Area Forecast Discussion
Issued by NWS State College, PA
FXUS61 KCTP 301014
Area Forecast Discussion
National Weather Service State College PA
614 AM EDT Thu Mar 30 2017
An active southern jet stream is expected over the next week
with a series of significant systems likely to affect Pa. Low
pressure over the Mississippi Valley will move east over the
next 48 hours, tracking just south of Pennsylvania late Friday.
Another low pressure system, following the same track, will
likely affect Pennsylvania late Monday into Tuesday. A third low
is likely to track west of Pa through the Great Lakes during
the later half of next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
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.
.SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/...
A soaking rain appears a certainty for central Pa later tonight
into Friday, as closed upper low tracks east from the Ohio
Valley. Associated anomalous southerly low level jet and plume
of +2SD PWATs overrunning dome of low level cold air provided
by blocking high north of New Eng will result copious rainfall
amounts across the state. Blend of model QPF ranging from around
1 inch in the north to close to 2 inches across the southeast
counties. Can`t rule out some elevated tsra across the southeast
counties late Friday, as surge of high PWATs and marginally
unstable air are drawn northward ahead of upper low.
This rainfall will add a healthy spike to the flow and levels
on smaller streams and creeks across the region with broader
moderate 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.
Will continue to lean toward the cooler NAM guidance through
Friday, a strategy which has worked well with cold air damming
scenarios over the last several months. Readings will likely
remain stuck in the 40s Friday.
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Any early showers should give way to improving conditions
Saturday, as low exits the coast and a drier northwest flow
takes hold. Some breaks in the cloud cover should occur
Saturday afternoon, esp across the Lower Susq Valley where
drying downslope flow will be enhanced. Max temps Saturday
should return to near seasonal norms.
Fair and mild weather appears likely Sunday, as high pressure
ridge builds across the state. However, the next potent and
moisture laden southern stream wave heads our way for Mon night
and Tuesday, bringing a likelihood of a widespread rain. A brief
break is likely around next Wednesday, then another round of
significant rainfall appears possible by the later half of next
week when all med range guidance tracks a closed low northeast
through the Grt Lks.
.AVIATION /10Z 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.