000
FXUS63 KDMX 040457
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1157 PM CDT FRI SEP 3 2010

.SHORT TERM /TONIGHT/...
WEAKENING PRESSURE GRADIENT TONIGHT AS A RIDGE OF HIGH PRESSURE
BUILDS INTO THE STATE FROM THE WEST. THE SURFACE RIDGE AXIS SHOULD
BE OVER WESTERN IOWA AROUND MIDNIGHT. ALTHOUGH STRONG WINDS
WILL BE PRESENT ALOFT OVER EASTERN IOWA TONIGHT...THE NIGHTTIME
INVERSION SHOULD PREVENT THOSE WINDS FROM REACHING THE SURFACE. AS A
RESULT OF THE CLEAR SKIES AND LIGHT WINDS...TEMPERATURES SHOULD DROP
INTO THE MID TO UPPER 40S...WELL BELOW NORMAL FOR THIS TIME OF
YEAR...BUT ABOUT 5 TO 10 DEGREES HIGHER THAN RECORD LOWS.

.LONG TERM /SATURDAY THROUGH FRIDAY/...
NW FLOW WITH UPPER TROUGH CONTINUES TO DRIVE TO THE SE THIS EVENING
WITH RATHER DRY AND COOL AIR TO QUICKLY FOLLOW INTO THE REGION FOR
SATURDAY. AS RIDGE BUILDS INTO THE AREA SAT...WIND FIELDS ALOFT WILL
WEAKEN TO THE POINT THAT ANY MIXING OF WINDS WILL RESULT IN ONLY
MODEST SFC WINDS OF 10 TO 18 MPH RATHER THAN THE ADV CRITERIA WINDS
OF TODAY. H850 TEMPS CONTINUE TO BE COOL ON SAT WITH 5 TO 10C OVER
THE REGION BY LATE AFTERNOON. THIS WILL LEAD TO QUITE COOL HIGHS
OVER THE EAST WITH UPPER 60S NORTHEAST TO THE MID 70S ACROSS THE
WEST. WITH THE HIGH PULLING EAST SATURDAY NIGHT...WEAK SOUTH FLOW
WILL RETURN WITH INCREASING WINDS ON SUNDAY. THOUGH SHORT TERM
MODELS INCREASE THETAE ADVECTION SUNDAY...DRY AIRMASS WILL RESULT IN
LITTLE OPPORTUNITY FOR ANY LEADING WAA PRECIPITATION. GUSTY
SOUTHERLY WINDS SHOULD HELP LIFT HIGHS BACK INTO THE LOWER TO MID
80S OVER MUCH OF THE REGION WITH SOME MID TO HIGH CLOUDS MOVING
ACROSS THE AREA. AS SOUTH FLOW REMAINS INTACT SUNDAY NIGHT AND
MONDAY...MILDER OVERNIGHT LOWS WILL RETURN TO THE REGION AHEAD OF
THE NEXT UPSTREAM SYSTEM. SOME TIMING QUESTION AS TO THE PASSAGE OF
THE FRONT MONDAY BUT CURRENTLY THE MED RANGE MODELS SUGGEST THAT THE
WARM SECTION WILL REMAIN ACROSS CENTRAL/SOUTHEAST SECTIONS LONG
ENOUGH TO DRIVE HIGHS IN THE MID/UPPER 80S PRIOR TO FRONTAL PASSAGE.
MODELS INCREASE INSTABILITY TO 500 TO 1000 J/KG BY LATE
AFTERNOON/EVE HOURS. WITH H700 TEMPS NEAR 12C BY LATE AFTERNOON...
ANY CONVECTION WILL BE HELD BACK UNTIL THE EVENING HOURS. BOTH GFS
AND EURO PICK UP ON THIS TREND WITH THE GFS BEING MORE AGGRESSIVE
WITH EVENING CONVECTION JUST EAST OF THE AREA. FOR NOW...WILL BE
LEANING TOWARD SLIGHT CHANCE EVE CONVECTION EAST. SVR LOOKS MUTED
WITH THE HIGHER LIKELIHOOD THAT ACTIVITY WILL BE EAST OF THE REGION
PRIOR TO IT REALLY GETTING GOING. ONE THING THAT NEEDS TO BE WATCHED
ON MONDAY WILL BE STRONG SUBSIDENCE BEHIND THE BOUNDARY. MODEST CAA
ALONG WITH THAT SHOULD HELP DRIVE WINDS BACK IN THE 30 TO 40 MPH
RANGE DEPENDING ON THE TIMING OF FEATURES.  WILL MONITOR THE NEXT
FEW DAYS. TUESDAY LOOKS TO BE ANOTHER BREEZY DAY...ESPECIALLY IN THE
MORNING NORTHEAST BUT THEN CALM DOWN AS HIGH BUILDS EAST. HIGHER
AMPLITUDE FLOW IS EXPECTED TO CONTINUE FOR THE REMAINDER OF THE WEEK
AS TROUGH OVER THE WEST BRINGS SW RETURN FLOW TO THE AREA BY TUES
NIGHT AND BEYOND. MED RANGE MODELS HAVE GENERAL TRENDS IN HAND BUT
DIFFER ON DETAILS OF TIMING. EURO/GEM ARE SLIGHTLY SLOWER AND WILL
LEAN TOWARD LATER ARRIVAL OF MORE SIGNIFICANT PRECIP THOUGH SLIGHT
CHANCES FOR SOME RETURN RAINFALL ARE POSSIBLE PRIOR TO THE ARRIVAL
OF THE MAIN SYSTEM BY LATE FRIDAY. TEMPS WILL GRADUALLY WARM BOTH
THURSDAY AND FRIDAY WITH HIGHS ONCE AGAIN CONSERVATIVELY REACHING
THE UPPER 70S TO LOWER 80S...THOUGH WITH SOME UNCERTAINTY IN AREAL
COVERAGE OF PRECIPITATION TEMPS MAY BE HIGHER BASED ON THERMAL
CONSIDERATIONS ALONE.

&&

.AVIATION...
04/06Z...HI PRES OVR THE DKTS INTO KS WILL MOVE OVR IA ON
SAT...PASSING EAST BY SAT EVE.  LGT WNWLY FLOW THRU SAT BCMG LGT SLY
TWD SNST.  NO WX OTR THAN SOME SCT TO BKN AC LATE IN TAF PD OVR THE
SW HLF OF IA.

&&

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

&&

$$

SHORT TERM/AVIATION...MS SEP 10
LONG TERM...REV

NWS DMX Office Area Forecast Discussion