... Tropical Storm Faye, centered over New Jersey, will move north toward eastern New York tonight. A frontal boundary will cross the region Saturday and stall. An upper level disturbance will follow on Sunday. High pressure builds over the Mid Atlantic next week bringing an extend stretch of hot weather.
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Dropping heights in association with an upper level disturbance and weak surface trough was enough to kick off a round of showers and thunderstorms in the mountains this afternoon and evening. In spite of little if any shear, mesoanalysis indicates plentiful instability (SBCAPE up to 2000-2500 J/kg), which was sufficient to support some stronger storms, albeit pulsy in nature. Even the mid-level lapse rates are poor, which is confirmed by the 00Z IAD RAOB.
With the loss of daytime heating, we're starting to see a weakening trend on KLWX radar. Still have some stronger storms on the edges...near CHO and approaching MRB/HGR. Current forecast confines storms along a line from Catoctins/northern Blue Ridge/Central Foothills, which leans heavily on latest CAMs.
No meaningful change to the low temperature forecast. Dewpoints are in the lower 70s, so there is a limit to how low they will fall.
SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... A weak cold front will approach from the west and move through our region Saturday morning. Compared to prior model runs from the past few days, this boundary is forecast to be much weaker as the strong upper forcing support remains to our north near the PA and MD border. Wind shifts in model solutions indicate a passage during middle to late morning periods to early afternoon. I don't see a lot of showers and thunderstorms with the front mainly due to the early day passage. The upper level trough to our north could provide enough forcing in a warm and humid environment to kick off showers and a few thunderstorms mainly near the Maryland PA border during the Saturday afternoon. Overall the strong thunderstorm threat has really decreased for Saturday but I still have included chance pops for most of our region with the highest near the MD/PA border and decreasing toward central Virginia. The threat for showers and thunderstorms should decrease after sunset as daytime heating drops off and the upper level trough lifts off to our northeast. Daytime temperatures on Saturday should easily reach back into the upper 80s to lower 90s on Saturday as winds become more west southwest during the afternoon periods with overnight lows in the mid 60s to low 70s.
The threat for showers and thunderstorms will end overnight and into early Sunday. A mainly westerly flow will lead to drier weather moving into our region Sunday morning and dry conditions should continue through Sunday morning. A weak southerly flow will form late Sunday morning leading to advection of warm and moist air into our region. Another stronger upper level shortwave trough will drop down into our region from the Great Lakes region Sunday afternoon and into early Monday. Increasing moisture and daytime temps will lead to modest instability with CAPE values upwards of 1500. The increased lift provided by the upper level trough and focused upper level jet coupled with fair instability will to an increased threat for the formation of showers and thunderstorms Sunday afternoon and evening. The one limiting factor will be that they may form after the sun sets. Sunday looks like the best chance for stronger thunderstorms to form especially during the late afternoon and early evening periods. The best area for strong storms will likely be west of the Blue Ridge at this time but there remains a lot of uncertainty on the strength and location of the upper level trough. Daytime temps will hover in the 90s once again with overnight lows in the mid 60s to lower 70s.
LONG TERM /MONDAY THROUGH FRIDAY/... A surface cold front will likely be near or east of I-95 on Monday. Showers and thunderstorms will be possible along and ahead of the front. Where rainfall does not occur, temperatures should easily reach 90 degrees or warmer.
The front should push through the region Monday night to allow an area of high pressure to develop overhead Tuesday through Wednesday. Drier air will keep convection down and temperatures will be a couple of degrees lower as well with highs reaching the middle 80s both days.
A light southerly flow develops Wednesday night and Thursday. The humidity will increase and so will the temperatures as we may look at temperatures reaching 100 degrees in places on Thursday.
By late in the day Thursday into Thursday evening, a weakness in high pressure and an approaching surface cold front could spark thunderstorms. A pre-frontal trough at the surface could be the trigger in igniting these storms that would be fueled by the heat and humidity.
On Friday, the actual surface cold front could set up across our region and ignite additional showers and thunderstorms. Storms that could produce heavy rainfall or damaging winds.