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Area forecast discussion 
National Weather Service Mount Holly New Jersey
619 am EST Tuesday Feb 9 2016

Synopsis...
a trough of low pressure will extend from the middle-Atlantic coast
into the eastern Great Lakes today. This low pressure will move
northeast of the region tonight and Wednesday. High pressure will
work eastward through the region Thursday into Friday before giving
way another area of low pressure with an Arctic cold frontal
boundary by the end of the week. On Sunday, another area of high
pressure will build southward into the region as low pressure forms
across the southern United States by Monday.

&&

Near term /until 6 PM this evening/...
630 am update...area of precipitation across Delaware-Maryland-Virginia is making progress
further north despite much drier dew points north of Delaware-Maryland-Virginia. And
under the heavier bands, we are beginning to see a rain and and
snow mix. Still think the bulk of the precipitation will be from middle day
on, but we might see some light accumulations with this area.

Previous near term discussion...
models trended warmer through the day, with some (including the
nam) even showing rain possible as far northwest as philly by this
afternoon. This is a considerable change from what the models were
showing just 24 hours ago. This trend, combined with the fact that
heavier snow has not really developed across our region overnight
(amounts so far have been less than one half inch) has lead to
some changes with the forecast. Still think that precipitation will be
mostly snow as once the heavier bands do develop, temperatures
could quickly drop to near the dew points which are generally near
or below freezing. The exception to this is central and southern
Delaware and far southeastern New Jersey which may see periods of rain this
morning before changing to mostly snow later this afternoon.

First the changes to the snow totals: given the lack of snow
accumulation overnight, and the higher boundary layer temperatures
during the day today leading to lower snow to liquid ratios,
forecast snow totals have generally been decreased across the
region, with one exception. Across northeastern NJ, high res models
are now showing a potential for frontogenetical bands this evening
or late tonight. So increased snow totals slightly in this area,
although i'm concerned that if the models trend even further north,
those bands may miss our region all together.

Changes to the headlines: given the generally lower snow totals,
much of the area that was in the Winter Storm Warning is now in a
Winter Weather Advisory, with the exception of Chester and Delaware
counties which have the highest risk of seeing mesoscale banding
this afternoon. For those two counties, the warning remains in
effect. The advisory was also expanded on the northern end to
include Morris County to account for potential banding overnight.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
snow should generally move out of the region by late this evening
except across northeastern New Jersey where it may linger through the
overnight hours.

As the surface trough lifts further north, winds should shift to
westerly which should help to continue to diminish the coastal
flooding threat.

&&

Long term /Wednesday night through Monday/...
an active wintry pattern to continue through the presidents day
Holiday.

Wednesday: snow associated with a trough of low pressure will be
ending across northern portions of the region in the morning.
However, a somewhat unstable airmass will be left across the region
in the afternoon hours with steeping low level lapse rates and tt
modeled near 50. Enough moisture may still be present to form a few
scattered snow showers and flurries across the region with the
higher terrain across eastern PA and northwest New Jersey helping to aid potential
development. A look at BUFKIT soundings shows the potential for a
favorable mixing as well which could result in some northwest wind
gusts around 25 miles per hour in the afternoon. High temperatures will likely
struggle to what met and mav guidance has due to some snow cover and
the strong cold air advection push during the day.

Wednesday night through Thursday night: our region will be
situated between Arctic high pressure building into the Midwest
and the departing low pressure system. This pressure gradient will
lead to continued strong northwest winds with cold air advection
into the region. The wind direction also looks to send moisture off
the Great Lakes into the region as well. Instability looks less than
during the day Wednesday but low level lapse rates should steepen
Thursday afternoon. This will result in the chances for some
scattered snow showers and flurries to continue. Any light snow
accumulation could lead to a few slick spots as temperatures will be
falling quite a bit below freezing. Clouds and wind should keep the
low temperatures up Wednesday night, say only the 10's to around 20
with afternoon highs in the 20's on Thursday. Winds will decrease
Thursday night with clearing skies allowing for a more favorable
setup for radiational cooling as high pressure builds toward the
region. Low temperatures will likely fall into the 10's regionwide
and continued to nudge them slightly lower than what most guidance
indicates.

Friday and saturday: high pressure will move through the region on
Friday. This high pressure system will give way to another Arctic
cold front with a clipper type low pressure system along it. This
moves through the region Friday night and Saturday. Modeling is
still trying to resolve if the more clipper like low pressure will
develop into a coastal low along the boundary. Right now about a
third of ensemble members from both the GFS and European model (ecmwf) suites are
showing the potential for a coastal low forming near or southwest of
the region. The other two thirds of ensemble members plus the 00z
CMC, UKMET and GFS form a low pressure much farther offshore. The
less likely coastal low formation scenario could result in
another period of accumulating snowfall for the region. However,
with the bulk of model guidance staying further offshore will just
add a generic low chance of snow showers to the forecast for
Friday night and Saturday. Even if the low forms offshore
Saturday, it will be a cold and windy with another round of northwest
flow snow showers and flurries with the highest coverage in the
high terrain areas in eastern PA and northwest NJ, similar to the middle
of this week.

Saturday night through Sunday night: another potent area of Arctic
high pressure will build into the region with the coldest shot of
air of the season so far. 850 mb look to dive well below -20c across
most of region as currently modeled. As in other periods will
continue to nudge temperatures a couple of degrees cooler than most
ensemble guidance sets. Strong northwest winds in the wake of the
departing system on Saturday will likely lead to below zero wind
chills, pushing advisory criteria in spots.

Presidents day: high pressure will gradually move east of the region
and will give way to a storm system that is currently modeled to
form across the southern United States. Right now it appears that a
typical GFS bias is at work focusing storm development in the
northern branch of the jet and being to progressive with moving the
trough eastward across the country. The ECMWF, UKMET and CMC seem to
have a better handle of a broader trough which gives the southern
branch more of a chance to be involved in the pattern. This allows
for a stronger system to form across the Southern Plains. Right now
it looks like Monday will start dry with precipitation chances
moving into the region by Monday afternoon and night. Timing can
always change by 24 hours or more this far out. Temperatures will
also rebound on the backside of the high pressure system. However,
given this is several days a lot of ensemble spread is still present
and the various features involved will not even sampled by
observational data for several more days.

&&

Aviation /11z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Widespread MVFR and IFR ceilings are expected through much of the taf
period. The lowest conditions, including visibility restrictions are
expected with snow bands, which are likely to move through the taf
sites this afternoon into the early evening hours.

After 00z, snow should begin to lift out of the area from south to
north, and with it, expect improving visibilities and eventually
(likely not until after 06z) improving ceiling conditions. Winds are
also expected to shift from northeasterly through the day to
westerly or northwesterly after 06z.

Outlook...

Wednesday through thursday: mainly VFR, some brief MVFR restrictions
in isolated snow showers and flurries. Northwest winds 15-25 knots
with higher gusts.

Thursday night and friday: VFR.

Friday night and saturday: mainly VFR, possible MVFR restrictions
in scattered snow showers. Northwest winds increasing Saturday
from 15-25 knots with higher gusts.

&&

Marine...
Small Craft Advisory conditions, especially for seas are expected to continue today
and tonight. There may be a bit of a lull in the winds during the
day today, but a shift to westerly or northwesterly winds is
expected tonight, and with it, and increase in wind speeds once
again.

Outlook...

The Small Craft Advisory has been extended till 6pm Wednesday based on a high
confidence of northwest wind gusts near 25 knots occurring throughout
the day and seas staying around five feet. Wind gusts near 25 knots
may continue through Thursday night even with decreasing
waveheights. Another round of strong northwest wind gusts over 25
knots is becoming likely Saturday. These gusts may even reach gale
force for a time.

&&

Tides/coastal flooding...
moderate coastal flooding, with isolated major coastal flooding is
possible with high tide this morning for the New Jersey shore, Delaware
beaches, and locations along the Delaware Bay. Minor coastal
flooding is expected for the tidal Delaware River with this high
tide cycle. Thanks to decreasing astronomical tides, and an expected
wind shift, we are not expecting coastal flooding with the high tide
cycle this evening, though it could get close to minor flooding
thresholds for the Oceanside.

Minor coastal flooding is possible for the northeastern shore of the
Chesapeake Bay with the high tide cycle early this morning and
again this evening. There is some risk that moderate coastal
flooding could be reached with the evening high tide, but
confidence is low, so will continue with the coastal Flood
Advisory for now.

The potential for blowout tides is present for the Thursday low
tidal cycles.

&&

Phi watches/warnings/advisories...
PA...Winter Weather Advisory until 6 am EST Wednesday for paz060-
061-071-103>106.
Winter Storm Warning until 6 am EST Wednesday for paz070-101-
102.
Coastal Flood Advisory until 5 PM EST this afternoon for
paz070-071-106.
New Jersey...Winter Weather Advisory until 6 am EST Wednesday for
njz008>010-012>027.
Coastal Flood Warning until 1 PM EST this afternoon for
njz012>014-020>027.
Coastal Flood Warning until 3 PM EST this afternoon for njz016.
Coastal Flood Advisory until 5 PM EST this afternoon for
njz015-017>019.
Delaware...Winter Weather Advisory until 6 am EST Wednesday for
dez001>004.
Coastal Flood Warning until 1 PM EST this afternoon for
dez002>004.
Coastal Flood Warning until 3 PM EST this afternoon for dez001.
Maryland...Winter Weather Advisory until 6 am EST Wednesday for mdz008-
012-015-019-020.
Coastal Flood Advisory until 10 PM EST this evening for mdz008-
012-015-019-020.
Marine...Small Craft Advisory until 6 PM EST Wednesday for anz450>455.

&&

$$
Synopsis...Gaines
near term...Johnson
short term...Johnson
long term...Gaines
aviation...Gaines/Johnson
marine...Gaines/Johnson
tides/coastal flooding...

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