Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 311815
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
115 PM CDT THU JUL 31 2014

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND FRIDAY
ISSUED AT 343 AM CDT THU JUL 31 2014

PCPN TRENDS...FOG TRENDS AND TEMPERATURES ARE THE MAIN FCST
CONCERNS.

SHOWERS HAD ENDED OVER CENTRAL WI...AND MID-LEVEL CLOUDS WERE
GRADUALLY ERODING OVER THE SW PART OF THE FCST AREA. AREAS OF
FOG HAD DEVELOPED OVER NC WI...WITH PATCHY FOG REPORTED
ELSEWHERE. DENSE FOG WAS OCCURRING OVER PARTS OF VILAS...
ONEIDA AND LINCOLN COUNTIES.

VSBYS HAD ALREADY DROPPED TO 1/4SM-3/4SM OVER VILAS...ONEIDA AND
LINCOLN COUNTIES EARLY THIS MORNING...AND WILL LIKELY LOWER
SOME MORE OVER THE NEXT FEW HOURS. THIS SAME AREA HAD DENSE FOG
YESTERDAY MORNING. GIVEN THE POTENTIAL FOR HAZARDOUS DRIVING
CONDITIONS FOR THE MORNING COMMUTE...HAVE DECIDED TO ISSUE A
DENSE FOG ADVISORY THROUGH 8 AM.

ALTHOUGH SOME WEAK SHORT-WAVE ENERGY MAY MOVE THROUGH THE RGN
TODAY...NO SIGNIFICANT FORCING IS EXPECTED. DRIER CANADIAN
AIR...WITH PWATS AROUND 0.75 INCH...WILL MOVE INTO NORTHERN WI
TODAY...SO ANY CONVECTION THAT DEVELOPS SHOULD BE ISOLD/SCT.
MODIFIED FCST SOUNDINGS SUPPORT CAPE OF 500-1000 J/KG...WITH THE
BEST INSTABILITY OCCURRING OVER THE SW HALF OF THE CWA. LLVL
CONVERGENCE IS EXPECTED TO BE STRONGEST OVER FAR NE WI. WILL
CARRY SLGT CHC OR CHC POPS OVER MOST OF THE CWA THIS AFTERNOON
AND EVENING...WITH THE HIGHEST POPS OVER CENTRAL AND FAR NE WI.
DRY CONDITIONS ARE EXPECTED OVERNIGHT...WITH PATCHY FOG EXPECTED
TO REDEVELOP. USED A BLEND OF THE TOP-PERFORMING GUIDANCE SETS
(WHICH HAVE BEEN TOUGH TO BEAT LATELY) FOR TEMPERATURES TODAY AND
TONIGHT. THEY SUPPORT HIGHS IN THE MIDDLE 70S TO LOWER 80S...
EXCEPT UPPER 60S AND LOWER 70S LAKESIDE...WITH LOWS IN THE MIDDLE
40S TO LOWER 50S NORTH...TO 55 TO 60 SOUTH.

ON FRIDAY...MOISTURE AND INSTABILITY IS EXPECTED TO INCREASE A
BIT DURING THE DAY. MODIFIED FCST SOUNDINGS SUPPORT CAPE OF
1500-2000 J/KG...WITH LI`S OF -5 TO -7. AN UPPER LEVEL TROF
WILL MOVE INTO THE REGION LATE IN THE DAY...AND SHOULD HELP
TRIGGER TSTM DEVELOPMENT. ALTHOUGH DEEP LAYER SHEAR IS FAIRLY
WEAK (10-20 KTS)...THE DEGREE OF INSTABILITY AND FAVORABLE WET
BULB ZERO HGTS AROUND 10K FT SUPPORT A THREAT OF ISOLD SVR TSTMS
WITH LARGE HAIL AND DAMAGING WINDS. HIGH TEMPERATURES SHOULD BE
QUITE SIMILAR TO TODAY...GENERALLY IN THE UPPER 70S AND LOWER
80S.

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 343 AM CDT THU JUL 31 2014

MEDIUM RANGE MODELS SHOW THAT SOME DEAMPLIFICATION WILL OCCUR TO THE
RIDGE TROUGH PATTERN ACROSS NORTH AMERICA BY EARLY THIS WEEKEND.
WILL STILL HAVE TO DEAL WITH FLATTENED TROUGHING OVER THE GREAT
LAKES...HOWEVER...THAT WILL PROVIDE PERIODIC PRECIP CHANCES.  THE
ECMWF AND GFS REMAIN IN GOOD AGREEMENT SO WILL CONTINUE TO BLEND
THESE MODELS.

FRIDAY NIGHT THROUGH SATURDAY NIGHT...THE DEEP UPPER TROUGH WILL
BEGIN TO LIFT TO THE NORTHEAST FRIDAY NIGHT...BUT WILL CONTINUE TO
PROVIDE SCT SHOWERS AND ISOLATED TSTORMS INTO THE EVENING BEFORE
DIMINISHING OVERNIGHT.  THEN AS THE TROUGH EXITS...WEAK SHORTWAVE
RIDGING BUILDS ACROSS THE REGION ON SATURDAY.  THE PREVIOUS SHIFT
FAVORED A DRY FORECAST...AND CANNOT ARGUE WITH THIS REASONING THOUGH
THE ECMWF CONTINUES TO SPIT OUT LIGHT QPF OVER NORTHEAST WISCONSIN.
THINK THIS IS OVERDONE THOUGH.  THEN A SHORTWAVE WILL MOVE INTO
ONTARIO AND DRAG A WEAK FRONT INTO NORTHWEST WISCONSIN LATE SATURDAY
NIGHT.  WILL INCREASE SKY COVER LATE BUT KEEP THE AREA DRY.

REST OF THE FORECAST...THE SHORTWAVE WILL PUSH THE FRONT ACROSS THE
REGION ON SUNDAY WHICH WILL GIVE THE REGION THE NEXT SIGNIFICANT
CHANCE OF SHOWERS AND THUNDERSTORMS.  THEN THE MODELS SHOW THE FRONT
STALLING ACROSS CENTRAL WISCONSIN SUNDAY NIGHT INTO TUESDAY...THOUGH
ITS NOT EXACTLY CLEAR WHERE THE FRONT ENDS UP BY TUESDAY.  SEEMS
THAT SUNDAY NIGHT AND MONDAY OFFER BETTER CHANCES OF PRECIP RATHER
THAN TUESDAY.  THEN ANOTHER SHORTWAVE ARRIVES BY THE MIDDLE OF NEXT
WEEK.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 114 PM CDT THU JUL 31 2014

DENSE FOG DISSIPATED AND CU DEVELOPED ACROSS THE AREA THIS
MORNING. LAPSE RATES FROM THE SURFACE TO 3KM WERE ALREADY VERY
STEEP AT MIDDAY...CAPES WERE GREATER THAN 1000J/KG ACROSS CENTRAL
WISCONSIN...AND AROUND 500J/KG FROM SUE TO RHI. EXPECT STORMS TO
DEVELOP WITH INSTABILITY AND SHORT WAVE ENERGY MOVING THROUGH THE
STATE. SHOWERS BEGAN TO DEVELOP EARLY THIS AFTERNOON...SO HAVE
INCLUDED VCSH AT TAF SITES. HAVE INTRODUCED VCTS A LITTLE LATER IN
THE AFTERNOON AND WOULD NOT BE SURPRISED IF THE STORMS HAD SOME HAIL
SINCE WBZ HEIGHTS WERE LESS THAN 9KFT. STUCK WITH CONVECTION
ENDING WITH LOSS OF DAYTIME HEATING...BUT WAS UNSURE ABOUT THIS AS SOME
SHOWERS PERSISTED UNTIL AFTER MIDNIGHT LAST NIGHT. RELATIVELY
LIGHT WINDS AND DECREASING CLOUDS WILL ALLOW FOR FOG DEVELOPMENT
DURING THE NIGHT...BUT KEPT MVFR VSBYS AT TAF SITES...EXCEPT FOR
RHI WHERE THERE WILL PROBABLY BE SOME IFR VSBYS AT TIMES.
&&

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

$$

SHORT TERM.....KIECKBUSCH
LONG TERM......MPC
AVIATION.......MG





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