


Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
848 FXUS61 KLWX 182003 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 403 PM EDT Fri Jul 18 2025 .SYNOPSIS... A stationary front over the area today will return northward as a warm front tomorrow. A cold front will move through Sunday night. High pressure will build to our north early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Current surface analysis shows a stationary front extending west-northwestward from just north of Richmond toward Charlottesville, Staunton, and Harrisonburg, and then eventually into central West Virginia. Storms are in the process of developing in the vicinity of and south of this boundary, but activity has struggle to develop north of roughly Harrisonburg, as earlier cloud cover/shower activity has limited daytime surface heating. Model guidance has struggled mightily with the evolution of storms thus far today, and there is a growing amount of skepticism regarding whether stronger storms will make it into the far northern reaches of the Flood Watch that is in effect. Based on the current evolution of the cumulus field, it appears as though the greatest threat for stronger storms and resultant risk for flash flooding will be from the Harrisonburg/Staunton/Waynesboro/Charlottesville vicinity eastward toward Fredericksburg. While confidence isn`t quite there to cancel the Watch further north, confidence in flooding occurring north of those locations is decreasing. Any stronger storms today will still be capable of producing very heavy rainfall, given high PWAT values, deep saturated profiles and ample instability. The background environment isn`t overly favorable for damaging winds with low DCAPE values (300-600 J/kg) and subpar low-level lapse rates (around 7 C/km), but a few instances of damaging winds may still be possible, especially if storms start to exhibit weak supercellular characteristics (as some of the storms near Roanoke have started to do). Further north toward the DC/Baltimore Metros, most of the precipitation is expected to occur as showers, but a few thunderstorms may try to drift northeastward toward the DC Metro late this evening. The threat for flash flooding looks to be low in the DC Metro, but not zero, with any potential chance coming if storms approach from the southwest during the late evening hours. Any activity will wind down by around or shortly after midnight, with dry conditions expected during the second half of the night. Low clouds may try to develop later tonight, and fog may form in locations that don`t get the low clouds. Overnight lows are expected to be in the upper 60s and lower 70s. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... The stationary boundary located over the area today will make slight northward progress as a warm front tomorrow. Flow aloft will remain primarily zonal. A weak convectively generated disturbance may approach from the west during peak heating. The combination of daytime heating and weak ascent associated with this feature will result in another round of showers and thunderstorms tomorrow afternoon into tomorrow evening. Currently it appears as though the highest coverage of these storms (much like today) will be in the Central Shenandoah Valley and Central Virginia. However, a brief afternoon or evening thunderstorm may be possible anywhere in the forecast area. Storms may be capable of producing isolated to scattered instances of flooding, as well as a damaging wind gust or two. High temperatures will be in the mid-upper 80s for most, with dewpoints holding in the 70s. Upper troughing will start to dig to our north across Northern New England on Sunday, while low pressure tracks through the Canadian Maritimes. This will cause a cold front to drop southward across NY, New England and PA over the course of the day. Storms may try to form along a pre-frontal trough Sunday afternoon. Some of these storms may be strong to severe. SPC currently has the entire area outlooked in a Marginal Risk for severe thunderstorms. && .LONG TERM /MONDAY THROUGH FRIDAY/... Characterized by 500-mb height anomalies running around 1.5 to 2 standard deviations below average, a formidable upper trough is forecast to continue tracking eastward across the Canadian Maritimes. This pattern shift allows for a broad dome of Canadian high pressure that settles over Quebec into New England through mid- week. On Monday, a steady northerly component to the surface winds will sufficiently lower dew points over the area. This ultimately results in a multi-day reprieve from the 2 to 3 weeks of continued heat and humidity. Although the current forecast package shows dew points in the upper 50s to mid 60s, plenty of solutions carry readings into the mid 50s. This is accompanied by daily high temperatures in the low/mid 80s (upper 60s to 70s in the mountains). Widespread overnight lows will be in the 60s, with some upper 50s along the mountain ridges. Any shower chances through Tuesday are tied to the Potomac Highlands into the central Shenandoah Valley. Some perturbations circulating clockwise around a ridge across the Lower Mississippi Valley could invigorate some localized lift. By Wednesday, some return flow picks up as the surface anticyclone exits the New England coast. The global ensemble consensus shows this scenario unfolding which helps increase dew points across the Mid-Atlantic region. At the same time, a broad upper ridge initially over the south-central U.S. will expand both north and east in time. Its influence on the local area is expected to come with rising daily temperatures, especially by Thursday and Friday. A return of temperatures in the low/mid 90s is looking more likely, but ensemble spread does increase as noted by sizeable box-and-whisker plots. While thunderstorms do not come back immediately, expect a better chance for such storms by late in the week. This is in response to some northern stream amplification noted in a number of models. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... The main concern through the rest of the day will be thunderstorm potential, with otherwise prevailing VFR conditions. The best chance for storms looks to be around CHO, which is located in the vicinity of a stationary front. Further north and east, conditions are a bit more stable, so chances for thunderstorms appear to be lower, albeit non-zero. At the moment, light rain is moving eastward from the vicinity of MRB toward the DC/Baltimore metros. This activity is expected to continue on as just showers. Any potential thunderstorms would likely develop off to the southwest in more unstable air and move northeastward toward the Metro terminals later this evening. As a result, the PROB30s for DCA and IAD have been pushed back a couple hours. The PROB30 has been removed at BWI, where confidence is increasing that storms will remain off to their south and west. Any thunderstorms should wind down during the first half of the night, but low clouds may move in later during the night. IFR ceilings appear possible for a time later tonight into early tomorrow morning, but gradual improvement back to VFR ceilings is expected over the course of the morning tomorrow. Thunderstorms will form again tomorrow afternoon, with most of the activity focused over central VA. Confidence is currently too low to introduce PROB30s in the DC/Baltimore Metro terminals, but at least a PROB30, if not a TEMPO will eventually be needed for CHO. Additional thunderstorms may be possible on Sunday afternoon. With precipitation chances looking pretty low on Monday through Wednesday, expect VFR conditions at all terminals. The shift in the pattern ushers in a northerly wind on Monday before turning more east-southeasterly by Tuesday. Once Canadian high pressure exits the New England coast on Wednesday, a return southerly flow is expected. && .MARINE... Light and variable winds are expected over the waters this afternoon. An SMW for thunderstorms may be needed later this evening, particularly over the middle to lower Tidal Potomac. Light south to southeasterly winds are expected tomorrow, and then light westerly winds on Sunday. Winds will shift to out of the north behind a cold front Sunday night, and potentially could near low-end SCA levels during that time. SMWs may potentially be needed for thunderstorms during the afternoon and evening hours both days this weekend. Winds across the marine waters should stay below advisory levels through Tuesday. A northerly wind may gust around 10 to 15 knots on Monday before shifting to east to northeasterly on Tuesday. There is no threat for thunderstorms as Canadian high pressure builds to the north. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Flood Watch until midnight EDT tonight for MDZ016-501-509-510. VA...Flood Watch until midnight EDT tonight for VAZ025>031-036>040- 050-051-055>057-501>504-507-508-526-527. WV...Flood Watch until midnight EDT tonight for WVZ050-055-501>506. MARINE...None. && $$ SYNOPSIS...KJP NEAR TERM...KJP SHORT TERM...KJP LONG TERM...BRO AVIATION...BRO/KJP MARINE...BRO/KJP