Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 010837
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
337 AM CDT WED OCT 1 2014

.SHORT TERM /TODAY/...
ISSUED AT 337 AM CDT WED OCT 1 2014

ONGOING PRECIP BAND WILL CONTINUE TO TRACK EAST-NORTHEAST THIS
MORNING BEFORE TRANSITIONING EAST OF THE FORECAST AREA EARLY THIS
AFTERNOON. THE LATEST HRRR/HOPWRF/ARW/NMM ALL HAVE THE MAIN PRECIP
SHIELD PUSHING EAST OF THE FORECAST AREA B/T 18-21Z THIS
AFTERNOON...WITH THE HOPWRF THE QUICKEST TO MOVE IT OUT. PLUS THE
NAM12/GFS/ECMWF AGREE ON THE MORE PROGRESSIVE NATURE OF THE PRECIP
DEPARTING THE FORECAST AREA SOONER. HENCE...TRANSITIONED
CATEGORICAL/LIKELY POPS EAST FASTER ABOUT 3 HOURS THAN PREVIOUSLY
EXPECTED. WITH THE SLIGHTLY FASTER MOVEMENT TODAY...TOOK OUT
MENTION OF HEAVY WORDING. HOWEVER...LIKELY COULD SEE SOME ISOLATED
POCKETS OF UP TO 1-2 INCHES WITH THE PRECIPITABLE WATER VALUES IN
THAT RANGE. BUT LOWER CONFIDENCE IN THE WIDESPREAD HEAVY RAIN
TODAY. STILL MAY SEE SOME LINGER LIGHT SHOWERS BEHIND FRONT WITH
SOME WEAK FORCING AND THETA-E ADVECTION.

TEMPERATURES AGAIN WILL BE PROBLEMATIC WITH THE RAIN COOLED AIR MASS
THIS MORNING...LEANED TOWARD THE COLDER SOLUTION OF THE NAM12. IT
SEEMED TO HAVE A BETTER HANDLE ON MAX TEMPS ON TUESDAY.

.LONG TERM /TONIGHT THROUGH TUESDAY/...
ISSUED AT 337 AM CDT WED OCT 1 2014

MAIN CHALLENGES SIMILAR TO
LAST NIGHTS FORECAST. WITH SUBTROPICAL MOISTURE PLUME FOCUSED ON
WESTERN IOWA NOW WITH TONIGHTS SHORT WAVE TRACKING NORTH...NEXT
UPSTREAM WAVE ARRIVING LATER THIS AFTERNOON AND TONIGHT AND FINALLY
THE THIRD SW WAVE IN A SERIES TOMORROW...THE ACTIVE WEATHER PATTERN
CONTINUES. AS USUAL...SOME MODIFICATIONS TO FCST MOVING FORWARD BUT
OVERALL THE GENERAL TRENDS REMAIN ON TRACK.  BY LATE TODAY THE
CURRENT SHORT WAVE IMPULSE OVER WESTERN IOWA WILL BE EXITING THE
EASTERN PORTION OF THE FORECAST AREA WITH SFC TROUGH/COOL FRONT
APPROACHING NORTHWEST IOWA. THE FRONT IS EXPECTED TO SLOW THURSDAY
NIGHT AND FRIDAY AS THE FINAL WAVE OVER THE SOUTHERN ROCKIES BEGINS
TO AMPLIFY INTO THE CENTRAL PLAINS. MODELS HAVE CONTINUED TO DIFFER
ON DETAILS WITH TRACK OF LOW AND TONIGHT THE 00Z GEM IS DIGGING THE
SFC LOW FARTHER SOUTHEAST AND THEN NORTHEAST THROUGH FAR EASTERN
IOWA ON THURSDAY. THE 00Z NAM IS FARTHEST WEST WITH THE TRACK AND
THE GFS IS LEANING TOWARD THE GEM...BETWEEN THE TWO. THE 12Z EURO
THIS MORNING AND TONIGHTS 00Z RUN CONTINUE TO BE THE MORE STABLE
SOLUTIONS...SIMILAR TO LAST NIGHTS WITH THE WAVE RIDING UP THROUGH
JUST EAST OF DES MOINES.  THE ONE CONSISTENCY BETWEEN ALL MODELS IS
THE 6 TO 10 HOUR BREAK IN ORGANIZED RAINFALL OVER THE ENTIRE AREA
TONIGHT...WITH ONLY THE SOUTH ONCE AGAIN SEEING THE BETTER FORCING
BEGINNING AGAIN AFTER 06Z AS AN H850 WARM FRONT WILL TAKE SHAPE OVER
CENTRAL OR NORTHERN MO BETWEEN 06Z AND 12Z TOMORROW. THE 12Z EURO
FOCUSES THE BEST LIFT OVER THE SAME LOCATIONS AND IN FACT...THE
ENTIRE RUN IS CONSISTENT WITH ITS PREDECESSOR WITH FORCING OVER
NORTHEAST KS...NORTHERN MO THROUGH 06Z AND THEN THE MOISTURE
TRANSPORT BEGINS VEERING OVER TIME WITH THE MOISTURE TRANSPORT
FOCUSED MORE TOWARD NORTHEAST MO BY 12Z. THIS STRONG ISENTROPIC LIFT
WITH A WEAK WAVE PEELING OFF THE MAIN UPPER SHORT WAVE WILL PROVIDE
FOR RAINFALL WELL EAST OF THE MAIN UPPER LEVEL SYSTEM. AS THE MAIN
H500 WAVE OVER CENTRAL NEBRASKA MOVES EAST...A SFC LOW WILL TRACK
NEAR TOPEKA BY 18Z...AND DEEPEN SLIGHTLY AS IT AND THE UPPER LOW
TRACK NORTHEAST THROUGH NORTHEAST IOWA THE REMAINDER OF THE
AFTERNOON. THERE IS SOME UNCERTAINTY AS TO HOW RAPID THE SYSTEM WILL
DEVELOP...THE BEST TRACK...AND EXPECTED PRECIP SHIELD BUT THE
CONSENSUS IS FOR A FALL CYCLONE WITH DEF ZONE PRECIP NORTHWEST OF
LOW AND AREAS OF THUNDER SOUTHEAST OF SYSTEM ON THURSDAY. THE
SOUTHEAST MAY BRIEFLY GET INTO THE WARM SECTOR THURSDAY AFTERNOON
AND WE HAVE BEEN INCLUDED IN A SLIGHT RISK FOR SEVERE WEATHER IN THE
FAR SOUTHEAST BUT WINDOW OF OPPORTUNITY LOOKS FAIRLY LIMITED FOR ANY
SEVERE WEATHER. FOR NOW...WILL PROBABLY HANG ON TO SIMILAR SOLUTION
AS LAST NIGHT WITH GENERALLY HIGH POP EVENT ACROSS THE FCST AREA
TOMORROW. PRECIPITABLE WATER WILL INCREASE TO ABOUT 1 TO 1.5 INCHES
BY THURSDAY AFTERNOON SOUTHEAST...BUT PROGRESSIVE NATURE OF THE
SYSTEM SHOULD KEEP RAINFALL TOTALS MANAGABLE WITH WIDESPREAD HEAVY
RAINFALL TOTALS NOT BEING MUCH OF AN ISSUE...THOUGH SOME QUICK
DOWNPOURS MAY BRING 1 TO 2 INCH RAINS DURING THE AFTERNOON
SOOUTHEAST. ONCE AGAIN...MUCH COLDER ON FRIDAY BUT SOME DIFFERENCES
ON HOW COLD TO GO. NEWEST 00Z GEM PAINTS A NOVEMBER SCENE ON FRIDAY
WITH HIGHS ONLY IN THE 40S...AND INCREASINGLY BLUSTERY NW WINDS. IT
ALSO DEEPENS THE SFC LOW CONSIDERABLY AND MAINLY EAST OF THE AREA AS
A SECONDARY H500 LOW DROPS SOUTH INTO THE LARGE SCALE TROUGH FRIDAY
NIGHT. H850 TEMPS FRIDAY HIT -2 TO -4C BY 00Z SAT. THE EURO IS
GENERATING H850 TEMPS OF 0 TO -2C BY 00Z SATURDAY WITH THE COLD CORE
LOW DROPPING QUICKLY SOUTH AS WELL. BOTH SOLUTIONS SUGGEST HIGHS IN
THE 40S TO LOWER 50S FRIDAY WITH PARTLY SUNNY SKIES EARLY GIVING
QUICKLY TO CLOUDY SKIES AND SHOWERS DEVELOPING INTO THE AFTERNOON
HOURS. THE COLD POOL ALOFT WILL CONTINUE TO PROMOTE SHOWER CHANCES
LATE FRIDAY AFTERNOON AND EVENING OVER THE REGION. OTHER MODELS ARE
NOT FAR BEHIND THIS GEM/EURO SCENARIO. THE OTHER WRINKLE THAT HAS
DEVELOPED IS THAT THE SHORTWAVE ACCOMPANYING THE COLD CORE LOW
FRIDAY EVENING HAS A VERY STRONG JETMAX ASSOCIATED WITH IT. LAPSE
RATES STEEPEN QUICKLY TOWARD 00Z SAT AND STRONG MIXING IS
ANTICIPATED LATE AFTERNOON THROUGH THE EVENING HOURS. SOLUTIONS
DIFFER SOMEWHAT...BUT WITH STRONG MIXING...HEADLINES FOR WIND NOW
LOOK MUCH MORE LIKELY ACROSS MUCH OF THE AREA. THE GFS SUGGESTS
WARNING CRITERIA WINDS...WHILE THE EURO SUGGESTS MID TO UPPER RANGE
ADVISORY POTENTIAL. WILL NEED ANOTHER RUN OR TWO TO SETTLE ON
DETAILS BUT WILL MENTION IN HWO AND PASS ALONG TO ONCOMING SHIFT.
HIGHS THROUGH THE WEEKEND HAVE BEEN KNOCKED DOWN AND MINS FRIDAY
NIGHT/SAT MORNING EASILY REACHING THE LOWER TO UPPER 30S OVER THE
AREA. FROST WILL MOST LIKELY BE AVOIDED THOUGH...DUE TO THE EXPECTED
MIXING THROUGH THE NIGHT. SATURDAY EXPECT SOME CLOUDS AND WINDY
CONDITIONS...AND A CRISP FALL DAY...EMPHASIS CRISP. AS THE SYSTEM
PULLS EAST ON SUNDAY SOME WARMING IS ANTICIPATED AS THICKNESS RISES
REPLACE THE STEEP FALL OF THE TWO PREVIOUS DAYS. ANOTHER WEAK
CLIPPER IS PROGGRED TO RACE THROUGH THE REGION SUNDAY WITH A FEW
SHOWERS AND ANOTHER SHOT OF COLD AIR SUNDAY NIGHT AND MONDAY. HIGHS
TO RECOVER TO NEAR NORMAL BY THE END OF THE PERIOD AS UPPER LEVEL
FLOW BEGINS TO TURN MORE ZONAL WITH TIME.

&&

.AVIATION...01/06Z
ISSUED AT 1153 PM CDT TUE SEP 30 2014

SHRA/TSRA EXPECTED TO EXPAND ACROSS THE AREA OVERNIGHT AND WED
MORNING...ESPECIALLY AFFECTING DSM/OTM...BEFORE MOVING OUT LATER
IN THE DAY ON WED. THE PRECIP WILL BE ACCOMPANIED BY MVFR
CIGS/VSBYS...POSSIBLY BRIEFLY IFR. FROM WED AFTN INTO WED NIGHT
THERE SHOULD BE SCATTERED REDEVELOPMENT BUT OF MORE CONCERN IS THE
POTENTIAL FOR WIDESPREAD FOG/STRATUS DEVELOPMENT. MOST OF THIS
POTENTIAL IS TOWARD OR AFTER THE END OF THE 06Z TAF PERIOD SO THIS
WILL BE ASSESSED IN MORE DETAIL FOR FUTURE TAF ISSUANCES.

&&

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

$$

SHORT TERM...PODRAZIK
LONG TERM...REV
AVIATION...LEE



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