Area Forecast Discussion
Issued by NWS Des Moines, IA

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040
FXUS63 KDMX 262034
AFDDMX

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

.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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON/
ISSUED AT 1226 PM CDT TUE APR 26 2016

EXPECT LOW CIGS ACROSS THE NORTH TO LIFT AND DISSIPATE THROUGH THE
AFTERNOON HOURS. SOME HIGH CLOUDS TO REMAIN AROUND THE AREA. CIGS
TO LOWER WITH CHANCES OF SHOWERS AND RAIN THIS EVENING INTO THE
OVERNIGHT HOURS. LOW MVFR POSSIBLY IFR CIGS EXPECTED WITH THE RAIN
SHIELD BY WEDNESDAY MORNING. HELD OFF THUNDER CHANCES SOME AS
UNCERTAINTY IS HIGH HOW FAR NORTHEAST THEY WILL MAKE IT THIS
EVENING.


&&

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

$$

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



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