Area Forecast Discussion
Issued by NWS Wakefield, VA

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179 FXUS61 KAKQ 221725 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 125 PM EDT Sat Jul 22 2017 .SYNOPSIS... Hot and humid conditions will continue over the region this 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/... Latest analysis indicates a weak sfc/lee trough lingering over the Mid- Atlantic region this morning from S NJ down into the piedmont of central VA/NC. Aloft, WNW flow prevails and with some weak shortwave energy passing through central VA currently, s few showers have actually developed approaching the NW zones as of 9 am. Appears this energy is weak, with main shortwave still well off the the WNW northern Ohio associated with ongoing MCS/MCV activity. Latest CAMs indicate this activity should be limited in coverage through the next few hrs, but did add a 20% PoP in the NW through late morning. Main headline today will again be the heat/humidity, with 9 am temperatures mainly 80 to 85 F and heat indices as high as the mid 90s on the eastern shore where dew pts are the highest (upper 70s/near 80 F). With the pattern perhaps showing its hand a little right now, think core of the hottest wx today will set up across the SE, aided by enough of a low level Jet and mixing to keep the seabreeze from developing as it has the past few days for places like Hampton Roads. Have raised highs to the upper 90s acrs these areas given a solid WSW flow all the way to the coast. Temperatures there will tend to be higher than the past 2 days, while inland (esp NW), highs will be a bit cooler to those of Friday, due to potential for more aftn clouds and as core of 850mb heat shifts a bit S. Heat advisory remains in effect for all zones except the far NW and Ocean City Beaches and Currituck Outer Banks NC. Though, depending on how clouds evolve later today, much of the area N/W of Richmond may not reach the 105 F heat index criteria. Other story today will be the convective potential for the mid to late aftn and evening. Expect main 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. Slight risk remains in place for most of the CWA, as the upper trough digs SE across the Ohio Valley. Sunday remains a bit of a conditional convective threat. Numerous convective boundaries are likely to be in place, which would serve as a focusing mechanism for afternoon and evening convection. However, uncertainty exists regarding the extent and degree of cloudiness from convective debris which hangs around into Sunday, thereby serving to dampen destabilization. Models are still split on extent of cloudiness through the early afternoon and have therefore elected to keep POP in chance range (40-50%) for now, highest over the NE CWA. Should convective debris clear out in a timely way on Sunday, it`s easy to visualize a scenario in which more widespread convection occurs, given better lift/lapse rates courtesy of the approaching upper trough and the strong heating/destabilization that would result from quicker clearing. Once again, damaging winds again the primary threat with storms on Sunday. Highs drop off slightly given increase in dewpoints and clouds. Highs in the low 90s along the coast to mid 90s just inland, with heat indices again right around heat advy criteria. 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 shifting south across SE VA & NE NC with 20% PoPs for the N. Slightly less humid Monday over the NW CWA. Not quite as hot, with 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 /18Z SATURDAY THROUGH WEDNESDAY/... VFR conditions expected through most of the forecast period as high pressure remains off the coast. Sct convection possible across northern TAF sites after 22Z as a series of convective complexes ride se along a stalled front well north of the fa. First complex tracking across northern VA/MD attm is progged to continue SE across the lwr MD eastern shore towards 00Z. Given decent agreement in high res data, added VCTS to SBY`s forecast for a few hours beginning at 22Z. Otw, kept thunder out of the other TAFs as any storms that do develop are not expected until after 00Z. Convection may not make it to the SERN TAF sites until late tonight if at all. Expect lcl MVFR CIGS/VSBYS in any storm with the potential for IFR VSBYS in any one downpour. Expect a repeat performance Sunday as the persistant pattern continues early in the week. Outlook: Convection slowly shifts 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 into the area for the mid week period. && .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 today 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 until 8 PM EDT this evening for MDZ021>024. NC...Heat Advisory until 8 PM EDT this evening for NCZ012>017- 030>032. VA...Heat Advisory until 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/MAM SHORT TERM...LKB/MAM LONG TERM...MAS AVIATION...MPR MARINE...BMD CLIMATE...AKQ is the U.S. government's official web portal to all federal, state and local government web resources and services.