329 FXUS61 KLWX 091917 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 317 PM EDT Wed Jul 9 2025 .SYNOPSIS... A surface trough will remain across the area through Thursday. Weak high pressure will build over the area for the end of the week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Low-level trough is expected to sharpen across the area through tonight as a shortwave-trough approaches from the OH Valley. This will provide stronger forcing and help sustain thunderstorms longer into the night tonight. In other hand, recent NUCAPS data from 1717Z indicate that air mass today is not as unstable as it was yesterday. Not seeing the 3500 J/kg CAPE that I saw yesterday. Northeast Maryland looks particularly more stable and less humid today than yesterday. The 925-850 mb moisture axis is also further west today and extends up the I-81 corridor from Augusta County VA up through Winchester, Martinsburg, Hagerstown into Chambersburg PA. The radar trends indicate that the cluster over Rockingham County will likely merge eventually with the other clusters approaching the Appalachians, posing a flood risk over parts of eastern WV. Given these trends and moisture axis further west, have expanded the Flood Watch to cover eastern WV and Washington County MD. With time, this moisture axis is expected to shift northeast on SSW winds. So, expect a later onset of thunderstorms in central and northeast MD this evening when compared to yesterday. Given the stronger forcing, expect thunderstorms to last well into the overnight hours, especially for the I-95 corridor. Overall, the flood risk looks higher than the severe threat. After the thundestorms exit late tonight, expect areas of low clouds/fog to form. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Low clouds to start the day will keep temperatures and instability down Thu. Weakening surface trough will result in less forcing for thunderstorm development. Expect thunderstorm coverage tomorrow to be significantly less than today. Strengthening low-level ridging Fri should result in a downward trend in areal coverage of convection. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Very little change to what is a typical Summertime pattern across the region. Sensible heat and humidity will remain along with daily shower and thunderstorm chances. This is a result of zonal flow aloft and no strong frontal boundaries set to cross the region. Overall, a stagnant airmass that will be hard to flip until at least the middle of next week. Synoptically, will continue to monitor an area of low pressure and shortwave trough tracking across the Great Lakes into eastern Canada this weekend. This shortwave trough combined with a dissipating frontal boundary will lead to an uptick in showers and thunderstorms this weekend into early next week. Once again. it will not be raining all the time with ample dry time for plans in between. Highest coverage will be during the afternoon and evening hours through at least Tuesday. As for severe weather, uncertainty remains given the placement of the wavering 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 this weekend into early next week 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 Monday, 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 Tuesday into Wednesday next week. This front does not appear cross until then with a secondary front to follow late next week. The GFS tends to remain more aggressive in holding the current pattern while ECWMF and Canadian turn the pattern over mid next week.Temperatures and precipitation will continue to remain above average within the back half of the long term period. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... Numerous to widespread showers and thunderstorms are expected late this afternoon through this evening. Heavy rainfall, freq lightning and reduced vsby are the main threats. Low clouds form late tonight with IFR cigs expected before mixing/scattering out late Thu morning. Less t-storm coverage expected Thu. Prevailing VFR conditions are expected Saturday through Monday. Sub- VFR reductions remain possible during the afternoon and evening hours as a result of showers and thunderstorms. Winds will remain light out of the south and southwest Saturday before turning light out of the west to northwest Sunday. && .MARINE... Gradient winds are expected to increase tonight across the southern waters which may require SCAs. Otherwise, higher winds and waves can be expected near thunderstorms. 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 Thursday as the front stalls nearby. 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 outside of the open waters. Sub-SCA level winds are expected through the upcoming weekend despite a stalled front nearby. Light southerly winds are expected Friday and Saturday with light west to northwesterly winds on Sunday. Thunderstorms may be possible during the afternoon and evening hours, potentially leading to the issuance of SMWs. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flood Watch until midnight EDT tonight for DCZ001. MD...Flood Watch until midnight EDT tonight for MDZ004>006-008-011- 013-014-016>018-503>508. VA...Flood Watch until midnight EDT tonight for VAZ025>027-029>031- 036>040-050-051-053>057-501-502-505>508-526-527. WV...Flood Watch until midnight EDT tonight for WVZ053. MARINE...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