Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180236 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 936 PM EST Tue Jan 17 2017 .SYNOPSIS... A warm front will stall out across Maryland tonight. A weak cold front will push through the area early Wednesday. High pressure returns Thursday followed by an approaching warm front Friday. High pressure returns again for Saturday. Low pressure will affect the area to start the new week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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The latest surface analysis (9pm) indicates that the warm front has reached the Potomac River, evidenced by the sharp dewpoint gradient in that vicinity, as well as light surface convergence. Visibility across Maryland (north of the front) has sharply dropped, with the development of fog. However, observations have been wavering. Ultimately, have decided to place the northern portion of the forecast area in a Dense Fog Advisory until 4am. Visibility observations outright support this action in metro Baltimore. For the rest of the Advisory area, believe that the low clouds (200-300 feet) have enshrouded most of the hills in fog. Still have a few showers crossing the area as well. The more organized activity departed by dusk. What`s left is weakly forced by overrunning. Am carrying chance PoPs to cover. The associated weak cold front presently (9pm) is across West Virginia. It will arrive during the overnight hours. Temperatures will either remain steady or rise slightly up until the frontal passage. Made those adjustments to the database earlier this evening. The fropa will also provide enough drier air, not to mention mixing, to break up any residual fog. Thus, expect fog to largely be gone by daybreak.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... Compact area of upper-level energy passes over the area tomorrow...with spotty light rain chances mainly across the Allegheny Front and along the Mason Dixon line. Elsewhere...expect drying/warming conditions as high pressure builds into the region through Thursday. Next system approaches late Thursday with showers approaching our SW zones by early Friday. Highs Wednesday and Thursday in the 50s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... A storm system over the western Ohio Valley will pivot northeastward into the Lower Great Lakes region Friday into Friday night. Some energy associated with this main low will push across our region during the same time. Light to moderate rain will gradually spread northeastward across the Shenandoah Valley early Friday. Rain should reach the District of Columbia and surrounding areas by Friday afternoon. Temperatures will remain mild with high temperatures about 10 degrees above normal. Drier air will work its way into our region from the west behind this wave low pressure energy and escorted by high pressure building in from the Ohio Valley. Weak high pressure will be overhead Saturday into Saturday night. Temperatures will stay mild throughout the period. A separate area of high pressure over New England could aid in some cloud cover with an upslope flow. A storm system will develop over the Mississippi Valley and deepen as it pivots northward Sunday and Sunday night. This low could send additional energy into our region Sunday into Sunday night, bringing the chance of rain showers once again. On Monday, the main low will move northward into the eastern Great Lakes. The threat for showers and perhaps a rumble of thunder exist Monday. Temperatures will remain mild. Drier air will push in behind the departing storm system Monday night. High pressure will usher in cooler and dry air on Tuesday. Clouds will breaking for sunshine, except for clouds and upslope rain and/or snow showers in the Potomac Highlands possible. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Flight conditions have been variable this evening. A warm front stretches along the Potomac River, with IFR to LIFR north of the front. CHO, on the other hand, has been VFR. Increasing fog northeast of the front may result in further deteriorating conditions until the arrival of a cold front. Anticipate the cold front to reach the terminals after midnight but before dawn, with improvement to come thereafter. Mainly VFR tomorrow...though gusty NW winds up to 25 mph possible in the wake of cold front. IFR to LIFR conditions Friday with rain showers. MVFR conditions Friday night. Winds southeast around 5 knots Friday. Winds light and variable Friday night. && .MARINE... Primarily southerly sub-SCA winds expected through tonight. However, with strong low-level wind field, may see some gusts approach SCA-criteria this evening and tonight. Have continued trend to keep winds just under Advisory criteria. Winds will then turn to the northwest on Wednesday following cold frontal passage. Gusts up to about 20 knots expected...a Small Craft Advisory is in effect. Winds will then subside for Wednesday night through Thursday night. No marine hazards Friday through Friday night. Winds southeast becoming light and variable 5 to 10 knots Friday through Friday night. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Dense Fog Advisory until 4 AM EST Wednesday for MDZ003>006-011- 502-503-505>508. VA...Dense Fog Advisory until 4 AM EST Wednesday for VAZ028-031-505. WV...Dense Fog Advisory until 4 AM EST Wednesday for WVZ050>053-504. MARINE...Small Craft Advisory from 7 AM to 6 PM EST Wednesday for ANZ530>543.
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&& $$ SYNOPSIS...HTS/MSE NEAR TERM...HTS SHORT TERM...MSE LONG TERM...KLW AVIATION...HTS/MSE/KLW MARINE...HTS/MSE/KLW is the U.S. government's official web portal to all federal, state and local government web resources and services.