691  
FXUS63 KGRR 290024  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
824 PM EDT FRI APR 28 2017  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 333 PM EDT FRI APR 28 2017  
 
A WEAK WAVE WILL MOVE ALONG A STATIONARY BOUNDARY THROUGH THE OHIO  
VALLEY LATE THIS EVENING INTO SATURDAY MORNING. THIS WILL BRING A  
ROUND OF LIGHT PRECIPITATION, MAINLY AFFECTING SOUTHERN SECTIONS OF  
LOWER MICHIGAN. THE BIGGER STORY WILL COME OVER THE WEEKEND AS A  
DEEPENING UPPER LEVEL LOW SWING FROM THE PLAINS INTO THE MIDWEST.  
ABUNDANT MOISTURE WILL SURGE NORTHWARD, RESULTING IN PERIODS OF  
SHOWERS AND THUNDERSTORMS FROM LATE SATURDAY INTO MONDAY. MUCH  
QUIETER WEATHER LIES BEYOND MONDAY WITH BELOW NORMAL TEMPERATURES.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY NIGHT)  
ISSUED AT 333 PM EDT FRI APR 28 2017  
 
A HEAVY RAIN EVENT IS LOOKING MORE LIKELY BEGINNING SATURDAY  
AFTERNOON AND EXTENDING THROUGH THE SECOND HALF OF THE WEEKEND.  
OTHERWISE, LIGHT RAIN SHOWERS ARE POSSIBLE LATE THIS AFTERNOON  
INTO EARLY SATURDAY MORNING.  
 
VISIBLE SATELLITE IMAGERY CONTINUES TO SHOW EXTENSIVE CLOUD COVER  
STREAMING IN FROM THE SOUTH THIS AFTERNOON. LIGHT TO MODERATE RAIN  
HAS DEVELOPED ALONG A QUASI-STATIONARY BOUNDARY, WHICH STRETCHES  
FROM CENTRAL ILLINOIS EASTWARD TO CENTRAL OHIO. THIS BOUNDARY WILL  
CONTINUE TO MEANDER SOUTH OF LOWER MICHIGAN THROUGH EARLY SATURDAY.  
IN THE MEANTIME, A DISTURBANCE MOVES ALONG THE BOUNDARY LATE THIS  
EVENING WITH RAIN SHOWERS LIFTING NORTHWARD IN LOWER MICHIGAN. MUCH  
OF THE ACTIVITY WILL BE LIGHT IN NATURE INTO SATURDAY MORNING BEFORE  
A LULL BETWEEN RAINFALL LATE SATURDAY MORNING AND EARLY SATURDAY  
AFTERNOON.  
 
FRONT BEGINS TO LIFT NORTH AS A WARM FRONT SATURDAY AFTERNOON WITH A  
STRENGTHENING RIDGE DEVELOPING OVER THE SOUTHEASTERN U.S. THE  
BOUNDARY REMAINS SOUTH OF LOWER MICHIGAN WITH SEVERAL WAVES OF  
ENERGY MOVING ALONG THE BOUNDARY FROM SW TO NE. MUCH OF THE RAINFALL  
WILL BE CONVECTIVE IN NATURE OVER MO/IL. AS IT TRAVELS NORTH, IT  
WILL PROVIDE A BROAD AREA OF RAINFALL WITH SOME EMBEDDED  
THUNDERSTORMS SATURDAY AFTERNOON AND EVENING.  
 
THE BOUNDARY LIFTS FURTHER NORTH SUNDAY WITH COPIOUS AMOUNTS OF  
MOISTURE STREAMING NORTHWARD OUT OF THE GULF. THE FRONT WILL ALSO  
PLAY A LARGE ROLE IN HIGHS REACHING THE 70S NEAR THE MI/IN BORDER  
AND 40S THROUGH CENTRAL LOWER MICHIGAN. PWATS REACH WELL ABOVE ONE  
INCH LATE SATURDAY AND STAY THERE THROUGH ALL OF SUNDAY,  
ESPECIALLY THROUGH THE HEART OF THE CWA. GUIDANCE IN GOOD  
AGREEMENT WITH PLACING THE HEAVIEST RAINFALL INTO THE SW CORNER OF  
LOWER MICHIGAN. TOTAL RAINFALL AMOUNTS LOOK TO REACH THE 2-4 INCH  
REALM THROUGH EARLY MONDAY MORNING. LOCALIZED AMOUNTS HIGHER THAN  
4 INCHES ARE POSSIBLE, ESPECIALLY IN/NEAR ANY CONVECTION.  
THEREFORE, A FLOOD WATCH WILL BE ISSUED FROM SATURDAY AFTERNOON  
THROUGH EARLY MONDAY TO COVER FLOOD POSSIBILITIES FOR LOW LYING,  
FLOOD PRONE AREAS.  
   
LONG TERM
 
(MONDAY THROUGH FRIDAY)  
ISSUED AT 333 PM EDT FRI APR 28 2017  
 
THE RAIN WILL GRADUALLY LIGHTEN UP AND BECOME MORE SCATTERED THROUGH  
THE EARLY PART OF NEXT WEEK. WE WILL SEE A CHILLY PERIOD MONDAY  
NIGHT THROUGH THURSDAY WHEN SOME PATCHY OVERNIGHT FROST WILL BE  
POSSIBLE. THEN A DRIER AND SLIGHTLY WARMER PERIOD IS EXPECTED  
LATE IN THE WEEK.  
 
SURFACE AND UPPER LOW SHOULD BE OVER NE IA MONDAY MORNING. THIS  
HEADS NORTHEAST INTO THE U.P. BY MONDAY NIGHT. MONDAY MORNING RAINS  
LOOK LIKELY STILL, BUT IT SHOULD BECOME LIGHTER AND MORE SCATTERED  
MONDAY AFTERNOON. THE SYSTEM ONLY SLOWLY HEADS INTO CANADA, SO IT  
WILL PROBABLY TAKE UNTIL TUESDAY AFTERNOON OR EVENING BEFORE WE  
FINALLY SEE THE RAIN COMPLETELY END.  
 
CHILLY AIR FOLLOWS THE SYSTEM, WITH H8 TEMPS DROPPING TO AROUND -3C  
BY TUESDAY NIGHT. AS SKIES CLEAR WE MAY HAVE THE RISK OF FROST LATE  
TUESDAY NIGHT AND AGAIN WED AND THU NIGHTS. AT THIS POINT LOW TEMPS  
APPEAR TO BE IN THE MID 30S EACH NIGHT, SO THE RISK TO AREA FRUIT  
TREES SHOULD BE LOW, BUT STAY TUNED. A SHORT WAVE COMES THROUGH THU  
NIGHT OR FRI, BUT IT APPEARS THE SURFACE REFLECTION IS WELL SOUTH,  
SO WILL KEEP THE FORECAST DRY FOR NOW.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)  
ISSUED AT 823 PM EDT FRI APR 28 2017  
 
A WARM FRONT WILL SHARPEN JUST SOUTH OF THE GREAT LAKES TONIGHT  
AND ESPECIALLY ON SATURDAY. THE TAF SITES ACROSS SOUTHWEST LOWER  
MICHIGAN WILL SEE CEILINGS LOWER AND THICKEN THE NEXT 24 HOURS.  
VFR CEILINGS AND MAINLY DRY WEATHER SHOULD BE IN PLACE TONIGHT.  
THERE IS A SMALL CHANCE AT SOME MVFR CEILINGS TONIGHT HOWEVER WE  
DID NOT FEEL THE THREAT WAS HIGH ENOUGH TO INCLUDE IN THE TAFS.  
CEILINGS SHOULD GRADUALLY LOWER TONIGHT FROM 7,000-10,000FT TO  
AROUND 3,500FT BY SATURDAY MORNING.  
 
ON SATURDAY, THE CEILINGS SHOULD LOWER INTO THE MVFR RANGE WITH  
RAIN DEVELOPING FROM SOUTH TO NORTH. RAIN SHOULD SPREAD INTO  
SOUTHERN LOWER MICHIGAN AROUND 15Z AND MOVE INTO THE I-96 CORRIDOR  
AROUND 18Z.  
 

 
   
MARINE
 
 
ISSUED AT 333 PM EDT FRI APR 28 2017  
 
WINDS WILL CONTINUE TO SHIFT THIS AFTERNOON, PREDOMINANTLY COMING  
FROM THE NORTH-NORTHEAST TONIGHT THROUGH MUCH OF THE DAY SATURDAY.  
SPEEDS WILL GENERALLY BE 5-15 KNOTS, INCREASING TO 15-25 KNOTS  
SATURDAY AFTERNOON. LOCALLY HIGHER WINDS MAY OCCUR IN/NEAR  
THUNDERSTORMS, BUT OFFSHORE FLOW SHOULD KEEP WAVES UNDER SCA  
CRITERIA. OTHERWISE, THE MAIN CONCERN WILL CONTINUE TO BE SHOWER  
AND THUNDERSTORM CHANCES EXTENDING FROM LATE SATURDAY INTO MONDAY.  
 
MONDAY BRINGS THE LIKELIHOOD FOR HAZARDOUS CONDITIONS. LOW PRESSURE  
WILL APPROACH THE AREA WITH BETTER SUPPORT FOR HIGH WIND AND WAVE  
ACTION INTO EARLY NEXT WEEK, ESPECIALLY WITH WINDS OUT OF THE SOUTH-  
SOUTHWEST.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 333 PM EDT FRI APR 28 2017  
 
IN GENERAL, A FAIRLY WIDESPREAD 2" TO POSSIBLY 4" OF RAIN IS  
EXPECTED THIS WEEKEND. THIS WILL CERTAINLY LEAD TO RIVER RISES AND  
SOME AREAS MAY REACH FLOOD STAGE BY EARLY NEXT WEEK. AT THIS POINT  
NO MAJOR FLOODING IS ANTICIPATED. FORECASTS WILL CONTINUE TO BE  
ADJUSTED WITH THE PROJECTED RAINFALL AND ONCE THE RAIN GETS INTO THE  
BASINS THE ACCURACY OF THE FORECASTS WILL INCREASE. IT IS IMPORTANT  
NOT TO FOCUS ON THE EXACT CREST VALUES NECESSARILY SINCE THEY MAY  
CHANGE WITH THE DAILY UPDATES AS THE RAIN GETS CLOSER TO THE REGION  
AND EVENTUALLY BEGINS OCCURRING OVERHEAD.  
 
THE GREATEST IMPACTS AT THIS POINT LOOK SOMEWHAT SIMILAR TO EARLIER  
THIS MONTH FOR THE SYCAMORE CREEK AND LOOKING GLASS RIVER. RISES  
ABOVE FLOOD STAGE LOOK LIKELY. ON THE GRAND, THE RIVER MAY HOLD JUST  
BELOW FLOOD STAGE. IF RAINFALL ENDS UP BEING MORE 3"-5" ACROSS THIS  
BASIN THEN HIGHER CRESTS WOULD BE ACHIEVED AND FLOODING WOULD LIKELY  
MATERIALIZE.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...FLOOD WATCH FROM SATURDAY AFTERNOON THROUGH MONDAY MORNING FOR  
MIZ043>046-050>052-056>059-064>066-071-072.  
 
LM...NONE.  

 
 

 
 
SYNOPSIS...JAM  
SHORT TERM...JAM  
LONG TERM...JK  
AVIATION...DUKE  
HYDROLOGY...HOVING  
MARINE...JAM  
 
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