239
FXUS63 KDMX 121215
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
715 AM CDT THU JUN 12 2025
KEY MESSAGES
- LULL IN STORM COVERAGE THIS MORNING WITH ADDITIONAL STORMS IN
THE AFTERNOON AND EARLY EVENING WITH LIMITED SEVERE CHANCES
- NOT A WASHOUT, BUT CHANCES FOR STORMS AT TIMES INTO EARLY NEXT
WEEK WITH ORGANIZED STORMS POSSIBLE EARLY NEXT WEEK
UPDATE
ISSUED AT 209 AM CDT THU JUN 12 2025
THE EFFECTIVE SURFACE FRONTAL BOUNDARY, REINFORCED BY OUTFLOW
FROM WEDNESDAY NIGHT STORMS, HAS SUNK INTO CENTRAL IOWA
OVERNIGHT AND LIES NEAR THE HIGHWAY 30 AND INTERSTATE 80
CORRIDORS. HOWEVER, THE 925-850 MB FRONTAL ZONE LIES WELL TO THE
NORTH, NEAR OR JUST NORTH OF THE IOWA/MINNESOTA BORDER. A FEW
CLUSTERS OF THUNDERSTORMS ARE LINGERING IN OUR NORTHEASTERN
COUNTIES AROUND WATERLOO AND WAVERLY EARLY THIS MORNING, BUT
THESE ARE SLOWLY MOVING OUT AND OTHERWISE THE BULK OF
CONVECTIVE ACTIVITY THIS MORNING SHOULD RESIDE IN THE NORTHERN
ZONE NEAR THE BORDER. MEANWHILE, A BROAD UPPER LOW IS DRIFTING
NORTHWARD ACROSS ARKANSAS AND INTO MISSOURI WHERE IT WILL STALL
THROUGH FRIDAY. AS OF THIS WRITING THE RAIN ASSOCIATED WITH THAT
FEATURE REMAINS WELL SOUTH OF IOWA.
LATER THIS MORNING, 500 MB STEERING FLOW OVER THE UPPER MIDWEST
WILL BACK JUST SLIGHTLY TO WEST SOUTHWEST, ALLOWING THE FRONTAL
ZONE NEAR THE IA/MN BORDER TO MOVE NORTH INTO MINNESOTA. MODEST
BUT ORGANIZED SOUTHERLY SURFACE FLOW WILL ALSO PUSH THE SHALLOW
SURFACE BOUNDARY BACK UP INTO NORTHERN IOWA. AS A RESULT, THERE
SHOULD BE A BREAK IN THE RAIN ACROSS MOST OF OUR AREA IN THE
LATE MORNING AND HAVE LOWERED POPS DURING THAT TIME ACCORDINGLY.
BY THIS AFTERNOON HOWEVER, POPS INCREASE AGAIN AS DIURNAL
HEATING WILL ALLOW FOR DESTABILIZATION TO OCCUR, WITH FORECAST
SOUNDINGS INDICATING SUFFICIENT CAPE AND LACK OF CAPPING TO
SUPPORT CONVECTIVE INITIATION. HOWEVER, THERE IS NO REAL FORCING
MECHANISM AND FLOW IS VERY LIGHT THROUGH THE COLUMN, WITH THE
NAM SOUNDING FOR DES MOINES SHOWING THAT AT NOON THE MAXIMUM
WIND SPEED BELOW 400 MB IS ONLY 13 KT. THAT MEANS THE
METAPHORICAL "POPCORN" STORMS, WHICH SHOULD REMAIN BENIGN AND
FAIRLY LIMITED IN COVERAGE. THE POSSIBLE EXCEPTION TO THIS WILL
BE IN OUR FAR NORTHERN/NORTHEASTERN COUNTIES, WHERE A SUBTLE
SHORTWAVE MOVING OVERHEAD WILL PROVIDE A BIT MORE FORCING, AND
THE RETREATING SURFACE BOUNDARY MAY FOCUS CONVECTION A BIT MORE.
HAVE CARRIED HIGHER POPS (40-60%) IN THOSE AREAS ACCORDINGLY,
WITH LOWER POPS (20-30%) FARTHER SOUTH. SPC HAS ALSO OUTLINED A
MARGINAL RISK OF SEVERE HAIL/WIND ACROSS OUR FAR NORTH/NORTHEAST
WHICH IS APPROPRIATE.
FROM LATE THURSDAY NIGHT THROUGH FRIDAY IT APPEARS WE WILL SEE
A PERIOD OF WEAK RIDGING WHICH SHOULD ALLOW FOR QUIETER AND
DRIER WEATHER OVERALL, AND HAVE LOWERED POPS TO 10-20% DURING
THIS TIME.
DISCUSSION
ISSUED AT 218 PM CDT WED JUN 11 2025
A MORE ACTIVE PERIOD OF THUNDERSTORM CHANCES IS IN STORE OVER
THE NEXT WEEK LARGELY DRIVEN BY SHORTWAVE TROUGHS BEING CARRIED
THROUGH THE LOW AMPLITUDE FLOW. THIS FLOW CAN BE VIEWED ON THE
UPPER LEVEL WATER VAPOR IMAGERY FROM GOES-EAST WITH ONE WAVE
OVER THE DAKOTAS AND NEBRASKA AND ANOTHER NEARING THE NORTHERN
ROCKIES. THIS FIRST SHORTWAVE IS REACHING THE STATE THIS
AFTERNOON INTERACTING WITH A STATIONARY FRONT THAT IS DRAPED
OVER FAR NORTHERN IOWA FROM JUST NORTH OF SHELDON TO JUST NORTH
OF ALGONA TO NORTH OF WATERLOO. THIS FRONT HAS PROVIDED SOME
LEVEL OF CONVERGENCE DESPITE THE WEAK SURFACE FLOW WITH A STORM
ALONG THE IOWA/MINNESOTA BORDER. EXPECTATION IS THAT ADDITIONAL
STORMS WILL BE ABLE TO FORM ALONG NORTHERN IOWA THIS AFTERNOON
AND PUSH EASTWARD INTO EARLY THIS EVENING. NOW, THE WEAK FLOW
DOES RESULT IN WEAKER EFFECTIVE SHEAR DESPITE THE TRADITIONAL
DEEP SHEAR VALUES LOOKING FAVORABLE FOR STORM ORGANIZATION.
SURFACE BASED CAPE VALUES OVER 1500 J/KG ARE COMMON SOUTH OF THE
FRONT ALREADY THIS AFTERNOON AND WITH THE DRY MID-LEVEL AIR,
DOWNDRAFT CAPE VALUES ARE OVER 1000 J/KG. THE STEEP LOW LEVEL
LAPSE RATES AND STILL MORE THAN SUFFICIENT SBCAPE VALUES SHOULD
ALLOW FOR GOOD PARCEL ACCELERATION ON STORM DEVELOPMENT PHASE
THAT PUSHES PAST THE 12KFT FREEZING LEVEL AND INTO THE HAIL
GROWTH ZONE. THIS WILL RESULT IN A LARGE HAIL THREAT. FURTHER,
THE LARGE DOWNDRAFT CAPE VALUES, INVERTED V SOUNDINGS, AND
SURFACE DEWPOINT DEPRESSIONS OVER 20 DEGREES F ALSO POINT TO THE
HAZARD OF DAMAGING WIND GUSTS. THIS IS SHOWN IN VARIOUS
CONVECTIVE ALLOWING MODELS (CAMS) SUCH AS THE 12Z HRRR, 0/12Z
ARW CORES, AND 12Z FV3, WHICH HAVE SMALL, BUT VARYING SWATHS OF
SEVERE WIND GUSTS (>50 KNOTS/58 MPH) OVER NORTHERN IOWA THIS
AFTERNOON INTO EARLY THIS EVENING. ALREADY HAVE SEEN SEVERE
GUSTS UP IN WFO SIOUX FALLS SERVICE AREA WITH THE ONE STORM THIS
AFTERNOON.
THIS FIRST WAVE OF STORMS WILL EXIT INTO NORTHEAST IOWA MID TO LATE
EVENING, BUT REGENERATION OF ADDITIONAL STORMS IS EXPECTED OVER
SIOUXLAND AS A WEAK LOW LEVEL JET POINTS INTO THAT REGION,
ESPECIALLY LATE TONIGHT INTO THE OVERNIGHT. WHILE SEVERE
WEATHER IS NOT EXPECTED, LOCALLY HEAVY RAINFALL WILL BE POSSIBLE
AS THESE STORMS TRACK ROUGHLY EASTWARD FOLLOWING THE WEAK
850-300MB FLOW ALONG THE STALLED FRONT OVER NORTHERN IOWA.
EFFICIENT RAINFALL IS CERTAINLY POSSIBLE GIVEN THE DEEP WARM
CLOUD DEPTHS AND PRECIPITABLE WATER VALUES OVER 1.5 INCHES
POOLING ALONG THE BOUNDARY. RAIN TOTALS OF 1 TO 2 INCHES ARE
POSSIBLE SOMEWHERE ALONG THIS BOUNDARY WHETHER IN NORTHERN IOWA
OR SOUTHERN MINNESOTA. A FEW CAMS (E.G. ARW, HRRR, FV3) ALSO
SHOW AMOUNTS OVER 4 INCHES IN VARYING LOCATIONS, WITH THESE CAMS
IMPACTING THE LOCALIZED PROBABILITY MATCHED MEAN OF THE 12Z
HREF. FLASH FLOOD GUIDANCE (FFG) VALUES OVER NORTHERN IOWA RANGE
FROM 1.75 TO 2 INCHES FOR 1 HOUR, 2 TO 2.5 INCHES FOR 3 HOURS,
AND 2.5 TO 3 INCHES FOR 6 HOUR. WITH RELATIVE SOIL MOISTURE
(RSM) PERCENTILES IN THE NORMAL RANGE (30TH TO 70TH PERCENTILE)
AT THE 0-10CM AND 10-40CM LAYERS, THE FFG SEEMS A BIT LOW FROM
AN EMPIRICAL SENSE FOR MID-JUNE. SO, URBAN AREAS AND/OR SMALLER
BASINS, IF THE HIGHER RAINFALL MOVES OVER THOSE AREAS, COULD
HAVE ISOLATED FLASH FLOODING. AS FOR RIVERS, MONTHLY AVERAGE
USGS STREAMFLOWS ARE AVERAGE AND THERE IS CAPACITY AND
EXPECTATION AT THIS POINT IS MAINLY WITHIN STREAM BANK RISES.
THE EXCEPTION WOULD BE IF ONE OF THOSE HIGHER QPF CAM SOLUTIONS
VERIFIES AND THIS COULD RESULT IN MORE THAN WITHIN STREAM BANK
RISE.
AS WE MOVE INTO THURSDAY, THERE SHOULD BECOME A MINIMUM IN COVERAGE
OF ANY SHOWERS OR STORMS IN THE MORNING HOURS THAT LASTS INTO AT
LEAST PART OF THE AFTERNOON. THE SECOND SHORTWAVE NEARING THE
NORTHERN ROCKIES TODAY LOOKS TO PASS LARGELY NORTH OF THE STATE
THURSDAY AFTERNOON AND NIGHT. THIS WOULD KEEP THE FOCUS FOR MUCH OF
THE STORM ACTIVITY NORTH OF THE STATE, THOUGH A FEW STORMS MAY MOVE
ACROSS NORTHERN IOWA MID TO LATE AFTERNOON INTO THE EARLY EVENING
HOURS. THESE COULD POSE AN ISOLATED HAIL OR GUSTY WINDS THREAT AND
IS CURRENTLY CAPTURED IN THE DAY 2 SPC OUTLOOK. FURTHER SOUTH
OUTSIDE THE MARGINAL RISK AREA, A FEW STORMS MAY DEVELOP DURING PEAK
HEATING OVER CENTRAL IOWA. INSTABILITY MAY REACH 1000 J/KG, BUT
SHEAR IS WEAK SO OUTSIDE OF PERHAPS SOME SUB-SEVERE HAIL AND WIND
GUSTS AS STORMS COLLAPSE, THE ACTIVITY OVER CENTRAL IOWA LOOKS TO BE
MORE OF THE SUB-SEVERE VARIETY. DEPENDING ON WHERE THE RAIN FALLS
TONIGHT (WEDNESDAY NIGHT/EARLY THURSDAY) WILL DETERMINE WHAT KIND OF
FLASH FLOODING OR RIVER FLOODING RISK, IF ANY, WILL EXIST LATER ON
THURSDAY.
LOW SHOWER AND STORM CHANCES WILL PERSIST IN PARTS OF THE STATE,
MAINLY NORTHERN AND EASTERN IOWA ON FRIDAY AS SHORTWAVE ENERGY
PASSES NORTH OF THE STATE AND A 500MB CLOSED LOW DRIFTS
NORTHEASTWARD OVER MISSOURI. A FRONT MAY CLEAR THE STATE BY SATURDAY
WITH THIS WEEKEND FAVORING DRIER, THOUGH NOT FULLY DRY CONDITIONS.
THE MACHINE LEARNING/ARTIFICIAL INTELLIGENCE (ML/AI) SEVERE
PROBABILITIES ARE ALSO LOW OR NON-EXISTENT IN THIS PERIOD. CHANCES
FOR MORE ORGANIZED STORMS MAY DEVELOP AS A WARM FRONT LIFTS OVER THE
REGION AND IOWA RETURNS TO THE WARM SECTOR EARLY NEXT WEEK.
INSTABILITY AND SHEAR PARAMETER SPACE WOULD POINT TO SOME STRONG TO
SEVERE STORM RISK WITH THIS SUPPORTED IN THE ML/AI SEVERE
PROBABILITIES AS WELL.
AVIATION /12Z TAFS THROUGH 12Z FRIDAY/
ISSUED AT 614 AM CDT THU JUN 12 2025
MAINLY VFR CONDITIONS ARE ANTICIPATED THROUGH THE TAF PERIOD.
THE EXCEPTION WILL BE THE POSSIBILITY OF BRIEF LOWERED
VISIBILITY/CEILINGS IN AND NEAR SHOWERS AND THUNDERSTORMS. THESE
WILL AFFECT MCW IN THE FIRST HOUR OR TWO OF THE TAFS, BUT
OTHERWISE HOLD OFF UNTIL THIS AFTERNOON/EVENING WHEN WIDELY
SCATTERED STORMS ARE EXPECTED. GIVEN PROBABILITY OF IMPACTS AT
ANY GIVEN TERMINAL, OPTED FOR TARGETED 3-4 HOUR PROB30 GROUPS
DURING THE MOST LIKELY TIME AND LEFT MENTION OUT OF THE
REMAINDER OF THE TAF PERIOD. AMENDMENTS WILL BE POSSIBLE LATER
TODAY BASED ON SHORT-TERM RADAR TRENDS.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...LEE
DISCUSSION...ANSORGE
AVIATION...LEE
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page