110  
FXUS63 KGRR 200833  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
333 AM EST THU FEB 20 2020  
 
LATEST UPDATE...  
SYNOPSIS/DISCUSSION/MARINE  
   
SYNOPSIS
 
 
ISSUED AT 334 AM EST THU FEB 20 2020  
 
- LAKE EFFECT SNOW SHOWERS INTO AFTERNOON  
 
- COLD INTO FRIDAY THEN A WARMING TREND INTO SUNDAY  
 
- SOME SORT OF SYSTEM WITH RAIN/SNOW MONDAY AND WEDNESDAY  
 

 
   
DISCUSSION
 
(TODAY THROUGH NEXT WEDNESDAY)  
ISSUED AT 334 AM EST THU FEB 20 2020  
 
-- LAKE EFFECT SNOW SHOWERS INTO AFTERNOON --  
 
OUR LAKE EFFECT SNOW SHOWERS HAVE DEVELOPED AS WE WERE THINKING,  
AFTER MIDNIGHT BUT THEY ARE FAIRLY LIGHT. I EXPECT THE SNOW  
SHOWERS TO BECOME SLIGHTLY MORE WIDESPREAD DURING THE DAYTIME  
HOURS DUE TO THE PASSAGE OF THE UPPER TROUGH AND COLDEST MID-LEVEL  
AIR IN CONJUNCTION WITH DAY TIME HEATING. INVERSION HEIGHTS ARE  
AT BEST 6000 FT MID TO LATE MORNING (HRRR SOUNDING) AND WITH 850  
TEMPS NEAR -18C AND LAKE NEAR 2C LITTLE QUESTION WE HAVE ENOUGH  
INSTABILITY FOR LAKE EFFECT. LIFT IS IN THE DGZ BUT IT IS SHALLOW  
DUE TO THE SHALLOW INVERSION HEIGHTS. WITH THE NORTH NORTHWEST  
WINDS AT CLOUD LEVEL THIS MORNING THE LAKE EFFECT SNOW SHOWERS  
WILL STAY CLOSE TO THE LAKE SHORE. AS WE CONTINUE TO SAY,  
ACCUMULATIONS WILL BE LIMITED, MOSTLY LESS THAN AN INCH (IF THAT)  
DUE TO THE LIMITED CLOUD DEPTH.  
 
AS THE UPPER TROUGH MOVES THROUGH WITH THE COLDEST AIR MOVING EAST  
WITH IT, WINDS AT CLOUD LEVEL TURN MORE WESTERLY DURING THE  
AFTERNOON AND THAT SPREADS THE SNOW SHOWERS INLAND SOME. THIS  
SHOULD BE LITTLE MORE THAN FLURRIES THROUGH.  
 
BY EVENING THERE IS ENOUGH WARM ADVECTION AND DRY AIR TO CLEAR  
SKIES.  
 
--COLD INTO FRIDAY THEN A WARMING TREND INTO SUNDAY --  
 
WE HAVE A DECENT WARM UP HEADING THIS WAY FOR SATURDAY INTO  
SUNDAY. THIS IS THANKS TO A PACIFIC SHORTWAVE THAT DIGS QUICKLY  
SOUTH JUST OFF THE WEST COATS CAUSING SPLIT FLOW THE JET STREAM  
LEVEL BY FRIDAY. WITH THE POLAR JET NEAR 55 NORTH MOST OF THE  
WEEKEND THAT PUTS US IN PACIFIC AIR AND ON THE BACK SIDE OF  
DEPARTING SURFACE HIGH. WHILE NOT STRICTLY IN OUR FORECAST HIGHS  
COULD REACH 50 SUNDAY.  
 
-- SOME SORT OF SYSTEM WITH RAIN/SNOW MONDAY AND WEDNESDAY --  
 
THAT SYSTEM THAT DIGS SOUTH OFF THE WEST COAST TOMORROW IS KICKED  
EAST BY A CLOSE WAVELENGTH PACIFIC SYSTEM. THAT CREATES A COMPLEX  
PATTERN FOR US NEXT WEEK. THE LEAD SYSTEM COMES OUT MONDAY BUT  
THERE IS CONSIDERABLE DISAGREEMENT ON HOW THIS PLAYS OUT. THE  
LATEST ECMWF HAS THE TRAILING SYSTEM AT THE MAIN STORM AND THAT  
WOULD IMPACT US WEDNESDAY. IT WILL TURN COLDER AFTER THAT FOR  
QUITE SOME TIME. IN ANY EVENT THERE IS TO MUCH UNCERTAINTY TO SAY  
JUST HOW THIS PLAYS OUT. I WOULD EXPECT AT LEAST ONE OF THESE  
SYSTEM TO BRING US SIGNIFICANT PRECIPITATION (TYPE A QUESTION).  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)  
ISSUED AT 1255 AM EST THU FEB 20 2020  
 
IT WOULD SEEM OUR LAKE EFFECT CLOUD AND SNOW SHOWER PROCESS IS  
SLOW TO GET UNDERWAY. EVEN IN NORTHERN LOWER MICHIGAN NEAR  
GAYLORD AT 0530Z WHERE IT WAS 2 1/2 MILES IN SNOW SHOWERS THE  
CEILING IS NEAR 4000 FT. I EXPECT LARGELY VFR CEILINGS TODAY AT  
ALL TAF SITES. BASED ON WHAT I AM SEEING WITH THE LATEST HI-RES  
MODELS AND LOOKING AT MODEL SOUNDINGS, SEEMS THE MOST ACTIVE  
PERIOD FOR THE SNOW SHOWERS WILL BE MIDDAY NOT EARLY THIS MORNING.  
 
ALSO CLOUD LEVEL WINDS TURN MORE WESTERLY LATER IN THE DAY SO THE  
SNOW SHOWERS WILL TRY TO MOVE INLAND FROM US-31 TO US-131 IN THE  
AFTERNOON. I DO NOT THINK THESE SNOW SHOWERS WILL BE ALL THE HEAVY  
BUT I COULD SEE ISOLATED IFR VISIBILITIES FOR A FEW MINUTES AT  
MKG, GRR, AZO AND MAYBE BTL, FROM MID MORNING TO MID AFTERNOON  
BUT I HAVE NOT PUT THAT IN THE TAF SINCE IT WOULD BE ISOLATED. I  
AM THINKING VCSH IS THE BEST WAY TO HANDLE THIS NOW. IF THE  
ACTIVITY BECOMES MORE ACTIVE I WILL UPDATE THE TAFS TO REFLECT THE  
SNOW SHOWER ACTIVITY MORE ACCURATELY.  
 
TAF LOCATIONS NEAR I-69 SHOULD HAVE CEILING NEAR 4000 FT DURING  
THE DAY TIME TODAY BUT THE SNOW SHOWERS SHOULD NOT REACH THAT FAR  
INLAND.  
 
IT ALL SHOULD CLEAR UP THIS EVENING ONCE THE AXIS OF THE COLDEST  
AIR MOVES THROUGH. BY 02Z OR SO I EXPECT SKIES TO BE CLEAR AT ALL  
TAF SITES.  
 

 
   
MARINE
 
 
ISSUED AT 334 AM EST THU FEB 20 2020  
 
DUE THE STRONG SYSTEM PASSING WELL NORTH OF MICHIGAN FRIDAY, WINDS  
WILL REALLY INCREASE. HOWEVER THIS IS SOME QUESTION AS TO HOW AIR  
TEMPS NEAR THE LAKE TEMP WILL IMPACT MIXING THE GALE WINDS JUST  
OFF THE SURFACE DOWN THE LAKE SURFACE. WE WILL ISSUE A GALE WATCH  
TO COVER THAT FRIDAY INTO EARLY SATURDAY.  
 
WE WILL LET THE SCA EXPIRE THIS AFTERNOON AND WE MAY NEED TO  
REISSUE ONE AHEAD OF THE GALE WATCH LATE TONIGHT INTO FRIDAY  
MORNING.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LM...SMALL CRAFT ADVISORY UNTIL 4 PM EST THIS AFTERNOON FOR  
LMZ844>849.  
 

 
 

 
 
SYNOPSIS...WDM  
DISCUSSION...WDM  
AVIATION...WDM  
MARINE...WDM  
 
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