275  
FXUS63 KDTX 292245  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
645 PM EDT MON MAY 29 2017  
 
   
AVIATION
 
 
WIDELY SCATTERED CONVECTION ACROSS SE MI, RESULTING FROM LATE DAY  
DIURNAL INSTABILITY ALONG A SFC TROUGH AXIS, WILL DIMINISH OVER THE  
NEXT HOUR OR SO WITH THE WANE IN DAYTIME HEATING. THE LOSS OF  
DAYTIME HEATING WILL ALSO REDUCE THE MIXED LAYER, LEADING TO A  
STEADY DROP IN THE SOUTHWEST WINDS AFTER 00Z. THE SFC TROUGH AXIS  
WILL DRIFT EAST OF SE MI BY LATE EVENING, ALLOWING WEAK SFC HIGH  
PRESSURE TO EXPAND INTO THE AREA FROM THE WEST. THIS WILL RESULT IN  
A FURTHER DROP IN THE WIND SPEEDS (TO LESS THAN 10 KNOTS) DURING THE  
LATER HALF OF THE EVENING.  
 
FOR DTW... REMNANT THUNDERSTORM ACTIVITY IN THE VICINITY OF METRO  
SHOULD EXIT WELL EAST BY 00Z. THUNDERSTORM OUTFLOW HAS ALREADY  
REDUCED WIND SPEEDS IN AND AROUND METRO.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* NONE.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 352 PM EDT MON MAY 29 2017  
 
DISCUSSION...  
 
FORECAST REMAINS DOMINATED BY AN UPPER LOW THAT WILL CONTINUE TO  
WOBBLE AROUND OVER ONTARIO AND QUEBEC THROUGH THE WEEK. A SERIES OF  
TROUGHS WILL ROTATE AROUND THIS LOW THROUGH THE GREAT LAKES  
PRESENTING SEVERAL OPPORTUNITIES FOR INCREASED CLOUD COVER AND  
POSSIBLY SOME PRECIPITATION. IN ADDITION, TEMPERATURES WILL  
FLUCTUATE AROUND NORMAL FOR THE END OF MAY, LOW 70S, AS THE  
SHORTWAVE TROUGHS AND RIDGES SLIDE THROUGH.  
 
THIS AFTERNOON WE ARE DEALING WITH POSSIBLY THE BEST SETUP FOR  
SHOWERS AND THUNDERSTORMS THROUGH THE END OF THE WEEK AS THE FIRST  
OF THESE SHORTWAVES WORKS THROUGH THE AREA. AIDED BY THE LEFT EXIT  
REGION OF A JET STREAK TO OUR SOUTH, DECENT VORTICITY LOBE EXPANDING  
OUTWARD FROM THE LOW, ENHANCED RIBBON OF THETA E, AND STRONG LOW/MID  
LEVEL LAPSE RATES TO UTILIZE AROUND 500 J/KG OF ELEVATED CAPE, WE  
SHOULD CONTINUE TO SEE A SCATTERED COVERAGE OF SHOWERS AND  
THUNDERSTORMS THROUGH THE EVENING HOURS. SHOULD ALSO MENTION THE  
LAKE BREEZE NOTED OVER MACOMB AND ST CLAIR COUNTIES THIS AFTERNOON  
AT THE ONSET OF THE SHOWERS. TYPICAL LEADS TO ENHANCED ACTIVITY NEAR  
LAKE ST CLAIR AND THE ST CLAIR RIVER. THE LOSS OF DAYTIME HEATING AS  
THE SHORTWAVE MOVES EAST THIS EVENING SHOULD END PRECIP CHANCES  
THROUGH THE OVERNIGHT.  
 
OTHER ISSUE FOR THE REMAINDER OF THE EVENING WILL BE THE ENHANCED  
WIND FIELD ACROSS THE AREA. FAIRLY TIGHT PRESSURE GRADIENT FROM THE  
TIGHTLY WOUND STACKED LOW COMBINED WITH DEEP BOUNDARY LAYER MIXING  
WILL ALLOW WINDS TO CONTINUE TO GUST TO AROUND 25 TO 30 KNOTS. THIS  
IS FAIRLY UNIFORM ACROSS SOUTHERN LOWER MI, ALTHOUGH THERE IS A  
SLIGHT UPTICK IN WINDS OVER THE SAGINAW VALLEY WITH A FEW GUST  
TOPPING 30 KNOTS. WITH THE OVERALL SETUP CHANGING LITTLE FOR  
TUESDAY, ONE CAN EXPECT GUSTS AGAIN TO REACH INTO THE MID 20 KNOT  
RANGE.  
 
THE NEXT SHORTWAVE WILL ARRIVE TUESDAY AFTERNOON BUT WITH A DRIER  
AIRMASS AND LESS INSTABILITY WE WILL EXPECT TO SEE LESS COVERAGE OF  
SHOWERS AS THEY LIKELY STRUGGLE TO DEVELOP. LAPSE RATES WILL STILL  
BE FAVORABLE AS COOLER AIRMASS SLIDES IN ALOFT, AND CAPE COULD STILL  
REACH A FEW HUNDRED J/KG, THUS WE'LL KEEP THE SLIGHT CHANCE MENTION.  
 
WEDNESDAY WILL BE A BIT OF A DIFFERENT SCENARIO AS THE MAIN UPPER  
LEVEL TROUGH AXIS SWEEPS THROUGH LOWER MI. STILL DEALING WITH A  
DRIER AIRMASS WHICH WILL MAKE SHOWERS STRUGGLE TO DEVELOP, BUT BROAD  
AREA OF DECENT LOW LEVEL LAPSE RATES, WITH SOME SKINNY CAPE ALOFT  
AND OVERALL LIFT INDUCED BY THE TROUGH COULD RESULT IN SOME  
SCATTERED SHOWERS. MUCH DRIER AIR WORKS INTO THE REGION LATER IN THE  
DAY BEHIND THE TROUGH AS FLOW MORE NORTHWESTERLY.  
 
EXTENDED FORECAST WEDNESDAY THROUGH TUESDAY: QUASI-STATIONARY LOW  
PRESSURE CENTER RETURNS OVER NORTHERN ONTARIO BY THURSDAY. THIS WILL  
RESULT IN THE FAMILIAR WEATHER PATTERN THAT HAS PERSISTED OVER THE  
PAST FEW WEEKS WITH SEVERAL SHORT WAVES BEING SHUTTLED THROUGH LOWER  
MICHIGAN. AT LEAST CHANCES FOR SHOWERS AND OR THUNDERSTORMS IN THE  
FORECAST FOR LATE THURSDAY NIGHT THROUGH EARLY SATURDAY MORNING.  
MEANWHILE, SURFACE LOW PRESSURE ORGANIZING OVER THE CENTRAL AND  
SOUTHERN PLAINS IS EXPECTED TO FEED WARM, MOIST AIR NORTHWARD INTO  
THE POCKET OF THE OHIO RIVER VALLEY BY EARLY NEXT WEEK. TRANSLATION:  
MORE CHANCES FOR RAIN DEVELOPING FOR SUNDAY AND MONDAY.  
 
MARINE...  
 
LATE DAY GUSTY SOUTHWEST WINDS WILL EASE SOME TONIGHT AS NOCTURNAL  
STABILITY TAKES HOLDS. RENEWED GUSTINESS WILL THEN COMMENCE ON  
TUESDAY AS THE REGION REMAINS UNDER THE INFLUENCE OF UPPER LEVEL LOW  
PRESSURE. GUSTS IN EXCESS OF 25 KNOTS MOST LIKELY OVER SAGINAW BAY,  
WHERE A SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH TUESDAY.  
PERSISTENT SOUTHWEST TO WESTERLY WINDS WILL A MODEST INCREASE IN  
SPEED AND GUSTINESS EACH AFTERNOON THROUGH THE MIDWEEK PERIOD.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EDT TUESDAY FOR LHZ421-422.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

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