Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 232139 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 539 PM EDT Tue May 23 2017 .SYNOPSIS... A potent low pressure system will track along a stationary frontal boundary through midnight, before pushing offshore overnight. Weak high pressure prevails Wednesday. Unsettled conditions return Wednesday night and Thursday as an upper level trough approaches from the west. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Current GOES WV imagery/model analysis depict a potent shortwave trough lifting ENE across the Tennessee Valley ahead of an upper low digging across the Upper Midwest. At the surface, a stationary front is aligned roughly W-E across NC with a broad area of low pressure along the boundary. Low pressure is expected to become more organized as it lifts ENE tonight tracking across SE VA/NE NC before moving offshore after 06z. Rain is expected to increase in coverage/intensity late this aftn through the evening, especially along and S of an FVX- RIC-WAL line. QPF late this aftn through the evening should average 0.75" to 1.5" for srn VA/NE NC and this will be in addition to 0.5-1.25" for these ares over the past 24 hrs. Thunder is possible across far SE VA/NE NC with the presence of elevated instability. Some localized flooding is possible mainly in urban and poor drainage areas. PoPs then taper off from W-E late tonight as the primary forcing pushes offshore. Remaining cloudy with some patchy fog possible across the Piedmont. Low temperatures range from the upper 50s N/NW to the low/mid 60s SE. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... A vigorous upper low gradually drops sewd through the Mid- Mississippi Valley late tonight through Wednesday. Some semblance of shortwave ridging develops over the Mid-Atlantic late tonight through much of the day Wednesday due to the combination of a departing shortwave trough and the upper low digging to the W. Therefore, PoPs drop below 15% for a roughly 12hr period. Lower clouds will struggle to erode despite some mid-level drying as the surface pressure gradient will be rather nebulous resulting in weak low-level flow. The best chc for any partial clearing will be across the MD Ern Shore. High temperatures will average 70-75F (highest SE). The upper low digs into the Tennessee Valley with yet another shortwave trough lifting NNE across the Carolinas and Mid- Atlantic Wednesday evening through the early overnight hours. A secondary wave lifts NNE across the Blue Ridge late Wednesday evening through the overnight hours. PoPs quickly ramp up to categorical across the SW piedmont early Wednesday evening and spreading NE into central/SE VA late evening through the early overnight hours, before shifting to the Ern Shore after midnight. Mid-level drying and subsidence will result in PoPs quickly diminishing from SW-NE late Wednesday night into early Thursday morning. There is a chc of thunderstorms across mainly the srn third of the area. 500mb flow strengthens to 40- 50kt across SE VA/NE NC and the presence of a surface warm front will result in a veering low-level wind field. However, forecast soundings depict a stable layer below 950mb, so it may be difficult to get surface based convection and at this time the severe weather threat is low (SPC has the SE counties in a marginal, 5% risk). Additional QPF Wednesday night averages 0.4-0.6". The upper low finally begins to lift NE across the mountains Thursday. A strong shortwave trough will lift across the Mid- Atlantic during the afternoon/early evening. Once again PoPs increase, to ~60% from the Piedmont to central VA to the MD Ern Shore, with 40-50% farther SE. 500mb flow of 45-55kt is expected along with modest instability. Therefore, a few stronger to marginally storms are possible. The main threat would be wind and hail as low-level shear is minimal. Additional QPF Thursday aftn/evening should average ~0.25" with locally higher amounts. High temperatures range from the mid 70s to around 80 after morning lows ranging through the 60s. The upper low continues to lift NE across PA/NY/New England late Thursday night into Friday. Drier conditions finally arrive as deep layered WNW flow develops over the region. Some lingering mid-level energy could result in some sct-bkn cu Friday aftn. Otherwise, drier and breezy with highs in the upper 70s to low 80s, after morning lows in the mid 50s to low 60s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Shortwave ridging builds over the Northeast Saturday as an upper level low tracks into the Great Lakes region. Weak area of surface high pressure slides off the Mid-Atlantic coast Saturday as a warm front lifts through the region. Weak perturbations in fast westerly flow aloft will result in low end chance POPs Saturday afternoon for showers and thunderstorms. Otherwise, warming trend continues with highs in the low to mid 80`s. The warm front locates/stalls over the northern Mid- Atlantic region Saturday night, resulting in continued chances for showers/thunderstorms over the northern local area as perturbations in the westerly flow track across the region. The upper low slowly pushes across the Great Lakes region Sunday with an associated cold front progged to reach the central Appalachians late Sunday. Pressure falls ahead of the approaching front will induce a lee side/thermal trough over the region and better chances for diurnally driven showers and thunderstorms. Highs Sunday generally in the mid 80`s. The cold front reaches the local area Monday, but is expected to stall over the region as subtropical high pressure strengthens off the Southeast coast. The weak front remains over the eastern local area through Tuesday, with chances for diurnally driven showers and thunderstorms. Highs Monday and Tuesday in the low to mid 80`s. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... Poor aviation conditions will continue through much of the TAF period. A frontal boundary is currently located just south of the region with waves of showers riding along the boundary. A more potent low pressure system will track along the boundary this evening. MVFR to IFR conditions with low clouds and reduced visibilities due to periods of moderate/heavy rain will persist through tonight. Heavier rain departs the area mainly after 06Z, but low ceilings and the potential for fog will persist through Wednesday morning. Outlook: A cold front is expected to impact the region Wednesday afternoon and into Wednesday night bringing the chance for more showers and thunderstorms/adverse aviation conditions. Scattered afternoon showers, and potentially a few thunderstorms, are expected to develop on Thursday allowing for the chance of more sub-VFR conditions. Dry/VFR conditions return for Friday and Saturday. && .MARINE... Latest surface analysis depicts weak area of high pressure centered just offshore the Delmarva, with an area of low pressure over Georgia. A quasi-stationary boundary was located along the Southeast coast. The result is a east to northeast wind of 10-20 knots over the waters. Few gusts to around 20-25 knots observed in the mouth of the Bay and adjacent coastal waters. Seas generally 3-4 feet and waves 2-3 feet. Low pressure progged to lift along the boundary into northeast North Carolina and southeast Virginia this evening. Pressure falls ahead of the low in tandem with increasing gradient winds will result in a period of 15-25 knot onshore winds over the waters. NAM guidance continues to be on the stronger side, indicating near gale conditions near the mouth of the Bay and in the lower Bay. Believe this is too aggressive as the hi-res guidance doesn`t back the NAM up. Have opted for a GFS/CMC solution, resulting in a period of SCA conditions in the Bay, Sound, coastal waters, and lower James River through late tonight into Wednesday morning. Seas build to 4-7 feet (highest north) with waves of 2-4 feet. Waves in the lower James build to 2-3 feet. The low pushes offshore late tonight/early Wednesday morning with flow becoming north to northwest. SCA conditions expected to linger in the Bay through late morning/early afternoon, with seas diminishing through Wednesday afternoon. Another area of low pressure lifts into the Ohio Valley Wednesday into Wednesday night as a meso-low lifts along the Appalachians. SCA conditions are anticipated again Wednesday night over the Bay and coastal waters with speeds of 15-25 knots and seas building to 3-5 feet. Southwest flow increases Thursday as the low lifts north of the region, with speeds of 10-20 knots expected. SCA conditions could again be possible Thursday night as the low tracks off the Northeast coast. && .TIDES/COASTAL FLOODING...
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A period of onshore flow and higher astro tides (moving toward a new moon) will result in elevated water levels through Wednesday night. Many tidal sites will reach action stage during this evenings/overnights high tide cycle. Coastal flood statements have been issued for the upper James and areas around Bishops Head, Maryland. Low pressure lifts over the region tonight, with onshore flow ramping up. However, the low is expected during periods of low tide. Lower astro tides are expected Wednesday morning. Higher levels are forecast Wednesday evening/night, with minor flooding possible along the the Bay, James River, and Atlantic waters.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...Small Craft Advisory until 10 AM EDT Wednesday for ANZ630>632- 634. Small Craft Advisory until 4 AM EDT Wednesday for ANZ633-638- 656-658. Small Craft Advisory until 4 PM EDT Wednesday for ANZ650-652- 654. && $$ SYNOPSIS...AJZ/JDM NEAR TERM...AJZ SHORT TERM...AJZ LONG TERM...SAM AVIATION...AJB MARINE...SAM TIDES/COASTAL FLOODING...

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