Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
357 PM EDT Sat Oct 10 2015
a high pressure system will remain across the area this weekend,
before receding offshore on Monday. A cold front is forecast to
cross the region on Tuesday, briefly followed by a high pressure
system on Wednesday. Multiple troughs or cold fronts should
then move through the northeast starting on Thursday.
Near term /until 6 am Sunday morning/...
high pressure centers itself across the area overnight tonight. Any
cloud cover late this afternoon/this evening is expected to clear
out overnight. As the high builds over, winds will diminish across
the area, becoming light and variable/calm in most areas. This will
allow good radiational cooling across the area. Temperatures are
expected to cool enough overnight across the north for areas of
frost to form, especially Carbon/Monroe, Pennsylvania and Sussex,
New Jersey. So we've put these three counties in a frost advisory.
For the next tier down, temperatures may be warm enough for most
places to prevent frost from forming, but we've included patchy
frost as there could be some frost for the more sheltered areas.
Short term /6 am Sunday morning through 6 PM Sunday/...
as high pressure builds offshore, winds will become more
southwesterly for most areas except across the south where winds
will be more variable. During the day across the area. Temperatures
should rebound nicely and end up a couple of degrees above normal in
most areas. Little cloud cover is expected with only some high level
cirrus clouds, and some patchy cumulus possible.
Long term /Sunday night through Saturday/...
a mixed bag initialization this morning with a GFS/NAM combo looking
good at 500mb, the NAM better at 850mb overall (gfs has errors in
both directions) and a GFS/NAM combo best at 925mb with an overall
cold bias with the latter. The deep/dt on the initialization showed
a slight increase in amplitude. GFS ensemble mean and op GFS very
close. The op NAM was about 6 hours slower than the sref mean
(which matched the gfs) with the cold front passage and timing was not used.
The long term will be dominated by ridging along the West Coast
of noam and troffing in the east. Neither's amplitude is robust,
but its enough: at or slightly below normal temperatures will return
to our County Warning Area after a warm start to the long term. In that latter part
of the long term while not necessarily wet, a cyclonic flow aloft
with a series of fronts and troughs will give US some light precipitation
chances as well as some days with cold air advection stratocu and/or self
destruct sun (esp northern cwa).
Sunday night does not appear as much as a slam dunk in our County Warning Area concerning
radiational cooling as tonight will be. But the overall predicted
wind field at and slightly above the boundary layer suggests that
the radiational inversion should form/hold in most places. Cloudiness
associated with the developing southeastern Continental U.S. Cut-off should not be a factor
yet. Thus we went toward the low end of stat guidance for mins
(closer to GFS mos). Given greater uncertainty about US actually
radiating and a slight air mass recovery, additional frost is not
A mild Columbus day on Monday is then predicted. By then our County Warning Area should
start seeing some cloudiness from both the southeastern Continental U.S. Disturbance
as well as the approaching cold front. Full sun macros are into the
70s. We are thus either around (mainly GFS mos) the high end of
stat guidance if not slightly higher based on the predicted
Cold frontal passage precipitation Monday night and Tuesday. While not chocked
full of available moisture, the kinematic support looks stronger than
average given the strong short wave, entrance region of the 250mb jet
and predicted middle level qvec convergence. As pmdhmd mentioned about the
cold front passage dry biases, our probability of precipitation are higher than stat guidance. The
timing is not going to be great and reason we did not up to
likely. Other reality is precipitation may be a trace just as much as a
couple of hundredths. Precipitation associated with the southeastern Continental U.S.
Disturbance has pretty much model consensus now of staying east
of our County Warning Area. Because of the clouds, confidence about Monday night
mins is less than average.
Was tempted to remove more probability of precipitation for Tuesday afternoon, but with most
models showing a double barrel short wave look, want to make sure
we are as dry with the second short wave as they are predicting. By
then, we are losing the qvec and jet support. Tricky maximum temperatures
Tuesday as the cold air advection is not robust, but convective temperatures will be
reached in the cooler air. Maximum temperature projections start drifting
downward during the afternoon. Thus our maximum temperatures are generally
below stat guidance, but not confidently.
Cooler weather will then arrive on Tuesday night and Wednesday. A
short wave predicted to pass through our County Warning Area and convective
temperatures being reached. Models are showing some light measurable precipitation
far north or approaching far north. We added a chance of sprinkles
over the higher terrain. We might see a repeat on Thursday, but
model short wave timing by then is beyond the Legal limit. So we
have more confidence about precipitation chances with the next approaching
cold front on Friday and Friday night. Its a chilly air mass and
we might come close or at least thinking about mentioning snow as
part of a mixed ptype in the Poconos. We started Saturday as a
chilly, but a dry weekend day.
Aviation /20z Saturday through Thursday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy, and surrounding areas.
VFR conditions will prevail through the taf period. Only high level
cirrus clouds expected the rest of today and and again Sunday.
Winds will become light and variable later this afternoon/evening
into the overnight hours as high pressure builds across the area. As
the high builds offshore Sunday, the wind will become more
southwesterly, but remain less than 10 knots.
Sunday night and Monday...mainly VFR conditions. Isolated fog at
more rural airports early Monday.
Monday night through Tuesday...some sub-VFR in passing shwrs,
otherwise VFR conditions.
Tuesday night through Thursday...mainly VFR conditions are
expected. Some gusty west winds possible during the day.
the Small Craft Advisory will remain in effect through 6 PM as seas
on the central/southern waters remain around 5 feet and winds gust
in the lower 20s. Winds will continue to diminish this evening as
high builds across the area, and seas will subside as well. Sub-
Small Craft Advisory conditions will then remain across the waters
the remainder of tonight into Sunday.
Sunday night and Monday...sub-advisory conditions are expected.
Monday night through Wednesday...sub-sca conditions look to continue at
this time, but some wind gusts around 20 knots plus may occur,
especially Tuesday night following a cold front passage.
Wednesday night and Thursday...a second surge of
stronger westerly winds expected, especially later Thursday.
So while sub-advisory conditions expected, we may come close again.
PA...frost advisory from 2 am to 9 am EDT Sunday for paz054-055.
New Jersey...frost advisory from 2 am to 9 am EDT Sunday for njz001.
Marine...Small Craft Advisory until 6 PM EDT this evening for