Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
847 PM EDT Sat Mar 15 2014
high pressure will move southeast from central Canada tonight and
settle over the Great Lakes region on Sunday. The high will slowly
build east Sunday night. Meanwhile...low pressure tracks northeast
from the lower Mississippi Valley on Sunday...and intensifies off
the Carolina coast Sunday night through Monday.
Near term /until 6 am Sunday morning/...
pleasant/dry/warm conditions across the region this afternoon...with most
areas into the upper 60s to lower 70s. Latest surface analysis depicts
999 mb surface low across the St Lawrence Valley with a strong upper
level low over Hudson Bay Canada. Confluent upper level flow
upstream of this upper low has allowed for a very cold surface high to
build into Saskatchewan (temps to nearly -40 f this morning).
Have an enhanced fire weather danger Special Weather Statement for Virginia/Maryland through 6 PM given
the continued dry conditions (see fire weather section below).
Otherwise...uneventful tonight with mainly clear skies and
temperatures falling through the 50s this evening. Increasing
clouds from the SW after midnight with lows primarily in the upper
30s to low 40s.
Short term /6 am Sunday morning through Tuesday/...
***have issued a Winter Storm Watch for mainly the northern half
of akq forecast area late Sun afternoon/Sunday night into monday***
Although some differences in exact placement of features still
exists between the latest suite of models...in general the
agreement is good enough to to warrant the issuance of a Winter
Storm Watch along and north of a line of counties from Prince Edward
to Chesterfield to the middle peninsula on east-northeast to Accomack Virginia.
Overall the setup for cold air is quite favorable in terms of the
placement of the surface high over the Great Lakes. The initial source
of this surface high was from central Canada and the airmass associated
with it is quite cold. However the strength of the surface high while
impressive initially (1038 mb) is prognosticated to weaken significantly
and only be about 1027-1028mb from 00-06z Monday. This suggests
that a thermal profile according to a general consensus of the
12z models may be a little too cold too fast (bringing the 0 c surface
wet bulb temperatures to the northwest zones around 00z...metropolitan Richmond
between 01-03z...and to Southside Virginia between 03-05z. European model (ecmwf) may be
the most realistic model with respect to the arrival of frozen
precipitation and have tried to follow this the closest. Thus...highest
snow totals (up to 8") are prognosticated to be over the northern tier...with
the southern portion of the watch a bit more uncertain (2-5").
Over far southern Virginia thinking is that initial burst of quantitative precipitation forecast with
best forcing between about 02z-10z...will be primarily rain...and
may tend to stay more as sleet rather than snow through 06-10z.
Thus these areas are more likely to see 1-3" or less of accumulation.
Rain will be the p-type south over far southeast Virginia/NE NC. Lows in the
u20s north to the Lower-Middle 30 S.
Monday forecast tricky for ptype (as wedge holds in through midday) but
bulk of forcing for heavy precipitation will have slid off to the east-northeast
leaving just light precipitation and only a light additional
accumulation. High pressure slides east by the afternoon allowing just
enough warmer air in to allow precipitation to mix with or change to rain.
Monday night/Tue...NAM suggests next batch of moderate to heavy precipitation
pushes back north into County Warning Area while the GFS confines it to the southeast zones.
Either way...generally a warmer scenario as surface high would be off the
New England coast so only the northwest zones really have much chance for
anything but rain. Still cold with highs mainly in the 40s.
Long term /Tuesday night through Saturday/...
the long term will see the southern stream trough moving off to the
east Tuesday night and then an active northern stream taking over
through the end of the week.
Surface high pressure ridge over the Piedmont will maintain a wedge
with overcast skies and a chance for light precipitation Tuesday night. Have
low temperatures in the low to middle 30s west of Interstate 95 and middle
30s to around 40 to the east.
A warm front moves slowly through the area Wednesday with a chance
for showers...mainly over northern portions Wednesday and eastern
portions Wednesday night. High temperatures in the 50s to lower 60s
Wednesday lower to the upper 30s to middle 40s for Thursday morning.
A cold front crosses the Middle Atlantic States Thursday morning. The
GFS and Euro agree with having precipitation to the east of the forecast area
by 12z Thursday. High pressure builds in through Friday. The
forecast is dry Thursday through Friday. Highs are expected to be
in the middle 50s to middle 60s both days with lows in the 30s Friday
morning and mainly lower 40s Saturday morning.
With a cold front approaching...went with wpc forecast for a chance
of showers on Saturday. High temperatures range from the upper 50s on
the lower Eastern Shore to the upper 60s well inland.
Aviation /01z Sunday through Thursday/...
VFR conditions will prevail through the 18z sun...but clouds will
increase and thicken early sun into the afternoon. Winds gradually
veer as a diffuse frontal system moves across the taf sites
tonight. Gusty northwest winds diminish late tonight and veer to the NE
during the overnight and early sun. Low pressure will move out of
the southeast/Gulf region and to off the NC coast by Sun afternoon. The low
will bring clouds and a wintry mix of rain/snow/sleet to the
region beginning in the afternoon and persisting into Monday.
Outlook...precipitation is in the forecast for much of the outlook period
with the potential for IFR conds at times. A period of precipitation begins
late Sunday and Sunday night. The main precipitation should diminish early
Monday with mixed precipitation types at ric sby and possibly phf.
Accumulation of frozen precipitation is possible at ric and sby.
Chances of precipitation is in the forecast Monday through Wednesday...
mainly southeast portions Monday afternoon through Tuesday and northern portions
Wednesday. Mainly dry weather is forecast Thursday.
a dry front drops through the area tonight. Breezy west winds at or below
15 knots with occasional gusts up to 20 knots will persist through early
this evening and then diminish shortly after sunset. Waves will
average 1-3 feet and on ches Bay waves will be around 1 foot.
Focus then turns to a low pressure developing along the frontal
boundary located just south of the forecast area on sun. The low
will travel eastward along this boundary and move into the Carolina Sun
night then push offshore on Monday. A persistent NE/onshore wind will
increase Sunday and especially Sunday night/early Monday as the low
deepens. Wind speeds will reach 25-30 knots with gusts up to 40 knots over
the ocean/ches Bay/Currituck Sound...and 20-30 knots for the rivers.
Seas should build to 6-10 feet Sun night into Monday. Small Craft Advisory wind speeds
will be short-lived Sun afternoon/early evening before gale conditions
will be met late sun evening. Therefore have issued gale warnings
for all coastal waters/ches Bay/Currituck Sound beginning early
sun evening and continuing into early Monday afternoon. Small Craft Advisory flags have
been issued for the rivers beginning early sun evening and
continuing into early Monday evening. Sca's may be extended until
midnight Monday night before winds subside on the rivers. Low
pressure lingers off the coast through Tuesday...as high pressure
remains north of the region. This will result in continued onshore
flow and slowly subsiding seas.
persistent dry/breezy pattern expected over the region again today.
Winds will be a little lighter than yesterday. However...SW to west
winds of 15-20 miles per hour will still be common. These winds coupled with
min relative humidity values dropping into the low/middle 20s across a large portion
of our forecast area...and dry fuels...will be enough to warrant an
enhanced Fire Danger Statement (sps) at least for our Virginia and Maryland
counties today. Critical relative humidity/wind criteria is expected to be more
marginal across NE NC.
Maryland...Winter Storm Watch from Sunday evening through Monday
afternoon for mdz021>025.
Virginia...Winter Storm Watch from Sunday afternoon through Monday
afternoon for vaz048-049-061>064-069.
Winter Storm Watch from Sunday evening through Monday
afternoon for vaz060-067-068-070>078-082>086-099.
Marine...Gale Warning from 5 PM Sunday to 2 PM EDT Monday for
Small Craft Advisory from 5 PM Sunday to 8 PM EDT Monday for