228
FXUS63 KDMX 142335
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
635 PM CDT SUN SEP 14 2025
...UPDATED FOR THE 00Z AVIATION DISCUSSION...
KEY MESSAGES
- MARGINAL RISK UP INTO CRAWFORD COUNTY. DAMAGING WINDS WILL BE
THE PRIMARY THREAT, BUT THE THREAT WILL DIMINISH AFTER SUNSET.
- THUNDERSTORMS WITH GUSTY WINDS POSSIBLE TONIGHT (<30%) AND
AGAIN TOMORROW NIGHT (<20%) MAINLY CENTRAL AND EAST.
- RAIN BECOMES MORE LIKELY (>50% CHANCE) BY WEDNESDAY.
DISCUSSION
ISSUED AT 252 PM CDT SUN SEP 14 2025
OUT OF THE SEQUENCE OF TROUGHS SEEN OVER THE WESTERN CONUS AND
PACIFIC TODAY, THE FIRST FEATURE CONTINUES ITS NEGATIVE TILT INTO
THE UPPER MIDWEST TODAY. MODERATE HEIGHT FALLS ON THE ORDER OF -5 TO
-6 DAM WILL STAY JUST TO THE WEST OF THE STATE LATER TODAY. AN UPPER
JET WILL ROUND THE BASE OF THE FEATURE THROUGH TODAY, BOOSTING DEEP-
LAYER SHEAR VALUES OVER 40KTS IN WESTERN IOWA. CONVECTIVE TRENDS
HAVE SLOWED WITH TIME, MEANING THAT LESS STORMS WILL INCH INTO
WESTERN IOWA TONIGHT AND, WHEN THEY DO, LESS OF THE SHEAR WILL BE
UTILIZED THANKS TO THE NOCTURNAL INVERSION. WITH THE SYNOPIC-DRIVEN
CONVECTION GETTING HELD TO THE WEST, THERE'S ANOTHER REGION OF LIFT
TO WATCH TONIGHT: THE AIRMASS BOUNDARY OVER EAST-CENTRAL IOWA.
CONVERGENCE IS DRIVEN BY THE CLASHING OF THE EASTERLIES FROM THE
ONTARIO HIGH AND THE WARM CONVEYOR BELT OF THE AFOREMENTIONED LOW TO
THE WEST. THIS BOUNDARY CAN BE SEEN THIS AFTERNOON IN THE SOUTHWEST
TO EASTERLY SURFACE WINDS CREATING A CUMULUS FIELD.
WHILE SHEAR THIS FAR EAST WILL BE LOW, MUCAPE VALUES OVER 1000 J/KG
RESIDE OVER EASTERN IOWA. OVERNIGHT CAM RUNS, MAINLY THE HRRR,
PRODUCED 40KT WINDS. THIS OCCURS IN THE POCKET OF THE HIGHEST DCAPE
VALUES (AROUND 400 J/KG, BUT DECREASING THROUGH THE NIGHT). CLOUD
LAYER SHEAR IS VALUED AT LESS THAN 20KTS, SO STORMS THAT DO BECOME
STRONG WILL BE SHORT-LIVED. THIS GRADIENT HANGS AROUND MONDAY AND
MONDAY NIGHT AND MAY ONCE AGAIN PROVIDE ENOUGH SUPPORT FOR SHOWERS
AND STORMS, ALTHOUGH THIS TIME WITH LESS MOISTURE AT PLAY. MOST ALL
HREF MEMBERS HAVE CONVECTION ACROSS NORTH CENTRAL IOWA MONDAY
AFTERNOON, BUT KEEP IN MIND THAT EARLIER RUNS THAT COVERED
TODAY/TONIGHT PERIOD HAD CONVECTION GOING BY NOW, SO IT'S POSSIBLE
THAT COVERAGE IS OVERDONE AGAIN IN A SIMILAR SETUP. HAVE AT LEAST
KEPT NON-ZERO POPS IN TO COVER POTENTIAL.
BROAD TROUGHING SWIRLS OVER THE WESTERN CONUS AND THE UPPER RIDGE
WILL ANGLE INTO THE GREAT LAKES REGION BY MIDWEEK. GIVEN THE
PROXIMITY TO THE FORCING, RAIN AND STORM CHANCES ARE NOT FAR AWAY
WITH SOME POTENTIAL BEGINNING ONCE CONVECTIVE TEMPERATURE IS
REACHED. THE MASS OF SYNOPTIC FORCING GETS CLOSE ENOUGH TO HAVE
HIGHER CONFIDENCE RAIN AND STORMS FOR THE SECOND HALF OF THE
WEEK. IT WILL BE WRAPPED UP ENOUGH AT THAT POINT TO ONLY HAVE
HEIGHT FALLS AROUND -2 DAM, SO LESS DYNAMIC.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 626 PM CDT SUN SEP 14 2025
SHOWER AND THUNDERSTORM POTENTIAL OVERNIGHT INTO MONDAY MORNING
CONTINUES TO BE THE PRIMARY CHALLENGE PRESENTED IN THE AVIATION
FORECAST THIS EVENING. GUIDANCE IS SHAKY ON COVERAGE, INTENSITY
AND LOCATION, MAKING IT DIFFICULT TO PIN DOWN EXACT TIMING AND
IMPACTS FOR A GIVEN SITE. THAT SAID, HAVE BEGUN TO INCLUDE -SHRA
MENTION AT KMCW, KALO, KDSM, AND KOTM AT THE MOST LIKELY TIMES
FOR PRECIPITATION. KEEP IN MIND THAT LIGHTNING MAY BE PRESENT
WITH THESE SHOWERS, BUT HAVE LEFT OUT OF THE TAFS FOR THIS
ISSUANCE GIVEN LOW CONFIDENCE IN OCCURRENCE. WILL CONTINUE TO
MONITOR OBSERVATIONS AND FORECAST TRENDS THROUGH THE EVENING,
AND PROACTIVELY UPDATE FORECASTS AS NEEDED. WHEN AND WHERE
PRECIPITATION ISN'T ONGOING, LIGHT WINDS AND SCATTERED TO BROKEN
MID- LEVEL CLOUD COVER IS EXPECTED.
ASIDE FROM OVERNIGHT SHOWERS, VFR CONDITIONS CONTINUE INTO
MONDAY. THERE IS A LOW CHANCE FOR ADDITIONAL SHOWERS OR
THUNDERSTORMS MONDAY AFTERNOON AND INTO THE EVENING, MAINLY TO
THE EAST NEAR KALO AND KOTM. THAT SAID, HAVE LEFT OUT OF TAFS
FOR THIS ISSUANCE GIVEN IT OCCURRING AT THE END OF THE FORECAST
PERIOD.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...JIMENEZ
AVIATION...DODSON
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