740
FXUS63 KDMX 191153
AFDDMX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
653 AM CDT MON MAY 19 2025
...UPDATED FOR THE 12Z AVIATION DISCUSSION...
KEY MESSAGES
- SHOWER AND STORM CHANCES REMAIN THIS MORNING, WITH GUSTY WINDS
AND HAIL THE MAIN THREATS SOUTHWEST.
- STRONG TO SEVERE STORMS ARE FORECAST THIS AFTERNOON INTO
MONDAY EVENING WITH THE HIGHEST RISK OVER SOUTHWEST INTO SOUTH
CENTRAL IOWA. THE MAIN HAZARD AGAIN IS LARGE HAIL WITH GUSTY
WINDS A SECONDARY HAZARD. A NON-ZERO TORNADO RISK IS ALSO
POSSIBLE.
- WIDESPREAD RAINFALL FORECAST WITH TOTALS FROM TONIGHT THROUGH
WEDNESDAY RANGING FROM 1 INCH OVER NORTHERN IOWA TO 3 INCHES OVER
PARTS OF SOUTHERN IOWA. LOCALLY HIGHER AMOUNTS ARE EXPECTED,
PARTICULARLY SOUTH OF I-80. MAINLY WITHIN RIVER BANK RISES ARE
EXPECTED. LOCALIZED FLASH FLOODING POTENTIAL HIGHEST OVER URBAN
AREAS FROM MONDAY NIGHT INTO EARLY TUESDAY.
- BREEZY TO WINDY TONIGHT INTO TUESDAY
UPDATE
ISSUED AT 424 AM CDT MON MAY 19 2025
THE ACTIVE WEATHER PATTERN HAS BEGUN OVER THE REGION AS SHOWERS AND
STORMS HAVE BEEN OCCURRING LARGELY OVER THE WESTERN AND
SOUTHERN PORTIONS OF IOWA THIS MORNING. THIS ACTIVITY WAS
DELAYED INITIALLY AS DRY AIR OVERHEAD LIMITED FALLING RAIN FROM
REACHING THE GROUND, BUT THE COLUMN GRADUALLY SATURATED THROUGH
THE EARLY MORNING HOURS. SO FAR, SEVERE POTENTIAL HAS BEEN QUITE
MUTED OVER MUCH OF THE STATE AS SURFACE ANALYSIS DEPICTS ALMOST
NO INSTABILITY ACROSS MUCH OF THE REGION, ALONG WITH NO NOTABLE
SHEAR, WHICH HAS LARGELY RESULTED IN STRATIFORM PRECIPITATION
AND LITTLE TO NO LIGHTNING IN THESE AREAS. SURFACE ANALYSIS
DEPICTS THE CENTER OF THE SURFACE LOW GENERALLY OVER WESTERN
NEBRASKA/KANSAS EARLY THIS MORNING, WITH AN ASSOCIATED WARM
FRONT DRAPED ALONG NORTHERN MISSOURI INTO FAR SOUTHWEST IOWA.
ALONG AND JUST SOUTH OF THE WARM FRONT, AREAS OF SCATTERED
CONVECTION ARE ONGOING, LATCHING ON TO THE 500-1000 J/KG OF
MUCAPE AND SHEAR VALUES AROUND 30-40 KNOTS, PAIRED WITH HIGHER
MOISTURE AVAILABILITY AS DEWPOINTS SIT IN THE UPPER 50S TO LOW
60S. FURTHER WEST INTO EASTERN NEBRASKA, DRY AIR JUST AHEAD OF A
LINE OF CONVECTION WITH GRAVITY WAVE INTERACTIONS HAS BEEN
LEADING TO ELEVATED GUSTS UP TO 40-45+ MPH IN THE AREA WHICH
HAVE BEEN FAIRLY CONSISTENT OVER THE PAST FEW HOURS. AS THIS
INITIAL WAVE CONTINUES TO TRACK NORTHEAST THROUGH ABOUT MID-
MORNING, SUB-SEVERE WINDS MAY CONTINUE TO BE A CONCERN MAINLY
OVER PORTIONS OF WESTERN IOWA, BUT OVERALL CONVECTION SHOULD
REMAIN LARGELY ELEVATED NORTH OF THE WARM FRONT AS IT REMAINS
OVER NORTHERN MISSOURI.
IT IS STILL EXPECTED THAT CONDITIONS DRY OUT FOR A LITTLE WHILE
LATER THIS MORNING, AS THE INITIAL WAVE MOVES OUT OF THE AREA,
WITH CAM GUIDANCE SHOWING SOME SPOTTY SHOWERS AT MOST. QUESTIONS
ARISE INTO THE AFTERNOON TIMEFRAME, AS CLOUD COVER POTENTIAL
WILL REMAIN CRUCIAL IN DETERMINING HOW THE SEVERE WEATHER RISK
ENDS UP PLAYING OUT. LATEST HRRR GUIDANCE GENERALLY KEEPS
WIDESPREAD STRATUS ACROSS THE STATE THROUGHOUT THE DAY, WHICH
WOULD LIMIT CONVECTION FIRING OFF THIS AFTERNOON TO EVENING FROM
BEING SURFACE-BASED AND MORE OF ELEVATED SETUP WITH WIND AND
HAIL THE MAIN THREATS. THE RAP HOWEVER SUGGESTS THAT CLEARING IS
POSSIBLE LATER THIS MORNING INTO THE AFTERNOON, WHICH WOULD
LIKELY ERODE ANY CAPPING OVERHEAD AND LEAD TO AN INCREASING
POTENTIAL FOR SURFACE-BASED CONVECTION INTO THE
AFTERNOON/EVENING. LOOKING BACK AT CURRENT CONDITIONS, CLEARING
IS STARTING TO OCCUR OVER EASTERN KANSAS AND NEBRASKA AS NOTED
IN SATELLITE IMAGERY, SO THE POTENTIAL CERTAINLY IS THERE FOR IT
TO EXTEND INTO SOUTHERN IOWA, WHERE THE UPPER 50 TO LOW 60S
DEWPOINTS WILL BE LOCATED, ALONG WITH FAVORABLE INSTABILITY AND
SHEAR PARAMETERS OVER THE AREA THAT COULD LEAD TO HAIL, WIND,
AND EVEN THE POTENTIAL FOR A FEW TORNADOES. A VERY CLOSE EYE
WILL REMAIN ON HOW CONDITIONS EVOLVE THROUGH THE REST OF THE
MORNING AND INTO THE AFTERNOON. THE SLIGHT RISK OVER THE
SOUTHERN/WESTERN PARTS OF IOWA REMAIN REASONABLE GIVEN THIS
INFORMATION, WITH THE ENHANCED RISK JUST TOUCHING OUR SOUTHERN
BORDER WHERE THE WARM FRONT IS EXPECTED TO GENERALLY BE LOCATED.
BREEZY SYNOPTIC WINDS ARE STILL EXPECTED THROUGHOUT THE DAY AS
THE LOW PRESSURE SYSTEM APPROACHES THE STATE, WITH GUSTS UP TO
30-40+ MPH EXPECTED. HIGHER GUSTS WITH AFTERNOON TO EVENING
CONVECTION IN RELATION TO GRAVITY WAVE INTERACTIONS PER GUIDANCE
SUCH AS THE HRRR LOOKS TO FURTHER ENHANCE WIND GUST POTENTIAL
OVER EAST/NORTHEAST IOWA, WITH GUSTS UP TO 50+ MPH.
ON THE HYDRO SIDE OF THINGS, LITTLE CHANGES HAVE OCCURRED, AS
THE BULK OF HEAVY PRECIPITATION IS EXPECTED TO OCCUR THIS
EVENING AND ESPECIALLY THROUGHOUT TUESDAY AS THE LOW PRESSURE
MOVES DIRECTLY ACROSS THE STATE. PWAT VALUES AROUND 1-1.5 INCHES
ARE STILL COMMON OVER THE AREA, WITH HIGHEST RAINFALL TOTALS OF
2-3 INCHES EXPECTED ACROSS THE SOUTHEAST, WITH 1.5-2.5 INCHES
GENERALLY ACROSS THE REST OF THE STATE. HEFS GUIDANCE IN
ASSESSING IMPACTS TO RIVERS LOOKS TO GENERALLY INDICATE LITTLE
IF ANY CONCERN FOR SITES TO REACH ACTION STAGE, UNTIL 10%
PROBABILITIES (WORST CASE) ARE CONSIDERED THAT WOULD ALLOW FOR
SITES ACROSS CENTRAL INTO NORTHERN IOWA TO REACH ACTION STAGE.
THEREFORE, LOW CONCERNS ARE IN PLACE FOR ANY MAJOR IMPACTS TO
RIVERS OUTSIDE OF NOTABLE RISES BUT STILL REMAINING WITHIN
BANKFUL. FLASH FLOODING CONCERNS WOULD GENERALLY BE LIMITED TO
URBAN AREAS AS WELL.
DISCUSSION
ISSUED AT 257 PM CDT SUN MAY 18 2025
EARLY AFTERNOON GOES-EAST VISIBLE SATELLITE IMAGERY SHOWS JUST AREAS
OF HIGH CLOUDS OVER THE STATE AS WEAK RIDGING PUSHES INTO THE
REGION. THE REST OF THE DAYTIME WILL BE BENIGN AS HIGH CLOUDS
CONTINUE TO ARRIVE, BUT A MORE ACTIVE PATTERN IS STILL FORECAST TO
TAKE SHAPE FROM TONIGHT INTO THE FIRST HALF OF THE UPCOMING WEEK.
THIS MORE ACTIVE PATTERN WILL BE DUE TO A MORE PRONOUNCED TROUGH
AXIS OVER THE WESTERN US THAT IS NEARING THE ROCKIES THIS AFTERNOON.
ONE SHORTWAVE TROUGH IS LIFTING OUT OF THE BASE OF THE TROUGH OVER
THE FOUR CORNERS REGION WHILE ANOTHER SHORTWAVE IS COMING DOWN EAST
OF THE SPINE OF THE CASCADES. THESE TWO SHORTWAVES STILL LOOK TO
PIVOT AROUND ONE ANOTHER BEFORE PHASING INTO ONE UPPER LOW TOWARD
TUESDAY BEFORE SLOWLY SLIDING ACROSS THE REGION AT MIDWEEK. AS I DID
YESTERDAY AFTERNOON, LET'S FIRST DISCUSS THE CONVECTIVE CONCERNS
FOLLOWED BY THE HYDROLOGY HAZARDS.
CLOUDS WILL THICKEN INTO TONIGHT AND LOWER AS THE FIRST SHORTWAVE
LIFTS TOWARDS THE REGION WITH A BROAD SURFACE LOW PRESSURE AROUND
THE MIDDLE OR UPPER 990MBS MOVING OVER CENTRAL NEBRASKA AND KANSAS.
A STRONG SLUG OF LOW LEVEL THETA-E ADVECTION AND QG CONVERGENCE WILL
MOVE OVER IOWA AND NORTH OF A WARM FRONT STRETCHED FROM
KANSAS/NEBRASKA INTO MISSOURI TONIGHT. MUCH OF TODAY'S GUIDANCE (THE
LATEST OF EITHER THE 0Z, 6Z, OR 12Z CONVECTIVE ALLOWING MODELS
(CAMS)) CONTINUES TO FOCUS THE STRONGEST CONVECTION TONIGHT OVER
MISSOURI. THAT'S NOT TO SAY WE WON'T SEE ANY SEVERE RISK OR
RAINFALL, BUT THE HIGHER CHANCE OF THE SEVERE HAZARDS LOOKS TO BE
OVER MISSOURI AS A MESOSCALE CONVECTIVE SYSTEM (MCS) MOVES THROUGH
SOME PORTION OF THAT STATE. MODELS DO SHOW VARYING DEGREES OF SHOWER
AND STORM COVERAGE OVER IOWA STARTING CLOSER TO MID-EVENING OVER OUR
SOUTHWESTERN FORECAST AREA (ATLANTIC, CRESTON, BEDFORD) THAT SPREADS
NORTHEASTWARD OVER ALL OF CENTRAL IOWA OVERNIGHT AND IS LARGELY EAST
OF THE FORECAST AREA (WATERLOO TO OTTUMWA) BY DAYBREAK TUESDAY. WITH
THE WARM FRONT REMAINING SOUTH OF THE STATE, STORMS ARE EXPECTED TO
REMAIN ELEVATED WITH A GOOD AMOUNT OF MUCAPE ABOVE THE INVERSION.
WHILE DEEP LAYER SHEAR LOOKS IMPRESSIVE, THE EFFECTIVE LAYER IS LESS
SO AND THUS THE FOCUS FOR SEVERE WEATHER LATER THIS EVENING INTO THE
EARLY MORNING HOURS OF MONDAY WILL BE A LARGE HAIL RISK OVER
SOUTHWEST INTO PORTIONS OF SOUTH CENTRAL IOWA. THE OUTLIER, UNLIKELY
CASE WOULD BE IF THE 6Z/12Z NAM CARRIES THE MCS INTO SOME PORTION OF
IOWA, WHICH WOULD BRING THE POTENTIAL OF STRONG WINDS INTO THE
SOUTHERN PORTION OF THE STATE. BUT AGAIN, THIS SEEMS UNLIKELY AT
THIS TIME.
AS THESE STORMS MOVE EAST EARLY IN THE DAYLIGHT HOURS OF MONDAY,
THERE SHOULD BE A RELATIVE LULL IN THE HEAVIER, STRONGER ACTIVITY.
HOWEVER, FORECAST SOUNDINGS AND HREF LOW CLOUD WOULD POINT TOWARD
LIMITED SUNSHINE AND THERE MAY BE ENOUGH DEPTH OF SATURATION FOR
DRIZZLE OR MIST. HOWEVER, FOR SIMPLICITY HAVE NOT INCLUDED THAT IN
THE FORECAST. AS MENTIONED YESTERDAY, WILL BE WATCHING THE WARM
FRONT'S POSITION, WHICH IS EXPECTED TO BE OVER NORTHERN MISSOURI AND
COULD SNEAK CLOSE TO THE IOWA STATE LINE. THIS WILL DEPEND ON THE
OVERNIGHT TONIGHT'S CONVECTION AND WHERE THE EFFECTIVE WARM FRONT
ENDS UP. THERE ARE A FEW MODELS THAT SHOW THE WARM FRONT SNEAKING
INTO SOUTHWEST OR SOUTH CENTRAL IOWA WITH THE MOST NOTABLE BEING THE
18/0Z C-SHIELD, WHICH THEN PROJECTS A MORE ACTIVE AFTERNOON/EVENING
OVER IOWA. HOWEVER, THIS IS AN OUTLIER AND WITH THE WARM FRONT
EXPECTED TO STAY LARGELY SOUTH OF THE MISSOURI BORDER, SURFACE BASED
HAZARDS ARE A MUCH LESSER CONCERN. DEPENDING ON THE CLOSENESS OF THE
WARM FRONT, WE MAY GET STORMS THAT FORM ON THE WARM FRONT OVER
NORTHERN MISSOURI THAT CROSS INTO OUR SOUTHERN ROW OF COUNTIES WITH
LARGE HAIL AND PERHAPS GUSTY WINDS. MUCAPE VALUES WILL BE HIGHEST
OVER OUR SOUTHWESTERN INTO PARTS OF OUR SOUTH CENTRAL FORECAST AREA
(ROUGHLY A DENISON TO LAMONI LINE), THOUGH EFFECTIVE SHEAR IS MUCH
LESS THAN THE DEEP LAYER SHEAR AGAIN SO THINKING IS LARGE HAIL WILL
BE THE PRIMARY RISK HERE WITH PERHAPS GUSTY WINDS A SECONDARY
THREAT. THE MAIN TIME AND AREA OF CONCERN FOR THESE STORMS WOULD BE
FROM LATE MONDAY AFTERNOON INTO MONDAY EVENING WITH THE SEVERE RISK
WANING AFTER MIDNIGHT. HOWEVER, SHOWERS AND STORMS WILL PERSIST
OVERNIGHT MONDAY INTO THE DAY TUESDAY.
AS FOR HYDROLOGY HAZARDS, NOTHING HAS CHANGED WITH ANTECEDENT
CONDITIONS SINCE THIS TIME YESTERDAY SO I REFER THE INTERESTED
READER TO LOOK AT THE FORECAST DISCUSSION FROM 228PM SATURDAY FOR
THOSE DETAILS. PRECIPITABLE WATER VALUES WILL TREND UP INTO TONIGHT
AND THEN REMAIN BETWEEN 1.25 AND 1.5 INCHES OVER SOUTHERN IOWA AND 1
INCH OVER NORTHERN IOWA FROM MONDAY THROUGH EARLY TUESDAY. THESE
VALUES ARE SEASONAL TO SEASONALLY HIGH AND CONFIRMED BY THE
CONTINUED 90TH TO 97.5TH PERCENTILE SHOWN IN THE NAEFS AND ECMWF
850MB SPECIFIC HUMIDITY FIELD. THE WARM CLOUD DEPTHS DON'T LOOK TOO
NOTABLE UNTIL MONDAY INTO MONDAY NIGHT WHEN THEY EXCEED 3000 TO
3500M OVER SOUTHERN IOWA. SO FOR TONIGHT INTO EARLY MONDAY, OUTSIDE
OF THE 6Z/12Z NAM THAT BRING THE MCS AND ITS HIGHER QPF AMOUNTS INTO
SOME PORTION OF OUR FORECAST AREA, RAINFALL AMOUNTS WILL GENERALLY
BE UNDER A HALF AN INCH OVER WESTERN INTO SOUTH CENTRAL IOWA.
THEREFORE, FLASH FLOODING AND RIVER FLOODING RISK REMAINS NEAR ZERO
FOR THIS TIME PERIOD.
THIS RISK WILL CHANGE AS WE HEAD INTO MONDAY NIGHT INTO EARLY
TUESDAY WHEN RATES ARE EXPECTED TO BE HIGHER AND STORM MOTIONS
SHOULD SLOW AS THE UPPER LOW BEGINS TO PUSH TOWARD THE STATE. THE
LATEST ECMWF EXTREME FORECAST INDEX HAS INCREASED TO 80 TO 90% OF
ITS ENSEMBLE MEMBERS POINTING TO AN ANOMALOUS, BUT NOT EXTREME EVENT
RELATIVE TO ITS MODEL CLIMATE AND THAT THE EVENT WILL OUTPERFORM THE
ENSEMBLE MEAN. FURTHER, THE OVERNIGHT'S FORECAST AS WELL AS INITIAL
NATIONAL BLEND OF MODELS (NBM) QPF IS NEARING DAILY RECORD VALUES IN
A FEW PLACES. DURING THIS PERIOD, AN ADDITIONAL THREE QUARTER OF AN
INCH TO AN INCH OVER NORTHERN IOWA TO AN ADDITIONAL 2 TO 3 INCHES OF
RAIN OVER SOUTHERN IOWA ARE FORECAST. DETERMINISTIC MODELS AND
LATEST HREF LOCALIZED PROBABILITY MATCHED MEAN DO SHOW BULLSEYES OF
HIGHER VALUES, LARGELY IN VARYING PLACES OVER SOUTHERN IOWA, WITH
THE MAGNITUDE BEING 3 TO 5 INCHES. WPC HAS MAINTAINED THEIR SLIGHT
RISKS OF EXCESSIVE RAINFALL OVER SOME PORTION OF THE STATE FROM
TONIGHT THROUGH EARLY TUESDAY. WHILE FLASH FLOOD GUIDANCE REMAINS
HIGH, LOCALIZED FLASH FLOODING OVER AN URBAN CENTER CANNOT BE RULED
OUT. HOWEVER, THERE ARE CONCERNS THAT THE QPF MAY BE OVERDONE IF THE
CONVECTION STAYS LARGELY SOUTH OF THE STATE WITH RATES AND AMOUNTS
PERHAPS LESSER ON THE COOL SIDE OF THE WARM FRONT.
TODAY'S LATEST QPF ENSEMBLE HYDROGRAPHS AND EXPERIMENTAL HYDROLOGIC
ENSEMBLE FORECASTING SERVICE (HEFS) SHOW AN INCREASE IN THE NUMBER
OF FORECAST POINTS THAT WOULD REACH OR EXCEED ACTION STAGE. HOWEVER,
THE QPF ENSEMBLE HYDROGRAPHS ASSUME 95TH PERCENTILE RAINFALL;
HOWEVER, WHEN EXAMINING THE EXPECTED RAINFALL ONLY ONE SITE REACHES
ACTION STAGE. THE SAME IS TRUE WITH THE HEFS AS YOU NEED TO REACH
THE 10% CHANCE OF EXCEEDANCE TO GET TO ACTION OR MINOR FLOOD STAGE.
THIS COUPLED WITH NO HIGHER THAN NORMAL STREAMFLOW AND LARGELY BELOW
NORMAL STREAMFLOW WHERE THE HIGHEST RAINFALL IS FORECAST TO FALL,
THERE IS CAPACITY WITHIN THE GAGES RIVERS AND STREAMS TO HOLD THIS
RAINFALL TO WITHIN BANK RISES.
SHOWERS ARE FORECAST TO BECOME MORE SCATTERED ON WEDNESDAY AS
LINGERING LIFT FROM THE UPPER LOW SLIDES OVER THE AREA. IT WILL ALSO
BE COOL ON WEDNESDAY WITH HIGHS MAINLY IN THE 50S AND WHILE IT DOES
'WARM' INTO THE 60S ON THURSDAY, THIS TOO IS COOL FOR THIS TIME OF
YEAR. WHILE THE INITIAL NBM HAS DRIED OUT THE FORECAST ON THURSDAY,
THERE IS LINGERING MID-LEVEL QG CONVERGENCE THAT KEEPS THE SCATTERED
SHOWERS OVER PORTIONS OF THE STATE IN THE DETERMINISTIC MODELS SO
WILL HAVE TO ASSESS THOSE TRENDS IN THE COMING DAYS. A SHORTWAVE
TROUGH WILL APPROACH THE AREA BY LATER FRIDAY AND COULD BRING
ADDITIONAL SHOWER AND STORM CHANCES BACK TO IOWA BY FRIDAY NIGHT
INTO SATURDAY.
AVIATION /12Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 653 AM CDT MON MAY 19 2025
WIDESPREAD SHOWERS WITH EMBEDDED THUNDERSTORMS ARE ONGOING
ACROSS MUCH OF THE STATE THIS MORNING, AND ARE EXPECTED TO
CONTINUE AT TIMES THROUGH THE REMAINDER OF THE MORNING HOURS,
WHICH WILL COME WITH PERIODS OF VSBY AND CEILING RESTRICTIONS
INTO MVFR/IFR CATEGORIES. DRYING CONDITIONS ARE EXPECTED LATE
MORNING INTO THE AFTERNOON, BEFORE SHOWER AND STORM CHANCES
RETURN MAINLY AFTER 20Z, WITH THE HIGHER PROBABILITIES OF
OCCURRENCE OVER THE SOUTHERN PART OF THE STATE. DETAILS ON
EXACT TIMING AND PLACEMENT ARE MORE UNCERTAIN, AS IT WILL DEPEND
ON HOW CONDITIONS EVOLVE THIS MORNING THROUGH THE AFTERNOON, SO
REFINEMENTS WILL BE REQUIRED THROUGHOUT TODAY. OTHERWISE WINDS
WILL BE BREEZY OUT OF THE EAST/SOUTHEAST WITH GUSTS INCREASING
TO 30-35+ MPH ACROSS MUCH OF THE STATE AND ESPECIALLY OVER
NORTHERN IOWA LATE THIS MORNING THROUGH THE AFTERNOON BEFORE
DECREASING SLIGHTLY INTO TUESDAY.
DMX WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...BURY
DISCUSSION...ANSORGE
AVIATION...BURY
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