000
FXUS63 KDMX 120453
AFDDMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DES MOINES IA
1153 PM CDT TUE JUN 11 2013

.SHORT TERM.../TONIGHT /...
ISSUED AT 303 PM CDT TUE JUN 11 2013

MAIN CONCERN IS OBVIOUSLY CONVECTIVE TRENDS INTO THE NIGHT.  CURRENT
SCENARIO HAS VERY UNSTABLE AIR MASS IN PLACE OVER MUCH OF THE AREA
WITH RAP2 MLCAPES 1-3K J/KG.  HOWEVER CINH BELOW NOTED ELEVATED
MIXED LAYER /EML/ IS QUITE HIGH AS WELL...150 J/KG OR MORE.
ALTHOUGH ISOLATED RELATIVELY WEAK ELEVATED CONVECTION MAY CONTINUE
INTO THE EARLY EVENING AS WEAK SHORT WAVES TOP THE RIDGE AND VERY
HIGH BASED WARM ADVECTION CONTINUES...THE MAIN ATTENTION WILL BE TO
THE WEST.

CURRENT MLCIN WEAKNESS IS OVER THE WRN THIRD OF SD AND THIS WOULD BE
THE AREA OF CONCERN FOR SURFACE BASED DEVELOPMENT LATE THIS
EVENING.  ALTHOUGH OBJECTIVE ANALYSIS INDICATES REDUCED CINH THERE
NOW...VISIBLE SATELLITE IMAGERY STILL SHOWS CAPPED ENVIRONMENT VIA
CLOUDS STREETS.  HOWEVER POTENT SHORT WAVE UPSTREAM ENTERING SWRN WY
WILL LIKELY MODIFY THE ENVIRONMENT...REDUCING CINH AND EVENTUALLY
PRODUCING AN MCS.  FORWARD PROPAGATING MCS MOTION SUGGESTS NEARLY
WEST-EAST MOVEMENT AT 50-60KTS...WHICH WOULD MAINLY POINT JUST NORTH
OF IOWA.  THIS IS ALSO THE AREA TARGETED BY SPC SSEO.  OVERALL
CONFIDENCE IN THIS EVOLUTION IS NOT GREAT HOWEVER AS HI RES
CONVECTION ALLOWING MODELS HAVE VARIOUS SOLUTIONS NOT INCREASING
FORECAST CONFIDENCE.  MOST DEVELOP AN MCS OVER SD 00Z-06Z BUT EWD
EVOLUTION IS IN QUESTION.  12Z HIRES ARW CORE DEPICTS A WELL DEFINED
MCS...POSSIBLY DERECHO...WHILE THE NMM VERSION HAS A LESS DEFINED
CONVECTIVE COMPLEX.  FAIRMONT FORECAST SOUNDINGS MAY SUGGEST THE
LATTER WITH EML BASE RISING AND VERY STABLE AIR MASS BELOW 3KM
THROUGH 06Z.  3KM WARM NOSE DOES MODIFY SOMEWHAT BY 12Z BUT IT MAY
BE DIFFICULT TO GET CONVECTION ROOTED TOO LOW AS IT APPROACHES IA AS
IT IS STILL SOMEWHAT STABLE...SO IT MAY BE ON THE DOWNWARD TREND.
THUS OVERNIGHT SEVERITY REMAINS IN QUESTION...BUT CONFIDENCE IS
THERE TO KEEP LIKELY POPS GOING NORTH LATE FOR PRECIP IN SOME FORM.

.LONG TERM.../WEDNESDAY THROUGH TUESDAY/...
ISSUED AT 303 PM CDT TUE JUN 11 2013

THE MCS MENTIONED IN THE TONIGHT DISCUSSION SHOULD HOLD TOGETHER
WEDNESDAY MORNING AS IT CROSSES NORTHERN IOWA. BASED ON SPC/S
PLACEMENT OF THE MOD RISK FOR DAY TWO THE FEELING IS THAT THERE
WILL BE SOME WEAKENING OF THE MCS DURING THE MORNING ACROSS
NORTHERN IOWA. HOWEVER...IF IT DEVELOPS INTO A DERECHO OVERNIGHT
AND CAN LAST THROUGH THE NIGHT TIME HOURS THEN IT SHOULD NOT HAVE
A PROBLEM SUSTAINING ITSELF ONCE THE SUN COMES UP. THUS WE COULD
SEE AN ACTIVE MORNING. ATTENTION THEN SHIFTS TO WEDNESDAY
AFTERNOON. THE SURFACE LOW WILL SHIFT ACROSS IOWA DURING THE DAY
AND WHERE IT WILL BE DURING PEAK HEATING...AS WELL AS THE COLD
FRONT LOCATION...WILL DEPEND SEVERE POTENTIAL FOR LATER WEDNESDAY.
THE AIR MASS WILL BE UNSTABLE ENOUGH THAT WHEN STORMS REFIRE THEY
WILL GO SEVERE FAIRLY QUICKLY. THE EURO IS AND HAS BEEN SLOWER
WITH THE MOVEMENT OF THE LOW AND FRONTAL BOUNDARY PLACING MORE OF
CENTRAL IOWA IN A THREAT BUT IT IS AN OUTLIER. THE REMAINING MODELS
ALL HAVE THE LOW IN EASTERN IOWA BY 18-21Z. IF ANY SEVERE THREAT
EXISTED OVER THE EASTERN THIRD OF CENTRAL IOWA...IT WOULD BE GONE
BY 00Z.

CONDITIONS WILL RAPIDLY IMPROVE FOR WEDNESDAY NIGHT AND
THURSDAY AS HIGH PRESSURE BUILDS INTO THE AREA. BY FRIDAY THOUGH
THE UPPER LEVEL RIDGE AXIS IS OVER WESTERN IOWA WITH A SHORT WAVE
EXPECTED TO TOP THE RIDGE BRINGING A CHANCE FOR THUNDERSTORMS TO
THE WESTERN HALF OF IOWA MAINLY FRIDAY. THE UPPER RIDGE GETS
PUSHED EAST AND FLATTENED FRIDAY NIGHT THROUGH SATURDAY IN
RESPONSE TO A POTENT SHORTWAVE OVER THE NORTHERN PLAINS. A FRONTAL
BOUNDARY WILL ALSO PUSH ACROSS THE AREA SATURDAY INTO SUNDAY FOR
ADDITIONAL THUNDERSTORM CHANCES. ANOTHER POTENT SHORTWAVE WILL
DROP ACROSS THE STATE ON SUNDAY NIGHT INTO MONDAY WHEN ADDITIONAL
THUNDERSTORMS...POSSIBLY AN MCS.. WILL TRAVEL ACROSS MAINLY
SOUTHERN IOWA.

FOR THE REST OF THE EXTENDED...UPPER LEVEL RIDGING WILL RE-
ESTABLISH ITSELF ACROSS THE ROCKIES INTO THE HIGH PLAINS BUT A
DEEP LOW OVER THE WEST COAST PROMISES TO SEND SHORTWAVES ATOP THE
RIDGE RIGHT INTO THE MIDWEST. TIMING OF SUCH FEATURES THIS FAR OUT
THOUGH ARE NEAR IMPOSSIBLE SO I EITHER WENT DRY OR PUT SOME
SLIGHTS IN FOR PERIODS I THOUGHT HAD A BETTER POTENTIAL.

&&

.AVIATION...12/06Z
ISSUED AT 1149 PM CDT TUE JUN 11 2013

THUNDERSTORMS IN NORTH CENTRAL NEBRASKA WILL PUSH EASTWARD
OVERNIGHT...AND ADDITIONAL DEVELOPMENT AHEAD OF STORMS MAY ALSO
AFFECT NORTHERN SITES. HAVE INCLUDED VCTS MENTION...THOUGH TS FROM
TIME TO TIME ARE POSSIBLE AT KMCW/KALO AND POSSIBLY KFOD. CEILINGS
WILL REMAIN PRIMARILY VFR...THOUGH LOW LEVEL SATURATION OCCURS
NEAR 12Z AND LOW VFR AND MVFR CEILINGS AND VISIBILITIES ARE POSSIBLE
AT SITES...BUT STILL HAVE LOW CONFIDENCE. CEILINGS WILL RAISE BY
18Z...BUT COULD SEE ADDITIONAL CHANCES FOR THUNDER AT ALL SITES IN
THE AFTERNOON HOURS. HAVE NOT INCLUDED THIS ATTM DUE TO UNCERTAINTY
IN TIMING AND LOCATION. WINDS WILL SHIFT TO THE NORTH THROUGH THE
PERIOD.

&&

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

&&

$$

SHORT TERM...SMALL
LONG TERM...FAB
AVIATION...AWB