986  
FXUS63 KGRR 230858 CCA  
AFDGRR  
 
AREA FORECAST DISCUSSION...CORRECTED  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
458 AM EDT SUN JUL 23 2017  
 
LATEST UPDATE...  
SYNOPSIS/SHORT TERM/LONG TERM/MARINE  
   
SYNOPSIS
 
 
ISSUED AT 330 AM EDT SUN JUL 23 2017  
 
LOW PRESSURE PASSING THROUGH THE STATE TODAY WILL BRING SCATTERED  
SHOWERS AND THUNDERSTORMS. HIGH PRESSURE WILL PROVIDE A STRETCH  
OF DRY AND LESS HUMID WEATHER MONDAY AND TUESDAY BEFORE THE NEXT  
FRONT BRINGS MORE SCATTERED SHOWERS AND STORMS LATER WEDNESDAY  
INTO EARLY THURSDAY.  
 

 
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 330 AM EDT SUN JUL 23 2017  
 
COMBINATION OF H5 UPR LOW/SHORTWAVE AND SFC COLD FRONT DROPPING  
SOUTHEAST THROUGH THE GREAT LAKES REGION WILL LEAD TO SCATTERED  
CONVECTION TODAY. CAPE/SHEAR PROFILES SUGGEST THE POSSIBILITY OF A  
FEW STRONG TO PERHAPS SEVERE STORMS BY AFTERNOON, WITH SB CAPES  
NEAR 1500 J/KG AND 0-6 KM SHEAR AROUND 35 KNOTS.  
 
HOWEVER THE LATEST RAP SOUNDINGS HAVE A RATHER DRY LOOK AND IT  
WILL BE SOMEWHAT OF A RACE AGAINST TIME OF BUILDING UP ENOUGH  
SURFACE BASED INSTABILITY BEFORE THE WEST/NORTHWEST LOW LEVEL FLOW  
OFF LAKE MICHIGAN DEVELOPS AND STRENGTHENS. MODELS DO SEEM TO BE  
A BIT SLOWER/LESS AGGRESSIVE IN THIS REGARD WHICH SUGGESTS THE  
POSSIBILITY OF A LONGER WINDOW OF TIME WITH DECENT SFC CONVERGENCE  
BEFORE THE LAKE SHADOW SPREADS INLAND.  
 
IN GENERAL, THE DEVELOPING WEST/NORTHWEST FLOW OFF LAKE MI SHOULD  
TEND TO FOCUS MOST CONVECTION EAST OF HIGHWAY 131 BY 18Z, AND  
EAST OF U.S. 127 BY 21Z. MOSTLY SUNNY SKIES SHOULD BE SWEEPING  
EASTWARD OFF THE LAKE AS WELL THIS AFTERNOON.  
 
ONE OTHER THING TO WATCH FOR LATER TODAY IS THE POTENTIAL OF A  
STRONGER CONVECTIVE CLUSTER THAT MAY IMPACT THE CHICAGO AREA WHICH  
COULD CLIP FAR SRN LAKE MICHIGAN/VAN BUREN COUNTY.  
 
OTHERWISE SOME OTHER THINGS OF NOTE IN THE SHORT TERM INCLUDE  
AREAS OF DENSE FOG EARLY THIS MORNING WHICH WILL LIFT BY MID  
MORNING, AND A POTENTIAL FOR CONSIDERABLE CLOUDS ON MONDAY. THE  
PRESENCE OF A THERMAL TROUGH ALOFT AND LOW LEVEL CYCLONIC FLOW  
WILL PROBABLY RESULT IN CONSIDERABLE DIURNAL CLOUDINESS, PARTICULARLY  
INLAND FROM LAKE MI.  
 
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 330 AM EDT SUN JUL 23 2017  
 
MAIN CONCERN IS THUNDERSTORM POTENTIAL LATE WEDNESDAY INTO EARLY  
THURSDAY. LATEST MEDIUM RANGE GUIDANCE SUGGESTS A LINE OF CONVECTION  
WILL ENTER THE AREA AROUND OR SHORTLY AFTER DARK WEDNESDAY NIGHT. AS  
NOTED ALREADY, THERE IS SUFFICIENT FORCING AND INSTABILITY FOR THE  
MENTION OF THUNDERSTORMS. STORM INTENSITY COULD DEPEND CHIEFLY ON  
WHEN THEY OCCUR RELATIVE TO PEAK AFTERNOON HEATING. REGARDLESS, THEY  
SHOULD PROGRESS RAPIDLY THROUGH THE AREA WITH LITTLE FLOOD CONCERNS  
ANTICIPATED AT THIS TIME.  
 
AFTER PRECIPITATION EXITS THURSDAY, DRY CONDITIONS AND SEASONABLE  
TEMPERATURES ARE EXPECTED TO PERSIST INTO SATURDAY.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)  
ISSUED AT 202 AM EDT SUN JUL 23 2017  
 
HIGH CONFIDENCE FOR WIDESPREAD IFR AND OCCASIONAL LIFR CONDITIONS  
THROUGH 12Z, ALTHOUGH ONSET MAY BE SLIGHTLY DELAYED FARTHER EAST  
AT LAN TERMINAL. WE ARE MUCH LESS CERTAIN AFTER 12Z, BUT THE  
GENERAL EXPECTATION IS FOR A RISE TO VFR VISIBILITIES / MVFR  
CEILINGS WITH THE POSSIBILITY FOR THUNDERSTORMS MOVING SOUTHEAST  
INTO THE AREA BEFORE 18Z. AFTER 18Z, VFR SHOULD PREDOMINATE WITH  
SCATTERED THUNDERSTORMS IN THE VICINITY. GUSTY WINDS WITH STORMS  
WILL BE MORE LIKELY FARTHER EAST AROUND JXN AND LAN TERMINALS.  
 

 
   
MARINE
 
 
ISSUED AT 330 AM EDT SUN JUL 23 2017  
 
AREAS OF DENSE FOG OVER LAKE MICHIGAN THIS MORNING ARE EXPECTED  
TO MIX OUT THIS AFTERNOON WITH ARRIVAL OF DRIER AIR/WESTERLY  
FLOW. SCATTERED STORMS WILL POSE A THREAT TO MARINERS, MAINLY  
THIS MORNING. ROUGH CONDITIONS WITH WAVES UP TO 4 FEET AND NORTH  
WINDS TO 20 KNOTS WILL DEVELOP ON LAKE MICHIGAN LATE TONIGHT AND  
CONTINUE INTO MONDAY. WILL HAVE TO MONITOR FOR THE POSSIBILITY OF  
SMALL CRAFT ADVISORY/BEACH HAZARD, BUT CURRENTLY IT'S BORDERLINE.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 1123 AM EDT SAT JUL 22 2017  
 
WE AGAIN ESCAPED THE HEAVY TO EXCESSIVE RAIN THAT FELL IN  
SOUTHERN WISCONSIN AND NORTHERN ILLINOIS. WHILE THAT AREA FLOODS,  
MOST OF OUR AREA CONTINUES TO RUN DRIER THAN NORMAL THESE PAST 1  
TO 2 WEEKS. WITH HIGH ATMOSPHERIC WATER VAPOR CONTENT, THE SHOWERS  
SATURDAY MORNING EFFICIENTLY PUT DOWN OVER A HALF INCH OF RAIN BUT  
ONLY IN A FEW ISOLATED SPOTS. SCATTERED SHOWERS OR STORMS SUNDAY  
WILL PROVIDE ONLY SPOTTY RELIEF TO THE DRY WEATHER. AFTER THAT, THE  
NEXT POTENTIAL FOR A STORM WILL BE WEDNESDAY.  
 

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

 
 

 
 
SYNOPSIS...MEADE  
SHORT TERM...MEADE  
LONG TERM...TJT  
AVIATION...TJT  
HYDROLOGY...CAS  
MARINE...MEADE  
 
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