Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 222050
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
250 PM CST MON DEC 22 2014

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND TUESDAY
ISSUED AT 249 PM CST MON DEC 22 2014

PLENTY OF POTENTIAL PITFALLS IN THIS FCST OVER THE NEXT 24 HOURS
AS A LARGE DYNAMIC SYSTEM GRADUALLY MOVES INTO THE REGION. THE
MAIN FCST DILEMA TO BE PCPN TYPE OVER MOST OF THE FCST AREA AS
WARMER AIR AT THE SFC TRIES TO LIFT NORTH AND WL BE COUNTERED BY
DYNAMIC COOLING TRYING TO KEEP THE ATMOSPHERIC COLUMN COOLER.

THE 20Z MSAS SFC ANALYSIS INDICATED A PAIR OF LOW PRES SYSTEMS
OVER THE NRN AND CNTRL PLAINS. A WRMFNT EXTENDED FROM THE CNTRL
PLAINS EWD INTO THE OHIO RIVER VALLEY. THE RADAR MOSAIC SHOWED A
LARGE BAND OF PCPN LIFTING NORTH FROM THE MIDWEST INTO THE GREAT
LAKES/UPR MS VALLEY. THIS PCPN WAS MAINLY IN THE FORM OF RAIN...
ALTHO SOME LIGHT SNOW OR SLEET WERE MIXING IN AT TIMES.

A CLOSED UPR LOW...LOCATED WITHIN THE BROAD CNTRL CONUS LONGWAVE
TROF...IS FCST TO MOVE FROM THE CNTRL PLAINS TO THE MIDWEST TNGT.
AS THIS TAKES PLACE...THE PAIR OF SFC LOWS WL CONSOLIDATE AND LIFT
NEWD INTO NE IA BY DAYBREAK WITH THE WRMFNT PULLING NORTH TO NEAR
THE WI/IL BORDER. THE LARGE SLUG OF GULF MOISTURE...OVERRUNNING
THE WRMFNT AND AHEAD OF A NRN MOVING SHORTWAVE...WL CONT TO
OVERSPREAD THE REST OF WI THIS EVENING WITH PCPN CONTINUING THRU
THE NGT. PCPN TYPE TO BE THE BIGGEST FCST ISSUE AS SFC TEMPS ARE
FCST TO BE AROUND FREEZING N-CNTRL WI TO THE MID 30S E-CNTRL WI
AND THE 8H 0C ISOTHERM TO BE LIFTING NW OVRNGT. CURRENT THINKING
IS FOR AN INCH OR TWO OF SNOW TO FALL NW OF A LINE FROM ISW-MNM
WITH LESSER AMOUNTS ACROSS E-CNTRL WI WHERE MORE RAIN IS
ANTICIPATED.

PCPN WL PICK UP IN INTENSITY LATE TNGT THRU TUE MORNING AS THIS
DYNAMIC SYSTEM HEADS INTO THE WRN GREAT LAKES REGION. PCPN TYPE WL
CONT TO BE A MAJOR FCST HEADACHE...ESPECIALLY OVER THE SE HALF OF
NE WI WHERE THE STRONG DYNAMICS MAY PROVIDE ENUF COOLING TO ALLOW
THE MIXED PCPN OR ALL RAIN TO BRIEFLY CHANGE TO ALL SNOW...DESPITE
SFC TEMPS IN THE UPR 30S. THIS COULD PROVIDE FOR A QUICK INCH OR
TWO OF SNOW FROM ROUGHLY STE-GRB-IMT BACK TO STE DURING THE
MORNING. THIS AREA IS ALSO TO RESIDE ON THE NOSE OF AN INCOMING
DRY SLOT WHERE LIFT WL BE MAXIMIZED. FOR N-CNTRL WI WHERE THE PCPN
TO REMAIN ALL SNOW...LOOK FOR AN ADDITIONAL 2 TO 4 INCHES OF
ACCUMULATION TO OCCUR.

.LONG TERM...TUESDAY NIGHT THROUGH MONDAY
ISSUED AT 249 PM CST MON DEC 22 2014

SLOW MOVING SYSTEM WILL CONTINUE TO DRIFT OVER THE GREAT LAKES
REGION TUESDAY NIGHT INTO WEDNESDAY NIGHT. LIGHT WRAP AROUND PCPN
WILL GRADUALLY DEPART THE NORTHWEST HALF OF THE STATE TUESDAY
EVENING WHILE A DRY SLOT DRIVES NORTHEASTWARD INTO MUCH OF EASTERN
WISCONSIN.

OF NOTICE FOR WEDNESDAY INTO WEDNESDAY NIGHT IS THE SUBTLE SHIFT
WESTWARD WITH THE NEW PCPN SHIELD DUE TO PHASING OF THE GREAT
LAKES SYSTEM WITH SOUTHERN STREAM ENERGY. WILL CONFINE HIGHER POPS
ALONG THE LAKESHORE AND LATER RUNS CAN CONTINUE TO UP POPS AND
INCREASE COVERAGE IF THIS TREND CONTINUES. OTHERWISE QUIET
WEATHER FOR XMAS DAY AT THIS TIME.

PROGS ARE IN GOOD AGREEMENT WITH A SURFACE LOW WITH MID LEVEL
TROUGH SLIDING OVER THE AREA TOWARD FRIDAY NIGHT. TEMPERATURES MAY
BE WARM ENOUGH FOR A RAIN SNOW MIX OVER EAST CENTRAL WISCONSIN
BUT WILL KEEP IT SNOW DUE TO OVERNIGHT TIMING. ANOTHER POSSIBLE
FRONTAL SYSTEM MAY SLIDE OVER THE AREA EARLY NEXT WEEK. THIS
EARLY NEXT WEEK SYSTEM MAY BE FOLLOWED WITH SOME COLDER AIR MASS
BUT THE DURATION LOOKS MINIMAL ON THE RECENT MODEL RUNS.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1132 AM CST MON DEC 22 2014

IFR CIGS/VSBYS TO REMAIN IN PLACE ACROSS CNTRL WI THRU THE
AFTERNOON MAINLY DUE TO FOG...WHILE ERN WI TO SEE PRIMARILY MVFR
CONDITIONS. FCST BECOMES MUCH MORE DIFFICULT STARTING TNGT AS A
PRONOUNCED LONGWAVE TROF OVER THE CNTRL CONUS HELPS TO DEEPEN AN
AREA OF LOW PRES OVER THE MIDWEST. THIS SFC LOW WL HELP TO PULL
WARMER AIR INTO THE SE HALF OF WI...MAKING PCPN TYPE AN ISSUE AS
THE AIR ALOFT IS STILL RELATIVELY COLD. FOR ERN WI...PCPN SHOULD
BEGIN EARLY THIS EVENING AS LIGHT SNOW BEFORE MIXING WITH RAIN AND
A LITTLE SLEET FOR THE OVERNIGHT HOURS. PROBLEM IN THE EAST IS
THAT THE AIR MASS GETS RELATIVELY UNSTABLE TUE MORNING AND ENUF
LIFT MAY BE PRESENT TO BRIEFLY BRING A FEW HOURS OF SNOW BEFORE
CHANGING BACK TO A MIX ONCE AGAIN. FOR CNTRL/NRN WI...AIR MASS
NEVER GETS WARM ENUF FOR RAIN AND EXPECT MAINLY ACCUMULATING SNOW
ESPECIALLY IN THE NORTH. CIGS/VSBYS TO SETTLE INTO THE IFR
CATEGORY TNGT INTO TUE WITH LOCALIZED LIFR CONDITIONS IN HEAVIER
PCPN.
&&

.HYDROLOGY...
ISSUED AT 249 PM CST MON DEC 22 2014

MILD CONDITIONS ARE EXPECTED OVER EAST CENTRAL WISCONSIN THROUGH
WEDNESDAY ALONG WITH THE POTENTIAL OF UP TO 0.25 TO 0.40 INCHES OF
RAIN TONIGHT INTO TUESDAY. WHILE THE RAIN WILL PRODUCE SOME
RUNOFF...PRIMARY ISSUE IS THE AFFECTS ON ICE CONDITIONS ON AREA
RIVERS AND LAKES.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM CST
TUESDAY FOR WIZ005-010>013-018>021-030-031.
&&

$$

SHORT TERM.....AK
LONG TERM......TDH
AVIATION.......AK
HYDROLOGY......TDH





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