Scientific Forecaster Discussion
fxus61 kctp 291900
Area forecast discussion
National Weather Service State College PA
300 PM EDT Wed Mar 29 2017
high pressure will provide dry weather tonight and early
Thursday. A storm system will approach the region from the Ohio
Valley on Thursday, bringing showery conditions Thursday night
through Saturday. A warm up is then in store over the weekend.
Near term /through tonight/...
GOES-r/16/freshman/newbie visible shots show about 3 cu over the
southern quarter of Centre County. That's about right. Sky has
cleared out over most of the area, with only a dissipating patch
of cu in the NE. Wind should die down tonight, but northerly
gusts into the upper teens are possible until sunset. High
clouds will slowly increase tonight. But, the clouds will only
lower slightly in the west by sunrise. There might be a sprinkle
before sunrise in the west, but not enough reason to mention at
Short term /Thursday/...
clouds lower and thicken through the morning. While a few
sprinkles are possible in the morning in the west, it is dry
under the clouds.
Evaporational/dynamic cooling of the airmass *may* help 925-850
mb temps dip to near 0c right as the precip starts across the
area Thursday afternoon/evening and Friday. The quantitative precipitation forecast is really
minimal during that brief time, so I will not mention it in the
wx grids for now. However, I do expect a pellet or two of sleet
or a flake of snow at the beginning of the warm advective
precip. Temps will be well above freezing during that time, and
column temp profile then rise to entirely above freezing. At the
worst a very thin coating of frozen stuff may occur on the
grass in the far NE miles of the County Warning Area. Ground/Road temps very
warm, now. Not expecting any problems.
Long term /Thursday 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 New Jersey 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.
Aviation /19z Wednesday through Monday/...
VFR conditions will continue tonight most of Thursday with
increasing high-to-mid level clouds/cigs. Showers are possible
by noon in the far west (jst/bfd), and the cigs do lower rapidly
during the day in much of the rest of the area. Expect one wave
of warm advection rainfall in the afternoon and evening rolling
through from SW-NE. But, there could be a few sleet pellets or
snow flakes mix in right at the very beginning of the precip.
Temps will be much too warm to have this make any kind of
trouble on the ground. Wind will go light/variable tonight, and
increase over the west later in the morning over the west as the
high pressure overhead currently slides to the E/NE.
Conditions go downhill in the evening and sub-VFR conditions in
rain showers and lowered cigs last into Friday night.
Sat: sub-VFR restrictions early; then gradually improving
conditions into Sat night.
Sun-Mon: VFR/no sig wx.