Forecast Discussion
Summary
SYNOPSIS
... An area of coastal low pressure will push northward from the Carolinas today as high pressure remains to the north of the local area. Rain chances will increase today and persists through at least Tuesday. High pressure builds back in by the middle part of next week with a moderating trend in temperatures.
NEAR TERM /THROUGH TONIGHT/... A cut-off UL low will meander over the SE US today while an extratropical low moves slowly inland near an area of low-level frontogenesis with high pressure to the north.
Latest ACARS imagery continues to show the abundant dry air in the low to mid-levels of the atmosphere as indicated on the 00Z RAOB from IAD. While radar imagery shows what looks to be showers advancing into central VA, Td depressions remain in the 10-15 degree range. WV imagery shows the gradient in moisture as well. It will take some time for the atmosphere to moisten as the better forcing associated with this system remains near the OBX as of this morning. Most of the radar returns in central VA are lightly forced and not reaching the ground as of 330 AM. Not expecting much in terms of rainfall through daybreak given the dry air, aside from our southernmost areas near Nelson Co, VA.
For the remainder of the overnight, expect continued high clouds in the form of cirrostratus. Amid a light east to southeasterly wind, tonight's low temperatures will fall into the 50s, locally into the mid/upper 40s over the higher terrain and near the Mason- Dixon Line.
For today, have continued the downward trend in POPs to the north of I-66. Those near I-70 and the Mason Dixon have the best shot at staying dry today. To the south near CHO and the central Blue Ridge, expect intermittent showers through the day. High temps in the 70s to the north where rain is not expected and in the 60s to the south where rain showers will lower temps.
By this evening/tonight, the main area of frontogenesis associated with the low will move into the area. The easterly flow will result in an upslope component to the precip and therefore the highest QPF amounts on the eastern facing slopes of the Blue Ridge. Toward the metros, it will still take time for the column to moisten and precip to reach the ground. These rain chances will still be greatest along/south of I-66. Lows in the 50s for most tonight.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... With the aforementioned low nearby, Atlantic moisture will continue to be advected into the area amidst the easterly flow through Tue. Memorial Day does not look like a washout, but the potential for intermittent rain showers certainly exists (especially along/south of I-66). The higher QPF amounts will be on the easterly facing slopes of the Blue Ridge given the added orographic lift where 48-60 hour totals of 1-3" are possible. Currently no flooding/flash flooding concerns given anteceding dry conditions and overall forecast rainfall rates that are expected to be light to briefly moderate in nature and below FFG. A few thunderstorms are possible during the afternoon/evening Mon and Tue. Highs Mon/Tue are somewhat uncertain given how widespread rain may or may not be, but overall expecting below normal temperatures again (60s/70s for most). Lows in the 50s each night (upper 40s for the mtns).
LONG TERM /WEDNESDAY THROUGH SATURDAY/...Persistent upper level low will be weakening and drifting east Wednesday into Thursday as troughing moving across Canada flattens the blocking ridge. There should still be some showers around Wednesday (mainly tied to the diurnal heating cycle) while max temperatures remain a little below normal. Thursday has more promise for dry conditions as ridging builds in from the northwest, although ensemble spread still indicates there's a chance the closed low will remain close enough by for a few showers. Friday has the lowest rain chances as high pressure is likely overhead. Temperatures will rebound above normal Thursday and Friday, potentially closing in on 90F on Friday.
A backdoor cold front is forecast to drop into the area sometime in the Friday night to Saturday time frame. Latest guidance indicates the front will be moisture starved, but temperatures will drop slightly behind the boundary.