Area Forecast Discussion
Issued by NWS Wakefield, VA

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000
FXUS61 KAKQ 240244
AFDAKQ

Area Forecast Discussion
National Weather Service Wakefield VA
1044 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/...
Latest surface analysis shows ~1005mb sfc low pressure over
Northeastern NC near ECG at 03z. Quasi-stationary boundary
extends SW to NE from East Central NC to the Northern Outer
Banks (PGV to ECG). Numerous perturbations on GOES WV imagery
moving along the front early this evening, with radar mosaic
showing swath of heaviest showers moving NE from Hampton Roads
up to the Lower Eastern Shore. Another batch of showers was
noted pushing along/just east of the front across the coastal
Carolinas.

Have updated pops, with only minor changes per latest trends.
Categorical PoPs through 06z over the east 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 /03Z WEDNESDAY THROUGH SUNDAY/...
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.

&&

.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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