Area Forecast Discussion
Issued by NWS Mt. Holly, NJ-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KPHI 010837
Area Forecast Discussion
National Weather Service Mount Holly NJ
337 AM EST Thu Dec 1 2016
Low pressure will be to our north today and tonight before slowly
moving into the Canadian Maritimes later Friday into Saturday. High
pressure over the Ohio Valley Saturday will move into the Mid
Atlantic during Sunday. Meanwhile, areas of low pressure in the
Midwest and Plains Tuesday will consolidate into one main storm as
it tracks into the Great Lakes later Wednesday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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 /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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/...
The synoptic setup starts with a closed low to our north that
eventually elongates and weakens eastward to the Canadian Maritimes
Friday. The southwestern flank of the trough however pivots across
the Northeast later Friday into Saturday before shifting east. A
rather busy flow regime occurs with several short waves involved.
The model guidance has been having trouble in handling the ejection
of a Southwestern U.S. upper-level low, corresponding to differences
regarding an interaction from the northern stream. As mentioned by
WPC, the 00z GFS, UKMET and CMC provide added support for staying a
little slower than the 12z ECMWF mean with the ejection of the upper-
level low. A deepening trough then in the West results in several
surface lows initially Tuesday, however this should consolidate into
the Great Lakes Wednesday as one storm. This may turn into a rather
potent trough and surface cold front as it shifts eastward. We used
a model/continuity blend Friday through Saturday night, then blended
in the 00z WPC Guidance. Some adjustments were then made following
additional collaboration with our neighboring offices.
For Friday through Sunday...An upper-level trough pivots across the
area Friday into Saturday then shifts east. Some ridging though
arrives Sunday before perhaps a weakening short wave trough arrives
Sunday night into Monday. This feature should be on the weak side,
and therefore kept some low PoPs going Sunday night. The low-level
airmass may remain dry enough to reduce the amount of precipitation
that can occur, however this could allow for a bit of snow across
the north. It will be chilly during this time frame, with a gusty
west-northwest wind especially during the daytime hours. There
should be more cloudiness especially across the northern and western
areas Friday and Saturday. Some lake effect moisture may allow for a
few snow/rain showers or flurries in the Poconos Friday night and
Saturday. We are expecting an increase in the clouds during Sunday
due to a general weak system arriving.
For Monday and Tuesday...This time frame features an amplifying
upper-level trough across the West, which will drive some ridging
downstream. There is the potential for a lead short wave trough that
ejects northeastward from the Gulf coast states well ahead of the
main trough. This would toss some precipitation our way Tuesday as
high pressure sits to our north. This surface high pressure anchored
to our north may provide enough subsidence and low-level dry air to
keep precipitation at bay despite a warm front developing to our
southwest. There looks to be an overrunning scenario potentially
setting up, therefore we will monitor this. Kept Tuesday during the
day dry, then brought in some low PoPs northward at night.
For Wednesday...A storm system organizes and strengthens into the
Upper Great Lakes region. This will push surface high pressure east
of New England with a southerly flow of warmer air surging
northward. It appears that a warm front will be approaching from the
south, with cooler air to its north. There is the potential for some
showers due to warm air advection and lift north of the warm front.
If enough low-level dry air remains longer, then this could set up a
cold air damming scenario north of the warm front.
.AVIATION /09Z 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 through Sunday...VFR overall. West-northwest winds 10-15
knots with gusts up to 25 knots both Friday and Saturday
afternoons, then diminishing Sunday.
Sunday night and Monday...Mainly VFR. Some rain or snow showers are
possible Sunday night into Monday morning, especially to the
north and west of PHL.
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 and Saturday...A cold air advection regime will be in place
during this time frame, however steeper lapse rates Saturday should
provide better mixing. As a result wind gusts from the northwest up
to 30 knots (especially Friday night and Saturday) are anticipated
and a Small Craft Advisory looks to be needed.
Sunday and Monday...High pressure builds in overall with lighter
winds. Therefore, the conditions are forecast to be below Small
Craft Advisory criteria.
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 3 AM EST Friday for ANZ431-450>455.
Small Craft Advisory until 10 PM EST this evening for ANZ430.