Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 240149 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 949 PM EDT Mon Oct 23 2017 .SYNOPSIS... A weakening cold front slowly push through the local area late tonight into early Tuesday. A second cold front crosses the area Tuesday night. High pressure builds across the Gulf of Mexico Wednesday and Thursday...as low pressure lingers from the Great Lakes to New England. && .NEAR TERM /THROUGH TUESDAY/...
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Current analysis indicates sfc high pressure well off the coast, with low pressure deepening to the lee of the central Appalachians (this out ahead of parent sfc low over MI). Areas of showers are overspreading much of the western Piedmont this evening. Earlier stronger line segments in vicinity of the Blue Ridge in NC and VA have weakened, with the stronger activity now in central NC. Little overall change in thinking with the scenario tonight, with a high shear/low CAPE event expected, which has prompted a Tornado Watch that extends into the Ern VA Piedmont and runs through 06z. The best lift/forcing for likely to categorical PoPs (60-90%) looks to reach to areas west of I-95 through midnight, then pushing E to the I-95 corridor from 03-06Z, and to the coast from 06-12Z. Strong low level jet and effective shear values to 50-60 KT (and some directional shear through 06Z as SSE sfc winds interact with SSW winds in the H85 to H7 layer. The last few runs of the HRRR depict the potential for some stronger convection to push into S-central VA prior to 06z, with a weakening trend thereafter. SPC has SLGT risk SVR for SW parts of the local area (shifting to the ern shore Tue morning). If it all comes together, an isolated severe tstm with damaging winds and even an isolated tornado can`t be ruled out. However, more likely it will be just a narrow line of showers with embedded convection with wind gusts staying below severe limits (to 40-45 mph). Will continue the mention of locally heavy rain and strong/gusty winds in the HWO. Expect skies to turn partly to mostly sunny by late morning W and by late aftn E...and have continued w/ lowering PoP trend W-E. Still rather warm as winds remain from the SW, with highs Tues in the mid 70s W to the lower 80s SE as cold air lags well behind off to the NW of the local area.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Latest 12Z/23 GFS/NAM/ECMWF remain in good agreement Tue night into Wed, but then show some fairly significant differences with respect to the strength of the upper low over the eastern CONUS by late Wed/Thu. The ECMWF the deepest/farthest south and the GFS the weakest/most progressive and the NAM somewhere in between but genly a little more like the ECMWF. Will side a little more to the NAM/ECMWF consensus, but not quite to the extent of how deep the upper low digs south. Thus, the sfc cold front reaches the coast early Tue night and is expected to exit the coast by daybreak Wed morning. Any RA tapers/ends at the coast Tue evening. Lows will range from the upper 40s west of I-95 to the mid/upper 50s closer to the coast by Wed morning. Dewpoints also fall from the lower 50s NW to lower 60s SE in the evening to 40-45F inland and 45F to around 50F by morning. On Wed...local area looks to remain in between the sfc cold front well offshore and deeper moisture/cold pool aloft to our WNW. Some SCT/BKN cu will tend to linger due to some shortwave energy aloft, but should be dry with highs mainly in the m-u60s (staying a little below MAV numbers as they are based off the warmer GFS). For Wed night/Thu, siding to the NAM/ECMWF allows for some digging SE of the upper level shortwave energy from the Great Lakes through the Carolinas by thu morning. Will keep it dry for now, with partly cloudy conditions. Lows Wed night mainly in the 40s and highs Thu 60-65 F under partly to mostly sunny skies. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Long term period starts off dry Thu night/Fri with sfc high pressure over the immediate area and W/SW flow aloft. With light sfc winds under a clear sky, expect low temps Thu night in the low/mid 40s most of the area, and highs in the mid/upr 60s Fri. Attention then turns to an approaching deep upper-level trough Sat. Although any pcpn will likely hold off until after daytime Sat, included a 20% chance of a shower in case the faster ensemble member solutions pan out. Better chance of rain (40-50%) arrives Sat night/Sun as strong sfc low pressure forms out ahead of the upper-level trough. There is still plenty of uncertainty over the track of this low, but the possibility is there for moderate to heavy rain Sun. High temps in the mid/upper 60s Sat drop to the upr 50s to mid 60s Sun. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... Low pressure and an associated cold front will approach fm the west this evening, then the actual cold front will gradually cross the region and move offshore later tonight into Tue evening. Increasing SE then S winds expected this evening thru Tue morning ahead of the front, with showers and possible tstms moving thru the CWA later this evening into Tue morning. SE or S winds 10-15 kt, with gusts up to 25 kt possible during this time period, with higher gusts possible in stronger showers or tstms. This front will bring the potential for MVFR/IFR conditions in showers and lower CIGS. Mainly VFR conditions expected later Tue aftn/evening through Fri. && .MARINE... Previous marine headlines remain in place ahead of an approaching cold front. Decided to put all headlines in effect with this package with SCA conditions expected to commence over all wtrs within 12 hr. The SCA is for 15-20 kt southerly winds over the rivers/Sound and 15- 25 kt winds with gusts up to 30 kt over the Bay and ocean. Waves up to 4 ft over the Bay with seas over the ocean up to 7-8 ft. A trough of low pressure ahead of the cold front slides through the area early Tue, with the pressure gradient relaxing a bit into the day Tue and winds decreasing to below SCA thresholds. Main cold front crosses the area Tue night with sub-SCA NW winds expected behind the front into Wed. Will maintain the SCA over the ocean through the day Wed due to a prolonged period of 5 ft seas. Lighter winds and sub- SCA conditions into Thu and Fri with sfc high pressure over the area. && .TIDES/COASTAL FLOODING...
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A modestly strong SSE wind ahead of a cold front will potentially push tidal anomalies to 1.0-1.5ft above normal late tonight into early Tuesday morning. This could push some locations near minor flooding thresholds (mainly Cambridge and Bishops Head) during high tide late tonight into early Tuesday morning. Water levels at these locations potentially remain elevated for the following high tide (aftn/early evening), which is the higher astronomical tide.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 10 AM EDT Tuesday for ANZ635>638. Small Craft Advisory until 4 PM EDT Tuesday for ANZ630>632-634. Small Craft Advisory until 7 PM EDT Tuesday for ANZ633. Small Craft Advisory until 7 PM EDT Wednesday for ANZ650-652- 654-656-658. && $$ SYNOPSIS...LKB NEAR TERM...LKB SHORT TERM...ALB/LKB LONG TERM...MAS AVIATION...LKB/TMG MARINE...AJB/MAS TIDES/COASTAL FLOODING...AJZ

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