Area Forecast Discussion
Issued by NWS Des Moines, IA

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000
FXUS63 KDMX 071748
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1248 PM CDT MON JUL 7 2014

.SHORT TERM /TODAY/...
ISSUED AT 355 AM CDT MON JUL 7 2014

TRANQUIL CONDITIONS TO START BUT THE WEATHER WILL LIKELY BECOME MORE
ACTIVE BY THIS AFTERNOON. JET SEGMENT CONTINUES TO TOP THE WRN
CONUS RIDGE INTO THE NRN PLAINS. NEXT UPSTREAM SHORT WAVE/PV
ANOMALY IN THE FLOW...CURRENTLY OVER SRN ALBERTA...IS STRONGER
THAN WHAT PASSED TODAY AND WILL HELP EXPAND CONVECTION NW-SE
DURING THE AFTERNOON WITH MODERATE KINEMATIC FORCING...AND
THERMODYNAMIC SUPPORT /THETA- E ADVECTION/ RESPONDING LATE CLOSER
TO THE NE/MO BAROCLINIC ZONE. AIRMASS HAS STABILIZED FOR THE
MOMENT...HOWEVER RECOVERY IS ANTICIPATED DURING THE AFTERNOON. 08Z
SURFACE ANALYSIS SHOWS WEAK WAVE ALONG ND/SD BORDER BUT THE
ASSOCIATED FRONTAL BOUNDARY SHOULD MATURE AS SHORT WAVE ADVANCES
ENHANCING LOW LEVEL CONVERGENCE FROM NE INTO IA. 06Z NAM IS NOW
MORE AGGRESSIVE ON INSTABILITY THAN PREVIOUS RUN WITH MLCAPES IN
EXCESS OF 2000 J/KG AS DEEP SHEAR TO AROUND 40KTS SUGGESTING
ORGANIZATION AND POTENTIAL SUPERCELL DEVELOPMENT. LARGE HAIL IS
POSSIBLE AND STEEP LOW LEVEL LAPSE RATES WILL ENHANCE THE DAMAGING
WIND THREAT AS WELL. TORNADO ENVIRONMENT WILL BE LESS FAVORABLE
THAN WHAT OCCURRED SUN...ESPECIALLY THERMODYNAMICALLY WITH LOWER
DEWPOINTS RESULTING IN HIGHER LCLS AND LOWER 0-3KM CAPES
RESPECTIVELY. RAW MODEL TEMPS AND SOUNDINGS SUGGEST AT OR ABOVE
THE WARMEST END OF MOS WHICH SEEMS REASONABLE CONSIDERING BETTER
MIXING POTENTIAL AND NO STRATUS TO OVERCOME UNLIKE YESTERDAY.

.LONG TERM /TONIGHT THROUGH SUNDAY/...
ISSUED AT 355 AM CDT MON JUL 7 2014

FAIRLY WIDESPREAD THUNDERSTORMS ARE ANTICIPATED TONIGHT AS A
COMPACT BUT POTENT 500 MB SHORTWAVE MOVES OVERHEAD AND PUSHES A
COLD FRONT ACROSS THE AREA. THE HIGHEST INSTABILITY WILL BE
PRESENT IN OUR SOUTH AND SOUTHWEST WHERE RECOVERY FROM YESTERDAYS
COOL FRONT WILL BE MORE ROBUST...AND THE THREAT OF SEVERE WEATHER
AND HEAVY RAIN SHOULD BE MAXIMIZED IN THOSE COUNTIES OR EVEN SOUTH
OF THE BORDER IN MISSOURI. A FLASH FLOOD WATCH HAS BEEN ISSUED
FROM ABOUT ATLANTIC TO BLOOMFIELD TO COVER THE HEAVY RAIN
THREAT...PARTICULARLY GIVEN THE AMOUNT OF RECENT RAINFALL AND THE
TOPOGRAPHY OF THOSE AREAS.

BEHIND THE COLD FRONT DRY AND COOL WEATHER WILL PREVAIL FROM
TUESDAY THROUGH THURSDAY. THERE WILL BE SMALL CHANCES FOR
OCCASIONAL POP UP SHOWERS AND STORMS GIVEN THE SEASON AND WEAK
REINFORCING 500 MB IMPULSES MOVING THROUGH THE CYCLONIC FLOW
OVERHEAD...HOWEVER INSTABILITY WILL BE SOMEWHAT LIMITED AND
COVERAGE/INTENSITY OF ANY STORMS THAT FORM SHOULD BE LOW WITH ONLY
SLIGHT POPS ADVERTISED AT TIMES. MEANWHILE TEMPERATURES AND
HUMIDITY WILL BE MUCH MORE COMFORTABLE...WITH HIGHS IN THE MID
70S TO LOWER 80S AND LOWS IN THE MID 50S TO LOWER 60S.

BY LATE THURSDAY AS SURFACE HIGH PRESSURE SLIDES OFF TOWARD THE
GREAT LAKES A RETURN OF SOUTH SOUTHEAST FLOW WITH ASSOCIATED WARM
AIR/MOISTURE ADVECTION IS ANTICIPATED...AND THIS WILL BE FOLLOWED
IN SHORT ORDER BY ANOTHER MID LEVEL TROUGH THAT WILL LIKELY
GENERATE SHOWERS AND STORMS ACROSS THE BULK OF THE AREA FROM
THURSDAY NIGHT INTO FRIDAY. THIS SIGNAL HAS BEEN PRETTY CONSISTENT
FOR A COUPLE OF DAYS AND FITS WITH SYNOPTIC CLIMATOLOGY...THUS
WITH INCREASING CONFIDENCE HAVE TAKEN POPS UP TO LIKELY FOR THESE
PERIODS. AT THIS TIME THE SEVERE WEATHER THREAT APPEARS LIMITED
BUT WE WILL BE MONITORING THAT IN THE COMING DAYS. THE FRIDAY
SYSTEM WILL PUSH A WEAK FRONTAL BOUNDARY OVER THE FORECAST AREA
THAT WILL LINGER SOMEWHERE NEARBY NEXT WEEKEND WITH LONG RANGE
MODELS STILL EXHIBITING A LOT OF VARIABILITY IN THEIR SOLUTIONS.

&&

.AVIATION...07/18Z
ISSUED AT 1248 PM CDT MON JUL 7 2014

MAIN CONCERNS THIS PERIOD WILL BE CONVECTIVE TRENDS AND WINDS FOR
TUESDAY FOLLOWING THE FRONTAL PASSAGE. AIRMASS AHEAD OF THE MAIN
SYSTEM CONTINUES TO DESTABILIZE...WEAKENING AREA OF CONVECTION
OVER NW IOWA WILL SHOULD BE NO MORE THAN A FEW SHOWERS AS IT
CROSSES THE AREA THERE THROUGH 20Z. MODELS INCREASE UPPER LEVEL
FORCING TOWARD 00Z WITH CURRENT AREA OF CONVECTION OVER NORTHEAST
NEBRASKA MOVING TOWARD WESTERN TAF SITES KFOD...KDSM AT THAT TIME.
SVR CONCERNS THIS AFTERNOON WITH POTENTIAL FOR WIND AND SOME HAIL
OVER THE AREA...WILL UPDATE AS NEEDED ONCE LINE BECOMES MORE WELL
DEFINED AND CONVECTIVE TRENDS MORE APPARENT. STORMS WILL MOVE
QUICKLY ESE THIS EVENING...WITH THE COLD FRONT HANGING UP OVER
NORTHERN MO THROUGH 09Z. THIS WILL ALLOW FOR CONTINUED CONVECTION
AND LOW CIGS ACROSS THE THROUGH 09Z SOUTHEAST AT KOTM...SOME
UNCERTAINTY AS TO HOW QUICKLY THE AREA WILL TRANSITION SOUTH OF
THE BORDER...AND MAY HAVE TO DELAY ENDING OF CONVECTION NEARER
KOTM. OTHERWISE...WINDS INCREASE WITH MIXING AFT 15Z TUESDAY WITH
NORTHWEST 13 GUST 24KTS THROUGH END OF TAF PERIOD.

&&

.HYDROLOGY...
ISSUED AT 355 AM CDT MON JUL 7 2014

THUNDERSTORMS ARE EXPECTED ACROSS MUCH OF THE FORECAST AREA
TONIGHT...BUT HEAVY RAIN PARAMETERS ARE LARGELY CONFINED TO AN
AXIS FROM SOUTHEASTERN NEBRASKA INTO NORTHERN MISSOURI AND
POSSIBLY SNEAKING INTO FAR SOUTHERN AND SOUTHWESTERN IOWA. GIVEN
THE SATURATION RESULTING FROM RECENT RAINS AS WELL AS THE
TOPOGRAPHY OF THESE AREAS...FELT IT PRUDENT TO ISSUE A FLASH FLOOD
WATCH DUE TO THE EXPECTED IMPACTS IF THE HEAVY RAIN AXIS IS FAR
ENOUGH NORTH TO AFFECT THOSE COUNTIES.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH TUESDAY
MORNING FOR ADAIR-ADAMS-APPANOOSE-CASS-CLARKE-DAVIS-DECATUR-
LUCAS-RINGGOLD-TAYLOR-UNION-WAYNE.

ENHANCING LOW LEVEL CONVERGENCE FROM NE INTO IA. 06Z NAM IS NOW
MORE AGGRESSIVE ON INSTABILITY THAN PREVIOUS RUN WITH MLCAPES IN
EXCESS OF 2000 J/KG AS DEEP SHEAR TO AROUND 40KTS SUGGESTING
ORGANIZATION AND POTENTIAL SUPERCELL DEVELOPMENT. LARGE HAIL IS
POSSIBLE AND STEEP LOW LEVEL LAPSE RATES WILL ENHANCE THE DAMAGING
&&

$$

SHORT TERM...SMALL
LONG TERM...LEE
AVIATION...REV


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