Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* a breezy and cooler week, but quiet in terms of rainfall *

12:45 p.m. Monday, October 20, 2025:

As expected, a line of heavy, gusty showers accompanied Sunday night's cold frontal passage and dumped 0.25-0.50" of beneficial rain across most of northern MD and the Lower Susquehanna Valley. Slightly less rain fell across southeastern PA, while parts of Franklin County received up to 0.75" (see below). The front moved through Millersville University around 11 PM Sunday evening and pushed east of the I-95 corridor by 2 AM this morning. In its wake, westerly winds of 12-25 mph with gusts up to 40 mph have ushered much cooler and drier air into the Commonwealth. After an unseasonably warm Sunday with high temperatures in the mid 70s, they'll peel back to around normal (low-to-mid 60s) this afternoon. Clouds will continue to dissipate throughout the rest of the day, as well (see below). Be alert for blowing objects and debris, such as small tree limbs, trash cans and holiday decorations, on roadways through the PM commute. In addition, keep a tight grip on the wheel, especially on north-south oriented highways and interstates. A bubble of high pressure will then settle into the mid-Atlantic States tonight and cause winds to subside quickly between 6-9 PM. Due to clear skies and light winds overnight, temperatures should fall rapidly and bottom out in the upper 30s to low 40s early Tuesday morning.

Breezy conditions will return Tuesday afternoon in advance of a weak cold front. The 10-20 mph southerly breeze will usher warmer air back into northern MD and southeastern PA (albeit briefly), and high temperatures should reach the upper 60s to low 70s! After a sunny morning, clouds will increase during the afternoon hours, but no more than a stray shower or two should accompany the frontal passage Tuesday evening (see below). Compared to last night's front, tomorrow's will be much weaker and more starved for moisture. Thus, rainfall amounts should not exceed a few hundredths of an inch in any location.

Behind the front, another round of gusty, westerly winds will usher cooler and more seasonable air back into the region on Wednesday, and the chilly air mass will then stick around through the upcoming weekend. A deep trough, or dip in the Jet Stream, will develop across southeastern Canada and the eastern United States in response to a substantial ridge over the Rockies and High Plains. In addition, a closed-off, upper-level low will track from the Great Lakes region into southeastern Canada spanning Tuesday into Wednesday and then "camp out" there through the end of the week. The mid-Atlantic States will be on the southern periphery of the chillier air mass, but high temperatures from Wednesday-Sunday should still be a few degrees below normal. A tight pressure gradient, or difference in pressure, between the upper low over southeastern Canada and a high pressure system over the Central States will be responsible for a continuation of relatively windy conditions. Westerly gusts from Wednesday-Friday probably won't be quite as high as this afternoon, but sustained winds will likely still be between 12-25 mph each afternoon with gusts up to 30 mph. The combination of chilly air in the mid-levels of the atmosphere and westerly flow over the still-warm waters of the Great Lakes will lead to lake-effect rain showers across the higher terrain of northern and western PA. While only a few sprinkles should reach the Lower Susquehanna Valley on Wednesday and Thursday afternoons, morning sunshine will be of the "self-destruct" variety and give way to afternoon clouds. With the loss of daytime heating, clouds will then dissipate around or shortly after sunset each evening, and winds will slacken. As a result, high temperatures will only be in the low 60s on Wednesday, near 60°F on Thursday and in the upper 50s Friday. Overnight lows should be in the seasonably chilly low-to-mid 40s Wednesday night, near 40°F Thursday night and in the upper 30s Friday night. The blustery conditions will make the outdoor air feel even chillier late this week, so grab a jacket or sweatshirt before heading out the door to work or school. Tie down loose objects and holiday decorations, as well, to prevent them from being blown away by the wind. 

The aforementioned high pressure system is expected to shift into the mid-Atlantic States on Saturday. As a result, I expect the weekend to start on a mostly sunny, pleasantly cool and much calmer note. After a cold start, high temperatures may still struggle to reach or exceed the 60-degree mark Saturday afternoon, but the combination of sunshine and very light winds should help to at least partially mitigate the chill. The high pressure system may then shift into the western Atlantic by Sunday and remain centered there early next week. If so, then southerly flow on its backside would usher increasingly warm and more humid air into the Commonwealth from Sunday-Tuesday. Uncertainty in the forecast increases dramatically during that time, but it's a "good bet" that clouds and perhaps a few showers return on Sunday and stick around through Monday. I'll refine and finesse the weekend forecast on Friday, so check back then for an update! To my dismay, summer warmth is now gone, and that "fall feeling" in the air is here to stay.. 🙁 -- Elliott