Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* More Frost Concerns Late This Week *

11:30 a.m. Tuesday, April 23, 2024:

After a windy but pleasant start to the weekend, an unseasonably cool air mass settled into the mid-Atlantic States on Sunday following a secondary cold frontal passage. A thick, mid- and upper-level cloud deck blotted out the sun on Sunday and prevented high temperatures from exceeding the low 50s.. some 15°F below average for late April. Skies then cleared on Sunday evening, and the combination of clear skies and light winds allowed temperatures to plunge into the 30s early Monday morning. Under sunny skies, highs rebounded into the more comfortable low 60s Monday afternoon, but residents in many outlying areas woke up to another frosty start this morning. Frost Advisories were in effect from 2-8 a.m. for northern MD and southeastern PA each of the last two mornings, and I expect at least one more widespread frost late this week. Before then, today will turn out warmer and more pleasant with only a few high clouds in the sky at times. A south-to-southwesterly breeze of 10-20 mph to the north of a high pressure system centered over the Carolinas is directing the warmer air mass into the Commonwealth. As of 11 a.m., temperatures were already in the low-to-mid 60s across most of south-central PA, and highs will top out in the upper 60s to perhaps low 70s this afternoon. Needless to say, it will be a great afternoon for outdoor activities, but allergy sufferers are and will continue to "take it on the chin" with pollen counts through the roof after our recent explosion of spring flowers/foliage. I for one can't stop sneezing the last few days.. 🤧

Skies will turn mostly cloudy this evening in advance of a weak cold front dropping southeastward from the Great Lakes region. An isolated shower or two may impact parts of the Lower Susquehanna Valley late tonight and again Wednesday afternoon, but many areas will remain dry. The air mass ahead of the front will be starved for moisture, and the atmosphere should remain quite stable Wednesday afternoon. Thus, I don't expect more than a rumble or two of thunder in one or two spots, and the bulk of the showers will be light and widely separated. In fact, most areas will receive a few hundredths of an inch of rain or less, and outdoor activities should not be interrupted for more than 15-30 minutes (at most). The front will not move through southeastern PA until Wednesday evening, so high temperatures should still reach the mid-to-upper 60s complements of partial sunshine and a downsloping, 12-25 mph northwesterly breeze. Tonight's lows will also be much higher than the last few nights and generally in the upper 40s to mid 50s.

Behind the front, a Canadian high pressure system will build into the Northeast from Wednesday night through the end of the week. Winds will turn northerly Wednesday night and usher another unseasonably cool air mass into the mid-Atlantic States. Due to clearing skies and diminishing winds Wednesday night, patchy frost is possible in outlying areas early Thursday morning. However, the better chance for widespread frost will come early Friday morning with the high positioned just north of the Commonwealth. Despite mostly sunny skies, high temperatures will be around 10 degrees below normal Thursday afternoon, or generally in the upper 50s to around 60°F. Yet again, they won't have too far to fall Thursday night for frost/freeze concerns early Friday morning, and I expect widespread Frost Advisories to be issued by the National Weather Service between ~2-8 a.m. Friday. Additionally, sub-freezing (30-31°F) temperatures are a real possibility in the coldest valleys and most outlying areas (see below). Residents in these locations should be sure to apply a protective covering to sensitive plants/vegetation or bring them inside before going to bed. That will ensure their protection from being damage or killed. Fortunately, temperatures will rebound quickly on Friday under mostly sunny skies, and the afternoon should turn out quite pleasant with highs similar to Monday (low 60s). 

Looking ahead into the upcoming weekend, we will deal with "a tale of two days" yet again. After a partly cloudy and chilly Friday night with lows still in the upper 30s to low 40s, a warm front will traverse the Commonwealth from southwest-to-northeast on Saturday and bring more showers to the state. Showers will be most widespread in western and northern parts of PA, but at least some intermittent showers should dampen the Lower Susquehanna Valley throughout the day. High temperatures will be confined to the low-to-mid 60s, at best, on account of the clouds and showers. However, another burst of 80-degree warmth won’t be far behind. Following the warm frontal passage, an upper-level ridge, or northward bulge in the Jet Stream, will amplify over the eastern United States from Sunday through early next week. Southwesterly winds will usher an unseasonably warm air mass into the mid-Atlantic States by Sunday, and highs should soar into the upper 70s to low 80s under partly sunny skies. With the ridge firmly in control of our weather, low temperatures will also be way above normal Sunday night and generally in the 50s or even low 60s. Humidity will also be on the rise as evidenced by dewpoints in the upper 50s to low 60s from Sunday through Tuesday. By all intents and purposes, it will feel like the heart of summer outside on Monday with highs well into the 80s. With enough sunshine, the record high of 87°F from 1974 at Millersville University could be in jeopardy.

After a warm and muggy Monday night with lows likely in the 60s, the next round of showers and thunderstorms should arrive later Tuesday or Tuesday night ahead of an approaching cold front. The exact timing of the front will have an impact on Tuesday’s high temperatures and determine whether severe weather could be a concern or not. However, those details will remain nebulous until late this week, so stay tuned for an update on Friday. Once thing is for certain: May does not look cool, and there should be no more frost or freeze concerns south of I-80/east of I-99 after this week. The warm-biased pattern we’ve been enjoying since last fall will persist next month, and I expect aggregate temperatures to end up around 2-4 degrees above normal in May. It should be a warm-weather lover’s paradise on most days, and I'm oh so ready for that! 😎 -- Elliott