Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
710 PM EDT Wednesday Jul 30 2014
Upper level low pressure will stay anchored over James Bay Canada
through Friday before weakening and moving to the northeast.
Another trough forming over the lower Ohio Valley will bring
increasingly humid and unsettled conditions for the weekend.
Temperatures will remain cooler than normals.
Near term /until 6 am Thursday morning/...
7 PM update...
A line of showers and thunderstorms is moving into the middle
susq valley. Storms are bringing downpours and wind gusts in the
Hrrr shows convection staying fairly active well into the
evening...not quieting down appreciably until after midnight.
The cold air aloft and cyclonic flow will likely keep low to middle
clouds around through the night with a few showers remaining
possible...mainly across the northwest mountains
Min temperatures will be closer to normal tonight...but some readings
in the 40s are still possible across the near mountains region and
perhaps a few of the cold spots across the high terrain of
Short term /6 am Thursday morning through Thursday night/...
The upper low throws one more uppercut at northern Penn Thursday
morning...before refueling temporarily for a day or so across the
lower Ohio Valley.
Scattered/numerous showers are expected to affect the northern third to half of
the County Warning Area in the morning. The afternoon should turn out to be mainly
dry - within an area of large scale subsidence and weak surface hi
pressure in the wake of the upper wave.
Temperatures aloft will still be cool and daytime instability should be
good enough for isolated-scattered showers in the west/north during the middle
to late afternoon.
Highs temperatures Thursday may try to sneak back to normal in the
southeast...but the north/west zones will probably still be 8-10 degrees below
seasonal normals given more in the way of clouds and scattered
The Thursday night period continues to look like the least likely
time for any showers to develop with 500 mb height rise of a few
dam...and weak ridging over the area at the surface. Lows early Friday
morning will be similar to the previous few nights with skies trying
to clear and winds generally light/variable.
Long term /Friday through Wednesday/...
the global models and ensemble members show the highly amplified
noam western ridge/eastern trough configuration relaxing into
early next week...but otherwise maintaining its orientation. The
rising 500mb heights should allow temperatures to edge back toward
early August climate normals. The general pattern remains unsettled
through the weekend.
The mean upper trough axis shifts westward to near 90w which should
allow the quasistationary frontal zone draped along the eastern Seaboard
to drift westward along the I-95 corridor. The 12z gefs shows plume of
hi precipitable waters pooling near the surface boundary along/east of the applchn
spine. This suggests the potential for heavy rafl setting up from
the southern Middle Atlantic States up into southeastern PA/Delmarva/NJ areas. There
are still some quantitative precipitation forecast differences but the latest runs seem to be
converging toward the idea the the main quantitative precipitation forecast axis will be east of
the applchns...although the diurnal cycle and individual shortwaves
moving through the lw trough will play a role in the duration and
Conditions should improve into early next week as the hi precipitable water
plume shifts S/east and drier air arrives accompanied by surface high
pressure on Monday. Northern stream energy is slated to push a cold front southward
into the area by next Tuesday/Wednesday which may stall out from the Ohio Valley
into the Middle Atlantic States.
Aviation /23z Wednesday through Monday/...
late afternoon update highlights ongoing precipitation and
movement through the area. Rainfall diminishing just to the west
of kjst and kaoo so went with better conditions than sites to the
north...where convection is ongoing and moving toward both kipt
and kunv. By the time the system reaches the southeast
sites...loss of daytime heating should diminish chances for any
precipitation and any reduction in VFR conditions.
Mainly VFR for tonight with lingering broken Alto cumulus clouds...and
perhaps a few stray light showers.
A stronger 500 mb trough will rotate across the area
on Thursday...accompanied by another round of scattered showers and storms
/mainly across northern Penn/.
A brief dry period with weak ridging at the surface and aloft over the
regional airfields Thursday night and Friday.
Afterward...a potent upper trough will form over the lower Ohio
Valley and lift slowly NE toward the middle atl region over the weekend.
Deep moisture surging northward from the Gulf and western Atlantic will
bring periods of showers and thunderstorms and rain over the weekend /focused across
the southeast half of the state/.
Thursday...scattered thunderstorms and rain impacts possible.
Fri-sun...scattered PM thunderstorms and rain impacts possible.
Mon-Tue...slow improvement expected with areas of MVFR possible
mainly in the morning.
near term...la corte/Lambert