Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
731 am EDT Sat Sep 5 2015
high pressure will ensure mainly dry weather for Labor Day
weekend with above normal warmth and just the chance of an
afternoon or evening pop-up shower or thunderstorm. The pattern
will start to change in the middle of the week as the upper level
flow flattens out and a cold front drops down from the north.
Near term /until 6 PM this evening/...
showers have been persistent in the southern tier through the night.
The wind shift/weak convergence and deep easterly moisture influx
are probably driving these showers since diurnal instability has
long since disappeared. Only light showers /no T/ left in the SC
mountains hrrr and rap move these slightly to the west before killing
them off just after sunrise. Low clouds have overspread/developed
over the entire region except for Warren Colorado. A few patches of
clear east of kipt can be imagined when perusing the 11-3.9
micron imagery this morning. Otherwise...it is cloudy. These
clouds could be tough to mix out - at least in a rapid fashion -
since they are generally above 1kft. Thus...will hang onto some of
these clouds into the middle to late morning. The east will be
breaking out into the sun and the mixing in the west could allow a
shower or two to develop in the afternoon. However...most of these will
remain west of the County Warning Area. Only the northwest is worthy of a chance pop for
late this afternoon/this evening as a lake breeze may kick off a few
rain showers. The clouds will make it more difficult to get to the lofty
maxes we have experienced recently - including ties of the record
highs at Harrisburg...Altoona and Bradford yesterday. Will go for
maxes based on an equal blend of MOS guidance minus one or two
degrees. This will result in only a 10 degree diurnal swing at many
Short term /6 PM this evening through Sunday night/...
the upper low over the upper Great Lakes will slowly fill and lose
character. The surface high will still nose into the state...but the
center of it will slide south into the western Atlantic by
Monday. Any showers this evening will likely be in the northwest...but
the expected cell motion should keep them either out of the state
to the north or make the few that do pop up go slowly to the north
and out of the area early this evening. The low clouds will
probably try to redevelop in the eastern mountains other areas may see
them try to form...but will keep it generally p/c overnight with
the clearing perhaps allowing for some morning fog on Sunday.
Sunday looks to be drier and sunnier...and probability of precipitation almost non-
existent. Temperatures will get a few degrees f warmer vs Saturday. Once
again...it will be the far northwest which could see a pop up shower -
perhaps again being generated along a lake breeze boundary.
Long term /Monday through Friday/...
the high pressure will keep it warm and mainly dry into Monday.
A weak cold front will slide slowly to the east-southeast from the Great
Lakes/Midwest states. This feature could bring some isolated
rain showers/thunderstorms and rain to our northwest zones beginning Tuesday afternoon and evening.
A slowly amplifying broad trough from the northern plains through the
NE U.S. Wednesday afternoon into next weekend will push a
second...stronger cfront east across the commonwealth Wednesday
night and Thursday.
This pattern transition will bring a few opportunities for
showers and thunderstorms...albeit mainly of the scattered
afternoon and evening variety.
12z gefs and 12z ec are in good agreement on the location of this
trough axis /from Lake Superior to the middle miss valley at 00z
Sat/...though as one would expect...the ensemble mean dampens out
the amplitude of the trough compared to the ec.
Details in the timing of any specific shortwaves rotating through
this amplifying trough are simply too Muddy at this time range.
One thing more certain in this medium range forecast is the cooling
temperatures for the latter half of the week and next weekend...when both
maximum and min temperatures could be up to several degree f below normal
/especially over the northern and western mountains of the state...where more
clouds and cooler temperatures aloft will be found/.
Aviation /11z Saturday through Wednesday/...
11.3.9u imagery at 11z shows stratus has become widespread across
central PA...the result of moist southeasterly flow and orographic
lifting. Blend of latest hrrr/surface observation suggest IFR ceilings are likely
between 12z-13z at kbfd/kjst and possible at kaoo. Lower elevations
further east should fare better with MVFR ceilings expected.
Diurnal heating/mixing will cause ceilings to rise by late am. Model
soundings indicate MVFR ceilings may linger across the central mountains
until around noon. However...by afternoon there is a high degree of
confidence in widespread VFR conds and light wind.
Mostly clear skies and a light wind will likely result in patchy
valley fog again early Sunday morning.
Sun-Tue...patchy fog in the morning...otherwise VFR.
Wednesday...isolated PM thunderstorms and rain impacts possible.