Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 110901 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EST Wed Jan 11 2017 .SYNOPSIS...
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A warm front will gradually cross the area today. A cold front will then drop back south across the region Friday. The front will stall to the south and a few waves of low pressure will ride east along the front over the weekend into early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Precipitation has moved east of the area, so have gone ahead and cancelled the Freezing Rain Advisory. The only air temperatures left below freezing are in Allegany and Highland Counties, although some road sensors still report subfreezing readings, so some icy untreated surfaces may still exist. The dissipating cold front is located over the Ohio Valley, with the theta-e gradient settling across the area today. The morning hours will be dry and we may even get some glimpses of the sun through the high clouds, as the lower clouds are currently clearing out. That, however, will be short lived as another low level jet rounds low pressure in the MS Valley, spreading rain back into the area this afternoon and evening. Overall amounts look to be less than a quarter inch, highest in the northwestern half of the area. P-type won`t be a concern, with highs today in the 40s (already there for many), and possibly 50s. The rain should push out of the area by midnight as the warm front surges northward. Guidance indicates fog and low clouds may linger though as the moist air gets trapped under warming aloft. However, with a steady southerly breeze, am not sure dense fog will be a concern. This will also hold low temperatures up into the 40s.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Thursday will be spent in the warm sector of the low pressure system which by that time will be moving up the St. Lawrence Valley. A few showers may brush by the Highlands, but otherwise it should be dry. Temperatures are progged to soar into the upper 50s and even 60s with gusty southerly winds. The associated cold front will push south through the area late Thursday night or Friday morning. The timing of the front will be important for highs, as temperatures likely reach the upper 50s again ahead of the front but fall into the 40s behind it. The front appears to be fairly uneventful in terms of precipitation as the flow becomes westerly...maybe a few light showers, with a better chance along the western slopes of the Appalachians. The Friday night period gets a little interesting as 1040+ mb high pressure builds into the Great Lakes and allows cold air to spill into the area. While the surface front will be well south of us, the midlevel front will be directly over the Mid-Atlantic, stall in the westerly flow. A disturbance will approach, although the extent of precipitation is uncertain. Thermal profiles support a mix, if not purely rain or freezing rain (depending on temperature) in the south. Highest confidence of precip is in the Highlands at this time, but stay tuned.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/...
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Guidance keeps the front south of the region through Monday before it starts to head back north on Tuesday ahead of a stronger wave of low pressure. Before that happens however, it now appears two weak waves of low pressure will ride eastward along the front, the first on Saturday and the second Sunday or Sunday night. The cold air will be most dominant with the first system while the high to the north is still strong and in the prime position to push cold air down the east side of the mountains, but some cold will linger Sunday as well. This means that both waves, but particularly the first one, can produce wintry weather, particularly some freezing rain. Kept wording in forecast generic given uncertainty, but definitely more than "rain or snow" is possible this weekend. Temperatures will be a bit below normal with the wedge in place. Later next week, some warming is expected as a stronger low pushes north into the Great Lakes.
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&& .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
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Precipitation has moved out of the area, and low level moisture does not seem to be lingering, so VFR looks to be a good bet through the remainder of the morning. Exiting low level jet should also abate LLWS concerns. The next disturbance will spread rain across the area late this afternoon (after 3PM most locations) into this evening. MVFR conditions appear likely with IFR possible, especially from evening on. Low clouds will likely linger into Thursday morning before they can mix out, aided by 25 kt southerly gusts. LLWS will once again be a concern tonight as well. The remainder of Thursday should be VFR. Low clouds may redevelop Thursday night. Cold front will slip south early Friday, but should have little impact other than the wind shift. The next disturbance could bring wintry precipitation late Friday night, but confidence is low. Sub-VFR with potential for icing is possible at the terminals through the weekend.
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&& .MARINE...
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Southerly flow will continue through Thursday night as a warm front generally stays north of the area. Gradient relaxes today, so SCA will drop off. Low level flow increases again tonight, but mixing is questionable. However, appears stronger winds will begin arriving over the Bay late, even without a large gust factor, so have hoisted an SCA. The SCA will expand to all waters Thursday morning, and may need to be continued into Thursday night. A cold front will move through early Friday. It`s a little uncertain if the northerly surge behind the front will be strong enough to warrant an SCA. Winds diminish over the weekend.
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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 7 AM EST this morning for ANZ530>543. Small Craft Advisory from 1 AM to 6 PM EST Thursday for ANZ530>534-537>543. Small Craft Advisory from 8 AM to 6 PM EST Thursday for ANZ535- 536.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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