Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 301138
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
638 AM CDT SAT APR 30 2016

UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND SUNDAY
ISSUED AT 350 AM CDT SAT APR 30 2016

THE INTERACTION OF AN UPPER LOW LIFTING NORTHEAST FROM THE CENTRAL
PLAINS AND A SHORTWAVE TROUGH DROPPING SOUTH FROM NORTHERN ONTARIO
WILL PRODUCE AN INTERESTING COMBINATION OF UPPER SUPPORT LATER TODAY
THROUGH MIDDAY SUNDAY. UPPER DIFFLUENCE IS EXPECTED FROM A EAST TO
WEST MOVING JET NORTH OF THE UPPER LOW AND AN UPPER JET MOVING ACROSS
NORTHERN WISCONSIN...THE UPPER PENINSULA AND LAKE SUPERIOR. THIS UPPER
SUPPORT WILL HAVE TO DO THE MAJORITY OF WORK TO PRODUCE RAIN AS LOW
LEVEL WARM ADVECTION IS MINIMAL AND LOW LEVEL CONVERGENCE IS MAINLY
TO OUR SOUTH. THE LOW LEVELS OF THE ATMOSPHERE ARE NOT NEARLY AS DRY
AS WHEN THE LAST UPPER SYSTEM APPROACHED...SO THINK THAT WE WILL SEE
LESS VIRGA AND MORE LIGHT RAIN OR SPRINKLES ACROSS THE SOUTHERN HALF
OF THE FORECAST AREA LATE THIS AFTERNOON THROUGH SUNDAY MORNING.

TEMPERATURES TODAY SHOULD BE ABOUT THREE TO FIVE DEGREES BELOW NORMAL
AGAIN DUE TO CLOUD COVER AND AN INCREASING NORTHEAST WIND FROM LAKE
MICHIGAN. THE NORTH MAY ACTUALLY BE WARMEST. LOWS TONIGHT WILL BE
HELD UP DUE TO CLOUD COVER AND WIND SO THEY WILL ACTUALLY BE A FEW
DEGREES ABOVE NORMAL. SUNDAY/S HIGHS SHOULD BE CLOSE TO NORMAL EXCEPT
COOLER NEAR THE LAKE AND BAY SHORES.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY
ISSUED AT 350 AM CDT SAT APR 30 2016

THE MAIN TAKEAWAY WITH REGARDS TO THE MEAN FLOW NEXT WEEK WILL BE
THE INCREASINGLY AMPLIFIED FLOW CONSISTING OF A WEST COAST UPPER
TROUGH...EASTERN ROCKIES UPPER RIDGE AND EASTERN CONUS UPPER
TROUGH. THIS WOULD PLACE NE WI UNDER A NW FLOW ALOFT WITHI
TEMPERATURES AVERAGING CLOSE TO SEASONAL NORMALS. PRECIPITATION
AMOUNTS SHOULD BE BELOW NORMAL WITH THE ONLY REAL THREAT OF SEEING
RAINFALL TO BE ALONG A COLD FRONT EITHER TUESDAY OR TUESDAY NIGHT.

A WEAK RIDGE OF HIGH PRESSURE IS FORECAST TO MOVE INTO THE WESTERN
GREAT LAKES SUNDAY NIGHT...BRINGING DECREASING CLOUDS...LIGHT
WINDS...AND SOMEWHAT COOL CONDITIONS FOR EARLY MAY. MIN
TEMPERATURES TO RANGE FROM THE LOWER TO MIDDLE 30S NORTH...MIDDLE
TO UPPER 30S SOUTH. THIS SURFACE RIDGE WILL SLIDE TO OUR SOUTH AND
EAST ON MONDAY WITH WEAK WAA OVERSPREADING WI ON WEST WINDS
(EXCEPT FOR EASTERN WI WHERE A LAKE BREEZE WILL TURN WINDS TO THE
SE MONDAY AFTERNOON). A VERY WEAK SHORTWAVE TROUGH IS ALSO
FORECAST TO DRIFT OVER THE AREA ON MONDAY AND MAY BRING SOME
CLOUDS TO THE AREA IN THE AFTERNOON. MAX TEMPERATURES ARE EXPECTED
TO REACH THE MID 50S NEAR LAKE MI...LOWER 60S EASTERN WI AND MID
60S OVER CENTRAL WI.

QUIET CONDITIONS TO CONTINUE THROUGH MONDAY NIGHT BEFORE ATTENTION
TURNS TO AN APPROACHING COLD FRONT FROM CANADA ON TUESDAY. MODELS
STILL DISAGREE ON BOTH THE TIMING OF THE COLD FRONT AND THE
STRENGTH OF THE ACCOMPANYING MID-LEVEL SHORTWAVE TROUGH. THE GFS
REMAINS THE FASTEST BY TAKING THE FRONT THROUGH ALMOST ALL OF NE
WI...WHILE THE ECMWF HAS CAUGHT UP TO THE GEM BY HAVING THE FRONT
REACH NORTHERN WI BY 00Z WEDNESDAY. MEANWHILE...THE GEM HAS THE
STRONGER SHORTWAVE TROUGH...THUS HIGHER PRECIPITATION AMOUNTS.
HAVE LEANED THE FORECAST CLOSER TO THE ECMWF/GEM SOLUTION...
KNOWING THE GFS` PROPENSITY FOR BEING TOO QUICK. THEREFORE...HAVE
SMALL CHC POPS GENERALLY ALONG AND NORTH OF HIGHWAY 29...MAINLY
FOR THE AFTERNOON HOURS. PRE-FRONTAL WARMING AND PERSISTENT WAA
COULD SEND MAX TEMPERATURES INTO THE 65-70 DEGREE RANGE OVER MOST
OF THE FORECAST AREA WITH SLIGHTLY COOLER READINGS NEAR THE LAKE.

CHANCE OF SHOWERS WOULD BE NEEDED OVER ALL OF NE WI TUESDAY NIGHT
AS THE COLD FRONT MOVES SOUTH THROUGH THE STATE. COOLER CONDITIONS
ARE EXPECTED ON WEDNESDAY BEHIND THE COLD FRONT AS N-NW WINDS
USHER A CHILLIER AIR MASS INTO THE GREAT LAKES. THERE IS A
POTENTIAL GLITCH TO WEDNESDAY`S FORECAST AS THE MODELS DIFFER ON
THE LOCATION OF THE DEVELOPING EASTERN CONUS UPPER TROUGH. THE GFS
IS STRONGER/FARTHER WEST AND WOULD SET OFF SOME INSTABILITY
SHOWERS OVER EASTERN WI. OTHER MODELS ARE EITHER WEAKER OR FARTHER
EAST WITH THE TROUGH DEVELOPMENT...THUS DRY CONDITIONS FOR NE WI.
MAY LEAVE A SMALL TOKEN POP IN THE EAST FOR WEDNESDAY...BUT
CONFIDENCE NOT VERY HIGH AT THE MOMENT. MAX TEMPERATURES FOR
WEDNESDAY TO RANGE FROM THE MID 50S NORTH/LAKESHORE...TO AROUND 60
DEGREES SOUTH.

THE HIGHLY-AMPLIFIED MEAN FLOW TO BE IN PLACE BY WEDNESDAY NIGHT
WITH A DEEP UPPER TROUGH HITTING THE WEST COAST...AN UPPER RIDGE
SITUATED OVER THE CENTRAL CONUS AND A STRONG UPPER TROUGH OVER THE
EASTERN CONUS. HIGH PRESSURE AT THE SURFACE IS FORECAST TO BUILD
TOWARD THE WESTERN GREAT LAKES WEDNESDAY NIGHT AND RESIDE OVER THE
REGION ON THURSDAY. LOOK FOR MOSTLY CLEAR SKIES AT NIGHT/MOSTLY
SUNNY SKIES DURING THE DAY...BUT TEMPERATURES TO STILL BE A BIT
BELOW NORMAL.

THIS AMPLIFIED PATTERN WILL SLOW THE MOVEMENT OF WEATHER SYSTEMS
ACROSS THE CONUS AND WITH THE UPPER RIDGE HOLDING OVER THE CENTRAL
CONUS...DO NOT ANTICIPATE MUCH CHANGE IN OUR WEATHER THROUGH
FRIDAY. TEMPERATURES ALOFT WILL BEGIN TO WARM A LITTLE BY
FRIDAY...SO MAX TEMPERATURES SHOULD AT LEAST BE CLOSER TO NORMAL.
&&

.AVIATION...FOR 12Z TAF ISSUANCE
ISSUED AT 638 AM CDT SAT APR 30 2016

CLOUDS WILL INCREASE FROM SOUTH TO NORTH TODAY AS AN
UPPER LEVEL SYSTEM APPROACHES FROM THE CENTRAL PLAINS. SOME LIGHT
RAIN MAY FALL FROM A MIDDLE CLOUD DECK BY EARLY EVENING SOUTH OF
A GREEN BAY TO STEVENS POINT LINE. THE LIGHT RAIN MAY MOVE FURTHER
NORTH OVERNIGHT POSSIBLY REACHING A MARINETTE TO MERRILL LINE.

MVFR CEILINGS ARE POSSIBLE LATE TONIGHT AND EARLY SUNDAY SOUTH OF
WAUSAU TO GREEN BAY BUT OTHERWISE IT SHOULD GENERALLY BE VFR. LOW
LEVEL WIND SHEAR IS POSSIBLE TONIGHT WITH EAST NORTHEAST WINDS
AROUND 10 KNOTS AT THE GROUND AND 30 KNOTS AROUND 1000 FEET AGL.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......KALLAS
AVIATION.......RDM



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