Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241952 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 252 PM EST Fri Feb 24 2017 .SYNOPSIS... A cold front will approach the area tonight and cross the area Saturday. High pressure will then build over the area Sunday through early next week. A warm front will then lift north into the area Tuesday followed by another cold front on Wednesday. && .NEAR TERM /THROUGH TONIGHT/... Very warm day ongoing today with the area ensconced in the warm sector of a low pressure system passing through the Great Lakes. Warm southerly flow will continue through the remainder of the afternoon and evening with mostly sunny skies and only scattered cumulus and some areas of high cirrus. Temperatures will max out in the 70s to near 80F, nearing daily records, and possibly even the all- time February record at Washington/Dulles (see climate section below). For tonight, very mild conditions will continue with persistent southerly flow and increasing low level moisture. This increasing moisture may lead to the development of low stratus overnight and into Saturday morning, especially from the DC metro eastward. There may also be some areas of fog, with the best chances along and near the Chesapeake Bay where cooler waters in the 40s interact with low level dew points in the 50s. Elsewhere, southerly flow should preclude widespread fog formation. Lows tonight generally in the 50s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... A strong cold front will cross the region on Saturday, noted by sharp wind shift from the south to west-northwest and tight low level temperature gradient (difference of around 12C at 925 mb). In addition, will see temperatures surge again out ahead of the front, although will be dependent on extent and dissipation rate of any morning fog/stratus. Current forecast of 70s ahead of the front combined with dew points in the 50s should yield 500-800 J/KG of MLCAPE. That combined with increasing uni-directional 0-6KM shear of 50-60 knots will set the stage for a high shear/low cape day. Expecting a fine-line or squall of convection moving along the front from west to east through the day, generally in the 10am-4pm timeframe. These forecast CAPE/shear profiles combined with the sharp front are favorable for at least a low- end severe threat. The strongest winds (50kt+) are progged to be generally 700mb and above, so will need some height to the convection to mix this down to the surface. In addition, the best upper level forcing will be located north of the region across Pennsylvania. Because of these factors, current thoughts are for more of a widespread 30-40 knots with the line, with localized severe gusts possible. The Storm Prediction Center has placed the Mid- Atlantic states in a Marginal risk for severe thunderstorms. Much cooler temperatures will crash in behind the front for Saturday night with temperatures falling back into the 20s and 30s by Sunday morning. Gusts of 30-35 mph, possibly higher, are likely behind the front Saturday evening. Will also see some light upslope snow showers develop in the northwest flow. Calmer and more seasonable conditions are expected for Sunday and Sunday night as high pressure builds into the region. Highs will be in the 40s to low 50s with lows in the 20s and 30s. && .LONG TERM /MONDAY THROUGH FRIDAY/... As high pressure moves offshore Monday, a warm frontal system will move parallel to the Ohio Valley and push into the mid- Atlantic Monday night. A chance of rain and snow showers are possible with the storm system for Monday night with rain showers continuing into Tuesday. The system moves to the east coast Tuesday then offshore Tuesday night. The next low pressure system will move across the Great Lakes, dragging its associated cold front across the mid- Atlantic Wednesday into Wednesday night. There is a chance for rain showers ahead of the front. As the main trough of low pressure pivots across the region Wednesday night into Thursday, cooler and drier air will follow with high pressure building in from the west. Some upslope snow showers could evolve as well through the day Thursday. A reinforcing shot of colder air will move in behind a cold dry front Friday, only to be followed by high pressure from the Midwest U.S. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... The region will remain in the warm sector of a low pressure system passing to the northwest this afternoon into tonight. No aviation weather concerns expected through the remainder of the day today with only some high cirrus and scattered cumulus. Otherwise, southerly winds with some gusts to 20 kt possible. Clouds will increase tonight. Areas of low stratus and possibly some patchy fog will develop overnight and persist into Saturday morning. MVFR/IFR conditions likely. Strong cold front will cross the area on Saturday, likely reaching the metros during the afternoon. Thin line of gusty showers/embedded thunderstorms likely (brief IFR possible) , followed by a several hour period of potential 30+ kt westerly gusts. Winds will subside through Sunday as high pressure builds in from the west. There is the potential for periods of MVFR conditions Monday through Wednesday with chances of rain showers. Winds will be generally out of the southwest. && .MARINE... Southerly flow 10-15 kt today and tonight with high pressure offshore and low pressure moving toward Great Lakes. There may be a few localized gusts to 20 knots this afternoon, mainly along the shorelines. Areas of fog possible tonight and into Saturday morning. A Small Craft Advisory goes into effect at 10am Saturday for increasing southerly flow ahead of an approaching cold front. The front will bring a dramatic change in conditions during the late afternoon to early evening. Line of gusty showers/possible thunderstorms will mark sharp wind shift to west. There is potential for strong to severe thunderstorms, so stay weather aware if out on the waters tomorrow. Behind the front, gale conditions are expected, and a gale warning is in effect. Winds slowly taper into Sunday morning, although SCA likely continues a good portion of Sunday. There should be a lull Sunday night with high pressure moving across the area. Periods of SCA conditions are possible in the Monday to Wednesday timeframe with southerly winds ahead of an approaching low pressure system. && .CLIMATE... Temperatures today are expected to be at least the second warmest Feb 24th on record (if not break or tie the record from Feb 24, 1985). High minimum records are possible for Friday and less likely for Saturday due to evening temperatures dropping behind an afternoon cold front. Record highs are less likely overall on Saturday as showers and clouds should limit how warm it gets, while DC/Baltimore both set their all-time February highs on that date back in 1930, making them hard to reach. Record high maximum temperatures for February 24 and 25: BWI 79F (1985), 83F (1930) DCA 78F (1985), 84F (1930) IAD 79F (1985), 79F (2000) Record high minimum temperatures for February 24 and 25: BWI 55F (1985), 52F (1930) DCA 52F (1975), 54F (1891) IAD 53F (1985), 47F (2000) Warmest temperatures ever observed in February BWI 83F (2/25/1930) DCA 84F (2/25/1930) IAD 79F (2/25/2000, 2/24/1985) Warmest Februaries (average temperature) DCA BWI IAD 1. 46.9 (1976) 44.0 (1976) 42.1 (1990) 2. 45.2 (1990) 43.9 (1949) 41.1 (1976) 3. 44.7 (1997) 43.3 (1890) 41.0 (1998) 4. 44.3 (2012) 42.7 (1932) 40.9 (2012) 5. 43.9 (1949) 42.6 (1909) 40.5 (1997) Feb 2017 (through the 23rd) DCA: 46.3 BWI: 43.0 IAD: 43.6 Warmest Winters (Dec 1-Feb 28/29) DCA BWI IAD 1. 44.7 (1931-32) 45.3 (1931-32) 40.0 (2011-12) 2. 44.3 (1889-90) 44.4 (1889-90) 39.7 (2001-02) 3. 43.3 (2011-12) 42.4 (1948-49) 39.4 (1997-98) 4. 43.2 (2001-02) 41.9 (1949-50) 39.0 (2015-16) 5. 42.8 (1949-50) 41.3 (1879-80) 38.3 (1990-91) Winter 2016-17 (through Feb 23) DCA: 43.4 BWI: 40.1 IAD: 40.4 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 10 AM to 2 PM EST Saturday for ANZ530>543. Small Craft Advisory from 1 AM to 6 AM EST Sunday for ANZ530>543. Gale Warning from 2 PM Saturday to 1 AM EST Sunday for ANZ530>543. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...KLW AVIATION...MM/KLW MARINE...MM/KLW CLIMATE...BAJ/DFH/RCM

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