426
FXUS63 KDMX 311758
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1258 PM CDT FRI JUL 31 2026
...UPDATED FOR THE 18Z AVIATION DISCUSSION...
KEY MESSAGES
- STORMS DEVELOP OVER EASTERN HALF OF IOWA EARLY THIS AFTERNOON.
QUESTIONS REMAIN ON IF FAVORABLE CONDITIONS WILL OVERLAP FOR
ANY TORNADO POTENTIAL. OTHERWISE, ISOLATED STORM WIND GUSTS
AND LOCALLY HEAVY RAINFALL POSSIBLE. ANY FLASH FLOOD RISK WILL
BE FOCUSED ON AREAS THAT RECEIVED THE HIGHEST RAINFALL FROM
EARLIER TODAY AND URBAN AREAS.
- INCREASING WINDS WITH GUSTS IN EXCESS OF 35 TO 40 MPH
SPREADING FROM NORTHWEST IOWA LATE THIS MORNING TO EASTERN
IOWA BY SUNSET.
- RELATIVELY COOLER AND QUIET WEATHER IS THEN FORECAST SATURDAY
THROUGH AT LEAST MONDAY.
SHORT TERM /THROUGH SATURDAY/
ISSUED AT 220 AM CDT FRI JUL 31 2026
EARLY MORNING RADAR IMAGERY SHOWS SEVERAL AREAS OF SHOWERS AND
STORMS IN AND AROUND THE STATE. THE FIRST IS ASSOCIATED WITH THE
WARM AIR ADVECTION WING JUST EAST OF I-35 AT THIS EARLY HOUR AND
THESE SHOWERS WILL CONTINUE TO SLOWLY PUSH OFF TO THE EAST. AN AREA
OF STRONGER STORMS FUELED BY THE NOCTURNAL LOW LEVEL JET IS PUSHING
SOUTHEASTWARD THROUGH SOUTHWEST IOWA AND SOUTHEASTERN NEBRASKA
MOVING INTO MISSOURI AND KANSAS. FINALLY, A SHORTWAVE TROUGH IS
GRADUALLY DEEPENING WITH SURFACE CYCLOGENESIS OCCURRING OVER
SIOUXLAND AND CAUSING ADDITIONAL SHOWERS AND STORMS IN SOUTH DAKOTA,
WHICH MAY RESULT IN NEW STORM DEVELOPMENT BETWEEN IT AND THE
SOUTHEASTWARD DIVING STORMS OVER THE NEXT SEVERAL HOURS. THE
DAMAGING WIND THREAT LOOKS VERY LOW AND WOULD BE MAINLY CONCERNED
WITH THE STORMS SCRAPING OUR SOUTHWESTERN FORECAST AREA. HEAVY
RAINFALL POTENTIAL STILL REMAINS FAVORABLE GIVEN THE PARAMETER SPACE
WITH DEEP WARM CLOUD DEPTHS AND PRECIPITABLE WATER (PWAT) VALUES
WELL OVER 2 INCHES. IN FACT, THE 0Z KOAX ROAB HAD A 2.4 INCH PWAT
VALUE, WHICH IS NOT ONLY A DAILY RECORD, BUT LOOKS TO BE THEIR ALL-
TIME HIGHEST ON RECORD! LOOKING AT DETERMINISTIC AND ENSEMBLE DATA,
THERE IS NO READILY IDENTIFIABLE CORRIDOR FOR THE HEAVIEST RAINFALL
IN IOWA. THE MOST FAVORABLE AREA WHEN LOOKING AT THE ENVIRONMENTAL
DATA WOULD BE NORTHERN IOWA WHERE THE 850-300MB FLOW IS RELATIVELY
LIGHTER AT GENERALLY 15 TO 20 KNOTS COMPARED TO 20 TO 30 KNOTS OVER
SOUTHERN IOWA. THUS, STORMS IN NORTHERN IOWA WILL BE SLOWER MOVING
THAN THOSE IN SOUTHERN IOWA. RAINFALL AMOUNTS THROUGH MIDDAY TODAY
RANGE BETWEEN 1 AND 3 INCHES WITH A FEW OF THE CONVECTIVE ALLOWING
MODELS SHOOTING BETWEEN 3 AND 4 INCHES. LOOKING AT ANTECEDENT
CONDITIONS, THE SOILS ARE DRY WITH THE PRE-RAINFALL SOIL MOISTURE
FROM NASA SPORT SHOWING 0-10CM AND 0-40CM GENERALLY AT OR BELOW THE
30TH PERCENTILE WITH PARTS OF WESTERN IOWA AT THE SECOND PERCENTILE.
WITH 3 HOUR FLASH FLOOD GUIDANCE (FFG) BETWEEN 2.5 AND 3.5 INCHES
AND 6 HOUR FFG BETWEEN 3.5 AND 4.5 INCHES AND MATURE CROPS, FLASH
FLOODING CONCERNS WILL BE ISOLATED MAINLY TO URBAN AREAS WHERE THERE
WILL BE LESS INFILTRATION COMPARED TO RURAL AREAS. ADDITIONAL
DETAILS ARE OUTLINED IN THE HYDROLOGY SECTION BELOW.
BY DAYBREAK FRIDAY, SHOWERS AND STORMS WILL BE MAINLY EAST OF I-35
AND PUSHING EASTWARD AS SURFACE LOW PRESSURE MOVES AND SLOWLY
DEEPENS AS IT ENTERS THE CENTRAL PART OF THE STATE. THIS SHOULD
OFFER A BREAK IN THE RAIN, THOUGH SHOWERS MAY LINGER OR MOVE BACK IN
OVER FAR NORTHERN IOWA LATE IN THE MORNING OR AFTERNOON. ATTENTION
BY MIDDAY OR EARLY AFTERNOON WILL BE MONITORING FOR POSSIBLE
STRONGER STORM DEVELOPMENT TO THE EAST OF THE LOW PRIMARILY EAST OF
I-35 AND PROBABLY SOUTH OF I-80. THERE ARE MANY QUESTIONS ON WHAT
HAZARDS MAY EVOLVE WITH THE FIRST BEING TORNADO POTENTIAL. SOUNDINGS
AT ALO AND OTM POINT TO VARIOUS CHALLENGES TO BE ABLE TO CALL IT A
FAVORABLE TORNADO ENVIRONMENT. AT ALO, HODOGRAPHS ARE CURVED AND
ELONGATED WITH 0-1KM STORM RELATIVE HELICITY (SRH) OVER 200 M2/S2
FROM THE RAP. HOWEVER, THERE IS NO SURFACE BASED INSTABILITY/CAPE OR
0-3KM CAPE FOR TORNADOES OR FUNNELS TO BE OF MUCH CONCERN. MOVING TO
OTM, 0-3KM CAPE IS GENERALLY ABOVE 75 J/KG WITH SURFACE INSTABILITY
OVER 1000 J/KG. HOWEVER, DUE TO BEING FARTHER FROM THE SURFACE LOW,
LOW LEVEL WINDS ARE AT BEST SOUTH-SOUTHWEST BEFORE VEERING MORE TO
THE SOUTHWEST AND WEST. THUS, THE HODOGRAPH AND SRH ARE NOT HIGHLY
SUPPORTIVE OF ROTATING STORMS, THOUGH FUNNEL CLOUDS MAY BE POSSIBLE
GIVEN THE 0-3KM CAPE. REGARDLESS OF LOCATION, THE ONE THING THAT IS
FAVORABLE EVERYWHERE WILL BE THE LOW LIFTING CONDENSATION LEVEL
(LCL)/CEILINGS. OF COURSE, THESE ARE FORECAST PARAMETERS SO IF MORE
CLEARING CAN OCCUR OR THE POSITION OF THE LOW DRIFTS MORE SOUTHWARD,
THIS MAY CHANGE THE RISK. THUS, THERE MAY BE A NARROW SPATIAL WINDOW
WHERE THERE IS FAVORABLE CAPE AND SRH FOR A TORNADO SO MESOANALYSIS
WILL BE KEY TO HONE IN ON ANY AREA THAT MAY EVOLVE. OTHERWISE,
ISOLATED DAMAGING WIND GUSTS MAY BE POSSIBLE AS THERE IS PLENTY OF
DRY AIR WORKING INTO THE BACKSIDE OF THESE DEPARTING STORMS IN THE
MID-LEVELS. FINALLY, THESE STORMS WILL STILL BE IN THE FAVORABLE
HEAVY RAINFALL PARAMETER SPACE THAT AN ADDITIONAL 1 TO 2 INCHES IS
POSSIBLE IN NARROW SWATHS. ANY FLASH FLOOD RISK WOULD SEEM TO BE
RELEGATED TO AREAS THAT RECEIVE HEAVY RAINFALL EARLIER TODAY OR AN
URBAN AREA. THE SEVERE RISK SHOULD END BY EARLY EVENING AS THE LOW
PRESSURE IS EAST OF THE AREA. HOWEVER, SHOWERS AND ISOLATED STORMS
WILL LINGER OVER EASTERN IOWA AS MOISTURE IS WRAPPED BEHIND THE LOW
THROUGH MUCH OF FRIDAY NIGHT.
AS THE SURFACE LOW MEANDERS EAST-SOUTHEASTWARD ACROSS IOWA ON
FRIDAY, SURFACE WINDS WILL BE INCREASING WITH A TIGHT PRESSURE
GRADIENT COUPLED WITH MODEST PRESSURE HEIGHT RISES ON THE BACKSIDE
OF THE LOW. FORECAST SOUNDINGS SHOW LOW LEVEL WINDS OF 35 TO 45
KNOTS THAT WILL BE IN THE SHALLOW MIXING LAYER. THUS, FORECAST
SUSTAINED WINDS FROM THE NORTH WILL BE AT 20 TO 30 MPH WITH GUSTS IN
EXCESS OF 35 TO 40 MPH. A SITE OR TWO MAY EVEN REACH WIND
ADVISORY CRITERIA GUSTS OF 45 MPH PER FORECAST SOUNDINGS, BUT
GIVEN LACK OF CONSISTENT SIGNAL AND LOCATION HAVE HELD OFF ON AN
ADVISORY AND WILL MONITOR TRENDS AND UPSTREAM OBSERVATIONS. THE
TIMING OF THE INCREASE IN WINDS WILL BE AROUND MIDDAY FROM
EMMET TO CRAWFORD COUNTIES, THE I-35 COUNTIES AROUND MID-
AFTERNOON, AND THE HIGHWAY 63 CORRIDOR TOWARD SUNSET. WINDS WILL
STAY BREEZY OVERNIGHT TONIGHT INTO MUCH OF SATURDAY, THOUGH
WILL NOT BE AS STRONG AS THEY WILL BE IN THE AFOREMENTIONED
TIMES. THESE WINDS ALONG WITH A GOOD AMOUNT OF LINGERING CLOUD
COVER SHOULD HELP STAVE OFF FOG DEVELOPMENT EARLY SATURDAY. ANY
LINGERING SHOWERS WILL END BY MIDDAY SATURDAY IN OUR
SOUTHEASTERN FORECAST AREA WITH THE CLOUDS ALSO GRADUALLY
DECREASING AS WELL. WITH THE NORTHERLY FLOW, WILL SEE A RETURN
OF HIGH LEVEL WILDFIRE SMOKE OVER THE AREA WITH THE CLOUDS
CLEARING OUT.
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
ISSUED AT 252 PM CDT THU JUL 30 2026
DRIER CONDITIONS RETURN ON SATURDAY AS AN UPPER RIDGE STARTS TO
BUILD BACK INTO THE AREA. TEMPERATURES REMAIN COOLER FOR THE SEASON
AND IN THE 70S SATURDAY TO 80S INTO EARLY NEXT WEEK MAKING FOR
ANOTHER PLEASANT STRETCH. THE NEXT CHANCES FOR PRECIPITATION START
TO MOVE IN MIDWEEK AS UPPER TROUGHING RETURNS WITH SEVERAL ROUNDS
POSSIBLE AS WAVES MOVE THROUGH THE OVERARCHING UPPER LEVEL PATTERN.
DETAILS WILL CONTINUE TO BE FINE-TUNED AS WE GET CLOSER.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1248 PM CDT FRI JUL 31 2026
VFR TO LIFR CONDITIONS ONGOING ACROSS THE STATE EARLY THIS
AFTERNOON. ALTHOUGH SOME IMPROVEMENT TOWARDS LOW VFR MAY OCCUR
AT TIMES, PREVAILING MVFR TO IFR WILL BE MORE COMMON WITH CLOUDS
AND ADDITIONAL DEVELOPING SHOWERS, FEW STORMS THIS AFTERNOON
THROUGH EVENING. THE STORM POTENTIAL REMAINS HIGHEST EAST OF
I-35 BUT CONFIDENCE IN TSRA ACTUALLY IMPACTING KALO OR KOTM WAS
NOT HIGH ENOUGH TO MOVE OUT OF PROB30 GROUP. HAVE OTHERWISE
TRIED TO UPDATE TIMING AND USED TEMPO/PROB 30S FOR VISIBILITY
REDUCTIONS WITH SHOWERS THOUGH SOME ADDITIONAL REFINEMENT TO
IMPACTS OR TIMING IS LIKELY WITH SCATTERED NATURE OF ACTIVITY
OUTSIDE OF KMCW WHICH MAY SEE MORE STEADY RAIN FOR A TIME.
ALTHOUGH SOME SITES ARE REPORTING FOG, AS WINDS INCREASE FOG
SHOULD CONTINUE TO BE LESS OF A CONCERN. NORTH WINDS CONTINUE
TO INCREASE NORTHWEST TO SOUTHEAST THIS AFTERNOON INTO EVENING AND
STAY BREEZY INTO SATURDAY. PEAK GUSTS MAY NEAR 30-40 KNOTS.
CEILINGS BEGIN TO IMPROVE SATURDAY MORNING INTO MIDDAY NORTHWEST
TO SOUTHEAST.
HYDROLOGY
ISSUED AT 1144 AM CDT FRI JUL 31 2026
RAINFALL FOR THIS EVENT HAS GENERALLY UNDERACHIEVED VS. EARLIER
FORECASTS THUS FAR, THUS HYDROLOGIC RESPONSES ON AREA RIVERS AND
STREAMS HAS BEEN LESS THAN ANTICIPATED. THE CEDAR BASIN FROM
SOUTHEAST MN INTO NORTHEAST IA RECEIVED THE HEAVIEST RAINFALL, AND
THE CEDAR RIVER ITSELF IS EXPECTED TO CREST AROUND ACTION STAGE
EARLY NEXT WEEK IN THE WATERLOO-CEDAR FALLS AREA. THE UPPER-MOST
PORTIONS OF THE DES MOINES BASIN IN SOUTHWEST MN RECEIVED SOME
LOCALLY HEAVY RAINFALL WHICH MAY LEAD TO MINOR RISES DOWNSTREAM INTO
NORTHWEST IA NEXT WEEK, BUT IS EXPECTED TO REMAIN BELOW ACTION STAGE.
ADDITIONAL MODERATE TO LOCALLY HEAVY RAIN IS EXPECTED THIS AFTERNOON
AND EVENING, MAINLY ACROSS THE EASTERN THIRD OF IA. GREATEST FLOOD
RISK IS PONDING OR POSSIBLE LOW-END FLASH FLOODING MAINLY IN TOWNS
AND CITIES, MAINLY EAST OF US 63, WHICH WOULD BE PRIMARILY WITHIN
THE CEDAR-IOWA BASIN. GOING CEDAR RIVER FORECASTS FOR THE WATERLOO-
CEDAR FALLS AREA INCORPORATE THE MOST LIKELY QPF SCENARIO THROUGH
12Z SATURDAY.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...ANSORGE
LONG TERM...05
AVIATION...05
HYDROLOGY...ZOGG
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