736  
FXUS63 KGRR 251107  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
707 AM EDT MON SEP 25 2017  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 328 AM EDT MON SEP 25 2017  
 
TWO MORE DAYS OF RECORD HIGH TEMPERATURES ACROSS MOST OF SOUTHWEST  
MICHIGAN THEN THE FIRST COLD FRONT COMES THROUGH EARLY WEDNESDAY  
LOWERING HIGH TEMPERATURES FROM NEAR 90 TO NEAR 70 (WHICH IS CLOSE  
TO NORMAL NOW). A SECOND COLD FRONT COMES THROUGH ON FRIDAY  
BRINGING MORE FALL LIKE TEMPERATURES AND SOME LAKE ENHANCED RAIN  
SHOWERS WITH IT. ANY SHOWERS WITH THE COLD FRONT EARLY WEDNESDAY  
WILL BE WIDELY SCATTERED AND NOT PRODUCE MUCH RAINFALL, EVEN WERE  
IT DOES RAIN. THE RAINFALL ON FRIDAY WILL BE MORE WIDESPREAD BUT  
BEING LAKE ENHANCED WILL MOSTLY BE NEAR THE LAKE MICHIGAN SHORE.  
 

 
   
SHORT TERM
 
(TODAY THROUGH WEDNESDAY)  
ISSUED AT 328 AM EDT MON SEP 25 2017  
 
WE GET TODAY AND TUESDAY IN THE CURRENT RECORD WARM WEATHER  
PATTERN, THEN A SIGNIFICANT CHANGE WILL OCCUR AND WE WILL HAVE A  
RATHER PROGRESSIVE UPPER AIR PATTERN INTO NEXT WEEK.  
 
THIS IS ONE OF THOSE HENRY RULE EVENTS. WE HAVE A CLOSED UPPER  
LOW OVER THE SOUTHWEST CONUS AND UNTIL WE GET A SYSTEM STRONG  
ENOUGH AND CLOSE ENOUGH IN WAVELENGTH IT WILL STAY THERE. WE IN  
FACT DO HAVE SUCH A SYSTEM CURRENTLY NEAR THE DATELINE. BY  
TOMORROW THE WAVE LENGHT GETS SHORT ENOUGH TO PUSH THE LOW  
CURRENTLY OVER THE SOUTHWEST CONUS NORTHEAST OVER THE TOP OF THE  
LONGWAVE RIDGE, WHICH IS OVER THE EASTERN CONUS.  
 
HOWEVER THIS IS WHY WE HAVE ONLY A VERY LOW CHANCE FOR SHOWERS  
WITH THE FRONT. THE LONGWAVE RIDGE IS STILL THERE AS THE FRONT  
COMES THROUGH SO ALL THE GOOD DEEP FORCING IS OVER NORTHERN  
MICHIGAN AND INTO ONTARIO CANADA. IT IS OVER UPPER MICHIGAN AND  
ONTARIO, NORTH OF LAKE SUPERIOR WHERE THE BEST 1000/850 MOISTURE  
TRANSPORT IS WEDNESDAY MORNING AHEAD OF THE FRONT. IN FACT THERE  
IS NOT EVEN ALL THAT MUCH INSTABILITY, DOWN HERE, THE MOST  
UNSTABLE CAPE IS MOSTLY LESS THAN 500 J/KG EARLY WEDNESDAY MORNING  
AS THE FRONT COMES THROUGH. SO I AM THINKING ONLY WIDELY SCATTERED  
SHOWER WITH THE OUTSIDE CHANCE OF A THUNDERSTORM.  
 
MEANWHILE WE ARE STILL IN THE WARM STREAM OF AIR SO EXPECT HIGHS  
BOTH TODAY AND TUESDAY TO BE FROM AROUND 90 TO THE LOWER 90S.  
THERE WILL BE SOME CIRRUS CLOUDS TODAY WHICH IS PARTLY FROM THE  
UPPER LEVEL OUTFLOW FROM HURRICANE MARIA. THIS SHOULD NOT BE  
ENOUGH TO KEEP US FROM BRAKING MORE RECORD HIGHS HOWEVER FOR TODAY  
AND TUESDAY.  
   
LONG TERM
 
(WEDNESDAY NIGHT THROUGH SUNDAY)  
ISSUED AT 328 AM EDT MON SEP 25 2017  
 
THE TRANSITION TO MORE FALL-LIKE WEATHER WILL CONTINUE FOR THE  
LATTER PART OF THE WEEK AND INTO THE WEEKEND. THERE WILL BE THE  
CHANCE FOR SCATTERED SHOWERS THURSDAY NIGHT AND FRIDAY.  
 
THE PATTERN SHOULD BE FAIRLY ZONAL ON THURSDAY, BRINGING US  
SEASONALLY COOL TEMPS. BUT THEN AN UPPER TROUGH DEEPENS OVER THE  
GREAT LAKES BY FRIDAY AND THIS SHOULD ACTUALLY BRING TEMPS TO BELOW  
NORMAL VALUES THAT SHOULD PERSIST INTO THE WEEKEND. THE MODELS HAVE  
TRENDED DEEPER WITH THIS TROUGH WHICH ALSO INCREASES THE CHANCE FOR  
RAIN IN THE THURSDAY NIGHT AND FRIDAY TIME FRAME. THIS DOESN'T LOOK  
LIKE A DROUGHT-BUSTER, BUT IT WOULD SEEM TO BE ENOUGH TO SETTLE THE  
DUST. THERE COULD BE SOME LAKE EFFECT SHOWERS INTO FRIDAY AFTERNOON  
AND EVENING, BUT THESE LOOK MINIMAL AS THE AIR MASS THAT FOLLOWS THE  
SHORT WAVE APPEARS QUITE DRY.  
 
A LARGE CANADIAN HIGH PRESSURE PUSHES IN FOR THE WEEKEND. DRY  
WEATHER SHOULD RETURN, BUT IT DOES NOT LOOK LIKE WE WARM UNTIL NEXT  
WEEK. SO EXPECT A PLEASANTLY COOL AND DRY WEEKEND. THERE COULD BE  
SOME PATCHY FROST FRIDAY AND SATURDAY NIGHTS TOWARD U.S. 10.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 707 AM EDT MON SEP 25 2017  
 
THERE IS SOME PATCHY LIGHT FOG AROUND EARLY THIS MORNING BUT THIS  
FOG SHOULD QUICKLY MIX OUT BY 15Z THEN JUST SOME CIRRUS CLOUDS  
(FOR THE MOST PART) INTO THIS EVENING. MORE PATCHY FOG TO EARLY  
TUESDAY MORNING TOO BUT THAT THIS POINT I DO NOT EXPECT ANY  
PERSISTENT IFR FOG.  
 

 
   
MARINE
 
 
ISSUED AT 328 AM EDT MON SEP 25 2017  
 
LIKELY WE WILL NEED A SMALL CRAFT ADVISORY WEDNESDAY ONCE WE GET  
INTO THE COLD AIR.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 1245 PM EDT SUN SEP 24 2017  
 
RIVERS ARE RUNNING AROUND NORMAL TO BELOW NORMAL FOR THE TIME OF  
YEAR. MEANWHILE, THE US DROUGHT MONITOR IS INDICATING DRY CONDITIONS  
ACROSS SOUTHERN LOWER MICHIGAN. NEAR-RECORD WARMTH IS EXPECTED TODAY  
AND MONDAY. THE NEXT CHANCE FOR RAIN IS WEDNESDAY, BUT IT'S NOT A  
GOOD CHANCE. NO RIVER ISSUES ARE EXPECTED THROUGH THE WEEK.  
 

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

 
 

 
 
SYNOPSIS...WDM  
SHORT TERM...WDM  
LONG TERM...JK  
AVIATION...WDM  
HYDROLOGY...63  
MARINE...WDM  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MI Page
The Nexlab IN Page Main Text Page