235
FXUS63 KDMX 240817
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
ISSUED BY NATIONAL WEATHER SERVICE DULUTH MN
317 AM CDT THU APR 24 2025
KEY MESSAGES
- MORE WIDESPREAD RAIN WITH SOME THUNDERSTORMS ARRIVES TODAY
INTO TONIGHT WITH A BROAD AREA THROUGH CENTRAL IOWA THAT COULD
SEE 1 OR MORE INCHES OF RAIN, WITH LOCALIZED AMOUNTS UP TO 2
INCHES.
- ADDITIONAL SHOWER AND THUNDERSTORM POTENTIAL FOR SUNDAY INTO
EARLY NEXT WEEK, SOME OF WHICH COULD BE SEVERE ON MONDAY INTO
TUESDAY.
DISCUSSION
ISSUED AT 315 AM CDT THU APR 24 2025
LAST NIGHT WAS ACTIVE ONCE AGAIN, WITH SHOWERS AND THUNDERSTORMS MOVING
THROUGH CENTRAL IOWA PRODUCING QUARTER TO GOLF BALL SIZED HAIL
ALONG THE I-80 AND HIGHWAY 20 CORRIDORS, COPIOUS AMOUNTS OF
SMALL HAIL IN THE CEDAR FALLS/WATERLOO AREA, AND SOME STRONG
WINDS IN SOUTHEASTERN IOWA. IN ADDITION TO THE SEVERE ASPECTS,
AREAS AROUND THE HIGHWAY 30 AND HIGHWAY 20 CORRIDORS HAVE PICKED
UP YET ANOTHER ROUND OF RAIN AFTER THE STORMS TWO NIGHTS AGO,
COMING OUT TO ROUGHLY 4.59” OF RAINFALL IN THE LAST WEEK AT
WATERLOO AND 2.48” OF THAT COMING JUST LAST NIGHT. THE SEVERE
THREAT HAS ONCE AGAIN WRAPPED UP AFTER MIDNIGHT, WITH ONLY RAIN
AND OCCASIONAL THUNDER PERSISTING IN NORTH CENTRAL AND EAST
CENTRAL IOWA EARLY THIS MORNING. AFTER THIS AREA OF MOSTLY
STRATIFORM PRECIPITATION DEPARTS, WE’LL SEE A BRIEF LULL IN
PRECIPITATION THROUGH THE NEXT FEW HOURS BEFORE YET ANOTHER
ROUND OF PRECIPITATION LIFTS NORTH AND EAST INTO THE AREA TODAY.
SHOWER AND STORM CHANCES TODAY WILL BE ASSOCIATED WITH A VERY
SUBTLE SHORTWAVE PROPAGATING EAST NORTHEAST THROUGH THE 500 MB
PATTERN, BRINGING A LOBE OF VORTICITY AND LIFT INTO THE FORECAST
AREA. AS THIS OCCURS, WARM, MOIST GULF AIR WILL AGAIN SURGE
INTO THE FORECAST AREA, BOOSTING PWAT VALUES INTO THE 1” TO 1.3”
RANGE THROUGH THURSDAY INTO FRIDAY MORNING, RESULTING IN DECENT
RAINFALL PRODUCTION FOR THIS TIME OF THE YEAR. THIS ROUND OF
PRECIPITATION WILL ALSO COME IN A SLIGHTLY DIFFERENT FLAVOR
COMPARED TO RECENT DAYS, AS IT WILL TEND TOWARDS MORE STRATIFORM
PRECIPITATION THAN CONVECTIVE. THIS IS INDICATIVE OF THE
HEAVILY SATURATED PROFILES AND THE RELATIVE LACK OF INSTABILITY
AND SHEAR. THERE MAY BE A FEW HOURS IN THE AFTERNOON/EARLY
EVENING OVER SOUTHERN AND SOUTHWESTERN IOWA WHERE A FEW STRONGER
UPDRAFTS COULD DEVELOP, BUT EVEN THEN, THE LACK OF DEEP LAYER
SHEAR WILL LIMIT ORGANIZED CONVECTION, MEANING THESE STORMS WILL
BE PULSEY WITH MINIMAL SEVERE WEATHER THREAT. OF GREATER
CONCERN WILL BE YET ANOTHER ROUND OF PRECIPITATION MOVING
THROUGH AREAS THAT HAVE ALREADY SEEN MULTIPLE ROUNDS OF RAINFALL
THROUGH THE LAST WEEK. ENSEMBLE GUIDANCE STILL INDICATES A
BROAD AREA OF MEAN 24 HR RAINFALL AROUND 1”+ THROUGH CENTRAL
IOWA, WITH THE HREF LOCAL PROBABILITY MATCHED MEAN FOR 24 HOURS
SHOWING A SWATH OF 1.5” TO 2+” AMOUNTS. THESE HIGHER END
AMOUNTS CERTAINLY WON’T BE WIDESPREAD, BUT DEPENDING ON HOW SOME
OF THE HEAVIER PRECIPITATION TRACKS COULD BE REALIZED LOCALLY.
WHEN LOOKING AT HREF PROBABILITIES FOR 1.5”+ RAINFALL IN 24 HRS,
THE HIGHEST PROBABILITIES AROUND 40-60% EXIST ROUGHLY FROM
INTERSTATE 80 TO HIGHWAY 30, AND WEST OF I-35. AREAS FURTHER
EAST OF I-35 HAVE SLIGHTLY LOWER PROBABILITIES (< 40%) BUT
STRETCH UP TO THE WATERLOO/CEDAR FALLS AREA WHERE RIVERS HAVE
ALREADY RISEN INTO ACTION STAGE. WHILE THE SHORTWAVE IS LIFTING
NORTH INTO THE AREA, THERE WILL ALSO BE A 500 MB TROUGH PUSHING
SOUTH OUT OF CANADA, BRINGING SURFACE HIGH PRESSURE, DRY AIR
AND SUBSIDENCE BEHIND THE SHORTWAVE. THIS WILL WORK TO SHOVE THE
MAIN BAND OF RAINFALL SOUTH AND EAST AS IT MOVES THROUGH THE
FORECAST AREA TODAY AND TONIGHT, LIMITING RAINFALL AMOUNTS OVER
NORTHWEST IOWA. NORTHWEST IOWA IS CURRENTLY WHERE NBM DEPICTS
THE HIGHEST AMOUNTS OF PRECIPITATION, BUT GIVEN THE RECENT TREND
IN GUIDANCE FOR THIS HIGH PRESSURE TO SHUT OFF RAINFALL SOONER,
EXPECTING THE HEAVIEST BAND OF PRECIPITATION TO VERIFY CLOSER
TO WHERE THE HREF HAS IT, RATHER THAN NBM.
AS WE GET INTO FRIDAY MORNING, PRECIPITATION WILL BEGIN TO
DEPART TO THE EAST AS THE HIGH PRESSURE FILLS IN BEHIND IT. THIS
SHOULD BRING US MOSTLY DRY CONDITIONS THROUGH FRIDAY AFTERNOON
AND SATURDAY, GIVING THE AREA A MUCH NEEDED BREAK FROM SHOWERS
AND STORMS. PRECIPITATION CHANCES THEN RETURN TO THE FORECAST
LATE SUNDAY NIGHT THROUGH MONDAY, ALTHOUGH DETAILS REGARDING
THESE CHANCES THROUGH THIS PERIOD REMAIN A BIT BLURRY AMONG
GUIDANCE. THESE DETAILS INCLUDE A RELATIVELY PROMINENT SYSTEM
DIGGING IN OVER THE WESTERN CONUS THROUGH THE WEEKEND AND THEN
LIFTING NORTH AND EAST THROUGH THE PLAINS AND IN THE VICINITY OF
THE STATE THROUGH THE BEGINNING OF NEXT WEEK. THE STORM
PREDICTION CENTER HAS A 15% RISK (SLIGHT RISK) FOR SEVERE
WEATHER OVER THE ENTIRE AREA AS THIS LIFTS NORTH, WHICH GIVEN
THE PARAMETER SPACE AND WIND FIELDS SEEMS UNDERSTANDABLE.
HOWEVER, MODEL GUIDANCE OVER THE LAST FEW RUNS HAS STRUGGLED TO
PRODUCE MUCH CONVECTION ASSOCIATED WITH THIS SYSTEM AS IT MOVES
THROUGH IOWA, POTENTIALLY DUE TO A LACK OF CONVERGENCE AS IT
MOVES THROUGH. THAT SAID, IT MAY ALSO BE DUE TO THE EXPECTATION
OF DISCRETE CONVECTION, WHICH MAY NOT BE GETTING CAPTURED WELL
BY THE COARSER GLOBAL MODELS. THEREFORE, THE POTENTIAL FOR
SEVERE WEATHER ON MONDAY IS CERTAINLY THERE, BUT WE WILL WANT TO
CONTINUE TO KEEP AN EYE ON GUIDANCE IN THE COMING DAYS,
ESPECIALLY ONCE WE GET NEARER TO THE HIGH RESOLUTION WINDOW.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1252 AM CDT THU APR 24 2025
A STATIONARY BOUNDARY STILL REMAINS STRETCHED FROM OMA TO NEAR
ALO TO JUST NORTH OF PDC AS OF 06Z THIS EVENING AND IS SLOWLY
LIFTING NORTH. SHOWER AND THUNDERSTORMS PERSIST ACROSS NORTHERN
AND NORTHEASTERN IOWA THROUGH THE NEXT SEVERAL HOURS AT MCW AND
ALO, WITH MVFR VISIBILITY AT TIMES AND BRIEF NORTHWESTERLY WIND
GUSTS TO 20 KNOTS AT ALO WITH THE PASSING STORMS. A MORE DIFFUSE
NORTH-SOUTH BOUNDARY JUST WEST OF OTM COULD PRODUCE A FEW
SHOWERS AT OTM BETWEEN 08-10Z, BUT CONDITIONS SHOULD REMAIN VFR
THERE. SCATTERED SHOWERS AND A FEW EMBEDDED STORMS COULD PUSH
INTO DSM/FOD/MCW/ALO MID MORNING INTO AFTERNOON, BUT THE BETTER
POTENTIAL FOR AN ADDITIONAL ROUND OF SHOWERS AND THUNDERSTORMS
IS FORECAST TO APPROACH FROM THE WEST LATE THIS AFTERNOON AND
SPREAD EASTWARDS ACROSS IOWA THIS EVENING INTO EARLY TONIGHT.
HYDROLOGY
ISSUED AT 326 PM CDT WED APR 23 2025
WIDESPREAD RAINFALL EXPECTED ACROSS CENTRAL IOWA (80-90%)
THURSDAY CONTINUES TO SIGNAL AN INCREASING POTENTIAL FOR
ADDITIONAL RAINFALL TOTALS AROUND AN INCH, WITH AN ISOLATED
HIGHER AMOUNT NEAR 1.5’’ ACROSS CENTRAL AND NORTHERN IOWA. RIVER
RESPONSES PER HEFS GUIDANCE SUGGESTS THAT A RISE ABOVE ACTION
STAGE IS LIKELY (70-90%) AT SHELL ROCK AND CEDAR RIVERS THURSDAY
INTO FRIDAY. THOUGH THE LIKELIHOOD FOR ADDITIONAL SITES TO SEE
RIVER FLOW EXCEEDANCE IS ON THE LOWER END (<=30) AT THE IOWA
RIVER, DES MOINES RIVER, AND RACCOON RIVER, RISES AT AND ABOVE
THE ACTION STAGE THRESHOLD IF HIGHER RAINFALL AMOUNTS WERE TO
OCCUR. CLOSE MONITORING WILL CONTINUE TO WATCH FOR THIS
POTENTIAL.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...DODSON
AVIATION...ROTHSTEIN
HYDROLOGY...BURY
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