Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* a beautiful saturday followed by a stormy sunday *

1:30 p.m. Friday, August 14, 2026, Update:

The last few days have provided residents of northern MD and southeastern PA with a much-needed reprieve from the recent onslaught of showers and locally heavy, drenching thunderstorms. A quasi-stationary frontal boundary draped from the Ohio Valley through the southern mid-Atlantic States has served as the "train tracks" for several violent thunderstorm complexes, or Mesoscale Convective Systems (MCS), since Tuesday. Fortunately, the activity has remained southwest of the Lower Susquehanna Valley, and this afternoon will be no exception. One last disturbance moving southeastward along the boundary may graze areas between Interstate 70 and the Mason-Dixon Line with a few brief showers through 5-6 PM, but areas farther north should remain dry (see below). Overall, the week is ending on a partly-to-mostly cloudy, dry and relatively pleasant note with high temperatures in the mid 80s for most. Light, northerly flow has also ushered slightly less humid air into the region, and dewpoints will hover in the low-to-mid 60s through this evening (see below).

Skies will clear rapidly during the late-afternoon and early-evening hours, and the first half of the weekend is shaping up to be absolutely spectacular in terms of the weather. After a mainly clear and mild Friday night with lows in the mid-to-upper 60s, Saturday will turn out mostly sunny and seasonably warm with low humidity. It's hard to ask for more comfortable conditions than high temperatures in the mid 80s and dewpoints around 60°F in mid-August. A high pressure system of Canadian origin will settle into the Northeast on Saturday and promote the beautiful weather (see below). If you have outdoor activities planned this weekend, Saturday will certainly be ideal and the better day (by far) for them. Just make sure to lather on the sunscreen!

Unfortunately, the weather will do a "total 180" during the second half of the weekend. Clouds will increase Saturday night in advance of an approaching storm system, and widespread showers and thunderstorms are then expected on Sunday. The exact path of the system is still somewhat uncertain, but it will essentially be another long-track MCS. The MCS will actually originate in Iowa and Illinois later this afternoon and evening and then move slowly east-southeastward in the 24-48 hours to follow. At this point, its most likely path will be through the upper Ohio Valley from Saturday into Saturday night and then Pennsylvania on Sunday. The most widespread storms and heaviest rain may actually impact the Lower Susquehanna Valley between ~7 AM and 1 PM on Sunday. In terms of severe weather potential, that's a good thing due to a lack of instability during the morning hours. The MCS will likely stabilize the atmosphere enough to prevent a second round of storms from developing later Sunday afternoon and evening. I won't rule out some additional showers during that time, but the activity should not be widespread or intense. The main threats from Sunday's storms will be lightning, heavy rainfall and localized flash-flooding of low-lying, urban- and poor-drainage areas. Most areas will pick up 0.50-1.00" of rain from the system with locally higher amounts up to 2" through Sunday evening (see below). Despite the recent surplus of rain, parts of the region are still in a moderate-to-severe drought, so the rain will be largely beneficial. That being said, expect reduced visibility and standing water on some roadways on the drive to-and-from Sunday morning church services. Drive within the speed limit to minimize the risk of hydroplaning or an accident, and grab an umbrella before heading out the door. Due to the clouds and wet weather, high temperatures may struggle to exceed the 80-degree mark Sunday afternoon despite higher humidity.

Looking ahead into early next week, northwesterly winds should usher much drier and less humid air into the mid-Atlantic States behind the MCS. A weak cold front will move through the Commonwealth Sunday night, and Monday may actually turn out quite nice with gradually lowering humidity under partly-to-mostly sunny skies. A sprawling high pressure system is then expected to settle into the Ohio Valley on Tuesday and shift into the mid-Atlantic States by Wednesday, so another welcome stretch of dry weather is a "good bet". Due to mainly clear skies, light winds and low humidity, overnight lows will be quite comfortable by mid-August standards and generally in the low-to-mid 60s on Monday and Tuesday nights. Afternoons will be warm but temperate with highs in the mid 80s on Monday/Tuesday and upper 80s Wednesday. Thereafter, southwesterly flow may return on Thursday and usher hotter and more humid air back into the region, but uncertainty in the forecast increases dramatically late next week. Regardless, any 90-degree days appear sparse and widely separated in the foreseeable future, and I doubt many of you will be complaining about that! Check back Tuesday for an update. -- Elliott

12:15 p.m. Tuesday, August 11, 2026: 

Following a partly-to-mostly sunny, hot and humid end to the weekend, more showers and thunderstorms rumbled through northern MD, southeastern PA and the Lower Susquehanna Valley on Monday. One round impacted south-central PA during the morning with the second right on its heels between 1-6 PM. Along with locally heavy rainfall and frequent lightning, the storms caused numerous downed trees and powerlines, as well as nickel- to quarter-sized hail, in parts of the region. Most areas received 0.50-1.00" of rain from the storms, but the I-83 corridor was hit particularly hard with 1-2" of rain. On the other hand, southeastern PA missed out on the worst storms, and just 0.36" of rain fell at Millersville University (see below).

Following some early-morning showers, this afternoon will turn out partly-to-mostly cloudy and generally dry. A Mesoscale Convective System, or MCS, is moving southeastward through Ohio and the central Appalachians at the time of this writing, and another is right on its heels across northern Illinois and Indiana. Showers and storms associated with the first MCS will stay well south of Interstate 70, and rarely do any additional thunderstorm complexes track farther north/east in the absence of a warm frontal boundary. This case should be no exception, so I only expect a few showers to graze northern MD and southeastern PA tonight (see below). Due to high amounts of moisture and instability in the atmosphere, a shower or thunderstorm separate from each MCS may pop up across parts of the Commonwealth later this afternoon and evening. However, most if not all of the day should be dry across the Lower Susquehanna Valley with high temperatures in the mid-to-upper 80s and dewpoints around 70°F (see below). The only threat from tonight's showers and any rogue thunderstorm will be locally heavy rainfall, but most areas will likely pick up 0.10-0.25" or less through Wednesday morning. Similar to the last few nights, temperatures will bottom out in the mid 60s to around 70°F tonight.

Behind tonight's disturbance, a bubble of high pressure will settle into southern New England and promote decreasing clouds, drier and less humid weather on Wednesday with dewpoints in the low-to-mid 60s and high temperatures in the mid-to-upper 80s. After a partly cloudy and mild Wednesday night with lows in the mid-to-upper 60s, west-southwesterly flow will then return on Thursday and boost dewpoints back into the upper 60s to perhaps 70°F. Temperatures should peak around or just shy of 90°F Thursday afternoon under partly sunny skies (see below). I won't rule out an isolated shower Wednesday night and again on Thursday, but most areas should remain dry. 

Uncertainty in the forecast increases late this week, but odds favor the passage of a weak cold frontal boundary later Thursday night or Friday morning. Some numerical computer models suggest a slower frontal passage and another round of showers/storms on Friday, but most indicate a partly sunny, dry and seasonable end to the week with lowering humidity and high temperatures in the mid 80s Friday afternoon. Given the track of today's MCS and gradual southward/westward progression of the quasi-stationary frontal boundary over the Ohio Valley and central Appalachians, I favor the model consensus of a dry and relatively pleasant Friday north of I-70. Behind the front, a high pressure system of Canadian origin is expected to settle into the Northeast during the first half of the weekend. If so, then Saturday will turn out mostly sunny and a bit cooler with low humidity (50s dewpoints) and no chance of rain. High temperatures should be in the comfortable low 80s Saturday afternoon following a mainly clear and refreshingly cool Friday night with lows around 60°F. Saturday night should also be ideal for sleeping with the windows wide open before warmer and more humid air returns on Sunday. The timing of another cold front will be key in determining our weather later Sunday into Monday, but only a foolish meteorologist would venture to give precise details at this distance. In an active pattern such as this, timing individual thunderstorm complexes and cold frontal passages is nearly impossible outside of just 1-2 days. Thus, I'll "punt" on the Sunday-Monday forecast for now and provide an update on Friday. Stay tuned! -- Elliott