Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* A Breezy and Showery Weekend, but heavier rain stays east *

11:45 a.m. Friday, October 10, 2025, Update: 

As anticipated, the first frost of the season occurred in many rural parts of northern MD, southeastern PA and the Lower Susquehanna Valley between 3-8 AM this morning. Temperatures bottomed out at 32°F at York Airport, 35°F at Millersville University, 38°F at Lancaster Airport and 39°F at Harrisburg International Airport. Fortunately, temperatures rebounded quickly after sunrise, and highs will reach the pleasantly cool low-to-mid 60s this afternoon (see below). An area of high pressure centered along the southern New England coastline will also promote mostly sunny and dry conditions on our TGIF, so get outside and enjoy after work or school!

Following a partly cloudy and seasonably cool Friday night with lows in the 40s, Saturday will turn out mostly cloudy but slightly milder with highs in the mid 60s to perhaps 70°F. Moist, easterly flow on the backside of the high pressure system will be responsible for the enhanced cloud cover, and an upper-level low pressure system tracking slowly eastward through northern PA and southern New England will then bring scattered showers to the region from Saturday afternoon into early Sunday morning. There has been talk on social media of a "powerful Nor'easter" over the weekend, but northern MD and southeastern PA will likely be on the system's western periphery and receive minimal amounts of rain through Monday. The upper-level low to our north would have to "phase," or join forces, with the low pressure system off the Carolina coastline by Saturday night or Sunday for heavier rain across our region, and that seems highly unlikely. Instead, there may be a relative "lull" in the wet weather during the daylight hours on Sunday before steadier, light rain or more widespread showers return Sunday night into Monday. The coastal storm should creep north-northeastward off the Carolina and mid-Atlantic coastline during the second half of the weekend and ultimately end up off the Delmarva or New Jersey coastline by Sunday night. Thereafter, the system could essentially stall there for 12-18 hours before finally making a "right turn" out-to-sea on Tuesday. 

Rainfall amounts from Saturday afternoon through Monday night may slowly increase from northwest-to-southeast across northern MD, southeastern PA and the Lower Susquehanna Valley. However, higher and more significant rainfall totals should occur south/east of I-95, and the distribution of rainfall amounts locally will depend on the exact track of the upper-level low and location/intensity of Saturday night's showers. At this point, I expect rainfall amounts to remain below 1" in areas north/west of I-95, and less than 0.50" may fall across most of the region. We may end up in the "subsidence zone" between the upper low and coastal storm from Sunday into Sunday night. If so, then rainfall amounts could actually be quite paltry across the region. Only time will tell! Regardless, you'll want to keep an umbrella handy throughout the entire weekend and be prepared to move inside at times. Fortunately, high temperatures should remain in the low-to-mid 60s both Sunday and Monday, so it won't be a particularly "cold rain." Dewpoints will rise back into the 50s tomorrow and remain there through early next week, so overnights will be much milder, too, with lows in the mid 50s Saturday night and low 50s Sunday/Monday nights. Northeasterly winds will also increase Saturday night, and they should be sustained at 12-25 mph with gusts up to 30 mph from Sunday through Monday night. Clouds will hang tough on Sunday and Monday on account of the northeasterly flow and proximity of the coastal storm, so it will certainly feel rather cool outside. Needless to say, you'll probably want to wear a jacket or sweatshirt while engaging in outdoor activities this weekend, and shorts/t-shirts certainly won't be the attire of choice for most. 

By the middle of next week, winds will turn northwesterly on the backside of the storm system and usher drier air into the Commonwealth. As a result, showers or light rain/drizzle should taper off Monday night, and skies may even turn partly sunny on Tuesday with highs still around average (mid 60s). Pesky, low-level moisture may prevent as much as clearing as I currently anticipate, but the weather will certainly turn much nicer on Wednesday as a bubble of high pressure settles into the mid-Atlantic States. Winds will also subside during the middle of the week, making it feel milder and more comfortable outside. Under mostly sunny skies, high temperatures may even reach or exceed the 70-degree mark Wednesday afternoon in advance of a moisture-starved cold front. No more than a stray shower or two will accompany that frontal passage Wednesday night, but another blast of chillier air will follow late next week. However, temperatures should still only be a few degrees below average next Thursday and Friday (low 60s), so the cool shot certainly won't make any headlines.. but fall is definitely here to stay now. Have a great fall break, Marauders, and check back next Tuesday for an update! -- Elliott

12:30 p.m. Tuesday, October 7, 2025:

In retrospect, the first week of October could certainly be classified as a "blowtorch" and virtual extension of summer. High temperatures have been in the low 80s across most of the Lower Susquehanna Valley since Saturday, and there has not been a day with a high temperature below 70°F since June 27th. In addition, no measurable rain has fallen at Millersville University since September 26th. However, both are about to change, and one in a big way. South-to-southwesterly winds of 10-20 mph on the backside of a high pressure system over the western Atlantic are still pumping unseasonably warm and humid air into the region this afternoon, but a much cooler, drier and more fall-like air mass is "waiting in the wings." High temperatures will still be around 80°F this afternoon.. about 10°F above average for early October.. with dewpoints around 60°F, but a cold front will sweep through the Commonwealth from tonight through Wednesday morning and put an end to our "extended summer." First, we'll receive some much-needed, beneficial rain along and just ahead of the front. Showers and some localized heavier downpours will impact northern MD and southeastern PA between ~6 PM this evening and 10 AM Wednesday. The showers will overspread the region from southwest-to-northeast between ~6-11 PM this evening, continue overnight and then taper off between ~6-10 AM Wednesday morning. Due to the abnormally dry conditions and parched ground, the rain will be largely beneficial (see below). The only real impacts to travel will be wet roadways and standing water in some low-lying, urban- and poor-drainage areas during the Wednesday morning commute. In terms of rainfall amounts, numerical computer models are all over the place. The ECMWF and ICON models suggest less than 0.50" of rain falls across most of northern MD and south-central PA, but the NAM and HRRR show as much as 1-2" of rain. Given the lack of instability and timing of the rain, I favor the lower amounts.. but only time will tell (see below)..

Behind the front, northerly winds of 12-25 mph will usher much cooler and drier air into the Lower Susquehanna Valley on Wednesday. After a mostly cloudy start, skies will gradually clear during the late-morning and early-afternoon hours (see below). In stark contrast to the last few days, high temperatures will be "near normal" on Wednesday (near 70°F) and then end up 5-10°F below average on Thursday (low 60s). The change in humidity will be even more extreme. Dewpoints should peak in the low-to-mid 60s tonight, tumble into the 40s by Wednesday evening and then bottom out in the upper 20s to low 30s Thursday night. Temperatures will only drop into the low-to-mid 60s tonight on account of the high humidity, clouds and showers, but lows will end up in the low-to-mid 40s Wednesday night under clear skies.

As mentioned above, Thursday will be the coolest day since late May despite abundant sunshine. It won't be as windy as tomorrow, but a north-northeasterly breeze of 8-16 mph will make the outdoor air feel even chillier. I then expect the first widespread frost of the season across northern MD and the Lower Susquehanna Valley Thursday night. A Canadian high pressure system will settle into southern New England and northern PA late this week and promote efficient, radiational cooling after sunset. Winds will be very light or calm Thursday night, and dewpoints should be in the upper 20s to low 30s under clear skies. Temperatures often bottom out near the dewpoint on clear, crisp fall nights, and this case should be no exception. In fact, temperatures may bottom out between 30-32°F in the deepest valleys and most outlying areas early Friday morning. They'll be significantly higher (38-40°F) in urban centers such as York, Lancaster and Harrisburg. In the majority of locations, lows will range from 32-36°F (see below). Regardless, the frost will likely put an end to the growing season in most spots, so bring tender plants/vegetation inside or apply a protective covering over them Thursday evening.

In terms of the weather, Friday will be virtually identical to Thursday with high temperatures in the low-to-mid 60s under sunny skies. Winds will be even lighter (5-10 mph or less), so it should feel slightly milder and more comfortable outside Friday afternoon. However, you'll definitely need to grab a jacket, sweatshirt or coat before heading out the door to work or school late this week and put shorts, t-shirts and flip-flops in the closet for awhile. Friday night won't be as cold with lows in the upper 30s to perhaps mid 40s, but it will take until the weekend for temperatures to be back around average. The aforementioned high pressure system will shift into the western Atlantic this weekend, and southeasterly flow on its backside should at least boost highs back into the mid-to-upper 60s from Saturday through early next week. There is some potential for a low pressure system to develop along or just off the southeastern U.S. or Carolina coastline over the weekend and then back into the mid-Atlantic States early next week, but the more likely outcome is for a track out-to-sea and continuation of partly-to-mostly sunny and pleasant conditions across the Lower Susquehanna Valley. Check back on Friday for an update on the potential system, and enjoy the "change of seasons" and "sweater weather" late this week. The "warm-weather party" is over.. ☹️ -- Elliott