Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
938 am EDT Sat Mar 15 2014
a few snow showers are possible across the north today as colder
air moves southward across the Great Lakes. Another crossing
disturbance may bring some snow on Sunday and Monday.
Near term /through tonight/...
as of this morning...forecast continues to remain on track. Cold
advection has brought a return of stratocu to most of the region
north of pit. This should continue to expand southward...so some
adjustments to cloud cover and temperatures were made.
Previous discussion follows...
cold air advection and a westerly flow behind the front may produce les snow
showers/flurries across the far north later this morning and
through the afternoon. Have kept probability of precipitation in the chance to slight
chance Cat for snow showers as the cold air advection is not real impressive and
the core of the main shortwave swings through southern New York.
The area will be under cold air advection throughout the day so expect stratocu
from time to time...particularly over the northern half of my forecast area.
Cooler temperatures today...most if not all readings below normal.
Short term /Sunday through Tuesday/...
the big conundrum continues to be the evolution and interaction of
multiple streams and middle-levels systems set to affect the area
from Sunday evening into early Monday. Model solutions have
continued to waffle quite a bit on the northward spread of
precipitation into the area...likely owing to inconsistent
handling of the phasing of a system that tracks southeastward down
the Front Range of The Rockies into the High Plains with a system
ejecting out of the southwest. Previous runs maintained a bit more
coherence of two separate systems longer into the cycle than the
current runs do...which resulted in a more well defined low level
circulation ejecting toward the area Sunday night. The newest 00z
runs from basically all model and ensemble families suggest a far
more ill-defined feature ejecting out with the southern stream
system lagging and really ingesting the bulk of the moisture and
upper dynamics. As a result...far weaker northward moisture flux
as well as warm advection is noted toward the area on Sunday
night. While this does certainly Bode well to keeping the p-type
primarily snow...the idea of rapid/heavy accumulation certainly
does seem to be becoming a bit less of a likely outcome as the
best lift and moisture are now seeming to likely remain south of
the forecast area.
Additionally...the upper low that ejects out of the southwest
takes a much more subdued track across Dixie without any northward
jaunt to its track early next week. This should result in dry
conditions by the second half of Monday that allow for some
clearing and moderating conditions from Monday afternoon into middle-
Long term /Tuesday night through Friday/...
another deep upper level system seems likely to move from the
Central Plains into the Great Lakes by Wednesday. As it moves into
the lakes...the preponderance of model guidance continues to
indicate the upper low/wave should take on an increasingly
negative tilt. That coupled with a fairly deep layer of 850-500 mb
negative Theta-E lapse rates...impressive 0-6 km shear...along
with a strong middle-level jet rounding the base of the upper low all
point toward some convective development along the cold front that
slices through the area sometime on Wednesday. Thunderstorms were
re-added to the forecast for this possibility.
After the passage of wednesday's system...global guidance becomes
increasingly divergent in its approach to handling the short wave
pattern. However...increasing heights should allow 850 mb
temperatures to start to moderate after the system's passage...so
temperatures should again start to nudge back up again short after
cold advection behind wednesday's cold front wanes. Fries
Aviation /14z Saturday through Wednesday/...
latest models soundings portray a strato cumulus deck across much of
the area today as the cold air aloft settles in. Will keep
primarily VFR at all locations except fkl and duj. However...some
occasional MVFR ceilings could still be possible at many sites through
the morning hours.
Surface winds will strengthen this morning with gusts of 25 to
30 kts possible through the afternoon.
Outlook.../Saturday night through Wednesday/...
the next chance of genl restrictions will come with northern flank precipitation of low
pressure crossing the middle Atlantic region on Sunday into Monday. Another
disturbance may spawn showers and restrictions later on Wednesday.