Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200846 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 346 AM EST Tue Feb 20 2018 .SYNOPSIS...
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A warm front will slowly pass through the region this morning into early this afternoon. Record warmth is possible behind the warm front later today through Wednesday. A cold front will pass through Wednesday night into Thursday before stalling out to our south Thursday night. The boundary will return north as a warm front Friday into Saturday before a stronger cold front passes through from the west on Sunday.
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&& .NEAR TERM /THROUGH TODAY/...
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Low clouds and some fog/drizzle exist early this morning from near the Blue Ridge eastward as warm/moist air aloft streams overhead of a cooler surface layer. Through the remainder of the morning, the surface warm front will continue crossing the area, with low clouds and fog eventually lifting and giving way to some scattered cumulus and scattered high clouds. Northeast Maryland and locations near the Chesapeake Bay will be the last to see this change. On the warm side of the surface boundary, south/southwest winds and very warm temperatures will be the main story as highly anomalous upper level ridge (heights 2-3 SD above climatology for Feb) sits parked off of the southeast US coastline. 850 mb temperatures will rise into the 13-15C range by this evening, which is very rare territory for Feburary. Expecting high temperatures to reach the 70s for most locations, except holding in the 60s in northeast MD and along the Chesapeake Bay where clouds clear last. Some locations west of the Blue Ridge will make a run at 80F.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
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Tonight, with plenty of low level moisture as dew points sit in the 50s, some fog and low clouds become possible again. Extremely mild conditions for this time of the year are expected with lows in the 50s to locally near 60F. Wednesday will be exceptionally warm again with another day of highs in the 70s to locally near 80F. As a cold front approaches from the northwest later in the day, some showers become possible west of the Blue Ridge. The cold front will push southward across the region Wednesday night, with surface northerly flow taking over. Aloft, with the strong ridge still positioned near the southeast US coastline, southwest flow will continue. This combined with some energy aloft, will set the stage for a day of rain and drizzle on Thursday, with temperatures crashing back towards normal, with daytime highs in the 40s/50s.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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A boundary to our south will return north as a warm front Friday and it will stall out near our area Friday night through Saturday. Most of the area should remain north of the boundary Friday...so low clouds along with chilly conditions are expected with perhaps even some light rain and drizzle. The boundary will likely move into the area Friday night and hang around through Saturday night. There is high uncertainty as to exactly where the boundary will be which means that there is high uncertainty with the forecast. The boundary will separate chilly marine air to the north vs unusually warm and moist air to the south. It does look like there will be shortwave energy passing through in the southwest flow aloft...so rain is likely although it will probably not be raining the whole time. Given the anomalously moist airmass in place...moderate to locally heavy rain is possible. A stronger cold front is still expected to pass through the area later Sunday into Sunday night from the west. More showers are likely ahead of the front. A few thunderstorms cannot be ruled out either...depending on whether or not the previously mentioned boundary is overhead or to our north. If it is to our north...then the warm sector may provide enough instability for some thunderstorms to develop.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/...
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Widespread IFR/LIFR exists east of the Blue Ridge this morning in low stratus and some areas of mist/fog. Improvement is expected this morning, first at IAD/CHO, followed by DCA, and eventually MTN/BWI by noon or so. At MRB, also seeing fog, but this should lift shortly after sunrise. VFR is then expected in the afternoon and evening. Additional low clouds and some fog are likely again tonight, with potential for IFR returning, especially BWI/MTN/DCA/CHO. Similar to today, these ceilings/visibilities will improve through Wednesday morning with VFR by the afternoon. As a cold front crosses Wednesday night with rain likely Thursday, another period of sub-VFR is likely. A boundary will approach from the south Friday as a warm front and it will stall out nearby or just to our north Saturday through Saturday night. Times of rain are likely along with subVFR cigs/vsbys ahead of the boundary Friday. In fact...IFR/subIFR conditions are likely during this time. SubVFR conditions are likely Friday night and possible Saturday depending on how far north the boundary makes it. Uncertainty in the position of the boundary remains high at this time.
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&& .MARINE...
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Southerly flow will increase through this morning and especially this afternoon and a Small Craft Advisory goes into effect for all waters at 10 AM. With warm air temperatures expected over considerably cooler waters, the strongest gusts will likely be observed along the shorelines. The same situation will occur Wednesday and a SCA is in effect. Additional Small Craft Advisories may become necessary on Thursday as well as northerly winds increase behind a cold front. A warm front will approach the waters from the south Friday and it will stall out nearby later Friday night through Saturday night. Confidence on where the boundary sets up remains low at this time. If the boundary sets up to the north...then SCA wind gusts are possible in the warm sector. However...the boundary may remain just to the south as well which would mean lighter winds but extended low clouds/fog. Times of rain are likely regardless of the frontal postion Friday through Saturday night.
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&& .CLIMATE... Some all-time February highest minimum temp records could be in jeopardy, but it depends on how quickly a cold front moves through Wednesday night. If the Wednesday calendar day 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 It almost goes without saying that daily records are in jeopardy. A table of those records follows: Record warm daily maximum temperatures Tue 2/20 Wed 2/21 DCA 76 (1930) 75 (1953) BWI 76 (1930) 74 (1930) IAD 70 (1971) 70 (1997) Record warm daily minimum temperatures Tue 2/20 Wed 2/21 DCA 59 (1939) 51 (1954) BWI 57 (1939) 49 (1981) IAD 46 (1981) 45 (1981) && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 10 AM this morning to 8 PM EST this evening for ANZ530>543. Small Craft Advisory from 9 AM to 6 PM EST Wednesday 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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