Area forecast discussion
National Weather Service State College PA
1142 PM EDT Tuesday may 21 2013
Synopsis...
a warm and humid summertime air mass will continue to bring well
above normal temperatures to central Pennsylvania through
Wednesday. A cold front will cross the region on Thursday. A
second front will push through on Friday and usher in high
pressure from central Canada into the northeast and Middle-Atlantic
States. This high will bring cooler and drier air to the area for
Memorial Day weekend that could last right through Monday.
&&
Near term /until 7 am Wednesday morning/...
storms only now touching northern Warren County as best moisture
convergence stays along the northern border. Temperatures have dropped off at
the surface...but instability still high aloft. Isolated/scattered showers
and storms moving through pit and crw right now are on track to
move into the southwestern cos by midnight and could last into the middle
of the night if they hold together. RUC holds onto the cells for
another hour or two...but then dissipates them. This seems
plausible since they are not looking very healthy right now. The
cluster from WV seems to have more organization and will keep on
with low chance probability of precipitation for the SW into the wee hours. The RUC and hrrr
are at odds with each other with respect to the convection along the New York
border. RUC continues it through much of the night...but hrrr
breaks it apart. Will also hold the line with chance probability of precipitation for the northern
tier of counties seeing no preponderance of guidance that is
against some measure of elevated instability and potential for
convection there. Will keep mentions of patchy fog as well..with
mainly clear skies right now and high dewpoints. Clouds from
upstream will probably level temperatures off in a few hours...but fog
may yet creep into the valleys.
&&
Short term /7 am Wednesday morning through 6 PM Wednesday/...
a short wave moving eastward across the upper MS valley in vicinity of Iowa will phase with a
Canadian upper low/trough dropping southward across Hudson/James Bay during
the day Wednesday...reaching the Midwest by f48. At the surface...a
cold front pushing eastward through the Ohio Valley will be the main focus for
thunderstorm development/severe potential this period.
Am clouds with some spotty showers and areas of 1-2sm figure will
combine with weak ridging within the predominant southwesterly flow
aloft...to limit diurnal heating to some extent across the day 2 Storm Prediction Center
slight risk area - which covers nearly all of the County Warning Area with the
exception of the far southeastern zones. Although low to middle level winds
will be strongest across the northwest half of Penn...latest sref and short
range model guidance paints the greatest probability for cape
greater than 1200 j/kg across the lower susq valley late Wednesday
afternoon.
Despite the tempered destabilization...expect an afternoon increase in
thunderstorm coverage /with lower cloud bases compared to tuesday's/ along
with some pick-up in intensity as belt of stronger flow aloft shifts
eastward ahead of the middle-upper trough. Bands of thunderstorms capable of
producing damaging winds/marginal hail will be possible and thus will
continue to highlight an elevated severe weather threat in the severe weather potential statement for
Wednesday. Better forcing portends higher probability of precipitation ranging from the
medium-high chance range in the southeast to low lklys in the northwest. Showers/thunderstorms
may persist after dark into Wednesday night.
Maximum temperatures will likely be 3-5f lower than Tuesday...but still around
12f above normal.
&&
Long term /Wednesday night through Tuesday/...
the upper ridge will break down as a trough deepens into the Great
Lakes region by Thursday afternoon. This will correspond with a
front moving through the northeast Thursday. Timing for this front
is still varying but current ec brings the front through midday
Thursday. Couple this front with daytime heating and strong
southwest flow...Thursday could be the best day for daytime
convection this week. Both the operational GFS and the European model (ecmwf) continue
to output the possibility of a low level jet Thursday
afternoon...which with 35-40kts of deep-layer shear will only
increase probabilities for precipitation Thursday afternoon. This
eastern North America trough axis extending from James Bay southward
through the Great Lakes/mid- south to the central Gulf Coast will push
slowly eastward and should reach the East Coast by 00z Sat. This will
allow for persistent instability over the area through the end of
the week...with cold northwesterly flow behind the front. The
guidance is showing some notable diffs with the 500 mb system. The
NAM/GFS/gefs are slower and sharper with trough as it crosses the
Ohio Valley into the middle- Atlantic. The 00z GFS even closes off the 500 mb low
over northern Virginia Friday evening. The last two runs of the CMC have been trying
to generate a tropical cyclone- like system near the Outer Banks.
The known slow/tropical biases of the NAM/CMC and strong/closed
solution of the GFS leads to a UKMET/European model (ecmwf) preferred solution which favors
more eastward progression with the trough and its associated cold front.
Behind the departing cold front...a strong and large anticyclone
should dominate pattern in the Friday-Monday timeframe...building southeastward
from Nunavut Canada across the Great Lakes into the northeast. An
unseasonably cold/dry airmass will accompany the high resulting in
below normal temperatures for Memorial Day weekend. Ecens MOS data shows
temperatures on Friday/Sat struggling to crack the 60f mark locally...with
several opportunities for a late-season frost over the northern mountains
Sat/sun/Mon mornings. However current low temperatures remain above 40
for most of the region with the exception being along the New York
border. Winds should remain gusty Saturday morning. The better
chance for frost will be Sunday morning...temperatures will be
slightly warmer but the winds should be light to calm. There
should be a moderation into the middle of next week with temperatures
getting back to near normal around 5/28.
&&
Aviation /04z Wednesday through Sunday/...
not a lot of change. Still an isolated storm possible near
the New York border overnight. Also maybe a brief shower close
to jst...left out the forecast for now.
Earlier discussion below.
Main front and action across New York state...took mention of showers
and storms out of all sites but bfd. Left vcsh in bfd until 03z.
Some fog later...based mainly on what went on last night.
Not seeing much difference for Wednesday...very similar to today...
will be in the warm sector...with not much going on.
More in the way of widespread showers and storms later Thursday
into Thursday night. Could by busy across the far southeast Thursday night...
if a wave forms on the front.
Cooler and breezy for Friday into Sunday...as a strong cold
front drops southeast of PA.
Ho
outlook...
Thursday...scattered thunderstorm impacts possible...mainly in the PM.
Fri-Mon...no sig weather expected.
&&
Ctp watches/warnings/advisories...
none.
&&
$$
Synopsis...Lambert/steinbugl
near term...dangelo
short term...Lambert/steinbugl
long term...ceru/steinbugl
aviation...Lambert/Martin
