281
FXUS63 KILX 201733
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1233 PM CDT TUE OCT 20 2026
KEY MESSAGES
- DRY CONDITIONS AND TRANQUIL WEATHER PREVAIL ACROSS CENTRAL AND
SOUTHEAST ILLINOIS THROUGH THIS WEEKEND.
- ABOVE NORMAL TEMPERATURES WILL DOMINATE THE REGION, WITH
AFTERNOON HIGHS CLIMBING INTO THE MID TO UPPER 70S.
DISCUSSION
ISSUED AT 1233 PM CDT TUE OCT 20 2026
EXPANSIVE SURFACE HIGH PRESSURE CENTERED SOUTH OF JAMES BAY
EXTENDS SOUTHWEST INTO THE MID AND LOWER MISSISSIPPI VALLEY
THIS AFTERNOON. BROAD SUBSIDENCE AND VERY DRY AIR BELOW 500 MB
WILL LEAD TO CLEAR SKIES THROUGH TONIGHT. HIGH TEMPERATURES TO
PEAK IN THE LOWER 70S TODAY, FOLLOWED BY OVERNIGHT LOWS IN THE
MID 40S.
A MODERATING TREND BEGINS WEDNESDAY AND CONTINUES THROUGH
THIS WEEKEND AS UPPER LEVEL RIDGING AMPLIFIES OVERHEAD. SUITE OF
MODEL GUIDANCE INDICATES 850 HPA TEMPERATURES WARMING TO +11C
TO +13C THROUGH THIS PERIOD. AFTERNOON MIX-DOWN OF THIS AIR WILL
LEAD TO DAILY HIGHS IN THE MID 70S THROUGH FRIDAY, THEN UPPER
70S TO AROUND 80F THIS WEEKEND WHEN SOUTHWEST LOW LEVEL FLOW
BECOMES BETTER ESTABLISHED. FORECAST SOUNDINGS SHOW DAYTIME
BOUNDARY LAYER MIXING REDUCING AFTERNOON DEWPOINTS INTO THE 40S,
YIELDING MINIMUM RELATIVE HUMIDITY VALUES BETWEEN 30 AND 40
PERCENT. NORMALLY IN LATE OCTOBER THIS WOULD RESULT IN AN
ENHANCED RISK OF FIRE SPREAD, BUT A WEAK MSLP GRADIENT WILL
PROMOTE LIGHT WINDS UNDER 10 MPH THROUGH FRIDAY.
A TRANSITION IN THE UPPER AIR PATTERN BEGINS MONDAY INTO
TUESDAY AS A POTENT UPPER-LEVEL TROUGH TRAVERSES THE NORTHERN
PLAINS AND LIFTS TOWARD THE UPPER MIDWEST. THE ECMWF-AI AND
OPERATIONAL ECMWF-ENS HAVE REMAINED CONSISTENT WITH A SLIGHTLY
SLOWER FRONTAL PASSAGE THAN THE GEFS MEMBERS, BRINGING THE
ATTENDANT COLD FRONT INTO WESTERN ILLINOIS MONDAY EVENING AND
CLEARING SOUTHEAST ILLINOIS TUESDAY AFTERNOON. THE NBM
INTRODUCES SLIGHT CHANCE POPS (15 PERCENT) WEST OF THE ILLINOIS
RIVER MONDAY AFTERNOON. WITH A LACK OF UPPER LEVEL SUPPORT AND
PROJECTED DRY AIRMASS, MODELS GENERALLY SHOW A DRY FRONTAL
PASSAGE FOR THE REMAINDER OF THE CWA.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1233 PM CDT TUE OCT 20 2026
VFR/SKC AND LIGHT WINDS 5 KT OR LESS THROUGH WED MORNING.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...25
DISCUSSION...25
AVIATION...25
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