899
FXUS63 KDMX 280816
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
316 AM CDT THU MAY 28 2026
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 /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1036 PM CDT WED MAY 27 2026
VFR CONDITIONS WILL PERSIST THROUGH THE PERIOD. SCATTERED CIRRUS
OVERNIGHT MAY BECOME BKN AT TIMES ON THURSDAY. LIGHT WIND
OVERNIGHT THE BECOMING EAST/SOUTHEAST AROUND 10 KTS BY MID TO
LATE MORNING.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...DODSON
LONG TERM...DE BRUIN/DODSON
AVIATION...DONAVON
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