National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KDMX 251737
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1237 PM CDT FRI JUL 25 2014

.SHORT TERM /TODAY/...
ISSUED AT 338 AM CDT FRI JUL 25 2014

PRIMARY CONCERN TODAY WILL BE CONVECTIVE TRENDS AND TEMPS. MCS
EXPANDED EARLY THIS MORNING DRIVEN BY BOTH KINEMATIC AND
THERMODYNAMIC FORCING. POSITIVE DIFFERENTIAL VORTICITY ADVECTION
FROM SHORT WAVES TOPPING THE SWRN CONUS RIDGE...TIED INTO LOBE FROM
SWRN CANADIAN UPPER LOW...CONTINUES FROM THE ERN DAKOTAS INTO IA.
STRONG H85/H7 THETA-E ADVECTION AND H85 MOISTURE TRANSPORT AHEAD OF
THE SHORT WAVES HAS ALSO GREATLY FUELED AND INFLUENCED THIS ELEVATED
CONVECTION.  MAIN CONCERNS APPEAR TO BE FREQUENT LIGHTNING AND
LOCALLY HEAVY RAINS. MUCAPE AXIS CONTINUES TO ADVANCE INTO IA WITH
SYSTEM AND THREE HOUR CHANGES 500-1500 J/KG.  EFFECTIVE SHEAR HAS
DECREASED SOMEWHAT...NOW PEAKING BEHIND CURRENT MCS...SO THIS AND
COMBINATION OF FREEZING LEVELS EXCEEDING 14KFT HAS APPEARED TO
DIMINISH SEVERE THREAT SOMEWHAT...HAIL IN PARTICULAR.  THIS LESS
FAVORABLE SEVERE ENVIRONMENT HAS ELEVATED THE HEAVY RAIN THREAT
HOWEVER WITH PWS RISING WELL THROUGH THE 1-2 INCH RANGE AND WARM
CLOUD DEPTHS OVER 4KM.  CELLS SEEM TO BE FOLLOWING SEWD UPWARD
PROPAGATION VECTOR.  WITH MEAN WIND NORMAL TO VEERING LOW LEVEL JET
THIS HAS KEEP THE MAGNITUDE HIGH ENOUGH TO KEEP THINGS SOMEWHAT
PROGRESSIVE. DO NOT EXPECT MUCH IN THE WAY OF FLASH FLOODING WITH
RECENT DRY SPELL...FLASH FLOOD GUIDANCE CONTINUING TO REBOUND...AND
MATURE CROPS.

LARGE SCALE FORCING LOOKS TO WANE INTO THE AFTERNOON SO SEE NO
REASON TO ARGUE WITH HI RES MODELS ENDING PRECIP BY AFTERNOON AS MCS
EXITS TO THE EAST. ATTENTION WILL THEN TURN TO TEMPS WITH WARM
SECTOR RAPIDLY SURGING NWD BEHIND MCS AHEAD OF APPROACHING SURFACE
TROUGH. CONSENSUS OF RAW MODEL TEMPS WOULD SUGGEST MAXES NEED TO BE
RAISED A TAD SO NOW HAVE M80S/LOW 90S NE-SW. RESULTANT HEAT INDICES
ARE STILL IN LINE WITH PREVIOUS ADVISORY HOWEVER SO NO CHANGES
THERE.

.LONG TERM /TONIGHT THROUGH THURSDAY/...
ISSUED AT 338 AM CDT FRI JUL 25 2014

MAIN FORCING EXITING TO THE EAST AND WEAK TROUGH EXPECTED TO PASS
SOUTH OF THE FORECAST AREA BY 12Z SATURDAY. HOWEVER...THAT BEING
SAID THERE WILL BE ONLY MODEST CHANGES IN AIRMASS THROUGH FRIDAY
NIGHT AND SATURDAY WITH WARM THICKNESS AND H850 TEMPS STILL HOLDING
ACROSS THE AREA...ESPECIALLY THE SOUTH HALF.  ALOFT...A RATHER WEAK
UPPER LEVEL WAVE AT H500 WILL TRANSLATE EAST INTO WESTERN IOWA BY
MIDDAY SATURDAY. THIS WILL CONTINUE TO SLIDE SOUTHEAST AND INDUCE
ANOTHER WEAK SFC WAVE OVER SOUTHERN/SOUTHEAST IOWA BY LATE AFTERNOON
AND EARLY EVENING SATURDAY.  WITH INSTABILITY REMAINING QUITE HIGH
ACROSS THE SOUTH SATURDAY AFTERNOON AND EVENING...WEAK LIFT AND SFC
CONVERGENCE...SOME SCT THUNDER IS EXPECT FOR THE LATE AFTERNOON AND
EVENING HOURS SOUTH THIRD. HAVE EXPANDED POPS A BIT OVER THE SOUTH.
OVERNIGHT SATURDAY NIGHT THE THERMAL GRADIENT AT H850 INCREASES
ALONG WITH A RENEWED...BUT WEAK INCREASE IN H850 FLOW INTO THE
BOUNDARY. THIS SHOULD RESULT IN A BUILDING OF THUNDERSTORMS OVER THE
SOUTH THIRD DURING THE MID TO LATE EVENING HOURS AS THE LOW LEVEL
JET BEGINS TO SHOW ITSELF.  LATER IN THE EVENING THE JET WILL
INTENSIFY AND WITH THE H500 WAVE MOVING EAST OF THE AREA...TAKE MOST
OF THE CONVECTION OUT OF THE AREA AFTER 06Z. AS HAS BEEN THE TREND
FOR THE PAST THREE DAYS...NO CHANGES TO THE TIMING AND EVOLUTION OF
THE STRONGER COLD FRONT EXPECTED TO DROP SOUTH INTO THE AREA ON
SUNDAY. TONIGHTS WATER VAPOR IMAGE SHOWS THE STRONG WAVE IN ALBERTA
WHICH IS EXPECTED TO MOVE EAST AND EVENTUALLY PHASE WITH THE H500
GYRE OVER HUDSON BAY... CAUSING THE ENTIRE EASTERN CONUS PATTERN TO
AMPLIFY NEXT WEEK. THE BEST FORCING WITH THE CANADIAN H500 WAVE
OVER THE NORTHERN PLAINS BY SUNDAY WILL DIG SOUTHEAST ACROSS MN
AND WISCONSIN WITH MAINLY DIURNAL SHOWERS ACROSS MN/NORTHERN IA
DISSIPATING BY SUNSET AS THE COLDER AIR RUSHES INTO THE REGION
SUNDAY AFTERNOON WITH THE PASSAGE OF THE FIRST COLD FRONT.
THUS...RAIN CHANCES LOOK SLIM OVER MOST OF THE REGION SUNDAY WITH
ONLY A SLIGHT CHANCE FOR RAIN OVER THE NORTHEAST. A SECOND
BACKDOOR FRONT WILL MARCH SOUTH DURING THE NIGHT AND EXIT THE
SOUTHEAST BY 12Z. NORTHEAST FLOW WILL INTENSIFY DURING THE
DAY...AND THIS IS WHEN WE WILL REALLY APPRECIATE THE COOLER
WEATHER. H850 TEMPS BY LATE AFTERNOON WILL HOLD TO NEAR 10C ACROSS
THE AREA. THIS SHOULD LEAD TO HIGHS IN THE LOWER 70S NORTHEAST TO
THE MID 70S IN THE SOUTH. CLOUDS WILL LIKELY BUILD INTO THE AREA
DURING THE LATE MORNING AND AFTERNOON HOURS AS WELL WITH THE
COLDER AIR ALOFT. COOL HIGH PRESSURE WILL DOMINATE THE AREA
THROUGH WEDNESDAY WITH ONLY A MODEST WARMING ALOFT. THUS...EXPECT
TEMPERATURES TO HOLD PAT IN THE 70S TO NEAR 80 DURING THE DAY AND
IN THE 50S TO LOWER 60S AT NIGHT. PATCHY FOG MAY OCCUR...
ESPECIALLY IN LOW LYING AREAS AT TIMES THROUGH THE PERIOD. BY
MIDWEEK A MODEST SHORTWAVE WILL DROP SOUTH IN THE NORTHWEST FLOW
ON THE BACK SIDE OF THE H500 LOW OVER THE EASTERN CONUS. THIS MAY
FIRE A FEW SHOWERS AND ISOLATED THUNDERSTORMS WED AFTERNOON...
THOUGH ANY INSTABILITY REMAINS QUITE LOW. ADDITIONAL WAVE ENERGY
TRACKING SOUTHEAST MAY AFFECT THE AREA THURSDAY AND FRIDAY...
THOUGH CONFIDENCE REMAINS LOW TOWARD THE END OF THE WEEK ON BOTH
TIMING AND PLACEMENT OF ANY SYSTEM DROPPING SOUTH WITH THE
NORTHWEST FLOW. COOL WEATHER WILL PERSIST THROUGH THE END OF NEXT
WEEK.

&&

.AVIATION...25/18Z
ISSUED AT 1233 PM CDT FRI JUL 25 2014

AREAS OF STRATUS WILL CONTINUE TO AFFECT KFOD AND KDSM THROUGH THE
EARLY AFTERNOON HOURS BEFORE LIFTING TO VFR. SOUTHEASTERLY WINDS
WILL CONTINUE TO BE STRONG AND GUSTY THROUGH 00Z. LOW WILL
APPROACH FROM THE WEST...AND WINDS WILL DECREASE. LIGHTER WINDS
AND VFR CEILINGS MAY ALLOW FOR BR/FG AT SITES...ESPECIALLY WITH
LOW LEVEL MOISTURE FROM OVERNIGHT STORMS LAST NIGHT. HAVE TRENDED
TOWARDS MVFR AND IFR VISIBILITIES NEAR 12Z FOR NOW. CONDITIONS
WILL AGAIN QUICKLY IMPROVE TO VFR BEYOND 12Z.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
HEAT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR ADAMS-CASS-
RINGGOLD-TAYLOR-UNION.

&&

$$

SHORT TERM...SMALL
LONG TERM...REV
AVIATION...AWB