378
FXUS63 KDMX 181135
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
635 AM CDT TUE AUG 18 2026
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- THUNDERSTORMS THIS MORNING WITH ISOLATED TO SCATTERED STORMS
THIS AFTERNOON. THE SEVERE WEATHER AND HEAVY RAINFALL THREAT
HAS DIMINISHED. A DAMAGING WIND GUST OR LOCALLY HEAVY RAIN
COULD STILL OCCUR.
- GUSTY WINDS POSSIBLE EARLY THIS MORNING ASSOCIATED WITH MESO-
HIGH/MESO-LOW OVER WEST CENTRAL IOWA. GUSTS OVER 40 MPH ARE
POSSIBLE.
- A FEW STORMS POSSIBLE AGAIN ON WEDNESDAY, MAINLY OVER WESTERN
IOWA. THE THREAT FOR SEVERE WEATHER IS LOW.
SHORT TERM /THROUGH WEDNESDAY/
ISSUED AT 249 AM CDT TUE AUG 18 2026
THUNDERSTORMS HAVE REMAINED TO THE NORTH AND TO THE WEST OF IOWA SO
FAR THIS MORNING. THE STRONGEST STORMS ARE NOW ENTERING SOUTHEAST
NEBRASKA. THESE STORMS HAVE MAINTAINED COLD POOL BALANCE AND THERE
IS EVEN AN EVIDENT MESO-HIGH PRESSURE ON THE LATEST SURFACE
ANALYSIS. THESE STORMS ARE TRACKING SOUTHEAST AND MAY STILL CLIP FAR
SOUTHWEST IOWA THOUGH THE CURRENT STABILITY FROM THE LINGERING
SURFACE HIGH WILL BE A CHALLENGE AND LIKELY RESULT IN A WEAKENING
ALONG ANY PART OF THE COMPLEX MOVING INTO IOWA. ADDITIONAL STORMS
ARE MOVING SOUTHEAST OUT OF SOUTH DAKOTA. WHILE THESE STORMS ARE NOT
CURRENTLY SEVERE, THESE MAY HAVE A BETTER POTENTIAL TO REMAIN INTACT
AS THEY ENTER IOWA WITH THE INSTABILITY AXIS LEANING INTO NORTHWEST
IOWA IN THE NEXT FEW HOURS. OVERALL THOUGH, THE THREAT FOR SEVERE
WEATHER AND HEAVY RAINFALL THROUGH TODAY IS ON THE WANE. THE
POTENTIAL REMAINS FOR A DAMAGING WIND GUST THIS MORNING ASSOCIATED
WITH STORMS. IN ADDITION, A MESO-LOW HAS DEVELOPED OVER NORTHWEST
IOWA, LIKELY IN RESPONSE TO THE MESO-HIGH. GUSTY WINDS ARE POSSIBLE
BETWEEN THESE TWO AND THERE IS A PRESSURE GRADIENT NEAR 40 UBARS/KM
THAT HAS DEVELOPED BETWEEN THE TWO. THIS MAY LEAD TO WIND GUSTS
GREATER THAN 40 MPH. THIS IS ALREADY SHOWING UP AROUND SIOUX CITY
WHERE PERSONAL WEATHER STATIONS ARE RECORDING GUSTS OF 30-40 MPH.
THE WIND DID TURN MORE SOUTHEAST WHEN THIS OCCURRED SO IT IS
POSSIBLE THIS COULD RESEMBLE MORE OF A WAKE LOW AS IT IS NEAR THE
BACK EDGE OF THE ERODING STRATIFORM PRECIPITATION.
THE SHOWERS AND THUNDERSTORMS THIS MORNING ARE LIKELY THE MAIN
PERIOD OF PRECIPITATION. SOME RECOVERY DOES OCCUR THIS AFTERNOON,
MAINLY ACROSS NORTHERN IOWA AND MAY RESULT IN ISOLATED TO SCATTERED
STORMS. THE RECOVERY INCLUDES SKINNY CAPES THROUGH THE
INSTABILITY LAYER SO NOT MUCH POTENTIAL FOR STRONG PARCEL
ACCELERATIONS. WITH THIS WEAKER CAPE, ANY STORM TOPS WILL LIKELY
BE STRONGLY SHEARED DUE TO QUICKLY INCREASING SPEED SHEAR
ALOFT. PERHAPS THAT CAN MAINTAIN UPDRAFT/DOWNDRAFT BALANCE. THE
HEAVY RAIN THREAT IS DECREASING AS WELL. MOISTURE RECOVERY HAS
NOT BEEN QUITE AS STRONG AS PREVIOUSLY ADVERTISED AND NOW MAX
PWAT VALUES ARE EXPECTED TO BE CLOSER TO 1.75 INCHES AND WITH
LACK OF TRAINING POTENTIAL OR VIGOROUS CONVECTION, WIDESPREAD
HEAVY RAIN ISN'T LIKELY. THE MAIN FOCUS FOR STORMS LATER TODAY
WILL BE ALONG THE RETREATING WARM FRONT ACROSS KANSAS WHERE THE
PRIMARY INSTABILITY AXIS WILL BE LOCATED. TRENDING DRIER TONIGHT
WHILE A FEW SHOWERS AND STORMS REMAIN POSSIBLE OVER WESTERN
IOWA ON WEDNESDAY.
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 /12Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 629 AM CDT TUE AUG 18 2026
SCATTERED THUNDERSTORMS ARE POSSIBLE TODAY WITH THE HIGHEST
CHANCES THIS MORNING. GUSTY WINDS AND MVFR CIGS ARE POSSIBLE
WITH ANY STORMS. MORE WIDESPREAD CIGS OF 3-4 KFT MAY DEVELOP
LATER TODAY BEFORE DIMINISHING THIS EVENING. A FEW AFTERNOON TO
EVENINGS STORMS ARE POSSIBLE BUT AREAL COVERAGE IS LIMITED. IF
CLEARING IS ABLE TO OCCUR OVERNIGHT, FOG IS POSSIBLE BUT AGAIN
CONFIDENCE IS LOW ENOUGH TO NOT INCLUDE WITH THIS FORECAST.
OUTSIDE OF THE GUSTY WINDS NEAR THUNDERSTORMS, THE WIND WILL BE
LIGHT.
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...DONAVON
LONG TERM...05
AVIATION...DONAVON
HYDROLOGY...ZOGG
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