|Dew Point:||64.4°F (18.0°C)|
|Sea Level Pressure:||28.50" (964.9 mb)|
Slight Chance Showers And ThunderstormsLow: 71
Chance Showers And Thunderstorms then Showers And Thunderstorms LikelyHigh: 83 Low: 65
Chance Rain ShowersHigh: 71 Low: 59
Mostly SunnyHigh: 75 Low: 60
SunnyHigh: 79 Low: 62
A slight chance of showers and thunderstorms before 5am, then a chance of showers and thunderstorms. Mostly cloudy, with a low around 71. West wind around 5 mph. Chance of precipitation is 30%. New rainfall amounts less than a tenth of an inch possible.
A chance of showers and thunderstorms before noon, then showers and thunderstorms likely. Some of the storms could produce heavy rain. Mostly cloudy, with a high near 83. Southwest wind 5 to 14 mph, with gusts as high as 21 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.
Showers and thunderstorms. Some of the storms could produce heavy rain. Cloudy, with a low around 65. West wind 7 to 13 mph. Chance of precipitation is 80%. New rainfall amounts between 1 and 2 inches possible.
A chance of rain showers. Mostly cloudy, with a high near 71. North wind around 9 mph. Chance of precipitation is 50%. New rainfall amounts between a half and three quarters of an inch possible.
Mostly cloudy, with a low around 59. North wind around 7 mph.
Mostly sunny, with a high near 75.
Partly cloudy, with a low around 60.
Sunny, with a high near 79.
Mostly clear, with a low around 62.
... A cold front will slowly approach from the Great Lakes through this afternoon before passing through tonight into Tuesday. High pressure will return for Wednesday into the weekend.
NEAR TERM /THROUGH TONIGHT/... The upper-level ridge that has brought the intense heat and humidity over the last few days will slowly break down in response to a cold front approaching from the north and west along with its associated upper-level trough axis. Therefore, today will not be as hot as recent days. However, for locations east of the Blue Ridge Mountains, there will be some more sunshine at least through midday. This will cause max temps to top off in the lower to middle 90s near and east of the Interstate 95 corridor with heat indices topping off in the lower 100s for most of these areas. With somewhat higher dewpoints expected in southern Maryland, a Heat Advisory is in effect for late this morning through this afternoon for heat indices to top off around 105 degrees. Confidence is too low at this time to expand the advisory farther north and west due to the cloud cover nearby. Either way it will be a hot and humid day across these areas, but not quite as oppressive as recent days. Farther west, cloud cover will allow for noticeably cooler conditions compared to recent days with highs in the 80s for most of these locations.
The lowering heights and an increasing southwest flow aloft will combine with forcing from an approaching cold front and strengthening pressure trough overhead, along with instability from the very warm and humid air in place to trigger showers and thunderstorms. With moderate to high CAPE, thunderstorms will contain heavy rainfall and despite stronger winds aloft making storms more outflow dominant, there may be multiple rounds of storms over any particular area since it is a favorable setup for training convection (low-level flow parallel to mean cloud layer wind). Given those concerns, the Flash Flood Watch was expanded in area to include the rest of the Shenandoah Valley and the Potomac Highlands.
Increased shear profiles along with the moderate to high instability suggests that storms will have the chance to be severe with damaging winds being the primary threat. The best chance for severe storms will be near and east of Interstate 81 through the Washington and Baltimore Metro areas into the Virginia Piedmont and southern Maryland, where instability is most likely to be higher due to some more sunshine through midday.
The cold front will drop into the area tonight while the upper- level trough associated with the boundary moves overhead. More showers and thunderstorms are expected during this time, and some may contain more heavy rainfall. Therefore, the Flash Flood Watch continues through late tonight. Drier air will slowly move into northwestern portions of the CWA late this evening and overnight, but precipitation is expected for most of the night farther southeast.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The cold front will continue to drop southeast Tuesday. Morning showers and possible thunderstorms are likely east of the Blue Ridge but drier air will gradually work its way in causing the widespread precipitation to diminish later Tuesday morning. However, with the upper-level trough overhead a few instability showers may pop up anywhere Tuesday afternoon and evening. Coverage should be isolated to scattered though. Tuesday will also turn out much cooler and less humid compared to recent days, thanks to a northerly flow behind the cold front.
Surface high pressure will build toward the area Tuesday night through Wednesday, but the upper-level trough will remain overhead. Cooler and less humid conditions are expected during this time. A popup shower cannot be ruled out Wednesday afternoon due to some instability with the trough overhead, but drier air from the high will cause any coverage to be isolated to perhaps widely scattered. High pressure will settle overhead Wednesday night while the trough begins to finally push off to the east.
LONG TERM /THURSDAY THROUGH SUNDAY/... High pressure will settle overhead Thursday through the weekend, bringing dry conditions for most areas along with lower humidity than what has been experienced in recent days. High temps Thursday will be in the 80s for most areas, and high temps for Friday through the weekend will be in the upper 80s to lower 90s for most areas, causing seasonable conditions.