Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
839 am EST Wednesday Nov 26 2014
high pressure over the Ohio Valley will weaken today as a clipper
system undercuts the region and passes to the south tonight. West
flow on Thanksgiving day will occur as an upper level trough
passes over the region...bringing some flurries and light snow.
High pressure will build in Friday and pass to the
east...initiating southerly flow and a warming trend for the
Near term /until 6 PM this evening/...
stratus deck across about the northwest half of our forecast area has been
slowly expanding eastward over the last several hours. Would
expect this eastward expansion to slow/stop through late morning
as the sun comes up with perhaps the periphery of the stratus deck
beginning to cumulus up. Temperatures will be dependent on the lower cloud
cover so expect highs across the northwest only in the low to
possibly middle 30s...increasing to the low to middle 40s across the
Short term /6 PM this evening through Friday night/...
a clipper system will cross the region tonight and undercut the
high pressure that is established and getting worked over in the
Ohio Valley today. An upper level trough will follow the clipper
system and spark scattered light snow showers and flurries through
the day on Thanksgiving. Little to no accumulations are expected
though temperatures will be hard pressed to rise out of the middle
30s with cold advection over the region. This cold air will
continue to be pulled into the area on west-northwest winds until the axis of
the high pressure behind the clipper crosses on Friday. Flow will
turn south later in the day Friday and the cooler than average
temperatures will begin to see a slight warmup that will be
reinforced over the weekend.
This weak warming will spark a few light snow showers over the
lower Great Lakes and could affect northern County Warning Area on Friday...but is
not very likely to be located that far south at this particular
time in the forecast process.
Long term /Saturday through Tuesday/...
although warm advection will occur at the surface heading into
Saturday...model soundings suggest that an inversion and
relatively thick layer of moisture will keep things from becoming
well mixed below 5000 feet. Even as most of the column will remain
quite dry...cloudy conditions with low ceilings appear fairly
likely...and there is even widespread model agreement in light
precipitation beginning by Saturday evening (somewhat unusual for
what looks like a drizzly profile). With warm advection and
plentiful cloud cover...min temperatures for Saturday night /
Sunday morning were increased by several degrees from the previous
Chances for precipitation will increase heading into Sunday...as
frontogenesis occurs over the Ohio Valley...with a strengthening
temperature gradient. A surface front is eventually forecast to
develop...and move very slowly southeast through the County Warning Area heading
into Monday. Temperature forecasts are somewhat uncertain...given
the sharp gradient...but above-normal temperatures are likely south
of the front on Sunday. A brief period of cooler conditions can be
expected on Monday...with occasional showers and a possible mix with
snow on Monday night. Overall model agreement on the precipitation
patterns with this front are fairly strong...with a slight trend
toward precipitation getting further south a little more quickly on
Monday into Monday night.
By Tuesday...strong surface high pressure is expected to move into
the northeastern states...allowing for a quick return to southerly
flow over much of the eastern part of the country. This should allow
for another period of mild (above normal) temperatures on Tuesday
and especially on Wednesday.
Aviation /14z Wednesday through Sunday/...
the eastern edge of MVFR clouds over Indiana into Northwest Ohio...that are
trapped under high pressure ridge...drifted eastward a little overnight
pushing into kday and kcmh. Models are keeping this area of clouds
pretty steady state as they stalling the southeast advancement of the
MVFR ceilings around I-71. Brought the MVFR ceilings into cvg/luk for a
couple of hours late this morning...then pulled them back to the
northwest. The tougher forecast is what will happen in central Ohio. The
clouds there are about 1k higher than the deck to the west. So
will the clouds retreat away from cmh/lck later this morning. Went
ahead and forecasted this scenario but confidence isnt high that
it will work out.
As East Coast storm pulls away later today...the weak clipper
system dives into the Tennessee Valley. It will help the flow to push
the MVFR clouds southeastward overnight. While the precipitation associated with the
clipper is expected to stay south of all the tafs...the MVFR
clouds are expected to work over all the tafs after 00z.
Outlook...MVFR ceilings possible Thursday into Thursday night and
again Saturday. MVFR/IFR ceilings and MVFR visibilities possible
Saturday night into Sunday.