381 
FXUS63 KDMX 300503 CCA
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1200 AM CDT TUE AUG 30 2011

...UPDATED 06Z AVIATION DISCUSSION...

.SHORT TERM /TONIGHT/...
LEE SIDE TROUGH IN FULL SWING OVER THE WESTERN PLAINS WITH SOUTHERN 
STREAM SYSTEM LOCATED OVER OK THIS AFTERNOON. WARM AIR ADVECTION HAS 
ALREADY BEGUN AND RETURN MOISTURE FLOW HAS RESULTED IN SOME 
CONVECTION OVER THE HIGH PLAINS.  MODELS CONTINUE IN GOOD AGREEMENT 
FOR THE OVERNIGHT WITH INCREASING LIFT AND THETAE ADVECTION BY 12Z. 
WITH CLOUDS ON THE INCREASE AND LIGHT SOUTH WINDS...NOT EXPECTING A 
RETURN OF FOG TO THE REGION...THOUGH SOME PATCHY FOG MAY DEVELOP 
NORTHEAST DURING THE EARLY MORNING HOURS. HAVE LEFT AREA DRY UNTIL 
AFT 06Z WITH INCREASING SATURATION FROM THE WEST. LOWS WILL DROP 
ONLY INTO THE 50S AND 60S WITH THE CLOUD COVER. SOUNDINGS SUGGEST 
THAT INSTABILITY WILL BE LIMITED OVERNIGHT UNTIL THE LOW LEVEL JET 
AND WARM AIR ADVECTION CREATE SOME ELEVATED INSTABILITY FROM 09-12Z 
TUESDAY. 

.LONG TERM /TUESDAY THROUGH MONDAY/...A COUPLE OF CONCERNS IN THE 
EXTENDED WITH THE FIRST ITEM FOR TOMORROWS RAINFALL CHANCES...THEN
THE HEAT THURSDAY...AND RAIN CHANCES BY THE END OF THE WEEK.
MODELS ARE IN GENERALLY GOOD AGREEMENT THROUGH THURSDAY WITH
TIMING OF SHORTWAVE TUESDAY AND WARM UP WEDNESDAY AND THURSDAY. NAM
IS THE WARMEST WEDNESDAY AND THURSDAY FOR MAX TEMPS...SO BLENDED
WITH THE GFS/NAM/SREF. BY FRIDAY...THE 12Z RUNS OF THE ECMWF AND
GFS ARE NOT IN GOOD AGREEMENT WITH TIMING OF COLD FRONT LATER THIS
WEEK. LATEST ECMWF HAS TWO SMALLER SHORTWAVES THROUGH FRIDAY AND
SATURDAY COMPARED TO THE GFS SHOWING ONE LARGER SYSTEM THROUGH ON
FRIDAY.

TUESDAY THROUGH THURSDAY...A MID-LEVEL SHORTWAVE AND 500MB VORT MAX 
WILL BRING SOME RAIN TO THE FORECAST AREA THROUGHOUT MUCH OF THE DAY 
TUESDAY. THETA-E ADVECTION AND MOISTURE TRANSPORT INTENSIFY BY 12Z 
TUESDAY ACROSS WESTERN IOWA AND TRANSITION EASTWARD BEFORE MOVING 
OUT BY 00-03Z WEDNESDAY. BUFR SOUNDINGS CONTINUE TO SHOW A 6 HOUR
PERIOD OF DEEP MOISTURE DURING MIDDAY AS WELL AS DECENT ISENTROPIC
LIFT ALONG THE 300K TO 310K SURFACES...SO EXPECTING A GOOD STEADY
RAIN THROUGH MUCH OF THE DAY TOMORROW BEFORE TAPERING OFF IN THE
LATE AFTERNOON/EARLY EVENING. QPF AMOUNTS AND HIGHEST POPS ARE IN
THE SOUTH WHERE THE BEST ISENTROPIC LIFT IS LOCATED.

WARMER TEMPERATURES IN STORE BY WEDNESDAY AND THURSDAY...WITH THE 
HOTTEST DAY LOOKING TO OCCUR ON THURSDAY. LARGE UPPER LEVEL RIDGE 
BUILDS INTO THE CENTRAL PORTION OF THE COUNTRY ON WEDNESDAY AND 
SHIFTS EAST INTO THE OHIO/TENNESSEE VALLEYS BY THURSDAY. THIS WILL 
SET UP THE STATE FOR VERY HOT CONDITIONS ON THURSDAY. GOOD MIXING
DEVELOPS THROUGHOUT THE DAY THURSDAY...GENERALLY MIXES DOWN FROM
ABOUT 900MB OR EVEN NEAR 875MB. NAM SOUNDINGS ARE THE WARMEST
ACROSS CENTRAL IOWA...WITH TEMPS NEAR 100 DEGREES OVER THE SOUTH.
850MB TEMPS WARM INTO THE +26C TO 27C RANGE BY 21Z THURSDAY.
SURFACE DEW POINTS RANGE IN THE LOWER 70S AND MAY PUSH THE HEAT 
INDEX INTO THE LOW 100S IN SOME AREAS. SO A CONSIDERATION FOR A
HEAT HEADLINE FOR FUTURE FORECAST PACKAGES.

FRIDAY INTO SATURDAY...AS MENTIONED ABOVE...THE ECMWF BRINGS ACROSS 
A SECONDARY COLD FRONT ON SATURDAY WITH ANOTHER SHORTWAVE THAT MOVES 
OVER THE DAKOTAS/NORTHERN MINNESOTA ON SATURDAY. THE FIRST COLD
FRONT THE ECMWF PREDICTS WILL QUICKLY MOVE THROUGH FRIDAY
MORNING...WHILE THE GFS IS SLOWER AND NOT UNTIL FRIDAY EVENING.
WENT DRY FOR SATURDAY AS THIS WAS FIRST HINT OF A SECONDARY COLD
FRONT FROM THE ECMWF...BUT MAY NEED TO ADD SOME POPS ON SATURDAY
AFTERNOON IF THIS TREND CONTINUES. 

SUNDAY AND MONDAY...COLDEST AIR MASS OF THE SEASON WILL AFFECT MUCH 
OF THE HOLIDAY WEEKEND.  LOW TEMPS SUNDAY NIGHT AND MONDAY NIGHT 
LOOK TO DROP WELL INTO THE 40S ACROSS NORTHERN IOWA WITH SURFACE 
HIGH PRESSURE DIRECTLY OVERHEAD. LOWERED TEMPS DURING THIS PERIOD.

&&

.AVIATION...30/06Z
CEILINGS SHOULD GRADUALLY LOWER DURING THE COURSE THE OVERNIGHT 
HOURS AS AN UPPER LEVEL SHORTWAVE NEARS THE AREA....BUT SHOULD 
REMAIN VFR THROUGH THE BEGINNING OF TODAYS RAIN EVENT. THE UPPER 
MIDWEST RADAR MOSAIC SHOWS WIDESPREAD WEAK TO MODERATE ECHOES ACROSS 
WESTERN IOWA...BUT SURFACE OBSERVATIONS SEEM TO INDICATE THAT MOST 
OF THIS IS VIRGA. ONCE THE MAIN SYSTEM ARRIVES...WIDESPREAD RAINFALL 
AND MVFR TO NEAR IFR CONDITIONS CAN BE EXPECTED FOR MUCH OF THE DAY 
BEFORE THE SYSTEM PULLS OUT AROUND SUNSET.

&&

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

&&

$$

SHORT TERM...REV
LONG TERM...KLP
AVIATION...SKOW