330
FXUS63 KDMX 260346
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1046 PM CDT FRI APR 25 2025
...UPDATED FOR THE 06Z AVIATION DISCUSSION...
KEY MESSAGES
- DRY AND QUIET, AND RELATIVELY COOL THROUGH THE DAY SATURDAY.
- SHOWER AND THUNDERSTORM CHANCES RETURN FROM SATURDAY NIGHT
INTO MONDAY NIGHT. THERE IS A LOW POTENTIAL OF SEVERE STORMS
SUNDAY NIGHT, MAINLY NORTHWEST AND WEST, THEN A MUCH HIGHER
AND MORE WIDESPREAD THREAT OF SEVERE WEATHER MONDAY AFTERNOON
TO MONDAY NIGHT. DETAILS REMAIN UNCERTAIN, SO CONTINUE TO
MONITOR THE FORECAST FOR UPDATES.
DISCUSSION
ISSUED AT 259 PM CDT FRI APR 25 2025
A SURFACE HIGH PRESSURE RIDGE WILL BUILD FROM MINNESOTA DOWN
ACROSS IOWA AND WISCONSIN THROUGH TONIGHT. CURRENTLY THICK
CLOUDS PERSIST ACROSS MUCH OF OUR FORECAST AREA, HOWEVER SOME
CLEARING IS WORKING INTO OUR NORTHWESTERN COUNTIES AS THE RIDGE
BUILDS IN AND THIS SHOULD PROGRESS STEADILY SOUTHWARD ACROSS
IOWA, WITH DIURNALLY GENERATED STRATOCUMULUS BEHIND IT
DISSIPATING AFTER SUNSET, RESULTING IN CLEAR SKIES FOR OUR AREA
BY SUNRISE SATURDAY. CLOSE TO THE RIDGE AXIS, OVER SOUTH CENTRAL
MINNESOTA, CALM WINDS AND LONGER RADIATIONAL COOLING TIME
OVERNIGHT COMBINED WITH HIGH NEAR-SURFACE MOISTURE DUE TO RECENT
RAINS MAY LEAD TO THE FORMATION OF FOG, POSSIBLY DENSE AS
DEPICTED BY RECENT HRRR AND RAP RUNS. HOWEVER, IT REMAINS
UNCLEAR HOW MUCH THIS WILL BE ABLE TO BUILD INTO NORTHERN IOWA
WHERE WINDS MAY REMAIN ORGANIZED BUT LIGHT. THE HRRR AND RAP DO
BRING FOG JUST BARELY INTO IOWA (AROUND ESTHERVILLE AND ALGONA)
FOR A COUPLE HOURS AROUND SUNRISE, SO THIS WILL BEAR WATCHING
TONIGHT. OTHERWISE, QUIET WEATHER IS ANTICIPATED THROUGH
SATURDAY AS THE HIGH PRESSURE SLIDES AWAY TO THE EAST RESULTING
IN A FAIRLY COOL BUT DRY AND PARTLY TO MOSTLY SUNNY DAY.
BY SUNDAY MORNING A LARGE 500 MB LOW WILL BE CENTERED OVER
NEVADA. WEAK RIDGING ALOFT WILL MOVE OVER IOWA BUT BE QUICKLY
SUCCEEDED BY INCREASINGLY SOUTHWESTERLY STEERING FLOW BY SUNDAY
NIGHT. THIS WILL PROMOTE STEADY MOISTURE ADVECTION AND WARM AIR
ADVECTION ALOFT FROM SATURDAY NIGHT THROUGH SUNDAY NIGHT, AND
SUBTLE SHORTWAVE IMPULSES EJECTING OUT OF THE LOW WILL INTERACT
WITH DIURNAL FLUCTUATIONS IN THE LLJ TO PRODUCE ROUNDS OF LIGHT
RAIN/CONVECTION ACROSS IOWA. THE FIRST ROUND WILL LIKELY MOVE
FROM WEST TO EAST ACROSS OUR AREA LATE SATURDAY NIGHT AND SUNDAY
MORNING IN ASSOCIATION WITH THE FIRST SURGE OF MOISTURE
ADVECTION, BUT INSTABILITY IS VERY LIMITED AND THE CLOUD LAYER
WILL BE UNDERCUT BY SOMEWHAT DRY AIR FLOWING OUT OF THE RECEDING
SURFACE HIGH, THUS MOSTLY SCATTERED LIGHT SHOWERS ARE
ANTICIPATED DURING THIS TIME. THE SECOND ROUND OF PRECIPITATION
POTENTIAL IS PEGGED OVERNIGHT SUNDAY NIGHT INTO EARLY MONDAY,
WHEN THE LLJ/WIND FIELDS WILL BE STRONGER AND MORE INSTABILITY
WILL BE PRESENT, ESPECIALLY IN OUR WESTERN AND NORTHWESTERN
COUNTIES. THIS WILL RESULT IN A WINDOW FOR ELEVATED
THUNDERSTORMS OVERNIGHT IN AN ENVIRONMENT OF STEADILY INCREASING
SHEAR, PERHAPS SUPPORTING A THREAT OF HAIL. SPC HAS A MARGINAL
RISK JUST WEST OF OUR SERVICE AREA, BUT THIS MAY NEED TO BE
EXTENDED INTO OUR WESTERN AND NORTHWESTERN COUNTIES AT SOME
POINT.
FINALLY, MONDAY PROMISES TO BE AN ACTIVE DAY AS THE SEVERE
THUNDERSTORM POTENTIAL RAMPS UP QUICKLY IN THE AFTERNOON AND
EVENING. THE 500 MB LOW WILL MOVE EASTWARD OVER THE HIGH PLAINS
BUT AS AN OPEN TROUGH, WITH AN ASSOCIATED SURFACE CYCLONE
DEEPENING OVER EASTERN SD AND SOUTHWESTERN MN DURING THE DAY.
ACROSS IOWA WE WILL SEE STRENGTHENING SOUTHERLY SURFACE FLOW AND
SOUTHWESTERLY FLOW ALOFT, RESULTING IN MUCH WARMER TEMPERATURES
PEAKING IN THE LOW TO MID 80S, HIGHER DEWPOINTS WELL INTO THE
60S, AND STRONG INSTABILITY AND WIND SHEAR BY THE AFTERNOON.
THIS CREATES A FAVORABLE PARAMETER SPACE FOR SEVERE
THUNDERSTORMS, HOWEVER, THERE ARE SEVERAL CAVEATS. THE FIRST IS
THE POSSIBILITY OF MORNING/MIDDAY CLOUDS AND PRECIPITATION
ASSOCIATED WITH DECAYING OVERNIGHT ACTIVITY AND ANY LINGERING
BOUNDARIES THIS MAY LAY DOWN, BUT GIVEN THE OVERALL
DISORGANIZED NATURE EXPECTED FROM THAT ACTIVITY AS WELL AS THE
STRONG FLOW BEHIND IT, IT IS MORE LIKELY THIS WILL BE BLOWN OUT
OF OUR AREA BY THE AFTERNOON. THEREAFTER, WHILE OVERALL CAPE
GROWS TO 2000-2500 J/KG SOME FORECAST SOUNDINGS INDICATE A
CAPPING EML WILL REMAIN IN PLACE ACROSS MUCH OF THE STATE DURING
THE AFTERNOON, PARTICULARLY THE NAM ALTHOUGH IT APPEARS TOO
SATURATED IN THE NEAR-SURFACE LAYER. HARDLY ANY MODEL SOLUTIONS
GENERATE DISCRETE CELLS IN THIS WARM SECTOR ACROSS OUR AREA,
LIKELY RESULTING FROM A COMBINATION OF WEAK CIN AND LACK OF
CONVERGENCE/FOCUS MECHANISM DURING THAT TIME. HOWEVER, IT IS
STILL THREE DAYS OUT AND IF THE FORECAST TRENDS TOWARD A LESS
INHIBITED AIRMASS OR ANY TRIGGERING MECHANISM BECOMES APPARENT,
ANY DISCRETE STORMS THAT FORM WITHIN THE WARM SECTOR WOULD HAVE
THE POTENTIAL OF SURFACE-BASED SUPERCELLS CARRYING A RISK OF ALL
MODES OF SEVERE WEATHER.
BY MONDAY EVENING, A COLD FRONT TRAILING FROM THE SURFACE LOW
OVER SOUTHWESTERN MN WILL MOVE INTO WESTERN IOWA AND IS MUCH
MORE LIKELY TO GENERATE A BROKEN LINE OF STORMS ACROSS AT LEAST
PORTIONS OF OUR FORECAST AREA FROM EVENING INTO EARLY MONDAY
NIGHT. FORECAST SOUNDINGS AND HODOGRAPHS ARE VERY SUPPORTIVE OF
SUPERCELLS FORMING ALONG AND JUST AHEAD OF THE BOUNDARY,
HOWEVER, A LACK OF SIGNIFICANT BACKING IN LOW-LEVEL FLOW MAY
HELP TO MITIGATE THE LACK OF STRONG TORNADOES AND SOUNDING
ANALOGS FAVOR LARGE HAIL, WITH SOME POTENTIAL FOR TORNADOES OF
THE RELATIVELY SHORTER/WEAKER VARIETY. OBVIOUSLY, THIS WOULD
STILL BE VERY HAZARDOUS AND SUCH DETAILS ARE VERY MUCH SUBJECT
TO CHANGE OVER THE NEXT FEW DAYS, SO THE LARGE 30% SEVERE
THUNDERSTORM RISK OUTLINED BY SPC IS VERY APPROPRIATE.
AVIATION /06Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1043 PM
CDT FRI APR 25 2025
MVFR STRATUS EDGE NEAR KDSM/KALO CURRENTLY SHOULD BE OUT OF
THOSE AREAS AT 06Z. THE STRATUS WILL LINGER A BIT LONGER AT KOTM
BEFORE SCATTERING. VFR CONDITIONS ARE THEN EXPECTED FOR THE
REMAINDER OF THE PERIOD. LIGHT NORTH TO NORTHEAST WINDS TO START
WILL INCREASE WITH MIXING SATURDAY MORNING WILL CAUSE THE WIND
TO BE NEAR TO ABOVE 12 KTS BY LATE MORNING INTO THE AFTERNOON.
THE WIND WILL GRADUALLY TURN FROM NORTHEAST TO EAST/SOUTHEAST
SATURDAY.
HYDROLOGY
ISSUED AT 259 PM CDT FRI APR 25 2025
SOME AREA RIVERS AND STREAMS CONTINUE TO RISE DUE TO RECENT
RAINS, HOWEVER, ALL WITHIN OUR FORECAST AREA ARE EXPECTED TO
CREST BELOW FLOOD STAGE AND NO ADDITIONAL RAIN IS FORECAST UNTIL
AT LEAST SATURDAY NIGHT.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...LEE
AVIATION...DONAVON
HYDROLOGY...05
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