Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 130905 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 405 AM EST Tue Feb 13 2018 .SYNOPSIS...
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High pressure will build north of the area today before pushing offshore tonight. A warm front will then cross the region during midweek, followed by a cold front late in the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 3 AM, high pressure is located along the PA/NY border, moving eastward towards New England. Skies are mostly clear across much of the CWA, with radiational cooling taking place allowing most places to drop down to near normal temps for lows. The exception is in the far SW, wher clouds have started overspreading Augusta, Nelson and Highland Counties in association with some warm advection in association with a weak passing disturbance, strong jet streak aloft and the stationary front currently located well south of the region. For most of the CWA, today will feature increasing clouds and chilly temperatures as the high pushes east but leaves a cold air wedge on the east side of the mountains. The increasing clouds should help reinforce this cold wedge, though it is noted that the forecast highs could end up a little too cold if there is a bit more sun than currently anticipated. The exception to this is down in the aforementioned counties where clouds have already moved in. Multiple models are showing some light precip breaking out across this region of west- central VA in the next few hours. BUFKIT soundings suggest the predominant p-type will be sleet versus snow or freezing rain, and with POPs still below 50 percent, decided not to issue any advisories as of yet. Will continue to review this situation over the next few hours in case as short-fused advisory becomes necessary, but as mentioned, precip could end up being predominantly light sleet (not advisory criteria), and it also may warm up just above freezing in many valley locales before precip starts. Tonight, this disturbance passes east, and it looks as though clouds could actually decrease for a time. This could allow temps to radiate back down below freezing. Late tonight, warm advection associated with another disturbance will get underway, resulting in another increase in clouds. This may allow temps to rise late, especially in western areas. Precip may start overspreading the area late tonight, but dry air and limited forcing will likely confine this to the Allegheny Front, and right now ridge temps look like they will actually be above freezing. If that changes, a winter weather advisory could become necessary, but right now rain appears to the main p-type late tonight.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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Warm air starts flooding the region on Wednesday as high pressure continues heading off the coast. However, moisture will be limited at first, so expect the majority of the day to be dry except along the Allegheny Front, where some light rain is expected. Late in the day, an upper disturbance will approach from the west, which when combined with the increasing low level moisture and warm advection aloft, should allow showers to break out from west to east during the afternoon and evening. Precipitation is not expected to be heavy, with a few hundredths to a few tenths of an inch expected. Most of this precip should clear the area later at night, though some mist and drizzle could linger early Thursday. After that breaks, there could be some sun, which would help boost temps up into the 70s across the region. Most guidance has the low level warm front pushing north of the region, so felt comfortable pushing most places into the low 70s. Late in the day, the next cold front will approach, and a wave of low pressure will pass by to the north during the night. This should bring showers across the region. Temps will remain very mild and it will likely remain breezy as well.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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A cold front will drop southward through the area Friday morning. Due to the west-to-east orientation of the frontal boundary and low- level westerly flow, precipitation amounts shouldn`t be too exorbitant. Though generally light, showers should be widespread given the presence of a favorably placed upper level jet streak. Rain winds down by Friday evening as drier and much cooler air rushes in behind the front. Though not usually an ideal setup for wintry precipitation, about half of the 00z GEFS/Canadian ensembles have (light) precipitation moving back into the area during the second half of Saturday, overrunning the marginally cold air in place. The 00z operational GGEM/ECMWF show this as well. Temps will be marginal, but cold enough to introduce low PoPs for snow during this period. Warmer air quickly builds back into the region Sunday into early next week as transient cool high pressure slides offshore to our north. Another frontal system may bring precipitation (mainly rain) early next week.
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&& .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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VFR throug the TAF period as high pressure remains in control, even as it passes eastward away from us late tonight and Wednesday. Clouds will increase during this time but cigs should remain above 3k ft. No visibility restrictions expected. Sub-VFR potential is much higher Wednesday night as a disturbance moving through brings some showers. Conditions likely improve on Thursday, accompanied by southwest wind gusting 20-30 knots. Sub-VFR likely again Thursday night as showers move across the region ahead of a cold front. Sub-VFR likely Fri in -SHRA with cold FROPA. LLWS possible. Surface winds generally SW around 10 kts. Some guidance hinting at -RASN Sat aft-eve. Otherwise mainly VFR over the weekend. NW winds Fri night 15 kts and gusty become lighter/variable over the weekend.
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&& .MARINE...
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Northerly flow should weaken over the next few hours as high pressure reaches closest approach to our north, allowing the gradient to diminish, but SCA remains in effect until mid morning. Light winds should prevail as ridge of surface high pressure on the east side of the Appalachians remains over the region later today through Wednesday. As high pressure slides further east Wednesday night and Thursday, the southerly gradient will increase as the wedge dissipates and a cold front approaches from the west. While this is a warm wind over chilly waters, we could still get 20 knot gusts especially near upwind shores. SCA may therefore be needed Wednesday night through Thursday night for some waters. SCA likely Friday and Friday night both ahead of and behind a cold front. A few gusts near gale force are not impossible but poor mixing may keep higher gusts at bay. Winds go light over the weekend.
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&& .CLIMATE...
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Unseasonably warm weather is expected on Thursday. While temps will be over 20 degrees above normal, it will be difficult to top the record highs in Baltimore and Washington. However, the record highs at Dulles could be smashed. Below are the current record highs for Thursday February 15: SITE RECORD MAX RECORD MIN DCA 77 in 1949 52 in 1909 BWI 77 in 1949 51 in 1949 IAD 68 in 1982 44 in 1984 and 1967
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 9 AM EST this morning for ANZ534- 537-543.
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&& $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...DHOF AVIATION...RCM/DHOF MARINE...RCM/DHOF CLIMATE...RCM

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