012  
FXUS63 KGRR 111129  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
629 AM EST SUN DEC 11 2016  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 326 AM EST SUN DEC 11 2016  
 
SNOW WILL CONTINUE TODAY...MODERATE TO HEAVY...AS LOW PRESSURE IN  
THE PLAINS MOVES TOWARD THE GREAT LAKES. TOTAL SNOWFALL IN THE 6 TO  
10 INCH RANGE IS EXPECTED.  
 
A BLAST OF ARCTIC AIR WILL ARRIVE MID WEEK AND RESULT IN HIGHS IN  
THE MID TEENS WEDNESDAY AND THURSDAY ALONG WITH LAKE EFFECT SNOW.  
THE BELOW NORMAL TEMPERATURES WILL CONTINUE THROUGH NEXT WEEKEND.  
 

 
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 326 AM EST SUN DEC 11 2016  
 
FORECAST CONCERNS DEAL WITH THE UNFOLDING SNOW EVENT AND THE CURRENT  
HEADLINES. THERE HASN'T BEEN TOO MUCH CHANGE IN REGARD TO THE  
DYNAMICS OF THIS SYSTEM AS IT REMAINS MULTI-FACETED WITH BOTH A LAKE  
EFFECT COMPONENT AND WARM AIR ADVECTION COMPONENT.  
 
LATEST RADAR SHOWS SNOW ONGOING ACROSS THE CWA WITH A DISTINCT LAKE  
EFFECT AREA MOVING NORTH ALONG THE LAKE SHORE OVER OTTAWA AND  
MUSKEGON COUNTIES. THESE COUNTIES ALONG WITH ALLEGAN WILL SEE  
SEVERAL INCHES OF LAKE EFFECT SNOW THAT WILL COMBINE WITH THE  
ONGOING WARM ADVECTION TO BOOST SNOW TOTALS. AFTER COMBINING QPF  
(WHICH IS A BIT HIGHER WITH THE 06Z MODEL RUN) WITH MODEL SNOW  
RATIOS, SNOW TOTALS AROUND 10 INCHES ARE FORECASTED FROM MUSKEGON  
COUNTY SOUTH THROUGH VAN BUREN AND 9 INCH TOTALS FROM KENT SOUTHEAST  
THROUGH INGHAM. FOR CONSISTENCY WITH SURROUNDING OFFICES, WE  
UPGRADED THE ADVISORY TO A WINTER STORM WARNING MAINLY ALONG AND  
SOUTH OF I-96. THE HEAVIEST SNOW WILL FALL IN THIS AREA FROM 14Z  
THROUGH 22Z OR SO. SOLID 3/4-1 INCH/HR SEEMS LIKE A REAL POSSIBILITY  
GIVEN THE STRONG ISENTROPIC LIFT AT 285K. STRONG PRESSURE ADVECTION  
WAS NOTED WITH 40KTS PERPENDICULAR TO THE THE PRESSURE SURFACES.  
THIS SNOW WILL BECOME INCREASINGLY WET AS THE DAY WEARS ON DUE TO  
CONTINUED WARM AIR FLOWING NORTH INTO THE SYSTEM. OUR CWA SHOULD  
REMAIN ALL SNOW THOUGH AS WE HAVE FAIRLY DEEP COLD AIR IN PLACE. AS  
THE SNOW BECOMES MORE MOIST, IT WILL LIKELY BECOME MORE SLIPPERY TOO  
CREATING BIGGER IMPACTS.  
 
THE SNOW WILL BEGIN TO DIMINISH LATER THIS EVENING AS THE LOW MOVES  
EAST OF THE STATE. MAINLY DRY WX IS EXPECTED MONDAY AND A FEW  
SCATTERED LAKE EFFECT SNOW SHOWERS POSSIBLE TUESDAY.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 326 AM EST SUN DEC 11 2016  
 
WE ARE LOOKING AT MORE UNSETTLED AND COLD WEATHER THROUGH THE LONG  
TERM PORTION OF THE FORECAST. WE WILL SEE THE NEXT SURGE OF ARCTIC  
AIR COMING IN JUST IN TIME FOR THE LONG TERM LATE TUE. NORMALLY THIS  
WOULD IGNITE THE LAKE EFFECT AND GET IT GOING STRONG. INDICATIONS  
ARE RIGHT NOW THAT THE SFC PATTERN WILL BE A BIT ANTI-CYCLONIC  
IMMEDIATELY BEHIND THE FRONT. WE SHOULD SEE THE LOW LEVEL FLOW  
BECOME MORE CYCLONIC THROUGH WED, HELPING LAKE EFFECT TO GET  
STARTED. AS MENTIONED BEFORE, THE DEGREE OF COLDER AIR AND THE FLOW  
WILL HAVE MOISTURE DEPTH FAIRLY LIMITED. THE DGZ WILL ALSO BE QUITE  
LOW WHICH WILL ALSO LIKELY LIMIT THE AMOUNT OF LAKE EFFECT.  
 
THE CYCLONIC FLOW ALOFT WILL LIFT OUT TOWARD FRIDAY, ALLOWING A  
BRIEF BREAK IN THE COLDEST OF THE AIR AND LAKE EFFECT. THIS WILL  
EVENTUALLY GIVE WAY TO A STRONG TROUGH THAT IS EXPECTED TO BE OVER  
THE WRN STATES MID-WEEK.THIS TROUGH WILL EVENTUALLY LIFT OUT, AND  
WILL LIKELY DEVELOP A DECENT SYSTEM AND SEND IT TOWARD THE REGION.  
WE ARE LOOKING AT LEAST ANOTHER BURST OF SNOW IN THE FRI/SAT TIME  
FRAME. MODELS ARE EVEN TRYING TO BRING WARM ENOUGH AIR UP FROM THE  
GULF, THAT A MIX WILL BE A POSSIBILITY.  
 
AS THE STORM MOVES THROUGH BY LATE SAT, THE AREA WILL BECOME  
ENTRENCHED UNDER THE UPPER LOW/CYCLONIC FLOW ONCE AGAIN. THIS WILL  
BRING BACK THE COLD WEATHER ALONG WITH LAKE EFFECT CHANCES.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 628 AM EST SUN DEC 11 2016  
 
MODERATE TO HEAVY SNOW WILL DEVELOP THIS MORNING RESULTING IN LIFR  
CONDITIONS AT THE TAF SITES. THE LOW VIS/CIG CONDITONS WILL LAST  
THORUGH THE EVENING AND THEN IMPROVE LATE TONIGHT ONCE THE SNOW  
DIMINISHES.  
 

 
   
MARINE
 
 
ISSUED AT 326 AM EST SUN DEC 11 2016  
 
WE EXTENDED THE SMALL CRAFT ADVISORY THROUGH MONDAY NIGHT. WINDS AND  
WAVES WILL BE HAZARDOUS FOR SMALL CRAFT DURING THIS TIME FRAME.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 129 PM EST SAT DEC 10 2016  
 
THE LATEST WATER TEMPS ON AREA RIVERS INCLUDE THE FOLLOWING  
SAMPLES: 33 ON THE MUSKEGON RIVER AT BIG RAPIDS, 34 ON THE  
KALAMAZOO RIVER, AND 35 ON THE GRAND RIVER AT EASTMANVILLE. EXPECT  
RAPID ICE FORMATION ON THESE RIVERS STARTING THE MIDDLE OF THIS  
UPCOMING WEEK AS AIR TEMPS RETREAT INTO THE TEENS AND SINGLE  
DIGITS. FRAZIL ICE DEVELOPMENT CAN OCCUR QUICKLY WITH THESE TEMPS  
COMBINED WITH HIGHER THAN NORMAL FLOWS. SNOW ALSO CONTRIBUTES TO  
ICE DEVELOPMENT. IN TERMS OF ICE JAM POTENTIAL, THERE IS SOME RISK  
AFTER ICE DEVELOPS GIVEN FLOWS RUNNING ON THE HIGHER SIDE OF  
NORMAL MAINLY FOR THE GRAND RIVER BASIN. HOWEVER, IT IS TOO EARLY  
TO TELL HOW MUCH OF A RISK THERE IS SINCE THE GRAND RIVER IS  
CURRENTLY ICE FREE. RESIDENTS IN JAM-PRONE AREAS SHOULD MONITOR  
ICE DEVELOPMENT OVER THE COURSE OF THE NEXT WEEK.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...WINTER STORM WARNING UNTIL 4 AM EST MONDAY FOR MIZ050-056>058-  
064>067-071>074.  
 
WINTER WEATHER ADVISORY UNTIL 4 AM EST MONDAY FOR MIZ037>040-  
043>046-051-052-059.  
 
LM...SMALL CRAFT ADVISORY UNTIL 7 AM EST TUESDAY FOR LMZ844>849.  
 

 
 

 
 
SYNOPSIS...04  
SHORT TERM...04  
LONG TERM...NJJ  
AVIATION...04  
HYDROLOGY...HOVING  
MARINE...04  
 
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