513  
FXUS63 KGRR 172322  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
722 PM EDT SUN JUN 17 2018  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 325 PM EDT SUN JUN 17 2018  
 
HOT AND HUMID CONDITIONS WILL CONTINUE LATE THIS AFTERNOON AND  
EARLY EVENING. IT WILL BE HOT AND HUMID AGAIN MONDAY OVER FAR  
SOUTHERN LOWER MICHIGAN WHERE HEAT INDICES WILL AGAIN REACH  
THE 100 DEGREE MARK. A COLD FRONT MOVING IN FROM THE NORTH WILL  
BRING SOME SHOWERS AND THUNDERSTORMS MONDAY THROUGH MONDAY NIGHT.  
SHOWERS AND STORMS WILL LINGER TUESDAY OVER FAR SOUTHERN LOWER  
MICHIGAN.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY NIGHT)  
ISSUED AT 325 PM EDT SUN JUN 17 2018  
 
A HEAT ADVISORY CONTINUES IN EFFECT FOR OUR ENTIRE FCST AREA UNTIL  
8 PM THIS EVENING. TEMPS IN THE LOWER TO MIDDLE 90S THROUGH THE  
REST OF THIS AFTERNOON AND EARLY EVENING IN CONJUNCTION WITH DEW  
POINTS IN THE LOW TO MID 70S WILL RESULT IN HEAT INDICES IN THE  
LOWER 100S.  
 
AN ISOLATED SHOWER DEVELOPED OVER OUR FAR NE FCST AREA WHERE  
MESOSCALE ANALYSIS SHOWS INSTABILITY IS MAXIMIZED IN AN AREA OF  
WEAK SFC CONVERGENCE. HOWEVER IT WILL CONTINUE TO DRIFT ENE AND OUT  
OF OUR AREA. ADDITIONAL SHOWER DEVELOPMENT IS UNLIKELY TO OCCUR  
GIVEN A LACK OF A FORCING MECHANISM FOR SHOWER OR CONVECTIVE  
INITIATION TO OCCUR IN SUBSIDENCE UNDER THE HIGH AMPLITUDE UPPER  
RIDGE. ISOLATED SHOWERS NEAR TO NE OF KORD WILL MOST LIKELY  
DISSIPATE BEFORE MAKING IT INTO OUR SOUTHERN FCST AREA.  
 
IT WILL REMAIN VERY WARM AND HUMID TONIGHT WITH MINS IN THE 70S  
AND DEW POINTS MAINLY IN THE 70 TO 75 DEGREE RANGE. THE COLD FRONT  
APPROACHING FROM THE NORTH VERY LATE TONIGHT WILL RESULT IN  
DEVELOPMENT OF A FEW SHOWERS AND PERHAPS AN ISOLATED STORM OVER  
OUR FAR NORTHERN FCST AREA AFTER MIDNIGHT.  
 
THE COLD FRONT WILL CONTINUE TO ADVANCE SOUTHWARD ACROSS LOWER  
MICHIGAN MONDAY AND TRIGGER DEVELOPMENT OF SHOWERS AND THUNDERSTORMS.  
THE BEST CHANCE FOR THUNDERSTORMS WILL COME IN THE AFTERNOON AND  
EVENING WHEN THERE IS POTENTIAL FOR MODERATE INSTABILITY TO  
DEVELOP (SB CAPE VALUES REACHING 2-2.5K J/KG NEAR TO SOUTH OF  
I-96).  
 
HOWEVER A CONSENSUS OF SHORT RANGE HIGH RES MODEL GUIDANCE AND  
THE HIGH RES CAMS ARE NOT TOO BULLISH ON CONVECTIVE DEVELOPMENT  
TOMORROW. THERE ARE SEVERAL FACTORS GOING AGAINST POTENTIAL FOR  
BETTER ORGANIZED/STRONGER CONVECTIVE DEVELOPMENT INCLUDING LACK  
OF FAVORABLE UPPER LEVEL DYNAMICS AND ONLY AROUND 20-30 KTS OF  
DEEP LAYER SHEAR. AS SUCH SEVERE WX POTENTIAL TOMORROW IS VERY  
LOW AND OUR AREA IS ONLY IN THE GENERAL THUNDER SPC DAY 2 OUTLOOK.  
 
IT WILL NOT BE QUITE AS HOT TOMORROW FOR MUCH OF OUR FCST AREA DUE  
TO CLOUDS AND SCATTERED SHOWERS/CONVECTION ALONG AND OUT AHEAD OF  
THE FRONT. HOWEVER GIVEN FRONTAL TIMING WE EXPECT AREAS SOUTH OF  
I-96 TO ONCE AGAIN HAVE HIGH TEMPS IN THE LOWER TO PERHAPS MIDDLE  
90S WITH DEW POINTS STILL WELL INTO THE 70'S. AS SUCH WE WILL  
ISSUE A HEAT ADVISORY FOR OUR SOUTHERN TWO TIERS OF COUNTIES FOR  
TOMORROW. SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE  
MONDAY NIGHT IN THE VICINITY OF THE FRONT.  
 
OVERALL GUIDANCE TRENDS FOR TUESDAY SUGGEST THAT SCATTERED SHOWERS  
AND THUNDERSTORMS WILL LINGER OVER OUR SOUTHERN FCST AREA. THE  
FRONT WILL BE SOUTH OF OUR AREA BY THEN AND EXTEND FROM WEST TO  
EAST ACROSS CENTRAL/SOUTHERN IL/IN/OH. ELEVATED INSTABILITY WILL  
STILL BE PRESENT OVER OUR SOUTHERN COUNTIES TUESDAY WITH H8 LI/S  
OF -1 TO -2. IN FACT SOME SHOWERS AND STORMS SHOULD CONTINUE TO  
DEVELOP OVER OUR SOUTHERN FCST AREA THROUGH TUESDAY NIGHT WITH  
ELEVATED INSTABILITY NORTH OF THAT BOUNDARY STILL PRESENT.  
 
THANKS FOR COORD ON HEAT ADVISORY HEADLINE DECISIONS DTX/IWX.  
   
LONG TERM
 
(WEDNESDAY THROUGH SUNDAY)  
ISSUED AT 325 PM EDT SUN JUN 17 2018  
 
TEMPERATURES WILL FOR THE MOST PART BE NEAR NORMAL THROUGH THE  
PERIOD. PRECIPITATION IS STILL A BIG QUESTION. THURSDAY INTO FRIDAY  
LOOK LIKE THERE WILL BE LITTLE IF ANY PRECIPITATION BUT A WAVE ON  
THE FRONT MAY BE FAR ENOUGH NORTH FOR SHOWERS/THUNDERSTORMS TO  
IMPACT SOUTHWEST MICHIGAN ON WEDNESDAY. OVER NEXT WEEKEND, ANOTHER  
SLOW MOVING SYSTEM MAY BRING A CONSIDERABLE AMOUNT OF RAIN TO THE  
AREA BUT THE TRACK AND TIMING FOR THIS ARE AN ISSUE.  
 
THE MAIN ISSUE IS WHAT HAPPENS TO THE SYSTEM OVER THE SOUTHWEST  
CONUS THIS COMING WEEK. MOST OF THE MODELS AND THEIR ENSEMBLES IN  
ONE FORM OR ANOTHER BRING THE SYSTEM THROUGH THE GREAT LAKES FRIDAY  
INTO SUNDAY. ONLY THE CANADIAN MODEL HAS THE NORTHERN STREAM  
EASTERN TROUGH SO BIG AND EXPANDED THAT THE SYSTEMS HEADS TO FAR  
SOUTHEAST TO IMPACT MI. GIVEN THAT THE MODELS TYPICALLY OPEN THESE  
SYSTEMS UP AND WEAKEN THEM TO FAST, I AM THINKING THIS COMING  
WEEKEND WILL BE RATHER WET.  
 
A WAVE ON THE FRONT MAY BRING US SHOWERS/THUNDERSTORMS ON WEDNESDAY.  
THIS TOO, DEPENDS ON OUR SOUTHWEST CONUS UPPER LOW AND HOW MUCH OF  
IT SHEARS OUT WHEN.  
 
 
OVERALL COOLER AND WET WOULD BE MY SPIN ON NEXT WEEK ESPECIALLY LATE  
IN THE WEEK INTO THE WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)  
ISSUED AT 721 PM EDT SUN JUN 17 2018  
 
VFR CONDITIONS EXPECTED THROUGH THE PERIOD. MAIN ITEM OF INTEREST  
WILL BE A COLD FRONT MOVING SOUTH ACROSS THE STATE MONDAY  
AFTERNOON. IT'S POSSIBLE WE COULD SEE A FEW SHOWERS/STORMS NEAR  
THE FRONT AFTER 20Z.  
 

 
   
MARINE
 
 
ISSUED AT 325 PM EDT SUN JUN 17 2018  
 
PATCHY FOG WILL POSE A HAZARD TO MARINERS THROUGH TONIGHT.  
THUNDERSTORMS WILL POSE A HAZARD TO MARINERS VERY LATE TONIGHT  
THROUGH MONDAY NIGHT INTO TUESDAY. WINDS AND WAVES WILL BE BRIEFLY  
HIGHER IN AND NEAR STORMS BUT OTHERWISE WINDS AND WAVES WILL  
REMAIN BELOW SCA CRITERIA THROUGH MONDAY.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 1210 PM EDT SUN JUN 17 2018  
 
RECENT RAIN HAS RESULTED IN A SLIGHT RISE ON A FEW RIVERS. WITH  
RIVER LEVELS RUNNING NEAR NORMAL, NO FLOODING IS EXPECTED.  
 
MORE RAIN IS EXPECTED ACROSS THE AREA SUNDAY NIGHT THROUGH WEDNESDAY  
NIGHT. SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL DEVELOP.  
VERY HEAVY RAINFALL WILL BE POSSIBLE WITH THE STORMS. THIS MAY  
PRODUCE LOCALIZED FLOODING.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...HEAT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR MIZ037>040-043>046-  
050>052-056>059-064>067-071>074.  
 
HEAT ADVISORY FROM NOON TO 6 PM EDT MONDAY FOR MIZ064>067-  
071>074.  
 
LM...NONE.  

 
 

 
 
SYNOPSIS...LAURENS  
SHORT TERM...LAURENS  
LONG TERM...WDM  
AVIATION...04  
HYDROLOGY...63  
MARINE...LAURENS  
 
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