Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231357 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 957 AM EDT Tue Aug 23 2016 .SYNOPSIS... High pressure remains over the region through much of the week with a cold front moving through on Friday. High pressure returns for the weekend. && .NEAR TERM /THROUGH TONIGHT/... High pressure is centered over the central Appalachians this morning. Overall the weather is quiet and non-impactful. Patch of mid-level clouds, mainly across Virginia, beginning to transition into a cu field; this should be areawide by afternoon, with scattered to perhaps broken coverage. (Aside from the subsidence inversion, the morning sounding is dry.) Thermal fields are similar to yesterday, which will result in another day of lower to mid 80s with dew points in the mid 50s to around 60. The high will begin to move offshore tonight, but the pressure gradient will remain weak. While some cirrus is possible, temperatures should otherwise be able to drop close to the dew points in the upper 50s and lower 60s away from the urban centers and waters (upper 60s in these locales). Patchy valley fog will be possible. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... The center of high pressure will move offshore for Wednesday and Thursday, while mid/upper ridging expands over the SE CONUS. While there will be an uptick for dew points on Wednesday, the more noticeable change will come Thursday, when temperatures will near 90F and dew points will rise into the mid and upper 60s. There is some model variation on how strong the SE ridge is. In general the NAM is the weakest and allows some shortwave troughs to more directly cross the area. Think Wednesday will be dry for most, although there is a slim chance of a shower on the spine of the Appalachians. Thursday will provide a better chance of mountain convection as instability will be greater. While most of this should be confined west of I-81, some of it could spill eastward during the evening depending on shortwave trough trajectory. A cold front will also be pushing south across PA late at night, but convection should be at a diurnal minimum as it nears the CWA. && .LONG TERM /FRIDAY THROUGH MONDAY/... Guidance remains in overall decent agreement through the long term with the cold front crossing the region Friday and high pressure passing to the north Saturday and exiting stage right slowly Sunday and Monday. Pops spike Friday with instability associated with the cold front then drop to sub-chance on Saturday. They start ramping up especially in the west again Sunday and Monday as upslope flow on southwest side of the high brings more moisture into the mountains where terrain influences may allow storms to pop. Probability looks low though without a larger forcing mechanism. Temperatures will spike Friday ahead of the front into the lower 90s then drop closer to normal through the weekend. They may start to rise again Monday. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... Stratocumulus near FL070 beginning to scatter into a cu field. Scattered to perhaps broken coverage by afternoon. Little aviation concern through Wednesday as high pressure moves offshore. Could be some morning BR at MRB, but not a strong enough signal to put in TAF yet. Scattered storms are expected to develop over the mountains on Thursday, perhaps reaching MRB, but unlikely in the metros at this point. VFR overall Friday through the weekend. Main issue will be if any thunderstorms impact the terminals on Friday. && .MARINE... Easterly flow on the waters this morning, generally around 10 kt. Flow will become SE today and S by Wednesday and Thursday as high pressure moves offshore. Sub- SCA expected through most of the period. The best chance for southerly channeling appears to be Thursday evening, but forecast is less than SCA criteria at this time. Front crossing the region Friday is a window for SCA conditions as well as thunderstorms, but confidence is low on both. High pressure likely keeps winds just below SCA over the weekend with easterly flow. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS/HTS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM/HTS MARINE...ADS/RCM/HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.