Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
812 PM EDT Wednesday Apr 1 2015
dry weather tonight will be followed by a warm Thursday with
increasing shower and thunderstorm chances.
Near term /through Thursday/...
815pm update...previous forecast in line. Only minor changes to
shortwave is in the process of exiting to the east at present.
What was a more solid deck of stratus/stratocu has lifted and
broken up into mainly high cumulus or low ac. These clouds will move
out/break up during the late afternoon and early evening...leading
to a mostly clear overnight period as h500 ridge axis arrives by
12z. With surface high moving off to the east...surface pressure
gradient starts to tighten up after midnight. This will help to
keep the boundary layer stirred and keep temperatures from falling
off too far. Tried to lean at or a touch above the model consensus
for low temperatures.
Southerly flow and warm advection increase on Thursday with h850
temperatures climbing to +9/+10 during the afternoon. This will help
drive temperatures around 15 degrees above normal...and have high
temperatures near the top end of guidance. Pit has a chance to reach 70
degrees for the first time since last November 11. This is in
advance of the next major weather system...with a frontal boundary
extending across the Great Lakes into the Mississippi Valley from
a Canadian low. Expecting the bulk of the precipitation to arrive
towards and after sunset from the west...and do have likely probability of precipitation
here by 00z. However...some meager instability and isentropic lift
may pop some rain showers from late morning on. Enough instability for a
few thunderstorms as well...but not enough for a severe weather
concern. Despite the strong southerly flow...model soundings are
not suggesting very deep mixing...which would keep 50+ knot h850
winds locked up aloft. Do expect some 25-30 knot gusts at the
surface but not enough for a Wind Advisory. Quantitative precipitation forecast through 00z should
remain below a quarter inch in general...with the more significant
rain to follow.
Short term /Thursday night through Saturday night/...
the front is still forecast to stall across the area through
Friday as several shortwaves ride along this boundary...bringing
rounds of showers. The last...and most significant wave that will
help push the front to the east will come later Friday night.
While there will be plenty of Gulf moisture present...as suggested
in the model with precipitable water values approaching 1.00 inch and the 1 to
2 inch rainfall amounts prognosticated areawide...the long duration of
the event should help to minimize water problems. However...if
there is enough instability for thunderstorm development...heavier
rainfall could cause some minor flooding issues. At this
time...will not add any concern for this in the severe weather potential statement with low
The upper trough axis is prognosticated to shift east of the area
Saturday morning...with the front and surface wave exiting. A
brief changeover to snow is possible as the precipitation ends. Any
remaining precipitation chances...mainly NE of pit...should diminish by
Generally kept a compromise of the GFS/European model (ecmwf) and to lesser extent
the NAM and sref for the forecast with minimal changes made to
probability of precipitation and temperatures from the last shift.
Long term /Sunday through Wednesday/...
a trailing shortwave is still prognosticated to generate some showers
along a southward sagging cold front on Sunday. Confidence in the
situation...especially southward progress of the front remains
questionable...so slight...to chance probability of precipitation were confined to
Otherwise...temperatures are expected to moderate to near...then above
the seasonal averages as a shortwave ridge develops over the
eastern half of the Continental U.S. In response to western states troughing.
Precipitation chances will rise as the week and trough progress.
The long term prognosis was primarily based on adjusted wpc
Aviation /00z Thursday through Monday/...
clear skies and light winds through the overnight under surface
ridges. Ridge will shift east ahead of approaching storm system
Thursday with middle deck arriving before 12z western ports with
winds increasing from the southwest 10 to 15 kts and becoming
gusty. Lowering ceilings to MVFR with scattered showers from late morning
west spreading east in the afternoon. Thunder possible with
increasing low level moisture ahead of shortwave aloft and
approaching cold front...but for now will leave out as coverage
and timing in doubt.
Outlook.../Thursday through Monday/...
restrictions expected with cold front Thursday night. Low
pressure will bring possible restrictions late Friday into