... A cold front will pass across the Mid-Atlantic tonight, with high pressure becoming wedged against the eastern face of the Appalachians Sunday. Atlantic moisture will support rain during the early half of the workweek, especially across the mountains. A strong cold front will pass across the region during the middle of the coming week, with cool high pressure building in behind it, making it feel like it should for late September.
NEAR TERM /THROUGH SUNDAY/... As of 110 PM EDT Saturday...
The area remains in a relatively dry air mass (dew points in the 60s and PWATS at or below 1.50 inches) as compared to the area from Tennessee to Florida where dew points are in the 70s with PWATS at or above 2 inches. A cold front will approach the region this afternoon and move into central Virginia tonight. Some of the moisture to our southwest may get draw into the Mountain Empire and NW NC mountains to help generate isolated moderate to heavy showers this afternoon and evening. Heating, orographics and the approaching front will trigger storms elsewhere. Modest CAPE values may bring a few strong storms, but overall picture appears to be scattered light showers that will wane this evening.
Surface high pressure moves over New England on Sunday, pushing the cold front south into the Carolinas. Behind the front is cooler drier air and easterly flow. It is possible that this wedge may not be deep enough across the southern portion of the CWA. If not, upslope flow may produce showers along the eastern slopes of the NW NC Blue Ridge.
Temperatures today warmed into the low 80s across the mountains to upper 80s east of the Blue Ridge. Temperatures will be around 3 or so degrees cooler tomorrow. Tonight's lows will drop into the low to mid 60s.
SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 215 PM EDT Saturday...
Showers start to increase this period...
Building ridge off the east coast with deep trough pushing into the central U.S. plus upper troughiness over the Gulf Coast states with tropical moisture (remains of Nicholas) will set our area into a southerly flow aloft.
At the surface, high pressure will wedge southwest from the Northeast into our region, and this will bring more of an easterly fetch off the Atlantic. The combo and both tropical moisture feeding in will start to produce showers especially along the Blue Ridge Sun night into Tuesday, with pops increasing area wide by Tuesday as better upper forcing occurs.
Overall, rainfall amounts look to be on the light side, but day in and day out of showers especially over the NC mountains will start to saturate things, and could see more of a hydro issue come the long range when the front moves across.
With the wedge in place, high temps will be tempered but sunshine at times should allow it overall to be at or just below normal, with highs mainly in the 70s, a few 80s in the piedmont. Lows will stay elevated in the 60s due to the increasing low level moisture.
Forecast confidence is high on increasing moisture and threat of showers being highest into the southern Blue Ridge, but less on rainfall amounts this period, and average on cloud cover and temps.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 121 PM EDT Saturday...
Looking at heavy rain threat Wednesday followed by dry/cool weather to close out the week...
Synoptic models show enough agreement that the midweek system should bring best chance of rain late Tue night-Wed evening, but some differences in speed beyond Wed afternoon occur with the GFS faster while the Euro/CMC are slower. Given trough axis staying sharp, leaned more toward slower solution which should keep higher pops into Wed night, before drier air works in behind the storm system Thursday.
Drier and cooler to end this forecast, though the amplification of the 5h trough and position of the high suggest it will not be as cool as earlier thought, but still temperatures/humidity will be feeling like fall, slightly below normal for late Sept.
Another trough amplification and front may bring a few showers to the central Appalachians Saturday but low threat for now.