717
FXUS63 KDMX 062348
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
648 PM CDT MON APR 6 2026
...UPDATED FOR THE 00Z AVIATION DISCUSSION...
KEY MESSAGES
- BAND OF MODERATE TO HEAVY SNOWFALL OVER SOUTHWEST IOWA THIS
EVENING INTO TUESDAY MORNING. SNOW AMOUNTS OF 2 TO 5 INCHES
LIKELY, WITH A NARROW SWATH OF 6+ INCHES POSSIBLE.
- LIGHT SNOW TRANSITIONING TO LIGHT RAIN POSSIBLE INTO MID-DAY
ON TUESDAY.
- WARMER AND WINDY CONDITIONS EXPECTED ON WEDNESDAY. SCATTERED
SHOWERS AND THUNDERSTORMS POSSIBLE WEDNESDAY AFTERNOON INTO
THE EVENING.
- ACTIVE WEATHER CONTINUES AT TIMES THURSDAY THROUGH THE
WEEKEND.
SHORT TERM /THROUGH TUESDAY NIGHT/
ISSUED AT 254 PM CDT MON APR 6 2026
NORTHERLY FLOW BEHIND LAST NIGHTS FRONTAL PASSAGE HAS LED TO COOL
AND BREEZY CONDITIONS TODAY. SURFACE HIGH PRESSURE FILLING IN OVER
IOWA HAS KEPT THINGS DRY AT THE SURFACE, BUT INCREASING
FRONTOGENESIS/LIFT ALOFT HAS LED TO WEAK RADAR RETURNS AND MID-LEVEL
CLOUD COVER OVER THE SOUTHWESTERN HALF OF IOWA. HOWEVER, WITH THE 20
DEGREE DEWPOINT SPREADS BELOW THESE RETURNS, AND THE PATCHINESS OF
CLOUDS ON SATELLITE IMAGERY, IT'S CLEAR THAT THE DRY AIR IS WINNING
OUT AND LITTLE IS REACHING THE GROUND. A FEW SPRINKLES REMAIN
POSSIBLE THIS AFTERNOON AND EVENING AS THIS MID-LEVEL MOISTURE
CONTINUES TO PRECIPITATE DOWN INTO THE LAYER, BUT CHANCES FOR ANY
APPRECIABLE PRECIPITATION IS LOW.
PRECIPITATION CHANCES INCREASE CONSIDERABLY THIS EVENING, AS THE
THETA-E ADVECTION FROM THE SOUTHWEST CONTINUES TO SMASH INTO THE
COOL, DRY AIR MASS OVERHEAD. THIS BATTLE BETWEEN THE TWO ADVECTION
REGIMES WILL LEND ITSELF TO A SLANTED REGION OF FRONTOGENESIS FROM
ROUGHLY 850 MB TO 650 MB. MODEL CROSS SECTIONS AND SOUNDINGS
INDICATE OVER -20+ MICROBARS OF LIFT ROUGHLY COLLOCATED WITH
THE DENDRITIC GROWTH ZONE AND SUPER SATURATION WITH RESPECT TO
ICE WITHIN THIS LAYER, RESULTING IN A BAND OF MODERATE TO
POTENTIALLY HEAVY SNOWFALL. THIS BAND WILL ALSO BE FAVORABLY
POSITIONED WITHING THE RIGHT ENTRANCE REGION OF THE UPPER LEVEL
JET, FURTHER PROMOTING BROAD-SCALE LIFT. HREF OUTPUT SHOWS 40
TO 50% OF MEMBERS WITH >1" PER HOUR SNOWFALL RATES OVERNIGHT
WITHIN THIS BAND, FURTHER EMPHASIZING THE POTENTIAL FOR HEAVY
SNOWFALL FALLING WITHIN THE BAND. SNOW RATIOS MAY BE A TAD ON
THE WETTER SIDE, BUT OVER 0.5" OF MODELED QPF WILL MORE THAN
MAKE UP FOR THE LACK OF HIGHER SNOW RATIOS. HOWEVER, WE CAN'T GO
WITHOUT MENTIONING THE INTRUSION OF DRY AIR THAT WILL STILL BE
ONGOING ON THE NORTHERN FRINGE OF THIS BAND, AS THE DRY AIR MASS
TO THE NORTH TRIES TO WORK AGAINST THE BAND. WHILE THIS WON'T
PREVENT SNOWFALL UNDERNEATH THE ZONE OF STRONGEST FORCING, THIS
WILL CUT INTO THE NORTHERN EDGE OF THE HEAVIEST BAND. THE NET
RESULT WILL BE A BAND OF SNOWFALL GENERALLY AROUND 2 TO 5" WITH
LOCALLY HIGHER AMOUNTS OF 6" OR MORE IN A NARROW SWATH WITHIN
THE BAND. GIVEN THE DRY AIR INTRUDING FROM THE NORTH, THIS BAND
WILL LIKELY HAVE A SHARP CUTOFF OF SNOWFALL AMOUNTS, ESPECIALLY
ALONG THE NORTHERN FRINGE. WITH THE HIGHER END POTENTIAL FOR
HEAVY SNOW EMBEDDED WITHIN THE BAND, HAVE ISSUED A WINTER
WEATHER ADVISORY FOR AREAS MOST LIKELY TO BE IMPACTED BY THE
BAND. AN UPGRADE TO WINTER STORM WARNING WILL LIKELY BE NEEDED
LATER THIS EVENING TO CAPTURE THE LOCATION OF THE NARROW SWATH
OF HIGHER AMOUNTS ONCE CONFIDENCE IN THE EXACT LOCATION
INCREASES. AREAS THAT DO RECEIVE THIS WETTER, HEAVIER SNOW
SHOULD EXPECT SLICK TRAVEL DURING THE TUESDAY MORNING COMMUTE.
WHILE THE HEAVIEST BAND OF SNOW IS EXPECTED OVER SOUTHWEST IOWA,
PRECIPITATION WILL DRIFT NORTHWARD INTO THE DAY ON TUESDAY AS
THE HIGH PRESSURE DEPARTS OFF TO THE EAST. HOWEVER, FORCING WILL
DIMINISH AS THIS OCCURS AND SATURATION WILL BE MORE DIFFICULT
TO COME BY FARTHER NORTH INTO THE DRIER AIR. THEREFORE, LIGHT
SNOW CHANCES WILL DRIFT NORTHWARD THROUGH LATE TUESDAY MORNING
INTO THE AFTERNOON, BUT ACCUMULATIONS WILL BE MINIMAL. A
TRANSITION OVER TO RAIN MAY ALSO OCCUR AS LOW LEVEL TEMPERATURES
WARM THROUGH THE DAY.
LONG TERM /WEDNESDAY THROUGH MONDAY/
ISSUED AT 254 PM CDT MON APR 6 2026
A 500 MB TROUGH DIGS INTO THE MIDWEST ON WEDNESDAY. A HEALTHY LOW
LEVEL JET WILL DEVELOP AHEAD OF THIS SYSTEM, ADVECTING WARM, MOIST
SOUTHERLY AIR UP INTO IOWA. WITH THIS JET ALOFT WINDS WILL BECOME
QUITE BREEZY ON WEDNESDAY. WARM AIR ADVECTION REGIMES AREN'T THE
MOST EFFICIENT AT TRANSPORTING WINDS ALOFT DOWN TO THE SURFACE, BUT
THERMAL MIXING ON THURSDAY TAPPING INTO A 50 TO 60 KT LOW LEVEL JET
WILL STILL RESULT IN WINDY CONDITIONS AT THE SURFACE, EVEN IF THE
ENTIRETY OF THOSE WINDS AREN'T REALIZED. NBM WINDS ARE ALREADY
SUGGESTING SUSTAINED WINDS AROUND 20 TO 30 MPH AND GUSTS UP TO 40
MPH, AND MODELED SOUNDINGS FROM THE GFS IMPLY WINDS COULD BE EVEN
STRONGER THAN THIS THANKS TO STEEP LOW LEVEL LAPSE RATES AND 50 KT
WINDS AT THE TOP OF THE MIXED LAYER. ALTHOUGH NOT A PRIME HIGH WIND
ENVIRONMENT, WOULD NOT BE SURPRISED TO SEE BOTH SUSTAINED WINDS AND
GUSTS APPROACHING WIND ADVISORY CRITERIA AND WILL BE ASSESSING THE
NEED FOR ANY WIND HEADLINES IN THE COMING DAYS. WITH THE PLUME OF
LOW LEVEL GULF MOISTURE THAT WILL COME UP WITH THIS SYSTEM, WE WILL
ALSO BE LOOKING AT THE POTENTIAL FOR SHOWERS AND A FEW THUNDERSTORMS
AHEAD OF THE TRAILING COLD FRONT. THAT SAID, INSTABILITY LOOKS
MINIMAL AND SEVERE WEATHER THREAT IS LOW AT THIS TIME.
AS HAS BEEN DISCUSSED IN MULTIPLE PREVIOUS DISCUSSIONS, THE
PROGRESSION OF THIS FRONT WILL DICTATE HOW WET IT WILL BE THROUGH
THE END OF THE WEEK. LAST NIGHT'S GUIDANCE SUGGESTED THE FRONT MAY
FALL THROUGH THE STATE AND KEEP MOST OF THE AREA DRY THROUGH
THURSDAY. HOWEVER, RECENT GUIDANCE SUGGESTS IT MAY STALL OVER IOWA,
BISECTING THE STATE AND KEEPING RAIN AND THUNDERSTORM POTENTIAL IN
PLACE OVER SOUTHERN IOWA ON THURSDAY BEFORE FULLY PUSHING THROUGH
THE AREA ON FRIDAY. THIS PROGRESSION WOULD GIVE US A BRIEF LULL IN
RAIN CHANCES THROUGH FRIDAY AND INTO SATURDAY, BEFORE THE BROAD
UPPER LEVEL TROUGH DEVELOPS OVER THE WESTERN CONUS INTO THE SECOND
HALF OF THE WEEKEND. THIS WILL OPEN THE STATE UP TO THE GULF ONCE
AGAIN AND PUT US INTO A MOIST, ACTIVE SOUTHWEST FLOW PATTERN. RAIN
AND THUNDERSTORMS ARE POSSIBLE THROUGHOUT THIS PERIOD, BUT WITH THIS
BEING AN EVER-CHANGING SCENARIO, WILL HOLD OFF ON ANY FARTHER
DETAILS AT THIS TIME.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 645 PM CDT MON APR 6 2026
A BAND OF SNOW WILL SET UP OVER SOUTHWEST IOWA TONIGHT,
LINGERING NEAR KDSM AND KOTM. IMPACTS AT THESE TWO SITES WILL BE
LIMITED TO MVFR CIGS OR VSBYS UNTIL THE BAND LIFT NORTH AFTER
12Z. SNOW WILL BEGIN TO MIX WITH RAIN, LIMITING THE VSBY IMPACTS
TO MVFR THROUGH THE DAY, BUT WITH CIGS PROGRESSIVELY BECOMING
MVFR OR IFR AT ALL SITES.
HYDROLOGY
ISSUED AT 250 PM CDT MON APR 6 2026
MANY STREAMS ARE CRESTING NOW OR WILL CREST OVER THE NEXT ~24 HRS
WITH AROUND 15 RIVER FORECAST POINTS REACHING ACTION STAGE. THE
CEDAR RIVER AT CEDAR FALLS HAS REACHED MINOR FLOOD STAGE AND THE
IOWA RIVER NEAR TAMA THAT IS EXPECTED TO CREST AROUND FLOOD STAGE
TUESDAY MORNING.
THE PRECIPITATION TODAY INTO TONIGHT, INCLUDING THE SNOW BAND,
WILL LARGELY FALL OVER AREAS THAT HAVE NOT SEEN THE HIGHER RAINFALL
THAT OCCURRED LAST WEEK. NASA SPORT GFS FORCED 0-10 CM AND 0-40 CM
SOIL MOISTURE PERCENTILES ARE FORECAST TO RECOVER TO BETWEEN THE
30TH AND 70TH PERCENTILES BY LATE THIS WEEK. WHILE OFFICIAL RIVER
FORECASTS ACCOUNT FOR ONLY 24 HOURS OF QPF, BOTH THE OFFICIAL
FORECASTS AND THE 120-HR CONTINGENCY FORECASTS SHOW ALL CURRENT
LOCATIONS IN ACTION OR MINOR FLOOD STAGE TO FALL BELOW ACTION STAGE
BY LATE THIS WEEK. THEY ARE UNLIKELY TO RETURN TO THEIR BASE FLOWS
OF EARLY LAST WEEK THOUGH.
RAINFALL UP TO 1-2 IN WILL FALL WITH A COLD FRONT WEDNESDAY INTO
THURSDAY, WHICH MAY TAKE AWAY SOME SOIL CAPACITY AS THE ACTIVE, WET
PATTERN SETS UP LATE THIS WEEKEND INTO EARLY NEXT WEEK. UP TO A FEW
ADDITIONAL INCHES ARE POSSIBLE OVER PORTIONS OF THE STATE, BUT
UNCERTAINTY ON AMOUNTS AND PLACEMENT WITHIN ANY GIVEN BASIN AT THIS
TIME RANGE REMAINS HIGH. THE GFS AND NBM FORCED NATIONAL WATER MODEL
HIGH MAGNITUDE FLOW ANNUAL EXCEEDANCE PROBABILITIES ARE GENERALLY
~50% ON LARGER STREAMS. THIS DATA SUGGESTS RENEWED GENERALLY WITHIN-
BANK RISES ESPECIALLY SHOWN OVER SOUTHERN INTO EASTERN IOWA, WITH
SOME ISOLATED MINOR FLOODING POSSIBLE. THE EXPERIMENTAL FLOOD HAZARD
OUTLOOK (FHO) CONTINUES HIGHLIGHTING MUCH OF IOWA FOR LIMITED
POTENTIAL FLOOD IMPACTS WITH THE EXPERIMENTAL HYDROLOGIC ENSEMBLE
FORECASTING SERVICE (HEFS) AT THE 30% CHANCE OF EXCEEDANCE WITH
STAGES SIMILAR TO CURRENT, BUT AT THE 10% CHANCE OF EXCEEDANCE WITH
SEVERAL MORE POINTS REACHING MINOR STAGE AND A FEW TO MODERATE
STAGE. TRENDS IN THE HEAVY RAINFALL SIGNAL WILL CONTINUE TO NEED TO
BE MONITORED.
DMX WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 1 PM CDT
TUESDAY FOR IAZ057-058-070>072-081>084-092>095.
SHORT TERM...DODSON
LONG TERM...DODSON
AVIATION...JIMENEZ
HYDROLOGY...ZOGG
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