Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Wakefield Virginia
132 am EST Monday Jan 26 2015

Synopsis...
low pressure over the lower Ohio Valley will weaken across the
southern Appalachians later tonight into Monday morning. A new low
pressure system will develop off the coastal Carolinas Monday
morning...and rapidly intensify off the middle Atlantic coast Monday
night. The low will continue to pull off to the northeast of the
area through Tuesday.

&&

Near term /until 6 am this morning/...
current GOES WV imagery this evening indicates a rather dynamic
middle/upper system tracking across KY/TN...with the upper pv maximum
diving across the lower Mississippi Valley. This system even
generated thunderstorms over Alabama earlier this evening. A quiet
evening is occurring locally with just a slow increase in clouds as
the system is slow to advance east. The latest high res data (rap/hrrr)
along with the 26/00z NAM suggest deep lift/uvm associated with the
system reaches the eastern Virginia Piedmont around 09-15z. It then weakens
from 15-18z as the main energy transfers to the developing surface low
off the coastal Carolinas. Given this...likely probability of precipitation will be forecast
mainly west of I-95 late tonight into Monday morning...before
transitioning to far northern portions through the remainder of the day.
The latest data does suggest higher quantitative precipitation forecast with the initial rain late
tonight/Monday morning...but still amounts should be 0.30" or less.
Lows in the middle-upper 30s /above freezing all areas so no p-type
concerns overnight.

&&

Short term /6 am this morning through Wednesday/...
a Winter Storm Watch remains in effect for the Maryland Eastern Shore Monday
night into Tuesday...

Favoring a blend of the 12z NAM/European model (ecmwf) and 15z sref this
period. Have noted 12z GFS has a spurious looking bullseye of quantitative precipitation forecast
over portions of the County Warning Area west of the Bay Monday night/early Tuesday. The
06z GFS had this as well (although a bit farther to the south). Of
note...the 26/00z NAM as well as the 25/18z GFS both indicate a
secondary zone of deformation and band of frontogenesis back over
central Virginia Monday night...which has could complicate the snow
forecast.

For Monday...the energy will continue to Transfer to the offshore surface
low and much of the akq County Warning Area will be in sort of a lull with fairly
weak lift despite mainly cloudy skies. Still have likely probability of precipitation across
the north and chance probability of precipitation south on Monday...just do not expect much in
the way of quantitative precipitation forecast. High temperatures have been raised a few more degrees
from previous forecast...into the middle 50s in NE NC...to the lower
40s over the far northern tier. We went closer to the met numbers
due to a lack of Faith in the GFS model this cycle.

The main event for our area begins Monday night...as colder air
plunges south in response to rapid intensification of the surface low
off the Virginia coast. Still mainly rain across the southern 2/3 of the
County Warning Area in the evening...becoming all snow between 03-06z for most
locations. During this time...best lift/frontogenesis will reside
off the coast. Will be relying on deformation zone and intense
banding developing from the Delaware-Maryland-Virginia to log island to "wrap
around" and drop south for most of our snow into the day Tuesday.
Thus...snow amounts will show a sharp cutoff. Any change in
position of this banding can have drastic effects on snow
amounts...so uncertainty remains rather high. Have forecast
roughly 3-6" of snow on the Maryland Eastern Shore in the watch area...with
2-3" across Northern Neck/Virginia Eastern Shore (areas that will probably need an
advisory)...tapered fairly quick to < 1" over most of the remainder of
the County Warning Area. Could see slightly more than 1" across Hampton Roads early
Tuesday however.

Snow is expected to taper off late Tuesday morning/aftn...but if European model (ecmwf)
is correct this would be slower and additional snow amounts may
need to be added. Mav/met guidance looks too warm Tuesday...especially
across the NE. Expect highs in the lower 30s NE to around 40 f SW.
Clearing/cold Tuesday night/Wednesday with lows in the upper teens to middle
20s and highs on Wednesday in lower 40s SW to the lower 30s NE.

&&

Long term /Wednesday night through Sunday/...
long term period will feature below normal temperatures with dry weather most
days. For Wednesday night...surface hi pressure builds over the middle Atlantic and southeast
states as the next low pressure systm approaches from the west. With a mostly
clear sky and light winds...temperatures will fall into the middle 20s in most
spots. Low pressure and an associated middle-level vorticity maximum will bring
precipitation (plain rain) into the area starting late Thursday. Favored the
slightly slower European model (ecmwf) solution...with a 30% chance of precipitation (ra/snow
north and rain south) Thursday night...with low temperatures in the low to middle 30s.
Conds then dry out into Friday and Sat as surface hi pressure builds in from the west.
Expect a prtly cloudy sky both days with northwest winds and hi temperatures
falling from the 40s on Friday to the middle 30s to lower 40s on Sat.

&&

Aviation /07z Monday through Friday/...

As of 06z...VFR conditions across area terminals will continue
into Monday morning. Middle and high level clouds slowly increase
over the next few hours, with cloud bases lowering later this
morning...first over ric/sby through 15z...then by late
morning/afternoon over phf/orf/ecg. Light rain is forecast to develop
mainly at ric this morning...with vcsh wording at sby by late
morning. Blended current probability of precipitation with some of the guidance for
starting times of precipitation. Ceilings and visibilities lower to MVFR and in some
cases IFR during the afternoon except at ecg. The lowest conditions for
this taf period and beyond appear to be lining up for sby where NE
winds will also become gusty.

Outlook...rain changes to snow during the late evening hours
Monday into early morning hours of Tuesday (02-06z/tuesday) and
continues trough midday Tuesday. Snow may be heavy at times at
sby through Tuesday morning where accumulating snowfallis
currently forecast. Elsewhere, a light accumulation of snowfall is
expected at ric/phf/orf with only a trace amts of snow expected at
ecg. IFR conditions are expected by late afternoon and through the
evening at sby and will continue overnight Monday especially during
periods of accumulating snow. IFR conds will be possible Monday
night at phf/orf/ecg, mainly towards the end of the taf period and
into Tuesday morning.

Dry and mainly VFR conds are expected during the rest of the week.
There will be a chance for precipitation late in the week mainly on Thursday
night.

&&

Marine...
headlines have been hoisted over all waters for the upcoming strong
coastal low. For tonight...10-15 knots southeast winds will slowly shift to the east as
surface low pressure approaches from the west. The low will redevelop off the
Carolina CST on Monday...and strengthen as it slowly advances newrd
into Monday night. A gale warng has been issued for coastal waters north of
Parramore Island where confidence for 34+ knots winds is hi on the back
side of the low. For the remainder coastal waters and the Bay...with this
being 3rd period and still some uncertainty...went ahead with a gale
watch for now and will be converted to either a gale warng or Small Craft Advisory in
future updates. Otws...went with a Small Craft Advisory for the sound and rivers.
Another thing of note is seas with this event...expected to rise to
at least 12 feet out 20nm over northern coastal waters. Waves over the Bay up to
5-6 feet. Northwest flow and marginal Small Craft Advisory conds may continue into Tuesday
night/Wednesday as surface hi pressure slowly builds in from the west. Sub-Small Craft Advisory conds then
for Wednesday night/Thu.

&&

Tides/coastal flooding...
low pressure intensifies rapidly off the middle-Atlantic coast
Monday night/Tuesday. The result will be a period of strong northerly
winds over the waters. Tidal anomalies are expected to reach 1 to
1.5 feet...possibly higher...during Monday night and Tuesday
mornings high tide cycles. Sites in the Lower Bay will reach
highest astro tide with water levels approaching minor flooding
thresholds at Sewells Point Monday night. For Ocean City...minor
flooding is expected with a small chance for moderate as
well...but not high enough likelihood to issue any watch/warning at this time
with this still three high tide cycles out. Will re-evaluate tonight.
High anomalies are expected again Tuesday...before anomalies drop off
late Tuesday into Tuesday night as the low lifts away from the region.

&&

Akq watches/warnings/advisories...
Maryland...Winter Storm Watch from this evening through Tuesday afternoon
for mdz021>025.
NC...none.
Virginia...none.
Marine...Small Craft Advisory from 7 PM this evening to 7 PM EST
Tuesday for anz635>638.
Gale watch from this evening through Tuesday evening for
anz630>632-634.
Small Craft Advisory from 7 PM this evening to 4 am EST
Wednesday for anz633.
Gale watch from this evening through Tuesday evening for
anz654-656-658.
Gale Warning from 4 PM this afternoon to 10 PM EST Tuesday for
anz650-652.

&&

$$
Synopsis...lkb
near term...ajz/lkb
short term...ajz/lkb
long term...mas
aviation...mam/lsa
marine...mas
tides/coastal flooding...

National Weather Service Glossary of Abbreviations