Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 061435

Area Forecast Discussion
National Weather Service Wilmington OH
935 AM EST Tue Dec 6 2016

An area of low pressure will move northeast through the Ohio
Valley today. Drier conditions will return on Tuesday, but
temperatures will drop for the second half of the week after a
cold front moves through on Wednesday.


Surface low in middle Tennessee will continue to lift northeast
through the day. Large shield of rain to the north of the low will
persist into the afternoon and then start to clear from west to
east later in the day. Temperatures will struggle to rise with
daytime highs less than 5 degrees warmer than mid morning


Aside from the low clouds, the rest of the air mass in place over
the Ohio Valley tonight will be quite dry. On the southeastern
periphery of a stacked low over northern Minnesota, a dry cold
front is expected to move through the ILN CWA early Wednesday
morning, with winds switching to the WNW. The surface reflection
of this front is not overly easy to pick out, and in fact, surface
winds are expected to back to the SW again by Wednesday afternoon.
The cold advection will do its best to stunt the diurnal cycle,
and much cooler conditions are expected going into Wednesday

By Thursday, the slowly-moving longwave pattern feature troughing
setting up across the western Great Lakes, with very quick WSW
flow aloft over the Ohio Valley and mid-Atlantic. Previous
forecasts have mentioned the possibility of snow on Thursday
morning, but models continue to back away from this proposition,
with both the 00Z GFS / 00Z ECMWF keeping conditions dry across
the ILN CWA. While a 20 PoP for a slight chance of light snow has
been maintained, a mention of flurries might eventually cover the
scenario. There are no signs of forcing in the low levels at all,
with only some weak/transient upper support on the south side of
the 300mb jet, and this no longer appears to be enough to generate
any reasonable chance of accumulating snow. The continued cold
advection just off the surface will keep the shallow boundary
layer well mixed through Thursday and Friday, which does present
the possibility of a persistent (though maybe broken)
stratocumulus deck. As the top of this mixed layer intersects the
lower end of the DGZ on Friday, some flurries may be possible
(particularly in the northern half of the ILN CWA). This has been
included in the forecast.

Until the advection pattern really starts to adjust itself over
the weekend, temperatures will only continue to cool each day this
week. Model blends for temperatures looked generally reasonable,
but NAM min temps appeared too high for the latter half of the
week, and were not used.


With the upcoming weekend, a warm front will cross northeast
through the Ohio Valley and increase the threat for rain on
Sunday, possibly a rain/snow mix as the warm air overspreads the
cooler air in place. Models continue to disagree in how this
system evolves with the ECMWF notably drier and further west than
the more progressive and much wetter GFS. Modelers from WPC also
seem to have split the difference here noting the warm frontal
passage similar to the GFS solution on Sunday, then bows to the
ECMWF on Monday morning with the surface low east of Lake
Superior. GFS occludes the front off of the east coast on Monday
morning and pushes in drier air. Meanwhile the ECMWF continues to
keep a strong baroclinic zone in the midwest with continued threat
for precipitation over the Ohio Valley during this same time

Tried to trend lower on the threat for precipitation on day 6 and
7 and culminated the pops on the high end category Sunday
afternoon, in line with the GFS. Against better judgment and
nodding towards ECMWF the pops have been lingered into Monday and
Monday night to account for lower confidence and natural
variability of the models on day 7.


IFR ceilings will spread in the Columbus area leaving all TAF
sites IFR. Rain will end late around 20-21Z for the wrn tafs and
a few hours later for the ern tafs. Behind the cdfnt, winds will
turn to the w and will increase, with gusts of 20 kts possible.
Cigs will try to lift to MVFR in the w behind the front, but the
should linger in the IFR range further e.

Some drizzle will be possible during the late afternoon and
evening hours of Tuesday as the forecast soundings are showing
drier air aloft coming in over the trapped low level moisture.

The low level moisture will finally begin to scour out aft 12Z

OUTLOOK...MVFR ceilings are possible again on Thursday and Friday.




LONG TERM...Franks
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