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FXUS63 KDMX 180408
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1108 PM CDT MON AUG 17 2026
...UPDATED FOR THE 06Z AVIATION DISCUSSION...
KEY MESSAGES
- DRY AND PLEASANT DURING THE DAYTIME TODAY!
- THUNDERSTORMS RETURN OVERNIGHT INTO TUESDAY. A FEW STRONG TO
SEVERE STORMS ARE POSSIBLE ALONG WITH LOCALLY HEAVY RAINFALL.
SHORT TERM /THROUGH WEDNESDAY/
ISSUED AT 308 PM CDT MON AUG 17 2026
HIGH PRESSURE CONTINUES TO MOVE ACROSS THE AREA TODAY KEEPING
CONDITIONS PLEASANT AND DRY WITH TEMPERATURES IN THE UPPER 70S TO
LOW 80S AS OF 2 PM. DEW POINTS HAVE ALSO BEEN LOWER THAN RECENT
DAYS, MAINLY IN THE UPPER 50S TO 60S AND LEADING TO MORE
REASONABLE HUMIDITY LEVELS.
DIURNAL CUMULUS WHICH HAS DEVELOPED THIS AFTERNOON WILL DISSIPATE
AFTER SUNSET BUT CLOUD COVER WILL GRADUALLY BUILD IN TO FOLLOW AS
SEVERAL ROUNDS OF SHORTWAVE ENERGY SWING THROUGH AT LEAST PORTIONS
OF THE AREA OVERNIGHT INTO TUESDAY, THE STRONGEST OF WHICH APPEARS
TO BE EARLY TUESDAY MORNING. ANOTHER WAVE THEN LOOKS TO MOVE
ACROSS LATER TUESDAY AFTERNOON-EVENING.
THETA-E ADVECTION REALLY RAMPS UP AGAIN TONIGHT WITH MOISTURE
GRADUALLY RETURNING INTO TUESDAY MORNING BEHIND THE DEPARTING HIGH
PRESSURE. THUNDERSTORMS ARE EXPECTED TO DEVELOP UPSTREAM IN SD/MN
ALONG A COLD FRONT THAT WILL MOVE SOUTHEAST WITH TIME INTO TUESDAY
MORNING, BUT DOESN'T REALLY REACH NORTHERN IOWA UNTIL CLOSER TO
MIDDAY TUESDAY. ALTHOUGH SOME CAMS BEG TO DIFFER, THESE STORMS ARE
LARGELY EXPECTED TO DISSIPATE OR AT LEAST WEAKEN AS THEY NEAR
NORTHERN IOWA AND WILL ALSO ENCOUNTER DRIER AIR. AS NOTED IN
THE PREVIOUS DISCUSSION, AN ISOLATED STRONG WIND GUST CAN'T
COMPLETELY BE RULED OUT BUT WITH THE LLJ POINTING TO THE SOUTH
OF NORTHERN IOWA, THE WEAKENING AND DISSIPATING TREND FOR SHOWERS/STORMS
LOOKS TO WIN OUT.
ANOTHER AREA OF STORMS TO WATCH THAT MAY BE OF GREATER IMPACT
ARE THE STORMS THAT DEVELOP NEAR THE PRE-FONTAL TROUGH IN
NEBRASKA. CAMS SUGGEST SEVERAL ROUNDS OF STORM CLUSTERS COULD BE
POSSIBLE BUT WHAT REMAINS UNCERTAIN IS THE LONGEVITY OF STORMS
AS THEY ENTER WESTERN IOWA. ALTHOUGH FORCING OVERALL MOVES EAST
WITH TIME, MOISTURE RETURN IS BETTER INTO NEBRASKA THAN INTO
IOWA BY AROUND 09Z AND DOESN'T REALLY BECOME MORE FAVORABLE
UNTIL CLOSER TO 12Z. THE LLJ STRENGTH IS ALSO IN QUESTION, NOT
NEARLY AS STRONG AS IN SOME CASES LAST WEEK AND ALSO LARGELY
POINTED INTO NEBRASKA THEN WEAKENING AS IT TURNS INTO IOWA
THROUGH THE MORNING HOURS. THE LATEST RUNS OF THE HRRR MAY BE
STARTING TO CAPTURE THIS WEAKENING TREND. THIS MORNING'S
SOLUTIONS OF THE HRRR BROUGHT A WIND THREAT INTO IOWA DURING THE
OVERNIGHT HOURS, BUT THE 18Z LARGELY DISSIPATES ALL ROUNDS
OVERNIGHT AND HAS THE MAIN THUNDERSTORM WINDOW ACROSS SOUTHWEST
TO SOUTHERN IOWA IN THE 6-9A TIMEFRAME TUESDAY MORNING. THE
OTHER LINGERING QUESTION IS THE LARGELY SCATTERED NATURE OF THE
STORMS WHICH COULD ULTIMATELY MAKE UPSCALE GROWTH AND THUS
SUSTENANCE DIFFICULT, AS WELL AS QUESTIONS OF HOW THE WARM MID-
LEVEL TEMPERATURES OVER NEBRASKA MAY FACTOR INTO STORM
STRENGTH/INTENSITY PRIOR TO REACHING THE IA/NE BORDER.
WHAT HAPPENS OVERNIGHT INTO TUESDAY MORNING WILL LARGELY DICTATE
WHAT IS ABLE TO DEVELOP TUESDAY AFTERNOON AND EVENING. THE WARM
FRONT LOOKS TO REMAIN SOUTH OF IOWA SO IT WOULD DEPEND ON ANY
LINGERING OUTFLOW BOUNDARIES FROM EARLY DAY CONVECTION AND WHAT KIND
OF ATMOSPHERE RECOVERY WE ARE ABLE TO SEE. AS NOTED IN THE
PREVIOUS DISCUSSION, IF WE DO GET SOME CLEARING/RECOVERY THERE
MAY BE SOME FUNNEL CLOUD POTENTIAL THIS AFTERNOON, AS WELL AS
THE POTENTIAL FOR A FEW STRONGER STORMS. HOWEVER, THIS
REDEVELOPMENT AND ASSOCIATED RISKS ARE STARTING TO LOOK FARTHER
SOUTH INTO MORE OF MO/KS/NE, AS HAS BEEN REFLECTED BY THE
SOUTHWARD SHIFT OF THE DAY 2 SPC SLIGHT RISK (LEVEL 2 OF 5) NOW
ONLY IMPACTING THE SOUTHWEST PORTIONS OF OUR FORECAST AREA.
THE OTHER THING TO NOTE WILL BE IN THE INCREASING MOISTURE INTO
THE AREA. PRECIPITABLE WATER (PWAT) VALUES START TO RETURN TO
1.5 TO EVEN 2" IN SOUTHWEST IOWA, WHICH COULD LEAD TO SOME
HEAVY RAINFALL POTENTIAL, AND RAIN RATES OF UP TO 1-2" PER HOUR.
THE QPF SIGNAL IN IOWA IS HIGHEST IN SOUTHWEST IOWA, LARGELY
OUT OF OUR AREA WITH MOST SEEING LESS THAN 1" AND HIGHLY
ISOLATED LOCATIONS SEEING 1-2", LOCALIZED HIGHER AMOUNTS. REFER
TO THE HYDROLOGY DISCUSSION BELOW FOR MORE INFORMATION ON FLOOD
POTENTIAL.
LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/
ISSUED AT 308 PM CDT MON AUG 17 2026
ADDITIONAL PRECIPITATION CHANCES ARE IN THE FORECAST ON WEDNESDAY AS
SHORTWAVE ENERGY CONTINUES TO MOVE THROUGH THE OTHERWISE
NORTHWESTERLY UPPER FLOW. DRIER CONDITIONS ARE THEN FORECAST ON
THURSDAY AS ANOTHER HIGH PRESSURE MOVES ACROSS BEFORE RETURNING
AGAIN THURSDAY NIGHT INTO FRIDAY WITH ANOTHER PUSH OF ENERGY.
THIS SEEMS TO BE A COMMON PATTERN INTO THE WEEKEND WITH ABOUT
EVERY OTHER DAY DRY- PRECIPITATION CHANCES BUT WITH OVERALL
LOWER CONFIDENCE IN THE PLACEMENT AND TIMING AT THIS RANGE.
TEMPERATURES REMAIN PLEASANT THIS WEEK IN THE THE 70S TO 80S.
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 1054 PM CDT MON AUG 17 2026
VFR CONDITIONS CONTINUE LATE TONIGHT/EARLY THIS MORNING.
THUNDERSTORM ACTIVITY IS STILL EXPECTED TO MOVE INTO IOWA EARLY
TUESDAY MORNING, ALBEIT DIMINISHING AS IT ARRIVES. CONFIDENCE
IS DECREASING IN THUNDER CHANCES AT MORE EASTERN SITES (KMCW,
KALO, KOTM) BUT STILL POSSIBLE AT MORE WESTERN SITES (KDSM AND
KFOD). SCATTERED SHOWER AND STORM CHANCES LINGER AT TIMES
THROUGH THE DAY TUESDAY, BUT LOW CONFIDENCE IN PERSISTENT
IMPACTS AT ANY GIVEN SITE SO HAVE KEPT AS PROB30S FOR THE TIME
BEING.
HYDROLOGY
ISSUED AT 308 PM CDT MON AUG 17 2026
ADDITIONAL FLOODING CONCERNS EXIST REGARDING THE POTENTIALLY HEAVY
RAIN TONIGHT INTO TUESDAY. AT THIS TIME, CONCERNS INVOLVE FLASH
FLOODING MORE THAN RIVER FLOODING.
ANOMALOUSLY HIGH RAINFALL OVER THE PAST WEEK ACROSS MUCH OF THE CWA
LED TO INCREASED SOIL MOISTURE IN MANY AREAS, WITH SIGNIFICANT
INCREASES IN SOME LOCATIONS. THAT SAID, THE PAST 1-2 DAYS OF DRY OR
RELATIVELY LOW RAIN AMOUNTS ACROSS MUCH OF THE CWA ALLOWED SOIL
INFILTRATION CAPACITY TO RECOVER MODESTLY. HIGHEST 0-10 CM (4 IN)
SOIL SATURATION VALUES MAINLY EXTEND FROM ALONG THE I-80 CORRIDOR
SOUTH TO US HWY 34, WITH A SECONDARY MAXIMUM EXTENDING FROM THE DES
MOINES TO FORT DODGE AREAS. ALL OTHER THINGS BEING EQUAL, THESE TWO
REGIONS WOULD BE MOST SUSCEPTIBLE TO FLASH FLOOD IMPACTS FROM THE
INCOMING RAIN. BASED ON CURRENT QPF AMOUNTS AND PLACEMENT, THE MOST
LIKELY SCENARIO IS PONDING OF WATER ESPECIALLY IN URBAN AREAS, WITH
SOME LOWER END FLASH FLOODING POSSIBLE ESPECIALLY IN THE
AFOREMENTIONED AREAS WITH ELEVATED SOIL SATURATION.
BASED ON CURRENT QPF AMOUNTS AND PLACEMENT, THE RIVER FLOOD RISK IS
MINIMAL. ISOLATED TO SCATTERED MODERATE TO SIGNIFICANT WITHIN-BANK
RISES ARE THE MOST LIKELY SCENARIO. OUR QPF ENSEMBLE HYDROGRAPHS AND
HEFS SUGGEST HIGHER-END RAIN AMOUNTS MAY RESULT IN SOME LOCATIONS
RISING TO BETWEEN ACTION STAGE AND FLOOD STAGE, ESPECIALLY BETWEEN I-
80 AND US HWY 34.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...05
LONG TERM...05
AVIATION...DODSON
HYDROLOGY...ZOGG
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