Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
936 PM EST Monday Dec 9 2013
a low pressure system is starting to form over the Carolinas. It
will move northeast out to sea Tuesday afternoon and yank in
colder air behind it Tuesday night. High pressure will then build
into the region from the west during middle and late week before
shifting into the western Atlantic Saturday. Low pressure and a
new cold front are slated to move across the Middle Atlantic States
late Saturday. Canadian high pressure should follow...arriving in
the northeast United States early next week.
Near term /until 6 am Tuesday morning/...
no big changes will be made with this update. Overall the nod to
the model that is verifying the best with the mass fields off the
00z soundings and 00z surface analysis GOES to the European model (ecmwf). The WRF-nmmb
overall was slow. If anything forecast errors at 925mb and 850mb were
around 1c too warm, so trending toward less mixing potential.
We are just getting into the rap and hrrr's time frame and they
are showing multiple banding potential on Tuesday in both PA and New Jersey.
The European model (ecmwf) and the Canadian model outputs favor New Jersey and Delaware more so
than Maryland and PA. Nevertheless all of the models are showing a quick
hitting snow event with a couple of hours of heavy snow where
these bands develop. Sref mean snowfall for phl has settled in at
3.6 inches. Sref snowfall probability of precipitation do favor the highest amounts east
In the interim, laps forecast soundings are showing plenty of dry air
and wind just above the boundary layer. The former will evap cool
the +6c air over phl at 800mb to snow while the latter should help
disperse the fog overnight.
We did not make any big changes to temperatures and dew points. Given
that the precipitation is racing out of Mississippi, we kept the present
timing as it looks as though precipitation should advance and develop
quickly come Tuesday morning.
We'll be in a lull most of tonight, between yesterday's snow and
what's to come tomorrow. Impacts tonight will be associated with fog
and restrictive visibilities and sub-freezing temperatures that
could refreeze what's currently on the ground.
Temperatures will fall into the lower 20s across the northwest zones
and into the upper 20s elsewhere.
Precipitation will be reentering the picture tomorrow morning.
Things could start to ramp up prior to 6am. Soundings suggest all
snow at the onset except for our southern counties where some
freezing rain and sleet is possible. The morning rush could be
impacted, although it appears, at least at this time, that when you
get north of Delmarva, the onset of precipitation will commence
during the second half of the commute.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
winter storm warnings and winter weather advisories have been
issued. Although banding predictability is fairly low, models are
pointing to the i95 corridor at this time.
800 mb-700 mb forcing is in place tomorrow morning as well Omega. Decent
snow growth is forecast and we're under the right rear of the 300 mb
jet. The feeling is...there will be at least moderate snow for a few
hours that will compensate for a daytime snowfall with temperatures
We like 3 to 5 inches across the i95 corridor and that's what is in
the west-southwest. Our graphics on the web will display 4 to 6 inches, with 3
to 5 not being an option. Less amounts should fall across the far
northwestern zones, the far southern zones and right along the coast.
The GFS quantitative precipitation forecast is on the high side of the spectrum while the Euro is on
the lower side. We're in the middle.
Long term /Tuesday night through Monday/...
500mb: a broad trough in eastern United States sharpens up a bit
Thursday as short waves move through the base of the trough. Ridging
follows Friday and then we wait to see how the middle week closed low
near baha California interacts with the northern stream for next
weekend. Lots of uncertainty in the models for next weekend which
includes temperatures...ptype and storm track. Troughing developing in
the eastern USA makes it probable that some sort of precipitation
should develop here next weekend.
Temperatures: much below normal cold for portions of this extended
period with calendar day average values expected to be 10 degrees or
more colder than normal Wednesday through Friday and possibly again
next Monday with fridays temperatures possibly 15 degrees below
normal! The mildest days should be Saturday and or Sunday.
Forecast basis... Tuesday night-Wednesday night is a 50 50 blend of the 12z/9
GFS/NAM MOS. Thursday is 100 percent 12z/9 GFS MOS and then Thursday night-
next Monday is the 1522z/9 wpc extended grids. This data is checked
against the 12z/9 European model (ecmwf)...modified and noted in the dailies when
significant. The 09z/9 sref was checked for probability of precipitation within its forecast
range the 12z/9 gefs 6hr probability of precipitation for .05 were checked for the extended
The dailies below...
Tuesday night...clearing and colder with freeze up of the Tuesday snow
event. Wintry looking night-scape. A bit of an added wind chill
Wednesday and Thursday...potential for bursts of snow showers
near and north of i80 in NE PA and northwest New Jersey as the southern extent
of windex events are suggested by the guidance to graze the northern
portion of our forecast area. The short waves are sending in bursts
of colder air in general west-northwest flow and you could argue that a secondary
cold frontal passage can occur Wednesday night. Blustery day times.
Overall south of i80...p/c...possibly a flurry or 2. The wci may
drop to 10 below zero in the Poconos Thursday night.
Friday...cold interlude with increasing clouds possible?
Next weekend...potential for periods of wintry precipitation...especially
Saturday...depending on surface low evolution on a new cold front
crossing eastward from the Appalachians. Right now our forecast is
hinged completely on wpc guidance. Its categorical that it will
precipitate but confidence on details including temperatures and ptype is
well below average.The forecast drawn up focuses precipitation on Saturday ending
Next Monday...blustery and cold...at least to start. The wci may
drop to 10 below in the Poconos early Monday but confidence on
cold temperatures Monday is less than the high confidence forecast for
Aviation /02z Tuesday through Saturday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Overnight...the 00z tafs have been issued. It appears the the fog
and lower clouds may remain for a bit longer than earlier forecast.
Some breaks are beginning to show up on the 11u-39.U satellite
images across the Delaware-Maryland-Virginia and southern New Jersey. We pushed back the return
to higher conditions to 05-06z for many sites.
Tuesday...MVFR will quickly transition into IFR as snow settles in
across the terminals. We tried to refine this somewhat in the 00z
tafs and indicated that it may be a hour or so earlier than
before. A period of LIFR is possible in some heavier snow. Some
improvement, maybe back to VFR, possible later in the day.
Tuesday night...VFR northwest wind gust to 20 knots. Confidence above average.
Wednesday - Thursday...VFR scattered-broken at or above 3500 feet. Chance of a flurry
except a few periods of MVFR or IFR conds in snow showers Arkansas
possible in the Poconos. West-northwest wind g 20-25 knots each afternoon.
Confidence above average. I did raise 12z/9 NCEP MOS guidance by
about 4 degrees primarily because of still relatively mild 850
temperatures and the 12z/9 UK and ec 2m temperatures.
Friday...VFR ceilings. Wind turning west or southwest in the afternoon.
Saturday...MVFR or IFR conds probable in precipitation.
tonight...no headlines with diminishing winds and seas in the 2 to 4
Tuesday...both northwest winds and seas will begin to build later
tomorrow. Guidance suggests that Small Craft Advisory conditions will be back in
place late tomorrow afternoon or early tomorrow evening.
Tuesday night - Thursday...a fairly tight gradient will persist with
periods of gusty winds to 25 knots and end of westerly fetch seas on
the Atlantic near 5 feet. We may have near gale force gusts Tuesday
night and Wednesday morning, especially across the northern ocean
waters. Small Craft Advisory has been started. An extension probable and it may
need an upgrade to a marginal gale in later forecast for a portion of Tuesday
Friday...winds and seas should subside below Small Craft Advisory
levels as high pressure builds across the region and remain below
as we end the work week.
Saturday...an Small Craft Advisory is possible. There is model spread on the
solutions but its even possible we'll need a southerly gale for a portion
of the Atlantic waters. This part of the forecast is very low
PA...Winter Weather Advisory from 6 am to 5 PM EST Tuesday for
Winter Storm Warning from 6 am to 5 PM EST Tuesday for paz070-
New Jersey...Winter Weather Advisory from 6 am to 5 PM EST Tuesday for
Winter Storm Warning from 6 am to 5 PM EST Tuesday for
Delaware...Winter Weather Advisory from 6 am to 5 PM EST Tuesday for
Winter Storm Warning from 6 am to 5 PM EST Tuesday for dez001.
Maryland...Winter Weather Advisory from 6 am to 5 PM EST Tuesday for
Winter Storm Warning from 6 am to 5 PM EST Tuesday for mdz008.
Marine...Small Craft Advisory from 5 PM Tuesday to 6 am EST Wednesday