Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 022032
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
332 PM CDT WED SEP 2 2015

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SYNOPSIS...
ISSUED AT 332 PM CDT WED SEP 2 2015

THE VERY WARM AND HUMID LATE-SUMMER WEATHER WILL CONTINUE WELL
INTO THE LABOR DAY WEEKEND...THEN COOLER AND DRIER WEATHER IS
EXPECTED NEXT WEEK.

THE LARGE SCALE PATTERN INVOF NOAM IS CURRENTLY DOMINATED BY A
TROF OVER ALBERTA...AND BROAD DOWNSTREAM RIDGING ACRS THE CENTRAL
AND ERN CONUS. THE WRN TROF WL SHARPEN AND DEEPEN SWD DOWN THE
WEST COAST THE NEXT COUPLE DAYS...RESULTING IN A SHARPENING OF
THE DOWNSTREAM RIDGE FM THE CENTRAL CONUS INTO SRN ONTARIO. THE
WRN TROF WL BEGIN TO ADVANCE EWD BY THE WEEKEND...EVENTUALLY
PUSHING THE RIDGE AXIS E OF THE FCST AREA BY EARLY NEXT WEEK.

THE PATTERN WL KEEP VERY WARM AND HUMID AIR ACRS THE AREA WELL
INTO THE UPCOMING HOLIDAY WEEKEND...THOUGH ACTUAL TEMPERATURES
COULD BE HELD DOWN BY CLDS AND PCPN AT TIMES /AS OCCURRED ACRS
THE N TDA/. TEMPERATURES AND HUMIDITIES WL FALL BACK CLOSER TO
SEASONAL NORMALS ONCE THE UPR TROF AXIS NEARS THE AREA EARLY NEXT
WEEK. ALTHOUGH ABUNDANT MOISTURE WL REMAIN ACRS THE AREA FOR
SEVERAL DAYS...FORCING WL BE SUBTLE AFTER TNGT. SO ALTHOUGH ISOLD
STORMS WL FORM AND PROBABLY PRODUCE LOCALLY HEAVY RAIN...COVERAGE
WILL PROBABLY BE LIMITED UNTIL THE UPPER TROUGH BEGINS TO NEAR THE
AREA DURING THE LATTER PART OF THE LABOR DAY WEEKEND. PCPN AMNTS
AT MOST AREAS WL FOR THE MOST PART DEPEND ON HOW MUCH RAIN OCCURS
WITH THAT FEATURE.
&&

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 332 PM CDT WED SEP 2 2015

MAIN FCST EMPHASIS OVER THE NEXT 24 HOURS SHIFT FROM DENSE FOG TO
PCPN POTENTIAL AS A WEAK FRONTAL BOUNDARY INTERACTS WITH A MID-
LEVEL SHORTWAVE TROF. THE PRIMARY FCST ISSUE IS WHERE TO PLACE THE
BEST CHC FOR PCPN.

THE 19Z MSAS SFC ANALYSIS INDICATED A WAVE FRONTAL BOUNDARY
STRETCHED FROM JUST SOUTH OF A MPX TO CWA TO SUE LINE. WATER
VAPOR SATL IMAGERY SHOWED A MID-LEVEL SHORTWAVE TROF OVER WRN
WI/ERN IA. THESE TWO FEATURES...COMBINED WITH A MOIST AND UNSTABLE
ATMOSPHERE ALLOWED FOR A NEW ROUND OF CONVECTION TO FIRE IN THE
VCNTY OF THE FRONTAL BOUNDARY.

NOT THE EASIEST OF FCSTS OVER THE NEXT 24 HOURS AS THE WEATHER
FEATURES BOTH AT THE SFC AND ALOFT AR WEAK. THE W-E ORIENTATED
BOUNDARY IS FCST TO VERY SLOWLY SAG SWD...BUT REMAIN IN THE
GENERAL VCNTY OF CNTRL/E-CNTRL WI TNGT. MEANWHILE...THE WEAK MID-
LEVEL SHORTWAVE TROF IS EXPECTED TO MOVE INTO THE GREAT LAKES
REGION. THESE TWO FEATURES...COMBINED WITH THE VERY MOIST/UNSTABLE
AIR MASS OVERHEAD...WL CONT TO BE THE DRIVING FORCES FOR
ADDITIONAL PCPN CHCS TNGT. MAIN PROBLEM IS TRYING TO PINPOINT
EXACTLY WHERE THIS CONVECTIVE BAND WL SET-UP...SINCE A COMPLEX CAN
CREATE ITS OWN MESOSCALE ENVIRONMENT. LATEST THINKING IS FOR THE
CURRENT ACTIVITY OVER NRN WI TO GRADUALLY DISSIPATE THIS EVENING
AND REFOCUS ACROSS CNTRL/E-CNTRL WI FOR THE BULK OF THE NIGHTTIME
HOURS. BESIDES THE EVERPRESENT MARINE FOG...WL HAVE TO WATCH NRN
WI FOR LOCALLY DENSE FOG LATE TNGT DUE TO RAINFALL...LIGHT WINDS
AND DEW POINTS STILL IN THE 60S. MIN TEMPS TNGT WL RANGE FROM THE
LWR 60S NORTH...TO THE MID TO UPR 60S SOUTH.

THE FRONTAL BOUNDARY CONTS ITS SLOW SWD MOVEMENT ON THU...HOWEVER
THE MID-LEVEL SHORTWAVE TROF REMAINS NEARLY STATIONARY OVER THE
MIDDLE OF THE GREAT LAKES. THIS KEEPS AT LEAST ERN WI SUSCEPTIBLE
TO ADDITIONAL PCPN CHCS...ESPECIALLY IF ANY CONVECTIVE BOUNDARIES
ARE LEFT BEHIND. THE REST OF THE FCST AREA IS PROGGED TO BE DRY...
PARTLY CLOUDY AND STILL HUMID WITH DEW POINTS HOLDING IN THE MID
TO UPR 60S. MAX TEMPS TO RANGE FROM THE MID TO UPR 70S NEAR LAKE
MI...80-85 DEGS ELSEWHERE.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 332 PM CDT WED SEP 2 2015

ALTHOUGH IT IS IMPOSSIBLE TO ABSOLUTELY RULE OUT PCPN DURING THE
END OF THE WORK WEEK AND MUCH OF THE WEEKEND...WEAK FORCING INVOF
UPPER RIDGE WL MAKE ORGANIZED STORMS UNLIKELY. ENDED UP CARRYING
LOW POPS AT TIMES. GIVEN THE HIGH MOISTURE CONTENT OF THE AIR
MASS AND LIKELY SLOW MOVEMENT OF THE STORMS...LOCALIZED HEAVY
RAINFALL WILL BE POSSIBLE. SOME FOG WILL ALSO DEVELOP OVERNIGHT...
AND COULD BECOME DENSE ENOUGH TO RESULT IN HAZARDOUS TRAVEL
CONDITIONS...MAINLY LATE AT NIGHT AND EARLY IN THE MORNINGS. STUCK
CLOSE TO A BLEND OF THE TOP PERFORMING GUIDANCE PRODUCTS FOR
TEMPERATURES.

NO SIG CHANGES WERE NECESSARY TO EXTENDED FORECAST INITIALIZATION
GRIDS GENERATED FROM A BROAD-BASED BLEND OF GUIDANCE PRODUCTS.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1239 PM CDT WED SEP 2 2015

A FRONTAL BOUNDARY DRAPED ACROSS CNTRL WI...COMBINED WITH A MID-
LEVEL SHORTWAVE TROF MOVING INTO THE GREAT LAKES REGION...WL CONT
TO BRING SEVERAL ROUNDS OF SHWRS/SCT TSTMS TO THE REGION THRU THU
MORNING. INITIAL BAND OF PCPN TO MAINLY REMAIN ACROSS NRN WI WHERE
VSBYS/CIGS COULD DROP AS LOW AS IFR CONDITIONS UNDER ANY STORMS.
AS THE BOUNDARY SAGS SLOWLY SOUTH TNGT...FOCUS FOR PCPN SHIFTS TO
CNTRL/E-CNTRL WI. EVEN IF THE PCPN BECOMES SCATTERED FOR A TIME...
PLENTY OF LOW-LEVEL MOISTURE AND LIGHT WINDS REMAIN OVER THE
AREA...THUS IF NOT PCPN...THEN AREAS OF FOG WITH LOW CIGS AND
VSBYS BECOME THE PROBLEM. VSBYS MAY DROP TO IFR LEVELS LATE TNGT
INTO THU MORNING. AS THE FRONT CONTS TO SAG SOUTH ON THU...PCPN
CHCS SHOULD PRIMARILY BE OVER THE SRN HALF OF THE STATE WITH
DECREASING POPS IN THE AFTERNOON. MVFR CIGS/VSBYS TO PREVAIL THU
MORNING BEFORE RETURNING TO VFR CONDITIONS IN THE AFTERNOON.
&&

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

$$

SYNOPSIS.......SKOWRONSKI
SHORT TERM.....KALLAS
LONG TERM......SKOWRONSKI
AVIATION.......KALLAS


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