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000 
FXUS61 KPBZ 060333
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
1033 PM EST Thu Dec 5 2019

.SYNOPSIS...
Dry and seasonable conditions are expected overnight under surface 
high pressure. A cold front will return precipitation chances Friday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...

Evening Update: No major changes have been made to this forecast 
period. 

Previous Discussion: 

Zonal flow has mostly been re-established allowing skies to clear in
several areas but high clouds will filter in gradually overnight 
ahead of an encroaching shortwave and its subsequent cold front.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY NIGHT/...
Low level wrly flow should shift swly early Friday as surface high
pressure advances eastward, with warm advection aiding in the
recovery to near average temperature through midday. A Great Lakes
shortwave trough is expected to advance across northern portions of 
the forecast area during the afternoon, increasing rain / snow 
chances through Friday evening. This disturbance appears weak as 
better forcing for ascent is progged across the Great Lakes. Forecast
soundings also suggest the presence of low- level dry air hampering 
the development of a deep, moist boundary layer, resulting in 
generally light rain / snow amounts. 

Meanwhile, a southern stream shortwave is progged to increase
rain / snow chances across northern WV and for the PA and MD ridges 
Friday. Similarly, forcing for ascent appears weak, thus 
precipitation accumulation amounts should be minor. 

Precipitation chances end Friday night with building sfc high 
pressure. Near-neutral temperature advection will maintain below 
average temperature given quasi-zonal flow aloft through Saturday. A
pattern shift is then anticipated Sunday as a Hudson Bay low 
deepens, returning swly flow and warm advection aloft. Above average
temperature is expected Sunday, with surface high pressure 
prevailing.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Stratiform rain chances increase Monday as a series of shortwaves 
impact the region on the van of the deepening Hudson Bay low and 
associated central Plains trough. Deep moisture transport is expected
given strong jet support, with PWAT values in exceedance of the
climatological 90th percentile. This should support widespread rain 
Monday into Tuesday.


Long term model blends agree on the arrival of an arctic front by 
Tuesday / Wednesday, changing rain over to snow given cold advection
in nwly flow behind the frontal passage. Wednesday high temperature 
should top out 15 to 20 degrees below average. Some moderation, 
albeit limited, is expected Thursday as flow aloft becomes quasi- 
zonal.

&&

.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Shortwave ridging has brought VFR to regional terminals. Cloud cover
is expected to increase once again tomorrow as the next in series of 
shortwaves affects area ports. A brief period of low- level wind 
shear is likely in the morning before surface wind responds to the 
trough. In addition, scattered showers are possible tomorrow 
afternoon, but given limited moisture, should not bring widespread 
restrictions other than a MVFR cloud deck. 

.Outlook... 
More restrictions are likely early next week with the next
disturbance.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...None.
OH...None.
PA...None.
WV...None.

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