Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wakefield Virginia
119 am EST Friday Jan 30 2015

Synopsis...
a cold front crosses the region overnight. 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 today/...
as of 930 PM EST...a cold front has reached The Spine of the
Appalachians and will push eastward through the local area
overnight. Pre-frontal showers have pushed offshore at this time...and a
period of dry weather is expected until around 09z. Then a slight chance
for some light precipitation over eastern areas is expected due to the front and
associated middle-level vorticity maximum despite little moisture. This precipitation
would be in the from of light snow or sleet across the lower Maryland
Eastern Shore...but no accumulation. Low temperatures in the low 30s
Piedmont to near 40 Virginia Beach.

For Friday...dry weather and decreasing cloudiness prevails 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 /tonight through Sunday night/...
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 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
m30s-l40s.

&&

Aviation /06z Friday through Tuesday/...
southerly winds averaging 10-15 knots will shift to the west-southwest between
09-12z...and then sharply to the northwest after 12z. There are
indications that a few showers may affect mainly eastern portions of
the area with the front...so have added -shra to korf/kphf/ksby
from 09-13z. Still do not expect ceilings to drop to more than about
4000 feet and visibilities will only drop slightly so retained p6sm
wording.

Gusty northwest wind will develop after 14z...with gusts increasing to
around 30 knots from 18z-22z. Winds slowly diminish later this
evening but should still be gusting to 20-25 knots (highest at ksby).

Dry/less windy Sat as the area of high pressure slides across the
region. A more moist frontal system impacts the region Sunday afternoon into
Monday. This looks to be mainly rain although there is a chance
for precipitation to mix with or change to snow at kric/ksby on the back
side of the system before the precipitation ends on Monday.

&&

Marine...
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.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...Gale Warning from 10 am this morning to midnight EST tonight
for anz630>632-634>636-638.
Small Craft Advisory from 10 am this morning to 6 am EST
Saturday for anz633-637.
Small Craft Advisory until 10 am EST this morning for
anz630>632-634-650-652.
Gale Warning from 10 am this morning to 6 am EST Saturday for
anz652-654.
Gale Warning from 1 PM this afternoon to midnight EST tonight
for anz656-658.
Freezing spray advisory from 7 PM this evening to noon EST
Saturday for anz650-652.
Gale Warning from 10 am this morning to noon EST Saturday for
anz650.

&&

$$
Synopsis...jdm/mas
near term...jdm/mas
short term...mas
long term...mpr
aviation...lkb
marine...mpr

National Weather Service Glossary of Abbreviations