Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
655 PM EST Wednesday Nov 25 2015
high pressure remains centered off the New England coast through
Friday night. A cold front approaches from the northwest late
Saturday...then stalls across the region Saturday night and Sunday.
Near term /until 6 am Thursday morning/...
surface high prs off New England coast will continue to extend SW across
the area. Low level warm air advection may lead to some SC along the Outer Banks
late. Some high level cloudiness this evening...otw a good evening to view the
full moon. Leaned toward the cooler MOS numbers given lows past few
nights were on the low side of guidance. Lows in the M-u30s west of
the Bay...40s to near 50 near the water.
Short term /6 am Thursday morning through Saturday/...
went with a GFS/sref blend this prd...but still xpctg a mainly
dry and mild period from Thanksgiving day through Friday night.
NAM appears to aggressive in its middle level moisture fields. Surface high
strengthens to ~1048mb (+3 St dev) Thursday / Friday as it slides east of
Nova Scotia. Low level winds shift to the east-southeast which results in scattered-broken
SC from time to time...but not the overcast cndtns the NAM depicts.
Models continue to feature development of a weak trough just off the
southeast coast. Any significant moisture / precipitation prognosticated to stay southeast of the
local area and out over the Gulf Stream. Thus...a dry forecast will be
maintained. A mild period ahead with 850 mb temperatures sprtg highs Thursday in
the M-u60s and 65-70 Friday. Lows Thursday and Friday nites in the 40s to near 50
southeastern coastal areas.
12z models even slower with the apprchg cold front. GFS/sref has
the boundary weakening as it sags south across the region late Sat
while the 12z European model (ecmwf) stalls it across northern Virginia past 00z sun. Little
sprt for any measurable precipitation seen with the actual frontal passage so at this
point I cut back probability of precipitation Sat but kept slght chance across northern most counties
aftr 18z as the boundary apprchs. Temperatures tricky and may depend on how
far south the boundary actually gets. Expect to see increasing cloudiness through
the day. Highs 60-65 xcpt in the u50s Eastern Shore / Northern Neck.
Long term /Saturday night through Wednesday/...
blocky pattern persists to begin the extended period over the western
Continental U.S....lending to a difficult/low confidence forecast. Frontal
boundary prognosticated to reside west to east across the middle-Atlantic
region Sun night as high pressure builds over the Great Lakes
region. The front will drift slowly southward during the day sun...with
increasing chances for precipitation during the day sun. Front weakens Sun
night...but will maintain chance probability of precipitation over the region. Surface high
pressure builds into New England Monday...ridging southward into the local
area with an in-situ cad wedge. Significant differences in medium
range guidance arise in the middle level flow and resultant
cyclogenesis over the Ohio Valley Monday and Tuesday. Will maintain slight
chance to low end chance probability of precipitation Monday. Have trended forecast toward the
European model (ecmwf) beginning Monday night and Tuesday...which pushes a cold front through
the region late Tuesday into Tuesday night. The result will be chance probability of precipitation
Tuesday and Tuesday night. Drying trend expected thereafter as high
pressure builds eastward from the Midwest.
Temperatures will remain rather steady...near to slightly below seasonal
norms through the extended. Lows generally in the upper 30s to 40s.
Aviation /00z Thursday through Monday/...
high pressure ridge over the eastern third of the country this
evening...remaining in place through 18z Thursday. VFR conditions
are expected through the 00z taf period. However...with the flow
becoming more easterly...expect to see some additional low level
moisture beginning to push to the west.
Outlook...the area of high pressure remains in place into Saturday
with VFR conditions expected. A slow moving cold front will drop
southward into the region late on Saturday evening and linger
across the region through Monday. Expect possible MVFR to IFR
ceilings and visibilities with this front with light rain possible.
high pressure has centered just off the northeast coast this
afternoon...ridging southwestward over the local water. The result is a light
onshore flow at or below 10-15 knots. Seas generally 3 to 4 feet and waves 1 to 2
feet. High pressure strengthens and pushes farther off the New England
coast tonight...but remains ridged over the local area. Onshore flow
remains light due to weak flow. While winds remain generally at or below 10
knots...stronger winds over the western Atlantic and a long east-NE fetch will
push seas toward 5 feet late Thursday...first in the southern coastal waters.
Seas build to 4 to 6 feet Thursday night all coastal zones...and will
likely remain in the 4 to 6 feet range through at least Sat night as
onshore flow persists. After inter-office coordination...uncertainty
remains as to how quick the seas can build in light flow so have
held off on 3rd period headlines for seas at this time. A cold front will
approach from the northwest Friday night...likely stalling/weakening
over the region through the weekend. Flow becomes northerly sun and
Monday...remaining at or below 15 knots as models indicate very little cold air advection. While
there remains a great deal of uncertainty...the next cold front is
forecast to impact the region Tuesday into Tuesday night.