FXUS63 KDTX 291137
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
637 AM EST SUN NOV 29 2009

.AVIATION...

STRATUS DECK STRUGGLING TO MATERALIZE THIS MORNING WITH DEVELOPMENT 
APPEARING TIED TO A SURFACE TROUGH STILL POSITIONED FROM NEAR GRAND 
RAPIDS UP INTO NORTHERN LOWER MI.  BETTER BOUNDARY LAYER COOLING AND 
LIGHT WINDS CONTRIBUTING INSTEAD TO MVFR FOG FORMATION.  LATEST 
SATELLITE AND OBSERVATIONAL TRENDS SUGGEST FOG WILL REMAIN THE 
PRIMARY ISSUE THROUGH MID MORNING...PREDOMINATELY AT MVFR LEVELS 
ALTHOUGH CANNONT RULE OUT BRIEF PERIODS OF IFR/LIFR RIGHT AROUND 
SUNRISE.  STRATUS DECK WILL EVENTUALLY EXPAND SOUTH/EAST AND INTO 
THE REGION BY AFTERNOON AS A LOW LEVEL FRONTAL BOUNDARY SLIDES 
THROUGH.  RAIN WILL FOCUS ALONG AND BEHIND THIS BOUNDARY INTO THE 
EVENING HOURS.  CEILINGS WILL LOWER TOWARD IFR/LIFR AT THIS POINT 
GIVEN THE DEPTH OF THE MOISTURE MOVING IN.  SOUTHWEST WINDS FOR MUCH 
OF THE DAY WILL BECOME NORTHWESTERLY TONIGHT BEHIND THE FRONT.

&&

.PREV DISCUSSION...ISSUED 332 AM EST SUN NOV 29 2009 

SHORT TERM...TODAY

POSITIVELY TILTED UPPER TROUGH CURRENTLY EXTENDING ACROSS THE 
DAKOTAS/MN WILL SHIFT EAST INTO THE GREAT LAKES TODAY.  AT THE 
SURFACE...COLD FRONT CONTINUING TO DRIFT SOUTHEAST INTO NORTHERN 
LOWER MI...ACCOMPANIED BY AN EXPANDING AREA OF STRATUS. THE 
INCREASING HEIGHT FALLS WILL ALLOW A SFC WAVE TO DEVELOP AND RIDE 
NORTHEAST ALONG THIS BOUNDARY AS IT SETTLES INTO THE SAGINAW VALLEY 
THIS MORNING.  DEEPER MOISTURE AND STRONGER FORCING WILL INITIALLY 
BE LACKING...ALTHOUGH THE EXPANDING STRATUS WILL MAKE RUN TOWARD THE 
NORTHERN FORECAST AREA OVER THE COURSE OF THE MORNING.  THIS WILL 
RESULT IN DRY CONDITIONS HOLDING THROUGH THE MORNING HOURS...SO 
WILL PULL POPS FOR THIS PERIOD.  

BY AFTERNOON...LATEST MODEL SOUNDINGS AND CROSS SECTIONS STILL 
INDICATE AN INCREASE IN MID LEVEL FRONTOGENESIS WITHIN AN AREA OF 
DEFORMATION AS THE LOW LEVEL FRONTAL BOUNDARY SAGS SOUTHEAST. THIS 
WILL OCCUR IN THE PRESENCE OF GOOD LEFT EXIT REGION UPPER JET 
DYNAMICS...DEEPER MOISTURE TRANSPORT AND A NARROW CORRIDOR OF LOWER 
STABILITY WITHIN THE 700-500 MB LAYER.  THIS SETUP WILL SUPPORT AN 
AREA OF RAIN DEVELOPING ALONG THE FRONTAL ZONE AS IT PROGRESSES 
SOUTHEAST THROUGH THE AFTERNOON/EARLY EVENING.  THE THERMAL PROFILE 
WILL BE COOLING DURING THIS TIME...BUT LATEST SOUNDINGS/THICKNESSES 
INDICATE PRECIPITATION WILL REMAIN IN THE LIQUID FORM ACROSS THE 
NORTH THROUGH 00Z.  

THICKENING CLOUD COVER AND THE ONSET OF COLD AIR ADVECTION 
ACCOMPANYING THE FRONTAL PASSAGE WILL RESULT IN A SLIGHTLY LARGER 
SPREAD IN HIGH TEMPERATURES AREAWIDE.  WEAK THERMAL RIDGE IN PLACE 
OVER THE SOUTHERN COUNTIES WITH A FEW PEAKS OF SUN EARLY AND A 
PERSISTENT SOUTHWEST LOW LEVEL FLOW WILL HELP READINGS REACH INTO 
THE UPPER 40S-LOWER 50S TODAY. THE SAGINAW VALLEY/THUMB WILL SEE 
LESS RECOVERY AS CLOUDS THICKEN EARLIER WHILE COLD AIR BEGINS TO
DRAIN IN BY AFTERNOON. THIS WILL KEEP HIGHS IN THE LOWER 40S...
STILL SLIGHTLY ABOVE NORMAL.

LONG TERM...

A COUPLE OF SHOTS AT ACCUMULATING SNOW DURING THE EXTENDED PERIOD.

DEEPENING LOW PRESSURE PULLING AWAY FROM SOUTHEAST MICHIGAN TONIGHT 
WILL USHER IN NOTICEABLY COLDER AIR...WITH 850 MB TEMPS FALLING TO 
BETWEEN -6 (SOUTH) TO -8 C (NORTH) BY 12Z MONDAY. 

MID LEVEL DRY SLOT MOVING INTO SOUTHEAST MICHIGAN WILL LIMIT 
PRECIPITATION CHANCES TONIGHT...BUT LAKE HURON LAKE BAND WILL LIKELY 
PROVIDE GLANCING BLOW OVERNIGHT TO EASTERN THUMB SHORELINE. 
HOWEVER...BOTH NAM/GFS INDICATING THE MAX 925 MB OMEGA/CONVERGENCE 
REMAINING OFFSHORE...AS LOW LEVEL WINDS REMAIN IN THE 330-340 RANGE. 
PRONOUNCED SURFACE RIDGING MONDAY MORNING WILL ALSO BE A 
HINDRANCE....AND WILL CARRY JUST A CHANCE OF FLURRIES ACROSS THE 
CWA. SNOW CHANCES WILL BEGIN TO RAMP UP MONDAY AFTERNOON AND 
ESPECIALLY MONDAY EVENING. 

SHORTWAVE/LEFT EXIT REGION OF AN UPPER LEVEL JET STILL PROGGED TO 
IMPACT SOUTHERN LOWER MICHIGAN MONDAY EVENING...WITH A GOOD SHOT 
(ALBEIT BRIEF) OF ISENTROPIC ASCENT...COUPLED WITH LAKE MICHIGAN 
ENHANCEMENT SHOULD PROVE ADEQUATE FOR SNOW (LIKELY POPS)...AS NAM 
ALSO SHOWS NICE LOW LEVEL FRONTAL CIRCULATION DEVELOPING NEAR 
6Z...WITH 3 G/KG OF SPECIFIC HUMIDITY AT 850 MB. A WELL DEFINED 
SURFACE TROUGH IS ALSO REFLECTED IN THE PRESSURE FIELDS. WITH THE 
SMALL WINDOW OF STRONG LIFT (JUST BEFORE MIDNIGHT)...THINKING WE
ARE LOOKING AT ACCUMULATIONS OF HALF AN INCH TO AROUND AN INCH
(PREDOMINATELY M59 NORTH). THIS ALSO MATCHES UP RATHER NICELY WITH
THE GFS.

UPPER LEVEL TROUGH/COLD POOL OVER THE GULF OF ALASKA WITH TWO TIGHT 
CIRCULATIONS NOTED ON THE WATER VAPOR IMAGERY WILL THEN BECOME THE 
FOCUS FOR THE MID TO LATE PART OF THE WEEK...AS PHASING WITH THE 
CUTOFF OVER THE FOUR CORNER REGIONS REMAINS A CONCERN...SETTING US 
UP FOR A POTENTIAL WINTER STORM. MEDIUM RANGE MODEL CONSENSUS 
TONIGHT CONTINUES TO SHOW A FASTER TREND WITH THE NORTHERN STREAM 
TROUGH ARRIVING OVER THE GREAT LAKES REGION...WITH PHASING OF THE 
CUTOFF LOW OVER TEXAS/WESTERN GULF STATES OCCURRING A BIT TOO LATE.
THE NORTHERN STREAM TROUGH AXIS REMAINS A BIT TOO POSITIVELY TILTED.
WILL NEED TO KEEP OUR GUARD UP ON THURSDAY AS CANADIAN 
GLOBAL/EUROPEAN ARE CLOSE CALLS...BUT BETTER CONFIDENCE IN THE 
COLD AIR BECOMING ESTABLISHED OVER THE REGION...WITH THE EUROPEAN 
AND THE ENSEMBLE MEAN SHOWING 850 MB TEMPS DOWN TO -12 C BY 
FRIDAY...LIKELY HOLDING MAXES IN THE MID 30S.

MARINE...

A RELATIVELY WEAK WIND FIELD WILL EXIST THROUGH THE AFTERNOON AS AN 
AREA OF LOW PRESSURE LIFTS THROUGH.  COLDER AIR FILTERING IN BEHIND 
THIS SYSTEM WILL RESULT IN INCREASING WINDS AND WAVES THIS EVENING 
AND TONIGHT ACROSS LAKE HURON.  NORTHWEST GUSTS MAY REACH 25 KNOTS 
AT TIMES...WHILE WAVES BUILD TO 3 TO 6 FEET ALONG THE NEARSHORE 
WATERS.  SMALL CRAFT CONDITIONS WILL CONTINUE INTO MONDAY FOR HIGHER 
WAVES.  WINDS WILL SHIFT TOWARD THE SOUTHWEST BRIEFLY MONDAY 
AFTERNOON/EVENING...WITH THE LONGER FETCH AGAIN BUILDING THE WAVE
HEIGHTS ON OUTER SAGINAW BAY.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.

LAKE HURON...
     SMALL CRAFT ADVISORY...SAGINAW BAY...FROM 7 PM SUNDAY TO 10 AM 
     MONDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS FROM PORT AUSTIN TO PORT 
     HURON...FROM 7 PM SUNDAY TO 4 PM MONDAY.

LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.

&&

$$

AVIATION.....MR
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR

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