Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
FXUS61 KPHI 301401
Area Forecast Discussion
National Weather Service Mount Holly NJ
901 AM EST Wed Nov 30 2016
Low pressure will slowly track across the Great Lakes today into
tonight, then across southeastern Canada by late Thursday. An
associated cold front will cross our area during tonight. High
pressure approaches later Friday, then settles over our region
during Saturday into Sunday. A warm front lifts to our northwest
late Monday as low pressure lifts into Canada, then a cold front
approaches later Wednesday.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Dense fog continues to impact the region this morning. As the
heavier/steadier rain moves into the area, it should help to lift
ceilings and improve visibilities from fog. As a result of the low
conditions, we have extended the dense fog advisory to last
through noon. Most areas should see improvement by that time,
especially in areas to the north and west of Philadelphia.
Rain will overspread the entire region during mid and late
morning, then shifts to mostly the I-95 region northward during
the afternoon as the little leftover wind shift this morning over
southern DE and far S NJ shifts northwest during the afternoon in
response to the next impulse of strong southwesterly 850mb winds.
Instability is significant enough to put in an isolated tstm this
morning over the Delmarva and s NJ. All this modeled by the SPC
WRF and NSSL WRF.
Thereafter, am unsure about thunder. GFS/EC have good instability
fields of NJ and DE near 21z/30-00z/01 but little in the way of
lift so not much convection may occur at that time in the gusty
southerly sfc flow of 15 to 25 mph. Winds will be light and variable
from KRDG and KMQS northward through the Lehigh Valley and Poconos
into far northwest NJ. Note: could see a burst of 30 mph wind
gusts near 18z in s DE.
A large north to south temperature gradient is forecast late this
afternoon across the forecast area with highs ranging from the
lower 70s (near record KGED) in southern DE to between 50 and 55
from I-80 north. Highs will be generally 15 to 20 degrees above
Fcst temps this aftn may be 1 to 3 degrees too warm from KMQS-
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/...
Showers with maybe an isolated tstm will accompany a cold frontal
passage, probably mostly in the 9 PM to 3 AM time frame tonight.
Clearing from west to east toward sunrise Thursday. Patches of dense
fog possible early tonight near near and north of I-78 where sfc
winds will be light and variable prior to the cfp.
Fcst was a 50 50 blend of the 00z/30 gfs/nam mos leaned toward
the warmer nam.
For qpf totals: I have storm totals of .6 to 1.25 inches. That
might be a tad high.
Lows will generally be around 15 to 20 degrees above normal.
.LONG TERM /THURSDAY THROUGH TUESDAY/...
The synoptic setup starts with a closed low Thursday that eventually
elongates and weakens eastward to the Canadian Maritimes Thursday
night and Friday. The southwestern flank of the trough then pivots
across the Northeast later Friday into Saturday before shifting
east. The flow tries to go more zonal over the weekend, however a
short wave undercutting a ridge looks to move through Sunday night
into Monday. There is however more uncertainty with this feature. As
a trough amplifies across the West later Monday, downstream ridging
builds across our area Tuesday. The western trough looks to amplify
quite a bit across the central part of the nation later Tuesday and
Wednesday, and its eastward progression may be slowed due to this.
As a result, did not rush in an associated cold front as the parent
surface low lifts up into Canada Wednesday. We used a
model/continuity blend Thursday through Friday night, then blended
in the 00z WPC Guidance. Some adjustments were then made following
additional collaboration with our neighboring offices.
For Thursday and Friday...An upper-level trough/closed low from the
Great Lakes to Ontario Canada is forecast to weaken and become
elongated during this time frame. This occurs as a surface low
develops on the triple point just to our northeast as the parent low
north of the Great Lakes gradually spins down. This places a cold
front offshore to start Thursday with cyclonic flow occurring.
Cooling will allow for lake effect precipitation to occur however
the flow looks westerly enough to keep it northwest of our area.
There will be stratocumulus though with this more notable across our
northwestern zones each day (potentially thinning out at night).
A breeze especially Thursday will add some chill to the air. The
axis of the trough looks to pivot across the area Friday night,
however it looks generally dry except for perhaps a snow shower or
flurries in the Poconos.
For Saturday and Sunday...The upper-level trough shifts east early
Saturday with the flow attempting to turn more zonal. Some ridging
though arrives Sunday before perhaps a weakening short wave trough
arrives Sunday night. The guidance is mixed with this feature,
however some solutions suggest it may shear out some as it runs into
a confluence area downstream (the 00z ECMWF is rather wet starting
Sunday night, which looks to phase systems resulting in a stronger
and faster scenario). The shearing out option is seen via some
guidance as a weakening precipitation shield. For now given the
uncertainty, we kept the PoPs on the low side and limited the amount
of precipitation types. There should be more cloudiness especially
later in the weekend with the incoming system.
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,
potentially robust, that ejects northeastward from the Gulf coast
states well ahead of the main trough. This would toss some
precipitation our way Monday into Tuesday as high pressure sits to
our north. As noted above, there is quite a bit of variability in
the guidance with this possible short wave and also timing
differences. The main system may be low pressure running
northeastward from the Plains to the Great Lakes then into Canada.
Given the sharpening associated trough, the eastward progression of
this system might be slowed and therefore delaying any precipitation
for our area. Given much more uncertainty, tried to keep the
forecast closer to continuity.
.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Today...IFR/lifr conds in stratus fog should improve soon after
onset of rain..some of the rain briefly heavy. Thereafter IFR
conditions should improve to MVFR CIGS during mid-late afternoon
KTTN/PHL/KPNE/KILG/KMIV/KACY as southerly winds increase, however,
IFR/LIFR conds in st/fog/periods of rain continue KRDG/KABE.
Thunder potential, especially this morning over the Delmarva to
vcnty KACY but no thunder in the TAFS attm.
Tonight...MVFR and IFR conditions in st/fog and band or two of moderate
to heavy showers with a small chance of thunder. Clearing and eventual
improvement to VFR from west to east after 06z. Low level wind shear
is possible in the evening due the the expectation of a 40 to 50
knot low level southwesterly jet at that time, especially affecting
airfields from KTTN, KPHL and KILG eastward, but not in the TAF
Thursday and Friday...VFR overall. West-northwest winds 10-15 knots
with gusts to 20 knots, however diminishing during each night.
Saturday and Sunday...VFR for much of time. A storm system may
approach Sunday night with some precipitation, however there is
uncertainty with this system.
Dense fog over the nearshore waters continues this morning and is
expected to continue through this afternoon. We have raised a
dense fog advisory for all of our area waters through 1pm. As
steadier/heavy rain moves into the area, conditions are expected
to improve. The dense fog may linger longer than 1pm and we will
reevaluate the need for an extension with the midday update.
otherwise...SCA continues. Added parts of De Bay late today and
tonight. Right now on the Atlantic waters its for seas of 5 feet
or greater but the southerly wind will once again gust 25-30 kt
this afternoon/evening, then gusty westerly late tonight. There
could be an hour of gales either side of the cold frontal passage
tonight handled with an SMW.
A thunderstorm is possible this morning over the DE waters and
then late today or this evening any of the waters but confidence
is below average on thunder occurrence this afternoon and tonight.
Thursday through Saturday...Pressure gradient hangs on enough for
much of this time frame with cooler air, therefore gusts to about 25
knots are anticipated mainly for the Atlantic coastal water zones.
This will keep seas elevated as well. Small Craft Advisory extended
through the day Thursday for now. The conditions should then be
below advisory criteria Saturday night.
Sunday...Winds and seas are currently forecast to be below advisory
criteria due to weaker flow.
For today and tonight...Additional rainfall is expected to favor
the 0.60 to 1.25 inch range.
We are still not expecting main stem flooding or even smaller
basin flooding since these rainfall amounts will be spread out and
the antecedent conditions were rather dry. Poor drainage flooding
is always a possibility especially during heavier rainfall rates
but impacts from this type of flooding are generally minor, except
for travel during the morning and evening commutes.
November based on the following calendar day max min temp.
PHL 64 55. Nov avg 50.0 or 2.4F above normal. Ranked 14th warmest
Nov in the PHL period of record (tied 14).
ABE 57 50. NOV avg 45.9 or 3.2F above normal. Ranked #16 warmest
in the ABE period of record.
ACY 66 54. NOV avg 48.3 or 1.5F above normal. Not ranked top 16.
Daily record High temperatures for today 11/30 where they appear
vulnerable to being within 2 degrees of record.
GED 74 - 2006
Daily record rainfall values for Nov 30.
ACY 1.25 1923
We just missed a record equaling amount for the 29th at ABE by
PA...Dense Fog Advisory until 11 AM EST this morning for PAZ054-055-
NJ...Dense Fog Advisory until 11 AM EST this morning for NJZ001-
DE...Dense Fog Advisory until 11 AM EST this morning for DEZ001>004.
MD...Dense Fog Advisory until 11 AM EST this morning for MDZ008-012-
MARINE...Dense Fog Advisory until 1 PM EST this afternoon for ANZ430-
Small Craft Advisory until 6 PM EST Thursday for ANZ450>455.
Small Craft Advisory from 7 PM this evening to 3 AM EST
Thursday for ANZ430.
Small Craft Advisory from 4 PM this afternoon to 3 AM EST
Thursday for ANZ431.