Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190129 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 929 PM EDT Sat Mar 18 2017 .SYNOPSIS... A storm system will move offshore tonight. High pressure then briefly builds over the area Sunday and Monday, before a cold front crosses the area Monday night. Stronger high pressure will take hold across the area for most of the remainder of the upcoming work week. && .NEAR TERM /THROUGH SUNDAY/...
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A few minor changes to the forecast for tonight. Light-to-moderate rain showers ongoing across roughly the eastern half of the CWA due to inverted trough and approaching upper-level low. Radar reflectivities are deceptively hot south of DC...as the 0.5 degree elevation angle is sampling melting hydrometeors in/near the melting layer. Though...still getting some much needed rainfall across these areas...with several reports of more than a half an inch of rainfall. Expect precipitation to continue through much of the night until upper-level low passes through the area. Rain showers will gradually transition to snow showers overnight from north to south. Best chance for some light snow accumulations across N MD (mainly Washington, Frederick, Carroll, N Baltimore, and Harford Counties). Have nudged low temperatures down a few degrees across these areas to account for observation trends and recent model performance. Even after lowering temperatures...they still remain rather marginal for anything other than light snow accumulations. Though, snowfall amounts up to an 1 inch are possible on grassy surfaces. While there might be some conversational snowflakes further south across the DC/Balt metros near sunrise...little-to-no accumulation expected. Previous Discussion (for Sunday)... Precip quickly ends Sunday morning, even in the upslope region, leaving a partly to mostly cloudy day, and temperatures around 10 degrees cooler than today with a brisk north/northwest wind.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... High pressure builds in for Sunday night and early Monday. A westerly wind on Monday afternoon will help boost temperatures into the mid/upper 50s or even lower 60s again. The 12z model suite has delayed the onset of the next round of rain Monday with another approaching cold front, and for most areas, Monday should be dry during the day now. This next shortwave is rather weak, with not much moisture return, so we are only carrying chance PoPs for now. && .LONG TERM /TUESDAY THROUGH SATURDAY/... A cold front will bring a chance for rain showers to the region Tuesday and Tuesday night. An area of high pressure will build southward from the Great Lakes Wednesday through Thursday night. Drier air and colder temperatures will ensue into the region. This high pressure will move to the coast to allow for a return flow to usher in milder air Friday and a chance for rain showers Friday night and Saturday with an advancing warm front. The warm front should move north of the region later Saturday, while even milder air moves in from the south. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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MVFR-to-IFR continues at many of the terminals due to rain showers. Though, marine stratus layer progressed far enough westward...that BWI/MTN cigs went IFR. Largely MVFR expected overnight though some IFR is possible in locations where rain changes to snow (MRB/IAD/BWI/MTN). Vsby improves once the rain/snow move out, and ceilings should follow suit by midday Sunday. VFR after that through Monday. Showers possible Monday night with some ceiling/visibility restrictions possible. MVFR conditions Tuesday and Tuesday night with a few rain showers. VFR conditions Wednesday and Wednesday night. Winds northwest 10 knots Tuesday and Tuesday night. Winds northwest 10 knots Wednesday becoming north 5 to 10 knots Wednesday night.
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&& .MARINE...
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By late evening, northerly channeling develops down the bay with sustained winds 15-20 knots and gusts 25-30 knots. Cannot rule out a gale force gust but for now believe those will be further down the bay into Virginia. As high pressure builds in Sunday night, winds will begin to decrease especially in the northern bay and tidal Potomac. Extended the SCA for the lower Potomac and lower half of the Bay through Sunday night; additional areas may need to be added to this if winds do not decrease as quickly as currently forecast. Winds light on Monday and Monday night with high pressure. Showers possible Monday night. Small craft advisories possible Tuesday, then again Wednesday. Winds on Tuesday will be northwest 10 to 15 knots gusts 20 knots. Winds Wednesday northwest becoming north 10 to 15 knots gusts 20 knots.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 7 PM EDT Sunday for ANZ530-531-535- 536-538-539-542. Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537- 540-541-543.
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&& $$ SYNOPSIS...JCE NEAR TERM...MSE/JCE SHORT TERM...JCE LONG TERM...KLW AVIATION...MSE/JCE/KLW MARINE...JCE/KLW

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