Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
375 FXUS61 KLWX 111830 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 230 PM EDT Thu Jul 11 2024 .SYNOPSIS... Shower and thunderstorm chances return Friday and Saturday especially east of the Blue Ridge with a stalled front nearby. Weak high pressure briefly builds back into the area Sunday then gradually slides offshore Monday into Tuesday allowing the high heat, humidity, and daily thunderstorm chances to return. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Dry conditions through this evening as a stalled front remains well to our south across SE VA. Abundant stratocu across the Potomac Highlands has kept temps very cool compared to recent days, only in the 60s to 70s. As the clouds continue to break up this afternoon, expect highs to reach the low 80s east of the Allegheny Front and around 70F in the higher elevations. Elsewhere, abundant sunshine with highs in the mid 80s to around 90F. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... The stalled front across the VA Tidewater slowly begins advancing north into our area tonight into Friday morning. A few showers push their way into southern MD by around midnight, then coverage increases during the second half of the night. A dramatic surge in PWATs accompanies the advancing front for areas east of the Blue Ridge. Values go from under 1.2" this evening to well over 2-2.2" come sunrise Friday. Widespread showers, some producing locally heavy rainfall, move into the I-95 corridor Friday morning. Multiple rounds of showers and scattered thunderstorms are likely throughout the day on Friday. A lull in activity is expected at some point Friday evening as the front lifts north of the area, though given the very saturated atmosphere some showers are likely to continue through Friday night. A tight QPF gradient is likely east of the Blue Ridge, and especially east of I-95. The current forecast calls for half to an inch of rain between the Blue Ridge and I-95, with 1-1.5" of rain along the I-95 corridor, and 2-4" of rain east of I-05. The heaviest rain is likely to occur late tonight through early Friday afternoon in Southern MD, where localized higher amounts up to 5" are possible. A Flood Watch may be needed for some areas east of I-95. For those west of the Blue Ridge, the downslope nature of east to southeast flow is going to reduce rain amounts significantly. Overall only expecting around a tenth to a quarter of an inch of rain reach the Shenandoah Valley, and stay mostly dry in the Alleghenies. Abundant cloud cover and precipitation keep highs well below normal for most of the area Friday, only reaching the low 80s. The warmest temps will be in the Potomac Highlands from Hagerstown to Cumberland to Petersburg where highs reach the upper 80s. Come Saturday the front itself washes out in vicinity of the area as the mid-level forcing supporting the system weakens and moves east over the Atlantic. Another wave of low pressure aloft approaches from the west Saturday afternoon, that could fire off another round of scattered showers/thunderstorms in the afternoon east of the Blue Ridge. There remains a good amount of uncertainty regarding coverage of storms Saturday afternoon as dry air filtering in from the west could put a cap on much of the activity. Still, highs in the upper 80s to low 90s, dew points in the mid to upper 70s, and some broad 20-25 knots of shear could lead to some organized convection. Conditions dry out Saturday night as another front that sweeps through the area. && .LONG TERM /SUNDAY THROUGH THURSDAY/... The long term period will generally be unsettled, with our region pitted between a strong upper ridge over the southern CONUS, and a building positively-tilted trough to our northwest. This will gradually swing through by mid-week, but the details on how strong this trough will be and exactly where it tracks are still a bit in question. Overall, pretty much every day during this time period looks quite hot, with highs well into the 90s, and even near 100 by the time we get to Wednesday. Dew points each day will be somewhat questionable, as model guidance suggests we get into the low to even mid 70s. However, wind direction aloft could play a key role, and we could mix down some lower dew points (mid-upper 60s) during the afternoons. This would be the one thing keeping us from another lengthy period of heat headlines, but will continue to monitor model trends as we get closer. Either way, it looks very hot once again, continuing an already very hot summer. Of course, with the threat of heat comes the inevitable afternoon thunderstorm threat. This will occur each afternoon, becoming increasingly likely by Wednesday as the trough inches closer to the region. Storms that develop Sunday will be very isolated and likely driven by terrain circulations, thus would probably move quite slow. Should a storm get locked over one location for an hour or two, could see some isolated instances of flooding in the higher terrain. However, the recent drought has flash flood guidance very high area- wide. This would continue into Monday as well, though coverage could be a bit higher. By Tuesday and Wednesday, we start to tap a bit more wind shear, thus there will be an increased threat for some strong to severe storms. Looking into some model soundings, do think we will run into a similar issue we have seen recently with a lack of substantial mid- level lapse rates. The very warm air mass in place aloft is just going to make it very difficult to get widespread severe convection going in the absence of some cold advection aloft. Could see a scenario where storms generally struggle to get developed, but the ones that do will have plenty of DCAPE to tap into. Any storm that manages to break through the mid-level warmth and grow a tall core will have the potential for some damaging winds. Think the greatest threat for this would be Wednesday into Wednesday evening, but we are getting to the end of the forecast period at that point, so details can certainly change this far out. Storms would also be capable of some heavy rainfall rates, thus introducing at least some risk for isolated instances of flooding. However, given the recent rapid-onset drought, that would likely be relegated to the metro areas. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... VFR conditions through most of tonight. A stalled front to our south slowly lifts north of the area early Friday into Friday night. Expect MVFR to IFR CIGs to slowly spread north by 12Z Friday, with the worst conditions most likely at CHO, IAD, DCA, BWI, and MTN Friday afternoon into Friday night. Persistent showers, some heavy at times, are expected Friday late morning through Friday evening, with MVFR or lower visibility likely. East winds around 5 knots Friday morning become southeast in the afternoon. Scattered to widespread showers continue into Saturday as the front remains stalled over the area. Additional periods of sub-VFR conditions are likely until another front sweeps through the area Saturday night. VFR conditions return Sunday. Sunday and Monday should both generally be characterized by VFR conditions across all terminals. Winds are generally going to be out of the SW at 5 to 10 knots throughout the period during the afternoons, with light and variable winds overnight. However, there is a slight chance for afternoon thunderstorms each day, primarily at MRB and perhaps CHO. However, cannot completely rule out an afternoon storm making it as far east as IAD Sunday, and even all the way to I-95 on Monday. If these were to make it over the terminals, could see some gusty winds, VSBY reductions, and of course lightning. Probability at this point is 20 percent, so still a low likelihood, but certainly not out of the question. && .MARINE... A stalled front over southeast VA lifts north over the local waters tonight, stalling there through Saturday, before another front sweeps through Saturday night. A period of SCA conditions is likely in the open waters of the central Chesapeake Bay Friday morning into Friday evening as southerly winds increase, gusting to around 20 knots. Elsewhere, variable wind pattern around 5-10 knots. Widespread showers and scattered thunderstorms are expected all day Friday into Friday night. A few Special Marine Warnings may be needed for wind gusts of 35+ knots. Rain/storm chances linger into Saturday, then a front sweeps through bringing sub-SCA conditions Sunday. Winds will generally be light out of the SW through Monday. However, during the evening/overnight time period winds could turn more southerly over the waters, resulting in channeled flow up the Chesapeake Bay. SCAs may be possible both evenings, but are not likely at this time. Additionally, while the chance of thunderstorms is there on Monday, they will be very isolated in nature. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 11 AM Friday to 6 AM EDT Saturday for ANZ534-543. && $$ SYNOPSIS...KRR NEAR TERM...KRR SHORT TERM...KRR LONG TERM...CJL AVIATION...KRR/CJL MARINE...KRR/CJL