Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 011758
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1258 PM CDT SAT AUG 1 2015

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND SUNDAY
ISSUED AT 259 AM CDT SAT AUG 1 2015

FAIR WEATHER CUMULUS CLOUDS ARE EXPECTED TODAY...HOWEVER WITHOUT
THE MID AND UPPER LEVEL SUPPORT SHOWERS ARE NOT EXPECTED AS
RIDGING GETS SQUEEZED SOUTH. HIGHS TODAY WILL GENERALLY BE IN THE
UPPER 70S TO LOWER 80S WITH WIND SPEEDS MUCH LIGHTER THAN THE
PREVIOUS FEW DAYS.

AN APPROACHING LOW PRESSURE SYSTEM WILL HAVE A SIGNIFICANT IMPACT
ON OUR WEATHER TONIGHT AND SUNDAY AS IT TRACKS THROUGH THE WESTERN
GREAT LAKES REGION. THE LOW WILL TRACK OVER MINNESOTA
TONIGHT...PUSHING A WARM FRONT NORTH THROUGH THE UPPER MISSISSIPPI
VALLEY. THE LOW WILL CONTINUE EAST THROUGH WISCONSIN ON SUNDAY
DRAGGING A COLD FRONT EAST THROUGH THE WESTERN GREAT LAKES AS IT
TRACKS EAST. THIS LOW WILL BRING A VERY UNSTABLE AIRMASS INTO THE
WESTERN GREAT LAKES REGION...ESPECIALLY SUNDAY WHEN MUCAPE VALUES
SOAR TO 2000 TO 4000 J/KG DEPENDING ON THE MODEL SOLUTION. THE GFS
IS NOT AS UNSTABLE WITH VALUES CLOSER TO 2000 J/KG WITH THE NAM
JUST ABOUT DOUBLE THAT AT AROUND 4000 J/KG. EVEN IF THE LESS
UNSTABLE GFS VERIFIES THAT IS STILL A VERY UNSTABLE
AIRMASS...WHICH WHEN COMBINED WITH 0-6 KM BULK SHEAR VALUES AROUND
40 KNOTS COULD LEAD TO SEVERE THUNDERSTORMS TONIGHT AND SUNDAY.
THE SOUTHERN PORTION OF THE CWA IS IN MARGINAL OR ON THE CUSP OF
SLIGHT RISK FOR SEVERE WEATHER PER THE SPC OUTLOOKS...WHICH IS
DEPENDENT ON HOW FAR NORTH THE THE UNSTABLE AIR WILL TRACK AND
WHERE STORMS DEVELOP NEAR THE WARM FRONT TONIGHT...AND THEN THE
COLD FRONT ON SUNDAY. THE ONLY REAL CHANGE FROM THE PREVIOUS
FORECAST WAS TO PUSH OFF POPS A FEW HOURS LATER INTO THE OVERNIGHT
HOURS AS THE WARM FRONT IS EXPECTED TO ARRIVE A BIT LATER THAN
PREVIOUSLY FORECAST.

WITH CLOUDS AND A WARM FRONT APPROACHING LOWS TONIGHT WILL BE
RELATIVELY WARM...GENERALLY IN THE LOWER TO MIDDLE 60S. HIGHS ON
SUNDAY WILL RANGE FROM THE MIDDLE 70S NORTH OF THE WARM
FRONT...WITH LOWER TO MIDDLE 80S ACROSS CENTRAL AND EAST CENTRAL
WISCONSIN SOUTH OF THE WARM FRONT.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY
ISSUED AT 259 AM CDT SAT AUG 1 2015

THE LATEST ENSEMBLE MEANS CONTINUE TO INDICATE MID-LEVEL RIDGING
WILL BE LOCATED UPSTREAM OVER THE CENTER OF THE CONTINENT FOR MUCH
OF NEXT WEEK.  THIS PATTERN WILL LEAD TO TROUGHING LOCATED OVER
ONTARIO AND MUCH OF THE GREAT LAKES INCLUDING WISCONSIN.  THE ECMWF
IS QUICKER SHIFTING THIS PATTERN TO THE EAST THAN OTHER GUIDANCE BY
THE END OF THE WEEK. BUT WILL CONTINUE TO LEAN ON THE ECMWF THROUGH
12Z TUESDAY.

SUNDAY NIGHT THROUGH MONDAY NIGHT...MODELS ARE QUICKER EXITING A
COLD FRONT ON SUNDAY EVENING...WHICH WILL BRING A CHANCE OF SHOWERS
AND THUNDERSTORMS TO CENTRAL AND NORTHEAST WISCONSIN.  WITH SB CAPES
GREATER THAN 1000 J/KG AHEAD OF THE FRONT...THE THREAT OF STRONG TO
ISOLATED SEVERE STORMS WILL CONTINUE UNTIL THE FRONT EXITS.  WITH 0-
6KM AROUND 45 KTS...STRONG GUSTY WINDS WILL BE POSSIBLE
WITHIN ANY STORMS.  BEHIND THE FRONT...COOLER AND DRIER AIR WILL
INVADE FROM THE NORTH.  SHOULD SEE A GOOD DEAL OF SUNSHINE ON MONDAY
THOUGH WILL SEE CLOUDS BUILD WITH HEATING OF THE DAY.  PROGGED
SOUNDINGS LOOKED CAPPED MONDAY AFTERNOON...BUT THERE IS COLDER AIR
ALOFT...AND POTENTIAL FOR SMALL SCALE IMPULSES TO KICK OFF SHOWERS.
WILL LEAVE A SMALL CHANCE ACROSS THE NORTH.  NOT UNREASONABLE THAT
ANY SHOWER THREAT COULD LINGER ACROSS THE FAR NORTH MONDAY
NIGHT...BUT FOR NOW WILL LEAVE THE FORECAST DRY.

REST OF THE FORECAST...SOME SHOWERS COULD ALSO OCCUR ON TUESDAY
AFTERNOON ACROSS THE FAR NORTH...THEN THE UPPER TROUGH BEGINS TO
PULL OUT ON WEDNESDAY.  HIGH PRESSURE WILL BE BUILDING INTO THE
REGION DURING THIS TIME...WITH TEMPS COOLING SEVERAL DEGREES ON
TUESDAY COMPARED TO MONDAYS READINGS. HIGH PRESSURE TO LINGER
WEDNESDAY AND THURSDAY BEFORE THE THREAT OF PRECIP RETURNS LATE IN
THE WEEK.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1258 PM CDT SAT AUG 1 2015

VFR CONDITIONS WILL PREVAIL AT LEAST 06Z SUNDAY WITH MAINLY HIGH-
BASED CUMULUS ACROSS NORTHERN WISCONSIN AND SOME SCT MID-LEVEL
CLOUDS ACROSS THE SOUTH. STILL SOME OCCASIONAL GUSTY W TO NW
WINDS TO ABOUT 20KTS THIS AFTERNOON.

LOW PRESSURE SYSTEM DEVELOPING OVER THE NORTHERN PLAINS AND AN
APPROACHING WARM FRONT AFTER MIDNIGHT WILL BRING AN INCREASINGCHANCE
FOR SCATTERED SHOWERS AND THUNDERSTORMS. STILL A FAIR AMOUNT OF
UNCERTAINTY ON THE TIMING AND LOCATION OF ANY SCATTERED
THUNDERSTORM ACTIVITY. BEST GUESS AT THIS TIME IS THAT MOST LIKELY
AREA TO SEE SCATTERED ACTIVITY WOULD BE OVER CENTRAL AND NORTHERN
WISCONSIN AFTER ABOUT 08Z. DUE TO LOW CONFIDENCE IN THIS
REGARD...WILL NOT INCLUDE MENTION OF THUNDER IN 18Z TAF PACKAGE.

AFTER 18Z SUNDAY...COLD FRONT DROPPING SOUTHEAST ACROSS THE
FORECAST AREA...ALONG WITH DEVELOPING LOW PRESSURE OVER EASTERN
WISCONSIN SUNDAY AFTERNOON WILL BRING ANOTHER CHANCE OF PERHAPS
MORE WIDESPREAD AND VIGOROUS CONVECTION BY MID-AFTERNOON SUNDAY.
GREATEST LIKELIHOOD FOR THUNDERSTORM ACTIVITY SUNDAY AFTERNOON
WOULD BE GENERALLY SOUTHEAST OF A LINE FROM MNM TO AUW.

SOME LLWS IS PSBL AT RHI/AUW/CWA AFTER 04Z...THEN AROUND 08Z AT
ATW/GRB/MTW.
&&

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

$$

SHORT TERM.....KURIMSKI
LONG TERM......MPC
AVIATION.......ESB



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