487  
FXUS63 KDTX 210350  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
1150 PM EDT SUN APR 20 2014  
 
   
AVIATION
 
 
//DISCUSSION...  
 
SKIES REMAIN CLEAR BELOW 10KFT TONIGHT AND MONDAY GIVEN THE  
EXISTENCE OF A VERY DRY LOW LEVEL ENVIRONMENT. A LIGHT SOUTH TO  
SOUTHEAST WIND TONIGHT WILL VEER TO SOUTHWEST WHILE INCREASING INTO  
THE 10 KNOT RANGE ON MONDAY. THE ARRIVAL OF A FRONTAL BOUNDARY WILL  
BRING AN INCREASING CHANCE FOR SHOWERS IN LOWER CEILINGS MONDAY  
EVENING/NIGHT. ISOLATED POTENTIAL FOR THUNDERSTORMS...PROBABILITY  
TOO LOW TO INCLUDE A MENTION AT THIS TIME.  
 
//DTW THRESHOLD THREATS...  
 
* NONE  
 

 
   
PREV DISCUSSION
 
ISSUED 354 PM EDT SUN APR 20 2014  
 
SHORT TERM...TODAY AND TONIGHT  
 
VERY DRY NEAR SURFACE AIR REMAINS IN PLACE OVER SOUTHEASTERN  
MICHIGAN THIS AFTERNOON EVIDENCED BY SURFACE DEWPOINTS THAT HAVE  
FALLEN DOWN INTO THE 20S AT MANY LOCATIONS. THE 20.12Z KDTX SOUNDING  
SHOWED THE DEPTH OF THIS DRY AIR TO BE SIGNIFICANT...FROM THE  
SURFACE THROUGH 11 KFT AGL. GEOPOTENTIAL HEIGHT SETTLING IS  
FORECASTED TO OCCUR AT A BROAD WAVELENGTH WHICH WILL ALLOW THE  
FRONTAL BOUNDARY BLOCKED TO THE NORTH...TO SETTLE SLIGHTLY  
SOUTHWARD. IT REMAINS POSSIBLE THAT SOME VIRGA OR ENHANCED MIDLEVEL  
CLOUD COULD BRUSH BAY/MIDLAND COUNTIES...ESPECIALLY BETWEEN THE  
01-06Z TIMEFRAME. KEPT A SLIGHT CHANCE OF PRECIPITATION IN THE  
FORECAST TO ACCOUNT FOR THIS. OTHERWISE...LOW DEWPOINTS AND  
PERSISTENT RIDGING SUGGESTS TEMPERATURES TONIGHT SHOULD COOL...WITH  
A MAX/MIN DIFFERENCE OF ROUGHLY 25 DEGREES. FORECASTED LOWS TONIGHT  
ARE EXPECTED IN THE LOWER INTO THE 40S IN THE FAR EASTERN SECTIONS  
OF THE CWA...WITH UPPER 40S TO NEAR 50 WEST.  
 
LONG TERM...MONDAY THROUGH NEXT SUNDAY  
 
DEEPENING OF THE MID LEVEL TROUGH APPROACHING THE WEST COAST ON  
MONDAY WILL LEAD TO AN OVERALL AMPLIFICATION IN THE DOWNSTREAM  
HEIGHT FIELD HEADING INTO MID WEEK. STRONG AGREEMENT IS NOTED AMONG  
THE 12Z MODEL SUITE IN SHOWING WEAK SFC LOW PRESSURE DEVELOPMENT  
OVER THE UPPER MS VALLEY ON MONDAY IN ADVANCE OF A MID LEVEL WAVE  
TRACKING ALONG THE US/CANADIAN BORDER. MEANWHILE...THE MID LEVEL  
CIRCULATION NOW OVER THE SRN HIGH PLAINS WILL LIFT INTO THE OHIO  
VALLEY ON MONDAY. THIS WILL FORCE WEAK MID LEVEL SHORT WAVE RIDGING  
OVER SE MI INTO EARLY TO MID AFTERNOON ON MON DESPITE THE WEAKENING  
OF THIS SYSTEM. OBSERVATIONS ACROSS THE REGION SUGGEST ONLY A NARROW  
RIBBON OF DEEP LAYER MOISTURE PRESENT ALONG THE RESIDUAL FRONTAL  
BOUNDARY NOW EXTENDING FROM NRN IOWA TROUGH THE STRAITS REGION.  
ENHANCED LOW LEVEL S-SW FLOW IN ADVANCE OF THE APPROACHING SFC LOW  
AND THE EXPECTED MID LEVEL RIDGING SHOULD HOLD THIS RIBBON OF  
MOISTURE NORTH OF THE FORECAST AREA WELL INTO MON AFTERNOON. IN  
LIGHT OF REGIONAL OBSERVATIONS...THE GFS APPEARS SIGNIFICANTLY TOO  
BULLISH ON TIMING THE LOW LEVEL MOISTURE INTO SE MI. THUS THE  
NAM/CANADIAN/ECMWF WHICH HOLD THE ARRIVAL OF THE DEEPER MOISTURE AND  
THUS PRECIP CHANCES LATER INTO THE AFTERNOON/EVENING APPEAR  
REASONABLE. THE LACK OF LOW LEVEL MOISTURE AND GOOD S-SW FLOW SHOULD  
THEN ENABLE FAIRLY DEEP MIXING DEPTHS INTO MON AFTERNOON...  
SUPPORTIVE OF HIGH TEMPS WELL INTO THE 70S.  
 
THE SFC LOW IS EXPECTED TO TRACK INTO NRN LOWER MI BY MON EVENING.  
INCREASING MOISTURE CONVERGENCE ALONG THE ASSOCIATED SFC FRONT AND  
WEAK INSTABILITY WILL PROVIDE INCREASING CHANCES FOR SHOWERS  
/ISOLATED THUNDER/ LATE IN THE DAY. AMPLIFICATION OF THE MID LEVEL  
WAVE TRACKING ACROSS THE NRN GREAT LAKES MON NIGHT WILL STRENGTHEN  
THE MAGNITUDE OF THE DOWNSTREAM UPPER JET MAX. THE ENHANCED RESPONSE  
WITHIN THE ENTRANCE REGION OF THIS JET WILL INVOKE A DEEPER FRONTAL  
CIRCULATION OVER THE FORECAST AREA MON NIGHT. THIS SHOULD RESULT IN  
AN INCREASE IN COVERAGE OF SHOWERS AFTER 00Z. CONTINUED LONG WAVE  
TROUGH AMPLIFICATION EAST OF THE REGION WILL USHER IN DRIER AND MUCH  
COOLER AIR BY DAYBREAK TUES. SO TEMPS WILL ONCE AGAIN BE ON THE  
COLDER SIDE OF THE TYPICAL MID APRIL SPECTRUM INTO MID WEEK. THE  
DEGREE OF DRY AIR SHOULD KEEP THE FORECAST AREA PRECIP FREE TUES AND  
WED. DIURNALLY ENHANCED DAYTIME CU/STRATO CU ARE HIGHLY POSSIBLE IN  
LIGHT OF THE STEEP LOW LEVEL LAPSE RATES...ESPECIALLY ON TUES  
CONSIDERING MODEL SOLUTIONS DEPICT A SECONDARY MID LEVEL SHORT  
WAVE TRAVERSING LOWER MI.  
 
THURSDAY AFTERNOON...THE LOW PRESSURE SETTING UP TO THE WEST OVER  
THE NORTHERN PLAINS WILL BRING INCREASING CLOUDS DURING THE DAY WITH  
RAIN CHANCES DEVELOPING LATE THURSDAY NIGHT INTO FRIDAY. WEAK  
CHANCES FOR SHOWERS WILL CONTINUE THROUGH SATURDAY. A STRONG  
CANADIAN HIGH BUILDS OVER THE AREA FOR SUNDAY AND MONDAY RESULTING  
IN DRYER AND SLIGHTLY COOLER CONDITIONS.  
 
MARINE...  
 
A STALLED FRONTAL BOUNDARY WILL LINGER OVER NORTHERN LAKE HURON INTO  
MONDAY AFTERNOON. HIGH STABILITY OVER THE COLD LAKES AND A  
RELATIVELY WEAK GRADIENT WILL SUPPORT LIGHT WINDS THROUGH THE DAY  
MONDAY. A LOW PRESSURE SYSTEM WILL THEN PASS ACROSS LAKE HURON  
MONDAY EVENING...DRAGGING A COLD FRONT ACROSS THE REGION. POST  
FRONTAL NORTHWEST WINDS WILL INCREASE INTO THE 20 TO 30 KNOTS RANGE  
EARLY TUES MORNING AND PERSIST INTO TUES AFTERNOON AS COLDER AIR  
ADVANCES SOUTH. THE CHANCES OF GALE FORCE WIND GUSTS STILL LOOK LOW  
AT THIS TIME...ALTHOUGH THE DEVELOPMENT OF SOME SMALL CRAFT ADVISORY  
CONDITIONS DOES LOOK POSSIBLE. HIGH PRESSURE WILL THEN BRING CALMING  
CONDITIONS THROUGH THE MIDDLE OF THE WEEK BEFORE SOUTHWEST TO WEST  
WINDS INCREASE LATE IN THE WEEK WITH THE APPROACH OF THE NEXT LOW  
PRESSURE SYSTEM.  
 

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

 
 

 
 
AVIATION.....MR  
SHORT TERM...CB  
LONG TERM....SC/DE  
MARINE.......SC  
 
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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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