Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
907 am EST Friday Dec 6 2013
a cold front over New Jersey and Delaware will move through the
rest of the forecast area today as a series of low pressures move
along the boundary. High pressure will briefly build across the
northeast Saturday night into Sunday. An area of low pressure will
develop across the lower Mississippi River valley, then strengthen
as it moves northward into the Great Lakes Sunday night. This will
lift warm front across the area early Monday, followed by a cold
front Monday night. A weak clipper system may skirt across the
northern tier of the country early next week before high pressure
builds across the region late in the week.
Near term /until 6 PM this evening/...
the cold front has cleared most of our forecast area and will
continue its trek. Estf update during the day was to try to better
time waves of precipitation and downward spiral of temperatures.
We will issue a Winter Weather Advisory for the Poconos starting
late this afternoon. There remain guidance conflicts, but they all
agree on bringing sub 925mb air into that part of our County Warning Area.
Differences abound as to when surface temperatures drop below freezing while
temperatures above 850mb are expected to remain above freezing.
1000-500mb thicknesses greater than 5460 meters have been non
snow and that trek into our County Warning Area is painfully slow. Thus the idea
of a prolonged period of sleet, even if the freezing rain does not
come to fruition will make for hazardous travel, possibly starting
as soon as the evening rush.
There will be a lull in precipitation activity later this morning before the
next wave rides up along the front and brings a renewal of precipitation
later today. Probability of precipitation will decrease back to chance range across the southern
areas and then ramp up later. P-type will be rain in 99 percent of the
area today with the exception being across the southern Poconos where ice pellets
will probably mix in before tonight. This transition with the cold
advection is a tricky call. Temperatures will fall steadily across
the area today with readings starting in the 50s/low 60s before dawn
and dropping in the to the 30s/low 40s (north) by late afternoon.
Short term /6 PM this evening through 6 am Saturday/...
what was described for the Poconos is expected to start occurring in
Sussex County New Jersey this evening. There is about a 50/50 split as to
where sub freezing temperatures stall in our County Warning Area overnight with half of
the models stopping it along the Pocono Lehigh Valley border and
in Sussex County New Jersey. Will wait on the 12z model data to
make any further changes. MOS/met guidance temperatures were verifying
fairly close to reality in the colder air to our northwest.
The next wave will arrive overnight and bring a decent round of rain
to much of the area. Temperatures across the southern Poconos and northern New Jersey
will be marginal and p-type issues abound. We expect that it will
become cold enough for some snow and in between a sleety mix and a
chance for some freezing rain also. Confid in freezing rain is
low...since ground temperatures will not have yet cooled enough to
freeze much. A slushy coating to ice pellets/snow with up to an
inch will be found over the northern most areas. Precipitation ends gradually
from west to east after midnight and will probably be done in most areas
by dawn Sat.
Long term /Saturday through Thursday/...
a break in the weather looks likely for Saturday into Saturday night
before a return of unsettled weather for the end of the weekend into
early next week. The front cold front affecting the area today will
have pushed to our south by Saturday morning. It is possible some
lingering showers may occur for our coastal and southern areas early
on Saturday, but drier air is expected to build across the area and
there will not be much of any vorticity impulses to help create any
shower activity for the remainder of the day. High pressure will
begin pushing into the area from the west late Saturday into
Saturday night which should help keep the weather dry into Saturday
The high pressure will lift into the northeast on Sunday, which will
allow a warm front to begin lifting into the area Sunday night into
Monday morning as an area of low pressure moves into the Great Lakes
region. As the low continues to lift into southeast Canada on
Monday, it will drag a cold front across our area. Several short
waves/vorticity impulses are expected to affect the area during this
period which will allow periods of precipitation to occur through
the time frame. The precipitation may start out as early as Sunday
across our southern areas as the first of the vorticity impulses
moves into the area. With cold air in place, this precipitation will
possibly start out as a wintry mixture for Sunday into Sunday night,
before possibly changing to rain Monday as warmer air moves in. A
good portion of the area could see a snow/sleet accumulation before
the change over to rain. There is also the potential for a period of
freezing rain to occur, especially for our northern half of the County Warning Area.
Our northern zones could hold on the the wintry mixture longer into
Monday morning as cold air could get dammed up before the warm surge
pushes through. The precipitation should begin to dissipate Monday
night into Tuesday as the frontal boundary pushes farther offshore.
However, there still will be a chance of precipitation into Tuesday
as couple of more vorticity impulses slide across the area.
A return of drier and cooler weather is currently expected for
Wednesday into Thursday as thicknesses drop across the area high
pressure begins to build into the area from the west. A weak clipper
system may skirt to our north on Wednesday, but is not expected to
affect our area. There is the possibility of some lake effect snow
showers/flurries later in the week, but we'll include those as we
get closer and confidence is higher.
Aviation /14z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Visibilities have improved somewhat early this morning ahead of the
approaching cold front. The showers have brought down some stronger
winds aloft. The visibilities will improve over the northern/eastern areas shortly.
Winds will be mostly srly/southwesterly for a few more hours...then frontal passage
with wrly winds becoming nwrly by late morning. Winds gusts around
20 kts possible. Conditions may improve to the higher part of MVFR
or perhaps even low ND VFR for awhile later this morning behind the
first batch of showers. Confid in VFR returning is rather low.
More rains arrive from SW to NE this afternoon and conditions will
again head back to IFR tonight over most of the area. Rains will
probably mix with sleet and snow across the far north. Winds will be
mostly nearly/nerly overnight.
Saturday-Saturday night...mostly VFR. Gusty north-northwest winds 15-20 knots
Sunday-Monday night...IFR/MVFR probable with rain/wintry mix
Sunday-Monday. Possible improvement Monday night.
Tuesday...mostly VFR...possible MVFR early. Rain/snow showers
possible. Gusty west-northwest winds possible.
prefrontal conditions on the waters are approaching Small Craft Advisory criteria.
Seas at buoy 44009 are lingering around 4 feet and the wind gusts are
picking up with some gusts around 20 kts. I will leave the Small Craft Advisory flag
in place...since higher gusts may occur with the arrival of the
colder air later this morning. The flag is a rather low-end event at
best and could be taken down before the 6pm expiration.
Saturday-Saturday night...Small Craft Advisory, or near advisory,
Sunday-Sunday night...sub-advisory conditions possible Sunday,
before a return to Small Craft Advisory conditions Sunday night.
Monday-Tuesday...Small Craft Advisory, or near advisory, conditions
PA...Winter Weather Advisory from 4 PM this afternoon to 7 am EST
Saturday for paz054-055.
New Jersey...Winter Weather Advisory from 7 PM this evening to 7 am EST
Saturday for njz001.
Marine...Small Craft Advisory until 6 PM EST this evening for