203  
FXUS63 KDMX 251734  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
1234 PM CDT TUE JUL 25 2017  
   
SHORT TERM
 
/TODAY THROUGH TONIGHT/  
ISSUED AT 338 AM CDT TUE JUL 25 2017  
 
SURFACE RIDGE CONTINUES TO SLIDE EAST EARLY THIS MORNING WITH  
INCREASING WARM ADVECTION AND AS SOUTHWEST SURFACE WINDS STRENGTHEN.  
LOW LEVEL JET IS FOCUSED INTO WESTERN MINNESOTA THIS MORNING WHERE  
BULK OF CONVECTION IS CURRENTLY FOUND. WHILE THESE STORM SHOULD  
REMAIN NORTH OF THE STATE THROUGH MID MORNING, AN ISOLATED STORM  
CANNOT BE RULED OUT IN FAR NORTHERN IOWA WHERE THETA-E ADVECTION  
WILL BE FAIRLY DECENT. HOWEVER, MUCH OF TODAY WILL SEE IOWA WITHIN  
THE WARM SECTOR OF THE SYSTEM WITH INCREASING SOUTHERLY FLOW THROUGH  
THE DAY. THERMAL RIDGING FROM THE PLAINS WILL EDGE INTO THE WESTERN  
HALF OF IOWA WITH TEMPERATURES CLIMBING INTO THE LOWER 90S IN THE  
WEST. DEWPOINTS WILL ALSO BE HIGHER AS MOISTURE TRANSPORT CONTINUES  
INTO THE STATE AND ANTICIPATE HEAT INDEX VALUES CLIMBING TO 100 TO  
105 IN THE SOUTHWEST QUARTER OF THE FORECAST AREA. THIS IS NOT QUITE  
ADVISORY CRITERIA AND WILL BE TODAY ONLY. IN ADDITION, CURRENT  
READINGS AND DEWPOINTS ARE QUITE SEASONABLE, THEREFORE NO HEADLINES  
ARE NECESSARY AT THIS POINT.  
 
FOR TONIGHT, MAIN AXIS OF INSTABILITY WILL BE FROM WESTERN IOWA INTO  
WESTERN MINNESOTA AND FAR EASTERN SD. FOCUS FOR CONVECTION WILL BE  
NEAR SURFACE LOW AND BOUNDARY FROM SOUTH DAKOTA INTO MINNESOTA.  
FARTHER SOUTH INTO IOWA, CONVECTIVE INHIBITION AND LACK OF  
SUBSTANTIAL FORCING WILL LIMIT THUNDERSTORMS CHANCES FOR MUCH OF THE  
NIGHT. EVENTUALLY, THE CONVECTION TO THE NORTH AND WEST WILL  
APPROACH THE FORECAST AREA TOWARD DAYBREAK ON WEDNESDAY. THEREFORE,  
HAVE INCLUDED POPS IN THE FAR NORTH AND WEST AFTER MIDNIGHT.  
OTHERWISE, TEMPERATURES WILL REMAIN QUITE WARM OVERNIGHT WITH DECENT  
SOUTH WINDS AND RELATIVELY HIGH DEWPOINTS OVER THE STATE.  
   
LONG TERM
 
/WEDNESDAY THROUGH MONDAY/  
ISSUED AT 338 AM CDT TUE JUL 25 2017  
 
SYNOPSIS...  
YET ANOTHER LARGE-SCALE RIDGE SETS UP OVER THE SOUTHERN THIRD OF THE  
CONUS... HOWEVER... THE CORE OF THIS RIDGE IS MUCH FURTHER EAST  
COMPARED TO THE SETUP FROM LAST WEEK THAT BROUGHT THE EXCESSIVE HEAT  
TO IOWA. IN FACT, FOR THE DURATION OF THIS LONG TERM FCST PERIOD  
THROUGH NEXT TUESDAY OR SO, IOWA HAS A LARGE NORTHERLY COMPONENT TO  
THE FLOW FROM 850MB. SUBSEQUENTLY, LONG-RANGE MODELS IN GREAT  
AGREEMENT WITH BRINGING 850MB TEMPS INTO THE +12C TO +15C RANGE FOR  
MOST OF THIS LONG-TERM FCST PERIOD...A STARK CONTRAST TO THE +22C TO  
+25C TEMPERATURES FROM LAST WEEK. WEDNESDAY PM INTO THURSDAY MORNING  
COULD FEATURE HEAVY RAINFALL ACROSS MUCH OF THE CWA. SFC HIGH  
PRESSURE THEN PROPAGATES ACROSS THE UPPER MIDWEST, GENERALLY KEEPING  
US DRY INTO THE WEEKEND.  
 
WEDNESDAY PM - THURSDAY AM HEAVY RAINFALL POTENTIAL  
CONFIDENCE: MEDIUM-HIGH  
 
BOTTOM LINE UP FRONT...  
HEAVY RAINFALL IS POSSIBLE ACROSS MUCH OF THE CENTRAL TO  
ESPECIALLY THE EASTERN/NORTHEASTERN PORTIONS OF THE DMX CWA.  
FLASH FLOOD/FLOOD HEADLINES MAY CERTAINLY NEED TO BE ISSUED FOR  
OUR EASTERN/NE COUNTIES THIS AFTERNOON, TO BEGIN SOMETIME  
WEDNESDAY PM.  
 
SYNOPTICS...  
06Z TUE WATER VAPOR IMAGERY PICKING UP ON A SHORTWAVE CENTERED  
NEAR THE FOUR CORNERS REGION. THIS WAVE IS EXPECTED TO RIDE ALONG  
THE ABOVE-MENTIONED RIDGE THROUGH THE PLAINS AND TOWARDS IOWA. A  
SFC REFLECTION IS SLATED TO PUSH THROUGH IOWA, MAKING IT TOWARDS  
THE EASTERN PART OF THE STATE BY 06Z THU. SLIGHT DISAGREEMENT IN  
PRECISE TRACK AS ECMWF/GEM REMAIN STRONG OUTLIERS TO THE  
NORTHEAST, AND THE NAM BEING MUCH MORE INTENSE WITH THE SYSTEM.  
HOWEVER, TRENDS ARE THE ECMWF PUSHING FURTHER SW AND THE GFS  
PUSHING SLIGHTLY NE, SO PERHAPS THERE IS SOME CONVERGENCE IN  
SOLUTION. OVERALL, AM FAVORING THE 00Z TUE GFS. GIVEN HOW LAST  
WEEK WENT CANNOT DISCARD THE INTENSITY OF THE NAM.  
 
MESOSCALE...  
THE PAST SEVERAL MODEL RUNS HAVE ACROSS THE BOARD SHOWN A SLUG OF  
PWATS OVER 2.5 INCHES TO PUSH THROUGH IOWA, WHICH WOULD BE NEAR-  
RECORD FOR THIS TIME OF YEAR. 0-6KM MUCAPE VALUES REACH THE 1000  
TO 1500 J/KG RANGE, WITH WIDESPREAD MIXING RATIOS OF 8 G/KG TO  
ACCOMPANY WARM CLOUD DEPTHS OVER 4500M. IN SHORT, SOMEWHERE IS  
GOING TO GET SOME HEAVY RAINFALL, WITH HIGHER TOTALS OVER 2 INCHES  
SEEMING VERY PLAUSIBLE. AS OF RIGHT NOW, THE FOCUS IS OVER  
CENTRAL TO EASTERN/NE IOWA. OBVIOUSLY NE IOWA IS VERY SATURATED  
AND CANNOT TAKE HIGH AMOUNTS OF RAIN ATTM, SO FLASH FLOOD/FLOOD  
POTENTIAL WILL NEED TO BE WATCHED VERY CLOSELY.  
 
THE KDSM NAM FCST SOUNDINGS COMPLETELY SATURATE THE PROFILE BY 00Z  
THU. RESULTINGLY, LOW TO MID-LEVEL LAPSE RATES ARE NOT THAT  
IMPRESSIVE, AND WITH THESE DEEP WARM CLOUD DEPTHS, THINK SEVERE HAIL  
WILL BE TOUGH TO COME BY. OVERALL DAMAGING WIND SETUP NOT VERY  
IMPRESSIVE EITHER, THOUGH CANNOT BE RULED OUT AS THE PRIMARY THREAT.  
TORNADO THREAT EARLY ON, PRIMARILY ACROSS SOUTHERN IOWA, CANNOT BE  
RULED OUT EITHER. AS NIGHT SETS IN, NOCTURNAL LLJ KICKS UP INTO  
IOWA, TRANSITIONING ANY REMAINING SEVERE THREAT INTO A HEAVY  
RAINFALL THREAT.  
 
THURSDAY AND BEYOND...  
CONFIDENCE: MEDIUM-HIGH  
 
BY MID-MORNING THURSDAY, MUCH OF THE PRECIPITATION SHOULD BE  
SOUTHEAST OF THE AREA. WITH HIGH PRESSURE AND LARGE- SCALE  
SUBSIDENCE RIDING IN QUICKLY UPON THE HEELS OF THIS SYSTEM, AM  
EXPECTING SUNSHINE BY THURSDAY AFTERNOON AND DRY CONDITIONS WITH  
NEAR-NORMAL TEMPERATURES INTO THE WEEKEND. PERHAPS BY EARLY NEXT  
WEEK, WE WILL SEE RETURN FLOW & WARMING CONDITIONS AND  
THUNDERSTORM CHANCES RETURN.  
 

 
   
AVIATION
 
/FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON/  
ISSUED AT 1233 PM CDT TUE JUL 25 2017  
 
MAIN CHALLENGES WILL BE ONSET OF CONVECTION TOWARD END OF PERIOD.  
RELATIVELY QUIET UNTIL 13Z WITH JUST DAYTIME MIXING EXPECTED  
THROUGH 23Z TODAY. OVERNIGHT LOW LEVEL WIND SHEAR POSSIBLE  
NORTHWEST NEARER KFOD...OTHERWISE SOUTH SOUTHWEST WINDS WILL RELAX  
TO 5 TO 15 MPH OVERNIGHT. CONVECTION PROGGED TO ARRIVE BETWEEN  
13-15Z NORTHWEST...HAVE INTRODUCED VCTS AT KFOD...WITH SOME EAST  
SOUTHEAST EXPANSION TOWARD END OF PERIOD BUT SHOULD STILL REMAIN  
WEST OF KDSM/KMCW UNTIL FOLLOWING TAF FORECAST PERIOD. /REV  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...COGIL  
LONG TERM...KOTENBERG  
AVIATION...REV  
 
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