Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 262341
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
641 PM CDT TUE AUG 26 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 329 PM CDT TUE AUG 26 2014

STILL LOOKS LIKE DECENT RAIN/THUNDERSTORM CHANCES TONIGHT...ALTHOUGH
TIMING LOOKS A BIT LATER THAN IN PREVIOUS FORECASTS. MAIN FOCUS
SHOULD BE LATER TONIGHT AS MOISTURE TRANSPORT ORIENTS INTO THE
WESTERN/CENTRAL PORTIONS OF THE CWA. MAIN PUSH OF MOISTURE NOT
EXPECTED UNTIL LATE TONIGHT...SO DID DECREASE POPS ACROSS THE CWA
THIS EVENING KEEPING THE HIGHER POPS UNTIL AFTER 06Z. STORM MOTION
TO BE SLOWER 5 TO 15 KTS AND PARALLEL TO THE BOUNDARY...SO
POSSIBILITY OF TRAINING/SLOW MOVING STORMS IS HIGH. PWATS CONTINUE
TO BE IN THE 1.75 INCH RANGE...AND A RELATIVELY HIGH FZ LVL SO
EFFICIENT RAIN PRODUCTION POSSIBLE. BEST CHANCES FOR HEAVIER
RAINFALL OVERNIGHT IN THE WEST CENTRAL PORTIONS OF THE CWA. THIS IS
THE SAME AREA THAT SAW SOME HEAVIER RAINFALL MONDAY NIGHT...SO WILL
GO AHEAD AND ISSUE A FLASH FLOOD WATCH FOR A FEW COUNTIES ACROSS THE
WEST WHERE THE HEAVIER RAINFALL COULD FALL OVER THE AREAS THAT ARE
NEAR SATURATION FROM PREVIOUS HEAVY RAINFALL.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 329 PM CDT TUE AUG 26 2014

MAIN CONCERN IN THE FIRST 2 TO 3 DAYS WILL BE PERIOD FROM WEDNESDAY
NIGHT THROUGH THURSDAY AFTERNOON...THEN AGAIN FRIDAY NIGHT THROUGH
SATURDAY BEFORE A BREAK OCCURS FOR SATURDAY AFTERNOON AND A PORTION
OF SUNDAY. PREDOMINANT UPPER LEVEL PATTERN TO PERSIST MOST OF THE
EXTENDED PERIOD WITH SOUTHWEST FLOW AND HIGHER THAN NORMAL MOISTURE
FOR THIS TIME OF YEAR. H850 SUBJECTIVE ANALYSIS THIS MORNING SHOWS
AN UPPER LEVEL AND NEARLY STATIONARY BOUNDARY DRAPED ACROSS LOWER
MICHIGAN WEST TO SOUTHERN IOWA/NORTHERN MO BACK WEST INTO KS AND
COLORADO. A LARGE RIDGE OF HIGH PRESSURE IS SADDLED FROM THE MID
MISSISSIPPI RIVER VALLEY EAST TO NEW ENGLAND...AND A RELATIVE STRONG
WESTERLY FLOW ALOFT CONTINUES OVER THE NORTHERN CONUS WITH A WEAK
TROUGH TO THE WEST. WITHIN THE STAGNANT RIDGE AXIS AND TROUGH TO THE
WEST...SOUTHWEST FLOW AND DEW POINTS OF 15C HAVE POOLED AT H850 AND
WILL CONTINUE TO PERSIST OVER THE NEXT FEW DAYS. AT START OF THE
FORECAST PERIOD 12Z WED...DECAYING MCS SHOULD BE OVER EASTERN
NEBRASKA OR WESTERN IA WITH LESSENING ACTIVITY DURING THE DAYTIME
HOURS...SIMILAR TO TODAY. MODELS GENERALLY IN AGREEMENT WITH BETTER
MOISTURE TRANSPORT THROUGH EARLY WED AS SHOWN BY SUBJECTIVE H850
ANALYSIS HEIGHT FIELD WHICH REMAINS TO THE WEST DUE TO LINGERING
RIDGE AXIS. MORNING ANALYSIS HAS PREFERRED LIFT/TRANSPORT OVER
CENTRAL AND WESTERN NEBRASKA AT THIS TIME...WITH GRADUAL SHIFT EAST
EXPECTED THROUGH 12Z WED. FOR THE REMAINDER OF WED SOME LINGERING
SHOWERS AND STORMS MAY OCCUR...BUT COVERAGE AND STRENGTH SHOULD
REMAIN MODEST AT BEST WITH EITHER LINGERING CLOUD COVER FROM THE
OVERNIGHT ACTIVITY OR SOME PARTIAL SUNSHINE AS DECAYING CONVECTIVE
SYSTEM WORKS EAST. HIGHS ONCE AGAIN WILL BE SOMEWHAT HELD BACK BY
EXPECTATION OF CLOUDS AND SOME PRECIPITATION. MODELS STILL SHOW BEST
FORCING ARRIVING FOR LATER WEDNESDAY EVENING...ESPECIALLY AFTER 03Z
WHEN H500 TROUGH BEGINS TO MOVE EAST OUT OF THE SOUTHWEST. BY THEN
H850 MOISTURE CHANNEL...DYNAMIC LIFT AND MOISTURE TRANSPORT WILL BE
MAXIMIZED OVER WESTERN AND NORTHERN IOWA. LOOKING AT MODEL
PARAMETERS...GFS AND EURO... GFS PRECIPITABLE WATER WILL INCREASE TO
OVER 2 INCHES BY MID AFTERNOON WEDNESDAY THROUGH 18Z THURSDAY ACROSS
THE NORTH. MEANWHILE WARM CLOUD DEPTHS AGAIN PROMOTE EFFICIENT
RAINFALL WITH VALUES FROM 12-13KFT ACROSS THE NORTH. BUFR SOUNDINGS
ALSO INDICATIVE SHOWING LONG THIN CAPE AND SATURATED THROUGH MOST OF
COLUMN. WITH LIKELIHOOD OF AN MCS DEVELOPING WEST OF THE AREA AND
THEN MOVING INTO AND ACROSS THE H850 WARM FRONTAL ZONE WEDNESDAY
EVENING OVER NORTHERN IOWA...RAINFALL TOTALS OF 2 TO 3 INCHES WITH
LOCALLY HIGHER AMOUNTS MAY OCCUR ACROSS THE NORTHWEST AND NORTH BY
00Z FRIDAY. FOR NOW WILL NOT GO WITH HEADLINES...SINCE ANY CHANGE IN
AREA OF EXPECTED HEAVY RAINFALL WOULD ALTER COVERAGE. MORE
IMPORTANTLY...PAST 10 DAYS RAINFALL TOTALS...QPE FROM Q3 SHOWS THE
NORTHWEST HAS A SLIGHTLY GREATER ABILITY TO TAKE HEAVY RAINFALL AT
THIS TIME. HEADLINES MAY BE NEEDED FOR THIS AREA AND SHOULD HAVE A
BETTER IDEA OF EXTENT BY TOMORROW. THROUGH THE WEEKEND...LITTLE
CHANGE EXPECTED INTO THE WEEKEND. TIMING OF WAVES AND EXITING OF
MAIN UPPER LEVEL WAVE STILL IN QUESTION...BUT CONSENSUS POINTS TO
SATURDAY MORNING OR AFTERNOON. THIS WILL RESULT IN A BREAK ON SUNDAY
WITH ANOTHER SET OF WAVES ARRIVING BY EARLY MONDAY THROUGH TUESDAY
WITH MORE RAINFALL EXPECTED AS THE OVERALL PATTERN PERSISTS. HIGHS
THROUGH THE PERIOD WILL CONTINUE IN THE 75 TO 85 RANGE WITH LOWS IN
THE UPPER 50S TO 60S. WITH ZONAL PATTERN STILL FORECAST BEYOND SEVEN
DAYS...LITTLE OVERALL CHANGE IS ANTICIPATED FOR NOW.

&&

.AVIATION...27/00Z
ISSUED AT 637 PM CDT TUE AUG 26 2014

WARM ADVECTION AND THETA-E ADVECTION WILL PERSIST FOR THE DURATION
OF THE FORECAST. CONVECTION IS FORECAST TO DEVELOP
OVERNIGHT...MAINLY IN WESTERN IOWA WITH SOME BLEED-OVER INTO THE
EAST. GENERALLY VFR CONDITIONS ARE EXPECTED DURING THIS
TIMEFRAME...HOWEVER MVFR TO IFR CONDITIONS ARE EXPECTED IN AND
AROUND CONVECTION LATE TONIGHT INTO WEDNESDAY MORNING.

&&

.HYDROLOGY...
ISSUED AT 329 PM CDT TUE AUG 26 2014

SOME HEAVY RAINFALL POTENTIAL EXISTS TONIGHT ACROSS PORTIONS OF THE
WEST CENTRAL CWA THAT ALREADY SAW HEAVIER RAINFALL IN PREVIOUS
NIGHTS. SOME AREAS RECEIVED IN EXCESS OF 2 INCHES OF RAINFALL MONDAY
NIGHT...WITH THE POSSIBILITY OF SLOW MOVING/TRAINING THUNDERSTORMS
LATE TONIGHT HEAVY RAINFALL WILL AGAIN BE POSSIBLE. WIDESPREAD 1
INCH TO 1.5 INCH AMOUNTS ARE POSSIBLE ACROSS THE WEST CENTRAL...WITH
LOCALIZED HIGHER AMOUNTS OF AROUND 3 INCHES POSSIBLE. WITH GROUNDS
SATURATED FROM RECENT RAINFALL...ADDITIONAL HEAVY RAINFALL WILL
CREATE THE POTENTIAL FOR FLASH FLOODING...THUS A FLASH FLOOD WATCH
WILL BE ISSUED FOR THIS AREA LATE TONIGHT INTO WEDNESDAY MORNING.

FLASH FLOOD GUIDANCE IN THESE AREAS AROUND 1.75 INCHES IN ONE HOUR
TO 3 INCHES IN 6 HOURS. POTENTIAL EXISTS FOR WIDESPREAD 1 TO 1.5
INCH AMOUNTS ACROSS THE WEST CENTRAL...WITH LOCALIZED HIGHER AMOUNTS
POSSIBLE.

ANTICIPATION OF MORE WIDESPREAD RAINFALL WEDNESDAY NIGHT THROUGH THURSDAY
MAY LEAD TO LOCALIZED FLASH FLOODING AND POTENTIAL RIVER RISES TO
ABOVE FLOOD STAGE FROM LATER THURSDAY THROUGH THE WEEKEND. WITH
NEAR ZONAL TO SOUTHWESTERLY PATTERN REMAINING IN PLACE...
ADDITIONAL ROUNDS OF MODERATE RAINFALL ARE EXPECTED INTO HOLIDAY
WEEKEND AND EARLY NEXT WEEK WHICH WILL KEEP THE AREA WET ENOUGH TO
MAKE SOME FLASH FLOODING AND RIVER FLOODING CONTINUED POSSIBLE
CONCERNS.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM 1 AM CDT WEDNESDAY THROUGH WEDNESDAY
MORNING FOR AUDUBON-CARROLL-CASS-CRAWFORD.

&&

$$

SHORT TERM...BEERENDS
LONG TERM...REV
AVIATION...COGIL
HYDROLOGY...BEERENDS/REV



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