340
FXUS63 KDMX 012005
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
305 PM CDT TUE SEP 1 2026
KEY MESSAGES
- SLIGHT RISK (LEVEL 2 OF 5) INTRODUCED ACROSS NORTHERN IOWA
TUESDAY NIGHT INTO WEDNESDAY MORNING. DAMAGING WINDS UP TO 75
MPH THE PRIMARY HAZARD.
- HEAT ADVISORY EXTENDED THROUGH THURSDAY WITH HEAT INDICIES
PUSHING UPPER 90S TO TRIPLE DIGITS ACROSS CENTRAL AND SOUTHERN
IOWA.
- ADDITIONAL HEAT AND STORMS CONTINUE THROUGH THE END OF THE
WEEK INTO LABOR DAY WEEKEND.
SHORT TERM /THROUGH WEDNESDAY NIGHT/
ISSUED AT 300 PM CDT TUE SEP 1 2026
TUESDAY WILL FEATURE A MIX BAG OF HOT TEMPERATURES ACROSS SOUTHERN
IOWA AND POSSIBLE STORMS TONIGHT WHICH COULD BE STRONG TO SEVERE
ACROSS NORTHERN IOWA. WHAT A WAY TO KICK OFF METEOROLOGICAL FALL
ACROSS CENTRAL IOWA.
TODAY
CURRENT SURFACE ANALYSIS REVEALS A WEAK BOUNDARY LIFTING NORTH,
WHICH MAY TRIGGER A FEW SHOWERS AND STORMS AS IT PUSHES THROUGH.
OUTSIDE OF TONIGHTS SEVERE WEATHER RISK,THE PRIMARY STORY REMAINS
THE OPPRESSIVE HEAT ACROSS CENTRAL AND SOUTHERN IOWA. HIGHS WILL
CLIMB INTO THE LOWER TO MID 90S ALONG AND SOUTH OF I-80. HEAT
INDICES WILL AGAIN REACH THE MID TO UPPER 90S, WITH A FEW LOCATIONS
MAKING A RUN AT THE TRIPLE DIGITS. THE ONGOING HEAT ADVISORIES
ACROSS SOUTHERN IOWA REMAIN IN EFFECT THROUGH THURSDAY.
TUESDAY NIGHT
ATTENTION THEN TURNS TO THE SEVERE WEATHER THREAT ACROSS NORTHERN
PORTIONS OF THE CWA TONIGHT. LATE MORNING ANALYSIS SHOWS AN H5
SHORTWAVE POSITIONED OVER WYOMING, PROGGED TO TRACK INTO THE HIGH
PLAINS BY THIS AFTERNOON. CONVECTION IS EXPECTED TO INITIATE THIS
EVENING ACROSS SOUTHERN SD AND NORTHERN NE. AS THESE STORMS PROGRESS
EASTWARD, THEY WILL TAP INTO A FAVORABLE ENVIRONMENT FOR UPSCALE
GROWTH INTO A MCS, AIDED BY A STRENGTHENING NOCTURNAL LLJ. HIGH RES
GUIDANCE (HRRR, RRFS AND NAM) CONSISTENTLY POSITIONS THE NOSE OF
THE LLJ ACROSS SOUTHERN MN AND NORTHERN IA. THIS MOISTURE
CONVERGENCE ZONE WILL COINCIDE WITH THE HIGHEST INSTABILITY AND OUR
HIGHEST CONFIDENCE (40-60%) IN SEVERE WEATHER. FORECAST SOUNDINGS
DEPICT MUCAPE VALUES AROUND 3000 J/KG AND STRONG DEEP LAYER (0-6KM)
SHEAR OF 40-50 KTS, EASILY SUPPORTING ROBUST UPDRAFTS. AS THE MCS
MATURES AND CONSOLIDATES A COLD POOL, DRY ENTRAINMENT IN THE LOWER
LEVELS WILL ENHANCE DOWNDRAFT POTENTIAL, INTRODUCING A SIGNIFICANT
DAMAGING WIND THREAT WITH GUSTS UP TO 75 MPH. WHILE STRAIGHT-LINE
WINDS ARE THE PRIMARY HAZARD, A QLCS TORNADO OR TWO CANNOT BE RULED
OUT. ROBUST 0-3KM SHEAR (35-40KTS) COUPLED WITH 50-100 J/KG OF 0-3KM
CAPE WILL PROVIDE AMPLE LOW LEVEL STRETCHING POTENTIAL FOR ANY LINE-
EMBEDDED VORTICES. ONE LIMITING FACTOR THAT MAY TEMPER THE OVERALL
SEVERE CEILING IS RELATIVELY WEAK MID LEVEL LAPSE RATES, GENERALLY
HOVERING AROUND 6-6.5C/KM. AS STORMS MOVE ACROSS THE NORTHERN PARTS
OF IOWA, PWAT VALUES WILL BE AROUND 2" WHICH WILL SUPPORT DECENT
RAINFALL RATES. FLASH FLOODING COULD BE CONCERN LATE TONIGHT IN THE
HEAVIER THUNDERSTORMS PRIMARY IN THE URBAN AREAS.
WEDNESDAY
FOLLOWING THE DEPARTURE OF THE MORNING MCS AND ANY LINGERING
PRECIPITATION, DANGEROUS HEAT RETURNS. SIMILAR TO TODAY, UPPER
RIDGING WILL BUILD OVER THE PLAINS AND MIDWEST, BRINGING ANOTHER
ROUND OF HOT TEMPERATURES AND TROPICAL DEWPOINTS. THE NEXT WINDOW
FOR CONVECTION ARRIVES WEDNESDAY NIGHT INTO THURSDAY AS A WARM FRONT
LIFTS INTO NORTHERN IOWA. LOW-LEVEL MOISTURE POOLING AHEAD OF THE
BOUNDARY WILL PUSH DEW POINTS INTO THE LOWER 70S, YIELDING 2000-2500
J/KG OF MUCAPE. HOWEVER, THERE IS CONSIDERABLE UNCERTAINTY REGARDING
STORM CONVERGENCE ACROSS THE NORTH,. DEEP-LAYER SHEAR LOOKS WEAKER,
AND AN INTENSE CAPPING INVERSION CHARACTERIZED BY H8 TEMPERATURES OF
23-25C, COULD SUPPRESS STORM INITIATION.
LONG TERM /THURSDAY THROUGH TUESDAY/
ISSUED AT 300 PM CDT TUE SEP 1 2026
AS WE HEAD INTO THE END OF THE WORK WEEK AND LABOR DAY WEEKEND,
ADDITIONAL SHOWERS AND STORMS WILL BE POSSIBLE AGAIN THURSDAY NIGHT
INTO FRIDAY MORNING. HIGHS ON FRIDAY WILL ONCE AGAIN CLIMB INTO THE
LOWER 90S, COUPLED WITH OPPRESSIVE DEW POINTS IN THE 70S. THE
ONGOING HEAT ADVISORY MAY EVENTUALLY NEED TO BE EXTENDED THROUGH
FRIDAY. HOWEVER, WE OPTED TO HOLD OFF ON ANY EXTENSIONS WITH THIS
FORECAST PACKAGE DUE TO LINGERING UNCERTAINTY REGARDING THE
SOUTHWARD EXTENT OF FRIDAY MORNING CONVECTION. ADDITIONAL SHOWERS
AND THUNDERSTORMS CHANCES WILL REMAIN IN THE FORECAST THROUGH THE
WEEKEND, ALONGSIDE CONTINUED WARM HIGHS IN THE UPPER 80S AND LOWER
90S.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1230 PM CDT TUE SEP 1 2026
VFR CONDITIONS TO PREVAIL THE REST OF THE EVENING. A FEW SHOWERS
AND STORMS ARE PRESENT AT 1PM NEAR KMCW BUT SHOULD CLEAR OUT BY
19Z. AS WE HEAD INTO THE OVERNIGHT HOURS, A NOCTURNAL LLJ WILL
GET GOING ACROSS CENTRAL IOWA PROVIDING SOME LLWS AT ALL STIES
FROM 06Z UNTIL 11Z. STORMS WILL BE POSSIBLE OVERNIGHT ACROSS
NORTHERN IOWA, SO PROB30 GROUPS HAVE BEEN INTRODUCED AT KMCW
FROM 06Z TO 10Z.
DMX WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY FROM 1 PM WEDNESDAY TO 7 PM CDT THURSDAY FOR
IAZ057-058-070-071-081-092.
HEAT ADVISORY UNTIL 7 PM CDT THURSDAY FOR IAZ059>062-072>075-
082>086-093>097.
SHORT TERM...TDR
LONG TERM...TDR
AVIATION...TDR
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