9:20 AM (Sat) | ***Unstable atmosphere today as colder air begins its push into the Mid-Atlantic…thunder possible with hail/graupel in some spots…below-freezing conditions on the way***
Paul Dorian
The atmosphere will become increasingly unstable today in part due to a strong vorticity max moving overhead. In addition, colder air will first make inroads in the upper part of the atmosphere later today making for steepening lapse rates and increasing chances for showers and scattered thunderstorms. Map courtesy NOAA, tropicaltidbits.com
Overview
In what seems to becoming more and more of an annual tradition, winter is going to make a comeback in early spring. Colder air will begin to make its presence felt later today in the Mid-Atlantic region; especially, in the upper part of the atmosphere where the freezing level will lower. As a result of the increasing cold air aloft, the atmosphere will become quite unstable and there will likely be “hit or miss” thunderstorms during the mid-day and afternoon hours. Given the lower freezing level aloft, hail or graupel (snow pellets) can be experienced in some areas during any gusty shower or thunderstorm later today. Winds will increase in strength tonight from the northwest and continue quite strong on Sunday and the passage of a secondary cold front will usher in very cold air for this time of year and below-freezing conditions for late Sunday night and late Monday night. There will be snow showers possible on Sunday associated with the secondary cold front and perhaps even a few heavier snow squalls for interior sections of the Mid-Atlantic.
Below-freezing conditions will dominate the scene early Monday morning as depicted here by the latest NAM model run - including in the urban areas along Route I-95. Map courtesy NOAA, tropicaltidbits.com
Details
The calendar says its spring, but as has been the case in many recent years, winter will not go away without a fight. An initial push of colder air later today will first make inroads in the upper part of the atmosphere and it will be accompanied by a vigorous wave of energy. The atmosphere in the Mid-Atlantic region will become increasingly unstable and showers will develop across much of the region. In addition, given the colder air aloft and overall unstable atmospheric conditions, there can be “hit or miss” thunderstorms later today in the Mid-Atlantic region. A lowering freezing level will add to the possibility that any gusty shower or “low-cap” thunderstorm can produce small hail or graupel (snow pellets) from later today into early tonight.
Temperatures will drop below-freezing in most areas late Sunday night and again late Monday night and will be way below-normal on Monday for the latter part of March. Map courtesy NOAA, tropicaltidbits.com
Winds will increase by tonight from a northwesterly direction and temperatures will drop well down into the 30’s for lows in the DC-to-Philly-to-NYC corridor. An even colder air mass will arrive on Sunday following the passage of a secondary cold front and winds will continue to be very noticeable from a northwesterly direction. There will be snow showers possible on Sunday associated with the secondary cold front and perhaps even a few heavier snow squalls for interior sections of the Mid-Atlantic.. After temperatures are limited to the 40’s for highs on Sunday in DC, Philly and NYC, they’ll drop to below-freezing by late Sunday night and remain way below-normal on Monday. In fact, temperatures on Monday will be some twenty degrees below-normal and are likely to hold in the 30’s in much of the Mid-Atlantic region paving the way for another late night where below-freezing conditions will prevail in the DC-to-Philly-to-NYC corridor. More snow showers and even heavier snow squalls are possible on Monday as the atmosphere will feature more upper-air disturbances moving through the region.
The latest radar image shows lots of “blue” around the Great Lakes. Indeed, today’s cold air outbreak will be accompanied by a good deal of “lake-effect” snows in and around the Great Lakes with the incoming colder air mass moving over the relatively warm waters. Map courtesy WSI (intellicast.com), NOAA
On Tuesday, the cold air will generally hold its ground and a frontal boundary zone oriented NW-to-SE may develop some precipitation along it as warmer air from the south and west tries to advance into the colder air to the north and east. As a result, there will be a chance for a bit of rain, ice or snow in parts of the Mid-Atlantic region by later Tuesday night or Wednesday before the advancing milder air wins out later next week.
One final note, this will very likely not be the final serious cold air outbreak of the season for the northeastern states as signs point to additional cold blasts going through the beginning part of April.
Meteorologist Paul Dorian
Arcfield
arcfieldweather.com