289 
FXUS63 KILX 212109
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
309 PM CST Wed Nov 21 2018

.SHORT TERM...(This evening through Thanksgiving Day) 
ISSUED AT 309 PM CST Wed Nov 21 2018

The cold front will push just south of our forecast area by early
this evening, then stall there before shifting north as a warm 
front on Thanksgiving day. Clouds into early evening will be 
limited to our far NE counties, roughly from Lacon to El Paso to 
Danville. HRRR indicates the clouds will generally linger across
the north into the overnight, with some dissipation on the
southern fringes at times. The overall affect on low temps in our
area should be minimal, with upper 20s to around 30 in
central/southeast IL. 

As high surface pressure pulls farther away to the east tomorrow,
winds will become southerly and increase to 10-15 mph by
afternoon. Periodic clouds will be lingering in the north
Thanksgiving morning, then should shift north of the forecast
area during the afternoon as the warm front moves into northern 
IL. With increasing sunshine during the day, we expect high temps
to climb toward seasonal normals on Thanksgiving, with upper 40s 
north and low to mid 50s south. 

&&

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 309 PM CST Wed Nov 21 2018

Clear skies will continue Thursday night, but steady south winds 
will result in low temps remaining above freezing in most areas,
except for possibly near Danville.

A longwave upper trough will amplify across the Plains on Friday,
resulting in increased moisture transport ahead of a deepening
surface wave. Time height cross-sections indicate we should
saturate through a deep enough layer of the atmosphere for rain to
overspread central IL quickly Friday afternoon, with widespread
rains in our entire forecast area by mid-evening. The models have
continued to handle this system consistently, with primarily an
open wave even at the surface until Saturday over the Great Lakes,
when our precipitation will be done. QPF amounts from Friday
afternoon and Friday night still look to remain in the 0.25" to
0.40" range. The increasing rain chances and cloud cover will
limit high temperature potential on Friday, as highs top out in
the upper 40s north and lower 50s S of I-70. 

By sunrise on Saturday, the rain should be limited to along the 
Indiana border for a couple hours, mainly east of Champaign to 
Lawrenceville. Cloud cover looks to break up from southwest to
northeast Saturday afternoon, with areas northwest of Peoria
possibly remaining cloudy all day. Despite limited sunshine,
central IL will remain under the influence of a warm air mass, as
high temps reach the 50s across the board. 

For the late weekend travel, a low pressure system is still
expected to track across Illinois. The 12Z GFS did a dramatic 
shift southward with the track of that low, on the order of 
250-300 miles, bringing colder air and accumulating snowfall into
our northwest counties as early as late Sunday morning, with snow
continuing into early evening. Several inches of snow could 
accumulate during a busy travel day. The GFS still indicates 
primarily rain in the eastern half of our counties, but a 
significant travel impact could occur if the GFS solution 
verifies. The overall consensus of other models continue to lean 
toward our current forecast, with light snow mainly Sunday night 
for areas mainly west of I-55. The 12z ECMWF and Canadian both 
continue to show much lower potential for significant snow accum 
in our area in the Sunday into Monday time frame, with QPF amounts
after rain changes to snow supporting mainly a half inch or less 
in our NW counties. The Canadian sends a secondary wave into IL 
from the NW on Monday, and triggers some additional light snowfall
through the day. The end result in our official forecast was for 
only minor adjustments on snowfall amounts Sunday night, with 
little to no snow during the day Sunday. The band of heavy snow 
from this event (4"-7") still appears to affect mainly Iowa into 
SW Wisconsin on Sunday-Sun eve, with rain changing to snow into 
our western counties Sunday night as isentropic downglide 
dominates in the wake of the surface low. 

This system will need to be watched closely, as the ECMWF and
Canadian surface low tracks did also show a slight southward
shift, but not nearly as major of a change in the southward surge
of cold air into Illinois on Sunday, when the bulk of our
0.25"-0.40" QPF (mainly rain) falls. 

A significant push of colder air under Canadian high pressure 
will dominate the late extended forecast, as high temps on Monday 
will settle out around 14 to 18 degrees colder than Sunday, with 
low 30s toward Galesburg, and near 40 toward Lawrenceville. The 
cold air will remain in place Tuesday and Wednesday, when high 
temps remain in the 30s across central and southeast IL. After
light snowfall or flurries end Monday night, dry weather will 
occur Tuesday and Wednesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1159 AM CST Wed Nov 21 2018

A cold front will continue to push southward through central IL
this afternoon, and move south of all TAF sites by 21z-22z. Low
clouds are trailing the front, at a slower pace than the front. The
progression of MVFR clouds southward toward PIA and BMI has 
slowed, but appears poised to still reach BMI between 19z- 20z. 
Those clouds are expected to stall out just north of PIA and CMI, 
so did not include them for those two TAFs. The clouds are 
projected to dissipate in place, with VFR cloud conditions at BMI 
by 23z. VFR conditions should then prevail the remainder of the 
18z TAF period. 

Mid-high clouds from the next shortwave will brush across the
northern terminals late tonight into Thanksgiving morning, but no
effect on aviation is expected. 

Winds will gradually shift from NE to E and then SE by tomorrow
morning. Speeds will climb to 10-12kt tomorrow morning from the
S-SE. 


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Shimon
LONG TERM...Shimon
AVIATION...Shimon