Area Forecast Discussion
Issued by NWS Sterling, VA

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435 FXUS61 KLWX 221527 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1027 AM EST Mon Jan 22 2018 .SYNOPSIS... High pressure will shift east off the Southeast coast today. A cold front will approach from the west tonight, then cross the region Tuesday. High pressure will build across the area during the second half of the week, then shift offshore this weekend as another frontal system approaches from the west. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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While guidance suggest we will lose the stratocu deck later today there will be a sig increase in high level clouds. So, expecting cloudy skies overall today. Still very mild with temperatures in the mid 60s in most places. Don`t think we`ll hit 70F in any areas today. Showers should hold off until evening in the west and after midnight in the east.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... Overall guidance has come into good agreement on timing a cold frontal passage around midday Tuesday. As the front approaches from the west Monday evening, clouds quickly lower and thicken. Expect showers to develop/advect into the region near and west of the Blue Ridge during the middle to late evening, then quickly spread eastward overnight. Elevated instability of 100-300 J/kg should be enough for a few isolated thunderstorms as well. It will be a rather mild and humid night for late January, with lows only in the mid 40s to lower 50s, and dew points not far behind. Since the front passes through around midday Tuesday, this allows for a little surface heating during the mid to late morning. This may allow a few thunderstorms to become rooted in the boundary layer, resulting in a few instances of gusty winds. The best chance for this would be south of US 50 into interior southern MD away from the cooler water. Gusty southerly winds are likely over the ridgetops as well since they will be poking into the low level jet, but at the moment it appears winds will be brief and sporadic enough to preclude a Wind Advisory ahead of the front at least for now. The front will pull offshore by Tuesday evening. NW winds will be a bit blustery, again especially on the ridges (where a Wind Advisory would be more likely in cold advection). These NW winds will usher in a more seasonable airmass for Wednesday and Wednesday night. Upslope snow showers are likely with about 1 to 2 inches of accumulation expected Tuesday night in NW flow. A secondary shortwave could reinvigorate some light upslope snow showers and keep extra clouds around the area Wednesday into Wednesday night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A reinforcing shot of cool air will cross the region on Thursday, resulting in what will likely be the coolest day of the week. However, with the air still having more of a Pacific than Arctic origin, it will only drop temps to around or perhaps just slightly below normal. Winds will gust a bit, but otherwise, a seasonable January day. High pressure will build overhead on Friday, and temps will begin to moderate already, but the big warming will get underway Saturday as the high shifts east and southwest flow kicks back in on the high`s west side. However, guidance is not in great agreement on how long the warm spell lasts, with the GFS quickly pushing a cold front across the area by Saturday night, while the EC lingers it until during the day Sunday. Accompanying the front will be some showers, but as with the front, timing on them varies, and is rather uncertain. Best chance of rain is Saturday night. By later Sunday, cooler air will be streaming back across the area, but with limited if any arctic air available, not expecting any severe cold, and even below normal readings will be a bit hard to find. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...
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VFR is expected. S winds around 10 kts, with a few gusts to around 20 kts are expected today. Clouds quickly lower and thicken tonight, especially after midnight, with widespread IFR CIGS likely by 9z. Vsbys drop in -SHRA as well after midnight. LLWS issues almost a certainty with strong LLJ about 50 kts around 2 kft. Iso thunder potential as well 9-18z Tue, possibly accompanied by gusty surface winds mainly SE of a line from DCA to CHO. VFR returns Tue aft. Gusty NW flow ensues 10 G 20 kts into Wed before gradually diminishing. VFR will prevail Thursday and Friday with high pressure in control overall. A dry cold front on Thursday may bring northwesterly gusts back to 20-25 knots, but they should subside by Friday.
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&& .MARINE... SCA gusts expected, albeit a bit sporadic due to poor mixing over cooler water starting this evening. Gusts should gradually become more widespread into Tuesday, with gales possible depending on mixing/convection. Winds shift to NW following cold FROPA Tue early aft. Gusts could persist through Tue night into Wed before diminishing as high pressure builds. Reinforcing shot of cool air moving south from Canada on Thursday will likely lead to more SCA conditions, but winds should relax Friday as high pressure builds overhead. && .TIDES/COASTAL FLOODING... Increasing southerly flow ahead of an approaching cold front will cause water levels to increase today through Tuesday. Minor coastal flooding is possible, especially during the midday high tide cycles Tuesday if the cold front isn`t through by then. However, confidence on any minor flooding is low. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 1 AM to 6 PM EST Tuesday for ANZ530>532-535-536-538>541. Small Craft Advisory from 7 PM this evening to 6 PM EST Tuesday for ANZ533-534-537-542-543. && $$ SYNOPSIS...DHOF NEAR TERM...LFR SHORT TERM...DHOF LONG TERM...RCM AVIATION...RCM/DHOF MARINE...RCM/DHOF TIDES/COASTAL FLOODING...DHOF

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