999  
FXUS63 KDTX 091400  
AFDDTX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI  
900 AM EST TUE FEB 9 2016  
   
UPDATE
 
 
INTEGRITY OF SPIRAL BANDS OF SNOW SHOWERS ACROSS SOUTHEAST  
MICHIGAN REMAINS RATHER HIGH. THESE BANDS ARE ASSOCIATED WITH A  
DEVELOPING LOWER LEVEL CIRCULATION OVER SOUTHWEST ONTARIO AND  
SOUTHERN LAKE HURON. THIS FEATURE WILL CONTINUE TO DEVELOP AS  
UPPER LEVEL TROUGH MAINTAINS A FAVORABLE ENVIRONMENT. GIVEN THE  
OVERACHIEVING NATURE OF THE BAND OF SNOW SHOWERS ALONG THE  
INITIAL SURFACE TROUGH EARLY THIS MORNING...AND THE PROSPECTS  
CONMTINUE FOR PERIODS OF MODERATE SNOW...ESPECIALLY ALONG AND  
NORTH OF M-59...HAVE OPTED TO EXPAND THE WINTER WEATHER ADVISORY  
INTO THE NORTHERN REACHES OF THE DETROIT METRO REGION.  
EXPECTATIONS ARE FOR AN ADDITIONAL 1 TO 3 INCHES IN THE EXPANDED  
AREA WITH LITTLE CHANGE OVER THE INITIALLY ADVISORY AREA.  
 

 
   
AVIATION
 
ISSUED 702 AM EST TUE FEB 9 2016  
 
A BAND OF HEAVY SNOW BECAME FOCUSED ON A SURFACE TROUGH AND SWUNG  
THROUGH SE MICHIGAN DURING THE EARLY MORNING. THE BAND WILL  
CONTINUE TO BREAK UP IN THE DTW TERMINAL CORRIDOR WHILE LOW  
PRESSURE OVER SOUTHERN LAKE HURON FEEDS BANDS OF SNOW INTO THE  
MBS-FNT-PTK REGION. EXPECT THIS AREA TO REMAIN IFR FOR MUCH OF THE  
DAY. THERE WILL BE SOME VARIATION...ESPECIALLY SOUTH OF PTK...BUT  
TIMING AND DURATION OF BREAKS HAS VERY LOW PREDICTABILITY AND WILL  
BE SUBJECT TO SHORT TERM UPDATES THROUGH THE DAY. THE RELATIVE  
BREAK IN THE SNOW PATTERN OBSERVED OVER WESTERN LOWER MICHIGAN  
DURING THE MORNING IS EXPECTED TO SLIDE EASTWARD OVER SE MICHIGAN  
TONIGHT AS THE LOW MOVES TOWARD LAKE ONTARIO. THE AREA OF SNOW  
OVER WISCONSIN AND ILLINOIS WILL HAVE A CHANCE TO MOVE INTO OUR  
AREA TOWARD SUNRISE WEDNESDAY.  
 
FOR DTW... BANDS OF SNOW SHOWERS WILL CONTINUE TO BREAK UP THROUGH  
MID MORNING AND ALLOW CONDITIONS TO IMPROVE DURING LATE MORNING  
WHILE CEILING REMAINS MVFR. THERE REMAINS POTENTIAL FOR ANOTHER  
SURGE OF SNOW MID TO LATE AFTERNOON BUT THIS IS SUBJECT TO UPDATE  
AS OBSERVATIONS REVEAL BETTER TIMING ON SMALLER SCALE MOVING DOWN  
FROM THE THUMB REGION.  
 
//DTW THRESHOLD PROBABILITIES...  
 
* HIGH FOR CEILING AOB 5KFT TODAY AND TONIGHT.  
 
* HIGH FOR SNOW AS PRECIPITATION TYPE.  
 
* LOW FOR EXCEEDING NORTHWEST CROSSWIND THRESHOLD TODAY.  
 

 
   
PREV DISCUSSION
 
ISSUED 314 AM EST TUE FEB 9 2016  
 
DISCUSSION...  
 
A 999MB SURFACE LOW NEAR EXETER, ONTARIO WILL CONTINUE TO GRADUALLY  
DEEPEN BY ANOTHER MB OR TWO OVER THE NEXT SEVERAL HOURS AS EMBEDDED  
ENERGY PIVOTS AROUND THE CLOSED LOW ALOFT. ONGOING ADVISORY EVENT IS  
PANNING OUT IN REASONABLE FASHION AND NO CHANGES ARE NEEDED TO THE  
EXISTING HEADLINE.  
 
0730Z RADAR MOSAIC REVEALS A BAND OF MODERATE TO HEAVY SNOW  
TRANSLATING SOUTHWARD THROUGH SOUTHEAST MICHIGAN. THIS BAND IS BEING  
FORCED BY THE LEAD EDGE OF COLD AIR ALOFT AND WILL LIKELY HOLD  
TOGETHER FOR THE MOST PART AS IT CONTINUES TO TRACK SOUTH, REACHING  
THE I-94 CORRIDOR BY 6AM AND EXITING THE AREA TO THE SOUTHEAST MID-  
MORNING. THIS BRIEF BURST OF SNOW WILL REPRESENT THE PEAK OF THIS EVENT  
SOUTH OF THE M-59 CORRIDOR, AS LARGE SCALE FORCING IS PROGGED TO  
REMAIN LARGELY STATIONARY OVER THE NE CWA.  
 
THE PRIMARY CHANGE TO THE FORECAST WILL BE AN INLAND ADJUSTMENT OF  
SNOWFALL AMOUNTS IN HURON, TUSCOLA, AND SANILAC COUNTIES. RADAR  
RETURNS AND COOLING CLOUD TOPS ON IR ARE INDICATIVE OF A  
STRENGTHENING VERTICAL MOTION FIELD. BROAD ELEVATED WAA/ISENTROPIC  
ASCENT IS SUPPORTING LIGHT SNOW FROM ONTARIO TO LAKE HURON. HOWEVER,  
IT APPEARS TO BE THE BACK EDGE OF THE TROWAL. FAR FROM A CLASSIC  
TROWAL, MAINLY DUE TO THE LACK OF ANY APPRECIABLE DEFORMATION, AN  
ELEVATED MOISTURE FEED INTO THIS REGION IS EVIDENT ON REGIONAL IR  
AND WV. THE SNOW BAND THAT HAS DEVELOPED IS DUE TO CONVERGENCE AND  
WEAK FGEN ALONG THE TROWAL'S BACK EDGE. THIS FEATURE WILL MOST  
LIKELY ONLY SHOW A SLOW CYCLONIC PIVOT THROUGH THE NOON HOUR, AND IT  
IS WITHIN THIS AXIS THAT THE HEAVIEST SNOW IS NOW FORECAST.  
UNFORTUNATELY, DISTANCE FROM THE RADAR, LACK OF REPORTS, AND A VOID  
IN SURFACE OBS IS SEVERELY LIMITING DIAGNOSIS OF ACTUAL SNOW  
INTENSITY. ALTHOUGH THE 00Z NAM HANDLED THE RELEVANT FEATURES WELL,  
ITS QPF OUTPUT HAS NOT BEEN USEFUL. THAT HAS CHANGED WITH THE 06Z  
NAM, WHICH APPEARS MORE REASONABLE IN SPATIAL EXTENT/INTENSITY AND  
CORRELATION WITH RELEVANT FEATURES. IT WILL REPRESENT THE PRIMARY  
QPF GUIDANCE THROUGH TODAY.  
 
AS THE UPPER LOW OPENS UP THIS AFTERNOON, THE TROWAL, OR WHAT  
REMAINS OF IT AFTER THE CIRCULATION OPENS, WILL RAPIDLY PIVOT  
THROUGH THE AREA BRINGING A ROUND OF LIGHT SNOW MAINLY TO LOCATIONS  
NORTH OF 8 MILE. TRAILING THIS ACTIVITY WILL BE THE LAKE ENHANCED  
SURFACE TROUGH THAT REMAINS OVER LAKE HURON AT THE MOMENT. THIS  
FEATURE WILL COME CRASHING ONSHORE WITH PEAK SNOWFALL INTENSITY  
FALLING IN THE 19-22Z TIME FRAME. THE INTRODUCTION OF COLDER AIR  
OVER THE LAKE 12-18Z WILL CONTRIBUTE TO MORE ROBUST, THOUGH STILL  
MODEST, OVERLAKE INSTABILITY. THIS WILL IN TURN HAVE A CHANCE TO  
STRENGTHEN THE LAKE ENHANCED TROUGH BEFORE IT PIVOTS ASHORE.  
OBSERVATIONS WILL THEREFORE BE WORTH MONITORING DURING THE  
AFTERNOON AS A BRIEF PERIOD OF INTENSE SNOW WILL BE ON THE TABLE  
FOR HURON AND SANILAC COUNTIES. PROGRESSIVE FLOW THEN TAKES OVER  
AS THE OPEN WAVE EXITS RESULTING IN A RAPID DIMINISHING OF SNOW  
COVERAGE AND INTENSITY BY 00Z.  
 
THE STORY WEDNESDAY THROUGH THURSDAY WILL BE COLD TEMPERATURES AS  
925MB TEMPERATURES FALL FROM -2C AT PRESENT TO -15C BY WEDNESDAY  
NIGHT. WITH THE BULK OF THE FIRST WAVE OF COLD ADVECTION OCCURRING  
TONIGHT, AND THEN CONTINUING IN WEAK FASHION THROUGH WEDNESDAY,  
LITTLE IN THE WAY OF DIURNAL RECOVERY IS EXPECTED. HIGHS WILL  
STRUGGLE TO 20 DEGREES IN MOST SPOTS. THERE WILL ALSO BE A GOOD  
CHANCE FOR SNOW SHOWERS, ESPECIALLY DURING THE FIRST HALF OF THE  
DAY, AS THE DGZ WILL BE SUPERSATURATED WRT ICE BEFORE LINGERING  
MOISTURE EXITS LATE. NW FLOW WILL TEND TO LIMIT PURE LES POTENTIAL,  
ALTHOUGH THE FETCH WILL FAVOR MONITORING POTENTIAL FOR A SUPERIOR-  
MICHIGAN BAND STRETCHING INTO SW PORTIONS OF THE AREA. CLOUDS AND  
A STRONG GRADIENT SHOULD KEEP LOWS EASILY ABOVE MODELED VALUES IN  
MOST LOCATIONS...RAISED LOWS WED NIGHT SEVERAL DEGREES INTO THE  
LOW TEENS. LITTLE CHANGE FOR THURSDAY IN TERMS OF TEMPERATURES,  
THOUGH THE EXIT OF DEEPER MOISTURE AND SLIGHTLY ANTICYCLONIC FLOW  
MAY ALLOW FOR PEEKS OF SUN BY AFTERNOON.  
 
EDGEWAVE RACING EAST ALONG THE LEAD EDGE OF A MUCH COLDER UPPER LOW  
WILL BRING A CHANCE OF LIGHT SNOW TO ALL LOCATIONS FRIDAY.  
TEMPERATURES WILL PLUMMET INTO THE SINGLE DIGITS OR LOWER FRIDAY  
NIGHT AND HIGHS ARE UNLIKELY TO REACH 10 DEGREES ON SATURDAY.  
SUBZERO LOWS WILL BE POSSIBLE AGAIN SATURDAY NIGHT. WIND CHILLS  
AROUND -15 WILL BE COMMON DURING THIS TIME. UNLIKE LAST FEBRUARY,  
THIS INTRUSION OF DANGEROUSLY COLD AIR WILL BE SHORT-LIVED AND LONG  
GONE BY EARLY NEXT WEEK.  
 
MARINE...  
 
LOW PRESSURE OVER THE SOUTH END OF LAKE HURON DURING THE MORNING  
WILL MAINTAIN INCREASING COVERAGE OF SNOW SQUALLS AND INCREASING  
NORTH WIND AS IT DRIFTS TOWARD LAKE ONTARIO TODAY. A WIND HEADLINE  
IS NOT ANTICIPATED BUT THE INCREASED WIND AND LONG NORTHERLY FETCH  
WILL BUILD WAVE ACTION WELL INTO CRITERIA FOR SMALL CRAFT ADVISORY  
BY TONIGHT AND LASTING INTO THURSDAY. THE NORTH WIND WILL ALSO BRING  
A SURGE OF ARCTIC AIR ACROSS THE LAKE DURING THIS TIME THAT WILL  
MAINTAIN SNOW SQUALLS AND SUPPORT INCREASINGLY FAVORABLE FREEZING  
SPRAY POTENTIAL BY WEDNESDAY MORNING WHICH WILL LIKELY BECOME HEAVY  
WEDNESDAY NIGHT INTO THURSDAY. THE WIND WILL DIMINISH LATER THURSDAY  
THROUGH FRIDAY WHILE ARCTIC AIR MAINTAINS A HOLD ON THE REGION INTO  
NEXT WEEKEND.  
 

 
   
DTX WATCHES/WARNINGS/ADVISORIES
 
 
MI...WINTER WEATHER ADVISORY UNTIL 9 PM EST THIS EVENING FOR MIZ047>049-  
053>055-060>063-068>070.  
 
LAKE HURON...HEAVY FREEZING SPRAY WARNING FROM 7 PM WEDNESDAY TO 7 AM EST  
THURSDAY FOR LHZ362-363-441>443-462>464.  
 
SMALL CRAFT ADVISORY UNTIL 4 PM EST THURSDAY FOR LHZ441>443.  
 
LAKE ST CLAIR...NONE.  
MICHIGAN WATERS OF LAKE ERIE...NONE.  

 
 

 
 
UPDATE.......RK  
AVIATION.....BT  
DISCUSSION...JVC  
MARINE.......BT  
 
YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE  
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).  
 
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