Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 211736
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1136 AM CST WED JAN 21 2015

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND THURSDAY
ISSUED AT 339 AM CST WED JAN 21 2015

PCPN TRENDS TODAY AND TONIGHT...SKY COVER LATE TONIGHT INTO
THURSDAY...AND TEMPERATURES THROUGH THE PERIOD...ARE THE MAIN FCST
CONCERNS.

A VERTICALLY STACKED LOW PRESSURE SYSTEM OVER NE IA WAS MOVG ESE
EARLY THIS MORNING...WITH ITS ASSOCIATED DEFORMATION ZONE SLOWLY
PIVOTING NE INTO C/EC WI. A LIGHT MIX OF SNOW AND FREEZING DRIZZLE
WAS OCCURRING SW OF A LINE FROM CWA-PCZ-OSH...AND WAS GRADUALLY
EXPANDING NE. A POCKET OF DRY AIR AT 850 MB OVER THE NE HALF OF
THE CWA WAS PREVENTING PCPN DEVELOPMENT THERE.

THE LIGHT BAND OF PCPN IS EXPECTED TO BECOME ORIENTED WEST TO EAST
OVER OUR SOUTHERN COUPLE TIERS OF COUNTIES...AS THE UPPER LOW
SHIFTS THROUGH FAR SOUTHERN WI THIS MORNING. RH/TEMP TIMESECTIONS
AND BUFKIT SUGGEST THAT PCPN TYPE SHOULD BE MAINLY SNOW. ONLY VERY
LIGHT QPF AND SNOWFALL AMOUNTS ARE ANTICIPATED...WITH PERHAPS A
HALF INCH OVER OUR FAR SW/S COUNTIES. LIGHT SNOW SHOULD TAPER OFF
AS THE UPPER SHIFTS EAST THIS AFTERNOON. LIGHT N-NW FLOW OVER LAKE
SUPERIOR MAY BRING SOME FLURRIES OR LIGHT SNOW SHOWERS INTO VILAS
COUNTY THIS AFTERNOON.

SCT SNOW SHOWERS OVER VILAS COUNTY...AND FLURRIES OVER THE REST
OF THE FORECAST AREA...CAN BE EXPECTED TONIGHT. THIS WILL COME
TO AN END AS HIGH PRESSURE BUILDS INTO THE REGION LATE TONIGHT.
THIS HIGH...COMBINED WITH LOW-LEVEL DRYING...DEVELOPING W-SW
FLOW AND INCREASING SUBSIDENCE...SHOULD BRING AT LEAST PARTIAL
CLEARING ON THURSDAY.

USED A BLEND OF THE BETTER PERFORMING GUIDANCE SETS FOR
TEMPERATURES THROUGH THURSDAY. HIGH TEMPS SHOULD BE MAINLY IN
THE MIDDLE 20S TO LOWER 30S...WITH LOWS TONIGHT IN THE TEENS.
IF WIDESPREAD CLEARING OCCURS OVER NORTHERN WI LATE TONIGHT...
LOW TEMPS MAY NEED TO BE ADJUSTED DOWNWARD.

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY
ISSUED AT 339 AM CST WED JAN 21 2015

500MB RIDGE EXPECTED TO DOMINATE THE WEATHER PATTERN DURING THE
PERIOD. UNLIKE THE LAST SEVERAL MONTHS AND OVER THE PAST YEAR OR
TWO...THE 500MB RIDGE IS GOING TO SET UP FURTHER EAST ACROSS THE
WESTERN HALF OF THE UNITED STATES. THE COMBINATION OF THE RIDGE
AXIS AND SPLIT FLOW ALOFT WILL KEEP THE TRUE ARCTIC AIR BOTTLED UP
IN CANADA EARLY IN THE PERIOD. BY THE END OF NEXT WEEK...ECMWF
BUILDS RIDGE FURTHER AND RETROGRADES THIS FEATURE...WHICH WOULD
ALLOW FOR COLDER AIR TO MOVE INTO THE AREA LATE NEXT WEEK IF THIS
SCENARIO HOLDS TRUE.

NOTHING NEW TO REPORT ABOUT SEVERAL CLIPPERS MOVING THROUGH THE
MEAN FLOW DURING THE PERIOD. MODELS CONTINUE TO SHOW SIGNIFICANT
DIFFERENCES IN TIMING AND LOCATION OF THESE FEATURES...SO HARD TO
PINPOINT WHEN AND WHERE HIGHEST SNOW AMOUNTS WOULD OCCUR DURING THE
FORECAST PERIOD. DID SPEED UP THE ARRIVAL OF THE COLD FRONT ON
FRIDAY AND FRIDAY NIGHT BASED ON ECMWF/CANADIAN MODELS. GFS/WRF
WERE SOME WHAT SLOWER. THE QUICKER ARRIVAL OF PRECIPITATION MAKES
FOR A CHALLENGING PRECIP TYPE FORECAST DUE LOW LEVEL THERMAL
PROFILE AND MOISTURE CONCERNS. BOUNDARY LAYER MAY BE WARM ENOUGH
FOR RAIN FRIDAY AFTERNOON WITH HIGHS IN THE MIDDLE AND UPPER 30S.
MODELS DO SHOW 850MB TEMPERATURES CRASHING FRIDAY EVENING...THUS
MOST OF THE PRECIPITATION SHOULD BE IN THE FORM OF SNOW...EXCEPT
ACROSS EASTERN WISCONSIN WHERE BOUNDARY LAYER TEMPERATURES MAY BE
WARM ENOUGH FOR RAIN IF QUICKER ARRIVAL OF PRECIPITATION DOES
OCCUR.

SECONDARY COLD FRONT WILL MOVE ACROSS THE REGION ON SATURDAY. WILL
NEED TO WATCH FOR THE POTENTIAL OF FLURRIES AS BOUNDARY PUSHES
THROUGH THE REGION. 00Z CANADIAN/ECMWF HAVE CONVERGED ON SOME SNOW
FOR SATURDAY NIGHT INTO SUNDAY EVENING...ALTHOUGH THE DETAILS IN
THE SOLUTION ARE DIFFERENT. THE GFS TAKES THIS CLIPPER SYSTEM
SOUTHWEST OF THE AREA. PAST HISTORY WOULD SUGGEST THAT WHEN THE
CANADIAN/ECMWF CONVERGE ON A SOLUTION THIS FAR OUT...THIS WOULD BE
THE WAY TO TREND PRECIPITATION CHANCES ON A SNOWIER SOLUTION.

DID MAKE SOME MINOR ADJUSTMENTS UPWARD ON MAX TEMPERATURES ON
MOST DAYS DURING THE PERIOD. PER COORDINATION WITH SURROUNDING
OFFICES...DID LOWER MIN TEMPERATURES A FEW DEGREES THURSDAY NIGHT.
THERE MAY BE A PERIOD OF LIGHTER WINDS EARLY THURSDAY EVENING TO
ALLOW TEMPERATURES TO FALL SOME.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1136 AM CST WED JAN 21 2015

MAINLY MVFR CEILINGS ACROSS THE AREA THIS AFTERNOON
AND TONIGHT WITH THE EXCEPTION OF CENTRAL WISCONSIN WHERE IFR
CEILINGS SHOULD GRADUALLY LIFT TO MVFR RANGE BY EVENING. SOME
LIGHT SNOW OR FLURRIES POSSIBLE IN LAKE EFFECT AREAS.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....KIECKBUSCH
LONG TERM......ECKBERG
AVIATION.......RDM





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