368
FXUS63 KDMX 261755
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1255 PM CDT SAT SEP 26 2026
...UPDATED FOR THE 18Z AVIATION DISCUSSION...
KEY MESSAGES
- RAIN CHANCES LINGERING THROUGH THE DAY TODAY AND ANOTHER ROUND
OF HEAVIER RAIN TONIGHT. HIGHEST AMOUNTS IN CENTRAL AND
SOUTHERN IOWA.
- 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 SUNDAY/
ISSUED AT 258 AM CDT SAT SEP 26 2026
A CLOSED LOW WAS CIRCULATING OVER SOUTHERN CANADA OVERNIGHT AND
A NEGATIVELY-TILTED SEGMENT WAS ANALYZED OVER THE CENTRAL PLAINS.
THE PRIMARY INSTABILITY AXIS IS STATES AWAY AND ONLY A HANDFUL OF
LIGHTNING STRIKES CAN BE FOUND THIS FAR NORTH. WARMER MIDLEVEL
TEMPERATURES REMAIN LOCKED BEHIND THE LEADING SHORTWAVE SEGMENT,
RESIDING OVER THE ROCKIES, MEANING LAPSE RATES WILL LEAN MORE
TOWARDS THE MOIST ADIABAT IN THE MIDLEVELS AND CAPE VALUES WILL STAY
MAINLY UNDER 1000 J/KG. THE MIDLEVEL WIND FIELD ALSO REMAINS WEAK
WITH THE UPPER JET MORE COLLOCATED WITH THE MAIN TROUGH IN THE
INTERMOUNTAIN WEST. THESE TWO FACTORS MEAN THAT THE RISK FOR SEVERE
WEATHER IS LOW OVER THE WEEKEND. THAT SAID, CONCERNS FOR HEAVY
RAINFALL REMAIN. WHILE THE WEAK CONVECTIVE PROCESSES WILL HELP CURB
THE RAINFALL AMOUNTS, MOISTURE CONTENT, THE SYNOPTIC SETUP, AND WEAK
FLOW WILL KEEP EFFICIENCY HIGH.
00Z CAMS TRENDED MORE LOCALIZED RATHER THAN WIDESPREAD QPF SWATHS
AND THEIR SIMULATED LOCATION DIFFERED. THE CONCEPTUAL MODEL FAVORS
THE QPF MAX TO THE MAIN CONVERGENCE ALONG THE LOW-LEVEL JET. IN
FACT, WON'T LEAVE COMPLETELY DURING THE DAY TODAY. RAIN CHANCES WILL
PERSIST AND INCREASE AS THE LLJ MAX REESTABLISHES ITSELF AT SUNSET.
SLOW-MOVING STORMS WILL PRODUCE HEAVY RAIN OVERNIGHT AND MOSTLY
LIKELY BE FOUND SOMEWHERE ACROSS CENTRAL AND SOUTHERN IOWA; THIS IS
THE SAME PART OF THE STATE THAT HAS SEEN THE MOST RAINFALL ALREADY
THIS MONTH. PONDING IS LIKELY AND THE FLASH FLOOD POTENTIAL IS LOWER
DUE TO THE WEAKER CONVECTIVE PROCESSES LIMITING RAINFALL RATES.
CONCERNS ARE MORE IN RIVER FLOODING. BASINS MENTIONED IN THE
PREVIOUS DISCUSSION REMAIN THE MAIN CONCERN TONIGHT: THE RACCOON,
NORTH AND MIDDLE RIVERS. SOIL MOISTURE PERCENTILES IN THESE BASINS
ARE OVER 80%, MEANING THAT MUCH OF THE RAIN RECEIVED THIS WEEKEND
AND BEYOND WILL BECOME RUNOFF. THAT BEING SAID, GIVEN THE DOWNTREND
IN QPF THIS WEEKEND, IT MAY BE MORE OF A PRIMER FOR THE RAINFALL
DURING THE WORK WEEK.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
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 SUNDAY/
ISSUED AT 1254 PM CDT SAT SEP 26 2026
A PATCH OF MVFR TO IFR SHOWERS AND CIGS ARE MOVING EASTWARD ACROSS
THE STATE CURRENTLY STRETCHING FROM DSM TO MCW. THESE SHOWERS WILL
MOVE OUT OVER THE NEXT COUPLE OF HOURS BUT MVFR STRATUS ARE FILLING
IN BEHIND AND MAY IMPACT MOST OF THE TERMINALS THIS AFTERNOON. INTO
TONIGHT, MORE SHOWERS BUILD ACROSS THE STATE, WITH HIGHEST
CONFIDENCE AT DSM/OTM. SHOWERS WILL LIKELY IMPACT NORTHERN PARTS OF
THE STATE TOO, BUT CONFIDENCE ON TIMING AND COVERAGE IS LOW AT THIS
TIME AND TOTAL COVERAGE HAS TRENDED LESS SINCE THE PREVIOUS
ISSUANCE. ADDITIONALLY, THERE IS A CHANCE FOR AN ISOLATED
THUNDERSTORM, THOUGH PROBABILITIES APPEAR LESS THAN 30 PERCENT AT
THIS TIME.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...JIMENEZ
LONG TERM...DONAVON
AVIATION...DE BRUIN
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