Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 291020
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
520 AM CDT WED APR 29 2015

UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND THURSDAY
ISSUED AT 257 AM CDT WED APR 29 2015

PRIMARY FOCUS DURING THIS PERIOD IS THE UNSTABLE UPPER LOW
SYSTEM PROGGED TO DROP SOUTHWARD OVER EASTERN WISCONSIN TODAY.
SYSTEM WILL INCLUDE A PERIOD OF A LFQ REGION OF A NORTH TO SOUTH
UPPER JET...TOTAL TOTALS CLIMBING INTO THE 50S...AND VERY STEEP
LOW LEVEL LAPSE RATES THIS AFTERNOON. HOWEVER THESE HEALTHY
DYNAMICS WILL BE SLIDING OVER A VERY DRY BOUNDARY LAYER. MORE THAN
LIKELY WILL GET A FEW SPRINKLES OVER EASTERN WISCONSIN THIS
AFTERNOON INTO EARLY EVENING. THE NEARLY DRY ADIABATIC BOUNDARY
MAY PRODUCE A FEW GUSTY WINDS TO 25-30 KTS WITH ANY LIGHT
SHOWERS...SPRINKLES AND EVEN VIRGA. IF ANY MID LEVEL MOISTURE CAN
POOL TOGETHER THIS AFTERNOON...AN ISOLATED TSRA REMAINS POSSIBLE.
NOT SEEING ANY NOTABLE CONVERGENCE AT THE SURFACE FOR MOISTURE
POOLING DUE TO THE NORTHERLY WINDS. THIS UPPER LOW IS DROPPING A
TAD TO THE EAST THAN COMPARED TO 24 HOURS AGO. CURRENTLY HAVE A
SLIGHT CHC OF TSRA THIS AFTERNOON...WILL REDUCE THE WINDOW OF
MENTION DUE TO THE LOW CONFIDENCE.

WRAP AROUND CLOUDS WILL CONTINUE TO PASS OVER EASTERN WISCONSIN
TONIGHT INTO THURSDAY WHILE A RIDGE OF HIGH PRESSURE BUILDS INTO
THE WESTERN GREAT LAKES REGION. SO EASTERN WISCONSIN MAY BE
DEALING WITH MORE CLOUDS UNTIL THE UPPER RIDGE NUDGES THE SYSTEM
TO THE EAST LATER THURSDAY. A FEW SPRINKLES WILL BE POSSIBLE FAR
EASTERN WISCONSIN LATE TONIGHT INTO THURSDAY IN THE LINGERING
CYCLONIC FLOW.

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY
ISSUED AT 257 AM CDT WED APR 29 2015

MEAN FLOW ACROSS THE LWR 48 IS STILL FCST TO BECOME MORE ZONAL
STARTING THIS WEEKEND WITH PACIFIC SYSTEMS QUICKLY MOVING THRU
THIS PROGRESSIVE FLOW. THE FIRST IS SET TO ARRIVE FRI/FRI NGT...
BUT IS RATHER WEAK AND WL NOT PRODUCE MUCH PCPN. THE SECOND SYSTEM
IS EXPECTED TO ARRIVE LATE SUNDAY INTO MON AND WL HAVE BETTER LIFT/
FORCING/INSTABILITY/MOISTURE AVAILABLE. TEMPS ARE FCST TO WARM TO
ABOVE NORMAL LEVELS ONCE THE FLOW TURNS ZONAL (SAT) AND STAY ABOVE
NORMAL INTO EARLY NEXT WEEK. THERE ARE SIGNS OF A MORE UNSETTLED
PATTERN JUST BEYOND THIS FCST CYCLE AS A SHORTWAVE TROF LIFTS NEWD
FROM THE SW CONUS. MORE ON THIS POTENTIAL WET PATTERN IN THE DAYS
TO COME.

COMBINATION OF WEAK SFC RDG AND WEAKENING UPR RDG TO RESIDE OVER
THE WRN GREAT LAKES THU NGT AND BRING A MOSTLY CLEAR SKY/LIGHT
WIND REGIME TO NE WI. NEAR IDEAL RADIATIONAL COOLING CONDITIONS WL
BRING A WIDE RANGE OF TEMPS WITH READINGS RANGING FROM THE UPR 20S
NEAR THE UPR MI BORDER...TO THE UPR 30S OVER MOST OF CNTRL/E-CNTRL
WI. CLOUDS ARE FCST TO GRADUALLY INCREASE OVER THE AREA ON FRI
AHEAD OF A WEAK SYSTEM PUSHING INTO THE WRN GREAT LAKES. THIS
SYSTEM TO BE COMPOSED OF A WEAK CDFNT AND A WEAK SHORTWAVE TROF...
WITH LITTLE IN THE WAY OF LIFT OR FORCING EVIDENT ON THE MODELS.
LATEST TIMING OF THE CDNT WOULD BRING A SMALL CHC OF SHWRS TO
N-CNTRL/CNTRL WI FRI AFTERNOON. FRI WL BE A MILD DAY WITH MAX
TEMPS MAINLY IN THE UPR 60S TO LWR 70S (COOLER LAKESIDE).

THE SMALL RAIN CHCS WOULD CONT INTO FRI NGT AS THIS WEAK SYSTEM
MOVES ACROSS THE FCST AREA. ANY PCPN AMOUNTS WL BE ON THE LIGHT
SIDE AND SCATTERED AT BEST...THUS THIS SYSTEM WL NOT END THE DRY
CONDITIONS THAT CURRENTLY EXIST ACROSS A LARGE PART OF WI. MIN
TEMPS FRI NGT TO RANGE FROM THE UPR 30S NORTH...TO THE MID 40S
SOUTH. THE MEAN FLOW TO ALREADY HAVE BECOME ZONAL OVER THE WRN
2/3RDS OF THE CONUS BY THE FIRST HALF OF THE WEEKEND. NE WI TO BE
SITUATED BETWEEN SYSTEMS WITH A SMALL AREA OF HI PRES MOVING
ACROSS THE GREAT LAKES. A DECENT AMOUNT OF SUNSHINE IS ANTICIPATED
FOR SAT AND WITH 8H TEMPS PUSHING +10C...WE COULD SEE MAX TEMPS
PUSH INTO THE LWR 70S ON AVERAGE (60S NEAR LAKE MI...MID 70S CNTRL
WI).

WL BE WATCHING TWO AREAS OF PCPN DEVELOP SAT NGT. THE FIRST AREA
TO BE OVER THE NRN PLAINS ASSOCIATED WITH A CDFNT. THE SECOND AREA
TO BE OVER THE MID-MS VALLEY ASSOCIATED WITH THE LOW-LEVEL JET/WAA.
THESE TWO AREAS OF PCPN ARE PROGGED TO CONVERGE ON THE GREAT LAKES
ON SUNDAY...ALTHO THE MAIN PCPN INGREDIENT WL BE THE INCREASING WAA
THRU WI. A PREVAILING SW WIND ON SUNDAY WL ALSO DRAW WARMER/MORE
MOIST AIR INTO WITH MAX TEMPS AGAIN IN THE LWR HALF OF THE 70S
(AWAY FROM LAKE MI) AND DEW POINTS CLIMBING INTO THE UPR 40S TO
MID 50S. ENUF INSTABILITY WL BE GENERATED (SUB-ZERO LI`S/CAPES
GREATER THAN 1K J/KG) TO WARRANT THE MENTION OF THUNDER.

THE BEST CHC OF SEEING A WIDESPREAD PCPN EVENT APPEARS TO BE
SUNDAY NGT/MON TIME FRAME AS THE CDFNT DROPS SEWD THRU WI. ENUF
INSTABILITY CARRIES OVER INTO SUNDAY NGT AND WITH LIFT FROM THE
CDFNT...HAVE KEPT THUNDER IN THE FCST. THERE IS SOME MINOR TIMING
DIFFERENCES WITH RESPECT TO THE MOVEMENT OF THE CDFNT AS THE GFS
IS THE FASTEST AND THE GEM IS THE SLOWEST. THIS BECOMES IMPORTANT
HEADED INTO MON WITH RESPECT TO HOW LONG TO HANG ON TO THE POPS...
ESPECIALLY OVER THE NORTH. FOR NOW...WL KEEP A SMALL CHC POP
N-CNTRL AND KEEP THE HIGHEST POPS OVER E-CNTRL WI. DESPITE THE
CLOUDS/PCPN IN THE VCNTY...MAX TEMPS ON MON ARE STILL EXPECTED TO
REACH THE UPR 60S NORTH...LWR 70S SOUTH (COOLER AGAIN NEAR THE
LAKE).

FCST ISSUE FOR MON NGT INTO TUE WL BE THE LOCATION OF THE CDFNT AS
THE MODELS INDICATE A SFC WAVE TO RIDE ALONG THE BOUNDARY AND SET
OFF ANOTHER ROUND OF SHWRS/TSTMS. THE MORE PROGRESSIVE GFS HAS THE
CDFNT DROP JUST FAR ENUF SOUTH (NRN IL) TO KEEP ANY ADDITIONAL
PCPN SOUTH OF THE FCST AREA. MEANWHILE...THE GEM/ECMWF ARE NOT AS
PROGRESSIVE WITH THE FNT STILL IN CNTRL/SRN WI RESPECTIVELY. THIS
KEEPS A CHC OF SHWRS/TSTMS IN THE FCST FOR CNTRL/E-CNTRL WI INTO
TUE MORNING. JUST NOT ENUF CERTAINTY TO CHOOSE A FAVORITE AND HAVE
USED A MODEL COMPROMISE WHICH KEEPS A POP IN THE FCST FOR
CNTRL/E-CNTRL WI THRU TUE.
&&

.AVIATION...FOR 12Z TAF ISSUANCE
ISSUED AT 519 AM CDT WED APR 29 2015

VFR CONDITIONS EXPECTED TODAY AND TONIGHT. MID LEVEL
CLOUDS WILL BE ON THE INCREASE FROM THE NORTH THIS
MORNING...FOLLOWED WITH A PERIOD OF SCATTERED 3500 TO 4000 FEET
LEVELS THIS AFTERNOON WITH ISOLATED SHOWERS. BRIEF GUSTY WINDS TO
30 KNOTS WILL BE POSSIBLE WITH SOME OF THE AFTERNOON SHOWERS OR
SPRINKLES WHICH CAN DEVELOP. &&

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

$$

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







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