Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 021113
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
613 AM CDT SAT MAY 2 2015

UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND SUNDAY
ISSUED AT 243 AM CDT SAT MAY 2 2015

FORECAST FOCUS WILL BE WITH THE ANTICIPATED SHOWERS AND
STORMS AND MUCH NEEDED RAIN FOR SUNDAY.

SAT IMAGERY SHOWS SCT-BKN MID LEVEL CLOUDS DRIFTING OVER MUCH OF
THE STATE EARLY THIS MORNING. THE CLOUDS WERE ASSOCIATED WITH THE
REMNANTS OF A WEAK TROUGH PASSING OVER AND WEAK WAA OVER THE
AREA. WILL CONTINUE TO MONITOR FOR A FEW SPRINKLES THIS MORNING
BUT MORE THAN LIKELY SOME VIRGA POSSIBLE THIS MORNING AS THE GRB
RAOB SOUNDING REMAINS DRY IN THE LOWER LAYERS.

WITH THE WAA AND 300 MB SUBTLE DIFFLUENT FLOW ALOFT...A FEW MODELS
PRODUCE LIGHT ISOLATED PCPN THIS AFTERNOON AND ESPECIALLY TONIGHT
INTO SUNDAY WELL AHEAD OF AN APPROACHING COLD FRONT. EARLY THIS
MORNING ISOLATED CONVECTION WAS NOTED OVER THE CENTRAL PLAINS AND
MAINLY ASSOCIATED WITH A WEAK SHORT WAVE. THE GEM AND ECMWF PASSES
THIS PIECE OF ENERGY WELL SOUTH OF THE AREA. GFS IS MORE NORTH AND
SPOTTY WITH PCPN LATE TODAY INTO SUNDAY MORNING. SINCE DEWPOINTS
STILL WORKING THROUGH THE 40S DURING THIS PERIOD...WILL THE CONTINUE
DRY FORECAST THROUGH TONIGHT AND MOST AREAS SUNDAY MORNING.

A STRONG COLD FRONT IN THE WESTERLY FLOW WILL APPROACH WISCONSIN
SUNDAY AND TRACK OVER SUNDAY NIGHT. ALONG WITH THE DIFFLUENT FLOW
ALOFT...INCREASING SURFACE DEWPOINTS WILL INCREASE SB CAPES TO
1000 TO 1500 J/KG DURING A PERIOD FROM 3 PM TO 9 PM SUNDAY
AFTERNOON. THIS INSTABILITY ALSO OCCURS DURING THE HIGHEST SHEAR
VALUES TO PROVIDE THE POTENTIAL OF ISOLATED NEAR SEVERE
STORMS. BEST UPPER JET DYNAMICS ALONG THE US/CANADA BORDER
HOWEVER WESTERLY MID LEVEL FLOW WILL PROVIDE SHEAR FOR CONVECTION.
ALTHOUGH MODEL SURFACE DEWPOINTS ARE IN THE 50S...SOME CONVERGENCE
OR POOLING TO NEAR 60 WILL AID WITH LOCALLY STRONGER CONVECTION.
TIMING OF DYNAMICS AND PEAK HEATING TIME INDICATE NORTH CENTRAL
AND CENTRAL WISCONSIN HAS THE STRONGER POTENTIAL OF MORE POTENT
STORMS.

TEMPERATURES WILL BE A FEW DEGREES HIGHER TODAY THAN FRIDAY DUE
TO THE WARM START AND ONGOING WAA. MAX TEMPS FOR SUNDAY WILL BE
MORE OF A CHALLENGE DUE TO TIMING OF THE START OF CONVECTION AND
RATE OF INCREASING CLOUDS.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY
ISSUED AT 243 AM CDT SAT MAY 2 2015

MEAN FLOW TO TRANSITION FROM ZONAL EARLY NEXT WEEK TO AMPLIFIED AS
A WRN CONUS UPR TROF DEVELOPS AND A SUBTROPIAL UPR RDG SETS UP
OVER THE SE CONUS. ONE FCST CONCERN TO BE THE LOCATION OF A
FRONTAL BOUNDARY THAT WL PASS THRU WI AS A CDFNT SUNDAY NGT...
STALL TO OUR SOUTH AND THEN RETURN NORTH AS A WRMFNT TOWARD MID-
WEEK. ANOTHER CONCERN TO BE THE MOVEMENT OF A LARGE PIECE OF MID-
LEVEL ENERGY THAT BREAKS AWAY FROM THE UPR TROF AND LIFTS NE INTO
THE CNTRL CONUS. THIS PATTERN SHIFT WL BRING A MORE ACTIVE WEATHER
SCENARIO TO NE WI WITH SEVERAL ROUNDS OF SHWRS/TSTMS EXPECTED. THE
LAST CONCERN TO BE WHETHER OR NOT ANY OF THESE STORMS MAY BECOME
STRONG TO SEVERE...ESPECIALLY SUNDAY NGT.

CDFNT TO DRIVE THRU NE WI SUNDAY NGT WITH A MARGINAL RISK OF
SEVERE WEATHER CONTINUING AS THE AIR MASS AHEAD OF THE FNT TO
STILL BE UNSTABLE AND UNCAPPED. THE THREAT WOULD BE LARGE HAIL AND
DAMAGING WINDS AS A LINE OF STORMS PUSHES THRU THE FCST AREA...
MAINLY DURING THE EVENING HOURS WHEN INSTABILITY IS STILL
RELATIVELY HIGH. DEW POINTS IN THE 50S AND PW VALUES IN THE 1.25
TO 1.50" RANGE WL ALSO BRING LOCALLY HEAVY RAIN TO MUCH OF THE
REGION SUNDAY NGT. WOULD NOT BE SURPRISED TO SEE ISOLATED AMOUNTS
OF 1+ INCH BY THE TIME THE PCPN BEGINS TO DIMINISH OVRNGT. MIN
TEMPS TO RANGE FROM THE LWR TO MID 40S N-CNTRL...MID 50S E-CNTRL
WI.

ANY LINGERING RAIN SHWR OVER E-CNTRL WI (MAINLY CALUMET AND
MANITOWOC COUNTIES) EARLY MON MORNING WL COME TO AN END AS THE
CDFNT PULLS AWAY. THE REST OF THE FCST AREA WL BE DRY AS A WEAK
AREA OF HI PRES BUILDS INTO NRN SECTIONS OF THE GREAT LAKES. MORE
SUN NORTH...MIX OF SUN/CLOUDS SOUTH SHOULD YIELD FAIRLY UNIFORM
TEMPS OVER NE WI WITH READINGS GENERALLY IN THE UPR 60S TO LWR 70S
(COOLER NEAR LAKE MI AS WINDS TURN NE).

THE AFOREMENTIONED CDFNT IS FCST TO STALL ACROSS NRN IL BY MON NGT
WITH CONVERGENCE AND MOISTURE POOLING ALONG THE FNT ALLOWING FOR
ADDITIONAL SHWRS/TSTMS TO DEVELOP. THE NRN EDGE OF PCPN MAY GET
CLOSE TO OUR SRN TIER OF COUNTIES LATE MON NGT...BUT HAVE KEPT THE
FCST DRY FOR NOW AS DRIER AIR GETS PUMPED INTO NE WI FROM THE HI
PRES OVER THE NE PART OF THE GREAT LAKES. MOSTLY CLEAR SKIES NORTH/
PARTLY TO MOSTLY CLOUDY SKIES SOUTH WL ALLOW MIN TEMPS TO RANGE
FROM 35-40 DEGS NORTH...MID 40S SOUTH. THERE IS SOME MODEL DEBATE
AS TO WHETHER THE STALLED BOUNDARY WL BEGIN TO SLOWLY EDGE NWD ON
TUE IN RESPONSE TO INCREASING SOUTH WINDS AHEAD OF NE-MOVING
SHORTWAVE TROF NEAR THE FOUR CORNERS REGION. ANTICIPATE THE MODELS
WL CONT TO WAFFLE ON THIS SUBJECT IN THE COMING DAYS...BUT WITH
THE OFF-CHANCE THAT A QUICKER RETURN IS CORRECT...HAVE ADDED A
SLGT CHC POP TO THE SRN TIER OF COUNTIES FOR TUE AFTERNOON. MAX
TEMPS ON TUE AWAY FROM LAKE MI SHOULD AGAIN BE ABLE TO REACH THE
UPR 60S TO LWR 70S.

AS THIS SHORTWAVE TROF LIFTS NEWD THRU THE SRN ROCKIES TUE NGT AND
INTO THE CNTRL PLAINS ON WED...THE STRENGTHENING SOUTHERLY WINDS
ACROSS THE CNTRL PLAINS WL LIFT THE STALLED BOUNDARY NORTH AS A
WRMFNT INTO WI. EXPECT TO SEE AT LEAST A CHC OF SHWRS/TSTMS MOVE
INTO NE WI AS THE WRMFNT PUSHES THRU MAINLY TUE NGT INTO WED
MORNING. THERE IS POTENTIAL THAT THE FCST AREA WL GET INTO THE
WARM SECTOR WED AFTERNOON AND IF WE CAN AVOID ANY FURTHER PCPN...
MAX TEMPS INLAND MAY AGAIN SOAR WELL INTO THE 70S.

PCPN CHCS MINIMIZE WED NGT AS THE WRMFNT TO HAVE CLEARED WI AND
THE SHORTWAVE TROF LIFTS INTO THE NRN PLAINS. THIS WOULD LEAVE
ONLY WEAK WAA AND PERHAPS A WEAK SHORTWAVE TO DEVELOP ANY SHWRS/
ISOLATED TSTMS. PCPN CHCS LOOK TO BE ON THE INCREASE ON THU AS THE
SHORTWAVE TROF SHIFTS ACROSS THE UPR MS VALLEY AND A PLUME OF GULF
MOISTURE SURGES NWD INTO THE WRN GREAT LAKES. PERSISTENT WAA WL
RAISE 8H TEMPS TO AROUND +15C AND WITH DEW POINTS CLIMBING BACK
INTO THE 50S...CAPE VALUES MAY SURPASS 1K J/KG THU AFTERNOON. MAX
TEMPS FOR THU SHOULD AGAIN WARM WELL INTO THE 70S WITH A FEW LWR
80S IN CNTRL WI IF THE PCPN CAN STAY AWAY LONG ENUF.

THE FCST FOR THE END OF THE WORK WEEK IS A BIT UNCERTAIN DUE TO
THE MODELS HANDLING THE MOVEMENT OF THE SHORTWAVE TROF AND ITS
ASSOCIATED CDFNT DIFFERENTLY. SINCE THIS SYSTEM TO BE IN OUR
GENERALY VCNTY...PREFER TO CONT THE MENTION OF SHWRS/TSTMS IN THE
FCST BASED OFF OF THE MODEL CONSENSUS. MAX TEMPS ON FRI WL NOT BE
AS WARM AS THU...BUT REMAIN ABOUT 10 DEGS ABOVE NORMAL.
&&

.AVIATION...FOR 12Z TAF ISSUANCE
ISSUED AT 612 AM CDT SAT MAY 2 2015

A PERIOD OF MID LEVEL CLOUDS WILL DRIFT OVER THE AREA
THIS MORNING...OTHERWISE VFR CONDITIONS EXPECTED TODAY AND
TONIGHT.
&&

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

$$

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






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