030  
FXUS63 KDTX 292350  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
750 PM EDT TUE JUL 29 2014  
 
   
AVIATION
 
 
//DISCUSSION...  
 
COVERAGE OF PULSE TYPE SHOWERS AND THUNDERSTORMS ALREADY SHOWING A  
DIMINISHING TREND WHICH SHOULD CONTINUE THROUGH THE EVENING HOURS.  
EXPECT VFR CONDITIONS THROUGH THE TAF CYCLE WITH CIGS SCATTERING OUT  
THROUGH THE OVERNIGHT FOR MOST LOCATIONS. COULD SEE CIRRUS DEBRIS  
FROM UPSTREAM SYSTEM STREAM INTO THE AREA THROUGH THE NIGHT. AS THE  
SHOWERS DIMINISH...ATTENTION WILL TURN TO FOG POTENTIAL FOR THE  
EARLY MORNING HOURS. WITH CLOUDS DIMINISHING AND AMPLE MOISTURE AT  
THE SFC DUE TO RAINFALL...RADIATIONAL COOLING COULD PRODUCE SOME FOG  
BY MORNING. CLOUDS CLEARING FASTER AND EARLIER ACROSS THE NORTH WILL  
PUT MBS AT THE BIGGEST RISK TO SEE FOG...LESS CONFIDENT FOR FNT AND  
PTK. WILL INCLUDE A PERIOD OF MVFR VSBY FOR MBS AND MONITOR TRENDS  
FOR THE OTHER SITES AS WE BEGIN NIGHTFALL.  
 
FOR DTW...STILL A CHANCE FOR SOME SHOWERS THROUGH ABOUT 02Z AS  
UPSTREAM CONVECTION DRIFTS SOUTHEASTWARD THROUGH SUNSET. VFR  
CONDITIONS THROUGH TOMORROW MOST LIKELY UNLESS A SHOWER PASSES OVER  
THE SITE.  
 
//DTW THRESHOLD THREATS...  
 
* MEDIUM CONFIDENCE IN CEILING BELOW 5000 FEET IN SHOWERS DURING  
THE EVENING.  
 
* LOW CONFIDENCE IN CEILING BELOW 5000 FEET WEDNESDAY AFTERNOON.  
 
* LOW CONFIDENCE IN AN ISOLATED THUNDERSTORM THROUGH 03Z.  
 

 
   
PREV DISCUSSION
 
ISSUED 339 PM EDT TUE JUL 29 2014  
 
SHORT TERM... TODAY AND TONIGHT  
 
DIURNAL CLOUDS AND CONVECTION HAVE BEEN BLOSSOMING IN THE WAKE OF  
A BAND OF MID CLOUDS. THESE MID CLOUDS /ASSOCIATED WITH THE LEAD  
EDGE OF A PLUME OF HIGHER LOW-MID LEVEL MOISTURE/ WILL BE EXITING TO  
THE EAST OF THE AREA BY FORECAST ISSUANCE. THE COLD AIR ALOFT IS A  
RESULT OF AN ANOMALOUSLY DEEP UPPER TROUGH EXTENDING ACROSS THE ERN  
US. WITH 500MB TEMPS AROUND -17C OVER SE MI...MID LEVEL LAPSE RATES  
WILL REMAIN STEEP WELL INTO THE NIGHT. THE 19Z SURFACE ANALYSIS  
SHOWS A TROUGH AXIS EXTENDING FROM THE THUMB DOWN TO SOUTH-CENTRAL  
LOWER MI. MOISTURE POOLING ALONG THIS TROUGH HAS SENT SFC DEWPOINTS  
INTO THE MID TO UPPER 50S...RESULTING IN 0-1KM ML CAPE ON THE ORDER  
OF 500 J/KG. THE COMBINATION OF THIS WEAK INSTABILITY AND COLD AIR  
ALOFT WILL CONTINUE TO SUPPORT BRIEF SHOWERS/THUNDERSTORMS INTO THIS  
EVENING THAT WILL BE CAPABLE OF PRODUCING SMALL HAIL. THE SURFACE  
TROUGH WILL MOVE INTO THE ERN PORTIONS OF THE AREA /PORT HURON-  
DETROIT-MONROE/ BY 21Z. THUS SCATTERED-NUMEROUS CONVECTION IS  
EXPECTED TO CONTINUE DEVELOPING TOWARD THE EAST OVER THE NEXT COUPLE  
OF HOURS.  
 
THE LOSS OF DAYTIME HEATING DURING THE EVENING WILL LEAD TO A  
DIMINISHING TREND IN COVERAGE AND INTENSITY OF RESIDUAL CONVECTION.  
IN LIGHT OF WHAT WAS OBSERVED UPSTREAM YESTERDAY AND CONSIDERING THE  
STEEP MID LEVEL LAPSE RATES...THIS PROCESS SHOULD BE GRADUAL. THE  
REGIONAL WATER VAPOR IMAGE SHOWS A MID LEVEL SHORT WAVE IMPULSE OVER  
WRN LAKE SUPERIOR...EMBEDDED WITHIN THE NORTHWEST FLOW. THIS WAVE  
WILL TRACK ACROSS SW LOWER MI INTO NRN OHIO TONIGHT. SOME ADDED  
ASCENT ASSOCIATED WITH THIS FEATURE COUPLED WITH A RESIDUAL LOW  
LEVEL MOISTURE AXIS OVER FAR SRN MI WILL WARRANT A CHANCE OF  
LINGERING SHOWERS/ISOLATED THUNDERSTORMS INTO THE OVERNIGHT. THERE  
WILL BE SOME OPPORTUNITY FOR CLEARING TONIGHT...ESPECIALLY ACROSS  
THE SAGINAW VALLEY AND THUMB. WITH SURFACE DEWPOINTS HOLDING WELL IN  
THE 50S UP THROUGH THE NRN GREAT LAKES...THERE WILL BE A CHANCE OF  
SOME FOG LATE TONIGHT PREDICATED UPON THE DEGREE OF RADIATIONAL  
COOLING.  
 
LONG TERM...  
 
LARGE UPPER LEVEL LOW CENTERED OVER THE SOUTHERN END OF JAMES BAY  
WILL DRIFT SOUTHWEST...DROPPING INTO NORTHEASTERN ONTARIO BY  
THURSDAY MORNING.  
 
MULTIPLE SPOKES OF ENERGY/SHORTWAVE TROUGHS WILL BE ROTATING AROUND  
THE MAIN CIRCULATION...WITH ONE MOVING THROUGH NORTHERN LOWER  
MICHIGAN LATE TOMORROW/TOMORROW EVENING...AS 500 MB TEMPS FALL INTO  
THE NEGATIVE UPPER TEENS TO AROUND -20 C. THERE LOOKS TO BE A SHARP  
MOISTURE GRADIENT STRADDLING SOUTHERN LOWER MICHIGAN TOMORROW...AS  
SEEN IN 850-700 MB THETA-E FIELDS...AND THERE IS A QUESTION MARK ON  
HOW MUCH MOISTURE AND SUBSEQUENT INSTABILITY WILL BE AROUND TO  
SUPPORT SHOWERS AND ISOLATED THUNDERSTORMS...AS NAM IS THE MOST  
AGRESSIVE...BUT LATEST EURO HAS ALSO TRENDED MORE UNSTABLE. WITH THE  
FAVORABLE LATE DAY TIMING AND MAGNITUDE OF THE MID LEVEL COLD  
POOL...CERTAINLY THINK SCATTERED POPS (ESPECIALLY TOWARD OHIO  
BORDER) ARE WARRANTED WITH ISOLATED THUNDERSTORMS.  
 
THURSDAY LOOKS FAIRLY SIMILAR WITH ANOTHER PIECE OF UPPER LEVEL  
ENERGY ROTATING THROUGH....WITH TIMING SENSITIVITY. 30 KNOTS OF 0-6  
KM WIND SHEAR AND INVERTED V SOUNDING MAKES WIND A BIT OF A CONCERN  
IF ANY THUNDERSTORM IS IN FACT ABLE TO MATERIALIZE...AS WELL AS HAIL  
WITH MAX CAP DENSITY CENTERED AROUND FREEZING LEVEL. ONCE  
AGAIN...NAM IS INDICATING THE MOST INSTABILITY WITH UP TO 1500 J/KG  
OF CAPE.  
 
LOW LEVEL AIRMASS WILL BE SLOWLY MODIFYING AS 850 MB TEMPS GO FROM  
UPPER SINGLE NUMBERS WEDNESDAY (SUPPORTING HIGH IN THE LOWER 70S) TO  
LOWER TEENS ON THURSDAY (MID/UPPER 70S).  
 
THE LONGWAVE PATTERN WILL CONTINUE TO SLOWLY DEAMPLIFY OVER THE  
REMAINDER OF THE FORECAST PERIOD...BUT IT STILL LOOKS TO FEATURE A  
GENERAL RIDGE WEST/TROUGH EAST PATTERN...PRECLUDING ANY BIG  
WARM-UPS. UPPER TROUGH AXIS/COLD POOL WILL STILL BE OVERHEAD FRIDAY  
AND SATURDAY SO DIURNALLY ENHANCED SHOWERS WILL BE A POSSIBILITY AT  
LEAST THROUGH SATURDAY. TEMPERATURES ARE EXPECTED TO BE NEAR TO  
SLIGHTLY BELOW NORMAL INTO EARLY NEXT WEEK.  
 
MARINE...  
 
A COOL BUT LIGHT NORTHWEST WIND WILL PERSIST OVER LAKE HURON AND  
LOWER MICHIGAN THROUGH TOMORROW. THE WIND WILL REMAIN LIGHT THROUGH  
THE END OF THE WEEK AND TEND TO SHIFT TOWARD THE SOUTHWEST BY FRIDAY  
WITH INCREASING INFLUENCE OF WEAK HIGH PRESSURE BY THE WEEKEND.  
OTHERWISE THERE WILL BE A LOW CHANCE OF BRIEF SHOWERS AND ISOLATED  
THUNDERSTORMS...PRIMARILY NEAR THE SHORELINES OVER LAKE ST CLAIR AND  
WESTERN LAKE ERIE.  
 

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

 
 

 
 
AVIATION.....DRK  
SHORT TERM...SC  
LONG TERM....SF/DT  
MARINE.......SF  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab MI Page Main Text Page