Heavy Snow in Michigan, December 23, 2002

AREA FORECAST DISCUSSION...CORRECTION OF TIME.
NATIONAL WEATHER SERVICE MARQUETTE MI
505 AM EST MON DEC 23 2002

MAIN FCST CONCERNS IN THE SHORT TERM ARE LES TRENDS/HEADLINES.

WV IMAGERY AND RUC ANALYSIS INDICATED ELONGATED MID/UPR LVL NRN
STREAM CUTOFF LO CENTERED OVER NRN QUEBEC. STRONG SHRTWV/VORT WAS
LOCATED UPSTREAM...JUST NW OF LK SUPERIOR. IR/WV LOOPS ALSO SHOWED
AREA OF DEEPER MOISTURE AND ENHANCED TOPS HAD DESCENDED ACRS NW UPR
MI. LOW LVL MOISTURE WAS ALSO PLENTIFUL UPSTREAM PER CWPL SNDG
(MOIST ISOTHERMAL AT -16C TO 700 MB) AND REPORTS OF 3-5SM -SN
EARLIER OVER NE MN AND AT CYQT. COMBINATION OF UPWARD MOTION WITH
700-300 QVECTOR CONV WITH DPVA AHEAD OF THE SHRTWV AND COLDER H8
TEMPS TO NEAR -16C (GIVING LK-H8 DELTA/T TO AROUND 19C) HAS BROUGHT
NOTABLE INCREASE IN COVERAGE AND INTENSITY OF LES INTO NW UPR MI AND
ERN LK SUPERIOR. HEAVIER SNOW BEGAN NEAR KCMX AT 07Z WITH VSBY
FREQUENTLY DOWN TO NEAR 1/4SM WITH +SHSN AND HOUGHTON WEBCAMS ALSO
SHOWED VSBY DOWN TO AROUND 1/2SM AT TIMES. KMQT 88D SHOWED 280-290
ALIGNED BANDS WITH CORES OF 28DBZ REFLECTIVITY OVER ERN LK SUPERIOR
WITH BANDS APPEARING TO BRUSH THE SHORELINE E OF GRAND MARAIS.

TODAY...00Z/06Z WAS SLIGHTLY SLOWER WITH MOVEMENT OF SHRTWV/VORT
UPR MI THAN THE 00Z GFS WITH THE VORT AXIS INTO INTO NW UPR MI AT
18Z WHILE THE GFS PLACES IT OVER SE UPR MI. GIVEN RECENT
TRENDS...SLOWER ETA PREFERRED WHICH IS ALSO SUPPORTED BY THE 06Z
RUC.SO...EXPECT LCLY HEAVY LES TO CONTINUE OVER NW UPR MI TIL THIS
AFTERNOON WHEN DNVA/SUBSIDENCE TAKES OVER WITH LOWER INVERSION HGTS
AND ASSOCIATED WARMING OF H8 TEMPS TO AROUND 13C. SNOWFALL RATES UP
TO 1 INCH/HR SHOULD CONTINUE WITH ADDITIONAL ACCUMULATIONS OF UP TO
6 INCHES. ETA 950 MB WIND FCST DEPICTS SLOW VEERING TREND WITH
WEAKENING CONVERGENCE ZONE SHIFTING GRADUALLY SOUTH FROM KCMX AFT
12Z TOWARD NE ONTONAGONA AND CNTRL HOUGHTON COUNTY. SHIFT TOWARD 300
WIND WILL ALSO SHORTEN FETCH INTO MOST OF THE KEWEENAW.
HOWEVER...CONTINUED LIFT AHEAD OF THE SHRTWV ALONG WITH LOW LVL
MOISTURE UPSTREAM WILL KEEP ACCUMULATING LES GOING.SO...WL LEAVE LES
WARNING HEADLINE IN PLACE THROUGH THIS MORNING. OVER THE EAST...ETA
LINES UP WELL WITH CURRENT TRENDS AND IS CONSISTENT IN KEEPING 950
MB CONVERGENCE ZONE ACRS FAR ERN ALGER (NEAR GRAND MARAIS) TO NRN
LUCE COUNTY THROUGH 18Z. AFT 18Z...WINDS VEER ENOUGH FOR SOME LES TO
REACH KERY. HOWEVER...SYNOPTIC SUPPORT FROM SHRTWV WILL BE
DEPARTING/WEAKENING BY THIS TIME. SO...EXPECT SHARP GRADIENT TO
HEAVIER SNOW OVER NRN PORTION OF LUCE COUNTY AND FAR NRN SCHOOLCRAFT
COUNTY. AGAIN LES WARNING HEADLINE MAINTAINED INTO THIS AFTERNOON AS
LATER EXIT OF THE SHRTWV AND LONGER FETCH KEEP HEAVIER LES GOING
WELL INTO THE AFTERNOON OVER THE NE CWA.

OVER THE REST OF UPR MI...EXPECT THAT SCT -SHSN WILL DIMINISH BY
AFTERNOON AS THE SHRTWV MOVES THROUGH WITH ACCUMULATIONS AMOUNTING
TO NO MORE THAN A HALF INCH.

CAA SHOULD COUNTER DIURNAL TREND WITH HIGHS NOT NEAR EARLY MORNING
READINGS.

JLB

THE SHORTWAVE WILL MOVE ACROSS THE FORECAST AREA THIS EVENING. LATER
TONIGHT...ANOTHER WEAK SHORTWAVE WILL SLIDE ACROSS NORTHERN
WISCONSIN. UPPER LEVEL JET WILL REMAIN JUST SOUTH OF THE FORECAST
AREA AND WILL HAVE VERY LITTLE AFFECT ON THE FORECAST AREA. A
THERMAL RIDGE WILL MOVE INTO NORTHERN PLAINS AND WILL LOWER THE
DELTA-TS ACROSS LAKE SUPERIOR OVERNIGHT. THE SURFACE RIDGE WILL
INTENSIFY OVER THE NORTHERN PLAINS. ANTI-CYCLONIC FLOW WILL KEEP THE
WINDS OVER LAKE SUPERIOR OUT OF THE NORTHWEST. LOW LEVEL Q-VECTOR
CONVERGENCE WILL INCREASE OVER CENTRAL LAKE SUPERIOR OVERNIGHT. THIS
WILL KEEP LAKE EFFECT SNOWS GOING. WARM AIR ADVECTION AT 850MB WILL
LOWER THE INVERSION OVER LAKE SUPERIOR TO AROUND 900MB. CONDITION
FAVORABLE FOR LAKE EFFECT SNOWS TO CONTINUE...BUT WILL NOT PRODUCE
SIGNIFICANT ACCUMULATION.

A CLOSED LOW WILL MOVE TO EAST CENTRAL QUEBEC ON TUESDAY. A BROAD
RIDGE WILL SHIFT OUT OF THE CANADIAN ROCKIES INTO THE WESTERN
CANADIAN PRAIRIES. AS A WEAK SHORTWAVE MOVE ACROSS THE FORECAST AREA
TUESDAY MORNING...ANOTHER MUCH WEAKER SHORTWAVE WILL SLIDE DOWN THE
LEE OF THE CANADIAN ROCKYS RIDGE AND REACH NORTHWEST ONTARIO BY
12Z TUE. AS A COLD FRONT SWINGS INTO NORTHERN ATLANTIC STATES...
ANOTHER COLD FRONT WILL FOLLOW THE FIRST THROUGH NORTHERN ONTARIO. A
BROAD SURFACE RIDGES WILL MOVE INTO THE CENTRAL AND NORTHERN PLAINS.
850MB TEMPERATURES ON TUESDAY WILL LOWER TO -10C...GIVING A
LAKE-850MB DELTA-TS OF 13C. LOW LEVEL MOISTURE BELOW 850MB WILL BE
90 PERCENT OR HIGHER ON TUESDAY. ANTI-CYCLONIC FLOW AROUND THE RIDGE
WILL KEEP THE SURFACE WIND MAINLY OUT OF THE NORTHWEST ON TUESDAY.
THESE CONDITIONS ARE FAVORABLE FOR LAKE EFFECT SNOW TO CONTINUE OVER
NORTHERN U.P...MAINLY OVER THE KEWEENAW PENINSULA AND BETWEEN
MUNISING AND WHITEFISH POINT. Q-VECTOR CONVERGENCE WILL BE THE
STRONGEST IN THE MORNING OVER CENTRAL LAKE SUPERIOR...BUT WILL
WEAKEN THROUGH THE DAY.

TUESDAY NIGHT WILL SEE DRIER AIR MOVING INTO THE FORECAST AREA. WARM
AIR ADVECTION OUT OF THE CENTRAL PLAINS WILL BRING UP THE 850 MB
TEMPERATURES. A WEAK SHORTWAVE WILL SWING ACROSS THE FORECAST AREA.
LOW LEVEL Q-VECTOR ANALYSIS FAVOR MAINLY DIVERGENCE ACROSS THE AREA
TUESDAY NIGHT. WINDS WILL REMAIN OUT OF THE NORTHWEST...AND START TO
BACK WEST.

THE WINDS WILL BACK WEST ON WEDNESDAY. DELTA-TS WILL DECREASE TO 8C
OVER THE WEST AND 11C OVER THE EAST. LOW LEVEL RELATIVE HUMIDITY
WILL BE AROUND 65 PERCENT. A WEAK SHORTWAVE WILL MOVE ACROSS THE
AREA ON WEDNESDAY. CONDITIONS WILL STILL BE FAVORABLE FOR LAKE
EFFECT SNOW TO CONTINUE BUT WILL BE LIGHT AND SCATTERED. 280K
ISENTROPIC ANALYSIS SHOWING WEAK ASCENT ACROSS THE AREA ON
WEDNESDAY. WILL KEEP A MENTION OF LAKE EFFECT GOING INTO EARLY
WEDNESDAY NIGHT.

A THERMAL RIDGE WILL EXPAND OUT OF THE NORTHERN PLAINS INTO THE
UPPER GREAT LAKES ON THURSDAY. WARM ADVECTION WILL LOWER THE
INVERSION TO 950MB AND WINDS WILL BACK SOUTHWEST. DELTA-TS WILL
LOWER TO 10C ACROSS THE LAKE. THIS SHOULD END LAKE EFFECT ACROSS THE
FORECAST AREA.

.MQT...LES WRNG MIZ006-007-085 THROUGH TODAY.
       LES WRNG MIZ001>003-084 THROUGH THIS MORNING.
       GALE WARNING E LK SUPERIOR.

DLG