Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
553 am EDT Sat Jul 26 2014
a series of disturbances will move across the forecast area this
weekend as a deep upper trough develops over the northeastern
United States. There will be several chances for precipitation
before another shot of unseasonably cool air moves in and remains
over the region throughout the new work week.
Near term /through tonight/...
a potent shortwave can be seen on water vapor imagery sliding east
through the region. Short range operational models aren't doing
particularly well handling the small tight area of light showers
associated with the system.
With the shortwave sliding through early in the day...ridging
aloft should give a respite in the shower activity. As a
result...I went below model probability of precipitation as heights aloft rise ahead of
the next trough that will be digging into the gr lakes. Middle level
lapse rates will be fairly steep so I cannot rule out a stray
shower or T-storm...but thinking is that coverage will be small
enough to avoid mention in most areas.
850 temperatures pop up to 16-18c which should be suitable for daytime
highs to hit 80 or above over most of the area. More clouds up
north will probably keep readings in the upper 70s. Humidity will
be on a slow rise...but not terrible given that we are in the
height of the climatological Summer.
Storm Prediction Center has a moderate risk for a good chunk of Illinois-in expecting an mesoscale convective system
to form ahead of a cold front that will be moving into the
Midwest. These developments will have to be closely monitored for
southwestern sections later tonight as models show a rare late
night surge of instability moving into western areas. With
convective placement confidence being low at this range...I opted
for chance probability of precipitation centered mainly after midnight.
Short term /Sunday/...
Sunday could be a busy day as an unseasonably strong upper low
drops through the lower lakes and takes aim at the local area. Storm Prediction Center
has outlooked much of Kentucky and WV with a moderate risk which looks
reasonable given the strength of the approaching dynamics and
instability. We could be vulnerable locally into the evening given
the expected timing of the cold front entering the region and the
amount of upstream instability the system will have available.
Where the Ohio Valley developments take place will have much to
say about how far north into central PA the strongest storms will
manage to move. As usual...being about 2 days out...this remains
murky but this is a remarkably robust system for middle Summer and it
will be surprising if it passes without causing severe storms.
Given current projections of wind and instability...the area south
of I-80 would seem to be the region most under threat for severe
Highs in the upper 70s to middle 80s will be trending down over the
next few days.
Long term /Sunday night through Friday/...
all the action of note will be pretty much over by Monday with
Post frontal showers gradually diminishing in coverage as the low
and front slide through New England.
In a pattern that looks more like it belongs in middle winter than
middle Summer...an anomalously deep upper trough is made to set up
over the eastern US and remain in place all week. The details of
minor shortwaves sliding into the trough differ among the
available guidance...but deep moisture will have moved east so
we'll be left dealing with mainly diurnal instability under the
cold air aloft.
We could see more significant moisture return later in the week as
the GFS/gefs/ECMWF all hint at the upper trough retrograding a
bit...possibly paving the way for some Atlantic moisture to work
up the eastern Seaboard.
500mb heights in the 3-4std dev below normal range and 850 temperatures
of 1-3 Standard dev below normal point to the most certain part of the
forecast being several days of temperatures averaging well below
normal. A slow moderation can be expected by late in the week.
Aviation /10z Saturday through Wednesday/...
several more hours of widely scattered showers...but
conditions should remain VFR.
Showers should end by late morning...as vorticity maximum
moves east of the area.
Another jet maximum moves across the area this evening.
Thus could be a few more showers across the northern
and western areas tonight.
The combination of strong directional shear and
dynamics will likely result in some storms being on
the strong side at times from Sunday into Monday.
Looking at mainly dry conditions after Monday.
sun...scattered thunderstorms and rain impacts expected.
Monday...am low ceiling poss West Mountains
Tue-Wed...no sig weather expected.
near term...la corte
short term...la corte
long term...la corte