Scientific Forecaster Discussion
fxus61 kpbz 181128
Area forecast discussion
National Weather Service Pittsburgh PA
728 am EDT Fri Oct 18 2019
dry weather will prevail through much of the weekend, though rain may
clip areas south of Pittsburgh Sunday as a low pressure system passes.
A cold front will bring the next widespread rainfall late Monday
Near term /through tonight/...
730am update...have updated morning temperature trends to better
capture cold pockets where cloud coverage was absent, allowing for
more efficient radiational cooling. Sky coverage also updated to
incorporate latest hi-res model and satellite imagery trends. The
rest of the forecast remains on track.
GOES east imagery shows streams of clouds coming off the lakes, as
cold northwest flow continues overrun the Warm Lake waters to produce clouds
below the low-level inversion. Clouds will slowly break through the
late afternoon as subsidence increases, northwest flow weakens, moisture
becomes mores negligible and 850mb warm advection commences. The warm
advection plus increased sunshine will begin a warming trend today,
but remain generally in the 50s, which is below seasonal averages.
Clear skies, light winds, and subsidence aloft will create ideal
radiational cooling and make the area more susceptible to frost
Saturday morning W/ lows in the 30s. Confidence not high enough for
product issuance at this time, but subsequent shifts will need to
monitor the frost potential.
Short term /Saturday through Sunday night/...
after a cool start Saturday morning, Saturday through Monday will
feature temperatures above the climatological mean and only a minimal
chance of rain.
The aforementioned ridge will cross the region, placing the area in
southwest flow. Plenty of sunshine and warm advection will bring
temperatures to near to just above the climatological mean.
Cloud cover will increase late Saturday as an extratropical low
moves up the eastern Seaboard in conjunction with a quick-moving
shortwave embedded within the southwest flow. Models diverge a bit
with regards to the western extent of precipitation Sunday morning.
That is, the GFS keeps precipitation along or east of I-95 while the
NAM/CMC/ecm bring precip all the way towards the Allegheny Front.
Have chosen a blend towards the latter solutions given storm track.
In doing so, have also reduced pops across the non-ridge locations.
Even with the transient shortwave, do not believe there'll be enough
lift and moisture to support showers. Furthermore, no model
solutions place precipitation in the lower elevations this far west.
Long term /Monday through Thursday/...
another deep trough will lift across the upper Midwest on Monday.
Strong warm air advection across the area will result in another warm
mid-October day... though increasing cloud cover through the day
will likely keep the temperature down just a bit.
The front and associated rainband will cross the region overnight
Monday into Tuesday morning. At this time, system/jet positioning do
not appear ideal for a big wind-making system, and a period of northwest
flow precipitation does not appear to be much of a threat. High
pressure and drier weather arrive for Wednesday and Thursday, along
with seasonably cool temperatures.
The next chance for rainfall looks to be late in the week (friday)
with the passage of another cold front.
Aviation /12z Friday through Tuesday/...
VFR stratocu is expected as cool northwest flow overruns the Warm Lake
waters, with moisture remaining stuck under a low-level inversion.
However, building sfc high pressure and ridge building aloft will
increase subsidence that will erode the cumulus from the SW to the NE
through the day, resulting in clear skies by tonight.
Efficient radiational cooling combined with Warm River waters will
make River Valley fog possible Saturday morning. More widespread fog
is unlikely to develop due to the lack of near sfc moisture.
restrictions will be possible with a cold frontal passage early next