Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 261853 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 153 PM EST Sat Nov 26 2016 .SYNOPSIS...
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High pressure will move across the region through Sunday, then move offshore on Monday, ushering in southerly winds and warmer temperatures. A storm system will begin to approach the region on Tuesday, but the associated cold front will not move through until Wednesday or Wednesday night.
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&& .NEAR TERM /THROUGH SUNDAY/...
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Plenty of clouds out this afternoon as a shortwave finishes rolling through the area. Forecast simulations show the existing low cloud layer beginning to dry after sunset tonight, and we should quickly clear in most areas. We will remain in a reasonably tight pressure gradient between the high over the southern Appalachians and the departing low in the Atlantic, so decoupling of winds should be limited to mainly sheltered valleys, especially in our southwestern counties. As a result, I leaned toward the warm side of guidance, with lows near 40 in downtown DC/Baltimore and in bayshore communities, but potentially mid 20s in Highland County. Still could see an upslope rain or snow shower out west, and I extended the ongoing PoPs through the entire night rather than just the evening hours. Cannot rule out a sprinkle further east but probability is way too small to include. For Sunday, high pressure and dry air will result in just a few clouds and an increasingly less breezy day. Temperatures will be fairly similar to today, but with less wind it will feel a little less chilly.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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Sunday night will be the coldest of the upcoming stretch, with high pressure allowing for fairly widespread decoupling of the winds. Lows mainly in the 20s except in the usual warm spots (and on ridgetops). Clouds increase Monday. There is a bit of model disagreement on temperatures. The consensus shows southerly flow by afternoon, but the GFS doesn`t have it at all, and therefore is cooler. Will stick with the consensus for now. The previous forecast seems to have a good handle on the precip onset Monday night. Of note, it looks like a good chance temperatures will warm at least for the second half of the night, so no precip type issues like we sometimes have at onset.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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A warm front will lift north across the region Tuesday morning, followed by a cold front moving northwest to southeast Tuesday evening. A persistent southerly flow will fuel rain showers throughout the day Tuesday. As the cold front slides across southern Maryland and east- central Virginia Tuesday evening, there could be a brief break in the rain shower activity into the overnight hours. A second storm system is expected to develop along the tail-end of the cold front over the interior Southeast U.S. Wednesday morning. The storm should ride northeast along the front Wednesday and Wednesday night, bringing more rain showers to the region. The storm system will continue to move northeastward toward southern New England Thursday. High pressure will build in behind the storm and its associated cold front Thursday and Thursday night. Drier and colder air will filter into the region. An upper level trough of low pressure is expected to sag southward into the region from the Eastern Great Lakes Thursday night and Friday. There may not be a lot of moisture available to fuel any showers with the trough. Plus, a downsloping flow over the Appalachian Mountains could encourage a dry day Friday. High pressure will build in behind the trough of low pressure Friday night and Saturday. Dry and chilly conditions expected.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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Ceiling heights have lifted above the MVFR threshold solidly and will remain so until the clouds break tonight. Ongoing wind gusts up to 25 knots will decrease after sunset. Could be a few more gusts to 20 knots tomorrow during the day. Otherwise, VFR through the TAF period and even through Monday. Outlook... Conditions will quickly deteriorate to IFR or even LIFR as precip onset occurs late Monday night or early Tuesday. Rain showers expected through the day with gusty southerly winds. Low clouds hang in for Tuesday night and a second round of showers Wednesday. Could be yet a third round of showers and low ceilings either Wednesday night or Thursday morning before drying and clearing occur.
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&& .MARINE...
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Seeing fairly widespread SCA gusts today, and high-res models say these will continue, except in the upper Tidal Potomac, through the night as the relatively warm water allows mixing down of gusts. Winds should gradually subside on Sunday, but uncertainty in how quickly they decrease prompts leaving up the SCA. It could be dropped early, however. No marine concerns Sunday night through Monday night. Small craft advisories likely Tuesday with winds southerly 15 to 20 knots and higher gusts. Channeling may lead to gale force gusts on Tuesday. Small craft advisory conditions are possible Tuesday evening. Winds southerly 10 to 15 knots with higher gusts Tuesday night. May be a second round of southerly channeling up the bay on Wednesday.
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&& .TIDES/COASTAL FLOODING...
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Water levels are dropping below normal. Model guidance was too early in creating a blowout so we are correcting to the observed anomaly. We could approach a foot below normal tides before winds shift on Monday and the anomaly starts to rebuild. The southerly channeling favors elevated water levels, but our model output is not handling it very well this far out. Bottom line is that minor coastal flooding is possible along the bay Tuesday/Wednesday but uncertainty is high.
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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 6 PM EST Sunday for ANZ530>534- 536>543. Small Craft Advisory until 9 PM EST this evening for ANZ535. Small Craft Advisory from 6 AM to 6 PM EST Sunday for ANZ535.
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&& $$ SYNOPSIS...JE NEAR TERM...JE SHORT TERM...JE LONG TERM...KLW AVIATION...JE MARINE...JE/KLW TIDES/COASTAL FLOODING...JE

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