Area forecast discussion 
National Weather Service Mount Holly New Jersey 
417 am EST Thursday Jan 29 2015 


Synopsis... 
high pressure overhead this morning will move offshore late in the 
afternoon. Low pressure will move across New York tonight and then 
across the New England waters Friday night. It will send an Arctic 
front across our area early Friday. High pressure will build in for 
most of the weekend. A low pressure system is expected to move just 
south of the area Sunday night through Monday night. High pressure 
will build back in for the middle of next week. 


&& 


Near term /until 6 PM this evening/... 
surface high pressure was centered between the East Coast and the 
Appalachians. There has been a fairly large temperature spread across the 
area. Temperatures have dropped into the single digits in the sheltered 
valleys of NE PA and northwest New Jersey where the high is directly overhead and 
winds were calm. There is enough of a pressure gradient farther 
south and east for a light northwest wind to keep temperatures steady in the upper 
teens/lower 20s across the Delmarva, far southeast PA and S New Jersey. However, 
these areas have a chance to cool several more degrees through daybreak 
as the high builds toward the coast. 


The high will move offshore in the afternoon while an area of low 
pressure that is currently over the Midwest tracks eastward toward 
the Middle-Atlantic States late in the day. After a sunny start to the 
morning, high and middle clouds ahead of this system will overspread 
our area later this morning and lower/thicken during the afternoon. 


There is good model agreement regarding the time of arrival for the 
precipitation late this afternoon in our far western zones (mpo-rdg-mqs-esn 
roughly between 4 PM and 6 pm). Note that we did speed up the onset 
an hour or two earlier as models often are too slow with the leading 
warm air advection band. Thermal profiles support ptype starting out as snow in PA, 
snow/ice pellets in NE Maryland/far north Delaware-Maryland-Virginia and rain/ice pellets toward Queen Anne's and 
Talbot. 


&& 


Short term /6 PM this evening through 6 am Friday/... 
low pressure will move through the eastern Great Lakes this evening. 
The initial shield of precipitation that is expected to be entering our far 
western zones by the start of the period will spread eastward during 
the early and middle evening as a leading shortwave trough aloft swings 
through. Ptype from philly and points northward will be all snow. A 
warm nose aloft is forecast to cause snow to mix with sleet in the 
northern Delaware-Maryland-Virginia and the southern most locations in New Jersey. Warmer surface 
temperatures will likely result in mainly rain across southern Delaware and 
adjacent Maryland zones. 


Probability of precipitation and snowfall amounts are highest along and north of the I-78 
corridor, where synoptic lift will be greatest and less transitory 
closer to the surface low. Forecast snowfall amounts with this event 
are around 1-2 for these areas. There is certainly a possibility for 
locally higher amounts up to 3 inches mainly across the higher 
elevations in northeast PA and northwest New Jersey but not expecting it to 
be widespread enough to warrant a Winter Weather Advisory. 


The majority of the snow is expected to move out of the area by 
midnight. However, some light snow may linger overnight in northeast 
PA and northern New Jersey. 


We are not anticipating temperatures to fall much during the overnight with 
cloud cover blanketing the area and a southwest wind ahead of a cold 
front. 


&& 


Long term /Friday through Wednesday/... 
Friday...the Arctic front and low pressure north of the region will 
be moving away. Scattered snows across the northern areas just after 12z 
will remain into the morning before diminishing. Cold and windy 
conditions developing with temperatures not changing much...remaining in 
the low 30s north and middle 30s south. Temperatures may begin to fall during 
the afternoon as the cold air advection increases. Winds gusting to 
25 to 35 miles per hour at times. Wind chills in the single digits over the southern 
Poconos...teens across the northern third of the area and low 20s 
elsewhere. 


Friday night through Sun morning...high pressure remains across the area. 
A dry forecast but bitter cold temperatures continue Sat with some moderation 
Sunday. Highs Sat mostly teens (north) and low 20s (south) wind 
chills mostly single digits early with sub zero far north. A wind 
chill flag may be needed. Wind chills in the teens across the 
Delaware-Maryland-Virginia and southern New Jersey. 


Sun afternoon through Monday...another low pressure system will affect 
much of the area. After more disorganized solutions for the system 
with the 12z Wednesday models...the 00z Thursday op models have again swung 
back to wetter solutions for our area. GFS...moves low pressure from 
the Carolinas up off the Delaware-Maryland-Virginia then just east of 40/70 Monday. A 
decent swath of moderate quantitative precipitation forecast (mostly snow) to much of the forecast 
area. Ec...weaker low pressure moves from the Carolinas up well east 
of the 40/70 mark with slower deepening. Still some snow to the 
area...but much lighter and the higher totals are across the 
Delaware-Maryland-Virginia and southern New Jersey. CMC...much closer...stronger and very wet. 
Areas S/east of I-95 would change to rain Monday with the CMC solution. 


There can be a tendency for a northward track bias with systems when 
a strong high is north/northwest of the system. The GFS/CMC models 
may be displaying this...so we have gone with the wpc numbers for 
now and offered the high chance/low likely probability of precipitation for these period. Not 
much of a change from previous forecast. With this written...an 
increasing chance for an accumulating snow for Sun night Monday for the 
southern/eastern parts of the County Warning Area. We will make mention of this in the severe weather potential statement 
and ask users to continue to follow this system over the next few 
days. Models have yet to lock on to a solution...but may be 
beginning to settle...with at least more agreement than this time 
last night. 


Monday night through Wednesday...more high pressure with cold temperatures Tuesday and a 
bit warmer Wednesday. A mostly dry forecast for this period. 


&& 


Aviation /09z Thursday through Monday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


VFR this morning and first part of the afternoon. Expect a band of snow to 
reach the western terminals late in the day (rdg around 22z and Abe 
23z). Visibilities will likely lower to IFR quickly after onset of snow. 
Snow moves eastward toward the I-95 terminals between 00z-02z. This 
will be a quick moving system, so only expecting a brief, 3-6 hour, 
period of snow. Sleet may mix in at ilg/miv/Acy but confidence in 
precipitation making it to Acy is relatively low for this close to the 
event. Snow may linger out toward Abe-ridge after midnight. 


Winds will be light this morning, becoming southerly this afternoon/evening and 
southwesterly overnight 5-10 knots. 


Outlook... 
Friday through Sun morning...VFR expected. Gusty winds Friday. 
Sun afternoon through Monday...lowering ceilings. Snow with MVFR/IFR possible. 


&& 


Marine... 
light winds today with high pressure overhead. The high shifts 
offshore tonight and southwest winds increase. Small Craft Advisory was issued for 
the coastal zones, which starts at 11 PM and continues through the 
overnight. Waves will build to near 5 feet during the overnight. 


Outlook... 
Sat through sun...gale warnings issued. Winds and seas subside back 
to Small Craft Advisory conditions Sunday. Freezing spray expected. 
Sun night...sub-sca conditions. 
Monday through Tuesday...Small Craft Advisory conditions. Winds/seas subside Tuesday afternoon. 
Tuesday night through Wednesday...Small Craft Advisory seas possible. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 11 PM this evening to 6 am EST 
Friday for anz450>455. 
Gale Warning from 6 am Friday to 6 am EST Saturday for anz430- 
431-450>455. 


&& 


$$ 
Synopsis...O'Hara 
near term...Klein 
short term...Klein 
long term...O'Hara 
aviation...Klein/O'Hara 
marine...Klein/O'Hara 



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