957
FXUS63 KDMX 010730 CCA
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
229 AM CDT THU OCT 1 2026
KEY MESSAGES
- MODERATE TO HEAVY RAINFALL CONTINUES THIS MORNING. FLASH
FLOODING REMAINS POSSIBLE, AND RIVER FLOODING LIKELY.
- RAIN THIS MORNING TAPERS OFF FROM NORTHWEST TO SOUTHEAST
THROUGH THE DAY TODAY, WITH POTENTIAL FOR AN ADDITIONAL 1 TO 2
INCHES OVER SOUTHERN INTO SOUTHEASTERN IOWA THIS AFTERNOON.
- ONCE RAIN ENDS ACROSS THE AREA TODAY, COOLER, DRIER AND
BREEZIER CONDITIONS DEVELOP WITH DRY, FALL-LIKE WEATHER
THROUGH THE WEEKEND.
SHORT TERM /THROUGH TONIGHT/
ISSUED AT 216 AM CDT THU OCT 1 2026
HEAVY RAIN IS ONGOING EARLY THIS MORNING, AS THE LOW PRESSURE
FORMERLY KNOWN AS HURRICANE POLO MAKES IT'S WAY INTO WESTERN IOWA.
FLASH FLOOD WARNINGS LITTER EASTERN NEBRASKA INTO WESTERN IOWA WHERE
A SLOW MOVING, CONVECTIVELY DRIVEN LINE OF STORMS BROUGHT
EFFICIENT RAINFALL TO THE AREA. RAINFALL AMOUNTS REPORTED OUT OF
THE OMAHA AREA HAVE RANGED FROM 4 TO AS HIGH AS 8 INCHES WITH
THIS LINE. UPON IT'S ARRIVAL IN THE DMX FORECAST AREA, THE LINE
HAS SINCE FALLEN APART, BUT THE REMAINING VORT MAX IS STILL
SLOWLY PUSHING ACROSS THE AREA. FUELED BY A MOISTURE RICH LOW
LEVEL JET, THIS VORT MAX IS PRODUCING A SWATH OF HEAVY RAINFALL
WITH EFFICIENT 1-2 IN/HR RATES. WHILE RATES LIKELY WON'T BE AS
ROBUST AS THE MORE CONVECTIVELY DRIVEN MODE SEEN TO OUR WEST,
THE LESS PROGRESSIVE NATURE OF THIS HEAVY RAINFALL WILL ALLOW
AMOUNTS TO RACK UP QUICKLY. MODEL GUIDANCE CONTINUES TO SHOW A
SWATH OF 2 TO 4 INCH RAINFALL FALLING OUT OF THIS, WITH EMBEDDED
POCKETS UP TO 6 INCHES. CURRENT RADAR TRENDS WOULD SUGGEST THIS
BAND IS GOING TO SET UP IN A ROUGHLY WEST SOUTHWEST TO EAST
NORTHEAST LINE, FOLLOWING ALONG US HIGHWAY 30 WEST OF AMES,
PASSING THROUGH THE AMES AREA, THEN DRIFTING SLIGHTLY NORTH OF
HIGHWAY 30 UP TOWARDS THE WATERLOO/CEDAR FALLS AREA. THIS
RAINFALL WILL LIKELY LEAD TO PONDING AND FLOODING THROUGHOUT
NORTH CENTRAL IOWA, AS HEAVY RAIN FALLS ON ALREADY SATURATED
SOILS. THE FLASH FLOOD WATCH CONTINUES THROUGH THIS EVENING,
ALTHOUGH SOME ADJUSTMENTS TO THE WATCH ARE LIKELY AS RAIN BEGINS
TO END TODAY.
AFTER THE VORTMAX PUSHES THROUGH LATER THIS MORNING, THE TRAILING
COLD FRONT WILL BEGIN TO PUSH SOUTHWARD, ENDING THE RAINFALL FROM
NORTHWEST TO SOUTHEAST THROUGH THE DAY. BARRING A FEW ELEVATED
SHOWERS, MUCH OF THE FORECAST AREA WILL SEE RAIN ENDING BY NOON, IF
NOT SOONER. BEFORE COMPLETELY PUSHING OUT OF THE AREA THIS
AFTERNOON, WE MAY SEE SHOWERS AND EVEN A FEW STORMS FESTER ALONG THE
BOUNDARY IN SOUTHERN AND SOUTHEASTERN IOWA. THESE WILL HAVE THE
POTENTIAL TO BRING ANOTHER 1 TO 3 INCHES TO SOUTHEASTERN IOWA,
ALTHOUGH IT'S POSSIBLE THIS SECONDARY BAND ENDS UP SOUTH AND
EAST OF OUR FORECAST AREA. REGARDLESS, GIVEN THE WIDESPREAD RAIN
THAT FELL YESTERDAY AND SATURATED SOILS OVER SOUTHERN IOWA, WPC
HAS MAINTAINED A SLIGHT RISK FOR EXCESSIVE RAINFALL (LEVEL 2 OF
4) TO ACCOUNT FOR THIS SECONDARY SWATH OF RAIN IN SOUTHEASTERN
IOWA LATER TODAY.
BEHIND THE COLD FRONT TODAY, CONDITIONS OVER IOWA WILL BE DRYING OUT
AND COOLER AIR FILLING IN. SLIGHTLY ENHANCED PRESSURE GRADIENTS
COMBINED WITH THE COOLER, DESCENDING AIR MASS WILL LEAD TO SOME
BREEZY POST-FRONTAL CONDITIONS TODAY. NORTHERLY WINDS OF 15 TO 20
MPH ARE EXPECTED TODAY, WITH GUSTS UP TO 30 MPH ESPECIALLY OVER
NORTHERN IOWA.
LONG TERM /FRIDAY THROUGH WEDNESDAY/
ISSUED AT 328 PM CDT WED SEP 30 2026
THE EXTENDED FORECAST PERIOD IS EXPECTED TO MARK THE FIRST TRUE
TRANSITION TO FALL-LIKE WEATHER. BEHIND THURSDAYS COLD FRONT,
SURFACE HIGH PRESSURE WILL BUILD BACK INTO THE REGION, BRINGING
SEVERAL DAYS OF DRY WEATHER AND COOLER TEMPERATURES. PREVIOUS
FORECAST ITERATIONS DEPICTED A SHORTWAVE DIVING SOUTHEASTWARD TOWARD
THE UPPER MISSISSIPPI RIVER VALLEY, BUT THIS AFTERNOONS MODEL
GUIDANCE HAS LARGELY REMOVED THAT FEATURE, LEAVING THE AREA MOSTLY
DRY UNTIL PRECIPITATION CHANCES RETURN LATE IN THE PERIOD.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1108 PM CDT WED SEP 30 2026
VFR TO LIFR CONDITIONS REMAIN TO START THE PERIOD AND WILL
CONTINUE THROUGH THE OVERNIGHT WITH IFR TO LIFR CONDITIONS
PERSISTENT DURING THE EXPECTED RAIN THROUGH THE OVERNIGHT. THE
HEAVIEST RAIN IS EXPECTED DURING THIS TIME PERIOD WHICH WILL
CAUSE VISIBILITY DROPS AT TIMES DUE TO THE INTENSITY OF THE
RAIN, POTENTIALLY EVEN LOWER THAN ADVERTISED IN THE CURRENT
TAFS. CEILINGS WILL ALSO BECOME LARGELY IFR TO LIFR TO GO ALONG
WITH THE RAIN AND ANY POTENTIAL FOG. HAVE KEPT LIMITED THUNDER
MENTIONS AT KDSM AND WILL MONITOR CLOSELY SHOULD THUNDER REMAIN
LONG ENOUGH TO AFFECT KOTM AS WELL INTO THURSDAY MORNING. TIMING
IN ALL CASES (RAIN/VISBY/CIG/THUNDERSTORM) MAY STILL NEED
FURTHER ADJUSTMENTS AND WILL WATCH TRENDS CLOSELY. RAIN
GRADUALLY ENDS NORTHWEST TO SOUTHEAST AS A COLD FRONT MOVES
THROUGH THE AREA ON THURSDAY WITH GRADUALLY IMPROVING CEILINGS
BEHIND. ADDITIONALLY, WINDS OUT OF THE NORTH WILL INCREASE
BEHIND THE FRONT BRINGING BREEZY CONDITIONS ON THURSDAY.
HYDROLOGY
ISSUED AT 216 AM CDT THU OCT 1 2026
ALL TYPES OF FLOODING, INCLUDING FLASH, AREAL AND RIVER, REMAIN
POSSIBLE AS ADDITIONAL MODERATE TO HEAVY RAIN FALLS ACROSS MUCH OF
THE CWA. RESPONSES ON AREA RIVERS ARE ALREADY ONGOING WITH THE
RAINFALL THAT'S FALLEN THROUGH EARLY THURSDAY MORNING, WITH
ADDITIONAL RAIN STILL ON THE WAY.
RIVER FLOOD WARNINGS HAVE BEEN ISSUED FOR LOCATIONS WHERE WE HAVE
HIGH CONFIDENCE (AT LEAST 80%) OF REACHING AT LEAST FLOOD STAGE.
A HANDFUL OF RIVER FLOOD WATCHES HAVE BEEN INTRODUCED AT RIVERS
WHERE CONFIDENCE IN FLOODING IS RELATIVELY LOWER. REFER TO THE
NATIONAL WATER PREDICTION SERVICE AT WEATHER.GOV/DESMOINES/WATER
FOR THE LATEST RIVER OBSERVATIONS AND FORECASTS.
THE RACCOON RIVER BASIN WILL LIKELY BE IMPACTED BY RAINFALL THIS
MORNING, BUT WILL SEE A MORE DELAYED RESPONSE WITH THE HEAVIEST
RAIN FALLING FARTHER NORTH (UPSTREAM) IN THE BASIN. RECENT
RAINFALL IN MUCH OF THAT BASIN HAS ALREADY PRIMED RIVERS FOR A
RESPONSE, WITH ADDITIONAL WATER FALLEN OR FALLING NOW EARLY THIS
MORNING.
FLASH FLOODING REMAINS POSSIBLE THROUGH THIS MORNING,
ESPECIALLY IN URBAN AREAS INCLUDING CREEKS AND SMALLER STREAMS.
SEASONALLY HIGH SOIL MOISTURE WILL LEAD TO FASTER AND MORE
SIGNIFICANT RUNOFF THAN NORMAL. WITH THE HEAVY RAIN THREAT
SHIFTING SLIGHTLY NORTHWARD, QUICK RESPONDING STREAMS IN THE DES
MOINES METRO (WALNUT AND FOURMILE CREEK) SEEM LESS LIKELY TO
SEE SIGNIFICANT RESPONSES, BUT IOWAY CREEK IN AMES MAY STILL
END UP UNDER THE HEAVIEST RAINFALL AND WILL BE MONITORED CLOSELY
THROUGH THE MORNING.
DMX WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH THROUGH LATE TONIGHT FOR IAZ024>028-033>039-
044>050-057>062-070>075-081>086-092>097.
SHORT TERM...DODSON
LONG TERM...VORST
AVIATION...05
HYDROLOGY...ZOGG/DODSON
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