Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210835 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 335 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 through 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 Friday into 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 /THROUGH TODAY/...
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Exceptional warmth for late February is expected again today with record high temperatures likely. Some low clouds will start the day again, albeit to a less degree than yesterday, and likely confined to near the I-95 corridor. With deep southwest flow, expecting these to lift by mid to late morning, similar to yesterday, giving way to partly/mostly sunny skies. 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 and evening.
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&& .SHORT TERM /TONIGHT 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. 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/...
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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.
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&& .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
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A period of MVFR/IFR is likely this morning across the TAF sites east of the Blue Ridge. Any ceiling/visibility restrictions will then lift by 15z with VFR and gusty southwest winds developing at all sites. As a cold front approaches and crosses the region this evening and tonight, rain showers and even an isolated thunderstorm are possible, mainly MRB. 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 will increase again during the mid to late morning hours with SCA conditions developing across the waters. With warm air temperatures expected over considerably cooler waters, the strongest gusts will likely be observed along the shorelines. A Small Craft Advisory is in effect for all waters beginning at 9 AM. As a cold front crosses the region tonight, winds will turn northerly behind the front, and may approach SCA criteria tonight and Thursday. Uncertainty with respect to wind speed remains, so have not issued a SCA at this time. A boundary will remain near the waters 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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A summary of the records broken on Tuesday...February 20th. IAD high was 77 degrees. That broke the old record of 70 set in 1971. The low temperature was 47 degrees. This was the warmest low on record for that date...breaking the old record of 46 degrees in 1981. DCA high was 78 degrees. That broke the old record of 76 set in 1930. BWI high was 76 degrees. That tied the old record of 76 set in 1930. If today`s calendar day...Wednesday February 21st low does not drop below 60 degrees, it would be the first time not dropping below 60 at DCA in February since 1891, and only the sixth time on record in the entire meteorological winter season. Even a low 56 or higher at DCA would be the warmest low in the month of February since 1976. 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 In addition, its not out of the question that all-time February maximum temperatures are tied or broken. 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 It goes without saying that daily records are in jeopardy. A table of those records follows. 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 from 9 AM this morning to 6 PM EST this evening for ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM CLIMATE...LWX

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