Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
418 FXUS61 KLWX 041956 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 356 PM EDT Thu Jul 4 2024 .SYNOPSIS... High pressure will remain in place offshore through early next week. A weak cold front will move through on Saturday, before stalling out in the vicinity through early next week. && .NEAR TERM /THROUGH TONIGHT/... Current radar imagery shows two large clusters of shower/thunderstorm activity. One stretches from south-central PA to just east of the Blue Ridge in Central Virginia. This activity is slowly progressing off toward the east, and should track through the remainder of the forecast area between now and roughly 7 PM. Behind that activity, there`s around a 100 mile gap where there isn`t much thunderstorm activity through western portions of our forecast area. Then another area of thunderstorms extends southward from Ohio through central West Virginia and into far southwestern Virginia. This activity is also tracking eastward, and will move into our area this evening. Most CAMs attempt to have these storms fall apart as they cross the mountains, but if they do hold together, they could have implications for fireworks shows in the evening. Extrapolating out the forward motion of this system puts it in the middle of our forecast area around 9 PM, with the ongoing storms in our area located off to the east. Thus far, storms have been rather unimpressive despite around 1000-2000 J/kg of MLCAPE present. Deep, saturated profiles (PWAT values around 2.2-2.3 inches according to SPC Mesoanalysis) have limited outflow accelerations, but have led to heavy rainfall producing storms. With around 20-25 knots of mid-level flow present, storms have remained progressive thus far. With storms moving along and background drought conditions in place, flooding isn`t expected in rural areas (where nearly 3 inches of rain in an hour is needed to cause issues). Some isolated instances of flooding can`t be ruled out in urban areas, but even that doesn`t look overly likely at the moment. A wet microburst or two can`t be ruled out as well, but it largely appears to be an environment that isn`t favorable for severe thunderstorms. Thunderstorm activity will wind down with loss of daytime heating through the first half of the overnight. Drier conditions are expected during the second half of the night. Some patchy fog may be possible later tonight, especially in locations to the west of the Blue Ridge that received rainfall today. Temperatures will remain mild overnight, with lows generally in the low-mid 70s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Hot and humid conditions will persist into Friday and Saturday. Highs both days are expected to make it into the low-mid 90s. When coupled with dewpoints in the mid 70s, this will lead to peak heat index values in excess of 100-105 degrees. Heat Advisories are in effect for portions of the area tomorrow, and additional Heat Advisories may be needed on Saturday. Afternoon/evening thunderstorms will also be possible both days. There won`t be much large scale forcing for ascent present tomorrow, so overall coverage of storms may be a bit lower. By Saturday, a shortwave trough will track to our northwest, driving a cold front into our area. This boundary may help to focus thunderstorm activity to the east of the Blue Ridge Saturday afternoon. && .LONG TERM /SUNDAY THROUGH THURSDAY/... A cold front is expected to push through the area by Sunday morning, stalling as a weak boundary just to our east. Brief ridging looks to keep us mostly dry on Sunday, with highs a little cooler than Saturday, but not as humid with dewpoints in the 60s. Any showers and thunderstorms that do develop will be restricted to near the stalled boundary, so far southern Maryland in our area. Heading into the work week, continuing moisture advection on southerly flow behind high pressure offshore will allow for scattered afternoon showers and thunderstorms on Monday. The focus of showers will be dependent on where the stalled boundary is (currently still expected to be to our east) and where there are any minor perturbations aloft. For Tuesday, as a low pressure system moves into the Great Lakes, a leading trough could act as the focus for convection in the afternoon and evening over our area. Showers and thunderstorms appear more likely Tuesday than Monday thanks to the added lift, with PoPs 50-70%. Precip chances on Wednesday will be dependent on how the cold front associated with the Great Lakes system evolves. With only weak boundaries moving through and southerly flow for most of the extended, high temperatures are expected to remain in the 80s to low 90s for much of the area. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Prevailing VFR conditions are expected at the terminals through Saturday. Afternoon/evening thunderstorms will be possible each day, potentially leading to temporary restrictions. Winds will be light out of the south. Storms are currently ongoing from near HGR southward to CHO. Those storms will progress eastward through the late afternoon and evening, eventually impacting the metro area terminals. Additional thunderstorms are present across central WV, and will move into the area during the late evening, after a few hour lull in-between. Sunday appears dry with high pressure building in behind a boundary stalled to our east. For Monday, scattered showers and thunderstorms are possible in the afternoon which could bring brief periods of sub- VFR conditions to the terminals. && .MARINE... SCAs remain in effect this afternoon in southerly flow in central portions of the Bay, as well as the lower tidal Potomac. Elsewhere, sub-SCA southerly flow is expected today. SMWs may be needed over the waters late this afternoon into this evening in association with any thunderstorms that move over the waters. Sub-SCA level southerly flow is expected on both Friday and Saturday. SMWs may be needed once again either afternoon as storms move over the waters. Light winds are expected on Sunday with high pressure over the waters and a boundary stalled to the east. Winds increase out of the south/southeast on Monday and could approach SCA criteria with southerly channeling. && .TIDES/COASTAL FLOODING... Steady southerly winds through Saturday night are likely to result in minor coastal flooding at the more sensitive locations each day. This is going to be during the highest diurnal tide, which is currently in the morning. Annapolis is most likely to hit minor flooding each day, with DC SW Waterfront, Havre de Grace, and Baltimore needing a close watch. A weak front pushes south of the area Sunday, bringing light northwest/north winds and a brief reprieve from coastal flooding. However, stronger southerly flow is expected again next week, likely leading to additional periods of coastal flooding. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory from noon to 8 PM EDT Friday for DCZ001. Heat Advisory until 8 PM EDT this evening for DCZ001. MD...Heat Advisory from noon to 8 PM EDT Friday for MDZ008-011-013- 014-016>018-504-506-508. Heat Advisory until 8 PM EDT this evening for MDZ011-013-014- 016-504-506. VA...Heat Advisory from noon to 8 PM EDT Friday for VAZ050-051- 053>057-502-527. Heat Advisory until 8 PM EDT this evening for VAZ053>056-527. WV...None. MARINE...Heat Advisory from noon to 8 PM EDT Friday for ANZ530. Small Craft Advisory until 8 PM EDT this evening for ANZ533- 537-541. Small Craft Advisory until 1 AM EDT Friday for ANZ534-543. && $$ SYNOPSIS...KJP NEAR TERM...KJP SHORT TERM...KJP LONG TERM...CAS AVIATION...KJP/CAS MARINE...KJP/CAS TIDES/COASTAL FLOODING...KRR