Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* warm and relatively tranquil pattern through end of april *

11:00 a.m. Friday, April 25, 2025, Update:

The weather has been nothing short of spectacular across northern MD, southeastern PA and the Lower Susquehanna Valley this week! A sprawling high pressure system of Pacific origin has promoted mostly sunny skies, low humidity and pleasantly warm conditions with highs in the mid 70s on Tuesday, mid-to-upper 70s Wednesday and upper 70s to low 80s Thursday. The high is still located over the western Atlantic today, so partly sunny and warm conditions will continue to grace the region on our "TGIF" with highs in the mid-to-upper 70s. However, clouds will gradually lower and thicken later this afternoon well ahead of an approaching cold front. The front will traverse the mid-Atlantic States from northwest-to-southeast spanning tonight through Saturday afternoon. Widespread showers and embedded thunderstorms will erupt along and well in advance of the front, but I don't anticipate any severe weather. Winds both at the surface and aloft are and will remain relatively light through Saturday morning, and clouds will greatly limit instability. In addition, the upper-level energy associated with the front will trek through southeastern Canada and New England this weekend and be displaced too far north/west from the surface front. Dewpoints should creep into the low-to-mid 60s later tonight through Saturday morning, so some of the storms will produce locally heavier downpours and cause areas of reduced visibility on the roads. The most concentrated activity will impact areas between I-81 and I-95 overnight, but a second round of storms should erupt Saturday afternoon after a relative lull during the morning hours. These storms will likely initiate near I-83 and Routes 11/15 before intensifying upon their southeastward journey toward I-95. The front/storms should finally push east of Washington, D.C., to Philadelphia between 6-8 PM. Through Saturday afternoon, most areas will receive 0.25-0.50" of much-needed rain with locally higher amounts up to 1.00-1.25" (see below). Be alert for standing water in some low-lying, poor-drainage and urban areas, and keep an umbrella handy over the next 24-36 hours. The timing of the storms isn't ideal, but we'll take whatever we can get.. and whenever we can get it! A wildfire broke out in Cumberland County on Thursday, and the rain should help firefighters with containment efforts and prevent new fires. Both fuels (leaves, grass, brush, etc.) and the ground are exceptionally dry, and the risk of wildfire development and spread will continue to be heightened in the absence of much rain.

Despite tomorrow's showers and storms, high temperatures should still peak in the mid-to-upper 70s prior to the frontal passage. Behind the front, skies should clear during the mid-to-late afternoon hours, and northwesterly winds of 15-30 mph with gusts up to 40 mph will then usher cooler and much drier air into the Commonwealth from Saturday night into Sunday. Dewpoints will tumble by ~30°F in less than 24 hours, ultimately ending up in the low-to-mid 30s by Sunday morning. The gusty winds should prevent temperatures from falling below the mid-to-upper 40s Saturday night, and highs will still reach the mid 60s to perhaps 70°F Sunday afternoon thanks to abundant sunshine (see below). It will definitely feel cooler outside compared to most days this week, but high temperatures in this range are actually "normal" for late April. The ongoing stretch of 70-to-80-degree warmth is what's unusual..

Anyhow, a Canadian high pressure system will settle over the Commonwealth from Sunday night into Monday before shifting into the western Atlantic during the middle of next week. As such, the last week of April will start on a gorgeous note! Sunshine and light winds will accompany highs near 70°F Monday afternoon, and dewpoints will still only be in the 30s. Low temperatures should be in the crisp low-to-mid 40s Sunday night and comfortable upper 40s to low 50s Monday night, as well, under clear skies. Thereafter, southwesterly flow on the backside of the high will direct another surge of unseasonably warm air into the region. I still expect high temperatures to soar into the 80s on Tuesday, but a cold front sweeping southeastward from the Great Lakes region will likely cut the anomalous warmth short and limit it to 1-2 days. The cold front may trigger a severe weather outbreak across the Ohio Valley and western NY/PA Tuesday afternoon and evening, but the storms should rapidly weaken and collapse south/east of the Appalachian Front later Tuesday night. At this point, the frontal passage will most likely occur on Wednesday morning in northern MD, southeastern PA and the Lower Susquehanna Valley. As a result, the region should be spared from any severe weather, and Wednesday's round of storms will probably fire up south of I-70 and east of I-95. If so, then Wednesday will turn out partly sunny and less humid.. but still rather warm.. with highs in the upper 70s to low 80s. Uncertainty in the forecast increases dramatically late next week, but odds favor a partly-to-mostly cloudy and seasonable Thursday (highs around 70°F) followed by another round of showers and storms on Friday. A Canadian high pressure may briefly settle into the Northeast on Thursday before the next storm system takes aim at the Ohio Valley and eastern Great Lakes region on Friday. However, the timing of these features and details of the forecast can and very likely will change over the weekend, so check back on Tuesday for an update! -- Elliott

11:30 a.m. Monday, April 21, 2025:

After an unseasonably warm start to Easter Weekend with highs in the upper 70s to mid 80s Saturday afternoon, a cold front sagged southward through the mid-Atlantic States Saturday night. Northerly winds of 10-20 mph ushered cooler air into northern MD, southeastern PA and the Lower Susquehanna Valley on Sunday, but high temperatures still reached the upper 60s to low 70s under partly sunny skies. Quite frankly, we couldn't have asked for better weather on Easter! 

In stark contrast to yesterday, the week is starting on a mostly cloudy note due to moist, southeasterly flow of 12-25 mph on the backside of a high pressure system over the western Atlantic. Despite the clouds, high temperatures will be near normal, or in the mid 60s to low 70s, from northeast-to-southwest across the region this afternoon. A storm system currently centered over the northern Great Lakes region will trek into southeastern Canada over the next 24 hours, and a weak, trailing cold front will traverse the mid-Atlantic States from west-to-east spanning this afternoon through tonight. However, only scattered showers should accompany its passage in northern MD and south-central PA with perhaps an embedded rumble or two of thunder north/west of I-81. I don't expect any severe weather due to poor (overnight) timing of the front, a lack of instability, and virtually no difference in temperature from one side of the front to the other. Showers should remain west of the Lower Susquehanna Valley until 6 PM and impact most areas between ~8 PM this evening and 3 AM Tuesday. The showers will push east of the I-95 corridor before daybreak, so the Tuesday morning commute won't be adversely affected by the weather. Rainfall amounts south/east of the Appalachian Front will generally remain below 0.25", but up to 0.50" could fall in a few spots north/west of I-81 (see below).

Behind the "cold" front, temperatures will actually be higher tomorrow than today on account of downsloping, westerly winds of 10-20 mph off the Appalachians. Temperatures will only bottom out in the mid-to-upper 50s tonight due to extensive cloud cover, but skies should rapidly clear early Tuesday morning. A thin veil of cirrus clouds may dim the sun a bit throughout the day, but high temperatures will still soar into the low-to-mid 70s north/west of I-81 to around 80°F along I-95. A high pressure system of Pacific origin will settle into the Northeast and mid-Atlantic States from Wednesday into Thursday and promote a continuation of mostly sunny and pleasantly warm conditions with highs in the 70s and lows in the mid-to-upper 40s (see below). The high will shift into the western Atlantic on Friday, but the week should still end on a partly sunny and dry note with highs in the 70s. With the high nearby or directly overhead, winds will be light on Wednesday and Thursday.. a welcome change from the seemingly continuous onslaught of blustery conditions so far this year. They'll turn south-to-southeasterly at 10-20 mph on Friday and remain like that through Friday night. The southerly flow will also pump more moisture into the region, so dewpoints may briefly climb into the low-to-mid 60s later Friday night and/or Saturday. Overall, this week's weather will be ideal for outdoor activities and a harbinger of things to come for the rest of spring and summer. As a warm-weather fan, I couldn't possibly be happier or more excited! 😊

Another storm system is expected to develop in the Midwest from Thursday night into Friday and track into New England by Saturday. To its south, a trailing cold front should sweep through the Commonwealth later Friday night through Saturday. Exact timing of the front is uncertain, but skies should turn mostly cloudy again Friday night before showers and perhaps a few thunderstorms arrive Saturday morning. At this point, the probability of severe weather appears low, but that could change if the front slows down by just 3-6 hours. As for temperatures, we'll be treated to an unseasonably warm Friday night with lows in the upper 50s to low 60s, but highs on Saturday should be "near normal" thanks to the clouds and wet weather. Be prepared to move outdoor activities inside for several hours, and keep an umbrella handy throughout the day. A widespread 0.25-0.50" of rain seems like a good first estimate for amounts on Saturday. Behind the front, winds will turn northerly on Sunday and usher drier and somewhat cooler air into the Commonwealth. Honestly, next Sunday's weather could be a virtual "rinse and repeat" of the weather on Easter. Dewpoints will tumble into the 30s or low 40s by Sunday morning, and mostly sunny skies should accompany highs in the mid 60s to perhaps 70°F during the afternoon hours. A Canadian high pressure system is then expected to settle over the Commonwealth from Sunday night through Monday before shifting into the western Atlantic during the middle of next week. As such, the last week of April will start on a beautiful note with sunny skies and light winds accompanying highs near 70°F Monday afternoon. Low temperatures should be in the crisp 40s Sunday night and comfortable low-to-mid 50s Monday night, as well. Thereafter, southwesterly flow on the backside of the high will direct another surge of unseasonably warm air into the region. Although not a "lock," high temperatures will probably soar into the 80s at least once or twice between next Tuesday-Friday, and we shouldn't have to worry about more showers/storms until late in the week. I'll take it!

As a whole and in aggregate, the Jet Stream will continue to exhibit a pronounced northward bulge over the Eastern States through the beginning of May. The final piece of the Tropospheric Polar Vortex (TPV) has settled over northwestern Canada and will remain over northern portions of the country through month's end. As a result, the last vestiges of winter's chill will fade over western parts of North America in the next few weeks. By contrast, unseasonably warm weather will "run rampant" over the eastern United States. In other words, spring is finally here to stay, and there may not even be a sub-40°F low temperature across northern MD and the Lower Susquehanna Valley until autumn. High temperatures should be in the 60s, 70s, and 80s most afternoons going forward, and I don't expect any more prolonged or noteworthy "cold shots" until October or November. Additionally, the Jet Stream should be relatively weak and located over New England or southeastern Canada for the majority of the next 1-2 weeks. Thus, our abnormally dry and tranquil pattern will continue with no "big rainmakers" in the foreseeable future. Bouts of scattered showers/thunderstorms will be separated by several or more days, and any severe weather should be highly localized. Overall, the weather pattern looks about as warm and quiet as possible for this time of year. That's good news for outdoor enthusiasts but bad news in terms of the drought. Instead of improving, it will only worsen in the days and weeks to come. The old saying "drought begets drought" continues to play out in real time. Not good heading into the summer months.. -- Elliott