Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211613 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1113 AM EST Wed Feb 21 2018 .SYNOPSIS...
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Southerly flow south of a warm front will bring near record warmth to the region this afternoon. A cold front will pass through tonight into Thursday before stalling out to our south Thursday night. The boundary may return north as a warm front Saturday before a stronger cold front passes through from the west on Sunday. High pressure will return for early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Exceptional warmth for late February is expected again today with record high temperatures likely. Most clouds have moved out/dissipated, with partly/mostly sunny skies at present. With 925 mb temperatures progged to be even slightly higher than on Tuesday, highs will likely be even a bit warmer with widespread upper 70s to even some low 80s. If these come to fruition, daily records will be set, and the all-time February max temperatures may be approached or exceeded, with Washington-Dulles having the highest chance (see Climate section below). A cold front moving through the Midwest this morning will then approach the region later this afternoon, crossing the area during the evening and overnight hours. Chances for rain showers will increase from west to east during the afternoon hours, and with the warmth and moisture, several hundred joules of CAPE will likely develop, and some thunder or gusty showers are also possible. The highest chances of rain showers will remain north/west of the metro areas through the day, then push south through the metros during the evening.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
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As the front sinks southward across the area during the overnight hours, falling temperatures and lowering clouds are expected. There may also be areas of light rain and showers, although significant rainfall isn`t expected during the overnight hours. Towards morning as an area of low pressure moves along the frontal zone through the Ohio Valley, more widespread rain will likely approach parts of eastern WV and western MD. Temperatures by morning will fall into the 40s/50s. Thursday will feature low clouds, periods of rain, and drizzle as the weak system passes by. The greatest forcing and most significant rain will likely pass north of the area across Pennsylvania, but the strong warm air advection over cool/moist low levels should still lead to rain and drizzle across the region. Temperatures not really expected to go far with daytime highs similar to the morning lows, in the 40s/50s. In fact, temperatures may be falling much of the day. With a strong high pressure center still over northern New England Thursday night, funnelling in cool northeast flow, and an anomalously strong upper level ridge over the southeast US providing warm southwest flow aloft, areas of light rain and drizzle will persist Thursday night and into Friday morning. By Friday afternoon, as the next wave of low pressure moves along the stalled frontal zone, some areas may break into the warm sector, but uncertainty on its position remains high. Will show 40s across northeast MD to upper 50s/low 60s south/west Friday afternoon.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... Low pressure will develop over the Rockies and central Plains Saturday. This will cause a boundary to our south to retreat north as a warm front. However...the boundary is likely to stall over our CWA which makes for a tricky forecast. The ECMWF has been consistent in keeping the boundary farther south over central Virginia into extreme southern Maryland. The GFS is a bit farther north closer to the Mason-Dixon Line. The boundary will separate chilly marine air to the north vs more very warm air to the south. Did tweak the forecast a bit closer to the ECMWF based on the latest trends of the guidance which shows the GFS edging a bit farther south with the boundary vs previous runs. Certainty remains very low. Shortwave energy will pass through in the southwest flow aloft...bringing the likelihood for some rain. Highest confidence for rain is across the northern portion of the CWA...where there is an increased chance for overrunning ahead of the boundary and closer to the shortwave energy. Max temps are forecast to range from the lower to middle 50s north of the boundary to the mid and upper 60s south of the boundary. The low over the Rockies and Plains Saturday will track through the Great Lakes Saturday night and into southern Canada Sunday. The cold front associated with this system will approach the area Saturday night into Sunday. This may cause the boundary overhead to move farther north as a warm front. A period of unusually warm conditions is likely during this time. An increasing low-level jet and shortwave energy will bring the chance for showers during this time as well. Again highest confidence in precipitation will be across the northern CWA into the Appalachian Mountains. The cold front associated with the low will pass through Sunday afternoon. A few showers and perhaps even a few thunderstorms will accompany the frontal passage. Will have to watch for the potential of heavy rain Saturday and Sunday. We will have an anomalously moist airmass in place. As of now it appears that the best chance for flooding from heavy rain will be to our north later Saturday into Sunday where forcing will be stronger. Will continue to monitor. High pressure will return for early next week bringing drier and more seasonable temperatures. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/...
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VFR and gusty southwest winds at all sites through the rest of today. As a cold front approaches and crosses the region this evening and tonight, rain showers and even an isolated thunderstorm are possible, with best odds being at MRB, then moving towards DCA/BWI/IAD later in the evening. Winds will turn northerly behind the front, and low ceilings with MVFR conditions are forecast develop by early Thursday morning. MVFR/IFR conditions are then likely in low clouds, areas of rain, and drizzle Thursday, Thursday night, and potentially lasting into Friday. A boundary will remain overhead Saturday before possibly retreating as a warm front Saturday night into Sunday. IFR conditions are likely on the north side of the boundary. Certainty in the position of the boundary remains low at this time. A cold front will pass through Sunday. A few showers and thunderstorms are possible along and ahead of the cold front.
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&& .MARINE...
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Southerly winds with SCA conditions across the waters today. With warm air temperatures expected over considerably cooler waters, the strongest gusts will likely be observed along the shorelines. As a cold front crosses the region tonight, winds will turn northerly behind the front, and now look more likely to reach SCA criteria, so have raised one for the bay and adjacent waters (except the Potomac) for after midnight. A boundary will remain near the waters through Saturday before possibly moving north as a warm front Saturday night into Sunday. A Small Craft Advisory may be needed on the south side of the boundary during this time. Confidence in the position of the boundary remains low at this time. A stronger cold front will pass through from the west Sunday. A few showers and thunderstorms may accompany the frontal passage.
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&& .CLIMATE...
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The all-time February highest minimums are: 61 at DCA/Washington (2/17/1891) 58 at BWI/Baltimore (2/17/1891) 55 at IAD/Dulles (2/17/1976) - records only go back to 1960 at IAD The all-time February highest maximums are: 84 at DCA/Washington (2/25/1930) 83 at BWI/Baltimore (2/25/1930) 79 at IAD/Dulles (2/24/1985 and 2/25/2000) - records only go back to 1960 at IAD Record warm daily maximum temperatures Wed 2/21 DCA 75 (1953) BWI 74 (1930) IAD 70 (1997) Record warm daily minimum temperatures Wed 2/21 DCA 51 (1954) BWI 49 (1981) IAD 45 (1981)
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530>543. Small Craft Advisory from midnight tonight to 6 PM EST Thursday for ANZ530>534-537>543.
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&& $$ SYNOPSIS...BJL/RCM NEAR TERM...MM/RCM SHORT TERM...MM/RCM LONG TERM...BJL AVIATION...BJL/MM/RCM MARINE...BJL/MM/RCM CLIMATE...LWX/RCM

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