Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 201752
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1252 PM CDT SAT SEP 20 2014

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND SUNDAY
ISSUED AT 356 AM CDT SAT SEP 20 2014

SHOWERS AND THUNDERSTORMS ASSOCIATED WITH LOW LEVEL WARM ADVECTION
AND UPPER JET SHOULD END EARLY TODAY AS FORCING SHOVES OFF TO THE
EAST. A WEAK COLD FRONT WILL MOVE ACROSS THE AREA DURING THE AFTERNOON
HOURS. MODEL FORECAST SOUNDINGS SUGGEST THERE MAY BE ENOUGH INSTABILITY
TO PRODUCE AT LEAST SCATTERED THUNDERSTORMS IN EASTERN WISCONSIN BEFORE
IT GOES BY. IF STORMS DO MATERIALZE SOME GUSTY WINDS AND HAIL ARE
POSSIBLE. HIGHS TODAY ARE DEPENDENT ON THE TIMING OF THE FRONT AND
CLOUD COVER BUT SHOULD BE 5 TO 10 DEGREES ABOVE NORMAL FOR THIS TIME
OF THE YEAR.

AN UNUSUALLY STRONG UPPER JET WILL APPROACH CENTRAL WISCONSIN THIS
EVENING AND MOVE ACROSS THE AREA OVERNIGHT. 300 MB WINDS OF 120 KNOTS
ARE STRONG FOR THIS TIME OF THE YEAR AND THE ASSOCIATED UPPER TROUGH
IS QUITE SHARP. IT SHOULD BE ABLE TO PRODUCE AN AREA OF SHOWERS AND
THUNDERSTORMS. WET BULB ZERO TEMPERATURES OF 6000FT TO 8000FT AND STRONG
VERTICAL MOTION SHOULD RESULT IN HAIL AND IT IS NOT OUT OF THE QUESTION
FOR SOME LARGE HAIL TO OCCUR. LOCALLY HEAVY RAIN IS ALSO POSSIBLE DESPITE
MODEST PRECIPITABLE WATER VALUES.

SUNDAY SHOULD BE BLUSTERY AND FALL LIKE IN THE MORNING WITH SHOWERS
AND GUSTY NORTH WINDS. IT SHOULD BECOME PARTLY SUNNY IN THE AFTERNOON
WITH HIGHS AROUND 5 TO 8 DEGREES BELOW NORMAL.

.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY
ISSUED AT 356 AM CDT SAT SEP 20 2014

HIGHLY AMPLIFIED PATTERN IN PLACE TO START THE PERIOD...CONSISTING
OF STRONG RIDGING OVER THE WESTERN PLAINS INTO WESTERN CANADA...
AND A DEEP TROUGH OVER THE EASTERN GREAT LAKES. THE TROUGH WILL
CONTINUE TOWARD THE EASTERN SEABOARD THROUGH MID-WEEK...AS THE
RIDGE FLATTENS SLIGHTLY AND MOVES INTO CENTRAL CANADA AND THE
UPPER MISSISSIPPI VALLEY. MEDIUM RANGE MODELS CONTINUE TO
ADVERTISE A WEAK SHORTWAVE TROUGH PUSHING ACROSS THE UPPER PLAINS
EARLY IN THE WEEK...AND ACROSS THE WESTERN GREAT LAKES DURING THE
MID TO LATE WEEK. THIS FEATURE WILL BRING THE ONLY CHANCE FOR
PRECIP DURING THE PERIOD. OTHERWISE...DRY AND VERY PLEASANT LATE
SUMMER/EARLY FALL WEATHER IS EXPECTED...WITH TEMPERATURES NEAR
NORMAL ON MONDAY...THEN ABOVE NORMAL FOR NEARLY THE REST OF THE
WEEK.

ONLY CONCERN SUNDAY NIGHT WILL BE HOW LOW CAN TEMPS DROP AND HOW
MUCH FROST AND FOG WILL DEVELOP. BOTH WILL DEPEND ON CLOUD
COVER...AS WINDS LOOK TO DIE OFF DURING THE EARLY EVENING. THERE
WILL BE SOME LINGERING MOISTURE UNDER THE CYCLONIC NW FLOW...WITH A
LITTLE INFLUENCE FROM LAKE SUPERIOR...AS THE UPPER TROUGH EXITS TO
THE EAST. MODEL SHOWING MOISTURE DECREASING THROUGH THE
NIGHT...AND THINK THERE WILL BE SOME CLEARING. HAVE LOWERED TEMPS
A LITTLE. WILL LIKELY HAVE SOME FROST ISSUES...ESPECIALLY OVER THE
NORTH...SO ADDED PATCHY FROST TO THE OVERNIGHT GRIDS. LIGHT WINDS
AND CLEARING SKIES WILL ALSO LEAD TO SOME FOG DEVELOPMENT...SO
ADDED THAT AS WELL.

MODELS HAVE COME INTO DECENT AGREEMENT AND CONSISTENCY REGARDING
THE WEAK SHORTWAVE TROUGH CROSSING THE NORTHERN U.S. DURING THE
WEEK. LIMITED SYNOPTIC FORCING AND MOISTURE...ESPECIALLY OVER
EASTERN AND SOUTHERN WI...WILL KEEP THE CHANCES FOR SHOWERS ON THE
LOW SIDE...BUT WILL CONTINUE WITH LOW CHANCE OR SLIGHT CHANCE POPS
WEDNESDAY NIGHT AND THURSDAY DURING THE "BEST" PERIOD OF FORCING
FROM THE SHORTWAVE.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1250 PM CDT SAT SEP 20 2014

A WEAK COLD FRONT IN CONCERT WITH AN UPPER-LEVEL DISTURBANCE WILL
GENERATE MVFR CIGS AND SCATTERED SHOWERS OVER EASTCENTRAL
WISCONSIN EARLY THIS AFTERNOON. AS THE UPPER LEVEL DISTURBANCE
PUSHES OFF TO THE EAST EXPECT MAINLY VFR CONDITIONS WITH SCT-BKN
SC AOA 3000 FEET OVER MOST OF THE FORECAST AREA.

A STRONG UPPER-LEVEL DISTURBANCE WILL THEN QUICKLY APPROACH THE
FORECAST AREA EARLY THIS EVENING GENERATING A BAND OF SHOWERS AND
THUNDERSTORMS NEAR THE MISSISSIPPI RIVER WHICH WILL QUICKLY MOVE
EASTWARD AFFECTING THE CENTRAL WISCONSIN TAF SITES BY 06Z.
SCATTERED SHOWERS MAY ALSO DEVELOP FURTHER TO THE EAST EARLY THIS
EVENING OVER NORTHEAST WISCONSIN. AS THE SHOWER AND THUNDERSTORM
ACTIVITY CONSOLIDATE OVER THE FORECAST AREA SHORTLY AFTER MIDNIGHT
EXPECT MVFR OR IFR CIGS THAT WILL LIKELY PERSIST INTO SUNDAY
MORNING. CONDITIONS SHOULD IMPROVE TO VFR CONDITIONS FROM NORTHWEST
TO SOUTHEAST TOWARD MIDDAY SUNDAY AS THE SYSTEM MOVES EAST OF THE
AREA.
&&

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

$$

SHORT TERM.....RDM
LONG TERM......BERSCH
AVIATION.......ESB





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