Winter Storm Watch 3, NWS Green Bay, WI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
253 PM CDT SUN MAR 20 2011

.SYNOPSIS...A MAJOR LATE-WINTER STORM TO AFFECT THE AREA MID-WEEK.
WINTER STORM WATCH WILL BE POSTED FOR THE NORTH WITH THIS ISSUANCE.

FLOW ACRS NOAM SPLIT. STG AND AMPLIFIED SRN STREAM WILL DOMINATE THE
CONUS WHILE BLOCKING NRN STREAM RIDGE SETS UP OVER CENTRAL CANADA.
SERIES OF STG SHRTWVS EJECTING OUT OF SRN STREAM TROF WL BRING A
SERIES OF SYSTEMS EWD ACRS THE AREA. WITH A SIG INFLOW OF GULF
MOISTURE AND STG BAROCLINIC ZONE IN PLACE ACRS THE RGN...HEAVY PCPN
IS LIKELY.

TEMPS WL START OUT NR NORMAL...BUT THEN COLD CANADIAN AIR BEING
DRIVEN SWD BY MASSIVE ANTICYCLONE OVER NWRN HUDSON BAY WL EVENTUALLY
SURGE ACRS THE AREA AND TAKE TEMPS BACK BLO NORMAL.
&&

.SHORT TERM...TONIGHT AND SUNDAY.

LATEST RUC ANALYSIS AND SATELLITE/RADAR IMAGERY SHOW A
DOUBLE-BARRELED LOW PRESSURE SYSTEM...ONE OVER NORTH DAKOTA...AND
THE OTHER OVER EASTERN NEBRASKA DRIVEN ENE BY SEVERAL SHORTWAVES
OVER THE NORTHERN PLAINS.  SLUG OF WARM/MOIST ADVECTION PRECIP IS
NOW SHIFTING OVER FAR NE WISCONSIN EARLY THIS AFTERNOON...BUT STILL
GETTING OBS OF SNOW MIXING IN WITH RAIN OVER NORTH-CENTRAL AND
NORTHEAST WISCONSIN WHERE 850MB TEMPS ARE HOVERING AROUND THE 0C
MARK. NOT A LOT OF PRECIP ACTIVITY UPSTREAM THOUGH THERE ARE PLENTY
OF SUB 1KFT CLOUD DECKS AND VSBYS BELOW 3SM.  AS A RESULT...WILL CUT
BACK ON PRECIP CHANCES FOR THE REST OF THE AFTERNOON OVER CENTRAL
AND NORTH-CENTRAL WISCONSIN.  PRECIP CHANCES ARE THE MAIN FORECAST
CONCERN TONIGHT.

TONIGHT...SHORTWAVE TROUGH OVER THE NORTHERN PLAINS WILL CONTINUE TO
MOVE ENE OVER THE GREAT LAKES TONIGHT.  DUAL SURFACE LOWS WILL
FOLLOW SUIT AS WELL AND STILL HAVE INDICATIONS THAT A SECONDARY
ROUND OF PRECIPITATION WILL MOVE ACROSS THE FORECAST AREA DURING THE
EVENING.  WILL SEE GOOD FORCING VIA -DPVA AND UPPER DIVERGENCE IN
THE LEFT EXIT REGION OF A JET STREAK THAT PROMOTES THIS IDEA TAKING
PLACE THOUGH STILL RATHER DIFFICULT AT THIS TIME TO IDENTIFY WHERE
THE HEAVIEST PRECIP WILL OCCUR.  THE LATEST NUMERICAL GUIDANCE
DOESNT APPEAR TO HAVE A GOOD HANDLE ON PRECIP ATTM...SO USED THE
HRRR FOR THE FORECAST THIS EVENING.  THIS WILL PLACE THE BEST
CHANCES OF PRECIP OVER N-C WISCONSIN...THOUGH ADMITTEDLY...EASTERN
WISCONSIN WILL SEE THE LONGEST DURATION OF FORCING.  CHANGED POPS
AROUND AT THE LAST MINUTE TO REFLECT THIS SCENARIO.  850MB TEMPS WILL
CONTINUE TO HOVER AROUND THE FREEZING MARK OVER NORTH-CENTRAL
WISCONSIN AND WILL KEEP A MENTION OF SNOW IN THE FORECAST THROUGH
THE LATE EVENING HOURS.  CANNOT RULE OUT AN ISOLD LIGHTNING STRIKE
BUT WITHOUT MUCH GOING ON UPSTREAM AND EXTREMELY MEAGER INSTABILITY
PROJECTED BY THE MODELS...WILL JUST LEAVE OUT OF THE FORECAST.
ANTICIPATE AREAS OF FOG DEVELOPING AS A RESULT OF LOW LEVEL
CONVERGENCE WITH THE SURFACE LOW...AND ABOVE FREEZING DEWPOINTS OVER
THE FROZEN GROUND.  CONDITIONS WILL IMPROVE AFTER MIDNIGHT ONCE THE
LOW PASSES TO THE EAST AND DRIER AIR WORKS IN FROM THE WEST.  MODELS
INDICATE LOW LEVEL MOISTURE WILL WRAP AROUND THE NORTHERN SURFACE
LOW BACK INTO NORTH-CENTRAL WISCONSIN WHERE LOW LEVEL COLD ADVECTION
WILL BE TAKING PLACE.  PLENTY OF LOW CLOUDS UPSTREAM SO THIS IDEA
APPEARS PLAUSIBLE.  DRY AIR ALOFT WILL MAKE PRECIP HARD TO GENERATE
HOWEVER...AND WILL ONLY LEAVE A MENTION OVER THE DOOR PENINSULA AND
N-C WISCONSIN.  LOWS MOSTLY IN THE MIDDLE 30S.

SUNDAY...HIGH PRESSURE RIDGE AXIS BUILDS INTO WISCONSIN WHICH WILL
LEAD TO A QUIETER DAY BUT NOT WITHOUT FORECAST CONCERNS.  WILL STILL
BE SLIGHTLY COLD ADVECTING AT 925MB WITH PLENTY OF LOW LEVEL
MOISTURE HANGING AROUND TRAPPED BENEATH THE INVERSION.  IF LOW
CLOUDS DO NOT HANG AROUND INTO THE MORNING HOURS...DIURNAL HEATING
AND STEEPENING LOW LEVEL LAPSE RATES SHOULD LEAD TO A GOOD STRATO-CU
FIELD FORMING IN THE AFTERNOON.  WILL GO WITH PARTLY SUNNY-MOSTLY
CLOUDY SKIES OVER NORTH-CENTRAL WISCONSIN AND PARTLY CLOUDY
ELSEWHERE...THOUGH WOULD NOT BE SURPRISED IF THERE ARE MORE CLOUDS
THAN CURRENTLY IN THE FORECAST.  THIS WILL ALSO IMPACT MAX
TEMPS...AND THE LEADING TEMP GUIDANCE STAYS ON THE COOL SIDE FOR
HIGHS.  WILL GO SLIGHTLY WARMER DUE TO SOME POTENTIAL FOR SUNSHINE
SO WILL PUT HIGHS IN THE LOWER 40S NORTH TO THE UPPER 40S SOUTH.

.LONG TERM...MON NGT THRU NEXT SUN. STG CYCLONE TRACKING OUT OF THE
PLAINS WL AFFEC THE AREA MID-WEEK. UPR PATTERN IN SRN STREAM WOULD
NORMALLY ALLOW THE SYSTEM TO TRACK W OF THE AREA...TAKING THE HVY
SNOW ACRS NW WI AND MN. BUT...NRN STREAM FLOWING SWD ARND DEVELOPING
BLOCK WL DEFLECT THE SYSTEM ON A MORE ELY COURSE...AND TRACK IT S OF
THE AREA. FCST DIFFICULTY IS THAT TEMPS AOA ABV 850 MB GET QUITE
WARM...AND COULD RESULT IN MIXED PCPN RATHER THAN SNOW.

HAVE THE BEST CONFIDENCE IN GETTING HEAVY SNOW ACRS THE N...SO WL
START WITH A WATCH THERE. AXIS FM AUW-GRB REALLY UP FOR GRABS.
NAM/ECMWF SUGGEST BIG SNOWS IN THIS AREA AS WELL...BUT GFS/SREF
WARMER. THAT AREA COULD ALSO DRY SLOT AND GO OVER TO L/ZL
WEDNESDAY...SO PERHAPS MODEL QPFS ALONG THAT AXIS ARE TOO HIGH.
SINCE THIS COULD BE A HIGHER-END EVENT...THOUGHT BEST APPROACH WAS
TO GET WATCH OUT NOW FOR AREA WITH GREATEST CONFIDENCE OF GETTING
HEAVY SNOW. WATCH CAN ALWAYS BE EXPANDED SWD LATER IF NEEDED.

EXTENDED LOOKS QUIET. GUID TEMPS STILL SEEMED TOO COLD GIVEN THAT
IT/S LATE MARCH. TWEAKED DOWN A LITTLE MORE...BUT NOT AS COLD AS
GUID WOULD INDICATE.
&&

.AVIATION...LOW PRESSURE MOVING OVER THE REGION FROM THE SOUTHWEST
WILL SPREAD IFR(LIFR) CIGS AND VSBYS INTO THE GRB/ATW (RHI/CWA/AUW)
THIS EVENING WITH SHOWERS AND ISOLD THUNDERSTORMS POSSIBLE.
UNCERTAINTY IS HIGH ENOUGH WITH THUNDER CHANCES TO LEAVE OUT OF
FORECAST.  AS THE LOW PASSES TO THE EAST...IMPROVING CONDITIONS WILL
GENERALLY BE FOUND ACROSS THE AREA TAF SITES SINCE DRIER AIR WILL BE
WORKING IN BEHIND THE LOW.  CIGS WILL LIKELY REMAIN LIFR AT RHI
THOUGH VSBYS WILL IMPROVE.  UNCERTAINTY IS FAIRLY HIGH WITH THE
AMOUNT OF CLEARING AT THE REMAINING TAF SITES.  STATISTICAL GUIDANCE
SUGGESTS A PERIOD OF SCT CONDITIONS LATE TONIGHT INTO TOMORROW
MORNING AT AUW/CWA/ATW/GRB THOUGH CHANCES ARE HIGHER AT GRB/ATW.
&&

.MARINE...SMALL CRAFT CONDITIONS WILL CONTINUE INTO TONIGHT.
ADVISORY ALREADY ISSUED.  ONCE THE SURFACE LOW PASSES THIS
EVENING..WINDS WILL SHIFT AROUND TO THE WEST BUT NOT WIND SPEEDS
WILL NOT BE HIGH ENOUGH FOR ANY HEADLINE.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
EVENING FOR WIZ005-010>013-018>022-073-074.

&&

MPC/SKOWRONSKI

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