Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 181847 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 247 PM EDT Sat Mar 18 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH SUNDAY/...
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As expected, showers have developed to our west this afternoon in association with an approaching shortwave and cold front. There have even been a couple thunderstorms near the surface low center, which will move across our southern counties this afternoon. As a result, showers look pretty likely with a chance of thunderstorms. The storms may be vigorous enough to produce small hail, perhaps close to severe-sized hail if a storm gets particularly strong. The window of occurrence looks pretty short -- perhaps 3 to 7 pm, but the convection has had a history of small hail over West Virginia, and we are a little bit warmer / more unstable. Thunder potential should generally be south of the US 48/I-66/US 50 combined corridor. The shortwave moves across the area, and as mentioned in the morning discussion, energy transfers to an offshore low, leaving an inverted trough behind, followed by the upper low itself. This combination will keep precipitation chances in the eastern half of the forecast area virtually all night. Forecast soundings show precipitation changing over to snow at the tail end of the precip (say after 08z tonight)...but temperatures are at or above freezing and today has been reasonably warm with a lot of sun. Temperatures do get close to freezing in extreme northeast Maryland -- places like Frederick, Westminster, and northern Baltimore and Harford Counties. I`ve added some light accumulations to these areas (1/2 inch or less, generally), but there`s some potential for around an inch of fresh snow there. Further south in the cities, some flakes may fly late tonight or early Sunday, but it currently looks too warm to accumulate. 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/...
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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.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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Although today turned out quite sunny, cigs/vsby will decrease as the showers/rain move back in. Most of what is out there now is VFR but after sunset, cigs will lower to MVFR and maybe even IFR (IFR was only included in the MRB TAF though). Vsby is a big question mark. Probably largely MVFR but a period of IFR is likely, especially if rain changes to snow for a while, accompanied by gusty winds. 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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Winds have been light on the waters on this Saturday. Showers move into the waters by early evening, and a thunderstorm is possible south of DC/Annapolis with some small hail. 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 from 11 PM this evening to 7 PM EDT Sunday for ANZ530-531-535-536-538-539-542. Small Craft Advisory from 11 PM this evening to 6 AM EDT Monday for ANZ532>534-537-540-541-543.
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&& $$ SYNOPSIS...JE NEAR TERM...JE SHORT TERM...JE LONG TERM...KLW AVIATION...JE/KLW MARINE...JE/KLW

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