Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 220758 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 358 AM EDT Sat Jul 22 2017 .SYNOPSIS... Hot and humid conditions will continue over the region over the weekend. A weakening cold front will gradually push across the area late Sunday through Monday, with temperatures cooling down to near normal levels Monday through Thursday. && .NEAR TERM /THROUGH TONIGHT/... Early morning analysis reveals a quasi-stationary frontal boundary draped from eastern new England back into the mid- Missouri Valley. A Weak sfc/lee trough is still lingering over the Mid-Atlantic region this morning from S NJ down into the piedmont of central VA/NC. And of course, Bermuda high pressure remains in control over the western Atlantic. Aloft, a quick- moving shortwave continues to dive across the Ohio valley toward the central Appalachians this morning. Associated late night MCS/MCV activity continues to roll across the Ohio River Valley early this morning. W-NW flow prevails aloft around the base of an upper level trough centered over eastern Canada. Headline today will again be the heat. We`re off to a very warm start once again, with early morning lows mainly 75 to 80 F. Temperatures will be similar to slightly cooler to those of Friday, due to potential for more aftn clouds and as core of 850mb heat shifts a bit S. Having said that, however...we will see slightly higher dewpoint values today compared to Friday. Therefore expect most of the area to reach heat advisory criteria by late morning (coast) into the aftn inland, even as highs avg only in the mid 90s. Only far NW counties should mix out enough to keep Heat index values in the low 100s this aftn. Other story today will be the convective potential for the mid to late aftn and evening. Expect convection to remain well to our NW through midday. However, majority of CAMs (including time lagged HRRR and NAM Conest...which have handled convection to the N/NW well over the past few days) showing convective outflows triggering some more iso-sct showers and T-storms today than we`ve seen locally over the past few days. This is a result of 1) a more unstable airmass by this aftn/early evening, courtesy of increasing PW values and lowering heights aloft, and 2) a bit more in the way of deep layer shear, especially over the northern 1/3 of the area, as upper trough to the NW deepens/amplifies. Convection developing over the foothills into N VA will therefore be more likely to hold together into our local area for at least a few hours from the mid to late afternoon. For that reason, have bumped POPs into high end chc to likely (50-60%) across the Northern Neck counties over to the lower Eastern Shore. POPs taper down to slight chance (20%-30% South central VA into NE NC). Most of the CWA is in a marginal risk for severe wx, with a slight risk for the northern half of the area. Damaging wind gusts will be the primary threat, though steepening mid-level lapse rates could portend to some strong updrafts and the potential for some large hail (best chance over the northern neck/eastern shore). lows again in the 70s to near 80 across the south. Slightly "cooler" across the north, especially in areas the do receive those showers. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Continued hot and humid with additional heat headlines likely needed for some of the region on Sun. Highs mainly in the mid to upper 90s Sunday. Slight risk remains in place for most of the CWA, but more uncertainty exists depending on how long convective debris from Sat night hangs around and potentially keeps more clouds around. Cold front slated to pass through while weakening late Sun night through Mon. Will maintain chc PoPs all zones Sun night, and favor highest PoPs Mon across the S with 20% PoPs for the N. Slightly less humid Monday, especially N. Highs Mon 90 to 95 F. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Cold front progged to push offshore Tuesday morning as the upper trough slides over the Northeast into the Canadian Maritimes. Deepest moisture pushes offshore late Monday night, but will keep mention of slight chance to chance POPs near the coast. Southern portion of the cold front expected to stall over the Carolinas Tuesday as a baggy trough locates over the Southeast. Combination of weak energy in the upper flow and a moist air mass near the boundary, will keep mention of slight chance to chance POPs across the far southeast local area Tuesday afternoon. Otherwise, cooler Tuesday with a light north to northeast wind. Highs generally in the upper 80`s to around 90 (near seasonable norms). High pressure at the surface and aloft slides north of the region Tuesday night into Wednesday as another trough tracks across Ontario. Meanwhile, a broad upper ridge over the Southern Plains expands eastward, but the baggy trough remains over the Southeast. Best chances for measurable precip expected to be south of the region Wednesday, but will carry slight chance to low end chance POPs across the southern portions of the forecast area. Highs Wednesday generally in the mid 80`s. Another trough tracks into the Great Lakes and Northeast Wednesday night and Thursday, pushing another weakening cold front into the Mid- Atlantic region Thursday afternoon. Will need to watch for upstream convection Wednesday night in northwest flow aloft, so have added chance POPs for the Maryland Eastern Shore. With the boundary and cyclonic flow over the region Thursday, have chance POPs for diurnally driven showers and thunderstorms. Highs Thursday generally in the upper 80`s to low 90`s. Medium range guidance depicts additional energy digging down the backside of the upper trough Friday, with a wave of low pressure progged to develop along the Mid- Atlantic front. Timing and spatial differences at that timeframe of the forecast cause a great deal of uncertainty, so have only mentioned 20-40% POPs at this time. Highs back around seasonal norms. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... VFR conditions at area terminals this morning, with VFR conditions to prevail through the 06z TAF period. High pressure will continue to prevail off the Southeast Coast tonight into Saturday, with a lingering trough to the lee of the central Appalachians. This will result in primarily light SW flow at ~5-10kt. Sct to occasionally bkn mid and high clouds overnight. Mainly dry conditions are expected tonight with a minimal chc of showers/tstms at SBY through 10z (SCT showers now crossing from north of an ESN to GED line at issuance time). Sct cu with bases ~5-6kft develop by late morning ahead of a weak upper level system. This feature should trigger isolated to scattered showers/tstms late this afternoon and evening. The best chc (30-50%) is from RIC-SBY and north, with a 20-30% chc for PHF/ORF/ECG. Have included Vicinity Thunder wording at SBY and RIC, but have held out elsewhere for now. Outlook: Another period of late aftn/evening showers/tstms expected Sunday, shifting south into south central VA and NC for Monday. VFR should dominate through this period, with periods of periods of sub-VFR possible in heavier showers/TSRA. A weak cold front pushes through the area Tuesday with high pressure building N of the region Wednesday. && .MARINE... High pressure is well-rooted over Bermuda with a sfc thermal trough in the lee of the mountains and flat/zonal flow aloft across the region. This pattern will persist through the weekend with a cold front approaching the waters on Monday...crossing the waters Monday night. Expect increasing potential for aftn/evening thunderstorms with each passing day. Main impacts will be locally strong wind gusts, heavy rainfall and frequent lightning. Winds will generally be SW aob 15kt with seas averaging 2-4ft and waves 1-3ft during this timeframe. Models are hinting at a brief uptick in wind speeds Sunday night, which is likely associated with thunderstorms than more synoptically-driven conditions. SCA flags are not anticipated at this time. The cold front stalls out just south of the area with weak troughing along the Mid Atlantic/Carolina coasts, which is expected to persist in this area from Tuesday through the rest of the week. Best chance for aftn/evening thunderstorms should remain confined to srn waters invof the weak trough as well as seabreeze boundaries. Wind speeds aob 15kt the rest of the week. Wind direction veers to the north behind the cold front late Monday night/Tuesday...becoming onshore/E-SE Tuesday night through Wednesday night...then becoming S-SW Thursday/Friday. Seas average 2-3ft; waves 1-2ft. && .CLIMATE... Heat wave is expected to continue through Sunday. The 2nd half of July is climatologically the hottest few weeks of the year, so we still may not set any daily records at our main climate sites. For reference, record highs for Saturday and Sunday are listed below: * Date: Sat(7/22) Sun(7/23) * RIC: 103/1952 103/1952 * ORF: 102/2011 103/2011 * SBY: 104/1930 103/2011 * ECG: 104/1952 104/1952 && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for MDZ021>024. NC...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for NCZ012>017-030>032. VA...Heat Advisory from 10 AM this morning to 8 PM EDT this evening for VAZ060>062-064>069-075>090-092-093-095>100-511>525. MARINE...None. && $$ SYNOPSIS...MAM NEAR TERM...LKB SHORT TERM...LKB/MAM LONG TERM...MAS AVIATION...AJZ/MAM MARINE...BMD CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.