Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 082056 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 356 PM EST Fri Dec 8 2017 .SYNOPSIS... A frontal boundary remains nearly stationary off the Mid Atlantic coast through Saturday. A series of low pressure systems will track northeast along this boundary through Saturday. Cold high pressure builds into the area Saturday night into Monday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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See latest WSWAKQ products for updated winter wx headlines including a winter wx advisory for much of the CWA and a warning encompassing portions of the Piedmont and mainly west side of metro Richmond. Updated discussion to be issued shortly. Latest short term forecast guidance continues to show a messy and complicated forecast, especially regarding where the rain/snow transition will occur. However, the models are coming into better agreement in showing much of the region west of I-95 and north of Richmond, and into the MD eastern shore will be mainly snow tonight given that the 1295m or less 1000-850mb thickness values in this area. In fact, the thicknesses remain quite low today in this same area so it would not shock me to see a rain/snow mix in this area during the day today given the very low wet bulb zero values at the sfc. Have already had a report of some snow in Chesterfield. However, no accumulation is expected today. Tonight will be a different matter given that the sfc temps will cool allowing some accumulation. Am still thinking that there will be a swath of 2-3 inches in the new advisory area. However, just to the cold side of the rain/snow line, there could be higher amounts of 4 inches but given that this will likely be such a narrow area and higher amounts will depend on heavier precipitation rates and sfc temperatures. It may be a case here where that narrow strip just into the cold air in the heaviest precip band sees 4+ inches of wet snow. Updated forecast package new advisory have already been issued. Previous discussion below... A messy forecast starting today. A frontal boundary remains aligned off the mid-Atlantic/SE CONUS coasts today. A couple of weak disturbances aloft in strong SW flow will ride NE invof the boundary...slowly pushing moisture NNW into/across the FA (initially from NE NC early this morning). Some light pcpn reaches srn-central VA by late morning/early afternoon...then points NNW of there by eve. Thermal profiles suggest mainly -RA (RA/occasional +RA possible invof far SE VA-NE NC by later today)...though would not rule out a touch of -SN or -IP interior srn VA this morning...and again later today in corridor from central VA to lower SE MD. Highs mainly 40-45F.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... Attention turns to the srn stream system currently over SE TX for tonight through Sat. The operational models have trended toward a (slightly) more amplified system (the past 24 hours)...allowing more pcpn to be thrown back to the NW. RA likely will be the dominant ptype in ern/SE VA and NE NC...while SN is favor far NW. In between...the battle line will be drawn (basically centered along a line from SBY-RIC-AVC). The more amplified the system...the more potential for warming (in the mid levels)...though w/ marginal thermal profile/cold air in place...more QPF doesn`t necessarily mean more SN accum. There are differences in thickness/thermal profiles from model to model...and since there has been no cold air up until now...any SN accums difficult to determine...and P-rate/SN-rate likely to determine whether there is any impact on roads. The arrival of the upper level system on Sat may be enough to aid in cooling the column (w/ better UVM)...and bring a higher potential for SN across the FA (esp from central VA to interior lower SE MD). For now...will be holding off on any winter headlines (after coordination w/ nearby offices). Also...will have a rather wide zone of mix RA/SN centered along a line from AVC-PTB/RIC-XSA-SBY from tonight into Sat. Forecast SN accums 1-4 inches over the piedmont in VA to far interior lower SE MD...up to 1 inch to an EMV-PHF-OXB line. RA may mix w/ or end as little SN near the coast in ern/SE VA and over NE NC as pcpn diminishes (W-E) Sat afternoon through Sat evening. Cold but dry Sun w/ highs around 40F. (Lows Sat night m-u20s inland...l30s right at the coast in SE VA-NE NC). && .LONG TERM /MONDAY THROUGH FRIDAY/...
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The long term period will be characterized by below normal temperatures and mainly dry wx as a long wave trough sets up over the eastern CONUS. A vigorous shortwave is shown to rotate through the mean trough and pivot across the local area late Tuesday into Wednesday. This feature will reinforce the already chilly air in place and probably bring our coldest readings so far this season. In addition, widely scattered snow showers may occur especially over eastern areas as the upper trough pivots through Tuesday night/Wednesday. Highs Mon/Tues from the mid 40s to around 50. Highs Wed in the mid to upper 30s. Highs next Thurs in the low to mid 40s. Similar into Fri. Low temps Sunday night in the 20s, to near 30 coast. Lows Mon night from the upr 20s Piedmont to the mid 30s coast. Lows Tues/Wed nights from around 20 Piedmont to nr 30 coast.
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&& .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... Frontal boundary remains (well) S and E of the local area through the 12Z TAF forecast period. BKN-OVC VFR CIGS (mainly aoa 8-10kft) continuing attm. Area of mainly -RA will be slowly spreading NNW today...w/ CIGS/VSBYS lowering gradually to low end MVFR or IFR. RA and IFR/MVFR CIGS expected tonight into Sat at PHF/ORF/ECG...while mixed RA/SN or perhaps periods of all SN expected at RIC/SBY. Pcpn...possibly as a mix of RA/SN even to the coast...is expected to move offshore between 18Z-22Z Sat. VFR conditions are expected after late Sat afternoon/eve and continue into early next week. && .MARINE...
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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 this aftn have increased to 15-20 kt over NC waters and will see these winds expand north through the evening. Have put many of the Small Craft Advisory headlines in effect over the lower Bay/lower James/srn coastal waters with the aftn issuance (and remaining zones will go into effect by 1 am). Kept the upper rivers out of the SCA headlines through Sat. A strong cold front passes through Saturday night, 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.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .CLIMATE...
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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
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Winter Weather Advisory from 7 PM this evening to 4 PM EST Saturday for MDZ024. Winter Storm Warning from 7 PM this evening to 7 PM EST Saturday for MDZ021>023. NC...None. VA...Winter Weather Advisory until 4 PM EST Saturday for VAZ048-509- 510. Winter Storm Warning from 7 PM this evening to 4 PM EST Saturday for VAZ062-064-075>077-511>513-515-517-519-521. Winter Weather Advisory from 7 PM this evening to 4 PM EST Saturday for VAZ078>083-085-514-516-518-520-522. Winter Storm Warning until 4 PM EST Saturday for VAZ060-061- 065>069. MARINE...Small Craft Advisory from 1 AM Saturday to 6 PM EST Sunday for ANZ650-652-654. Small Craft Advisory until 1 PM EST Sunday for ANZ633-638-656- 658. Small Craft Advisory until 4 PM EST Sunday for ANZ632-634. Small Craft Advisory from 1 AM Saturday to 4 PM EST Sunday for ANZ630-631.
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&& $$ SYNOPSIS...MRD NEAR TERM...MRD SHORT TERM...ALB/MRD LONG TERM...MAS AVIATION...ALB MARINE...LKB TIDES/COASTAL FLOODING... CLIMATE...

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