Winter Weather in Illinois, January 5, 2017

Area Forecast Discussion
National Weather Service Paducah KY
330 AM CST Thu Jan 5 2017

.SHORT TERM...(Today through Saturday night)
Issued at 330 AM CST Thu Jan 5 2017

Will not be making any changes to winter headlines at this time.
00Z and later guidance shows many scenarios for today and this
evening with respect to timing and amounts, but the overall trend
is drier in most places and a general shift to the south with
the light snows for much of the day. Also seeing trends for a
quicker end to the snow.

One area of concern is southeast Missouri early this morning.
Observations indicate a solid area of 1-2SM snows over southwest
and central Missouri that is forecast by the latest HRRR runs to
move rapidly eastward through much of southeast Missouri by 12Z.
Although the HRRR is diminishing the intensity as it enters the
dry air over southeast Missouri, it would still likely result in
at least a coating on roads prior to sunrise. However, with the
speed it is moving/spreading eastward, it is not likely to last
long enough to result in much more than a dusting, so will not
expand the Advisory to this area. However, did increase PoPs to
50% and have non-zero accumulations.

The HRRR takes this area of light snow eastward through west
Kentucky well before 18Z, so also increased PoPs to 50% there
12Z-18Z. Still not seeing much more than a dusting, but it is
likely to begin earlier than previously forecast.

Now for what was expected early this morning. The snow band over
northern Missouri into central Illinois overnight has not lived
up to expectations, and latest short term guidance has it pushing
southeast into our area shortly and then quickly dries it up
toward midday. Once again the residence time of what should be
MVFR snow will not likely add up to what has been forecast. Figure
much of the I-64 corridor will see around an inch with possibly 2
inches right along the northern border of the forecast area.

What is uncertain is how far south the accumulating snows will
make it this morning, and the influence of the snow moving across
southern Missouri. There may be a narrow swath of little or no
snow across the mid-section of the area this morning.

As stated earlier, the overall trend in guidance is for a more
rapid southward spread and cessation of the accumulating snows
this morning toward midday. For this afternoon, there area various
solutions indicating one or more areas of light snow developing
over the region and moving quickly eastward as the main upper-
level trough pivots through the region late this afternoon and
evening. Will keep decent chance to low end likely PoPs going for
most of the area this afternoon, and even linger low chance PoPs
into the evening across the southeast half of the area. It appears
that the precipitation should be east of the area by 03Z this
evening. With so much uncertainty and numerous adjustments in the
latest guidance, will leave the Advisory going as is, but will not
be surprised to see it be cancelled early, possibly even early
this afternoon for western portions of the area.

Another punch of Arctic air will push into the area this afternoon
and tonight, as the upper trough passes. Winds at or above 5kts
through the night will take wind chills down to just under 5 above
along the I-64 corridor late tonight and early Friday. The surface
high will ridge into the area Friday and Friday night. This will
result in good radiational cooling potential, especially if there
is any significant snow cover. This will definitely be the coolest
night for straight temperatures. Winds only around 5 kts over the
southeast corner of the region will result in wind chills near
zero in the Elkton, Hopkinsville and Ft Campbell areas early
Saturday morning. The surface high will sink south of the area
Saturday, allowing a light west wind to develop. Highs may not be
warm enough, especially if we do not have the expected snow cover.

.LONG TERM...(Sunday through Wednesday)
Issued at 330 AM CST Thu Jan 5 2017

The medium range model solutions appeared to be in good agreement
for the overall extended period forecast.

For the first couple of days, the PAH forecast area will be under
dry northwesterly flow aloft, with the center of surface high
pressure over the region on Sun, and low level return flow starting
up early on Mon. This return flow is expected to last until a cold
frontal passage early on Wed, resulting in a warming trend to
eventually above average levels.

Deeper Gulf moisture should become more prominent by Mon night.
Thus, ahead of a low-amplitude mid level shortwave (00Z ECMWF
suggests a bit higher amplitude), isentropic lift should enable the
development of widespread pcpn across a wide swath of the eastern
CONUS by early Tue, including our region. The 00Z ECMWF seemed to
downplay initial QPF amounts however. It is tough to get frozen pcpn
with a southerly wind in these parts. However, model thermal
profiles suggested the possibility of a rather brief rain/snow mix
as early as Mon evening in the higher elevations of the MO Ozark
foothills, and for a few hours after midnight in southeastern IL,
southwestern IN, and the Pennyrile region of KY. Surface temps in
the 30s will rise overnight, from west to east. At this time, what
little impact that is possible should be confined to a small part of
southwestern IN (a dusting). After daybreak Tue, all rain can be
expected.

Meanwhile, as an area of associated low surface pressure deepens
over IA/MO by midday Tue, the pressure gradient will tighten across
the PAH forecast area, resulting in winds gusting to around 30 mph
Tue afternoon. QPF amounts in rain should ramp up Tue night with the
enhanced lift associated with the surface frontal passage. No tstm
activity is forecast at this time. Almost all pcpn should be out of
the region by mid morning Wed. We may see the sun later in the day
as high surface pressure begins to build in. The front is expected
to yield only a modest dip in temps.

&&

.AVIATION...
Issued at 1149 PM CST Wed Jan 4 2017

As alluded to with the 00z Thursday TAF issuance, the visibilities
and ceilings for KEVV and KOWB were dropped to MVFR and IFR,
respectively. KEVV will see two periods of low ceilings and
visibilities, the first between 08-10z and then again from 11z to
23z. These changes were primarily necessitated by the sharp
gradient of lift and saturation of the atmosphere at the onset of
precipitation, then again as the main shortwave sharpens and
deepens during the day.

The impact of lowered ceilings and visibilities at KOWB is
delayed until the 15z-23z time frame.

The 12km NAM-WRF appears to have a decent handle on the lowered
ceilings and visibilities. The NAM-WRF model visibilities were
nearly half of the observed visibilities in Missouri, so adjusted
upward to MVFR/VFR levels, mainly 4-6 miles.

Little change to the KPAH and KCGI TAF's, except to prolong
ceilings and precipitation beyond 00z Friday.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory until 6 PM CST this evening for
     ILZ075>078-080>087.

MO...Winter Weather Advisory until 6 PM CST this evening for MOZ076.

IN...Winter Weather Advisory until 6 PM CST this evening for INZ081-
     082-085-086.

     Winter Weather Advisory until midnight CST tonight for INZ087-
     088.

KY...Winter Weather Advisory until midnight CST tonight for
     KYZ014>016-018>021.

&&

SHORT TERM...DRS
LONG TERM...DB
AVIATION...Smith

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PADUCAH KY
257 PM CST WED JAN 4 2017

ILZ075>078-080>094-INZ081-082-085>088-KYZ001>022-MOZ076-086-087-
100-107>112-114-051000-
JEFFERSON-WAYNE IL-EDWARDS-WABASH-PERRY IL-FRANKLIN-HAMILTON-
WHITE-JACKSON-WILLIAMSON-SALINE-GALLATIN-UNION-JOHNSON-POPE-
HARDIN-ALEXANDER-PULASKI-MASSAC-GIBSON-PIKE-POSEY-VANDERBURGH-
WARRICK-SPENCER-FULTON-HICKMAN-CARLISLE-BALLARD-MCCRACKEN-GRAVES-
LIVINGSTON-MARSHALL-CALLOWAY-CRITTENDEN-LYON-TRIGG-CALDWELL-
UNION KY-WEBSTER-HOPKINS-CHRISTIAN-HENDERSON-DAVIESS-MCLEAN-
MUHLENBERG-TODD-PERRY MO-BOLLINGER-CAPE GIRARDEAU-WAYNE MO-CARTER-
RIPLEY-BUTLER-STODDARD-SCOTT-MISSISSIPPI-NEW MADRID-
257 PM CST WED JAN 4 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHERN
ILLINOIS...SOUTHWEST INDIANA...WESTERN KENTUCKY AND SOUTHEAST
MISSOURI.

.DAY ONE...THIS AFTERNOON AND TONIGHT

ACCUMULATING SNOWFALL IS POSSIBLE GENERALLY ACROSS THE NORTHERN
HALF OF THE OUTLOOK AREA STARTING LATE TONIGHT. SEE THE WINTER
WEATHER ADVISORY FOR ADDITIONAL DETAILS.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

ACCUMULATING SNOWFALL WILL CONTINUE ON THURSDAY GENERALLY ACROSS
THE NORTHERN HALF OF THE OUTLOOK AREA. TOTAL SNOW ACCUMULATIONS
OF ONE TO THREE INCHES ARE EXPECTED IN THIS AREA BEFORE ENDING BY
MIDNIGHT THURSDAY. SEE THE WINTER WEATHER ADVISORY FOR ADDITIONAL
DETAILS.

SNOW ACCUMULATIONS ACROSS THE SOUTHERN HALF OF THE AREA WILL
RANGE FROM JUST UNDER AN INCH TO A DUSTING OR LESS NEAR THE AR/MO
AND KY/TN BORDERS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED BUT ANY REPORTS OF
SNOWFALL/SNOW DEPTH WOULD BE GREATLY APPRECIATED.

JP