... In the wake of a frontal passage, high pressure will build into the region for the balance of the holiday weekend, lingering across the eastern half of the U.S. into the middle of next week. A cold front will then approach from the Ohio Valley and Great Lakes Wednesday night into Thursday before an expansive area of high pressure builds eastward from the central U.S. leading into next weekend.
NEAR TERM /THROUGH TONIGHT/... The GOES-16 visible channel imagery shows the slow moving upper low centered over central New Jersey. The cooler air aloft within the cyclonic flow regime has led to a broad fair weather cumulus field. Closer to the better forcing, updrafts are slightly stronger over northeastern Maryland where some showers and a few lightning strikes have been observed. Any such activity should be focused closer to the Mason-Dixon Line through the afternoon and into the early evening hours. For the rest of the area, temperatures should be fairly close to late May normals. With the 12Z KIAD sounding depicting around 10C at 850-mb, a dry and well-mixed boundary layer will favor highs in the upper 70s. Compared to yesterday, dew points have dropped off by around 10 degrees leading to a drier feel to the air.
Heading into the evening and overnight, any cumulus will dissipate with the loss of daytime heating. Aside from some high clouds streaming overhead, tranquil conditions are anticipated at night. Some patchy fog is possible from I-81 westward where the lower troposphere can near saturation. Low temperatures are forecast to drop into the 50s to low 60s, locally near the upper 40s along the Allegheny ridgetops.
SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Heading through the remainder of the Memorial Day holiday weekend, the upper trough will exit well offshore. This allows upstream heights to build leading to a gradual increase in temperatures. The ridge axis settles over the Mid-Atlantic region on Monday with mid-level heights increasing to 588-mb and above. Dry conditions will present themselves under this anticyclone with highs reaching the 90 degree mark by Monday/Memorial Day. Before that occurs, Sunday is forecast to sit closer to the low 80s with 70s across the mountain locales. Similarly, overnight temperatures will also increase into early next week with widespread 60s to near 70 degrees by Monday night. During the period, southerly winds persist which should lead to increasing humidity as well.
LONG TERM /TUESDAY THROUGH FRIDAY/... Ridge aloft will be squarely over the Mid Atlantic and southeast on Tuesday, likely resulting in the hottest day of the upcoming week. Highs in the lower to mid 90s will be common, with heat indices in the upper 90s to near 100. The ridge will be suppressed to the south a bit on Wednesday by a series of northern stream troughs. It's possible a backdoor front could work into the area late Tuesday or Wednesday in association with these features. However, it appears temperatures will still reach 90 for another day in many areas. There could also be a few showers and storms Wednesday, but forcing isn't notable at this time.
The more active day will likely be Thursday as another cold front drops into the area from the northwest. Some shear and instability will be in place, but there are questions surrounding the magnitude of each as well as the frontal position and timing. Some severe storms are possible if the ingredients can come together. Temperatures will be dependent on the frontal position, but will likely be a bit cooler than prior days.
The front may be slow to push to the south, and some clouds and showers may hang around Friday as upper level troughing remains overhead. Temperatures will likely drop back closer to seasonable values. Model forecasts start diverging on the synoptic pattern by Saturday, so for now have a dry and seasonable forecast.