869  
FXUS63 KGRR 191140  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
740 AM EDT FRI SEP 19 2014  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 312 AM EDT FRI SEP 19 2014  
 
HIGH PRESSURE OVER NEW ENGLAND WILL TRACK SLOWLY EAST TODAY.  
SOUTHWEST WINDS AROUND THIS FAIR WEATHER SYSTEM WILL DRAW UP A  
MILDER AIRMASS INTO MICHIGAN THROUGH TODAY. A COLD FRONT IN THE  
UPPER PLAINS WILL TRACK THROUGH MICHIGAN SATURDAY INTO SATURDAY  
NIGHT. THIS SYSTEM WILL BRING WITH IT A ROUND OF POTENTIALLY  
STRONG THUNDERSTORMS. A COOLER AIRMASS WILL FILTER IN BEHIND THIS  
COLD FRONT FOR SUNDAY.  
 

 
   
SHORT TERM
 
(TODAY THROUGH SUNDAY)  
ISSUED AT 312 AM EDT FRI SEP 19 2014  
 
THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE POTENTIAL FOR  
SEVERE WEATHER ON SATURDAY. OVERALL...CONFIDENCE IS HIGHER THAT WE  
WILL SEE SOME SEVERE WEATHER.  
 
DEEP LAYER SHEAR STRENGTHENS AS THE COLD FRONT PUSHES IN FROM THE  
WEST SATURDAY AFTERNOON AND EVENING. THE SYSTEM RESPONSIBLE FOR  
THE INCREASING WIND FIELDS WAS MOVING ONSHORE IN WESTERN CANADA  
AND THE NW U.S. MODELS ARE FAIRLY SIMILAR IN TRACKING THIS SYSTEM  
INTO THE GREAT LAKES REGION DURING THIS TIMEFRAME. THIS  
STRENGTHENING SHEAR WILL ALLOW FOR ORGANIZED STORMS TO DEVELOP WITH  
A POTENTIAL FOR DAMAGING WINDS AND LARGE HAIL. SOME UNCERTAINTY  
EXISTS IN HOW MUCH INSTABILITY WE DEVELOP HERE IN SW MICHIGAN...OVERALL  
THOUGH IT LOOKS LIKE THAT WILL END UP SUFFICIENT AS WELL. THE 0 TO  
1 KM SHEAR AND HELICITY DO SUPPORT AND ELEVATED RISK FOR TORNADOES.  
FORECAST SOUNDINGS FAVORED THE 18Z TO 02Z TIMEFRAME FOR THE  
POTENTIAL SEVERE WEATHER. OVERALL I KEPT THE HIGH POPS GOING.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 312 AM EDT FRI SEP 19 2014  
 
FAIR AND TRANQUIL WEATHER IS ANTICIPATED THROUGH THE LONG RANGE  
FORECAST PERIOD AS A LARGE SFC HIGH PRESSURE RIDGE BUILDS IN. ANY  
LINGERING SHOWERS ON SUNDAY SHOULD EXIT OUR AREA BY SUNDAY NIGHT AS  
THE UPPER TROUGH AXIS MOVES FURTHER EAST.  
 
TEMPERATURES WILL AVERAGE RATHER CLOSE TO NORMAL SUNDAY NIGHT  
THROUGH MIDWEEK BEFORE UNDERGOING A GRADUAL MODERATING TREND LATE  
NEXT WEEK.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)  
ISSUED AT 731 AM EDT FRI SEP 19 2014  
 
A PATCH OF LIFR CLOUDS/FOG WAS DRIFTING NORTHWEST FROM KGRR TO  
KMKG AND THIS WILL IMPACT THESE TAF SITES EARLY THIS MORNING.  
ELSEWHERE THE IFR AND LOWER CONDITIONS WERE VERY LOCALIZED. STILL  
MVFR FOG WAS FAIRLY WIDESPREAD...AND THERE IS A SMALL CHANCE THAT  
THE IFR COULD EXPAND OVER THE NEXT HR. BY 15Z IT APPEARS THAT VFR  
WEATHER WILL PREVAIL. LATER TONIGHT LOCALIZED SHOWERS WILL ARRIVE.  
SOME INSTABILITY MOVES IN AS WELL...SO AN ISOLATED THUNDERSTORM IS  
POSSIBLE. I DID NOT INCLUDE THIS IN THE FORECAST DUE TO THE  
ISOLATED NATURE OF ANY CONVECTION.  
 

 
   
MARINE
 
 
ISSUED AT 312 AM EDT FRI SEP 19 2014  
 
WILL ISSUE A SMALL CRAFT ADVISORY WITH THIS PACKAGE. WINDS AND  
WAVES WILL INCREASE ESPECIALLY THIS AFTERNOON AND EVENING. BY  
MIDNIGHT ALL ZONES WILL SEE SMALL CRAFT CONDITIONS. THE SOUTHERLY  
FLOW SUPPORTS THE HIGHEST WAVES UP NORTH. THE GRADIENT WEAKENS  
LATER SATURDAY AS THE LOW LEVEL JET PULLS AWAY. BY 00Z MOST  
LOCATIONS SHOULD SEE CONDITIONS UNDER SMALL CRAFT CRITERIA.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 312 AM EDT FRI SEP 19 2014  
 
LOCALLY HEAVY RAIN WILL ACCOMPANY THE THUNDERSTORMS ESPECIALLY  
SATURDAY AFTERNOON INTO THE EVENING. IT DOES NOT LOOK LIKE THE  
STORMS WILL STALL OUT...THUS 1 TO 2 HR HEAVY RAIN DURATION IS THE  
MOST LIKELY SCENARIO. THIS TYPICALLY LEADS TO URBAN AND POOR  
DRAINAGE ISSUES IF ANY.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LM...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EDT  
SATURDAY FOR LMZ847>849.  
 
SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 8 PM EDT  
SATURDAY FOR LMZ844>846.  
 

 
 

 
 
SYNOPSIS...MJS  
SHORT TERM...MJS  
LONG TERM...LAURENS  
AVIATION...MJS  
HYDROLOGY...MJS  
MARINE...MJS  
 
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