578
FXUS63 KDMX 201154
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
654 AM CDT TUE MAY 20 2025
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- LOCALIZED FLASH FLOODING POTENTIAL REMAINS THIS MORNING,
PARTICULARLY OVER URBAN AREAS. WITHIN RIVER BANK RISES ARE
EXPECTED WITH ADDITIONAL RAINFALL AMOUNTS OF 1-2 INCHES
EXPECTED OVER THE NORTHEAST HALF OF THE STATE
- BREEZY TODAY AND COOLER
UPDATE
ISSUED AT 401 AM CDT TUE MAY 20 2025
ANY CONCERN FOR SEVERE WEATHER HAS DIMINISHED AS OF LATE LAST NIGHT
INTO EARLY THIS MORNING, GIVEN THAT INSTABILITY HAS LARGELY
DIMINISHED, THOUGH A FEW WEAK STORMS ARE CURRENTLY PUSHING INTO
SOUTHWEST IOWA BUT SHOULD CONTINUE TO WEAKEN AS THESE STORMS MOVE
INTO MORE STABLE AIR. OTHERWISE, MUCH OF IOWA THIS MORNING IS
EXPERIENCING AREAS OF MODERATE TO HEAVY RAINFALL IN THE FORM OF
STRATIFORM PRECIPITATION ACROSS THE NORTHERN TWO-THIRDS OF THE
STATE. RAINFALL TOTALS SINCE YESTERDAY SO FAR GENERALLY RANGE IN THE
1-2.5 INCH RANGE ACROSS THE SOUTHEAST HALF OF THE STATE, WITH
ISOLATED POCKETS OF 3+ INCHES AND A FEW HIGHER TOTALS NEARING 4+ AS
THE DES MOINES INTERNATIONAL AIRPORT RECEIVED 3.74 INCHES OF
RAINFALL IN 24 HOURS. GIVEN THIS GENEROUS AMOUNT OF RAINFALL IN THE
DES MOINES METRO AND VICINITY, RIVERS HAVE GENERALLY SEEM
SUBSTANTIAL RISES OF SEVERAL FEET, ONE PARTICULARLY BEING WALNUT
CREEK AT DES MOINES 63RD STREET, WHICH SO FAR HAS RISEN ROUGHLY 3.7
FEET TO NEAR 9 FEET IN THE LAST 24 HOURS, NEARING ACTION STAGE AT
THIS TIME. SURFACE ANALYSIS EARLY THIS MORNING SHOWS THE LOW
PRESSURE SYSTEM CENTERED OVER SOUTHERN IOWA INTO NORTHERN MISSOURI,
WHICH PER GUIDANCE IS STILL ON TRACK TO PASS ACROSS THE STATE
THROUGH TODAY. WITH THIS, THE MAIN CONCERN WILL BE ASSESSING THE
REMAINING RAINFALL AMOUNTS EXPECTED TODAY AND HOW THIS WILL IMPACT
AREAS THAT HAVE ALREADY TAKEN THE HIGHER AMOUNTS OF RAINFALL OVER
THE LAST 24+ HOURS. AS IT STANDS PER LATEST GUIDANCE, CONVECTIVE
ALLOWING MODELS DEPICT THIS BROAD SWATH OF PRECIPITATION ONGOING TO
GRADUALLY CIRCULATE NORTH/NORTHEASTWARD THROUGH SUNRISE INTO
MID- MORNING, BEFORE CONDITIONS GENERALLY DRY OUT. CANNOT RULE
OUT VERY LIGHT RAIN OR DRIZZLE POTENTIAL THIS AFTERNOON TO
EVENING AS MODEL SOUNDINGS INDICATE LOW LEVEL SATURATION IN THE
COLUMN AND LIFT WITHIN THIS SAME AREA. ADDITIONAL RAINFALL
TOTALS THROUGH THE REST OF TODAY LOOK TO RANGE UP TO 0.5 TO 2
INCHES, WITH THE HIGHEST VALUES ACROSS THE NORTHEASTERN HALF OF
THE STATE WHERE THE MAIN SWATH OF CURRENT RAINFALL IS LIFTING
TOWARDS. HEFS GUIDANCE INDICATES A 30 PERCENT CHANCE THAT AT
LEAST A FEW RIVER SITES MAY REACH OR JUST EXCEED ACTION STAGE IN
THE DES MOINES METRO AREA TODAY, THOUGH GIVEN THE HIGHER
TRENDING RAINFALL AMOUNTS, THE 10% PROBABILITIES ARE NOT
COMPLETELY OUT OF THE QUESTION FOR A HANDFUL OF SITES IN THE
METRO AREA TO MEET OR EXCEED ACTION STAGE TO EVEN MINOR FLOOD
STAGE. THIS WILL BE MONITORED VERY CLOSELY THROUGHOUT TODAY.
THERE IS ALSO A POTENTIAL FOR THUNDERSTORMS BY LATE MORNING TO
AFTERNOON, LIMITED GENERALLY OVER FAR SOUTHEASTERN IOWA AS THE MORE
FAVORABLE CONDITIONS SUCH AS WARM SECTOR SETS UP OVER THE AREA. RAP
SOUNDINGS INDICATE SURFACE TO 3KM MLCAPE VALUES UP TO 50 J/KG WITH
NOTABLE SURFACE VORTICITY THAT COULD ENHANCE STRETCHING
POTENTIAL, LEADING TO A NON-ZERO CHANCES OF FUNNEL CLOUDS.
DISCUSSION
ISSUED AT 254 PM CDT MON MAY 19 2025
MORNING SHOWERS AND STORMS HAVE PUSHED WELL EAST OF THE AREA
LEAVING BEHIND SOME SUNSHINE OVER PARTS OF EASTERN IOWA, BUT A
GENERALLY CLOUD FILLED SKY OVER WESTERN INTO CENTRAL IOWA PER
GOES-EAST DAY CLOUD PHASE DISTINCTION RGB. THE RESIDUAL AND
CURRENT WARM FRONTS ARE TO THE SOUTH OF IOWA, THOUGH SOME LOW
LEVEL MOISTURE WITH DEWPOINTS INTO THE 60S ARE INTO THE
SOUTHWESTERN PART OF THE STATE. SURFACE WINDS HAVE BEEN BLUSTERY
WITH SUSTAINED WINDS SPORADICALLY - BOTH TEMPORALLY AND
SPATIALLY - REACHING ADVISORY CRITERIA WITH WIND GUSTS OF 25 TO
40 MPH COMMON. A FEW SHOWERS HAVE BEEN BUBBLING AT TIMES OVER
OUR FORECAST AREA, BUT OVERALL WE ARE RAIN FREE. FARTHER TO THE
WEST, THUNDERSTORMS HAVE DEVELOPED OVER EASTERN NEBRASKA WHERE
SPC MESOANALYSIS SHOWS UNCAPPED SURFACE BASED INSTABILITY
(SBCAPE) OF 1500 J/KG AND VERY FAVORABLE EFFECTIVE SHEAR VALUES
OVER 50 KNOTS. TO OUR SOUTHWEST, STORMS HAVE ALSO DEVELOPED
ALONG THE KANSAS/MISSOURI LINE, BUT THESE ARE LIKELY ELEVATED
STORMS DUE TO INHIBITION AND THE STABLE LAYER, WHICH IS
PREVENTING REALIZATION OF THE HIGH EFFECTIVE SHEAR AND SURFACE
INSTABILITY VALUES. OVER IOWA, SBCAPE HAS BEEN BUILDING TO
AROUND 1000 J/KG OVER THE SOUTHWEST CORNER AND FORECAST
SOUNDINGS SHOW UPWARDS OF 500 J/KG OF SBCAPE AT CSQ; HOWEVER,
WITH THE CLOUD COVER AND EASTERLY FLOW, THE STABLE LAYER IS
PROVIDING QUITE A BIT OF INHIBITION. WHILE THERE IS A VERY LOW
CHANCE OF SURFACE BASED STORMS OVER OUR SOUTHWESTERN FORECAST
AREA IF INHIBITION CAN BE OVERCOME BY ANY CLEARING AND/OR
COOLING OF THE ELEVATED WARM LAYER, WE ARE GENERALLY EXPECTING
ELEVATED STORMS. MUCH OF OUR STORM ACTIVITY IS EXPECTED TO
ARRIVE FROM STORMS THAT MOVE OUT OF NORTHERN MISSOURI OR UP OUT
OF NORTHEASTERN KANSAS/FAR SOUTHEASTERN NEBRASKA. THESE ARE
FORECAST TO REACH OUR SOUTHWESTERN FORECAST AREA BETWEEN AROUND
4PM AND 6PM, AND THEN WILL SPREAD NORTHEASTWARD INTO THE REST OF
SOUTHERN AND CENTRAL IOWA WITH SOME DEGREE OF FILL IN OF
SCATTERED SHOWERS AND STORMS FARTHER NORTH AND NORTHWEST IN THE
STATE. WHILE STORMS WILL BE ELEVATED, MUCAPE VALUES OVER 1000
J/KG AND EFFECTIVE SHEAR OF 30 TO 40 KNOTS WILL ALLOW FOR
INITIAL STORM ORGANIZATION WITH THE MAIN HAZARD BEING LARGE HAIL
AND A SECONDARY HAZARD OF GUSTY, THUNDERSTORM WINDS. FORECAST
SOUNDINGS SHOW INSTABILITY WANING INTO TONIGHT AND EFFECTIVE
SHEAR ALSO WEAKENS AS THE UPPER LOW APPROACHES AND THE SPEED
SHEAR LESSENS. THIS WILL LARGELY IF NOT COMPLETELY END ANY
SEVERE RISK BY MIDNIGHT WITH THE CONCERNS TRANSITIONING TO
HYDROLOGY AND MONITORING FOR FLASH FLOODING.
ON THIS FRONT, THE NAEFS AND ECMWF 850MB SPECIFIC HUMIDITY
PERCENTILES REMAIN ABOVE SEASONAL LEVELS TONIGHT AT BETWEEN THE 90TH
AND 97.5TH PERCENTILE WITH BETWEEN AROUND 1.5 INCHES OVER SOUTHERN
IOWA TO AROUND 1 INCH OVER NORTHERN IOWA. WARM CLOUD DEPTHS DO
INCREASE UP TO 3500M AND 850-300MB WINDS SLOW DOWN TO BETWEEN 10 AND
20 KNOTS THIS EVENING THROUGH TUESDAY MORNING. THESE POINT TO A
FAVORABLE SETUP FOR EFFICIENT RAINFALL PROCESSES AND/OR PROLONGED
RESIDENCE TIME OF HEAVY RAINFALL. 24 HOUR RAINFALL FROM NOW THROUGH
MIDDAY TUESDAY FROM THE NATIONAL BLEND OF MODELS SHOWS THE
INTERQUARTILE RANGE OF ADDITIONAL RAINFALL BETWEEN 0.75 INCHES TO
1.75 INCHES AT THE LOWER END (25TH PERCENTILE) TO 2 TO 3 INCHES AT
THE UPPER END (75TH PERCENTILE). DETERMINISTIC MODELS SHOW THE
HIGHEST QPF VALUES OVER SOUTHERN INTO PERHAPS PARTS OF CENTRAL IOWA
OF 3 TO 6 INCHES OVER THE NEXT 24 HOURS. PAST TWO RUNS OF THE HREF
LOCALIZED PROBABILITY MATCHED MEAN SHOW 1.5 TO 3 INCHES WITH MAX
VALUES OF 3 TO 5 INCHES OVER ROUGHLY THE SAME AREA. WHILE IT'S NOT
POSSIBLE TO PINPOINT THE MAXIMUMS, CURRENT FORECAST ACROSS MOST OF
OUR FORECAST AREA IS 1.5 TO 3 INCHES.
RAINFALL SINCE LAST NIGHT HAS AVERAGED GENERALLY FROM HALF AN INCH
TO AN INCH WITH THE HIGHEST AMOUNTS ALONG OUR SOUTHERN TIER OF
COUNTIES AND THEN ALONG AND WEST OF HIGHWAY 169 WITH AMOUNTS OVER AN
INCH FARTHER INTO FAR WESTERN IOWA. LARGER RIVERS HAVE SHOWN LITTLE
IF ANY RESPONSES WITH RESPONSES ON SMALLER STREAMS GENERALLY MINOR.
SO, OVERALL THE RAINFALL SO FAR HASN'T GREATLY CHANGED THE
ANTECEDENT DRY CONDITIONS. USGS STREAMFLOW IS SHOWING BELOW NORMAL
OVER THE SOUTHERN IOWA BASINS WITH A MIXTURE OF NORMAL TO BELOW
NORMAL STREAMFLOW OVER CENTRAL AND NORTHERN IOWA. AS FOR FLASH FLOOD
GUIDANCE (FFG), 1 HOUR FFG VALUES RANGE FROM 1.75 INCHES OVER
NORTHERN IOWA TO AROUND 2.5 INCHES OVER SOUTHERN IOWA WITH 6 HOUR
FFG VALUES RANGING FROM 2.75 INCHES OVER NORTHERN IOWA TO AROUND 4
INCHES OVER SOUTHERN IOWA. FLASH FLOODING CONCERNS CONTINUE TO BE
HIGHEST OVER URBAN CENTERS, INCLUDING THE DES MOINES METRO. IF
RAINFALL OF A FEW TO SEVERAL INCHES FALLS OVER A GIVEN BASIN IN A
SHORT PERIOD OF TIME, THIS COULD CAUSE FLASH FLOODING ISSUES AND
URBAN STREAM RISES. AS FOR RIVER RESPONSES, LATEST QPF ENSEMBLE
HYDROGRAPHS BASED ON BEST ESTIMATE RAINFALL AND EXPERIMENTAL
HYDROLOGIC ENSEMBLE FORECASTING SERVICE (HEFS) AT 50% OR EVEN 30%
CHANCE OF EXCEEDANCE SHOW WITHIN BANK RISES. THEREFORE, THAT IS THE
OVERALL EXPECTATION ON GAGED STREAMS AND RIVERS THAT RIVER FLOODING
WOULD BE ISOLATED AT WORST.
THE INTENSITY OF RAINFALL WILL LESSEN THROUGH THE DAY TUESDAY WITH
SCATTERED SHOWERS AND STORMS LIFTING LARGELY NORTHEAST AND NORTH
THROUGH THE DAY AS THE UPPER LOW MOVES OVER THE STATE. IT WILL BE A
CLOUDY, CHILLY, AND BREEZY DAY OTHERWISE. THIS UPPER LOW AND
LINGERING FORCING WILL KEEP A GOOD DEAL OF CLOUDS OVER A BIG PART OF
THE STATE WITH SCATTERED TO SPOTTY SHOWERS OVER NORTHERN INTO
PERHAPS CENTRAL IOWA WEDNESDAY INTO THURSDAY WITH COVERAGE
DECREASING THROUGH THIS PERIOD. CONDITIONS WILL REMAIN COOL WITH
HIGHS IN THE 50S TO LOW 60S ON THESE DAYS WITH WARM CONDITIONS BY
FRIDAY. A SHORTWAVE TROUGH WILL APPROACH FROM THE NORTHWEST ON
FRIDAY WITH SHOWER AND STORM CHANCES RETURNING TO AT LEAST WESTERN
IOWA BY FRIDAY NIGHT INTO SATURDAY.
AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 654 AM CDT TUE MAY 20 2025
IFR/LIFR CONDITIONS REMAIN ACROSS THE MAJORITY OF TERMINALS THIS
MORNING, AND WILL LARGELY CONTINUE AS LOW STRATUS PASSES
OVERHEAD, DESPITE BRIEF PERIODS OF CLEARING SKIES. VISIBILITIES
WILL ALSO REMAIN LOWER AT TIMES GIVEN THE RECENT RAINFALL, WITH
ADDITIONAL SHOWERS LARGELY EXPECTED THIS MORNING YET ACROSS
MAINLY THE NORTHERN TERMINALS. A LOW CHANCE FOR THUNDERSTORMS IS
POSSIBLE LATE MORNING THROUGH THE AFTERNOON NEAR KOTM, BUT
TRENDS GENERALLY KEEP THIS ACTIVITY FURTHER EAST BUT WILL BE
MINITORED CLOSELY. FOR NOW HOWEVER, PROB30 MENTIONS AT THE
TERMINAL AT THIS TIME AND WILL BE UPDATED AS NEEDED. WINDS WILL
BE BREEZY, ESPECIALLY AT THE NORTHEASTERN PORTION OF THE STATE
THIS MORNING WITH GUSTS UP TO 30-35 KNOTS OUT OF THE
EAST/SOUTHEAST, DECREASING GRADUALLY THROUGH THE DAY.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...BURY
DISCUSSION...ANSORGE
AVIATION...BURY
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