672  
FXUS63 KDTX 221030  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
630 AM EDT SUN OCT 22 2017  
 
   
AVIATION
 
 
LOW LEVELS WILL REMAIN DRY FOR ONE MORE DAY (CEILING FREE BELOW 12  
KFT), BUT INCREASING SOUTHERLY FLOW AHEAD OF A COLD FRONT WILL ALLOW  
FOR QUICKLY LOWERING CEILINGS NEAR AND JUST AFTER SUNSET, WITH MVFR  
SHOWERS LIKELY MAKING IT INTO MBS AND FNT TOWARD MIDNIGHT. SHOWERS  
WILL GRADUALLY CONTINUE TO SPREAD EASTWARD OVERNIGHT INTO MONDAY  
MORNING.  
 
SOUTHERLY WINDS EXPECTED TO REACH AROUND 15 KNOTS SUSTAINED THIS  
AFTERNOON, AND STILL HOLDING AROUND 10 KNOTS THIS EVENING.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* MEDIUM CONFIDENCE IN CIGS AOB 5000 4-12Z MONDAY, HIGH CONFIDENCE  
AFTER.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 328 AM EDT SUN OCT 22 2017  
 
DISCUSSION...  
 
MILD AND BREEZY CONDITIONS WILL END THE WEEKEND ACROSS SE MI AS DEEP  
SOUTHERLY FLOW WILL BE IN PLACE TODAY AHEAD OF A SLOW MOVING COLD  
FRONT TRACKING ACROSS THE WRN GREAT LAKES. DESPITE SOME OCCASIONAL  
MID/HIGH LEVEL CLOUDS TODAY, THE SOUTHERLY FLOW SHOULD BOOST MIXING  
DEPTHS SLIGHTLY, SUPPORTING HIGH TEMPS FROM THE MID 70S TO NEAR 80  
(15 TO 20 DEG ABOVE LATE OCTOBER NORMS). AN EVOLVING SPLIT FLOW  
WITHIN AN APPROACHING LONG WAVE MID LEVEL TROUGH WILL SUPPORT A  
DECELERATION OF THE APPROACHING SFC COLD FRONT AS IT TRACKS INTO SE  
MI TONIGHT INTO THE DAY MONDAY. WHILE MID LEVEL MOISTURE ADVECTION  
LATE THIS AFTERNOON THROUGH TONIGHT MAY LEAD TO SOME SPRINKLES/LIGHT  
SHOWERS OUT AHEAD OF THE SFC FRONT, THE MAIN FORCING FOR PRECIP WILL  
BE POST FRONTAL LOWER TROPOSPHERIC FGEN. BASED ON 00Z MODEL  
GUIDANCE, TIMING OF THIS FORCING WILL FOCUS THE BETTER RAINFALL  
CHANCES ACROSS THE WESTERN HALF OF THE FORECAST AREA TONIGHT.  
 
MID LEVEL TROUGH AMPLIFICATION ACROSS THE NRN PLAINS/UPPER MIDWEST  
IS SHOWN BY THE ENTIRE 00Z MODEL SUITE. THERE DOES HOWEVER REMAIN  
DIFFERENCES IN HANDLING OF THE SOUTHERN STREAM WAVE SET TO AMPLIFY  
OVER THE SRN MS VALLEY TODAY AND ITS INTERACTION WITH THE DEEPENING  
NORTHERN STREAM TROUGH. THE GFS/NAM SOLUTIONS DAMPEN THE SRN STREAM  
WAVE MORE RAPIDLY AS IT LIFTS INTO THE UPPER OHIO VALLEY MON NIGHT  
AND KEEP A GOOD DEAL OF PHASE SEPARATION WITH THE NORTHERN STREAM  
WAVE. THIS RESULTS IN THE BETTER LARGE SCALE DYNAMICS DEVELOPING  
OVER THE ERN HALF OF THE FORECAST AREA INTO SRN ONTARIO MON/MON  
NIGHT. THE ECMWF/CANADIAN HOWEVER INDICATE THE SRN STREAM WAVE  
LIFTING ACROSS SE MI MONDAY NIGHT, RAPIDLY PHASING INTO THE NRN  
STREAM. THE RESULT IS A REGION OF PERSISTENT MID LEVEL FORCING OVER  
LOWER MI WITH A RAPIDLY DEEPENING SFC LOW OVER LAKE HURON MON NIGHT.  
THIS SOLUTION SUGGESTS THE POSSIBILITY OF SEVERAL INCHES OF RAIN  
ACROSS SE MI MON/MON NIGHT (WHEREAS THE GFS CAMP IS MORE IN THE ONE  
TO TWO INCH RANGE). THERE REMAINS A FAIR AMOUNT OF ENSEMBLE SPREAD  
WITH THE ECMWF MEMBERS IN THE HANDLING OF THIS SYSTEM. THERE IS ALSO  
CONCERN THAT THE ECMWF MAY BE OVER DEEPENING THIS SYSTEM (A TREND  
NOTED IN SEVERAL SYSTEMS LAST COOL SEASON). PERHAPS BETTER SAMPLING  
OF THE NORTHERN STREAM ENERGY NOW ENTERING THE PACIFIC NORTHWEST  
TODAY WILL LEAD TO A CONVERGENCE IN MODEL SOLUTIONS OVER THE NEXT  
COUPLE FORECAST CYCLES.  
 
THE AFOREMENTIONED CONCERNS WITH THE ECMWF SOLUTION WILL STEER THE  
FORECAST TOWARD THE GFS CAMP THIS FORECAST CYCLE, WITH THE MAIN  
IMPACT BEING A LITTLE LOWER FORECAST RAIN TOTALS AND SLIGHTLY LOWER  
WIND SPEEDS ON TUES. AS THE SOUTHERN STREAM WAVE ENTERS THE TN/OH  
VALLEYS MON/MON NIGHT, MID LEVEL DEFORMATION WILL INTENSIFY ACROSS  
THE SLOW MOVING FRONT OVER SE MI. TIGHTENING OF THE MID LEVEL THETA  
E SURFACES WITHIN GOOD UPPER LEVEL DIVERGENCE AND CONDITIONAL MID  
LEVEL INSTABILITY WILL LEAD TO ROBUST MID LEVEL ASCENT OVER SE MI.  
THIS COMBINED WITH A GOOD INFLUX OF MOISTURE INTO THE FRONTAL SLOPE  
(PWATS AROUND 1.5 INCHES) WILL SUPPORT HIGH CHANCES FOR RAIN,  
ESPECIALLY MON AFTERNOON AND EVENING.  
 
A DEEP UPPER LOW IS FORECAST TO DEVELOP OVER THE GREAT LAKES BY  
TUESDAY. COLD CANADIAN AIR WILL BE DRIVEN INTO THE REGION BY THIS  
SYSTEM, WITH 850MB TEMPS EXPECTED TO DROP INTO THE NEGATIVE DIGITS.  
DIVERGING MODEL SOLUTIONS AND POOR RUN TO RUN CONTINUITY LEAD TO  
HIGH FORECAST UNCERTAINTY MID WEEK INTO NEXT WEEKEND. THE EXPECTED  
PERSISTENCE OF MID LEVEL TROUGHING OVER THE REGION THROUGH MID WEEK  
WITH PERIODIC MID LEVEL WAVES WILL SUPPORT OCCASIONAL SHOWERS  
TUES AND WED.  
 
MARINE...  
 
SOUTHERLY WINDS IN THE 15 TO 20 KNOT RANGE TODAY AHEAD OF A COLD  
FRONT, WHICH WILL SLOWLY WORK INTO SOUTHEAST MICHIGAN TONIGHT. WIND  
GUSTS UP AROUND 25 KNOTS OVER SOUTHERN LAKE HURON THIS EVENING WILL  
DIMINISH AS WE HEAD INTO MONDAY AS THE FRONTAL BOUNDARY STALLS OVER  
THE AREA. LOW PRESSURE COMING UP FROM THE SOUTH ON MONDAY WILL BE  
DEEPENING, BUT IT APPEARS THE TRACK WILL BE TOO CLOSE TO THE CENTRAL  
GREAT LAKES TO GENERATE GALE FORCE WINDS, AND THE GALE WATCH WILL BE  
DROPPED. ALTHOUGH, THERE STILL IS A LESS THAN 30 PERCENT CHANCE THE  
LOW COULD DEEPEN GREATER THAN ADVERTISED TO PRODUCE GALES, BUT WOULD  
NOT BE UNTIL LATE TUESDAY AS COLDER AIR WRAPS INTO THE SYSTEM.  
 
HYDROLOGY...  
 
A COLD FRONT CARRYING A BAND OF SHOWERS WILL WORK INTO THE AREA LATE  
THIS EVENING INTO EARLY MONDAY MORNING BEFORE A RAPIDLY  
STRENGTHENING LOW DEVELOPS ALONG IT CAUSING IT TO BECOME NEARLY  
STATIONARY OVER LOWER MICHIGAN. ALTHOUGH THE STRENGTH AND TRACK OF  
THE LOW REMAIN UNCERTAIN AT THIS TIME, THERE IS POTENTIAL FOR MORE  
THAN 2 INCHES OF RAIN OVER A PORTION OF THE AREA MONDAY INTO MONDAY  
NIGHT AS STRONG DEFORMATION FORCING LIFTS THROUGH THE PENINSULA.  
URBAN AND SMALL STREAM FLOODING WILL BE A POSSIBILITY DURING THIS  
TIME.  
 

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

 
 

 
 
AVIATION.....SF  
DISCUSSION...SC  
MARINE.......SF  
HYDROLOGY....SF  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT.  
 
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