Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 262344
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
644 PM CDT TUE APR 26 2016

...UPDATED AVIATION DISCUSSION...

.SHORT TERM.../TONIGHT/
ISSUED AT 330 PM CDT TUE APR 26 2016

AREA OF SFC LOW PRESSURE SITUATED ACROSS CENTRAL KS WITH AN
OUTFLOW BOUNDARY FROM MORNING CONVECTION EXTENDING THROUGH
THROUGH ERN KS. AREA OF PRECIPITATION AND MCS THAT MOVED THROUGH
NRN MO THIS MORNING HAS PUSHED ANY CHANCES FOR AFTERNOON STORMS
MUCH FURTHER TO THE SOUTH/WEST TODAY. WINDS HAVE EVEN PUSHED
FURTHER ENE REINFORCING THE DRIER AIR IN THE LOWER LEVELS...AND
CLOUD COVER HAVING KEPT TEMPS DOWN MUCH OF THE DAY. THEREFORE HAVE
PUSHED BACK ONSET OF CHANCES FOR STORMS TO MAINLY THIS EVENING
INTO THE OVERNIGHT HOURS. LATEST HI-RES NAM ARW WEST SEEMS TO HAVE
A DECENT HANDLE FIRING STORMS NEAR THE VICINITY OF THE OUTFLOW
BOUNDARY AS IT LIFTS NORTHWARD OVER THE NEXT FEW HOURS AS A WARM
FRONT. IT WILL BE ANY CONVECTIVE DEVELOPMENT ACROSS SE NE/NE KS
THAT COULD LIFT NE INTO SOUTHWEST IOWA BY MID/LATE EVENING TO
BRING THE POTENTIAL FOR A STRONG TO SEVERE STORM. TIMING WILL
LIKELY LIMIT THE THREAT TO MAINLY DAMAGING WINDS AND SOME LARGE
HAIL WITH ANY OF THE STRONGER STORMS.

OTHERWISE AS THE LOW LIFTS NORTHWARD INTO SE NE AND SHORTWAVE
ALOFT ROTATING THROUGH THE BASE OF THE TROUGH LIFT THROUGH
IOWA...SHOULD SEE A LARGE AREA OF SHOWERS AND ISOLATED
THUNDERSTORMS SPREAD THROUGH THE STATE IN THE LATE NIGHT HOURS.
EXPECT A LARGE RAIN SHIELD TO BE IN PLACE BY 12Z WEDNESDAY...WITH
MUCH OF THE SOUTHWESTERN CWA HAVING RECEIVED AROUND A HALF INCH TO
POSSIBLE OVER AN INCH OF RAIN OVERNIGHT.

.LONG TERM.../WEDNESDAY THROUGH TUESDAY/
ISSUED AT 330 PM CDT TUE APR 26 2016

THE FIRST 24 HOURS OF THE LONG TERM FORECAST WILL HINGE HEAVILY ON
CONVECTIVE TRENDS THIS AFTERNOON AND TONIGHT. STRATIFORM REGION
OF PRECIPITATION...THE REMNANTS OF THIS EVENING`S THUNDERSTORMS...
SHOULD BE PROGRESSING THROUGH CENTRAL IOWA AT THE ONSET OF THE
PERIOD ATTENDANT TO BROAD 295-300K ISENTROPIC LIFT AHEAD OF THE
NE/KS LOW. THIS AREA OF PRECIPITATION SHOULD WEAKEN THROUGH THE
MORNING AND EARLY AFTERNOON AS THE DEEP MOISTURE TRANSPORT BECOMES
REESTABLISHED FURTHER TO THE SOUTHEAST OVER THE OHIO RIVER VALLEY
AND THE MIDLEVEL INSTABILITY DECAYS.

THE GFS/EC/NAM HAVE COME INTO AGREEMENT IN LIFTING THE SURFACE LOW
AND WARM FRONT INTO SOUTHWEST IOWA DURING THE EARLY AFTERNOON ON
WEDNESDAY AND THIS WILL SERVE AS THE SOURCE FOR CONVECTIVE
INITIATION. STEERING FLOW WILL BE RELATIVELY WEAK THROUGH THE
AFTERNOON AND IS REFLECTED WELL IN THE BUNKERS RIGHT MOVING
SUPERCELL VECTORS FROM 18-03Z...GENERALLY LESS THAN 20 KTS AND
BACKING WITH TIME. STRONG EASTERLY FLOW NORTH OF THE WARM FRONT
WILL RESULT IN IMPRESSIVE LOW LEVEL HODOGRAPHS WITH 0-1 KM
HELICITY VALUES OF 200-300 M2/S2 IN THE CRESTON NAM BUFR SOUNDING
AT 21Z. MLCAPE VALUES RISE TO OVER 1000 J/KG DURING PEAK HEATING
WITH MUCH OF THE INSTABILITY IN THE LOWEST 3 KM OF THE SOUNDINGS.
SUFFICE TO SAY...A MULTI-MODAL SEVERE WEATHER THREAT EXISTS SHOULD
ISOLATED SUPERCELLS DEVELOP ALONG OR NEAR THE WARM FRONT. THE
POSSIBLE LONG RESIDENCE TIME ON THE BOUNDARY INCREASES THE THREAT
FOR TORNADOES AND THE NORTHWESTWARD EXTENSION OF THE SPC DAY 2
SLIGHT RISK INTO SOUTHWEST IOWA IS WARRANTED. TRENDS WITH THIS
SYSTEM WILL NEED TO BE WATCHED CAREFULLY AS CLOUDS/OUTFLOW
ASSOCIATED WITH THE CONVECTION EARLIER IN THE MORNING MAY
INFLUENCE HOW THIS EVENT PANS OUT.

THE WEDNESDAY AFTERNOON STORMS WILL LIFT NORTHWARD AND WRAP AROUND
THE NEARLY STATIONARY H500 LOW LOCATED OVER EASTERN KANSAS
OVERNIGHT. THE THREAT OF THUNDER SHOULD DIMINISH AFTER THE LOSS OF
SOLAR INSOLATION. BROAD CYCLONIC FLOW ALOFT AND EASTERLY FLOW AT
THE SURFACE WILL KEEP THE REST OF THE CWA COOL AND CLOUDY THROUGH
FRIDAY. THE UPPER LEVEL LOW FINALLY ELONGATES AND DEPARTS LATE
THURSDAY WITH H300 SHORTWAVE RIDGING BRINGING A BREAK TO THE DAMP
WEATHER. PREVIOUSLY ADVERTISED WEEKEND SYSTEM STILL REMAINS ON
TRACK TO PASS SOUTH OF THE CWA...KEEPING IOWA IN THE COOL SECTOR
WITH PERIODS OF SHOWERS AND POSSIBLY THUNDERSTORMS TOWARDS THE
IA/MO BORDER WHERE TOKEN AMOUNTS OF MUCAPE MAY BE REALIZED.
SURFACE HIGH PRESSURE SINKS SOUTH FROM CANADA FOR THE BEGINNING OF
NEXT WEEK...REINFORCING COOL NORTHERLY FLOW INTO MIDWEEK.

&&

.AVIATION.../FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING/
ISSUED AT 638 PM CDT TUE APR 26 2016

DELAYED THE ONSET OF PRECIP A COUPLE HOURS LATER THAN PREVIOUSLY
ANTICIPATED. THUS...THE MVFR CIGS REALLY DO NOT MOVE INTO THE TAF
SITES UNTIL AROUND 06Z OR LATER. IFR TO LIFR CIGS LIKELY TOWARDS
WEDNESDAY MORNING AS PRECIP SHIELD IS EXPECTED TO SPREAD ACROSS
CENTRAL IOWA DURING MUCH OF THE MORNING. THE STRONG EAST WINDS
WILL PERSIST THROUGH THE ENTIRE FORECAST TIME FRAME AS THE SURFACE
LOW SLOW TO MOVE EAST OF THE STATE.

&&

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

&&

$$

SHORT TERM...BEERENDS
LONG TERM...SKOW
AVIATION...PODRAZIK



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