188  
FXUS63 KGRR 182003  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
303 PM EST THU DEC 18 2014  
 
LATEST UPDATE...  
LONG TERM  
   
SYNOPSIS
 
 
ISSUED AT 240 PM EST THU DEC 18 2014  
 
LIGHT SNOW AND FREEZING DRIZZLE ARE EXPECTED TO DIMINISH OVERNIGHT.  
QUIET WEATHER IS EXPECTED THROUGH THE WEEKEND WITH SOME SUN ON  
FRIDAY. HIGHS WILL BE IN THE 30S OVER THE WEEKEND WITH A WARM UP  
INTO THE LOWER 40S EARLY NEXT WEEK.  
 
UNSETTLED WEATHER IS EXPECTED NEXT WEEK...WITH MULTIPLE  
OPPORTUNITIES FOR BOTH RAIN AND SNOW. RAIN OR SNOW WILL BE POSSIBLE  
BEGINNING SUNDAY AFTERNOON INTO SUNDAY NIGHT. THEN A PERIOD OF RAIN  
IS EXPECTED MONDAY AND TUESDAY. COLDER AIR SHOULD ARRIVE ABOUT  
TUESDAY NIGHT WHICH SHOULD CHANGE THE PRECIPITATION TO SNOW WHICH  
SHOULD CONTINUE INTO CHRISTMAS DAY.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SATURDAY NIGHT)  
ISSUED AT 240 PM EST THU DEC 18 2014  
 
MAIN CONCERN IS DRIZZLE/FREEZING DRIZZLE THIS AFTERNOON LASTING INTO  
THE EVENING. SURFACE BOUNDARY HAS STALLED ROUGHLY ALONG A HOLLAND TO  
GRAND RAPIDS TO LANSING LINE. TEMPERATURES SOUTH OF THIS BOUNDARY  
HAVE BEEN SLOW TO RISE...BUT EXPECT A SLOW CLIMB ABOVE FREEZING THE  
REST OF THIS AFTERNOON. SHORT RANGE GUIDANCE INCLUDING THE HRRR  
SHOWS THE BOUNDARY DROPPING SOUTH TO I-94 BY 10 PM. THERE IS A  
NARROW WINDOW FOR FREEZING DRIZZLE AGAIN THIS EVENING AS  
TEMPERATURES BEGIN TO FALL. PRECIPITATION IS MOST LIKELY TO OCCUR  
OVER FAR SOUTHWEST LOWER MICHIGAN WHERE SPEED CONVERGENCE OF WINDS  
OFF LAKE MICHIGAN WILL SUPPLEMENT BOUNDARY CONVERGENCE. LIGHT SNOW  
WILL ALSO CONTINUE TO BE POSSIBLE EARLY TONIGHT IN THE VICINITY OF  
THE BOUNDARY.  
 
OTHERWISE NO SIGNIFICANT WEATHER IS EXPECTED THROUGH SATURDAY NIGHT  
WITH HIGH PRESSURE IN CONTROL.  
   
LONG TERM
 
(SUNDAY THROUGH THURSDAY)  
ISSUED AT 303 PM EST THU DEC 18 2014  
 
STILL A FAIR AMOUNT OF UNCERTAINTY AS TO THE DETAILS OF THE STORM  
SYSTEM EXPECTED TO IMPACT THE REGION JUST PRIOR TO CHRISTMAS AND  
INTO CHRISTMAS DAY.  
 
THE MODELS HAVE TRENDED FURTHER NORTH WITH THE SURFACE LOW...NOW  
TAKING IT ACROSS NORTHERN LOWER TUESDAY NIGHT. THEY ARE ALSO  
HINTING AT AN EAST COAST LOW WHICH MAY TRANSFER ENERGY FROM THE  
GREAT LAKES LOW. BOTTOM LINE...THIS APPEARS TO BE A SLOW MOVING  
STORM AND A FEW WOBBLES EITHER WAY WILL BE MAKE A DIFFERENCE ON  
TIMING PCPN TYPE.  
 
THE STORM BECOMES NEGATIVELY TILTED BY TUESDAY NIGHT WHICH SHOULD  
FAVOR A QUICKER ARRIVAL TO THE COLDER AIR. BEST BET RIGHT NOW IS  
THAT THIS MOVES IN TUESDAY NIGHT. SO EXPECTING A WET MONDAY AND  
TUESDAY...FOLLOWED BY A COOL DOWN AND A SWITCH TO SNOW TUESDAY  
NIGHT. AND EVEN THOUGH SOME OF THE STORM/S ENERGY MAY SHIFT TO THE  
EAST COAST...WE SHOULD REMAIN UNDER A MOIST CYCLONIC FLOW LINGERING  
INTO CHRISTMAS DAY. THIS SHOULD RESULT IN LIGHT SNOW CONTINUING  
RIGHT INTO THE THURSDAY. H8 TEMPS SHOULD BE AROUND -8C BY CHRISTMAS  
DAY SO EXPECT LAKE MICHIGAN WILL HELP ENHANCE THE SNOW A BIT. ALL  
IN ALL IT APPEARS A WHITE CHRISTMAS IS A GOOD BET FOR MUCH OF SW MI.  
 
UNTIL THEN...I ADDED POPS TO SUNDAY AFTERNOON AND EVENING...MOSTLY  
ALONG AND NORTH OF I-96. MODELS SHOW A SHARPENING WARM FRONT MOVING  
NORTH INTO THE AREA WITH DECENT ISENTROPIC LIFT AHEAD OF IT. WOULD  
EXPECT SOME LIGHT SNOW WITH THIS...ALTHOUGH ACCUMS SHOULD REMAIN  
UNDER AN INCH. THEN WARMER AIR ARRIVES LATE SUNDAY NIGHT/MONDAY  
WHEN THE PCPN SHOULD SWITCH TO RAIN.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 1255 PM EST THU DEC 18 2014  
 
PILOTS WILL NEED TO BE AWARE OF THE THREAT OF AIRCRAFT ICING TODAY  
AND INTO TONIGHT. SOME REPORTS OF FREEZING DRIZZLE HAVE BEEN  
RECEIVED. AND THE IN CLOUD TEMP WILL BE IN THE -8 TO -11C RANGE  
BETWEEN 3000 AND 5000 FT. THIS IS AN IDEAL RANGE FOR SUPER-COOLED  
LIQUID TO EXIST WITHIN THESE CLOUDS. CLOUD TOPS ARE EXPECTED TO BE  
AROUND 10,000 FT MUCH OF THE DAY...SO IT MAY BE DIFFICULT TO CLIMB  
OUT OF THE ICING. CLOUD TOPS ARE NOT EXPECTED TO LOWER UNTIL  
02-04Z WHEN THE ICING THREAT SHOULD DIMINISH.  
 
MUCH OF THE REGION REMAINED UNDER MVFR CONDITIONS EARLY THIS  
AFTERNOON...WITH PATCHY IFR IN LOWER CEILINGS AND FREEZING  
DRIZZLE. EXPECT LITTLE OVERALL CHANGE IN CONDITIONS...ALTHOUGH THE  
FREEZING DRIZZLE THREAT SHOULD END ACROSS THE I-96 TAF SITES BY  
21-22Z. THIS THREAT COULD LINGER NEAR THE I-94 TAF SITES UNTIL  
ABOUT 01Z.  
 
DRIER AIR SLOWLY MOVES IN FROM THE NORTH TONIGHT AND EXPECT AN  
IMPROVEMENT IN CEILINGS PRIOR TO DAYBREAK TO MOSTLY VFR.  
 

 
   
MARINE
 
 
ISSUED AT 240 PM EST THU DEC 18 2014  
 
NO CONCERNS AT THIS TIME. WINDS AND WAVES WILL CONTINUE TO SUBSIDE  
THIS EVENING AND STAY LOW INTO THE WEEKEND WITH HIGH PRESSURE IN  
CONTROL.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 240 PM EST THU DEC 18 2014  
 
NO SIGNIFICANT HYDRO IMPACTS EXPECTED FOR THE FORESEEABLE FUTURE.  
 

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

 
 

 
 
SYNOPSIS...EBW/JK  
SHORT TERM...TJT  
LONG TERM...JK  
AVIATION...JK  
HYDROLOGY...EBW  
MARINE...TJT  
 
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