Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1156 PM EDT Tuesday may 26 2015
high pressure at the surface and aloft will remain anchored just off
the East Coast through the end of this week. A cold front will
likely push across the region Saturday night...then stall just
south of the state early next week.
Near term /until 6 am Wednesday morning/...
1015 PM update...
mesoscale convective complex is moving into far eastern Ohio...but
weakening as it does so. Most of the very sparse convection that
did form this evening dies very quickly over central PA. The
warmer temperatures aloft closer to the upper ridge and the loss of
daytime heating will most likely weaken this stuff even further.
Some/slight development is seen at this time on the southern
flank. If this diminishes as well...little to no precipitation will get
into the County Warning Area...or certainly cross rte 219 before daybreak. Will
paint low probability of precipitation in for the west and none for the east. While a very
isolated shower may pop over the central mountains or susq valley...it
is not Worth probability of precipitation at this point. A muggy and warm night is in
store and some fog is possible in the morning.
deep south-southwesterly flow on the western periphery of the
dominant coast ridge will continue to transport Gulf of mex
moisture northward into central PA.
Water vapor loop and rap 300-400 mb wind forecasts indicate that a
well-defined...albeit compact short wave will be moving NE across
Lake Erie late this afternoon...while an associated 45-50 knots
jetlet crosses northern and western Penn.
Enhanced mesoscale lift from this feature will team up with the
growing cape values /locally as high as 1000-1500 j/kg/ across
the Allegheny plateau to produce increasingly numerous
showers...and a few thunderstorms and rain late this afternoon and early this
Blend of the latest NAM/sref and hrrr continue to favor the northern
mountains...and portions of the Laurel Highlands for the greatest chance
of showers/scattered thunderstorms and rain.
For areas south and east of kcbe to kseg and kavp line...the
period through 21z should remain dry. However...differential
heating at the southeast edge of the middle level cloud shield...and a
ribbon of highest 850 mb Theta-E air advecting east into the
middle susq valley should help to focus and enhance another area
of showers there late today.
Storm Prediction Center paints their marginal risk of severe thunderstorms and rain across roughly the western
half of Penn this afternoon and evening.
Basin average rainfall will be generally around 0.10 of an inch in
most places through midnight...with some spotty 0.25-0.50 inch
amounts in thunderstorms and rain.
Temperatures are nearing their highs for the day ranging from the middle-
upper 70s over the Allegheny plateau...to the m80s across the lower
Short term /6 am Wednesday morning through 6 PM Wednesday/...
a potent shortwave lifting through the Great Lakes will introduce a
better chance of rain showers/thunderstorms and rain on Wednesday. Model timing of this feature
suggests showers could arrive early in the day across the west
counties...with a greater risk of PM thunderstorms and rain across eastern PA.
Gefs mean convective available potential energy peak around 1200 j/kg across the southeast counties Wednesday
afternoon. However...middle level winds and associated deep-layer shear are
not particularly strong in the latest model data...so the severe weather
threat just marginal...and that's what Storm Prediction Center covers practically all of
the County Warning Area with in their day 2 convective outlook.
Mcldy skies will hold temperatures down a bit...but consall still
suggests high temperatures between the m70s- l80s...several degree above normal
for late may.
Long term /Wednesday night through Tuesday/...
upper level trough will deepen as it propagates eastward. Expect
cold front to move through PA...Wednesday night into Thursday
morning. This will bring northwesterly flow and cooler and drier
air. High pressure at the surface and aloft will build over the
region through Friday...reducing any precipitation chances through
the latter half of the week as the bulk of medium range guidance
implies drier weather as lower precipitable water air mass works into central PA.
A cold front will likely bring an end to the Summer-like
warmth/humidity next weekend. A fair amount of agreement among medium
range guidance for rainy weather Saturday night into Sunday along an
incoming frontal boundary. Scattered showers could follow Sunday/Monday
as wave of low pressure rides eastward along stalled frontal boundary
south of PA.
Aviation /04z Wednesday through Sunday/...
a Summer-time pattern will persist through the week.
Radar continues to be quiet across central PA at 04z...though some
convection beginning to edge eastward across the Ohio/PA border into
west PA. Majority of County Warning Area will remain dry overnight...but some showers
may slip into far western counties from kbfd-kjst after 10z. VFR
conditions have been the rule so far /except at kipt where rain
fell late Tuesday afternoon/ but as sunrise approaches and moist low
level flow picks up a bit...expect MVFR ceilings/visibility to develop over
much of County Warning Area.
Sref model guidance suggests /and even NAM MOS hints/ that the
lower ceilings may linger into late morning from kipt-kmdt before a
return to VFR...middle morning elsewhere. Chances for
showers/isolated thunderstorms peak across western half of County Warning Area between
12-18z...and slide eastward after 16z.
Wednesday...patchy a.M. MVFR fog/br. Scattered showers/tstms.
Thu-Fri...patchy a.M. MVFR fog/br. Isolated p.M. Thunderstorms.
Sat...patchy a.M. MVFR fog/br. Scattered-numerous p.M thunderstorms west/cold frontal passage.
Sun...MVFR ceilings poss northwest. Otherwise mainly VFR in scattered showers.