882  
FXUS63 KGRR 221135  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
735 AM EDT SUN OCT 22 2017  
 
LATEST UPDATE...  
AVIATION  
   
SYNOPSIS
 
 
ISSUED AT 316 AM EDT SUN OCT 22 2017  
 
RAIN WILL MOVE INTO LOWER MICHIGAN TODAY WITH A SLOWLY APPROACHING  
COLD FRONT. POTENTIALLY HEAVY RAINFALL IS EXPECTED MONDAY AFTERNOON  
AND MONDAY NIGHT BEFORE WINDY AND COOL WEATHER ARRIVES ON TUESDAY  
AND WEDNESDAY. TEMPERATURES THROUGH THE WEEK WILL DECLINE STEADILY  
FROM HIGHS AROUND 60 MONDAY TO HIGHS IN THE 50S THIS COMING  
WEEKEND.  
 

 
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 316 AM EDT SUN OCT 22 2017  
 
WILL ISSUE A FLOOD WATCH FOR MONDAY AFTERNOON AND MONDAY NIGHT  
FOR THE EASTERN TWO THIRDS OF OUR FORECAST AREA. THIS IS BASED ON  
VERY STRONG RUN TO RUN CONSISTENCY WITH THE ECMWF/ECE AND WITH THE  
GLOBAL GEM FOR DEEPENING A SIGNIFICANT LOW OVER LAKE HURON AND  
PROVIDING A STRONG TROWAL/DEFORMATION AREA OF HEAVY RAIN WRAPPING  
BACK INTO THE AREA. THE UPPER PATTERN PRECEDING THIS DEVELOPMENT IS  
A MINOR TROUGH/PV MAXIMUM APPROACHING THE AREA. A LARGER AND  
BROADER TROUGH/PV MAX FARTHER UPSTREAM IS DIGGING TOWARDS THE  
MINOR TROUGH. THIS OFTEN RESULTS IN A QUICK AND SIGNIFICANT  
TRANSFER OF ENERGY FROM THE UPSTREAM BROAD TROUGH TO THE  
DOWNSTREAM MINOR TROUGH PRIOR TO PHASING, WHICH CAN BE VERY  
FAVORABLE FOR RAPID CYCLOGENESIS. ECE MEMBERS SHOW A MUCH TIGHTER  
CLUSTERING OF FORECAST LOW POSITIONS OVER LAKE HURON WHICH  
REINFORCES THE IDEA OF A TROWAL IN OUR EASTERN FORECAST AREA.  
 
JUXTAPOSED WITH THE PROSPECTS FOR RAPID CYCLOGENESIS IS AN  
ATMOSPHERE THAT IS ANOMALOUSLY MOIST. UPSTREAM OBSERVED SOUNDINGS  
CONTINUE TO SHOW PRECIPITABLE WATER VALUES AROUND 200 PERCENT OF  
NORMAL FOR THIS TIME OF YEAR.  
 
OUR INITIAL FORECAST GUIDANCE TYPICALLY IS BASED HEAVILY ON THE GFS,  
WHICH HAS ITSELF BEEN VERY CONSISTENT WITH PLACING PRECIPITATION  
FARTHER EAST. CONSEQUENTLY, WE HAVE MADE UPWARD ADJUSTMENTS TO  
INHERITED POP AND QPF FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING  
TO BETTER AGREE WITH THE WATCH. EVEN SO, LOCAL PRECIPITATION AMOUNTS  
OF 5 INCHES OR MORE ARE QUITE POSSIBLE EAST OF US-131 BY TUESDAY  
MORNING.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 316 AM EDT SUN OCT 22 2017  
 
THE WORST OF THE POTENTIAL WET AND WINDY PERIOD IN THE SHORT TERM  
SHOULD BE OVER WITH BY THE BEGINNING OF THE LONG TERM ON TUE NIGHT.  
EVEN THOUGH THE MORE EXTREME WEATHER WILL BE MOVING OUT, WE LOOK TO  
REMAIN RATHER DAMP INTO WED BEFORE WE SEE A TEMPORARY DRY PERIOD.  
THIS OCCURS AS THE LONG WAVE TROUGH OVER THE AREA WILL BE REINFORCED  
BY ONE MORE WAVE COMING IN ON THE BACKSIDE OF THE TROUGH. LAKE  
ENHANCEMENT WILL BE A FACTOR WITH H850 TEMPS EXPECTED TO BE BELOW  
0C.  
 
THE DRY PERIOD IS THEN EXPECTED TO BE CENTERED AROUND THE THU-FRI  
TIME FRAME. THE LAST SHORT WAVE COMING IN ON THE BACKSIDE OF THE  
TROUGH WED WILL SWEEP THE LONG WAVE TROUGH OUT OF THE REGION. AN  
UPPER RIDGE WILL TRAVERSE THE AREA FOR THU AND FRI, ALLOWING FOR  
DRIER AND SOMEWHAT MILDER WEATHER.  
 
THE WEATHER IS EXPECTED TO BECOME SOMEWHAT WET ONCE AGAIN NEXT  
WEEKEND. THE UPPER RIDGE WILL BE PUSHED TO THE EAST, AND A FAIRLY  
STRONG LONG WAVE TROUGH LOOKS TO DIG OVER THE ROCKIES. THIS WILL  
INDUCE A LOW LEVEL SRLY FLOW AHEAD OF THE DEVELOPING SFC LOW, ALONG  
WITH MORE MOISTURE COMING IN FROM THE GULF. TEMPERATURES SHOULD STAY  
SOMEWHAT MILD NEXT WEEKEND, UNTIL THE FRONT PUSHES THROUGH. AT THAT  
TIME, ANOTHER COLD PERIOD WILL BE LIKELY AFTER NEXT WEEKEND.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 735 AM EDT SUN OCT 22 2017  
 
HIGH CONFIDENCE FOR VFR THROUGH 18Z AREAWIDE. LOW LEVEL WIND SHEAR  
REMAINS A CONCERN THROUGH MID MORNING AND RETURNS EARLY TONIGHT.  
SHEAR SHOULD NO LONGER BE AN ISSUE AFTER SURFACE WINDS SWITCH TO  
THE NORTHWEST TONIGHT.  
 
CEILINGS WILL GRADUALLY DECREASE FROM WEST TO EAST THIS AFTERNOON  
INTO TONIGHT WITH IFR POSSIBLE AT MOST TERMINALS AFTER 06Z  
MONDAY. VISIBILITY RESTRICTIONS IN FOG AND LIGHT RAIN SHOULD  
REMAIN MOSTLY MVFR WITH THE LOW CEILINGS, BUT THERE COULD BE SPOTS  
WITH VISIBILITY BELOW 3 MILES NEAR THE LAKESHORE.  
 

 
   
MARINE
 
 
ISSUED AT 316 AM EDT SUN OCT 22 2017  
 
LATEST WW3 GUIDANCE SUGGEST WAVES WILL DECREASE TO BELOW SMALL CRAFT  
ADVISORY LEVELS THIS AFTERNOON IN THE HOLLAND-GRAND HAVEN-WHITEHALL  
REGION AND THEN EARLY TONIGHT NORTH OF WHITEHALL. THE SCA IS SET TO  
EXPIRE AREAWIDE AT 8 PM TONIGHT WHICH IS WITHIN A FEW HOURS ON  
EITHER SIDE OF THE FORECAST. HAVE NO PLANS TO GET ANY MORE PRECISE  
THAN THIS.  
 
MONDAY NIGHT AND PARTICULARLY TUESDAY COULD SEE SIGNIFICANT WINDS  
AND WAVES WITH NORTHWEST GALES LIKELY DEVELOPING.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 155 PM EDT SAT OCT 21 2017  
 
SHOWERS WILL SPREAD INTO THE AREA FROM THE WEST SUNDAY AND SUNDAY  
NIGHT AS A COLD FRONT BEGINS TO TRACK THROUGH THE GREAT LAKES. RAIN  
MAY BE MODERATE AT TIMES IN INTENSITY, BUT IS NOT EXPECTED TO LEAD  
TO FLOODING. TOTAL RAINFALL THROUGH 8AM MONDAY WILL BE UP TO ONE-  
HALF INCH.  
 
AN AREA OF LOW PRESSURE WILL LIFT NORTHWARD ALONG THIS FRONTAL  
BOUNDARY, ALLOWING AN AREA OF HEAVIER RAINFALL TO DEVELOP LATE  
MONDAY THROUGH TUESDAY OVER THE GREAT LAKES. WHILE CONFIDENCE IN  
THIS SCENARIO IS INCREASING, THE PRECISE LOCATION OF WHERE THE  
HEAVIEST SWATH OF RAIN WILL OCCUR, WHERE AMOUNTS COULD EXCEED 2  
INCHES, IS STILL UNCERTAIN. LATEST FORECAST GUIDANCE PLACES A NORTH  
TO SOUTH-ORIENTATED BAND OF HEAVIER RAIN TOTALS ANYWHERE FROM LAKE  
MICHIGAN TO EASTERN OHIO. LOCALIZED FLOODING AND RISES IN RIVERS,  
CREEKS, AND STREAM COULD OCCUR IN THIS SWATH. THE POTENTIAL FOR  
HEAVY RAINFALL ACROSS THE WESTERN HALF OF MICHIGAN LATE MONDAY  
THROUGH TUESDAY WILL CONTINUE TO BE MONITORED.  
 

 
   
GRR WATCHES/WARNINGS/ADVISORIES
 
 
MI...FLOOD WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY MORNING FOR  
MIZ039-040-045-046-051-052-057>059-065>067-072>074.  
 
LM...SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR LMZ846>849.  
 

 
 

 
 
SYNOPSIS...TJT  
SHORT TERM...TJT  
LONG TERM...NJJ  
AVIATION...TJT  
HYDROLOGY...HLO  
MARINE...TJT  
 
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