|Dew Point:||66.9°F (19.4°C)|
|Wind:||From the West at 4.0 MPH Gusting to 10.0 MPH|
|Sea Level Pressure:||30.28" (1025.3 mb)|
Chance Showers And Thunderstorms then Slight Chance Showers And ThunderstormsLow: 70
Chance Showers And Thunderstorms then Showers And Thunderstorms LikelyHigh: 76 Low: 62
Showers And Thunderstorms LikelyHigh: 67 Low: 57
Mostly SunnyHigh: 69 Low: 59
SunnyHigh: 72 Low: 60
A chance of showers and thunderstorms before 9pm, then a slight chance of showers and thunderstorms between 9pm and 5am, then a chance of showers and thunderstorms. Some of the storms could produce heavy rain. Mostly cloudy, with a low around 70. Southwest wind around 8 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter 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. Partly sunny, with a high near 76. West wind 8 to 15 mph, with gusts as high as 23 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch possible.
Showers and thunderstorms likely. Some of the storms could produce heavy rain. Cloudy, with a low around 62. West wind 10 to 15 mph, with gusts as high as 22 mph. Chance of precipitation is 70%. New rainfall amounts between a half and three quarters of an inch possible.
Showers and thunderstorms likely. Cloudy, with a high near 67. North wind 6 to 10 mph. Chance of precipitation is 60%. New rainfall amounts between 1 and 2 inches possible.
A slight chance of rain showers before midnight. Mostly cloudy, with a low around 57. North wind around 9 mph. Chance of precipitation is 20%.
Mostly sunny, with a high near 69.
Mostly clear, with a low around 59.
Sunny, with a high near 72.
Mostly clear, with a low around 60.
... A cold front will slowly approach from the Great Lakes through Monday, then cross the region Monday night into Tuesday. High pressure will follow for much of the rest of the week.
NEAR TERM /THROUGH TONIGHT/... Isolated to widely scattered showers and thunderstorms are expected into this evening given height falls starting to encroach on the region in tandem with peak heating. Westerly flow usually dries the low levels out a bit due to downsloping, but the air coming up and over the mountains is so humid to begin with that dew points are holding in the lower 70s for many areas this afternoon. Even so, westerly flow reduces convergence a bit, so convection should remain widely scattered. Two possible areas of focus are: 1) north-central Maryland along and ahead of an old outflow boundary moving south out of Pennsylvania, and 2) portions of central Virginia in association with a weak perturbation in the mid levels (which has sparked convection near Roanoke/Lynchburg and is drifting north).
Any thunderstorms that do develop with have the potential to produce brief very heavy rain and strong, gusty winds due to PWATs nearing 2 inches and steep low-level lapse rates/DCAPE of over 1000 J/kg. Mid- level lapse rates are around 7.0 C/km which is pretty decent for the Mid-Atlantic in late July, which could cause even pulse-type updrafts to overperform a bit (in the form of downbursts when they come back down); some severe hail can't be ruled out, either, but is less likely overall due to high freezing levels.
Tonight will remain very warm, humid, and unstable. Another shortwave approaching from the Tennessee Valley coupled with weak theta-e advection in the low-levels may touch off a couple heavy thunderstorms late overnight into early Monday morning. Given the lapse rates in place in the mid levels and the amount of CAPE just above the surface inversion, some gusty winds or hail can't be completely ruled out, though overall the severe threat should be minimized due to the time of day.
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The cold front approaching from the Great Lakes crawls into Pennsylvania Monday. Ahead of it, a surface lee pressure trough and differential heating boundary on the southeast side of an anticipated cloud shield (leftover from early morning shower activity across eastern WV/northern MD) will likely act as the impetus to initiate convection near the higher terrain around midday. CAPE approaching 2000 J/kg and increasing effective shear of up to 40 kts spells the potential for more organized severe weather. Of note, most of the shear is in the 2-6 km AGL layer, which may be more favorable for sustaining linear segments, enhancing the threat for gusty winds. A tornado or some severe hail can't be ruled out with any discrete cells or boundary interactions with a frontal circulation/low-level veering developing overhead. The best chance for severe weather appears to be generally east of I-81 and north of I-64.
In addition to the severe threat is the threat for flash flooding. A Flash Flood Watch has been issued for northern and central Maryland and portions of northern and northwestern Virginia, as well as the eastern panhandle of West Virginia where the greater instability to the south and synoptic forcing with the front approaching from the north are expected to intersect. See hydro section for more details.
Southeast of the developing clouds and precipitation, portions of southern Maryland should heat up rather readily through early afternoon. Therefore, a Heat Advisory has been posted for these areas, where heat indices will likely reach 105 for a few hours.
The front only slowly moves south across the area overnight Monday night, and with high PWAT air in place, periods of showers and thunderstorms will remain likely through much of the night across the region.
The front and its associated precipitation should clear to our southeast by Tuesday afternoon, with much cooler temperatures and lower humidity to follow.
LONG TERM /WEDNESDAY THROUGH SUNDAY/... The long term period is shaping up to be one of the nicest stretches of weather we've experienced all summer. Starting off on Wednesday, the surface front will be located well off to our southeast, but the mid-level trough axis and upper level jet will still be situated overhead. With the trough axis lingering overhead, some fair weather clouds may form with daytime heating, but conditions will stay dry. Winds will be light out of the north, with below normal temperatures and low humidity levels. High temperatures will reach the low 80s along the urban corridor, while higher elevation locations will struggle to make it out of the 70s. Dewpoints will only be in the 50s.
The mid-upper level trough will slide off to the east Wednesday Night, allowing high pressure to build in from the west for Thursday and Friday. The surface high will slide offshore on Saturday, allowing return flow to start redeveloping. Other than a few passing fair weather clouds, each day should feature near wall to wall sunshine. Temperatures will gradually moderate from below normal, to near normal, with highs in the low to mid 80s on Thursday and highs in the upper 80s on Saturday. Low temperatures will start off in the 50s to low 60s on Wednesday, and moderate to the 60s by Saturday. Humidity levels will remain relatively low, with dewpoints starting in the 50s on Wednesday, then gradually climbing into the low-mid 60s by Saturday.