Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
356 PM EDT Friday Jul 25 2014
surface high pressure, overhead, will move offshore on Saturday
setting up a return flow. A warm front crosses the region late on
Saturday while the parent low pressure system moves through the
Great Lakes. The attendant cold front swings through late on Sunday
into Monday followed by another high pressure system.
Near term /until 6 am Saturday morning/...
the WRF-nmmb initialization did look better than the GFS at 500mb,
especially upstream. At 850mb and 925mb it was a mixed bag between
the models, but nearly all errors that there were, were 1c. No big
changes in the models deep/dt from yesterday. The best of this air
mass is now behind US.
A pocket of higher dew points at 850mb over New Jersey corresponded to the
convective temperature being reached. Just looking at how the cumulus field is
already gasping shows how long it will last (not at all) into this
Tonight is a flip of last night as the evening should be the clearer
half before high clouds from the former and ongoing mesoscale convective system in the
Midwest work their way into our County Warning Area overnight. The WRF-nmmb
especially and the GFS somewhat also take some of the lower level
moisture in southwest Virginia and advect it into our County Warning Area late
tonight. Dont see much Omega at that level, so emphasis remains more
with the high clouds. That being said, we had temperatures drop overnight
in the more traditional typical fashion. Dew point errors today have
been too low and they are rising to the Lee of the sea breeze front.
So we did not buy into the lower radiational cooling mins on stat
guidance for this reason.
Short term /6 am Saturday morning through 6 PM Saturday/...
confidence is not high in either direction about convection and the
end result for now is a rather generic vanilla summer's day forecast
The models have been pretty consistent in pooling dew points as
Saturday progresses in our County Warning Area. Partly because of the aforementioned
short waves and also looks to be some surface wind convergence. They
actual spike upward has become more logical from yesterday where
some of the model forecast surface dew points were reaching the middle 70s.
Still MOS guidance is forecasting dew points 5 to 10f lower than
their own model guidance. This plus teetering close to the edge of
the available cape for thunder and whether or not the cap would
hold. Given the short waves aloft, thinking the cap wont. This leaves
the dew points. If they dont get into the middle 60s along the coastal
plain, chances are there wont be enough cape. North and west there
is always the orographic influence that may compensate for lower dew
points. Modified sounding convective temperatures are predicted to be
reached, so we did expand the mention of during the afternoon
thunder geographically. Conversely since most mesoscale models are
converging south and east toward the higher dew point pooling, we
did lower probability of precipitation in the northwest part of our County Warning Area.
Predicted 1395 1000-850mb thicknesses are not buying maximum temperatures as
high as they have done in past Summers. Full sun macros look
overcooked and maximum temperatures were kept closer to 10-11c over predicted
925mb temperatures. This is close to stat guidance and continuity. GFS
thermal guidance went down about 1-2c from thursday's levels at or below
Long term /Saturday night through Friday/...
Sunday...a decaying mesoscale convective system should be diving well to the southwest of
our region as one middle-level shortwave cruises through. Surface warm
front should be lifting through during the early part of the morning.
Moisture will continue to increase with a southwest surface flow
with precipitable waters exceeding 1.5 inches. Early morning showers and
thunderstorms should be waning by late morning as most of the
operational guidance shows the region breaking out. Not quite sure
how long lived the break will be as convective temperatures should
easily be met as highs approach 90f so we continue with chance probability of precipitation.
Better forcing moves in aloft with a much stronger shortwave and
approaching cold front later on Sunday. Better height falls, shear
profiles and less capping should allow for much more organized
convection to occur. Storm Prediction Center has US in day 3 outlook at this time so
will continue with the severe weather potential statement highlighting.
Monday...cold front will continue to move through the region, though
not at a blistering pace. Weak surface cyclogenesis is possible on
Monday as the front sits just to our east so we keep chance probability of precipitation
in place during the day. Temperatures should end up being around
average across the east and slightly below across the west.
Tuesday - Thursday...drying trend should commences across a majority
of the region, but with the middle-level trough/cold pool aloft, and
the slightest hint of instability around, isolated showers are
possible on Tuesday...better further north. The chances for
showers decreases each afternoon thereafter. Temperatures should
end up being below normal for late July standards.
Aviation /20z Friday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
18z tafs continued VFR forecast.
Rest of this afternoon few to scattered VFR cumulus with the
greatest concentration at New Jersey terminals and airports.
A sea and Bay breeze fronts have formed. The sea breeze front has
made decent progress and is already from Bridgeton to Hammonton to
Jackson and Middletown in New Jersey. The Bay breeze is harder to discern.
This front should continue to move northwest with a weakened version
predicted to get to the kphl area airports between 23z and 00z. Wind
speeds even behind the front should be 10 knots or less. Preceding the
front and at other terminals light west to southwest winds will
For tonight winds will become light and variable, southwest if
there is a direction. The cirrus in the tafs is more for the
second half of the night. No fog is expected to form.
On Saturday. VFR ceiling expected. Most of the remaining taf time it
should be at the altocu level. Southwest winds will be increasing
as the morning progress. Winds in the last forecast group represent
more of the latter half of the morning/early afternoon
Isolated showers and thunderstorms should occur, but coverage for now
appears too small and likely after 18z to include in any
terminals. Confidence too low for kphl inclusion.
Sunday - Monday...sub-VFR conditions expected in areas of showers and
Tuesday - Wednesday...VFR.
sea and Bay breeze flow should dominate the nearshore and Delaware
Bay waters into this evening before winds becoming lighter
The high pressure system will be moving offshore and a slightly
stronger synoptic scale return flow is predicted for Saturday. As is
typically the case, model guidance over the waters is normally
overdone in cases like this and winds and seas were kept below Small Craft Advisory
criteria through the day on Saturday.
Sunday...sub-sca expected with scattered showers and thunderstorms.
Monday...seas may build to Small Craft Advisory levels under a strengthening
southwest surface flow.
Tuesday - Wednesday...sub-sca conditions expected.