218  
FXUS63 KDTX 301105  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
705 AM EDT SAT JUL 30 2016  
   
AVIATION
 
 
BETTER COVERAGE OF SHOWERS AND THUNDERSTORMS TODAY ACROSS  
SOUTHEAST MICHIGAN WILL WARRANT VICINITY SHOWERS FOR MUCH OF THE  
DAY. LONGEST AND MOST PERSISTENT SHOWERS EXPECTED ACROSS MBS  
DURING THE MORNING WHILE A PROB30 GROUP FOR THUNDERSTORMS IS IN  
THE FORECAST LATE THIS AFTERNOON FOR FARTHER SOUTH LOCATIONS.  
OUTSIDE OF THIS ACTIVITY, LOOKING AT CEILINGS AT OR MOSTLY ABOVE  
5000 FEET. SCATTERED SHOWER ACTIVITY IS EXPECTED TO PERSIST  
TONIGHT (DID NOT INCLUDE IN TAFS DUE TO COVERAGE CONCERNS), BUT IF  
CLOUDS BREAK UP, FOG WILL BECOME LIKELY. CONFIDENCE IS SHAKY WITH  
THIS SCENARIO, BUT WILL INCLUDE LIGHT (MVFR) FOG DEVELOPMENT FOR  
NOW.  
 
FOR DTW...DIURNAL HEATING SHOULD LEAD TO ADDITIONAL SHOWERS AND  
POSSIBLE THUNDERSTORMS TODAY. TIMING REMAINS DIFFICULT TO DETERMINE.  
CONTINUED LIGHT NORTHEAST WINDS DURING THE DAY, BECOMING LIGHT AND  
VARIABLE LATE TONIGHT.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* LOW IN THUNDERSTORMS AND CEILINGS AOB 5000 FEET.  
 

 
   
PREV DISCUSSION
 
 
ISSUED AT 405 AM EDT SAT JUL 30 2016  
 
DISCUSSION...  
 
PERSISTENT MID LEVEL DEFORMATION REMAINS IN PLACE OVER LOWER  
MICHIGAN EARLY THIS MORNING. LEFT OVER FROM YESTERDAY, IT IS NOW  
GETTING A BOOST FROM AN UPPER WAVE SLIDING EASTWARD FROM THE SOUTH  
END OF LAKE MICHIGAN. EARLY MORNING OBSERVATIONAL DATA INDICATES  
EXPANSION OF ELEVATED CONVECTION OVER LOWER MICHIGAN OCCURRING  
WITHIN THE MID LEVEL THETA-E RIDGE ANALYZED ROUGHLY ALONG THE I-69  
CORRIDOR AT 00Z. THERE IS LOOSE MODEL AGREEMENT THAT INDICATES THE  
MOISTURE AXIS WILL SHIFT NORTHWARD DURING THE REMAINDER OF THE  
MORNING AS THE UPPER WAVE MOVES FROM THE SOUTH END OF LAKE MICHIGAN  
EASTWARD ALONG THE OHIO BORDER. THIS SHOULD FAVOR THE TRI CITIES AND  
THUMB REGION FOR LIKELY/NUMEROUS POP COVERAGE DURING THE SHORT TERM  
BUT PLAN TO BROADEN HIGHER POPS SOUTHWARD TOWARD THE M-59 CORRIDOR  
AS WELL TO ACCOUNT FOR POTENTIAL OF ENHANCED FORCING NEAR THE MID  
LEVEL DRY SLOT INTERFACE. CONVECTIVE TRENDS IN THIS SCENARIO REMAIN  
DIFFICULT TO PIN DOWN AS CLUSTERS OF SHOWERS/STORMS WILL NOT BE WELL-  
BEHAVED WITHIN THE LARGER SCALE PATTERN. THE GENERAL WEST TO EAST  
ORIENTATION OF THE MOISTURE AXIS AND WEST TO EAST CELL MOTION WILL  
KEEP LOCALLY HEAVY RAINFALL AS THE PRIMARY HAZARD THROUGH THE  
MORNING.  
 
THE TRANSITION TO SURFACE BASED CONVECTION WILL TAKE PLACE AS  
DIURNAL HEATING PEAKS DURING THE LATE AFTERNOON. THIS WILL SHIFT THE  
HIGHER CONCENTRATION OF CONVECTION TOWARD THE OHIO BORDER CLOSER TO  
THE SURFACE LOW. THE SURFACE LOW AND FRONTS WILL REMAIN SOUTH OF THE  
BORDER BUT THE TENDENCY FOR INVERTED TROUGHINESS EXTENDING NORTHWARD  
INTO LOWER MICHIGAN WILL HELP WITH LOW LEVEL CONVERGENCE. THE  
GENERAL CONSENSUS OF MESOSCALE MODELS (HRRR, NMM, ARW, 4KM NAM)  
INDICATES SURFACE BASED CAPE BUILDING INTO THE 1500-2000 J/KG RANGE  
AS FAR NORTH AS THE M-59 CORRIDOR BUT MOSTLY I-96/696 SOUTHWARD.  
GIVEN THE WEAK WIND PROFILE, EXPECT CONVECTIVE MODE SIMILAR TO  
YESTERDAY WHICH TURNED OUT TO BE PULSE-TYPE, SLOW-MOVING MULTICELL  
CLUSTERS PRONE TO HEAVY RAINFALL. MEASURES OF DEEP MOISTURE REMAIN  
HIGH AS PW IS PROJECTED AROUND 1.7 INCHES WITH 700 MB DEWPOINT  
AROUND 3C. THE WPC DAY 1 SLIGHT RISK AREA FOR EXCESSIVE RAINFALL  
SEEMS REASONABLY PLACED OVER THE SOUTH 1/2-1/3 OF SE MICHIGAN AND  
WITHIN THE SPC DAY 1 GENERAL THUNDER OUTLOOK. THE DIFFICULTY IN  
PINNING DOWN CONVECTIVE TRENDS PRECLUDES LONGER FUSED HEADLINE  
ISSUANCE AT THIS POINT BUT SHORT FUSED ISSUANCES MAY BE NEEDED  
AGAIN DURING LATE AFTERNOON INTO EARLY EVENING.  
 
THE UPPER WAVE MOVING INTO THE NORTHERN PLAINS DURING THE EARLY  
MORNING WILL BE THE CULPRIT IN DELAYING THE EXIT OF THIS UNSETTLED  
PATTERN DURING SUNDAY. THE COLLECTIVE OUTPUT AMONG THE 00Z MODELS  
SUGGEST THIS FEATURE WILL SLIDE OVER ABOUT THE SAME REGION AS  
TODAY'S WAVE AND BOTH FEED OFF AND REINFORCE THE LOW TO MID LEVEL  
MOISTURE AXIS. THE ECMWF REMAINS MORE PROGRESSIVE THAN THE NAM, GFS,  
AND GEM AND WOULD CONFINE CHANCE POPS TO THE MORNING WHILE THE OTHER  
MODELS ARE SLOWER AND MORE INTENSE WITH THE OCCLUSION. DEFINITELY  
TRENDED THE SUNDAY FORECAST MORE PESSIMISTIC IN THIS PACKAGE TO  
BUILD IN THE TREND FOR UPCOMING MODEL CYCLES.  
 
THE SHORT WAVE RIDGE TRAILING THE SUNDAY WAVE WILL SUPPORT SURFACE  
HIGH PRESSURE SLIDING INTO THE GREAT LAKES DURING MONDAY WHICH WILL  
THEN LAST THROUGH ABOUT MID WEEK. THE SURFACE HIGH IS PROJECTED TO  
PRODUCE WARM TEMPERATURES FOR THE START OF AUGUST BUT WITH LOWER  
HUMIDITY. THERE ARE SIGNALS FOR A ROUND OF MCS TYPE ACTIVITY NEARBY  
TO OUR WEST DURING THE SECOND HALF OF THE WEEK AND POSSIBLY THE NEXT  
FRONT DUE IN LOWER MICHIGAN BY NEXT FRIDAY.  
 
MARINE...  
 
NORTHEAST WINDS HOLDING AROUND 20 KNOTS OVER CENTRAL AND SOUTHERN  
LAKE HURON THROUGH TODAY WILL MAINTAIN ELEVATED WAVE HEIGHTS IN THE  
NEARSHORE WATERS. SMALL CRAFT ADVISORIES HAVE BEEN REISSUED THROUGH  
THIS EVENING. NORTHEAST WINDS WILL DECREASE TO AROUND 10 KNOTS OVER  
THE REMAINDER OF THE WEEKEND INTO EARLY NEXT WEEK, ALLOWING FOR  
SIGNIFICANT WAVE LESS THAN 4 FOOT RANGE.  
 
HYDROLOGY...  
 
A BETTER COVERAGE OF SHOWERS (SCATTERED-NUMEROUS) AND A FEW  
THUNDERSTORMS ARE EXPECTED TODAY OVER SOUTHEAST MICHIGAN, BUT STILL  
NOT WIDESPREAD. NONE-THE-LESS, THE STRONGER SHOWERS AND  
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL IN EXCESS  
OF HALF AN INCH WITHIN AN HOUR, WITH ISOLATED CELLS PRODUCING 1 INCH  
OR GREATER NOT OUT OF THE QUESTION DUE TO THE SLOW MOVEMENT.  
LOCALIZED URBAN FLOODING WILL BE POSSIBLE. ACTIVITY WILL PERSIST  
TONIGHT, BUT IN A WEAKENING STATE WITH THE LOSS OF DAYTIME HEATING.  
ANOTHER ROUND OF SCATTERED ACTIVITY EXPECTED ON SUNDAY.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...BEACH HAZARDS STATEMENT THROUGH THIS EVENING FOR MIZ048-049-055-063.  
 
LAKE HURON...SMALL CRAFT ADVISORY UNTIL 10 PM EDT THIS EVENING FOR LHZ421-422-  
441>443.  
 
LAKE ST CLAIR...NONE.  
 
MICHIGAN WATERS OF LAKE ERIE...NONE.  
 

 
 

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