000
FXUS63 KDMX 132111
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
411 PM CDT THU JUN 13 2013

.SHORT TERM.../TONIGHT /...
ISSUED AT 410 PM CDT THU JUN 13 2013

A VORT MAX RIDING THE UPPER RIDGE COMBINED WITH WEAK SURFACE FRONTAL
CONVERGENCE HAS INITIATED SOME THUNDERSTORMS OVER EASTERN NEBRASKA
IN AN AREA OF STEEPER LAPSE RATES.  EXTRAPOLATING THEIR MOVEMENT...
AND ASSUMING THEY HOLD TOGETHER...WOULD PUT THEM IN FAR SOUTHWEST
IOWA FOR A COUPLE HOURS LATER THIS AFTERNOON THEN INTO THE EARLY
EVENING BEFORE MOVING SOUTHEAST OUT OF THE STATE.  I HAVE ADJUSTED
EARLY EVENING POPS TO REFLECT THIS.

THE REST OF THE EVENING SHOULD BE QUIET WITH JUST PARTLY CLOUDY
SKIES.  AS THE SURFACE HIGH SHIFTS EAST TONIGHT WE GET INTO A
SOUTHEAST FLOW...MAINLY OVER THE WEST THIS EVENING THEN FORECAST
AREA WIDE OVERNIGHT WITH INCREASING WIND SPEED ACROSS THE WEST.  THE
FRONTAL BOUNDARY OVER THE PLAINS WILL SLOWLY PROGRESS TO THE
MISSOURI RIVER DURING THE EVENING AND BE IN OR NEAR WESTERN IOWA
OVERNIGHT.  THERE IS STRONG THETA-E ADVECTION THAT OCCURS
OVERNIGHT...ESPECIALLY AFTER 09Z AND THERE IS EVIDENCE OF A WEAK TO
MODERATE LOW LEVEL JET DEVELOPING OVER THE WEST.  IN ADDITION...
THERE ARE SEVERAL WEAK VORT MAXES RIDING THE UPPER RIDGE AND WITH
THE INCREASING THETA-E ADVECTION WE SHOULD SEE SOME THUNDERSTORMS
DEVELOP OUT WEST AND PROBABLY MOVE INTO THE WESTERN FORECAST AREA
AFTER 09Z...POSSIBLY MAKING IT TO KDSM BY 12Z.

SOME CAVEATS TO THIS ARE THAT SOUNDINGS SHOW A WELL DEFINED DRY
LAYER BETWEEN 750MB AND 850 MB AND THERE IS A WARM NOSE AT 800 MB.
ANY STORMS THAT DO DEVELOP WOULD BE ELEVATED AND LIKELY VERY HIGH
BASED SINCE THEY WOULD HAVE TO FORM ABOVE 700 MB...WHERE WE HAVE
BETTER MOISTURE.  RAINFALL IS NOT EXPECTED TO BE GREAT THROUGH 12Z
EITHER FOR REASONS ALREADY MENTIONED.  SOUNDING AND TIME HEIGHT
CROSS SECTIONS DO SHOW POCKETS OF LOW LEVEL MOISTURE SO I DO THINK
WE WILL SEE A CLOUD DECK AT 4-6KT IN AREAS...AND POSSIBLY EVEN LOWER
THAN THAT LOCALLY.  AS FOR TEMPS...THEY WILL VARY QUITE A BIT FROM
NORTHEAST TO SOUTHWEST.  WHERE THE WINDS TURN SOUTHEASTERLY EARLIER
AND INCREASE OVERNIGHT...TEMPS SHOULD REMAIN IN THE LOWER TO MID 60S
BUT IN THE NORTHEAST AND EAST WHERE WE WILL BE UNDER THE INFLUENCE
OF THE HIGH...TEMPS WILL DROP INTO THE MID TO UPPER 50S.

.LONG TERM.../FRIDAY THROUGH THURSDAY/...
ISSUED AT 410 PM CDT THU JUN 13 2013

FAIRLY ACTIVE WEATHER PATTERN CONTINUES FRIDAY AND THROUGHOUT THE
WEEKEND THE 500MB RIDGE TRANSITIONING TO MORE ZONAL FLOW BY
SATURDAY. SEVERAL SHORTWAVES MOVE ACROSS THE STATE FRIDAY THROUGH
SUNDAY...WITH FINALLY A COLD FRONT AND UPPER LOW TRACKING ACROSS
THE REGION BY MONDAY. LEANED TOWARD A BLEND OF THE SREF/NAM AND
THE 12Z HIRES WEST-NMM FRIDAY...THEN GFS/ECMWF OVER THE WEEKEND
INTO EARLY NEXT WEEK.

GOOD THETA-E ADVECTION CONTINUES OVER THE FORECAST AREA THROUGH
THE DAY TOMORROW WITH BEST FORCING BY THE AFTERNOON HOURS AS THE
FIRST OF SEVERAL VORT MAXES MOVE ACROSS THE STATE. HIGHEST POPS
ARE ACROSS CENTRAL TO NORTHERN IOWA PAST 18Z AND CUT BACK ON
EASTWARD MOVEMENT DURING THE MORNING HOURS FRIDAY. ANOTHER 500MB
VORT MAX MOVES ACROSS THE STATE BY AROUND 06Z SATURDAY. VERY GOOD
MOISTURE TRANSPORT INTO THE STATE WITH PRECIPITABLE WATER VALUES
RANGING FROM 1.5 TO 2 INCHES. CONCERNED ABOUT ADDITIONAL FLOODING
AND FLASH FLOODING ACROSS PORTIONS OF NORTHERN IOWA FRIDAY NIGHT
AND MAY CONSIDER A FLASH FLOOD WATCH WITH NEXT FORECAST PACKAGE
WITH HIGHER CONFIDENCE IN TIMING AND LOCATION OF HEAVIEST
RAINFALL.

ANOTHER VORT MAX MOVES THROUGH THE STATE BY SATURDAY AFTERNOON AND
SHIFTS TO THE SOUTHEAST BY SATURDAY NIGHT. BEST INSTABILITY LOOKS
TO BE CONFINED TO SOUTHERN IOWA AND DECENT DEEP LAYER SHEAR
PRESENT WITH THIS SHORTWAVE.

DECENT COLD FRONT AND UPPER LOW MOVE ACROSS THE REGION BY MONDAY
AND DRY THINGS OUT FOR A FEW DAYS NEXT WEEK. LEANED TOWARD
TWEAKING MAX TEMPS UP SLIGHTLY BY THE MIDDLE OF NEXT WEEK WITH THE
UPPER RIDGE SHIFT EAST AND ALLOWING FOR RETURN FLOW ACROSS THE
FORECAST AREA.

&&

.AVIATION...13/18Z
ISSUED AT 1250 AM CDT THU JUN 13 2013

VFR CONDITIONS CONTINUE THROUGH 06Z.  WARM AND MORE MOIST AIR WILL
RETURN TO THE STATE OVERNIGHT THOUGH AS WINDS BECOME SOUTHEAST AND
HIGH PRESSURE SHIFTS TO THE EAST.  AN APPROACHING SURFACE LOW OVER
THE PLAINS WITH A WARM FRONT ACROSS EASTERN IOWA WILL BE THE FOCUS
FOR SOME HIGH BASED THUNDERSTORMS THAT WILL MOVE INTO WESTERN IOWA
AFT 09Z AND APPROACH KFOD AND POSSIBLY AS FAR E AS KDSM BY 12Z.  CIG
WILL DEVELOP AND LOWER TO BETWEEN 8-10KFT WITH LOWER CIGS
POSSIBLE.

&&

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

&&

$$

SHORT TERM...FAB
LONG TERM...PODRAZIK
AVIATION...FAB