Scientific Forecaster Discussion
fxus61 kctp 282022
Area forecast discussion
National Weather Service State College PA
422 PM EDT Tue Mar 28 2017
an area of low pressure will move along the Mason-Dixon line
through tonight...bringing showers to central PA and isolated
thunderstorms to southeastern sections today. High pressure
will build down out of southern Canada and bring cooler and
drier weather for Wednesday and Thursday.
A new storm system will approach for the end of this week with
the potential for more inclement weather.
Near term /until 6 PM this evening/...
still some areas of light rain over eastern areas and drizzle
with low clouds in central areas. But the main energy has moved
off to our east. GOES-16 shows all the cold cloud tops to our
east and cold conveyor lifting into New York.
A lot of dry air in western PA and the upper level low to our
south. So most of the significant rain is over. Gradual
improvement later this afternoon and evening.
Best probability of precipitation now in the eastern areas.
Short term /6 PM this evening through 6 PM Wednesday/...
the rain threat should mostly be off to our east by 8-10 PM.
Improving conditions as the strong anticyclone to our northwest
slides slowly over the area. Should be near seasonal day with
mostly sunny skies and little chance of quantitative precipitation forecast.
Long term /Wednesday night through Tuesday/...
a nearly north-South Ridge of high pressure with dry air, and
normal to slightly below normal 850 hpa and 925 hpa temperatures
will be overhead Wednesday night, creating nearly optimal
conditions to radiate strongly/cool off into the 20s to low 30s.
The one factor to watch closely that could impact min temps
will be the timing of thickening mid/high clouds that will be
spilling over the top of the upper ridge just to our west.
For Thursday...should the timing of thickening clouds occur
during the morning (prior to the late March sun having much of a
chance to warm the sfc) then the much cooler NAM temps (ranging
from the 40s to around 50f in the south) may be in store for
US, accompanied by a light southeasterly flow.
12z GFS/ec and their respective ensembles are in good agreement
with the onset timing of warm frontal rain that streaks quickly
east from the Ohio Valley Thursday afternoon and evening.
Evaporational/dynamic cooling of the airmass helps 925-850 mb
temps dip to around or slightly below 0c across our NE counties
Thursday night and Friday as the steadier light-mdtly heavy,
warm advection rain begins there. Included mention of a
rain/sleet and snow mix to the north and east of a kipt and kseg
line (mainly across elevations at or above 1800 ft msl, where even a
light coating of snow/sleet is possible by daybreak friday).
There's a low prob for a light coating of snow on the high
terrain across Sullivan County.
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 /20z Tuesday through Sunday/...
considerable areas of MVFR and IFR remain this afternoon,
however latest satellite image shower the sfc low moving
eastward. The rain, mist and fog should persist through this
afternoon though clearing has already begun at aoo. Upslope flow
will keep jst in IFR cigs and vsbys but west to east expect cigs
and vsbys to improve between 21z to 00z. MVFR could persist
until around 03z, especially at bfd.
The trend for improvement will continue overnight with fair
weather and VFR conditions tomorrow.
Wed...early a.M. Restrictions; becoming VFR.
Thu...VFR/no sig wx.
Thu night-Fri...sub-VFR restrictions/rain likely.
Sat...gradually improving conditions.