Area Forecast Discussion
Issued by NWS Wakefield, VA

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064 FXUS61 KAKQ 281112 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 712 AM EDT Fri Apr 28 2017 .SYNOPSIS... A cold front stalls over the area this morning before weakening. Strong high pressure then prevails just off the Southeast Coast for the rest of Friday through the weekend...bringing warmer and more humid conditions to the area. A cold front pushes across the region Monday night. && .NEAR TERM /THROUGH TONIGHT/... Latest GPS water vapor imagery depicts an anomalously moist air mass over the local area, with precipitable waters progged ~1.5 inches (although, about 20% lower than predicted 24 hours ago). Plume of moisture also visible on water vapor ahead of an elevated mixed layer spreading over the Piedmont. RAP analysis indicates marginal instability over the region this morning thanks to steepening mid level lapse rates ahead of the mixed layer (MUCAPE 500-1000 j/kg). However, forcing remains rather meager with the latest radar trends depicting the limitation. RAP indicates some weak vorticity advection across the southeast to go along with 30-40 knots of deep layer shear. This will be enough to maintain scattered showers with embedded thunder as a weak pre-frontal trough pushes across the region. The cold front is progged to weaken, stall over the central Appalachians/western Piedmont mid morning as the remaining showers push offshore. Deepest moisture pushes offshore late morning as a weak perturbation in southwest flow pushes across the region. Rapid destabilization is progged across the southeast local area as dewpoints in the upper 60`s to around 70 degrees pool along the weak surface trough and dry/cool air advects into the upper levels. NAM indicates MLCAPE values of 2500-3000 j/kg. However, strong capping is expected between 850-700mb. Given lingering mid level moisture and instability, and low level convergence near the coast from the weakening surface trough or potential sea-breeze boundary have kept mention of slight chance to chance POPs across the southeast this afternoon. Limitation will be if the shallow forcing is enough to break the cap. Hi-res updraft helicity fields indicate that may not be possible, hence low POPs/confidence. Parameters are quite impressive, so any storms that can form could produce hail and gusty winds. Meanwhile, the subtropical ridge amplifies off the Southeast coast this afternoon. Early morning clouds and convection will temper temperatures from reaching their full potential this afternoon, but still quite warm. Highs generally in the mid 80`s. Cooler near the coast. Atmosphere stabilizes tonight, with some overnight stratus expected due to return flow. Mild, with lows in the mid to upper 60`s. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... Heights continue to build into Saturday as 850mb temps warm to +17 to +19C (+2 standard deviations). The result will be the warmest day of the season with widespread readings in the low 90`s inland. Some records may be challenged with temperatures 10-20 degrees above normal. Dewpoints in the 60`s will push heat index values into the mid 90`s inland. Given the warm temps and dewpoints in the mid to upper 60`s, along with steep mid level lapse rates from an elevated mixed layer, instability is progged to be quite impressive Saturday afternoon. However, a lack of appreciable forcing and a strong cap will limit any chances for diurnally driven showers/thunderstorms to sea-breeze boundaries. Although, a lack of deep layer moisture and shear will ultimately limit the storm coverage. Will need to keep an eye on a potential vorticity anomaly progged to lift from the Gulf into the Southeast Saturday, which could help provide some additional forcing across the south. A backdoor front progged to drop into the northern Mid-Atlantic region late Saturday, dropping over the Maryland Eastern Shore late Saturday night. Will need to keep an eye on upstream convection that develops along the front Saturday afternoon, potentially dropping over the northeast local area Saturday evening/night. Mild, with lows in the upper 60`s to around 70. The subtropical ridge retreats offshore Sunday as a deep/anomalous upper trough pushes across the central CONUS. The backdoor front progged to stall over the northern local area Sunday before slowly lifting northward late Sunday into Sunday night as a warm front. Warm advection aloft (in wake of the mixed layer) and a drier air mass will owe to more stable and dry conditions Sunday. Have retained silent POPs Sunday afternoon. Lower heights and 850mb temps will knock a few degrees of of high temperatures, but still warm with highs in the mid to upper 80`s. Heat indices forecast in the upper 80`s to around 90 with a southwest wind of 10-15 mph. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... There will be increasing chcs for showers and tstms fm the west late Sun night into Mon morning, as a cold front pushes into the mtns. That cold front will push thru the mts by late Mon, then cross the area and move off the coast Mon night into Tue morning. Have maintained high chc to likely Pops for showers/tstms fm Mon aftn into Tue morning. Lows Sun night will range thru the 60s. Highs on Mon in the upper 70s to mid 80s. Lows Mon night mainly in the upper 50s to mid 60s. Weak high pressure will provide dry wx for later Tue morning thru Wed, as it slides from the Gulf coast states to off the SE coast. Highs on Tue and Wed mainly in the mid to upper 70s. Lows Tue night ranging thru the 50s to near 60. Another low pressure area will lift fm the lower MS valley twd the OH valley Wed night thru Thu. This will result in increasing chcs for showers or tstms, esply during Thu. Lows Wed night in the mid 50s to lower 60s. Highs on Thu in the upper 60s to mid 70s. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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Scattered showers and thunderstorms over southeast Virginia and northeast North Carolina will push offshore mid morning, with improving conditions mid to late morning. A weakening cold front stalls over the Piedmont this morning, with additional isolated to scattered thunderstorms expected across southeast Virginia and northeast North Carolina. Coverage is expected to be limited, so have no included in TAFS. Winds become southwest then south at or below 10 knots. Overnight stratus is expected thanks to warm return flow. IFR conditions are possible. Outlook...Mainly dry weather expected over the weekend. Next frontal boundary expected late Monday into Tuesday with possibility of shwrs and tstms.
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&& .MARINE... A weak cold front will stall just north of the waters this morning before dissipating. Winds will remain from the south as high pressure off the Southeast coast strengthens over the area. SCA in the northern coastal waters are barely up to 5 feet this morning. SCA remains in effect north of Parramore Island until 1 PM EDT but may be cancelled prior to that. A period of sub-SCA conditions is expected late today through Sunday. Deep low pressure develops over the southern Great Plains Saturday and moves through the upper Midwest. A cold front will move east and is expected to cross the Mid Atlantic States Monday night or early Tuesday. Southerly winds ahead of the front will likely generate SCA conditions Monday and Monday night. Seas build to 5 to 8 feet and stay 5 feet or higher through Tuesday. && .CLIMATE... It appears likely that Richmond and Norfolk will end the month with the warmest April on record. Warm temperatures during most of the month combined with an unseasonably warm period to end April are expected to push the average temperature above that which occurred in 1994. At Richmond, the previous record was 63.2 and at Norfolk it was 64.7. Both were set in 1994. This month`s temperatures could be around a degree above those values. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 1 PM EDT this afternoon for ANZ650- 652. && $$ SYNOPSIS...MAM/SAM NEAR TERM...BMD/SAM SHORT TERM...SAM LONG TERM...TMG AVIATION...SAM MARINE...LSA CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.