Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
505 am EDT Thursday Jul 31 2014
a closed upper level low pressure centered over James Bay will
lift slowly northeast today. However...the associated long wave
trough will sharpen up off to our west through the weekend.
Thus...increasingly humid and unsettled conditions are expected
for the weekend. Temperatures will remain cooler than normal.
Near term /until 6 PM this evening/...
waves of fog seem to be occurring as many locations/observation -
including out the window - have a rapidly changing visibility.
Will mention areas of fog for the morning in the central cos where
it rained the most yesterday.
Infrared and WV loops depict a rather consolidated short wave trough
than earlier forecasts have shown. The only clusters of thunderstorms and rain at 09z
are to our north and moving generally northeast. Newest echoes
popping over the Middle-Lake convergence area are headed east. This
could strafe the northern tier as the sun rises. Working off the
premise of a more compact area of forcing and not two separate
vorticity maxima...there should be a quicker exit to the main bunch of
showers across the north today. The best forcing will be during
the morning...but the best instability will be in the middle- day
hours. So there might be convection form as the tail end of the
forcing presses through the County Warning Area. Highest probability of precipitation will be in the
morning across the north. But low chance probability of precipitation still a good idea for
much of day...inching off to the east by sunset. Good sunshine
this morning over much of the area will help temperatures get a few degrees
warmer than Wednesday - very near normal in the southern tier but still 5-10f
below normal in the rest of the area.
Short term /6 PM this evening through 6 PM Friday/...
NAM and GFS both hint at a minor chance of a shower in the northern tier
in the evening. Will just leave a 20 pop there for the time being
while dropping probability of precipitation off in the east. Winds over the Ohio Valley
remain srly at the surface and the upper low rotates up to the
northeast - allowing heights to rebound. But the yin of rising
heights will be accompanied by a yang of a dip in the long wave
trough. The axis of this trough will remain to our west into the
next week. Continued unsettled conditions are in store as precipitable waters
rise on good poleward flow and an inverted surface trough forms along
the East Coast. The northward surge of moisture will likely
trigger showers and thunderstorms over the middle-Atlantic tonight
which will rise into the area for Friday and into the long term
period. Temperatures do get nearer to normal on Friday.
Long term /Friday night 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/30th 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 placement.
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 /09z Thursday through Monday/...
light showers diminishing over the southeast at 06z...with new area of
showers/thunderstorms riding next shortwave across Lake Erie. It appears
most of this activity will remain to our north...though isolate
showers poss mainly in western sections overnight /esp near kjst/.
With earlier rains...clouds scattering out and light
winds...expect some drops in visibility in fog overnight...with impacts
varying quite a bit from site to site.
A stronger 500 mb trough will rotate across the upper Great Lakes
the first half of Thursday...accompanied by another round of scattered
showers and storms mainly over New York...and likely sneaking
into the northern mountains /kbfd/ as well.
Thursday...scattered thunderstorms and rain impacts possible.
Fri-sun...scattered PM thunderstorms and rain impacts possible.
Monday...slow improvement expected with areas of MVFR possible
mainly in the morning.