Area Forecast Discussion
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FXUS61 KCTP 300909
Area Forecast Discussion
National Weather Service State College PA
509 AM EDT Thu Mar 30 2017
High pressure will provide dry weather tonight. A storm system
will approach the region from the Ohio Valley later today,
bringing rainy and cool weather that will last through Friday.
A warm up is then in store over the weekend.
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Mid and high level cloudiness overspreading central Pa early
this morning, as WAA aloft develops in advance of approaching
warm front. Made some minor adjustments upward to overnight min
temps based on cloud cover across the north. Otherwise, forecast
on track for a dry overnight with temps bottoming out from the
upper 20s north to the mid 30 south.
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
An increasingly moist southwest flow aloft will work into
western Pa today, overrunning the cool/dry air mass in place.
GEFS PWATS rise to between 1-2SD above climo by late today.
Based on this scenario, have raised POPs considerably across the
region later today. Latest SREF/GEFS, as well as 00Z EC, GFS and
Canadian, all support categorical POPs across the western half
of the state, with less chance of showers across the east.
Increasing fgen forcing noted in the models by late morning
over the western counties, as nose of low level jet works toward
the area from the Ohio Valley. Thus, have ramped up the chance
of showers beginning late morning into the afternoon.
An examination of model soundings shows a persistent shallow
layer of sub-freezing air around 900mb, suggesting that sleet
pellets could mix with the rain over the central and northern
mountains. Surface temps should be safely above freezing, so no
travel impacts expected.
Have trended max temps downward slightly today, based on an
earlier arrival of precip and thick overcast. NAM has a good
track record with temps in cold air damming scenarios this
winter and have thus leaned toward its cooler numbers today,
with highs ranging from the upper 30s over the higher terrain of
the Alleghenies, to the upper 40s over the southern valleys.
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Model consensus is also for a quasi Miller-B type of low track
heading just north of the Ohio River during the day Friday, then
a pressure jump and slight intensification of the sfc low (to
996 mb) off the southern NJ and New England Coast Saturday.
Under normally colder winter-time circumstances, this low track
would be pretty favorable for a significant snowfall across
much of central and northern PA. However, a quite warm boundary
layer (and 850 mb temps) to begin with, coupled with the lack
of a stronger anchoring high over southeast Canada and New
England will mean a widespread/soaking rain evening with 24-36
hour rainfall at the majority of places here in Central PA
coming in between 0.75-1.00 inch.
This rainfall will add a healthy spike to the flow and levels on
smaller streams and creeks across the region with broader mdt
rises on rivers, but no significant threat for flooding as
headwater flash flood guidance is averaging 2-2.5 inches for a
12 and 24 hour period respectively.
Periods of light rain, drizzle, and ridge shrouding dense fog
will persist Friday night into Saturday as slightly colder air
wraps around behind the storm. Some breaks in the cloud cover
should occur Saturday afternoon, esp across the Lower Susq
Valley where drying downslope flow will be enhanced. Forecast
temps Friday may be a bit warm considering the aforementioned
storm track just to our south, and amount of rain expected.
Max temps Saturday will near to a few deg F above normal in
High pressure building over the region (coupled with the
offsetting effect of abundant sunshine and GEFS mean 850 mb
temps cooling by 3-4 deg C imply max temps close to what we`ll
see Saturday, which is upper 40s to lower 50s across the nrn
mtns...and mid to upper 50s elsewhere. Dry and slightly milder
conditions are in the forecast for Monday as the ridge of high
pressure slides just to our east and ens mean 850 mb temps
rebound by a few to svrl deg C (atop a light serly sfc flow).
The next, rather potent and moisture laden southern stream wave
heads our way for Mon night and Tuesday, bringing a likelihood
of a widespread rain. Next Wednesday looks dry in the wake of
the early weak system with temps rising above normal.
.AVIATION /09Z THURSDAY THROUGH MONDAY/...
No big changes for the 09Z TAFS.
Some mid level clouds early today with VFR conditions.
Expect a few showers across the west later today. Perhaps
some snow or sleet for a brief time, but ground temperatures
too warm for any accumulation.
Widespread rain tonight into Friday night will result
in poor conditions for aviation, as low pressure tracks
northeast across the Great Lakes.
Improving conditions for the weekend, as high pressure
builds eastward from the Northern Plains.
Sat: Sub-VFR restrictions early; then gradually improving
conditions into Sat night.
Sun-Mon: VFR/No sig wx.