Bryce Resort / Basye

Summary

SYNOPSIS

... A backdoor cold front will sink south of the area tonight. The boundary will return north as a warm front Sunday into Monday before secondary cold front approaches and stalls near the area for the middle and latter portions of next week.

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... High pressure remains centered over the New England Coast this afternoon while an upper-level ridge axis is slowly moving off to our east. An upper-level trough is building over the central CONUS and a backdoor cold front is currently located near the Potomac Highlands into central Virginia.

The backdoor boundary will most likely stall out near the area through late this afternoon before eventually pushing off to our south and west tonight as high pressure strengthens along the New England Coast.

As convergence strengthens along the backdoor boundary into this evening, this will combine with moisture advection (southerly flow aloft around periphery of the high) and instability, triggering some showers and thunderstorms over the Allegheny and Potomac Highlands into the Shenandoah Valley. This activity will likely advect eastward into the metro areas late this evening and overnight. A rumble of thunder is possible overnight as well due to limited elevated instability above the marine layer.

Low clouds and noticeably cooler conditions are expected overnight as the onshore flow continues behind the backdoor cold front. Lows will be in the 50s for most areas, with upper 40s in portions of northern Maryland.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... The backdoor boundary will remain to the south and west through Saturday night while high pressure remains centered near the New England Coast. An onshore flow will continue during this time while warm and moist air overruns the marine layer in response to an upper-level trough pushing into the Midwest. This will result in plenty of clouds along with periods of rainfall and unseasonably cool conditions. There may be some breaks in the rain, but for most of the time near and west of Interstate 95, there will be some rain around. Perhaps there will be some more breaks east of Interstate 95 where the overrunning moisture may not be quite as deep.

The overrunning moisture will deepen Saturday night into Sunday morning as the boundary begins to push north as a warm front, and the low-level flow develops a fetch from the Gulf of Mexico. Therefore, more rain is expected.

The warm front will move into the area Sunday while a weak upper-level trough axis passes through. More unsettled conditions are expected with showers and perhaps even a couple thunderstorms. Sunday afternoon will turn out a bit warmer and more humid as well, but temps still near and below climo. Highs will range from the 60s north of the boundary in northern MD into the metro areas/eastern WV/northern VA to the 70s south of the boundary. The upper-level trough axis will move off to the east Sunday night while the surface boundary remains nearby. While a few showers are possible, coverage of precipitation should wane behind the departing trough axis. There may be areas of dense fog overnight with plenty of low-level moisture and light winds.

LONG TERM /MONDAY THROUGH FRIDAY/... The unsettled weather pattern is likely to continue across the region for virtually all of next week. Nearly zonal flow aloft favors numerous passing shortwaves that bring enhancements to the daily afternoon showers and thunderstorms. Even at night, isolated showers/storms are possible given the increased moisture and lingering elevated instability.

At the surface, a stalled frontal boundary is likely to be just north of the area Monday, slide south to around I-70 Monday night, then be pushed back north of the area through mid week. However, any change in the position of the stalled front could result in higher or lower rain chances than currently forecast for some areas. A stronger shortwave trough is forecast to cross the area Wednesday night into Thursday, possibly bringing some heavier rainfall and stronger storms to the area.

Afternoon highs in the upper 70s to low 80s Monday and Tuesday warm to the mid 80s Wednesday and Thursday. Very mild overnight lows in the 60s each night due to increased dew points and cloud cover.