201  
FXUS63 KDMX 181052  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
552 AM CDT SAT AUG 18 2018  
   
DISCUSSION
 
/TODAY THROUGH FRIDAY/  
ISSUED AT 342 AM CDT SAT AUG 18 2018  
 
RIDGE OF HIGH PRESSURE HAS MOVED OVER WESTERN AND CENTRAL IOWA  
THIS MORNING WHERE THE WIND HAS BECOME LIGHT IN VARIABLE. AREAS OF  
FOG ARE DEVELOPING AND THUS FAR HAS MAINLY REMAINED CONFINED TO  
THE LARGER RIVER VALLEYS. DEW POINT DEPRESSIONS ARE DROPPING INTO  
THE 1-2 DEGREE RANGE. SEVERAL HIGH RESOLUTION SOLUTIONS INCLUDING  
THE HRRR AND RAP ARE SUGGESTING THAT THE FOG WILL CONTINUE EXPAND  
ESPECIALLY OVER NORTH CENTRAL/NORTHWEST IOWA OVER THE NEXT SEVERAL  
HOURS. DENSE FOG WILL BE LIKELY IN SOME AREAS AND QUITE POSSIBLE A  
DENSE FOG ADVISORY MAY BE REQUIRED.  
 
THE UPPER LEVEL FLOW WILL BE FROM THE NORTHWEST AND THIS FLOW WILL  
CONTINUE TO ALLOW SOME SMOKE TO CONTINUE TO MOVE OVERHEAD AND  
RESULT IN SOME FILTERED SUNSHINE. THE HIGHEST CONCENTRATIONS WILL  
BE OVER THE NORTHERN HALF OF THE STATE AND IN COLLABORATION WITH  
NORTHERN OFFICES, HAVE INCREASED SKY COVER AS THE RESULT OF SMOKE.  
SOME INSTABILITY WILL DEVELOP BY THIS AFTERNOON AND LEAD TO  
CUMULUS DEVELOPMENT. AT THIS TIME, ANY ISOLATED SHOWERS/STORMS  
APPEAR TO REMAIN OUT OF THE FORECAST AREA.  
 
AN UPPER LOW WILL APPROACH IOWA FROM THE WEST TONIGHT INTO SUNDAY.  
THIS SYSTEM WILL BEGIN TO DRAW GULF MOISTURE NORTHWARD TOWARD THE  
STATE. PRECIPITATION CHANCE WILL INCREASE THROUGH THE DAY SUNDAY  
THOUGH THE LARGE AREA OF HIGH PRESSURE TO EAST BRINGING SOUTHEAST  
WIND AND DRIER AIR TO IOWA, LIKELY WILL DELAY THE ONSET OF  
PRECIPITATION UNTIL LATER IN THE DAY AND INTO THE EVENING. SHOWERS  
AND THUNDERSTORMS SHOULD BECOME WIDESPREAD SUNDAY NIGHT INTO  
MONDAY AS THE BROAD MOISTURE PLUME LIFTS NORTH INTO THE STATE.  
THE BROAD MOISTURE PLUME WILL HAVE GOOD WARM CLOUD DEPTHS AS IT  
ARRIVES LEADING TO AN EFFICIENT RAINFALL PROCESS. WIDESPREAD  
PRECIPITATION AMOUNTS OF 1-1.5 INCHES ARE POSSIBLE AND HIGHER  
AMOUNTS ARE POSSIBLE NEAR ANY PIVOT POINTS LEADING TO A MORE  
PROLONGED RAINFALL. THE SYSTEM WILL END AND MOVE OUT MONDAY NIGHT  
THEN A RETURN A LARGE SCALE NORTHWEST FLOW WITH A LARGE RIDGE  
DEVELOPING TO THE WEST. COOLER TEMPERATURES WILL ARRIVE TUESDAY  
AND WEDNESDAY. THIS PATTERN WILL ALSO BE CONDUCIVE TO THE RETURN  
OF SMOKE ALOFT AND COULD LOWER HIGH TEMPERATURE POTENTIAL EVEN  
FURTHER ON WEDNESDAY. GENERALLY QUIET WEATHER CONDITIONS THE  
REMAINDER OF THE FORECAST PERIOD. WARM ADVECTION WILL ARRIVE  
THURSDAY INTO FRIDAY WITH WARMER TEMPERATURES ARRIVING. THE WARM  
ADVECTION WILL ALSO BRING THE NEXT CHANCE OF PRECIPITATION BY  
FRIDAY.  
 

 
   
AVIATION
 
/FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING/  
ISSUED AT 549 AM CDT SAT AUG 18 2018  
 
AREAS OF FOG IS THE PRIMARY AVIATION HAZARD EARLY IN THE PERIOD  
THEN AGAIN LATE TONIGHT. PRIMARY IMPACTS THIS MORNING ARE IN  
VICINITY OF KFOD/KMCW WHERE VSBYS DOWN TO 1/4SM MAY OCCUR THROUGH  
14Z. CIGS AT 200 FT OR BELOW LIKELY WILL ACCOMPANY THE LOWER  
VSBYS. SOME VSBY REDUCTIONS ALSO POSSIBLE AT OTHER SITES. VFR THEN  
REMAINDER OF TODAY WITH LIGHT EAST/SOUTHEAST WIND. POSSIBLE FOG  
AGAIN TONIGHT. BEST CHANCE FOR RESTRICTIONS ARE EASTERN SITES  
KMCW/KALO/KOTM.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
DISCUSSION...DONAVON  
AVIATION...DONAVON  
 
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