Lake Effect Snow Warning 1, NWS Milwaukee, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
355 AM CST WED JAN 1 2014

.TODAY AND TONIGHT...FORECAST CONFIDENCE IS MEDIUM.

PRESSURE GRADIENT AND SHIFTING WINDS CAUSING SOME SLIGHT INCREASE
IN WIND SPEEDS ACROSS NORTHERN CWA WHERE TEMPERATURES HAVE FALLEN
TO AROUND -3. WIND CHILLS WL CONTINUE TO HOVER AROUND -20 THROUGH
THE EARLY MORNING ACROSS THE NORTHERN TIER SO WL POST WIND CHILL
ADVISORY.

FAR SOUTHERN WI WILL GET CLIPPED BY LAYER Q-VECTOR CONVERGENCE
AND RIGHT ENTRANCE REGION OF UPPER JET FOR A TIME THIS MORNING
BEFORE SHIFTING OFF TO THE EAST. HENCE EXPECT A PERIOD OF -SN THIS
MORNING WITH UP TO ONE INCH ADDITIONAL ACCUMULATION. -SN SHOULD
BEGIN TO TAPER LATE MRNG THRU MID-AFTN.

PRIMARY FOCUS IS ON LAKE EFFECT SNOW SHOWERS. 1000-850MB WINDS IN
THE PROCESS OF TURNING ONSHORE IN RESPONSE TO DEVELOPING LOW
PRESSURE SAGGING INTO THE SOUTHERN PLAINS. MAIN SYSTEM SNOW WITH
THIS LOW EXPECTED TO REMAIN JUST SOUTH OF WI TODAY AND TONIGHT AS
LOW MOVES EAST ACROSS THE SOUTHERN PLAINS AND HEADS TOWARD THE TN
VALLEY AND UNDERGOES CYCLOGENESIS TNGT INTO THU.

THIS SCENARIO WILL RESULT IN A PROLONGED PERIOD OF ONSHORE WINDS
TODAY THRU THU. AVERAGING LAKE MI TEMP AROUND 36...RESULTS IN
DELTA T VALUES OF 15 TO 18 DEGREES CELSIUS TODAY...INCREASING TO
20 DEGREES CELSIUS TNGT INTO THU. FOR THE BULK OF THE
TIME...ENHANCED SYNTOPTIC SCALE LIFT REMAINS SOUTH OF THE AREA.

DEEP MOISTURE IN DENDRITIC GROWTH ZONE HOWEVER PERIODS OF DRYING
NOTED ABOVE 3500FT INVERSION TODAY AND TONIGHT. INCREASING
CONVERGENCE AND DELTA T VALUES WILL RESULT IN OCNL SHSN IN
EASTERN CWA DEVELOPING THIS MRNG. BEST THREAT FOR HEAVIER SHSN MAY
BE TNGT INTO THU WHEN FETCH BACKS SLIGHTLY AND INCREASES TO AROUND
100 MILES AND INVERSION HEIGHT INCREASES RESULTING IN GREAT LAKE
INDUCED CAPE.

WL CONVERT WINTER WX ADVY TO LAKE EFFECT SNOW ADVISORY AND EXPAND
NORTH TO INCLUDE REST OF LAKE SHORE AND WASHINGTON COUNTIES FOR
POTENTIAL OF 3 TO 5 INCHES TOTAL ADDITIONAL...WITH HIGHER AMOUNTS
LIKELY IN SOME SOUTHERN LAKESHORE AREAS BUT SPREAD OVER A GREATER
PERIOD. NOT ENOUGH CONFIDENCE AT THIS TIME TO INCREASE TO WARNING
BUT WL DEFINITELY NEED TO BE WATCHED...ESPECIALLY FOR TNGT AND
THU.

.SHORT TERM...THURSDAY THROUGH FRIDAY NIGHT...FORECAST CONFIDENCE
IS HIGH.

LAKE EFFECT SNOW ADVISORY INTO THURSDAY ACROSS LOCATIONS NEAR
LAKE MICHIGAN. MODELS SHOWING MAIN SINGLE LAKE EFFECT SNOW BAND
SHIFTING SOUTHWARD THROUGH THE LAKESHORE COUNTIES THURSDAY
MORNING...THEN MOVING SOUTHWARD AND OUT OF THE AREA BY LATE
THURSDAY AFTERNOON. NAM MOST AGGRESSIVE WITH BRINGING IT FURTHEST
INLAND...WITH THE OTHER MODELS JUST GRAZING THE SHORELINE.

FAVORABLE SETUP CONTINUES THURSDAY WITH DELTA T VALUES OF 18 TO
21 DEGREES CELSIUS...SATURATED LOW LEVELS IN DENDRITE SNOW GROWTH
ZONE AND LOW LEVEL CONVERGENCE. CONTINUED HIGH POPS IN LAKESHORE
COUNTIES...LOWERING TO THE WEST.

SHOULD SEE ANOTHER 1 TO 2 INCHES OF SNOW NEAR THE LAKE WITH THIS
BAND. GIVEN SOME UNCERTAINTY WITH THE EXACT SETUP OF THE
BAND...COULD SEE HIGHER AMOUNTS THAN CURRENTLY FORECAST. THE REST
OF THE AREA WILL BE DRY...WITH COLD AND DRY AIRMASS IN PLACE.

HIGH PRESSURE PASSES SOUTHEAST THROUGH THE REGION THURSDAY
NIGHT. LIGHT WINDS AND CLEARING SKIES AND SOLID SNOWPACK SHOULD
ALLOW LOWS TO DROP INTO THE TEENS BELOW ZERO AWAY FROM THE
LAKE...SINGLE DIGITS BELOW ZERO NEAR IT. COULD EVEN BE A BIT
COLDER GIVEN THIS SETUP.

WARM AIR ADVECTION PATTERN THEN SETS UP ACROSS THE AREA FRIDAY AND
FRIDAY NIGHT...AS WINDS PICK UP OUT OF THE SOUTH SOUTHWEST. LOW
PRESSURE SHIFTS EAST ALONG THE CANADIAN BORDER. AIRMASS SHOULD
REMAIN DRY ACROSS THE AREA FOR MOST OF THIS PERIOD.

GFS/CANADIAN MODELS TRY TO BRING IN LIGHT QPF TO THE NORTH OR
NORTHWESTERN COUNTIES BY 12Z SATURDAY...WITH THE OTHERS DRY. LEFT
LOW POPS FOR LATER FRIDAY NIGHT. TEMPERATURES SHOULD REBOUND INTO
THE UPPER 20S TO LOWER 30S SATURDAY.

.LONG TERM...SATURDAY THROUGH TUESDAY...FORECAST CONFIDENCE IS
MEDIUM.

COLD FRONT IS EXPECTED TO SHIFT SOUTHEAST THROUGH THE AREA
SATURDAY PER GFS...OR SATURDAY EVENING PER ECMWF. LOW PRESSURE
THEN STRENGTHENS AND SHIFTS FROM THE SOUTHERN PLAINS TO THE OHIO
RIVER VALLEY BY 00Z MONDAY...BEFORE MOVING FURTHER NORTHEAST
MONDAY NIGHT.

THE GFS IS FURTHER SOUTHEAST THAN THE ECMWF WITH THIS LOW
TRACK...WHICH KEEPS SOUTHERN WISCONSIN DRY. THE ECMWF IS NOT AS
FAR SOUTHEAST AS THE GFS...AND KEEPS THE SOUTHEAST COUNTIES ON THE
EDGE OF THE QPF SHIELD SATURDAY NIGHT INTO SUNDAY EVENING. SOME
UNCERTAINTY HERE WITH THE LOW TRACK. FOR NOW...USED CONSENSUS
POPS WHICH HAVE SLIGHT CHANCES FOR SNOW ACROSS MOST OF THE AREA.

STRONG COLD AIR ADVECTION SUNDAY INTO MONDAY WILL BRING THE
COLDEST AIRMASS SO FAR THIS WINTER SEASON INTO THE REGION.
1000/500MB THICKNESSES FALL IN THE 490S DECAMETER RANGE...WITH A
DRY AIRMASS IN PLACE. THIS SHOULD LEAD TO BITTER COLD TEMPERATURES
AND WIND CHILLS SUNDAY NIGHT INTO TUESDAY.

LOWERED TEMPERATURES SEVERAL DEGREES FROM THE CONSENSUS BLEND FOR
THIS PERIOD. FOR NOW...COULD SEE WIND CHILLS DROP INTO THE 25 TO
35 BELOW ZERO RANGE SUNDAY NIGHT...AND IN THE 30 TO 40 BELOW ZERO
RANGE MONDAY NIGHT AND INTO EARLY TUESDAY. TEMPERATURES WILL ALSO
DROP INTO THE TEENS TO NEAR 20 BELOW ZERO RANGE MONDAY NIGHT. WILL
CONTINUE TO WATCH THIS PERIOD FOR THE BITTER COLD TEMPERATURES
AND WIND CHILLS.

&&

.AVIATION/12Z TAFS/...

PERIODS OF LAKE EFFECT SNOW SHOWERS WILL AFFECT EASTERN TAF SITES
FOR THE DURATION OF THE PERIOD. SNOW SHOWERS COULD BE BRIEFLY
HEAVY TNGT INTO THU.

&&

.MARINE...

PERSISTENT NORTHEAST WINDS OF 10 TO 20 KNOTS WILL CAUSE HIGHER
WAVE HEIGHTS THROUGH THURSDAY. OCCASIONAL GUSTS TO 25 KNOTS ARE
ALSO LIKELY DUE TO TIGHTENING PRESSURE GRADIENT. WL CONTINUE SMALL
CRAFT ADVISORY BEGINNING THIS MORNING...AND EXTEND TO 00Z/03.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...LAKE EFFECT SNOW ADVISORY UNTIL 3 PM CST THURSDAY FOR WIZ065-066-
     070>072.

     WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR WIZ046-047-
     051-052.

     LAKE EFFECT SNOW ADVISORY FROM NOON TODAY TO NOON CST THURSDAY
     FOR WIZ052-059-060.

LM...SMALL CRAFT ADVISORY FROM 9 AM THIS MORNING TO 6 PM CST
     THURSDAY FOR LMZ643>646.

&&

TODAY/TONIGHT AND AVIATION/MARINE...MBK
THURSDAY THROUGH TUESDAY...WOOD

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