Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 201704
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1204 PM EST THU NOV 20 2014


.AVIATION...

//DISCUSSION...

LOW LEVEL CONVERGENCE HAS ENHANCED SNOW SHOWERS OFF LAKE MICHIGAN
AND BROUGHT THEM WELL INLAND INTO SE MI. INCREASED LOW LEVEL
INSTABILITY HAS FRACTURED SOME OF THE MORE PERSISTENT SNOW BANDS.
WHAT THIS MEANS IS THAT THERE WILL BE INTERVALS OF BREAKS AND BRIEF
INTENSE SNOW SHOWERS...IMPACTING MAINLY FNT AND PTK THROUGH THE
AFTERNOON. VISIBILITIES WITHIN SOME OF THE HEAVIER SNOW SHOWERS WILL
BE REDUCED TO LESS THAN A QUARTER MILE. THE LOW LEVEL WINDS WILL
VEER TOWARD THE W-NW THIS EVENING...PUSHING THE HIGHER CONCENTRATION
SNOW BANDS FARTHER SOUTH AND LEADING TO SOME CLEARING FROM NORTH TO
SOUTH.

FOR DTW...THROUGH THE AFTERNOON...THE MORE WIDESPREAD AND INTENSE
SNOW SHOWERS WILL REMAIN NORTH OF METRO. THE WINDS WILL TURN MORE
TOWARD THE WEST-NORTHWEST THIS EVENING /AFTER 00Z/ AND THIS MAY
BRING SOME OF THE HIGHER INTENSITY SNOW SHOWERS INTO METRO...
POSSIBLY LEADING TO SOME MINOR ACCUMULATIONS. CONTINUED VEERING OF
THE WINDS OVERNIGHT SHOULD PUSH LINGERING SNOW SHOWERS SOUTH OF
METRO AFTER MIDNIGHT.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5KFT.

* LOW CONFIDENCE IN BRIEF INTERVALS OF VISIBILITY BELOW A HALF MILE
  IN SNOW THIS EVENING.

&&

.PREV DISCUSSION...ISSUED 932 AM EST THU NOV 20 2014

UPDATE...

AN ENHANCED REGION OF CONVERGENCE HAS LED TO A BAND OF HEAVY SNOW
JUST SOUTH OF THE I-69 CORRIDOR ACROSS SHIAWASSEE...GENESEE AND
LAPEER COUNTIES. THIS RIBBON OF CONVERGENCE WILL PERSIST AT LEAST
INTO EARLY AFTERNOON. BASED OFF THE 12Z DTX SOUNDING...DECENT LOW
LEVEL INSTABILITY AND MOISTURE IS LEADING TO THE HEALTHY RESPONSE
TO THE LAKE EFFECT ACTIVITY OFF LAKE MI. THERE MAY BE SOME BREAK
UP OR REORIENTATION OF THE BANDING THIS AFTERNOON...POSSIBLY
LEADING TO ENHANCED CONVERGENCE FARTHER SOUTH. OBSERVATIONAL DATA
AT THIS POINT SUGGESTS THE BAND NEAR THE I-69 CORRIDOR WILL BE
PERSISTENT ENOUGH TO SUPPORT SOME LOCALIZED ACCUMULATIONS IN
EXCESS OF THREE INCHES. THERE HAS ALSO BEEN A SPOTTER REPORT OF
WHITE OUT CONDITIONS IN THIS BAND. THIS HAS PROMPTED THE ISSUANCE
OF A WINTER WEATHER ADVISORY FOR SHIAWASSEE...GENESEE AND LAPEER
COUNITES THROUGH 4 PM.

PREV DISCUSSION...ISSUED 349 AM EST THU NOV 20 2014

SHORT TERM...TODAY AND TONIGHT

LAKE EFFECT SNOW SHOWERS WILL CONTINUE TO FUNNEL WEST TO EAST ACROSS
LOWER MICHIGAN AND IMPACT PARTS OF THE CWA...ESPECIALLY BETWEEN I 69
AND I 94 TODAY. AFTER AN INITIAL BURST OF LOCALLY INTENSE SNOW
SQUALLS ENHANCED BY SHORTWAVE TROUGH USHERING IN NEXT SHOT OF ARCTIC
AIR...THE REMAINING SNOW SHOWERS SHOULD REMAIN ON THE LIGHT TO
MODERATE SIDE AND REMAIN QUITE A BIT LESS ORGANIZED. SO...GENERALLY
DO NOT EXPECT MORE THAN AN ADDITIONAL INCH OR SO OF ACCUMULATIONS
EARLY THIS MORNING THROUGH TODAY. THAT SAID...DIURNAL ENHANCEMENT OF
THE SNOW SHOWER ACTIVITY MAY LEAD TO ISOLATED AMOUNTS UP TO 2 INCHES
IN THE I 69 TO M 58 CORRIDORS WHERE CONVERGENCE WILL BE STRONGEST.

A GRADUAL VEERING OF LOW LEVEL FLOW FROM WEST TO WEST/NORTHWEST WILL
RE-FOCUS SNOW SHOWERS OVER THE SOUTHERN CWA BY THE EVENING...WITH
SUBSTANTIAL WEAKENING OF ACTIVITY EXPECTED AFTER MIDNIGHT TONIGHT A
RIDGE OF HIGH PRESSURE BEGINS TO BUILD INTO THE AREA. A DUSTING TO
INCH OF SNOW CANNOT BE RULED OUT DURING THE EVENING I 94 SOUTH
BEFORE THIS WEAKENING TREND ENSUES.

WITH THE RE-ENFORCING SHOT OF ARCTIC AIR...TEMPERATURES WILL NOT GO
ANYWHERE TODAY...HOLDING GENERALLY IN THE LOWER/MID 20S...AND THEN
FALLING WELL INTO THE TEENS TONIGHT. IN FACT...SINGLE DIGITS WILL BE
COMMON OVER THE NORTHERN CWA WHERE SKIES WILL BECOME CLEAR/PARTLY
CLOUDY AND ALLOW FOR DECENT RADIATIONAL COOLING...HELPED ALONG BY
DECREASING WINDS WITH THE APPROACHING RIDGE.

LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY

SOME MOVEMENT IN THE LONGWAVE PATTERN WILL HELP PUSH THE PERSISTENT
AND COLD TROUGH OUT TO THE ATLANTIC. A SPLIT FLOW PATTERN THEN TRIES
TO TAKE SHAPE AS RESIDIUAL NORTHERN STREAM ENERGY LINGERS OVER
EASTERN CANADA AND SOUTHERN STREAM INTENSIFIES ACROSS THE SOUTHERN
CONUS WITH THE NEXT SERIES OF WAVES. THIS WILL LEAD TO A WARM UP
OVER THE GREAT LAKES OVER THE WEEKEND BUT COOLER WEATHER RETURNS
NEXT WEEK.

FRIDAY WILL BE A TRANSITIONAL DAY AS THE TROUGH EXITS THE GREAT
LAKES BUT THE THERMAL TROUGH LINGERS ONE MORE DAY. AS HEIGHTS BUILD
AND HIGH PRESSURE SLIDES THROUGH THE AREA...850MB TEMPS WILL RISE
FROM AROUND -18C AT 12Z FRI UP TO -4C BY 00Z SAT. LESS OF A CHANGE
WILL BE REALIZED AT THE SFC AS COLD AIR REMAINS LOCKED IN PLACE
UNDER THE INVERSION. THIS WILL KEEP MAX TEMPS IN THE MID 20S. WAA
KICK IN FRI NIGHT WITH THE AIDE OF A 50 KNOT LL JET. THIS STRONG SW
FLOW WILL HELP RAISE 925MB AND 850MB TEMPS ABOVE ZERO BY 12Z SAT.
MODELS CONTINUE TO SHOW A LAG IN SFC TEMPS WARMING...KEEPING SUB
FREEZING TEMPS IN THE LOWEST 1000+FT OF THE COLUMN. THOUGH THE
SOUTHERN STREAM TROUGH AND ASSOCIATED SFC LOW AREA STILL COMING
TOGETHER AT THIS TIME...MODELS HAVE CONSISTENTLY BEEN SHOWING A
SHORTWAVE LIFTING THROUGH SOUTHERN MI AHEAD OF THE MAIN SYSTEM. WITH
THE AFOREMENTION THERMAL PROFILE...LIGHT FREEZING DRIZZLE/RAIN WILL
BE POSSIBLE ACROSS THE AREA EARLY IN THE DAY. AS THE DAY PROGRESSES
AND WAA CONTINUES...THE PTYPE WILL EVENTUALLY CHANGE OVER TO A PURE
RAIN SCENARIO. SO WILL CONTINUE TO HIGHLIGHT THESE PTYPE CONCERNS IN
THE GRIDS.

TEMPERATURES WILL CLIMB SAT THROUGH MON AS THE TROUGH DEEPENS OVER
THE CENTRAL PLAINS CAUSING THE DOWNSTREAM AMPLIFICATION OF THE RIDGE
OVER THE EAST COAST. TEMPERATURES LOOK TO RETURN TO NEAR NORMAL FOR
MID NOVEMBER REACHING INTO THE UPPER 40S TO NEAR 50 AS 850MB TEMPS
CLIMB TO +6C SUN AND +7C EARLY MON. THIS WILL CHANGE ALL PRECIP OVER
TO RAIN FOR THE NEXT FEW DAYS AS AN UPPER LEVEL SHORTWAVE OVER TEXAS
LIFTS NE AND PHASES WITH A NORTHERN STREAM WAVE SUNDAY NIGHT INTO
MONDAY. THE LEAD EXTENSION OF THE WARM FRONT WILL DRAPE ACROSS THE
REGION THROUGH THE WEEKEND AS THE SFC LOW LIFTS INTO THE MIDWEST
WHILE STRENGTHENING. THE LEAD FRONTAL SFC WILL RESULT IN PERIODS OF
SHOWERS AS RIPPLES EJECTING OUT OF THE TROUGH LIFT OVER THE REGION
INCREASING ISENTROPIC ASCENT AND WEAK FGEN. THE BULK OF THE RAIN
SHOWERS WILL OCCUR SUNDAY EVENING THROUGH MONDAY MORNING AS THE LOW
PASSES OVER THE NORTHERN GREAT LAKES. A COLD FRONT WILL THEN SLIDE
THROUGH ON MONDAY USHERING MORE ARCTIC AIR INTO THE STATE. THE COLD
AIR WILL CHANGE THE RAIN OVER TO SNOW LATE MONDAY NIGHT. THEN ON
TUESDAY THE BACKSIDE TROUGH/DEFORMATION AXIS WILL SLIDE THROUGH THE
AREA KEEPING SNOW CHANCES AROUND. HIGH TEMPERATURES WILL FALL BACK
TO THE LOW 30S MIDWEEK WITH THIS LATEST BATCH OF ARCTIC AIR.

MARINE...

A DEEPENING LOW PRESSURE SYSTEM OVER THE NORTHEASTERN GREAT LAKES IS
PRODUCING A VERY TIGHT PRESSURE GRADIENT OVER THE REGION. THE
INFILTRATION OF YET ANOTHER SURGE OF ARCTIC AIR HAS DECREASED THE
STABILITY...AND IN COMBINATION WITH THE GRADIENT FLOW HAS LEAD TO
ANOTHER ROUND OF GALES OVER LAKE HURON. OBSERVATIONS HAVE BEEN
STEADILY IN THE 35 TO 40 KNOT RANGE OVER MOST OF THE BASIN EXCLUDING
ONLY A FEW NEARSHORE ZONES. THESE WESTERLY GALES WILL CONTINUE INTO
TONIGHT BEFORE HIGH PRESSURE BUILDING INTO THE AREA HELPS RELAX THE
GRADIENT AND WINDS SOME ON FRIDAY. COLD UNSTABLE AIR WILL CONTINUE
TO RESIDE OVER THE EASTERN LAKES INTO THE WEEKEND BUT A LOWER MIXED
LAYER WILL RESULT IN WINDS LESS THAN GALE FORCE DURING THAT TIME.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MIZ060>063-
     068>070.

LAKE HURON...GALE WARNING UNTIL 3 AM EST FRIDAY FOR LHZ362-363-421-441-462>464.

     SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LHZ442-443.

     GALE WARNING UNTIL 7 PM EST THIS EVENING FOR LHZ361.

     GALE WARNING UNTIL 1 PM EST THIS AFTERNOON FOR LHZ422.

LAKE ST CLAIR...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LCZ460.

MICHIGAN WATERS OF LAKE ERIE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR LEZ444.

     LOW WATER ADVISORY UNTIL 4 AM EST FRIDAY FOR LEZ444.

&&

$$

AVIATION.....SC
UPDATE.......SC
SHORT TERM...DG
LONG TERM....DRK
MARINE.......DRK


YOU CAN OBTAIN YOUR LATEST NATIONAL WEATHER SERVICE FORECASTS ONLINE
AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).



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