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Area forecast discussion 
National Weather Service State College PA
346 PM EST sun Mar 1 2015

Synopsis...
weak low pressure and a disturbance at upper levels of the
atmosphere will track northeast up the Ohio Valley and cross
Pennsylvania this evening. This pair of weather features will
bring periods of light to briefly moderate snow...then some mixed
precipitation to south-central PA and the lower susq valley into
this evening. High pressure will bring fair and cold conditions
to region Monday and Monday night. A stronger area of low pressure
will likely track west of Pennsylvania late Tuesday and early
Wednesday...bringing mainly rain to the area. Colder temperatures
will follow for the later part of the week.

&&

Near term /until 11 PM this evening/...
did adjust the area of freezing rain some...to fit in with the
current observation.

Earlier discussion below.

Bright banding and elevated ccs showing the precipitation transition zone
well as it translates north of the Maryland border into the south
central mountains and far lower susq River Valley. 3" of new snow
o.G. Near Greencastle from a trusted weather spotter and now
freezing rain occurring at 27f. Sleet had briefly mixed in earlier
across southern York. A general 2-4" is expected south of
Interstate 80 and east of Route 99...with the additional
changeover to ice across southern portions of the south central
mountains and lower susq River Valley adding another .1 to .15"
of ice on top in those areas.

Overall scenario playing out with with periods of snow (of
varying intensity) continuing to increase in areal coverage this
afternoon from southwest to northeast. Strong vertical shear
evident across the region with 150+ knots 250 mb jet slicing east-northeast
across the Northern Ohio valley and eastern glaks. Boundary layer
convergence and forcing is best across southern PA this afternoon
and evening...in vicinity of 850 mb jet features...first of which
has spawned a few hours of moderate to locally heavy precipitation rates
from northern Maryland into my southeast counties. This is prognosticated
to exit eastward by late afternoon/evening before a more broad
area of boundary layer convergence develops as the upper trough
nears.

12z rap handled the ongoing changeover quite well for areas along
the Maryland border...and expect MDT to be changing over in the next
hour or two...starting with a mixture of sleet and then mainly
light freezing rain afterward with around 0.10 inch quantitative precipitation forecast. Will
continue to ride with a blend of current and upcoming high res
guidance for ice across our southern zones...unless we see reason to
significantly deviate.

We will continue to hold off on any upgrades to winter storm/ice
storm warnings at this time...as amounts are expected to remain in
the .1 to .15" range overall...with some approaching .20" on top
of the 2-4" of snow accumulate.

Elsewhere...good consistency of past several model/ensemble cycles
continues this afternoon with respect to ptype...with bulk of
this wintry event falling as snow to the north of the rt22/322
corridor in central Penn. Amounts and distribution have been
tricky given the lack of forcing farther north...but in general it
appears that 2-4" will be common for most...while better upslope
and moisture transport into the west central mountains and Laurel
Highlands produce maximum amounts there...generally up to 6" but we
could see some spot amounts come in higher.

Temperatures will will continue to slowly rise to a late day high in the
upper 20s across the central and northern mountains...and lower to middle
30s across the lower susq valley and Laurel Highlands respectively.
Winds will be south to SW at 5-8 kts in most places through today.

&&

Short term /11 PM this evening through Monday night/...
precipitation looks to taper off in all areas during the late evening
through very early morning hours of Monday.

Low temperatures tonight /under plenty of lingering and more
shallow...warmer lower clouds/ will range from near 20 degree in the
north to 30f in across the south.

Blustery and colder conditions will make a return on Monday as
system number one slides off to our east. Other than the usual
Post frontal snows showers...favoring western higher
elevations...conditions will be gradually improving overall
throughout the day.

Did not make any large changes to Monday.

&&

Long term /Tuesday through Sunday/...
high pressure and its fair weather and light wind will be short
lived Monday night into Tuesday when the next in the series of
storm systems is slated to enter the local weather scene. This one
promises more of a messy outcome as it should track well to our
northwest...meaning warm air eventually invading the region...with a snow
to sleet/freezing rain and even rain scenario.

Snow amounts do not look to be the biggest part of the midweek
storm as we are prognosticated to warm aloft rather quickly. With a deep
snow pack and a lot of cold air to displace...we will likely see
a period of icing before warm air eventually changes everything to
rain Tuesday night into Wednesday.

Main change was to adjust probability of precipitation some Tuesday into Tuesday night.

Think main type of precipitation will be rain Tuesday night into Wednesday. Did
put small amts of .01 ice across the area...given that object
temperatures will still likely be cold. Temperatures Tuesday night may
drop a little...before coming back up late.

Rain should taper off to scattered showers with the passage of
the trailing cold front early Wednesday.

For Wednesday...took snow showers out of the northwest. Tight thickness pattern
across the area...support a large temperature gradient from northwest PA
to southeast PA. There could be a few show showers across the far
northwest...but it looks like mainly northwest of our area. Left probability of precipitation up...think
front will be slow to move out.

A trend toward colder weather again later in the week...given
split flow.

Push of Arctic air will bring temperatures and probability of precipitation back well below
normal for late Thursday into Friday. The only good thing seems to
be each Arctic shot is a little less potent than the last as we
leave the record cold of February behind.

&&

Aviation /21z Sunday through Friday/...
expect best radar returns to occur across central and southern PA
this afternoon and evening in the best low level convergence. Mix
transition to ice across south central mountains and lower susq
will lift north of kmdt middle to late afternoon as weak low
pressure from the Ohio Valley tracks eastward into the Laurel
Highlands and secondary weak low pressure forms near the Delaware-Maryland-Virginia
coast. Across the northern mountains of PA visibilities should average nearly 1sm
higher in the light snow.

Generally IFR to LIFR conditions in snow expected to continue all
day and into this evening. Ceilings remain above 1500ft at 1530z
across most central and eastern PA airfields...but have dropped off to
below 1kft above ground level across the western mountains...and will continue to
gradually drop in all areas as the day wears on. Still the threat
of some freezing rain mixing in for the southern tier counties later this
after and this evening.

Visibilities will improve overnight as snow comes to an end...but ceilings
will remain low keeping mainly IFR conditions going before lifting
to MVFR in the central and east late.

Conditions should continue to slowly improve on Monday...but
expect restrictions to linger in the western and northern higher
terrain on cold northwest winds and typical orographic snow
showers.

Brief respite later Monday into early Tuesday...before the next
system pushes another round of precipitation and reduced flying
conditions into the area later Tuesday and Wednesday.

Outlook...

Tuesday...VFR am. Mixed precipitation with ceiling/visible reductions possible late.
Wednesday...cig/vis reductions continue in wintry mix/rain.
Thursday...slowly improving conditions...lingering MVFR northwest and southeast.
Friday...mainly VFR.

&&

Climate...
the books have closed and we now have /and made it through/ the
coldest February on record.

Monthly mean temperatures were...ipt 18... 20.9.

The previous records for the coldest February...ipt 19...
21.4 both set in 1934.

This February ranked as the third coldest calendar month ever at
ipt...and fourth coldest ever at MDT.

&&

Ctp watches/warnings/advisories...
Winter Weather Advisory until 2 am EST Monday for paz019-027-
028-037-041-042-045-046-049>053-056>059-063>066.
Winter Weather Advisory until 7 am EST Monday for paz004>006-
010>012-017-018-024-033.
Winter Weather Advisory until 11 PM EST this evening for
paz025-026-034>036.

&&

$$
Synopsis...devoir/Lambert/Martin
near term...devoir/Lambert/Martin
short term...devoir/Lambert/Martin
long term...la corte/Lambert/Martin
aviation...devoir/Lambert/Martin
climate...Lambert

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