243  
FXUS63 KDMX 082358  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
558 PM CST THU DEC 8 2022  
   
..UPDATED FOR THE 00Z AVIATION DISCUSSION
 
 
   
DISCUSSION
 
/TONIGHT THROUGH THURSDAY/  
ISSUED AT 345 PM CST THU DEC 8 2022  
 
KEY MESSAGING HIGHLIGHTS:  
 
* HEAVY SNOW NOW ANTICIPATED ACROSS NORTHERN IA. SMALL, TARGETED  
WINTER STORM WARNING NOW IN EFFECT. LESSER SNOW AND MINOR  
GLAZING POSSIBLE JUST TO THE SOUTH.  
* LIGHT RAIN/SNOW CHANCES SAT  
* LARGE SYSTEM NEXT WEEK, APPRECIABLE RAIN LIKELY CENTRAL AND SOUTH  
 
THE FORECAST BEGINS WITH WIDESPREAD STRATUS ACROSS THE AREA IN  
PERSISTENT EASTERLY LOW LEVEL FLOW WITH A FRONT AND MATURING  
SURFACE LOW TO OUR SOUTH AND SOUTHWEST RESPECTIVELY. THIS WILL  
CONTINUE INTO THE EVENING WITH SOME FOG COMING BACK INTO PLAY AS  
WELL. IN FORESHADOWING OF WHAT'S TO COME, STRONG, PHASED  
THERMODYNAMIC AND KINEMATIC FORCING CONTINUES TO ADVANCE INTO THE  
MO VALLEY JUST UPSTREAM, BUT IT DOES STILL HAVE SOME MOISTURE  
DEFICIENCIES FOR THE TIME BEING. THERE ISN'T MUCH PRECIP UPSTREAM  
YET, BUT VISIBLE SATELLITE IMAGERY IS ALREADY SHOWING CONVECTIVE  
ELEMENTS.  
 
LATER THIS EVENING, THE STRONG H85/H7 QG FORCING WILL EXPAND  
SATURATION IN THAT LAYER AND START TO DEVELOP PRECIP, BUT THE MID  
LEVELS AND DENDRITIC GROWTH ZONE WILL BE NARROWER AS IT MATURES  
INTO NORTH CENTRAL IA INTO TONIGHT. ONCE THIS OCCURS, SNOWFALL  
RATES ARE EXPECTED TO JUMP CONSIDERABLY WITH THE HREF AND SEVERAL  
HI RES MODELS SUGGESTING RATES APPROACHING OR REACHING 1"/HR FOR  
SEVERAL HOURS. DENDRITIC SNOW PRODUCTION IS EXPECTED WITH  
TREMENDOUS OMEGA/VERTICAL MOTION IN THE DGZ, ALONG WITH  
SUPERSATURATION WITH RESPECT TO ICE. THIS IS ALSO ALIGNED WITH  
NEGATIVE H5/H6 EPV, AND EVEN FORECAST SOUNDINGS SHOWING ELEVATED  
CAPES OF A FEW J/KG. WOULD NOT BE SURPRISED TO SEE A FEW RUMBLES  
OF THUNDER. THE GFS/HRW FV3 COMPANION CORES SEEM UNDERDONE AND TOO  
FAR NORTH, BUT MUCH OF THE REMAINING GUIDANCE SUPPORTS 6 HOUR QPF  
IN THIS WINDOW TO 0.6"+ FROM ALGONA TO MASON CITY. THUS HAVE  
RAISED SNOW AMOUNTS TO 5-7" AND ISSUED A TARGETED SHORT-TERM  
WARNING DURING THE WORSE EXPECTED CONDITIONS, WHICH WILL BE A  
HEAVY WET SNOW AND ACCUMULATE QUICKLY, POSSIBLY WEIGHING DOWN  
WEAKER TREES. AN ADVISORY WILL REMAIN IN PLACE, BOOK-ENDING THE  
WORSE CONDITIONS WHEN MORE OF A WINTRY MIX IS ANTICIPATED WITH THE  
LOSS OF APPRECIABLE ICE INTRODUCTION. FARTHER SOUTH INTO CENTRAL  
AND SOUTHERN IOWA, ONLY RAIN IS ANTICIPATED WITH THIS SYSTEM. MUCH  
OF THE PRECIP WILL END IN OUR AREA FRIDAY MORNING, BUT SOME  
ADDITIONAL LIGHT FREEZING DRIZZLE IS POSSIBLE FAR NORTHEAST BY  
FRIDAY NIGHT.  
 
TO START THE WEEKEND, WE'LL LOOK TO THE SHORT WAVE CURRENTLY OFF  
THE OR/CA COAST. THE WARM ADVECTION AND DCVA IS FAIRLY STRONG, BUT  
FAIRLY MOISTURE STARVED OF PACIFIC ORIGIN, SO THERE IS ONLY LIGHT  
RAIN/SNOW CHANCES WITH LITTLE IF ANY QPF. HIGH PRESSURE WILL THEN  
SETTLE IN BEHIND WITH SEASONAL TEMPERATURES TO END THE WEEKEND,  
BUT THERE MAY BE YET ANOTHER ROUND OF FOG DEVELOPMENT DUE TO THE  
LIGHT FLOW AND RECENT SNOW AND/OR RAIN.  
 
ANOTHER BIG SYSTEM IS EXPECTED TO ARRIVE TUESDAY, AND LINGER  
THROUGH THE REMAINDER OF THE PERIOD WITH A LARGE CLOSED LOW  
CYCLONE DRIFTING FROM THE MO INTO THE MS VALLEYS OVER THREE DAYS.  
BOTH EPS AND NAEFS MOISTURE PARAMETERS (PWAT, SPECIFIC HUMIDITY,  
INTEGRATED MOISTURE TRANSPORT) ARE APPROACHING CLIMATOLOGICAL  
MAXES ALONG AND AHEAD OF THIS SYSTEM, SO APPRECIABLE PRECIPITATION  
IS ANTICIPATED. SOME SNOW IS POSSIBLE NORTH, BUT MUCH OF THIS  
EVENT WILL LIKELY BE RAIN WITH EPS, GEFS, NBM ENSEMBLES FAIRLY  
CONFIDENCE IN HALF-INCH TO INCH AMOUNTS. BOTH THE LOW LEVEL AND  
DEEP SHEAR IS TREMENDOUS, BUT IT APPEARS THAT TEMPS, DEWPOINTS,  
AND RESULTANT INSTABILITY WILL BE TOO LOW FOR MUCH IN THE WAY OF  
CONVECTION TO REALIZE THE ALARMING KINEMATICS. MUCH OF THE  
APPRECIABLE PRECIPITATION WILL OCCUR TUESDAY, BUT LINGERING  
LIGHTER RAIN OR SNOW, BREEZY CONDITIONS, AND EVENTUALLY ALL PATCHY  
LIGHT SNOW, WILL PERSIST THROUGH THE REST OF THE PERIOD.  
 

 
   
AVIATION
 
/FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING/  
ISSUED AT 544 PM CST THU DEC 8 2022  
 
MVFR TO LIFR CONDITIONS ACROSS THE AREA NEAR 00Z WITH CONDITIONS  
STILL EXPECTED TO DEGRADE THROUGH THE EVENING AND OVERNIGHT HOURS,  
WITH LIFR CONDITIONS LIKELY TO IMPACT ALL SITES AT SOME POINT.  
RAIN HAS BEGUN AND CONTINUES TO ADVANCE SW TO NE WITH SOME ICE  
REPORTED IN FAR WESTERN IOWA AND IMPACTFUL SNOW NORTH STILL  
EXPECTED TONIGHT. SNOW RATES NEAR KMCW MAY REACH 1"/HR LATER THIS  
EVENING WITH A MIX OF RAIN/SNOW/FOG/FREEZING FOG IMPACTING OTHER  
SITES INTO TOMORROW MORNING. PRECIPITATION MOVES OUT TOMORROW  
MORNING BUT IFR CEILINGS LOOK TO PERSIST FOR AWHILE AFTERWARDS. HAVE  
KEPT LARGELY WITH PREVIOUS FORECAST WITH THIS ISSUANCE BUT WILL  
CONTINUE TO MONITOR PRECIP TRENDS AND ISSUE AMENDMENTS IF  
NECESSARY.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL 9 AM CST FRIDAY FOR IAZ004-015-  
025>028-039.  
 
WINTER WEATHER ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR  
IAZ005>007-016-017.  
 
WINTER WEATHER ADVISORY FROM 6 AM TO 9 AM CST FRIDAY FOR  
IAZ005>007-016-017.  
 
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 AM CST FRIDAY  
FOR IAZ005>007-016-017.  
 
WINTER WEATHER ADVISORY UNTIL 6 AM CST FRIDAY FOR IAZ023-024-  
034>038.  
 
WINTER WEATHER ADVISORY UNTIL 6 AM CST FRIDAY FOR IAZ033-044-045-  
057.  
 

 
 

 
 
DISCUSSION...SMALL  
AVIATION...KCM  
 
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