192 
FXUS63 KILX 231627
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1027 AM CST Fri Nov 23 2018

.UPDATE...
Issued at 1027 AM CST Fri Nov 23 2018

Latest visible satellite imagery indicated high and mid level
clouds had overspread all of central and southeast Illinois. 
These clouds will lower and thicken this afternoon as moisture 
increases ahead of an approaching surface trough and mid level 
wave. Regional 12z soundings showed quite a bit of dry air that 
needs to be overcome before more widespread precip reaches the 
surface.

Regional radar mosaic and surface obs show much of the leading
edge of precip progressing through Missouri and into western IL is in
the form of virga, and will likely take several more hours before
rain begins to affect the western CWA. As a result, have delayed
the onset of precip this afternoon, with likely pops confined west
of a Peoria to Springfield line by 00z. The area of rainfall will
overspread the remainder of the CWA this evening, but with that
initial stage of drier air to overcome, have lowered event QPF to
0.25" or less for areas west of I-57, with slightly higher amounts
near a third of an inch south of I-70.


A tight pressure gradient ahead of the surface wave will lead to 
brisk and gusty S/SE winds today with some gusts likely reaching 
30 MPH. This will help push highs near 50 or into the lower 50s 
for most areas, despite thickening cloud cover.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 329 AM CST Fri Nov 23 2018

Short-wave trough evident on 09z/3am water vapor imagery over the
Central Plains will track eastward...spreading clouds and rain 
into central Illinois later today. The airmass is initially quite
dry as evidenced by 00z KILX/KDVN upper air soundings, so precip
will take awhile to spread into the area. Latest regional radar
mosaic shows only scattered light showers beginning to develop
across Kansas/Oklahoma, as the system has not yet intercepted 
much Gulf of Mexico moisture. This will change as the day 
progresses, resulting in rain becoming widespread west of the 
Mississippi River by early this afternoon. High-res models such as
the HRRR are suggesting a slower eastward progression of the 
steady rain, with much of it staying west of the CWA until late 
this afternoon into the evening. Have adjusted hourly PoPs to keep
the morning dry across the board, then have limited likely to 
categorical PoPs to locations along/west of a Bloomington to 
Shelbyville line by late afternoon. High temperatures will top out
in the lower 50s. Rain will overspread the entire area tonight 
before rapidly exiting into Indiana by early Saturday morning. 
Total rainfall with this system will generally range from one 
quarter to one third of an inch. 

.LONG TERM...(Saturday through Thursday)
ISSUED AT 329 AM CST Fri Nov 23 2018

Any lingering showers across the E/NE CWA will quickly come to an
end early Saturday, followed by a return to mostly sunny and mild
conditions with highs in the lower to middle 50s.  

The main forecast challenge with this package will be a stronger
storm system expected to impact the region Sunday into Monday. The
short-wave in question is currently off the coast of British
Columbia and will track E/SE into Washington later today. Once it
arrives over the CONUS, upper air soundings will be able to 
provide additional data for the models to work with and will thus
result in a clearer picture of what this feature will do once it 
crosses the Rockies. Previous model runs had shown the wave 
amplifying into a closed upper low over the Plains by Sunday 
morning:however, the 00z Nov 23 models now mostly keep it an open 
wave. The exact degree of amplification will be pivotal to the 
upcoming forecast, as that will determine how far south the 
surface low will develop. With a weaker upper wave as shown by the
latest models, the trend has been further south. The operational 
GFS continues to be the furthest south solution, while the NAM, 
GEFS, and GEM are clustered around a further north solution. 
Following the northern consensus still results in a slightly 
further south track than was seen 24 hours ago. As a result, think
the low will track from eastern Kansas Sunday morning to north- 
central Indiana Sunday night. This particular track will lead to a
rainy day across central Illinois for Sunday, with the rain 
mixing with and changing to snow northwest of the Illinois River 
Sunday afternoon. As the low passes into Indiana, colder air 
arriving on its backside on strong/gusty northwesterly winds will 
help change the rain to snow eastward to the I-57 corridor Sunday 
evening...then everywhere overnight before quickly ending from 
southwest to northeast by dawn Monday. The heaviest snowfall with 
this system is favored in a swath from northern Missouri across 
southern/eastern Iowa into northern Illinois. Accumulations will 
be likely across the W/NW KILX CWA...particularly along/north of a
Rushville to Bloomington line. The forecast low track will be 
fine-tuned over the next couple of model runs as the short-wave 
trough becomes better resolved, so stay tuned for updates.

Deep upper troughing will take hold across the eastern CONUS in
the wake of the early week system, resulting in wintry
temperatures for the remainder of the extended. High temperatures
will only be in the 20s and 30s, while overnight lows drop into
the teens Monday through Wednesday. 

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 556 AM CST Fri Nov 23 2018

Ceilings will steadily lower today...with rain developing from
west to east across the area late this afternoon into the evening.
Based on latest HRRR, it appears predominant rain will begin at
KPIA/KSPI by around 22z...then further NE to KCMI by 03z. Ceilings
will initially be VFR, but will lower to MVFR at all terminals
between 02z and 03z. The rain will gradually taper off overnight:
however, the MVFR ceilings will persist through dawn Saturday.
Morning upper air sounding revealed 40kt winds at around 1500ft,
so have included low-level wind shear at all sites through 15z.
After that, the higher momentum air will mix to the surface
creating southerly gusts of 25-30kt through the afternoon. Winds
will veer to the SW later tonight. 


&&

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

$$

UPDATE...25
SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...Barnes