255  
FXUS63 KDTX 131120  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
720 AM EDT THU AUG 13 2020  
   
AVIATION
 
 
HIGH PRESSURE CENTERED OVER NORTHERN ONTARIO AND QUEBEC HOLDS  
CONTROL OF CONDITIONS ACROSS SE MI TODAY AND TONIGHT. LIGHT EASTERLY  
LOW LEVEL WIND SUPPLIES DRY AIR INTO THE REGION RESULTING IN JUST  
SOME SCATTERED TO BROKEN CIRRUS AT TIMES. NO BIG CHANGES TONIGHT  
INTO FRIDAY AS VFR IN THE FORM OF HIGH CLOUDS CONTINUES ALONG WITH  
PERHAPS A STEADIER NE WIND COMPARED TO RECENT NIGHTS.  
   
DTW THRESHOLD PROBABILITIES
 
 
* NONE  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 349 AM EDT THU AUG 13 2020  
 
DISCUSSION...  
 
LITTLE CHANGE IN THE FORECAST AS MODELS ARE IN LOCK STEP ON THE  
LARGE SCALE PATTERN HEADING INTO THE WEEKEND. THE ONCE ZONAL FLOW  
ACROSS THE NORTHERN TIER OF THE US IS AMPLIFYING AS A SERIES OF WAVES  
ENTER THE NW CONUS DEEPEN THE TROUGH OVER WESTERN CANADA. THE  
STEEPENING RIDGE AXIS WILL NOT MAKE IT TO MI UNTIL FRIDAY KEEPING US  
UNDER CONFLUENT FLOW AND SUBSIDENCE UNTIL THEN. MEANWHILE AT THE  
SURFACE, HIGH PRESSURE WILL HOLD OVER THE REGION WHILE SHIFTING ITS  
CENTER FROM THE CENTRAL GREAT LAKES WEDNESDAY UP TO HUDSON BAY THIS  
AFTERNOON. THIS WILL KEEP A LIGHT EASTERN FLOW INTO THE AREA HELPING  
TO KEEP THE CURRENT DRY AIRMASS IN PLACE. PWATS WILL STILL BE AROUND  
0.75 INCHES AS SURFACE DEWPOINTS LINGER IN THE MID 50S TO NEAR 60  
THIS AFTERNOON. THIS WILL KEEP HEAT INDICES DOWN ONCE AGAIN AS TEMPS  
RISE INTO THE MID-UPPER 80S. RETURN OF SOUTHERLY FLOW ON FRIDAY WILL  
START TO ALLOW A LITTLE BETTER MOISTURE INTO THE REGION BUT A CUTOFF  
LOW MEANDERING AROUND THE MID MS VALLEY INTO TN/KY WILL BLOCK THE  
DEEPER GULF MOISTURE SO EXPECTING DEWPOINTS INTO THE LOW TO MID 60S  
THROUGH THE WEEKEND.  
 
THERE IS ONE FEATURE IN THE NEAR TERM TO KEEP AN EYE ON FOR THE  
FORECAST TODAY AND TONIGHT. A SHORTWAVE AND ASSOCIATED CLUSTER OF  
CONVECTION IS CURRENTLY WORKING ACROSS NORTHERN WI AND WILL CONTINUE  
ACROSS THE STRAITS TODAY. THOUGH THE UNFAVORABLE ATMOSPHERE WILL  
LIKELY MINIMIZE RAIN CHANCES, CLOUDS WILL LIKELY PERSIST. THE MID  
LEVEL FEATURE IS ADVERTISED TO GET CUT OFF FROM THE FLOW AND STALL  
OVER NORTHERN LOWER TODAY. THIS COULD BRING SOME THICKER CLOUDS INTO  
THE SAGINAW VALLEY. FOR NOW, I INCREASED CLOUDS OVER NORTHERN LAKE  
HURON BUT HELD OFF OVER LAND AS WE SEE HOW MUCH IT CAN HOLD TOGETHER  
IN THE INCREASINGLY LESS FAVORABLE ENVIRONMENT.  
 
ATTENTION THEN TURNS TOWARD THE WEEKEND AND THE RETURN OF RAIN  
CHANCES. NOT MUCH HAS CHANGED IN THE MODELS WHICH ISN'T NECESSARILY  
A GOOD THING BECAUSE THEY STILL DIFFER ON HOW THEY MANAGE THE TWO  
MAIN FEATURES, THE AFOREMENTIONED WEST COAST TROUGH THAT WILL  
EVENTUALLY PUSH ACROSS THE GREAT LAKES SUNDAY AND THE CUTOFF LOW TO  
OUR SOUTH. IF THE LOW DRIFTS FAR ENOUGH NORTH IT CAN THEN FEEL THE  
HEIGHT FALLS OF THE TROUGH AND SHIFT FARTHER NORTH. THIS WOULD MAKE  
FOR A RAINY SATURDAY WITH THE WEAK WAVE OVERHEAD ALL DAY. OTHERWISE  
THE FEATURES WILL REMAIN DISCONNECTED AND THE SURFACE HIGH WILL HOLD  
THROUGH SATURDAY KEEPING US DRY. THE TROUGH AND COLD FRONT WILL  
THEN SWEEP ACROSS LOWER MI LATE SUNDAY INTO SUNDAY NIGHT OFFERING  
THE CHANCE OF SHOWERS AND THUNDERSTORMS.  
 
IN THE WAKE OF THE FRONT, MUCH COOLER AIR WILL OVERTAKE THE REGION  
WITH 850MB TEMPS DROPPING FROM THE PERSISTENT MID TEENS THIS WEEK,  
DOWN INTO THE UPPER SINGLE DIGITS BY TUESDAY. FORECAST HIGHS ARE IN  
THE 70S WITH LOWS DROPPING INTO THE LOWER 50S.  
 
MARINE...  
 
DRY CONDITIONS PERSIST ACROSS THE CENTRAL GREAT LAKES AS HIGH  
PRESSURE CONTINUES TO BUILD OVERHEAD. LIGHT AND VARIABLE WINDS WILL  
GRADUALLY BACK TO THE NORTHEAST, WITH WINDS INCREASING TO 10 TO 15  
KNOTS BY MIDDAY THURSDAY. GUSTS COULD REACH AROUND 20 KNOTS THURSDAY  
AFTERNOON/EVENING, PARTICULARLY ACROSS SAGINAW BAY DUE TO ITS  
NORTHEASTERLY FETCH. OVERALL BOATING CONDITIONS ARE EXPECTED TO  
REMAIN FAVORABLE THROUGH THE END OF THE WEEK BEFORE ANOTHER  
POTENTIAL SYSTEM APPROACHES THE CENTRAL GREAT LAKES THIS WEEKEND.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...NONE.  
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  
 

 
 

 
 
AVIATION.....BT  
DISCUSSION...DRK  
MARINE.......SS  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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