Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
534 am EDT Wednesday Jul 23 2014

Synopsis...
a cold front will approach our area from the northwest today and
cross the region tonight into Thursday morning. High pressure
will build in behind the departing front for the end of the week
into the first part of the weekend. Then, a complex system will
affect the region for Sunday into Monday.

&&

Near term /until 6 PM this evening/...
fair early this morning...patchy IFR fog/stratus has formed over
southern Delaware with scattered clouds developing elsewhere near 5000
feet as the ki builds with a leading edge of instability aloft.

Today...little change from prior forecasts. Model guidance states
widespread lower 90s (near 18c 850 mb and 925mb hottest temperatures are
just west and northwest of our forecast area). Poconos and immediate
Atlantic shore a bit cooler. European model (ecmwf) seems to hold back slightly. The
forecast temperatures issued at 330 am may be a degree too warm.

Heat index upper 90s....close to 100 but no heat advisory issued at this time.

Thunderstorms probably restricted to northwest New Jersey and east central and NE PA after
21z...possibly a second cluster crossing Chesapeake Bay per multi
model ki consensus? Tt 48+ swi -2 ki increasing to 38c vicinity pocs
and east Virginia. Appears to be a see text case...unlikely severe through 00z
due to lack of bulk shear...500mb winds under 30 knots and MLCAPE
closer to 1600j.

Note that there should be cumulus fields forming this morning over nnj
in a leading edge area of ki 33c but with little or no primary
forcing...am not expecting to yield any late morning thunderstorms in nnj
as this leading patch of instability shoves east-northeast to Li by 18z.

Todays forecast basis: NAM temperatures (50 50 blend of 00z/23 NAM metmos and
the NAM 2m temps). Otherwise...other elements a 50 50 blend of
the 00z/23 NAM/GFS guidance in this 330 am issuance.

&&

Short term /6 PM this evening through 6 am Thursday/...
slow southeastward progress of the cold front into the unstable airmass should
yield bands of thunderstorms into the night but not necessarily widespread.
One or 2 thunderstorms could be severe but bulk shear for severe is marginal at
worst and only the tt and some cape allow for modest isolated severe
potential.

Precipitable water 1.8 inches offers a chance of narrow paths of 2 inch rains
beneath the biggest storms.

Lightning strikes might be the big problem?

Forecast basis; 50 50 blend of the 00z/23 GFS/NAM guidance in this 330
am issuance except mostly NAM metmos temperatures.

&&

Long term /Thursday through Tuesday/...
the cold front will be exiting the area Erly Thu, but lingering showers
and thunderstorms are still expected with any instability still around.
The best chances are Erly. Then, high pressure will build in from the
west and dominate the weather pattern through the Erly part of the weekend.

Dry weather is then expected through Sat. As the high slowly moves ewd,
the flow will become more southerly and southwesterly and expect a rise in temperatures
and humidity by the weekend.

Then, by sun, an area of low pressure near the Great Lakes will be moving
eastward. While its exact track is still a matter of debate between the
mdls, they do agree that there will be some kind of double
barreled-low structure by Sun night. There could be a weak cold front passage with
the first low Sun night or Mon, the main cold front passage will be Monday night or
Tuesday with the second low. Again, the details will still need to be
resolved at this time scale, but the sun into Monday time frame could
be stormy depending on how things ultimately play out.

High pressure will build in behind this departing cold front for Tuesday. Temperatures
look to be at or slightly above normal through the pd, until the cold front passage on
Tuesday when temperatures will be below normal. Expect comfortable humidity
Erly in the pd, then increasing humidity in advance of the cold front passage
Erly next week.

&&

Aviation /10z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.

Early this morning before 12z...primarily VFR with scattered clouds at or above
4000 feet. Patchy 2 to 5 Michigan fog possible in the Countryside taf
locations but confidence is less than it was at this time ydy.
Temperature-dewpoint spreads at 5 am are just too large for fog.
Exception southern Delaware to the S tip of New Jersey where IFR ceilings have
recently developed. Light S-SW wind.

Today after 12z...VFR scattered at or above 5000 feet. IFR ceilings may graze kmiv
this morning until 13-14z? Otherwise...briefly broken ceilings near 5000
feet vicinity kabe and krdg this afternoon and chance of a thunderstorm there after 22z
with gusty west wind 30-40 knots. Otherwise non thunderstorm gradient winds
suggest SW wind gust 17 knots this afternoon most taf locations.

Tonight...VFR ceilings with a better chance of brief IFR conds in thunderstorms.
Light SW wind shift north toward morning when patchy IFR St/fog might
form in the frontal zone or where it rains this evening. Strong
gusty west wind in a thunderstorm possible between 00z and 04z for kttn
kpne kphl and kilg but less confidence than for kabe and krdg
outlined in the previous paragraph.

Outlook...
Thursday...MVFR and IFR conditions at times in showers and
thunderstorms, especially early. Patchy fog Thursday morning. Moderate
confidence.

Thursday night through Sat...mainly VFR under high pressure. High
confidence.

Sun...sub-VFR possible in scattered showers and thunderstorms.
Moderate confidence.

&&

Marine...
no headlines through tonight.

Mainly S-SW wind g under 20 knots shift to north toward dawn Thursday.

Wave heights on our ocean waters should be 2 to 4 feet. Waves on
Delaware Bay are expected to be 2 feet or less.

Scattered thunderstorms tonight.

Outlook...
Thursday through Sat...no marine headline expected with high pressure
overhead.

Sun...increasing seas ahead of next system may yield sca, especially
north by later in the day.

&&

Rip currents...
low risk today even if the current 8 second period increases to
10 seconds for a 1.5 to 2 feet southeast swell. The forecast was factored with
a late afternoon strongest south-southeast wind to 15 knots. To be safest...swim
in life guarded areas. The no swimming signs mean just that and
likely were posted because of some sort of highly adverse event at
those locations in the past.

&&

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

&&

$$
Synopsis...nierenberg
near term...drag 535
short term...drag
long term...nierenberg
aviation...drag/nierenberg 535
marine...drag/nierenberg
rip currents...drag 535

National Weather Service Glossary of Abbreviations