Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Typical, "Up-and-down" March Pattern With Beneficial Rain on Wednesday *

12:30 p.m. Tuesday, March 4, 2025:

The first week of March kicked off on a sunny but chilly note with high temperatures around 10°F below normal Monday afternoon. However, a warm front moved through the mid-Atlantic States early this morning, and southerly winds have since ushered substantially milder air into northern MD, southeastern PA and the Lower Susquehanna Valley. In stark contrast to yesterday, high temperatures this afternoon will be around 10°F above average, or in the mid-to-upper 50s for most. Following a partly-to-mostly sunny afternoon, clouds will return tonight ahead of an approaching storm system. As discussed last week, the southerly flow will pump a deep fetch of moisture originating from the Gulf of America and southwestern Atlantic into the region tomorrow. Dewpoints will rise dramatically (by ~20-25°F) over the next 24 hours and peak in the low 50s Wednesday afternoon and evening. Despite cloudy skies and wet weather, unseasonably mild conditions will also persist over the next 42 hours with highs in the mid 50s to perhaps 60°F tomorrow afternoon and lows in the upper 30s to mid 40s both tonight and Wednesday night.

A powerful storm system currently centered over the south-central Plains will track northeastward into the Great Lakes region over the next 24-36 hours and then reach southeastern Canada on Thursday. The entire mid-Atlantic region will be in the system's warm sector and experience a soaking rain event. A single storm system has not produced liquid equivalent precipitation of 0.50" or more at Millersville University since December 11, 2024, but that should change tomorrow. A few showers may reach northern MD and western parts of the Lower Susquehanna Valley later tonight, but steadier rain and embedded thunderstorms should hold off until the mid-to-late morning and afternoon hours. In fact, there may be very few weather-related issues across the region during the morning commute, but the same cannot be said for the afternoon one. There may actually be a brief lull in the action during the PM commute, especially west of Route 11/I-83, and during the early-evening hours farther east. However, a cold front trailing southward from the storm system will cross the region Wednesday evening and produce another round of showers and embedded thunderstorms. The wet weather will finally taper off and push east of the I-95 corridor later Wednesday night. Regardless of the system's exact evolution, most areas will receive 0.50-1.00" of rain with up to 1.50" in the hardest-hit locations. Due to the ongoing, moderate-to-severe drought, the rain is much needed and most welcome (see below). Motorists should be alert for standing water in low-lying, urban and poor-drainage areas Wednesday afternoon and evening, as well as slow travel on highways and interstates, but the benefits of the rain will far outweigh its impacts. Just make sure to keep an umbrella and rain gear handy at all times tomorrow. 

In addition to the rain, south-to-southeasterly winds of 15-30 mph with gusts up to 40-45 mph will buffet the region tomorrow. The Storm Prediction Center (SPC) has also placed northern MD and the Lower Susquehanna Valley in a "slight risk" for severe weather, but I personally don't see much potential for it. Winds around 5,000 feet above the ground will be very strong and on the order of 70-90 mph, but a low-level temperature inversion (↑ temperatures with ↑ height above the ground) should keep the surface layer of the atmosphere "separated" from layers above it. Essentially, it would take a powerful line of thunderstorms with heavy rainfall and strong downdrafts to drag the wind energy, or momentum, from the mid-levels down to the ground, and I don't expect that to happen (see below). The atmosphere won't be unstable ahead of the cold front due to dense cloud cover and relatively low dewpoints, so that's yet another reason for my skepticism on the severe weather threat. It may be a different story south/east of I-95 and west of the Appalachian Front, but areas in between should be spared from damaging wind gusts. 

Behind Wednesday night's cold frontal passage, the week will end on a drier, cooler and more seasonable note with highs in the upper 40s to perhaps 50°F on Thursday and Friday. Winds will turn northwesterly and strengthen again on Thursday after a brief lull Wednesday night. Peak gusts should be similar to Wednesday and in the 40-45 mph range. Factor in mostly cloudy skies, and it will definitely feel chillier outside than the actual air temperature suggests on Thursday. Tie down loose objects and be alert for downed tree limbs and debris on roadways over the next two days, but any power outages will likely be spotty/isolated. It will still be brisk on Thursday night but not as brutal as during the daytime hours. Temperatures and wind chills should only bottom out in the upper 20s to low 30s and teens or low 20s, respectively, Thursday night, and that's not out of the ordinary in early March. March is indeed known for its strong winds, so the blustery conditions are simply "par for the course." Winds should continue to slacken on Friday as a bubble of high pressure briefly nudges into the mid-Atlantic States. In addition, skies should clear Thursday night and be partly-to-mostly sunny on Friday. Thus, the first Friday in March should be favorable for outdoor activities with only a light jacket or sweatshirt. I'll take it!

Looking ahead to the upcoming weekend, a fast-moving, moisture-starved disturbance may zip eastward along or south of I-70 from Friday night into Saturday. It could bring a few rain and snow showers to parts of the region during that time, but the system should become even more disorganized east of the Appalachians. The system will also be running into strong, upper-level confluence and subsequent sinking motion along the Eastern Seaboard. As a result, very little if any precipitation should reach areas south/east of I-81. Needless to say, I anticipate no accumulating snow through the end of the weekend and all of next week. Behind the disturbance, northwesterly winds of 12-25 mph will usher a reinforcing shot of cooler air into the region, but high temperatures should still only be around 5-10°F below average.. or in the low-to-mid 40s.. on Saturday. Another clipper-type disturbance or two will likely zip across the northern tier of the nation from the Great Lakes region to New England spanning Sunday-Monday. The exact track of each disturbance is still rather uncertain at this distance, but both will be starved for moisture and fail to bring more than a few sprinkles to the Lower Susquehanna Valley. Instead, we should be in both systems' warm sectors and well south of their track. If so, then partly-to-mostly sunny skies and west-to-southwesterly winds would accompany highs in the low-to-mid 50s both Sunday and Monday. Overnight lows will likely be in the 20s Saturday night, but they could be in the balmy 30s or 40s by Sunday and/or Monday nights. Even warmer air should then surge into the mid-Atlantic States by the middle and latter parts of next week. The Jet Stream will undergo a major reconfiguration and exhibit a pronounced, northward bulge over the Eastern States in response to a deep trough along the West Coast. With plenty of sunshine and dry air in place, high temperatures should easily soar into the 60s and perhaps even low-to-mid 70s on at least one or two days next week. As a warm-weather lover, I couldn't be more excited. Spring mode: activated! -- Elliott