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000
FXUS63 KGRB 090118
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
718 PM CST SUN DEC 8 2013

NEW INFORMATION ADDED TO UPDATE SECTION

.UPDATE...
ISSUED AT 644 PM CST SUN DEC 8 2013

SYSTEM AFFECTING THE FORECAST AREA HAS BEEN RATHER DISORGANIZED
AND DISJOINTED THUS FAR. SO FAR...SNOWFALL AMOUNTS HAVE BEEN
AROUND AN INCH OR SO THROUGH 6 PM. HOWEVER...WATER VAPOR IMAGERY
SHOWS SOMEWHAT MORE ROBUST SHORTWAVE DISTURBANCE ENTERING
SOUTHWEST WISCONSIN. THIS FEATURE HAS HELPED TO CREATE A SOMEWHAT
MORE SOLID AND ORGANIZED AREA OF LIGHT SNOW ACROSS SOUTHEAST
WISCONSIN WITH VSBYS GENERALLY BETWEEN ABOUT 1 AND 2 MILES. THIS
AREA OF LIGHT SNOW CONTINUES TO DRIFT NORTHEAST AND WILL LIKELY CLIP
THE SOUTHEAST PORTION OF THE FOX VALLEY GENERALLY SOUTH OF A LINE
FROM OSH TO KEWAUNEE OVER THE NEXT FEW HOURS.

FURTHER AS ANTICIPATED...AN AREA OF LAKE ENHANCED SNOW CONTINUES
TO DEVELOP OVER CENTRAL LAKE MICHIGAN AND IS DRIFTING NORTHWEST.
RADAR REFLECTIVITIES HAVE BEEN GRADUALLY INCREASING AND EXPNADING
IN AREA COVERAGE OVER THE LAST HOUR. APPEARS ACTIVITY AHEAD OF
APPROACHING SHORTWAVE ENTERING SOUTHWEST WISCONSIN CONTRIBUTING TO
LES ENHANCEMENT OVER CENTRAL LAKE MICHIGAN VIA SEEDER-FEEDER
MECHANISM.

THUS...EXPECT TO SEE SOMEWHAT HIGHER SNOWFALL RATES ACROSS THE
FOX VALLEY THIS EVENING IN ASSOCIATION WITH SHORTWAVE MOVING
ACROSS SOUTHEAST WISCONSIN AND LAKE ENHANCEMENT OFF LAKE MICHIGAN.
COULD SEE ANOTHER INCH OR PERHAPS TWO MY MIDNIGHT ESPECIALLY
SOUTHEAST OFF A LINE FROM STURGEON BAY TO GREEN BAY TO OSHKOSH.

LOOKING FURTHER UPSTREAM...PRIMARY SHORTWAVE DISTURBANCE NOW
ENTERING NORTHWEST IOWA. THIS FEATURE IS ALSO FORECAST TO MOVE
ACROSS THE SOUTHERN WISCONSIN AFTER MIDNIGHT AND MAY HELP TO KEEP
SOME LIGHT SNOW GOING AFTER MIDNIGHT ESPECIALLY OVER THE
SOUTHEAST HALF OF THE FORECAST AREA. HOWEVER...LOOKING AT SURFACE
OBSERVATIONS OVER IOWA...VSBYS NOT VERY LOW AND WERE IN THE 2 TO 4
MILE RANGE. IN FACT THE LATEST HRRR AND RUC FORECASTS SEEM TO
SIGNIFICANTLY DISSOLVE THE AREA OF QPF AS THIS FEATURE APPROACHES
WISCONSIN.

FORCING ACROSS THE NORTHWEST THIRD OF THE FORECAST AREA NOT
EXPECTED TO BE VERY STRONG AND THUS FAR SNOWFALL RATES UP THERE
HAVE BEEN QUITE LIGHT WITH VSBYS GENERALLY IN THE 2 TO 4 MILE
RANGE. WILL SEE HOW THE SHORTWAVE MOVING OUT OF IOWA EVOLVES LATER
THIS EVENING...BUT IF CURRENT TRENDS CONTINUE MAY NEED TO CANCEL ADVISORY
UP THERE.

FOR NOW WILL KEEP ADVISORY GOING OVER ENTIRE FORECAST AREA AND
WILL REVIST A BIT LATER THIS EVENING. BOTTOM LINE IS IT APPEARS
MOST SIGNIFICANT SNOWFALL WILL BE FOCUSED OVER THE FOX VALLEY AND
LAKESHORE. APPEARS FINAL SNOWFALL TOTALS WILL BE ON THE LOW END OF
CURRENT FORECAST.

.SHORT TERM...TONIGHT AND MONDAY
ISSUED AT 232 PM CST SUN DEC 8 2013

LATEST RUC ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW ONE SHORTWAVE
TROUGH MOVING INTO SOUTHWEST WISCONSIN THIS AFTERNOON...WHILE
ANOTHER WAVE NOW ENTERING THE CENTRAL GREAT PLAINS.  AHEAD OF THE
FORMER SHORTWAVE...WEAK ISENTROPIC ASCENT IS PRODUCING A WIDESPREAD
SWATH OF LIGHT SNOW ACROSS THE STATE.  THE BETTER SNOWS WITH THE
FIRST WAVE ARE STILL ACROSS IOWA AT THE MOMENT...WHERE VSBYS ARE
DOWN TO A HALF MILE AND WIDESPREAD 1-2 INCHES ARE BEING REPORTED SO
FAR.  FURTHER CONCERNS RESIDE ALONG THE LAKE SHORE WHERE LAKE
ENHANCEMENT IS OCCURRING OVER CENTRAL AND SOUTHERN PARTS OF THE LAKE
MICHIGAN SHORELINE.  EARLIER REPORTS SHOWED 1-1.5 INCH PER HOUR
SNOWFALL RATES IN THOSE LAKE ENHANCED BANDS.  ONE OF THESE BANDS IS
APPROACHING MANITOWOC...BUT APPEARS TRANSIENT IN A LOW LEVEL
CONVERGENT ZONE.  LOW LEVEL WINDS ARE JUST STARTING TO TURN TO THE
SOUTHEAST SO WILL NEED TO WATCH THESE TRENDS FOR THE REST OF THE
AFTERNOON.  AS THE SHORTWAVES MOVE ACROSS THE ARE TONIGHT...SNOWFALL
AMOUNTS AND IMPACTS ARE THE MAIN FORECAST CONCERN.

TONIGHT...SHORTWAVE TROUGH OVER COLORADO WILL QUICKLY EJECT
NORTHEAST A DRIVE A STRENGTHENING...ALTHOUGH STILL RELATIVELY
WEAK...AREA OF LOW PRESSURE FROM THE CENTRAL GREAT PLAINS AND ACROSS
SOUTHEAST WISCONSIN TONIGHT.  FORCING AHEAD OF THE SHORTWAVE IN THE
FORM OF -DIVQ...UPPER DIVERGENCE...AND ISENTROPIC ASCENT IS ONLY
MODEST...BUT BUFKIT SOUNDINGS FROM THE NAM/GFS/SREF ALL INDICATE A
150-200MB DEEP DENDRITIC GROWTH ZONE BETWEEN APPROX 850-650MB OVER
CENTRAL AND NORTHEAST WISCONSIN.  THIS SUGGESTS THAT WHATEVER WEAK
TO MODERATE LIFT THAT OCCURS...SNOW FLAKE PRODUCTION WILL BE VERY
EFFICIENT AND SNOW TO LIQUID RATIOS WILL BE QUITE HIGH.  GENERALLY
WENT WITH A 19-20:1 RATIO...ALTHOUGH A LITTLE LOWER NEAR THE LAKE
MICHIGAN SHORELINE WHERE ONSHORE FLOW WILL LEAD TO SLIGHTLY WARMER
LOW LEVEL THERMAL PROFILES.  THE BULK OF THE SNOW LOOKS TO OCCUR IN
A COUPLE WAVES. THE FIRST WILL ARRIVE LATE THIS AFTERNOON INTO EARLY
THIS EVENING FROM THE FIRST AREA OF SNOW OVER IOWA AND SE
MINNESOTA...FOLLOW BY THE MAIN SHORTWAVE AND SURFACE LOW OVER
COLORADO.  PLENTY OF 1-3" INCH REPORTS UPSTREAM OVER IOWA...AND FEW
4-6 INCH REPORTS OVER EASTERN NEBRASKA AS WELL.  WILL INCREASE
AMOUNTS A LITTLE OVER N-C WISCONSIN TO AROUND 3 INCHES.  THE PRIMARY
CONCERN THOUGH WILL BE ALONG THE LAKE SHORE WHERE WINDS WILL BE
TURNING TO THE EAST AND SOUTHEAST THIS EVENING. THE LAKE ENHANCEMENT
OVER SOUTHEAST WISCONSIN APPEARS TO BE FLUCTUATING...AS A CONVERGENT
BAND LIFTS NORTH.  BUT EARLIER SNOWFALL RATES WHERE ENHANCEMENT TOOK
PLACE ARE ALARMING. LOOKS LIKE A GOOD 9-12 HOURS OF ENHANCEMENT
POSSIBLE OVER NORTHEAST WISCONSIN.  WILL GO WITH WIDESPREAD 2-4
INCHES EXCEPT NEAR THE LAKESHORE WHERE 5-6 INCHES WILL BE POSSIBLE.
HEADLINES WILL REMAIN THE SAME...AND WILL PASS ALONG LAKE
ENHANCEMENT CONCERNS TO THE EVENING SHIFT.

MONDAY...THE SNOW WILL BE ENDING EARLY MONDAY MORNING OVER NORTHEAST
WISCONSIN AS THE SURFACE LOW PULLS AWAY.  WEST WINDS WILL BE
STRENGTHENING IN THE WAKE OF THE LOW AND COLD ADVECTING AT THE SAME
TIME.  TEMPS WILL REMAIN NEARLY STEADY OR FALL SLIGHTLY DURING THE
DAY...DESPITE CLEARING TAKING PLACE.  WITH WINDS GUSTING TO 30
MPH...APPARENT TEMPS WILL BE FALLING TO NEAR 20 BELOW ZERO OVER
CENTRAL AND NORTH-CENTRAL WISCONSIN DURING THE AFTERNOON.  WILL
LIKELY NEED WIND CHILL HEADLINES...BUT WITH THE ONGOING SNOW
ADVISORY...WILL NOT ISSUE ANOTHER HEADLINE.  MORNING TO MIDDAY HIGHS
IN THE MIDDLE SINGLE DIGITS NORTH TO THE UPPER TEENS NEAR THE LAKE
SHORE.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY
ISSUED AT 232 PM CST SUN DEC 8 2013

VERY COLD AIR WILL REMAIN FIRMLY ENTRENCHED ACROSS THE AREA
MONDAY NIGHT. EXPECT WINDS CHILLS TO DROP TO AROUND 25 BELOW
ACROSS THE NORTH. HOWEVER...TEMPERATURES ARE EXPECTED TO
MODIFY SOME LATE MONDAY NIGHT DUE TO INCREASING CLOUDINESS
AND AHEAD OF APPROACHING SYSTEM. INCREASED CHANCES OF SNOW
ACROSS THE NORTHWEST HALF OF THE FORECAST AREA. INCREASED SNOW
CHANCES SIGNIFICANTLY ON TUESDAY MORNING AS SYSTEM MOVES ACROSS
THE AREA. ALSO...PRECIPITATION TOTALS WILL BE LIGHT...SNOW RATIOS
WOULD SUGGEST LESS THAN AN INCH OF NEW SNOW TUESDAY MORNING. THE
HIGHEST SNOWFALL TOTALS WILL BE ACROSS THE NORTH.

MOST OF THE MODELS NOW BRING CLIPPER SYSTEM SOUTH OF THE AREA
TUESDAY NIGHT. THE ONLY EXCEPTION WAS THE ECMWF...THUS WILL CONTINUE
CHANCES ACROSS THE SOUTHERN HALF OF THE FORECAST AREA. THE GFS MODELS
HAS BEEN WAFFLING ON NORTHWARD EXTENT OF THE PRECIPITATION FIELD. VERY
COLD AIR IS EXPECTED WEDNESDAY MORNING. ANOTHER SYSTEM EXPECTED TO
PASS ACROSS THE NORTH THURSDAY/THURSDAY NIGHT. LOW CONFIDENCE ON WHEN
THIS SYSTEM WOULD BRING A SMALL CHANCE OF LIGHT SNOW DURING THIS PERIOD.
CURRENT FORECAST HAS LIGHT SNOW IN THE FORECAST THURSDAY NIGHT...BUT
LATER SHIFTS MAY NEED TO SPEED UP THE SNOW AND ADD A CHANCE TO THE
THURSDAY PERIOD. THE ARCTIC AIR WILL MODIFY FRIDAY INTO NEXT WEEKEND
WITH HIGHS IN THE UPPER TEENS TO MIDDLE 20S.
&&

.AVIATION...FOR 00Z TAF ISSUANCE
ISSUED AT 608 PM CST SUN DEC 8 2013

WEAK LOW PRESSURE WILL MOVE NORTHEAST ACROSS SOUTHERN
WISCONSIN INTO LOWER MICHIGAN OVERNIGHT BRINGING LIGHT SNOW TO THE
AREA. SYSTEM OVERALL IS SOMEWHAT DISJOINTED AND DISORGANIZED THUS
SNOWFALL RATES NOT VERY IMPRESSIVE SO FAR THIS EVENING. MAINLY
MVFR CIGS AND VSBYS CAN BE EXPECTED THROUGH 06Z AT CENTRAL AND
NORTHERN WISCONSIN TAFS SITES. SOMEWHAT STRONGER UPPER-LEVEL
FORCING OVER SOUTHEAST WISCONSIN HAS HELPED TO GENERATE SOMEWHAT
MORE ORGANIZED AREA OF LIGHT SNOW THERE WHERE IFR CIGS AND VSBYS
ARE MORE WIDESPREAD. EXPECT THIS AREA OF IFR CIGS AND VSBYS IN
LIGHT SNOW TO DRIFT NORTHEAST TO OSH AND ATW TAF SITES AFTER ABOUT
02Z. LAKE ENHANCED SNOW BANDS OFF OF LAKE MICHIGAN WILL ALSO DRIFT
NORTHWESTWARD AND AFFECT LAKESHORE COUNTIES DURING THE EVENING
RESULTING IN IFR CIGS AND VSBYS FROM TIME TO TIME...WHICH COULD
ALSO AFFECT THE GRB TAF SITE THROUGH ABOUT 08Z.

AS SYSTEM MOVES EAST INTO LAKE MICHIGAN AFTER MIDNIGHT...LIGHT
SNOW SHOULD BEGIN TO DIMINISH...BUT CIGS SHOULD GENERALLY REMAIN
IN THE IFR CATEGORY...ESPECIALLY AT GRB...ATW AND OSH TAF SITES.
WESTERLY WINDS WILL DEVELOP BEHIND THE SYSTEM AND BECOME GUSTY BY
MORNING LATE MORNING MONDAY. THE GUSTY WEST WINDS WILL LIKELY
CREATE SOME BLOWING AND DRIFTING OF THE NEW SNOW PARTICULARLY OVER
THE FOX VALLEY.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 6 AM CST MONDAY FOR WIZ005-010>013-
018>022-030-031-035>040-045-048>050-073-074.
&&

$$

UPDATE.........ESB
SHORT TERM.....MPC
LONG TERM......ECKBERG
AVIATION.......ESB