Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
456 FXUS61 KLWX 051430 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1030 AM EDT Fri Jul 5 2024 .SYNOPSIS... A cold front will slowly approach from the Ohio River Valley through tonight, then cross the region Saturday. High pressure will briefly follow for Sunday as the front stalls just to the south and east. The high will move offshore early next week as additional weak fronts impinge upon the area. && .NEAR TERM /THROUGH TONIGHT/... MID-MORNING UPDATE... Low clouds and fog from earlier this morning quickly burnt off after sunrise, leaving mostly sunny to partly cloudy skies east of the Blue Ridge. Some denser cu has begun to develop along the terrain west of the Shenandoah Valley. This scattered to broken fair weather cu is expected to develop further east through the afternoon. As we head into late afternoon and the early evening hours, a more convective presentation is expected. As in the previous discussion, guidance has continued to back off on PoPs during the early afternoon, instead focusing more on this evening. Consequently, trimmed PoPs a bit more this afternoon, mostly limited to south of I-66 and west of the Blue Ridge. Based on latest CAMs, isolated storms could develop along terrain near and west of the Blue Ridge to start. SPC still has us in a Marginal Risk for severe storms (level 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). This will be the feature to monitor for the potential of severe storms this evening. The heat continues today, with Heat Advisories and Excessive Heat Warnings in effect. PREVIOUS DISCUSSION FOLLOWS... The latest guidance has really backed off on convection during the first half of the day, with little to no precip expected. Rain chances have been cut back through early afternoon, then ramp up during the late afternoon to evening. The frontal boundary to our north slowly starts to sag southward, with some clusters of showers and thunderstorms forecast to develop in the highlands of WV. These showers/storms push east into our area, though the highest coverage is expected to be along and south of I-66 this evening. SPC continues to highlight a Marginal Risk for severe storms (level 1 of 5) along/west of I-81. As storms move across that area this evening, a severe storm or two will be capable of producing damaging wind gusts. The biggest story today is going to be the exceedingly hot and humid conditions. The latest guidance continues to trend upwards in regards to temperatures this afternoon. The forecast calls for mid to upper 90s across most of the area, with low to mid 80s in the mountains. A few spots are likely to could hit 100, including DC, Fredericksburg, and others in Central VA east of the Blue Ridge. On top of the heat, dew points during peak heating are likely to be in the low 70s, and upper 60s for those west of US-15. Around the Fredericksburg area and in far southern MD, dew points are forecast to be in the low to mid 70s for most of the day. The combination of hot temps and high humidity is expected to produce oppressive conditions. An Excessive Heat Warning has been issued for the Fredericksburg area and southern MD, due to peak heat indices of 110-112F. Heat Advisories are in effect for the rest of the area of the Alleghenies. Heat indices reach 100-105 west of the Blue Ridge, and 105-110 to the east. If you plan to be outdoors today, it is recommended you stay hydrated, wear light colored clothing, and take plenty of breaks in an air conditioned building. Shower/storm activity pushes east across the area through late evening, then conditions dry out overnight. Still, given the very moist environment, cannot rule out a stray shower tonight. Overnight lows settle in the mid to upper 70s. Some urban centers won`t drop below 80F until after midnight. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... A stout mid/upper-level wave will most likely be located over lower Michigan by daybreak Saturday. Flow aloft will increase ahead of this trough, but the trough itself is expected to buckle and lift up the Saint Lawrence River Valley and away from the region as it encounters persistent ridging over the northwest Atlantic Ocean. This actually results in weak height rises as the trough`s associated surface cold front slowly crosses the Mid-Atlantic. Low-level flow looks to be west to northwesterly for much of the area west of I-95. This flow pattern would reduce surface moisture (due to downsloping effects) and convergence. Therefore, convective coverage west of I-95 may be very sparse. Further east, higher low- level moisture and surface flow backed a bit more to the south results in a bit more favorable environment. The best large scale forcing for ascent will be lifting away from the region, so any activity will have to result from a combination of the slowing surface front, heating, and bay/river breeze boundaries. Given the hot and humid airmass in place, any thunderstorms that do form could produce heavy downpours, gusty to damaging winds, and frequent lightning during the afternoon to evening hours. The front looks to move just south and east of the local area heading into Sunday as high pressure briefly builds in. This greatly reduces the prospects for precipitation. Temperatures will still be hot, but it will be much less humid. && .LONG TERM /MONDAY THROUGH THURSDAY/... Ridging is forecast to persist over the northwest Atlantic Ocean while broad troughing slowly drifts east over the central CONUS much of next week. This pattern results in several weak surface fronts drifting into the area and washing out, with daily low-end chances for showers and thunderstorms each afternoon/evening. Without a more obvious large scale feature, the prospects for any widespread drought busting rainfall look rather slim. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... VFR conditions are expected for most of today as mostly dry conditions prevail through early afternoon. Scattered showers and thunderstorms are expected once again this evening, though the highest chances will be at CHO, IAD, and DCA. TEMPO groups may be needed for gusty winds and brief periods of sub-VFR conditions if any stronger storm moves over a terminal. Convection ends late this evening, with mostly dry conditions overnight. Given the saturated environment, additional low stratus is possible late tonight. Prevailing VFR conditions are forecast Saturday through early next week. Shower and thunderstorm coverage looks rather sparse, except east of I-95 on Saturday. W/SW flow is generally expected at 5-10 kts with occasional gusts to around 15 kts possible in the afternoon. && .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 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. Westerly to southwesterly flow is expected to continue right through early next week. The wind should stay generally light, though some strong thunderstorms may be possible particularly Saturday afternoon into Saturday evening. && .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. && .CLIMATE... Hot temperatures are today across the entire area, though this heat is likely to fall just short of record for the day. Below is a list of record high temperatures for July 5, and the current forecast high temperatures for those days. RERs are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. Friday Jun 21st Climate Site Record High Forecast High Washington-National (DCA) 102F (1999) 100F Washington-Dulles (IAD) 99F (1999) 99F Baltimore (BWI) 102F (1999+) 99F Martinsburg (MRB) 103F (1999) 97F Charlottesville (CHO) 104F (2012) 99F Annapolis (NAK) 100F (1999) 95F Hagerstown (HGR) 102F (1919) 96F && .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 from 4 PM this afternoon to 6 AM EDT Saturday for ANZ534-543. && $$ SYNOPSIS...DHOF NEAR TERM...CAS/KRR SHORT TERM...DHOF LONG TERM...DHOF AVIATION...DHOF/KRR MARINE...DHOF/KRR TIDES/COASTAL FLOODING...DHOF CLIMATE...KRR