942  
FXUS63 KGRR 181309  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
909 AM EDT WED JUL 18 2018  
 
LATEST UPDATE...  
FIREWEATHER  
   
SYNOPSIS
 
 
ISSUED AT 307 AM EDT WED JUL 18 2018  
 
A LARGE HIGH PRESSURE SYSTEM CENTERED OVER NORTHERN LOWER MICHIGAN  
THIS MORNING WILL REMAIN NEARLY STATIONARY THROUGH TODAY AND INTO  
TONIGHT. THIS FAIR WEATHER SYSTEM WILL ACT TO KEEP THE SKIES  
MAINLY CLEAR AND TEMPERATURES BELOW NORMAL FOR THIS TIME OF THE  
YEAR. THIS SYSTEM TRACKS EAST OF THE REGION ON THURSDAY. A  
SOUTHWESTERLY FLOW OF WARMER AND INCREASINGLY MOIST AIR WILL  
DEVELOP. RAIN SHOWERS WILL BE ON THE INCREASE BY FRIDAY AS A  
RESULT.  
 

 
   
SHORT TERM
 
(TODAY THROUGH FRIDAY)  
ISSUED AT 307 AM EDT WED JUL 18 2018  
 
THE MAIN CHALLENGE DEALS WITH THE TIMING AND COVERAGE OF THE RAIN  
FORECASTED TO ARRIVE FOR THE END OF THE WEEK.  
 
MODELS ARE IN RELATIVE AGREEMENT ON TRACKING A NEGATIVELY TILTED  
UPPER LEVEL TROUGH INTO THE REGION THURSDAY NIGHT INTO FRIDAY AS  
IT BECOMES A CLOSED LOW. INSTABILITY IS FORECASTED AS PRECIPITABLE  
WATER VALUES RISE TO OVER 1.5 INCHES AHEAD OF THIS APPROACHING  
WAVE. GIVEN THE SYNOPTIC FORCING...MOIST AND UNSTABLE AIRMASS THAT  
IS SHOWN TO BE IN PLACE...WILL THEREFORE RAISE POPS...ESPECIALLY  
FRIDAY AFTERNOON. MOST LOCATIONS WILL BE IN THE LIKELY RANGE FOR  
SEEING MEASURABLE RAINFALL.  
 
THE INITIALLY DRY AIRMASS IN PLACE FOR THURSDAY IS EXPECTED TO  
HOLD OFF THE RAIN UNTIL THURSDAY NIGHT. WILL FEATURE INCREASING  
POPS FROM WEST TO EAST THURSDAY NIGHT AS THE LOW PRESSURE SYSTEM  
NEARS FROM THE WEST.  
 
WILL MAINTAIN THE SEASONABLY WARM DAYS AND COOL NIGHTS TODAY INTO  
THURSDAY WITH THE LARGE HIGH PRESSURE SYSTEM STILL IN PLACE OVER  
MICHIGAN. I DID LOWER TEMPERATURES TONIGHT MAINLY TO THE NORTHEAST  
OF GRAND RAPIDS WHERE TEMPERATURES TYPICALLY COOL OFF QUICKER AT  
NIGHT WHEN THE AIRMASS IS RELATIVELY DRY.  
   
LONG TERM
 
(FRIDAY NIGHT THROUGH TUESDAY)  
ISSUED AT 307 AM EDT WED JUL 18 2018  
 
UNSETTLED WEATHER IS ANTICIPATED THIS WEEKEND WITH OCCASIONAL  
SHOWERS AND THUNDERSTORMS AS A RESULT OF AN UPPER LEVEL LOW PRESSURE  
SYSTEM THAT WILL MOVE SLOWLY EAST ACROSS THE GREAT LAKES REGION.  
GREATEST COVERAGE OF PRECIPITATION SHOULD OCCUR DURING THE AFTERNOON  
AND EVENING HOURS AS A RESULT OF INSTABILITY FROM DAYTIME HEATING  
AND WITH THE POOL OF COLDER AIR ALOFT.  
 
FAIR WX WILL BRIEFLY RETURN EARLY NEXT WEEK AS THE UPPER TROUGH  
AXIS MOVES EAST OF OUR REGION AND WEAK RIDGING NUDGES IN FROM THE  
WEST. HOWEVER ANOTHER SYSTEM WILL BRING POTENTIAL FOR MORE SHOWERS  
AND STORMS BY TUESDAY OR WEDNESDAY. TEMPERATURES WILL AVERAGE  
FAIRLY CLOSE TO NORMAL FOR THIS TIME OF YEAR THROUGH THE LONG  
RANGE FCST PERIOD.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)  
ISSUED AT 651 AM EDT WED JUL 18 2018  
 
THE DRY AIRMASS WILL CONTINUE THROUGH TONIGHT. THUS LITTLE IN THE  
WAY OF CLOUD COVER IS EXPECTED. THERE COULD BE SOME PATCHY FOG  
AROUND LATER TONIGHT. THE POTENTIAL AT THIS TIME LOOKED TOO LOW TO  
INCLUDE IT N THE FORECAST. THE PRESSURE GRADIENT WILL REMAIN WEAK  
THROUGH TONIGHT SO NOT MUCH WIND IS FORECASTED.  
 

 
   
MARINE
 
 
ISSUED AT 307 AM EDT WED JUL 18 2018  
 
I CANCELLED THE SMALL CRAFT ADVISORY AND BEACH HAZARDS. CONDITIONS  
HAVE FALLEN UNDER CRITERIA...LIMITING THE HAZARD POTENTIAL. THE  
WINDS ARE FORECASTED TO INCREASE AGAIN FOR LATER THURSDAY AND MORE  
SO THURSDAY NIGHT. WITH A SOUTHERLY FETCH...THAT WILL SUPPORT THE  
HIGHEST WAVES UP TOWARDS THE POINTS. THERE ARE SOME INDICATIONS  
THAT THE 4 FOOT WAVES MAY STAY FAR ENOUGH OFFSHORE TO LIMIT THE  
NEED FOR A HAZARD. WILL THEREFORE NOT ISSUE ANY HAZARDS AT THIS  
TIME.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 855 AM EDT WED JUL 18 2018  
 
THE COMBINATION OUR DEVELOPING DROUGHT WITH WARM TEMPERATURES  
AND LOW AFTERNOON HUMIDITIES BOTH TODAY AND TOMORROW WILL CONTINUE  
TO SUPPORT HIGH FIRE DANGER. WINDS TODAY ARE EXPECTED TO BE  
LIGHT, STAYING UNDER 10 MPH, WITH LAKE BREEZES DEVELOPING DURING  
THE AFTERNOON. WIND SPEEDS WILL INCREASE A LITTLE FOR TOMORROW,  
INCREASING TO 10 TO 15 MPH FROM THE SOUTH BY LATE MORNING.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 326 PM EDT TUE JUL 16 2018  
 
DRY WEATHER IS EXPECTED THROUGH THURSDAY. A SLOW-MOVING LOW PRESSURE  
SYSTEM WILL THEN BRING A PERIOD OF WET AND UNSETTLED WEATHER TO THE  
REGION FRIDAY THROUGH SUNDAY. EARLY THOUGHTS ON TOTAL RAINFALL  
AMOUNTS OVER THE THREE DAYS ARE FOR BETWEEN 0.5 AND 1.5 INCHES TO  
FALL OVER THE WHOLE AREA. THERE WILL BE HIGHER AMOUNTS WHERE  
THUNDERSTORMS DEVELOP. LOCALLY HEAVY RAINFALL WILL BE POSSIBLE IN  
THESE STORMS.  
 

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

 
 

 
 
SYNOPSIS...MJS  
SHORT TERM...MJS  
LONG TERM...LAURENS  
AVIATION...MJS  
FIRE WEATHER...WDM  
HYDROLOGY...HLO  
MARINE...MJS  
 
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