Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 270939 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 439 AM EST Mon Feb 27 2017 .SYNOPSIS... High pressure will shift east of the area today. A warm front will then lift north into the area Tuesday into Wednesday followed by another cold front Wednesday night. After a brief period of high pressure Thursday, a weak low pressure will cross the region early Friday. && .NEAR TERM /THROUGH TONIGHT/... Updated climate section below. Current surface analysis shows high pressure near Cape Hatteras. A developing low pressure and attendant warm front is located over the southern Plains. This system will be the focus of our attention through the next several days. The main upper level component of this system is still well to the west near the West Coast, but well ahead of that, a weak trough aloft with little surface reflection is currently crossing the mid-Mississippi Valley. As this weak system moves into the area today, clouds will be on the increase as warm advection occurs aloft. Low levels remain dry, but some guidance brings the warm advection precipitation into our western zones as early as around sunrise, and with temperatures near or below freezing, some freezing or frozen precipitation is possible. For now have included a chance of rain, sleet and snow in the western zones for this morning, changing to rain as southerly winds bring milder air northward this afternoon. Will be watching radar trends over the next few hours to determine if any winter weather headlines need to be issued, but right now believe odds accumulating snow or ice this morning are less than 50 percent. Further east, high pressure and dry air will win out and it should stay dry, if turning out somewhat cloudy, today. Southerly flow should bring warmer air back up from the south, however, so it should turn out to be a milder day compared to yesterday despite the clouds. Highs in most places will be around 10 degrees warmer than yesterday, but this is just the beginning. Tonight, weak ridging returns aloft and the chance of any precip fades. In fact, we may get some clearing, which could again allow some radiational cooling. However, with the milder southerly flow, expect lows to also be around 10 degrees warmer than this morning. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Deep trough from the Pacific hooks up with the developing low in the southern Plains and sends a maturing storm system northeastward into the Great Lakes by Wednesday. As this system develops, increasing southerly flow will bring another surge of very warm air northward to our region. Warm advection clouds and then showers will overspread the area Tuesday, but with weak forcing, it seems coverage and QPF will be rather modest for a warm front. Southerly flow with the warm front should nudge highs on Tuesday up into the 60s, with lows staying very mild Tuesday night, likely well into the 50s. The low and strong upper trough then pass to our north on Wednesday, dragging the surface front across our region Wednesday night. Temps look to surge well into the 70s and perhaps into the 80s ahead of the front, and this may set the stage for another round of severe weather. The SPC has placed the entire CWA in slight risk for Wednesday given this potential. The front should clear the area near or just after midnight, with drying and cooling on gusty NW winds after midnight Wednesday night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Thursday looks to be post-cold frontal with low pressure lifting north from Maine. Despite rapid growth progged, the strong wind threat continues only through Thursday morning as the low center is progged by 00Z GFS and ECMWF to reach Labrador late in the day. Notable cold air advection from mid- continental air Thursday night into Friday. An Alberta clipper system scoots east across or just north of the area. Will need to monitor this rare shot at snow in one of the warmest winters on record (see climate section below). While accumulating March snow in the central Mid- Atlantic is rare, there has been measurable snow each of the past four Marches across the area. This is the first shot at a fifth. Generally raised PoPs to chance for both Thursday night and Friday with the highest along the Mason-Dixon line with likelies west of the Allegheny Front. Alberta clippers lack Gulf of Mexico moisture and thus have maximum snowfall of a few inches with dusting to one inch most common result east of the Allegheny Front. Eastern Region Superblend (our default forecast for Days 4-7) progs low 50s max temps for the lower southeastern portion of the CWA Friday despite reinforcing cold air behind the clipper. Undercut this by a few degrees and made the chance PoPs for Friday snow showers due to the cold column under the upper trough. The subtropical ridge then sets back up over the SErn CONUS with a warming trend through the weekend. && .AVIATION /10Z MONDAY THROUGH FRIDAY/... VFR through the next 30 hours. CIGS should stay above 5k ft and no precip or fog is expected at terminals through early Tuesday. Rain and sub-VFR threat increases later Tuesday and Tuesday night. Gusty thunderstorms with sub-VFR cigs and vis are possible later Wednesday and Wednesday night as a strong cold front passes. 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 at night. Gusty NW flow behind a Wednesday night cold front eases through Thursday as cold air spills into the region. An Alberta Clipper crosses Thursday night/Friday morning with a shot for brief accumulating snow. && .MARINE... Winds likely to stay sub SCA today and tonight. Southerly flow may bring SCA by tomorrow afternoon to the bay, but held off on SCA for now given uncertainty. Southerly winds increase further just ahead of cold front on Wednesday, with gusty thunderstorms possible along the front and gales possible behind it. Gales taper off Thursday (possibly in the morning) as a brief bout of cold air settles into the region. An Alberta Clipper crosses the waters Friday morning with a reinforcing shot of cold air through Friday with another gale possible. && .CLIMATE... Another period of unseasonably warm weather is forecast to culminate in near-record warmth ahead of a cold front late Wednesday. 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 all three sites. 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 26th) DCA: 47.4 BWI: 44.0 IAD: 44.8 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 26th) DCA: 43.8 BWI: 40.4 IAD: 40.8 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 26th) DCA: 0.34 BWI: 1.21 IAD: 0.33 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/RCM MARINE...BAJ/RCM CLIMATE...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.