Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 270436
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1136 PM CDT FRI SEP 26 2014

.SHORT TERM /TONIGHT/...
ISSUED AT 341 PM CDT FRI SEP 26 2014

UPPER LOW WILL CONTINUE TO LINGER ACROSS IOWA THROUGH THE
OVERNIGHT...LIFTING BACK NORTH SLIGHTLY OVERNIGHT. WITH CONTINUED
FORCING NEAR LOW...WILL SEE ADDITIONAL CHANCES FOR PRECIPITATION
OVERNIGHT. GIVEN PREVIOUS TRENDS...HAVE KEPT PRECIPITATION CHANCES
CONFINED TO AFTER 06Z...AND ANTICIPATE SCATTERED PRECIPITATION.
HOWEVER...MOISTURE AND FORCING APPEARS TO BE MORE FAVORABLE TONIGHT.
THEREFORE HAVE INCREASED POPS TO CHANCE ACROSS SOUTHERN IOWA...WITH
SYSTEM LIFTING NORTH. MOISTURE IS BEST NEAR 12Z...AND THEREFORE MAY
BE A BIT EARLY WITH ONSET OF PRECIPITATION CHANCES. HAVE KEPT
TEMPERATURES NEAR GOING...GIVEN AMOUNT OF WARMING TODAY...THOUGH
HAVE DROPPED TEMPERATURES SLIGHTLY ACROSS THE SOUTH WHERE
PRECIPITATION MAY HELP COOL TEMPS.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
ISSUED AT 341 PM CDT FRI SEP 26 2014

INITIAL CONCERN CONTINUES TO BE HOW TO HANDLE SUBTLE POP TRENDS WITH
PESKY SHORT WAVE DRIFTING ACROSS THE MIDWEST. FEATURE SEEMS TO HAVE
SHOWN ITS HAND SOMEWHAT WITH MAINLY A DIURNAL CYCLE SUGGESTING
THERMODYNAMIC RATHER THAN KINEMATIC EMPHASIS.  EXPECT ANOTHER ROUND
TONIGHT INTO SAT MORNING...LIKELY DRIVEN BY VERY MINOR AND HIGH
BASED DIURNAL WARM ADVECTION INCREASE...WITH COVERAGE STILL VERY
LIMITED. HOWEVER WITH LOCALIZED MODERATE RAIN AND WEAK
CONVECTION/LIGHTNING VS LIGHT SHOWERS NO LONGER FEEL COMFORTABLE
WITH A DRY FORECAST. FORCING CONTINUES TO BE NONDESCRIPT SO HAVE
TRIED TO FOCUS LOW END POPS MORE ON BETTER MOISTURE. BOTH GFS AND
ECMWF HAVE DECENT HANDLE ON POCKET OF MID LEVEL MOISTURE AND
CLOUDS FROM N CENTRAL MO INTO CENTRAL IA. THIS OOZES SLOWLY
NORTHWARD INTO SAT SO HAVE SLIGHTS MENTIONED THROUGH THE HEART OF
THE FORECAST AREA AND DIMINISHING BY EARLY AFTERNOON. WAVE SEEMS
TO OPEN UP AND DRIFT AWAY SAT NIGHT INTO SUN SO WILL LEAVE THOSE
PERIODS DRY. SOUNDINGS WITH PROJECTED MIXING AND 0-2KM MODEL
TEMPS SUGGEST LITTLE CHANGE IN TEMP REGIME THROUGH THE WEEKEND
WITH HIGHS AND LOWS CLOSE TO PERSISTENCE.

SHORT WAVE RIDGE PASSAGE WILL KEEP THINGS DRY INTO MON WITH
ATTENTION THEN TURNING UPSTREAM TO APPROACHING WRN CONUS LONG WAVE
TROUGH. NEGATIVELY TILED LOBE OF FORCING CROSSES THE MO VALLEY LATE
TUE WITH FAIRLY DEEP THERMODYNAMIC AND KINEMATIC FORCING INTO TUE
NIGHT.  DETAILS ARE MORE DIFFICULT TO COME BY WED INTO FRI...BUT
PERSISTENT SW FLOW AND DIVERGENCE ALOFT SUPPORTS POPS CONTINUING
THROUGH THAT PERIOD WITH BOTH ECMWF AND GFS SUGGESTING ANOTHER
SHORT WAVE PASSAGE AND SURGE OF FORCING EITHER WED NIGHT OR THU.
LONG WAVE TROUGH WILL BE PROGRESSIVE ENOUGH TO GET IA INTO NW LOW
LEVEL FLOW BY FRI WITH COOLER TEMPERATURES AND PRECIP CHANCES
DIMINISHING IN EXTENT AND MAGNITUDE.

&&

.AVIATION...27/06Z
ISSUED AT 1136 PM CDT FRI SEP 26 2014

LITTLE CHANGE TO PREVIOUS FORECAST. HIGHER CONFIDENCE THAT
VICINITY SHOWERS AND STORM ARE POSSIBLE AT KDSM. STILL POSSIBLE AT
OTHER SITES BUT POTENTIAL NOT AS HIGH AT ANY OTHER SITES. LEFT
LOCAL MVFR FOG LATE. INCREASING SOUTH WINDS ON SATURDAY WITH VFR
CONDITIONS.

&&

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

$$

SHORT TERM...AWB
LONG TERM...SMALL
AVIATION...DONAVON


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