Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
636 PM EDT Wednesday may 6 2015
high pressure will build across our area through Thursday. The high
will then build to our east Friday and through the weekend, leading
to a return flow across our region. Low pressure is forecast to lift
through the Great Lakes region early next week and toward the
northeast by Wednesday, pulling a cold front to the East Coast
Near term /until 6 am Thursday morning/...
the water vapor imagery shows fast west-northwest flow aloft near
our area. Meanwhile, a surface front has cleared just about our
entire area as it worked southwestward. This is leaving more of a
marine influenced airmass over our area, thus more stability.
A short wave embedded in the fast flow aloft looks to be glancing
our area this evening. This along with some weak warm air advection near 850 mb may
be assisting the light shower/sprinkle development across the
central part of the County Warning Area. This is generally weakening as it slides
southeastward, however some renewed development is occurring in the
Harrisburg to Lancaster corridor. It appears that any thunder will
remain to our west and southwest where the greater instability
remains this evening.
Any showers should dissipate late this evening, however any subtle
short waves within the flow aloft may be enough to keep a few
showers going overnight. This is of lower confidence as the lift may
not be strong enough or the instability aloft is rather weak. The
hourly grids were adjusted with the latest observations, and then
the lamp/lav guidance was blended in to assist through the
Short term /6 am Thursday morning through 6 PM Thursday/...
Thursday...right now think it should overall average partly cloudy
with considerable convectively driven midday cloud cover. 50 50
blended 12z/6 NCEP MOS guidance temps/dews/winds.
Long term /Thursday night through Wednesday/...
high pressure builds offshore of the East Coast Thursday night into
Friday, and our area will remain on the western side of the high
through the upcoming weekend. Meanwhile, ridging aloft builds over
the area, which will allow temperatures to remain warm through the
upcoming weekend. Temperatures through Sunday will remain close to
10 degrees above normal each day. Mostly dry weather is expected as
there is no strong, discernible short wave/vorticity impulses
forecast to traverse the area around the ridge aloft. However,
with return flow in place and the warm, moistening low levels,
there is be some daytime instability. This could lead to some
diurnal, instability induced showers/thunderstorms, especially
Saturday and Sunday. We have slight chance/chance
showers/thunderstorms possible over the weekend. With the added
low level moisture and stable air overnight, there is the
possibility of overnight/early morning fog development each night
from Friday night through Sunday night.
As we move into Monday, a backdoor type front tries to sag southward
from the north, while the ridge aloft begins to break down and move
eastward. The front may not make it into our area, but will remain
instability across the area. If any vorticity impulses are able to
slide across the area in the southwest flow aloft, the would help
enhance our shower/thunderstorm potential. So we will continue with
low end chance probability of precipitation for Monday.
An broad area of low pressure is forecast to move out of the Great
Lakes Monday night, and into the northeast US/southeastern Canada
through Tuesday. As it does so, it will pull a cold front across the
area. Showers and thunderstorms chances increase from Monday night
into Tuesday/Tuesday night. The most likely period of
showers/thunderstorms would be with the frontal passage which is
currently expected during the day Tuesday.
An area of low pressure off the southeast coast is forecast to
meander near the Carolina coasts through the upcoming weekend. By
the time it starts to move northward, it should get caught up in
the southwest flow aloft and begin moving offshore early next
week. For now it is expected to remain far enough to our south,
but we'll need to watch the forecast over the next several days.
Aviation /00z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight...VFR with a ceiling at or above 4000 feet, which may
scatter out for some areas especially late. A few mainly light
showers moving through mainly this evening. Northeasterly winds 4-8
knots, possibly turning locally light southeast.
Thursday...VFR with cloud bases /ceiling at times/ at or above 4000
feet. Easterly winds 4-8 knots turning south-southeast then
southwest during the afternoon /remaining more southeast mainly at
kilg and kacy due to Bay/sea breeze influence/.
Thursday night-Friday night...generally VFR expected.
Saturday-Monday...generally VFR during the day. Isolated/scattered
showers/thunderstorms each afternoon. Fog/stratus possible
overnight/early morning with reduced cigs/vsbys.
winds and seas should remain below Small Craft Advisory criteria through Thursday.
Northeast /locally southeast/ this evening, then light east-
northeast overnight and turning southeast on Thursday. Seas
generally at or below 2 feet.
Thursday night-Monday...sub-Small Craft Advisory conditions
continue to be expected through the weekend. Winds may gust around
20 knots Saturday-Monday, with seas building to 4 feet.