Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
522 FXUS61 KLWX 051910 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 310 PM EDT Fri Jul 5 2024 .SYNOPSIS... A cold front will approach the area from the Ohio River Valley late tonight into Saturday. The front will bring shower and thunderstorm chances to areas west of the Blue Ridge tonight and to areas further east Saturday. Humidity decreases Sunday in the wake of the front with high pressure briefly building overhead. Heat, humidity, and daily thunderstorm chances return early next week as high pressure pushes offshore and several weak fronts push through the region. && .NEAR TERM /THROUGH TONIGHT/... Scattered to broken fair weather cumulus accompanied by high clouds have developed over the area early this afternoon. Temperatures have risen into the 90s for most of the area, with heat indices climbing to 100-110 from along the Blue Ridge to the Bay. Heat Advisories and Excessive Heat Warnings remain in effect until 8PM tonight. Convection later this afternoon will be mostly limited to south of I-66 and west of the Blue Ridge. Based on latest CAMs, storms are expected to initialize along terrain near and west of the Blue Ridge. SPC still has us in a Marginal Risk for severe storms (1 of 5) for areas along the Blue Ridge and west, with a Slight (2 of 5) just to the west of our CWA. An MCS that is currently crossing Kentucky is progged to move into our area this evening (or the remnants of it). Hires guidance such as the HRRR maintains somewhat organized convection through the mountains and into our area as shortwave energy passes aloft, while other guidance is less persistent with it. Will need to monitor the MCS closely as it evolves, as severe potential this evening will be dependent on if enough energy from the MCS persists into our area and tap into instability in our area despite the loss of daytime heating. Dry air aloft could keep us capped, or contribute to potential downbursts if the energy granted from the remnant MCS allows us to break the cap. As such, some storms this evening could be strong to severe. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... On Saturday, an upper shortwave and associated surface low pressure system are expected over the Great Lakes. By Saturday morning an associated weak cold front is expected to approach from our west and then slowly move through the area through Sunday morning. Guidance continues to quickly fill in the upper trough and takes it northeast, resulting in a continuing drier trend for Saturday west of the Blue Ridge as the best forcing leaves with it. Scattered showers and thunderstorms remain possible Saturday afternoon and evening with PoPs focused east of the Blue Ridge. This based on the current progged location of the boundary, due to westerly flow behind the boundary drying from downsloping, and along and east of the boundary having the better forcing and moisture from southerly flow. We`re continuing to monitor the potential for severe thunderstorms and isolated flooding. Currently the I-95 corridor east is under a Marginal ERO, but only a general thunder from SPC. Additionally, Temperatures on Saturday are expected in the low to mid 90s for most of the non-mountainous areas and heat indices near 100-105 east of the Blue Ridge. We`re monitoring the heat threat which could necessitate Heat Advisories, but appears thresholdy at this time, and only for an hour or so. Regardless, one can expect hot and humid conditions, with the highest heat indices in the Virginia Piedmont and along the waters due to the higher dewpoints. The weak boundary stalls just to our east on Sunday morning. 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. && .LONG TERM /MONDAY THROUGH FRIDAY/... Synoptically, not too much of a change in the extended as we enter the true crux of Summer. Upper level ridging/broad high pressure will continue it`s influence over the north-central Atlantic while broad upper level trough/low pressure over the central CONUS slowly progresses east mid to late next week. Meanwhile, upper level low pressure will continue to meander off the Carolina coast Monday before washing out toward the middle of the workweek. This will result in an uptick of moisture across the region along with the threat of daily diurnally/terrain driven showers and thunderstorms. Chances will be relatively low (25-50 percent each day) with no large scale features to point to for widespread drought busting rain. A cold front looks to potentially cross the area Tuesday into early Wednesday bringing with it the highest potential for widespread rainfall. Even here precipitation chances have been capped to 50 percent or less given some uncertainty amongst the models. Severe weather and even the potential for flooding could be an issue on this day given the unstable airmass ahead of the boundary. Learning machine probabilities also highlight this concern, so we`ll continue to monitor. High pressure builds back in behind the front Wednesday into the weekend. Most of the area will remain dry during this time although a few diurnally/terrain driven thunderstorms cannot be ruled out. Temperatures will drop back close to seasonal norms during this period. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... VFR conditions prevail through early this afternoon. Later this afternoon, isolated showers and thunderstorms could develop along the Blue Ridge. CHO and possibly MRB could see brief restrictions but confidence is low given the limited coverage. Heading into the evening, another round of convection is possible, reaching the terminals around 01z-07z west to east if it persists east of the mountains and through the loss of daytime heating. Given the low confidence, kept it to VCSH mention at the most. Will continue to monitor through the afternoon, hopefully getting a better idea of how convection will evolve in the next few hours. Terminals can expect scattered diurnal showers and thunderstorms once again on Saturday, but primarily along and east of the Blue Ridge, so MRB might miss out on the action. Prevailing VFR conditions are expected through Wednesday as the influence of upper level ridging remains nearby. Shower and thunderstorm chances are expected each afternoon and evening as a series of weak fronts push through. Sub-VFR conditions are possible for a brief period of time in and around these storms with a focus on terminals west of the Blue Ridge Monday and further east Tuesday as a cold front pushes through. High pressure briefly returns Wednesday and into the weekend ahead. W/SW flow is generally expected at 5-10 kts with occasional gusts to around 15 kts possible in the afternoon (both Monday and Tuesday). && .MARINE... Southerly winds prevail through tonight, with varying from southwest to southeast over parts of the water throughout the day. Southerly channeling is expected to produce SCA winds in the middle portion of the Chesapeake Bay between Smith Point and Drum Point this evening. A Small Craft Advisory has been issued for those waters through tonight, and it may need to be expanded a bit further up the Bay this evening if winds are stronger than forecast. Otherwise, sub-SCA winds gusting to around 10-15 knots. Mostly dry conditions today, then scattered showers and thunderstorms are possible this evening. Winds diminish heading into the weekend, but stronger gusts remain possible during any scattered showers and thunderstorms over the waters on Saturday. Sunday should be mostly dry, but will be dependent on where the stalled cold front sets up in relation to the waters. Southerly channeling looks to become a concern for portions of the waters Monday into Tuesday as the gradient tightens between upper level low pressure off the Carolina coast and the incoming cold front from the Ohio River Valley. SCA level winds return Tuesday into Wednesday in the wake of the cold frontal boundary. High pressure builds over the waters later next week. && .TIDES/COASTAL FLOODING... Generally light southerly to southwesterly flow will result in elevated tide levels through the weekend. Vulnerable shoreline may come close to minor flooding during the early morning high tides. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 8 PM EDT this evening for DCZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ003>006-008- 011-013-014-503>508. Excessive Heat Warning until 8 PM EDT this evening for MDZ016>018. VA...Heat Advisory until 8 PM EDT this evening for VAZ025>031- 036>040-050-051-053-054-501-502-505>508-526-527. Excessive Heat Warning until 8 PM EDT this evening for VAZ055>057. WV...Heat Advisory until 8 PM EDT this evening for WVZ051>053. MARINE...Heat Advisory until 8 PM EDT this evening for ANZ530. Small Craft Advisory until 6 AM EDT Saturday for ANZ534-543. && $$ SYNOPSIS...EST NEAR TERM...CAS SHORT TERM...CAS LONG TERM...EST AVIATION...CAS/EST MARINE...KRR/CAS/EST TIDES/COASTAL FLOODING...EST