459
FXUS63 KDMX 311943
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
243 PM CDT MON AUG 31 2026
KEY MESSAGES
- THE HOT AND HUMID CONDITIONS WILL CONTINUE THROUGHOUT THE
WEEK, ESPECIALLY OVER SOUTHERN IOWA THE NEXT FEW DAYS WHERE
HEAT INDEX VALUES WILL PEAK AROUND 100 DEGREES. A HEAT
ADVISORY REMAINS IN EFFECT FOR PORTIONS OF SOUTHERN IOWA THROUGH
WEDNESDAY AFTERNOON.
- THUNDERSTORMS WILL BE POSSIBLE AT TIMES FOR THE NEXT SEVERAL
DAYS, BUT GENERAL COVERAGE AND FREQUENCY WILL BE LOW. ONLY 20%
CHANCES ARE CARRIED AT TIMES THROUGH TUESDAY NORTH OF I-80.
THERE IS SOME POTENTIAL FOR ISOLATED SEVERE WEATHER TUESDAY
NIGHT/WEDNESDAY MORNING OVER NORTHERN IOWA.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 242 PM CDT MON AUG 31 2026
SURFACE CONDITIONS THIS AFTERNOON ARE QUITE WARM AND HUMID ACROSS
THE FORECAST AREA, DESPITE THE PUSH OF UPPER-LEVEL CLOUD COVER
TRACKING NORTHEAST ACROSS IOWA PER SATELLITE IMAGERY. TEMPERATURES
RANGE IN THE LOW TO MID 80S ACROSS THE NORTHWEST HALF OF THE STATE,
WITH WARMER VALUES SOUTH/EAST IN THE UPPER 80S TO LOW 90S, WHILE
DEWPOINTS SIT IN THE UPPER 60S TO 70S. THESE CONDITIONS ARE THANKS
TO THE PROMINENT SOUTHWESTERLY FLOW IN THE LOW LEVELS ALL THE WAY UP
TO 250MB, AS THE LARGE RIDGE AND ASSOCIATED HEAT DOME REMAINS PARKED
OVER THE SOUTHEAST CONUS. FURTHER WEST, A NEGATIVELY TILTED AND
RATHER STRONG SHORTWAVE TROUGH IS NOTED OVER SOUTHERN SASKATCHEWAN,
WHILE ANOTHER TROUGH, ALBEIT WEAKER IN COMPARISON, IS LOCATED OVER
CALIFORNIA/NEVADA. AT THE SURFACE, A SOUTHWEST TO NORTHEAST ORIENTED
BOUNDARY SITS OVER FAR EASTERN NEBRASKA THROUGH NORTHWEST IOWA AND
SOUTHERN MINNESOTA, TIED TO THE AFOREMENTIONED CANADIAN TROUGH.
AHEAD OF THIS BOUNDARY AND CLOSER TO THE WEAKENED LOW LEVEL JET,
SOME ISOLATED WEAK STORMS HAD OCCURRED AT TIMES THROUGH THE MORNING,
BUT WERE SHORT LIVED AS THEY LIFTED NORTHEAST ACROSS THE STATE, ONLY
PRODUCING OCCASIONAL LIGHTNING STRIKES AND SOME BRIEF RAINFALL.
THESE EARLIER STORMS STRUGGLED DUE TO THE NEAR SURFACE WARM LAYER
THAT IS WINNING OUT, PAIRED WITH DRIER AIR AND A LACK OF NOTABLE
FORCING TO KEEP STORM ACTIVITY GOING. THE REMAINDER OF THE AFTERNOON
IS EXPECTED TO REMAIN DRY, WITH A VERY LOW CHANCE FOR ADDITIONAL
STORMS TO DEVELOP GIVEN SIMILAR CONDITIONS WORKING AGAINST STORM
DEVELOPMENT BEING MORE PERSISTENT. CONTINUED WARMING WILL PUSH
TEMPERATURES A BIT HIGHER YET INTO THE LOW TO MID 90S, WARMEST
SOUTHEAST, WHERE HEAT INDICES ARE EXPECTED TO TOP OUT AROUND 100-105
DEGREES. THE HEAT ADVISORY IS IN EFFECT FOR THE REST OF TODAY AND
WILL REMAIN THROUGH WEDNESDAY, AS LITTLE CHANGE IN THE EXPECTED
LARGER SCALE PATTERN WILL RESULT IN OVERNIGHT LOWS IN THE 70S
OFFERING LITTLE RELIEF AND SIMILAR EXPECTED HIGH TEMPERATURES AND
HEAT INDICES TO TODAY'S VALUES. THOSE WHO PLAN TO SPEND TIME
OUTDOORS SHOULD STAY HYDRATED AND LIMIT TIME DIRECTLY IN THE SUN TO
AVOID HEAT ILLNESS.
INTO THE EVENING AND OVERNIGHT, THE AFOREMENTIONED BOUNDARY WILL
HAVE PUSHED FURTHER INTO IOWA, WHICH GUIDANCE POINTS ITS LOCATION
SOMEWHERE OVER CENTRAL TO NORTH CENTRAL IOWA IN MORE OF A WEST TO
EAST ORIENTATION, AS THE QUICKER EASTWARD MOVING UPPER LEVEL
CANADIAN TROUGH MENTIONED ABOVE TRACKS INTO ONTARIO. AT THE SAME
TIME, INCREASING FLOW IN RELATION TO THE LOW LEVEL JET MAXIMIZES
OVER KANSAS AROUND 30-35 KNOTS, AND LESS SO OVER IOWA AROUND 20-25
KNOTS. IN TERMS OF OVERALL ENVIRONMENT, SHEAR VALUES INCREASE AROUND
30-35 KNOTS, ALONG WITH MLCAPE VALUES AROUND 1000-2000 J/KG, WHILE
LAPSE RATES SIT AROUND 6.5-7 C/KM. THE ELEVATED WARM LAYER OVERHEAD
THOUGH, ALONG WITH RATHER WEAK FORCING FOR SURFACE CONVERGENCE AND
LIFT NEAR THE BOUNDARY WOULD SUGGEST RATHER LIMITED POTENTIAL FOR
STORMS THAT MAY DEVELOP DURING THIS TIMEFRAME, WHICH WOULD BE BRIEF
IN NATURE AND RELATIVELY WEAK. THEREFORE, HAVE KEPT POP COVERAGE LOW
INTO TUESDAY MORNING, WITH THIS LOW COVERAGE LIFTING NORTH ACROSS
THE STATE.
DESPITE THE LOW POTENTIAL FOR SHOWERS AND STORMS IN THE MORNING, THE
OVERALL TREND IS FOR DRY CONDITIONS TO KEEP HOLD FOR MUCH OF THE
FORECAST AREA THROUGH TUESDAY AFTERNOON/EARLY EVENING, WITH
CONTINUED HEAT AND HUMIDITY BEING THE PRIMARY CONCERN GIVEN HIGHER
CERTAINTY OF OCCURRENCE AND OVERALL IMPACTS. THE NEXT WINDOW OF
OPPORTUNITY FOR SHOWERS AND STORMS RETURN THROUGH THE EVENING INTO
WEDNESDAY MORNING, WITH A FOCUS IN DEVELOPMENT NEAR THE LINGERING
SURFACE BOUNDARY OVER IOWA. IN TERMS OF LOCATION OF THIS BOUNDARY,
MODEL GUIDANCE CONTINUES TO BE VARIED ON WHERE EXACTLY THIS FEATURE
WILL END UP, AS SOLUTIONS VARY FROM OVER NORTH-CENTRAL IOWA TO
SOUTHERN MINNESOTA. REGARDLESS OF LOCATION, DEVELOPMENT OF ELEVATED
SHOWERS AND STORMS IS SUGGESTED TO OCCUR LATE TUESDAY NIGHT TO
WEDNESDAY NEAR AND BEHIND THE BOUNDARY, WITH AN ENVIRONMENT MORE
FAVORABLE FOR AT LEAST STRONGER STORMS GIVEN MORE FAVORABLE FORCING
AS A STRONGER LLJ AROUND 30-40 KNOTS LOOKS TO DEVELOP, PAIRED WITH
INSTABILITY VALUES AROUND 1000-1500 J/KG AND MID-LEVEL LAPSE RATES
AROUND 7.5 C/KM. THERE IS A LOW POTENTIAL FOR ISOLATED STRONG STORMS
GIVEN THIS BETTER ENVIRONMENT FOR ORGANIZED STORMS, WITH DAMAGING
WINDS THE MAIN CONCERN GIVEN DCAPE VALUES AROUND 1000-1500 J/KG WITH
THE PRESENCE OF LOW-LEVEL DRY AIR PER SOUNDINGS, THOUGH HAIL IS ALSO
POSSIBLE IF ANY STONES CAN SURVIVE THE STEEP WARM LAYER BELOW. ANY
SHOWERS AND STORMS WOULD GRADUALLY TAPER OFF THROUGH MID-LATE
MORNING AS THE LOW-LEVEL JET FADES, WITH CAPPING OVERHEAD AND A LACK
OF FORCING LIKELY ALLOWING FOR DRY CONDITIONS THROUGH THE REST OF
THE DAY.
LONG TERM /THURSDAY THROUGH SUNDAY/
ISSUED AT 242 PM CDT MON AUG 31 2026
INTO THE END OF THE WORK WEEK, THE RIDGE OVER THE SOUTHEASTERN CONUS
FLATTENS OUT SOMEWHAT, BUT STILL GENERALLY KEEPS ITS INFLUENCE OVER
IOWA, WHICH WILL ALLOW FOR THE CONTINUATION OF RATHER UNCOMFORTABLE
CONDITIONS WITH THE HEAT AND HUMIDITY. FORECAST HIGHS IN MID 90S AND
HEAT INDICES AROUND 100-105 DEGREES OVER MUCH OF SOUTHERN IOWA ARE
EXPECTED, WHICH COULD LEAD TO AN EXTENSION IN CURRENT HEAT
HEADLINES INTO FRIDAY IF FORECAST TRENDS CONTINUE TO LEAN THAT
WAY, SO STAY TUNED FOR UPDATES. ADDITIONAL SHORTWAVES TRAVELING
THROUGH THE WESTERN PERIPHERY OF THIS RIDGE WILL CONTINUE TO
BRING CONTINUED PERIODS OF SHOWERS AND THUNDERSTORMS,
PARTICULARLY DURING THE OVERNIGHT AND MORNING THURSDAY AND
FRIDAY. LOCATION OF THE ASSOCIATED BOUNDARY(S) AND THE INFLUENCE
OF THE CAP OVERHEAD ARE STILL GENERALLY UNCERTAIN IN THIS
RANGE, AND EVEN MORE SO THROUGH THE WEEKEND CONSIDERING HOW
EARLIER ACTIVITY IN THE WEEK PLAYS OUT, SO WILL NEED TO MONITOR
TRENDS OVER THE COMING DAYS. FOR NOW, HAVE LEFT AT LEAST LOW POP
MENTIONS OVER PORTIONS OF THE FORECAST AREA THROUGH THE PERIOD
GIVEN THIS OVERALL POTENTIAL.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1242 PM CDT MON AUG 31 2026
VFR CONDITIONS ARE EXPECTED TO CONTINUE ACROSS ALL TERMINALS
THROUGH THE TAF PERIOD. UPPER-LEVEL CLOUDS WILL CONTINUE TO
PASS OVERHEAD INTO TUESDAY MORNING, WITH A REMAINING LOW
POTENTIAL (<20%) FOR SOME ISOLATED SHOWERS AND STORMS BETWEEN
06-12Z. GIVEN LOW CONFIDENCE IN OCCURRENCE THOUGH, AS WELL AS
EXACT LOCATION AND TIMING OF ANY STORM COVERAGE, HAVE LEFT OUT
AND WILL CONTINUE TO MONITOR. LLWS IS EXPECTED DURING THIS
GENERAL TIME PERIOD AT KDSM AND KOTM, BEFORE FADING FOLLOWING
SUNRISE. THERE IS A SLIGHT INCREASE IN FOG POTENTIAL BASED ON
LATEST GUIDANCE OVER KALO AND KMCW, SO HAVE CONTINUED WITH 6SM
BR MENTIONS AND MAY HAVE TO LOWER VSBYS FURTHER IF TRENDS
CONTINUE OR IF THE INCREASE THE OVERALL POTENTIAL OCCURS.
DMX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 7 PM CDT WEDNESDAY FOR IAZ059>062-072>075-
082>086-093>097.
SHORT TERM...BURY
LONG TERM...BURY
AVIATION...BURY
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