Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 212049
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
349 PM CDT MON APR 21 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 322 PM CDT MON APR 21 2014

SURFACE FRONT CROSSING FORECAST AREA THIS AFTERNOON AND WILL QUICKLY
DEPART TO THE SOUTHEAST EARLY THIS EVENING.  WILL CONTINUE TO SEE A
FEW ISOLATED STORMS IN THE INSTABILITY AXIS PRECEDING THE FRONT...
BUT THIS ACTIVITY WILL EXIT TO THE SOUTHEAST QUICKLY WITH THE FRONT.
OTHERWISE...MUCH DRIER AIR WILL ENTER THE STATE FOR THE OVERNIGHT
WITH WIDESPREAD SUBSIDENCE AS HIGH PRESSURE BUILDS INTO THE MISSOURI
RIVER VALLEY.  THE GUSTY WINDS FROM THIS AFTERNOON WILL DIMINISH
THIS EVENING AS MIXING DECREASES AND PRESSURE GRADIENT WEAKENS THE
HIGH PRESSURE MOVES CLOSER. TEMPERATURES WILL DROP NICELY AS WELL IN
THE DRIER AIRMASS AND HAVE UNDERCUT GUIDANCE IN FAVORED NORTHERN
LOCATIONS AS WELL AS THE NISHNA VALLEYS IN THE WEST.

.LONG TERM /TUESDAY THROUGH MONDAY/...
ISSUED AT 322 PM CDT MON APR 21 2014

TUESDAY INTO TUESDAY NIGHT THERE WILL BE AN UPPER RIDGE THAT WILL
MOVE INTO THE UPPER MIDWEST PROVIDING FOR A RELATIVELY COOLER AND
DRY DAY.

LATER TUESDAY NIGHT INTO WEDNESDAY THE UPPER RIDGE WILL SLOWLY
SHIFT TO THE EAST AS A STRONG UPPER LOW OVER CANADA DEVELOPS AN
INVERTED TROUGH THAT DIGS INTO THE PLAINS. BY LATE IN THE DAY
WEDNESDAY THE RIDGE AXIS WILL BE OVER EASTERN IOWA AND MOISTURE
AND INSTABILITY WILL BEGIN TO INCREASE ACROSS THE WEST. ALL OF THE
MODELS KEEP THE INSTABILITY WELL WEST OF THE CWA THROUGH 00Z THEN
SPREAD IT ACROSS THE STATE OVERNIGHT. THERE IS A BROAD AREA OF
THETA-E ADVECTION THAT PUSHES ACROSS IOWA ON WEDNESDAY ALONG WITH
SOME QC FORCING SO THERE WILL LIKELY BE SOME SHOWERS OR AN
ISOLATED THUNDERSTORM DEVELOPING ACROSS THE AREA THROUGH THE DAY
BUT AT THIS POINT ANY SEVERE POTENTIAL LOOKS TO BE
LATER...WEDNESDAY NIGHT INTO THURSDAY WHEN THE BETTER INSTABILITYARRIVES.
THE CAVEAT THEN IS THAT THE BEST SHEAR PROGRESSES TO THE EAST BY
THAT TIME. LOCATION OF ANY SEVERE THREAT IS STILL UNCERTAIN BUT IT
WOULD APPEAR WEDNESDAY EVENING INTO EARLY THURSDAY WOULD BE THE
BEST TIME.

BY LATE THURSDAY THROUGH FRIDAY THE LOW MOVES OFF INTO THE
NORTHERN GREAT LAKES WITH A RIDGE BUILDING INTO THE INTERMOUNTAIN
WEST. THE EURO KEEPS THE ASSOCIATED TROUGH NEAR EASTERN IOWA AND
SOME LINGERING PRECIP POSSIBLE...MAINLY FAR NORTHEAST BUT I HAVE
KEPT OUR CWA DRY.

THERE ARE STILL BIG DIFFERENCES WITH THE HANDLING OF THE WEEKEND
SYSTEM. THE GFS REALLY AMPLIFIES A RIDGE OVER THE MIDWEST AND
NORTHERN PLAINS AS A STRONG LOW DIGS INTO THE SW U.S. THE EURO IS
NOT AS AS STRONG WITH THE FEATURES AND MORE PROGRESSIVE...SIMILAR
TO YESTERDAY. AS A RESULT THE EURO IS FAR MORE PROGRESSIVE WITH
THE ADVANCE OF THE TROUGH AND PRECIP WHILE THE GFS REMAINS MORE
FOCUSED WITH THE DEEPER TROUGH. TO ME THE GFS SEEMS TOO
EXAGGERATED WITH THE DEEPENING LOW AND AMPLIFYING THE RIDGE. I
LEFT LOW CHANCE POPS IN FOR SATURDAY FOR CONSISTENCY SAKE BUT
SATURDAY COULD VERY WELL BE DRY IF THE GFS VERIFIES. BOTH MEDIUM
RANGE MODELS HOLD ON TO THEIR SOLUTIONS THROUGH THE WEEKEND SO
THE EURO IS WETTER THAN THE GFS BUT BOTH ARE COOL. WITH LOW
CONFIDENCE I KEPT CHANCE POPS GOING THROUGH THE WEEKEND. OBVIOUSLY
IT WONT BE RAINING THE WHOLE TIME BUT THE MODELS ARE TOO FAR APART
TO ATTEMPT TIMING AT THIS POINT. LOWS SATURDAY NIGHT AND SUNDAY
NIGHT UP NORTH WILL BE COLD ENOUGH AND ANY PRECIP COULD BE A
RAIN/SNOW MIX POSSIBLY EVEN CHANGING BRIEFLY TO SNOW. WE WILL NEED
TO CONTINUE TO MONITOR THE DEVELOPMENT OF THE WEEKEND SYSTEM.

&&

.AVIATION...21/18Z
ISSUED AT 1257 PM CDT MON APR 21 2014

COLD FRONT ACROSS CENTRAL IOWA WILL EXIT INTO ILLINOIS AND
MISSOURI BY LATE THIS AFTERNOON. STRONG NORTHWEST SURFACE WINDS
ARE EXPECTED ON THE BACKSIDE OF THE FRONT THIS AFTERNOON BEFORE
DIMINISHING SOME THIS EVENING AS MIXING DECREASES. SCATTERED
SHOWERS AND THUNDERSTORMS IN THE VICINITY OF KOTM WILL DEPART WITH
THE FRONT AS WELL. SCATTERED AREAS OF MVFR CEILINGS WILL GIVE WAY
TO WIDESPREAD VFR CONDITIONS BY THIS EVENING ACROSS ALL OF
CENTRAL IOWA WITH THESE CONDITIONS PERSISTING FOR THE REMAINDER OF
THE FORECAST PERIOD.


&&

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

$$

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



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