Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 171837
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1237 PM CST Sat Feb 17 2018

.UPDATE...
Issued at 1227 PM CST Sat Feb 17 2018

For aviation discussion only.

&&

.SHORT TERM...(Today through Monday night)
Issued at 230 AM CST Sat Feb 17 2018

The first order of business is a fast-moving system that will
bring rain and some snow this morning. A 500 mb shortwave will
move east from the Missouri Valley, preceded by a developing area
of precipitation. The precip should overspread se Missouri by 12z,
and then most of the remainder of the area from 12z to 16z.
Although temperatures aloft will be initially too warm for snow,
wet-bulbing of an elevated dry layer will result in a period of
wet snow in some places. Some wet snowflakes could mix in
anywhere across the area early this morning. The best chance of
any minor accumulations will be across portions of srn Illinois
and se Missouri, mainly north and west of a kcgi to kmdh line. The
00z href depicts a small area of 1-inch amounts in the hilly
terrain north and west of kcgi. The forecast will follow suit,
however accumulations will be mainly on grassy areas. Very little
if any impact on travel is anticipated.

The heaviest precip will occur over west Kentucky this morning,
where upwards of one-half inch of liquid equivalent is expected.
Most of the precip will end by noon, however an area of light
showers will graze parts of srn Illinois, sw Indiana, and nw
Kentucky this afternoon. Highs will be mainly in the 40s.

As for tonight, high pressure will bring clearing skies and light
winds. There is some potential for fog due to the wet ground and
good radiational cooling. Lows will be near freezing.

Partial sunshine is expected Sunday. Winds will become southeast
on the back side of the high. High temps will be in the 50s.

Sunday night through Monday night, a strengthening southerly low
level jet will develop ahead of a deepening 500 mb trough over the
western states. The strong warm advection pattern will help boost
highs to around 70 on Monday. Some warm advection clouds and
showers are likely, however a strong 500 mb high off the Carolina
coast will shunt much of the precip to the north and west of the
Ohio Valley. There could be enough instability for some thunder
Monday night, but the primary heavy rainfall potential will be
during the long-term period.

.LONG TERM...(Tuesday through Friday)
Issued at 230 AM CST Sat Feb 17 2018

The pattern will be high amplitude with an anomalously strong ridge
off the Southeast U.S. coast, and a deep trof over the Western U.S.
This will allow for unidirectional flow to set up from Arklatex
northeast across the Ohio and Tennessee River Valley regions.
Periods of heavy rain will be likely. Confidence is above average
for the Tuesday through Wednesday night time frame. We are seeing
MAX Percentiles from the ECMWF 51 ensemble member data for Tuesday
through Wednesday night for heights, PW`s and specific humidity.
These values exceed all (and are outside the latest 30 year climo
time frame) for a 3 week period centered on these days. For Thursday
through Saturday, confidence lowers a bit as timing differences
develop. Therefore we backed off the numbers slightly and based the
forecast more off the ensemble mean solutions of the EC and GFS. We
tend to believe the pattern will remain active even into the
weekend, resulting in a continued heavy rain threat. The key will be
placement. Some thunder is possible. But at this time, the chances
look limited. Most of the time, just rain showers.

In terms of temperatures, we will be well above average Tuesday with
highs into the 70s most areas. A front is forecast to move through
late Tuesday night into early Wednesday. We will stay on the cool
side until Friday and Saturday, when the models forecast the warm
sector will surge back northeast across the area. QPF wise, the
heaviest rain axis should set up across southeast Missouri, into
southern Illinois, and extending over to the Wabash River. For
Thursday through Saturday, the forecast is more broad brush for now
again factoring in uncertainty. When all is said and done, some
areas, especially along and north of the Ohio River and into
southeast MO may see 4 or more inches of total rainfall.

&&

.AVIATION...
Issued at 1227 PM CST Sat Feb 17 2018

Snow/rain IFR cigs/vsbys coming to an end from west to east early
this afternoon. Will leave behind IFR cigs for much of the day,
possibly into the evening over sw IN/Pennyrile of wrn KY. Should
then see clearing form west to east during the overnight. Models
may be a bit quick, as per usual, in clearing too quickly.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

UPDATE...GM
SHORT TERM...MY
LONG TERM...CN
AVIATION...GM


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