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fxus61 Kiln 090552 
afdiln

Area forecast discussion
National Weather Service Wilmington Ohio
1252 am EST Fri Dec 9 2016

Synopsis...
a cold air mass will remain over the region for the next several
days. Some flurries are expected tonight into Friday morning,
before an area of high pressure moves into the region for Friday
afternoon into Saturday. A complex low pressure system will
affect the Ohio Valley Saturday night into Monday, bringing a mix
of snow and rain.

&&

Near term /through today/...
flurry/light snow shower coverage and intensity has increased
over the past several hours as the flow off Lake Michigan has
become better aligned for such activity in the local forecast area. The
numerous flurries/light snow showers will continue through the
overnight period into early Friday morning. As the flow slowly
becomes more westerly late Friday morning, expect that the light
snow shower activity will become more confined to the northern or
northeastern third of the forecast area before drier conditions move in
everywhere for the second half of the afternoon.

Did bump temperatures down several degrees for tonight despite
extensive cloud cover. Obs are already showing several locations
in the upper teens, particularly across the Miami Valley, and
expect that in the cold air advection regime, temperatures may fall by an
additional couple of degrees. High temperatures are still on track
for Friday afternoon to reach near 30 degrees across the entire
forecast area. Am concerned that if cloud cover persists a bit longer across
the north/northeast, that temperatures may stay in the upper 20s.

&&

Short term /tonight through Saturday night/...
as the period begins, the coldest 800 mb air will have settled across
the region. Surface high pressure will begin to build in from the
west and the 500 mb flow will become more zonal. 800 mb temperature
advection will be neutral. So SC will probably be slow to erode
across the region. This will limit solar insolation and will keep
highs around 30 degrees. A chance of flurries will continue to be
used for the majority of the forecast area. Though most locations
will not receive any accumulation, a quick tenth or two could
occur in a snow shower on Friday morning, likely limited to west
central Ohio counties.

The surface high will continue to build east Friday night. The
low clouds will begin to erode, but they will be replaced by some
mid to high clouds streaming east in the zonal flow. Temperatures
will drop back to 15-20 degrees.

Saturday will be the calm before the storm. While temperatures
will still be below normal, conditions should be dry with a mix
of clouds and sun. Highs will range from the upper 20s across the
nrn counties while making the lower 30s around the Ohio River.

Models are showing differences in the solution for Saturday
night. The 12z NAM has come in dry as it is deeper with its
surface low and therefore keeps the better convergence and pcpn
across the Great Lakes. The GFS/European model (ecmwf) and canadiannh are showing
more of a general sly flow with broad isentropic lift advancing
from the nrn plains into the srn Great Lakes and Ohio Valley.

There is still uncertainty where the srn edge of the pcpn will
be, but there is enuf confidence to up pops across the nrn third
of the fa to likely. Thicknesses will be cold enuf for the pcpn to
fall as all snow. Right now it is looking like the possibility of
1-2" of snowfall north I-70. Will keep mention of accumulating
snow for the northern half of the County Warning Area in the severe weather potential statement.

&&

Long term /Sunday through Thursday/...
zonal upper level flow will be found over the conus with a h5
shortwave pivoting northeast through the Great Lakes region on
Monday. Ahead of the S/W, a baroclinic zone will set up in the Ohio
Valley and surface low pressure will strengthen through the day. As
the baroclinic zone takes form, precipitation is expected to develop
over the north and northwestern of the County Warning Area early Sunday and increase
coverage through Sunday afternoon.

The upper level shortwave quickly exits east on Monday and
precipitation ends from west to east with high pressure building in
the Midwest. A broad trough will cross the northern Great Lakes
region Tuesday night and Wednesday with zonal westerly flow found
underneath it. GFS and Canadian models are sharper with the trough
and influences a lot more lift in the region on Wednesday while the
European model (ecmwf) is more muted and shifts the forcing off of the East Coast
with very little precip in the Ohio Valley. Given the precipitation
was already in the forecast, continued the low chances for the
middle of next week and dried out the region on Wednesday.

Models are in a sharply cool pattern for the end of the valid period
on days 5-7 but show a strong variability in the ensembles of 30
degrees or more in both daytime highs and nighttime lows. While the
model spreads for any period are large, the average of the runs and
the deterministic run are definitely on the colder side of the
ensemble members. Kept the cold pattern of the forecast but tried to
trend slightly warmer to account for the variability that in
inherent in the longer range forecast.

Precip on these days will likely see snow on Sunday, mixing with
rain along and south of the Ohio River. Temperatures will warm
overnight and the rain/snow line will lift to the I-70 corridor by
daybreak Monday. Precipitation on Tuesday at this moment in time
would start as a mix or plain rain in the southern half of the County Warning Area
and then change to snow in the evening before ending overnight.

&&

Aviation /06z Friday through Tuesday/...
MVFR ceilings and snow flurries will persist in a cold cyclonic
flow. Improvement to VFR could occur around 13z at cvg and luk,
but observations will need to be closely monitored to determine
if that will happen. Otherwise, all sites should see VFR about 01z
Saturday with the arrival of high pressure and a drier airmass.
Winds will stay out of the west, with speeds around 10 knots
becoming light by the end of the forecast.

Outlook...MVFR/IFR ceilings and visibilities possible Sunday into
Monday.

&&

Iln watches/warnings/advisories...
Ohio...none.
Kentucky...none.
In...none.

&&

$$

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