February 8-9, 2025 southern New England Winter Storm (Overnight)

 We have entered an active stretch of weather with multiple winter storm threats between Super Bowl weekend and the upcoming week. Let's get right to it and discuss the Super Bowl weekend winter storm potential. 

Low pressure develops within eastern Colorado and central Plains Saturday along a baroclinic zone evolving into a frontal system as it rapidly tracks east-northeast across the country. Meanwhile an abundance of shortwave energy embedded within a fast zonal jet stream aloft traverses the northern Plains. This shortwave energy is expected to give a bit of a boost to the system as this shortwave energy has some interaction with the frontal system:

Moving into Saturday evening, computer forecast model guidance indicates very strong upper-level diffluence (faster jet stream winds moving into slower jet stream winds) with increasing upper-level divergence across the Northeast (evident by the wind barbs moving away from each other). The increasing upper-level divergence will help precipitation blossom within the region Saturday evening which will be further aided by increasing warm-air advection (supplying moisture) and strengthening area of surface low pressure:

Increasing precipitation Saturday afternoon and evening across the Northeast:

As the system lifts northeast and then east across the Northeast, we'll see a several hour window of strong upward vertical motion (lift) traverse the region:

Latest bufkit profiles across the region from the 18z/06 run of the GFS show a several hour period where omega values range between -20 to -30 ubar/s within the dendritic snow growth zone with snowfall ratios in excess of 10:1 and potentially greater than 15:1. This is suggestive of heavy snowfall rates (perhaps in excess of 1inch per hour) with excellent snow growth. Below is an example from Worcester, MA (ORH):

So, what can we expect? This will be another fast-moving, quick hitting winter storm with the brunt of the storm impact occurring in a 3-5 hour window. 

• Snow arrives from southwest to northeast across the region, beginning first across western Connecticut between 6:00-8:00 PM EST Saturday evening and 8:00-10:00 PM EST across northeastern Massachusetts. 
• Heaviest snowfall occurs between the hours of 11:00 PM - 4:00 AM EST. This is when snowfall rates could approach 1 inch per hour under the heaviest echo's. 
• Snow begins tapering off southwest-to-northeast during the pre-dawn hours southwest and around or shortly after daybreak Sunday northeast. 
• The fast forward speed of this storm limits accumulations. 
• Outside of the immediate coastal Plain and outer Cape, precipitation will be all snow. Sleet is expected to mix in across the immediate shoreline of Connecticut and Rhode Island and outer Cape Cod. This holds down totals slightly in these areas.
• Below is what I am currently expecting:

Sunday, January 19, 2025 Winter Storm

 Technical Discussion:

Low pressure develops within the mid-Atlantic region Sunday afternoon ahead of a southeastward advancing cold front. Computer forecast models are all in great agreement in shortwave energy rounding the base of an amplifying upper-level trough aiding in the development and strength of the low pressure. However, there are some uncertainties on the strength of this shortwave energy, however, there is a consensus towards this piece of energy to be on the stronger side:

Low pressure is then expected to pass to the south and east of Connecticut, a very favorable track for moderate-to-heavy snow to traverse much of the state. However, with some warmer in place out ahead of this system; particularly along the shoreline and southeastern Connecticut, this will ultimately cut down on snow potentials there:

Despite being so close to the storm, there are some uncertainties regarding the overall track and this could have a big impact on snowfall totals; particularly across south and eastern sections which are on the line between colder and warmer temperatures and where the heaviest banding and subsequent totals may reside. One of the more consistent forecast models with the evolution of this system has been the GFS. The GFS advertises potential for some heavy banding to traverse much of southern New England:

In fact, the latest 12z GFS bufkit for Worcester, MA (ORH) exhibits a crosshair signature with as much as -40 to -50 ubar/second within the dendritic snow growth zone. This is indicative of tremendous lift and would likely result in snowfall rates in the 2-3 inch per hour range with snowfall ratios of 15:1:

Forecast:

• Light snow begins to breakout across western Connecticut and western Massachusetts between 1-3 PM Sunday and the remainder of the region by 5-6 PM. 
• Snowfall rates intensify rapidly during the evening with the heaviest snowfall rates between 7-10 PM (hold on as late as 12-1 AM across northeast Massachusetts). Snowfall rates will approach 1 inch per hour and as much as 2-3 inches per hour under the heaviest banding. 
• Snow tapers off during the early overnight. 
• This will be a quick hitting and fast moving storm.
• There are some uncertainties; particularly around the Boston market and where the heaviest banding occurs. 
• Where the heaviest banding occurs, we will likely see a swath of snowfall accumulations more in the 8-12 inch range. 
• There will also be some mesoscale subsidence zones where snow growth and intensities struggle. Where this occurs totals will end up closer to the lower ends of the ranges. 
• Frigid temperatures and dangerously cold wind chills build in for Sunday night and Monday behind the system. 
• Below is what I am currently thinking. Keep in mind, where the heaviest banding snowfall occurs, totals will be in the 8-12 inch range, however, it is very difficult to determine where that will occur.

Wednesday, December 11, 2024 Southern New England Rain/Wind Event

 General Synoptic Overview: A northern stream shortwave trough with an associated surface cold front amplifies (strengthens) as it digs across the upper-Midwest interacts with shortwave energy and an associated frontal system lifting northeast out of the southern Plains overnight Tuesday:  

As these two systems interact the result will be a rapidly developing and deepening area of low pressure at the surface along a strengthening cold front. Low pressure begins developing within the mid-Atlantic early Wednesday morning and strengthens as it lifts northeast towards New England late in the afternoon:

With surface low pressure passing to the west of southern New England and strengthening while doing so, this should propel a warm front through much of the region yielding a surge of unseasonably strong theta-e characterized by surface temperatures climbing into the upper 50's to lower 60's and dew points into the mid-to-upper 50's across much of the region Wednesday afternoon:

With an intensifying system the response will be an increase in jet stream dynamics aloft, characterized by a potent 50-60 knot jet at 925mb (about 2,500 feet above the ground) overspreading much of southern New England through the day Wednesday with as much as 70-80 knots overspreading costal Connecticut and eastern southern New England:

What to Expect: Heavy rain is expected across the entire region Wednesday with a widespread 2-4 inches of rain and locally higher amounts. While this is great news for the drought situation there will be concern for flash flooding, particularly within typical flood prone areas and northern portions of the region where the is snow cover and some frozen ground. 

In addition to heavy rain, strong winds are expected, both sustained and potential gusts. A strengthening pressure gradient from the deepening low pressure and strong pressure falls should result in sustained winds of 20-30 mph within the region. Winds will be less in more sheltered areas, however, towards the coast (but just a bit inland) and towards eastern sections of New England winds could become sustained as high as 30-35 mph. 

There is also potential for widespread damaging wind gusts of 50-60 mph which could yield downed tree limbs and scattered power outages. As usual with these setups, the wind gust potential will be contingent on the strength of a temperature inversion just above the surface. Given the potential for temperatures to push 60 with dew points well into the 50's this may limit any inversion; increasing potential for damaging wind gusts. Another factor which could inhibit the max gust potential is stability produced by rainfall. 

With such a vigorous weather system, combined with the anomalously warm temperatures and higher dew points, there atmosphere will also become weakly unstable. Some forecast model guidance suggests a fine line of intense rainfall, potentially accompanied by thunder/lighting will develop across eastern Pennsylvania, northwest New Jersey, and southeast New York and strengthen as it progresses across southern New England during the late afternoon and evening. Should this materialize, this would increase the potential for wind gusts as high as 55-65 mph on the leading edge of it as it crosses the region. 

The worst of the weather conditions are expected to be from about noon to midnight Wednesday with improving conditions from western southern New England during the evening and eastern southern New England around midnight. 

Clipper System to Bring Accumulating Snow within southern England overnight 12.04.24 into 12.05.24

A shortwave trough entering the upper-Midwest early Wednesday afternoon amplifies (strengthens) as it traverses the Great Lakes region through the evening and overnight. 

As the shortwave trough amplifies, an area of surface low pressure across southeast Canada will continue strengthening as it progresses southeast and slides across northern New England during the overnight hours. With strong upper-level divergence just south of New England, combined with strong warm air advection in the lower-levels of the atmosphere. precipitation is expected to blossom later this evening and overnight within the region:

Where the thermal profile is expected to support all snow, snow will come down moderate at times. While this 18z/Dec 4 NAM bufkit run for Worcester, MA doesn't show impressive upward vertical motion, it does show around -5 units of omega bisecting the snowgrowth zone (purple and yellow contours) for much of the late evening and overnight:

The solid light blue line shows snowfall ratios. Farther inland, away from the coast and northwest of the I-84 corridor snowfall ratios should be as high as 12:1 to 15:1 during the peak of the snowfall.

What to Expect:

• Due to warmer air at the surface and within the lowest 2,500 feet of the atmosphere, areas south and east of the I-84 corridor are expected to be a rain/snow mix with all rain likely for the immediate coastal areas. 
• The heaviest snow and greatest accumulations will be within Berkshire County of Massachusetts into the northwest hills of Connecticut. Here precipitation will fall as all snow. A second area of greatest accumulations will be within the higher elevations of Worcester County Massachusetts into the northeast hills of Connecticut where there will be greater precipitation totals and stronger upward vertical motion. In fact, some areas just northwest of Worcester, Massachusetts could pick up 6-7''.
• Precipitation begins to break out anywhere between 8:00 PM - 10:00 PM EST Wednesday from a west to east direction with the heaviest snowfall rates (and rainfall rates for the coast) occurring between 1:00 AM - 7:00 AM EST Thursday morning. 
• Expect a very slow Thursday morning commute and give yourself extra travel time. 
• Precipitation winds down early Thursday morning, however, scattered snow squalls are expected throughout the day which can quickly lead to brief, but quickly diminished visibility and dangerous travel and even drop a quick inch of snow. Some thunder and lighting is also possible with the more intense squalls. 
• Below is what I am thinking:

Sunday, June 30, 2024 southern New England Thunderstorm Discussion

 Currently, a northwest to southeast oriented warm front resides from the northern Great Lakes region into Canada southeast across Pennsylvania and into portions of the mid-Atlantic. This warm front accelerates northeast through the remainder of Saturday, advecting in a moisture rich, high theta-e airmass into New England with dewpoints likely into the lower 70's by early Sunday morning. 

Warm front position - early Saturday afternoon

Through the day today, a shortwave trough dives into the upper-Midwest and amplifies as it progresses across the northern Great Lakes region towards the northeast. The result will be unseasonably strong wind shear overspreading the region characterized by 40-50+ knots of bulk shear. In addition, winds in the lowest levels of the atmosphere in the wake of the warm front may remain more southerly with winds more west-southerly aloft. Where low-level winds remain more backed, large helicity values in the 0-1km and 0-3km are likely with as much as 150 m2s2 in the 0-1km layer and 150-200 m2s2 in the 0-3km layer. 

Forecast bulk shear values of 40-50+ knots. More than sufficient for thunderstorm organization.

At the surface, temperatures are expected to climb into the upper 70's to lower 80's with dewpoints into the lower 70's (even as high as 73-75°F should dewpoint pooling result). Depending on the extent of morning cloud cover and degree of heating, temperatures, especially in the valley, could soar as high as 83-85. Despite marginal mid-level lapse rates (~6 C/KM), the combination of surface temperatures into the lower 80's and dewpoints into the lower 70's may yield moderate instability characterized by mixed-layer CAPE values in the 1500-2000 J/KG range and surfaced-based CAPE values around 2000-2500 J/KG. It should be interesting to note some forecast model guidance is suggesting mixed-layer CAPE values could approach 2500+ J/KG with surface-based CAPE values exceeding 3000 J/KG. These values are difficult to obtain without mid-level lapse rates ~7 C/KM and greater, however, if surface temperatures can near 85 and dewpoints climb into the 74-75°F range, these values could become obtained. 

NAM forecast model developing 1500-2000+ J/KG of mixed-layer CAPE Sunday afternoon.

The combination of moderate instability and strong wind shear ahead of an approaching cold front and likely pre-frontal trough development will be more than favorable for scattered-to-numerous thunderstorms developing by early afternoon and organizing into one or multiple convective lines. This combination of ingredients is also supportive for the strongest thunderstorms to produce locally damaging wind gusts and perhaps even a tornado. 

There are some caveats, however, which may reduce a more organized severe weather episode from occurring. In addition to the marginal mid-level lapse rates, the strongest shortwave forcing remains displaced well to the west of the best overlap of shear/instability with forecast model guidance showing the best shortwave forcing still in southeast Canada between the mid-to-late afternoon. 

All in all, the expectation is scattered-to-numerous thunderstorms develop across interior southeast New York by early afternoon with activity quickly organizing into one or more convective lines. Should the more extreme instability scenarios verify (mixed-layer CAPE > 2000-2500 J/KG) potential for a more widespread damaging wind producing event will increase. Given the larger helicity values, there would even be potential for an embedded tornado or two. Any tornado potential would be highest with any discrete cells which form initially or out ahead of the line. Localized flash flooding will be a concern as well given PWAT values approaching and exceeding 2''. 

Sunday, June 23, 2024 New England Thunderstorm Discussion

Synopsis

Scattered showers and thunderstorms are expected to develop within New York and Pennsylvania by early Sunday afternoon with this activity spreading east through the day with additional thunderstorm development within New England. The potential will exist for some of these thunderstorms to become strong-to-severe and capable of producing localized damaging wind gusts and/or hail. There is also potential for a few tornadoes within the region. In addition, torrential downpours with any thunderstorms may contribute to flash flooding within typical, low-lying, flood-prone areas.

As of Saturday morning, an elongated stationary front stretched from off the New England coast westwards through the Great Lakes region and into the upper-Midwest. Across New England, the north of the boundary is characterized by a much cooler and less humid airmass than what is in place south of the boundary.

Also as of Saturday morning, multiple pieces of shortwave energy were embedded within the jet stream across the north-central Plains and upper-Midwest with multiple weak areas of low pressure at the surface.

Forecast model guidance is in general agreement this shortwave energy will amplify (strengthen) some as it traverses the Great Lakes region and advances towards New England. This will result in a deepening low pressure at the surface and help to lift the stationary front across New England northwards as a warm front, advecting much warmer and more humid air into northern New England on Sunday morning. This will help set the stage for scattered afternoon and evening thunderstorms.

Dynamics

With a strengthening weather system, we’ll see an increase in winds throughout the troposphere. Forecast model guidance overspreads 40-50 knots of bulk shear by Saturday night through Sunday. These values are more than sufficient for thunderstorms to become organized, and these values are more than sufficient for the more mature storms to take on supercell characteristics.

In addition to winds increasing with height through the troposphere (speed shear) winds will also change direction through the atmosphere (directional shear) with the greatest turning of the winds occurring within the lowest 3 km thanks to the presence of a surface warm front. Forecast model guidance suggests 0-1km helicity (a measure of how winds are changing with speed and height) values on the order of 150-200+ m2s2 with 0-3km helicity values on order of 200-250+ m2s2. These values are more than sufficient for any mature, discrete thunderstorms to become supercells.

Thermodynamics

The combination of temperatures climbing into the 80’s with dewpoints into at least the lower 70’s will contribute to a moderately unstable airmass characterized by mixed-layer CAPE values ranging between 1500-2500 J/KG. What will hold back from an even more volatile atmosphere will be the lack of stepper mid-level lapse rates (change of temperature with height) in the 700-500mb level (typically associated with an elevated mixed-layer). One thing to watch for, however, is the potential for dewpoint pooling, especially within the Connecticut River Valley. Should this occur, a narrow corridor of dewpoints rising into the 74-76°F range would be likely, this could further boost mixed-layer CAPE values (in the 2500-3000 J/KG range) and compensate some for the weaker mid-level lapse rates.

Expectation

Combination of approaching shortwave energy, moderate instability, and sufficient wind shear will result in scattered-to-numerous showers and thunderstorms develop by early afternoon across New York and Pennsylvania with this activity spreading east through the day with showers and thunderstorms firing across New England by early-to-mid afternoon. While there is some potential for widespread strong-to-severe thunderstorms, the overall potential will be held back due to;

1)        The lack of an elevated mixed-layer and associated very steep mid-level lapse rates (> 7-7.5 C.KM).

2)        Assessing some forecast soundings within the region, it is noted there are some subtle warm layers aloft. These subtle warm layers (contributing to weaker lapse rates) will have a negative impact on parcel upward acceleration which can make it difficult for thunderstorms to become explosive and very intense, at least on a widespread scale.

The greatest potential for any thunderstorms to become strong-to-severe will be eastern eastern New York, Vermont, New Hampshire, western and central Massachusetts, and northwestern Connecticut. This is where the strongest thunderstorms will be capable of producing localized damaging wind gusts and hail. There will also be potential for a few tornadoes and some localized flash flooding. 

Significant Early April Winter Storm Potential

 Forecast model guidance remains in strong agreement in an anomalous evolution and structure of the 500mb pattern moving through the week of April characterized by strong ridging building into the Pacific-Northwest region during the early part of the week and shifting into the Inter-mountain West region along with significant trough amplification within the Northeast as the ridging within the Inter-mountain West continues building northeast into the Arctic domain, it will connect with the ridging within the Arctic domain, characterizing a highly negative Arctic Oscillation and North Atlantic Oscillation. This enhances the amplification of the trough across the Northeast:

12z March 30, 2024 run of the GEFS valid for 12z Tuesday:

12z March 30, 2024 run of the GEFS valid for 0z Thursday:

Highly anomalous weather patterns tend to produce anomalous weather and should this evolution verify, which is becoming increasingly likely, there will surely be some anomalous weather within New England. That anomalous weather would be in the form of accumulating snow and potential for significant accumulations. The period of interest is Wednesday, April 3 - Thursday, April 4, 2024.

Accumulating snow within New England during April can and does happen, however, climatologically speaking it is typically the higher terrain (generally above 1,000 feet in elevation), especially the farther north into New England one goes. In the case of this setup, these areas would stand the greatest potential for significant snowfall accumulations and winter storm impacts. However, given the anomalous nature of this setup, plus plenty of available low-level cold air, The 12z March 30, 2024 run of the GFS shows temperatures across New England at 925mb (~2,500 feet above ground level) just below freezing Wednesday morning:

Now it is important to understand where we are in the calendar. We are moving into the first week of April, average temperatures are much warmer than they are in the previous few months. In fact, during early April the average high temperature across many of the climatological stations is pushing into the 50's. So clearly, there has to be one heck of a cold anomaly in the lowest levels and a strong source of low-level cold advection to obtain temperatures cold enough to support snow for elevations below 1,000 feet and towards the coastal Plain. 

There is another factor to consider with this system as well. The premise of this post focused on the 500mb pattern, however, we did not divulge into the surface. Associated with this anomalous 500mb pattern will be a low pressure system at the surface which slowly progresses eastwards across the mid-western states during the first few days of the week. There is potential for secondary low pressure develop and rapid strengthening. If this occurs, and where it occurs, will have great implications on the sensible within the region. Development and strengthening around or south of Long Island would result in colder low-level airmass to the coast and dynamic cooling could result in even colder temperatures down to the surface. This scenario would increase the potential for snow, even down to the coast and increase the potential for accumulating snow for elevations below 1,000 feet. 

This is going to be a wild few days of storm tracking and this one has potential to yield some major surprises. As of now, the highest potential for a significant winter storm will be for elevations above 1,000 feet and within northern New England: