Stormy Monday (6/25/12)?

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.