027 
FXUS63 KILX 130820
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
320 AM CDT Mon Sep 13 2021

.SYNOPSIS...
Issued at 311 AM CDT Mon Sep 13 2021

Temperatures remain above average to start the week, with highs in
the upper 80s today and Tuesday. A cold front moves into the area 
Tuesday evening bringing a chance for scattered thunderstorms, 
some of which could be strong to severe.

&&

.SHORT TERM...(Today and tonight)
ISSUED AT 311 AM CDT Mon Sep 13 2021

A stationary front remains draped across northern IL and southern
IA as of early Monday morning. Temperatures were in the mid 60s 
across the area at 3am/08z...a few degrees cooler than last night 
but still above average. The above average temperatures are set to
continue into the work week as central Illinois remains firmly to
the south of the stationary boundary in a southwesterly surface 
flow regime. Overall, a similar conditions to Sunday are expected 
today, with the primary difference being that the wind 
speeds/gusts will be lower today than Sunday. The wildfire smoke 
that dulled sunshine over the weekend should begin to lift north 
out of the area today. Highs today will once again be in the upper
80s. 

Tonight, a shortwave lifts across the upper Midwest. The track of
this wave is such that as it passes by to the northwest, it will 
induce weak ascent across the northwest portion of the CWA. 
However, the expectation is for these areas to remain dry due to 
dry air in the mid-levels beneath cloud base. By Tuesday morning, 
the surface low associated with this shortwave will be located in 
the upper Great Lakes.

&&

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 311 AM CDT Mon Sep 13 2021

A cold front will extend from the aforementioned surface low into
Wisconsin and Iowa on Tuesday morning. In response to the pressure
falls, the pressure gradient tightens across the Midwest 
resulting in breezy southwest winds gusting to 25 mph ahead of the
cold front. This front will push into the ILX CWA Tuesday 
evening, with scattered thunderstorms expected along the front. 

Moisture advection and pooling along/ahead of the front will
result in PWAT values near 2" and dewpoints around 70 degrees. 
This, in conjunction with fairly steep mid-level lapse rates of 
about 7 degC/km, will lead to the development of robust 
instability Tuesday afternoon, with forecast soundings indicating 
upwards of 3000 J/kg of MLCAPE. The latest high-res guidance 
suggests there could be a subtle wind shift/convergent zone out 
ahead of the actual cold front, which could act to initiate 
thunderstorms in central IL by around 00z Wednesday. That would 
allow storms to tap into the more robust instability than if they 
did not develop until the overnight hours. There is still 
uncertainty as to the timing of these features, and some guidance 
maintains that the front/storms will not move into the area until 
well after sundown, but the trend has been towards earlier arrival
times. 30-40 knots of deep layer shear is expected to develop, 
but the better flow may lag behind the front which would limit the
severe potential somewhat. Nonetheless, the potential exists for 
severe storms Tuesday evening with damaging winds as the primary 
hazard, and large hail also possible.

On Wednesday, the front lingers in the southeastern half of the
CWA, keeping precip chances in the forecast. The post-frontal air
mass will provide a short-lived return to seasonable temperatures
with highs near 80 on Wednesday. Temperatures rebound quickly as 
ridging builds over the eastern half of the CONUS late in the 
week. Southerly flow will reestablish across the local area and 
boost high temperatures back above average, into the upper 80s by 
Friday and remaining there into the weekend. There doesn't appear 
to be much in the way of widespread precip chances after the mid-
week cold front, but the evolution of Tropical Storm Nicholas 
bears monitoring. If moisture from the system streams northward 
late in the week it could result in isolated showers/light rain 
for the eastern portions of the CWA on Friday/Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1115 PM CDT Sun Sep 12 2021

VFR conditions will persist through the TAF period as an elongated
upper-level high remains anchored over the Tennessee Valley. Some
scattered high clouds are anticipated into Monday as a frontal
system lurks to the north. Low- level winds will maintain a 
southwest component ahead of this frontal system, which will 
impact the regional terminals later this week. Sustained speeds 
will be SW at 5-10 kts with occasional gusts to 20 kts.


&&

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

$$

SYNOPSIS...Erwin
SHORT TERM...Erwin
LONG TERM...Erwin
AVIATION...MJA