Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 210105 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 905 PM EDT Tue Mar 20 2018 .SYNOPSIS... Low pressure will develop off the Outer Banks tonight and then intensify off the Delmarva coast Wednesday, before gradually pushing offshore Wednesday night. High pressure gradually builds into the area late in the week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 9 pm update...Afternoon forecast in good shape, with only minor tweaks to temps necessary. Latest satellite imagery shows significant tstm activity off the SC/NC coast, as upper shortwave interacts with the Gulfstream. In addition, band of shwrs/tstms has continued rotating around upper low from srn WV into central NC. Hi-res models suggest this feature will rotate into the region overnight, then be north of the area before noon Wednesday. Hi- res models also suggest this feature may contain the most important precip for the rest of the event, with NAM suggesting much of the snow behind this system will be light, and therefore have difficulty accumulating. Will not make any changes to current advisories/warnings, as there is not enough information to begin changing snow amounts. However, mid shift will need to closely monitor the band of shwrs/tstms to our W/SW being the main precip producer the next 24 hours. In addition, large tstm complexes offshore often lead to mitigating the amount of QPF for a system developing to the N/NW. All of this will need to be evaluated by mid shift. For now, no changes to current precip forecast next 24-30 hours. 4 pm discussion...Current wv imagery depicts a powerful upper trough pushing across the Southeast Conus, with an area of surface low pressure off the VA Capes and another area of broad low pressure developing across SC, and this will become the primary low tonight into Wednesday. High pressure N of the Great Lakes is presently ridging swd through the Piedmont, which is resulting in a CAD airmass under extensive stratus, and largely a lull in rain with the exception of the Ern Shore. Temperatures range from the mid 30s over the NW Piedmont to the mid 40s/around 50F for coastal SE VA/NE NC. This powerful complex system will continue to impact the region tonight. The 20/12z GFS/NAM/ECMWF continue to depict the surface low deepening tonight in vicinity of the Outer Banks. Pcpn arrives from the SW later this evening, with the potential for NW portions transitioning to snow after midnight, with the change to snow for the RIC metro occurring from 3-6 am. Much of the overnight accumulation of snow should be NW of RIC and mainly 1-2". More discussion on accumulation, warnings, and advisories is discussed in the short term section below. PoPs ramp up to categorical tonight. Lows range from the low 30s NW to the upper 30s/around 40F SE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... The upper level system passes ewd in vicinity of the VA/NC border Wednesday morning, with surface low pressure intensifying off the Mid-Atlantic coast. The upper level system slides offshore during the aftn with the overall system becoming stacked and nearly stationary off the coast during the 18-00z time period. This will bring the potential for banded pcpn (in the form of snow) across the Delmarva and perhaps the Nrn Neck. The upper level system pulls in enough cold air to allow a transition to snow for ern portions of the are Wednesday. Likely to categorical everywhere through through midday Wednesday as the forcing from the upper level system taps into moisture, and categorical PoPs over the Ern Shore into the aftn. Thicknesses suggest rain mixing with snow over the Ern Shore Wednesday morning (Dorchester may become all snow by daybreak), then becoming all snow by aftn evening. Farther W (I-95 corridor to the Piedmont) thicknesses suggest all snow while pcpn occurs, with snow tapering off from SW-NE during the aftn, and possibly mixing with light rain at the tail end. A cold rain for SE VA/NE NC could mix with some snow Wednesday aftn/early evening. The current forecast is for 3-5" for Caroline County and the Nrn Neck, and Somerset/Wicomico MD, with the potential for 4-6" for Dorchester MD. These areas have a winter storm warning. Elsewhere, 1-3" of snow is forecast in a corridor along a FVX-RIC-WAL line where winter weather advisories are in effect. The primary impact will be falling snow with conditions improving once the snow ends. Accumulation on roads will be dependent on intensity, otherwise, expected accumulation mainly on the grass and elevated surfaces. Accumulation farther S should be 1" or less, and little to no accumulation for far SE VA/coastal NE NC. Highs Wednesday will be in the mid 30s where snow falls to the upper 30s/low 40s where rain prevails. Highs in south central VA may rise to around 40 F later in the aftn as the precip intensity diminishes. Drier air arrives late Wednesday night through Friday as the system pulls to the northeast. Partly to occasionally mostly cloudy under the upper trough. Lows Wednesday night range from the mid/upper 20s NW to the low 30s SE, with highs Thursday in the mid to upper 40s, possible cooler over the MD Ern Shore depending on snowfall Wednesday. Some re-freezing could occur early Thursday morning especially if there is (partial) clearing late Wednesday night. Lows Thursday night range from the mid 20s to low 30s, with highs Friday in the mid 40s to around 50F. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Region remains influenced by large scale upper trof through most of the extended period. Area is between systems Friday night and most of Saturday. A shortwave trof will be approaching from the west Saturday night, and move across the area on Sunday. 12Z GFS/ECMWF are at odds with regard to how far north precip gets with this shortwave. Have gone with a blended solution, which gives a chance of rain/snow across much of the area. Shortwave moves offshore Sunday night, with ridging surface and aloft gradually building into the region Monday through Tuesday. Overall, cold high pressure building in from the the NW will provide a continuation of below/much below normal temperatures for much of the forecast period. For temperatures, Highs Sat around 50F inland...m40s at the coast. Lows Sat night generally 30-35, with some upper 30s NE NC. Highs Sun in the 40s to around 50 F, and Mon mid to upper 40s N/DELMARVA to mid 50s southern portions of interior NE NC. highs Tuesday around 50 Lower MD Eastern Shore to the upper 50s interior NE NC. Lows Sunday night/Monday night in the low to mid 30s. && .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/... Low pressure is located east of the DELMARVA at 23z, with another area of low pressure situated over eastern SC. Meanwhile, high pressure centered N of the Great Lakes is ridging swd through the Piedmont. Little if any precipitation occurring across the region at 00Z. However, there are showers/tstms along the NC coast lifting NEWD, and additional showers/tstms in SW VA/wrn NC, also moving NEWD. Expect precipitation to re-develop/move back into the area in the 04-06Z time frame, later at KSBY. In the meantime IFR cigs should prevail this evening although there could be occasions where cigs lift to MVFR around 1.0-1.5kft. As the 2 low pressure areas mentioned above begin to consolidate off the DELMARVA coast, rain will change to snow from NW to SE across the area. The changeover should reach KRIC by 12Z, KSBY/KPHF around 16Z, and KORF around 18Z. All in all, the 00Z TAF period will be dominated by IFR/LIFR in low ceilings and precip. A N wind of 10-15kt with gusts to around 20kt is expected, especially near the Bay/Ocean. Snow potentially lingers at SBY Wednesday evening. Otherwise, drier conditions arrive later Wednesday night, with dry and VFR conditions prevail Thursday and Friday. Low pressure approaches from the W late Saturday, with the potential for sub-VFR flying conditions by early Sunday. && .MARINE... A couple of low pressure areas will combine into one and intensify just off the Mid Atlc coast tonight into Wed morning. That strong low pressure system will then slowly lift NE off the Delmarva and New England coasts Wed into Thu. This will produce strong NE-NW winds over the waters tonight thru Thu, with Gale warnings now in effect for the nrn three coastal zns until 7 pm Wed, and SCA`s now in effect for the remainder of the marine zns until 1 pm or 4 pm Thu. Expect wind gusts to arnd 40 kt over the nrn two coastal zns thru tonight, then gusts to around 35 kt during Wed. Seas will be between 8 and 13 ft over the nrn coastal zns thru Wed, and between 6 and 9 ft over the srn coastal zns. Low pressure will move away twd/into the nrn Atlc late Thu thru Fri, allowing for conditions to slowly relax. High pressure will finally build over the area by Sat. Another low pressure system may impact the waters by Sun. && .TIDES/COASTAL FLOODING... Tidal departures build this evening through Wednesday and there will be the potential for at least minor coastal flooding for locations adjacent to the lower Bay and the Atlantic coast. Went ahead and issued a Coastal Flood Watch for coastal portions of Worchester County where guidance continues to indicate the potential for Moderate flooding Wednesday. Expect for tide departures to run from 2 to 3 feet above normal tide around times of high tide. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...Coastal Flood Advisory until 4 AM EDT Thursday for MDZ024-025. Winter Weather Advisory from 9 AM Wednesday to midnight EDT Wednesday night for MDZ024-025. High Surf Advisory until 8 PM EDT Wednesday for MDZ025. Wind Advisory until 2 PM EDT Wednesday for MDZ025. Winter Storm Warning from 6 AM Wednesday to midnight EDT Wednesday night for MDZ021>023. NC...Coastal Flood Advisory until 4 AM EDT Thursday for NCZ102. VA...Winter Storm Warning from midnight tonight to 6 PM EDT Wednesday for VAZ048-509-510. Coastal Flood Advisory until 8 AM EDT Thursday for VAZ089-090- 093-096-524. Coastal Flood Advisory until 8 AM EDT Thursday for VAZ078- 084>086-095-097-523-525. Winter Weather Advisory from 3 AM to 6 PM EDT Wednesday for VAZ060>062-068-069. Coastal Flood Advisory until 4 AM EDT Thursday for VAZ098>100. Winter Weather Advisory from 9 AM Wednesday to midnight EDT Wednesday night for VAZ099. High Surf Advisory until 8 PM EDT Wednesday for VAZ099-100. Winter Weather Advisory from 9 AM to 9 PM EDT Wednesday for VAZ078-082-083-085-518>520-522. Winter Weather Advisory from 6 AM to 6 PM EDT Wednesday for VAZ511>517. Winter Storm Warning from 3 AM to 9 PM EDT Wednesday for VAZ064-075>077-521. MARINE...Gale Warning until 7 PM EDT Wednesday for ANZ650-652-654. Small Craft Advisory until 4 PM EDT Thursday for ANZ630>632- 634-656-658. Small Craft Advisory until 1 PM EDT Thursday for ANZ633- 635>638. && $$ SYNOPSIS...AJZ/LKB NEAR TERM...AJZ/LKB SHORT TERM...AJZ/LKB LONG TERM...WRS AVIATION...AJZ/WRS MARINE...TMG TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.