Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
346 PM EST Tuesday Jan 27 2015
a strong low pressure system will push northeast into the Canadian
Maritimes tonight into Wednesday as high pressure slowly builds
east into the middle Atlantic. The high slides offshore
Thursday...before a cold front crosses the area Thursday night.
High pressure then returns for late Friday into Saturday.
Near term /through tonight/...
latest surface analysis reveals ~981 mb low pressure just east of Cape Cod
with ~1024 mb hi pressure centered over Wisconsin. The low will advance
newrd towards the Gulf of ME then Canadian Maritimes tonight as the
hi moves into the Ohio Valley. With the middle Atlantic between these
two features...northwest flow continues tonight with decreasing clouds.
Cannot rule out a flurry for some areas this eveng but this should
be isoltd. Temperatures will be about five degrees below normal for late
Jan...with lows mainly in the low to middle 20s. Wind chill values
will fall into the teens everywhere...with upper single digits possible
over the lower Maryland Eastern Shore.
Short term /Wednesday through Friday/...
short term period will feature mainly dry conds with continued below
normal temperatures. For Wednesday/Wednesday night...strong surface hi pressure builds east from the
Ohio Valley into the middle Atlantic region as a highly-amplified upper-
level trough pulls offshore. Expect a mostly sunny-mostly clear sky
with slowly diminishing northwest winds. Highs Wednesday range from the middle 30s
over the lower Eastern Shore to the upper 30s/lower 40s elsewhere. Similar
lows Wednesday night as tonight...low to middle 20s...but wind chill values
will not be quite as low due to the light winds.
Southerly flow returns Thursday ahead of the next cold front which crosses the
region Thursday night. Despite decent forcing...moisture will be lacking
a bit so will go no higher than 20-30% probability of precipitation at this time with the best
chance over northern areas. Ptype is rain Thursday afternoon/eveng transitioning to
a rain/snow mix overnight. Any precipitation will be light. Hi pressure then slowly
builds in from the west Friday leading to dry conds...decreasing
clouds...and hi temperatures in the upper 30s to middle 40s.
Long term /Friday night through Tuesday/...
northern stream remains active during the extended period with below
normal temperatures prevailing. Trough exits the coast Friday night/Sat
morning...as cold Canadian high pressure builds over the
middle-Atlantic during the day Sat. The result will be mostly sunny
skies and temperatures in the low-middle 30s. 850 mb temperatures prognosticated to be around
-10c (-1 Standard dev). Thereafter...models in good agreement now with
pushing the surface high offshore sun as the next northern stream shortwave
digs into the southern states. Associated surface low prognosticated to lift
from the lower MS valley northeastward over the central Appalachians sun...and
north of the region Sun night. Trailing cold front prognosticated to cross
the region Sun night. Deep 850 mb trough expected to advect moisture
northward from the eastern Gulf into the region in advance of the front.
Combined with height falls and increasing winds aloft...widespread
precipitation is expected to overspread much of the area late sun into Sun
night. Return flow will warm temperatures into the low-middle 40s (possibly
warmer) sun...with the coldest air remaining over the Great Lakes
region. The result will be predominately rain...but a brief rain/snow
mix is possible at the onset as warm air advection kicks in. However...no
accumulation is expected. All rain late sun-Sun night...with a
possible change over across the northern zones late Sat night as cold air
punches into the region. Westerly push behind the shortwave will result in
drying conditions Monday-Tuesday as cold Canadian high pressure builds in
from the northwest. By Tuesday...temperatures forecast to be back into the middle-upper
Aviation /20z Tuesday through Sunday/...
the effects of the storm in terms of snow and IFR conds have just
about ended. There are still light snow showers or flurries SW ric
as of 18z. Clouds (mostly MVFR cigs) are thinning out and should
clear late aftn/evening. Winds will continue gusty from the north/northwest
through the taf period and followed close to lavmos for those winds.
Outlook...VFR/dry weather is expected Tuesday night through Thursday afternoon. A
weak system may drop ceilings and visibilities in light rain Thursday night/early
Friday. A return to dry weather is expected during most of the weekend.
pressure gradient over the waters remains strong between low pressure
off the NE coast and high pressure over the Ohio Valley/Midwest. The
result is ongoing Small Craft Advisory conditions over all waters. Northwest gusts up to 25
knots over the Bay and 30 knots over the coastal waters observed this
afternoon. Low pressure will continue to lift northeastward along the NE
coast and into the Canadian Maritimes as cold Canadian high pressure
slowly builds in from the west. Another surge of low-level cold air advection is
expected tonight to go along with the already strong pressure
gradient. Have bumped up winds slightly overnight...into the 20-25
knots range in the Bay and 25 to 30 knots range in the coastal waters.
However...gale conditions are not anticipated as the strongest
gradient will be north of the waters. Seas will remain
elevated...ranging from 6-9 feet over the coastal waters through the
night and into tomorrow...before slowly subsiding through the day Wednesday
to 5-7 feet. High pressure finally arrives Wednesday night...with winds
finally diminishing at or below 15 knots. Seas will continue to subside through
the night...falling below 5 feet late Wednesday night. High pressure and
southerly flow briefly return to the waters Thursday before the next front
crosses the waters late Thursday night. Another cold air advection northwest surge is
expected late Thursday night through Friday night. Small Craft Advisory conditions appear
likely at this time. High pressure returns to the waters Sat and sun in
advance of yet another cold front set to cross the waters Sun
Marine...Small Craft Advisory until 6 PM EST Wednesday for anz633-
Small Craft Advisory until 10 PM EST Wednesday for anz630>632-
Small Craft Advisory until midnight EST Wednesday night for