What a difference a week makes! This time last week we were gearing up for some high heat and humidity as temperatures were forecasted to soar into the 90's and dewpoints into the 60's and 70's. Once a cold front passed through on Friday sparking off some severe storms across the region and a mid/upper level passed through on Saturday producing a few more severe storms that hot/humid airmass was pushed off the east coast. Today we dealt with much more seasonable weather. As we move into the first full week of summer we won't be dealing with any high heat (although we will warm up into perhaps the mid 80's by next weekend!) but we will have to deal with some humidity with high dewpoints on Monday and we will have to deal with temperatures that will run well below-average for this time of year (Tuesday-Thursday).
Currently a sharpening and deepening mid/upper level trough is working through the upper Mid-west working towards the Northeast. Associated with this feature will be a cold front that is also sliding eastward with the advancing trough. As the trough continues to sharpen and deepen this will turn our winds from a more northwesterly/westerly direction to a more southwesterly direction beginning later tonight. As this occurs we will see an ample increase in moisture and dewpoints will be rising from the 50's where they currently are to well into the 60's to possibly even near 70°F. This increasing moisture will also lead to an increase in instability through the overnight hours.
Wind fields aloft will also be increasing through the overnight hours and into the morning hours. The low-level jet is expected to increase to around 25-30 knots with the mid-level jet increasing to 35-45 knots and the upper-level jet increasing to 70 knots and portions of western southern New England entering the left entrance region of this upper-level jet max by tomorrow afternoon.
With the increase in moisture overnight and the wind fields aloft along with no cap in place showers are expected to develop across the region and move into the region from New York during the overnight hours and tomorrow morning. With an increase in instability t'storms can't be ruled out either during the overnight or early morning hours tomorrow. Given the presence of of increasing shear/high dewpoints/increasing instability it's possible we could even see a couple storms become strong to perhaps even severe. If this were to occur damaging winds and large hail would certainly be possible. If low-level wind fields and winds in the boundary layer work to be more southerly this will increase the level of helicity over the region which could lead to some storms exhibiting rotation...this will have to be watched closely.
As we head through the morning and into the afternoon hours things become a little more unclear as to how they will unfold...
After morning shower/t'storm activity a break in the action is expected to occur. Some computer models are indicating enough of a dry punch working in the mid-levels of the atmosphere to warrant the development of some sunshine as the clouds break up. If any breaks of sunshine occur this would boost temperatures fairly quickly thanks to strong June sun angle and warm low-level airmass over the region. As of now temperatures are expected to be in the mid-70's, however, if any sun breaks out some areas could close in on 80°F. This coupled with dewpoints into the 60's to near 70°F and cooling temperatures in the mid-levels of the atmosphere could create quite an unstable airmass across portions of the region. Some computer models are also indicating some very steep mid-level lapse rates across the region, possibly as steep as 7.5 C/KM! A few other computer models are only indicating mid-level lapse rates around 5.5 C/KM. If we see the steeper mid-level lapse rates pan out this would further increase the chances of stronger instability being realized, especially if any breaks of sun were to occur.
Along with the potential for stronger instability during the late morning and early afternoon hours wind shear aloft is expected to remain fairly strong with 0-6km shear values in the 35-45 knot range and western portions of southern New England ending up in the left entrance region of the 70 knot upper-level jet max as it slides just east of the area.
If the stronger instability is realized we will again see more t'storms develop across the region out ahead of the cold front during the late morning and early afternoon hours. The combination of stronger instability and very good shear in place will once again pose the threat for some strong to severe t'storms capable of producing large hail and damaging winds. Given the presence of high dewpoints all storms will produce torrential downpours and the threat for some isolated flash flooding. Something else to keep an eye on will be the direction of the winds at the surface and in the boundary layer just above the surface. If winds here stay more southerly and can maintain a speed of about 15 knots or so this will greatly increase the helicity across the region, especially in the CT River Valley. Given the presence of 35-45 knots of 0-6km shear this would lead to a threat for an isolated supercell or two. An isolated tornado couldn't be ruled out either.
All in all while at this time a severe weather outbreak and significant severe weather seems unlikely given the questions regarding how much heating/instability will develop across the region, however, given the signals on the models at least a few strong to severe t'storms will be possible. There also may be multiple rounds of storms; one during the overnight/early AM hours then again during the late morning/afternoon hours. If we end up seeing more in the way of sunshine than expected across the region this will certainly increase for severe weather later on in the day across the region. These details will have to be worked out on an hour-to-hour basis during the morning hours tomorrow. Down from New York City on south across NJ computer forecast models are generating much stronger instability and with very strong shear values. Only issue is these areas may be a bit removed from the stronger lift, however, the stronger instability/shear combo could lead to some of the strongest storms occurring across this area.
Once the front reaches southern New England the front is expected to stall over us tomorrow night as a weak wave of low pressure develops and rides up along the front. This will keep the threat for showers/t'storms throughout the night tomorrow. We will also have to deal with the potential for storms on Tuesday as a cold pool aloft may lead to afternoon thunderstorms but we'll worry about this after tomorrow's potential action.
Sunday, June 24, 2012
Friday, June 22, 2012
More storms on Saturday? (6/23/12)
The forecast for widespread thunderstorms across the region on Friday worked out perfectly as several clusters/ of t'storms developed from ME all the way down through NJ. There even turned out to be a little more in the way of severe weather than expected as there were numerous reports of damaging winds across the region, especially across western and northern CT including some reports of large hail! While wind shear was not overly strong it was sufficient enough to help storm updrafts become organized and moderate instability gave the storms the fuel they needed to become strong and severe. While the cold front which was responsible for providing the lift to spark today's thunderstorms will have moved off the coast by tomorrow morning the cooler/drier air is actually lagging a bit behind the front. This cooler air will work into the region once a mid/upper level trough work through the region. This will be occurring tomorrow, however, it will not be occurring quietly.
While temperatures tomorrow won't be nearly as warm today as the warmest of the low-level airmass will have worked off the coast with the front temperatures are still expected to be into the lower to perhaps mid 80's. With still an abundance of low-level moisture around dewpoints will once again be into the mid 60's. The combination of warm temperatures and high dewpoints will once again set the stage for moderate instability to develop across the region. Some computer models are indicating as much as 1000-1500 J/KG of SBcape will develop tomorrow with the potential for as much as 2000 J/KG of SBcape along with LI values in the -3C to -5C range. Unlike today, we will also be dealing with steeper mid-level lapse rates as mid-level cooling occurs with the approaching mid-level trough. This will actually aid in some higher instability values tomorrow.
Not only will we be dealing with steeper mid-level lapse rates tomorrow but we will also be dealing with more in the way of wind shear as 0-6km shear values are expected to increase to the 35-45 knot range. This will be more than sufficient to allow for storm organization and also lead to some mid-level storm rotation and some storms perhaps taking on supercell characteristics, especially if the stronger instability is realized.
All in all with the approaching mid/upper level trough and cold pool (500mb temps lowering to around -15C during the day) and potential for moderate instability along with adequate shear the potential once again will exist for the development of thunderstorms across the entire region. While the entire region is under the threat the most numerous activity may occur across NH, southern ME, eastern MA and northern RI. Any storms that develop tomorrow will have the potential to produce hail and gusty winds while the stronger/more severe storms will be capable of large hail and damaging winds. All storms will produce torrential rainfall which could lead to pockets of flash flooding, especially for the areas which were hit hard by Friday's storms.
The timeframe for storms tomorrow should be anywhere from as early as 11 AM lasting to about 8 PM or so, however, far eastern sections of southern New England may see activity linger until 9-10 PM. Once the trough passes through ,cooler and drier air will usher into the region and the threat for storms will be over...until Monday at least but we'll worry about this another day :)
While temperatures tomorrow won't be nearly as warm today as the warmest of the low-level airmass will have worked off the coast with the front temperatures are still expected to be into the lower to perhaps mid 80's. With still an abundance of low-level moisture around dewpoints will once again be into the mid 60's. The combination of warm temperatures and high dewpoints will once again set the stage for moderate instability to develop across the region. Some computer models are indicating as much as 1000-1500 J/KG of SBcape will develop tomorrow with the potential for as much as 2000 J/KG of SBcape along with LI values in the -3C to -5C range. Unlike today, we will also be dealing with steeper mid-level lapse rates as mid-level cooling occurs with the approaching mid-level trough. This will actually aid in some higher instability values tomorrow.
Not only will we be dealing with steeper mid-level lapse rates tomorrow but we will also be dealing with more in the way of wind shear as 0-6km shear values are expected to increase to the 35-45 knot range. This will be more than sufficient to allow for storm organization and also lead to some mid-level storm rotation and some storms perhaps taking on supercell characteristics, especially if the stronger instability is realized.
All in all with the approaching mid/upper level trough and cold pool (500mb temps lowering to around -15C during the day) and potential for moderate instability along with adequate shear the potential once again will exist for the development of thunderstorms across the entire region. While the entire region is under the threat the most numerous activity may occur across NH, southern ME, eastern MA and northern RI. Any storms that develop tomorrow will have the potential to produce hail and gusty winds while the stronger/more severe storms will be capable of large hail and damaging winds. All storms will produce torrential rainfall which could lead to pockets of flash flooding, especially for the areas which were hit hard by Friday's storms.
The timeframe for storms tomorrow should be anywhere from as early as 11 AM lasting to about 8 PM or so, however, far eastern sections of southern New England may see activity linger until 9-10 PM. Once the trough passes through ,cooler and drier air will usher into the region and the threat for storms will be over...until Monday at least but we'll worry about this another day :)
Heat/humidity to end with a bang?
Multiple locations across southern New England has experienced mid-summer heat/humidity over the past few days as many areas saw the thermometer soar well into the 90's and even close to 100F. When you coupled dewpoints which have been in the mid 60's to at times even lower 70's the combination of the heat/humidity as made it almost unbearable for some. Good news though for those who don't like the heat or humidity as there is relief in sight. However, we have to go through about one more day of heat/humidity along with the potential for thunderstorms.
A cold front is slowly pushing eastward across New York state and will close in on southern New England later this morning and afternoon hours. Out ahead of this cold front a pre-frontal trough is expected to develop and this will be the focal point in the development of showers and t'storms later this morning and afternoon.
With the cold front still well off to our west this once again means we will be under a southwesterly flow giving us another day of heat/humidity. With computer forecast models trending slower with the approaching and passage of the cold front this will give us yet another day of temperatures in the 90's with dewpoints around 70F. With cloud cover and showers/t'storms expected to develop a little later on this will likely prevent temperatures from reaching their full potential, however, it does appear many areas away form the immediate coastline will once again approach 90F and even get into the lower 90's. Down towards the coast a more southwesterly flow will make for the development of the sea-breeze which will hold back on temperatures here. With 90F expected across many inland locations this afternoon this will give us our 3rd consecutive day of 90F+ temperatures which will give us our first official heat wave of the 2012 summer season!
With the combination of heat/humidity and a cold front/pre-frontal trough approaching from the west this will set the stage for showers and thunderstorms to develop later this morning/afternoon. While it will be very hot and humid the atmosphere will become fairly unstable with Surface-Based Cape (Convective Available Potential Energy) values and Most Unstable Cape values expected to be in the 1500-2500 J/KG range. Lifted Index values are expected to get to -3C to -5C. Given the presence of this moderate instability some of the storms that develop could approach the strong or even severe side and the main threat would be strong winds which could be capable of knocking down large limbs or small trees. Given the presence of high dewpoints and abundant low-level moisture all storms will produce torrential downpours and this could lead to areas of localized flash flooding/poor drainage flooding.
While thunderstorm activity will be widespread today widespread severe weather is not expected this afternoon. The presence of marginal mid-level lapse rates (change of temperature with height) in the 700-500mb (~10,000ft ASL to ~18,000ft ASL) will inhibit much stronger instability from being realized as Mix-Layer Cape values are only expected to be around 1500 J/KG at most. Winds aloft, while they do increase as the afternoon goes on are marginal as well as shear in the 0-6km layer is only expected to be around 20-25 knots though it does increase to around 30 knots late in the afternoon.
All in all showers/t'storms will begin developing as early as late morning and should last through the afternoon hours and well into the evening hours. Multiple rounds of storms are expected to develop given the presence of heat/humidity and should form into multi-cells or multi-cell clusters. While widespread severe weather is not expected a few of the storms will have the potential to become strong to severe posing a risk for gusty winds capable of knocking down large limbs or small trees. While hail isn't expected to be a high threat can't rule out some hail in the strongest of storms. Torrential rains will also occur with all storms.
The front is expected to finally clear the region early tomorrow afternoon so we can't rule out some showers/t'storms tomorrow, however, instability will be much less than today so activity won't be as widespread or as strong. Once the front passes more seasonable temps will work into the region and this oppressive humidity will make an exit.
A cold front is slowly pushing eastward across New York state and will close in on southern New England later this morning and afternoon hours. Out ahead of this cold front a pre-frontal trough is expected to develop and this will be the focal point in the development of showers and t'storms later this morning and afternoon.
With the cold front still well off to our west this once again means we will be under a southwesterly flow giving us another day of heat/humidity. With computer forecast models trending slower with the approaching and passage of the cold front this will give us yet another day of temperatures in the 90's with dewpoints around 70F. With cloud cover and showers/t'storms expected to develop a little later on this will likely prevent temperatures from reaching their full potential, however, it does appear many areas away form the immediate coastline will once again approach 90F and even get into the lower 90's. Down towards the coast a more southwesterly flow will make for the development of the sea-breeze which will hold back on temperatures here. With 90F expected across many inland locations this afternoon this will give us our 3rd consecutive day of 90F+ temperatures which will give us our first official heat wave of the 2012 summer season!
With the combination of heat/humidity and a cold front/pre-frontal trough approaching from the west this will set the stage for showers and thunderstorms to develop later this morning/afternoon. While it will be very hot and humid the atmosphere will become fairly unstable with Surface-Based Cape (Convective Available Potential Energy) values and Most Unstable Cape values expected to be in the 1500-2500 J/KG range. Lifted Index values are expected to get to -3C to -5C. Given the presence of this moderate instability some of the storms that develop could approach the strong or even severe side and the main threat would be strong winds which could be capable of knocking down large limbs or small trees. Given the presence of high dewpoints and abundant low-level moisture all storms will produce torrential downpours and this could lead to areas of localized flash flooding/poor drainage flooding.
While thunderstorm activity will be widespread today widespread severe weather is not expected this afternoon. The presence of marginal mid-level lapse rates (change of temperature with height) in the 700-500mb (~10,000ft ASL to ~18,000ft ASL) will inhibit much stronger instability from being realized as Mix-Layer Cape values are only expected to be around 1500 J/KG at most. Winds aloft, while they do increase as the afternoon goes on are marginal as well as shear in the 0-6km layer is only expected to be around 20-25 knots though it does increase to around 30 knots late in the afternoon.
All in all showers/t'storms will begin developing as early as late morning and should last through the afternoon hours and well into the evening hours. Multiple rounds of storms are expected to develop given the presence of heat/humidity and should form into multi-cells or multi-cell clusters. While widespread severe weather is not expected a few of the storms will have the potential to become strong to severe posing a risk for gusty winds capable of knocking down large limbs or small trees. While hail isn't expected to be a high threat can't rule out some hail in the strongest of storms. Torrential rains will also occur with all storms.
The front is expected to finally clear the region early tomorrow afternoon so we can't rule out some showers/t'storms tomorrow, however, instability will be much less than today so activity won't be as widespread or as strong. Once the front passes more seasonable temps will work into the region and this oppressive humidity will make an exit.
Wednesday, June 20, 2012
First Heat Wave of 2012 Imminent? Threat of storms as well?
The official first day of summer is now less than 24-hours away and it won't take very long at all for the weather to feel like summer as a very hot and humid airmass is currently on it's way to southern New England!
Currently a warm front is located just to the west of southern New England and this warm front will continue working eastward towards the region and eventually clearing the region by late tomorrow morning. Once the warm front passes through a blast of hot and humid air will invade the region lasting through the next few days.
The airmass working into the region is something more commonly seen during those hottest periods of July/August. The degree of the heat that will be seen across the region tomorrow is something that isn't typically seen in these parts this early in the summer.
The combination of strong sunshine, temperatures at 925mb and 850mb (~25000ft ASL and ~5000ft ASL respectively) ranging from around +25C to +28C (~80F) at 925mb to +19C to +21C (~70F) at 850mb, and strong atmospheric mixing will all lead to surface temperatures ranging from about the mid to upper 90's across much of the region...a few locations may even tough 100F! The only areas which will be cooler will be the immediate coastline and elevations above 1000', but even here it will be tough to escape the heat as many of these locations will range from the upper 80's to the lower 90's!
While Wednesday will be incredibly hot with these temperatures it's possible Thursday is even a few degrees higher across some locations. In fact, Thursday maybe the best chance for a few locations to hit 100F. The areas which have the best shot at 100F are Windsor Locks/Hartford, CT, Taunton, MA, Ashford, NH, and Chicopee, MA. The reason being some computer models are hinting at surface winds on Thursday to be mainly from the west to even slightly northwest. A wind direction from here causes down slopping. This is when winds moving down the edges of mountains/very large hills warms the air as it works down the slope of the mountains/very large hills. This down slopping can often tack on as much as 2-3F on surface temperatures.
Besides the high heat over the next few days we will also have to contend with some fairly high humidity levels and high dewpoints. Normally in these cases with extreme heat we don't normally have to contend with high dewpoints throughout the course of the entire day. Normally it is the morning and evening hours which have the higher dewpoints as during the afternoon hours strong mixing brings drier air down form higher up in the atmosphere and this helps to mix out the low level moisture resulting in lower dewpoints. This case will be a little different, however. With the passage of this warm front there is expected to be an abundance of low-level moisture that will work in place. Computer models are showing 925mb dewpoints to be around +20C (~68F) and 850mb dewpoints to be around +15C (59F). With a strong cap in place at 700mb (~10,000ft ASL) it will be very difficult to mix down the much drier air that exists about 10,000ft ASL and higher up. With all this said dewpoints on both says should be into the mid and upper 60's and even a 70F reading or two is possible, especially in the morning hours and then again during the evening hours. Now it's possible dewpoints on Thursday end up being a few ticks lower across the areas affected by down slopping as down slopping will help to dry the air out a little more.
The combination of the hot temperatures and dewpoints over the next few days will make it feel more like 105F at times, especially during the hottest hours of the day.
As we move into Friday things become a bit more interesting. In order for a "heat wave" to be official one of the several major reporting climo stations must see temperatures hit at least 90F for at least 3-consecutive days. Friday does have the potential to hit 90F, however, there will be a cold front slowly moving towards the region. With the approach of the cold front along with height falls in the mid-levels of the atmosphere this should allow for clouds to develop along with showers and t'storms. While computer models have trended a little slower with the cold front it does appear that we may start clouding over as early as 1-2 PM. This would be just before peak heating which would mean a limit on how high temperatures get.
With a cold front working into such a hot and humid airmass the potential will exist for t'storms and some could become strong to severe given how the atmosphere will be quite unstable. There are several factors though to consider when dealing with the potential for strong to severe t'storms;
1) Timing of the cold front. While computer models have trended slower with the cold front it appears the front will be close enough to at least western sections of southern New England to where clouds/showers/t'storms may develop too early on in the afternoon. This would limit the level of heating we would see and would also cut back on the amount of instability that would be in place.
2) Low-level airmass drying out too quickly. Some computer models have winds in the lower level of the atmosphere coming from a more westerly/northwesterly direction. As mentioned above this is something that could really help to dry out the low level airmass much quicker thus decreasing the surface dewpoints and also decreasing the level of instability that would be in place. These westerly/northwesterly low-level winds would also tend to limit the level of convergence along the cold front which would decrease the degree of upward motion along the front meaning storms may not be as widespread.
3) Wind Shear aloft. Winds aloft aren't exactly very strong. In fact, the strongest winds aloft are well behind the cold front are are located along the leading edge of an eastward progressing mid/upper level trough which won't arrive until Saturday AM. Vertical wind shear values are rather modest at around 25-30 knots and there region just appears to be in the right exit region of a very modest 60-70 knot secondary upper-level jet max. Given the lack of shear this would reduce the level of lift along/ahead of the cold front which would also lead to less in the way of t'storm development.
4) Mid-level lapse rates. Mid-level lapse rates could be a concern although computer models do increase them as mid-level heights continue to fall and some cooler air works in aloft. Computer models do show mid-level lapse rates to be right around 6.5 C/KM which is decent. Any less, however, and that would be another negative factor in updraft strength.
Given the above Friday has the potential to generate a cluster of t'storms, which would likely evolve into a squall line or perhaps even multiple lines given how the wind alignment will be unidirectional. The main threat would be strong winds which could knock down small trees, limbs, and power lines. Given the presence of high dewpoints any storms would likely produce very heavy rainfall, possibly leading to minor street flooding/poor drainage flooding. It's still a bit uncertain though as to how widespread the t'storm threat will be given the above factors mentioned.
It's possible a threat for strong t'storms could exist on Saturday as well, especially across central/eastern sections of southern New England if the cold front has not cleared these areas. By Saturday that mid/upper level trough will have worked into the region and this is when the stronger winds aloft would be present. Computer models are also indicating some instability present early AM Saturday so this will have to be watched.
Once the front/trough clear the region we will return to much more seasonable weather temperature wise along with lower dewpoints and humidity levels.
Currently a warm front is located just to the west of southern New England and this warm front will continue working eastward towards the region and eventually clearing the region by late tomorrow morning. Once the warm front passes through a blast of hot and humid air will invade the region lasting through the next few days.
The airmass working into the region is something more commonly seen during those hottest periods of July/August. The degree of the heat that will be seen across the region tomorrow is something that isn't typically seen in these parts this early in the summer.
The combination of strong sunshine, temperatures at 925mb and 850mb (~25000ft ASL and ~5000ft ASL respectively) ranging from around +25C to +28C (~80F) at 925mb to +19C to +21C (~70F) at 850mb, and strong atmospheric mixing will all lead to surface temperatures ranging from about the mid to upper 90's across much of the region...a few locations may even tough 100F! The only areas which will be cooler will be the immediate coastline and elevations above 1000', but even here it will be tough to escape the heat as many of these locations will range from the upper 80's to the lower 90's!
While Wednesday will be incredibly hot with these temperatures it's possible Thursday is even a few degrees higher across some locations. In fact, Thursday maybe the best chance for a few locations to hit 100F. The areas which have the best shot at 100F are Windsor Locks/Hartford, CT, Taunton, MA, Ashford, NH, and Chicopee, MA. The reason being some computer models are hinting at surface winds on Thursday to be mainly from the west to even slightly northwest. A wind direction from here causes down slopping. This is when winds moving down the edges of mountains/very large hills warms the air as it works down the slope of the mountains/very large hills. This down slopping can often tack on as much as 2-3F on surface temperatures.
Besides the high heat over the next few days we will also have to contend with some fairly high humidity levels and high dewpoints. Normally in these cases with extreme heat we don't normally have to contend with high dewpoints throughout the course of the entire day. Normally it is the morning and evening hours which have the higher dewpoints as during the afternoon hours strong mixing brings drier air down form higher up in the atmosphere and this helps to mix out the low level moisture resulting in lower dewpoints. This case will be a little different, however. With the passage of this warm front there is expected to be an abundance of low-level moisture that will work in place. Computer models are showing 925mb dewpoints to be around +20C (~68F) and 850mb dewpoints to be around +15C (59F). With a strong cap in place at 700mb (~10,000ft ASL) it will be very difficult to mix down the much drier air that exists about 10,000ft ASL and higher up. With all this said dewpoints on both says should be into the mid and upper 60's and even a 70F reading or two is possible, especially in the morning hours and then again during the evening hours. Now it's possible dewpoints on Thursday end up being a few ticks lower across the areas affected by down slopping as down slopping will help to dry the air out a little more.
The combination of the hot temperatures and dewpoints over the next few days will make it feel more like 105F at times, especially during the hottest hours of the day.
As we move into Friday things become a bit more interesting. In order for a "heat wave" to be official one of the several major reporting climo stations must see temperatures hit at least 90F for at least 3-consecutive days. Friday does have the potential to hit 90F, however, there will be a cold front slowly moving towards the region. With the approach of the cold front along with height falls in the mid-levels of the atmosphere this should allow for clouds to develop along with showers and t'storms. While computer models have trended a little slower with the cold front it does appear that we may start clouding over as early as 1-2 PM. This would be just before peak heating which would mean a limit on how high temperatures get.
With a cold front working into such a hot and humid airmass the potential will exist for t'storms and some could become strong to severe given how the atmosphere will be quite unstable. There are several factors though to consider when dealing with the potential for strong to severe t'storms;
1) Timing of the cold front. While computer models have trended slower with the cold front it appears the front will be close enough to at least western sections of southern New England to where clouds/showers/t'storms may develop too early on in the afternoon. This would limit the level of heating we would see and would also cut back on the amount of instability that would be in place.
2) Low-level airmass drying out too quickly. Some computer models have winds in the lower level of the atmosphere coming from a more westerly/northwesterly direction. As mentioned above this is something that could really help to dry out the low level airmass much quicker thus decreasing the surface dewpoints and also decreasing the level of instability that would be in place. These westerly/northwesterly low-level winds would also tend to limit the level of convergence along the cold front which would decrease the degree of upward motion along the front meaning storms may not be as widespread.
3) Wind Shear aloft. Winds aloft aren't exactly very strong. In fact, the strongest winds aloft are well behind the cold front are are located along the leading edge of an eastward progressing mid/upper level trough which won't arrive until Saturday AM. Vertical wind shear values are rather modest at around 25-30 knots and there region just appears to be in the right exit region of a very modest 60-70 knot secondary upper-level jet max. Given the lack of shear this would reduce the level of lift along/ahead of the cold front which would also lead to less in the way of t'storm development.
4) Mid-level lapse rates. Mid-level lapse rates could be a concern although computer models do increase them as mid-level heights continue to fall and some cooler air works in aloft. Computer models do show mid-level lapse rates to be right around 6.5 C/KM which is decent. Any less, however, and that would be another negative factor in updraft strength.
Given the above Friday has the potential to generate a cluster of t'storms, which would likely evolve into a squall line or perhaps even multiple lines given how the wind alignment will be unidirectional. The main threat would be strong winds which could knock down small trees, limbs, and power lines. Given the presence of high dewpoints any storms would likely produce very heavy rainfall, possibly leading to minor street flooding/poor drainage flooding. It's still a bit uncertain though as to how widespread the t'storm threat will be given the above factors mentioned.
It's possible a threat for strong t'storms could exist on Saturday as well, especially across central/eastern sections of southern New England if the cold front has not cleared these areas. By Saturday that mid/upper level trough will have worked into the region and this is when the stronger winds aloft would be present. Computer models are also indicating some instability present early AM Saturday so this will have to be watched.
Once the front/trough clear the region we will return to much more seasonable weather temperature wise along with lower dewpoints and humidity levels.
Sunday, June 17, 2012
The Heat Is On...but not for long
The official first day of summer is Wednesday, June 20th, 2012 and boy will it sure feel like summer outside as a major ridge builds in from the central Plains allowing for a very hot airmass to invade pretty much the entire eastern third of the United States.
While there were stretches of April/May that sure felt like mid-summer the month of June has not been so kind as temperatures are actually running below-average for the month! This, however, will be changing as we move through the work week!
A trough which has been plaguing much of the Northeast will finally be lifting out as ridging which has been in place across much of the Plains and Southern States continues to strengthen and build northward and eastward. As this occurs a warm front is going to be lifting northward and moving through New England during the day on Tuesday and moving well into northern New England by early Wednesday morning. Once that warm front moves through a very hot airmass will have worked into the region.
Several computer forecast models are indicating temperatures at 925mb (~2500ft ASL) will approach +25°C (77°F) along with 850mb temperatures (~5000ft ASL) approaching +21°C (~72°F) to +23°C (74°F). With full sunshine and full mixing this would support temperatures well into the mid 90's across much of the region with the exception of the extreme coast and elevations above 1000'.
Right now it appears that Wednesday and Thursday will be the hottest days as temperatures both days have a very good possibility of reaching the mid to upper 90's across a large chunk of the region and it is even possible that a few locations could flirt with the 100°F mark! This will all depend on exactly how high the 850mb temps are and what the surface wind direction is. If surface winds stay more westerly this will enhance the downsloping component and across a few locations which will increase the likelihood of some locations getting to 100°F.
The next question is do we see an official heat wave out of this? At this point in time I would lean towards this NOT occurring. Remember, to have an official heat wave you must have at least three-consecutive days of 90°F or more. Tuesday looks like we'll only see lower to mid 80's and a cold front will be moving towards the region on Friday. It is the timing of this front which will play a major factor in whether or not we can hit 90°F on Friday. As of now computer guidance is suggesting the cold front will move through the region during the late morning or early afternoon hours. There would also likely be showers/t'storms associated with the front and the increase in cloud cover along with early timing of the front would likely prevent anyone across southern New England from hitting the 90°F mark. However, if the front slows down by several hours than it's very possible some locations can get to the magic number.
Once the cold front passes through on Friday a secondary cold front will work through the region on Saturday bringing in a much more cooler and dry airmass. This front may also be associated with a few showers/t'storms. It also appears that with the passage of this front we will yet again see another pattern change and the final week of June moving forward into July look like it will feature cooler than average temperatures...but we'll save this for another post!
While there were stretches of April/May that sure felt like mid-summer the month of June has not been so kind as temperatures are actually running below-average for the month! This, however, will be changing as we move through the work week!
A trough which has been plaguing much of the Northeast will finally be lifting out as ridging which has been in place across much of the Plains and Southern States continues to strengthen and build northward and eastward. As this occurs a warm front is going to be lifting northward and moving through New England during the day on Tuesday and moving well into northern New England by early Wednesday morning. Once that warm front moves through a very hot airmass will have worked into the region.
Several computer forecast models are indicating temperatures at 925mb (~2500ft ASL) will approach +25°C (77°F) along with 850mb temperatures (~5000ft ASL) approaching +21°C (~72°F) to +23°C (74°F). With full sunshine and full mixing this would support temperatures well into the mid 90's across much of the region with the exception of the extreme coast and elevations above 1000'.
Right now it appears that Wednesday and Thursday will be the hottest days as temperatures both days have a very good possibility of reaching the mid to upper 90's across a large chunk of the region and it is even possible that a few locations could flirt with the 100°F mark! This will all depend on exactly how high the 850mb temps are and what the surface wind direction is. If surface winds stay more westerly this will enhance the downsloping component and across a few locations which will increase the likelihood of some locations getting to 100°F.
The next question is do we see an official heat wave out of this? At this point in time I would lean towards this NOT occurring. Remember, to have an official heat wave you must have at least three-consecutive days of 90°F or more. Tuesday looks like we'll only see lower to mid 80's and a cold front will be moving towards the region on Friday. It is the timing of this front which will play a major factor in whether or not we can hit 90°F on Friday. As of now computer guidance is suggesting the cold front will move through the region during the late morning or early afternoon hours. There would also likely be showers/t'storms associated with the front and the increase in cloud cover along with early timing of the front would likely prevent anyone across southern New England from hitting the 90°F mark. However, if the front slows down by several hours than it's very possible some locations can get to the magic number.
Once the cold front passes through on Friday a secondary cold front will work through the region on Saturday bringing in a much more cooler and dry airmass. This front may also be associated with a few showers/t'storms. It also appears that with the passage of this front we will yet again see another pattern change and the final week of June moving forward into July look like it will feature cooler than average temperatures...but we'll save this for another post!
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