Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 281458 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 958 AM EST Tue Feb 28 2017 .SYNOPSIS...
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A warm front will lift north across the area through today, followed by a strong cold front late Wednesday and Wednesday night. After a brief period of high pressure Thursday, an area of weak low pressure will cross the region Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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It`s a mostly sunny start to the day for much of the region, but as a warm front located over the Ohio Valley moves towards the region, will see rapidly increasing clouds as well as increasing chances for rain showers by later this afternoon. Currently monitoring the progress of ongoing showers/thunderstorms along the warm frontal boundary across West Virginia/Ohio/Kentucky. NAM/HRRR seem to have the best handle of its evolution this morning, and leaned towards their solutions, while also slightly speeding up their arrival across our region. Expecting the first showers to make their entrance towards the Allegheny Front by noon-1pm, spreading eastward and reaching the metros around 3-5pm. Forecast CAPE/Showalters indicate that much of the initial activity should be plain rain with no thunder activity, but some elevated instability does work in later in the evening and overnight, so thunder chances increase then. Temperatures have already risen into the 50s, and highs in the 60s to around 70F prior to rain seem on track. After the disturbance passes later tonight, the chance of precipitation declines. Warm southerly flow and clouds will keep temps elevated, with lows well into the 50s in most of the area. Warmest spots may not fall below 60.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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Wednesday is the big show. Very powerful cold front pushes in from the west as low pressure slides past to our north, with a strong upper level shortwave and considerable low level instability (for March 1st, at least). There is a LOT of wind aloft to tap into, with 850s 50 knots plus at times. Given this, the SPC continues the slight risk for severe thunderstorms, with damaging winds still expected to be biggest threat, though more organized cells could bring hail. Some early sun should push temps close to, if not past, 80 in parts of the region, aiding the thunderstorm threat. Timing is still a little uncertain, and some storms may linger towards midnight. After that, quick drying and cooling takes place on a gusty NW wind. Potential for some gusts up to 40 mph behind the front late Wednesday night and Thursday. Pressure gradient declines as we head thru the day Thursday so winds should diminish later on. Highs will struggle to rebound much with considerable cold advection. Then we have to watch the clipper system which looks to push into the region later Thursday night with a reinforcing shot of cold air to boot. Right now guidance favors northern areas seeing any snow before dawn on Friday, with lows much colder than recent days supporting it.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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Friday the Alberta clipper scoots east from the area in the morning with the upper trough axis shifting east across the area late morning through midday. Instability under this low looks to produce snow streamers/showers/flurries over the area during daylight hours Friday. Guidance consensus max temps still is in the 40s across the area to around 50F well south of DC in gusty NWly flow. However, with the 850mb temps around -10C, wet bulb zero temps are less than 1000ft (a critical level for snow/rain). Therefore, went for snow exclusively for NWrn suburbs and rain or snow metro areas and south. Downsloping plays an important role in snow streamers in NWly flow. Elevation increases from the Laurel Ridge of PA south along the Allegheny Front of MD/WV. Therefore, accumulating snow chances generally decrease south from the Mason-Dixon line due to increased downsloping. However, the narrow bands that develop can produce localized accumulating snow wherever they set up. Above freezing temperatures will limit impact. Surface high pressure settles overhead Friday night, then shifts south to the SErn CONUS with a warming trend Saturday through Monday.
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&& .AVIATION /15Z TUESDAY THROUGH SATURDAY/...
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VFR expected into early this afternoon. Showers and sub-VFR potential increases later this afternoon and evening. Gusty thunderstorms with sub-VFR cigs and vis are also likely later Wednesday and Wednesday night as a strong cold front passes. Some thunderstorms may become strong to severe. Winds will be increasing out of the south, light today, but steady and gusty by Wednesday afternoon, then turn gusty from the NW after the front passes Wednesday night. VFR conditions expected Thursday and Thursday night. An Alberta Clipper shifts east from the area Friday morning with a shot for brief accumulating snow through the day Friday across the DC metros. High pressure/tranquil and cold Friday night.
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&& .MARINE... Generally sub-SCA winds expected for most of today. SCA goes into effect at 4 PM as southerly winds increase late in the day and overnight. Southerly winds increase further Wednesday with gale conditions possible, but confidence is low so went with SCA for now. In addition, there is the potential for strong to severe thunderstorms late Wednesday and Wednesday evening as a cold front crosses the region. Winds then turn northwest Wednesday night with gale conditions possibly continuing into Thursday morning before winds subside Thursday afternoon and evening. An Alberta Clipper shifts east from the Chesapeake Bay region Friday morning with a reinforcing shot of cold air through Friday and another gale possible into Friday night. High pressure overhead Saturday with south flow and warming Sunday and Monday. && .CLIMATE... Another period of unseasonably warm weather is forecast to culminate in near-record warmth ahead of a cold front that crosses the area Wednesday evening. Here is a list of record daily warm temperatures for March 1st (Wednesday). Site Record High Record Warm Low DCA 80 (1976) 57 (1910) BWI 80 (1972) 53 (1910) IAD 77 (1972) 43 (1997/1987/1976) Here are updated February and Winter records. A warm Tuesday will ensure the warmest February at DCA and IAD and probably a close new record at BWI. 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 27th) DCA: 47.3 BWI: 43.9 IAD: 44.6 Washington is on pace for the third warmest winter on record, Baltimore will have a top 10 warmest winter, and this will be the warmest winter on record for Dulles. 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 the 27th) DCA: 43.7 BWI: 40.4 IAD: 40.7 This has been a very dry February. Showers and isolated thunderstorms are expected this evening across the Baltimore- Washington area, so rainfall before midnight will be added to these totals. Driest Februaries (total precipitation) DCA BWI IAD 1. 0.35 (2009) 0.26 (2009) 0.25 (1978) 2. 0.42 (1978) 0.36 (2002) 0.35 (2009) 3. 0.47 (2002) 0.56 (1978) 0.46 (2002) 4. 0.62 (1901) 0.63 (1977) 0.49 (1977) 5. 0.66 (1977) 0.65 (1901) 0.68 (1968) Feb 2017 (through the 27th) DCA: 0.34 BWI: 1.21 IAD: 0.33 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 6 PM EST Wednesday for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...MM/RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/MM/RCM MARINE...BAJ/MM/RCM CLIMATE...BAJ/DFH

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