Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232343
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
643 PM CDT TUE SEP 23 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 340 PM CDT TUE SEP 23 2014

CLOSED UPPER LEVEL LOW OVER SOUTH DAKOTA WILL BE THE PRIMARY WEATHER
DRIVER FOR THE OVERNIGHT HOURS. CURRENT CLUSTER OF SHOWERS MOVING
NORTHEAST THROUGH NORTH CENTRAL IOWA WILL CONTINUE ON THIS TRACK AS
IT PIVOTS AROUND THE LOW AND WEAKEN THROUGH THE EVENING. DESPITE
AMPLE MID LEVEL MOISTURE...THE RAIN TODAY HAS BEEN FIGHTING DRY
SOUTHEASTERLY FLOW OFF A SOUTHERN GREAT LAKES HIGH. FLOW
TRAJECTORIES ARE NOT EXPECTED TO CHANGE MUCH DURING THE OVERNIGHT
HOURS AND MODEL SOUNDINGS REFLECT THIS WEDGE OF DRY AIR THROUGH THE
PERIOD. MAINTAINED A BAND OF SLIGHT CHANCE TO CHANCE POP ACROSS THE
CWA THROUGH THE EVENING AS THE UPPER LEVEL FORCING TRACKS THROUGH
DESPITE THIS WEDGE OP DRY AIR. HIGH RES MODELS DEVELOP A SECOND WAVE
OF SHOWERS AND STORMS OVER NE NEBRASKA AND SE SOUTH DAKOTA BETWEEN
03-06Z ON THE NOSE OF 925-850 MB THETA-E ADVECTION AND TRACK IT INTO
WESTERN IOWA BETWEEN 06-12Z. USED A BLEND OF THE WRF ARW/NMM MODELS
FOR PRECIP TRENDS AND COVERAGE...WHICH HAVE BEEN HANDLING THE
DAYTIME PRECIP PROGRESSION QUITE WELL.

.LONG TERM /WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 340 PM CDT TUE SEP 23 2014

THE FORECAST OUTLOOK IS LITTLE CHANGED FROM YESTERDAY WITH
PERSISTENT SEASONAL TEMPERATURES AND TWO PRECIP WINDOWS...EARLY AND
LATE. CURRENT KINEMATIC FORCING AND THETA-E ADVECTION DRIVING LOBE
OF SHOWERS AHEAD OF NE/SD SHORT WAVE/PV ANOMALY SHOULD DRIFT
EASTWARD OVERNIGHT BUT STILL REMAIN OVER IA BY THE START OF THE
PERIOD. MID LEVEL KINEMATIC FORCING WILL WEAKEN WITH TIME AND
EVENTUALLY EXIT THE FORECAST AREA...HOWEVER H85/H7 THETA-E
ADVECTION AND MOISTURE WILL LINGER THROUGH THE DAY KEEPING
SCATTERED WEAK CONVECTION IN THE FORECAST. LEADING EDGE OF SEVERAL
HUNDRED MUCAPES WILL REACH THE WRN HALF OF IA WED BUT DIMINISH TO
THE SOUTH BY WED NIGHT ELIMINATING MENTION OF THUNDER BY THAT
TIME.

FORECAST SHOULD BE DRY THU-MON WITH PERSISTENT NORMAL TO JUST ABOVE
NORMAL TEMPS.  SYSTEM EVENTUALLY WEAKENS AS IT LIFTS THROUGH THE
GREAT LAKES INTO THU...BUT REMNANTS DO GET TRAPPED UNDER THE
ANOMALOUS U.S./CANADIAN BORDER RIDGE AND FLOAT THROUGH THE MID MS
VALLEY TO VARIED DEGREES. THE GFS APPEARS STRONGER VS THE
ECMWF...BUT NONE OF THE MODELS SUGGEST ENOUGH FORCING OR MOISTURE TO
JUSTIFY ADDING POPS AT THIS TIME.  THE NEXT PRECIP CHANCES DO NOT
ARRIVE UNTIL A PATTERN CHANGE COMMENCES OVER THE WEEKEND WITH
PROGRESSIVE WRN CONUS TROUGH. THIS WILL EVENTUALLY LOWER HEIGHTS
INTO THE MO VALLEY...ESPECIALLY THE OFTEN FAVORED ECMWF
SOLUTION...SO HAVE RE-INTRODUCED LOW POPS MON NIGHT INTO TUE.

&&

.AVIATION...24/00Z
ISSUED AT 643 PM CDT TUE SEP 23 2014

AREA OF LIFT CONTINUES INTO NORTH CENTRAL IA WITH WEAKENING
SHOWERS. MEANWHILE...SCT THUNDER DEVELOPING OVER NORTHWEST MO WILL
MIGRATE EAST NORTHEAST AND WEAKEN WHILE SECOND UPPER LEVEL
SHORTWAVE MOVES EAST LATE THIS EVENING AND OVERSPREADS THE WESTERN
TWO THIRDS OF THE AREA BY 12-15Z WED WITH LIGHT SHOWERS. CIGS
SHOULD REMAIN VFR WITH WINDS INCREASING FROM THE SOUTH AFT 12Z
GUSTING NORTH TO 18-24 KTS. EASTERN AREAS WILL EXPERIENCE LIGHTER
WINDS.

&&

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

$$

SHORT TERM...SKOW
LONG TERM...SMALL
AVIATION...REV



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