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Area forecast discussion 
National Weather Service Mount Holly New Jersey
259 PM EST Thursday Feb 11 2016

Synopsis...
high pressure will settle across the area tonight and then move to
the east Friday. A low pressure area will move across southern
Canada and cause an Arctic front to cross our area Friday night.
High pressure will build in over the weekend and crest over the
region Sunday night. Low pressure will affect the are early next
week.

&&

Near term /until 6 am Friday morning/...
through 8 PM...continuing snow shower forecast, possibly briefly
heavy with brief small accumulations. I think mostly higher
terrain unless we can see some bands organize late this afternoon.
Not giving up, though drier dewpoints and 20+ tt/dew point spreads argue
against accums anywhere southeast of a kabe-kmmu line. However, have seen
bands organize before and a slight increase in relative humidity can permit
problem snow squalls. Will check at 320 PM for a final decision on
how to hopefully best forecast the period 330 PM to 8 PM.

The science behind the snow showers...extreme and moist boundary
layer lapse rates associated with the cold pool up through middle
levels--- roughly 500mb. Both the bgm windex tool and the btv
snowsquall parm tools indicated huge values both this morning,
this afternoon and probably again Saturday with real deal true
Arctic plunge.

Tonight...snow showers dry out or trail east-southeastward out to sea this
evening as the surface heating wanes and the cold pool aloft warms a
bit. Skies clear most of the area and winds diminish as a ridge of
high pressure pokes from the southwest in with some radiational
cooling on todays freshened snow cover. Ran a 50 50 blend of 12z/11
GFS/NAM MOS but will probably allow for cooler than this forecast by
2-3 degrees over east PA and northwest New Jersey radiators. Should get close to zero
in parts of east PA radiatiors per GFS 2m temperatures. Westerly winds
diminish and become light late.

Confidence: average.

&&

Short term /6 am Friday morning through 6 PM Friday/...
sunny, then increasing and thickening clouds ahead of the James
Bay Arctic vortex diving southeastward...mainly high clouds until late in
the day. Winds turn SW and the unstable and moistening boundary
layer lapse rates over the still open waters of the bays may yield
some Bay effect flurries late in the day. Otherwise, snow showers
in the warm air advection pattern in PA could develop flurries or snow showers in
the Poconos near 5 PM. SW wind.

50 50 blended 12z/11 GFS/NAM MOS guidance.

Confidence: average.

&&

Long term /Friday night through Thursday/...
a bitterly cold Arctic air mass will be across the area during the
beginning of the long term. A cold front will cross the area Friday
night accompanied by snow showers and gusty winds. This will usher
in the cold winds with temperatures dropping through the teens in
most areas and reaching the single digits across the north. The
temperatures will not recover much Saturday with highs mostly in the
teens north and low 20s south. Wind chill values much of the day
will be in the single digits with sub-zero readings north. We have
issued a wind chill watch for the southern Poconos and northwest New Jersey for Sat night
into Sunday morning...when the coldest air will be over the area.
Wind chill readings in these areas will be -25 to -30 degrees. A few
snow showers across the higher elevations of NE PA / northern New Jersey
Saturday.

Temperatures will moderate Monday and then trend back above normal for
Tue/Wed. These warmer temperatures will arrive at the same time as a wet
weather system approaches from the SW. Precipitation will probably
begin Monday night and continue into Wednesday. Many of the
operational models are indicating enough of a warm-up so that most
of the precipitation will be rain. It looks possible that some of
the precipitation initially could be snow or some sleet/freezing
rain. We will just have rain/snow in the grids for now with limited
confid in placement of any frozen precipitation.

The storm will pull away from the region next Wednesday and more high
pressure will arrive later in the day and last into Thursday.
Temperatures for this period will be within a few degrees of
seasonal norms.

&&

Aviation /20z Thursday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

Rest of today...VFR scattered-broken at or above 4000 feet. Brief MVFR/IFR conds in
snow showers may develop around kabe/krdg and kttn during middle to
late afternoon and may slip south toward the vicinity of kphl and
kpne around 22z. A westerly wind will continue to be quite gusty
to around 30 knots, with a few isolated gusts to 35 knots.

The snow showers are associated with extremely large and moist low
level lapse rates. Also aiding may be the Lake Erie moisture plume
(recently largely non ice covered).

This evening and tonight...VFR scattered-broken clouds at or above 4000 feet during the
evening becoming mainly clear or with just a little cirrus overhead.
Any leftover snow showers should end between about 0z to 02z. Gusty
west-northwest winds 20-30 knots into the evening will slowly diminish later
during the night.

Friday...VFR conditions are expected. Cirrus ceilings arrive and then
lower during the afternoon. Southwesterly winds are expected, mainly
around 10 knots or less.

Outlook...

Friday night and saturday: mainly VFR, possible MVFR restrictions
in scattered snow showers. Northwest winds increasing Saturday
from 15-25 knots with gusts up to 40 knots Saturday afternoon.

Saturday night and Sunday...VFR conditions expected. Northwest winds
10 to 25 knots.

Monday...VFR conditions for most of the day then becoming MVFR and
IFR by evening with rain and snow.

Tuesday...widespread lower ceilings/visibilities with rain and possibly snow.

&&

Marine...
gales in progress and glw continues as posted. An Small Craft Advisory will be needed
for much if not all of the over night hours once the gales subside.

Light freezing spray is occurring and continues to be expected on
the Bay as well as the near coastal waters through tonight.

Friday no headline! A good day to finish up any marine related activity.

Outlook...
gales will continue Friday night through Sunday morning. Conditions
will decrease back to Small Craft Advisory conditions for awhile Sunday before
returning to sub-Small Craft Advisory conditions. More Small Craft Advisory conditions possible Tuesday.

&&

Climate...
near record cold is expected for portions of our area Sunday
morning and by far the coldest air of the season so far.

Anticipating temperatures throughout our forecast area within several degrees
of zero (wind is the equalizer) anytime from midnight through 8 am
Sunday except colder kmpo (near -12f). This has been advertised by
the GFS/European model (ecmwf) 2m temperatures cyclically since at least the 00z/7
operational cycles. Therefore, best chance for record equaling or
exceeding for Valentines day the 14th would be kabe, kttn, kphl
and kmpo.

Snow cover may help a bit I-95 northwestward...and we'll see
where we are with snow cover by Thursday evening. New dustings
appear on the way through Friday night.

Please note... guidance in part is being climatology biased higher than
what the oncoming GFS/European model (ecmwf) literal airmass and 2m temperatures are indicating
for Sunday morning. Temperatures Sunday morning in the urban areas should
be about 25 colder than normal. That means guidance temperatures for phl
of 5 and 6 degrees appear too warm...especially with a normal
Philadelphia low on Sunday of 28.

Have seen the 12z/11 2m temperatures for phl...1 above ranging down to
-11 at kmpo and am liking those values as within 2f of the
upcoming reality.

Record low Max's can only occur for this event on Sunday the
14th, if then. Those have been added recently below.

Site 2015-16 coldest so far record low Feb. 14th ----rer low maximum
---------------------- --------------------

Abe 8 -1 in 1979 14-1979

Acy 10 -6 in 1979 13-1979

Phl 12 +2 in 1979 14-1979

Ilg 12 -4 in 1979 13-1979

Ridge 10 -4 in 1983

Ttn 9 0 in 1916

Ged 13 -7 in 1979

Mpo -1 -12 in 1970

So, this will be wind driven cold with many areas experiencing
wind chill values of 15 to 25 below zero...possibly 30 below in
the hills and mountains of northwest New Jersey and northeast
Pennsylvania.

&&

Phi watches/warnings/advisories...
PA...wind chill watch from Saturday evening through Sunday morning
for paz054-055.
New Jersey...wind chill watch from Saturday evening through Sunday morning
for njz001.
Delaware...none.
Maryland...none.
Marine...gale watch from late Friday night through Sunday morning for
anz430-431-450>455.
Gale Warning until 1 am EST Friday for anz450>455.
Gale Warning until 11 PM EST this evening for anz430-431.

&&

$$
Synopsis...O'Hara
near term...drag
short term...drag
long term...O'Hara
aviation...drag/O'Hara/Gaines
marine...drag/O'Hara
climate...

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