806  
FXUS63 KDTX 152313  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
713 PM EDT MON JUL 15 2019  
   
AVIATION
 
 
THE WARM FRONT, EXTENDING NW-SE ACROSS LOWER MICHIGAN MOVES INTO  
CANADA DURING THE EVENING AND TAKES THUNDERSTORMS OUT OF THE AREA.  
THAT LEAVES VFR IN PLACE AT THE TERMINALS WITH LIGHT SW WIND THROUGH  
EARLY TUESDAY MORNING. CLEAR SKY DEVELOPING BY LATE EVENING SHOWS AN  
INCREASE OF HIGH CLOUDS LATE AS THE NORTHERN FRINGE OF BARRY  
REMNANTS MOVE IN FROM THE SOUTH. LIGHT SHOWERS REACH DTW FIRST  
AROUND NOON TUESDAY AND SPREAD NORTHWARD TOWARD FNT DURING THE  
AFTERNOON. THERE IS ALSO A GRADUAL LOWERING OF CEILING TOWARD ENTRY  
LEVEL MVFR WHICH IS INDICATED IN OBSERVATIONS TODAY MOVING INTO THE  
OHIO VALLEY. AFTERNOON TIMING BRINGS DURATION INTO QUESTION AND THE  
FORECAST WILL TIE RESTRICTION TO SHOWERS FOR NOW. TIMING AND  
COVERAGE OF ANY THUNDERSTORMS WOULD BE LATE IN THE DAY WITH  
INSTABILITY IN QUESTION DUE TO THE EARLIER CLOUDS AND SHOWERS.  
PREFER TO SAVE THE MENTION OF STORMS FOR EVALUATION IN LATER  
UPDATES.  
 
FOR DTW... THUNDERSTORMS EXIT EAST OF DTW TO START THE FORECAST LEAVING  
VFR UNDER DECREASING CLOUDS THROUGH MIDNIGHT WITH LIGHT SW WIND.  
HIGH CLOUDS INCREASE LATE AND LOWER TOWARD 5000 FT TUESDAY MORNING  
LEADING TO A CHANCE OF VFR SHOWERS.  
   
DTW THRESHOLD PROBABILITIES
 
 
* MODERATE FOR CEILING 5000 FT OR LESS TUESDAY.  
 
* LOW FOR THUNDERSTORMS LATE TUESDAY.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 322 PM EDT MON JUL 15 2019  
 
DISCUSSION...  
 
CONVECTION HAS FIRED AS EXPECTED, WITH LATEST SPC MESOSCALE ANALYSIS  
INDICATING MLCAPES 1000-1500 J/KG ON THE WESTERN FRINGE OF THE CWA,  
WITH EFFECTIVE BUILD SHEAR ABOVE 30 KNOTS GENERALLY NORTH OF I-69.  
AN ISOLATED MARGINALLY SEVERE THUNDERSTORM OR TWO REMAINS POSSIBLE  
THROUGH THE BULK OF DAYLIGHT HOURS, BUT WEAK MID LEVEL LAPSE RATES  
SUGGESTS OTHERWISE WITH JUST TORRENTIAL DOWNPOURS DUE TO THE  
TROPICAL NATURE OF THE AIRMASS. SUBSIDENCE/MODEST DRYING OUT AT THE  
700 MB LEVEL BEHIND THE MID/UPPER WAVE EXITING LAKE HURON IS  
EXPECTED TO PRODUCE A DRY LATE EVENING INTO THE EARLY MORNING HOURS  
OF TUESDAY.  
 
REMNANT CIRCULATION/MOISTURE OF BARRY OVER THE LOW-MID MISSISSIPPI  
RIVER VALLEY BEING SHEARED OFF TO THE NORTHEAST AND NORTHERN FRINGE  
LOOKS TO CLIP SOUTHEAST MICHIGAN TOMORROW, AS THE CLOSED 500 MB LOW  
OPENS UP. PW VALUES EXCEEDING 2 INCHES SOUTH OF I-69 WITH 700 MB DEW  
PTS PUSHING 7 C AND POSSIBLY EVEN 8 C, RECORD TERRITORY FOR MID JULY  
AROUND HERE. THE MAIN MOISTURE SURGE IS ACTUALLY GOING TO OCCUR  
AROUND 12Z TUESDAY WHEN NOSE OF THE 800-700 MB JET CROSSES JUST  
ACROSS THE SOUTHERN MICHIGAN BORDER. STRONGER WINDS THEN ARE SHUNTED  
OFF TO THE EAST DURING TUESDAY, WITH 0-6 KM BULK SHEAR GENERALLY  
UNDER 20 KNOTS. THUS, NO SEVERE WEATHER IS EXPECTED WITH THE WEAK  
INSTABILITY/MID LEVEL LAPSE RATES. ONCE AGAIN, TORRENTIAL RAINFALL  
WILL BE THE MAIN HAZARD AND SHOULD NOT TAKE MUCH TO SET OFF DIURNAL  
ENHANCED SHOWERS AND EMBEDDED THUNDERSTORMS (SEE ARW), LINGERING  
INTO THE EARLY EVENING. WITH ACTIVITY/CLOUDS ALREADY ARRIVING TO  
START THE DAY, TEMPERATURES LIKELY HOLDING IN THE 80S, WITH TRI-  
CITIES AND NORTHERN THUMB REGION LIKELY SEEING THE WARMEST TEMPS.  
 
REASONABLE AGREEMENT AMONGST MODELS WITH AN UPPER LEVEL DISTURBANCE  
COMING OUT OF THE CENTRAL PLAINS AND TRACKING THROUGH LOWER MICHIGAN  
ON WEDNESDAY, HELPING TO KICK REMNANT OPEN 500 MB TROUGH OF BARRY  
OFF TO THE EAST. STILL A LOT OF MOISTURE TO WORK (PW VALUES AROUND 2  
INCHES/700 MB DEW PTS STILL AOA 5 C) WITH TO GENERATE SHOWERS AND  
THUNDERSTORMS, AS MLCAPES PUSH ABOVE 1000 J/KG AND POTENTIALLY UP TO  
2000 J/KG, DEPENDING ON TIMING AND STRENGTH OF THE DISTURBANCE.  
LOCALIZED ENHANCEMENT OF 0-6 KM BULK SHEAR REACHING AROUND 30 KNOTS  
(PROBABLY ALONG/NORTH M-46 ONCE AGAIN PER NAM) COULD SUPPORT AN  
ISOLATED SEVERE THREAT, BUT MID LEVEL LAPSE RATES STILL LOOK TO BE  
WEAK (UNDER 6 C/KM). 850 MB TEMPS AROUND 18 C, SUPPORTIVE OF MAXES  
AROUND 90 DEGREES, BUT WITH SHOWERS AND THUNDERSTORMS AROUND AND  
MOIST LOW LEVELS (SURFACE DEW PTS AOA 70 DEGREES), PROBABLY GOING TO  
HOLD TEMPS MORE IN THE 85-90 DEGREE RANGE.  
 
HEAT WILL INCREASE AT THE END OF THE WEEK AS AN UPPER LEVEL RIDGE  
SETS UP OVER THE CENTRAL PLAINS BEFORE EXPANDING EASTWARD ALLOWING  
THE 591DAM TO MOVE INTO SOUTHERN MI ON FRIDAY AND SATURDAY. BOTH OF  
THOSE DAYS WILL HAVE HIGHS IN THE MID 90'S (POSSIBLY UPPER 90'S IN  
DETROIT ITSELF) WITH DEWPOINTS IN THE MID 70'S GIVING HEAT INDEX  
VALUES WELL INTO THE 100'S. LOWS THURSDAY NIGHT ON WILL ONLY GET  
DOWN INTO THE MID 70'S.  
 
A LOW BEGINS TO DEVELOP OVER THE NORTHERN PLAINS THURSDAY MORNING  
AND MOVES OVER THE UPPER PENINSULA THURSDAY NIGHT. THIS SYSTEM PULLS  
HOTTER MUGGIER AIR INTO SE MI HELPING TO CREATE THOSE MID-90'S ON  
FRIDAY AND SATURDAY. THERE WILL BE A MODERATE CHANCE OF RAIN  
THURSDAY NIGHT THROUGH FRIDAY WITH THIS SYSTEM'S PASSAGE. A WEAK MID-  
LEVEL DISTURBANCE LOOKS TO MOVE FROM WISCONSIN INTO SE MI SATURDAY  
AFTERNOON WITH COULD BRING A CHANCE OF SCATTERED SHOWERS AND  
THUNDERSTORMS.  
 
MARINE...  
 
PREVAILING LATE DAY SOUTHEASTERLY WINDS WILL INCREASE MODESTLY WHILE  
GRADUALLY VEERING TO SOUTHWEST OVERNIGHT AS A WARM FRONT LIFTS  
THROUGH THE REGION. A 10 TO 20 KNOT SOUTHWEST WIND WILL REMAIN IN  
PLACE THROUGH TUESDAY. STRONGEST WINDS LIKELY NOTED ACROSS SAGINAW  
BAY DURING THIS TIME, WHERE CONDITIONS MAY NEAR ADVISORY LEVELS FOR  
SMALL CRAFT. SOUTHWEST WINDS WILL DIMINISH TUESDAY NIGHT AS THE  
GRADIENT EASES. WINDS WILL THEN TURN LIGHT AND VARIABLE FOR  
WEDNESDAY. INCREASINGLY MOIST AND UNSTABLE AIR ACROSS THE REGION  
OVER THE NEXT COUPLE DAYS WILL LEAD TO INCREASING CHANCES FOR  
THUNDERSTORMS.  
 
HYDROLOGY...  
 
A WARM FRONT WILL LIFT ACROSS SOUTHEAST MICHIGAN DURING THE  
AFTERNOON AND EVENING HOURS. THIS FRONTAL PASSAGE TIMED FAVORABLY  
WITH DIURNAL DESTABILIZATION WILL PROVIDE THE FOCUS FOR A SCATTERED  
COVERAGE OF SHOWERS AND THUNDERSTORMS DURING THIS TIME. ANY  
THUNDERSTORM ACTIVITY WILL BRING THE POTENTIAL FOR LOCALIZED HEAVY  
RAINFALL, WITH AMOUNTS IN EXCESS OF AN INCH POSSIBLE. THERE WILL  
AGAIN BE A CHANCE FOR SHOWERS AND THUNDERSTORMS BOTH TUESDAY AND  
WEDNESDAY, PARTICULARLY DURING THE AFTERNOON AND EVENING HOURS, AS  
TROPICAL MOISTURE ASSOCIATED WITH REMNANTS OF BARRY ENTER THE  
REGION. POTENTIAL EXISTS FOR LOCALLY INTENSE RAINFALL RATES TO  
DEVELOP WITHIN ANY ACTIVITY GIVEN THE HIGH MOISTURE CONTENT. THIS  
COULD LEAD TO POOR DRAINAGE FLOODING OF SUSCEPTIBLE LOW LYING AND  
URBAN AREAS.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
 
LAKE HURON...SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EDT TUESDAY FOR LHZ421-422.  
 
LAKE ST CLAIR...NONE.  
 
MICHIGAN WATERS OF LAKE ERIE...NONE.  
 

 
 

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