Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 202348
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
648 PM CDT WED AUG 20 2014

UPDATED AVIATION PORTION FOR 00Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 337 PM CDT WED AUG 20 2014

PRECIPITATION TIMING IS THE PRIMARY CONCERN DURING THIS PART OF
THE FORECAST AS A SURFACE LOW AND UPPER CYCLONE CONTINUE TO SLOWLY
MOVE AWAY FROM THE AREA. MOST OF THE CLOUDS ACROSS THE SOUTHWEST
1/2 TO 2/3 OF WISCONSIN SHOULD DISSIPATE WITH LOSS OF DAYTIME
HEATING...AND THE CLOUDS ACROSS MUCH OF THE FORECAST AREA WILL
MOVE AWAY WITH THE DEPARTING SYSTEMS. DEW POINTS WERE MAINLY IN
THE UPPER 50S AND LOWER 60S EARLY THIS AFTERNOON SO THERE WAS
PLENTY OF LOW-LEVEL MOISTURE. THE MOIST CONDITIONS...DEPARTING
CLOUDS AND WEAK SURFACE FLOW SHOULD RESULT IN AT LEAST PATCHY FOG
TONIGHT.

12Z VERSIONS OF THE NAM/GFS/ECMWF ALL BROUGHT QPF INTO THE
FORECAST AREA BETWEEN 06Z AND 12Z AHEAD OF AN APPROACHING WARM
FRONT. THERE IS ALSO SOME SHORT WAVE ENERGY PROPAGATING THROUGH A
WEAK UPPER LEVEL RIDGE THAT SHOULD REACH THE STATE ON
THURSDAY...SO HAVE GRADUALLY SPREAD AND INCREASED POPS FROM
SOUTHWEST TO NORTHEAST OVERNIGHT THROUGH THURSDAY. COULD BE SOME
HEAVY RAINFALL WITH THE STORMS CONSIDERING THE FACT THAT PWAT FROM
THE 12Z GRB SOUNDING WAS 1.41 INCHES...WHICH IS IN THE 75TH
PERCENTILE CLIMATOLOGICALLY. THERE CONTINUES TO BE SOME UNCERTAINTY
REGARDING SEVERE POTENTIAL WITH SPC SHOWING A 5 PERCENT CHANCE FOR
SEVERE ACROSS MUCH OF THE FORECAST AREA.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 337 PM CDT WED AUG 20 2014

THE 500 MB LEVEL PROGS BUILD A RIDGE LATE THIS WEEK AND INTO THE
WEEKEND. WARMER TEMPERATURES ARE EXPECTED UNDER THE BUILDING RIDGE
ALONG WITH SEVERAL CHANCES OF RAIN. THE MOST SIGNIFICANT RAIN WILL
LIKELY BE NEAR OR ALONG A FRONTAL BOUNDARY BUT LOCATION OF THIS
BOUNDARY IS STILL IN QUESTION BUT LATEST MODEL RUNS ARE HINTING
THE SURFACE BOUNDARY WILL SAG A BIT FURTHER SOUTH IN NORTHERN
ILLINOIS LATE THIS WEEK AND INTO THE WEEKEND. AS THE RIDGE BREAKS
DOWN NEXT WEEK...THE PATTERN LOOKS TO BE SETTING UP WITH A TROUGH
SETTLING INTO THE NORTHERN PLAINS AND THE SOUTHWEST FLOW ALOFT AND
LIKELY SHORT WAVE TROUGHS WILL BRING SEVERAL CHANCES OF RAIN...HOWEVER
TIMING THESE PRECIPITATION CHANCES BECOMES CHALLENGING.

FOR THURSDAY NIGHT...THERE IS SOME POTENTIAL FOR THUNDERSTORMS TO
AT LEAST PRODUCE HEAVY RAINFALL AS WELL AS STRONG TO SEVERE
STORMS. THE SURFACE WARM FRONT LIFTS INTO SOUTHERN WISCONSIN WHILE
THE H850 FRONT LIFTS INTO THE SOUTHWEST WISCONSIN ALONG WITH A
MODEST 30 KNOT LLJ WHICH EVENTUALLY VEERS TO THE WEST. AN UPPER
JET LIFTING NORTHWARD AS THE UPPER BUILDS MAY PROVIDE A FEW JET COUPLETS
TO ENHANCE THE CONVECTION...AND THE LATEST ECMWF SUGGEST A RRQ
REGION LINGERS INTO FRIDAY OVER SOUTHEAST WISCONSIN INCLUDING
PORTIONS OF EAST CENTRAL WISCONSIN. PWATS CLIMB TO A HEALTHY 1.60
INCHES WHICH MAY PRODUCE ROUNDS OF HEAVY RAIN...HOWEVER SINCE THE
FRONTAL BOUNDARY AND HIGHER PWATS OF 2.00 INCHES ARE TRENDING
SOUTHWARD AND THE LIKELY LOCATION OF SIG RAINS...WILL NOT ISSUE AN
ESF FOR NOW AND HIGHLIGHT IN THE HWO.

THE FOCUS OF ANY CONVECTION FRIDAY INTO SATURDAY NIGHT WILL LIKELY BE
ANY NORTHERN PLAINS SHORT WAVE AND CONVECTION WORKING OVER THE
RIDGE...AND ESPECIALLY IN THE REGION OF UPPER JET DYNAMICS OVER
THE NORTHERN GREAT LAKES REGION. BUT IN GENERAL WILL GO DRY OR
LOW POPS FRIDAY INTO SATURDAY.

THE WARM FRONT IS THEN PROGGED TO MOVE NORTHWARD SATURDAY INTO
SATURDAY NIGHT FOLLOWED WITH A COLD FRONT SUNDAY NIGHT INTO
MONDAY...HOWEVER MODEL DIFFERENCES REMAIN WITH THE TIMING OF THESE
FEATURES DUE TO TIMING OF THE BREAKDOWN OF THE UPPER RIDGE.

TEMPS POTENTIALLY BE RATHER WARM ALONG WITH INCREASED
HUMIDITY...ESPECIALLY IF CONVECTION BECOMES SPARSE AND CLOUDS
DIMINISH.
&&

.AVIATION...FOR 00Z TAF ISSUANCE
ISSUED AT 637 PM CDT WED AUG 20 2014

ALTHOUGH CLEARING HAD OCCURRED OVER MUCH OF C/EC WI THIS AFTERNOON...
STRATOCUMULUS WITH BASES OF 2500-3500 FT PERSISTED OVER NORTHERN WI.
EXPECT A GRADUAL DECREASE IN THE CLOUDS OVER N WI THIS EVG.

CLOUDS WILL INCREASE AGAIN FROM THE SOUTH LATER TONIGHT AS A WARM
FRONT CREEPS NORTHWARD TOWARD FAR SW WI. THIS FRONT MAY BRING SCT
SHRA/ISOLD TSRA TO PARTS OF C/EC WI LATE TONIGHT INTO THURSDAY
MORNING...AND A BETTER CHANCE OF SHRA/TSRA AS IT GETS CLOSER
CLOSER THURSDAY AFTERNOON AND EVENING. HAVE ADDED A TEMPO GROUP
FOR TSTMS IN THE TAFS DURING THE MID TO LATE AFTERNOON PERIOD...
BUT THE TIMING WILL LIKELY NEED TO BE ADJUSTED.

PATCHY/AREAS OF FOG SHOULD DEVELOP LATER THIS EVENING AND
OVERNIGHT...WITH VSBYS/CIGS POSSIBLY LOWERING TO IFR/LIFR. THE
THICKER FOG SHOULD DISSIPATE EARLY THURSDAY...BUT LIGHT FOG OR
HAZE MAY LINGER THROUGH THE DAY DUE TO A MOIST AIR MASS.
&&

.HYDROLOGY...
ISSUED AT 337 PM CDT WED AUG 20 2014

RIVERS ROSE A LITTLE A FEW DAYS AGO WITH THE SPOTTY
HEAVY RAINFALL...BUT OVERALL WAS NOT IMPACTED BY THE HEAVY RAIN
AND CAN HANDLE MORE RAIN.  POTENTIAL OF MORE HEAVY RAINFALL NEXT
SEVERAL DAYS. TRENDS OF THE MODELS SUGGEST THE DEEP MOISTURE WITH
PWATS OF 2.00 INCHES HAVE TRENDED SOUTH OF THE AREA WHILE THE
PRIMARY FRONT WITH THE DEEP MOISTURE PROGGED TO DROP INTO ILLINOIS
ON FRIDAY. BUT PWATS OF 1.60 INCHES CAN STILL PRODUCE HEAVY RAIN
AND NEEDS TO BE WATCHED...ESPECIALLY WHEN THE UPPER JET LIFTS
NORTH AND WINDS BECOME LIGHTER IN THE RIDGE...AND POTENTIALLY
SLOWER MOVEMENT OF THE CONVECTION.
&&

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

$$

SHORT TERM.....MG
LONG TERM......TDH
AVIATION.......KIECKBUSCH
HYDROLOGY......TDH





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