000 
FXUS63 KILX 021722
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1222 PM CDT Mon Jun 2 2025

.KEY MESSAGES...

- Wildfire smoke will maintain hazy skies again today. While 
  dense near surface smoke is not expected, the Illinois 
  Environmental Protection Agency (EPA) suggests air quality may 
  be degraded into the moderate category at times.

- High temperatures will approach 90 degrees west of the IL River
  today. Uncertainty in temperatures is higher tomorrow, but
  increasing humidity will bring heat risk into the moderate
  category (level 2 of 4).

- Periods of scattered thunderstorms late tomorrow through
  Thursday may generate localized heavy rain. In addition, there 
  is a level 2 of 5 (slight) risk for severe weather west of the 
  IL River Tuesday evening.
  

&&

.DISCUSSION...
Issued at 140 AM CDT Mon Jun 2 2025

A shortwave ridge will build into the Midwest through early 
tomorrow, then slide east as a large upper level trough approaches 
later Tuesday. Ahead of that trough, several transient disturbances 
embedded within a large southwest flow regime will glide over the 
Midwest and Ohio Valley late Tuesday through Thursday, resulting in 
periods of scattered showers and thunderstorms. Friday and beyond, 
the storm track becomes less clear, resulting in continued slight 
(20-40%) chances for periods of scattered storms across central and 
southeast IL.

***** HAZE LINGERS *****

Like yesterday, surface smoke concentrations this morning remain 
relatively low with air quality indices (AQIs) ranging from 30-60 
due to PM2.5 particulates; for reference, AQI values < 50 are 
considered good, while 50 < AQI < 100 they're "moderate." However, 
the RAP and HRRR suggest near surface smoke concentrations will 
increase again this afternoon due to deep mixing. The Illinois EPA 
maintains a forecast for moderate air quality through today. Both 
the smoke and haze are expected to depart tomorrow as southwest flow 
kicks it into the Great Lakes.

***** SEASONABLY WARM THROUGH TOMORROW *****

High res guidance, most notably the HRRR and Consshort, continue to 
indicate deep mixing today will maintain seasonably dry low levels, 
favoring efficient radiational warming beneath sunny skies. Highs 
are forecast to reach the mid 80s east of roughly I-55, and upper 
80s further west, perhaps touching 90 in a few spots (20-40% 
chance). As southerly flow strengthens tomorrow, low level 
moisture will increase with dewpoints surging well into the 60s, 
making it feel more muggy. While the cold front is forecast to 
take its sweet old time reaching us tomorrow night, several CAMs 
depict convective remnants entering our area during the late 
morning or afternoon. Even if we don't have any precip with this 
activity, the rain cooled air may prevent our highs from reaching 
forecast values (upper 80s), mainly west of I-55. Temperatures 
will turn cooler with highs in the 70s to around 80 south of the 
front Wednesday across our northwest and area-wide Thursday.

***** BREEZY TOMORROW *****

As surface high pressure is slow to shift east out of the area 
tomorrow and the cold front approaches from the west, the gradient 
will tighten leading to increasing southerly winds. Bufkit soundings 
suggest top of channel winds tomorrow afternoon and evening reach 
~30-35 kt (35-40 mph), so one shouldn't be surprised to encounter a 
few such gusts (NBM chances for 35+ mph are 40-60%) though 25-35 mph 
will be more common.

***** STORMS LATE TOMORROW THROUGH THURSDAY *****

As the cold front approaches from the west tomorrow evening, 
clusters of storms are forecast to move southwest to northeast 
through west-central IL. As dewpoints surge into the upper 60s, 
MUCAPE values are forecast to climb to anywhere from 1500-3000 J/kg 
ahead of the front where deep layer shear reaches 30-40 kt. Given 
steep low level lapse rates with an inverted V sounding profile, 
thinking is the biggest risk from these storms will be from gusty 
outflow winds, mainly in any organized linear segments. However, we 
cannot rule out localized, marginally severe hail. Later in the 
evening and into the overnight period, as the storms shift east of 
the IL River, abating diurnal instability and lower wind shear 
suggest the severe risk diminishes.

There will be some hydrological risk as well, primarily in urban and 
poor drainage areas. NBM suggests a 10-20% chance rain totals exceed 
2.5 inches (6h FFG is 2.5-3.5 inches), with the highest chances west 
of the IL River. However, the global models comprising the NBM at 
this time range lack the resolution to effectively handle 
convection, so we'll be interested to see what the HREF reveals when 
it begins to capture this event.

As the front becomes displaced from the stronger forcing aloft 
Wednesday, the severe risk diminishes but we could still have some 
localized hydrological issues with enough training. Thursday into 
Friday, model differences increase with the timing and location of 
another shortwave lifting through the district, but another period 
of showers and storms is expected. While we suspect there will be 
plenty of breaks in showers and storms during this latter part of 
the forecast period, our confidence is low in when those will occur. 
As a result, we maintain 20-50% precip chances right into the 
upcoming weekend.

Bumgardner

&&

.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1222 PM CDT Mon Jun 2 2025

VFR conditions continue through the 18z TAF period. Winds out of the 
south pick up to 10-15 knots tomorrow morning, gusting to 20-30 
knots. The western sites (SPI, PIA) have a PROB30 group as scattered 
showers may move into the area near the end of the TAF period. There 
still is a layer of smoke aloft, but shouldn't affect visibilities 
near the surface.

Copple

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$