Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
939 PM EDT Wednesday may 27 2015
high pressure remains off the coast and a cold front will move
across the area Thursday into Thursday night. High pressure
reestablishes itself off the East Coast Friday into Saturday. A
cold front is forecast to move across the area Saturday night into
Sunday. High pressure will return to the northeast early next week
while the front stalls to the south.
Near term /until 6 am Thursday morning/...
a moist airmass continues to advect into the region under a
southerly flow. The exception is along the coast where the dew
points have fallen some due to the marine influence. The level of
moisture present combined with some leftover boundaries should
continue to produce a few showers and even a thunderstorm for awhile
tonight. The buoyancy of the airmass is good given the moisture,
therefore it may just take a little bit of low-level convergence to
pop a shower. The instability is less therefore most should be
mainly showers. As a result, we maintained some low probability of precipitation for many
areas for awhile.
The hourly grids were adjusted based on the latest observations, and
then the lamp/lav guidance was used. We should see patchy fog
develop especially where more notable rain occurred, however we have
lower confidence at this time whether this will have much of an impact and
therefore it was not added at this time.
Short term /6 am Thursday morning through 6 PM Thursday/...
during the daytime Thursday, the previously mentioned surface cold
front is expected to approach our forecast area during the morning
and gradually cross the region through the afternoon to evening.
Similar to Wednesday, an increase in instability is expected during
the day, and with the approaching front and a shortwave aloft acting
as lifting mechanisms, more scattered shower/thunderstorm activity
is anticipated. We begin probability of precipitation a little earlier in the day, during
the morning, for our western zones. Highest chance pops, though, are
focused into the afternoon, before decreasing then into the evening
as the front passes by to the east. Met/mav guidance blended with
continuity yields high temperatures mostly into the middle and upper
80s for the region.
Long term /Thursday night through Wednesday/...
a cold front will be moving across the area at the start of the
period and could have some showers and thunderstorms with it. The precipitation
should be winding down early in the period.
On Fri, high pressure builds back into the region, and dry conds are
Low pressure then advances across Quebec on Sat and its associated cold front
will approach from the west on Sat. There is quite a bit of
uncertainty as to precipitation chances on Sat. The GFS is faster with the
front, and has some precip, mainly north. The GFS is slower and drier.
For now will go with low probability of precipitation. The GFS has cold front passage Sat night, with the
European model (ecmwf) on sun. Showers/thunderstorms will accompany fropa, but there still
remain questions as to the timing.
The front then stalls to the S of the region as high pressure builds
over Quebec. Yesterday, the models had dried out early next week.
Now, they are making it wetter. Again, confidence is low as the
models try to Iron things out. Lowered probability of precipitation a bit yesterday, and
raised them a bit today, but don't want to make any wholesale
changes. Also, some questions remain as to areal extent and
placement of the precipitation.
By Tue, the low move northeastward out to sea and precipitation chances either move
northward (gfs) or decrease (ecmwf).
The forecast is contingent on the stalled front and where it stalls,
whether it washes out and if any waves develop upon it. The models
are having a difficult time resolving the forecast early next week and
as a result, the confidence in this forecast is much below average.
There will likely be some precipitation beyond sun, but where, when, and
to what extent remain big questions.
Temperatures look to start above normal but could be below normal Erly next week
depending on how things play out.
Aviation /02z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Rest of tonight...VFR through much of the night. An isolated shower
or thunderstorm for awhile, however the coverage is rather small to
include in the taf. Some low clouds are anticipated to develop
toward morning, therefore continued with a 1000-1500 foot ceiling.
Some fog should develop, although this may be more likely where the
heaviest rain occurred. Southerly winds less than 10 knots.
Thursday...any low clouds/fog are expected to lift by middle morning,
then VFR. While some showers/thunderstorms should develop during the
day /which may locally reduce ceilings and visibilities/, the timing
and coverage of these is too low at this time to include in the
tafs. Southwesterly winds will gradually become more westerly and
increase to around 10 knots.
Thursday night...generally VFR. Scattered rain showers/thunderstorms and rain early. MDT confidence.
Friday...generally VFR. Isolated showers/thunderstorms possible for
Friday night...VFR early, then lowering ceilings/visibilities possible
overnight. MDT confidence.
Sat...IFR/MVFR possible early, then becoming VFR during the day.
Scattered rain showers/thunderstorms and rain possible which may reduce cigs/vsbys. Gusty
south- southwest winds around 20 knots. Low to MDT confidence on
thunderstorms and rain.
Sat night-sun...sub-VFR conditions possible, especially with
shra/tsra. Low to MDT confidence.
through tonight, some wind gusts to around 25 knots are expected,
along with wave heights in the 3 to 5 foot range for the coastal
waters. We therefore maintain the current Small Craft Advisory
through 10z Thursday. Thereafter, while some wind gusts to around 20
knots may still occur for the coastal waters, mainly sub-Small Craft
Advisory conditions are expected for the coastal waters and for
Delaware Bay through Thursday.
Thu-Sat...sub-sca conds expected, although winds may gust around
20 knots at times.
Sat night...seas may return to 5 feet or greater overnight ahead
of an approaching cold front.
Sun...Small Craft Advisory conds likely with cold front passage.
Marine...Small Craft Advisory until 6 am EDT Thursday for anz450>455.