502  
FXUS63 KDMX 240540  
AFDDMX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DES MOINES IA  
1140 PM CST TUE JAN 23 2018  
   
SHORT TERM
 
/TONIGHT THROUGH WEDNESDAY/  
ISSUED AT 322 PM CST TUE JAN 23 2018  
 
LITTLE IMPACTFUL WEATHER IS EXPECTED THROUGH THE WEEK WITH REGARD TO  
STORMS CROSSING THE REGION THOUGH CLOUDS/SNOW COVER WILL DRIVE  
TEMPERATURES AND SOME UNCERTAINTY REMAINS REGARDING AREAS OF CLEARING  
TONIGHT AND WEDNESDAY. MID LEVEL WATER VAPOR CHANNEL SHOWS AN  
UPSTREAM WAVE CROSSING THE EASTERN DAKOTAS NOW WITH A REFLECTION  
IN THE HEIGHT FIELD ALOFT AND A WEAK REFLECTION A THE SURFACE.  
CLOUD COVER ASSOCIATED WITH THIS FEATURE WILL SLIDE SOUTHEAST  
OVERNIGHT TONIGHT. MODELS NOT IN GREAT AGREEMENT WITH THE HANDLING  
OF THE EXPANSIVE STRATUS DECK STRETCHING FROM EASTERN MANITOBA  
SOUTH INTO IOWA AND MISSOURI. HIRES MODELS CONTINUE TO SUGGEST  
THAT THAT MOISTURE SUPPORTING THE DECK WILL REMAIN TRAPPED  
OVERNIGHT INTO WEDNESDAY AND SLOWLY DRIFT EAST. SYNOPTIC MODELS  
BARELY RECOGNIZE THE LINGERING EFFECTS OF THE STRATUS CLOUD COVER  
AT THIS TIME. SUPPORTING THIS THESIS IS THE WARM AIR ADVECTION  
EXPECTED TO OVERSPREAD THE REGION BY 12Z WEDNESDAY WHICH WILL  
RESULT IN A STRENGTHENING INVERSION. 12Z H850 TEMPERATURES OVER  
THE AREA VARY LITTLE WITH -5C TO -6C ACROSS THE BOARD. BY 12Z  
WEDNESDAY THE AIRMASS IS EXPECTED TO MODERATE ABOUT 2 TO 3C ALOFT.  
THE AREA OF CLOUDS OVER THE OUR WESTERN COUNTIES SHOULD BE SLOW  
TO LIFT TONIGHT WHILE MID LEVEL CLOUDS OVERRIDE IT TONIGHT. WILL  
KEEP CLOUDS GOING THROUGH THE OVERNIGHT AND LINGERING IN THE WEST  
DURING THE MORNING HOURS WEDNESDAY...PARTIALLY DISSIPATING IN THE  
LATE MORNING BEFORE ANOTHER AREA OF CLOUDS STREAMS SOUTHEAST WITH  
THE NEXT RESURGENCE OF WARMER AIR MOVING INTO THE REGION BY THURSDAY.  
HIRES MODELS ALSO BEGINNING TO SUGGEST SOME FOG FORMATION. ALREADY  
SOME LIGHT FOG HAS DEVELOPED OVER NORTHEAST NEBRASKA. THIS IS  
PRIMARILY DUE TO SOME MELTING TAKING PLACE WEST OF THE GENERATION  
AREA AND THEN ADVECTING EAST OVER THE LARGE SNOWPACK. SOME CONCERNS  
AS TO HOW FAR EAST THIS WILL ADVECT/MOVE OVERNIGHT. THE RAP/HRRR  
EXPAND FOG ALONG THE MISSOURI RIVER VALLEY SOUTHEAST INTO THE OUR  
WEST. THE ARW EXPANDS THE AREA THROUGH MOST OF THE SNOWPACK ALL  
ACROSS NORTHERN IOWA. ARRIVAL OF MID TO HIGH LEVEL CLOUDS MAY KEEP  
THE MORE WIDESPREAD FOG FROM DEVELOPING...BUT GIVEN THE POTENTIAL  
FOR ADVECTION OVERNIGHT THE ONCOMING SHIFT MAY HAVE TO UPDATE THE  
FORECAST NORTH/WEST FOR MORE WIDESPREAD FOG. LOWS TONIGHT WILL  
REMAIN IN THE TEENS AND 20S WITH HIGHS WEDNESDAY IN THE 20S NORTH  
TO THE LOWER 40S SOUTH.  
   
LONG TERM
 
/WEDNESDAY NIGHT THROUGH TUESDAY/  
ISSUED AT 322 PM CST TUE JAN 23 2018  
 
BOTH THE EURO/GFS REMAIN IN GENERALLY GOOD AGREEMENT THROUGH THE  
WEEKEND. MODIFIED ZONAL FLOW WILL CONTINUE TO REPLACE THE HIGHER  
AMPLITUDE FLOW OF EARLY/MID JANUARY. ONCE AGAIN THE MAIN EMPHASIS  
WILL BE FOR WARMING CONDITIONS WITH WEAK COLD INTRUSIONS PUSHING  
SOUTH FOLLOWING A COOL FRONT FRIDAY EVENING. CLOUDS REMAIN THE  
LIMITING FACTOR ON HIGHER CONFIDENCE IN THE EXTENDED FORECAST. WITH  
INCREASING WARM AIR ADVECTION ACROSS THE DEEP SNOWPACK OVER NEBRASKA,  
NORTHERN IOWA AND SOUTHERN MINNESOTA...IT'S LIKELY THAT THE PERSISTENT  
SOUTHWEST FLOW OVER THE LONGER FETCH OF SNOWPACK WILL RESULT IN  
AN AREA OF HIGHER SFC DEWPOINTS AND GREATER POTENTIAL FOR EITHER  
FOG OR STRATUS - ESPECIALLY WEDNESDAY NIGHT INTO EARLY THURSDAY.  
RATHER THAN TRY TO DEFINE THE EXACT AREA THAT MAY SEE FOG TODAY...WILL  
WAIT TO SEE WHERE SFC WIND INFLUENCES ARE LEAST AND CONVERGENCE  
IS MAXIMIZED OVERNIGHT AS WELL AS ANY INFLUENCE FROM HIGH LEVEL  
CLOUDS EXPECTED TO MOVE OVER THE REGION. BY THURSDAY THE DEEPENING  
TROUGH OVER THE WESTERN US WILL BUILD HEIGHTS ACROSS THE PLAINS  
AS H850 TEMPERATURES INCREASE INTO THE LOWER TEENS OVER THE  
WESTERN HALF OF THE FORECAST AREA. BOTH THE GFS/EURO LOWER H850  
TEMPERATURES FRIDAY THOUGH WITH RATHER MILD OVERNIGHT LOWS ANTICIPATED  
THURSDAY NIGHT...EVEN MODEST INSOLATION FRIDAY WILL LIKELY BRING  
HIGHS BACK INTO THE LOWER 50S SOUTH WITH UPPER 30S TO LOWER 40S  
OVER THE NORTH. THE GREATEST THREAT FOR ANY PRECIPITATION WILL BE  
FRIDAY AFTERNOON/EVENING ACROSS THE SOUTHEAST AS A WAVE WILL  
DEVELOP ALONG THE COOL FRONT AND POSSIBLY BRING SOME PRECIPITATION  
TO THOSE AREAS. GFS HAS BACKED OFF ON CHANCES WITH THE 12Z RUN  
WITH THE 12Z EURO ALSO SHOWING A MORE SOUTHEASTERLY TRACK OF THE  
SYSTEM. FOR NOW WILL LEAVE A SMALL CHANCE OF PRECIPITATION OVER  
THE SOUTHEAST FRIDAY NIGHT INTO SATURDAY MORNING. INTO THE  
REMAINDER OF THE WEEKEND A STRONGER COLD FRONT WILL PASS SOUTHEAST  
OF THE REGION SATURDAY NIGHT INTO SUNDAY. THIS QUICK ARCTIC  
INTRUSION WILL LOWER HIGHS SUNDAY BUT EXIT QUICKLY WITH WARMING  
RETURNING MONDAY INTO TUESDAY. AFTER HIGHS SUNDAY IN THE 20S AND  
30S WITH NORTHWEST FLOW CONDITIONS WILL IMPROVE BY TUESDAY WITH  
SOUTHWEST FLOW AND HIGHS BACK INTO THE 40S NORTH TO LOWER 50S  
SOUTH.  
 

 
   
AVIATION
 
/FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT/  
ISSUED AT 1140 PM CST TUE JAN 23 2018  
 
LOW STRATUS IN PLACE ACROSS MUCH OF THE AREA WITH SOME CLEARING  
IN THE NORTHEAST INITIALLY. LOW CLOUDS SHOULD MOVE BACK IN. FOG  
WILL BE POSSIBLE IN THE FAR WEST, BUT MORE CONFINED TO AREAS WHERE  
THE STRATUS DECK HAS MOVED OUT OF THE AREA FURTHER WEST OF THE  
FORECAST AREA. CIGS TO BE MAINLY IFR/MVFR AND WILL BEGIN TO ERODE  
THROUGH LATE MORNING/MID-DAY WEDNESDAY. WINDS TO STILL SHIFT  
AROUND TO THE WEST TO SOUTH THROUGH THE PERIOD. CHANCE FOR FOG  
AGAIN WEDNESDAY NIGHT JUST BEYOND THE CURRENT FORECAST PERIOD.  
 

 
   
DMX WATCHES/WARNINGS/ADVISORIES
 
NONE.  
 

 
 

 
 
SHORT TERM...REV  
LONG TERM...REV  
AVIATION...BEERENDS  
 
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