Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
352 PM EST Friday Dec 20 2013
high pressure offshore of the Carolinas will continue to March
eastward tonight and tomorrow. A weak cold front tries to move in
from the north tonight but stalls to our north while multiple waves
of energy pass along it through Sunday. The frontal boundary should
then move through the forecast area on Monday as the last low
pressure system moves into the Canadian Maritimes. Another Canadian
high pressure system should reach the Midwest on Tuesday and our
forecast area on Christmas day before moving offshore on Thursday.
Near term /until 6 am Saturday morning/...
snowpack will continue to drive some of the more significant weather
impacts during this time period. Have increased the mention of fog
in the forecast, and it will have the potential to be more
widespread and with lower visibilities over northwest portions of
the forecast area. Winds will drop off to near calm over snowpack
with inversion setting up while a light southwest winds is expected
Based on latest radar data and 12z guidance from both hrw-nmm and
hrw-arw models, as well as latest run from hrrr, have trimmed back
precipitation to far northwest zones for the evening period, and then
expanded them a little further south after midnight. Probability of precipitation are
relatively low as are the quantitative precipitation forecast amounts.
Used lav guidance for early evening, and then a met'mav blend for
the over night low temperature.
Short term /6 am Saturday morning through 6 PM Saturday/...
very little change to coverage/probability for precipitation in this
time period. Probability of precipitation are mainly over the northwest third of the area,
and quantitative precipitation forecast amounts are still relatively low.
Used a met/mav blend for the the daytime high temperature.
Southwest wind gradient picks up during the day. Wind speed were
cut back over the snowpack, where the surface inversion will
continue to be an issue.
Long term /Saturday night through Friday/...
the start of the longterm still appears murky in regards to the
advertised warmup we have been forecasting for several days now.
The biggest issue will be how clean of a warm sector can we
accomplish given the strengthening of the low-level jet and
steepening inversion Sunday morning. Given the amount of snowpack on
the ground during the day Saturday, we will likely have melting
taking place leading to fog formation by Sunday morning. This
combined with a moistening southerly flow will throw some low
stratus into the mix which will take quite a while to burn off given
the extremely weak late December sunangle...you have the perfect
ingredients for a high forecast bust potential. Not saying it won't
be warm, just not 70s warm north of southern Delaware-Maryland-Virginia. The only
thing that truly would help reach into the 70s would be a much
stronger low level jet that allows for a bit more momentum Transfer Sunday
morning and could wipe some the stratus out, or not let it form at
all. This will be tough given the models have been weakening the low level jet
the past couple of days.
Besides the record breaking temperatures we still have a meandering
pseudo-cold front to our north to contend with through at least the
first part of next week. The GFS continues to be the outlier based
on the timing of the frontal passage late Sunday night into Monday
while the other operational models show a much slower progression.
As was noted by tg earlier this morning, with the upper level trough
sharpening the system looks to go anafrontal Sunday night into
Monday as moisture surges in late at night, also bringing with the
better instability across our southern zones. We scaled the probability of precipitation
back a bit on Sunday and increased them a bit across the east on
Monday as guidance continues to suggest a final wave moving along
the front...front is now across our southern half or slightly
The flooding threat has not completely diminished Sunday night and
Monday morning though the best quantitative precipitation forecast with this event looks to bisect
the region fairly well. We will continue to highlight our severe weather potential statement for
late Sunday night across the faster responding streams and creeks in
our northern and western zones (where the snowpack currently
exists). The ground is relatively soggy so it should be able to
handle what is thrown at it, unless the snow doesn't melt in time.
Across the south, where the front should be on Monday, we could see
an enhancement with some added convection but given the dry
antecedent conditions flooding looks unlikely.
No big changes then for the rest of the long term. A blustery
Christmas evening followed by a dry and seasonably cold Christmas day.
It could be a cold radiating Christmas morning. A bit of an air mass
recovery should occur on Thursday. Next precipitation shot its in our
Thursday night grid. For now we are forecasting it more like a cold front passage
than what the op European model (ecmwf) has been depicting. The southern stream
system is literally born from convection which lessens the chances
of it being correct. The ec's 12z and 00z ensemble mean have not
agreed with the op run on this given how broad the middle-level
troughing to the west is which should allow for a more progressive
Aviation /20z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Tonight...generally VFR conditions late this afternoon will drop
down to MVFR conditions in fog this evening and IFR/MVFR conditions
in fog after 06z. Winds will be light and variable at kabe and
krdg. Winds elsewhere will be southwest around 6 to 12 knots early
this evening dropping to under 5 knots after 04z.
Saturday...general MVFR/IFR conditions improve to VFR during
Saturday morning. Light southwest winds at 12z become southwest at
10 to 15 knots after 16z.
Saturday night...MVFR to IFR because of ceilings and also visibilities
northwest. Low level wind shear potential.
Sunday through Sunday night...predominately MVFR. IFR at times in
low clouds, fog and precipitation. Strong gusty southwest winds potentially
exceeding 30 kts on Sunday.
Monday and Monday night...predominately MVFR becoming VFR during the
day northwest airports and by evening southeast airports.
Tuesday...VFR conditions with continued gusty northwest winds.
forecast continues essentially unchanged. Small Craft Advisory
continues on the ocean waters for both tonight and Saturday mainly
for seas but with some winds gusts hitting the 25 knot criteria,
particularly on Saturday.
Conditions are expected to remain sub-advisory on the Delaware Bay,
so no advisory has been issued. There will be some wind gusts into
the 20 knot range on Saturday.
No precipitation expected tonight or Saturday.
Saturday night and Sunday...extended the small craft on the ocean
front through Saturday night...for the time being. Conditions look
better for Small Craft Advisory on the Bay later on Sunday...higher confidence. Not
seeing much in the way of gales on our waters at this time.
Sunday night and Monday...high confidence of Small Craft Advisory
for swells on the ocean. Winds should diminish below criteria. On
Delaware Bay, winds and seas are expected to become sub Small Craft
Advisory Sunday night and continue on Monday.
Monday night and Tuesday...another ramp up of potential Small Craft
Advisory criteria winds in the northwest flow over all of the area
waters. Slow improvement late.
daily record maximum temperatures that are vulnerable to be exceeded.
12/21 kged 65-1956 por back to 1949
Kacy 65-1998 por back to 1874
kphl 64-1998 por back to 1872
kilg 64-1998, 1984 por back to 1894
kabe 61-1998 por back to 1922
kttn 64-1998 por back to 1865
kged 68-1949 por back to 1949
krdg 61-1998, 1949 por back to 1869
kmpo 58-1990 por back to 1901
For the month we've taken a look at the records and for the time
being we will only list the vulnerable short period of record
kged 77 set 12/1991. The monthly records for all our County Warning Area long term
climate stations are in the 70s and in most cases featured the
period of 12/4-7 1998. The mpo all time December record is 66.
Marine...Small Craft Advisory until 6 am EST Sunday for anz450>455.