


Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
052 FXUS61 KLWX 081921 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 321 PM EDT Tue Jul 8 2025 .SYNOPSIS... A cold front will drop closer to the area tonight and will then stall and waver nearby through the weekend. && .NEAR TERM /THROUGH TONIGHT/... Line of storms has formed east of I-81 and is progressing to the east around 23 kt. Latest NUCAPS data from 1736Z shows an instability gradient east of Route 15, so expecting storms to strengthen as they moved east of the Blue Ridge Mountains. NUCAPS data also showed 925-850 mb moisture maximized across northeast MD from Carroll east to Cecil Counties. Expect new storms to develop in that area along the bay breeze well in advance of line of storms currenly crossing I-81. Mid-level lapse rates are poor, but strong instability with CAPE values upward of 3500 J/kg will offset the warm temps aloft. Damaging winds, very high instantaneous rain rates, and freq lightning are the main threats. The current line is moving around 23 kt, but line may slow down as it approaches/encounters the bay breeze. Convection will gradually wane this evening with areas of fog/low clouds late given the warm and moist airmass overhead. Lows will fall back into the upper 60s over the mountains with mid 70s along and east of I-81. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Sharper low-mid level trough will cross the area Wed afternoon and provide better/stronger sfc convergence to trigger more widespread convection than today. Looks like areas along and east of I-95 will be the areas with the most concentrated activity. Signal for heavy rain for Wed is stronger than today due to better/stronger forcing and better moisture pooling along the front. Anticipate another Flood Watch tomorrow with greater risk of flooding/flash flooding. Scenario repeats itself Thursday with more showers and thunderstorms as frontal zone dissipates over the area. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Not much change in the extended pattern as there is no real progressive storm system to clean us out of this warm, muggy, and stormy pattern. Temperatures will trend slightly cooler for the end of the workweek and into the weekend given added cloud cover with the stalled front nearby. Pieces of shortwave energy will continue to ride along the stalled boundary as it bisects the area. Current 12z synoptic guidance shows the front stalling somewhere in the vicinity of southwest PA, central MD, and northern VA during the Saturday and Sunday timeframe. With the front nearby expect continued chances for showers and thunderstorms during the afternoon and evening hours. As for severe weather, uncertainty remains given the placement of the front and timing of shortwave energy as it pivots across. Current CSU learning machine guidance, CIPS pattern recognitions, and long range NSSL probs are leaning toward the Saturday and Sunday timeframe as the next potential period for organized convection. Either way thunderstorms will have the potential of producing locally damaging winds and instances of flash flooding each afternoon. This is due largely in part to the stagnant warm and moist airmass hanging tough over the region. Temperatures Friday through the weekend will range from the mid to upper 80s and low 90s. Heat indices will make it feel more like the mid to upper 90s. Beyond Sunday, uncertainty continues in regards to a potential frontal passage. 12Z synoptic/ensemble guidance show a cold front ejecting out of the Midwest and Ohio River Valley some time Monday into Tuesday next week. This front does not appear to arrive until mid next week leading to a continuation of daily shower and thunderstorm chances until it passes through. Temperatures and precipitation will continue to remain above average within the back half of the long term period. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... Temporary sub-VFR reductions are likely at all terminals beyond this point through 01-02z due in part to scattered to numerous thunderstorms bubbling up over the area. Clusters of storms will gradually work from west to east across the area first impacting KMRB/KSHD before 21z. Storms will work into the corridor between 19-21z with a slow lag to the east of DCA/BWI heading into the early evening hours. Repetitive round of thunderstorms are likely with chaotic and erratic storm motions expected leading to further uncertainty in when and where they pop up. For that reason, tried to keep 3 to 4 hour TEMPO windows at each terminal. Storm threats will include very heavy rain, frequent lightning, and potential downbursts to 50 kt. Winds will remain out of the south and southwest at less than 10 kts. Storm coverage decreases after 02-03z with areas of fog and low clouds expected overnight. This is especially true for terminals west of the corridor and in deeper river valleys. Another round of strong to severe thunderstorms are possible Wednesday afternoon and evening. This threat appears to be across the lower half of the corridor from IAD/DCA points south toward KCHO/KRIC. Once again damaging winds and instances of flash flooding will be the primary concerns. Expect sub-VFR reductions in around storms along with chaotic/erratic winds/storm motions. A similar pattern is expected Thursday through the weekend with daily afternoon/evening thunderstorms. This will lead to continued sub-VFR reductions at times mainly during the afternoon/evening and during the overnight with patchy fog/low clouds developing in the wake any thunderstorms. Winds will remain less than 10kts. && .MARINE... Scattered to numerous thunderstorms look to impact the waters anytime after 18-20z/2-4pm this afternoon. Special Marine Warnings will be needed to cover this threat with storms capable of producing severe downbursts winds and heavy rainfall. Highest coverage of storms look to be between 4-9pm this evening before diminishing overnight. Additional showers and thunderstorms are possible Wednesday as the front shifts further south and stalls across the waters. Storm coverage will once again be widespread, mainly confined to waters near southern MD and the northern neck of VA. Wind will be the primary threat with storms along with frequent lightning and heavy rainfall. Additional SMWs will be needed to encompass this threat. Winds will remain light out of the south outside of thunderstorms, with outflows likely disrupting opportunities for southerly channeling. Sub-SCA level winds are expected Thursday through the upcoming weekend despite a stalled front nearby. Gradients will remain fairly weak with variable wind directions dictated by the placement of the front. Once again SMWs will be needed at times during the afternoon and evening hours given daily convective development. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 7 PM EDT this evening for DCZ001. Flood Watch until midnight EDT tonight for DCZ001. MD...Heat Advisory until 7 PM EDT this evening for MDZ008-011-013- 014-016>018-508. Flood Watch until midnight EDT tonight for MDZ005-006-008-011- 013-014-016>018-503>508. VA...Heat Advisory until 7 PM EDT this evening for VAZ053>057-527. Flood Watch until midnight EDT tonight for VAZ053-054-506-526- 527. WV...None. MARINE...Heat Advisory until 7 PM EDT this evening for ANZ530. Flood Watch until midnight EDT tonight for ANZ530. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...EST AVIATION...LFR/EST MARINE...LFR/EST