Area Forecast Discussion
Issued by NWS Wakefield, VA

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323 FXUS61 KAKQ 092006 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 306 PM EST Sat Dec 9 2017 .SYNOPSIS... A frontal boundary remains nearly stationary off the Mid Atlantic coast through tonight. Low pressure will track northeast along this boundary today. Cold high pressure builds into the area tonight into early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Latest wx analysis indicates elongated ~1002 mb sfc low pressure from off Cape Hatteras NC NNE to well off the Delmarva as of late this morning. Precipitation has been rather light over the past few hrs with either light snow or a light mix along and west of the I-95 corridor and over the interior MD eastern shore...with mainly rain farther SE. However, latest radar is beginning to fill back in and a more prominent band of snow is now situated from between Farmville and South Hill on NNE through Goochland/western Hanover and Caroline Counties. This band is expected to persist and likely become enhanced through the next few hrs as the forcing increases with RRQ of ~175 KT upper Jet streak and 500 mb shortwave moves into the region. Latest RAP/NAM 12 approximate the changeover to all snow with the 1295 m 1000-850mb thickness and 32F sfc wet bulbs. Initially, there is enough of a warm nose aloft and higher 850-700mb thicknesses to support some sleet or a light mix through 18Z, but after that P-type should become just rain vs. snow. Made some minor adjustments to the forecast to lower additional snow amts slightly/mainly to 1-2" for much of central and eastern VA, though will maintain higher amts of 2-3" (locally up to 4") over the northern Neck and interior MD eastern shore as the band will tend to pivot and slow down a bit late this aftn and into the early evening in these areas. Also, models shows the cold air aloft/1000-850 mb thicknesses crashing below the critical 1295-1300 m over interior SE VA between 19-22Z and reaching the coast after about 22-23Z. Thus, increased snow amts for up to an inch of snow by late aftn in the SE. Confidence not high enough to add any advisories there, but will continue to monitor for a potential winter wx advy over some of SE VA where there is currently no headline in effect if the band were to expand more to the SE. Otherwise, no changes necessary to going winter weather headlines, with warnings bounding a South Hill to Richmond to Salisbury MD line, flanked by Advisories on either side. Highs today remaining steady in the low to mid 30s inland...upper 30s to lower 40s SE coast. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... By this evening, sky will gradually clear out in subsidence behind the departing upper trough, though some clouds will persist through 06-09Z on the ern shore. The clearing combined with the strong cold advection will allow temps to drop into the 20s late this evening/overnight. Roads may become slick and any snow that remains on the ground will become quite compacted. Sunday should be a cool day with temps only in the upper 30s/lower 40s even with mostly sunny skies. && .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
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The long term begins with the longwave trough entrenched over the eastern half of the US with multiple shortwave troughs expected to rotate through the longwave trough on Tuesday night/Wed and again Thurs night/Friday. Each of these shortwaves will have a strong clipper like surface low that will accompany the trough and swing a strong cold front through the region. At this point, the track of the shortwave does not appear to be far enough south or have enough moisture to cause any significant weather problems, other than to reinforce a cold air mass that will be in place through the work week. But there is some uncertainty with the models as the 12z GFS keeps the low track to the north of the area, but the 12z ECMWF now brings the second low on Thursday into Friday further to the south and has a little more moisture to work with. For now, have left a mention of some light snow showers of possibly a few flurries across northern portions of the CWA on Tuesday night in Wed morning and again for the second wave on Thursday into Thursday night. The warm advection with the second wave could be a little stronger and if enough moisture could be advected northward from the gulf coast, there could be a little more interest in this wave, but right now any pcpn would be expected to be light. The pattern finally breaks heading into the weekend with the long wave trough exiting and the flow become more zonal as a weak subtropical ridge begins to build over Southern Gulf of Mexico and Western Caribbean. For temperatures have leaned toward the colder Superblend/National blend of models on Tues night into Friday, which is a few degrees cooler than the MEX numbers. For the weekend, have remain on the cool side, but with the high sliding off the coast, could see temperatures recovering a little more than shown.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Have noted widespread IFR conditions across area terminals this morning. Conditions will deteriorate once again across terminals over the next few hours this morning, as precipitation moves back in over the next few hours. FZDZ/very light snow at RIC will transition back to a period of RASN then SN by 15z before ending late afternoon/early evening. Snow continues at SBY, possibly mixed with PL at times. RA at PHF/ORF/ECG today before ending tonight. Quieter wx returns behind the departing system from Saturday night through early next week. && .MARINE... An active period expected for the next several days with sfc low pressure currently along a frontal boundary from the eastern gulf of Mexico to off the NE FL Atlc coast. N/NE winds currently range from 15 to 25 knots over the waters with waves of 3-5 feet and seas of 4- 7 feet. Small Craft Advisories remain in effect for all of the waters minus the upper rivers through Sunday. A strong cold front passes through tonight, shifting winds to the WNW, and allowing for Small Craft conditions to prevail for all zones (including the upper rivers). Small Craft Advisories have been extended for much of Sunday with the passage of the front. While there may be a brief gust to near gale force Sunday morning it will be limited and Gales are not expected. Elevated westerly flow of 15-20 kt to continue Mon- Tue and will increase to 20-30 kt late Tue night and Wed. && .TIDES/COASTAL FLOODING... Water levels in the lower Bay and NC Outer Banks may approach minor flood thresholds during late morning/early aftn Sat high tide, but do not anticipate headlines being needed attm. && .CLIMATE... Avg 1st Date with Measurable Snowfall at Sites (Data based on 1981-2010): * Richmond: Dec 25th * Norfolk: Jan 12th * Salisbury: Dec 25th * Wallops: Dec 26th * Louisa: Dec 18th * Farmville: Dec 24th && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Winter Weather Advisory until 4 PM EST this afternoon for MDZ024. Winter Storm Warning until 7 PM EST this evening for MDZ021>023. NC...None. VA...Winter Weather Advisory until 4 PM EST this afternoon for VAZ048-078>083-085-509-510-514-516-518-520-522. Winter Storm Warning until 4 PM EST this afternoon for VAZ060>062-064>069-075>077-511>513-515-517-519-521. MARINE...Small Craft Advisory until 7 PM EST Sunday for ANZ650-652-654. Small Craft Advisory until 1 PM EST Sunday for ANZ633-656-658. Small Craft Advisory until 4 PM EST Sunday for ANZ630>632-634.
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&& $$ SYNOPSIS...MAM NEAR TERM...LKB SHORT TERM...ALB/MAM/MRD LONG TERM...ESS AVIATION...ALB MARINE...AJB/LKB TIDES/COASTAL FLOODING... CLIMATE...

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