Area Forecast Discussion
Issued by NWS Wakefield, VA

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572 FXUS61 KAKQ 240027 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 827 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/... Early evening surface analysis shows ~1005mb sfc low pressure just SW of Edenton at 00z. Quasi-stationary boundary extends W to E and has lifted up along/South of the Albemarle Sound. Numerous perturbations on GOES WV imagery moving along the front early this evening, with KAKQ radar showing swath of heaviest showers moving NE from NE NC into the Eastern Tidewater area. Have updated pops, with only minor changes per latest trends. Maintained heavy rainfall wording early this evening across the SE third of the area...and some localized flooding is possible mainly in urban and poor drainage areas across SE VA. PoPs then taper off from W-E late tonight as the primary forcing pushes offshore. Remaining cloudy with some patchy fog expected once again 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 /00Z WEDNESDAY THROUGH SUNDAY/...
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A frontal boundary will remain just to the southeast of the area with waves of low pressure moving along it. An area of rain will move across the area through early Wednesday morning. Widespread IFR ceilings will prevail this evening and overnight. With northeast winds and plenty of moisture remaining... ceilings will only improve slightly on Wednesday. Visibilities will lower to IFR in heavier precipitation but otherwise should be MVFR and improve to VFR on Wednesday morning. Winds will generally be from the northeast and east and may veer toward southeast on Wednesday at around 10 knots or less. OUTLOOK...Other rounds of showers are expected Wednesday into early Thursday morning and again late Thursday. Aviation conditions will likely be impacted through Thursday night. Dry weather returns Friday as weak high pressure builds over the region. Unsettled conditions return for the weekend when another frontal boundary affects the Mid Atlantic States.
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&& .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... 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. && .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/MAM SHORT TERM...AJZ LONG TERM...SAM AVIATION...LSA MARINE...SAM TIDES/COASTAL FLOODING...

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