Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240757 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 357 AM EDT Sat Aug 24 2019 .SYNOPSIS... A cold front will move into the southern mid-Atlantic today. Strong high pressure will build north of the region through early next week. A tropical cyclone could form over the weekend and move near the southeast coast and out to sea. && .NEAR TERM /THROUGH TONIGHT/... Isolated light rain showers are moving west to east across Nelson and parts of Albemarle Counties in Virginia. Rain amounts will be only a few hundredths of an inch at best. Aside from the showers, patches of dense fog have formed in valleys in the Potomac Highlands and Shenandoah Valley. These are areas where wind has grown calm and dewpoint temperatures are near 60. Visibility has fluctuated in most of these areas from around 2 miles to one-quarter mile then back up to 1 mile. Low confidence in a prolonged period of dense fog but will closely monitor the situation over the next hour or so to decide if an advisory will be needed or not. As for today, high pressure will continue to build to our north and usher in drier and cooler air than during the early to middle of last week. Obviously, the cloud cover and light to moderate rain showers with the passing front on Friday had kept our temperatures in the 60s throughout the day for the most part. However, we are anticipating a little more sunshine today that will inevitably lift our temperatures from the lower 60s to the lower to middle 70s over most of the region. A few showers can`t be ruled out near the Chesapeake Bay area with a northeast to onshore flow during the afternoon. Dry conditions will continue tonight as temperatures drop to the middle to upper 50s on a light northerly wind and partially clearing skies. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... With high pressure in control to our north and soon to be to our northeast Sunday into Sunday night, another dry and cool day in store for us during the period. High temperatures Sunday will be about the same as today, if not about 3 degrees warmer. The cooler scenario would rely on whether we have a northerly component to our wind or an easterly component to our wind Sunday into Sunday night. Again, a stray shower or two can`t be ruled out along the Chesapeake Bay during the afternoon. As for Monday into Monday night, the high pressure center makes a move toward the northeast to allow for an easterly wind and then a gradual southeast wind. These change in direction will allow for warmth and moisture to return to the region Monday into Monday night, primarily the moisture. Temperatures will still only reach the middle to upper 70s Monday afternoon. There is a chance that rain showers will develop not just along the Chesapeake Bay, but in other places as well. Rain amounts will be light, if they occur. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Coastal low pressure will be sliding offshore Tuesday, increasing the threat of showers. Onshore flow may provide a bit of a cooler wedge, but its too soon to rule embedded thunderstorms out-- a small deviation in the details would allow for sufficient heating. Ample moisture will be in play, and heights will be dropping by the end of the day. That trough axis, with a surface cold front, will be crossing the area Wednesday...making this period the most likely time frame for precipitation. Given the humidity of the air mass ahead of the front, thunderstorms also possible, but its uncertain whether there will be enough upper level support for strong storms. Continental high pressure will gradually build Thursday-Friday, with the 500 mb trough axis gradually dampening. Given the low heights, wouldn`t completely rule out a diurnally driven shower on Thursday, but the trend will deviate toward seasonable/dry conditions by the end of the week. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Patchy dense fog has been causing visibility to fluctuate in the Shenandoah Valley and toward the Mason-Dixon line. Although we are anticipating IFR conditions near MRB, there is a chance that LIFR could occur at some point near daybreak. All in all for the remainder of the terminals, and for MRB from mid-morning on, VFR conditions are expected with building high pressure. Winds will be northwest at first becoming northerly then northeasterly over the course of today, tonight and Sunday. VFR conditions expected again Monday into Monday night. Any isolated showers could bring lower ceilings to the TAF sites Monday afternoon. Winds northeast becoming southeast Monday into Monday night. Onshore winds Tuesday may bring a marine layer inland. While confidence in details low, flight restrictions due to ceilings possible. If low ceilings do form, they would be likely to lift Wednesday; however, as a cold front advances, the threat for showers and thunderstorms increase. Restrictions on Wednesday likely to be more brief/spotty in nature. && .MARINE... A Small Craft Advisory is in effect through Noon today for all zones, then for the Tidal Potomac and central Chesapeake Bay this evening and overnight. Additional small craft advisories may be imminent for the marine zones Sunday afternoon and then again for Monday. One factor could be the pressure gradient between the high pressure to the north and northeast and the developing coastal sub- tropical or tropical low pressure system over the Southeast U.S. East/northeast winds Tue will become west Wed. At this point, the strongest winds appear as though they may be associated with showers/thunderstorms due to a cold front Wednesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until noon EDT today for ANZ531>534-537- 539>541-543. Small Craft Advisory from 6 PM this evening to 6 AM EDT Sunday for ANZ534-537-543. && $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...HTS AVIATION...KLW/HTS MARINE...KLW/HTS

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