232
FXUS63 KDMX 172009
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
309 PM CDT MON AUG 17 2026
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 TUESDAY NIGHT/
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, AND DEW POINTS LOWER THAN RECENT DAYS AND IN THE
UPPER 50S TO 60S LEADING TO MORE REASONABLE HUMIDITY LEVELS AS WELL.
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, THOUGH ANOTHER 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 DRY AIR. AS NOTED IN THE
PREVIOUS DISCUSSION, AN ISOLATED STRONG WIND GUST CAN'T COMPLETELY
BE RULED OUT BUT WITH THE LLJ POINTED TO THE SOUTH OF NORTHERN IOWA,
THE WEAKENING/DISSIPATING SHOWERS/STORMS LOOKS TO WIN OUT.
ANOTHER AREA OF STORMS TO WATCH THAT MAY BE OF GREATER IMPACT IS 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 AND LARGELY WEAKENS AS IT
TURNS INTO IOWA INTO THE MORNING HOURS. THE LATEST RUNS OF THE HRRR
MAY BE STARTING TO CAPTURE THIS WITH EARLIER RUNS BRINGING A WIND
THREAT INTO IOWA DURING THE LATER OVERNIGHT HOURS BUT THE 18Z, AS
ONE EXAMPLE, LARGELY DISSIPATES ALL ROUNDS PRIOR AND HAS THE MAIN
THREAT WINDOW ACROSS SOUTHWEST TO SOUTHERN IOWA AND IN THE 6-9A
TIMEFRAME. 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 ALL 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. IF WE DO GET SOME
CLEARING/RECOVERY, THERE MAY BE SOME FUNNEL CLOUD POTENTIAL, AS
NOTED IN THE PREVIOUS DISCUSSION, WITH STORM REDEVELOPMENT STARTING
TO LOOK FURTHER SOUTH INTO MORE OF MO/KS/NE, AS HAS BEEN REFLECTED
IN THE SHIFT OF THE DAY 2 SPC SLIGHT (LEVEL 2 OF 5) RISK TOWARDS
THAT AREA AND ONLY REMAINING IN OUR SOUTHWEST.
THE OTHER THING TO NOTE IS AS WE GET MORE MOISTURE INTO THE AREA,
PWATS START TO RETURN TO 1.5 TO EVEN 2" IN SOUTHWEST IOWA. THIS
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.
LONG TERM /WEDNESDAY THROUGH MONDAY/
ISSUED AT 308 PM CDT MON AUG 17 2026
ADDITIONAL PRECIPITATION CHANCES ARE IN THE FORECAST ON WEDNESDAY AS
SHORTWAVE ENERGY MOVES 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 SHORTWAVE 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 /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1246 PM CDT MON AUG 17 2026
VFR CONDITIONS ONGOING AND EXPECTED TO CONTINUE THROUGH THE
DAYTIME INTO THE EVENING TONIGHT. SOME SCATTERED CUMULUS HAS
BEGUN TO DEVELOP THIS AFTERNOON AS EVIDENCED ON SATELLITE. WINDS
OUT OF THE WEST TODAY BECOME OUT OF THE SOUTH TONIGHT BUT WILL
LARGELY STAY LIGHT, UNDER 10 KNOTS BEFORE SHIFTING BACK TO OUT
OF THE WEST DURING THE DAYTIME TOMORROW. MAIN AVIATION CHALLENGE
IS THE CHANCE FOR SHOWERS AND STORMS OVERNIGHT THROUGH MUCH OF
THE DAY TUESDAY. UNCERTAINTY IN STORM TIMING AND EVOLUTION
REMAINS ON THE HIGHER SIDE SO ONLY MINOR EDITS TO PREVIOUS PROB
30 GROUPS. THERE ARE AT LEAST SHOWER IF NOT THUNDERSTORM CHANCES
AT ALL SITES DURING THE LATER PORTION OF THE TAF PERIOD BUT
COVERAGE, INTENSITY, AND TIMING MAY ALL STILL CHANGE AND THE
COVERAGE/INTENSITY WILL AFFECT THE IMPACTS AT ANY ONE TAF SITE.
EXPECT UPDATES IN FUTURE ISSUANCES. STRONGER STORMS COULD HAVE
GUSTY WINDS AND LOCALLY HEAVY RAIN AT TIMES WHICH COULD LEAD TO
LOWER VISIBILITIES AND CEILINGS THAT MAY BECOME AT LEAST
SCATTERED MVFR.
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...05
HYDROLOGY...ZOGG
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