Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 090006

Area Forecast Discussion
National Weather Service Wilmington OH
706 PM EST Thu Dec 8 2016

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.


Northwest flow on the backside of the low pressure in ern Canada
will continue the caa tonight. This will push the cold air sc down
through the entire fa. Scattered flurries can`t be ruled out at
anytime where there are clouds, so included a mention of a flurry
everywhere there is sc.

As the night progresses, the flow across Lake Michigan lines up
better, and lake effect snow showers will work down into NW OH
after 06Z. Still kept the snow showers in a chance category across
portions of W Central OH as we will have to wait as see the exact
location that where the band sets up.

The cloud cover will stop temperatures dropping to rock bottom as
the arctic air works in. Lows in the upper teens to lower 20s
still look reasonable.


As the period begins, the coldest H8 air will have settled across
the region. Surface high pressure will begin to build in from the
west and the H5 flow will become more zonal. H8 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 OH 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/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 CWA in the HWO.


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 CWA 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
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 CWA
and then change to snow in the evening before ending overnight.


MVFR cigs are expected for most of the TAF period, however some
brief VFR cigs will be possible at the start of the TAF period and
also at the end of the KCMH, KLCK, and KCVG TAF. Wind gusts will
continue this evening before gradually decreasing overnight. Winds
will stay up however around 10 knots. Some snow flurries or light
snow showers will be possible overnight with favorable winds off
of the lake.

OUTLOOK...MVFR ceilings may linger into Friday night. MVFR/IFR
ceilings and visibilities possible Sunday into Monday.




LONG TERM...Franks
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