Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1253 am EST Sat Feb 28 2015
a large area of high pressure will build across the area for the
first half of the weekend. A low pressure system will lift out of
the Midwest...bringing snow and mixed precipitation to central
Pennsylvania Sunday and Sunday night. A stronger area of low
pressure will likely track west of Pennsylvania in the middle of
the week...producing another round of mixed precipitation and
rain in central Pennsylvania.
Near term /until 8 am this morning/...
wind has gone calm across the northwest mountains...allowing temperatures to plummet
late this evening. At 05z...mesonet observation indicate the colder
valleys of the northwest mountains have already dropped to around -15f. Across
the eastern half of the state...a light breeze has kept temperatures from
falling too quickly. However...as high pressure builds in...expect
diminishing wind and plummeting readings toward dawn. Have
tweaked min temperatures a bit...with lows averaging from around -15f over
the northwest mountains...to 0-5f across the lower susq valley. However...given
the ideal rad cooling conds...expect a wide range in lows from
hilltops/urban locations to normally colder rural valleys.
A bit of thin cirrus will overspread the area early this am in
response to developing warm air advection aloft. However...it should not
significantly affect rad cooling. Rec min for the 28th is -18f at
ipt and -1f at MDT. Even the -1f at MDT seems like a long shot
given current readings.
Short term /8 am this morning through 6 PM Sunday/...
fair and still cold weather expected Saturday...as surface high will
be right overhead. A fast-moving middle level shortwave is prognosticated by
all models to track across the area late in the day. Low precipitable water air
mass will preclude any precipitation concerns. However...cirrus may dim
the sunshine at times. Ens mean 850/925mb temperatures remain well blw
normal for the date...likely supporting highs only in the 20-25f
Long term /Sunday night through Friday/...
a relatively mild/active southwest flow aloft should prevail
through the period as the persistent upper ridge over the western U.S.
Temporarily breaks down. Numerous shortwaves within the northern and
southern streams will move east during the period providing potential
for precipitation...some of it rain...for a change.
An Arctic high pressure system over central PA at the start of
the period will move east of the region by Sunday night. The
combination of shortwave energy in the southern stream ejecting from a
trough and a digging northern stream trough moving southeastward from south
central Canada toward the upper Midwest seems to drive an
expanding area of warm air advection type snowfall spreading eastward sun-Mon.
While there appears to be little indication of a strong surface
low...models still generate 0.25-0.50 inch quantitative precipitation forecast amts along the
baroclinic zone. Thermal profiles seem to favor snow across the northwest
1/2 of central PA with mixed ptypes possible in the
south/southeast. Medium range...ensemble and wpc guidance suggest
sufficient qp for a significant snow event across part of central
PA. Accordingly...have issued a Winter Storm Watch across the
northwest most 5 counties starting late Saturday night/early
Sunday morning through Monday morning.
Another northern/southern stream combo looks to affect the region middle week
as energy from the southern cal upper low begins to eject eastward. Timing
differences are evident with the GFS more bullish on precipitation
returning early Tuesday vs. Slower European model (ecmwf) (tue ngt). Mixed ptype issues
are expected again with this next system...with a lean toward
rain as significant warm air moves north ahead of the system.
Behind the middle week system...another push of Arctic air will bring
temperatures and probability of precipitation back well below normal for late Thursday into
Aviation /06z Saturday through Wednesday/...
the northwesterly breeze will become light and variable
overnight. Expect widespread VFR conds overnight through
Saturday...with little more than some high cloudiness passing
Conditions will deteriorate later Saturday night into Sunday...as
clouds thicken and lower...and snow develops from west to east
across the area. The snow is expected to change to a wintry mix
across southern PA on Sunday.
Things should begin to improve on Monday and remain good into
early Tuesday...before the next system pushes another round of
precipitation and reduced flying conds into the area later Tuesday into Wednesday.
Overnight into Sat...generally VFR. No sig weather expected.
Sat night-sun...snow overspreading the area. Precipitation should remain
all snow across northern PA...while mixing west/ sleet and freezing rain
across the south.
Monday...continued ceiling/visible reductions possible...mainly am.
Tuesday...VFR am. Mixed precipitation with ceiling/visible reductions possible late.
Tuesday night-Wed...cig/vis reductions continue in wintry mix/rain.
the coldest February on record is still looking likely. Monthly
mean temperatures through the 26th...ipt 18... 20.7.
The current record coldest February..ipt 19... 21.4 both set
So far...this month is the third coldest ever at ipt...and fourth
coldest ever at MDT.
kmdt and kipt temperatures reading far too warm. Observer at kmdt
reported 27f as the maximum based on backup observation and nearest
neighbor. Parts on order for kmdt but kipt temperature spike/trouble is
new today and will be investigated. Using 28f for maximum in kipt
for today 2/27 based on nearest neighbor observations.
Winter Storm Watch from late tonight through Monday morning