160  
FXUS63 KDMX 140800  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
300 AM CDT WED APR 14 2021  
   
DISCUSSION
 
/TODAY THROUGH TUESDAY/  
ISSUED AT 300 AM CDT WED APR 14 2021  
 
FORECAST HIGHLIGHTS:  
-- FROST POTENTIAL REMAINS AS BELOW NORMAL TEMPERATURES LARGELY  
PERSIST INTO NEXT WEEK  
-- RAIN CHANCES LATER FRIDAY INTO SATURDAY, MAINLY SOUTHERN IOWA  
-- ADDITIONAL PRECIPITATION CHANCES EARLY NEXT WEEK WITH A FRONT  
 
DETAILS: THE UPPER LEVEL PATTERN HAS NOT GREATLY CHANGED OVER THE  
PAST 24 HOURS WITH THE UPPER LOW SLIGHTLY FARTHER EAST NEAR DULUTH  
AND THE WESTERN US UPPER LOW OVER THE INTERMOUNTAIN WEST PER GOES-  
EAST WATER VAPOR IMAGERY. NIGHTTIME MICROPHYSICS RGB SHOWS PLENTY OF  
CLOUDS ROTATING AROUND THE UPPER LOW INTO NORTHERN IOWA. SOME SITES  
IN FAR SOUTHERN MINNESOTA HAVE REPORTED LIGHT SNOW AND CONFIRMED BY  
MINNESOTA DOT CAMERAS. THERE COULD BE A BIT OF LIGHT SNOW FALLING  
NEAR THE IOWA-MINNESOTA BORDER, BUT NOT MUCH FARTHER SOUTH WITH  
LARGER DEWPOINT DEPRESSIONS. THESE LARGE DEWPOINT DEPRESSIONS ARE  
ALSO A CONCERN OVER THE CURRENT FROST ADVISORY OVER SOUTHERN IOWA AS  
WIDESPREAD FROST FORMATION MAY NOT OCCUR. THE MOST LIKELY AREA AT  
THIS POINT MAY BE IN THE NISHNABOTNA VALLEY WHERE DEPRESSIONS ARE  
NOT QUITE AS LARGE. FOR TODAY, TEMPERATURES WERE TRENDED LOWER AGAIN  
AS INITIAL NATIONAL BLEND OF MODELS GUIDANCE REMAINS ABOVE THE 75TH  
PERCENTILE OF AVAILABLE GUIDANCE. WINDS WILL ONCE AGAIN BE BREEZY,  
BUT SHOULD NOT BE AS STRONG AS YESTERDAY WITH BOUNDARY LAYER DEPTH  
SHALLOWER ONLY REACHING TO BETWEEN 900 AND 850MB.  
 
ADDITIONAL NIGHTS WITH FROST ARE SEEMINGLY LIKELY. AT THIS POINT,  
THE MAIN AREA OF CONCERN IS OVER SOUTHERN IOWA DUE TO THE PROGRESS  
OF THE GROWING SEASON, WHICH ISN'T TO SAY THAT THE TEMPERATURES WILL  
BE WARMER FARTHER NORTH. FOR TONIGHT, A BETTER FROST POTENTIAL  
EXISTS LOOKING AT THE TEMPERATURE AND DEWPOINT SPREADS COMPARED TO  
THIS MORNING.  
 
AS THE UPPER LOW SLOWLY SAUNTERS EASTWARD TODAY, THIS WILL ALLOW THE  
WESTERN US UPPER LOW TO BEGIN TO SLOWLY ADVANCE EASTWARD AS WELL  
THROUGH THE REMAINDER OF THE WEEK. FORCING WILL INCREASE THROUGH THE  
DAY FRIDAY OVER SOUTHERN IOWA AND EVEN MORE SO SOUTH OF IOWA. MID-  
LEVELS IN FORECAST SOUNDINGS AT CSQ AND LWD ARE DRY SO IT MAY TAKE  
UNTIL AFTERNOON OR EVENING FOR LIGHT RAIN TO BEGIN. FARTHER NORTH  
TOWARD I-80, THERE MAY BE TOO MUCH DRY AIR FOR MUCH RAIN. OVERALL,  
THE HIGHER RAIN AMOUNTS WILL BE SOUTH OF THE STATE WITH SOUTHERN  
IOWA MAYBE PICKING UP A FEW TENTHS THROUGH SATURDAY. BY LATE IN THE  
WEEKEND, A STRONGER COLD FRONT WILL BE HEADING TOWARDS THE STATE.  
THIS COULD MEAN WARMER TEMPERATURES AHEAD OF THE FRONT ON SUNDAY.  
THEN, PRECIPITATION CHANCES INCREASE ON MONDAY INTO MONDAY NIGHT AS  
THE FRONT PASSES THROUGH IOWA. GFS FORECAST SOUNDINGS AND CROSS  
SECTIONS SHOW THE PROFILE WILL BE COLD ENOUGH ALOFT WITH SATURATION  
WITHIN THE DENDRITIC GROWTH LAYER FOR SNOW. HOWEVER, THE NEAR  
SURFACE BOUNDARY LAYER TEMPERATURES ARE ABOVE FREEZING, WHICH WOULD  
SUGGEST MELTING. THE QUESTION IS WHETHER THESE NEAR SURFACE  
TEMPERATURES ARE TOO WARM WITH PRECIPITATION ONGOING AND WHETHER  
THAT TRANSLATES TO A COLD RAIN OR PERHAPS A WET SNOW. WHILE  
DETERMINISTIC MODELS ALL SHOW PRECIPITATION SLIDING THROUGH DURING  
THIS TIME PERIOD, THERE ARE OF COURSE ENSEMBLE MEMBERS ACROSS THE  
GLOBAL SUITE THAT SHOW PRECIPITATION SPLITTING THE STATE OR BEING  
JUST DRIER IN GENERAL. OVERALL, FAIRLY CONFIDENT IN A FRONT PASSING  
THROUGH THE STATE EARLY NEXT WEEK AND MODERATELY CONFIDENT THERE  
WILL BE PRECIPITATION ALONG THE BOUNDARY WITH GREAT UNCERTAINTY  
AROUND PRECIPITATION TYPE. IT IS A DAY 6 FORECAST SO WILL BEAR  
WATCHING.  
 

 
   
AVIATION
 
/FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT/  
ISSUED AT 1157 PM CDT TUE APR 13 2021  
 
THE MN/GREAT LAKES UPPER LOW WILL CONTINUE TO INFLUENCE OUR  
WEATHER THROUGH THE PERIOD WITH CURRENT VFR CEILINGS NORTH  
TRANSITIONING TO MVFR OVERNIGHT AND INTO MUCH OF TUESDAY WITH VFR  
CEILINGS PUSHING FARTHER SOUTH AS WELL. WINDS WILL CHANGE LITTLE,  
STAYING NW WITH MINOR PEAK HEATING MIXING GUSTS DURING THE  
AFTERNOON.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
FROST ADVISORY UNTIL 8 AM CDT THIS MORNING FOR IAZ070>075-  
081>086-092>097.  
 

 
 

 
 
DISCUSSION...ANSORGE  
AVIATION...SMALL  
 
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