000
FXUS63 KDTX 111747
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1247 PM EST WED DEC 11 2013

.AVIATION...

//DISCUSSION...

AN ARCTIC COLD FRONT MARKED BY A BAND OF HEAVIER SNOW SHOWERS WILL
MOVE THE REST OF THE WAY THROUGH SE MICHIGAN DURING THE AFTERNOON,
IMPACTING MAINLY THE DETROIT AREA TERMINALS THROUGH ABOUT 21Z. THE
SNOW ALONG THE FRONT WILL BRING IFR TO BRIEFLY LIFR VISIBILITY
RESTRICTION FOR AN HOUR OR TWO BEFORE CONDITIONS IMPROVE IN THE
COLDER AIR BEHIND THE WIND SHIFT. THERE IS A CONSIDERABLE DIURNAL
COMPONENT IN THE CLOUDS OBSERVED IN THE MBS AREA WHICH SUPPORTS THE
IDEA OF A CLEARING TREND AFTER SUNSET LASTING THROUGH MUCH OF THE
NIGHT. BACKING LOW LEVEL FLOW WILL THEN BRING SOME STRATOCU INTO THE
TERMINAL CORRIDOR FROM LAKE MICHIGAN DURING THURSDAY MORNING WITH
THE BEST POTENTIAL FOR MVFR CEILING NORTH OF PTK.

FOR DTW...A QUICK POWDERY INCH OF SNOW IS LIKELY AS AN ARCTIC FRONT
MOVES THROUGH THE REGION DURING THE AFTERNOON. THE BURST OF SNOW
WILL BE BRIEF, LASTING ABOUT AN HOUR ASSOCIATED WITH THE IMMEDIATE
FRONTAL PASSAGE AROUND 20Z.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILING BELOW 5000 FT DURING THE AFTERNOON.
MODERATE CONFIDENCE THURSDAY MORNING.

* HIGH CONFIDENCE IN SNOW AS PRECIPITATION TYPE.

&&

.PREV DISCUSSION...ISSUED 1010 AM EST WED DEC 11 2013

UPDATE...

A FAST-MOVING SHORT WAVE IS ON THE WAY THROUGH THE SOUTHERN GREAT
LAKES DURING THE LATE MORNING AND WILL EXIT EASTWARD BY MID
AFTERNOON. THERE IS A GENEROUS PATTERN OF LIGHT SNOW WITH THE
SYSTEM BASED ON VISIBILITY OBSERVATIONS LESS THAN 1 MILE REPORTED
FROM NORTHERN ILLINOIS THROUGH NORTHERN INDIANA AND A FASTER ONSET
IN SE MICHIGAN EARLIER IN THE MORNING. AUGMENTATION OFF THE SOUTH
END OF LAKE MICHIGAN IS IN THE PROCESS OF DEVELOPING ALONG THE
ARCTIC COLD FRONT ENTERING THE SAGINAW VALLEY AT PRESS TIME.
EXPECT POCKETS OF HEAVIER SNOW SHOWERS TO EXTEND EASTWARD INTO OUR
AREA FROM SW LOWER, ALONG AND SOUTH OF THE INTERSTATE 69
CORRIDOR. THIS WILL PROVIDE THE NECESSARY BOOST IN ACTIVITY FOR
ACCUMULATION UP TO AN INCH ALONG AND SOUTH OF THAT LINE TO THE
OHIO BORDER BEFORE THE UPPER WAVE AND FRONT EXIT SOUTHWARD AND
EASTWARD BEFORE THE EVENING PEAK TRAVEL PERIOD.

PREV DISCUSSION...ISSUED 353 AM EST WED DEC 11 2013

SHORT TERM...TODAY AND TONIGHT

PERSISTENT AREA OF LIGHT SNOW SHOWERS/FLURRIES CONTINUE TO FOCUS
EARLY THIS MORNING WITHIN THE M-59/I-69 CORRIDOR...ANCHORED ON A
TEMPORARILY FADING LAKE MOISTURE FLUX COMPONENT AND WEAK CONVERGENCE
SIGNAL EMBEDDED WITHIN A SLIGHTLY BACKED WESTERLY FLOW.
MEANWHILE...EARLY MORNING WATER VAPOR IMAGERY SHOWING THE NEXT
SHORTWAVE WORKING THROUGH THE PREDOMINANT LONGWAVE TROUGH NOW
CENTERED OVER EASTERN IA/NORTHERN IL.  THE MAIN VORTICITY LOBE WILL
TEND TO TRANSLATE EAST-SOUTHEAST WITH TIME...THE CORE OF THE DPVA
ALIGNING JUST SOUTH OF THE AREA.  HOWEVER...THIS WAVE WILL PROVIDE A
GLANCING SHOT OF MID LEVEL ASCENT ACROSS SOUTHERN SECTIONS BY EARLY
AFTERNOON GIVEN SOME DEFORMATION FORCING CONTAINED WITHIN THE
ENTRANCE REGION OF AN ESTABLISHED UPPER LEVEL JETLET.   IN
ADDITION...THIS WAVE DOES ARRIVE WITHIN THE SOUTHERN PERIPHERY OF A
BROADER REGION OF HEIGHT FALLS/TROUGHING.  THIS APPEARS TO TRANSLATE
INTO A STRONGER DOWNSTREAM RESPONSE IN ESTABLISHING A WELL DEFINED
LOW LEVEL TROUGH/CONVERGENCE ZONE COMING OFF LAKE MICHIGAN.  THE NET
RESULT WILL LIKELY BE FOR THE RESIDENT CONVERGENCE FIELD CURRENTLY
IN PLACE ACROSS THE M-59/I-69 TIER TO STRENGTHEN WITH TIME THROUGH
THE MORNING HOURS...BEFORE TRANSLATING SOUTHWARD INTO THE AFTERNOON
AS THE MEAN 850-925 MB LAYER WINDS VEER.

THIS EVOLUTION IN THE MASS FIELD IN ADDITION TO SOME INCREASE IN
OVERLAKE MOISTURE DEPTH IS EXPECTED TO AUGMENT THE ONGOING LAKE
EFFECT ACTIVITY...PROVIDING A FAVORABLE ENVIRONMENT FOR DOWNSTREAM
PENETRATION OF SNOW SHOWERS INTO MAINLY CENTRAL AND SOUTHERN
SECTIONS OF SOUTHEAST MICHIGAN TODAY.  THE OVERALL DRYNESS OF
THE RESIDENT ARCTIC AIRMASS PRESENTS A CHALLENGE IN DEFINING
POSSIBLE ACCUMULATION...SPECIFIC HUMIDITY OF NO MORE THAN 1 G/KG
TRANSLATING INTO A LIMITED LIQUID EQUIVALENT /A FEW HUNDREDTHS/.
WITH THAT SAID...THIS ENVIRONMENT WILL ALLOW FOR SNOW RATIOS ON THE
ORDER OF 20:1.  MOISTURE/THERMAL PARAMETERS WITHIN THE LOWEST 2 KM
POINT TOWARD SEEING A PERIOD OF GOOD DENDRITIC ICE CRYSTAL
GROWTH...A SOUNDING CHARACTERIZED BY STEEPER LAPSE RATES AND A
PERIOD OF MARKED ASCENT WITHIN THE -12 TO -16C LAYER. THUS DESPITE
THE LACK OF BETTER MOISTURE QUALITY...A GENERAL ACCUMULATION OF A
HALF TO ONE INCH WITH THE POTENTIAL FOR SOME LOCALLY HIGHER TOTALS
REMAINS ACHIEVABLE ALONG AND SOUTH OF I-69. POCKETS OF LIGHT SNOW
MAY GENERATE SOME MINOR ACCUMULATION FOR POINTS TO THE NORTH OF
THIS LINE...BUT A GENERAL DISPLACEMENT FROM BOTH THE MAIN FORCING
AND LAKE MOISTURE WILL CONTAIN BOTH THE COVERAGE AND DURATION.

NO REAL CHANGE IN EXPECTATIONS ON TEMPERATURES...HIGHS AGAIN
ARRIVING WITHIN THE UPPER TEENS TO LOWER 20S RANGE.  A DEEPER
NORTHWEST FLOW AND THE ATTENDANT INCREASE IN COLD/DRY AIR ADVECTION
WILL SUPPORT A PROGRESSIVE CLEARING TREND FROM NORTH TO SOUTH FROM
LATE AFTERNOON INTO THE EVENING HOURS.  THIS SETS UP A SOLID
RADIATIONAL COOLING OPPORTUNITY IN FRESH SNOW COVER AND CLEAR SKY.
A 5 TO 10 KNOT LOW LEVEL GRADIENT WILL KEEP THE BOUNDARY LAYER FROM
FULLY DECOUPLING...SO NOT THE PERFECT SETUP.  REGARDLESS...A -17C
925 MB TEMPERATURE IN THIS ENVIRONMENT WILL SUPPORT SINGLE DIGIT LOW
TEMPERATURES.  THE ADDED WIND ELEMENT WILL YIELD WIND CHILLS NEAR OR
JUST BELOW -10 DEGREES ACROSS MOST LOCALES OUTSIDE METRO DETROIT.
THIS WILL PLACE NORTHERN PORTIONS OF THE TRI-CITIES AND THUMB AT THE
CUSP OF AN ADVISORY /-15/.

LONG TERM...THURSDAY THROUGH TUESDAY.

INTERESTING DUAL AXIS JET STREAK WILL NOSE INTO THE GREAT LAKES ON
THURSDAY AS THE NEXT JET SURGE WORKS INTO THE EASTERN NORTH AMERICA
LONGWAVE TROUGH AXIS. EXIT DYNAMICS AND ATTENDANT THETA E INFLECTION
IN THE MID TO UPPER LEVELS BETWEEN 18-00Z WILL HAVE A VERY DIFFICULT
TIME COMMUNICATING DOWN INTO THE LOWER TROPOSPHERE DUE TO HIGH
STATIC STABILITY SFC-20 KFT AGL. A RATHER ATYPICAL FORECAST WITH
HIGH CERTAINTY CONCERNING THE CEILING FOR QPE AMOUNTS WHICH IS A
HUNDREDTH OR TWO FOR THE NORTHERN HALF OF THE CWA.

THE ARCTIC COLD WILL PERSIST THURSDAY AND THURSDAY NIGHT WITH
TEMPERATURES LIKELY READING IN THE TEENS FOR A MAJORITY OF THE 24
HOUR PERIOD. WIND CHILLS ARE FORECASTED TO REMAIN SUBZERO THROUGH
THE LATE MORNING HOURS...ONLY RECOVERING INTO THE SINGLE DIGITS
ABOVE ZERO DURING THE AFTERNOON. AN AGGRESSIVE AND STABLE SURFACE
RIDGE IS PROJECTED TO BUILD NORTH OF THE GREAT LAKES FRIDAY CAUSING
A PSEUDO BACKDOOR COLD ADVECTION RESPONSE DOWN INTO THE HEART OF
LOWER MICHIGAN BY FRIDAY AFTERNOON.

NO SURPRISES WITH 11.00Z NWP WITH REGARDS TO THE POTENTIAL FOR
ACCUMULATING SNOWFALL THIS WEEKEND. LATEST RUNS AGAIN SUPPORT LARGE
SEPARATION BETWEEN A STRONG PV ANOMALY IN THE NORTHERN STREAM THAT
WILL DIVE OUT OF MANITOBA AND IDEAL LEFT EXIT REGION DYNAMICS OF A
SOUTHERN STREAM JET STREAK THAT WILL SLIDE THROUGH THE TENNESSEE
RIVER VALLEY. THE NARRATIVE WILL DEPEND ON WHETHER OR NOT THESE TWO
FEATURES WILL PHASE.

MARINE...

THE COMBINATION OF VERY COLD TEMPERATURES WITH A TIGHTENED PRESSURE
GRADIENT CONTINUE TO BRING WESTERLY GALES THIS MORNING FOR MUCH OF
LAKE HURON. A HEAVY FREEZING SPRAY WARNING ALSO REMAINS IN EFFECT TO
ACCOMPANY THE GALE WARNING. A WEAK SURFACE RIDGE WILL TRY TO PUSH
THROUGH THE GREAT LAKES ON THURSDAY... HOWEVER...THIS HIGH IS
EXPECTED TO BE SQUEEZED SOUTHWARD WHICH WILL KEEP RESPECTABLE FLOW
OVER THE GREAT LAKES WELL INTO FRIDAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

LAKE HURON...
     HEAVY FREEZING SPRAY WARNING...LHZ361-LHZ362-LHZ363...UNTIL 4 PM
     WEDNESDAY.

     GALE WARNING...LHZ361-LHZ362-LHZ363...UNTIL 4 PM WEDNESDAY.

     SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
     FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 7 PM THURSDAY.

LAKE ST CLAIR...NONE.

MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....BT
UPDATE.......BT
SHORT TERM...MR
LONG TERM....CB
MARINE.......CB


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