Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 260640
Area Forecast Discussion
National Weather Service State College PA
240 AM EDT Sun Mar 26 2017
A cold front will sag south of Pennsylvania this
evening, then return north as a warm front Sunday night.
Unsettled conditions will continue through the middle of next
week before high pressure returns with drier air.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Backdoor cold front has pushed south and west of the entire CWA
as of late this evening. Parent shortwave and associated large
scale forcing has passed east of the region, so no precip is
currently falling across central Pa as of 02Z. However, GOES-16
water vapor loop is showing a weak shortwave lifting northward
from West Virginia. As this feature and associated southerly low
level jet lift into the region later tonight, expect a few
showers to result, mainly where WAA is strongest along and north
of baroclinic zone across northern Pa. In addition, moist
easterly flow is likely to produce some patchy drizzle late
tonight, especially over the higher terrain.
Overnight lows will range from the mid 30s over the mountains
north of Williamsport, to mid 40s in the southern valleys.
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Any rain showers should lift north of the border by early
Sunday afternoon, as weak shortwave and baroclinic zone lift
into upstate NY. However, persistent, moist easterly flow should
result in lingering drizzle/ridge top fog the rest of the day.
Upper low will approach from the Ohio Valley late in the day,
bringing a renewed chance of showers across the Alleghenies and
central mountains toward evening. Can`t rule out a rumble of
thunder across the Alleghenies, although any convection will be
weakening rapidly as it encounters stable air mass over central
Local experience suggests we lean away from blended model
guidance for max temps in such low level cold air damming
situations. As such, I lowered tomorrrow`s highs by a few
degrees counting on a day not nearly as nice as today,
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
This period starts out with above normal heights over the
eastern US. Several lows weaken as they move into this blocked
flow and are forced to move to our west.
The first wave is comes overnight Sunday into early Monday. It
has a good surge of moisture and a boundary related to the
cooler weather on Sunday. Thus nearly all guidance shows a very
high probability of rain overnight Sunday into Monday. Most of
the NCEP guidance shows the peak chance of rain from 0000-1200
UTC Monday. Then things improve during the day Monday.
Our POPS Monday may be too high but they are consistent with
nearby offices. GEFS implies little or no rain in our CWA much
after 1800 UTC. Most rain before than would be in the east. Our
850 hPa temperatures are above normal too so should be a warm
later afteroon and evening.
The second wave moving up to our west comes in overnight Monday
into Tuesday. Clearly the uncertainty with this and the longer
forecast length introduces more uncertainty. But at this time
peak rain probabilities are during the day Tuesday but lower
probabilities than the first event.
The second event will push the warm moist air to our south
Tuesday night into Wednesday. Chance of rain should drop
overnight Tuesday into Wednesday. Wednesday should be a
relatively good day as high pressure builds in from the
northwest. The dry air and high pressure are in all the guidance
implying Wednesday and Thursday should be relatively nice days.
High pressure, dry air, and normal to slightly below normal 850
hPa and 925 hPa temperatures imply near normal daytime highs.
The storm track shifts to our south and some models show a
southern stream wave Thursday night and Friday. This could bring
clouds to our region. GEFS and CMCE imply we could be on the
northern edge of an expanding precipitation shield Friday and
Saturday as the southern stream wave slides to our south and
east. Thus POPS increase Friday and Saturday. Could be a cold
rain across south-central PA Friday and Friday night.
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --IR satellite confirms observational trends and near-term model
guidance in developing widespread low clouds/ceilings across the
airspace this morning. A moist east/southeast low level flow
will support sub-VFR conditions with low MVFR to IFR fcst
terminal-wide by afternoon. Question remains how quickly cigs
could lower to IFR and timing adjustments/amendments may be
necessary going forward. Aside from some patchy drizzle or mist,
the main period of rain should be from around 27/00z to 27/12z.
Mon-Tue...Sub-VFR with periods of rain.
Wed...MVFR with chance of rain early in the morning, then
Thu...Increasing chance of rain late in the day into Thursday
-- End Changed Discussion --
SHORT TERM...Fitzgerald/La Corte