248  
FXUS63 KGRR 310406  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
1206 AM EDT WED AUG 31 2016  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 324 PM EDT TUE AUG 30 2016  
 
SCATTERED SHOWERS AND A FEW STORMS WILL REMAIN POSSIBLE TONIGHT,  
BEFORE GRADUALLY SHIFTING SOUTH OF THE AREA ON WEDNESDAY AS A COLD  
FRONT PUSHES THROUGH THE AREA. MUCH COOLER AND DRIER AIR WILL THEN  
FILTER IN FOR THE REST OF THE WEEK.  
 
MUCH OF THE UPCOMING HOLIDAY WEEKEND LOOKS DRY FOR THE AREA WITH  
GRADUALLY WARMING TEMPERATURES. THE THREAT FOR RAIN WILL INCREASE  
STARTING ON LABOR DAY AND CONTINUE INTO TUESDAY.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY NIGHT)  
ISSUED AT 324 PM EDT TUE AUG 30 2016  
 
OUR MAIN FOCUS OF THE FORECAST IS ON PRECIPITATION TRENDS THROUGH  
WED AS THE COLD FRONT TO OUR NW WILL GRADUALLY PUSH THROUGH THE AREA.  
 
SOME SCATTERED SHOWERS WITH ISOLATED THUNDER HAS DEVELOPED THUS FAR  
THIS AFTERNOON. COLLIDING BOUNDARIES FROM THE WEAKLY SHEARED STORMS  
COULD POP UP A FEW ADDITIONAL SHOWERS/STORM THROUGH THE AFTERNOON.  
THE SHOWERS/STORMS HAVE BEEN UNIMPRESSIVE THUS FAR, AND WE DO NOT  
EXPECT MUCH OF AN UPTICK IN INTENSITY THIS AFTERNOON. THE ONLY REAL  
THREAT IS LOCALLY HEAVY RAINFALL DUE TO THE SLOW MOVEMENT AND RICH  
MOISTURE CONTENT OF THE AIR.  
 
A FEW MORE SHOWERS AND STORM WILL REMAIN POSSIBLE TONIGHT AS THE  
FRONT SINKS SOUTH INTO THE AREA. INSTABILITY WILL BE ON THE WANE AS  
WE LOSE THE DIURNAL COMPONENT. SOME INSTABILITY WILL REMAIN AS THE  
FRONT BEGINS TO ENCOUNTER THE RICHER MOISTURE FURTHER SOUTH. A LACK  
OF A LOW LEVEL JET AND ORGANIZED SHORT WAVE TONIGHT WILL LIMIT THE  
COVERAGE TO THE CHC/SCT CATEGORY.  
 
A FEW SHOWERS/STORMS WILL REMAIN ACROSS THE SOUTH ON WED, AND THEN  
CLEAR OUT OF THE CWFA IN THE AFTERNOON. THE FRONT LOOKS TO BE  
LOCATED TOWARD I-94 AROUND 12Z WED AND WILL SINK SOUTH. THERE WILL  
NOT BE AN OPPORTUNITY FOR ANY DIURNAL INSTABILITY TO BUILD, SO ANY  
STORMS THAT WOULD OCCUR WILL STAY WELL BEHAVED.  
 
THE ONLY OTHER PERIOD TO NOTE IN THE SHORT TERM IS THE WED  
NIGHT/EARLY THU TIME FRAME WHERE A SHOWER IS NOT OUT OF THE REALM OF  
POSSIBILITIES. WE WILL SEE A FAIRLY STRONG SHORT WAVE DROP SSE  
THROUGH THE AREA AT THAT TIME. IT WILL BE LACKING MOISTURE, AND  
SHOULD BE 2/3RDS THROUGH THE CWFA BY 12Z THU. SOME LAKE ENHANCEMENT  
COULD BE OCCURRING, BUT WITH A NNE FLOW AT THAT TIME, WE WILL STAY  
DRY INLAND. WE WILL NOT HAVE A REAL GOOD OPPORTUNITY TO TAP DIURNAL  
INSTABILITY EITHER WITH THE WAVE MOVING OUT EARLY THU.  
   
LONG TERM
 
(FRIDAY THROUGH TUESDAY)  
ISSUED AT 324 PM EDT TUE AUG 30 2016  
 
CONSIDERABLE MID LEVEL HEIGHT RISES OCCUR FRIDAY INTO SATURDAY AS A  
RIDGE REPLACES THE TROUGH. THIS RIDGE REMAINS IN PLACE AS WE GO  
THROUGH SUNDAY. AS A RESULT...THE REGION WILL BE LOOKING AT A DRY  
PERIOD. TEMPERATURES WILL BE MODERATING...ESPECIALLY IN THE  
SATURDAY TO SUNDAY TIMEFRAME.  
 
THE RIDGE PUSHES EAST OF THE AREA SUNDAY INTO MONDAY. DEEP  
SOUTHWEST FLOW DEVELOPS. THIS WILL SUPPORT A CONTINUED WARMING  
TREND ALONG WITH THE ARRIVAL OF HIGHER PRECIPITABLE WATER VALUES.  
THIS WILL RESULT IN AN INCREASINGLY UNSTABLE AIRMASS AS WE GO FROM  
MONDAY INTO TUESDAY. AS A RESULT...WILL FEATURE A RISK FOR SHOWERS  
AND THUNDERSTORMS EARLY NEXT WEEK. WELL ABOVE NORMAL TEMPERATURES  
ARE EXPECTED. SOME UNCERTAINTY IN HOW THE EAST COAST STORM TRACKS  
NEXT WEEK...WHICH WILL PLAY A FACTOR WHEN OUR NEXT COLD FRONT  
PASSAGE OCCURS. FOR NOW...WILL KEEP IT WARM THROUGH TUESDAY.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 1203 AM EDT WED AUG 31 2016  
 
PRIMARILY VFR CONDITIONS WILL GRADUALLY DETERIORATE TO MVFR  
OVERNIGHT DUE TO LOW CLOUDS AND PATCHY FOG. POCKETS OF IFR  
ARE ALSO POSSIBLE PARTICULARLY AT KMKG WHERE CONDITIONS HAVE  
JUST DIPPED TO IFR DUE TO FOG. ISOLATED RAIN SHOWERS WILL CONTINUE  
TO DEVELOP OVERNIGHT. THE THREAT FOR A STORM IS NOW TOO LOW TO  
WARRANT INCLUSION IN ANY OF THE TERMINAL FORECASTS OVERNIGHT.  
 
CONDITIONS WILL IMPROVE TO VFR EARLY TO MID MORNING AND THEN STAY  
VFR THROUGH WEDNESDAY AFTERNOON AND EVENING AS FAIR WEATHER  
RETURNS AND A DRIER AIRMASS MOVES IN.  
 

 
   
MARINE
 
 
ISSUED AT 324 PM EDT TUE AUG 30 2016  
 
MAIN IMPACTS FOR MARINE INTERESTS WILL BE THE HIGHER WINDS AND WAVES  
EXPECTED TO DEVELOP ON WEDNESDAY, AND LAST THROUGH THURSDAY. GOOD  
COLD AIR ADVECTION WILL TAKE PLACE BEHIND THE FRONT, AND INTERACT  
WITH LAKE WATER TEMPERATURES NEAR THEIR PEAK FOR THE SEASON. THIS  
SHOULD BUILD UP THE WAVES WELL. THUS, WE HAVE ISSUED A BEACH HAZARDS  
STATEMENT AND SCA. THE ONLY CAVEAT TO THIS IS THAT THERE MAY BE  
TIMES WHERE THE WIND DIRECTION WILL TEMPORARILY SHIFT TO MORE NNE.  
 
THE OTHER THING TO WATCH FOR ALSO WILL BE WATERSPOUT POTENTIAL,  
ESPECIALLY WED NIGHT AND THU. THIS IS WHEN THE CORE OF THE COLDEST  
AIR ALOFT WILL BE OVERHEAD AND WILL INTERACT WITH THE WARMER LAKE  
TEMPS.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 105 PM EDT TUE AUG 30 2016  
 
SCATTERED SLOW-MOVING THUNDERSTORMS TUE AFTERNOON ARE CAPABLE OF  
PRODUCING LOCAL RAINFALL AMOUNTS OVER A HALF INCH IN A SHORT  
AMOUNT OF TIME. DEEPER ATMOSPHERIC HUMIDITY AND CORRESPONDINGLY  
HIGHER PW VALUES ARE IN SOUTHERN MICHIGAN BUT GREATER INSTABILITY  
AND STORM COVERAGE WILL BE IN CENTRAL MICHIGAN TUE AFTERNOON.  
SMALL BASINS WILL LIKELY BE ABLE TO HANDLE ANY LOCALLY HEAVY  
RAINFALL, BUT MINOR PONDING OF WATER ON ROADWAYS IS POSSIBLE.  
AFTER THE COLD FRONT CLEARS ON WED, THE NEXT CHANCE FOR  
APPRECIABLE RAINFALL WILL HOLD OFF UNTIL NEXT WEEK.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...BEACH HAZARDS STATEMENT FROM 10 AM EDT THIS MORNING THROUGH  
THURSDAY EVENING FOR MIZ037-043-050-056-064-071.  
 
LM...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 11 PM EDT  
THURSDAY FOR LMZ844>849.  
 

 
 

 
 
SYNOPSIS...NJJ  
SHORT TERM...NJJ  
LONG TERM...MJS  
AVIATION...LAURENS  
HYDROLOGY...CAS  
MARINE...NJJ  
 
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