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000
FXUS63 KGRB 212013
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
313 PM CDT TUE MAY 21 2013

FORECAST DISCUSSION FOR ROUTINE AFTERNOON FORECAST ISSUANCE

.SHORT TERM...TONIGHT AND WEDNESDAY
ISSUED AT 305 PM CDT TUE MAY 21 2013

MAIN FORECAST CONCERN WILL BE THE PRECIPITATION CHANCES ON
WEDNESDAY...INCLUDING THE POTENTIAL FOR SOME SOAKING RAIN EAST
CENTRAL WISCONSIN.

FOR TONIGHT...A WEAK SFC BOUNDARY WAS SITTING ACROSS NORTHERN
WISCONSIN LATE THIS AFTERNOON...IN THE VICINITY OF AN IRON MT TO
EAU CLAIRE LINE. THIS BOUNDARY HAS BEEN THE FOCUS FOR SHOWERS AND
A FEW THUNDERSTORMS FROM NEAR MARINETTE TO MERRILL. A FEW OF THESE
STORMS MAY CONTAIN PEA TO DIME HAIL AND BRIEF HEAVY DOWNPOURS INTO
THE EARLY EVENING. ACTIVITY SHOULD QUICKLY WEAKEN AFTER SUNSET AS
INSTABILITY WANES. DECREASED POPS IN CENTRAL AND EAST CENTRAL
WISCONSIN AFTER MIDNIGHT FROM PREVIOUS FORECAST AS FRONTAL
BOUNDARY MOVES NORTH...BUT KEPT CHANCE POPS IN NORTHERN WISCONSIN
OVERNIGHT WITH THE BOUNDARY HANGING AROUND THAT AREA. MOSTLY
CLOUDY CONDITIONS SHOULD PREVAIL TONIGHT KEEPING LOW TEMPERATURES
FAIRLY MILD.

FOR WEDNESDAY...UPPER LEVEL DISTURBANCE THAT HAS BEEN SITTING OVER
THE NORTHERN PLAINS THE PAST FEW DAYS WILL FINALLY SHIFT EAST.
MEANWHILE...SFC BOUNDARY THAT MOVED NORTH TUESDAY NIGHT IS THEN
EXPECTED TO COLLAPSE BACK SOUTH. IT LOOKS LIKE TOMORROW AFTERNOON
WILL BE OUR BEST CHANCE THIS WEEK FOR WIDESPREAD PRECIPITATION AS
THE UPPER LEVEL LOW AND SURFACE BOUNDARY SHIFT ACROSS THE STATE.
MODELS SHOWING AMPLE QG FORCING WITH WITH THE UPPER LEVEL TROUGH
WHICH WILL HELP TO INITIATE AN AREA OF RAIN SHOWERS IN THE
VICINITY OF THE SFC BOUNDARY IN CENTRAL WISCONSIN...STARTING
AROUND 12Z. EXPECT THE AREA OF SHOWERS TO EXPAND QUICKLY THROUGH
OUT ALL OF NORTHEAST WISCONSIN THROUGH THE MORNING. ATMOSPHERE
SHOULD REMAIN FAIRLY STABLE WITH WEAK CAPE AND VERY LITTLE
SHEAR...SO NOT EXPECTING ANY SEVERE STORMS WITH ONLY AN ISOLATED
RUMBLE OF THUNDER POSSIBLE. INCREASED POPS A BIT IN THE MORNING
GIVEN THE MODEL TRENDS AND THE AMOUNT OF FORCING THAT WILL BE
MOVING OVER THE AREA...OTHERWISE SEEMS PREVIOUS FORECAST IS ON
TRACK.

THE WRF ARW/NMM AND ECMWF ALSO SUGGEST AN AREA OF HEAVIER
PRECIPITATION ASSOCIATED WITH A SECONDARY SHORTWAVE DISTURBANCE MOVING
NORTHEAST OUT OF THE SOUTHERN PLAINS DURING THE AFTERNOON
WEDNESDAY. THE PRECIPITATION SHIELD WITH THIS SYSTEM MAY ALSO
AFFECT THE EASTCENTRAL WISCONSIN WEDNESDAY AFTERNOON.  DEW POINTS
WILL REMAIN IN THE MIDDLE TO UPPER 50S IN NORTHEAST WISCONSIN WITH
PRECIPITABLE WATER VALUES OVER 1 INCH...THUS AMPLE MOISTURE WILL BE
AVAILABLE. COULD SEE SOME HEAVY RAIN IN EAST CENTRAL WISCONSIN AS
MODEL SOUNDINGS SUGGEST HIGH PRECIPITATION EFFICIENCY....WITH LONG
SKINNY CAPE AND WEAK WIND PROFILES. GIVEN THE MODEL TRENDS AND
MOISTURE ABUNDANCE...ADDED MENTION OF HEAVY RAIN TO THE FORECAST
FOR THE FOX VALLEY AND LAKESHORE.

TEMPERATURES WILL BE MUCH COOLER ON WEDNESDAY GIVEN THE RAIN AND
CLOUDS.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY
ISSUED AT 305 PM CDT TUE MAY 21 2013

MODELS FORECAST UPPER LOW TO MOVE EAST WEDNESDAY
NIGHT AND THURSDAY WITH NORTHWEST UPPER FLOW RETURNING AS UPPER
RIDGE SLOWLY APPROACHES FROM THE PLAINS. MUCH COOLER AIR WILL
ARRIVE THURSDAY AND THURSDAY NIGHT AS 850MB TEMPERATURES FALL
BELOW FREEZING ACROSS THE NORTH. A FROST OR FREEZE IS LIKELY
THURSDAY NIGHT EXCEPT NEAR THE LAKE AND BAY AS WINDS DIMINISH.
ANOTHER FROST OR FREEZE MIGHT BE POSSIBLE FRIDAY NIGHT BUT THE
MODELS HAVE A SHORT WAVE TROUGH MOVING QUICKLY SOUTH ACROSS THE
WESTERN GREAT LAKES IN THE NORTHWEST UPPER FLOW. THIS WOULD
PROBABLY PRODUCE ENOUGH CLOUDS AND WIND TO KEEP A FROST OR FREEZE
FROM OCCURRING FRIDAY NIGHT. THE UPPER RIDGE GETS CLOSER SUNDAY AND
MONDAY BUT THE UPPER FLOW STAYS NORTHWEST AND THERE IS A BIG
SURFACE HIGH TO OUR EAST. THAT WILL PROBABLY BE SUFFICIENT TO KEEP
ANY PRECIPITATION TO OUR WEST. TEMPERATURES WILL SLOWLY WARM AS
HEIGHTS RISE.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 107 PM CDT TUE MAY 21 2013

VARIABLE WEATHER CONDITIONS EXPECTED THIS AFTERNOON
AND TONIGHT AS BANDS OF SHOWERS AND THUNDERSTORMS MOVE ACROSS THE
REGION. CONDITIONS WILL GENERALLY BE VFR EAST OF A MARINETTE TO
SHAWANO TO WAUPACA LINE LINE WITH MVFR CONDITIONS FURTHER WEST.
BRIEF IFR POSSIBLE IN SHOWERS AND THUNDERSTORMS. IN
ADDITION...THERE IS DENSE FOG ALONG THE LAKE MICHIGAN SHORE. IT
WILL PROBABLY STAY JUST EAST OF THE MANITOWOC AND STURGEON BAY
AIRPORTS BUT IT WILL BE CLOSE.
&&

.MARINE...
ISSUED AT 305 PM CDT TUE MAY 21 2013

DENSE FOG NEAR THE LAKE MICHIGAN COULD DIMINISH THIS EVENING AS
SLIGHTLY DRIER AIR MOVES TOWARDS THE LAKE BUT THERE IS A LOT OF
UNCERTAINTY. THERE IS A POSSIBILITY THAT IT COULD STAY ALONG THE
SHORE OVERNIGHT. A COLD FRONT WILL MOVE THROUGH WEDNESDAY
AFTERNOON OR EVENING AND PRODUCE STRONG NORTHEAST WINDS AND LARGE
WAVES HAZARDOUS TO SMALL CRAFT WEDNESDAY NIGHT THROUGH THURSDAY.
&&

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

$$

SHORT TERM.....WOLF
LONG TERM......RDM
AVIATION.......RDM
MARINE.........RDM