000
FXUS63 KDTX 092311
AFDDTX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
611 PM EST MON DEC 9 2013


.AVIATION...

//DISCUSSION...

DRY AIR ADVECTING IN FROM THE WEST AND LOWERING INVERSION HEIGHTS
HAS EFFECTIVELY ENDED THE LAKE EFFECT SNOW OVER THE TAF SITES THIS
EVENING...HOWEVER LOW LEVEL MOISTURE WILL REMAIN CAUSING A BKN-OVC
DECK AROUND 3K FT. THE HEIGHT OF THE DECK WILL CAUSE ISSUES IN THE
FORECAST AS IT BOUNCES BETWEEN 2500 AND 3500 FT...OR MVFR TO
VFR...HOWEVER CIGS ARE EXPECTED TO SETTLE AROUND 3500 FT ACROSS THE
SOUTH WITH 2500 FT ACROSS THE NORTH. FLURRIES ARE STILL POSSIBLE FOR
THE FIRST FEW HOURS...MAINLY FROM PTK NORTH TO MBS. WEST-SOUTHWEST
WINDS WILL GUST AROUND 20 KNOTS UNTIL SUBSIDING LATER THIS EVENING.
ANOTHER COLD FRONT WILL PUSH ACROSS THE AREA ON TUESDAY. THIS WILL
ONCE AGAIN BRING GUSTY WINDS FROM THE SOUTHWEST. GUSTS TO 30 KNOTS
CAN BE EXPECTED THROUGH THE AFTERNOON AND EVENING.

//DTW THRESHOLD THREATS...

* HIGH CONFIDENCE IN CEILINGS BELOW 5000 FT THROUGH THIS
  EVENING...MEDIUM CONFIDENCE LATER TONIGHT AND INTO TUESDAY.

&&

.PREV DISCUSSION...ISSUED 359 PM EST MON DEC 9 2013

SHORT TERM...THROUGH TONIGHT

RESURGENCE IN LAKE EFFECT HAS OCCURRED OVER THE PAST HOUR...WITH
SNOW BANDS OFF LAKE MICHIGAN HAVING RE-EXPANDED NORTH OF THE I-94
CORRIDOR AFTER ONLY A FEW HOUR BREAK. THIS IS LIKELY DUE TO COLDER
AIR PUSHING ACROSS LAKE MICHIGAN AND INTO SOUTHEAST MICHIGAN BEHIND
A COLD FRONT. THIS HAS EFFECTIVELY INCREASED LAPSE RATES OVER THE
LAND AND SENT LAKE TO 850MB TEMPERATURE DIFFERENTIALS OVER THE LAKE
ABOVE 20 C. PRIOR TO THE COLDER AIR`S ARRIVAL...DRIER AIR HAD BEEN
MAKING INROADS INTO THE LOWER LEVELS AND LIMITING ICE NUCLEI. AS THE
COLDER AIR HAS SETTLED IN HOWEVER...THE MOISTURE HAS BECOME PLACED
SOLIDLY WITHIN THE DENDRITIC GROWTH ZONE...DESPITE DEPTH OF
SATURATION SHRINKING. THIS CHANGE IS APPARENT WHEN LOOKING AT THE
CHANGE THAT HAS OCCURRED IN THE SNOWFLAKES OVER THE PAST
HOUR...LOOKING MORE LIKE DENDRITES HERE AT DTX. POPS WERE INCREASED
TO LIKELY/CATEGORICAL FOR FAVORED AREAS NORTH OF THE I-94 CORRIDOR
THIS EVENING...AND DID CARRY AT LEAST SOME CHANCES ALL THE WAY DOWN
TO THE OHIO BORDER AS WINDS SHIFT SLIGHTLY FROM SOUTHWEST TO WEST
AND POTENTIAL FOR A FEW BANDS TO FOCUS SOUTH OF M-59 INCREASES.
LIGHT ACCUMULATIONS ARE POSSIBLE...UP TO ONE HALF INCH UNDER THE
MORE PERSISTENT BANDS.

TRICKY FORECAST THEN FOR THE REMAINDER OF THIS EVENING AS COLD AIR
CONTINUES TO STREAM OVER THE WARMER LAKE AND DRIER AIR CONTINUES TO
WORK IN BEHIND THE FRONT. FORECAST SOUNDINGS DO SHOW SOME DRYING IN
THE LOWER LEVELS OVERNIGHT. THIS IS A LITTLE UNCERTAIN CONSIDERING
MOISTURE CONTINUING TO STREAM IN FROM OFF THE LAKE UNDER AN
INVERSION. SATELLITE IMAGERY FROM OVER LAKE MICHIGAN THE PAST FEW
HOURS HAS SHOWN A PRONOUNCED EROSION OF THE LAKE EFFECT BANDS FROM
WEST TO EAST OVER THE LAKE AS THE DRIER ARRIVES...AND DID KEEP POPS
OVERNIGHT ONLY IN THE CHANCE CATEGORY.

TEMPERATURES WILL BECOME QUITE COLD OVERNIGHT AS DEWPOINTS PLUMMET
INTO THE SINGLE DIGITS AND GUSTY WINDS SUBSIDE. AREAS THAT HAVE
SEVERAL INCHES OF SNOW ON THE GROUND FROM THE PAST FEW DAYS WILL
ESPECIALLY SEE TEMPS FALL...AS THE FRESH SNOW COVER HELPS THE GROUND
RADIATE AND WINDS DECOUPLE. LOOKING FOR ONLY SINGLE DIGIT MIN TEMPS
IN MANY LOCATIONS ACROSS THE THUMB AND TRI-CITIES...WITH LOW/MID
TEENS ELSEWHERE.

LONG TERM...TUESDAY THROUGH SATURDAY

THE BROAD LONGWAVE TROUGH OVER THE GREAT LAKES DOES NOT LOOK TO GO
ANYWHERE SOON. BOTH GFS AND ECMWF SHOW THIS TROUGH HOLDING FOR AT
LEAST THE NEXT WEEK. SEVERAL SHORTWAVES WILL DROP INTO THE TROUGH
BRINGING SOME CHANCES OF SNOW AND REINFORCING SHOTS OF ARCTIC AIR IN
THEIR WAKE.

ON TUESDAY...AFTER A BRIEF PERIOD OF SFC RIDGING IN THE WAKE OF
MONDAYS LOW PRESSURE SYSTEM...A SECOND LOW WILL TRACK ACROSS LAKE
SUPERIOR DRAGGING A COLD FRONT THROUGH LOWER MI IN THE AFTERNOON.
GUSTY SW FLOW AHEAD OF THE FRONT WILL VEER WESTERLY BEHIND THE
FRONT. WIND SPEEDS WILL BE SOLIDLY AROUND 30 KNOTS IN THE LOWEST FEW
THOUSAND FEET. THE INVERSION LOOKS TO WASH OUT ALLOWING DECENT
MIXING THROUGH THE DAY. THIS SHOULD ALLOW GUSTS TO REACH 30 MPH OR
SO AT THE SFC FOR MOST OF SE MI. MODELS SHOW A NARROW BAND OF
MOISTURE WITH THE FRONT ACROSS THE SAGINAW VALLEY BUT THE CAA BEHIND
THE FRONT WILL PROMOTE LAKE EFFECT. QUESTION AS ALWAYS IS HOW FAR
EAST WILL THE LAKE EFFECT MAKE IT? MODELS SHOW DRY AIR MOVING IN AT
850MB WITH THE BEST LAKE CONVERGENCE SIGNATURE NOT ARRIVING TIL ITS
TOO LATE.

BETTER CHANCE OF SNOW WILL COME ON WEDNESDAY ALTHOUGH STILL NOT
OVERLY IMPRESSED. A COMPACT MID LEVEL VORT MAX WILL ROUND THE BASE
OF THE TROUGH AND PASS THROUGH THE NORTHERN OHIO VALLEY. THE BEST
FORCING AND LIFT APPEARS TO PASS TO OUR SOUTH BUT STILL WEAK
TROUGHING AND FRONTOGENESIS SHOULD PROVIDE SOME LIFT OVER THE AREA.
IN ADDITION IT COULD RECEIVE A BOOST FROM THE CONVERGENT BAND
ALREADY LOCATED OVER SW LOWER MI. OVERALL A MARGINAL EVENT AS
MOISTURE CANNOT REALLY BE FOUND IN ANY MODEL. AN AFTERNOON TOTAL OF
ONLY A FEW HUNDREDTHS IS THE COMMON THEME WHICH WOULD AMOUNT TO LESS
THAN AN INCH. SOME LAKE EFFECT WILL LINGER THROUGH THE EVENING
HOURS. THIS SYSTEM WILL USHER IN SOME OF THE COLDEST AIR WE HAVE
SEEN SO FAR WITH 850 MB TEMPS POSSIBLY COOLER THAN -20C ENTERING THE
CWA. WIND CHILLS WILL RARELY EXCEED 10F THROUGH MID WEEK WITH
WEDNESDAY NIGHT FALLING TO NEAR -10F.

HIGH PRESSURE BUILDS TO THE OHIO VALLEY AND SOUTHERN GREAT LAKES ON
WEDNESDAY NIGHT AND INTO THURSDAY WHILE ANOTHER CLIPPER SYSTEM
TRACKS ACROSS THE NORTHERN GREAT LAKES. THIS SYSTEM WILL BRING YET
ANOTHER CHANCE FOR SOME SNOW SHOWERS ON THURSDAY THROUGH FRIDAY TO
MAINLY THE NORTHERN CWA /SAGINAW VALLEY AND NORTHERN THUMB/.
WEST-NORTHWEST WINDS WILL PREVAIL THOUGH THE EXTENDED TIMEFRAME
KEEPING HIGH TEMPERATURES IN THE LOW TO MID 20S THROUGH THE END OF
THE WEEK. THE NEXT MAJOR SYSTEM TO IMPACT SOUTHEAST MICHIGAN WILL BE
ON SATURDAY AND SATURDAY EVENING AS A LOW PRESSURE SYSTEM TRACKS
ACROSS THE OHIO VALLEY. AT THIS TIME...SOUTHEAST MICHIGAN WILL BE
NORTH OF THIS SYSTEM KEEPING PRECIPITATION AS ALL SNOW.
HOWEVER...BEING NEARLY A WEEK OUT DID NOT FEEL CONFIDENT PUTTING
MUCH MORE THAN CHANCE POPS IN THE FORECAST FOR FRIDAY NIGHT THROUGH
SATURDAY NIGHT.

MARINE...

AN ACTIVE STRETCH OF WEATHER OVER THE GREAT LAKES THROUGH MID WEEK.
A TIGHTENING PRESSURE GRADIENT WILL PRODUCE GALES OVER MOST OF LAKE
HURON THIS EVENING AND INTO THE OVERNIGHT. THE ARCTIC AIRMASS
OVERHEAD COMBINED WITH THESE WIND SPEEDS WILL MAKE FREEZING SPRAY AN
ISSUE THUS A WARNING HAS BEEN ISSUED TO ACCOMPANY THE GALE WARNING.
AFTER THIS SYSTEM MOVES OUT A SECOND LOW WILL PASS ACROSS NORTHERN
LAKE HURON. ONCE THE LOW EXITS TO ONTARIO...THE GRADIENT LOOKS TO
TIGHTEN UP QUICKLY WITH FAIRLY STRONG DROPS IN PRESSURE GRADIENT
MAGNITUDE FORCE OVER THE LAKES AND GOOD COLD AIR ADVECTION PRODUCING
YET ANOTHER CHANCE FOR GALES WEDNESDAY NIGHT. THOUGH A MARGINAL
EVENT...MODELS HAVE BEEN CONSISTENT WITH WINDS REACHING LOW END
GALES THUS A GALE WATCH HAS BEEN ISSUED.

&&

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

LAKE HURON...
     HEAVY FREEZING SPRAY WARNING...LHZ361-LHZ362-LHZ363-LHZ421-LHZ441-
     LHZ462...UNTIL 4 AM TUESDAY.

     GALE WARNING...LHZ361-LHZ362-LHZ363-LHZ421-LHZ441-LHZ462...UNTIL 4
     AM TUESDAY.

     GALE WATCH...LHZ462-LHZ463-LHZ464...FROM 7 PM TUESDAY TO 4 AM
     WEDNESDAY.

     GALE WATCH...LHZ361-LHZ362-LHZ363...FROM 7 PM TUESDAY TO 10 AM
     WEDNESDAY.

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

&&

$$

AVIATION.....KURIMSKI
SHORT TERM...HLO
LONG TERM....DRK/RK
MARINE.......DRK


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