337
FXUS63 KILX 310640
AFDILX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
140 AM CDT SUN MAY 31 2026
KEY MESSAGES
- ABOVE NORMAL TEMPERATURES ARE LIKELY TO PERSIST INTO MID-JUNE, WITH
HIGHS GENERALLY IN THE 80S. HUMIDITY VALUES ARE EXPECTED TO
INCREASE LATE THIS WEEK INTO THE WEEKEND.
- WIDELY SCATTERED SHOWERS AND STORMS ARE POSSIBLE THROUGH
MONDAY, WITH THE BEST CHANCE (30-40%) BEING SOUTH OF A
GALESBURG TO LAWRENCEVILLE LINE TONIGHT. DRY CONDITIONS ARE
EXPECTED TUESDAY THROUGH THURSDAY.
DISCUSSION
ISSUED AT 138 AM CDT SUN MAY 31 2026
THE SYNOPTIC PATTERN CONTINUES TO EVOLVE AS ANTICIPATED, WITH
AN AMPLIFIED OMEGA BLOCK THAT FEATURES A RIDGE AXIS OVER IL
BEING PINCHED BY A NEGATIVELY TILTED TROUGH TO THE WEST AND A
DEEP LOW OFF THE EASTERN SEABOARD. CENTRAL IL REMAINS POSITIONED
WITHIN A MOISTURE GRADIENT BETWEEN A BROAD MOIST SECTOR TO THE
SOUTHWEST AND A DRIER AIR MASS ASSOCIATED WITH A 1024-MB SFC
HIGH PRESSURE OVER THE GREAT LAKES. AS OF 06Z/1AM, DEWPOINTS
RANGED FROM THE LOW 40S ALONG THE I-74 CORRIDOR TO THE LOW 60S
IN THE SOUTHERN IL RIVER VALLEY TO THE LOW 70S INTO CENTRAL MO.
THIS DRIER AIRMASS LEAVES SOME QUESTION AS TO HOW FAR NORTHEAST
ANY PRECIP WILL REACH OVER THE NEXT 48 HOURS, BUT THE
EXPECTATION IS THAT THE SFC HIGH WILL WEAKEN WHILE MID-LEVEL
LIFT AND THE MOIST AXIS BOTH GRADUALLY LIFT NORTHEAST, OFFERING
BETTER CHANCES FOR RAIN THAN PREVIOUS DAYS. POPS WERE A
CHALLENGE OWING TO TIMING AND PLACEMENT DIFFERENCES AMONG THE
LATEST HIGH-RES GUIDANCE. IN GENERAL, POPS STILL DECREASE WITH
NORTHEASTWARD EXTENT (LESS THAN 20% NORTH OF I-74). THE MOST
CONSISTENT SIGNAL IN RECENT DAYS HAS BEEN FOR A WAVE TO PASS
JUST SOUTHWEST OF THE ILX CWA SUNDAY NIGHT, MAINLY TO THE SOUTH
OF A SPRINGFIELD-TO-EFFINGHAM LINE. HAVE 20-40% POPS IN THE
FORECAST FOR THIS DISTURBANCE, BUT THE POPS INCREASE QUICKLY
JUST TO THE SOUTH ACROSS NWS ST. LOUIS FORECAST AREA (60-80%).
OUTSIDE OF THIS WAVE, ANY PRECIP ACTIVITY WOULD MAINLY BE IN THE
FORM OF ISOLATED TO WIDELY SCATTERED SHOWERS.
PRECIP CHANCES COME TO AN END BY MONDAY NIGHT AS A NEW SFC HIGH
PRESSURE SETTLES IN OVER THE GREAT LAKES. BETWEEN HEIGHT RISES
ALOFT AND THIS EXPANSIVE SFC HIGH PRESSURE, DRY CONDITIONS ARE
EXPECTED LOCALLY TUESDAY THROUGH THURSDAY. THE NBM UNDER-
FORECAST TEMPS ONCE AGAIN ON SATURDAY (ACTUAL HIGHS REACHED THE
MID-UPPER 80S VS A LOW- TO-MID 80S NBM FORECAST), AND THIS HAS
BEEN AN ONGOING BIAS WITH OUR CURRENT PATTERN. WITH A SIMILARLY
DRY AIRMASS AND GREAT LAKES HIGH PRESSURE IN PLACE DURING THE
MID-WEEK PERIOD, WOULD NOT AT ALL BE SURPRISED TO SEE THE
OBSERVED HIGHS COME IN SEVERAL DEGREES WARMER THAN THE CURRENT
NBM FORECAST, WHICH HAS HIGHS IN THE UPPER 70S TO LOW 80S TUES-
WED, THEN MID 80S BY THURS. THE GOOD NEWS IS THAT DEWPOINTS WILL
BE SEASONABLY LOW TUES-WED, IN THE UPPER 40S AND LOW 50S.
BY LATE WEEK, THE UPPER RIDGE BECOMES FLATTENED, SFC HIGH
PRESSURE SHIFTS TO TOWARDS THE SE CONUS, AND SOUTHERLY SFC FLOW
IS ESTABLISHED ACROSS IL. THIS WILL LIKELY MARK THE BEGINNING
OF A MORE SUMMER-LIKE PATTERN WITH A SLIGHT INCREASE IN TEMPS
BUT A MORE NOTABLE INCREASE IN THE HUMIDITY. FORECAST HIGHS FOR
THE FRI JUN 5 - MON JUN 9 PERIOD PEAK IN THE MID TO UPPER 80S,
BUT HEAT INDICES ARE FORECAST TO CLIMB INTO THE LOW 90S.
EXPERIMENTAL PROBABILISTIC HEAT RISK DEPICTS A 30- 60% CHANCE OF
MODERATE HEAT RISK ACROSS MUCH OF THE AREA ON THESE DAYS. A
MODERATE HEAT RISK IMPLIES HEAT IMPACTS FOR THOSE WHO ARE
SENSITIVE TO THE HEAT OR DO NOT HAVE ADEQUATE COOLING AND
HYDRATION. THE TRANSITION TO A MORE HUMID AIRMASS AND A MORE
ZONAL SYNOPTIC PATTERN RESULTS IN INCREASING PRECIP CHANCES,
WITH THE MODEL BLEND DELIVERING A 30-50% CHANCE OF SHOWERS AND
STORMS NEXT WEEKEND.
AVIATION /06Z TAFS THROUGH 06Z MONDAY/
ISSUED AT 1150 PM CDT SAT MAY 30 2026
ANOTHER SET OF VFR TAFS AS DRY EASTERLY LOW LEVEL FLOW REMAINS
IN PLACE. AN AREA OF -SHRA/TSRA TO OUR WEST IS FORECAST TO MOVE
INTO WEST CENTRAL IL LATER THIS MORNING, THEN TURN SOUTH. KEPT
KPIA-KSPI DRY FOR NOW BUT WILL MONITOR TRENDS AS THE AREA OF
CONVECTION DEVELOPS. E-SE WINDS WILL PERSIST NEAR/UNDER 10 KT
THROUGH THE FORECAST.
ILX WATCHES/WARNINGS/ADVISORIES
NONE.
KEY MESSAGES...ERWIN
DISCUSSION...ERWIN
AVIATION...25
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