Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
348 PM EST Thursday Nov 20 2014
a cold front will shift to our east through early this evening, then
high pressure from the lower Ohio Valley will build into our area
later Friday. The high will move offshore Saturday, then a warm
front lifts across our area Sunday night and Monday as a strong low
pressure system tracks into the Great Lakes region. A cold front is
forecast to move through later Monday night and Tuesday, followed by
high pressure late Wednesday and Thursday.
Near term /until 6 am Friday morning/...
a cold front has been slow to move through our region today.
As a result, we were able to get a few hours of more southerly flow
and a few degrees tacked on to the high temperatures. A nice break
from the early season cold. However, tonight with the passage of the
front, winds will go back more northwesterly with another shot of
Arctic air entering the region. A dry airmass will continue to
prevent any chances for precipitation. For temperatures, started
with lav guidance through the evening since it has a better handle
on recent temperature trends. Went at or a touch cooler in spots
with lows, sustained winds argue for warmer lows but the degree of
the airmass may be underestimated by stat guidance.
Short term /6 am Friday morning through 6 PM Friday/...
high pressure will move from the Ohio Valley into our region
throughout the day. Continued dry with mostly sunny skies outside of
the Poconos and northwest New Jersey. Northwest flow will continue with some
moisture off the Great Lakes possibly interacting with the higher
terrain areas. Maintaining some scattered flurries in the grids for northwest
New Jersey and the Poconos. Modeled two meter temperatures and 850/925 mb temperatures
along with met and mav guidance sets show our region only having the
potential for highs in the middle 30's on Friday. Given the strong caa,
that seems reasonable.
Long term /Friday night through Thursday/...
the overall synoptic setup features a pattern change, which is a
result of energy driving across the southwestern U.S. Friday night
which ejects into the Southern Plains Saturday. This will allow
downstream ridging to push eastward as an upper-level trough lifts
out of the east. The southern energy looks to amplify an upper-level
trough across the central portion of the nation early next week,
with the potential for a deep cyclone tracking up across the Great
Lakes region. This trough eventually arrives in the east late
Tuesday and Wednesday, although it may deamplify into Thursday. We
used a model blend overall for Friday night through Sunday, then the
12z wpc guidance thereafter. Some adjustments were made following
additional collaboration with our surrounding offices.
For Friday night and Saturday...a pattern change gets underway as a
strong upper-level trough lifts out of the northeast through Friday
night. As this occurs, strong high pressure at the surface is
forecast to settle nearly right over the middle Atlantic Friday night
before shifting offshore during Saturday. This should result in good
radiational cooling conditions Friday night. As the upper-level
trough departs, the flow is forecast to start backing allowing warm air advection
to get underway. This ribbon of warm air advection along with an increase in the
flow just to our northwest especially will team up with a weakening
surface frontal boundary. This thermal boundary is more defined
around 850 mb though and there appears to be enough lift to generate
some light quantitative precipitation forecast around the Great Lakes. Some of this may settle
southeastward during Saturday night before weakening. Given the
warming aloft, any light quantitative precipitation forecast that can get to our far north/northwest
zones could be a little freezing rain. This looks like a low
probability at this time along with low confidence and therefore kept probability of precipitation
at 30 percent or less. The southwesterly flow along with the warm air advection
will allow some moderation in the surface temperatures Saturday,
although there should also be high cloudiness around.
For Sunday and Monday...an amplifying upper-level trough across the
plains and Midwest will drive a deepening surface low into the Great
Lakes region late Sunday and Monday. Downstream, increasing warm air advection and
Theta-E advection will combine with an area of large scale lift to
produce some rain. This will be with a warm front lifting north
Sunday night and Monday. This should be aided by an increasing
low-level jet, and it is possible that some convective elements
develop within the overrunning regime with a warmer and more moist
airmass surging northward. As the deepening surface low tracks
across the Great Lakes Monday, a cold front should arrive in our
area late. However, a dry slot looks to overspread our area during
Monday therefore after some early rain the chance of lingering showers
looks on the low side. We carried categorical probability of precipitation Sunday night,
then these taper down rapidly around daybreak Monday. Given the
strong low-level flow and warm air advection, a surge in the surface temperatures
are anticipating with some areas nearing 70 degrees for a time
despite being the second half of November. The record highs for
Monday are mainly in the upper 60s to lower 70s, and if we can get
enough sunshine and mix decently then some spots could have a shot
at these records.
For Tuesday through Thursday...a cold front is forecast to
be shifting gradually offshore and this will allow cold air advection to kick in as
the upper-level trough arrives. The actual trough axis looks to
remain to our west, and this could slow the front down as it eases
offshore. Some short wave energy rounding the base of the trough may
induce a surface low along the front. This feature however looks to
track offshore though Tuesday into Wednesday. We mostly followed the
12z wpc probability of precipitation during this time frame.
There becomes more uncertainty with the upper-level trough moving
across the east, due to what occurs across the west. Some guidance
shows a much stronger trough digging across the east late Wednesday
and Thursday. As of now, we went much closer to the 12z wpc guidance
which favored a blend of continuity and the European model (ecmwf) mean for
Wednesday and Thursday.
Aviation /21z Thursday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Only scattered middle-level clouds are expected through Friday.
However, the main story will be gusty winds. Sporadic gusts around
25 knots have occurred this afternoon and will continue gusts in the
tafs through 22z. The environment is favorable again Friday for
afternoon wind gusts around 25 knots. The wind direction will be
more north of west on Friday around 300 compared to the south of
west today around 250/260.
Friday night and Saturday...VFR, with some increase in high level
clouds late Saturday. Northwest winds less than 10 knots Friday
night becoming southwest, then southwest around 10 knots during the
Sunday and Monday...VFR for awhile Sunday with an increase in
clouds, then ceilings lowering to MVFR /potentially IFR/ Sunday
night into Monday as a period of rain moves across the area. The
ceilings may improve to VFR during Monday although a few showers may
linger. Southwesterly winds may gust to around 20 knots each
afternoon. A period of low-level wind shear may occur Sunday night
into Monday as a low-level southerly jet around 50 knots moves
Tuesday...mostly VFR with a shower possible especially closer to the
coast as a cold front shifts offshore. The winds becoming
seas will continue to be at or over five feet through a good
portion of Friday. Once again the potential is present for gusty
west to northwest to increase tonight to around 35 knots with the
highest chance from 07-11z. Some uncertainty is present in exactly
when the winds will start to slacken off between 12 and 16z Friday.
Given the uncertainty will only have the Gale Warning go to 12z Friday
at this time.
Friday night and Saturday...some gusts near 25 knots Friday evening,
then generally the conditions are anticipated to below Small Craft
Advisory criteria. An increasing southerly flow however may allow
wind gusts to near 25 knots Saturday night.
Sunday and Monday...a strong south-southwest low-level jet is
forecast to move across the area Sunday night into Monday. This will
be associated with a warmer airmass that is moving in, which tends
to not allow for a favorable mixing setup. Therefore, kept gusts
below gale criteria. Given the southwesterly flow, did go below
wavewatch by about a foot as it tends to overdo the seas within this
Tuesday...the winds are anticipated to be below advisory criteria,
and the seas should be subsiding below 5 feet.
a strong offshore flow will develop over the area as the cold front
moves off the coast. This flow will create low water conditions
along the coast and associated inlets tonight through Friday
afternoon. There is even some concern for blowout tides near the
time of high tide...which tonight occurs within an hour either side
of midnight along the coast...and later tonight in the Delaware Bay.
Dbofs and cbofs indicate water levels getting within a tenth of a
foot or so of blowout conditions (minus 1.8 feet mllw), while
etsurge guidance is not nearly as aggressive. Based on the fact that
one model is just barely bringing US to blowout conditions and
another isn't so close, we will hold off on any statements at this
point in time. We will obviously be watching the situation this
evening and issue later statements, if necessary.
Marine...Gale Warning from midnight tonight to 7 am EST Friday for
Small Craft Advisory until 6 PM EST Friday for anz430.