Area forecast discussion 
National Weather Service Mount Holly New Jersey 
941 PM EST Sat Nov 22 2014 


Synopsis... 
strong high pressure is edging offshore. Low pressure developing 
over the Central Plains will rapidly intensify as it moves into the 
Great Lakes Sunday night...drawing a strong warm front north through 
our area. The low will be near James Bay Monday evening as it sends 
a cold front eastward across the eastern Seaboard states. High 
pressure follows later Tuesday. Low pressure develops off the 
Carolina's Wednesday and moves east of New England on Thanksgiving. 
Canadian high pressure heads southeast into the Ohio Valley Friday. 


&& 


Near term /until 6 am Sunday morning/... 
high pressure will continue to shift off the middle Atlantic coast 
through tonight. As the flow backs some more in combination with a 
surface high sliding to our southeast, a large area of warm air advection will 
occur through tonight. This is more noted to our west and northwest 
closer to the core of a low-level jet. This will maintain some 
isentropic lift as the warming chips away at the remaining cooler 
airmass at the surface. This process is leading to an area of 
cloudiness that continues to spread east across much of the County Warning Area. 


The warm air advection and associated lift with the aforementioned short wave has 
been generating an area of light precipitation from central New 
York/Pennsylvania on northeastward. Some of this will move across 
our region through this evening in the form of sprinkles, however 
with the main low- level jet passing to our north along with the 
better lift there, any precipitation should be rather light and 
spotty. The forecast soundings continue to show a rather dry layer 
in the lowest levels and this combined with weak forcing results 
very light precipitation. There is little model support to bring 
in measurable precipitation, and the wpc quantitative precipitation forecast is pretty much dry. 
Temperatures through the evening in the coldest spots look just 
warm enough to prevent any frozen precipitation. 


Did raise low temperatures some with the latest 9:30 PM update. Cloud 
cover has kept temperatures up across most of the region. Down in 
the southern Delaware-Maryland-Virginia temperatures are running several degrees 
cooler outside the cloud shield. 


&& 


Short term /6 am Sunday morning through 6 PM Sunday/... 
an upper-level trough is forecast to be amplifying during Sunday 
across the plains. This will allow some ridging to develop 
downstream, resulting in the surface high to become anchored 
offshore. This will provide a southerly flow and with warm air advection continuing 
and even strengthening some during the day, a warmer day is 
anticipated. 


The location of a low-level jet in combination of some short wave 
energy and isentropic lift should keep any morning light 
precipitation focused to our north. Meanwhile, a warm front will 
continue to organize to our south as low pressure consolidates in 
the vicinity of the Tennessee Valley by late in the day. While there 
will be some clouds around, some thinning should occur for a time 
before an increase develops again toward evening. It appears that 
any organized lift remains away from our area, therefore we will 
carry a dry forecast during the daylight hours. 


As for high temperatures, a GFS/NAM MOS blend was generally used. 


&& 


Long term /Sunday night through Saturday/... 
**record warmth Monday followed by a potential winter storm/event 
for portions of our area wednesday** 


Another high amplitude trough near 100w longitude to start Sunday 
night lifts northeastward into Quebec by Tuesday with a new trough evolving 
over the eastern USA Wednesday but full of uncertainty regarding 
the short wave interactions - amplitude and translation speeds. So 
while a middle Atlantic coastal winter event is forecast, it is not 
yet a lock due to the previously mentioned uncertainty. A general 
cyclonic flow at middle levels continues over the northeast USA Thursday 
into the weekend with uncertainty regarding the embedded short waves. 


Temperatures: calendar day averages have been below normal since the 
13th (9 consecutive days). Models agree on temperatures about 15 to 20 
degrees above normal Monday...maybe 5 degrees above normal Tuesday... 
below normal Wednesday-Friday and 5 to 10 degrees below normal Saturday. 


Forecast basis: unless otherwise noted the long term period of this 
forecast is generally based on a 50 50 blend of the 12z/22 NAM/GFS 
MOS for the period Sunday night-Monday night. Then the 12z/22 GFS 
MOS is applied Tuesday and Tuesday night. Thereafter (wednesday 
onward) the 1522z/22 wpc gridded guidance which at times is blended 
50 50 with the 12z/22 GFS mexmos. All this is eventually checked 
against the 12z/22 European model (ecmwf) to see if we're in the ballpark with 
European model (ecmwf) cyclically persistent 18z 2 meter temperatures. Precipitation 
probability guidance is checked against the 09z/22 sref 3hrly probability of precipitation 
for .01 through 00z Wednesday and thereafter the 12z/22 gefs 6hr 
probability of precipitation for 0.05. 


The dailies... 


Sunday night...warm air advection with periods of showery rains...mainly after 
midnight and possibly heavy for a time. An isolated severe thunderstorm is 
not impossible in del/New Jersey with swi -1, tt 48, ki 32 and 60-70kt 
wind at 850 mb on the European model (ecmwf) in the 3am-6 am (08z-11z) time frame. 
12z NAM has similar elevated instability at 09z Monday. 12z GFS 
least robust of the three 12z models mentioned. Grids have the chance 
thunderstorm in snj and the Delaware-Maryland-Virginia early Monday morning. 


Monday...becoming partly sunny...windy and warm (after early 
morning showers race NE at 50 kts (near 60 mph). Record warmth 
expected and southwest wind gusts of 35-40 miles per hour. Blended transport 
wind supports 40 miles per hour gusts in the afternoon...possibly 45. 


Monday night...partly cloudy with maybe a low topped sprinkle or 
shower accompanying the cold front prior to midnight. 


Tuesday...partly to mostly sunny (mostly cirrus)...breezy and 
still with temperatures about 5 degrees above normal. 


Wednesday...a coastal storm is likely. The operational European model (ecmwf) is 
pretty stable these past two cycles and has been consistently 
furthest west with this opportunity for precipitation the past several 
days. The 12z GFS has moved west with the track. No lock on the 
track since short wave interactions show variability in the 
ensembles. Still...it looks as if the boundary layer temperature is going 
to govern where its mostly snow. Daytime temperatures 5 to 10 degrees 
below normal. 


Advise all with travel plans Wednesday afternoon and night in our 
forecast area to closely monitor future forecasts. This could become 
a snow storm for portions of our forecast area with plowable snow 
and near freezing temperatures....especially the Interstate 95 corridor. 


That would mean a significant impact due to Holiday travel and one 
of the busiest air travel days of the year. 


If this forecast remains similar Sunday...briefing packages would 
begin Sunday afternoon around 330 PM. 


Thursday into Friday morning...considerable cloudiness with a chance 
of snow showers or flurries as the prime trough shifts across the area. 


Friday-Saturday...wpc guidance with colder than normal temperatures as a 
low level west-northwest flow appears to prevail with Canadian high pressure 
heading east-southeastward through the Ohio Valley to the Middle Atlantic States. 


&& 


Aviation /03z Sunday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 






Tonight...VFR, with areas of ceilings at or above 5,000 feet. 
Southwesterly winds diminishing to 5 knots or less. 


Sunday...VFR, with ceilings at times above 5,000 feet. Southwest 
winds 5-10 knots, becoming southeast late. 


Sunday night... VFR through the evening with increasing clouds and 
gradually lowering ceilings. Light rain possible after 03z from 
phl south. 


Outlook... 
04z Monday through 12z Monday...very poor flying conds with MVFR 
expected and IFR possible if not probable in periods of showery rains. 
Rain could be heavy at times with a possible thunderstorm after 06z/24 
Sunday night. East to southeast wind could gust in the 25 to 30 knots range 
toward 09z Monday. Low level wind shear potential at kacy near 09z Monday. High 
confidence. 


Monday and Monday night...improving to VFR scattered-broken at or above 3500 feet 
(after any lingering showers rapidly depart northeastward by 14z). SW wind 
gust 30-38 knots. Cold front passage/shift Monday evening with a possible brief shower or 
sprinkle...especially east PA. MDT confidence. 


Wednesday...much uncertainty depending on the track of a coastal 
low. Could be VFR if low is far enough east or MVFR/IFR in rain/snow 
and wind if low is far enough west. As it stands with todays model and 
NCEP collaborated guidance...plan on precipitation changing to some 
snow and a period of IFR conditions. Confidence low to moderate. 


Thursday...VFR ceilings with a possible brief period of MVFR conds in 
scattered snow showers or flurries. 


&& 


Marine... 
a southwesterly flow will occur through Sunday as strong high 
pressure shifts offshore and into the western Atlantic. As this 
occurs, the pressure gradient is forecast to tighten some through 
much of tonight. A low-level jet is forecast to track mainly to our 
north, however the 925 mb winds increase to near 30 knots tonight. 
The forecast soundings indicate some mixing occurs, although surface 
gusts may be marginal. The southwesterly flow should also build the 
seas, however the strongest winds and highest seas may setup to our 
northeast. Since there is still potential, we will maintain the 
Small Craft Advisory through 11z Sunday for all but the Delaware 
Bay. The conditions should generally be below advisory criteria 
Sunday. 


Outlook... 
Sunday night through Monday...gale watch has been issued with 
strongest inflow southeast winds of potential 35-40 knots gusts near dawn 
Monday. Winds shift SW in the warm sector and may gust 35 knots along 
the coast where near record warmth prevails. 


Blended 12z/22 NAM/GFS transport wind supports gale gusts 06z Monday- 
02z Tuesday. For now the gale watch ends at 22z Monday. 


Monday night into Tuesday....a cold frontal passage and Small Craft Advisory conds as seas 
and wind eventually subside late Tuesday. 


Wednesday-Thursday...plan on Small Craft Advisory conditions redeveloping as a coastal 
low develops. Small potential for a gale late Wednesday. 


&& 


Climate... 
for our eight climate sites, here are the record high temperatures 
for November 24th and the most recent year of occurrence. 


Record highs 11/24: 


Acy: 72 set in 1999 
phl: 71 set in 1979 
ilg: 73 set in 1979 
abe: 69 set in 1931 
ttn: 71 set in 1979 
ged: 75 set in 1992 
rdg: 69 set in 1979 
mpo: 64 set in 1931 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...gale watch from late Sunday night through Monday afternoon for 
anz430-431-450>455. 
Small Craft Advisory until 6 am EST Sunday for anz450>455. 


&& 


$$ 
Synopsis...drag 
near term...Gaines/gorse 
short term...gorse 
long term...drag 
aviation...drag/Gaines/gorse 
marine...drag/gorse 
climate... 



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