Forecast Discussion
Summary
SYNOPSIS
... Cooler and drier air will follow for Sunday in the wake of a backdoor front. Shower and thunderstorm chances return the first half of next week as another cutoff low pressure system approaches from the north. Temperatures next week will likely remain seasonable with low humidity.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... A backdoor front was moving west/southwestward from the I-95 corridor as of mid afternoon as an upper-level low drops toward the region from New England. A pool of instability (1000-1500 J/kg MLCAPE) was apparent over north-central to western MD, eastern WV and far northwestern VA. Effective shear of 20-30 kts over this area along with FROPA just after peak heating and some added lift from nearby terrain is expected to result in a cluster of loosely organized thunderstorms capable of producing gusty to damaging winds, hail, heavy downpours and lightning generally between 5-10 PM this evening. DCAPE around 1000 J/kg may aid in downburst potential over these areas.
Elsewhere, weaker forcing, shear, and instability should result in more widely scattered showers or a thunderstorm or two. A stronger storm can't be ruled out over the Shenandoah Valley or perhaps into the central VA Piedmont.
Any activity will weaken overnight with the loss of heating and as the front exits the region.
SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Subsidence on the back side of an upper-level low will scour out a great deal of cloud cover by Sunday afternoon (after what may be a bit of a cloudy start). Thus, expect mostly sunny skies to conclude the weekend with below average temperatures. Expect highs to remain in the mid 70s with 60s more commonplace across mountains. For early June standards, these forecast highs are about 3 to 6 degrees below average. Given the dry northerly flow, dew points fall into the 40s to low 50s; so unlike typical Mid-Atlantic summer days, it will not feel muggy at all. The dry nature of the air mass will allow nighttime lows to fall into the upper 40s to low/mid 50s.
Dry weather continues into Monday as the slow moving upper low pushes away from the New England coast. With a large mid/upper- level anticyclone across the northern U.S. into central Canada, additional disturbances will slide southward from Quebec into the northeastern U.S. This comes in the form of another upper low which nears northern New England by late Monday. 1000-500 dm thicknesses rise a bit as the initial upper low exits. This brings Monday's temperatures back into the upper 70s to low 80s, but with low humidity thanks to northerly winds. Expect fairly seasonable conditions into the night as well.
LONG TERM /TUESDAY THROUGH SATURDAY/... An upper-level low off to the north will play the most important role in the period. Ensemble guidance suggests that temperatures will be slightly below normal for this time of year. With the proximity of the upper low to the Mid-Atlantic, a few showers and isolated thunderstorms will be possible through the early part of the period, but probabilities remain low at this time. Temperatures will likely begin to increase late in the period as the upper low moves further north and east. Winds will also be elevated through the early to middle part of the workweek next week with high pressure off to the west and the upper low to the north and east keeping a tighter pressure gradient.