Area Forecast Discussion
Issued by NWS Wakefield, VA-- Remove Highlighting --
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FXUS61 KAKQ 281112
Area Forecast Discussion
National Weather Service Wakefield VA
712 AM EDT Fri Apr 28 2017
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/...
-- Changed Discussion --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.
-- End Changed Discussion --
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.
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
MARINE...Small Craft Advisory until 1 PM EDT this afternoon for ANZ650-