Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
936 am EDT Monday Oct 20 2014
a high pressure system near Norfolk will move offshore today.
A low pressure system with an associated cold front over Lake
Superior will dive southeast reaching our region during the day on
Tuesday. Another low pressure system will form off the middle Atlantic
coast line on Tuesday and then drift slowly northeast, reaching Cape
Cod on Thursday and Nova Scotia on Friday. High pressure will
then briefly move in from the west late Friday. A cold front
should pass through the northeast around Saturday night, with
another high pressure system reaching the Great Lakes on Sunday.
Near term /until 6 PM this evening/...
the frost advisory and freeze warning were expired at 8am. A huge
chunk of our region saw shelter temperatures drop into the upper-
20s to low-30s so we were able to end the growing season in a lot
of places. The counties and zones below indicate where the growing
season has ended as of today.
Berks, Bucks, Carbon, Chester, Lehigh, Monroe, Montgomery, Northampton
In new jersey:
Atlantic (including coastal strip), Burlington, Hunterdon, Mercer,
Middlesex, Monmouth (including coastal strip), Morris, ocean
(including coastal strip), Somerset, Sussex, Warren.
The update this morning looks in good shape. Did bump up todays
highs a couple degrees as we see better warm air advection taking shape. We
should be able to mix upwards of 925mb where 8 to 10c temperatures
advect in by the late afternoon hours. Not much change otherwise.
High pressure will be shifting offshore today allowing a
southwesterly flow at the surface to develop. This flow will be
much less compared to the gustiness that was observed yesterday. A
robust short wave diving southeastward from the Midwest will help
carve out another upper-level trough across the Great Lakes and
Ohio Valley during the course of today. Downstream from this, some
warm air advection is forecast to occur across the middle Atlantic. This combined
with the presence of an upper-level jet will spread areas of middle
and high level cloudiness across the region. The main lift
associated with the amplifying upper-level trough is forecast to
remain to our west, therefore we maintained a dry forecast today.
We did carry some additional cloudiness though for many areas.
Short term /6 PM this evening through 6 am Tuesday/...
an upper-level trough will continue to amplify across the Great
Lakes and northeast. As this occurs, low pressure organizing at the
surface is forecast to be in the general vicinity of the eastern
Great Lakes later tonight.
There is some warm air advection being maintained ahead of this system, but overall
the best focus for this is forecast to be to our south and east. In
addition, a decent shot of low-level Theta-E advection is forecast
to arrive through the night. As the atmosphere moistens and the
large scale ascent begins to overspread the region late, some
showers could develop. This looks to be across our western zones
which is where we have the highest /chc/ probability of precipitation late. There may also
be another area of focus, which is offshore where the leading edge
of the stronger Theta-E advection interacts with some instability
partially due to the Gulf Stream. Overall, the clouds are forecast
to lower some through the night from west to east and the probability of precipitation were
gradually increased as well.
As for low temperatures, with the thickening clouds and a weak
southwesterly flow in place it will be a milder night. Overall, we
used a MOS blend with some minor adjustments.
Long term /Tuesday through Sunday/...
the WRF-nmmb 500mb initialization was better than the GFS or the
European model (ecmwf). The latter was too amplified from the Mississippi Valley
westward. This presents the forecast conundrum as the deep/dt is showing
stronger ridging in central noam vs last night's sounding run. We
seem to be vacillating around a line vs trending steadily in any
specific, consistent direction. East.G. At 78 hours the can
ggem/WRF/GFS/gefs ensemble mean surface lows are stacked on top of one
another. This forecast package is going to go with this consensus
as it includes the better initialized clustering plus there is no
clear cut dp/dt. In the grand scheme, it will not make the middle
of the week pleasant, just a slightly faster improvement than the
European model (ecmwf) has for the latter part.
There is fairly good modeling agreement on Tuesday morning of our
County Warning Area being in a relative precipitation lull between impulses. Probability of precipitation increase
during the afternoon as the primary low pressure system approaches
our County Warning Area and it becomes more unstable aloft. Other than the WRF-nmmb,
other models are not unstable enough for thunder. The 18z WRF was
the most unstable of the 21 sref members in our cwa, so showers yes,
but no thunder. Maximum temperatures close to a stat guidance blend.
On Tuesday night there is still a convective look to the soundings
and instability is forecast to be just offshore. This gets tricky
with the secondary cyclogen as to how quickly will precipitation get generated
plus any leftover convective triggering. The convective element
to it has been producing very little consistency in the quantitative precipitation forecast fields
other than to suggest heavier rain becomes a possibility east. The
secondary development has been in a steady line trending a little
bit slower. So for now while we have likely probability of precipitation across most of
our cwa, we do not have moderate rain mentioned.
Wednesday looks to be the most likely forecast time period for rain,
especially east as our County Warning Area will be in the most divergent location of
the upper level jet and the strongest forecast middle level qvec convergence.
We upped probability of precipitation and are carrying some moderate intensity rain east.
The ongoing secondary cyclogenesis appears to be occurring too close to
our County Warning Area to produce a long enough fetch or period of onshore winds
for tidal flooding. If the low does form farther to the south, the
chances for tidal flooding would increase. We are assisted also that
the moon's perigee does not coincide with the new moon and the
highest Spring tides with this lunar phase are on the weekend, two
days after the new moon.
Models start diverging come Wednesday night as to how much precipitation will
get wrapped into our County Warning Area. The consensus is a longer more circuitous
Route for it to get back into our area. We lose the predicted higher
level moisture and leans more toward smaller rain drops or drizzle
as a predominate ptype. This divergence in the models continues on
Thursday as to how much precipitation can wrap back into our County Warning Area. The
consensus clustering is that most of this will be north of our County Warning Area.
Probability of precipitation were kept as chance, but the persistent NE flow will not make
for too nice a day. By Wednesday and especially Thursday we are
going below stat guidance for temperatures.
Slow improvement the rest of the work week with at least a well
timed break come the weekend. An approaching cold front is not
expected to have any moisture to generate showers. As previously
mentioned a predicted teleconnection switch to a positive ao/nao and
negative pna will bring a milder regime back into the Continental U.S.. not
surprising we are having a precipitation event during this switch either. So
by the weekend fair weather returns along with above normal
Aviation /13z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR, with a ceiling at times mainly at or above 15000 feet.
Light and variable winds, becoming southwesterly and increasing to
around 10 knots.
Tonight...VFR, with a ceiling lowering to between 5000-8000 feet.
Some showers may approach kabe and krdg toward daybreak.
South-southwest winds diminishing to 5 knots, and even becoming
light and variable at some terminals.
Tuesday...some MVFR conditions mainly due to ceilings are possible
during the afternoon.
Tuesday night through Wednesday night...prevailing MVFR conditions
(mainly cigs) with some IFR conditions (mainly due to ceilings again)
should occur. Highest possibilities eastern terminals and airports.
Gustier northeast to north winds expected Wednesday and Wednesday
Thursday...prevailing MVFR conditions. Greatest duration northern
airports and terminals. Gusty northwest winds.
Thursday night and Friday...becoming VFR Thursday night and VFR
Friday. Gusty northwest winds possible.
today and tonight...the conditions are expected to be below Small
Craft Advisory criteria. High pressure shifts to the east allowing a
south-southwest flow to develop. This will be on the lighter side
for much of today, however is is forecast to increase some later
today and tonight for a time. The overall boundary layer flow should
be light enough though to keep the winds below 25 knots. The seas
are anticipated to be at or below 4 feet.
Tuesday and Tuesday night...sub Small Craft Advisory conditions
Wednesday through Friday...a protracted period of Small Craft
Advisory conditions is possible through the period. A secondary low
pressure system development should increase the gradient on
Wednesday and more confidently Wednesday night. Winds and seas
should likely peak on Wednesday night and Thursday with slow
improvement thereafter with Delaware Bay first to loose Small Craft