FXUS63 KDTX 050231
AFDDTX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
931 PM EST FRI DEC 4 2009
.UPDATE...
EARLIER SNOW SHOWER ACTIVITY HAS DIMINISHED TO JUST FLURRIES WITH
LOWERING INVERSION HEIGHTS. WEST-SOUTHWESTERLY FLOW OFF LAKE
MICHIGAN WILL HOWEVER SUSTAIN THE FLURRIES THROUGH A GOOD PORTION
OF THE NIGHT...BEFORE THE LOW LEVEL FLOW BACKS MORE SOUTHERLY.
WHILE A LARGE CLEARING HAS OCCURRED ACROSS THE DETROIT AND ANN
ARBOR METRO AREAS...LOW CLOUDS HAVE BEEN SLOWLY CREEPING TOWARD
THE METRO AREAS FROM THE SOUTHWEST. THESE CLOUDS ARE UNDERNEATH A
STRENGTHENING LOW LEVEL INVERSION. WITH VERY WEAK COLD AIR
ADVECTION FORECAST UNDERNEATH THE INVERSION BASE...THESE CLOUDS
SHOULD REMAIN OVER THE REGION THROUGH THE NIGHT. THEREFORE...WILL
BOOST THE OVERNIGHT CLOUD COVER A BIT.
&&
.PREV DISCUSSION...ISSUED 604 PM EST FRI DEC 4 2009
AVIATION...
CONTINUED SOUTHWEST FLOW WILL MAINTAIN QUITE A BIT OF STRATO CU AT
FNT AND MBS THROUGH A GOOD PORTION OF THE NIGHT...WITH PERIODIC
FLURRIES/LIGHT SNOW SHOWERS CONTINUING AT MBS. FROM PTK INTO
DETROIT...SKIES SHOULD CONTINUE TO CLEAR OUT AS HIGH PRESSURE
NUDGES IN FROM THE SOUTH. CEILINGS FOR THE MOST PART WILL REMAIN
VFR. HOWEVER...SOME OCCASIONAL MVFR CONDITIONS ARE POSSIBLE NEAR
MBS IN SOME OF THE HEAVIER SNOW SHOWERS.
PREV DISCUSSION...ISSUED 410 PM EST FRI DEC 4 2009
SHORT TERM...THIS AFTERNOON AND TONIGHT
A FLAREUP OF SNOW SHOWER ACTIVITY HAS TAKEN PLACE AGAIN THIS
AFTERNOON ACROSS SOUTHEASTERN MICHIGAN. THIS APPEARS TO BE IN
RESPONSE TO THE STEEPENING/LINKAGE OF MIXED LAYERS DIURNALLY...AND
INCREASED CVA IN ADVANCE OF A VERY VERY WEAK/SUBTLE SHORTWAVE OVER
NORTHERN ILLINOIS. IN ADDITION...SAGINAW BAY HAS BEEN PROVIDING A
BETTER THERMODYNAMIC PROFILE IN THAT VICINITY...ALTHOUGH CELLS TO
THIS POINT HAVEN/T RESPONDED MUCH IN IMPROVED ORGANIZATION.
CONVECTIVE DEPTHS ACROSS THE SOUTH REMAIN VERY LIMITED...EXPECTING
FLURRIES MAINLY SOUTH OF M 59.
AN UPPER LEVEL CONFLUENT REGIME WILL SET UP OVER SOUTHEASTERN
MICHIGAN OVERNIGHT AS COUPLED JET STRUCTURE ORGANIZES EAST OF THE
STATE. THIS WILL SUPPORT A SURFACE RIDGE AXIS TO SWEEP ACROSS
SOUTHERN PORTIONS OF THE FORECAST AREA INTO TONIGHT. WITH THE
ANTICYCLONIC FLOW....SURFACE TRAJECTORIES WILL TREND SOUTHERLY.
THEREFORE...WITH A NON FAVORABLE TRAJECTORY/A LACK OF A NEAR SURFACE
INVERSION/AND INVERSION HEIGHTS THAT FALL TO ROUGHLY 6KFT...NOT
EXPECTING MUCH UPSTREAM ACTIVITY TO SURFACE INTO LOWER MICHIGAN.
CONTINUED CYCLONIC FLOW CALLS FOR A CHANCE POP FOR -SHSN OVERNIGHT
NEAR/NORTH OF I 69. SNOWFALL ACCUMULATIONS THIS EVENING AND
OVERNIGHT WILL BE A DUSTING FOR MOST AREAS...WITH 1 TO 2 INCHES
POSSIBLE ALONG THE IMMEDIATE SAGINAW BAY SHORELINE OF TUSCOLA/HURON
COUNTIES. CLOUDS SHOULD SCATTER OUT THIS EVENING SOUTH OF I69. WITH
A RESIDUAL TRACE OF SNOW REMAINING...LOWS TONIGHT WILL TAKE A
PLUNGE...UPPER TEENS TO LOWER 20S.
LONG TERM...
ACTIVE PATTERN EXPECTED TO CONTINUE THROUGH NEXT WEEK WITH A
STRONG UPPER LEVEL RIDGE OVER THE GULF OF ALASKA AND DOWNSTREAM
LONGWAVE TROUGH OVER THE CENTRAL CONUS. SEVERAL SHORT WAVES WILL
ROTATE SOUTHWARD THROUGH THE BASE OF THIS TROUGH AND MOVE INTO OUR
AREA BRINGING A CHANCE OF PRECIP.
LAKE EFFECT SNOW WILL BE TAPERING OFF TOMORROW MORNING AS THE COLUMN
DRIES OUT AND WINDS BECOME MORE SOUTHERLY. A FEW BREAKS IN THE
CLOUDS WILL ALLOW MAX TEMPS TO REACH THE MID TO UPPER 30S. WITH WEAK
HIGH PRESSURE TO OUR SOUTH...DRY CONDITIONS ARE EXPECTED TO CONTINUE
THROUGH THE WEEKEND BEFORE OUR FIRST SYSTEM APPROACHES THE AREA ON
MONDAY. VORT MAX WILL GET SHEARED OUT AS IT EJECTS FROM THE DESERT
SOUTHWEST WITH FAST WESTERLY FLOW ALOFT. WAA IS ALSO WEAK WITH VERY
LITTLE ISENTROPIC LIFT. GFS AND ECMWF AGREE ON TIMING AND TRACK WITH
THE NAM FARTHER NORTH. EVEN WITH A TRACK FURTHER TO THE
NORTH...FORECAST SOUNDINGS SUGGEST AN ALL SNOW EVENT. GIVEN HOW FAST
THIS SYSTEM IS EXPECTED TO MOVE ACROSS THE AREA...ACCUMULATIONS WILL
GENERALLY BE AROUND 1-2 INCHES. HIGH PRESSURE WILL SLIDE ACROSS THE
REGION MONDAY NIGHT/TUESDAY MORNING WITH THE POTENTIAL FOR GOOD
RADIATIONAL COOLING.
SECOND STORM APPROACHING ON WED MORNING APPEARS TO BE THE MORE
SIGNIFICANT SYSTEM WITH BETTER DYNAMICS ALOFT AND STRONG LOW LEVEL
THERMAL ADVECTION. VORT MAX CURRENTLY OVER NORTHERN ALASKA WILL DIVE
SOUTHWARD ALONG THE WEST COAST EARLY NEXT WEEK AND EJECT OUT OF THE
SOUTHWEST. THIS WILL ALLOW A STRONG SURFACE LOW PRESSURE SYSTEM TO
MOVE ACROSS THE CENTRAL PLAINS AND INTO OUR REGION. MODELS GENERALLY
AGREE ON THIS SCENARIO BUT SUBTLE DIFFERENCES ON TRACK AND RESULTING
PTYPE PERSIST. 00Z ECMWF IS MORE AMPLIFIED AND FURTHER NORTH WITH
THE LOW RESULTING IN MAINLY A RAIN EVENT. 12Z ECMWF AND GFS ARE MORE
PROGRESSIVE WITH THE LOW FURTHER SOUTH. GFS BUFKIT SOUNDINGS SUGGEST
THERMAL PROFILES FROM THE SURFACE TO 850 MB WILL HOVER NEAR OR JUST
ABOVE 0C DURING THE DAY WED SO MAINTAINED MIX DURING THAT TIME
FRAME. OTHERWISE...LOOKS LIKE MAINLY SNOW. BUMPED UP POPS TO LIKELY
GIVEN THE MODEL CONSISTENCY ON TIMING. HIGH PRESSURE AND STRONG
WINDS WILL BUILD IN BEHIND THE LOW WITH ANOTHER FRONT APPROACHING
THE AREA BY FRIDAY.
MARINE...
A SURFACE RIDGE AXIS WILL PUSH ACROSS THE NORTHERN OHIO RIVER VALLEY
OVERNIGHT. THIS WILL ALLOW SURFACE WINDS TO BEGIN EASING WHILE
TURNING MORE SOUTHERLY. THE GRADIENT WILL HOLD ENOUGH DURING THE
EVENING TO CONTINUE WINDS OF 20 TO 25 KNOTS. LATER TONIGHT GRADIENT
FLOW WILL EASE AND ALLOW WAVE HEIGHTS TO GRADUALLY SUBSIDE. WILL
MAINTAIN THE CURRENT SMALL CRAFT ADVISORIES INTO THIS EVENING FOR
INNER SAGINAW BAY...TO TOMORROW MORNING FOR THE TIP OF THE THUMB
AREA. WINDSPEEDS ARE EXPECTED TO INCREASE AGAIN LATE SATURDAY NIGHT
AND SUNDAY MORNING AS A WEAK SURFACE TROUGH PASSES TO THE NORTH.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LAKE HURON...
SMALL CRAFT ADVISORY...INNER SAGINAW BAY...UNTIL 10 PM FRIDAY.
SMALL CRAFT ADVISORY...OUTER SAGINAW BAY AND THE NEARSHORE WATERS
FROM PORT AUSTIN TO HARBOR BEACH...UNTIL 4 AM SATURDAY.
LAKE ST CLAIR...NONE.
MI WATERS OF LAKE ERIE...NONE.
&&
$$
UPDATE.......SC
AVIATION.....SC
SHORT TERM...CB
LONG TERM....AGD
MARINE.......CB
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AT WWW.WEATHER.GOV/DETROIT (ALL LOWER CASE).
