... A cold front will pass through the area tonight. The front will stall over the Carolinas Monday and Tuesday before returning north as a warm front Wednesday through Thursday as low pressure passes by to the west. The cold front associated with that low may cross the area by Friday.
NEAR TERM /THROUGH TONIGHT/... A southerly flow ahead of a cold front has led to hot and humid conditions this afternoon. Max temps will be in the upper 80s to lower 90s for most locations (70s and lower 80s in the mountains and near the Bay).
The heat and humidity will lead to moderate amounts of CAPE. The latest mesoanalysis shows around 1-2KJ/KG of SBCAPE west of the Blue Ridge and 2-3KJ/KG of SBCAPE east of the Blue Ridge.
Stronger lifting mechanisms will continue to lead to the likelihood for showers and thunderstorms. A surface trough will act as a lifting mechanism along with an MCV moving in from the west and a strong cold front that will be moving into the area tonight. A couple rounds of showers/thunderstorms are possible, first with the pressure trough, and then with the MCV and cold front. Shear profiles are marginal (deep layer shear around 20-30 kts) and mid-level lapse rates are marginal as well. However, the heat and humidity has led to moderate CAPE ahead of the cold front. The moderate CAPE combined with steep low- level lapse rates and mid-level dry air will increase threat for damaging wind gusts. Latest mesoanalysis shows over 1000 j/kg of DCAPE for much of the area. A Severe Thunderstorm Watch is in effect for areas east of the Allegheny Highlands through 9 PM.
Storm motion should be fast enough to keep any flood threat localized, but non-zero due to the fact that there may be a couple rounds of heavier rain associated with thunderstorms. Storms should exit southern MD around midnight, and the cold front will drop to our south overnight. Much cooler conditions are expected behind the boundary. lows will fall into the 50s to lower 60s.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The cold front will stall out over the Carolinas for Monday through Tuesday night while high pressure remains to the north. An upper-level trough will develop over the Rockies and central CONUS during this time.
An upper-level disturbance will pass nearby to our south in the southern stream Monday through Monday night, and this combined with the upper-level trough out west will cause warm and moist air to overrun cooler air in place. This will bring plenty of clouds along with the likelihood for rain across portions of the area. The main uncertainty is how far north and east the rain makes it before it runs into drier air and subsidence associated with the high to the north. As of now, it looks like the best chance for rain Monday will be south and west of the Potomac River.
Plenty of clouds and cool weather will hang around for Monday night through Tuesday night due to an onshore flow around high pressure to our north. Some rain is possible, especially across central and southern areas closer to upper-level disturbances and shortwaves just to the south. However, there is still some divergence among guidance so confidence is low at this time.
LONG TERM /WEDNESDAY THROUGH SUNDAY/... A warm front will continue moving north through the region on Wednesday. Uncertainty exists regarding how far north the warm front will make it due to a strong area of high pressure displaced to the north. This will result in a return flow developing out of the south resulting in a moisture and temperature return. Ahead of the warm front, an on-shore flow will likely lead to mostly cloudy skies and cooler conditions.
Thursday the region likely remains in the warm sector with the associated cold front to the west of the region across the Ohio valley. A strong southerly flow is likely to form which will lead to strong warm air advection. WAA will lead to daytime temperatures peaking in the low to mid 80s and will likely lead to an increasingly unstable air mass with CAPE values potentially over 1500 J/kg. PW values may reach above 1.6 inches Thursday afternoon into early Friday which could prime the environment for isolated heavy downpours. Showers are likely on Thursday with a chance for pulse thunderstorms from the relative unstable airmass. The greater threat for strong to severe thunderstorms will likely occur late Thursday into Friday. The forcing is better to the north, but the negative tilt of the trough could result in added dynamics in an unstable environment increasing the potential for showers and thunderstorms. The timing of the frontal passage may hamper the initiation of convection Thursday evening, though details will be refined with the frontal passage timing. Showers along with a chance for strong thunderstorms will be possible through early Friday afternoon as the front progress through our region.
Behind the frontal passage, high pressure is forecast to build into our region through the weekend leading to a return of dry and somewhat cooler conditions.