270  
FXUS63 KDTX 301715  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
115 PM EDT TUE SEP 30 2014  
 
   
AVIATION
 
 
//DISCUSSION...  
 
FOR THE MOST PART DRIZZLE IS COMING TO AN END ACROSS SOUTHEAST  
MICHIGAN. HOWEVER...RECENT RADAR IMAGERY STILL IS SHOWING SOME  
SPOTTY DRIZZLE TRYING TO FORCE INTO THE REGION. THEREFORE...HAVE  
KEPT A TEMPO OF DRIZZLE IN THE FORECAST UNTIL 22Z. CEILINGS WILL  
REMAIN OVERCAST AND BELOW 2000 FEET THROUGH THE WEDNESDAY  
AFTERNOON AS LOW LEVEL MOISTURE CONTINUES TO FILTER ACROSS THE TAF  
SITES.  
 
FOR DTW...LINGERING DRIZZLE WILL BE POSSIBLE AT METRO THIS  
AFTERNOON. CURRENTLY EXPECTING THE CHANCE FOR DRIZZLE DEVELOPMENT TO  
END BY 22Z...HOWEVER LOW CLOUDS /BELOW 2000 FEET/ WILL STICK AROUND  
THROUGH WEDNESDAY MORNING.  
 
//DTW THRESHOLD THREATS...  
 
* HIGH PROBABILITY THAT CEILINGS WILL REMAIN BELOW 5000 FT THROUGH WEDNESDAY.  
 

 
   
PREV DISCUSSION
 
ISSUED 335 AM EDT TUE SEP 30 2014  
 
SHORT TERM...TODAY AND TONIGHT  
 
LOW LEVEL COLD AIR ADVECTION WILL PREVAIL THROUGH THE MORNING BEHIND  
THE SURFACE COLD FRONT WHICH EXITED THE FORECAST AREA SHORTLY AFTER  
06Z. LINGERING POST FRONTAL SHOWERS WILL EXIT TO THE SOUTHEAST OF  
THE STATE BEFORE DAYBREAK. THE SHOWERS OVERNIGHT DEVELOPED WITHIN A  
RIBBON OF STRONG LARGE SCALE ASCENT ALONG THE LEAD EDGE OF AN  
AMPLIFYING UPPER WAVE. RECENT WATER VAPOR IMAGERY ALREADY SHOWS THE  
EVOLUTION OF THIS SYSTEM INTO A CLOSED MID LEVEL LOW...WHICH IS  
FORECAST TO ROTATE ACROSS THE THUMB THIS MORNING AND INTO NE OHIO  
THIS AFTERNOON. THE ASSOCIATED SFC LOW...NOW LOCATED OVER SRN  
ONTARIO...WILL IN TURN TRACK INTO WRN PA/WV THIS AFTERNOON.  
 
RESIDUAL LOW LEVEL MOISTURE AND A DEEPENING POST FRONTAL INVERSION  
HAS LED TO A STRATUS DECK NOW EXTENDING ALL THE WAY TO SRN LAKE  
SUPERIOR. THIS INVERSION WILL ONLY DEEPEN DURING THE COURSE OF THE  
MORNING AS 925MB TEMPS FALL THROUGH THE SINGLE DIGITS. LOW CLOUDS  
WILL THUS REMAIN IN PLACE INTO AT LEAST LATE EVENING. THIS WILL  
LIMIT ANY DIURNAL RECOVERY AND HOLD DAYTIME TEMPS IN THE 50S. THE  
EVOLVING COMPACT MID LEVEL LOW WILL SUPPORT THE DEVELOPMENT OF AN  
ENHANCED REGION OF MID LEVEL DEFORMATION /TROWEL FEATURE/ TARGETING  
NRN/CNTL LAKE HURON AND NE LOWER MI. MODEL SOLUTIONS THEN INDICATE  
THIS FEATURE FALLING APART AS IT ADVANCES INTO SE MI TONIGHT AS THE  
UPPER LOW WEAKENS AND QUICKLY ADVANCES EAST. SO THE BETTER FORCING  
WILL REMAIN NORTH OF THE AREA TODAY. HOWEVER...MODEL SOUNDINGS ARE  
VERY SUPPORTIVE OF DRIZZLE TODAY /RADAR AND SFC OBS OVER NRN LOWER  
MI OVERNIGHT HAVE ALSO BEEN SHOWING A LOT OF DRIZZLE/. THIS IS DUE  
TO A MOIST BOUNDARY LAYER...LOW CLOUD BASES...SUBSTANTIAL DRY AIR  
ABOVE THE INVERSION...AND GOOD DIRECTIONAL SHEAR NEAR THE TOP OF THE  
MOIST LAYER. THE DRIZZLE IS EXPECTED TO BE QUITE WIDESPREAD OVER  
MUCH OF THE THUMB TODAY AS N-NW FLOW OVER LAKE HURON ADDS A LITTLE  
BETTER MOISTURE TO THE BOUNDARY LAYER AND ENHANCES CONVERGENCE ALONG  
THE SHORELINE.  
 
SFC RIDGING WILL BUILD ACROSS LOWER MI TONIGHT...WHILE ENHANCED  
THERMAL TROUGHING WILL RESIDE OVER LAKE HURON. THE FLOW ABOVE THE  
BOUNDARY LAYER WILL TURN TOWARD THE EAST WHICH WILL ACTUALLY SUPPORT  
SOME LOW LEVEL WARM AIR ADVECTION. THIS WILL WEAKEN /POSSIBLY EVEN  
ERODE/ THE LOW LEVEL INVERSION AND MAY SUPPORT SOME CLEARING ACROSS  
AT LEAST THE WRN PORTIONS OF THE AREA AS THE SFC HIGH BUILDS IN FROM  
THE NORTH. CLEARING POTENTIAL STILL HOWEVER CARRIES A LOW CONFIDENCE  
AS THE EASTERLY FLOW WILL ALSO ADVECT SOME HIGHER MOISTURE IN FROM  
THE EAST. SO FOG AND/OR ADDITIONAL STRATUS DEVELOPMENT SEEM  
POSSIBLE. THE POTENTIAL CLOUD COVER AND LOW LEVEL MOISTURE ADVECTION  
WILL WARRANT A LIMITED DROP IN TEMPS TONIGHT /LOWS FROM THE MID 40S  
TO LOW 50S/.  
 
LONG TERM...  
 
CONFIDENCE IS NOT VERY HIGH IN LOW CLOUDS SCOURING OUT COMPLETELY  
ON WEDNESDAY...AS NAM/GFS/GEM/EURO ALL SUGGESTING SOME 925-850 MB  
RESIDUAL MOISTURE UNDERNEATH THE MODEST UPPER LEVEL  
RIDGE...ESPECIALLY BACK ACROSS THE THUMB REGION. WITH JUST PARTIAL  
INSOLATION EXPECTED...LOOKING AT MAXES COMING UP JUST SHORT OF 70  
DEGREES. WE SHOULD HOWEVER HAVE NO PROBLEM CLIMBING INTO THE 70S ON  
THURSDAY AHEAD OF A COLD FRONT...WITH GOOD WARM ADVECTION ALLOWING  
925 MB TEMPS TO CLIMB INTO THE UPPER TEENS TO LOWER 20S PER 00Z  
EURO. HOWEVER...WITH INCREASING AND THICKENING CLOUDS...BACKED  
SOUTHEAST FLOW AT THE SURFACE...BOUNDARY LAYER MIXING WILL PROBABLY  
COME UP JUST SHORT OF 925 MB AND WILL HOLD MAXES IN THE MID TO  
UPPER 70S.  
 
WITH A VERY GOOD MOISTURE FEED...PW VALUES IN EXCESS OF 1.5  
INCHES...COUPLED WITH GOOD HEIGHT FALLS AND MODEST INSTABILITY  
THURSDAY NIGHT...RAIN SHOWERS CAN BE EXPECTED...WITH EVEN COLDER AIR  
ON TAP FOR THE WEEKEND AS UPPER LEVEL ENERGY OVER THE GULF OF ALASKA  
AND OFF THE COAST OF BRITISH COLUMBIA/PACIFIC NORTHWEST CONSOLIDATE  
OVER THE GREAT LAKES REGION...LEADING TO DEEP 500 MB LOW. IN  
FACT...THE LONGWAVE UPPER LEVEL TROUGH AXIS WILL BE ATTEMPTING TO GO  
SLIGHTLY NEGATIVE FRIDAY MORNING...WHICH IS YIELDING A SLOWER  
FRONTAL PASSAGE COMPARED TO LAST NIGHT...AND IT APPEARS SHOWERS WILL  
LIKELY LINGER INTO FRIDAY. COLD CYCLONIC FLOW AND 850 MB TEMPS  
FALLING BELOW ZERO OVER THE WEEKEND WILL LIKELY TRANSLATE TO AT  
LEAST SCATTERED LAKE ENHANCED SHOWERS AND MOSTLY CLOUDY SKIES...WITH  
FORECASTED 850 MB TEMPS OF -2 C YIELDING HIGHS ONLY IN THE LOW TO  
MID 50S ON SATURDAY.  
 
MARINE...  
 
A STRONG COLD FRONT WILL CLEAR THE CENTRAL GREAT LAKES THIS  
MORNING...WITH RELATIVELY SHORT LIVED WINDS OF 15 TO 20 KNOTS WITH  
GUSTS TO 25 KNOTS ACROSS CENTRAL AND SOUTHERN SECTIONS OF LAKE  
HURON. THIS WILL PROMPT AN INCREASE IN WAVE HEIGHTS...WITH HEIGHTS  
TOPPING OUT SLIGHTLY ABOVE 4 FEET OVER MUCH OF SOUTHERN LAKE  
HURON...AND THE PREVIOUS SMALL CRAFT ADVISORIES WILL CONTINUE  
THROUGH THE DAY. WINDS WILL DIMINISH BY TONIGHT AS HIGH PRESSURE  
BUILDS BACK INTO THE REGION...BUT THE NORTHEAST DIRECTION WILL  
MAINTAIN SOME MODEST WAVES OVER THE NEARSHORE WATERS. LIGHT WINDS  
AND LOW WAVES WILL PERSIST WEDNESDAY INTO THURSDAY.  
HOWEVER...SOUTHERLY WINDS DEVELOPING AHEAD OF A COLD FRONT LATE  
THURSDAY COULD RESULT IN WINDS UP TO 30 KNOTS OVER THE OPEN WATERS  
OF LAKE HURON THURSDAY NIGHT.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
 
LAKE HURON...  
SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS  
FROM PORT AUSTIN TO PORT SANILAC...UNTIL 6 PM TUESDAY.  
 
LAKE ST CLAIR...NONE.  
MI WATERS OF LAKE ERIE...NONE.  
 

 
 

 
 
AVIATION.....RK  
SHORT TERM...SC  
LONG TERM....SF  
MARINE.......SF  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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