000
FXUS63 KGRB 191934
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
234 PM CDT WED JUN 19 2013

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND THURSDAY
ISSUED AT 234 PM CDT WED JUN 19 2013

SFC ANALYSIS SHOWED AN AREA OF HIGH PRESSURE THAT CONTINUED TO
SHIFT EAST THIS AFTERNOON. A RELATIVELY MOIST LAYER BETWEEN
850-700MB COMBINED WITH A WEAK 300MB JET DIVING DOWN OVER LAKE
SUPERIOR LED TO THE DEVELOPMENT OF FAIR WEATHER CU IN CENTRAL AND
NORTH CENTRAL WISCONSIN. FURTHER EAST...LOCATIONS CLOSER TO THE
CENTER OF THE HIGH PRESSURE SYSTEM REMAINED SUNNY AS DRIER AIR
DOMINATED. AFTER A COOL START TO THE DAY...WARM SOUTHERLY FLOW
ALLOWED TEMPERATURES TO CLIMB QUICKLY AND RETURNED TO NEAR NORMAL
LEVELS...HOWEVER DEWPOINTS HAVE BEEN SLOW TO INCREASE. MAIN
FORECAST CONCERN WILL BE TIMING OF PRECIP CHANCES ON THURSDAY.

AS MENTIONED BEFORE...DEWPOINTS HAVE BEEN SLOW TO INCREASE
TODAY...WITH THE SURGE OF MOIST HOLDING OFF UNTIL THURSDAY
AFTERNOON. THEREFORE...CLIPPED A COUPLE OF DEGREES OFF THE
OVERNIGHT LOW IN MOST LOCATIONS. ONLY EXCEPTION WAS IN THE
NORTHWOODS WHERE CLOUDS STREAMING IN FROM THE NEXT SYSTEM SHOULD
KEEP IT A BIT WARMER. OTHERWISE...NOT MUCH CHANGE MADE TO THE
OVERNIGHT HOURS FROM THE PREVIOUS FORECAST TONIGHT AS HIGH
PRESSURE WILL KEEP THINGS DRY.

A LOW MOVING THROUGH CANADA WILL DRAG A COLD FRONT OVER THE UPPER
PENINSULA ON THURSDAY...AND WILL BE IN THE VICINITY OF THE
WI/YUPPER BORDER BY THURSDAY EVENING. IN ADDITION...A WEAK
SHORTWAVE WILL SLIDE ACROSS WISCONSIN DURING THE LATE AFTERNOON.
THESE TWO FEATURES WILL RESULT IN SCATTERED SHOWER AND
THUNDERSTORM ACTIVITY ON THURSDAY. MODELS HAVE BEEN TOO MOIST
RECENTLY/OVERDOING THE PRECIP...SO SLOWED DOWN THE PROGRESSION OF
CHANCE POPS EASTWARD FROM PREVIOUS FORECAST. IN FACT...LOCATION
IN FAR EASTERN WISCONSIN MAY SEE A COMPLETELY DRY THURSDAY...WITH
CENTRAL AND NORTH CENTRAL WISCONSIN SITTING UNDER MOSTLY CLOUDY
SKIES AND SCATTERED SHOWER ACTIVITY. TEMPERATURES TOMORROW WILL BE
WARMER THAN TODAY...AND MUGGY CONDITIONS SHOULD DEVELOP BY LATE
AFTERNOON AS DEWPOINTS INCREASE INTO THE LOWER 60S ON SOUTHWESTERLY
FLOW.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 234 PM CDT WED JUN 19 2013

MEAN FLOW INTO EARLY NEXT WEEK TO CONSIST OF AN UPR TROF OVER THE
ERN PACIFIC/WRN CONUS AND A BROAD/SOMEWHAT FLAT UPR RDG TO EXTEND
FROM THE SRN PLAINS TO THE MID-ATLANTIC. THIS PATTERN WL BRING
WARM...HUMID AND UNSETTLED WEATHER TO NE WI THRU MUCH OF THE
EXTENDED PERIOD. TRYING TO FIND A DRY PERIOD WL BE THE BIGGEST
FCST CHALLENGE AS RIPPLES OF SHORTWAVE ENERGY AND A FRONTAL
BOUNDARY IN THE VICINITY ACT AS A FOCUS.

PREVAILING W-SW FLOW ALOFT TO GRADUALLY BRING WARMER/MORE MOIST
AIR MASS INTO WI THU NGT. WHILE RELATIVELY TAME WAA-INDUCED SHWRS/
TSTMS TO BE IN OUR GENERAL VICINITY THU EVENING...THE POTENTIAL
DEVELOPMENT OF A MCS OVER THE UPR MS VALLEY ON THE NOSE OF A 40 KT
LOW-LEVEL JET WL NEED TO BE WATCHED DURING THE OVRNGT HOURS. THIS
CONVECTIVE COMPLEX WOULD BE ROLLING TOWARD N-CNTRL/CNTRL WI PRIOR
TO SUNRISE WITH A THREAT OF DAMAGING WINDS IF IT WERE TO
MATERIALIZE. HAVE PLACED HIGHEST POPS GENERALLY WEST OF AN IMT-SUE
LINE WITH LOW-END CHC POPS OVER THE LAKESHORE. CHANGE IN AIR MASS
WL PROVIDE AN ACTUAL SUMMERLIKE FEEL AS MIN TEMPS TO ONLY DROP
INTO THE 60-65 DEG RANGE.

REMAINS OF THE MCS TO MOVE THRU THE REST OF NE WI FRI MORNING...
BUT SHOULD BE WEAKENING AS THE LOW-LEVEL JET WEAKENS. THE PROBLEM
THEN RESIDES FOR FRI AFTERNOON AND WHETHER ADDITIONAL CONVECTIVE
ACTIVITY CAN DEVELOP. ATMOSPHERE WL BE ABLE TO DESTABILIZE WITH
CAPES SURPASSING 4K J/KG WITH LITTLE CIN INDICATED. THE KEY COULD
BE IF ANY CONVECTIVE BOUNDARIES ARE LEFT BEHIND BY THE MCS. THIS
IS HARD TO DETERMINE AT THIS TIME...THUS HAVE LEFT AFTERNOON POPS
IN THE LWR TO MID 80S (COOLER LAKESIDE) AND DEW PTS IN THE MID TO
UPR 60S.

PERSISTENT SW WINDS ALOFT IS FCST TO LIFT A WRMFNT THRU SRN WI TO
CNTRL WI BY 12Z SAT. GULF MOISTURE WL CONT TO FEED INTO THE REGION
WITH THE FNT ACTING AS A FOCUSING MECHANISM. EVEN WITH THE LOSS OF
DAYTIME HEATING...THE ATMOSPHERE TO REMAIN UNSTABLE WITH MID-LEVEL
LAPSE RATES AROUND 7 C/KM AND LI`S AROUND -6. HAVE BLANKETED THE
FCST AREA WITH HI CHC POPS FOR NOW...BUT EXPECT SOME CHANGES ONCE
THE LOCATION OF THE WRMFNT BECOMES MORE OBVIOUS. THIS WRMFNT IS
THEN EXPECTED TO EITHER HOLD NEARLY STEADY OVER CNTRL WI OR SLOWLY
EDGE NORTH TOWARD NRN WI ON SAT. THERE COULD EASILY BE A LULL IN
THE PCPN DURING THE MORNING AS THE ATMOSPHERE RELOADS FROM EARLIER
CONVECTION...HOWEVER AS THE ATMOSPHERE DESTABILIZES ONCE AGAIN
DURING THE AFTERNOON (CAPES AROUND 2K J/GK/LI`S AROUND -5)...A NEW
ROUND OF SHWRS/TSTMS SHOULD DEVELOP ESPECIALLY NEAR THE WRMFNT. 8H
TEMPS IN THE +15 TO +20C RANGE SHOULD YIELD MAX TEMPS TO REACH
INTO THE LWR-MID 80S INLAND/75-80 NEAR LAKE MI ON SAT.

SUBTLE MDL DIFFERENCES OCCUR SAT NGT AS THE GFS SHARPENS THE UPR
RDG OVER THE GREAT LAKES AND FORCES THE NEXT SHORTWAVE WELL TO OUR
NW. MEANWHILE...THE ECMWF KEEPS THE UPR RDG SOMEWHAT FLAT AND
ALLOWS THIS SHORTWAVE TO ENTER THE WRN GREAT LAKES. HARD TO
DETERMINE WHICH SOLUTION IS CORRECT...BUT WITH THE WRMFNT STILL
LURKING OVER NRN WI...WL PLACE HIGHEST POPS OVER THE NORTH WITH
SLIGHTLY LESS POPS FARTHER SOUTH. MUCH LIKE SAT...ANY OVRNGT
CONVECTION WOULD TEND TO WEAKEN IN THE MORNING ON SUNDAY...ONLY TO
REFIRE IN THE AFTERNOON AS INSTABILITY SOARS. PCPN FOR SUNDAY
WOULD BE SCATTERED AT BEST DUE TO THE WRMFNT TO HAVE LIFTED NORTH
AND NO PROMINENT SHORTWAVE ADVERTISED BY THE MDLS. IF WE COULD
STAY PCPN-FREE...A FEW LOCATIONS COULD REACH THE 90 DEG MARK AS
THE HEAT AND HUMIDITY CONT TO OVERSPREAD THE AREA.

A NEW TWIST OCCURS SUNDAY NGT AS A CDFNT ATTEMPTS TO PUSH TOWARD
WI. THIS FNT WL LOSE THE BATTLE AGAINST THE ENTRENCHED UPR RDG AND
EVENTUALLY STALL (OR EVEN WASHOUT) SOMEWHERE OVER NRN OR CNTRL WI
BY MON. THIS FNT COULD STILL BRING ANOTHER ROUND OF SHWRS/TSTMS TO
PARTS OF THE FCST AREA SUNDAY NGT AND DEPENDING ON WHERE THE FNT
HANGS UP ON MON...BRING ADDITIONAL PCPN CHCS. TOO MUCH UNCERTAINTY
HERE TO TRY AND PINPOINT HIGHER POPS...SO ESSENTIALLY FOLLOWED A
CONSENSUS SOLUTION WHICH BRINGS CHC POPS TO ALL OF NE WI. WHILE
THE EXTENDED MDLS AGREE THAT THE UPR RDG WL EVENTUALLY REBUILD
OVER THE ROCKIES BY THE END OF THE PERIOD...HOW WE GET THERE IS A
MATTER OF CONJECTURE. THE ECMWF SUBTLELY FLATTENS THE MEAN FLOW
WITH THE GFS SHOWING A SUBSTANTIAL SHORTWAVE TROF TO MOVE THRU WI
AROUND TUE NGT. NE WI TO REMAIN IN THE WARM SECTOR THRU TUE...SO
CANNOT RULE OUT AT LEAST A CHC OF SHWRS/TSTMS. BY WED...THE CDFNT
PUSHES THRU THE REGION WITH A CONTINUED CHC FOR MORE PCPN.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1140 AM CDT WED JUN 19 2013

HIGH PRESSURE OVER THE WESTERN LAKES WILL CONTINUE TO SHIFT EAST
ALLOWING SOUTHERLY WINDS TO BRING IN WARMER AND MORE HUMID AIR
INTO THE REGION. VFR CONDITIONS WILL CONTINUE FOR TODAY AND
TONIGHT. A DISTURBANCE WILL APPROACH THE AREA OUT OF THE
NORTHERN PLAINS ON THURSDAY....BRINGING WITH IT INCREASING VFR
CLOUDS THROUGH THE DAY FROM NORTHWEST TO SOUTHEAST. SCATTERED
SHOWERS POSSIBLE IN THE NORTHERN TAF SITES LATE IN THE MORNING.
&&

.MARINE...
ISSUED AT 234 PM CDT WED JUN 19 2013

A WARM AND HUMID AIR MASS WILL OVERSPREAD THE COOLER WATERS OF
THE BAY OF GREEN BAY AND LAKE MICHIGAN THURSDAY NIGHT OR
FRIDAY...LEADING TO THE FORMATION OF LOCALLY DENSE MARINE FOG.
THIS LOCALLY DENSE MARINE FOG WILL CONTINUE AT TIMES INTO EARLY
NEXT WEEK AS THE WARM AND HUMID AIR MASS REMAINS FIRMLY ENTRENCHED
ACROSS THE REGION. SEVERAL COMPLEXES OF THUNDERSTORMS ARE EXPECTED
FROM TIME TO TIME FRIDAY INTO EARLY NEXT WEEK. THESE STORMS WILL
POSE A SIGNIFICANT RISK FOR MARINERS WITH STRONG WINDS...LOCALLY
HIGHER WAVES...LARGE HAIL AND TORRENTIAL RAINS WHICH WILL REDUCE
VISIBILITIES BELOW ONE MILE.
&&

.HYDROLOGY...
ISSUED AT 234 PM CDT WED JUN 19 2013

SEVERAL COMPLEXES OF THUNDERSTORMS ARE EXPECTED FROM FRIDAY INTO
EARLY NEXT WEEK. A VERY WARM AND HUMID AIR MASS WILL BECOME
ENTRENCHED ACROSS THE REGION LATE THIS WEEK AND PERSIST INTO EARLY
NEXT WEEK. PRECIPITABLE WATER VALUES SHOULD RUN 150 TO 200
PERCENT OF NORMAL...LEADING THE LIKELIHOOD ON TORRENTIAL RAINS AND
POTENTIAL FOR URBAN FLOODING DUE TO THE INTENSE RAINFALL RATES.
ANY TRAINING OR SLOW MOVING THUNDERSTORMS WILL INCREASE THE RISK
OF FLOODING.
&&

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

$$

SHORT TERM.....WOLF
LONG TERM......KALLAS
AVIATION.......WOLF
MARINE.........KALLAS
HYDROLOGY......KALLAS