Sunday, January 14, 2024 Snow Squalls

 A potent Arctic cold progresses across New England Sunday. While the brunt of the Arctic air remains confined to the central United States, upper-Midwest, Ohio Valley, and Tennessee Valley regions, it will still be very cold and wintry across southern New England behind the front. 

The leading edge of the Arctic air will be defined by elongated and potent vorticity. A vorticity maximum will round the base of an amplifying trough across our region and strengthen, resulting in a great deal of positive vorticity advection across New England Sunday:

This system will be associated with vigorous dynamics characterized by a 500mb mid-level jet streak which may approach or exceed 150 knots. This is about as strong of a mid-level jet you'll ever see and will help promote vigorous lift across the region:

Associated with the feature will be steep mid-level lapse rates ranging between 6.5 C/KM to as high as 7.7-7.8 C/KM. These lapse rates will help aid in weak instability within the region. This weak instability will aid in lift:

In addition, there will be a very steep lapse rate from the surface to about 15,000 feet above the ground. This bufkit sounding for Windsor Locks, CT illustrates this well. This look is suggestive of instability:

The response from the strengthening shortwave and positive vorticity advection will be a strengthening southerly flow in the low-levels of the atmosphere which will help transport sufficient moisture into the region to interact with the front. The steep low-level lapse rates will also help to promote the mixing down of stronger winds aloft:

What are we looking at? 

As moisture increases along and ahead of the Arctic front, scattered snow squalls are likely to develop ahead of the cold front with potential for a line of moderate-to-heavy snow to develop along the Arctic front. This can be thought of like summer downpours and thunderstorms where you get a 15-30 minute period of heavy precipitation, but in this case instead of rain you have snow occurring. 

These snow squalls could produce 2-3 inches of snow in a very short amount of time on a local level. Strong wind gusts would occur as well and this would contribute to extremely dangerous travel conditions for a brief period of time as visibility drops to almost zero and roads become icy very quickly. There is even potential for thunder and lightning given the steep lapse rates and instability. If you are caught in a snow squall the best thing you can do is pull over or off the road (in a safe spot) and let the squalls pass. Snow under squalls becomes intense very quickly and conditions can deteriorate in the blink of an eye.

The time frame for these snow squalls is between 1:00 - 5:00 PM. 

Sunday, January 7, 2024 southern New England Winter Storm

 Our first widespread, accumulating snowfall event of the season is upon us! Snow lovers were starved after pretty much a shutout (some places did get some snow) during the month of December. If you happened to read my winter outlook, I mentioned January and February were going to be active and we are off to those races! Anyways, let's get right into all the fun science and meteorological applications and thought process behind the forecast.

Synopsis

A frontal system moving across the Gulf Coast states Friday lifts northeast across the mid-Atlantic region during the day Saturday. An area of surface low pressure develops within the mid-Atlantic and strengthens as it lifts northeast off the mid-Atlantic coast and passing south and east of Long Island:

Discussion

As the low moves over the open waters, this is where the fun begins! Thanks to the temperature gradient which exists between the water and land this time of year, combined with the jet stream dynamics, the surface low will begin to strengthen. As the surface low strengthens and the circulation elongates we'll see a low pressure center develop about 5,000 feet above the ground. Thanks to a strong latitude horizontal gradient, this will help to strengthen this low pressure circulation as the system is passing northeast south of Long Island.:

This track of the 850mb low, combined with the fact that it will be strengthening places a good portion of southern New England in a very favorable spot for an intense band of snow to traverse. This is indicated very well assessing 850mb frontogenesis on both the GFS (left) and NAM (right) forecast models:

Several forecast soundings across the region all show good cross hair signature (when maximum lift bisects the snow growth zone). When/where this is occurring, snowfall rates will be heaviest, snow growth will be best, and snow ratios will be highest. We'll look at a few examples below:

This system will also have a copious amount of moisture to work with. Forecast model guidance develops 50+ knots of easterly inflow at 850mb, throwing a great deal of moisture into a cold low-level airmass. The result will be plenty of snowflakes developing:

While we're well within the 48-hour window of start time, there remain a quite a bit of uncertainties within our forecast model guidance. This has become an increasingly annoying theme the past few years. There are differences with the overall track and speed of development. Some forecast models are on the more amped side, resulting in a farther north and west track and development. This introduces warmer air into southern areas and would also result in the greatest frontogenesis and subsequent banding shifting farther north. This would also increase potential for subsidence in southern areas. 

Forecast 

• The highest totals should be confined to interior east-central Massachusetts into southern New Hampshire, and southwestern Maine. This is where snowfall ratios should be the greatest throughout the duration of the storm and where the intense banding is likely to persist the longest. In fact, there may be a swath of snowfall of 12-16 inches within this zone!
• Towards southern Connecticut. snow ratios will be held back due to some warmer air in the lower levels, just above the surface. Snowfall ratios improve briefly as the intense banding lifts north. 
• Easterly surface winds off the warmer water will hold back accumulations greatly across extreme coastal Connecticut, southern Rhode Island, and far eastern Massachusetts. 
• Snow will also be on the wet side across southern Connecticut into interior southeast Massachusetts. This could result in isolated downed tree limbs and power outages. 
• Snow begins Saturday evening (between 7:00 PM-10:00 PM from southwest to northeast), with intensity quickly picking up through the evening. 
• The worst of the storm is between 11:00 PM - 5:00 AM, however, for northeastern areas this will be extended through much of Sunday morning. 
• Light snow lingers through much of Sunday with moderate to at times, heavy snow across interior northeast Massachusetts. 

Below is my snowfall forecast: