995
FXUS63 KDMX 251905
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
205 PM CDT FRI SEP 25 2026
KEY MESSAGES
- TWO MORE ROUNDS OF RAINFALL BEGINNING TONIGHT/SATURDAY MORNING
AND AGAIN SATURDAY NIGHT AND SUNDAY MORNING. AREAS WITH HEAVY
RAINFALL ARE POSSIBLE.
- ANOTHER POTENT SYSTEM ARRIVES MONDAY NIGHT AND THROUGH MID
WEEK. ADDITIONAL AREAS OF HEAVY RAIN MAY OCCUR.
- MONITORING POTENTIAL ACCUMULATIVE IMPACTS ON AREA STREAMS AND
RIVERS. SIGNIFICANT RISES ARE EXPECTED ON SOME STREAMS,
POTENTIALLY REACHING FLOOD STAGE OR HIGHER BY MID NEXT WEEK.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED AT 200 PM CDT FRI SEP 25 2026
PRECIPITATION CHANCES AND AMOUNTS ARE THE CHALLENGE THROUGH AT LEAST
SATURDAY NIGHT THEN AGAIN LATE MONDAY NIGHT THROUGH MID NEXT WEEK.
WIDESPREAD RAIN HAS BEEN ONGOING THIS MORNING AND INTO EARLY THIS
AFTERNOON, MAINLY ALONG AND SOUTH OF HIGHWAY 30. THE RAIN WILL
GRADUALLY DIMINISH OVER THE REMAINDER OF THIS AFTERNOON AS DRY AIR
ENTRAINMENT BEGINS AND FORCING CONTINUES TO DIMINISH. RAINFALL
WITH THIS ACTIVITY HAS BEEN QUITE EFFICIENT AND HAS RESULTED IN A
BAND OF 1.00" TO 1.50" WEST OF THE DES MOINES METRO ALONG THE
HIGHWAY 141 CORRIDOR.
EXPECTING TWO MORE PERIODS OF SHOWERS AND STORMS FROM TONIGHT INTO
SATURDAY NIGHT. EACH ROUND WILL BE DRIVEN BY AN INCREASING NOCTURNAL
LOW LEVEL JET AND ASSOCIATED WAVES OF THETA-E ADVECTION ALONG WITH
SHORT WAVE FRAGMENTS. FOR TONIGHT, A 35 TO 40 KT LOW LEVEL JET WILL
DEVELOP AND SIMILAR TO LAST NIGHT, THE OVERALL INSTABILITY AND MID-
LEVEL LAPSE RATES (~5.5 C/KM) ARE WEAK, THEREFORE, ANY POTENTIAL FOR
LIGHTNING IS LOW, BUT NON-ZERO OVER WESTERN PARTS OF IOWA. PWATS
WILL BE HIGHER TONIGHT AND IN THE 1.50" TO 1.75" RANGE AND THE 850
MB DEW POINTS WILL BE NEAR 12C. WARM CLOUD DEPTHS WILL BE AROUND
12500 FT. THE COMBINATION OF ALL OF THE ABOVE WILL RESULT IN ANOTHER
ROUND OF EFFICIENT RAINFALL PROCESSES AND WITH MORE MOISTURE
AVAILABLE AND A STRONG LOW LEVEL JET, MAX RAINFALL AMOUNTS WILL
LIKELY EXCEED TODAY'S TOTALS WITH THE MOST LIKELY LOCATION BEING
OVER WEST CENTRAL IOWA AND JUST WEST OF AMES/DES MOINES METRO. OF
NOTE, A LARGE HIGH PRESSURE SYSTEM REMAINS OVER THE GREAT LAKES
REGION AND RIDGED SOUTH INTO ILLINOIS. A WAVE OF DRIER AIR WILL BE
MOVING WESTWARD TONIGHT INTO EARLY SATURDAY MORNING. AT THIS TIME,
THE COLLISION OF MOISTURE ADVECTION EAST/NORTHEAST AND THE DRY AIR
APPEARS TO OCCUR OVER FAR NORTHEAST/EAST CENTRAL IOWA AND THIS WILL
BE THE AREA WHERE PRECIPITATION WILL STRUGGLE TO ADVANCE FURTHER.
THIS ZONE IS ALSO EAST OF THE FORECAST AREA, SO THE CONFIDENCE IN
PRECIPITATION OVER MUCH OF THE FORECAST AREA IS HIGH AND
ADJUSTED THE POPS ACCORDINGLY.
THE NEXT ROUND OF PRECIPITATION WILL BEGIN LATE AFTERNOON TO EARLY
EVENING OVER WESTERN IOWA. CONVECTIVE INSTABILITY WILL BE GREATER
ALONG WITH INCREASING MID-LEVEL LAPSE RATES. CONFIDENCE IN
THUNDERSTORMS IS GREATER AS WELL OVER THE WESTERN HALF OF IOWA
BEFORE THE INSTABILITY WANES TO THE EAST. THE LOW LEVEL JET AND
SHORT WAVE ENERGY WILL FUEL PRECIPITATION THROUGH THE NIGHT. THE
DEEPER CONVECTION AND THE NEARLY STAGNANT TO WEAK CORFIDI VECTORS
AND SLOW STORM MOTIONS COULD PROMOTE HEAVY RAIN POTENTIAL,
ESPECIALLY IF TRAINING OF STORMS/PRECIPITATION DOES OCCUR. THIS MAY
BE AN ACCUMULATIVE EFFECT WITH TOTAL RAINFALL AMOUNTS SINCE EARLY
THIS MORNING TOP 4-5 INCHES IN SOME SPOTS OF WEST CENTRAL TO CENTRAL
IOWA. WHILE THIS MAY NOT RESULT IN FLASH FLOODING, SIGNIFICANT RISES
ON AREA STREAMS AND RIVERS ARE POSSIBLE INCLUDING ALONG THE RACCOON,
NORTH AND MIDDLE RIVERS IN ADDITION TO THE SMALLER URBAN RELATED
STREAMS. SIGNIFICANT PONDING IS ALSO LIKELY.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED AT 200 PM CDT FRI SEP 25 2026
PRECIPITATION CHANCES WILL DIMINISH DURING THE DAY SUNDAY FROM WEST
TO EAST. MONDAY IS EXPECTED TO BE MOSTLY DRY BUT THAT DRY WEATHER
WILL BE SHORT LIVED AS ANOTHER POTENT SYSTEM IMPACTS THE STATE. AN
UPPER LOW PRESSURE SYSTEM WILL DIG INTO SOUTHERN CALIFORNIA ON
MONDAY THEN WILL TRANSITION INTO ARIZONA AND NEW MEXICO MONDAY NIGHT
AND TUESDAY. THAT WILL CREATE AN AMPLIFIED SOUTHWEST FLOW OVER IOWA
AND CREATE A MONSOONAL FLOW MOISTURE CONNECTION. WHILE THIS IS
ONGOING, A GOOD CONNECTION TO GULF MOISTURE WILL ALSO BE ESTABLISHED
WITH THE TWO MOISTURE SOURCES OVERLAPPING ACROSS IOWA AND PUSH PWAT
VALUES BACK OVER 2", WHICH IS CLIMATOLOGICALLY SIGNIFICANT FOR LATE
SEPTEMBER. SHOWER AND STORM POTENTIAL WILL INCREASE MONDAY NIGHT AND
PERSIST INTO TUESDAY NIGHT. HEAVY RAINFALL IS POSSIBLE WHICH COULD
FURTHER EXACERBATE HYDROLOGY CONDITIONS. STILL MONITORING THE
WEDNESDAY AND THURSDAY TIMEFRAME AS THE UPPER LOW TRANSLATES INTO
THE KANSAS REGION. ALSO DURING THIS TIMEFRAME, MONITORING THE
POTENTIAL FOR HURRICANE POLO BEING INGESTED INTO THE SOUTHWEST FLOW
AHEAD OF THE UPPER LOW, WHICH IS LIKELY DEPENDENT ON IF THAT
TROPICAL SYSTEM CAN MAINTAIN A NORTHEAST PATH ACROSS THE BAJA
CALIFORNIA. SHOULD THIS OCCUR, IT COULD BE A SOURCE FOR MORE
HEAVY RAINFALL MID-WEEK.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1235 PM CDT FRI SEP 25 2026
SHOWERS WILL BE MOVING ACROSS THE KDMX/KOTM AREAS THROUGH MID
AFTERNOON AND WILL BE IN VICINITY OF KFOD. IFR OR LOWER
CIGS/VSBYS ARE POSSIBLE AT TIMES. VFR WITH A FEW PERIODS OF MVFR
CIGS ARE EXPECTED AT KMCW/KALO THIS AFTERNOON. ANOTHER ROUND OF
PRECIPITATION AND LOWERING CIGS ARRIVES TONIGHT AND WILL PERSIST
INTO SATURDAY MORNING. THIS ROUND OF PRECIPITATION IS EXPECTED
TO IMPACT ALL SITES. SOUTHEAST WIND IS EXPECTED THROUGH THE
PERIOD. A FEW GUSTS MAY OCCUR LATE SATURDAY MORNING.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...DONAVON
LONG TERM...DONAVON
AVIATION...DONAVON/FOWLE
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