561  
FXUS63 KDTX 212352  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
752 PM EDT TUE MAY 21 2019  
 
   
AVIATION
 
 
DOWNSTREAM RESPONSE TO DYNAMIC UPPER LEVEL LOW PRESSURE OVER CENTRAL  
U.S. WILL FORCE GEOPOTENTIAL HEIGHT RISES AND SIGNIFICANT WARM AIR  
ADVECTION EVENT OVER SOUTHEAST MICHIGAN THE NEXT 12 TO 18 HOURS.  
EFFICIENCY TO SYSTEM RELATIVE ISENTROPIC ASCENT IS NOT IMPRESSIVE  
AND WILL RELY UPON FORCED, TANGIBLE INCREASE IN LOW TO MIDLEVEL  
THETA E CONTENT TO GENERATE PRECIPITATION. MID TO HIGH CLOUD DURING  
THE OVERNIGHT WITH THE POTENTIAL FOR SHOWER ACTIVITY IN THE 12-17Z  
TIME WINDOW FOR SOUTHEAST MICHIGAN. THIS BETTER POTENTIAL WILL COME  
WITH A RIBBON OF DEEPER MIDLEVEL MOISTURE. LOWER CONFIDENCE EXISTS  
WITH WHAT SORT OF COVERAGE WILL EXIST WITHIN THIS MOISTURE PLUME AS  
SOME MODEL GUIDANCE SHOWS LACK OF MOISTURE DEPTH WITH A VERY QUICK  
ONSET TO ACTIVE MIDLEVEL SUBSIDENCE. BOUNDARY LAYER CLOUD IS  
ANTICIPATED WEDNESDAY AFTERNOON IN THE WAKE OF THE PASSING SHORTWAVE  
ENERGY. A WELL MIXED SOUTHEASTERLY WIND IS EXPECTED FOR MUCH OF THE  
DAY WEDNESDAY.  
 
FOR DTW...SHOWERS ARE POSSIBLE IN THE 13-16Z TIMEFRAME WEDNESDAY AT  
DTW WITH CIGS IN THE 2500 TO 5000 FT AGL LAYER.  
   
DTW THRESHOLD PROBABILITIES
 
 
 
* LOW CONFIDENCE IN THUNDERSTORMS WEDNESDAY.  
 
* MEDIUM CONFIDENCE IN CIGS AOB 5000 FEET LATE WEDNESDAY MORNING,  
OTHERWISE LOW FOR WEDNESDAY.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 312 PM EDT TUE MAY 21 2019  
 
DISCUSSION...  
 
A REGION OF LIGHT RAIN ALONG THE MI/IN/OH BORDER REGION IS  
ASSOCIATED WITH A NARROW MID LEVEL FRONTAL ZONE. THIS FRONT HAS BEEN  
WEAKENING AS A RESULT OF MID LEVEL HEIGHT RISES ASSOCIATED WITH A  
SHARPENING OF THE MID LEVEL RIDGE AXIS NOW BUILDING OVER LOWER MI.  
THE RESULTANT RAIN SHOULD IN TURN CONTINUE TO DIMINISH. OTHERWISE,  
SFC HIGH PRESSURE WILL SLOWLY EXIT THE REGION TO THE EAST DURING THE  
NIGHT AS THE MID LEVEL RIDGE AXIS SLIDES INTO THE ERN GREAT LAKES.  
DESPITE THE ABUNDANCE OF LOW LEVEL DRY AIR THROUGH MUCH OF THE  
NIGHT, AMPLE MID/HIGH LEVEL CLOUDS STREAMING IN FROM THE SOUTHWEST  
AND AN INCREASING SOUTHEAST GRADIENT THROUGH THE NIGHT WILL LIMIT  
NIGHTTIME RADIATIONAL COOLING, LEADING TO A LITTLE WARMER NIGHT IN  
COMPARISON TO LAST NIGHT; MINS IN THE 40S.  
 
THE DEPARTING SFC HIGH AND SFC LOW LIFTING NORTHWARD ACROSS THE  
PLAINS LATE TONIGHT/WED MORNING WILL INCREASE THE SOUTHEAST GRADIENT  
ACROSS THE EASTERN LAKES. THE LOW LEVEL AIRMASS LOOKS TO BE COLD  
ENOUGH TO SUPPORT SLIGHTLY UNSTABLE CONDITIONS ACROSS LAKES ST CLAIR  
AND ERIE, SUPPORTING GUSTY SE WINDS FOR A PERIOD WED. THIS AND GIVEN  
THE HIGH LAKE LEVELS WILL AGAIN RAISE FLOODING CONCERNS ALONG THE  
LAKES ST CLAIR AND ERIE SHORELINES.  
 
AS THE UPPER LOW NOW CHURNING OVER THE CENTRAL PLAINS LIFTS INTO  
SOUTH DAKOTA BY WED MORNING, A 60+ KNOT LOW LEVEL JET WILL DRIVE A  
PLUME OF DEEP LAYER MOISTURE AND MODEST ELEVATED INSTABILITY INTO  
WESTERN LOWER MI TOWARD 09 TO 12Z WED MORNING. THE REMNANT MID LEVEL  
THETA E PUSH/ELEVATED INSTABILITY AXIS WILL BE DRIVEN ACROSS SE MI  
WED MORNING (LINGERING IN THE THUMB INTO EARLY AFTERNOON), POSSIBLY  
AIDED BY CONVECTIVELY ENHANCED SHORT WAVE IMPULSES. THERE IS SOME  
CONCERN THAT WITH THE BETTER DYNAMIC SUPPORT RESIDING NORTHWEST OF  
THE AREA AND HIGHER INSTABILITY ACROSS INDIANA, COVERAGE OF  
CONVECTION MAY SUBSTANTIALLY DECREASE OVER SE MI WED MORNING, SO  
CHANCE TYPE POPS WILL SUFFICE ATTM. LOW LEVEL SW FLOW WILL DRIVE A  
SFC WARM FRONT NORTHWARD INTO SE MI DURING THE DAY WEDNESDAY,  
EVENTUALLY REPLACING THE COOL MARINE MODIFIED AIR WITH A WARMER MORE  
SUMMER-LIKE AIRMASS. MODEL SOUNDINGS SUGGEST STRONG MID LEVEL  
CAPPING TAKING HOLD FAIRLY QUICKLY IN THE WARM SECTOR. THE EXCEPTION  
IS ALONG THE FAR EAST FROM MONROE UP THROUGH PORT HURON WHERE THERE  
APPEARS TO BE A SHORT WINDOW OF OPPORTUNITY OF DECENT INSTABILITY  
BEFORE CAPPING TAKES HOLD.  
 
THE UPPER LEVEL LOW IS FORECAST TO DAMPEN AS IT TRAVERSES THE  
NORTHERN LAKES ON THURSDAY, BUT WILL STILL DRIVE A COLD FRONT INTO  
SE MI THURS MORNING. CONVECTIVE CHANCES THURS MAY ACTUALLY HINGE ON  
CONVECTIVE DEVELOPMENT/PROPAGATION UPSTREAM ACROSS ILLINOIS/NRN  
INDIANA AND THE POTENTIAL FOR THE NORTHERN PORTIONS OF THIS TO  
IMPACT SE MI. BY THURS AFTERNOON, MODEL SOUNDINGS SUGGEST STRONG  
CAPPING TAKING HOLD WITHIN THE POST FRONTAL WESTERLY FLOW. A DECENT  
WESTERLY GRADIENT WILL LEAD TO WARM AND BREEZY CONDITIONS.  
 
ANOTHER WAVE FORECAST TO LIFT FROM THE CENTRAL ROCKIES INTO THE NRN  
PLAINS ON FRIDAY. THIS SYSTEM WILL LIKELY DRIVE THE SFC FRONT BACK  
INTO LOWER MI AS A WARM FRONT IN THE FRIDAY TO SATURDAY TIME FRAME,  
SUPPORTING ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS. DESPITE  
SOME DIFFERENCES, THE EURO SOLUTION SUGGESTS NORTHERN STREAM  
TROUGHING WILL DRIVE HIGH PRESSURE INTO THE AREA BY SUNDAY AND HOLD  
ITS INFLUENCE INTO EARLY NEXT WEEK, OFFERING DRY AND RELATIVELY COOL  
CONDITIONS FOR THE END OF THE FORECAST PERIOD.  
 
MARINE...  
 
HIGH PRESSURE WILL BUILD OVER THE AREA PROVIDING LIGHT WINDS AND  
SUBDUED WAVES INTO THIS EVENING. EAST TO SOUTHEAST FLOW WILL  
INCREASE OVERNIGHT INTO WEDNESDAY AS THIS HIGH SHIFTS OFF TO THE  
EAST AND A WARM FRONT BEGINS TO ENCROACHES FROM THE SOUTH.  
HOWEVER, WIND GUSTS ARE GENERALLY EXPECTED TO STAY UNDER 25 KNOTS  
ALONG THE NEARSHORE WATERS, AND SMALL CRAFT ADVISORIES ARE NOT  
ANTICIPATED AT THIS TIME. WINDS BECOME SOUTH TO SOUTHWEST LATE  
WEDNESDAY NIGHT AHEAD OF A COLD FRONT WHICH PASSES THROUGH ON  
THURSDAY. GUSTS UP TO 25 KNOTS ARE POSSIBLE RIGHT ALONG THE  
SHORELINE AREAS OF THE NEARSHORE WATERS, BUT WITH LOW LEVEL  
STABILITY OVER THE OPEN WATERS WILL MAIN GUSTS GENERALLY UNDER  
20 KNOTS.  
 
HYDROLOGY...  
 
SCATTERED SHOWERS AND A FEW THUNDERSTORMS WILL PASS THROUGH  
SOUTHEAST MICHIGAN LATE TONIGHT AND WEDNESDAY MORNING AS A WARM  
FRONT LIFTS NORTH. BASIN AVERAGE RAINFALL EXPECTED TO AVERAGE LESS  
THAN A QUARTER OF AN INCH.  
 
INCREASING SOUTHEAST FLOW ASSOCIATED WITH THIS WARM FRONT WILL BRING  
ANOTHER PERIOD OF FLOODING CONCERNS ALONG THE SHORELINES OF LAKE ST  
CLAIR AND WESTERN LAKE ERIE. THIS PERIOD OF STRONGER ONSHORE WINDS  
WILL BE RATHER BRIEF AND LIMITED TO LATE TONIGHT AND WEDNESDAY  
MORNING. NONE-THE-LESS, LAKESHORE FLOODING ADVISORIES HAVE BEEN  
ISSUED ONCE AGAIN.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...LAKESHORE FLOOD ADVISORY FROM 6 AM TO 6 PM EDT WEDNESDAY FOR MIZ070-  
076.  
 
LAKESHORE FLOOD ADVISORY FROM 6 AM TO 2 PM EDT WEDNESDAY FOR MIZ083.  
 
LAKE HURON...NONE.  
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY FROM 4 AM TO NOON EDT WEDNESDAY FOR LEZ444.  
 

 
 

 
 
AVIATION.....CB  
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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