Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
806 PM EDT sun Aug 30 2015
low pressure pushes across the area late tonight through Monday
night. High pressure builds back across the southeast and Middle
Atlantic States for the midweek period.
Near term /until 6 am Monday morning/...
middle-afternoon surface analysis reveals ~1020 mb surface high pressure
in place across the Lower Middle-Atlantic into the Carolinas. Latest
infrared/WV satellite imagery continues to show areas of middle/high
clouds streaming north-northeast across the Carolinas and eastern Tennessee Valley
toward our region...as weakening upper level low lifts north from
the Gulf Coast into the southeast Continental U.S.. regional radar mosaic
showing showers as far north as coastal SC...and expect these
showers to continue to slowly lift north this evening. Despite
only weak overrunning/minimal isentropic lift and dry air in low
levels, middle/upper dynamics could be enough to generate some
scattered showers late tonight. Have adjusted pop timing to be
mainly around and after midnight, with majority of 30% pop
oriented across the NE NC coastal plain. Forecast soundings
indicate low levels moisten up enough that as this moisture pushes
across, a passing shower or two are also possible across Hampton
Roads and south central Virginia late tonight. Have therefore gone with a
slight chance mention over these areas. Overall, partly cloudy
conditions tonight will become mostly cloudy to overcast and
milder overnight, with early morning lows generally 65 to 70.
Short term /6 am Monday morning through Wednesday/...
lingering 20-30% rain chances continue for all but Maryland Eastern
Shore areas from Monday morning into the afternoon. Accounted for a
little bit of a lull in the late morning/early afternoon hours as
first slug of light overrunning precipitation pushes offshore/ however,
with SW flow bringing a gradual increase in precipitable water values Monday/Monday
night...another round of showers is expected as low level
lift/additional upper support arrives coincident with diurnal
heating. Moved probability of precipitation a bit farther into the night Monday night with
timing slowing slightly. A bit more muggy Monday west/ highs Monday mainly
in the upper 80s to around 90f. By all indications, surface front
locates from near Hatteras to just off the Florida/Georgia coast...and thus
expect any issues with heavy rainfall to remain confined to our
south. However, with an influx of tropical moisture from the
remnants of Erika, brief heavy downpours will be possible across
southeast coastal plain.
weak surface high pressure will remain in place across the region,
with showers diminishing to begin the period Tuesday morning. The
southeast (subtropical) ridge builds back west across the southeast
coast on Tuesday, as weak troughing taking shape from the western
Gulf Coast to the Ozarks. Models eventually close this wave off
by Wednesday morning...and this in tandem with the antecedent
moist airmass and upper ridge aloft will bring increasing heat and
humidity for the midweek period. The good news is that forcing
for any late day showers/storms is weak and mainly to our
south...and thus probability of precipitation remain low both days. Will carry a 20% pop
across the far S/southeast for isolated afternoon/early evening showers/thunderstorms
each day. Expect highs Tuesday in the upper 80s to lower 90s...and
around 90/lower 90s for most on Wednesday. Early morning lows
each day upper 60s to low 70s.
Long term /Wednesday night through Sunday/...
the longwave pattern next week is expected to be characterized by
broad middle/upper ridging from the north-central to northestern US...with a
weak trough in vicinity of the Gulf Coast. Broad east-southeast flow beneath
the ridge is expected to bring increasing tropical moisture into
the southeastern US. The bulk of this moisture is expected to be from ts
Erika...or its remnants at that time. The general model consensus
shows the middle-level anticyclone centered from the Ohio Valley to
middle-Atlantic through at least Wednesday...which should keep
moisture suppressed S of the region. If the middle-level high center
retreats far enough north some of this moisture could spread into the
area later in the week. However...if the high remains overhead
moisture should remain S of the region. Weak cold front and upper
trough pass through the middle-Atlantic on Thursday but this looks to
have little affect on the current weather pattern.
Warm and increasingly humid through the week with forecast highs in
the upper 80s to low 90s with middle-upper 80s at the immediate coast.
By Thursday/Friday forecast highs drop into the middle/upper 80s...with
low 80s at the beaches. Forecast lows are in the upper 60s to low
Aviation /00z Monday through Friday/...
weak high pressure will continue to dominate the weather during the
00z taf period. An upper level low over the Gulf Coast states was
helping to trigger scattered precipitation over the Carolinas. The upper low
will move northeast and shear out on Monday.
Early Sunday evening...radar and satellite as well as surface
observations indicated layered cloudiness above 10k feet over the taf
sites. The column was relatively dry below that. NAM bufr soundings
indicate a lowering of the moist air to around 5-8k feet over southern
portions of the area. Lift will be weak but sufficient to produce a
chance to likelihood of light rain at orf and ecg by Monday morning.
Kept visibility at 7 plus as there are doubts that the surface will get
close to saturation but did include MVFR ceilings at ecg. The rest of
the taf sites could get a few sprinkles during the taf period but
not enough to mention for the tafs. Winds will remain at or below 10 knots
and generally from a southerly component.
Outlook...high pressure will continue to dominate with a few periods
of slight to low chances for rain. Most of the period through Friday
will be dry. Some limited cigs/vsby...mainly no lower than MVFR...
may occur during the early morning hours.
high pressure remains over the local waters. The result is a light
onshore flow (se to e) at or below 10 knots. Seas 2 feet in the north and 2-3 feet
south. Waves across the Bay 1-2 feet. A slight strengthening of the
gradient tonight will push speeds to 10-15 knots. An extended period of
sub-Small Craft Advisory conditions is expected through middle week as high pressure
prevails over the water. Wind directions generally SW to west through
Wednesday...at or below 15 knots. A backdoor cold front will attempt to drop into
the region late in the week. Seas average 2-3 feet and waves 1-2 feet.