Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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508
FXUS63 KDTX 091202
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
702 AM EST TUE FEB 9 2016

.AVIATION...

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 MIZ049-054-
     055-062-063.

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.

&&

$$

AVIATION.....BT
DISCUSSION...JVC
MARINE.......BT


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