Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
754 am EDT Wednesday Mar 12 2014
a strong late-winter storm will impact the area today...followed
by cold and blustery conditions with well-below normal
temperatures for Thursday. Temperatures will rebound to near
seasonal levels Friday into the weekend...ahead of a frontal
system pushing southeast from the Great Lakes. This front may
produce some rain or snow showers on Saturday.
Near term /through tonight/...
Strong and fast moving storm system over western Ohio will spread
snow...rain...thunder and perhaps severe weather to our region
later today. Temperatures in northwest will remain in low-middle 30s and in
southeastern areas...they should top 60. Strong baroclinic zone.
A frontal boundary is sagging into northwestern PA which will
produce the quick change over to snow in northwest Pennsylvania this
morning. Radar and observations show snow over southern Michigan and Ohio.
Implied snow bands over Lake Erie. The track of the low will keep
the cold air from pushing too deep into Pennsylvania this morning
and early afternoon. Thus west-southwest for heavy snow currently confined to
northwestern area. With advisory to south and east as cold air
Models suggest fast system with rain and potential thunder later
this afternoon/early evening in central and southeastern areas.
coupled jet structure still looking like a classic example...and
interaction should drop the pressure of the main surface low as it
traverses the PA Turnpike through the late morning and into the
evening. It will take it/S own toll by bringing moderate to heavy
rain to most of the state today...but RUC points to a lowering of
the Li/S and true instability across the southern third/half of the
area late this afternoon and early this evening. Storm Prediction Center has a slight risk
area covering that rough area...and have added gusty wind wording
to the grids for that time frame - right as the low passes
The snow will be heaviest in the north in the middle day and afternoon.
Quantitative precipitation forecast is impressive but may be tainted by convective feedback on
some model solutions. Still...the overall picture of 1-1.25 inches north
and 0.5-0.75 S is looking good. Thus...with the bulk of the precipitation
falling as snow along the New York border...especially Warren and McKean
cos...the going storm totals look solid with 8-10 there. The snow
accumulation gradient will be tight - especially during the daytime -
with almost no snow south of Route 6 in the morning and not far S
of the northern tier of cos this afternoon...despite falling temperatures. The
warm air aloft is just too much and sun angle now high enough to
make the snow forecast a real trouble. As the temperatures get cold this
afternoon/evening...there is a danger of the rain-wet roads
becoming icy quickly as the precipitation type change over occurs from north
The surface low should continue to deepen as it moves into New Jersey this
evening. The precipitation should taper rather abruptly in the central
and southeastern zones this evening. By 01z...little if any precipitation is left
there. So by the time the profiles get cold enough for snow
there...it should be ending. Will keep all snow totals and timing
as is with just minor editing.
The winds will get strong/gusty in the northern mts late this
morning...but the passage of the low and any storms in the south
will kick them up there in the early evening.
Short term /Thursday/...
Made minor changes to grids with overnight lows mainly near 0 in
northwest to teens southeast. Still forecast to be very cold day.
Updated guidance was similar to previous forecast. Changes were
the snow should be tapering off to scattered shsn in the evening across
the northern and western mts...but will keep current timing on west-southwest flags to
allow for lingering snow and blowing snow problems. Low pressure
continues to deepen as it moves away and creates wind problems for
the local area. The winds will get faster across the southern half of
the area tonight and sustained speeds and gusts may both reach
Wind Advisory criteria. Have thus posted an advisory for those areas
through Thursday noon. While winds will be strongest there in the
south...the temperatures do not drop fast enough to get wind chills below
advisory the line of -15f. Will issue an advisory for the northwest half as the
criteria should easily be met. If the timing of the snow were to
be ending later Thursday morning...we may have been able to forgo a
Wind Chill Advisory and just wrap it into the west-southwest. But the chills will
last much longer than the accumulating snow...through the entire
morning...whereas the snow should be virtually done by 2 am/06z.
Thursday should be one of the coldest we have seen yet this
winter. This is even more impressive given the middle-March timing.
800 mb temperatures drop into the minus 20s c in the morning...but this
nastiness gets dragged through the area rather quickly due to the
sharpness of the trough and progressive nature of the flow aloft.
Little breaks in the clouds over the S/southeast overnight should lead
to greater breaks in the morning over the southern tier and southeastern areas
could clear up totally by the end of the morning. Will play it
more-cloudy than that for now. Even with the sun and
downslope...the maxes in the southeast will only be in the M/u20s. That
would be welcome in the northern tier where maxes may not make it into
the tweens /10-12f/.
The gusty winds will gradually subside during the day Thursday with
daytime highs 25-30f below normal. Daily record low/mini-maxes are
in jeopardy. In addition...low temperatures Thursday morning across western PA
will also be near daily record. Suffice it to say...it may not be
this cold again /especially during the daylight hours/ until next
Long term /Thursday night through Tuesday/...
the good news is that the cold blast will be short-lived...with a
rapid moderation occurring on Friday. Breezy SW return flow in
advance of northern clipper surface low tracking across the upper Great Lakes
and downsloping should help to boost temperatures into the 40s north and
50s south. The models turn the low to the northeast up the St.
Lawrence Valley on day 5/Sat...dragging a trailing/weak cold front
across the northeast and middle-atl states. Model consensus indicates
some light precipitation is possible with chance probability of precipitation as the front shifts southeastward
across the County Warning Area.
Gefs/ec ensemble means show the large scale pattern reverting back
to a western ridge/eastern trough configuration into early next week. This
has been the favored/prevailing flow regime this winter...with a
cold polar vortex over eastern Canada. A strong surface high pushing
southeastward from the upper MS valley should direct colder air into the region
behind a reinforcing frontal passage on Sunday...with temperatures likely trending
lower by day 7/Mon. The non-NCEP oprnl models /12z CMC and European model (ecmwf)/
are more bullish on cyclogenesis in vicinity of the Gulf Stream just east
of the Carolinas...with the northwest edge of potnl precipitation shield possibly
reaching southern/southeastern PA on St. Patrick's day. Confidence is low given
the large spread between the GFS and ECMWF/CMC. Something to monitor
in the days to come.
Aviation /12z Wednesday through Sunday/...
conditions now IFR across the northwest. Steadier rain across the northwest.
Expect conditions to to go down hill across the rest of the
area...as rain becomes more widespread.
The big concern is strong winds and low level wind shear...along with heavy
rain...and perhaps some strong to severe thunderstorms along
the Maryland Line. Also snow across the north by after.
Then tonight the concern is still strong wind gust...rapid drop
in temperatures...and more snow.
Thursday will still feature gusty winds...as a deep storm pulls
away from the area.
Thursday...strong/gusty north/northwest winds...gradually diminishing in
Fri-sun...no sig weather expected.
with warmer temperatures rainfall today...we expect moderate
rises on rivers and streams. There is still enough ice in spots to
lead to ice jams...though significant decay has occurred at many
locations due to the recently warm weather. Any ice jams will be
isolated in nature. Monitor water levels closely for the rest of
Wind Chill Advisory from midnight tonight to noon EDT Thursday
Winter Weather Advisory from 3 PM this afternoon to 8 am EDT
Thursday for paz017-024-033.
Wind Advisory from 5 PM this afternoon to noon EDT Thursday
Winter Weather Advisory until 8 am EDT Thursday for paz006-010-
Winter Storm Warning until 8 am EDT Thursday for paz004-005.