Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wakefield Virginia
358 PM EST Thursday Jan 29 2015
a cold front crosses the region late tonight. Cold high pressure
then returns to the middle Atlantic region late Friday through
Saturday night. A strong low pressure system will affect the area
Sunday into Monday.
Near term /through Friday/...
latest surface analysis reveals ~1006 mb low pressure centered over the eastern
Great Lakes with its attendant cold front stretching down to the
south-southwest. Some light precipitation is occurring ahead of a weak associated warm
front now over western Virginia. Most areas will remain dry...but some rain
and sleet is possible over western and northern portions of the forecast area through Erly this
eveng. The cold front slides through the area late tonight/Friday
morng...with just a slight chance for some precipitation over eastern areas due
to the front and associated middle-level vorticity maximum despite little
moisture. Low temperatures in the low to middle 30s.
For Friday...dry weather and decreasing cloudiness as the front pushes
farther offshore and strong hi pressure slowly builds in from the west. Main
story on Friday will be the wind...with gusts up to 40 miles per hour NE areas
and 30-35 miles per hour SW areas. With hi temperatures in the upper 30s to middle
40s...wind chill values will be in the 20s to lower 30s much of the
day over most areas.
Short term /Friday night through Monday/...
dry weather continues into Friday night and Sat as the surface hi slides in from
the west and becomes centered over the middle Atlantic and southeast states.
Expect westerly flow Sat with a mostly sunny sky and hi temperatures only in
the middle 30s to lower 40s under continued cold air advection.
Attention then turns to another approaching storm systm which will
impact the area sun through Monday. Key players are an approaching northern
stream trough over the central/northern plains sun and southern stream energy
over Mexico. Subsequent surface low development will occur over the Tennessee
Valley late sun. The surface low will further strengthen as it
approaches the middle Atlantic Sun night...with its exact track
important in determining ptypes throughout the region. As for 12z
data...the European model (ecmwf) has trended northward to be more in line with the
GFS and takes the low directly over Virginia...while the CMC has shifted
south leading to a colder solution. There have also been some run-
to-run consistencies with these models as well. A blended solution
continues to favor a rain/ip/sn mix at the onset sun morng over north
and west areas...becoming mostly rain Sun afternoon/eveng with some snow mixed
in over northern areas. As the low passes east of the area Sun night into
Monday...thicknesses will fall and snow will be more likely over more
of the area...with still plain rain for extreme southeast Virginia/NE NC. The
precipitation then ends from west to east on Monday with hi temperatures only in the low 30s
north to low 40s S under strong cold air advection. The general idea with this storm
is that the current track favors mainly a rain event for much of
the forecast area with some wintry precipitation mixed in at the beginning and end of
the event especially over north and west areas. This is still several
days out and slight changes in the track will make a difference
over where the rain/snow line develops.
Long term /Monday night through Thursday/...
any precipitation assctd with Monday storm is offshore by 00z Tuesday. Clearing skies
and cold Monday night as 1030 mb high apprchs forecast area. Lows in the teens to
l20s southern most counties.
Ridge axis moves ovrhd Erly Tuesday then shifts offshore. Mostly sunny
and cold. Highs l-m30s. Clouds increases Tuesday night ahead of next systm.
Kept it dry for now as any precipitation should stay s&w of forecast area through 12z Wednesday.
Lows may occur in the evening then steady or rise aftr midnight as a S
wind develops. Lows in the 20s to l30s southeastern areas.
Models solutions differ a bit with the middle week systm. GFS takes surface low
NE into the Great Lakes region with the trailing cdfrnt prognosticated across the
forecast area Wednesday night. It also develops a low on southern end of boundary. This allows
said boundary to stall just offshore allowing the low to track NE along
the southeastern US coast but stay just south of akq forecast area. This scenario
brings milder air in ahead of the boundary for mainly rain...but a mix
with then change to snow Wednesday night as cold air advection develops behind it. European model (ecmwf) has
the low going into the Great Lakes but shows a strngr and wetter southern
stream low moving NE along the middle atlntc coast before lifting NE away
from region Thursday. Went with chance (liquid) probability of precipitation Wednesday. May start off as a
brief rain/sleet mix across Piedmont Erly depending on how fast the
precipitation moves in. Highs in the 40s. Went with chance probability of precipitation for a rain to
snow scenario Wednesday night for now. This a rather low confidence call
and will likely all depend on how much moisture is available when
the cold air ovrsprds the region. Lows m20s-l30s.
Cold with some lingering rain/snow showers along the coast Thursday morning.
Otw...clrd and cold as strong high prs builds in from the west. Highs
Aviation /20z Thursday through Tuesday/...
high pressure moves offshore this afternoon as a cold front
approaches from the northwest. A southerly wind averaging 5-10kt is
expected this afternoon and evening under broken-overcast middle/high clouds
(cigs at or above 15kft).
The cold front will cross the area late tonight with only a
minimal chance of -shra mainly at sby...which could end as a mix of
-rasn. Ceilings will average 5-10 k feet. A gusty northwest wind is expected
Friday with gusts to 30 knots (maybe as high as 35 knots at ksby) as
Canadian high pressure builds in from the northwest. That area of high
pressure slides across the region Friday night and Saturday...with
a more moist frontal system impacting the region Sunday into
Monday. High pressure is expected to return by Monday night and
expect winds to increase into marginal Small Craft Advisory levels later this evening
ahead of apprchg cold front. Only change to the Small Craft Advisory headline was to
add the lower zone and mouth of the ches Bay. Main headline will be
the gales Friday and Friday night as strong cold air advection develops behind the front and
ahead of the high prs apprchg from the west. Went ahead and extended
the gale headline through Sat morning over the Maryland coastal waters as the strong
gusts will be slower to dmnsh. Wind gusts 40-45 kts across northern coastal
waters with 35-40kts further south. Seas & waves respond to these gusty
winds. Seas average 7-10 feet with waves in ches Bay 4-5 feet.
Given the temperatures/wind gusts and current water temperatures...per coordinate with phl...
went ahead and issued a freezing spray advisory for the coastal waters
north of Parramore Island. This is where some moderate icing is
likely. Kept light icing mentioned further south & in the ches Bay
at this time.
Winds dmnsh to Small Craft Advisory Sat then quickly dmnsh below Small Craft Advisory levels by Sat evening
as high prs builds into and over the area Sat night.
Next low crosses the area Monday with anthr cold air advection surge seen behind
this systm Monday afternoon and night. Kept winds in Small Craft Advisory range and capped
gusts across coastal waters at 30 kts for now.
Marine...Gale Warning from 10 am Friday to midnight EST Friday night
Small Craft Advisory from 10 am Friday to 6 am EST Saturday
Small Craft Advisory from 10 PM this evening to 10 am EST
Friday for anz630>632-634-650-652.
Gale Warning from 10 am Friday to 6 am EST Saturday for anz652-
Gale Warning from 1 PM Friday to midnight EST Friday night for
Freezing spray advisory from 7 PM Friday to noon EST Saturday
Gale Warning from 10 am Friday to noon EST Saturday for anz650.