Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
356 PM EST Tuesday Jan 27 2015
a strong storm system east of New England tonight will reach the
Canadian Maritimes on Wednesday. High pressure will move in from
the Ohio Valley Wednesday and settle over the region Wednesday night
and Thursday morning. Low pressure will move through the Great Lakes
on Thursday and reform east of New England on Friday. High pressure
will move in from the Great Lakes on Saturday...followed by a low
pressure system moving through the Appalachians early next week.
Near term /until 6 PM this evening/...
all winter storm warnings and advisories were canceled early this
afternoon. Some scattered snow showers or flurries are possible
early this evening in the southern Poconos and northwest New
Jersey...but any such activity is expected to end before midnight.
The low pressure system responsible for the wintry weather the past
day or so will continue to move slowly northeast
overnight...reaching the Canadian Maritimes by morning. Skies are
expected to gradually clear from west to east during the overnight
hours as this low moves further away. On the other hand, northwest
winds in the 10 to 20 miles per hour range...with higher gusts...will continue
as the gradient between this low and incoming high pressure from the
west persists into Wednesday. Once the clouds clear...the fresh snow
cover up north should allow temperatures to drop into the single
digits. Lows in the middle-teens to around 20 are expected further
south were the snow cover isn/T as deep or widespread. A blend of
mav/met guidance was used for overnight temperatures, undercut by a
degree or two up north to account for snowcover.
Short term /6 PM this evening through 6 PM Wednesday/...
mostly sunny conditions are expected...except for morning
cloudiness in northern New Jersey (lingering effects from the departing
low). Northwest winds will pickup once again as daytime mixing takes
place...then gradually decrease late in the day as the sun begins to
set and as the pressure gradient continues to decrease. Temperatures are
expected to maximum out in the low to middle 20s far north, and in the low
30s south. Again...a blend of mav/met guidance was used for high
temperatures with a slight cut in the locations of deeper snowpacks.
Long term /Wednesday night through Tuesday/...
the middle level pattern at 00z Thursday is comprised of a deep trough at
70w with a northern stream ridge along the British Columbia coast
and a southern stream closed low in vicinity of the California coast.
Between these two features...shortwave ridge will crest over the middle
atl on Thursday...then northern and southern stream shortwave energy is
prognosticated to phase in vicinity of the Mississippi Valley and become negative
tilted as it reaches 70w around 00z Sat. This leads to low
pressure moving through the Great Lakes on Thursday with redevelopment
currently modeled in vicinity of Georges Bank on Friday. By Sat...northern
stream shortwave energy entering the northern plains is expected to
interact with southern stream shortwave energy ejecting out of a closed
low in vicinity of The Four Corners region. This leads to a complex area of
low pressure...which is currently prognosticated to move through the
Appalachians early next week.
The best chances for precipitation in the long term will be Thursday night into
early Friday and then again early next week...with ptype issues likely
with both systems...as temperatures roller coaster from near normal
to well below normal throughout the period.
Wednesday night and Thursday...
generally tranquil weather as a ridge of high pressure crests over the
region. Expecting ideal conditions for radiational cooling Thursday am as
atmos decouples with clear skies...light winds...and fresh snow
cover. Expecting min temperatures 10 to 15 degrees below normal region-
wide. On Thursday large scale flow becomes southwest and model x-secs
indicate middle level moisture streaming into the region...especially
in the afternoon. The GFS and Canadian are most aggressive in bringing
precipitation in prior to 00z along and west of the Delaware River...and this
timing is reflected in the fcsr. Maximum temperatures will generally be
5 to 10 degrees below normal.
Thursday night through Friday night...
low pressure moves through the Saint Lawrence valley with good model
agreement on the strongest dynamics just to the north and west...
and thus resultant quantitative precipitation forecast bullseye. At this time...model quantitative precipitation forecast is generally a
trace over the Delaware-Maryland-Virginia to 0.2 inches over the far northwest. The
greatest uncertainty is in model thermal profiles and thus ptype.
This does not appear to be a cold air damming situation with high
pressure offshore and the absence of an inversion. Nevertheless...low
pressure well northwest will lead to boundary layer winds insufficient
for warm air advection. Model soundings indicate a rain/snow event
with current profiles confining rain to southeast New Jersey...de...and Maryland
where model quantitative precipitation forecast is lightest. Expecting snow-liquid ratios ranging
from 5:1 to 10:1 which would give accumulations up to 1 inch in vicinity of
I-95 to 3 inches over the northwest...but this is preliminary...
stay tuned. Precipitation ends early Friday with strong cold air advection
as low pressure redevelops east of new eng...as temperatures fall through
the day after morning maximums. There is also the potential for snow
squalls...particularly over the Poconos...with a cold frontal
passage Friday afternoon. Model soundings show mixing to 850 hpa
with potential for wind gusts around 30 knots. The combination
of blustery winds and below normal temperatures on Friday night
will lead to low wind chills...therefore...a Wind Chill Advisory
may eventually be needed.
Sat and sun...
middle-level cyclonic flow over the region on Sat gradually gives way
to brief ridging on sun. On Sat the column will dry out...aside
for possibility of stratocumulus beneath a modeled subsidence
inversion...with one last brisk day in northwest flow behind
departing low. Middle level flow on Sunday becomes southwest...and
the column will gradually moisten in advance of storm system to
the southwest. Temperatures expected to be 10 to 15 degrees below normal.
Sunday night through Tuesday...
complicated forecast as low pressure traverses the Appalachians
late Sunday into early Monday. Strong middle-level vorticity maximum approaches
the coast with dual jet setup favoring redevelopment in vicinity of middle atl
or New England. At this time...thermal profiles generally favor snow with
rain mixing in closer to the coast...but this is highly uncertain.
Redevelopment could lead to colder air being drawn in...which
would bring snow further south along the coast. Any winter weather
would be exacerbated by cold antecedent conditions...making
surfaces more prone to icing.
Aviation /20z Tuesday through Sunday/...
The following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Conditions have gradually improved to VFR and skies will transition
to broken and scattered throughout the evening. Northwest wind gusts
around 20 knots will continue at all taf sites. For tonight there is
potential for some scattered low clouds around 2,000 feet to form.
However, with continued northwest winds over 10 knots there is
little to moderate confidence this will occur.
Wednesday will be a VFR day with northwest gusts again around 20
knots. Some higher gusts are possible in the afternoon. Gusts
will again decrease after sunset.
Wednesday night...primarily VFR.
Thursday into Friday morning...primarily VFR for much of Thursday. Light
snow is expected to overspread the area from west to east Thursday night
but may reach Abe/ridge by late afternoon. MVFR/IFR possible with the
snow. Highest confidence is at northern terminals.
Friday afternoon...VFR with northwest winds gusting around 30 knots.
Friday night...VFR with gusty northwest winds expected to continue.
Sunday...light snow is expected to overspread the area from west to
east during the day...low confidence on timing. MVFR/IFR possible
with the snow.
gale wind gusts have tapered off in conjunction with the departing
low pressure system. However, on the backside of the low pressure
strong northwest winds with Small Craft Advisory gusts will likely continue till
around 18z Wednesday in all marine zones, with some scattered Small Craft Advisory
gusts through 23z. Wave heights will gradually decrease by Wednesday
afternoon to around five feet. We have cancelled the remainder of
the Gale Warning and replaced with a Small Craft Advisory through 23z Wednesday,
ending earlier on the Bay.
Wednesday night through Thursday night...no marine headlines
are anticipated. Some freezing spray possible Wednesday night.
Friday...near gale-force northwest gusts behind departing low pressure.
Friday night...possible leftover northwest gale force gusts. Freezing
Saturday...Small Craft Advisory conditions possible. Freezing spray possible...
Sunday...conditions are expected to remain below Small Craft Advisory thresholds.
Marine...Gale Warning until 6 PM EST this evening for anz430-431-