Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 120908
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
408 AM CDT SAT APR 12 2014

.SHORT TERM /TODAY/...
ISSUED AT 339 AM CDT SAT APR 12 2014

SURFACE LOW PASSING THROUGH SOUTH DAKOTA EARLY THIS MORNING WITH
STRONG WARM ADVECTION ACROSS IOWA.  STRONG LOW LEVEL THERMAL
GRADIENT EXISTS NEAR THE IA/MN BORDER AND HIGH BASED SHOWERS AND A
FEW THUNDERSTORMS HAVE DEVELOPED ALONG THIS BOUNDARY.  LACK OF
DEEPER MOISTURE HAS LIMITED COVERAGE AND INTENSITY AND ANTICIPATE
THIS ACTIVITY TO PROGRESS EASTWARD ACROSS THE NORTHERN HALF OF THE
STATE THIS MORNING.  MEANWHILE...LOW LEVEL MOISTURE HAS BEEN SURGING
NORTHWARD ACROSS KANSAS AND INTO FAR SOUTHERN NEBRASKA EARLY THIS
MORNING.  THIS MOISTURE WILL CONTINUE TO PUSH RAPIDLY NORTHWARD
TODAY AHEAD OF AN APPROACHING BOUNDARY.  INSTABILITY WILL RAPIDLY
INCREASE DURING THE DAY AS THE MOISTURE ADVECTS INTO THE STATE AND
DEWPOINTS CLIMB INTO THE MID TO UPPER 50S BY AFTERNOON.  MLCAPES
WILL BE ON THE ORDER OF 1000-2000 J/KG BY LATE AFTERNOON AS BOUNDARY
SETTLES INTO NORTHERN IOWA.  WILL THERE IS SUFFICIENT BULK SHEAR FOR
ORGANIZATION OF STORMS WHEN DEVELOPMENT OCCURS BY LATE AFTERNOON
WHEN CAP SHOULD BREAK NEAR THE BOUNDARY.  SOME SUPERCELLS WILL BE
POSSIBLE WITH LARGE HAIL AND SOME DAMAGING WINDS AS THE PRIMARY
THREAT.  THESE STORMS WILL INITIALLY HAVE HIGHER BASES AND 0-1KM
HELICITY IS NOT OVERLY IMPRESSIVE...THEREFORE THE TORNADO
THREAT...WHILE NOT NON-EXISTENT...APPEARS TO BE LIMITED.  WITH PWATS
CLIMBING TO ABOVE ONE TO ONE AND A QUARTER INCHES BY LATE IN THE
PERIOD...MAY BEGIN TO SEE SOME LOCALIZED HEAVY RAINFALL AS WELL.
HAVE STAYED ON THE WARM SIDE OF GUIDANCE TODAY WITH THERMAL RIDGE
PASSING OVER THE STATE.

.LONG TERM /TONIGHT THROUGH FRIDAY/...
ISSUED AT 339 AM CDT SAT APR 12 2014

FOR TONIGHT THE FRONTAL BOUNDARY STALLS ACROSS THE SOUTHERN
PORTION OF THE CWA AS A PRETTY IMPRESSIVE SHORTWAVE RIDES EAST
ALONG THE BOUNDARY. THIS WILL PUSH EAST INTO THE OVERNIGHT HOURS.
WE REMAIN UNSTABLE AND STORMS SHOULD INCREASE THIS EVENING. WITH
CAPES AT 1500-2500 J/KG AND SHEAR REMAINING DECENT EXPECT STORMS
TO REMAIN THIS EVENING. SOME WILL ALSO BE SEVERE WITH HAIL AND
DAMAGING WIND REMAINING THE MAIN THREATS.

THE FRONT FINALLY PASSES TO THE EAST ON SUNDAY BY MID AFTERNOON
THECOLDER AIR LAGS BEHIND THE FRONT HOWEVER AND BY THE TIME IT
WORKS INTO THE CWA PRECIP WILL BE WINDING DOWN. THERE WILL BE A
CHANGE OVER TO SNOW FROM NORTHWEST TO SOUTHEAST...PROBABLY NOT
MAKING IT COMPLETELY OVER TO SNOW IN THE FAR SOUTHEAST. GIVEN THE
PRECIP WILL BE ENDING BY THIS TIME I AM NOT LOOKING FOR MUCH IN
THE WAY OF SNOWFALL...MAINLY A TENTH OR TWO ON GRASSY AREAS.

THE COLDEST TEMPS WILL ARRIVE MONDAY AND MONDAY NIGHT AND A
SHORTWAVE PASSES AND BRINGS DOWN EVEN COLDER AIR. BY LATE TUESDAY
NIGHT AND WEDNESDAY THE FLOW BECOMES WESTERLY THEN BACK AROUND TO
THE SOUTH. AFTER HIGHS IN THE 40S FOR MONDAY AND TUESDAY AND LOWS
IN MANY SPOTS BACK BELOW FREEZING...HIGHS ON WEDNESDAY WILL BE
BACK IN THE 50S WITH LOWS IN THE MID 30S TO LOWER 40S.

FOR THE REST OF THE EXTENDED THERE ARE SUBSTANTIAL DIFFERENCES IN
THE MODELS WITH THE GFS DIGGING A DEEP TROUGH OVER THE
INTERMOUNTAIN WEST WHILE THE EURO HAS MORE OF A WEAKER WAVE
PUSHING ACROSS THE NORTHERN PLAINS. THE GFS IS OBVIOUSLY SLOWER
WITH THE DIGGING SYSTEM BUT NEITHER SOLUTION GIVE US MUCH PRECIP
THROUGH EARLY THURSDAY. BY THURSDAY NIGHT/FRIDAY...IF YOU BELIEVE
THE GFS...THE SYSTEM WILL PULL GULF MOISTURE OVER THE REGION AND
BRING US A CHANCE FOR PRECIP AGAIN. GIVEN THE SLOWER MOVEMENT IT
WOULD BE ANOTHER PRECIP EVENT THAT WILL EXTEND OVER SEVERAL
PERIODS...FROM LATE THURSDAY NIGHT THROUGH FRIDAY NIGHT. BOTH
MODELS THEN AGAIN BRING A SHORTWAVE ACROSS THE NORTHERN PLAINS
AGAIN FOR NEXT WEEKEND BUT AGAIN DIFFERENCES ARE SUBSTANTIAL AS TO
SPEED AND STRENGTH OF THE SHORTWAVE. BROAD-BRUSHED CHANCE POPS
ACROSS THE AREA MAINLY THURSDAY THROUGH FRIDAY NIGHT.

&&

.AVIATION...12/06Z
ISSUED AT 1159 PM CDT FRI APR 11 2014

VFR CONDITIONS EXPECTED THRU THE TAF PD. CHC OF SHRA/TSRA SAT MORN
AT NORTHERN TERMINALS. CONFIDENCE IS NOT HIGH ENOUGH TO CARRY
PREVAILING OR TEMPOS SO WENT VCTS. THIS AREA OF CONVECTION WILL BE
MOVING EASTWARD. A SECOND THREAT OF SHRA/TSRA WILL DEVELOP LATER IN
THE DAY IN CONJUNCTION WITH AN ADVANCING SFC COLD FRONT. THIS AREA
OF CONVECTION WILL BE MOVING SE. BEST CHANCES OF SHRA/TSRA WILL BE
ACROSS THE SOUTHEAST HALF OF IOWA.


&&

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

$$

SHORT TERM...COGIL
LONG TERM...FAB
AVIATION...ZOGG



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