Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 060923 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 423 AM EST Tue Dec 6 2016 .SYNOPSIS... Low pressure lifts along the Southeast and Mid-Atlantic coasts today, bringing widespread rainfall to the region. Low pressure pushes offshore tonight as high pressure briefly returns Wednesday. A potent cold front pushes across the region Thursday. Arctic high pressure builds in Friday and Saturday, accompanied by the coldest temperatures so far this season. && .NEAR TERM /THROUGH TONIGHT/... Latest GOES water vapor imagery depicts mid level low pressure lifting from the Southern Plains into the lower Mississippi River Valley, with a plume of moisture stretching from the eastern Gulf of Mexico northeastward into the Mid-Atlantic states. Meanwhile, an upper level ridge stretches from the local area northwestward over the Great Lakes. At the surface, high pressure centered over the Northeast is ridging southward over the local area as a coastal front remains along the Southeast coast. Upper/surface high pressure has kept the brunt of the precipitation at bay this morning, with only light rain being reported over the southwest Piedmont. Expect this trend to change as the upper low de-amplifies and lifts into the Deep South and the ridge axis pushes offshore. Deep layer southwest flow will advect anomalous precipitable water values into the region (+200% based on latest blended total precipitable water product). Add in a departing 170+ kt exiting jet streak with the height falls ahead of the upper low and forcing for ascent will be quite impressive, especially by mid to late afternoon. Expect light rain to spread northeast into central Virginia by daybreak as isentropic lift/WAA overspreads the region. Low pressure develops along the coastal front as another area of low pressure weakens over the central Appalachians. The high retreats, as widespread rainfall spreads over the entire region by mid to late morning. Rainfall persists through the afternoon as the upper low finally reaches the area by late today. Hi-res guidance indicates rainfall rates increase to 0.1 to 0.25 inches/hour this afternoon, aided by strong dynamics. However, moisture flux remains rather meager with the best theta-e advection remaining offshore, so any chance for locally heavy rainfall will be tied to better forcing late today. Have increased QPF slightly, with amounts generally ranging from around an inch in the south to around an inch and a quarter for the Northern Neck through today. The upper low quickly kicks offshore this evening, with rainfall winding down southwest to northeast. Light rain lingers for the Maryland Eastern Shore through late tonight as wrap around moisture from the surface low impacts the region. Soundings indicate low levels will remain quite moist through the overnight thanks to a northerly wind. Have increased cloud cover, especially along and east of Interstate 95. In-situ wedge over the region today will result in a large temperatures spread across the local area. Daytime temperatures across the Piedmont forecast to be lower than the current temperatures. Thus, daytime temperatures will range from the low 40`s northwest to low 60`s southeast. Central Virginia forecast in the mid/upper 40`s to low 50`s. Temperatures drop into the mid/upper 30`s west to mid 40`s east tonight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... Wednesday will be a transition day as a weak secondary front pushes across the region in fast westerly flow aloft. Low pressure pushes well offshore as high pressure builds southward along the Northeast coast. A dry day is in store with near seasonable temperatures. Highs generally in the mid 50`s. Sky averages partly cloudy as soundings indicate mid level moisture trapped under a strong subsidence inversion. Anomalous northern stream low builds into southeast Canada Wednesday night as the associated trough digs into the eastern US. A strong, fast moving cold front will reach the central Appalachians by late Wednesday night. Clouds increase, but dry conditions expected. Lows in the mid to upper 30`s. Strong cold front quickly pushes across the forecast area Thursday as the trough axis lags behind. Moisture will be limited with precipitable waters at or below three quarters of an inch. While the front is progged to outrun the best height falls, potential is there for a narrow line of isolated to scattered showers along the boundary. Will maintain slight chance to chance POPs, with the best chances across the north and northeast, nearest the better moisture. Front reaches the coast Thursday afternoon as thicknesses inland plummet ahead of a surging arctic air mass. Any POPs Thursday afternoon will be tied to the coast. Temperatures warm into the upper 40`s to low/mid 50`s Thursday before plummeting Thursday night. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Long term period starts off Thu night/Fri with dry weather behind an offshore moving cold front. Main story in the extended will be cold temps, with lows in the mid/upr 20s Thu night dropping to the low/mid 20s Fri night and Sat night under continued dry weather with sfc high pressure in the vicinity. High temps Fri and Sat avg in the low 40s both days. Next chance of pcpn arrives Sun night/Mon with an approaching cold front, but have capped pops for now at 20-30% with this several days out. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... Latest surface analysis centers high pressure over the Delmarva, ridging southward over the local area. Subsidence over the local area and overcast cloud decks from 9-15k feet AGL are keeping the precipitation at bay, as the light echoes over the southwest are not reaching the ground. Expect this trend to continue through 9-12Z as cloud decks slowly lower. MVFR ceilings expected to spread into the Piedmont by 10-12Z, but VFR conditions expected otherwise. Surface winds are generally calm to light out of the northeast. Rain expected to overspread the region from south to northeast in earnest after 12Z this morning as low pressure lifts along the coast. Model consensus indicates MVFR conditions at onset and lowering quickly to IFR by mid to late morning. IFR and locally LIFR conditions are expected across the entire region by 18Z in the form of ceilings of 400-700 feet AGL and moderate rainfall. IFR/LIFR conditions expected to persist through the remaining 06Z TAF issuance all sites. Northeast winds increase to around 10 knots inland and 15 to 20 knots with occasional gusts of 25 to 30 knots near the coast. Conditions begin to slowly improve southeast to northeast late tonight as the storm system pulls away from the region. VFR conditions return Wednesday. A strong cold front impacts the area on Thursday, with only a quick chance for showers Thursday afternoon. High pressure returns Friday into the weekend. && .MARINE... Low pressure continues to deepen and lift NE through the Gulf Coast states this morning heading toward the Ohio Valley. Meanwhile high pressure that is along the eastern seaboard is beginning to retreat northeastward while a coastal front is developing along the Southeastern US Coast. Winds are currently around 10 to 15 kt across the waters but will begin to increase later today as the gradient tightens as the coastal front develops and low pressure begins to form along it on the Carolina coast. This area of low pressure will continue to strengthen this evening as is slides of the Virginia coast and then heads eastward on Wednesday. At this point, it appears that winds will increase to around 15 to 25 kt on the Chesapeake Bay and 25 to 30 kt across the coastal waters. The models show the 950 mb winds getting up to around 40 kts, especially to the north of the low. but getting all that winds to mix down does not look likely as lapse rates are marginal along the coast. So have decided to drop the Gale Watch and extend the SCA through Wednesday afternoon. There could be an occasional gust to 35 kt between 00z and 6z Wednesday, but the probabilities in the model are low, around 10%. Once the low pulls off the coast, high pressure builds in on Wednesday and should allow the winds to relax, but with seas being slow to drop, have kept the SCA running for the coast through Wed afternoon. They may linger into Wednesday night but for now did not want to extend the SCA beyond Wednesday. The next front pushes into the area on Thursday as an area of low pressure now over the northern plains slides across the Great Lakes and into Southern Canada. The models are differing on the timing with the GFS and ECMWF both bring the front through early with little moisture, while the NAM is slower and more amplified. With the strong upper flow and cold high pressure coming behind the front, have leaned toward the faster solution which limits any southerly flow ahead of the front. But once the front clears, much colder air will sweep through the waters and should produce another round of solid small craft to near gale force conditions into Friday night before high pressure settles over the east for the coming weekend. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory from 1 PM this afternoon to 1 AM EST Wednesday for ANZ635>638. Small Craft Advisory from 10 AM this morning to 7 AM EST Wednesday for ANZ630>634. Small Craft Advisory from 10 AM this morning to 4 PM EST Wednesday for ANZ650-652-654. Small Craft Advisory until 4 PM EST Wednesday for ANZ656-658. && $$ SYNOPSIS...MPR/SAM NEAR TERM...SAM SHORT TERM...SAM LONG TERM...MAS AVIATION...AJB/SAM MARINE...ESS

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