Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
513 am EDT Monday Jul 14 2014
a cold front will approach from the northwest during today and
Tuesday and it should arrive on Tuesday night. The boundary is
forecast to pass off the coast on Wednesday allowing high pressure
to build into our region from the west for Thursday into Friday.
The high is expected to pull away to our northeast over the
weekend with low pressure and a warm front arriving from the west
Near term /until 6 PM this evening/...
a Flash Flood Watch has been issued for the I-95 corridor
A brief break in the rain has mostly occurred early this morning
except some scattered showers and thunderstorms associated with a
couple of short wave/vorticity impulses moving across the area.
However, showers and thunderstorms are expected to increase in
coverage and intensity as we progress through the day. Several
ingredients are setting up for a heavy rainfall threat today
across the area. A surface low pressure system will begin
developing across the Great Lakes region today as a middle/upper low
continues to slowly swing southeastward out of the upper
Mississippi Valley. This surface low will not be affecting our
area today, but instead, the pre-frontal/Lee-side trough will
remain in place across the east Seaboard and remain the focus for
shower/thunderstorm development. These showers and thunderstorms
will be aided by several short wave/vorticity impulses that are
forecast to move across the area today. Also, we will remain in
the right-rear quadrant of an upper level jet streak lifting into
the northeast states through the day. In addition to all of this,
precipitable water values remain very high, ranging from 2-2.25
inches. All of this together increases the threat for heavy rain
and the potential for flash flooding across the area. Therefore a
Flash Flood Watch has been issued. We start it at 12 noon since
the heaviest rain will likely develop during the afternoon into
the evening hours. However, there remains the possibility for
showers and thunderstorms through the day.
Another concern will be the threat for severe weather. In
addition to everything listed above, instability remains high with
lifted indice's forecast well below zero and cape values forecast to exceed
1,000-1,5000 j/kg. Also, shear values approach 35-40 knots which
should be sufficient enough to increase the potential for damaging
winds. Storm Prediction Center keeps our entire area outlined in a slight risk for
severe weather today, with the greatest threat damaging winds.
Short term /6 PM this evening through 6 am Tuesday/...
we expect showers and thunderstorms to be ongoing at the start of
the evening time period, but there is the possibility we could get
a needed break in shower/thunderstorm action during the nighttime
hours. The strongest short wave/vorticity impulses are forecast to
pass through during the day, and as instability wanes overnight,
this could allow for showers and thunderstorms to decrease in
coverage and intensity. However, there will remain the possibility
for precipitation overnight, and with heavy rain again possible
Tuesday, we will keep it going through the night.
Long term /Tuesday through Sunday/...
a middle level low is forecast to be over northern lower Michigan on
Tuesday morning. The feature should lift northeastward and over
Quebec on Wednesday. A middle level trough is expected to remain over
our region into Thursday with a bit of a ridge from the west
building overhead for Friday. Another middle level low is anticipated
to be located over the eastern Great Lakes during the weekend.
A middle level pattern featuring a low over the Lake Huron and
southern Ontario vicinity has produced flash flooding in our
region in the past with a southerly surface wind and with the wind
direction veering to the southwest with height. The condition
favors training thunderstorms. Of course, other factors need to be
present and that should be the case from Tuesday into Tuesday
night. We will have a slow moving surface front along with
precipitable water values in excess to 2 inches. Also, we will be
under the right entrance region of an upper level jet. As a
result, we have a Flash Flood Watch in place for Tuesday into
Tuesday night for the Interstate 95 corridor northwestward.
In addition to the Flash Flood Watch, the Storm Prediction Center
has southern New Jersey, Delaware and northeastern Maryland under
its slight risk designation for severe thunderstorms on Tuesday.
The rain and the frontal boundary should begin to pass off the
coast on Tuesday night with the threat of heavy rain ending
gradually from west to east at that time. The precipitation should
move well out to sea on Wednesday.
Dry air is anticipated to build into our region from the west for
Wednesday night through Thursday night with a bit of an increase
in moisture possible on Friday in a developing southeasterly flow
on the back side of the surface high.
Another middle level low over the eastern Great Lakes and a warm
front from the south and southwest may bring precipitation next
High temperatures from Tuesday through Sunday should be mainly in
the 80s, with maximum readings mostly in the 70s in the elevated
terrain. Low temperatures are forecast to be mainly in the 50s and
Aviation /09z Monday through Friday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
The showers and thunderstorms have ended for most taf sites early
this morning, although more is on the way. There is a patch moving
into southern New Jersey early this morning, and another moving
across southern Pennsylvania/central Maryland which could impact
some taf sites early this morning. Where it rained yesterday,
Abe/rdg/ttn, we have we expect IFR conditions to develop, which
Abe has shown signs of already. The remainder of the taf sites
could still see some light MVFR fog develop toward daybreak. Any
fog/low clouds should dissipate and lift after sunrise, and
everyone should return to VFR. The showers and thunderstorms are
expected to return to the taf sites later today into this evening.
We tried to time the thunderstorms with tempo grounds, and will
fine tune them in subsequent tafs.
Showers and thunderstorms will likely become less widespread
again overnight Monday, and patchy fog could once again develop.
Winds today are generally expected to be southwest, except in and
around thunderstorms where winds will vary based on any outflow
boundaries. The winds could get gusty later today into this
evening around 15-18 knots, but gusts were kept out of the tafs
Tuesday and Tuesday night...MVFR and IFR conditions at times in
showers and thunderstorms. The rain may become heavy.
Wednesday through Friday...mainly VFR.
five foot seas have not manifested themselves and wind gusts have
dropped below 25 knots; so we will cancel the current Small Craft
Advisory. It looks like we could get close to 25 knots again later
today into this evening as well as have 5 foot seas return. So we
will issue another Small Craft Advisory for later today/this
evening into the overnight hours.
Showers and thunderstorms are possible today and tonight. Winds
and seas will be locally higher around any thunderstorms.
Tuesday through Friday...no marine headlines are anticipated.
there is a moderate risk for rip currents along the New Jersey
PA...Flash Flood Watch from noon EDT today through Tuesday evening
New Jersey...Flash Flood Watch from noon EDT today through Tuesday evening
Delaware...Flash Flood Watch from noon EDT today through Tuesday evening
Maryland...Flash Flood Watch from noon EDT today through Tuesday evening
Marine...Small Craft Advisory from 5 PM this afternoon to 6 am EDT
Tuesday for anz450>455.