Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
229 PM EDT Wednesday Aug 20 2014

Synopsis...
low pressure in Great Lakes region will weaken as it moves to near Lake
Ontario Thursday. A second area of low pressure will develop near
the Chesapeake Bay Thursday night. High pressure in eastern Canada
will build down along the East Coast later this weekend into next week.

&&

Near term /through tonight/...
a weak short moving east-southeastward through northern PA should shove the band of
showers and isolated thunderstorms in central PA eastward into parts of our
area this evening and tonight with a tendency for the band to
probably diminish during the night. Still a precipitable water of 1.5" plus
permits some of the showers this evening to be potentially briefly
heavy in east PA.

Forecast basis: probability of precipitation were blended NCEP MOS probability of precipitation with the 09z sref and
that gives the best chance for some needed rain to east PA. Otherwise a 50
50 blend of 12z/20 NCEP MOS except blended rgem sky with NAM sky
and GFS MOS guide.

Near or slightly above normal temperatures.

&&

Short term /Thursday/...
Thursday...another short wave in the west-northwest flow over southern New
York state should redevelop heavy convection during the afternoon over
east PA...possibly extending into west New Jersey and the Maryland East Shore closer to the
convergence of the surface low and inverted trough extending northward from
the vicinity of dca. Precipitable water values are generally forecast around
1.5-1.75 inches, so some showers/storms could produce a period of
moderate to heavy rainfall. Isolated small hail not impossible as
tt near 50 in area of maximum instability in New Jersey (near the Delaware
river).

Forecast basis: probability of precipitation were blended NCEP MOS probability of precipitation with the 09z sref and
that gives the best chance for some needed rain to east PA. Otherwise a 50
50 blend of 12z/20 NCEP MOS except blended rgem sky with NAM sky
and GFS MOS guide.

Near or slightly above normal temperatures.

&&

Long term /Thursday night through Tuesday/...
the long term forecast starts off with rain chances, before a drying
out period sets in across the area.

Thursday night...a second area of surface low pressure is forecast
to develop near the Chesapeake Bay along the stationary boundary
to our south. It is possible that this may help keep a focus for
precipitation Thursday night, before it sags to our south.

For Friday into the weekend, the middle/upper low will remain to our
northeast, keeping a northwest flow aloft across our area.
Meanwhile, high pressure will begin building down across the East
Coast from eastern Canada. Before the high takes full control of the
weather, there will remain a chance of scattered showers Friday and
Saturday as there may be a few short wave/vorticity maxes that affect the
area in the northwest flow aloft.

By Sunday into early next week, the surface high builds further into
the middle-Atlantic region, which should bring dry weather to the area.

Highs are expected to start out close to or slightly above normal
Thursday into Friday, but as the high builds down out of eastern
Canada and the northwest flow aloft remains across the area over the
weekend, 925/850 mb temperatures and thicknesses lower. This will allow for
slightly below normal temperatures over the weekend. As we move into
early next week, we should start to get more of a return surface
flow and ridging aloft begins to take place once again, allowing
for rebounding temperatures.

&&

Aviation /19z Wednesday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Rest of today...VFR scattered-broken at or above 4000 feet. Light southeast to S wind.

Tonight...VFR ceilings at or above 4000 feet spread eastward during the night with a
period of showers possible. Light south wind.

Thursday...generally VFR ceilings. Light south wind. Scattered showers
and thunderstorms which may lower ceilings/visibilities to briefly IFR conditions.

Outlook...
Thursday night...generally VFR. Chance of showers and thunderstorms
which may lower cigs/vsbys.

Friday-Sunday...periods of low end VFR or MVFR ceilings possible with a
chance of showers, especially Friday into Saturday.

&&

Marine...
no marine related headlines through Thursday.

East-southeast winds between 5-15 knots.

Outlook...
Thursday-Friday night...sub-Small Craft Advisory conditions expected.

Saturday-Sunday...seas may begin to approach Small Craft Advisory
levels as a long fetch develops around high pressure building in
from the northeast out of eastern Canada.

&&

Climate...
we are aware how dry its been recently in far northern New Jersey...i80
north and in fact 70 to 90 percent of normal there the past year and 5 o
25 percent of normal there the past month. Whatever rainfall occurs there
needs to develop between tonight and Friday evening...otherwise we probably
need to wait until the end of next week.

&&

Phi watches/warnings/advisories...
PA...none.
New Jersey...none.
Delaware...none.
Maryland...none.
Marine...none.

&&

$$
Synopsis...drag/Robertson
near term...drag 229
short term...drag 229
long term...Robertson
aviation...drag/Robertson
marine...drag/Robertson
climate...

National Weather Service Glossary of Abbreviations