Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 181959 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 259 PM EST Sun Feb 18 2018 .SYNOPSIS...
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High pressure moving overhead this afternoon will shift 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As expected, cloud cover has cleared this afternoon as high pressure builds in to our area. The exception to this would be those residing along and west of the Alleghenies, where mostly cloudy skies are still transitioning to partly sunny conditions. Temperatures range from the lower 40s in the colder spots to the lower 50s along our southern zones. Radar is echo free thanks to the aforementioned high pressure transiting our region. As the high pressure slides offshore overnight, this will turn winds light and southerly. Guidance in pretty good agreement with warm air advection picking up overnight, which is in response to the departing high and an approaching warm front to our southwest. As a result, we will see clouds increase towards morning from the southwest to northeast. We could even see a little light rain creep in to the the southern and western portions of the Central Foothills, Shenandoah Valley, and the Potomac Highlands. But guidance has favored on holding off on much of the precipitation until after daybreak Monday. Will maintain no more than chance POPs overnight for the above mentioned areas. Overnight lows will generally remain above freezing, with the middle 30s observed for most of our area, while the lower 30s will be measured in the coldest spots and along the Mason Dixon Line.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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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.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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Clouds have mostly eroded across the terminals, but some SCT clouds remain at BWI/MTN. With high pressure moving overhead the remainder of the and residing to our east overnight, light southerly winds will prevail with no VIS/CIG restrictions forecast. Clouds will increase once again toward daybreak Monday, but remaining VFR. CIGs will approach MVFR to potentially IFR categories Monday morning and afternoon as light rain slides across the terminals. Could see some VIS reductions as well. Confidence in timing and occurrence of rain is too low at this time to include in the TAF. 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.
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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 high pressure shifts offshore and a warm front pushes through the area by Monday evening, southerly breezes will increase across our waters Tuesday and Tuesday night, likely reaching SCA criteria. 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... 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 NEAR TERM...BKF SHORT TERM...BKF LONG TERM...IMR AVIATION...IMR/BKF MARINE...MM/BKF CLIMATE...JE

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