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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
388 FXUS61 KLWX 301858 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 258 PM EDT Sun Jun 30 2024 .SYNOPSIS... A cold front will then push through this evening. A strong area of high pressure settles over the area Monday and Tuesday before drifting offshore the second half of the week. A warm front nears the region by mid-week yielding a warming trend. && .NEAR TERM /THROUGH TONIGHT/... Earlier mid and high level cloud cover delayed heating and thus convective initiation. However, cumulus fields are gradually developing now. Instability will likely be greatest east of a surface trough located near the Blue Ridge, and it appears the first round of storms will develop in this area from mid to late afternoon. A few storms could approach southern Maryland as well, originating from the storms in southeast Virginia. Additional showers and thunderstorms may form along the surface cold front which is currently across central and southwestern Pennsylvania. With bulk shear of 30-35 kt, storms could organize and grow upscale, presenting predominantly a damaging wind threat. Isolated hail is possible, and a brief tornado could occur near the bayshore if winds remained backed. The greatest storm coverage may ultimately be across southern Maryland this evening. Precipitable water values near or above 2 inches will mean heavy rain rates are possible with any storm, but the greatest QPF signal is across southern Maryland with the conglomerated and potentially briefly repetitive storms. The dry ground conditions should keep the flood threat limited however. There is still uncertainty with whether two rounds of storms occur in any one location. This may be dependent on how widespread initial storms are and if the atmosphere recovers by the time the cold front arrives this evening. Given the timing of the front and moist/unstable airmass ahead of it, storms may not finally clear southern Maryland until around midnight. Even though heating was delayed, temperatures are still rising into the 90s, and dew points are not mixing down too much given the moist profile, light winds, and warm water temperatures. Localized heat index values are topping out near or just above 105 along the I-95 corridor, although only for an hour or two. Gusty northerly winds behind the cold front will usher in much cooler and drier air late tonight. Lows will drop back into the mid 50s to mid 60s, with 40s possible in the higher elevations. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Upper trough axis will pass through Monday as strong (1025 mb) surface high pressure build in from the Great Lakes. This will result in gusty northerly winds through the day and very comfortable conditions for early July standards. Highs will be in the upper 70s to lower 80s with dew points ranging from the upper 40s to mid 50s. Winds diminish Monday night with the high passing to the north. Lows in the 50s will be common, but the I-95 corridor likely stays in the 60s. With the ridge axis progressing to the east Tuesday, it will be a little milder, and there may be some extra cloud cover at times. Dew points will remain in the 50s though, resulting in continued comfortable weather. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Mostly dry conditions are expected Wednesday as high pressure holds on before scooting further offshore with large disturbance approaching from the west. Warm, moist air will build in during the day on Wednesday, allowing a warm up compared to the previous few days with highs in the upper 80s to low 90s. Winds will be elevated out of the SSE, gusting to 20 knots at times during the afternoon. Overnight lows fall into the upper 60s to low 70s for most areas. A large area of low pressure center over the central Canadian provinces will slowly track further east along a secondary low across the heart of the CONUS. Showers and thunderstorm chances will continue from July 4th holiday through the early part of the weekend with renewed PoPs each afternoon and evening. Should the forcing became more sufficient locally and convective parameters increase, strong to severe thunderstorms may be possible during the period but there remains a lot of uncertainty in this. The heat continues through the remainder of the week with highs in the low to mid 90s and heat indices reaching triple digits. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Thunderstorms will likely develop in a surface trough near the Blue Ridge around 19-20Z. Additional thunderstorms may develop along a cold front that approaches this evening. Main update to the 18Z TAFs was to delay thunderstorm timing by a few hours. There is still potential for two rounds, especially near Baltimore/Washington, but confidence is low in that solution. Have a broad brush TEMPO group for now given varied models signals and lack of convective development so far. Impacts are also uncertain since storms may not form a solid line, but strong wind gusts, very heavy rain, and frequent lightning will be threats. Details will be refined in amendments. Storms may not completely move southeast of DCA/BWI until 01Z. South to southwest winds will shift to the northwest behind the cold front this evening. Gusts of 20-25 kt will be possible behind the front and through the day on Monday. VFR conditions will prevail after storms exit. As the ridge of high pressure pushes off toward the New England coast, winds shift to east-southeasterly on Tuesday, before becoming southerly Tuesday night. VFR continues. VFR conditions are expected Wednesday and Thursday for the terminals. Showers and thunderstorms return Thursday, especially further west, so some isolated instances of sub-VFR conditions is not completely out of the question for the holiday period. && .MARINE... Southerly winds persist through early this evening which could near Small Craft Advisory thresholds, especially around southern Maryland. Have not extended the Small Craft Advisory for now due to uncertainty, but this potential will be monitored. Strong to severe thunderstorms are possible late this afternoon and through the evening as a cold front approaches. Thus, Special Marine Warnings may be needed at times, mainly between 4 PM and midnight, although storms may not completely exit southern Maryland waters until a little after that. In the wake of the cold front, a gusty northwesterly wind eventually shifts to northerly on Monday. Small Craft Advisories have been issued late tonight through Monday during period of cold advection. The Advisories may need to be extended into Monday evening for portions of the waters. Winds turn more east- southeasterly on Tuesday with high pressure to the north, staying below advisory thresholds. SCAs are expected Wednesday as high pressure exits to the east and incoming low pressure and associated frontal features approach from the west. Winds diminish by July 4th but SMWs may be needed Thursday afternoon for any strong showers or thunderstorms that cross the waters. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 10 PM this evening to 2 PM EDT Monday for ANZ530-531-535-536-538-539. Small Craft Advisory from midnight tonight to 6 PM EDT Monday for ANZ532>534-537-540>543. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...ADM AVIATION...ADS/ADM MARINE...ADS/ADM