Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
827 PM EDT Tuesday Mar 31 2015
high pressure provides a mainly dry and seasonable Wednesday.
Warmer temperatures arrive Thursday...before a wet weather system
closes out the work week.
Near term /until 6 am Wednesday morning/...
830pm update...removed probability of precipitation from the overnight period...adjusted
temperatures to latest guidance and lower cloud cover as stratocu
continues to move eastward with exiting low. Rest of overnight in
Surface low dropping across western PA into the
Appalachians currently...with frontal boundary recently passing
through pit. Steadier precipitation has moved off to the east...but some
scattered Post-frontal rain showers are firing in modest instability.
Expect these to progress to the south and east with the front over
the next few hours. Kept the thunder chances going in the
southeast before sunset...where more sun has been seen today. Only
expect a few lingering rain showers around 00z in the southeast before
ending during the evening. 25-35 miles per hour wind gusts will diminish
during that time as well.
Band of Post-frontal low clouds will swing through during the evening
as well. A short period of partial clearing will occur during the
predawn hours. Then...another weak disturbance currently in
Michigan yooper country will approach from the northwest around
12z. Expect this to manifest mainly in the form of reinforced
cloud cover...but there may be just enough juice to get a few
flurries or light snow showers north of I-80 by sunrise.
Previous low temperature forecast was at the lower end of the
guidance envelope. Considering the wind and expected
clouds...raised temperatures more towards the mean of the guidance.
Short term /6 am Wednesday morning through Friday/...
beyond maybe a few flurries and some cloud cover associated with
the weakening upper level disturbance as it passes just north of
the region early Wednesday....expect clearing skies and near
normal temperatures as surface ridge builds overhead. Wind shift
to the SW is not anticipated until late Wednesday and while ridge
will be shifting to the east...think that much of the region will
be allowed to decouple. Thus...opted to stay closer to the
MOS/European model (ecmwf) values and not the warmer name temperatures.
Cold front will be slow to make it's approach Thursday...with
strong southwesterly winds expected out ahead of it. This
should...despite increasing cloud cover...bringing temperatures
well into the 60's and lower 70's across the region as 850hpa
temperatures approach +10c. Precipitation continues to slow with the
boundary so very low probability of precipitation were kept in the forecast until late.
However...the NAM and to a lesser degree the European model (ecmwf)...suggest an
area of moisture may be advected northward out ahead of the
front...bringing a chance for rain to some of the region by
Thursday afternoon. With low confidence on the placement and
development of these showers...thought it best to just keep probability of precipitation
low for now. Very strong southwesterly low level jet will result
in gusty winds of 20-30 miles per hour Thursday and a chance of thunder may
be possible late with thin cape suggested on model soundings.
Cold front will remain just north of the forecast area until late
Friday when a upper wave and its associated surface low develop
and move across the upper Ohio Valley. Still some uncertainty on
the strength of this low and placement but likely to low-categorical
probability of precipitation were maintained through the period. Temperatures should
remain elevated until the cold front passes late Friday...but
precipitation will keep highs from being as warm as they were on
Long term /Friday night through Tuesday/...
a drying trend is indicated for the weekend although a trailing
shortwave may generate some showers on Saturday. The cool down
will not be significant though as flat ridging is European model (ecmwf) and GFS
prognosticated to build and moderate temperatures for next week.
Aviation /01z Wednesday through Sunday/...
scattered MVFR ceilings in cold advection being swept southeast as surface
ridge axis and subsidence are clearing skies across northwest PA.
General VFR expected at all ports by 02-03z. Winds will quickly
diminish as well with light north winds overnight. Weak shortwave
will bring some middle deck toward 12z Wednesday mainly kpit north.
Outlook.../Wednesday night through Sunday/...
restrictions possible with low pressure later Thursday into the
first half of Saturday.