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[Printable]
891
FXUS63 KGRB 220350
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
950 PM CST SUN DEC 21 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE
AND NEW INFORMATION ADDED TO UPDATE SECTION

.UPDATE...
ISSUED AT 939 PM CST SUN DEC 21 2014

NO MAJOR CHANGES TO THE FCST THIS EVENING. REPORTS FM CENTRAL WI
INDICATED SOME GLAZING ON THE ROADS DURING THE LATE AFTN...THOUGH
CONDITIONS NOT AS BAD THIS EVENING AFTER THE ROADS WERE TREATED
AND TEMPS GENERALLY AOA FZG. REDUCED SNOW ACCUMULATIONS IN THIS
AREA AS NOT MUCH SNOW HAS OCCURRED THUS FAR...AND MID-LVL
MOISTURE SHOULD DECR DURING THE NGT. EXPECT PCPN ACRS N-C WI TO
CONT AS PERIODS OF S-/ZL-...WITH THE ZL BECOMMING MORE PREVLAENT
LATER IN THE NGT.

WL CONT TO HANDLE THE SITN WITH AN SPS.

OTHERWISE...EDGED MIN TEMPS UP A LITTLE AS TEMPS AT MOST AREAS
HAVE GENERALLY HELD STEADY THE PAST FEW HRS.
&&

.SHORT TERM...TONIGHT AND MONDAY
ISSUED AT 313 PM CST SUN DEC 21 2014

FIRST ROUND OF PCPN CURRENTLY MOVING ACROSS WI...MAINLY IN THE
FORM OF LIGHT SNOW. MAIN FCST ISSUE FOR TNGT IS HOW LONG TO HANG
ON TO THE SNOW BEFORE TAPERING DOWN TO FREEZING DRIZZLE OR
FLURRIES. MAIN FCST ISSUE FOR MON WL BE PCPN TYPE IN THE AFTERNOON
AS THE NEXT SURGE IN MOISTURE OVERSPREADS THE REGION.

THE 19Z MSAS SFC ANALYSIS SHOWED HI PRES JUST EAST OF THE GREAT
LAKES WITH LOW PRES OVER THE CNTRL HI PLAINS. A BROAD S-SW WIND
WAS PUMPING WARM/MOIST AIR ALL THE WAY TO THE CANADIAN BORDER WITH
DEW POINTS IN THE LWR 30S AND TEMPS ABOVE NORMAL. RADAR MOSAIC
INDICATED LIGHT SNOW OVER THE NW HALF OF WI ASSOCIATED PRIMARILY
WITH WAA.

THIS INITIAL BAND OF MAINLY LIGHT SNOW (MIXED WITH A LITTLE RAIN
PERHAPS OVER CNTRL/E-CNTRL WI) WL CONT THRU THE EVENING HOURS WITH
THE GREATEST IMPACT NORTH OF A LINE FROM ISW-MNM. POTENTIAL FOR
AROUND AN INCH OR TWO OF ADDITIONAL ACCUMULATION IN THESE
LOCATIONS WITH LITTLE IF ANY ACCUMULATION FOR E-CNTRL WI. FCST
SOUNDINGS INDICATE A LOSS OF SATURATION IN THE MID-LEVELS OF THE
ATMOSPHERE LATER TNGT...THUS THE SNOW SHOULD TAPER OFF TO PATCHY
FREEZING DRIZZLE OR FLURRIES. DUE TO THE CONINUATION OF WAA THRU
THE NGT...DO NOT EXPECT TEMPS TO FALL MUCH WITH UPR 20S TO LWR 30S
AREA-WIDE.

NE WI TO RESIDE IN BETWEEN AREAS OF LIFT MON MORNING AS THE
INITIAL WAA WEAKENS A BIT AND THE MAIN/FORCING ASSOCIATED WITH A
LONGWAVE TROF STILL TO OUR SOUTH AND WEST. THUS...HAVE TONED DOWN
MORNING POPS ESPECIALLY ACROSS ERN WI. BY MON AFTERNOON...A JET
STREAK ROUNDS THE BASE OF THIS UPR TROF AND HELPS TO LIFT AN 8H
WRMFNT NWD TO THE WI/IL BORDER BY 00Z TUE. INCREASING LIFT/FORCING
WL BRING PCPN FROM SOUTH TO NORTH INTO NE WI WITH THE HIGHEST POPS
OVER CNTRL/E-CNTRL WI FOR THE AFTERNOON. THE MAIN FCST ISSUE TO BE
PCPN TYPE AS THE 8H 0C ISOTHERM APPROACHES CNTRL WI AND SFC TEMPS
RISE INTO THE LWR TO MID 30S NORTH...MID TO UPR 30S SOUTH. BY THE
TIME THE PCPN ARRIVES IN EARNEST...CNTRL/E-CNTRL WI WOULD SEE A
MIX OR EVEN CHANGE TO ALL RAIN. NRN WI WOULD BE MOSTLY SNOW THRU
THE DAY...BUT WITH TEMPS AT OR ABOVE FREEZING...SNOW ACCUMULATIONS
WOULD BE LIMITED TO UNDER AN INCH.

.LONG TERM...MONDAY NIGHT THROUGH SUNDAY
ISSUED AT 313 PM CST SUN DEC 21 2014

PROGS LAST FEW DAYS WERE HINTING OF DEEPENING STORM SYSTEM BY MID
WEEK WITH HIGH IMPACTS FOR THE GREAT LAKES. MORNING RUNS USING A
BETTER SAMPLING OVER WESTERN STATES HAS BACKED OFF ON IMPACTS FOR
THE AREA THIS WEEK.

FROM MONDAY NIGHT INTO TUESDAY...BRUNT OF THE WAA SURGE OF PCPN
FROM AROUND 0.20 TO 0.45 INCHES WATER EQUIVALENT DURING A 24 HOUR
PERIOD SPREADS NORTHWARD OVER THE AREA. THE PRIMARY ISSUE WITH
THIS SYSTEM IS PCPN TYPE AS FORECAST SOUNDINGS SUGGESTS MIXED
PCPN. PARTS OF NC AND CENTRAL WISCONSIN COULD TURN TO MORE SNOW AS
UPPER HEIGHTS FALL AND TEMPS COOL ALOFT AND COULD REACH THE BETTER
SNOW GROWTH REGION ALOFT. OTHERWISE SNOW RATIOS ARE EXPECTED TO BE
LOW SO A COMPACT SNOW MAY BE THE RULE. THE SNOW MIX MAY BE ENOUGH
FOR ADVISORY OF SOME TYPE FOR THE FORECAST AREA DURING THIS
PERIOD. MEANWHILE OVER EASTERN WISCONSIN...PRECIPITATION APPEARS
TO BE MOSTLY RAIN.

THE SYSTEM IS PROGGED TO EVOLVE EAST OF THE AREA WEDNESDAY INTO
THURSDAY. COLDER AIR WRAPPING AROUND THE SYSTEM WILL TURN THE MIX
BACK OVER TO SNOW OVER AT LEAST THE NORTHWEST HALF OF THE STATE.
MUCH OF EAST CENTRAL WISCONSIN REMAINS IN THE DRY SLOT. SOUTHERN
STREAM ENERGY WITH A SURGE OF PCPN WHICH EVENTUALLY PHASES INTO
THE NORTHERN LOW...OCCURS A BIT FURTHER EAST OF THE AREA FOR A
DIMINISHED THREAT OF ACCUMULATING SNOW OVER THE AREA. EVEN WINDS
EXPECTED TO BE LESS BUT STILL BLUSTERY OVER EASTERN WISCONSIN
THROUGH THURSDAY...WITH THE TREND TO LESS SNOW TO DRIFT AROUND.

PROGS HAVE BEEN GOING BACK AND FORTH WITH A WEAKENING SYSTEM PASSING
OVER OVER THE REGION THURSDAY NIGHT INTO FRIDAY THAT COULD
PRODUCE AN ADVISORY TYPE OF SNOW OVER THE SOUTHEAST TWO THIRDS OF
THE STATE.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 939 PM CST SUN DEC 21 2014

POOR FLIGHT CONDITIONS EXPECTED TO PERSIST FOR THE NEXT 24 HRS AND
BEYOND. LOW CLDS WITH GENERALLY IFR/LIFR CIGS WL REMAIN WIDESPREAD
ACRS THE AREA. PCPN LIKELY TO DIMINISH SOMEWHAT DURING THE
NGT...WITH ANOTHER ROUND OF MORE SIG PCPN OVERSPREADING THE AREA
STARTING LATE TOMORROW. HARD TO SEE A SIG LONG-LIVED IMPROVEMENT
IN CONDITIONS UNTIL THE MAIN UPR TROF AXIS SHIFTS E OF THE AREA
MIDWEEK.
&&

.HYDROLOGY...
ISSUED AT 313 PM CST SUN DEC 21 2014

RELATIVELY WARM SLOWLY WINTER STORM SYSTEM WILL TRACK OVER THE
GREAT LAKES REGION FROM TONIGHT INTO WEDNESDAY. WHILE SNOW OR A
SNOW MIXTURE IS EXPECTED OVER NORTH CENTRAL...CENTRAL
WISCONSIN...MAINLY RAIN IS EXPECTED OVER EASTERN WISCONSIN. LATEST
MODEL DATA SUGGESTS UP TO A HALF INCH OF RAIN IS EXPECTED FROM
MONDAY EVENING INTO TUESDAY MORNING WITH TEMPERATURES POSSIBLE
RISING TO NEAR 40 ON TUESDAY. WHILE THE RAIN WILL PRODUCE SOME
RUNOFF...PRIMARY ISSUE IS THE POTENTIAL AFFECTS ON ICE CONDITIONS
ON AREA RIVERS AND LAKES.
&&

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

$$

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









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