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FXUS61 KCTP 130242

Area Forecast Discussion
National Weather Service State College PA
942 PM EST Thu Dec 12 2019

Fair weather pattern from last couple days will turn stormy 
Friday through the weekend with risk of icy spots, heavy rain, 
and lake effect snow. Temperatures will trend milder into 
Saturday before gusty winds direct colder air back into the 
region by Sunday. Winter weather threat continues for Monday 
into Tuesday with the potential for snow and ice accumulation.


Forecast on track with clouds increasing overnight and
temperatures not falling much more. POPs increase across
southern PA at the very end of the period. Temperatures just 
close enough to freezing to have some freezing drizzle in spots.


Increasing southerly flow ahead of an amplifying upper trough
and low pressure system will gradually spread precipitation 
northward into retreating cold air damming surface ridge early 
Friday. Hires models suggest some patchy freezing drizzle is 
possible during the predawn hours Friday over south central PA. 
Confidence is low at this point, but any ice could result in 
high impact to AM commute. HREF and NBM show light QPF spreading
north of the PA/MD line after 12Z. The timing/onset of precip in
the 12Z to 18Z window is critical for ice threat with ramp-up of
POP/QPF coincident with sfc temps climbing just above freezing.
Considered an advisory in collaboration with PBZ/LWX MD zones
but overall confidence is just not there yet.

Continued to trend max temps Friday on the low-side or below 
NBM given moisture overrunning the cold air damming pattern
early in the day. Temps will be warm enough for rain in most 
areas by 00Z Saturday. The western Allegheny ridgetops could 
see freezing rain risk extend into early Friday night. Soaking 
rain is expected Friday night into early Saturday morning with 
a narrow diurnal range over the 24 hour period. Highest QPF
between 0.50 to 0.75 inches is forecast over east-central PA.


*Heavy rain possible (1-2 inches) in east-central PA Friday
 night into Saturday 
*Period of snow with higher amounts in the NW mtns Saturday
 night into Sunday. 
*Mixed precipitation likely later Monday into Tuesday; potential for
 winter weather should be monitored

Low pressure system will draw deep moisture/above normal PW
northward into the area Friday night resulting in widespread
moderate to briefly heavy rainfall. 

Models have some disagreement on timing and intensity. However,
given an adjustment to the NBM. The Storm total rainfall should
remain in the 1 to 1.5 inches range across east-central PA. Will
need to watch for a transition back to snow on the backside of
the system as the upper low pivots into the Northeast. Gusty
northwest flow in the wake of the system will usher cold air
back into the region. Lake effect snow accumulation is likely in
the favored upslope high terrain and snowbelts Sat night into
Sunday. Due to lake moisture and the strength of flow have
increased snow amounts slightly. Temperatures trend colder
Saturday to Monday with another winter weather threat early next
week. There will be a potential for snow and ice to impact the
area later Monday into Tuesday. Updated local winter storm
outlook graphics on the web and HWO to reflect the latest
trends/probs.Below average temps are forecast into the second 
half of next week.


VFR for next several hours with deteriorating conditions after
09Z for southern PA with lower cigs and freezing drizzle in the
colder locations close to KLNS and KMDT. Wet weather with low
cigs across the entire area on Friday and Friday night.


Fri...Rain/low cigs likely, especially late.

Sat...Rain/low cigs likely, especially early. Windy late.

Sun...Gusty west wind. AM low cigs/snow showers possible W Mtns. 

Mon...PM low cigs/wintry mix possible.





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