Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220057 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 857 PM EDT Wed Sep 21 2016 .SYNOPSIS... High pressure will build over the region through early Thursday then weaken through Friday. A cold front will move through the area early Saturday. High pressure builds again over the region early next week. && .NEAR TERM /THROUGH THURSDAY/...
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Low pressure continues to spin across the coastal Carolinas. Associated showers this evening have been confined to southeast Virginia. With northeast winds, don`t believe there will be support for these showers to spread north again; therefore, it will be a dry night. However, the same cannot be said with confidence regarding low clouds. There are mixed signals in synoptic and mesoscale guidance at this point. NARRE ceiling probabilities carry about 25% chance of low clouds moving in overnight, to about I-95. Have made the tonight forecast much cloudier, and am carrying this into Thursday morning. If a solid maritime deck does moves in tonight, it will be harder to dislodge it in late September heating. That could affect the Thursday daytime forecast. West of the stratocumulus, mostly sunny still likely. Therefore, am making no additional changes at this point.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... Weak high pressure in control during this period. Temperatures are expected to warm up into the upper 80s and possibly reach 90F in a few spots on Fri. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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Surface cold front will likely have passed south of the region by Saturday morning, being pushed along by a 1030+ mb high pressure center originating near Hudson Bay Canada. The center of this high and coolest air will pass over New England, but much cooler weather is expected over the Mid-Atlantic as well especially during the second half of the weekend into early next week. Onshore flow may result in elevated humidity and low clouds and drizzle especially early next week. The operational GFS runs have been the quickest with an approaching cold front next week but have been trending slower towards a GEFS/EC blend. A slower solution seems more likely given the large blocky nature of the high pressure center that will be stationed just northeast of the region next week. This should keep more substantial rain chances at a minimum through much of the forecast period.
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&& .AVIATION /01Z THURSDAY THROUGH MONDAY/...
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Forecast currently not looking as clear-cut as it was earlier. An IFR stratus/stratocumulus deck is moving inland, and has made it to RIC as of 00Z. This is more aggressive than most guidance. NAM seems to have caught on, but am not sure if its solution is now overdone, as it plunges DCA into IFR for the morning push, and brings the western edge to IAD and BWI for that same time frame. Meanwhile, NARRE only indicates about a 25% chance of IFR ceilings along I-95. Have therefore kept any IFR ceilings just southeast of DCA/BWI, and thus out of the TAFs, but am giving the potential much more weight than most models. This deserves close attention tonight. Once the low clouds and fog-- whatever there is-- burns off, the remainder of the TAf period will feature VFR. Mainly VFR expected Saturday with northerly winds 10 to 15 knots. Sub-VFR possible later in the weekend with lower clouds as winds become easterly around 10 knots.
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&& .MARINE...
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Winds will gust to around 15kt in the mid Bay through midday Thu before they begin to diminish. A pressure surge, aided by northerly channeling, will likely push winds into Small Craft Advisory territory on Saturday. Winds should gradually diminish and veer to the east Saturday night into Sunday.
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&& .TIDES/COASTAL FLOODING...
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Water levels running less than a foot above astronomical normals. Nonetheless this is proving to be enough to flirt with minor inundation thresholds at sensitive locations. Forecast has been running right on track...adding confidence in projected water level at high tide tonight. Current Advisory status...DC and Alexandria 11pm-2am, Anne Arundel County til midnight. Elevated water levels persist through the rest of the week due to low pressure off the Carolina coast.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 2 AM EDT Thursday for DCZ001. MD...Coastal Flood Advisory until midnight EDT tonight for MDZ014. VA...Coastal Flood Advisory until 2 AM EDT Thursday for VAZ054. WV...None. MARINE...None.
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&& $$ SYNOPSIS...LFR NEAR TERM...HTS SHORT TERM...LFR LONG TERM...DFH AVIATION...HTS/DFH MARINE...LFR/DFH TIDES/COASTAL FLOODING...HTS

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