Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 010700
Area Forecast Discussion
National Weather Service Mount Holly NJ
200 AM EST Thu Dec 1 2016
Low pressure over southeast Canada will redevelop eastward to the
Canadian maritimes by Friday. Its cold front will be crossing the
mid Atlantic states early this morning. High pressure over the
Ohio Valley on Saturday will move into the mid-Atlantic states on
Sunday. Meanwhile, a complex low pressure system stretching from
the midwest to the Gulf of Mexico will impact our weather early
or the middle of next week.
.NEAR TERM /THROUGH TODAY/...
Boundary between modified warm air to the north (Wednesdays max
temps 10F warmer than normal) and the 15-20F warmer than normal
air to the south, never made it past ILG/PHL. it was an overestimation
on the northward push on my part. In this case, the combined
GFS/EC was a little better on handling the area temps on
One more band of showers will race newd through the area between
now and 5 am, then it clears with the variable turning southerly
flow(except gusty southwest flow 30-35 mph along the coastal
plain) shifts to west.
After sunrise...a sunny or mostly sunny starts gives way to
diurnal caa cloudiness with a bkn deck for a time during midday-
afternoon. Gusty west winds of 25-030 mph are expected midday and
afternoon. Temps during the day still warmer than normal.
The forecast - already posted at 1230 AM - was based on a 50 50
blend of the 00z/01 GFS/NAM MOS, favoring the slightly warmer
.SHORT TERM /TONIGHT/...
Clear or mostly clear skies with diminished wind and some radiational
cooling. Lows maybe a couple of degrees warmer than normal.
Forecast basis: a 50 50 blend of the 00z/01 GFS/NAM MOS.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
A cyclonic flow aloft will be maintained over the region through at
least Friday, w/Friday night being the inflection point/transition
to an anticyclonic flow. Mid-level ridging will be prominent across
the area through Saturday night, with the eventual breakdown of the
ridge and subsequent unsettled weather being the primary source of
uncertainty for the remainder of the long term. This uncertainty
derives from the models` handling of multiple shortwave impulses
over the midwest, and the resultant degree of phasing between the
northern and southern streams.
There are two camps of model solutions for Sunday and beyond: GFS
/UKMET/Canadian, and the Euro. The GFS/UKMET/Canadian show minimal
stream phasing, which leads to a flatter eastern conus ridge, and
allows a quick moving clipper-like system to move through the
mid Atlantic Sunday into Monday. The Euro/Canadian indicate a more
robust phasing between the streams, leading to a higher amplitude
eastern conus ridge, and a primary storm system moving from the
lower Mississippi Valley on Sunday to the mid Atlantic in the Mon-
Tue time frame.
A look at both the ECENS and GEFS ensemble means tell a similar
story to the operational runs, with no additional clarification as
to which of the two solutions may be favored. Given the degree of
model disparity, it`s also unrealistic to compromise between the
extremes. Per WPC, the operational ECMWF appears to be the outlier,
so this forecast will lean more toward the GFS/UKMET/Canadian camp.
The end result is the best chance of precip focused in the late
Sunday into Monday period. Temperature-wise, dailies will not stray
too far from their climatological means, ending up near normal.
Thursday night through Saturday night...
The cyclonic flow aloft will eventually transition to shortwave
ridging over the region by Saturday. Friday is shaping up to be
a nice day with dry weather. Cannot rule out patchy fog Thursday
night in the normally prone locations where the boundary layer
decouples more, especially given the recent rainfall. With the
cyclonic flow aloft and westerly downsloping flow off the Great
Lakes, expect extensive stratocumulus across the far northwest,
otherwise mostly sunny. By Friday night, a shortwave swings by
just northeast of the area, with little in the way of moisture
and lift. Just an increase in cloudiness expected, in addition
to the upper jet cirrus over the area. On Saturday, similar to
Friday in terms of sky conditions. Cannot rule out a flurry in
northwest NJ and the Poconos, given greater low-level moisture
and instability across this area.
Clipper-type system approaches the region, but enough short-
wave ridging should be maintained aloft to stave off precip
during the day. At this point, an increase in cloudiness is
expected thru the day.
Sunday night thru Monday...
A weak shortwave moving quickly thru the northwest flow aloft
will traverse the region. There is inherent uncertainty in
the timing of this feature, given it`s over four days out,
but the primary period of impact is expected to be Sunday
night. Given the origins of the system and the absence of
Atlantic inflow (northwest flow), feel the precipitation
will be light, focused northwest of the area closer to the
Great Lakes. The thermal profile is supportive of snow, but
with limited moisture, amounts will be light. The primary
concern is the timing, as a minor shift forward could lead
to impacts for the Monday morning rush hour. Otherwise, a
clearing trend will take hold from southwest to northeast
during the day.
Monday night thru Wednesday...
At this time, fair weather is expected the first half of
this period, Monday night thru Tuesday. As the mid-level
ridge crests over the region late Tuesday, precipitation
could make it into the region as early as Tuesday night.
Model profiles indicate a warming trend, but cannot rule
out some wintry precip, especially at the onset given a
cold air damming signature. Given the time frame, above
average model uncertainty, and borderline thermal profile,
it`s too early to speculate any further on the sensible
.AVIATION /07Z THURSDAY THROUGH MONDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Through 12z...mixed variable conditions in showers, patches of
stratus/fog, becoming vfr CIGS everywhere by 09z. gusty southwest
winds 25-30 kt VCNTY KACy through 08z. otherwise light winds
tending to briefly become south or southwest before shifting to
west and gusty to 20 kt everywhere between 07z-10z subsequent to
an eastward moving cold front.
After 12z today...VFR sct-bkn aoa 4000 ft. Westerly winds will
gust 25-30 kt by 17z.
Tonight...VFR clear with sct cirrus possible late. West winds,
generally under 10 kt.
Friday thru Sunday...Predominantly VFR conditions expected. Winds
out of the west-northwest may gust up to around 20 to 25 knots at
all TAF sites both Friday and Saturday afternoons.
Sunday night and Monday...Predominantly VFR conditions. A brief
period of light snow is possible Sunday night into Monday morning,
especially to the northwest of I-95.
Monday night and Tuesday...Predominantly VFR.
Marine dense fog advisory was just cancelled at 120am. Considering
a GLW for ANZ450-451 but no decision on that til 3am. Otherwise
the SCA continues posted as previously. More at 300 am.
Friday...West-northwest winds expected to be predominantly below
SCA criteria, but cannot rule out a couple of gusts to 25 knots,
especially in the afternoon. This will need to be monitored, and
upgrade to SCA will be needed if more frequent 25 knot gusts are
Friday night and Saturday...Return of SCA conditions in a north-
westerly more likely during this period. A shortwave disturbance
will traverse the waters, leading to cold air advection/steeper
lapse rates, and more efficient momentum transfer. Thus, expect
frequent northwest wind gusts around 25 knots during this time-
frame over the ocean waters, with highest confidence northern
NJ waters (ANZ450-451).
Saturday night thru Monday...some residual SCA wind gusts over
the northern NJ waters possible early Saturday night. Otherwise,
sub-SCA conditions expected.
November averaged 1 to 3 degrees above normal throughout our
forecast area of responsibility.
PHL Nov avg 50.0 or 2.4F above normal. Ranked 14th warmest Nov in
the PHL period of record (tied 14).
ABE NOV avg 45.9 or 3.2F above normal. Ranked #16 warmest in the
ABE period of record.
ACY NOV avg 48.3 or 1.5F above normal. Not ranked top 16.
Georgetown missed equaling their record high by 2F. No matter the
average temperature yesterday at Georgetown DE was 23 degrees
Additionally: Allentown - 1.05 and Trenton-0.95 posted RER daily
Atlantic City`s monthly total of 1.08" tied for 13th driest
November in the period of record.
We will post 24 hour storm totals by 515am.
It`s possible our office will compile 2 day storm totals in a PNS
late this morning, as time allows. We do know widespread 2-3"
amounts occurred to the northwest of Interstate 95.
MARINE...Small Craft Advisory until 6 PM EST this evening for
Small Craft Advisory until 3 AM EST early this morning for