Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
210 PM EST Friday Mar 6 2015
an Arctic high pressure system will move across the forecast area
today and then sink south on Saturday. A weak low pressure system
will track to our north late Saturday into Sunday. A weak cold front
should pass across our region Monday. A low pressure system is
predicted to form on this frontal boundary off the North Carolina
coast Tuesday and then move farther offshore. A high pressure
system should then build into the eastern United States on
Wednesday and Thursday.
Near term /until 6 PM this evening/...
with the early afternoon update, only a few adjustments to hourly
temperatures and dewpoints were needed through the afternoon to early
evening period. We mainly used the lav/lamp guidance to edit
these elements, as this data was representative of the latest
observations and trends.
Otherwise, fair weather and cold temperatures today with high
pressure building in from the Ohio Valley. Skies will be clear this
morning...and then there will be some high clouds this afternoon.
High temperatures today will be well below normal...with low/middle
20s north and middle 20s to perhaps low 30s over metropolitan Philadelphia
and over the Delaware-Maryland-Virginia. Winds will be north or northwest at 5 to 10
miles per hour this morning and then become west or southwest around 5 miles per hour by
Short term /6 PM this evening through 6 am Saturday/...
short term... high pressure will continue to remain over the area
tonight. Winds will be lighter than Thursday night and with the ample
snow cover across the region...low temperatures could be as cold (or
perhaps colder) than Thursday nights readings. Presently we have single
digits across most areas with teens along the shore and 12 for phl.
Winds will be light tonight.
Long term /Saturday through Thursday/...
the 500mb initialization looked better off the WRF vs the GFS, overall
they were split at 850mb and both about 1c too cold at 925mb on
average. After having three wintry precipitation events in the first five days
of March, the long term remains relatively more subdued with a much
anticipated return (even if its just for a couple of days) of near
normal temperatures. The one change tonight vs last night is the
increasing chance that a southern stream system might bring some rain
into the region on Tuesday.
The moderating trend will start on Saturday after a cold cold cold
morning. Middle level warm air advection associated with a clipper low pressure
should bring middle and high level clouds into our cwa, especially
north. In spite of this, we went toward the higher set of stat
guidance. Today (friday) will be a good litmus test if stat
guidance cold bias in spite of ample snow cover continues. As far
as snow showers, there has not been much of a change to the
geographical extent of measurable precipitation reaching deeper into our
County Warning Area. Only change we made, was to start the low chance of snow
showers far north on Saturday afternoon.
The weak cold front associated with the clipper should pass through
our County Warning Area on Saturday night. Not much deep moisture to generate
showers. Low chance for snow showers was kept far north. Models are
indicating more low level clouds (possibly trapped under an
inversion north) around and this is reason for much higher mins.
On Sunday, some weak positive vorticity advection and a jet streak are predicted to pass
across our cwa, leaning north. Still too early to tell if we have
the geography straight, the jet streak itself looks more certain. We
put in a chance of flurries north as a proxy. While soundings
suggest lack of ice could be a problem (especially on the moisture
trapped NAM soundings), westerly winds are normally not a freezing
drizzle direction in our area. While colder air (relative to
saturday) is predicted to move into our area, it warms beyond
Saturday at 925mb. Thus reason for bump up in maximum temperatures.
A high pressure system briefly builds into the area on Monday. By
then air mass is even slightly warmer and we expect the snow cover
to be losing its effectiveness on slowing the rise of maximum temperatures.
Change then comes late Monday night and more so Tuesday as all the
runs have trended north with a low forming off the old stalled
front. Unless precipitation flies in on Monday night, thermally it looks warm
enough for rain, especially given south is favored over north.
Faster timing coupled with a more northern extension might be
problematic for ptype. In its wake, an even milder day is
predicted for Wednesday before a Canadian high pressure system
brings colder air back into our County Warning Area possibly as soon as Thursday.
Aviation /19z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
VFR conditions expected tonight and Saturday. Mostly clear tonight
with winds shifting from northwest to west through the early
evening under 10 knots. A general increase in middle and high level
clouds throughout the day tommorow ahead a cold front. Some wind
gusts from 15-20 knots are possible around 18z with moderate
confidence for these gusts.
Saturday night through Sunday...some MVFR conditions due mainly
to ceilings as a weak system moves by later Saturday. However,
any precipitation looks to remain north and west of the
Sunday night through Monday night...VFR overall.
Tuesday...chance of MVFR conditions at southern airports and
terminals. Ptype should be rain.
the Small Craft Advisory for our central to southern coastal waters has been
allowed to expire early this afternoon. Winds for all of our
coastal waters and Delaware Bay will be out of the north-northwest
at 15 knots or less through the remainder of the day, with seas
ranging from 2 to 4 feet for the coastal waters and 1 to 2 foot
seas for Delaware Bay.
Saturday and Saturday night...the conditions are
expected to be below Small Craft Advisory criteria, however the
winds will increase some from the west-southwest during Saturday.
There is a chance for some light freezing spray Saturday morning.
Sunday through Monday night...we are anticipating sub Small Craft
Advisory conditions as a weak front moves through.
Tuesday...there is a chance of Small Craft Advisory conditions
pending the proximity of the track of a low pressure system
predicted to form off the North Carolina coast.
with a snow cover in place and another Arctic airmass settling
into the region and radiational cooling occurring we have another
chance for more record lows across the region.
Acy 10 1888
phl 10 1978
ilg 11 1926
Abe 7 1960
ttn 7 1872
Ged 10 1978
ridge 7 1978
mpo -5 1909
Acy 10 1890
phl 9 1960
ilg 11 1960
Abe 1 1960
ttn 7 1890
Ged 3 1960
ridge 10 1989
mpo -18 1911
It appears that reading and Atlantic City have the better chance
of getting to their record low Saturday morning.
Record daily snowfall for Thursday March 5
Rer's posted for kilg and kacy...both 7.0 inches.
Phl had 7.5 and Allentown 6.7.
Kacy 0.3 - 1960
kilg 3.7 - 1981
kabe 7.0 - 1917
kphl 8.8 - 1981
Fwiw...water equivalence of total snow depth in portions of eastern
PA is now well over 3 inches.