fxus61 kctp 251151
Area forecast discussion
National Weather Service State College PA
751 am EDT Thu may 25 2017
soaking rain this morning will become more showery later today
with a few strong thunderstorms possible mainly across south-
central PA. Scattered showers will linger into Friday followed
by a period of mainly dry conditions Friday night into Saturday.
Showers and thunderstorms will likely impact the area Sunday
into Memorial Day. Today will be the coolest day this week with
temperatures rebounding through the Holiday weekend.
Near term /through tonight/...
10z: band of heavier rain focusing over the western 1/2 of the
County Warning Area early this morning. Highest rainfall totals in the past 12
hours are concentrated over this area with Max rainfall amounts
around 1 inch over parts of the Laurel Highlands.
Previous: all near term hires guidance shows steady light to
moderate rain overspreading central PA through 12z. Peak
rainfall intensity between 09 and 15z still looks good
coincident with Max 850 mb mflux anoms and strong southeast low level jet. Multi-
model derived quantitative precipitation forecast amounts between 0.50 and 1 inches expected
through midday with areas of 1"+ amounts in the southern
alleghenies aided by orographics and robust dynamics. Negligible
instability will inhibit short-term rain rates resulting in a
soaking rain with no runoff issues anticipated. The steadier
rain should lift over the northern 1/2 of the area later this
morning with overall Mode of precipitation becoming more showery
this afternoon with partial sunshine/cloud breaks expected in-
and- out of shower spells.
Occluded front pushes north of the Mason-Dixon line this
afternoon which should allow for at least modest destablization
with cloud breaks most likely across south-central PA. Storm Prediction Center has
expanded marginal risk northward into this area with thinking that
thunderstorm development will concentrate near the frontal
boundary over south-central PA. Instability is not that great
but shear profiles are supportive of at least low risk severe
probs. There is also plenty of large scale forcing to work with
given strong height falls/negative tilt trough and favorable
left-exit region jet dynamics. Will include risk for isolated
strong/severe storms in severe weather potential statement. Anticipate a gradual decrease in
shower activity tonight into early Friday morning with consensus
Max pops focused over the far NE and SW portions of the County Warning Area.
Short term /Friday through Saturday night/...
broad cyclonic/west-northwest flow on southern end of exiting
upper trough will support terrain-enhanced showers on Friday
before precip winds down Friday night/am Saturday. A lower-
amplitude but moderately strong westerly (zonal) mid level flow
will set up in the wake of the departing upper trough with
modest height rises/weak will ridging aloft into the weekend. A
warm front is progged to extend east from surface low in the
western Ohio Valley to the mid-Atlantic coast on Saturday.
Central PA should reside on the North/East fringe of high
instability convective corridor/mesoscale convective system type pattern expected to
evolve from the central and Southern Plains to the southern mid-
Atlantic coast into Saturday night. The greatest risk for
scattered thunderstorms remains over the SW 1/4 to 1/3 of the
County Warning Area which is consistent with previous fcsts. Storm Prediction Center has introduced
a marginal risk into this area for d3. The remainder of the area
should see a mainly dry start to the Holiday weekend but will
maintain slight chance pops.
Long term /Sunday through Wednesday/...
the large scale pattern will evolve into a broadly cyclonic
flow regime by Monday with upper trough parked over the Great
Lakes and southeast Canada into midweek. The aforementioned warm
front will lift north across the area on Sunday followed by a
series of weaker cold front associated with shortwave trough
rotating around parent upper low centered to the south of Hudson
Bay. Ensemble blend still supports Max pops on Sunday/Sunday
night into Monday with some additional shower opportunities into
midweek as series of shortwaves rotate around mean upper trough.
Temps should average pretty close to normal/seasonal to close
out the month of may.
Aviation /12z Thursday through Monday/...
low pressure located over Ohio will bring a steady rain with
widespread IFR/low MVFR cigs to central PA this morning. The
rain will taper off from south to north during the late morning
hours as a warm front works into the region. Rapidly improving
cigs and a wind shift from east to south are likely as the warm
front arrives during early to mid afternoon in the south and
late afternoon in the north. A few evening tsra could form in
the unstable air mass south of the warm front, so isold tsra
impacts are possible across the southern half of PA.
Winds will shift to the west this evening, as the low pressure
system passes north of PA. Residual low level moisture ascending
the Allegheny mtns is likely to result in IFR cigs at bfd/jst by
late this evening, while downsloping flow results in more
favorable cigs further east. Across eastern PA, light wind, wet
ground and light winds could result in areas of fog late tonight.
Fri...am low cigs/showers likely bfd/jst.
Sat...am fog possible bfd.
Sun...showers/reduced cigs possible, esp Sun night.
Mon...am low cigs poss west. Sct PM tsra impacts poss east.