Area forecast discussion 
National Weather Service Mount Holly New Jersey 
1226 am EDT sun Oct 23 2016 

strong low pressure over Maine will move north through eastern 
Quebec Sunday. A cold frontal passage occurs late Sunday night, then 
strong high pressure over central Canada gradually builds to our 
north by Wednesday. A frontal system will approach from the west on 
Thursday and probably move east of the mid Atlantic coast on Friday. 


Near term /until 6 am this morning/... 
a dramatic change in our weather compared to the last several days. 
This is courtesy of a negatively tilted upper-level trough in the 
northeast. This feature will continue to pivot to the north- 
northeast through tonight, driving deepening surface low pressure 
into eastern Canada. The light showers and sprinkles associated with 
the axis of the strong trough aloft will continue to shift eastward 
for the remainder of the night. Any showers with the axis of 
deformation to our north are ending and the rest of the night is 
expected to be dry. 

As for the low temperatures, we used a MOS/continuity blend 
however did not undercut these given the expectation that a breeze 
remains through the night. Temperatures were raised with the 
updates this evening slightly based on the wind gusts and updated 
metar observations. 

Clouds have pretty much dissipated over the region, so have 
adjusted the grids accordingly. Otherwise, just have made cosmetic 


Short term /6 am this morning through 6 PM Monday/... 
the upper-level trough weakens across the area during Sunday as it 
shifts toward the Canadian Maritimes. Strong surface low pressure 
however well to our north-northeast combined with high pressure to 
our southwest will keep a tight pressure gradient across our region. 
This will result in a gusty west-northwest wind through the day, 
which should increase quite a bit by mid to late morning as the 
boundary layer warms. The warming aloft though may temper the true 
mixing a bit. The gradient does relax toward late afternoon and 
therefore we are expecting the winds to start diminishing. 

The airmass overall looks rather dry through the day, however as 
some warming occurs around 850 mb and with residual cyclonic flow 
areas of stratocumulus may result especially across the northwestern 
areas. Given the low-level warming expected to occur, a milder 
afternoon is expected. High temperatures were mostly a blend of MOS 
and continuity. 


Long term /Monday night through Saturday/... 
500 mb: cold closed low in Quebec weakens over the Maritimes 
Wednesday as a short wave amplifies over the western Great Lakes 
region. That short wave moves off the mid Atlantic coast Friday 
followed by ridging Saturday. 

Temperatures...October through the 21st has averaged around 4 degrees 
above normal. The chill during midweek will make a significant Dent 
in that above normal departure. Calendar day averages Monday should 
be around 3 to 5 degrees above normal, cooling to between 5 and 10 
degrees below normal Wednesday and Thursday, then warming at or above 
normal Friday and Saturday. 

Forecast basis: unless otherwise noted, a 50 50 blend of the 12z/22 
GFS/NAM MOS guidance Sunday night-Monday night, thereafter the 
12z/22 GFS mexmos Tuesday and then the 15z/22 wpc guidance Tuesday 
night - Saturday, at times blended with the 12z/22 GFS mexmos guidance. 

The dailies... 

Sunday night...a secondary surface cold front slides through the 
region late (after midnight). As mentioned by previous shifts, a 
tight band of frontogenetic forcing along and just ahead of this 
front should lead to some showers. However, limited synoptic 
scale lift means that coverage should be limited across our 
region, mainly north of I-78, possibly focused along I-80. Precipitable water 
does increase to three quarter inch from the 0.3 inches 12 hours 
earlier. Lows several degrees above normal. Confidence: above 

Monday and Tuesday...a gusty northwest flow pattern sets up to start 
the work week, resulting in cold air advection taking hold Monday 
night and Tuesday. Gusty northwest winds each afternoon to 25 
mph. Diurnal cloud cover, with greatest coverage during each 
afternoon. Confidence: well above average. 

Frost or freeze will probably occur early Wednesday morning across 
much of eastern PA and New Jersey late Tuesday night as winds decrease- 
decouple with the approaching ridge of the Canadian centered and 
originating airmass. The growing season has ended in the Poconos 
and Warren-Sussex counties of NW New Jersey. GFS 2m temps, combined with 
the wpc guidance and 12z/22 GFS mex, suggests that we may be able 
to Post a freeze watch followed by a freeze warning for the I-78 
region northward. It appears likely that if this forecast scenario 
is close to reality that the growing season will likely end for 
much of the area are along and north of I-78. 

Wednesday...sunny and rather cool with a light northerly flow. 
Confidence: above average. 

Wednesday night...if its clear through 08z/27, there would be a 
repeat of frost or freezing conditions, similar to that of 24 
hours earlier. However, there is uncertainty regarding skycover, 
associated with a developing warm front to our west. Confidence: 
average or just below average with the primary uncertainty being 

Thursday...modestly interesting for late October. Chilly high to the 
northeast and an approaching frontal system from the west with the 
associated short wave in the Great Lakes heading east southeast. 
Thickening clouds with a cold rain possible by late in the day. 
Confidence: average. 

Rain looks quite likely for Thursday night. 

This appears to be a possible developing occlusion with low 
pressure forming on the occlusion by Friday morning along the mid 
Atlantic coast. 

Friday...quite a bit of uncertainty. For now, have forecast the 
progressive solution...any morning showers should end allowing a 
rainfree afternoon with a solution of a surface low moving east 
from the mid Atlantic coast, as per wpc and 00z/22 naefs guidance. 
However, there is uncertainty and so our skycover forecast is a 
little heavier than what might normally be associated a 
progressive drying out solution. 

Saturday...looks nice with high pressure dominating. 


Aviation /06z Sunday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 

Tonight...VFR. West-northwest winds around 15 knots with some 
lingering gusts around 25 knots till around midnight. 

Sunday...VFR. West-northwest winds increase to 15 knots with gusts 
up to 30 knots by mid to late morning, then diminish late in the 


Sunday night...VFR cigs developing during the night but there is 
a small chance of MVFR conditions in showers after midnight, 
primarily for taf sites north of kphl. Confidence: above average. 

Monday through Wednesday...mostly VFR conditions expected. Gusty 
northwest winds 20 to 30 kt both Monday and Tuesday afternoons. 
Confidence: well above average. 

Thursday...VFR cigs developing by midday, probably deteriorating 
to IFR or MVFR conds later Thursday night in showery rains. 
Easterly wind becoming southeast to south late. Confidence: 


the glw on the upper portion of Delaware Bay has been replaced 
with a Small Craft Advisory. For lower Delaware Bay, conditions are marginal, so 
have let the Gale Warning continue and extend it for a few hours. 
Just when it seemed like gusts would be below criteria, therewould 
be some gusts at or above gale criteria. Will reassess with the morning 
package issuance. 

Deepening low pressure tracking into eastern Canada will continue to 
circulate a colder airmass across our area. This combined with a 
tight pressure gradient and stronger flow is working with efficient 
low-level mixing. As a result, wind gusts of 35-45 knots are 
expected although these will diminish from south to north overnight 
and during Sunday. No changes were made to the ending times and 
trends will be monitored. A Small Craft Advisory will be needed for 
a time following the end of the Gale Warning. Given the strong 
offshore wind, seas will be elevated however the highest will be in 
lower Delaware Bay and then farther from the Atlantic coast. 

Sunday night...Small Craft Advisory conditions may continue into Sunday night, 
especially outer waters. Confidence: average 

Monday and Tuesday...Small Craft Advisory conditions with northwest winds occasionally 
gusting above 25 kt, though seas may drop off below 5 ft. 
Confidence: well above average. marine headlines anticipated. Northerly winds gusting 
under 20 kt expected to turn northeast at night. Confidence: above 
average. Small Craft Advisory may be needed for the Atlantic waters Thursday 
night. Confidence: below average. 


have quickly rereviewed the monthly departures. Will focus much 
more closely in the Sunday afternoon afd. For now...still expecting 
around a #15 warmest October in phl/Abe, that said with average 
confidence. Will probably have a much better handle on the monthly 
ranking in late sundays afd. 


Phi watches/warnings/advisories... 
New Jersey...none. 
Marine...Gale Warning until noon EDT today for anz452>455. 
Gale Warning until 6 PM EDT this evening for anz450-451. 
Small Craft Advisory until 4 PM EDT this afternoon for anz430. 
Gale Warning until 4 am EDT early this morning for anz431. 


near term...Gaines/gorse/nierenberg 
short term...gorse 
long term...drag 

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