Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Mount Holly New Jersey
346 PM EDT Wednesday Jul 29 2015

Synopsis...
high pressure will continue to move offshore tonight. A weakening
cold front will slowly move through our region on Thursday night.
The next weak cold front should cross our area late Saturday into
Sunday, followed by high pressure early next week. A potentially
stronger cold front is expected to arrive on Wednesday.

&&

Near term /until 6 am Thursday morning/...
there were scattered showers and isolated thunderstorms in
northeastern Maryland, Delaware and on Delaware Bay at middle
afternoon. As the convection continues to turn over the atmosphere
in those areas, the shower and thunderstorm activity should diminish
as we get into the early evening hours.

A middle level ridge axis is forecast to be overhead this evening and
it should continue to drift eastward overnight.

We are anticipating the daytime cumulus to diminish this evening
with just some high clouds overhead early tonight. Most of the model
guidance is suggesting that some remnant convection from Virginia
and vicinity will drift northeastward and over our forecast area
late tonight. As a result, we have indicated an increase in cloud
cover along with a chance of showers at that time.

Conditions will remain very warm and humid overnight. Minimum
temperatures should be mostly in the 70s with a light southwest wind.

&&

Short term /6 am Thursday morning through 6 PM Thursday/...
Thursday is forecast to begin with a mostly cloudy sky along with
some lingering rain showers. The clouds are expected to decrease for
the late morning and early afternoon hours before the convection
associated with the frontal boundary approaching from the northwest
arrives in our region.

We are anticipating that showers and thunderstorms will begin to
spread into our northwestern counties around 200 to 300 PM on
Thursday. The precipitation will work its way southeastward,
reaching the Interstate 95 corridor about 400 PM to 500 PM and the
coast toward 700 PM. Precipitable water values are forecast to
increase in excess of 2 inches so we will continue to mention the
potential for heavy rainfall. Also, some of the more well developed
thunderstorms may bring strong wind gusts.

We are expecting high temperatures near 90 degrees in much of our
forecast area. The air will remain very humid and heat index values
should reach the middle and upper 90s before the afternoon showers
and thunderstorms arrive. As a result, we will keep the excessive
heat warning in effect until 600 PM Thursday for our highly
urbanized areas along the Interstate 95 corridor.

A southwest wind around 10 miles per hour is anticipated for Thursday.

&&

Long term /Thursday night through Wednesday/...

Overview...

A closed middle-level low over hudson's Bay will maintain a trough
in the east Continental U.S. And a general cyclonic flow aloft through the
period. There is some model disagreement regarding shortwave energy
entering the Great Lakes region on Sunday...and to what extent the
trough amplifies as a result. The European model (ecmwf) is more amplified than the
GFS...which results in more tropical moisture moving into the
region...associated with low- pressure development in the greater Mexico. A
lot of uncertainty here at the d+5 time frame. The best chances
for precipitation will be with a cold frontal passage on Sat...and another late
Tuesday/early Wednesday. Above normal temperatures expected through the period.

Details...

Thursday night...cold front will slowly move offshore...as a wave
of low pressure develops along it in vicinity of the Outer Banks. This
will result in chances for rain showers/thunderstorms and rain through much of the night over
Delaware-Maryland-Virginia. With precipitable water values of 1.5 to 2 inches
and slow storm motion...the main concern will be heavy down-
pours. Conditions will also be favorable for the development of
some patchy ground fog in the normally prone locations.

Friday...shortwave ridging aloft along with a very dry air mass will
result in a mostly sunny day. Convective temperatures may be out of
reach...so even cumulus may be few and far between. The gradient
may weaken enough for a sea-breeze development late in the
afternoon. Maximum temperatures will be in the 80s west/ l90s in Delaware-Maryland-Virginia along
with a noticeably less humid air mass.

Sat through sun...thunderstorms are possible over the Lehigh
Valley and Poconos late Sat afternoon/early evening...then southeast
toward the coastline Sat night. Shortwave trough aloft will lead
to steep middle-level lapse rates...while a cold front moving
into the region pools low level moisture...and provides a
source of lift. Ml cape is modeled around 1.5 kj...while
bulk shear approaches 40 knots. Both of these factors are
most favorable over the Lehigh Valley and Poconos. At this time...
main threat appears to be gusty winds...with inverted-v model
soundings...as well as d-cape approaching 1.4 kj. Hail is
also a threat...as wbz values fall blw 10 kft in the afternoon....
as well as h50 temperatures around -12c. Otherwise...a partly to
mostly sunny Saturday is anticipated. Sun...shortwave ridging
aloft as high pressure briefly builds in behind departing cold
front. This will promote a mostly sunny and dry day.

Monday through Wednesday...there is a lot of uncertainty during this
time frame. The outcome hinges on just how much the East
Coast trough amplifies...which will determine whether or
not Gulf moisture makes it this far north on Mon/Tue.
Some diurnally driven rain showers/thunderstorms and rain are possible Monday...W/
a better chance with the approach of a cold front Tuesday.
The front may slow down as it moves through the region...
so Wednesday may be unsettled.

&&

Aviation /20z Wednesday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.

Mainly VFR conditions are expected at all eight of our taf sites
into tonight. The daytime cumulus should dissipate this evening.

Middle level clouds and scattered showers are forecast to overspread
our region late tonight. Some MVFR ceilings may develop around krdg
and kabe. The clouds and showers are expected to lift to our north
and northeast during the late morning and early afternoon.

Showers and thunderstorms are anticipated to approach from the
northwest early in the afternoon. The line of showers and
thunderstorms is forecast to move across our eight taf sites from
northwest to southeast between about 1900z and 2300z.

A southwest wind at 5 to 10 knots into this evening should decrease
to 6 knots or less for tonight. A southwest wind around 8 to 10
knots is expected for Thursday.

Outlook...

Thursday night and Friday...VFR conditions expected...except for patchy
ground fog in the 06z-12z Friday time frame.

Sat and Sat night...mainly VFR...with MVFR possible Sat evening and
early Sat night in shra/tsra.

Sun and Monday...VFR conditions expected.

&&

Marine...
weak high pressure will influence the coastal waters of New Jersey
and Delaware for tonight.

A frontal boundary is forecast to approach from the northwest on
Thursday. A south southwest wind is expected to increase to 10 to 15
knots with gusts around 20 knots on Thursday afternoon. Wave heights
on our ocean waters may build to around 4 feet. Conditions should
remain just below the Small Craft Advisory criteria.

Showers and thunderstorms associated with the frontal boundary are
expected to arrive late on Thursday.

Outlook...

Friday through Monday...sub-sca winds and seas expected during this time.

&&

Phi watches/warnings/advisories...
PA...excessive heat warning until 6 PM EDT Thursday for paz070-071-
102-104-106.
New Jersey...excessive heat warning until 6 PM EDT Thursday for njz015-
017>019.
Delaware...excessive heat warning until 6 PM EDT Thursday for dez001.
Maryland...none.
Marine...none.

&&

$$
Synopsis...franck/gorse
near term...iovino
short term...iovino
long term...franck
aviation...franck/iovino
marine...franck/gorse/iovino

National Weather Service Glossary of Abbreviations