Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
890 FXUS61 KLWX 121911 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 311 PM EDT Fri Jul 12 2024 .SYNOPSIS... A boundary will remain stalled near the Blue Ridge Mountains through tonight before weakening a bit for Saturday. High pressure will build over the southeastern CONUS Sunday through Wednesday of next week bringing a return of hot and humid conditions. A cold front will approach Wednesday before passing through Wednesday night into Thursday. High pressure will approach the area late next week. && .NEAR TERM /THROUGH TONIGHT/... Latest surface analysis shows a boundary that retrograded to the west, currently located near the Blue Ridge an Catoctin Mountains. The boundary separates tropical moisture from drier air (note the dewpoints on the moist side of the boundary are in the 70s and dewpoints are in the 60s along the drier side of the boundary). Low pressure will continue to weaken as it stalls out over the southeastern CONUS tonight. However, plenty of low-level moisture will continue to stream into the area from the south, with the deepest moisture near and east of the Blue Ridge Mountains (along and east of the boundary). This has resulted in showers near/east of the Blue Ridge Mountains along with a couple thunderstorms near southern MD. There may actually be a break in the precipitation late this afternoon before another round of convection upstream over the Carolina`s moves into the area this evening. Locally heavy rain is possible given the instability and abundant low-level moisture. However, confidence for flooding is low for most areas given the recent dry conditions and the fact that most of the activity should be moving (given a somewhat stronger low and mid-level flow 15-25 kt). Will continue with the Flood Watch for areas along the Bay into southern MD (where heavier rain has already occurred or FFG is lower near the urban areas around Baltimore). A weak upper-level disturbance will pass by to the north late tonight into Saturday morning and this may cause forcing along the boundary to strengthen just a bit. More showers are likely with possible thunderstorms, especially east of the Blue Ridge Mountains. Another round of heavy rain is possible, especially east of Interstate 95 where moisture will be deepest. The Flash Flood Watch continues locations along the Bay from Anne Arundel County northward (where forcing may be a bit stronger closer to the upper-level disturbance along with the deepest moisture). && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... The aforementioned frontal boundary will remain nearby on Saturday, perhaps pushing further south and east. With the Bermuda High still holding strong in the western Atlantic, plenty of moisture will interact with that boundary, resulting in more showers and storms. The best chance will be over southern Maryland tomorrow, with much lower chances west of I-95. Depending on how much rain ends up falling today, there could be a very marginal flood risk over southern MD as well. However, again, with the antecedent conditions being so dry, just don`t see it being a widespread threat at this time. The last thing to note about Saturday is that it will mark the first day in yet another warming period. Temperatures will be in the upper 80s to low 90s for most, and upper 70s in the mountains. Lows overnight will be up in the 70s. Sunday will generally be dry for most and much hotter as a strong upper ridge begins to build over the region. Meanwhile, the Bermuda High starts to break down and shift eastward, cutting off our supply of very high dew points. Temperatures Sunday afternoon look to reach the mid to upper 90s, with dew points in the mid to upper 60s. This should yield heat indices in the low 100s or so. We may not quite hit criteria for Advisories, but it will be close. With heat comes the chance for afternoon convection, which will likely be confined to the higher elevations. Steering flow will be pretty weak, so any storms that develop will move fairly slow. Given the ongoing drought however, they will have to maintain themselves for at least an hour or two over the same location to pose a flood threat. At this point, just don`t see that happening as Sunday looks to have very isolated coverage of storms at best, and lasting maybe 30 minutes given weak lapse rates in the mid-levels. Another mild night expected Sunday with lows only dropping into the low 70s (mid to upper by the water). && .LONG TERM /MONDAY THROUGH FRIDAY/... Another period of excessive heat and humidity is expected during the early to middle portions of next week. For Monday and Tuesday, forecast high temperatures are slated to reach the century mark across portions of the area. Between the two days, Tuesday looks a bit hotter as more locations could cross 100 degree days. The added element of humidity will help usher heat indices into the 105 to 110 degree range. This easily pushes into Heat Advisory to near Excessive Heat Warning territory. The continued summertime heat and humidity will add fuel to the atmosphere for daily showers and thunderstorms. A strong cold front tracking in from the Ohio River Valley is expected to cross the Mid- Atlantic region on Wednesday. Depending on the exact timing of this system coupled with any morning clouds or showers will ultimately dictate the degree of severe weather threat. At face value, the best chance for any severe convection would be Wednesday afternoon/evening given the approaching front, seasonably hot/humid air mass in place, and sufficient deep-layer flow within the column. This system is expected to slowly push east of the area into Thursday and Friday. However, it does appear to stay in the vicinity as heights quickly rebound over the southeastern U.S. into the Carolinas. While the frontal zone does not completely stall, it could remain close enough to keep showers and thunderstorms around into the latter half of the work week. The post-frontal air mass should provide some relief from the heat as daily high temperatures hold steady in the 80s, accompanied by low temperatures falling back into the 60s. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... A light southeast flow will bring plenty of low-level moisture into the area through Saturday morning. Showers are expected along with a chance for a thunderstorm for the eastern terminals. Confidence for a thunderstorm was too low to put in the TAFS as of now, but the best chance for a storm will be between 23z and 03z. Low clouds are expected to develop this evening with CIGS deteriorating to IFR levels during this time. IFR and possible subIFR conditions (from low clouds and fog) are likely overnight into early Saturday before cigs gradually improve. VFR cigs are likely to return Saturday afternoon. A shower or thunderstorm is possible Saturday, but much of the time should turn out dry. VFR conditions are expected most of the time Sunday and Sunday night. With convective chances increasing through the early/mid portions of the work week, there will certainly be a threat for restrictions at the area terminals. This is especially the case by mid-week ahead of a potent cold front. However, the hot and humid air mass early in the week will support daily chances for showers and thunderstorms. Wind fields should largely be out of the southwest with occasionally some diurnal shifts at times. The cold front will shift winds over to northwesterly by late Wednesday. && .MARINE... A Small Craft Advisory is in effect for southerly winds along the middle portion of the Bay and lower Tidal Potomac River. Showers are expected at times through tonight along with possible thunderstorms. Thunderstorms may contain locally strong winds, especially this evening. For Saturday, the slow moving frontal boundary remains setup over central/southern portions of the waters. This will be the focal point for thunderstorms to develop throughout the day. Any storms could produce locally strong wind gusts, which may necessitate SMWs at times. By Sunday, winds should generally be light out of the W to start the day, turning out of the SW mid-late morning, then S by the evening. As winds turn more southerly, would expect an uptick as the channel up the main portion of the Chesapeake Bay. SCAs may be needed during the late afternoon into Sunday evening, before tapering off overnight as the nocturnal inversion sets in. A hot and humid air mass will increase the chances for showers and thunderstorms over the waters early next week. Special Marine Warnings may be needed for any of the stronger thunderstorms. Some uptick in south-southwesterly flow may approach advisory levels on Tuesday. Thus, Small Craft Advisories may be needed over portions of the waters. && .CLIMATE... Here are some daily high temperature records during the July 15-17 timeframe next week. Records (RERs) are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. A `+` sign indicates multiple years currently hold that record. ***MONDAY, JULY 15TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 100F (1988) 100F Washington-Dulles (IAD) 98F (1995) 99F Baltimore (BWI) 102F (1995) 99F Martinsburg (MRB) 107F (1936) 97F Charlottesville (CHO) 102F (1954) 99F Annapolis (NAK) 101F (1995) 96F Hagerstown (HGR) 102F (1954) 100F ***TUESDAY, JULY 16TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 104F (1988) 102F Washington-Dulles (IAD) 104F (1988) 101F Baltimore (BWI) 104F (1988) 101F Martinsburg (MRB) 107F (1988) 100F Charlottesville (CHO) 102F (1988) 100F Annapolis (NAK) 98F (1997)+ 97F Hagerstown (HGR) 104F (1988) 101F ***WEDNESDAY, JULY 17TH, 2024*** LOCATION RECORD (YEAR) FORECAST Washington-National (DCA) 102F (1980) 98F Washington-Dulles (IAD) 100F (1997)+ 96F Baltimore (BWI) 101F (1988) 97F Martinsburg (MRB) 102F (1988)+ 93F Charlottesville (CHO) 100F (1988)+ 97F Annapolis (NAK) 100F (1900) 95F Hagerstown (HGR) 100F (1953)+ 94F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Flood Watch through Saturday morning for MDZ008-011-014-508. Flood Watch until midnight EDT tonight for MDZ017-018. VA...None. WV...None. MARINE...Flood Watch through Saturday morning for ANZ530. Small Craft Advisory until 6 AM EDT Saturday for ANZ532>534- 537-540>543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...CJL LONG TERM...BRO AVIATION...BJL/BRO/CJL MARINE...BJL/BRO/CJL CLIMATE...BRO