Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wakefield Virginia
951 PM EST Sat Dec 20 2014

Synopsis...
weak low pressure will push off the southeast coast tonight...as high
pressure remains over the local area through Sunday evening. Another
low pressure area moves northeast out of the Gulf of Mexico and up
along the Carolina coast late Monday into Tuesday...as high pressure
drifts off the New England coast into the Canadian Maritimes. A cold
front will cross the Wednesday night with high pressure returning
by Christmas day.

&&

Near term /through Sunday/...
widespread broken-overcast ceilings mainly 6-9kft continuing over the forecast area at this time...and
west/o any drying noted on the satellite...expected to remain over the forecast area
through the night. Nudged temperatures up a few degrees f most places due to
the cloudiness. Coldest spots right now on the Eastern Shore. Most low temperatures
from the M/u20s to l30s.

High pressure remains entrenched over the middle-Atlantic Sunday with
a mix of sun and clouds. Light winds overall with a light onshore
NE flow over the southeast coastal zones...seasonable highs in the Lower-
Middle 40s NE to around 50 f in south central Virginia.

&&

Short term /Sunday night through Tuesday/...
models show next shortwave trough amplifying across the northern
plains Sun night/Mon...as strong upper level ridging holds strong
from Florida to the Caribbean. Middle/upper level flow prognosticated to
turn more SW and this will help steer low pressure NE from the
Gulf Coast states into the southeast and middle Atlantic coastal waters Monday/Monday
night. Position of surface high to our north...shifting east to the New
England coast by 12z/Monday is not favorable for locking cold air
over the akq County Warning Area. Still should see enough cold air initially over
the region Sun night/Monday morning due to clear skies through part
of the night. This will lead to the chance of a few hours Worth of
overrunning frozen precipitation over climatology favored Piedmont zones northwest of
Richmond (with little chance for anything but all rain over the rest
of the cwa). Low level thicknesses (1000-850mb) are marginal but
BUFKIT soundings show a narrow layer of below freezing temperatures at
the surface from about 09-15z/Monday at kcho (and likely at klku). Still
some question as to how fast precipitation arrives but overall looks like
chances ramp up significantly during the 09-12z timeframe. Will go
with a chance for sleet over the Piedmont between
09-12z...transitioning to sleet/freezing rain from about
12-15z/Monday (although becoming confined to the far northwest by this
point). In any event...this looks light as bulk of deeper moisture
likely arrives after a changeover to all rain. Also...not
anticipating temperatures in middle 20s...generally closer to 30-32 f...so
impacts are expected to be minimal for the most part.

Highs Monday only in the upper 30s/around 40 northwest to the middle 50s far southeast in
cad setup. Maintaining likely to categorical probability of precipitation through Monday
afternoon...although quantitative precipitation forecast amounts only average 0.25-0.50". Low pressure
lifts to the NE Monday night with probability of precipitation slowly diminishing from
SW-NE overnight. Middle-level ridging briefly builds into the region
Tuesday. However...moist southerly flow originating from the Gulf
Stream will prevail so low chance (30%) probability of precipitation will be maintained.
Highs in the low 60s far southeast to the upper 40s northwest.

&&

Long term /Tuesday night through Saturday/...
a coastal low just off the middle Atlantic coast continue to wash out
Tuesday night as a warm front starts to lift north through the region.
Meanwhile...a very strong and vigorous surface low deepens over the
Ohio/Tennessee valleys and pushes a strong cold front toward the area. Initial
push of stratiform precipitation associated with the warm front Tuesday
night will likely give way to more showery precipitation as the middle
Atlantic region becomes warm-sectored ahead of the approaching cold
front. The surface pressure gradient tightens significantly on Wednesday as
the parent low deepens over the Great Lakes and a strong jet streak
(90-150 kt) noses into the region from the south-southwest. Highs should range
from 60-65 northwest and Maryland/Virginia lower Eastern Shore to 65-69 from roughly
Richmond to southeast Virginia/NE NC. In addition to dewpoints approaching 60
degrees across the southeastern half of the County Warning Area...a Theta-E ridge is
expected to surge northward along the southeast Wednesday morning into the southern middle
Atlantic coast by Wednesday aftn/evening. The combination of these
features/convective parameters means that a slight chance for
thunderstorms has been added to the forecast across southeast Virginia and NE NC
during the afternoon/early evening hours. The front exits the region late
Wednesday night and precipitation will taper off from west to east...coming to an
end early Thursday morning.

The upper trough associated with the Great Lakes surface low swings
through the region late Wednesday night through Thursday afternoon. Upper level
instability and abundant surface moisture from recent precipitation
should keep scattered-broken cumulus over the area through the day on Thursday.
Cold air advection occurring behind the cold front and a continued tight surface
pressure gradient will result in gusty west-southwest winds of 20-25mph with
gusts around 35mph...and should be fairly uniform across the region.
The gusty winds should decouple by Thursday evening. Overall conditions
Friday through the weekend should be dry. A Lee trough forms across the
area on Friday and a weak cad wedge develops. The pressure gradient
relaxes briefly Friday/Friday night as high pressure building over the southeast
states extends up into the middle Atlantic region. Meanwhile...a broad
upper trough pushes a dry cold front across the region on Sat which
will usher much colder 850mb temperatures over the area (-5 to -15c). Cold air advection
and a re-tightening of the surface pressure gradient will bring a return
to breezy SW winds on Sat and breezy northwest winds on sun behind the next
cold frontal passage.

&&

Aviation /03z Sunday through Thursday/...
no precipitation is expected during the 00z taf period. Broken clouds were over
much of the area. Model soundings indicated dry air above 10k feet but
metars have bases just below that level. A thin cloud deck of around
8-10k feet is expected to diminish toward morning. Some clouds at 5k
feet were reported at ecg. A mostly clear sky is forecast on Sunday.
Winds will be light through the period.

Outlook...a series of low pressure systems and complex frontal
boundaries will bring chances for rain and periods of low ceilings
and visibilities Monday through Wednesday. A cold front passes
through Wednesday night with VFR conds and dry weather Thursday.

&&

Marine...
quiet/benign conditions expected across all waters tonight through
most of Sunday night as weak high pressure ridging resides over the
middle Atlantic region. Winds will generally be north 5-10kt with
waves/seas averaging 1-2ft. Meanwhile...low pressure currently
stalled off the southeast coast gets absorbed into another low pressure
system tracking NE out of the northestern Gulf of Mexico to just off the southeast
coast tonight (riding along the boundary left by the current southeast
coast low). The newly formed southeast coast low slowly moves up the
Carolina coast on Monday and the middle Atlantic coast Monday night...washing
out on Tuesday/Tuesday night as a very strong and vigorous surface low deepens
over the Ohio Valley/Great Lakes regions and pushes a strong cold
front toward the area. Winds turn to the NE Sun night and gradually
increase to 15-20kt from south to north on Monday. Low-end Small Craft Advisory
conditions are anticipated to develop by Monday afternoon and persist over
southern waters through early Monday evening...and over northern waters through
late Monday evening.

A brief reprieve in Small Craft Advisory conditions is expected Tuesday/Tuesday night as the
coastal low gets washed out over the middle Atlantic region. A warm
front lifts north across the waters on Wednesday as a very strong cold
front approaches the region from the west. The surface pressure gradient
tightens significantly on Wednesday as a strong jet streak (90-150kt) also
noses into the region from the south-southwest. South winds will increase to
speeds of 15-25kt in the southern waters during the morning and in the
northern waters by the afternoon with Small Craft Advisory conditions likely developing during
the aforementioned timeframes. Seas should respond to the southerly winds
prior to seeing the increased wind speeds with seas building from
2-4ft Tuesday night to 4-5ft by Wednesday morning. Waves will build to 3-4ft
on ches Bay on Wednesday. The cold front is expected to cross the waters
Wednesday evening and solid Small Craft Advisory conditions will likely occur ahead of and
behind its passage. Am not anticipating gale force gusts unless they
are associated with convective showers Wednesday aftn/evening. Seas
continue to build to 5-9ft Wednesday night through Thursday before starting to
subside. S-SW winds of 20-30kt Wednesday night become westerly on
Thursday...remaining strong through the day Thursday. The pressure gradient
relaxes briefly Friday/Friday night as high pressure building over the southeast
states extends up into the middle Atlantic region. Meanwhile...a broad
upper trough pushes a dry cold front across the region on Sat which
will bring a return to breezy northwest winds across the waters late Sat
night.

&&

Akq watches/warnings/advisories...
Maryland...none.
NC...none.
Virginia...none.
Marine...none.

&&

$$
Synopsis...alb/lkb
near term...alb/lkb
short term...jdm/lkb
long term...bmd
aviation...lsa
marine...bmd

National Weather Service Glossary of Abbreviations