Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 170732 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 232 AM EST Wed Jan 17 2018 .SYNOPSIS... High pressure will slide offshore tonight. A cold front crosses the area Wednesday morning with low pressure moving northeast along the coast Wednesday afternoon and night. A second surge of arctic air pushes across the area Wednesday night into Thursday before temperatures moderate into next weekend. && .NEAR TERM /THROUGH TODAY/... Update...Main change this cycle was to upgrade portions of south central VA and Northampton NC to a winter storm warning and added Northampton Co. VA to a winter wx advisory. Evening analysis indicates a potent positively tilted upper trough all the way south into the lower MS/TN Valley. Frigid airmass down into the south central CONUS today and this will continue to migrate eastward tonight. In the near term tonight, low clouds and some patchy fog will persist near the coast and eastern shore while most of the remainder of the CWA is mainly cloudy with mid/high clouds thickening in advance of the approaching system. Lows tonight will be mainly in the mid 20s to around 30 F. The upper trough will pivot ESE and is progged to take on more a neutral tilt with the associated cold front pushing across the mountains and into the Piedmont well after midnight, genly by 09-12z Wednesday. The upper level is then progged to take on a negative tilt or even become cutoff for a time during the day Wed. This will place a narrow zone from central NC to south central VA into optimal placement for deformation banding within a deep upper level diffluent zone. Have raised snow amounts to 3-5" within the warning area and locally higher amounts will be possible especially if the upper feature were to slow down further. Previous Discussion... The vigorous upper level feature will continue to trundle ewd across the region Wednesday as the cold front gradually pushes through the region with snow overspreading the region and affecting the commute Wednesday morning across wrn and central portions. Pcpn could briefly begin as rain, especially toward the coast. 16/12z GFS/ECMWF/NAM/CMC demonstrate decent agreement with this feature, with some slight timing differences in the latter stages, mainly 18-00z Wednesday with the ECMWF/CMC slightly slower. Given this, PoPs have been increased to categorical across the Piedmont after 06z tonight into midday Wednesday, and for central and s- central VA Wednesday morning. Likely PoPs have been maintained for SE VA/NE NC, with likely PoPs for the Middle Peninsula/Northern Neck/Lower Ern Shore tapering to chc for the Lower MD Ern Shore. Overall, not much has changed with the synoptic weather details/preferences in the near and short term. Have gone ahead and extended Winter Weather Advisories east to include all zones west of the Chesapeake Bay, including for the Hampton Roads area for their evening commute. Have held out Accomack/Northampton for now with accumulations ~1" and some mixed pcpn expected. 12z/16 suite once again have trended slightly slower and upward with QPF. Have nudged forecast snow totals up slightly from the peninsula into Tidewater/Hampton Roads areas. Model consensus supports QPF of 0.25-0.35" across the Piedmont and s-central VA and Northampton NC, bordered by ~0.1 to 0.2" from central VA to E VA and NE NC, with 0.1" or less over the lower eastern shore. Expect some variability in SLRs, but generally ratios of 12-15:1 are expected during the highest PoPs, which supports 2-4" of snow across the Piedmont, with 1-3" for the I-95 corridor of central and s-central VA into Northampton NC. Confident in period of moderate snow inland, given well-modeled narrow band of negative EPV dropping over the SW zones in the Piedmont (I-85 corridor). There could be a very narrow corridor of 4-6" of snow in this band. However, expect this would be very localized and hard to pin- down, so there is no need for a watch or warning at this time. Slightly less confident into SE VA. To reiterate...we have issued a Winter Weather Advisory over Hampton Roads for the late morning and afternoon. However, we are still a bit concerned with sharpening axis of F-Gen/OPRH depicted by the 12z (and now 18z) high-res NAM. Issue will be that we will have a very narrow window within which to receive moderate snows into Tidewater area, before best axis of moisture slides offshore. Potential is there for warning criteria snows (and criteria is 3" for SE VA). However, after collaboration with neighboring offices and WPC, will hold off with warning for now. Narrow window of potential snowfall is the primary issue. Should later model runs continue to depict this potential, an upgrade to a Winter Storm Warning for all or part of the Hampton Roads area may be needed. High temperatures will generally be 30-35F, but will likely fall into the mid/upper 20s across the NW half of the area by early aftn and to the upper 20s/around 30F elsewhere by mid/late aftn. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... The sky will clear quickly Wednesday night as well-advertised quick shot of arctic air surges into the region. Shallow mixing is expected to persist overnight, which should inhibit temperatures from plummeting too far. Still cold nonetheless with lows in the teens inland to the upper teens/low 20s for coastal SE VA/NE NC. Mid-level WAA resumes rather quickly Thursday with 850mb temperatures of -2 to -4C at 12z warming to +4-6C by 21z. A cold start to the day, limited mixing, and mid- level WAA should result in rather stable lapse rates and surface high temperatures Thursday should only reach the upper 30s to low 40s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Pattern change looks to occur during the medium range period with a significant warmup expected through the upcoming weekend/early next week. It will still be on the cold side early Fri morning with sfc high pressure centered across the deep south, and one last upper trough moving ESE to the New England coast. Latest GFS/ECMWF/CMC depict the upper trough moving well off the New England coast Fri with a broad upper level ridge building over the eastern CONUS Fri aftn through the weekend. Expect continued dry conditions with warming temperatures, highs in the upper 40s/lower 50s Fri, rising well into the 50s (possibly near 60F) Sat, and into the upper 50s to lower 60s for Sun. Lows Fri night/Sat am in the mid 20s to mid 30s, and Sat night/Sun am in the 30s to around 40F. Minor timing differences arise by Mon between the models, but the overall trend is for a slower arrival of the cold front and with the upper pattern amplifying quite a bit this makes sense. Expect increasing clouds ahead of the next front Sun night but have genly slowed down the main chance for for showers until Mon aftn/Mon night. Mild with lows in the 40s Sun night/Mon am and highs Mon mainly in the 60s (could even be near 70F in the SE if more sun develops and the precip is slower to arrive). High chc PoPs for now/40-50% all zones mon night. The ECMWF is slower by this time than the GFS/CMC so will linger PoPs through 12Z. Drying out/becoming partly-mostly sunny Tue with highs mainly in the 50s. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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Complex scenario overnight with fog/low ceilings confined mainly to the waters and right at the coast. Conditions look to improve as we head through the early morning hours with even the potential for a brief return to VFR conditions this morning. Mainly VFR conditions are anticipated inland for the time being. Expect widespread flight restrictions on Wed in snow as clipper and associated cold front crosses the region. KRIC will likely experience the worst conditions from 12-18Z while KORF/KPHF/KECG will lag behind by several hrs with worst conditions not starting until between 15-18Z and lasting through most of the remainder of the TAF period. KSBY will overall see only light snow showers with vsbys down to about 2SM. Winds will be from the N and gust to 20-25kt near the coast by aftn. Outlook: Clearing Wed night with breezy N winds near the coast. Predominate VFR then likely Thu-Sat as the trough ejects NE offshore.
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&& .MARINE... Light winds and saturated conditions this evening over portions of the Bay and southern VA coastal waters. Cams show limited vsbys over these waters and raised a Marine Dense Fog Advisory through the evening hrs. High pressure will slide into the Atlc this evening. A surface cold front crosses the the coast late tonight into Wed morning, with strong CAA lagging behind until the upper trough arrives Wed evening into Thu. NNW winds increase to 15 to 25 knots Wed aftn/evening with gusts up to or arnd 30 kt, esply later Wed evening and Wed night, as the storm system moves out to sea and high pressure starts to build back in fm the west. SCAs are in effect over the coastal waters into Thu aftn, with SCAs for the Ches Bay and Currituck Snd now in effect fm Wed morning (7-10 am) into Thu morning (7-10 am). High pressure settles over the area later Thu aftn into Sat, then slides off the SE coast Sun. && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...None. NC...Winter Weather Advisory from 6 AM this morning to 6 PM EST this evening for NCZ013-014-030. Winter Weather Advisory from 10 AM this morning to 9 PM EST this evening for NCZ015>017-031-032-102. Winter Storm Warning until 6 PM EST this evening for NCZ012. VA...Winter Weather Advisory until 3 PM EST this afternoon for VAZ048-060>062-069-509-510. Winter Weather Advisory from 6 AM this morning to 6 PM EST this evening for VAZ084-086-088>090-092-093-096-523>525. Winter Weather Advisory from 10 AM this morning to 9 PM EST this evening for VAZ095-097-098-100. Winter Weather Advisory until 6 PM EST this evening for VAZ064- 067-068-075>078-080>083-085-511>522. Winter Storm Warning until 6 PM EST this evening for VAZ065- 066-079-087. MARINE...Small Craft Advisory until 1 PM EST Thursday for ANZ650-652- 654-656-658. Small Craft Advisory from 7 AM this morning to 7 AM EST Thursday for ANZ630>632. Dense Fog Advisory until 7 AM EST this morning for ANZ633-658. Small Craft Advisory from 7 AM this morning to 10 AM EST Thursday for ANZ634. Small Craft Advisory from 10 AM this morning to 7 AM EST Thursday for ANZ633-638.
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&& $$ SYNOPSIS...MAM NEAR TERM...LKB/MAM SHORT TERM...MAM LONG TERM...LKB AVIATION...AJB/LKB MARINE...TMG

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