Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 110520
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1120 PM CST Wed Jan 10 2018

.UPDATE...
Issued at 1120 PM CST Wed Jan 10 2018

Updated for 06Z aviation forecast discussion.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 245 PM CST Wed Jan 10 2018

For tonight through Thursday...

High Resolution (1-4km) and short to medium resolution (12-20km)
numerical guidance have quite similar solutions on the trajectory of
the conveyor belt/isentropically lifted rainfall through the WFO PAH
forecast area through 6 pm on Thursday. Not totally convinced there
will be enough instability to support any thunderstorms on Thursday,
so left a mention of it out of the gridded forecast for Thursday.
Given the saturated atmosphere, and mixing within the boundary
layer, should be little change in temperatures from the upper 50s
tonight to lower 60s tomorrow, allowing for direct warm air
advection.

For Thursday night through Friday night...

Models are beginning the hone in process, with the amount of
disparity amongst them starting to narrow. Looking at the recent
solutions and the primary differences with the 12Z run today, the
NAM is a little sharper/faster with its cold air plunge, but is
not too much faster than the GFS. WPC liked a GFS/NAM/UKMET
blended approach, stating the ECMWF seemed too fast. This approach
is mirrored in our regional blend, and not too many adjustments
were needed off of it. The ones that were made included smoothing
the qpf amounts in southern IL, where the blend created a dearth
between the higher qpf to the south and east, and the upper Low
influenced snowfall to the northwest. Also, the rapid drop in wet
bulb temps aloft played into our smoothing out slightly lower qpf
totals in our southeast, to more closely match our neighbors in
snow/ice amounts. The net creation is impact based Watch headline
accumulations basically along/east of the Mississippi river, where
confidence was reasonably high that accumulations of snow will
push 2 inches or more, and ice will be in the one tenth to one
quarter inch range. Higher end snowfall totals of 3 to 4 inches
are possible in our northern, eastern, and southeastern most Watch
counties. Highest end ice totals will be along/to our south and
east on the Ky/Tn border, esp from Murray and the Lakes, eastward
toward Hopkinsville, where 0.25-0.30" ice is possible. Note that WPC
outlooks a 25 percent chance of greater than 1/4" icing in this
zone. Another impact factor is wind/gusts, which will sharpen late
Thursday night-early Friday, just after the initial burst of
freezing/frozen pcpn. This could result in at least some isolated
to scattered downed power lines, so be prepared for that
additional impact danger as well.

.LONG TERM...(Saturday through Wednesday)
Issued at 245 PM CST Wed Jan 10 2018

Following the passage of the wintry system on Friday into early
Saturday, the upper level flow will keep the mean trough axis
fixed over the WFO PAH forecast area through at least next
Tuesday.

With any remaining snow cover/ice on the ground, this will enhance
and reinforce cold air advection with the lowest temperatures
expected initially Saturday night.

As waves rotate around the mean trough, another surge of cold air
will move into the area next Monday, returning low temperatures into
the single digits and teens on Monday and Tuesday. With moisture
limited to the systems themselves, very light snow or snow flurries
can be expected intermittently from Sunday night through Tuesday
night. Little, if any, accumulation is anticipated with these
systems.  Local snowfall amounts, less than a half inch, may be
possible along the I-64 corridor in southern Illinois and southwest
Indiana Sunday night into Monday morning.

&&

.AVIATION...
Issued at 1120 PM CST Wed Jan 10 2018

Cigs will remain MVFR or IFR with some gusts out of the south from
time to time with VFR or MVFR vsbys. There will be pockets of
drizzle overnight. Rain showers will start to become more probably
as we head toward daybreak on Thursday with the bulk of the rain
arriving by late afternoon and early evening. We will see a wind
shift between 00z to 06Z with a cold front and gusts will really
increase with the FROPA. Cold air will start to filter in at KCGI
late in the period which could cause some sleet.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Watch from Thursday evening through Friday evening
     for ILZ075>078-080>094.

MO...Winter Storm Watch from Thursday evening through Friday evening
     for MOZ112-114.

IN...Winter Storm Watch from Thursday evening through Friday evening
     for INZ081-082-085>088.

KY...Winter Storm Watch from Thursday evening through Friday evening
     for KYZ001>022.

&&

$$



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