Area Forecast Discussion
Issued by NWS Sterling, VA

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509 FXUS61 KLWX 181527 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1027 AM EST Sun Feb 18 2018 .SYNOPSIS...
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High pressure builds overhead today before shifting offshore tonight. A warm front will then lift northward through the area on Monday, ushering in another round of unseasonably warm temperatures. A cold front will approach the region during the middle portion of the work week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Ample stratocumulus across the CWA this morning with GOES-East picking up a healthy field of mountain wave clouds north and west of the metro areas. Patchy dense fog was also observed early this morning over portions of our area, thanks to the added ground moisture from yesterdays precipitation, but conditions have been improving the last couple of hours. High pressure will build overhead today, and as the ~800mb inversion measured by the 12z KIAD sounding weakens, clouds are expected to erode this afternoon with skies turning partly to mostly sunny. Temperatures will rebound nicely, topping out in the upper 40s to near 50 degrees, which is a couple degrees above normal for this time of year. The aforementioned high pressure will move offshore tonight, helping turn winds to a more southerly trajectory. Clouds will make a return once again as a warm front moves toward our region from the southwest, and warm air advection commences. This could spark some light rain showers over our far western and southwestern zones by daybreak Monday, however only minor accumulations of less than a tenth of an inch would result. Overnight lows will hold generally above freezing, with the middle 30s observed for most of our area, while the lower 30s will be measured in the coldest spots.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The new work week begins with a warm front swinging northward through the area. Although I hate using a 50 PoP because it feels like a hedging of bets, I`m looking at a pretty even mix of model guidance that shows virtually nothing and guidance that paints a period of light rain. Will keep likely PoPs west of the Blue Ridge, where there`s just slightly more moisture available. Regardless, I think we are talking about less than a tenth of an inch of rain in most areas -- so nothing like the precip events we`ve had recently. Can`t rule out a bit of light lingering rain into Monday night, mainly near the Bay. Temperatures Monday night probably don`t move much, and might even perhaps rise slightly during the night. Tuesday begins a two-day period of significant heat for mid- February, reminiscent of the warm spell in the second half of February last year. 00 UTC GFS MOS guidance is a jaw-dropper in our western CWA and points west, giving Cumberland MD a high of 79 and Petersburg WV a high of 81. I`m not willing to go there quite yet but it`s not out of the realm of possibility either. The notable difference between this upcoming Tuesday and last Thursday (which was similarly warm) is that it will be even more humid. Given good model consensus on expected dewpoints and wind, I think many places may struggle to drop below 60 Tuesday night. I went several degrees above guidance, and my gut feeling is I may still be on the cool side of reality. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... An anomalously strong upper level ridge (heights 2-3 SD above climatology for February) will be positioned near the southeastern US coastline through the end of the week and into the weekend. This will provide for strong and persistent southwest flow aloft and continued bouts of moisture/warm air advection, which will lead to an active period with above normal temperatures and precipitation chances. A cold front will be on the approach during the day Wednesday, and models are beginning to form more of a consensus with frontal passage likely late Wednesday or Wednesday night, and therefore increasing chances for rain showers by Wednesday afternoon and Wednesday night. Out ahead of the front, southwest flow and very warm conditions are expected. After a morning start in the 50s to around 60F, with 850mb temperatures progged to be from 12-14C and 925mb temperatures from 14-17C, widespread 70s are expected for highs across the region. These temperatures will be in (something that is incredible for me to type)the realm of 25-30 degrees above climatological normals for the day (49/32F at DCA). As the front shifts southward Wednesday night and Thursday strong high pressure will build into southeast Canada and New England. This will create a cold air damming set-up across the Mid-Atlantic, as low level northeasterly flow is overrun by continued southwest flow and additional warm air advection aloft. This will create an unsettled day weather-wise for Thursday with cloudy skies and rain chances. Temperatures will be significantly cooler than Wednesday, although still near or above daily normals. The frontal zone will remain nearby through Friday and Saturday, and current model guidance depicts the boundary surging back northward with the region back in the warm sector by Saturday. But with the zone still nearby, a wet and active pattern will be in place with numerous chances for rain showers. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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Earlier low clouds and fog that plagued IAD/BWI, which resulted in LIFR/IFR conditions, have since lifted and conditions are improving, heading to VFR status. CHO is still locked in to LIFR CIGs and IFR VIS. Satellite imagery indicates we should see improving conditions there over the next hour or two, with a return to VFR by 17z. BKN clouds AOA 050 across all terminals this morning will dissipate this afternoon, with dry conditions and light winds prevailing. VFR conditions forecast overnight and through 18z Monday for all terminals. Monday afternoon, there is a 50-60 percent chance of rain, and an even higher likelihood of lowering ceilings, with MVFR likely and IFR possible. Sticking with MVFR in the forecast for now. If the rain materializes, visibility could be similarly restricted. Those restrictions should improve as a warm front passes late in the day. Tuesday will be extremely warm and a bit breezy, but dry. Predominantly VFR expected Wednesday with gusty southwest flow. Chances for showers will be on the increase by late Wednesday, and periods of sub-VFR conditions become possible from Wednesday evening through Thursday with rain and low cloud potential.
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&& .MARINE...
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High pressure traversing the region today, shifting offshore tonight will promote light winds across our waters, thus no headlines expected during this period. As the high shifts offshore and a warm front pushes through Monday afternoon (perhaps accompanied by some light rain), southerly winds will pick up, with gusts to SCA criteria possible Tuesday and Tuesday night. Small Craft Advisories may be needed Wednesday with gusty southwest winds. With warm air temperatures expected over considerably cooler waters, the strongest gusts will likely be observed along the shorelines. SCA potential continues into Thursday behind the frontal boundary as well as winds turn to the north.
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&& .CLIMATE...
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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 morning "low" that we are currently forecasting ends up being the Wednesday calendar day low (60 at DCA), 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)
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...JE/BKF NEAR TERM...BKF SHORT TERM...JE LONG TERM...MM AVIATION...JE/MM/BKF MARINE...JE/MM/BKF CLIMATE...JE

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