Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 240914
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
414 AM CDT FRI APR 24 2015

.SHORT TERM /TODAY/...
ISSUED AT 329 AM CDT FRI APR 24 2015

SOUTHEAST FLOW OF DRY AIR CONTINUES TO FEED INTO THE STATE  SOME
ECHOS HAVE DEVELOPED FROM CENTRAL INTO NORTHWEST IA. THESE ARE DUE
TO THETA-E ADVECTION AS WELL AS SOME WEAK SPEED CONVERGENCE IN THE
LOWER LEVELS.  WITH 25 TO 30 KTS FLOWING INTO SLOWER 10 TO 15 KT
AIR...IT IS JUST ENOUGH TO KICK OFF SOME SHOWERS WITH AN OCCASIONAL
CLAP OF THUNDER. AT THE DAY PROGRESSES...MOISTURE WILL INCREASE WITH
PRECIPITATION BECOMING WIDESPREAD.  LIMITED INSTABILITY EXISTS BEING
NORTH OF THE SURFACE LOW PRESSURE TRACK...BUT THERE IS SOME ELEVATED
INSTABILITY.  THAT IS ENOUGH TO GO WITH THE ISOLATED ON THUNDER
CHANCES.  TEMPERATURES TODAY WILL HAVE A TOUGH TIME GOING UP WITH
THE CLOUDS AND INCREASING SHOWERS.  LITTLE RISE IS EXPECTED IN THE
WEST...AND MODEST RISES IN THE EAST.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 329 AM CDT FRI APR 24 2015

FORECAST ABOUT ON TRACK WITH LITTLE CHANGE FROM THE PREVIOUS
MODEL RUNS. THE MAIN DIFFERENCE WITH THE SYSTEM FOR TODAY THROUGH
SATURDAY IS THAT EXCEPT FOR THE GFS...THE MODELS HAVE ALL BUT
REMOVED OR WEAKENED THE INSTABILITY ACROSS IOWA. THE SHEAR ACROSS
US IS ALSO WEAKER AND MORE QUESTIONABLE.  EVEN THE GFS IS
CONSIDERABLY LESS BUT IT DOES HANG ON TO INSTABILITY LONGER THAN
ANY OTHER MODEL. THE RESULT IS THAT THUNDERSTORMS WILL BE ISOLATED
AT BEST FOR IOWA AND SHOULD BE CONFINED TO AREAS MAINLY SOUTH OF
INTERSTATE 80 TONIGHT INTO SATURDAY WHEN THE BULK OF THE PRECIP
WILL FALL. TONIGHT A FAIRLY POTENT SHORTWAVE WILL MOVE ACROSS THE
SOUTHERN/CENTRAL PLAINS. THE SHORTWAVE WILL BE MOVING OFF TO THE
EAST BY LATE DAY SATURDAY AND PRECIP SHOULD BE ENDING BY THAT
TIME WITH RIDGING ALREADY BUILDING BACK INTO THE UPPER MIDWEST
SATURDAY EVENING.

AS FOR THE REMAINDER OF THE EXTENDED...WHAT A DIFFERENCE A DAY
MAKES. THE MODELS ARE NOW IS MUCH BETTER AGREEMENT WITH THE NEXT
SYSTEM AND NOW CLOSE THE LOW OFF OVER THE SOUTHERN PLAINS MONDAY
INTO TUESDAY BEFORE PUSHING IT EAST. ACROSS THE NORTH A SECOND
SHORTWAVE DEVELOPS BUT NEVER REALLY INTERACTS WITH THE SOUTHERN
STREAM SYSTEM. MOISTURE NOW LOOKS TO BE LACKING WITH THIS SYSTEM
AND PRECIP IS LOOKING LESS LIKELY FOR IOWA.

UPPER RIDGING BUILDS INTO THE ROCKIES FOR MID TO LATE NEXT WEEK
AND THE EURO PARKS THE RIDGE OVER THE UPPER MIDWEST WHILE THE GFS
KEEPS US MORE IN NORTHWEST FLOW WITH THE RIDGE AXIS FURTHER WEST
AND BACK OVER THE ROCKIES. SO NEXT WEEK LOOKS SEASONABLY COOL AND
MAINLY DRY.

&&

.AVIATION...24/06Z
ISSUED AT 1114 PM CDT THU APR 23 2015

LITTLE CHANGE TO PREVIOUS THINKING...CHALLENGES THIS PERIOD WILL
BE CHANCES FOR THUNDER...AND CIGS. MODELS IN AGREEMENT WITH NEXT
WAVE ARRIVING OVERNIGHT WITH ISENTROPIC LIFT/SATURATION TAKING
PLACE ACROSS THE REGION BY EARLY MORNING WEST. HAVE INTRODUCED
VCSH NEAR 12Z-13Z WEST SITES WITH -RA/RA INCREASING THROUGH 18Z TO
EAST. ISO THUNDER LOOKING LESS LIKELY AS COVERAGE STILL IN
QUESTION WITH LIMITED TO NO MUCAPE AND DRY AIR TO OVERCOME...MORE
LIKELY THE AIRMASS WILL JUST STABILIZE MID LEVELS AND SQUELCH
ELEVATED CONVECTION. VFR CIGS WILL GRADUALLY DROP TO MVFR WITH
HEAVIER RAINFALL AND VSBY DROP TO MVFR AS WELL. WINDS WILL
INCREASE FROM THE SOUTHEAST GUSTING TO 22-24KTS AT TIMES THROUGH
00Z. THERE SHOULD BE A LULL IN THE SHOWERS UNTIL THE MAIN SYSTEM
ARRIVES BETWEEN 02-04Z...WHEN COVERAGE OF RAIN AND POTENTIAL OVN
THUNDER RAMPS UP AGAIN./REV

&&

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

$$

SHORT TERM...MS
LONG TERM...FAB
AVIATION...REV



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