518
FXUS63 KLOT 271725
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
1225 PM CDT MON OCT 27 2025
KEY MESSAGES
- A PASSING STORM SYSTEM MAY PROVIDE PERIODS OF RAIN ACROSS THE
AREA DURING THE MIDDLE OF THE WEEK, FAVORING AREAS SOUTH OF
INTERSTATE 80.
- EXPECT SEASONABLE TEMPERATURES THROUGH NEXT WEEKEND.
DISCUSSION
ISSUED AT 310 AM CDT MON OCT 27 2025
AN UPPER-LEVEL LOW CENTERED NEAR THE BOOTHEEL OF MISSOURI EARLY
THIS MORNING WILL MOVE ESE TO THE CAROLINAS THROUGH TONIGHT AS
A STRONG RIDGE OVER ONTARIO REMAINS MOSTLY STATIONARY. A DEEP
RESERVOIR OF DRY AIR ADVECTING FROM THE EAST AND NORTHEAST WILL
SUPPRESS PRECIP WELL SOUTH OF THE AREA, WITH ONLY SOME CIRRUS
ATTEMPTING TO LIFT NORTHWARD THROUGH THE DAY.
A LONGWAVE TROUGH OVER WESTERN CANADA AND THE NORTHWEST U.S.
WILL BECOME CONSIDERABLY ELONGATED ACROSS THE GREAT PLAINS OVER
THE NEXT 24-48 HOURS BETWEEN THE RIDGE OVER ONTARIO AND A
RAPIDLY BUILDING WEST COAST RIDGE. A NARROW NORTH TO SOUTH
ORIENTED BAND OF RAIN IS EXPECTED TO DEVELOP WEST OF THE
MISSISSIPPI RIVER LATE TONIGHT INTO TUESDAY IN ASSOCIATION WITH
A MODEST AREA OF MID-LEVEL MOISTURE BELOW A BROAD ENTRANCE
REGION OF A NORTHWEST POINTED UPPER-JET MAXIMUM. EXTENSIVE LOW
TO MID-LEVEL DRY-AIR ADVECTION FROM A PSEUDO-HUDSON BAY HIGH TO
THE NORTHEAST WILL STEADILY ERODE THE EASTERN EDGE OF THE
PRECIP BAND TUESDAY INTO TUESDAY NIGHT BEFORE THE MAIN VORTICITY
LOBE OF THE TOUGH DETACHES AND PIVOTS SOUTHWEST OF THE AREA.
EXPECTATIONS ARE THAT MUCH OF THE AREA WILL REMAIN DRY ON
TUESDAY, WITH RAIN POTENTIAL RANGING FROM LOW-END CHANCE POPS
(30%) NEAR THE WISCONSIN LINE TO LIKELY POPS (UP TO 70%) TOWARD
CENTRAL ILLINOIS TUESDAY NIGHT INTO WEDNESDAY MORNING. IT IS
HIGHLY LIKELY THAT THERE WILL BE A SHARP NORTH TO SOUTH GRADIENT
IN PRECIPITATION SOMEWHERE OVER THE FORECAST AREA, WITH A
DISTINCT POSSIBILITY THAT MUCH OF NORTHERN ILLINOIS REMAINS DRY
WITH THIS EVENT.
THE NEWLY FORMED LOW TO THE SOUTHWEST, THE ORIGINAL LOW OVER
THE CAROLINAS, AND EVEN THE REMNANTS OF HURRICANE MELISSA WILL
CONGEAL INTO A LONGWAVE TROUGH OVER THE NORTHEAST LATE IN THE
WEEK, WITH SIGNALS OF A COUPLE REINFORCING WAVES CROSSING THE
AREA FROM THE NORTHWEST THIS WEEKEND INTO EARLY NEXT WEEK.
ENSEMBLE GUIDANCE CONTINUES TO DEPICT A LOOSE OMEGA BLOCK
DEVELOPING AS THE WEST COAST RIDGE AMPLIFIES. OUR AREA WOULD BE
SITUATED ON THE WESTERN EDGE OF THE MAIN LONGWAVE TROUGH TO THE
EAST, YIELDING SPORADIC BOUTS OF SCATTERED RAIN SHOWERS AND
PERHAPS SOME LAKE EFFECT RAIN SHOWERS DURING THIS TIME. TEMPS
WILL REMAIN SEASONABLE AS ARCTIC AIR REMAINS WELL NORTH OF THE
AREA.
KLUBER
AVIATION /18Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 1225 PM CDT MON OCT 27 2025
NO SIGNIFICANT AVIATION WEATHER CONCERNS FOR THE 18Z TAFS.
FORECAST AREA SITS BETWEEN SURFACE HIGH PRESSURE OVER EASTERN
CANADA, AND LOW PRESSURE OVER THE PLAINS. THIS WILL CONTINUE TO
PROVIDE RELATIVELY DRY, EASTERLY LOW-LEVEL FLOW TO THE REGION
THROUGH TUESDAY. SURFACE WINDS NEAR 15 KTS WITH A FEW HIGHER
GUSTS THIS AFTERNOON WILL DIMINISH TO AROUND 10 KTS WITH SUNSET
THIS EVENING. WINDS WILL INCREASE AGAIN LATE MORNING TO MIDDAY
TUESDAY, WITH SOME HIGHER GUSTS AROUND/A LITTLE ABOVE 20 KTS
POSSIBLE IN THE AFTERNOON.
OTHERWISE, VFR CONDITIONS ARE EXPECTED THROUGH THE PERIOD, WITH
INCREASING HIGH CLOUD COVER TUESDAY. SPOTTY LIGHT RAIN IS
POSSIBLE OVER EASTERN IA AND EVENTUALLY CENTRAL IL BY LATE
TUESDAY, THOUGH THIS IS EXPECTED TO REMAIN SOUTH OF THE
TERMINALS.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 7 AM CDT WEDNESDAY FOR THE IL
NEARSHORE WATERS.
VISIT US AT WEATHER.GOV/CHICAGO
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