554  
FXUS63 KDTX 192321  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
721 PM EDT FRI AUG 19 2022  
   
AVIATION
 
 
LINGERING POCKETS OF HIGH BASED DIURNAL CU WILL FADE WITH THE LOSS  
OF DAYTIME HEATING, LEAVING PLENTY OF CLEAR SKY FOR THE OVERNIGHT  
PERIOD. PROSPECTS FOR A MINOR VISIBILITY RESTRICTION IN SHALLOW FOG  
NEAR DAYBREAK LIMITED BY CONTINUED WEAK SOUTHERLY FLOW, PRECLUDING A  
DEFINED MENTION ATTM. A GRADUAL INCREASE IN MOISTURE MAY INTRODUCE A  
FEW WIDELY SCATTERED SHOWERS BY EARLY SATURDAY. GREATER POTENTIAL  
FOR SHOWERS AND THUNDERSTORMS WILL EXIST DURING THE AFTERNOON AND  
EVENING HOURS AS A LOW PRESSURE SYSTEM GRADUALLY APPROACHES THE  
REGION.  
 
DTW THRESHOLD PROBABILITIES...  
 
* LOW FOR CEILINGS AT OR BELOW 5000 FT SATURDAY AFTERNOON.  
 
* LOW FOR THUNDERSTORM SATURDAY AFTERNOON AND EVENING.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 355 PM EDT FRI AUG 19 2022  
 
DISCUSSION...  
 
UPPER LOW CURRENTLY CIRCULATING OVER SOUTHERN MINNESOTA/SOUTH  
DAKOTA, EVIDENT PER WV IMAGERY, LARGELY GOVERNS THE FORECAST OVER  
THE NEXT SEVERAL DAYS, SUPPORTIVE OF WIDESPREAD SHOWER AND  
THUNDERSTORM ACTIVITY THROUGHOUT THE WEEKEND. FOR THE REST OF THIS  
EVENING, SOUTHEAST MI RESIDES WELL AHEAD OF THE LOW, KEEPING SKIES  
GENERALLY CLEAR ASIDE FROM DIURNAL CU. TEMPERATURES HOVERING IN THE  
MID 80S AND DEWPOINTS IN THE LOW 60S CONTRIBUTE TO AN OVERALL  
COMFORTABLE AND DRY EVENING, WITH LOWS DIPPING INTO THE LOW TO MID  
60S OVERNIGHT.  
 
MAIN FOCUS FOR THIS UPDATE IS ON SHOWER AND THUNDERSTORM ACTIVITY  
TOMORROW. INITIAL RIBBON OF VORTICITY EMANATING OFF THE PARENT LOW  
PUSHES INTO SE MI EARLY TOMORROW MORNING, INCREASING HIGH CLOUD  
COVERAGE AND KICKSTARTING A PERIOD OF MOISTURE ADVECTION INTO THE  
CWA. GENERALLY DRY START TO THE DAY GIVEN LACKLUSTER LOW LEVEL  
MOISTURE, ALTHOUGH COULD SEE A FEW ELEVATED SHOWERS WHERE LAKE  
MOISTURE AUGMENTS THE PROFILE. THUNDERSTORM CHANCES THEN INCREASE  
AFTER NOON AS DIURNAL HEATING AND ASSOCIATED INSTABILITY RAMP UP,  
ALTHOUGH THE DEGREE TO WHICH THE ATMOSPHERE DESTABILIZES WILL BE  
HIGHLY DEPENDENT ON BOTH CLOUD COVER AND EXTENT OF LOW LEVEL  
MOISTURE ADVECTION (12Z GUIDANCE SUGGESTS MLCAPE BUILDING TO 500-  
1000 J/KG BY 18Z). ALTHOUGH SOME CELLS MAY DEVELOP EARLY AFTERNOON  
IN THE WAKE OF BOUNDARY LAYER HEATING, A MORE FOCUSED REGION OF  
MULTICELLULAR CONVECTION DEVELOPS UPSTREAM (ACROSS NORTHERN IL/IN)  
ALONG RESIDUAL OUTFLOW AND PUSHES NORTHEAST INTO THE CWA MID  
AFTERNOON TO EARLY EVENING (BETWEEN ABOUT 2 TO 8 PM LOCAL TIME).  
ORGANIZED CONVECTION WILL BE LIMITED GIVEN WEAK DEEP LAYER SHEAR  
(~20 KNOTS IN THE 0-6 KM LAYER), ALTHOUGH A FEW STRONG TO ISOLATED  
SEVERE DOWNBURST WINDS ARE PLAUSIBLE GIVEN FAVORABLE MOISTURE  
PROFILES AND STEEP LOW LEVEL LAPSE RATES. THUS, SPC DAY 2 MARGINAL  
RISK LOOKS REASONABLE, KEEPING THE HIGHLIGHTED AREA SOUTH OF I-69  
WITH INCREASING FAVORABILITY FOR STRONG TO ISOLATED SEVERE STORMS  
TOWARD THE OHIO BORDER.  
 
THUNDERSTORM INTENSITY WANES AFTER SUNSET TOMORROW, ALTHOUGH  
ELEVATED THUNDERSTORMS DO REMAIN POSSIBLE OVERNIGHT INTO SUNDAY  
MORNING AS MUCAPE HOVERS AROUND 500-1000 J/KG. VORT MAX AND  
ASSOCIATED SYNOPTIC ASCENT TRANSITION OVERHEAD DAYTIME SUNDAY,  
TAPPING INTO A DEEPLY SATURATED PROFILE WITH PWATS IN EXCESS OF 1.5"  
(NEAR 90TH PERCENTILE FOR MID AUGUST). DEEP LAYER SHEAR REMAINS  
MEAGER IN THE OVERALL WEAK AMBIENT FLOW PATTERN, ONCE AGAIN  
INHIBITING ORGANIZED CONVECTION. STILL LOW CONFIDENCE IN COVERAGE OF  
SHOWERS AND STORMS ON SUNDAY, ALTHOUGH ABUNDANCE OF MOISTURE AND AT  
LEAST SOME RESIDUAL INSTABILITY LIKELY KEEP ON AND OFF SHOWERS GOING  
THROUGH MUCH OF THE DAY IN THE WAKE OF BACKGROUND SYNOPTIC FORCING.  
 
STUBBORN UPPER LEVEL PATTERN THEN EJECTS EASTWARD LATE SUNDAY INTO  
MONDAY, SHIFTING FLOW TO THE NORTHWEST AND USHERING IN COOLER AND  
DRIER CONDITIONS. SOME LINGERING SHOWER ACTIVITY WILL BE POSSIBLE  
MONDAY MORNING AS RESIDUAL MOISTURE CLEARS OUT, FOLLOWED BY A  
CLEARING TREND FOR THE AFTERNOON. OVERALL SEASONABLE CONDITIONS  
EXPECTED THROUGH MID-WEEK WITH TEMPERATURES IN THE LOW 80S ON MONDAY  
REBOUNDING SLIGHTLY INTO THE MID 80S BY MID WEEK AS HIGH PRESSURE  
BUILDS IN.  
 
MARINE...  
 
A RIDGE OF HIGH PRESSURE WILL CONTINUE TO BRING DRY WEATHER AND  
LIGHT WINDS OVER THE WATERS THROUGH THE FIRST HALF OF SATURDAY. A  
SLOW MOVING LOW PRESSURE SYSTEM WILL THEN BRING ACTIVE WEATHER LATER  
IN THE DAY ON SATURDAY AND AGAIN ON SUNDAY, AS WIDELY SCATTERED TO  
NUMEROUS SHOWERS AND SOME THUNDERSTORMS ARE EXPECTED TO DEVELOP.  
THERE WILL BE AN ISOLATED RISK FOR SEVERE WEATHER, WITH THE MAIN  
THREAT COMING AS HIGHLY LOCALIZED DOWNDRAFTS TO 34 KNOTS. THIS  
SEVERE THREAT IS EXPECTED TO REMAIN CONFINED ACROSS THE SAGINAW BAY  
INTO SOUTHERN LAKE HURON, AND LOCATIONS SOUTH. OUTSIDE OF ANY  
THUNDERSTORM ACTIVITY, WINDS WILL REMAIN LIGHT GIVEN THE WEAK  
PRESSURE GRADIENT AND STABLE LAKE CONDITIONS. SOME RESIDUAL RAIN  
SHOWERS WILL AGAIN BE POSSIBLE ON MONDAY, WITH HIGH PRESSURE THEN  
BUILDING IN THROUGH THE MIDWEEK PERIOD, BRINGING CONTINUED LIGHT  
WINDS AND THE RETURN OF DRY WEATHER.  
 
HYDROLOGY...  
 
WIDESPREAD SHOWERS AND THUNDERSTORMS DEVELOP TOMORROW AFTERNOON AS A  
MID LEVEL CLOSED LOW AND ATTENDANT FRONTAL FEATURES MOVES INTO  
SOUTHEAST MI. PWATS INCREASE TO 1.50 INCHES OR GREATER BY SATURDAY  
EVENING, PROVIDING AMPLE MOISTURE FOR HEAVY RAINFALL. OVERALL  
PRECIPITATION RESULTS IN BASIN TOTALS AVERAGING BETWEEN A HALF TO  
THREE QUARTERS OF AN INCH, ALTHOUGH EMBEDDED THUNDERSTORMS WILL BE  
CAPABLE OF PRODUCING LOCALIZED TOTALS IN EXCESS OF 1 INCH. WHILE  
WIDESPREAD FLOODING IS NOT A CONCERN, MINOR FLOODING MAY OCCUR IN  
LOW LYING AND FLOOD PRONE AREAS WITH ANY HEAVIER DOWNPOURS OR IF  
CELLS REPEATEDLY IMPACT ANY SINGLE LOCATION.  
 

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

 
 

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