Scientific Forecaster Discussion
fxus61 kctp 261417
Area forecast discussion
National Weather Service State College PA
1017 am EDT Wed Apr 26 2017
a moist east-northeast inflow from the Atlantic Ocean will
provide a cloudy and misty start today, followed by clearing
through the afternoon. A few strong to severe storms are
possible across the northwest alleghenies Thursday afternoon and
evening. Warmer temperatures are expected through the end of the
Near term /through tonight/...
GOES-16 shows the closed low circulation south of Long Island.
Vertically stacked system slowly drifting to the north. A trough
extends back over US. Lucky US!
Clear skies to our west and low clouds stuck over our region and
at least two distinct wrap around high cloud bands above the low
clouds. Not much on radar.
The hrrr implies the sun will erode the clouds. Areas between
bands and farther west will see peaks of sun. This will increase
as the day GOES on. The hrrr and sref have only slight chances
of any showers this morning in southeast PA close to the last
band seen on radar earlier today.
Kept the patchy fog in southern PA through this am. Probably
patchy drizzle in a few places too. But this should steadily
Warmer we get this afternoon the more we will erode the clouds
and temperatures should rebound with late afternoon highs
probably in the 70s in many locations.
Short term /Thursday through Friday night/...
overnight still some lingering clouds. We should see a surge of
warm air into the region. Most guidance shows 15-18c at 850 hpa
implying a well above normal day temperature-wise.
But the front to our west is trying to move into the western
flanks of the ridge. Thus the gefs and sref generate some cape
and there is a modest surge of wind into westernmost PA. Thus
marginal risk in western PA.
The sref/gefs timing is pretty late in the afternoon and
evening. Gefs clearly generates quantitative precipitation forecast in afternoon and evening
with efs mean cape generally in the 600-1000jkg-1 range moving
by. Thus both systems general quantitative precipitation forecast/pop mainly after 21z in
western PA which moves into central areas after 0000 UTC. This
implies these efss release the cape so to speak and imply
convection mainly in the 21 to 03 UTC timeframe.
Drier air as indicated in the precipitable water field implies sweeps across the
state west to east in the 0000 to 0600 UTC range implying
similar timing as the pop/cape maximums. Not big event. But good
chance of thunderstorms in northwestern PA and at least a chance
in central areas.
Long term /Saturday through Tuesday/...
model and ensemble guidance remained in good agreement with
large scale pattern amplification this period with a vigorous
closed 500 mb low ejecting northeast from the southern rockies into
the upper Great Lakes/Canada and deep surface cyclone expected
to lift out of the MS valley. Meanwhile, an anomalous upper
ridge centered over the southeast U.S./Western Atlantic will
gradually weaken and shift east.
The details of weekend forecast are still uncertain with rain
risk likely focusing along/north of quasi-stationary frontal
zone progged to shift south of PA by early Sunday before lifting
back to the north as warm front. Therefore continued to utilize
a nbm/ecens/wpc blend for Max/min temps and probability of precipitation which
maintained good continuity with previous fcst. While unsettled
with a period of rain likely at some point, the fcst does not
look like a washout. Temperatures should remain above late-
April climo but could be too warm/cool depending what side of
the boundary you are on.
Max probability of precipitation remain centered on Monday/may 1st as the aforementioned
cold front crosses the Appalachians and continues toward the
Atlantic Seaboard. A severe weather threat may evolve downstream
from the Ohio Valley into the mid Atlantic, but at this time it is
unclear whether instability will be sufficient to support severe
Temperatures will decline to near normal behind the cold front by
next Tuesday may 2nd.
Aviation /14z Wednesday through Sunday/...
lots of clouds and low clouds around this am. Some isolated
bands of light rain too. Most areas are MVFR only patchy infrared.
Conditions should slowly improve later this morning and
afternoon from west to east as the low to our east drifts away
Model relative humidity profile support VFR conditions at bfd/jst by midday,
while more gradual clearing takes place across the eastern half
of the state during the afternoon. Poorest flying conditions
will likely hang on the longest (perhaps until 16-17z) across
the lower susq valley invof kmdt, klns and kmui.
Patch MVFR/IFR overnight expecting areas of fog. We also
anticipate late afternoon/eve showers and thunderstorms over
western areas spreading into eastern areas. Highest probability
in the 21 UTC to 03 UTC range.
Thu...am fog possible. Isolated PM tsra impacts possible west.
Fri...no sig wx expected.
Sat...rain/low cigs possible northwest mtns. Isolated tsra impacts
Sun...low cigs possible east. Isolated PM tsra impacts possible