017  
FXUS63 KGRR 300055  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
855 PM EDT MON MAY 29 2017  
 
LATEST UPDATE...  
UPDATE  
   
SYNOPSIS
 
 
ISSUED AT 325 PM EDT MON MAY 29 2017  
 
THE REGION WILL STAY COOL TUESDAY AND WEDNESDAY WITH HIGHS IN THE  
60S TO AROUND 70. THIS COMPARES TO AVERAGE HIGHS IN THE 70S FOR  
THIS TIME OF YEAR. SCATTERED SHOWERS, OR EVEN A THUNDERSTORM, WILL  
DOT THE LANDSCAPE FROM TUESDAY AFTERNOON INTO MID DAY WEDNESDAY,  
THEN THE PRECIPITATION WILL EXIT SOUTHWEST MICHIGAN.  
 
IT APPEARS A BETTER CHANCE OF SHOWERS AND STORMS MOVE BACK INTO  
THE AREA THURSDAY NIGHT THROUGH FRIDAY NIGHT. NEXT WEEKEND LOOKS  
MAINLY DRY. WE SHOULD CONTINUE TO SEE SLIGHTLY BELOW NORMAL  
TEMPERATURES, WITH HIGHS MAINLY IN THE UPPER 60S TO MID 70S.  
 

 
   
UPDATE
 
 
ISSUED AT 856 PM EDT MON MAY 29 2017  
 
I AM WATCHING AN AREA OF SHOWERS OVER CENTRAL LAKE MICHIGAN MOVING  
LARGELY TOWARD THE EAST (HEADING TOWARD MKG). THERE IS A  
SIGNIFICANT TWIST IN THE H20 VAPOR IMAGE LOOPS AND THERE IS ALSO  
A 400 MB PV FEATURE WITH THIS AREA OF SHOWERS TOO. THE INSTABILITY  
IS FEEBLE AT BEST BUT THE MODEL SOUNDING SHOW THE AIR TO BE MORE  
MOIST IN THAT AREA SO IT JUST MAY BE THE AREA FROM MKG TO LDM WILL  
SEE A FEW SHOWERS OVER THE NEXT 3 TO 4 HOURS.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH WEDNESDAY NIGHT)  
ISSUED AT 325 PM EDT MON MAY 29 2017  
 
THE UPPER LOW OVER THE SUPERIOR REGION WILL CONTINUE TO DRIFT  
SLOWLY EAST. SEVERAL SHORT WAVES PASS THROUGH BETWEEN NOW AND MID  
DAY WED, BRINGING SHOWER CHANCES.  
 
WEAK LIFT REMAINS OVER SW MI INTO TONIGHT. CANNOT RULE OUT AN  
ISOLATED SHOWER OR STORM OVER THE NW HALF OF THE CWA, BUT 20 POPS  
SHOULD COVER THESE.  
 
A BETTER CHANCE OF SHOWERS AND STORMS WILL ARRIVE TUESDAY  
AFTERNOON AS A SHORT WAVE PINWHEELS AROUND THE UPPER LOW AND INTO  
SW MI BY EVENING. ANOTHER SHORT WAVE ARRIVES WED MORNING. SO THIS  
LEADS TO CARRYING SLIGHTLY HIGHER POPS FROM ROUGHLY 18Z TUESDAY  
THROUGH 18Z WEDNESDAY. WILL KEEP THE MENTION OF THUNDER IN THE  
FORECAST FOR TUESDAY AFTERNOON AND EVENING, AS THE DAYTIME HEATING  
AND CHILLY AIR ALOFT LEADS TO DECENT LAPSE RATES. SAME IS TRUE  
TOWARD I-94 ON WEDNESDAY, UNTIL THE FINAL SHORT WAVE COMES  
THROUGH. EXPECT THE SCATTERED PCPN WILL BE EAST OF THE AREA AFTER  
18Z WED, WITH THE EXITING SHORT WAVE. SKIES WILL BEGIN TO CLEAR  
BEHIND THE WAVE INTO THE EVENING.  
 
WEDNESDAY NIGHT WILL BE MOSTLY CLEAR AND COOL WITH LOWS DIPPING TO  
THE 45 TO 50 RANGE.  
   
LONG TERM
 
(THURSDAY THROUGH MONDAY)  
ISSUED AT 325 PM EDT MON MAY 29 2017  
 
SHOWERS AND THUNDERSTORMS WILL BE ON THE INCREASE THURSDAY NIGHT AND  
FRIDAY AS AREA OF ISENTROPIC ASCENT IN OVERRUNNING PATTERN SETS UP  
ACROSS LOWER MICHIGAN, ALTHOUGH IT APPEARS THAT THE BULK OF THE  
PRECIP COULD REMAIN JUST TO OUR SOUTH WHERE ONE OR MORE CLUSTERS OF  
CONVECTION FORM ALONG A WELL DEFINED SFC BOUNDARY THURSDAY NIGHT  
INTO FRIDAY NIGHT.  
 
THERE IS LOWER THAN AVERAGE CONFIDENCE IN THE FORECAST OVER THE  
WEEKEND AS ENSEMBLE SPREAD REMAINS LARGE. THE MAJORITY OF SOLUTIONS  
SUGGEST A CANADIAN SFC HIGH WILL BE CENTERED ACROSS SOUTHERN CANADA  
OR THE NORTHERN GREAT LAKES WITH A SFC LOW TRACKING ACROSS THE  
STALLED SFC BOUNDARY SOUTH OF LOWER MICHIGAN. DRY NORTHERLY FLOW  
SHOULD RESULT IN FAIR WEATHER OVER MUCH OF THE WEEKEND ALTHOUGH  
SOUTHERN ZONES COULD BE IN THE NORTHERN EDGE OF THE RAIN AT TIMES.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)  
ISSUED AT 720 PM EDT MON MAY 29 2017  
 
VFR CONDITIONS WILL CONTINUE THROUGH TUESDAY (AND WELL BEYOND  
THEN). A COLD CORE UPPER LOW OVER THE AREA WILL BRING AFTERNOON  
SHOWERS TO THE AREA TOMORROW AS IT DID TODAY. ALSO, AS TODAY  
THERE, WILL BE A "LAKE SHADOW" TO THE CONVECTION. LOCATIONS LIKE  
GRR AND MKG WILL VERY LIKELY SEE NO SHOWERS. ON THE OTHER HAND,  
AZO,BTL, LAN, AND JXN HAVE A BETTER CHANCE OF HAVING ONE OF THOSE  
SHOWERS. EVEN THEN THROUGH I WOULD EXPECT VFR CONDITIONS TO RULE.  
LIKE TODAY TOMORROW WILL BE BREEZY WITH GUST TO NEAR 25 KTS AT  
TIMES. THE SHOWERS ARE EXPECTED TO DISSIPATE WITH SUNSET  
TOMORROW.  
 

 
   
MARINE
 
 
ISSUED AT 325 PM EDT MON MAY 29 2017  
 
WINDS HAVE COME UP TODAY AND WAVES WILL CONTINUE TO GRADUALLY  
BUILD TONIGHT. NOT EXPECTING WE WILL REACH SMALL CRAFT ADVISORY  
CRITERIA, BUT IT WILL BECOME ROUGHER ON THE LAKE BY MIDNIGHT.  
THESE CHOPPY WAVES WILL CONTINUE INTO TUESDAY, BUT DIMINISH BY  
LATE AFTERNOON AND INTO THE EVENING. LOWER WAVES CAN BE EXPECTED  
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 206 PM EDT MON MAY 29 2017  
 
NO HYDROLOGIC CONCERNS FOR A FEW DAYS. SMALL RIVERS AND STREAMS  
MAY BE SUSCEPTIBLE TO RISES THURSDAY NIGHT INTO FRIDAY IF  
CONVECTION MATERIALIZES ACROSS THE REGION. PWAT VALUES ARE  
EXPECTED TO INCREASE TO 1.25-1.50" ACROSS SOUTHERN LOWER MI DURING  
THAT TIME. HARD TO SEE THIS BECOMING A PROBLEM ON MAINSTEM RIVERS  
UNLESS WIDESPREAD, TRAINING THUNDERSTORMS OCCUR. WE'LL KEEP AN EYE  
ON TRENDS.  
 

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

 
 

 
 
UPDATE...WDM  
SYNOPSIS...JK  
SHORT TERM...JK  
LONG TERM...OSTUNO  
AVIATION...WDM  
HYDROLOGY...HOVING  
MARINE...JK  
 
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