194 FXUS63 KDMX 111124 AFDDMX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE DES MOINES IA 624 AM CDT TUE JUN 11 2013 .SHORT TERM.../TODAY /... ISSUED AT 349 AM CDT TUE JUN 11 2013 TRICKY FORECAST TODAY...WITH REGARDS TO TEMPERATURES AND PRECIP CHANCES. CURRENTLY HAVE A DEVELOPING AREA OF LOW PRESSURE OFF TO THE WEST ACROSS WESTERN HIGH PLAINS...WITH AN EXITING AREA OF SURFACE HIGH PRESSURE. WEAK IMPULSES CONTINUE TO TOP THE UPPER LEVEL RIDGE IN PLACE ACROSS THE REGION...AND ARE EXPECTED TO MOVE THROUGH THE CWA ALOFT TODAY. ALSO HAVE STRONG SOUTHWESTERLY FLOW ALOFT...PUMPING MOISTURE INTO STATE WITH MOISTURE TRANSPORT ORIENTED INTO CENTRAL IOWA AND BOUNDARY MOVING THROUGH ALOFT. THIS COULD SPARK SOME CONVECTIVE ACTIVITY ACROSS THE CWA THIS MORNING INTO THE AFTERNOON HOURS. HOWEVER THERMAL RIDGE ALSO BUILDING INTO THE CWA...LIMITING POTENTIAL ACTIVITY AND CAPPING OFF ANY SURFACE BASED STORMS. SOUNDINGS INDICATE ANY ACTIVITY WOULD BE VERY HIGH BASED AT AROUND 10 TO 15KFT. HAVE CONFINED THEM TO THE NORTHEASTERN HALF OF THE CWA THIS AFTERNOON WHEN THETA-E ADVECTION IS STRONGEST...SOME UPPER LEVEL ENERGY APPROACHES AND SOUNDINGS GO NEAR ADIABATIC ALOFT SUGGESTING GREATER CHANCE FOR ELEVATED ACTIVITY. TEMPERATURES ALSO TRICKY AS MID/HIGH CLOUD COVER EXPECTED TO BE FAIRLY EXTENSIVE THROUGHOUT THE MORNING...POSSIBLY INTO THE AFTERNOON LIMITING HEATING. SFC WARM FRONT TO LIFT THROUGH THE CWA AND BE SITUATED ACROSS CENTRAL/NORTHERN IOWA BY LATE TODAY. THEREFORE STILL EXPECT SOUTHERN CWA TO WARM QUITE A BIT TODAY...WITH HIGHS IN THE UPPER 80S TO AROUND 90 SOUTH OF THE FRONT AND HIGHS IN THE LOW TO MID 80S NORTH OF THE FRONT. .LONG TERM.../TONIGHT THROUGH MONDAY/... ISSUED AT 349 AM CDT TUE JUN 11 2013 WARM FRONT WILL BE ESTABLISHED ACROSS THE CENTRAL PORTION OF THE STATE TONIGHT NEAR THE HIGHWAY 30 CORRIDOR. GENERALLY...LITTLE IF ANY PCPN IS EXPECTED SOUTH OF THE FRONT OVERNIGHT WHERE LIFT REMAINS WEAK. FARTHER NORTH...ISENTROPIC LIFT IS EXPECTED TO INCREASE OVERNIGHT AS LOW LEVEL LOW INCREASES INTO THE STATE. INITIALLY...EXPECT CONVECTION TO BE ISOLD/SCT THIS EVENING AND ELEVATED. AS THE NIGHT PERSISTS...MID LEVEL KINEMATIC FORCING WILL INCREASE IN ADVANCE OF THE SHORTWAVE WITH COVERAGE OF CONVECTION INCREASING. THE THREAT WILL EXIST FOR SOME DAMAGING WINDS GIVEN THE DRY SUBCLOUD LAYER. MAIN UPPER SYSTEM WILL ARRIVE ON WEDNESDAY WITH THE THREAT OF CONVECTION PERSISTING ACROSS THE NORTH IN THE MORNING. MAIN CONCERN IS TIMING OF PASSAGE OF SURFACE WAVE DURING THE AFTERNOON. ANTICIPATE RAPID DESTABILIZATION IN ADVANCE OF THE SURFACE WAVE IN THE FAR EAST BY EARLY AFTERNOON. SHEAR PARAMETERS ALSO INCREASE DURING THE DAY WITH 0-6KM BULK SHEAR OF 50-70KTS. 0-3KM HELICITY VALUES ARE FROM 100-200 BUT LIKELY HIGHER NEAR ANY BOUNDARIES. APPEARS ALL MODES OF SEVERE WEATHER WOULD BE POSSIBLE WITH INITIAL DEVELOPMENT AS SUPERCELLS LIKELY BEFORE TRANSITIONING INTO FORWARD PROPAGATING MCS FARTHER EAST. BY 18Z ON WEDNESDAY...MODELS GENERALLY HAVE SURFACE LOW/TRIPLE POINT NEAR TAMA IN THE EASTERN FORECAST AREA. AT THIS POINT...IT APPEARS THE BEST THREAT FOR THE MOST INTENSE CONVECTION WILL OCCUR JUST EAST OF THE DES MOINES FORECAST AREA ALTHOUGH CLOSE ATTENTION WILL BE PAID TO THIS AS THE TIME NEARS. FARTHER NORTH...SHOWERS AND THUNDERSTORMS WILL PERSIST FOR MUCH OF THE DAY IN NORTHERN IOWA WHERE MID LEVEL QG FORCING BEHIND SURFACE BOUNDARY WILL SUPPORT PCPN. THIS SYSTEM WILL DEPART QUICKLY ON WEDNESDAY EVENING WITH RELATIVELY TRANQUIL CONDITIONS THROUGH THURSDAY. WILL BEGIN TO SEE WARM ADVECTION AND MOISTURE TRANSPORT INCREASE LATE THURSDAY NIGHT INTO FRIDAY WITH ISOLD TO SCT THUNDERSTORM CHANCES INCREASING MAINLY WEST AND CENTRAL IOWA. MORE ORGANIZED AND WIDESPREAD CONVECTION IS ANTICIPATED FRIDAY NIGHT INTO EARLY SATURDAY AS A SHORTWAVE PASSES THROUGH THE MIDWEST. ADDITIONAL CHANCES FOR THUNDERSTORMS WILL PERSIST FOR MUCH OF THE FORECAST PERIOD...HOWEVER MORE RECENT MODELS RUNS INDICATE THE BEST THREATS MAY BE IN SOUTHERN IOWA INTO MISSOURI WITH DRIER AND COOLER CONDITIONS FARTHER NORTH. && .AVIATION...11/12Z ISSUED AT 624 AM CDT TUE JUN 11 2013 HIGH CLOUDS MAINLY ACROSS THE AREA CURRENTLY...WITH SOME LOW VFR/POSSIBLY HIGHER MVFR CIGS EXPECTED AS CU DECK DEVELOPS BY LATE MORNING INTO THE AFTERNOON HOURS. CHANCE FOR SOME THUNDERSTORMS MAINLY ACROSS THE NORTHEASTERN SITES THIS AFTERNOON AND THEN AGAIN LATE TONIGHT. THEREFORE HAVE TRIED TO TIME BEST CHANCES AND INSERTED VCSH AT KMCW AND KALO FOR NOW. MAINLY SOUTHEASTERLY WINDS EXPECTED THROUGHOUT THE PERIOD. && .DMX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...BEERENDS LONG TERM...COGIL AVIATION...BEERENDS