611  
FXUS63 KDTX 200757  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
357 AM EDT WED AUG 20 2014  
   
SHORT TERM
 
TODAY AND TONIGHT  
 
SHOWERS AND THUNDERSTORMS HAVE TRACKED EAST AS A COLD FRONT HAS  
SWEPT THROUGH THE CENTRAL GREAT LAKES. HOWEVER THIS COLD FRONT WILL  
NOT BRING MUCH RELIEF WITH REGARDS TO MOISTURE AS DEW POINTS ARE  
STILL IN THE LOWER TO MIDDLE 60S. THE LACK OF DRY AIR BEHIND THE  
FRONT AND FAIRLY CALM WINDS BRINGS WITH IT THE POTENTIAL FOR FOG  
ACROSS THE AREA. LINGERING CLOUDS SHOULD DELAY THE ONSET OF FOG  
FORMATION...WITH AREAS TO THE EAST PROBABLY NOT GOING DOWN UNTIL  
AROUND SUNRISE. ALTHOUGH THERE ARE EXPECTED TO BE AREAS OF DENSE FOG  
THIS MORNING...IT IS NOT EXPECTED TO BE WIDESPREAD ENOUGH TO WARRANT  
A DENSE FOG ADVISORY AT THIS POINT. HOWEVER IF VISIBILITIES DROP  
SIGNIFICANTLY WILL ISSUE THE APPROPRIATE HEADLINES AS NEEDED. THE  
LINGERING MOISTURE MAY STILL SPARK OFF SOME LIGHT SHOWER ACTIVITY  
EARLY THIS MORNING AS A RIBBON OF HIGH LOW LEVEL THETA-E AIR REMAINS  
OVER SOUTHEAST MICHIGAN.  
 
DAYTIME HEATING WILL ONCE AGAIN CAUSE AN UNSTABLE ATMOSPHERE AS IT  
COMBINES WITH A STILL MOIST BOUNDARY LAYER TO PRODUCE MUCAPES OF  
1500 TO 2000 J/KG. THIS SHOULD ONCE AGAIN SPARK OFF THUNDERSTORMS  
ACROSS THE AREA AS THE MID LEVEL LOW PRESSURE SYSTEM TRACKS THROUGH  
THE SOO TODAY. HOWEVER UNLIKE YESTERDAY 0-6KM BULK SHEAR VALUES WILL  
BE MUCH WEAKER AT AROUND 20 KNOTS...MAKING THE THREAT FOR SEVERE  
WEATHER MUCH LOWER. STORMS TODAY MAY PRODUCE WIND GUSTS UP OF 40 TO  
50 MPH WITH HAIL AROUND ONE HALF OF AN INCH UP TO DIME SIZE WITH THE  
STRONGEST STORMS.  
 
ALTHOUGH THE MID LEVEL LOW WILL REMAIN OVER LAKE HURON  
OVERNIGHT...RAIN CHANCES WILL DROP OFF WITH THE LOSS OF DAYTIME  
HEATING. RAIN SHOULD BE CONFINED TO THE AREAS NEAR THE LOW WHICH  
WILL BE THE THUMB REGION...WITH CHANCES CREEPING IN ACROSS THE  
EXTREME SOUTHERN CWA LATE TONIGHT AS A QUICK MOVING SHORTWAVE TRACKS  
THROUGH THE SOUTHERN GREAT LAKES.  
 

 
   
LONG TERM
 
 
A LONGWAVE AMPLIFIED RIDGE AXIS WILL BUILD AGGRESSIVELY INTO  
NORTHEASTERN NORTH AMERICA DURING THE NEXT 48 HOURS. IT GOES WITHOUT  
SAYING...BUT AN EXTREMELY ATYPICAL EVENT FOR THIS SUMMER. WHAT THIS  
WILL DO IS ESSENTIALLY THROW A CURVE BALL TO THE LOCAL WEATHER  
PATTERN...LIKELY BRINGING IN THE LARGEST RUN OF SUMMER WARMTH THIS  
REGION HAS SEEN ALL SEASON LONG. BEFORE THIS CAN REALLY BECOME  
ESTABLISHED DURING THE LATTER HALF OF THE WEEKEND...SOUTHEASTERN  
MICHIGAN WILL HAVE TO CONTEND WITH AN INTERNAL RIDGE STRUCTURE AND  
SECONDARY JET CORE. IT IS THIS SECONDARY JET OVERHEAD THAT WILL  
DIRECT SHORTWAVE ENERGY AND POTENTIAL RIDGE RIDER TYPE MCS INTO THE  
AREA LIKELY ANYTIME THROUGH SATURDAY. AN ACTIVE PERIOD IS IN STORE  
THROUGH THE END OF THE WEEK.  
 
THURSDAY...A LOWER GEOPOTENTIAL HEIGHT ANOMALY WILL BUILD OFF OF  
LAKE HURON AND INTO THE NORTHEASTERN UNITED STATES DURING THE DAY ON  
FRIDAY. IT IS THE COMBINATION OF THIS ACTION AND AN UPPER LEVEL JET  
CORE CRESTING THE RIDGE AXIS OVER THE PLAINS/NORTHERN MISSISSIPPI  
RIVER VALLEY THAT THAT WILL FREEZE THE HEIGHT PATTERN OVER LOWER  
MICHIGAN. QUITE THE GRADIENT IN TEMPERATURES IS EXPECTED WITH A  
STATIONARY FRONTAL BOUNDARY DRAPED FROM PORTIONS OF OHIO  
NORTHWESTWARD TO CENTRAL LOWER MICHIGAN NW TO PORTIONS OF THE U.P.  
THE FRONTAL BOUNDARY IS NOT EXPECTED TO MOVE MUCH KEEPING THE HEAT  
TO THE SOUTHWEST. MODELS KEEP THE BULK OF THE CWA DRY...ALTHOUGH THE  
FRONTAL BOUNDARY WILL BRING THE POTETNIAL FOR SHOWERS AND  
THUNDERSTORMS PARTICULALRY SOUTH AND WEST OF M 59. TEMPERATURE  
SHOULD TICK ABOVE THE 80 DEGREE MARK FOR MANY AREAS.  
 
THE AFORMENTIONED 300MB JETLET IS FORECASTED TO CREST THE RIDGE  
THURSDAY EVENING AND SLIDE DIRECTLY INTO SOUTHEASTERN MICHIGAN  
THURSDAY NIGHT/FRIDAY MORNING. MODELS ARE EXTREMELY NOISY...BUT  
OVERALL THERE IS A VERY GOOD SIGNAL THAT AN MCS COULD BUILD ACROSS  
THE NORTHERN MISSSIPPI RIVER VALLEY THURSDAY AND RELEASE TOWARDS THE  
AREA THURSDAY NIGHT. ALOT OF TIME TO FIGURE THIS OUT...BUT DEGREE OF  
INSTABILITY IMMEDIATELY TO THE SOUTH DUE TO STRONG LAPSE RATES ALOFT  
COULD LEAD TO SEVERE WEATHER RISK FRIDAY MORNING. ONE THING TO  
MONIOR IS THE MCS WILL LIKELY ORGANIZED/INTENSIFY IN AN AREA OF  
STRONG LEFT EXIT REGION DYNAMICS. THE OVERALL SYSTEM IS THEN SHOWN  
TO OUTRUN THE UPPER LEVEL JET SUPPORT BY DIVING TO THE SOUTH.  
 
FRIDAY...FRIDAY IS A DIFFICULT FORECAST PERIOD. WILL LIKELY NEED TO  
COMBAT SUBSIDENCE AND MIDLEVEL LATENT HEATING LEFTOVER FROM THE MCS  
IMPACTING THE REGION. UPPER LEVEL JET CORE WILL MAINTAIN ENOUGH  
INTEGRITY TO BRING PESKY SHORTWAVE ENERGY INTO PLAY. MODELS SUPPORT  
ADVECTING HIGH THETA E INTO THE STATE ENOUGH FOR WHAT COULD END UP  
TO BE A VERY HIGH CAPE SETUP.  
 

 
   
MARINE
 
 
A WEAK AREA OF LOW PRESSURE WILL SLIDE ACROSS LOWER MICHIGAN TODAY  
BRINGING A WEAK SOUTHEASTERLY WIND TO MANY AREAS. A SECOND WEAK AREA  
OF LOW PRESSURE WILL PUSH INTO THE NORTHERN GREAT LAKES ON  
FRIDAY...MAINTAINING A RATHER SIZABLE SURFACE TROUGH STRUCTURE OVER  
THE GREAT LAKES REGION. OUTSIDE OF CONTINUAL SHOWER AND THUNDERSTORM  
CHANCES...AN EXTENDED STRETCH OF MARINE WEATHER IS ANTICIPATED.  
 

 
   
AVIATION
 
ISSUED 1207 AM EDT WED AUG 20 2014  
 
//DISCUSSION...  
 
UPPER LEVEL LOW PRESSURE SPINNING OVER THE GREAT LAKES WILL SUPPORT  
SCATTERED THUNDERSTORM COVERAGE DURING THE EARLY MORNING. THE LATEST  
RADAR TREND INDICATES FNT AND THE DTW CORRIDOR MOST LIKELY TO  
AFFECTED IN THE 06-09Z TIME WINDOW. IN BETWEEN AND AFTER...VARYING  
AMOUNTS OF MID AND HIGH CLOUDS WILL ALLOW ENOUGH BOUNDARY LAYER  
COOLING FOR FOG DEVELOPMENT. IFR CONDITIONS WILL INITIALLY CONSIST OF  
STRATUS BUT THEN COMBINE WITH FOG THROUGH MID WEDNESDAY MORNING AS  
THE UPSTREAM SURFACE LOW DRIFTS INTO NORTHERN LOWER MICHIGAN. A  
TYPICAL CYCLE OF CEILING AND VISIBILITY IMPROVEMENT WILL THEN BE  
ACCOMPANIED BY INCREASING SHOWER COVERAGE WITH DAYTIME HEATING  
DURING THE AFTERNOON INTO WEDNESDAY EVENING.  
 
//DTW THRESHOLD THREATS...  
 
* HIGH CONFIDENCE IN CEILING AOB 5000 FT THROUGH MORNING.  
 
* MEDIUM CONFIDENCE IN THUNDERSTORM COVERAGE AND TIMING.  
 
* LOW CONFIDENCE IN CEILING AOB 200 FT/VISIBILITY 1/2SM AROUND  
SUNRISE.  
 

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

 
 

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