654  
FXUS63 KMPX 210349  
AFDMPX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN  
1049 PM CDT FRI SEP 20 2019  
   
UPDATE
 
 
ISSUED AT 1037 PM CDT FRI SEP 20 2019  
 
UPDATED TO INCLUDE 06Z AVIATION DISCUSSION BELOW.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY NIGHT)  
ISSUED AT 300 PM CDT FRI SEP 20 2019  
 
MORNING FOG AND LOW CLOUDS WAS SLOW TO DISSIPATE THIS MORNING DUE  
TO DEEP LOW LEVEL MOISTURE AND WEAK MIXING IN THE BOUNDARY LAYER.  
HOWEVER, THE BOUNDARY LAYER WINDS ARE EXPECTED TO INCREASE  
SIGNIFICANTLY OVER THE NEXT 12-24 HOURS, LEADING TO GUSTY WINDS  
OVERNIGHT AND SATURDAY.  
 
THE MAIN FORECAST CONCERNS ARE TIMING AND AREAL EXTENT OF THE  
THUNDERSTORM ACTIVITY LATER TONIGHT, AND INTO SATURDAY.  
 
FIRST, I CAN'T RULE OUT AN ISOLATED STORM THIS AFTERNOON, AND  
EARLY EVENING ACROSS THE UPPER MIDWEST. THE COMBINATION OF  
DIURNAL HEATING AND A WEAKENING CAP, SHOULD LEAD TO VERY ISOLATED  
STORMS, BUT THERE REMAINS NO TRIGGER FOR INITIATION. FORECASTERS  
NEED TO WATCH FOR ANY BUILDING CUMULUS FIELD AND WEAK CONVERGENCE  
NEAR THE SURFACE TROUGH FOR DEVELOPMENT.  
 
REGIONAL SATELLITE IMAGERY NOTED A CONCENTRATED AREA OF CLOUDS AND  
WEAK CONVECTION ACROSS EASTERN KANSAS THIS AFTERNOON. THIS AREA OF  
CONVECTION WILL MOVE RAPIDLY NORTHWARD DURING THE EVENING, AND  
WILL TRIGGER SHOWERS AND THUNDERSTORMS ALONG IT. THE COLD FRONT,  
AND MAIN UPPER LEVEL TROUGH, WILL STILL BE FAR ENOUGH AWAY IN THE  
DAKOTAS TO NOT HAVE ANY IMPACT UNTIL LATER IN THE DAY. THE  
OVERNIGHT AND FIRST PART OF SATURDAY WILL BE ASSOCIATED WITH THE  
LOW LEVEL JET AND DEEP MOISTURE ADVECTION. I CAN'T RULE OUT A FEW  
STRONG STORMS AS DEEP LAYER SHEAR INCREASES OVERNIGHT. HEAVY  
RAINFALL WILL BE THE MAIN THREAT AS PWATS CONTINUE TO BE VERY  
ANOMALOUS FOR LATE SEPTEMBER. THE BEST TIME FRAME OF PRECIPITATION  
WILL OCCUR AFTER MIDNIGHT, AND THROUGH NOON SATURDAY. BY SATURDAY  
AFTERNOON, THE WEAKENING LOW LEVEL JET AND DRY MID-LEVELS SHOULD  
DECREASE CHANCES OF PRECIPITATION. HOWEVER, THE COLD FRONT SHOULD  
INITIATE SOME ACTIVITY BY LATE SATURDAY AFTERNOON IN EASTERN  
MINNESOTA/WEST CENTRAL WISCONSIN. DUE TO DEEP LAYER SHEAR ALONG  
THE COLD FRONT, ANY STORMS WILL BE CAPABLE OF BECOMING SEVERE. SEE  
THE LATEST SPC OUTLOOKS FOR MORE INFORMATION.  
 
BEHIND THE COLD FRONT SATURDAY NIGHT, HUMIDITY LEVELS WILL RAPIDLY  
DECREASE AS A CANADIAN AIR MASS MOVES OVERHEAD.  
   
LONG TERM
 
(SUNDAY THROUGH FRIDAY)  
ISSUED AT 300 PM CDT FRI SEP 20 2019  
 
OVERALL PATTERN SHIFTS TO MORE ZONAL ALOFT INTO EARLY NEXT WEEK,  
WITH COOLER AIR IN THE WAKE OF THE SATURDAY TROUGH. THE PATTERN  
SHIFTS ABRUPTLY/MORE AMPLIFICATION AGAIN BY LATE IN THE WEEK AS  
MORE TROUGH ENERGY DIGS INTO THE SOUTHWEST CONUS WITH RIDGING OVER  
THE CENTRAL AND EAST.  
 
CLOUDS WILL GRADUALLY DEPART SUNDAY WITH CAA PATTERN IN THE WAKE  
OF THE COLD FRONT AND UPPER LOW. MORE WEST TO EAST FLOW DEVELOPS  
INTO EARLY NEXT WEEK WITH THE DETERMINISTIC MODELS TIMING OF THE  
MIDWEEK FRONTAL BOUNDARY STILL IN QUESTION. THE GFS REMAINS  
FASTEST WITH THE FRONT, MOVING IT THROUGH TUESDAY/TUESDAY NIGHT  
WITH PERHAPS SOME RESIDUAL SHOWERS TO THE NORTHEAST WEDNESDAY.  
OTHERWISE, THE ECMWF BRING THE BOUNDARY THROUGH ABOUT WEDNESDAY.  
FOLLOWING THIS FEATURE, THE MODELS LIFT A CLOSED LOW NORTHEAST  
ACROSS THE CENTRAL PLAINS TOWARD THE WESTERN GREAT LAKES THURSDAY  
NIGHT INTO SATURDAY AS MORE SIGNIFICANT TROUGH ENERGY DROPS IN  
OVER THE PACIFIC NORTHWEST AND EVENTUALLY SOUTHWEST INTO THE  
WEEKEND. THIS FEATURE PROMISES TO BE MOISTURE LOADED AND HAS A  
GOOD SHOT OF PRODUCING HEAVY RAIN ACROSS PORTIONS OF THE CWA  
FRIDAY/SATURDAY PERIOD. WILL CONTINUE TO MONITOR OVERALL MODEL  
TRENDS INTO THE COMING WEEK.  
 
TEMPERATURES REMAIN ABOVE NORMAL FOR THE MOST PART FOR THE FIRST  
PART OF THE EXTENDED PERIOD. MAY SEE NEAR NORMAL HIGHS SUNDAY.  
OTHERWISE, WARMER THAN NORMAL TRENDING BACK TO COOLER LATE IN THE  
WEEK DEPENDING WHERE THE FRONTAL BOUNDARY SETS UP ACROSS THE  
NORTHERN PLAINS.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)  
ISSUED AT 1037 PM CDT FRI SEP 20 2019  
 
ALL SITES TO START OUT AS VFR THIS SET BUT THE COMPLICATIONS BEGIN  
AFTER MIDNIGHT WITH THE TIMING OF POTENTIALLY MULTIPLE ROUNDS OF  
PRECIP FROM AROUND DAYBREAK THEN THRU THE DAY SATURDAY. AS A COLD  
FRONT SLOWLY PUSHES EAST OVER THE DAKOTAS TONIGHT, SHRA/TSRA WILL  
DEVELOP OVER WESTERN MN OVERNIGHT THEN STEADILY PUSH EAST,  
REACHING EASTERN MN AROUND DAYBREAK THEN CONTINUING INTO WESTERN  
WI DURING THE LATE MORNING HOURS. CONDITIONS WILL LIKELY DROP TO  
MVFR LEVELS WITH THE MORNING ROUND OF PRECIP, AND THIS ROUND WILL  
HAVE THE HIGHEST POTENTIAL FOR CB/TS. ONCE THIS ROUND MOVES THRU,  
THEN THERE MAY WELL BE A BREAK IN THE ACTION AND NOT JUST LESSER  
COVERAGE. IN ADDITION, IFR CEILINGS LOOK LIKELY TO DEVELOP DURING  
THE DAY TOMORROW IN CLOSE VICINITY OF THE COLD FRONT. ADDITIONAL  
SHOWERS MAY REACH THE TERMINALS TOMORROW AFTERNOON BUT INTENSITY  
IS EXPECTED TO BE LESS AND CB/TS CHANCES ARE MUCH LOWER.  
CONDITIONS LOOK TO IMPROVE AROUND TOMORROW EVENING AND BEYOND.  
 
KMSP...TWO MAIN ROUNDS LOOK TO PUSH THRU MSP, WITH BEST TIMING  
AROUND AND SHORTLY AFTER 12Z THEN A SECOND ROUND LATE TOMORROW  
AFTERNOON. CHANCES FOR TS/CB HIGHER FOR THE MORNING PRECIP, SO  
HAVE OMITTED MENTION FOR THE AFTERNOON TEMPO AT THIS POINT. BREEZY  
CONDITIONS ALSO LIKELY WITH SLOWLY VEERING WIND DIRECTION.  
 
/OUTLOOK FOR KMSP/  
SUN...VFR. WIND W 5-10 KTS.  
MON...VFR. WIND LIGHT AND VARIABLE.  
TUE...VFR. WIND SW 5-10 KTS.  
 

 
   
MPX WATCHES/WARNINGS/ADVISORIES
 
 
WI...NONE.  
MN...NONE.  

 
 

 
 
UPDATE...JPC  
SHORT TERM...JLT  
LONG TERM...DWE  
AVIATION...JPC  
 
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