321  
FXUS63 KGRR 141925  
AFDGRR  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE GRAND RAPIDS MI  
325 PM EDT TUE AUG 14 2018  
 
LATEST UPDATE...  
SYNOPSIS/SHORT TERM/LONG TERM/MARINE/HYDRO  
   
SYNOPSIS
 
 
ISSUED AT 325 PM EDT TUE AUG 14 2018  
 
DRY CONDITIONS ARE EXPECTED TO CONTINUE THIS AFTERNOON AND OVERNIGHT  
WITH CLOUD COVER INCREASING TOWARD TOMORROW MORNING. PRECIPITATION  
CHANCES WILL INCREASE TOMORROW AND THURSDAY AS A LOW PRESSURE SYSTEM  
TRACKS THROUGH THE GREAT LAKES. THE RISK OF HEAVIEST RAINFALL  
APPEARS TO BE SOUTH AND EAST OF OUR AREA. AFTER A SLIGHT CHANCE OF  
RAIN ON FRIDAY, A DRY WEEKEND IS EXPECTED BEFORE ANOTHER SYSTEM  
TRACKS TOWARD THE AREA EARLY NEXT WEEK.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH THURSDAY NIGHT)  
ISSUED AT 325 PM EDT TUE AUG 14 2018  
 
A QUICK LOOK AT WATER VAPOR IMAGERY DEPICTS A SCENE MUCH MORE  
TYPICAL OF FALL THAN MID-AUGUST WITH TWO LOW PRESSURE SYSTEMS OVER  
THE EASTERN HALF OF THE UNITED STATES. LOWER MICHIGAN IS BETWEEN  
BOTH TODAY WITH CONTINUED DRY AND MOSTLY SUNNY CONDITIONS (SAVE FOR  
UPPER-LEVEL HAZE FROM SMOKE). PATCHES OF CUMULUS CLOUDS HAVE ONCE  
AGAIN DEVELOPED THIS AFTERNOON THOUGH ON A MORE CONCENTRATED BASIS  
ALONG AND EAST OF THE LAKE SHADOW WHEN COMPARED TO YESTERDAY.  
 
TONIGHT, THE EXPECTATION IS FOR CLOUDS TO SLOWLY INCREASE IN  
COVERAGE WITH LOWS DROPPING TO THE LOW TO MID 60S. A SUBTLE  
INCREASE IN THE PRESSURE GRADIENT SHOULD ALLOW FOR WINDS TO REMAIN  
EVER SO SLIGHTLY HIGHER THAN LAST NIGHT WHICH WHEN COMBINED WITH  
INCREASING CLOUD COVER, SHOULD LIMIT THE EXTENT OF FOG DEVELOPMENT  
COMPARED TO THE PAST FEW DAYS. SO, WHILE A FEW AREAS OF FOG MAY  
DEVELOP (SEEMINGLY FAVORED NORTH OF I-96), COVERAGE IS EXPECTED TO  
BE SPOTTY.  
 
ATTENTION THEN TURNS TO THE STORM SYSTEM APPROACHING FROM THE  
SOUTHWEST. COMPARED TO 24 HOURS AGO, CONFIDENCE HAS INCREASED  
CONSIDERABLY THAT THE LOW WILL TRACK RIGHT THROUGH LOWER MICHIGAN IF  
NOT A BIT FURTHER SOUTH ALONG THE IN/MI BORDER. SUCH A TRACK  
WOULD FAVOR THE HEAVIEST RAIN TO REMAIN SOUTH AND EAST OF WESTERN  
LOWER MICHIGAN. THERE LOOKS TO BE TWO MAIN ROUNDS OF PRECIPITATION  
ACROSS WESTERN LOWER MICHIGAN--WEDNESDAY AFTERNOON AND EVENING  
FAVORING THE SOUTH, AND THURSDAY FAVORING THE FAR SOUTHEAST.  
THURSDAY STILL APPEARS TO BE THE MAIN SHOW WITH REGARD TO HEAVY  
RAIN POTENTIAL AS THE LOW ACTUALLY LIFTS THROUGH THE AREA.  
 
ALL THE SIGNS ARE THERE FOR THIS SYSTEM TO OVERACHIEVE IN RAINFALL  
PRODUCTION, INCLUDING ANOMALOUSLY HIGH AMOUNTS OF MOISTURE (PWATS  
APPROACHING DAILY RECORD LEVELS AT DTX), THE MEANS TO CONVERT THE  
MOISTURE TO HEAVY PRECIPITATION RATES VIA DIURNAL  
INSTABILITY/CONVECTION, THE ABILITY TO REPLENISH THE MOISTURE WITH A  
STRONG SOUTHERLY LOW-LEVEL JET, WEAK SHEAR/STEERING FLOW PROMOTING  
SLOWLY-MOVING AND TRAINING CONVECTIVE ELEMENTS, AND AMPLE SYNOPTIC-  
SCALE LIFT. AT THIS POINT, THESE ALL APPEAR TO BE LINING UP RIGHT  
OVER FAR SOUTHEASTERN LOWER MICHIGAN AND THUS OUTSIDE OF OUR AREA  
OF FORECAST RESPONSIBILITY. BUT, ALL IT TAKES IS FOR A SUBTLE  
SHIFT NORTHWEST IN STORM TRACK FOR THIS TO BECOME A PROBLEM FOR  
OUR AREA.  
 
IT IS WORTH NOTING THAT THERE IS A SIGNAL IN THE MODEL GUIDANCE THAT  
A LOCALIZED ZONE OF HEAVIER RAIN MAY DEVELOP ACROSS OUR AREA  
APPARENTLY TIED TO SOME SORT OF MCV/MESOLOW FEATURE IN TANDEM WITH  
THE PARENT SYSTEM WEDNESDAY NIGHT AND INTO EARLY THURSDAY. SUCH  
FEATURES ARE NEARLY IMPOSSIBLE TO PREDICT AND/OR TRUST AT THIS POINT  
IN TIME...HOWEVER, SHOULD CONFIDENCE INCREASE THAT ONE WOULD MOVE  
THROUGH OUR AREA, THE FORECAST WOULD HAVE TO BE UPDATED TO INCREASE  
RAINFALL AMOUNTS OVER A LOCALIZED AREA.  
 
SO, THE BOTTOM LINE IS THAT THE MOST LIKELY SCENARIO IS FOR THE  
HEAVIEST RAIN FROM THIS SYSTEM TO PASS SOUTH AND EAST OF WESTERN  
LOWER MICHIGAN.  
   
LONG TERM
 
(FRIDAY THROUGH TUESDAY)  
ISSUED AT 325 PM EDT TUE AUG 14 2018  
 
IN THE WAKE OF THE LOW MID-WEEK LOW PRESSURE SYSTEM, MODEL FORECAST  
GUIDANCE INDICATES THAT A WEAK SHORTWAVE TROUGH MAY SNEAK SOUTH  
THROUGH LOWER MICHIGAN ON FRIDAY PERHAPS LEADING TO AN UPTICK IN  
SHOWERS AND A FEW THUNDERSTORMS. OTHERWISE, DRY CONDITIONS ARE  
EXPECTED ON SATURDAY AND SUNDAY AS AN UPPER-LEVEL RIDGE AXIS MOVES  
OVERHEAD. PRECIPITATION CHANCES WILL THEN INCREASE NEXT WEEK AS A  
POTENT UPPER-LEVEL TROUGH APPROACHES FROM THE NORTHWEST.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1227 PM EDT TUE AUG 14 2018  
 
VFR CONDITIONS ARE EXPECTED TO CONTINUE AT ALL TAF SITES THROUGH  
THE FORECAST PERIOD. SCATTERED CUMULUS ROOTED AT 3-4KFT WILL  
CONTINUE THIS AFTERNOON BEFORE ABATING JUST AFTER SUNSET. WINDS  
STAYING AT/ABOVE 5 KTS AS WELL AS SLIGHTLY DRIER AIR SHOULD  
IMPEDE WIDESPREAD FOG FROM DEVELOPING DURING THE OVERNIGHT HOURS,  
THOUGH VERY LOCALIZED PATCHES ARE STILL POSSIBLE. AS SUCH, MENTION  
OF FOG AS WELL AS ASSOCIATED RESTRICTIONS IN VISIBILITY AND CIGS  
ARE BEING LEFT OUT OF THE CURRENT TAF PACKAGE.  
 

 
   
MARINE
 
 
ISSUED AT 325 PM EDT TUE AUG 14 2018  
 
WINDS AND WAVES ARE EXPECTED TO REMAIN BELOW SMALL CRAFT/BEACH  
HAZARDS CRITERIA OVER THE NEXT FEW DAYS. THE NEXT CHANCE FOR  
HAZARDOUS CONDITIONS APPEARS TO BE WITH A STORM SYSTEM EARLY NEXT  
WEEK.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 325 PM EDT TUE AUG 14 2018  
 
THE MAIN CONCERN OVER THE NEXT FEW DAYS IS THE POTENTIAL FOR  
LOCALIZED HEAVY RAINFALL WHICH MAY LEAD TO URBAN AND SMALL STREAM  
FLOODING. THE AREA MOST PRONE TO FLOODING WOULD BE ACROSS CENTRAL  
INGHAM COUNTY WHERE 2-5" OF RAIN HAS FALLEN OVER THE PAST 5-7  
DAYS. ELSEWHERE, DRIER SOIL MAY ACT TO SOAK UP THE MOISTURE MORE  
EASILY. HOWEVER, THE MOST LIKELY AREA TO RECEIVE HEAVY RAINFALL  
APPEARS TO BE JUST SOUTH AND EAST OF OUR AREA, POTENTIALLY  
AVERTING ANY LOCALIZED FLOODING CONCERNS.  
 
EVEN WITH LOCALIZED HEAVY RAINFALL, RIVERS AND STREAMS ARE  
EXPECTED TO REMAIN WITHIN BANKS UNLESS THE RAIN ENDS UP BECOMING  
MUCH MORE HEAVY AND WIDESPREAD THAN EXPECTED (THOUGH THIS IS A LOW  
PROBABILITY SCENARIO).  
 

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

 
 

 
 
SYNOPSIS...BORCHARDT  
SHORT TERM...BORCHARDT  
LONG TERM...BORCHARDT  
AVIATION...BORCHARDT  
HYDROLOGY...BORCHARDT  
MARINE...BORCHARDT  
 
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