Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
650 am EST Monday Dec 22 2014
midwestern low pressure will bring warmer temperatures and rain to
the region for the first half of the week. Snow shower chances will
come with the passage of that systems cold front on Christmas.
Near term /until 6 PM this evening/...
Made some minor adjustments to hourly temperatures to better align
with observational trends but otherwise no changes needed early
this morning. Previous discussion below..
Clouds are expd to increase today in warm advection. A weak surface low is expd to
advance up the East Coast into the Carolinas today...though recent upper air
charts and mesoscale data indicate most if not all precipitation should remain to
our east. With cold air damming in southeast flow...if any precipitation were to reach
Garrett or Tucker counties...a brief period of light freezing rain is possible.
Continued with low chance probability of precipitation in these areas. Highs should average a little above
the seasonal levels.
Short term /6 PM this evening through Thursday/...
the advancing weak surface low is prognosticated to continue to advance up and eventually
off the middle Atlantic coast tonight. Again...most precipitation should remain to
our east however mentioned low chance probability of precipitation for areas NE-southeast of pit where
again a brief period of light freezing rain is possible for the Maryland/WV mountains
and in colder valley locations NE of pit.
A digging upper trough is prognosticated to advance from the central Continental U.S. Into the
Great Lakes region by Thursday. Model solutions vary...but given the digging trough
think the NAM is significantly underdoing the development of surface features...
so sided closer to the GFS/ECMWF. Several shortwaves rotating around the
trough will bring increasing rain chances into middle weak. Developing surface low pressure is
prognosticated to advance from the Gulf Coast into the lower Great Lakes Tuesday night into
Wednesday evening. An associated cold front is prognosticated for a Wednesday evening/night
passage...with the upper trough axis prognosticated for a Christmas day passage.
Any rain showers should mix with and change to snow showers as colder air
advects in after frontal passage...and the upper trough crosses...though no significant
accums are expd at this time. Tightening pressure gradient Wednesday night and Thursday
should also bring gusty winds.
Above average Erly to middle weak temperatures should rtn to seasonal levels by Thursday.
Long term /Thursday night through Sunday/...
minimal changes were made to the extended as latest guidance
showed both poor agreement and continuity...and any changes that
were made were primarily based on ensemble means. With that...dry
conditions and temperatures approximately 10 degrees above normal
are forecast on Friday as ridging transitions over the region. A
trough of low pressure will then result in unsettled conditions
Saturday and Sunday.
Aviation /12z Monday through Friday/...
VFR conditions expected as cloud coverage increases over the
course of the day ahead of an approaching low pressure system. Any
precipitation during the day will be limited to mainly Garrett and
Tucker counties before more widespread precipitation develops on
Tuesday along with ceiling/visible restrictions across the region. Ceilings
in general will drop to between 4-5kft initially late this
afternoon and early evening...with precipitation and MVFR
restrictions developing mainly after midnight.
Outlook.../tonight through Saturday/... low pressure will result
in restrictions Tuesday and Wednesday as precipitation develops
over the region....with gusty winds expected Wednesday and Thursday.