Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190217 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 917 PM EST Sun Feb 18 2018 .SYNOPSIS... High pressure will move offshore overnight. A warm front will then lift northward through the area on Monday, ushering in another round of unseasonably warm temperatures that will last through mid week. A cold front will approach the region Wednesday night into Thursday before stalling nearby through the end of the work week. && .NEAR TERM /UNTIL 7 AM MONDAY MORNING/... High pressure is centered over the Jersey shore per the latest surface analysis. Cirrus is already wafting overhead, and satellite imagery detects a patch of low clouds developing over Nelson County...a consequence of onshore flow around the periphery of the high. Surface flow should be veering south overnight as strong warm advection ensues aloft. Thus, expect clouds to be thickening and lowering. However, high-res guidance (HREF/NMM/ARW) has generally be holding precip off through dawn, a trend that recent RAP/HRRR runs continue to show. Will hold off likely PoPs to south of Charlottesville/Harrisonburg by sunrise. Will have some chance PoPs creeping into central Virginia and into the Potomac Highlands after midnight though. There is a low-end probability in some datasets that there could be freezing rain across the ridge tops at onset. However, believe that warm advection will offset any wet-bulb cooling. Most guidance sets continue to indicate lows above freezing across all but MD/PA border east of the Catoctins-- where PoPs will be at or below 15%. Therefore, am going with an all rain solution. Consensus temperature forecasts suggest that temperatures will only be dropping a few more degrees from current values; accepted this solution in light of warm advection aloft and increasing clouds. && .SHORT TERM /7 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... Warm front lifts through our region on Monday and by Monday evening will reside to our north. This will deliver increasing rain chances area wide during the day, and allow cloudy skies to prevail. Global model consensus not too keen on much in the way of QPF, maintaining a tenth of an inch or less through Monday evening, with our southern zones having the best chance to see the most rainfall. High res guidance shows light rain trying to make its way through the metro areas during and after the morning rush, with lowering rain chances in the afternoon, with the exception of western Maryland and the eastern WV Panhandle where the warm front will be nearby. Warm air advection will be ongoing throughout the day on Monday, and by Monday evening, 850 temps will have increased by around 12C from what our upper air sounding will observe this evening (19/00z). Highs Monday will be in the 50s for all, maybe even cracking 60 degrees over the Potomac Highlands. With the warm front to our north Monday evening, expecting drying conditions and continued cloudiness with warm air advection continuing. Lows Monday night will settle in the upper 40s to near 50 degrees, or nearly 20 degrees above normal values. Unseasonably warm conditions will continue Tuesday and Tuesday night, as strong ridging persists over the Mid Atlantic region, as 500mb heights will be near the 99th percentile for this time of the year. Deep south southwesterly flow will also be realized throughout the atmospheric column. Highs on Tuesday will surpass 70 degrees once again, which will be 25 to perhaps 30 degrees above normal for some locations. Tuesday night, some spots in and around the cities may not even drop below 60 degrees, but mid 50s to around 60 degrees can be expected area wide. One consequence as a result the much warmer temperatures will be the increase in dewpoints or moisture in the air. By Tuesday afternoon, dewpoints will reach the lower 60s, bringing a feeling of stickiness to the air. On the other hand, with dry air and subsidence dominating aloft, rain chances will be near nil Tuesday and Tuesday night. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... The warming trend will continue into Wednesday with a strong upper level ridge... and at the surface we remain between a high pressure settled off of the southeast coast and a cold front to our west. Temperatures are expected to reach the mid to upper 70s... that is about 25 to 30 degrees above normal. Wednesday should start dry with chance of showers increasing as the slow moving front approaches. The front will move across our CWA late Wednesday or early Thursday, before stalling to our south Thursday into Friday. The front will then push north as a warm front Friday night or Saturday, with another boundary pushing through on Sunday. Chance of showers will remain for most the long term period with temperatures remaining above normal. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Clouds have already begun to increase once again...a trend that will continue through daybreak Monday, but remaining VFR. CIGs will approach MVFR to potentially IFR categories midday Monday as light rain slides across the terminals. Could see some VIS reductions as well. Confidence in occurrence of rain is too low at this time to explicitly include in the TAF, but is is implied via cigs and vsbys. Conditions improve Monday evening as a warm front lifts north of the terminals, and VFR CIGs and VIS return through Tuesday night under the influence of deep ridging. South southwesterly winds AOA 10 knots can be expected during this period, and they will be gusty during the day on Tuesday, upwards of 20 knots. VFR conditions expected part of the day Wednesday before sub VFR periods possible late on Wednesday and into Friday when unsettled weather could affect our area as a front moves across and stalls nearby. && .MARINE... High pressure will move offshore tonight, supporting light south flow. As a warm front pushes through the area by Monday evening, southerly breezes will increase across our waters, likely reaching SCA criteria by Tuesday. 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. && .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 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) && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BKF/HTS NEAR TERM...HTS SHORT TERM...BKF LONG TERM...IMR AVIATION...HTS/BKF/IMR MARINE...HTS/BKF/IMR CLIMATE...JE

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