Area Forecast Discussion
Issued by NWS Sterling, VA

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234 FXUS61 KLWX 231556 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1056 AM EST Mon Jan 23 2017 .SYNOPSIS... Low pressure over North Carolina will track northeast off the Delmarva tonight. A cold front will pass through the area Wednesday night. An upper-level trough will build overhead for the end of the week into the weekend. && .NEAR TERM /THROUGH TONIGHT/... A year ago today we were beginning the dig out from 2-3 feet of snow from the blizzard. Strong low pressure is impacting the area today - but the big differences are this one`s path is 150 miles farther to the west...and temperatures are 20 degrees warmer. Morning surface analysis showed low pressure centered over northern NC. A large swatch of precip (rain) is affecting southwestern VA, which is south of our forecast area. There is a strong pressure gradient between the low and high pressure over northern ME. This is causing strong easterly winds across the area. We are seeing gusts of 30-40 mph across much of the region. These will remain strong throughout the day. So far Upper Sherando reports 1.83" of rain. Big Meadows has received 2.28" in the past 12 hours. Previous discussion: Greatest rain totals expected along the eastern slopes of the Blue Ridge...as upslope enhances precipitation efficiency there (could see > 2 inches). Generally 1-2 inches expected elsewhere. Not entirely out of the question to see a rumble of thunder in some convective elements across S MD this afternoon as weak mid- level instability develops due to cold temperatures aloft as upper low passes by. However, chances remain too low to add at the moment. Lastly, some wintry precipitation could develop late this afternoon through tonight across the higher terrain of W MD, WV, and VA as the column continues to cool. Some uncertainty remains as to when this occurs...and the type of wintry precipitation. Could be a period of sleet/freezing rain as low levels cool slightly faster than mid- levels. Increased snow totals a bit to account for greater faster cooling of the column...though...any accumulations will initially be hampered by warm ground temperatures. Generally 1-2 inches at the higher elevations with less than an inch elsewhere...though a few isolated spots at higher elevations could pick up a bit more. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Tuesday remains a transition day...as center of surface low continues its eastward progression off the Jersey coast and high pressure across the gulf states gradually builds northward toward the area. A few lingering light showers remain possible through midday mainly from DC and to the N/NE. Additionally, upslope snow/rain showers could continue into mid-afternoon before moisture becomes too shallow and upslope winds turn to southerly as high pressure nudges up into the area. While rain will shift out of the area by midday...breezy W/NW winds gusting up to 25 kts remain...with relatively warm conditions on the drying flow. Heights crest over the area through midday Wednesday...with unseasonably warm temperatures (e.g., highs near 60F). Cold front crosses the region late Wednesday into Thursday...and, with limited moisture east of the mountains, expect most areas to remain dry. Upslope flow will allow for some rain/snow showers to develop by late Wednesday night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A sharp shortwave axis will cross the forecast area Thursday morning, which will carve out a deeper 500mb trough axis and pave the way for a series of disturbances into the weekend. The bulk of the moisture will be squeezed out by the Appalachians, but a northwest flow/cold advection pattern will be maintained areawide. In terms of temperatures, that means we`ll be much closer to normal. (Thursday will be the transition day; the temperature trace may not be truly diurnal, but its still quite far out to deviate from the norm.) Any precipitation would be snow, and it could be significant. However, it seems as though this would be a case of a couple of inches each day/night. It`s already mentioned in the Hazardous Weather Outlook, so will leave it there. && .AVIATION /16Z MONDAY THROUGH FRIDAY/... IFR will continue through tonight. Steadier/Heavier rain will impact all terminals through mid afternoon...before showers become more scattered. Gusty winds up to 30-40 knots are also possible today. MVFR may linger at a few sites (mainly BWI/MTN) for a few hours Tuesday morning...before showers move out of the area and all sites become VFR by afternoon. However, breezy conditions will continue with NW wind gusts 20-25 kts...before subsiding Tuesday night. High pressure briefly nudges into the area late Tuesday into Wednesday with dry weather and VFR prevailing. Weak front moves through late Wednesday...though at the moment it appears showers should avoid terminals. Mainly VFR conditions should prevail Thursday-Friday in northwest flow. MRB has the best chance at receiving impacts from cold air stratocumulus and potential MVFR/scattered snow showers; low confidence in that outcome though. Winds (from the northwest) will be gusty. && .MARINE... Gale Warning in effect until 6 PM. Expect solid SCA conditions to continue into Tuesday behind departing low pressure system...with an SCA in effect from 6 PM tonight to 6 PM Tuesday. Winds slacken late Tuesday as influence from low wanes. Mostly dry cold front crosses the waters late Wednesday into Thursday...with gusty winds possibly to SCA criteria behind it Thursday afternoon. Northwest flow on the waters Thursday/Friday as cold(er) air invades area. Small Craft Advisories appear likely. Wouldn`t completely rule out gales. && .HYDROLOGY... We have issued a flood watch along the I-81 corridor from Rockingham to Berkeley. Only water to show much response at the moment is Wardensville...but is is still only half way to flood stage. Area of moderate rainfall is on its way to that area. We will continue to monitor. The heavy rain should be north of the watch area by midnight. && .TIDES/COASTAL FLOODING... Persistent easterly flow has lead to elevated water levels. Coastal Flood Advisory was issued for Straits Point through the evening high tide cycle. Elsewhere...action stage is expected at Annapolis and Solomons...though further increase in anomalies could lead to tidal levels near minor stage. DC/Alexandria also forecast to reach minor stage late this afternoon. Developing westerly flow should allow for some decrease in anamolies by later Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Advisory until 4 PM EST this afternoon for DCZ001. MD...Wind Advisory until 4 PM EST this afternoon for MDZ004>006-011- 013-014-016>018-503>508. Coastal Flood Advisory until 3 AM EST Tuesday for MDZ016-017. VA...Flood Watch through this evening for VAZ026>031-038>040-507. Wind Advisory until 4 PM EST this afternoon for VAZ053-054. Coastal Flood Advisory until 3 AM EST Tuesday for VAZ057. WV...Flood Watch through this evening for WVZ052-053. MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST Tuesday for ANZ530>543. Gale Warning until 6 PM EST this evening for ANZ530>543. && $$ UPDATE...WOODY! PREVIOUS...MSE/HTS

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