Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
401 am EDT Monday Mar 30 2015
a weak frontal boundary crosses the region this morning...with
high pressure returning this afternoon into tonight. Low pressure
tracks across the northern middle Atlantic Tuesday with the
associated cold front dropping through the region Tuesday night.
Canadian high pressure builds into the region Wednesday.
Near term /until 6 PM this evening/...
current GOES WV imagery shows a middle-level trough lifting NE of the
Great Lakes region...with a middle-level frontal boundary trailing
back through the Ohio Valley. At the surface...low pressure is
centered north of the Great Lakes...with high pressure off the
southeast coast. The surface boundary (associated with the cold
front aloft) consists mainly of a wind shift from SW to west-northwest.
Locally...the airmass remains rather dry with dewpoints ranging
from the upper teens to low 20s...with temperatures in the upper
30s to middle 40s. The initial band of radar echoes that have passed
across the region have at most produced a brief period of -ip
across the far northern tier counties. The next batch is passing across
the central Appalachians. This will produce isolated/scattered -shra over the
northwest half of the area through mid-morning. The surface airmass will
remain dry throughout so expect very little measurable qpe. The
boundary is expected to encounter somewhat better moisture over southeast
Virginia/NE NC later this morning...so a period of likely -shra has been
maintained. Still eventual qpe amounts are expected to average
~0.1in or less.
Otherwise...mostly cloudy to overcast conditions this morning
should become partly to mostly sunny by afternoon...with the
clearing trend progressing NW-se. Favorable downslope flow (a west-northwest
wind of 10-15mph with gusts to around 20mph) should push highs
into the low/middle 60s over interior Virginia/NE NC. Farther east...highs
should be in the middle/upper 50s where cloud cover will persist
through early afternoon.
Short term /6 PM this evening through Wednesday/...
high pressure builds across the southeast states tonight as low
pressure moves into the Great Lakes. A clear and seasonably cool
night is expected with lows ranging from the upper 30s to low 40s.
The aforementioned low pressure system driven by zonal flow aloft
quickly tracks across the northern middle Atlantic Tuesday afternoon.
Expect mostly sunny conditions to begin the day with increasing
clouds across the north by afternoon. A ribbon of 20-30% probability of precipitation (for
-shra) has been maintained primarily for the northern interior Virginia
counties and the Maryland lower Eastern Shore during the
afternoon/evening hours. It will be difficult to get any precipitation S of
the low track with deep layered west-southwest flow.
Low-level thickness values continue to support highs around 70f
on Tuesday over interior Virginia/NE NC. This is certainly possible with
low pressure tracking north of the region resulting in deep layered
west-southwest flow. Forecast highs remain in the upper 60s to low 70s across
much of the area...with middle 60s over the interior Eastern Shore...and
locally cooler values along the immediate Atlantic coast.
Low pressure exits the Delaware-Maryland-Virginia after midnight Tuesday night.
Cooler conditions are expected Wednesday under a sunny sky as
Canadian high pressure builds into the area. Highs are forecast to
range from the low 50s along the coast...to the upper 50s/low 60s
over interior Virginia/NE NC...after morning lows in the upper 30s
north...to middle 40s S.
Long term /Wednesday night through Sunday/...
split flow continues to be problematic during the extended
period...but models continue to come into better agreement with a
late week frontal passage. To begin the extended...high pressure
pressure slides offshore Wednesday night. Increasing southerly flow on the back
side of the departing high and a flattening southern stream wave will
push a warm front through the local area Thursday. Resultant warm air advection will push
temperatures into the low 70s inland and low-upper 60s Eastern Shore and
coastal areas. Model consensus is to keep Thursday frontal passage dry
thanks to limited moisture and a lack of appreciable forcing. Have
removed slight chance probability of precipitation over the Piedmont Thursday. Potent northern
stream wave locates over the Great Lakes region Thursday night-Friday
pushing an associated/deepening surface low into southeast Canada. Attendant
cold front prognosticated to reach the central Appalachians during the late
Thursday-Friday timeframe. GFS continues to be less amplified with the northern
stream system...pushing the front through the region around 12 hour
quicker than the more amplified/slower European model (ecmwf). Regardless of spatial
and timing differences...expect increasing chances for precipitation
beginning Thursday night and continuing through Sat. 28/12z European model (ecmwf) pushes
the precipitation offshore Friday night...but the GFS stalls the front over
the region through Sat. Have maintained slight chance to low end
chance probability of precipitation Sat to account for uncertainty. Mild temperatures expected
Thursday night behind the warm front...with temperatures generally in the low-
middle 50s. Warm sector/southwesterly flow pushes temperatures into the middle 70s inland
(possibly warmer depending on cloud cover) and upper 60s-low 70s Eastern
Shore and coastal areas. Cooler Sat with highs middle 60s inland and
upper 50s-low 60s Eastern Shore and coastal areas. High pressure prognosticated
to build over the southeast states Sat night-sun...with decreasing chances
Aviation /08z Monday through Friday/...
center of surface hi pressure has shifted off the southeast coast as of
06z. This has allowed winds to shift to the SW. A weak cold front
will cross the area today... bringing a chance for showers mainly
across the southeastern half of the area after daybreak this morning. All
shower activity is expected to end by the afternoon. Winds will shift
to the northwest behind the front before quickly backing to west/SW by tonight.
High pressure builds back into the southeast US Tuesday but a cold front
moving through the area may bring a few showers to ksby Tuesday
evening. Wednesday/Wednesday night will be dry as high pressure builds in from
latest surface analysis reveals surface hi pressure centered off the southeast CST with
a cold front pushing ewrd through the Ohio Valley. Between these two
features...a prefrntal southerly surge is now beginning over the local
waters. Tricky call regarding Small Craft Advisory headlines...but looking at current
winds and expected slight increase through the first half of the day to
frequent gusts ~20 knots...hoisted a Small Craft Advisory for the Bay and lower James. A
Small Craft Advisory has also been issued for the northern coastal waters due to seas out 20 nm
close to 5 feet and gusts up to ~25 knots. Only marginal Small Craft Advisory conds
expected due to weak warm air advection over cold water preventing the highest
winds from mixing down to the surface. The cold front crosses the waters this
aftn/eveng...with sub-Small Craft Advisory conds anticipated Post frontal tonight due
to weak gradient winds and limited cold air advection. High pressure briefly builds
over the waters late tonight-Tuesday morning with the flow switching
from the northwest back to the SW Tuesday. Low pressure and an attendant cold
front approach the waters Tuesday...crossing the region Tuesday night. Small Craft Advisory
conditions are possible Post frontal Tuesday night-Wednesday morning. But
again it would be marginal. High pressure returns to the area Wednesday-
Thursday...resulting in sub-Small Craft Advisory conditions.
Marine...Small Craft Advisory until 1 PM EDT this afternoon for
Small Craft Advisory until 4 PM EDT this afternoon for anz650-