539
FXUS63 KDMX 281730
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1230 PM CDT THU MAY 28 2026
...UPDATED FOR THE 18Z AVIATION DISCUSSION...
KEY MESSAGES
- WARM AND MOSTLY DRY CONDITIONS CONTINUE TODAY. HIGHS IN THE
80S CONTINUE INTO THE WEEKEND.
- SCATTERED SHOWER/STORM CHANCES (20 TO 30%) RETURN TO THE
WESTERN AND SOUTHWESTERN PORTIONS OF THE AREA OVERNIGHT INTO
EARLY FRIDAY MORNING, THEN AGAIN FRIDAY AFTERNOON AND EVENING.
THE POTENTIAL FOR SEVERE WEATHER LOOKS LOW AT THIS TIME.
- ADDITIONAL SCATTERED SHOWER AND STORM CHANCES (20 TO 30%)
PERSIST INTO THE WEEKEND, ALTHOUGH MUCH OF THIS ACTIVITY
SHOULD REMAIN WEST OF THE AREA.
SHORT TERM /THROUGH FRIDAY NIGHT/
ISSUED AT 311 AM CDT THU MAY 28 2026
AFTER MULTIPLE NIGHTS OF SCATTERED SHOWERS AND SUB-SEVERE
STORMS, NORTHERN IOWA FINALLY GETS TO JOIN THE REST OF THE STATE
IN HAVING A DRY AND UNEVENTFUL NIGHT. SURFACE HIGH PRESSURE HAS
BEGUN TO BUILD OVER THE GREAT LAKES REGION, WHICH NOW SPILLS
INTO IOWA EARLY THIS MORNING. CURRENT SURFACE WINDS ARE FAIRLY
LIGHT, BUT A SUBTLE SHIFT FROM SOUTH SOUTHEAST TO NORTHEAST IN
NORTHEASTERN IOWA IS A SIGN OF THIS DRIER AIR MASS TRYING TO
WORK IT'S WAY INTO IOWA. THE EXPANSION OF THIS GREAT LAKES HIGH
INTO IOWA WILL HAVE A NOTABLE INFLUENCE ON OUR FORECAST OVER THE
DAYS TO COME, PARTICULARLY IN REGARDS TO RAIN CHANCES.
THROUGH THE DAY TODAY, THE HIGH PRESSURE OVER THE GREAT LAKES
WILL GENERALLY DOMINATE THE SURFACE FLOW PATTERN. THIS WILL KEEP
A PERSISTENT STREAM OF DRY AIR AT THE SURFACE, INHIBITING
PRECIPITATION OVER MOST OF IOWA THROUGH THE DAY. A STRIPE OF
WEAK INSTABILITY (~500 J/KG) OVER WESTERN IOWA IS CAUSING SOME
SHOWER/STORM DEVELOPMENT IN CAM GUIDANCE THIS AFTERNOON, BUT A
DEEPER LOOK INTO MODEL SOUNDINGS SHOWS VERY DRY PROFILES AND A
SHALLOW UNSTABLE LAYER SITTING ATOP OF A WELL-MIXED BOUNDARY
LAYER. THESE PROFILES SUGGEST SOME SCATTERED CUMULUS DEVELOPMENT
UNDER THE HIGH CLOUDS TODAY, AND MAYBE EVEN SOME VIRGA, BUT NOT
EXPECTING HYDROMETEORS TO REACH THE GROUND BEFORE EVAPORATING.
OTHERWISE, HIGHS WILL ONCE AGAIN REACH THE MID 80S UNDER PARTLY
CLOUDY SKIES.
AN INCREASING GULF MOISTURE STREAM WILL PUSH NORTHEASTWARD INTO
SOUTHWEST IOWA TONIGHT INTO EARLY FRIDAY MORNING, WHICH WILL
WORK TO SATURATE THE MID AND UPPER LEVELS. EASTERLY FLOW FROM
THE SURFACE HIGH WILL KEEP THE LOW LEVELS DRY, BUT THE SURFACE
HIGH'S INFLUENCE WON'T BE AS STRONG OVER WESTERN IOWA. AS A
RESULT, WE'LL SEE INCREASING RAIN CHANCES (~20%) OVER FAR
SOUTHWESTERN IOWA BY EARLY FRIDAY MORNING, AS THE WEAK LIFT AND
INSTABILITY SATURATES DOWN THROUGH THE DRY LOW LEVELS. BREEZY
WINDS MAY OCCUR AS THIS SATURATION OCCURS, BUT WITH ONLY A FEW
HUNDRED J/KG OF MUCAPE AND MINIMAL SHEAR FRIDAY MORNING, NOT
ANTICIPATING ANY SEVERE WEATHER.
OUR GREAT LAKES SURFACE HIGH WILL TRY TO HOLD OFF THE
ENCROACHING MOISTURE STREAM AS IT ATTEMPTS TO BRING BETTER
SATURATION INTO IOWA ON FRIDAY. THE STRENGTH OF THE HIGH ON
FRIDAY WILL GREATLY DICTATE HOW FAR EAST RAIN CHANCES GET, WITH
SOME OF THE 00Z CAM GUIDANCE SUGGESTING WE COULD SEE SCATTERED
SHOWERS/STORMS AS FAR EAST AS CENTRAL IOWA FRIDAY AFTERNOON AND
EVENING. HOWEVER, SOME OF THE 06Z GUIDANCE THAT HAS BEEN ROLLING
IN HAS ALREADY BACKED OFF ON THE EASTWARD EXTENT OF RAIN
FRIDAY, SUGGESTING THE DRY AIR FROM THE HIGH PRESSURE MAY WIN
OUT. TYPICALLY IN THESE CASES, WE SEE THE HIGH PRESSURE AND EAST
SOUTHEASTERLY FLOW WIN OUT OVER THE MOISTURE ADVECTION,
ESPECIALLY IN WEAKLY FORCED SCENARIOS LIKE THIS ONE. THE WILD
CARD WILL BE IF ANY INSTABILITY WILL BE ABLE TO TAKE ADVANTAGE
OF THE INCREASING MOISTURE CONTENT, LEADING TO ISOLATED OR
SCATTERED CONVECTION. FORTUNATELY, IF ANY SHOWERS OR STORMS DO
OCCUR, THE INSTABILITY VALUES STILL LOOK LOW (< 1000 J/KG) AND
WIND SHEAR STILL WEAK, SO THE POTENTIAL FOR ORGANIZED STORMS AND
SEVERE WEATHER LOOKS MINIMAL AT THIS TIME.
LONG TERM /SATURDAY THROUGH WEDNESDAY/
ISSUED AT 225 PM CDT WED MAY 27 2026
REMARKABLY SIMILAR MID-80S HIGHS ARE EXPECTED THROUGH THE END
OF THE PERIOD, THOUGH CONFIDENCE DECREASES AFTER MONDAY. THE
MOISTURE AXIS MENTIONED ABOVE WILL REMAIN JUST WEST OF OUR AREA
UNTIL SUNDAY, KEEPING SOME POTENTIAL PRECIPITATION CHANCES OVER
WEST/SOUTHWEST IOWA INTO SATURDAY. ON SUNDAY, A SHORTWAVE
EMBEDDED WITHIN THE WESTERN LONGWAVE WILL PIVOT ACROSS THE HIGH
PLAINS. IT IS LIKELY THIS WILL BE TOO FAR WEST TO CREATE ANY
MEANINGFUL SHEAR, BUT MAY BE ENOUGH TO BRING THE MOISTURE AXIS
FARTHER INTO IOWA. GEFS SBCAPE PROBABILITIES INCREASE
SIGNIFICANTLY SUNDAY AND BEYOND, AND MORE QPF OUTLIERS SHOW UP
IN THE NBM MEMBERS SUNDAY NIGHT AND AFTERWARDS (THOUGH AN
OVERALL DRY PATTERN WILL LIKELY STILL DOMINATE). ENSEMBLES
SUGGEST THE OMEGA BLOCK PATTERN WILL BEGIN TO BREAK DOWN EARLY
NEXT WEEK, AND THE EXACT EVOLUTION OF HOW THE RIDGE BREAKS DOWN
AND THE LONGWAVE FINALLY EJECTS WILL DETERMINE WHETHER OUR
HAZARDS FOR NEXT WEEK ARE GARDEN VARIETY SINGLE CELL
THUNDERSTORMS OR STRONGER, MORE ORGANIZED STORMS.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1230 PM CDT THU MAY 28 2026
THERE ARE NO AVIATION CONCERNS THROUGH THE TAF PERIOD. ONLY
HIGH CLOUDS ARE FORECAST (ABOVE FL100), WITH MODEST BREEZES
SLOWLY TURNING FROM EAST TO SOUTHEAST THROUGH THE PERIOD.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...DODSON
LONG TERM...DE BRUIN
AVIATION...LEE
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