Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
736 PM EST Friday Jan 30 2015
cold high pressure builds into the region through Saturday night.
A strong low pressure system will affect the area Sunday into
Monday. High pressure returns to area through middle week.
Near term /until 6 am Saturday morning/...
trough aloft swinging off the CST this evening...resulting in deep layered
northwesterly flow of colder air into the forecast area. Vrb clouds/mcldy conds on going
at this time...even scattered sprinkles/flurries have been moving through
areas mainly east of I 95 past couple of hours. Northwest winds have incrsd to
average 15-25 miles per hour...W/ gusts to 30-40 miles per hour (highest mainly on the eastern
shore). Remaining windy through the night. Wind Advisory to remain through
mdngt on the Eastern Shore for possible 45-50 miles per hour gusts. Otherwise...expecting gusts
to 30-40 miles per hour on average elsewhere before beginning to subside (well) after
mdngt. Expecting cloudiness to dissipate through the evening hours...resulting in
mainly sky clear overnight. Current temperatures in the 40s will drop quickly this
evening...then drop out mainly from the upper teens to l20s late. Combo winds
and temperatures result in wind chills dropping to the single digits and
Short term /6 am Saturday morning through Monday/...
Canadian surface hi pressure arrives from the west-northwest on Sat resulting in
dry/chilly conds. Starting out mainly sunny...W/ (mid/hi lvl) cloudiness
beginning to spread into the region from the west by lt in the day. Hi
temperatures from the l30s over the lower Maryland Eastern Shore to the u30s to l40s
elsewhere. Meanwhile...low pressure now in the SW Continental U.S. Will be moving into
the Southern Plains. Moisture will be incrsg significantly in advance
of that system through the plains and toward the Lower/Middle MS valley lt Sat.
Models over the past couple of days have had difficulty west/ the
handling of the SW storm system...and a system in the northern branch of the
jet stream digging into the north central Continental U.S.. a more southern track to that
storm as it headed into the eastern states was the case Wednesday/Thursday (thus a
much higher ptntl for colder/wintry p-type)...but now there is
more of a Transfer/combo of northern/southern stream systems in vicinity of nation's
midsection Sat night into Sun morning. This results in a more northern track
to the entire storm...W/ primary surface low pressure developing in vicinity of MO
instead of to the S closer to the Gulf CST. The pattern in vicinity of
mdatlc in not conducive for a widespread winter p-type event lt in
the weekend into Monday west/ surface hi pressure to drift to off the southeast Continental U.S. CST
(by sun aftn)...combined west/ lack of any northern surface hi pressure and a more
northern west-east track to the surface low pressure.
The air over the forecast area (esp north-northwest portion) on sun may be dry/cold enough
for rain/ice pellets mixture at onset of precipitation. Trend of models past 24 hours has
been to bring precipitation a little slower into the forecast area from the west through
the day sun. Expecting moderation of the airmass over the forecast area as S winds
develop. All models (nam/GFS/ecmwf) agree west/ the more northern track
(w-e) through the mdatlc states lt sun into Monday. Thus...rain will be
the primary forecast p-type Sun night into Monday morning. Temperatures to bottom out
early sun evening (in the M/u30s north...l/m40s s)...then rise a few degrees
f thereafter into Monday morning.
By midday/afternoon Monday...drying trend to beginning but suspect a bit
of a delay in low level cold air advection (or enough cold air to catch the precipitation
before it exits) to cause any significant snow threat (on mon). Will have
a mix rain/snow showers for mainly north-northeast portions (aft Monday mrng)...mainly chance
showers elsewhere. Hi temperatures from the l40s north-northwest to the l/m50s southeast.
Long term /Monday night through Friday/...
other than some some lingering snow showers over coastal waters Erly Monday
evening...expect clearing skies and cold Monday night as 1030 mb high apprchs
forecast area from the Ohio Valley. Lows in the middle teens north to l20s south
xcpt m20s southeastern beach areas.
Ridge axis moves ovrhd Erly Tuesday then shifts offshore. Mostly sunny
and cold. Highs in the 30s. Mostly clear Tuesday night. Lows in the 20s.
Models continue to have difficulty with middle week systm and offer
up different timing and moisture scenarios...so a low confidence
forecast continues until some kind of consistance in seen. However...
the trend is slower in bringing moisture north into the forecast area as southern
stream low develops in the northern gom then tracks NE along the southeast and
possibly middle atlntc coast before pulling NE and away from the area.
Model guidance suggests leaning more toward the GFS solution. Expect increasing
cloudiness Wednesday. Went with low chance probability of precipitation across NC counties late in the day.
Highs 45-50. Chance (liquid) probability of precipitation Wednesday night with mixed snow/rain late
across northern most counties. Lows around freezing northern most counties to the
M-u30s over the south. Rain chances continue Thursday xcpt for some rain/snow mix
Erly across the north. Highs in the 40s to near 50 southeast.
If the 12z European model (ecmwf) verifys...the strong high prs keeps southern stream low
south with little if any impact on forecast area. This has been the case most
of this winter given no real blocking pattern seen. Its solution would
be colder and drier.
Anthr Arctic high pressure builds into the area from the northwest behind
this systm by Friday. Decreasing cloudiness Thursday night. Lows in the 20s. Mostly
sunny Friday. Highs in the 30s.
Aviation /01z Saturday through Wednesday/...
gusty northwest winds will continue through most of the 00z taf period.
Due to cold air advection and a tightening pressure gradient...a
surge in winds will affect areas near the coast through early
Saturday morning. Gust values will occasionally spike overnight at
sby and orf but selected values fairly close to lavmos that are
expected to be within 10 knots of the observations. The sky will
be mainly clear with an 8k foot broken deck moving southeast of ecg first
couple of hours. Scattered high clouds start to move in Saturday afternoon.
Winds diminish late Saturday.
Outlook...clouds increase Sunday as low pressure approaches from the
west. The low crosses the Middle Atlantic States to the north of our
area Sunday night. Mainly a rain event is expected with some IFR
possible at the taf sites...especially at ric and sby. Rain ends late
Monday. Dry weather returns Monday night through most of Wednesday.
Another chance of rain develops late Wednesday.
current headlines remain in place with gales most places tonight and
into Sat morning across the northern coastal waters. Strngst cold air advection to ovrsprd
the marine area next several hours. Strongest winds...with gusts to 45 knots
over northern coastal waters...35-40 knots in the Bay and southern coastal
waters...and ~35 knots in most of the rivers will occur this evening.
This is when the pressure gradient will be the tightest and when
much colder air (850 mb temperatures dropping below -12c) really surge over
the relative warmth of the waters (+5 to +8 c). Seas & waves respond
to these gusty winds. Seas average 7-11 feet with waves in ches Bay 4-6
Freezing spray advisory continues tonight into Sat mornind across coastal
waters nrth of Parramore Island given the forecasted temperatures/wind gusts and
current water temperatures. This is where some moderate icing is likely.
Kept light icing mentioned farther south & in the ches Bay at this time.
Expect sca's to replace gales Sat morning with winds quickly falling
below Small Craft Advisory levels Sat evening as high pressure builds into the area.
Next low crosses the area Monday with another cold air advection surge seen behind
this system Monday afternoon and night. Have winds in Small Craft Advisory range with
gusts capped at 30 kts at this time.
Maryland...Wind Advisory until midnight EST tonight for mdz021>025.
Virginia...Wind Advisory until midnight EST tonight for vaz099-100.
Marine...Gale Warning until midnight EST tonight for anz635-636-638.
Small Craft Advisory until noon EST Saturday for anz633-637.
Gale Warning until 4 am EST Saturday for anz630>632-634-656-
Gale Warning until 7 am EST Saturday for anz652-654.
Freezing spray advisory from midnight tonight to noon EST
Saturday for anz650-652.
Gale Warning until noon EST Saturday for anz650.