FXUS63 KDTX 291715
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1215 PM EST SUN NOV 29 2009
.AVIATION...
EXPANSIVE AREA OF RAIN ACROSS THE WESTERN HALF OF LOWER MICH GAIN WILL
SPREAD INTO THE AREA THIS AFTERNOON AHEAD OF AN ADVANCING COLD
FRONT. THIS AREA OF RAIN IS EXPECTED TO EXPAND IN COVERAGE OVER
SOUTHEAST MICHIGAN THIS AFTERNOON AS IT ENCOUNTERS MORE FAVORABLE
UPWARD FORCING. WILL ALSO SEE A BIT OF A CONVECTIVE ELEMENT FROM
PTK SOUTHWARD...WITH A SLIGHT CHANCE TO SEE A THUNDERSTORM AT DTW
AND DET. MVFR CEILINGS/VISIBILITIES WILL BECOME PREVALENT OVER THE
NEXT FEW HOURS AS THE COLD FRONT APPROACHES...WITH A FEW DIPS INTO
IFR ASSOCIATED WITH THE HEAVIEST RAIN. COLD FRONT WILL PUSH DOWN
ACROSS SOUTHEAST MICHIGAN 18-23Z...FLIPPING WINDS TO THE
NORTHWEST...ALLOWING PRECIPITATION TO TAPER OFF WHILE TURNING TO A
RAIN/SNOW MIX...AND LOWERING CEILINGS TO LOW MVFR/IFR. THESE LOW
CEILINGS ARE EXPECTED TO REMAIN OVERHEAD INTO TOMORROW...LIFTING
BUT STILL REMAINING MVFR.
&&
.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.....HLO
SHORT TERM...MR
LONG TERM....SF
MARINE.......MR
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