Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 260440
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1140 PM CDT MON MAY 25 2015

.SHORT TERM /TONIGHT/...
ISSUED AT 304 PM CDT MON MAY 25 2015

FORECAST CHALLENGES FOR THE SHORT TERM PERIOD INCLUDE TIMING AND
LOCATION OF CONVECTION DEVELOPMENT LATER THIS AFTN INTO THIS
EVENING...AS WELL AS CONVECTIVE TRENDS OVERNIGHT.

CONVECTION ACROSS FAR NORTHERN IOWA...FORCED BY ELONGATED VORT MAX
WILL CONTINUE LIFTING NORTHEASTWARD INTO MN/WI. ATTENTION THEN TURNS
UPSTREAM TO KS/NE/MO REGION. CONVECTION HAS BEGUN FIRING IN KS THIS
AFTN...IN A QUITE UNSTABLE AIRMASS. IMPULSE MOVING INTO WRN OKLAHOMA
IS EXPECTED TO PROVIDE REGION OF ASCENT AS IT TRACKS NORTHEASTWARD.
UNSTABLE AIRMASS EXTENDS NORTHEAST INTO SOUTHERN IOWA...WHERE
MUCAPES ARE AS HIGH AS 2000 J/KG PER SPC MESOANALYSIS. THUS
CONVECTION IS EXPECTED TO CONTINUE DEVELOPING NORTHEASTWARD LATER
THIS AFTN INTO THIS EVENING AS THE IMPULSE AND PRECEDING ASCENT
REGION TRACKS NORTHEAST. BUFR FCST SOUNDINGS SHOWING AN ELEVATED
WARM LAYER ACROSS WESTERN AND SOUTHWESTERN IOWA...HOWEVER...WHICH
DECREASES IN TIME THIS EVENING. THUS ORGANIZED CONVECTION
DEVELOPMENT MAY BE DELAYED UNTIL THE WARM LAYER DECREASES
SUFFICIENTLY. ALTHOUGH DEEP LAYER SHEAR IS NOT EXPECTED TO BE
PARTICULARLY IMPRESSIVE...THE COMBINATION OF THE SHEAR VALUES THAT
WILL EXIST...ALONG WITH THE THERMODYNAMIC PROFILE...WOULD SUPPORT
ENOUGH ORGANIZATION TO PROVIDE DAMAGING WINDS AND LARGE HAIL. HEAVY
RAINFALL WOULD ALSO BE POSSIBILITY...BUT DO NOT ANTICIPATE ANY
WIDESPREAD OR SIGNIFICANT FLASH FLOOD THREAT.

SLIGHTLY WEST OF THE AFOREMENTIONED REGION...AND CLOSER TO THE
SURFACE BOUNDARY IN NORTHWEST IOWA...THERE IS ADDITIONAL RISK FOR
CONVECTION DEVELOPMENT. AREA OF STEEP MIDLEVEL RATES HAS BEEN
WORKING NORTHEASTWARD THROUGH KANSAS THIS AFTERNOON AND INTO
SOUTHEASTERN NEBRASKA. AS THOSE STEEP MIDLEVEL LAPSE RATES WORK INTO
WESTERN IOWA THIS EVENING...CONVECTION MAY DEVELOP ACROSS WEST
CENTRAL AND NORTHWESTERN PARTS OF THE STATE...AGAIN CLOSER TO THE
SURFACE BOUNDARY. IF CONVECTION DOES BECOME ESTABLISHED THERE THEN
THERE WILL BE A POTENTIAL FOR TRAINING STORMS AS THE CORFIDI VECTORS
WOULD BE NEARLY PARALLEL TO THE MEAN STORM MOTION...AS THE SURFACE
BOUNDARY MOVES LITTLE IF ANY OVERNIGHT.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 304 PM CDT MON MAY 25 2015

ACTIVE WEATHER PATTERN WILL CONTINUE THROUGH EXTENDED. EXPECT
ONGOING PRECIPITATION TO LINGER THROUGH THE MORNING
HOURS...ESPECIALLY IN THE EAST AS WEAK TROUGH BEGINS TO PUSH EAST
THROUGH IOWA THROUGH THE DAY TUESDAY. BOUNDARY WILL LINGER ACROSS
THE STATE...WHICH MAY ALLOW FOR CONTINUED SHOWERS AND
THUNDERSTORMS THROUGH THE DAY...AGAIN PRIMARILY IN THE CENTRAL AND
EAST. HOWEVER...FEEL WILL SEE SIMILAR SET UP TO TODAY WITH
GENERALLY A BREAK FROM PRECIPITATION CHANCES IN THE LATE MORNING
AND EARLY AFTERNOON AS LLJ DIMINISHES. BOUNDARY WILL GENERALLY BE
ACROSS CENTRAL IOWA BY 00Z WEDNESDAY WHICH MAY BE THE FOCUS FOR
THUNDERSTORM DEVELOPMENT IN THE LATE AFTERNOON. CAPE VALUES WILL
GENERALLY BE NEAR 1000 J/KG WITH GENERALLY WEAK SHEAR...THOUGH
SUFFICIENT ENOUGH TO ALLOW FOR ANY STORMS WHICH DEVELOP TO PERSIST
AND MAY SEE A SEVERE THUNDERSTORM OR TWO. SYSTEM WILL CONTINUE TO
PUSH EASTWARD THROUGH THE EVENING BRINGING AN END TO PRECIPITATION
CHANCES...AND MAY HAVE HELD ONTO PRECIPITATION TOO LONG TUESDAY
NIGHT.

WEDNESDAY WILL BE DRY AS WEAK RIDGE BUILDS ACROSS AREA.
HOWEVER...THIS WILL BE SHORT LIVED AS LARGE UPPER LEVEL LOW
PRESSURE SYSTEM PUSHES EAST ACROSS CANADA...BREAKING RIDGE DOWN
AND BRINING BOUNDARY TO IOWA WHICH WILL BE PRIMARILY WEATHER FOCUS
THROUGH THE END OF THE PERIOD. BOUNDARY WILL BE SLOW
MOVING...FINALLY BEGINNING TO PUSH INTO IOWA LATE FRIDAY.
HOWEVER...AHEAD OF BOUNDARY WILL SEE GOOD SOUTHERLY SURFACE FLOW
AND MOISTURE PUSHING INTO IOWA. THIS WILL HELP TO WARM
TEMPERATURES...BUT ALSO LEAD TO PRECIPITATION CHANCES THROUGH THE
PERIOD...THOUGH DO NOT HAVE HIGH CONFIDENCE WITH TIMING OF
PRECIPITATION TRENDS THROUGH FRIDAY...BUT HAVE KEPT POPS NEAR
GOING. BEST CHANCES FOR WIDESPREAD RAIN WILL COME FRIDAY. GFS
REMAINS LEAST PROGRESSIVE WITH SYSTEM...HANGING BOUNDARY ACROSS
NORTHERN MISSOURI THROUGH SUNDAY...WHILE ECMWF IS PROGRESSIVE.
HOWEVER...GEM HAS BEGUN TO TREND TOWARDS GFS...AND HAVE LEFT
CHANCE POPS INTO LATE SUNDAY. TEMPERATURES WILL AGAIN BE MUCH
COOLER BEHIND BOUNDARY...WITH HIGHS SATURDAY AND SUNDAY EXPECTED
TO BE WELL BELOW NORMAL.

&&

.AVIATION...26/06Z
ISSUED AT 1140 PM CDT MON MAY 25 2015

FIRST ROUND OF THUNDERSTORMS WILL BE OUT OF THE AREA BY 06Z WITH
JUST ISOLD SHRA/TSRA REMAINING. HOWEVER...MORE STORMS ARE ALREADY
FORMING ACROSS MISSOURI AND SHOULD EXPAND UP ACROSS IOWA LATER
TONIGHT...MAINLY AFTER 09Z...AND WILL PRIMARILY AFFECT OTM AND
PROBABLY DSM AND ALO. HAVE INCLUDED TEMPOS FOR MVFR CONDITIONS IN
TSRA AT DSM/OTM...BUT IT IS POSSIBLE THAT BRIEF IFR CONDITIONS MAY
ALSO OCCUR DURING THIS WINDOW. FROM ABOUT MIDDAY TUESDAY ONWARD
THERE MAY STILL BE ISOLD SHRA/TSRA BUT THE PROBABILITY IS
LOWER...AND FORECAST SOUNDINGS INDICATE LOW VFR CIGS AROUND
FL030-045 FOR MUCH OF THE DAY.

&&

.HYDROLOGY...
ISSUED AT 320 AM CDT MON MAY 25 2015

RAIN EXPECTED ONCE AGAIN TODAY...BUT THREAT FOR ANY FLASH FLOODING
REMAINS LOW. RAINFALL RATES EARLY TODAY NOT EXPECTED TO BE HIGH
ENOUGH AND RAINFALL PERSISTENT ENOUGH. LATER TODAY...SCATTERED
NATURE OF STORMS SHOULD NOT LEAD TO ANY WIDESPREAD COVERAGE UNTIL
THE EVENING HOURS. MAIN CONCERNS ARE ADDITIVE EFFECTS OF YESTERDAYS
THROUGH TUESDAYS RAINFALL...AND SUBSEQUENT EVENTS. SOME URBAN
RUNOFF AND PONDING OF WATER MAY BE POSSIBLE WITH STRONGER STORMS.

IN TERMS OF RIVER FLOODING...MINOR TO MODERATE WITHIN-BANK RISES ARE
EXPECTED AT MULTIPLE LOCATIONS ESPECIALLY WITHIN THE MIDDLE TO LOWER
DES MOINES RIVER BASIN...AS WELL AS THE LOWER RACCOON RIVER BASIN.
IF RAINFALL OVER THE NEXT 24-36 HRS COMES IN HEAVIER THAN
EXPECTED...THEN MINOR FLOODING COULD BE EXPECTED AT SOME
LOCATIONS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...ZOGG
LONG TERM...AWB
AVIATION...LEE
HYDROLOGY...ZOGG/REV



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