976  
FXUS63 KDTX 200355  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
1155 PM EDT FRI SEP 19 2014  
 
   
AVIATION
 
 
//DISCUSSION...  
 
CONTINUED STRENGTHENING OF THE SOUTHERLY SFC GRADIENT AND THE ONSET  
OF DAYTIME HEATING LATER THIS MORNING WILL LEAD TO AN INCREASE IN  
THE WINDS. GUSTS ARE EXPECTED TO TOP 20 KNOTS DURING PEAK AFTERNOON  
HEATING. MID LEVEL MOISTURE ADVECTION ACROSS THE SAGINAW VALLEY THIS  
MORNING MAY LEAD TO SOME HIGH BASED SHOWERS AT MBS. CONFIDENCE IS  
NOT HIGH ENOUGH TO INCLUDE IN THE TAFS AT THIS TIME. STRONGER  
FORCING ALONG A SFC TROUGH WILL LEAD TO A MUCH BETTER CHANCE FOR  
SHOWERS AND A FEW THUNDERSTORMS LATE THIS AFTERNOON AND EVENING.  
 
FOR DTW...THE BETTER INSTABILITY IS FORECAST TO RESIDE MAINLY NORTH  
AND WEST OF METRO SAT AFTERNOON AND EVENING. THUS THE CHANCES FOR  
THUNDERSTORMS IMPACTING METRO DETROIT LATE IN THE FORECAST PERIOD  
ARE STILL LOW ATTM.  
 
//DTW THRESHOLD THREATS...  
 
* LOW CONFIDENCE IN THUNDERSTORM POTENTIAL FRIDAY AFTERNOON AND  
FRIDAY NIGHT.  
 

 
   
PREV DISCUSSION
 
ISSUED 1004 PM EDT FRI SEP 19 2014  
 
UPDATE...  
 
CONVECTION ACROSS THE STRAITS REGION HAS DEVELOPED ALONG THE NOSE  
OF A MID LEVEL THETA E RIDGE SURGING NORTHWARD...LIKELY ENHANCED  
WITHIN STRONGER S-SW FLOW OVER LAKE MI. FARTHER WEST OVER THE  
MN/WI BORDER...CONVECTION HAS BEEN GROWING UPSCALE THIS EVENING.  
THESE SHOWERS/TSTMS ARE OCCURRING IN ADVANCE OF A MID LEVEL TROUGH  
AXIS AND ARE WITHIN A MUCH MORE UNSTABLE ENVIRONMENT. THE MID LEVEL  
TROUGH WILL ADVANCE INTO NW LOWER MI TOWARD DAYBREAK SAT. THE MID  
LEVEL THETA E RIDGE WILL HOWEVER NUDGE INTO THE SAGINAW VALLEY AND  
NORTHERN THUMB BETWEEN 09Z AND 12Z. THIS ALONG WITH SOME MODEST  
MID LEVEL DESTABILIZATION WILL AT LEAST SUPPORT A CHANCE OF SOME  
LATE NIGHT/EARLY MORNING CONVECTION IN AND AROUND THE TRI CITIES  
AND NRN THUMB REGION. NO OTHER UPDATES WILL BE MADE TO THE  
FORECAST PACKAGE.  
 
PREV DISCUSSION...ISSUED 342 PM EDT FRI SEP 19 2014  
 
SHORT TERM...THIS AFTERNOON AND TONIGHT  
 
VERY PLEASANT WEATHER WILL HOLD THROUGH THE EVENING AS TEMPERATURES  
GRADUALLY DROP THROUGH THE 60S AS WE APPROACH SUNSET. THESE MILD  
TEMPERATURES WILL PERSIST OVERNIGHT AS THETA-E RIDGE IN ADVANCE OF  
APPROACH SHORTWAVE OVERSPREADS THE AREA. WITH THIS INCREASE IN  
MOISTURE AND OVERALL CLOUD COVER...RADIATIONAL COOLING POTENTIAL WILL  
BE GREATLY REDUCED. COMBINE THIS WITH STEADY WARM AIR ADVECTION AS  
SOUTHWEST FLOW INCREASING AFTER MIDNIGHT AND LOW TEMPERATURES WILL  
LIKELY HOLD IN THE 50S IN MOST...IF NOT ALL...LOCATIONS.  
 
WHILE SHOWER POTENTIAL WILL BE RATHER MEAGER DURING THE PRE-12Z TIME  
FRAME...WILL MAINTAIN A SLIGHT CHANCE FOR THE FAR NORTH TO NORTHWEST  
CWA AS MOISTURE/LIFT GRADUALLY INCREASE WITH THE APPROACH OF THE  
AFOREMENTIONED TROUGHING.  
 
LONG TERM...  
 
UPPER AIR PATTERN WILL CONTINUE TO AMPLIFY SATURDAY THANKS TO A  
130KT JET STREAK DIGGING INTO THE MN/DAKOTAS REGION. COLUMN MOISTURE  
WILL INCREASE MARKEDLY AS THE MOISTURE PLUME NOW EXTENDING INTO THE  
NORTHERN PLAINS/SOUTHERN CANADA FOLDS EASTWARD. PWATS WILL INCREASE  
TO 1.5-1.75 IN...NEAR +2SD FOR SEPTEMBER. LARGE SCALE FORCING FOR  
ASCENT WILL INCREASE DURING THE DAY AS BETTER HEIGHT FALLS APPROACH  
THE REGION. ADDITONALLY...ANOTHER JET STREAK DOWNSTREAM OF THE  
TROUGH AXIS WILL STRENGTHEN DURING THE DAY...WITH ASSOCIATED RIGHT  
ENTRANCE REGION FORCING TRANSLATING THROUGH THE AREA. THIS SETUP  
SHOULD SUPPORT SHOWERS INCREASING TO SCATTERED TO NUMEROUS COVERAGE  
BY THE AFTERNOON.  
 
H5 WINDS OF AROUND 50 KT WILL SUPPORT BULK SHEAR VALUES AROUND 40  
KT...MORE THAN ENOUGH TO WORRY ABOUT ORGANIZED CONVECTION AND SEVERE  
WEATHER. LOW LEVEL JET WILL ALSO PEAK AROUND 30-40 KT DURING THE  
AFTERNOON. LIMITING FACTOR TO SEVERE WEATHER...AND THUNDERSTORMS IN  
GENERAL...IS INSTABILITY. A GOOD COVERAGE OF CLOUDS IS  
EXPECTED...WHICH WILL DIMINISH MIXING DEPTHS AND MUTE THE SURFACE  
TEMPERATURE RESPONSE DESPITE 925 MB TEMPS REACHING THE UPPER TEENS.  
LOW-LEVEL CAPPING BECOMES A CONCERN AS WELL. MIDLEVEL LAPSE RATES  
INCREASE SOMEWHAT...BUT ARE NOT TERRIBLY IMPRESSIVE AT AROUND 6.5  
K/KM. ANOTHER LIMITING FACTOR FOR DEEP CONVECTION WILL BE THE LACK  
OF ANY WELL-DEFINED BOUNDARY/SURFACE CONVERGENCE...AS THE MAIN COLD  
FRONT WITH THIS SYSTEM WILL LAG BACK OVER NORTHERN LOWER MI/WI. WITH  
SURFACE TEMPS IN THE 75-80F RANGE...AND DEWPOINTS INCREASING INTO  
THE LOWER/MID-60S...AND THE AFOREMENTIONED LIMITING FACTORS...IT  
LOOKS LIKE WE WILL STAY IN THE 500-750 J/KG MLCAPE RANGE. CANNOT  
RULE OUT A FEW STORMS APPROACHING SEVERE LIMITS GIVEN THE SHEAR  
EXPECTED...BUT WIDESPREAD SEVERE EVENT APPEARS UNLIKELY.  
 
MAINTAINED CHANCE POPS SATURDAY NIGHT AS MOISTURE LINGERS AND  
FORCING ASSOCIATED WITH THE INBOUND NOSE OF THE UPPER JET AND  
IMPRESSIVE PV ANOMALY INCREASES LATE. RAISED POPS SUNDAY TO LIKELY AS THE  
CORE OF THE MIDLEVEL COLD POOL /-21C AT H5/ MIGRATES OVER THE LOCAL  
AREA DURING PEAK HEATING. AREA BUFR SOUNDINGS INDICATE UNCAPPED  
PROFILES DEVELOPING WITH MLCAPE VALUES IN THE 500-1000 J/KG RANGE.  
THIS SHOULD AGAIN SUPPORT THE DEVELOPMENT OF SCATTERED TO NUMEROUS  
SHOWERS AND A FEW THUNDERSTORMS...WITH SOME SMALL HAIL POSSIBLE IN  
THE MORE VIGOROUS UPDRAFTS GIVEN FREEZING LEVELS DROPPING TO AROUND  
8KFT. MODELS DIFFER WITH HOW AGGRESSIVELY THE ANTICYCLONE BUILDS  
INTO THE UPPER MIDWEST IN THE WAKE OF THIS SYSTEM SUNDAY NIGHT...BUT  
PRECIPITATION SHOULD BE ON THE WANE SUNDAY EVENING WITH THE LOSS OF  
DAYTIME HEATING.  
 
THE WORK WEEK WILL START OFF QUITE COOL WITH LOW THETA E VALUES  
INDICATING A COOL AND DRY AIRMASS. SURFACE HIGH PRESSURE WILL SLIDE  
EAST...HELPING RETURN FLOW START TO WARM THE COLUMN BOTH TUES AND  
WED. THIS WILL BRING NORMAL TEMPERATURE VALUES BACK TO THE AREA.  
FLOW REMAINS RATHER WEAK...AND WE BECOME QUITE STAGNANT ALOFT BY THE  
END OF THE PERIOD. THE LACK OF ANY UPPER WAVES OR MOISTURE ADVECTION  
WILL KEEP A DRY FORECAST INTACT FOR THE EXTENDED FORECAST PERIOD.  
 
MARINE...  
 
SOUTHWEST FLOW WILL CONTINUE TO INCREASE TONIGHT INTO SATURDAY.  
DESPITE THE WARM AIR WITH THIS SYSTEM...GUSTY WINDS WILL DEVELOP  
GIVEN THE STRENGTH OF THE WIND FIELD AT LOW LEVELS OF THE  
ATMOSPHERE. SHOWERS AND THUNDERSTORMS WILL ACCOMPANY THE WARMER AIR  
SATURDAY AND SATURDAY NIGHT...WITH ADDITIONAL ACTIVITY EXPECTED  
DURING THE DAY SUNDAY AS UPPER LEVELS COOL AND UNSTABLE CONDITIONS  
DEVELOP. SOME SHOWERS MAY LINGER INTO SUNDAY NIGHT ALONG WITH A  
RENEWED INCREASE IN WINDS BEFORE HIGH PRESSURE EXERTS MORE OF AN  
INFLUENCE ON THE WATERS TO BEGIN NEXT WEEK.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...NONE.  
 
LAKE HURON...  
SMALL CRAFT ADVISORY...SAGINAW BAY AND THE NEARSHORE WATERS FROM  
PORT AUSTIN TO HARBOR BEACH...UNTIL 8 PM SATURDAY.  
 
LAKE ST CLAIR...NONE.  
MI WATERS OF LAKE ERIE...NONE.  
 

 
 

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