Weather

168 
fxus61 kctp 060541 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
1241 am EST Tuesday Jan 6 2009 


Synopsis... 
high pressure moves to the east and allows a somewhat significant 
storm to move in from the southwest. Expect mixed wintry 
precipitation from Tuesday morning through noon Wednesday. 
Another...colder storm could move in from the west by Saturday. By 
the end of next weekend there should be a cold upper level trough 
parked over the eastern U.S. 


&& 


Near term /until 8 am this morning/... 
skies not as clear as we might expect...but lots of moisture 
upstream...so temperatures not falling off quite yet. Mins may hold close 
to freezing in the southeast...but the northern mts will dip into the 
lower teens and dewpoints only in the single digits. 


&& 


Short term /8 am this morning through Wednesday night/... 
mixed precipitation event in store for Tuesday into Wednesday. Retreating high 
pressure will be in the right spot to trap cold temperatures in the 
central mts Tuesday morning and keep precipitation freezing/frozen for much 
of the event there...especially if the weak secondary low forms along 
the coast. The main low is going to our west and warm air will 
gradually flow up and over our cold dome. Central PA is once again 
the location that should see some of the worst of the weather with this 
system. Will therefore upgrade to a warning for much of the previous 
watch area...with an eye toward sig freezing rain accums...and Post Winter Weather 
Advisory for the rest of the area. Timing earlier in the SW and 
later in the NE. 


Light precipitation arrives in southern tier by middle morning Tuesday mainly in 
the form of snow. Precipitation continues to spread north and by 19z 
should see light snow covering much of northern half of County Warning Area. 
Southern half will be getting into heavier precipitation and beginning to 
transition from snow and sleet to mainly sleet for much of the 
afternoon in lots of places. Then...we should have a long period 
of freezing rain that continues through much of the night. Quantitative precipitation forecast looks to be 
a tenth to quarter inch through 00z though...with higher amounts 
Tuesday night. 


Deepening surface low is forecast to track west of the Appalachians 
Tuesday night into early Wednesday...moving northward through the 
upper Ohio Valley and into the lower Great Lakes by Wednesday 
night. Latest 21z sref plume ptypes have indicated mostly sleet 
and freezing rain with slightly lower amounts /compared to the 15z 
nums/ shown in the mean...but still warning-level fz rain in the 
ridge and valley region and laurels. Far southeastern cos may turn to rain 
faster than everyone else...but will still have a period of mixed 
precipitation to contend with. 


Warm air will eventually win out by Wednesday afternoon...briefly changing 
any lingering precipitation over the plain rain across most of the County Warning Area. 
The cold/occld fnt associated with the departing surface low pressure will move 
across the commonwealth Wednesday night. Colder air/gusty winds will 
follow in the wake of the frontal passage...with les developing across the 
north/west. 


&& 


Long term /Thursday through Monday/... 
overall...not much change early in period with regard to the 
large scale pattern. Temperatures are forecast to be below normal 
within marginally cold cyclonic flow...in the wake of the 
departing/deep low pressure system moving northeastward away from New England. This 
should result in lake effect/orographic snow showers across the 
western high terrain. 


Latest GFS/gefs have trended more toward a split flow in the west 
during the second half of the period...or closer toward the ec 
solution. This will certainly impact timing of next system forecast to 
affect the region around Sat 1/10. Colder air in the wake of this 
system suggests below normal temperatures continue to round out the week. 


&& 


Aviation /06z Tuesday through Saturday/... 
straight forward forecast for the next 12 hours as high pressure builds 
across central PA...providing light winds and VFR conds through early 
this morning. A storm system will track northward from the Gulf Coast 
states today...producing deteriorating flying conds as mixed precipitation 
overspreads the region from the south from late morning to middle after. 


Latest model data supports arrival of light snow/sleet across southern 
PA during the late morning hours...then northern PA by early evening. 
As warm air flows in aloft...precipitation should change to freezing rain over all 
but the north tier by evening. IFR ceilings likely to develop over the 
Laurel Highlands /kjst/ as early as 17z...then spread north over 
the remainder of central PA by early evening. Cold air damming/inversion 
should result in generally light east-southeast winds over the bulk of central 
PA. However...the Laurel Highlands /kjst/ will likely experience 
gusts to near 20kts by afternoon. 


Widespread IFR ceilings and freezing rain expected Tuesday night...with significant 
ice accumulations possible across the southern half of the state. 


Improving conds by late Wednesday as storm system moves north of the 
region. Gusty northwest flow behind this system will likely produce lake 
effect shsn and predominantly MVFR conds across the alleghenies 
/kbfd and kjst/ Wednesday night and Thursday. Areas southeast of mountains should 
experience predominantly VFR conds. A weak storm system may approach 
from the Great Lakes Friday night...possibly bringing a period of light snow 
to northwest PA. 


&& 


Ctp watches/warnings/advisories... 
Winter Weather Advisory from 11 am this morning to 1 PM EST 
Wednesday for paz004>006-010>012-017-018-037-041-042. 
Ice Storm Warning from 11 am this morning to 1 PM EST 
Wednesday for paz019-027-028-045-046-049>053-056>059-063. 
Ice Storm Warning from 8 am this morning to 10 am EST 
Wednesday for paz024>026-033>036. 
Winter Weather Advisory from 11 am this morning to 7 am EST 
Wednesday for paz064>066. 


&& 


$$ 
Synopsis...dangelo/rxr 
near term...dangelo/rxr 
short term...dangelo/rxr/steinbugl 
long term...steinbugl 
aviation...Fitzgerald/Martin