677  
FXUS63 KGRR 200728  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
328 AM EDT WED OCT 20 2021  
 
LATEST UPDATE...  
SYNOPSIS/DISCUSSION/MARINE  
   
SYNOPSIS
 
 
ISSUED AT 328 AM EDT WED OCT 20 2021  
 
-SHOWERS AND STORMS LATE WEDNESDAY INTO THURSDAY  
 
-COOLER WEATHER FRIDAY THROUGH MOST OF THE WEEKEND  
 
-CHANCE FOR SIGNIFICANT PRECIPITATION MID NEXT WEEK  
 

 
   
DISCUSSION
 
(TODAY THROUGH NEXT TUESDAY)  
ISSUED AT 328 AM EDT WED OCT 20 2021  
 
--SHOWERS AND STORMS LATE WEDNESDAY INTO THURSDAY --  
 
TODAY BEGINS WITH A CRISP CLEAR AUTUMN MORNING DUE TO STRONG  
OVERNIGHT RADIATIONAL COOLING. HOWEVER, OVERNIGHT LOWS AS WELL AS  
TODAYS HIGH TEMPERATURES, WILL BE ABOVE NORMAL. THE ABOVE NORMAL  
TEMPERATURES WILL BE AIDED BY WARM SOUTHWESTERLY FLOW IN THE MID-  
LEVELS, ALONG WITH MOIST FLOW AHEAD OF ANY APPROACHING LOW  
PRESSURE SYSTEM. THE LATEST NAFES ENSEMBLES ARE SHOWING MEAN  
TEMPERATURES ANOMALIES ARE +2 SIGMA, INDICATING A SLIGHTLY  
ANOMALOUS SIGNAL.  
 
AHEAD OF THE APPROACHING SYSTEM WILL BE A WEAK LLJ AT ABOUT 35KTS  
AT 2KFT. WHILE NOT NECESSARILY STRONG, IT SHOULD PROVIDE ENOUGH  
LOW LEVEL MIXING COUPLED WITH THE UNSEASONABLY WARM AIR FOR  
AFTERNOON SHOWERS AND STORMS. ONE OF THE LIMITING FACTORS WILL BE  
THE TIMING AS THIS SYSTEM WILL REACH THE REGION LATE IN THE DAY  
WITH THE STRONGEST PWATS MOVING THROUGH NORTHERN MICHIGAN AND  
ARRIVING WELL AFTER SUNSET. SO WHILE STORMS ARE POSSIBLE, THEY  
WILL TEND TO BE SCATTERED THROUGH SOUTHWEST MICHIGAN AND WILL LACK  
ORGANIZATION AND WILL NOT BE SEVERE. SHOWERS ARE LIKELY, BUT AS  
STATED ABOVE, THE STRONGEST MOISTURE WILL BE TO THE NORTH SO  
FLOODING IS NOT A CONCERN, ESPECIALLY WITH THE SPEED THAT THESE  
SHOWERS/STORMS WILL BE MOVING.  
 
SHOWERS AND STORMS WILL MOVE THROUGH NORTHEAST OVERNIGHT  
WEDNESDAY INTO THURSDAY AND AS THEY MOVE THROUGH CENTRAL INTO  
EASTERN MICHIGAN, THE MID TO NEAR RANGE MODELS SHOW THE OVERNIGHT  
CONVECTION ORGANIZING INTO A COHESIVE LINE TOWARDS THURSDAY  
MORNING. WHILE THIS WILL MAINLY EFFECT THE EASTERN HALF OF THE  
STATE, ANY LINE OF SHOWERS AND STORMS THAT FORM COULD AFFECT THE  
US 127 CORRIDOR INCLUDING LANSING AND JACKSON. AS STATED ABOVE,  
NONE OF THIS IS EXPECTED TO BECOME SEVERE.  
 
--COOLER WEATHER FRIDAY THROUGH MOST OF THE WEEKEND  
 
AS THE MID TO UPPER LEVEL LOW TRAVERSES THE GREAT LAKES, IT WILL  
BE PULLED INTO A LARGER UPPER LEVEL TROUGH EXTENDING FROM AROUND  
HUDSON BAY THROUGH THE MIDWEST. STRONG NORTHERLY FLOW WILL DROP A  
COLD FRONT ACROSS MICHIGAN THURSDAY EVENING INTO FRIDAY MORNING.  
THE MID RANGE MODELS ARE IN DECENT AGREEMENT THAT COLDER AIR, 0C  
TO -2C AT 850MB, WILL ADVECT INTO THE AREA BY 12Z FRIDAY MORNING.  
THE STRONG NORTHERLY FLOW ALONG WITH GUSTY WINDS WILL ALLOW FOR A  
BLUSTERY DAY ON FRIDAY.  
 
THE COLDEST TEMPERATURES IN THIS PERIOD WILL BE SATURDAY MORNING  
WITH PATCHY FROST POSSIBLE SO IF YOU HAVE ANY VEGETATION LEFT IT  
WOULD BE A GOOD IDEA TO PROTECT IT. THERE ARE SOME OUTLINING  
MODELS ALONG US 10 THAT HAVE THE POTENTIAL FOR SNOW FLURRIES.  
HOWEVER, GIVEN THE LACK OF MOISTURE IT IS UNLIKELY AND IF IT DOES  
OCCUR WILL NOT AMOUNT TO ANYTHING.  
 
THE COLDER AIR MASS WILL LINGER OVER THE STATE INTO SUNDAY BEFORE  
THE NORTHWESTERLY FLOW SHIFTS TO THE EAST SUNDAY AFTERNOON AS THE  
UPPER LEVEL TROUGH GIVES WAVE TO ANOTHER SYSTEM MOVE IN FROM THE  
CENTRAL US. THAT WILL MODERATE TEMPERATURES AND BRING WARMER AIR  
INTO THE REGION LATE SUNDAY INTO THE UPCOMING WORK WEEK. THE  
MODEL SOLUTIONS BEGIN TO DIVERGE AS THE GFS HAS A BETTER CHANCE OF  
PRECIPITATION SUNDAY. HOWEVER THE EC HAS THE STRONG, DRY EASTERLY  
FLOW MAINLY FENDING OFF ANY APPROACHING PRECIPITATION. SO WHILE  
PRECIPITATION IS POSSIBLE SUNDAY INTO MONDAY, IT WILL BE  
INHIBITED INTO COMING INTO A DRIER AIR MASS AND WILL HAVE CONTEND  
WITH DRY AIR ADVECTING INTO IT. THE BEST CHANCE FOR PRECIPITATION  
SUNDAY INTO MONDAY WILL BE ALONG THE I-94 CORRIDOR  
 
--CHANCE FOR SIGNIFICANT PRECIPITATION MID NEXT WEEK --  
 
STRONG, DIVERGENT UPPER LEVEL FLOW WILL MOVE ANY PRECIPITATION TO  
THE NORTHEAST MONDAY MORNING WITH NORTHWESTERLY FLOW ONCE AGAIN  
TAKING THE STAGE INTO TUESDAY. A WEAK UPPER LEVEL RIDGE WILL MOVE  
OVER THE AREA BEFORE A DEEPENING LOW WAVE TROUGH DEVELOPS IN THE  
MIDWEST AS TRAVERSES THE GREAT LAKES STATES WEDNESDAY INTO  
THURSDAY. THERE IS SOME SIGNAL FOR DECENT QPF THOUGH THE BEST  
PWATS ARE TO THE NORTH OF THE REGION.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 147 AM EDT WED OCT 20 2021  
 
VFR WEATHER CONTINUES TODAY INTO THE EVENING AS INCOMING  
CLOUDINESS HAS HIGH BASES, MOSTLY AT OR ABOVE 10,000 FT. A FEW  
SHOWERS ARRIVE LATER IN THE DAY BUT NO APPRECIABLE VSBY  
REDUCTIONS ARE EXPECTED AT THIS TIME.  
 
THE RISK FOR THUNDER WITH LOWER CIGS WITH BRIEF VSBYS  
RESTRICTIONS RAMPS UP A BIT AFTER 03Z TONIGHT, BUT HAVE EXCLUDED  
THAT IN THE TAFS FOR NOW. SHOULD CONFIDENCE IN TIMING AND COVERAGE  
OF CONVECTION INCREASE, THUNDER/CBS MAY NEED TO BE ADDED FOR  
TONIGHT IN LATER TAF UPDATES.  
 

 
   
MARINE
 
 
ISSUED AT 328 AM EDT WED OCT 20 2021  
 
WINDS AND WAVES WILL BE LIGHT TODAY, THOUGH THEY WILL INCREASE AS  
THE DAY CONTINUES. STRONG NORTHWESTERLY FLOW IS EXPECTED TOMORROW  
WITH WINDS INCREASING TO AT LEAST ADVISORY THOUGH IF THE STRONG  
FLOW INTENSIFIES ON THURSDAY IT COULD FLIRT WITH GALE CRITERIA.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LM...NONE.  

 
 

 
 
SYNOPSIS...CERU  
DISCUSSION...CERU  
AVIATION...MEADE  
MARINE...CERU  
 
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