Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 250526
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1226 AM CDT FRI JUL 25 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND FRIDAY
ISSUED AT 253 PM CDT THU JUL 24 2014

THE MAIN CONCERN DURING THIS PART OF THE FORECAST IS THE POTENTIAL
FOR SHOWERS AND THUNDERSTORMS LATE TONIGHT AND FRIDAY IN WARM
ADVECTION BEHIND A DEPARTING SURFACE HIGH. A WEAK UPPER LEVEL SHORT
WAVE IS FORECAST TO MOVE INTO WISCONSIN WHILE AN UPPER LEVEL RIDGE
STARTS TO BREAK DOWN AS FLOW ALOFT BECOMES MORE ZONAL.

12Z VERSIONS OF THE NAM/GFS/ECMWF ALL KEEP ANY QPF WEST OF THE
AREA THROUGH 06Z SO HAVE A DRY FORECAST GOING UNTIL AFTER THAT.
THE NAM/GFS BRING SOME QPF INTO CENTRAL WISCONSIN LATER IN THE NIGHT
WHILE THE EC IS MORE AGGRESSIVE WITH NORTHEAST EXTENT OF
PRECIPITATION. INSTABILITY IS NOT THAT IMPRESSIVE TONIGHT...BUT
HAVE KEPT THUNDERSTORMS AS THE MAIN PRECIPITATION TYPE TO BE ON
THE SAFE SIDE. BUFKIT TIME SECTIONS INDICATED SOME ELEVATED CAPE ON
FRIDAY MORNING...AND MID LEVEL LAPSE RATES ARE EXPECTED TO INCREASE
DURING THE DAY SO HAVE THUNDERSTORMS CHANCES THROUGH THE
AFTERNOON...WINDING DOWN IN PARTS OF CENTRAL WISCONSIN BY THE END
OF THE DAY.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY
ISSUED AT 253 PM CDT THU JUL 24 2014

PCPN TRENDS FOR THE WEEKEND WILL BE THE MAIN FCST CHALLENGE.

MODELS OFFER A VARIETY OF SOLUTIONS WITH REGARD TO PCPN TRENDS
FROM FRIDAY NIGHT THROUGH SATURDAY NIGHT...BUT GENERALLY AGREE
ON THE SCENARIO FOR SUNDAY...WITH A STRONG S/W TROF AND CANADIAN
COLD FRONT MOVG THROUGH THE REGION.

ON FRIDAY NIGHT...MODELS SHOW A WARM FRONT SITUATED OVER NORTHERN
IL...WITH A SUBTLE WEAKER BOUNDARY NEAR THE WI/UPPER MI BORDER. A
25-35 KT WEST-SOUTHWEST LLJ WILL BE DIRECTED INTO THE SOUTHERN
PART OF GRB CWA EARLY IN THE EVG...BUT IS EXPECTED TO WEAKEN AND
VEER W-NW OVERNIGHT. THE LFQ OF AN UPPER LEVEL JET WILL BE
POSITIONED OVER THE CWA THROUGH THE NIGHT...WITH PSBL SHORT-WAVE
ENERGY MOVG THROUGH N WI. THINK THAT MOST OF THE PCPN WILL OCCUR
SOUTH OF GRB CWA...CLOSER TO THE MAIN WARM FRONT AND THE DEEPER
MOISTURE/INSTABILITY. HOWEVER...ELEVATED INSTABILITY DOES ADVECT
ACROSS THE CWA...AND SOME UPPER FORCING FROM THE JET STREAK MAY
SUPPORT ISOLD/SCT CONVECTION...ESPECIALLY DURING THE EVENING. A
SIMILAR SETUP CONTINUES INTO SATURDAY...WITH W-NW FLOW AND
DRIER AIR AT 850 MB...AND AN 80-100 KT JET STREAK OVERHEAD. A
LACK OF LOW-LEVEL CONVERGENCE AND DRIER AIR ALOFT SUGGESTS THAT
ANY CONVECTION SHOULD REMAIN ISOLD.

ON SATURDAY NIGHT...THE APPROACHING UPPER LOW/STRONG SHORT-WAVE
TROF WILL ARRIVE IN OUR NW COUNTIES LATE...SO THE HIGHEST POPS
WILL BE FOCUSED OVER NC WI AFTER MIDNIGHT. THE POTENT UPPER
TROF WILL SWING THROUGH THE REGION ON SUNDAY...ACCOMPANIED BY
A CANADIAN COLD FRONT. GIVEN THE STRONG FORCING...WILL BOOST POPS
TO LIKELY OVER MOST OF THE CWA. THE SEVERE THREAT APPEARS TO BE
MARGINAL...WITH THE POTENTIAL FOR ABUNDANT CLOUD COVER...CONTINUED
WESTERLY FLOW AT 850 MB (WEAK CONVERGENCE)...AND THE UPPER FORCING
AND FRONT ARRIVING A LITTLE TOO EARLY IN THE DAY. HOWEVER...CAPE
OF 1000-1500 J/KG...LI`S OF -4 TO -6 AND DEEP LAYER SHEAR OF 25-35
KTS...COMBINED WITH THE EXPECTED FORCING...MAY LEAD TO ISOLD SVR
TSTMS WITH LARGE HAIL.

THE EXTENDED FCST FOR THE UPCOMING WORK WEEK IS EXPECTED TO BE
COOLER THAN NORMAL...WITH A THREAT OF MAINLY AFTERNOON AND EARLY
EVENING SHOWERS AND TSTMS. A STRONG UPPER LEVEL RIDGE WILL BE
PARKED OVER THE ROCKIES...WITH AN UPPER LOW SITUATED NEAR JAMES
BAY. THIS WILL RESULT IN NW FLOW OVER THE WESTERN GREAT LAKES
REGION THROUGH THE WORK WEEK. ALTHOUGH S/W TROFS IN THE NW FLOW
MAY GENERATE SOME PCPN AT TIMES...IT APPEARS THAT MOST OF THE
RAIN WILL BE DIURNALLY-DRIVEN DUE TO DAYTIME HEATING/INSTABILITY.
NONE OF THESE DAYS SHOULD BE WASHOUTS...WITH MAINLY ISOLD/SCT
CONVECTION EXPECTED.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1223 AM CDT FRI JUL 25 2014

MARGINAL LOW LEVEL WIND SHEAR MAY BE A CONCERN TO LIGHT AIRCRAFT
OVERNIGHT OVER THE WEST HALF OF THE STATE AS SURFACE WINDS DROP TO
AROUND 5 KTS FROM THE SOUTH WHILE SOUTHWEST WINDS INCREASE TO
AROUND 30 KTS AT 1000 FT AGL. MAINLY VFR CONDITIONS EXPECTED
THROUGH FRIDAY...WITH AN INCREASING CHANCE OF SHOWERS AND STORMS
LATER FRIDAY INTO FRIDAY NIGHT.

&&

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

$$

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





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