Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
757 PM EDT Sat Apr 18 2015
a cold front drops south across the area tonight...then stalls
over central North Carolina on Sunday. The stalled front lifts
back northeast as a warm front Sunday night...before another cold
front crosses the area Monday night.
Near term /until 6 am Sunday morning/...
seasonably warm this afternoon across forecast area...mainly sunny north...partly sunny
S. Isolated/scattered rain showers/thunderstorms have developed over (interior) NE NC in
region of MUCAPE avgg 1000 j/kg. Additional rain showers/thunderstorms extend westward
just S of the Virginia/NC border in vicinity of low level boundary. Continuing low probability of precipitation in vicinity of
NE NC through the (early) evening hours before waning. Backdoor cold front
presently dropping S toward the forecast area at this time...and will be pushing S across
the forecast area overnight as stronger surface hi pressure builds southeast out of eastern Canada.
Mainly clear to partly cloudy and cooler tonight west/ low temperatures in the
u40s north to the l/m50s S.
Short term /6 am Sunday morning through Tuesday/...
surface hi pressure shifts off the coast Sun morning with low level flow becoming
east-southeast. Meanwhile...low pressure will be tracking toward the lower
Great Lakes states...pushing a warm front NE toward the middle-
Atlantic region. Models do hint at possible stratus early Sun morning...especially
over NE NC/southeast Virginia...otherwise starting out sunny-partly cloudy. Expecting
incsg clouds midday through the afternoon (from W-e). Latest models
agree west/ previous run with respect to timing of arrival of any rain. Have
chance probability of precipitation as far east as a line from lku-ric-ntu by 16-18z
sun...incrsg to likely/categorical probability of precipitation from about ecg-occluded frontal passage on west by
00z...while keeping probability of precipitation at or below 20% on the Eastern Shore. Hi temperatures in
the M/u60s...with some l70s southeast.
Significant inflow of deep layered moisture into the region Sun night as
warm front makes progress NE through the forecast area. May be periods of
moderate/heavy rain...and would not rule out isolated (elevated)
thunder. The area of rain to shift off the CST Monday morning...W/
trough aloft approaching from the west by late Monday afternoon (likely
leading to scattered shwrs/tstms). Will continue to highlight possible
strong/isolated severe storms (in hwo) for (lt) Monday aftn/eve. Otw...vrb
clouds-partly sunny midday/afternoon on Monday. High temperatures in the 70s
at the CST...80 to 85f elsewhere.
Cold front crosses the forecast area Monday night (w/ scattered probability of precipitation...highest NNE-cntrl)...W/
drying/cooler westerly flow taking over into Tuesday. Partly/mostly sunny Tuesday
west/ hi temperatures in the u60s to near 70f at the CST...and l/m70s elsewhere.
Long term /Tuesday night through Saturday/...
upper low remains in vic of the Great Lakes through the extended period
thanks to blocky flow over the higher latitudes. Fast westerly/zonal flow
prognosticated over the local area. Surface high pressure builds over the southeast
states/southern middle Atlantic Tuesday night-Wednesday morning...sliding offshore
Wednesday afternoon. The result is a mostly sunny to partly cloudy sky
Wednesday with highs right around normal...upper 60s to 70 inland and middle-
upper 60s coastal areas. Potent shortwave rounds the base of the
stacked upper low into the Ohio Valley late Wednesday-Wednesday night.
Associated fast moving cold front reached the central Appalachians
Wednesday night...crossing the local area early Thursday. Front expected to
stall vic NC Thursday night due to westerly flow aloft. Question will be how
much moisture return there is Thursday as European model (ecmwf) remains dry and the GFS
rather moist. Difference is low level southwesterly flow in GFS compared to
westerly flow in the European model (ecmwf). Trended toward drier European model (ecmwf)...dropping probability of precipitation to
silent Thursday-Thursday night. Highs Thursday remaining around
normal...generally in the middle-upper 60s. Cool Canadian high pressure
prognosticated to build into the Ohio Valley Thursday night-Fri...extending into
the middle-Atlantic region. The result will be dry conditions...northwesterly
winds and below normal temperatures Friday...generally in the low-middle 60s
inland to upper 50s-low 60s coastal areas. Models picking up on a
southern stream system crossing the southeast states Sat. Mentioned slight
chance probability of precipitation southern Virginia/NE NC...closest to the frontal boundary and best
Aviation /00z Sunday through Thursday/...
a cold front over southern PA at 00z will move S overnight and pass
through the taf sites Sunday morning. Expect light onshore flow
which may help to produce some stratus or fog at some locations. IFR
conds are already present near the coast east of ecg which is handled
well by the NAM MOS. The NAM MOS also puts IFR at orf by 00z which
will not happen...at least not that early. NE winds develop behind
the front as low pressure approaches from the west. Rain overspreads
the area (except at sby) toward the end of the 00z taf period. IFR
conds may develop soon after the rain begins per the GFS MOS.
Outlook...Sunday night...rain and associated degraded flight
conditions are expected to affect all areas...with precipitation
diminishing from SW to NE during the 08z to 13z time frame Monday.
Another impulse tracks across the region Monday afternoon/evening
bringing a chance of showers/tstms. High pressure builds across the
southeast states Tuesday and Wednesday as low pressure lingers over
the Great Lakes. This will allow dry conditions to return and
continue into Thursday.
latest weather analysis depicts weak high pressure over the water this
afternoon with low pressure over New England. Winds generally at or below 10
knots...seas 2-3 feet and waves 1-2 feet. Low pressure pushes off the New
England coast tonight as a backdoor cold front drops north-S along the
coast. Front drops over the waters late tonight. Winds shift to
the NE behind the front...increasing to 10-15 knots. Select hi-res
guidance indicating a brief uptick in winds to ~20 knots immediately
behind the front over the Bay and coastal waters. Surge expected
to be short lived...so will handle with short fused products if
needed. High pressure builds across New England sun as low
pressure lifts into the Great Lakes region. Resultant gradient
will produce Small Craft Advisory conditions over all waters late sun-Sun night
(minus the upper james). Persistent NE flow of 15-20 knots over the
coastal waters will result in seas building to 4-6 feet Sun
afternoon (possibly sooner). Secondary low pressure prognosticated to
develop just west of the waters Sun night...helping ramp up speeds
to 20-25 knots over the Bay/coastal waters and 15-20 knots eastern Virginia
rivers/sound. Surface low and attendant warm front lift north of the
waters Monday with southerly winds diminishing to 10-15 knots. Small Craft Advisory headlines
for the Bay/rivers/sound drop off late Sun night...but 4-6 feet seas
persist through the day Monday. Headlines have been extended for the
coastal waters through 4th period/Mon. Cold front approaches from the
west late Monday-Monday evening...crossing the waters late Monday night-
Tuesday morning. Small Craft Advisory conditions are not anticipate at this time. High
pressure builds across the southeast states-southern middle Atlantic tues-weds.
period of onshore flow is expected through Sunday...before winds
switch to the south Sunday night and Monday. The result will be
tidal anomalies around 1 feet above normal most tidal gages.
Combination of tidal anomalies and high astro tides (new moon
phase) will push most sites over hat during high tide Sunday
night and Monday. Portions of the Upper Bay and Ocean City will
approach minor flooding thresholds.
Marine...Small Craft Advisory from 4 PM Sunday to 7 am EDT Monday for
Small Craft Advisory from noon Sunday to 6 PM EDT Monday for
Small Craft Advisory from 4 PM Sunday to 6 PM EDT Monday for