Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231327 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 927 AM EDT Thu Mar 23 2017 .SYNOPSIS... High pressure will build across the area today, and move offshore tonight. A warm front will cross the region Friday. Low pressure may affect the area Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure directly overhead this morning will shift offshore by late today. This will allow for light and variable winds this morning to gradually turn light southerly during the day today. Otherwise, a mostly sunny day is in store with highs about 10 degrees below climatological normals, in the mid 40s to low 50s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/...
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Tricky forecast tonight into early Friday. Skies may be clear enough early this evening for radiational cooling to bring temperatures back below freezing in many areas. Then, southerly winds and increasing clouds look likely to start temps on the upward trend after midnight, with many areas likely to return back above freezing by morning. However, a warm front will also be approaching from the west, and some rain is possible especially closer to the Mason-Dixon line. Guidance is not in great agreement, but the Canadian and European models do support a period of light rain, while the NAM and GFS both are dry. With temps possibly near or just below freezing at onset, a period of freezing rain is possible overnight, most likely close to the Mason-Dixon line and inland from the bay. Future shifts will need to closely monitor this potential. Right now probability is well below the 80% advisory criteria, so will just mention in the HWO. Otherwise, Friday will feature a significant warming as the warm front crosses the area. Skies will feature plenty of clouds, but southerly winds will become rather gusty, and temperatures should warm through the 50s into the lower 60s in spots. Some areas could even crack 70, but most places won`t just yet. Southerly flow will continue Friday night, keeping it much milder than the previous few nights. Saturday will remain relatively cloudy, but enough breaks of sun are expected to allow most places to soar into the 70s. This will be the first widespread 70-degree day since March 9th. Records are in the 80s at DCA and BWI, but only 76 at IAD, so the latter is within reach. A backdoor cold front may try to drop back south on Saturday night. Some guidance has backed off on this thought, which would result in another mild night. Otherwise, an approaching system may bring a few showers west, but generally dry weather expected.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Low pressure currently over the Great Basin will slowly make its way east across the country. The system is expected to be cutoff and weakening/filling by the time it reaches the Midwest Saturday night per 00Z ECMWF/GFS. Gulf moisture will stream ahead of this system with rain over the area Sunday and Sunday night. This looks to be a much better chance (likelies across the CWA) for a soaking rain than the quick hitter mainly north this Friday. Persistent warm/above normal conditions at least to the middle of next week in continued southerly flow. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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Expecting mainly VFR through Saturday night. Biggest concern right now, concentrated mainly on MRB, is a chance of some light freezing rain late tonight into early Friday. It will be a race of warmer air moving in at the surface versus precip (if there is some) moving in from the west. Further south and east, the chance of precipitation is less and the chance of temps warming up before it arrives is greater. Winds will become southerly and a bit gusty (20-25 knots) on Friday, and remain gusty as they swing more southwesterly Saturday. An occluded or warm front looks to cross the area Sunday into Monday with likely rain/potential for MVFR conds across the area in southerly flow.
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&& .MARINE...
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Winds will gradually diminish over the bay this morning as high pressure builds overhead with sub-SCA conditions. After that, southerly flow up the bay should start to increase as a warm front approaches, with SCA threat spreading up the bay overnight and then to the adjacent waters during the day Friday. Winds may diminish a bit overnight Friday but look likely to return to SCA levels on Saturday with continued south to southwest flow. With the water still rather chilly, mixing will reduce gusts a bit over the water, but still expect 20 knots or so especially near shore. Sly flow prevails Sunday into next week. Sly/SEly channeling into SCA levels possible at times through this time.
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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 6 AM to 6 PM EDT Friday for ANZ530- 531-537-539-542-543. Small Craft Advisory from noon to 6 PM EDT Friday for ANZ535- 536-538. Small Craft Advisory from midnight tonight to 6 PM EDT Friday for ANZ532>534-540-541.
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&& $$ SYNOPSIS...RCM NEAR TERM...MM/RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/MM/RCM MARINE...BAJ/MM/RCM

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