Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1152 am EDT Friday Oct 9 2015
an area of low pressure will track to our north during today,
however an associated strong cold front will move through our area
this evening. High pressure will then build into our region Sunday
and Monday. The next cold front arrives during Tuesday, briefly
followed by high pressure Wednesday. It appears that another cold
front then arrives late Wednesday into Thursday.
Near term /until 6 PM this evening/...
a line of showers with embedded thunderstorms associated with an
approaching cold front is now progressing through western/central
Pennsylvania late this morning and will move into eastern
Pennsylvania later this afternoon. A few scattered showers have
developed across portions of the area associated with a couple of
weak vorticity impulses and will continue to affect the area. The
atmosphere is becoming weakly unstable this morning and should
remain unstable into the afternoon as sunshine allows for more
daytime heating to occur. This should allow the line of showers
and thunderstorms to maintain themselves and possibly intensify as
they approach the area. With the weak instability expected,
MLCAPES approaching 500-1000 k/kg and negative Li's, along with
bulk shear around 30-35 knots, a few stronger storms with gusty
winds are possible. A brief period of moderate to heavy rain will
also occur with any thunderstorms with precipitable water values around 1.5
Short term /6 PM this evening through 6 am Saturday/...
tonight...again no change from the previously written Thursday
afd scenario. Any lingering showers and scattered thunderstorms near the cf at 8
PM this Friday evening (mainly southeast New Jersey and the southern portion of the
delmarva) should quickly move out to sea along the cold front.
There might be some lagging sprinkles behind the cold front in southeast
PA and S New Jersey this evening but essentially it dries out tonight.
High cloud cover may remain most of the night but there will be a
noticeable cooling and drying in the boundary layer overnight with
northwest surface winds gusty to 20 miles per hour and becoming northerly
Confidence: above average.
Long term /Saturday through Thursday/...
the synoptic setup is comprised of a trough in place across the east
Saturday, however a stronger short wave in the base of this trough
allows for more amplification to our south. This should result in a
closed low forming to our south during the course of the weekend and
early next week. The next trough slides across the northern tier of
states Monday and arrives into the northeast Tuesday, before
relaxing some Wednesday into Thursday. We used a model blend with
continuity for Saturday into Monday, then blended the 00z wpc
guidance with continuity thereafter. Some adjustments were then made
following additional collaboration with our neighboring offices.
For Saturday...a stronger short wave at the base of the trough looks
to result in the flow becoming cut off and therefore a closed low
develops to our south. This should maintain at least some clouds for
a time in the morning mainly across the southern portions of our
County Warning Area. High pressure at the surface is forecast to be building in
through the day with a northerly wind expected. This will help
advect drier air southward across our area, therefore more sunshine
should occur from north to south. It appears that enough drying
should prevent much stratocumulus developing within the cold air advection. It will
be much cooler, however less wind should occur in the afternoon as
the surface high builds in. Given enough clearing and lighter winds
at night, temperatures may near the middle/upper 30s across portions of
the northern zones toward daybreak Sunday with possibly some frost.
For Sunday and Monday...a chilly start to Sunday. The upper-level
trough generally starts to weaken Sunday as ridging builds up the
Ohio Valley, however a closed low looks to linger to our south. We
are left with lingering high pressure at the surface Sunday before
it weakens into Monday. The aforementioned closed low and associated
surface low should remain south and east as it slowly moves out to
sea Monday. This occurs as the next upper-level trough begins to
amplify across the Great Lakes region. We are anticipating a warming
trend during this time frame as the flow starts to turn
southwesterly ahead of the next cold front. We maintained a dry
forecast based on surface high pressure working in for a time.
For Tuesday through Thursday...the model guidance overall shows a
decent upper-level trough swinging across the Great Lakes and into
the northeast for a time. This pushes a cold front into the area
Tuesday. It still appears though that the main surface low tracks
well to our north although perhaps a weak surface low develops near
coastal New England. This leaves our area removed from the better
large scale lift. In addition, the deeper moisture looks to reside
offshore and therefore is more limited here for the frontal boundary
to work with. As a result, some low probability of precipitation were left for Tuesday. A
brief return of high pressure for Wednesday, however another system
quickly tracking just north of the Great Lakes may send another cold
front into our area Wednesday night into Thursday. The timing of the
individual features is less certain this far out especially as the
short waves may be on the weaker side. A surface cold front, perhaps
weakening, may therefore still be lurking in our area during
Aviation /16z Friday through Tuesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Some MVFR ceilings developed across Abe/rdg/ttn during the middle morning
hours, but should be lifting shortly. Otherwise, tafs should be
VFR, outside of any scattered showers through early this
afternoon. The main line of showers and embedded thunderstorms is
progressing through western/central Pennsylvania. It now looks
like the line should be reaching Abe/ridge between 19-21z,
ilg/phl/pne/ttn between 20-22z, and Acy/miv between 21-23z. We
will keep the mention of lower vsby, gusty winds, and
thunderstorms where they are currently in the tafs, and we may add
this to the Acy/miv 18z tafs.
Tonight...any lingering showers should quickly exit offshore between
00z-02z/10 with VFR ceilings clearing to reveal only cirrus after 06z/10.
Winds becoming predominantly northwest with gusts around 20 kt, then turning
northerly toward 10z Saturday. Confidence: above average.
Saturday...VFR. North-northeast winds mainly 10-15 knots, then
diminishing in the late morning and afternoon /becoming mostly light
and variable at night/.
Sunday and Monday...mainly VFR.
Tuesday...mainly VFR, however a cold front moving through may
produce some showers.
Small Craft Advisory headlines. Small Craft Advisory SW wind begins around midday nearshore ports
where navigation may be hindered. Further out over the water, the
southwest wind may be a little less due to less Transfer. Easterly
swell this morning will be overrun by a developing southerly short
period chop this afternoon,
Today...winds are expected to increase to 25 knots, and and seas
on the ocean are expected to increase to 5 feet during the day
ahead of the frontal boundary.
Tonight...wind shift to northwest with gusts 25 kt, especially New Jersey waters
after midnight. Atlantic seas 4-5 feet.
Saturday...high pressure building in from the west and weak low
pressure to our south will result in a northerly wind. The presence
of cold air advection initially and a tightened pressure gradient will result in
gusty winds, however as the high builds closer the winds are
expected to decrease from north to south in the afternoon. As a
result, we will extend the Small Craft Advisory through midday for
the Atlantic coastal waters and lower Delaware Bay. The winds and
seas are expected to lower at night.
Sunday through Tuesday...the winds and seas are anticipated to be
below Small Craft Advisory criteria at this time. A cold front
however arrives during Tuesday.
Marine...Small Craft Advisory until noon EDT Saturday for anz431-
Small Craft Advisory until 6 PM EDT this evening for anz430.