Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 211738
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1238 PM CDT THU MAY 21 2015

UPDATED AVIATION PORTION FOR 18Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND FRIDAY
ISSUED AT 322 AM CDT THU MAY 21 2015

SKIES WILL START OUT MOSTLY SUNNY ACROSS MOST OF THE FORECAST AREA
THIS MORNING AS HIGH PRESSURE CONTINUES TO DOMINATE THE WESTERN
GREAT LAKES. A QUICK MOVING MID LEVEL SHORTWAVE...SHOWN ON WATER
VAPOR IMAGERY ACROSS SOUTHERN MINNESOTA EARLY THIS MORNING...WILL
PASS THROUGH SOUTHERN WISCONSIN LATER THIS MORNING. AS THE
SHORTWAVE PEELS AWAY A SURFACE COLD FRONT WILL SINK SOUTH FROM THE
UPPER PENINSULA OF MICHIGAN...TRACKING THROUGH NORTHERN WISCONSIN
LATER THIS AFTERNOON AND INTO THE EVENING HOURS.

AS THE COLD FRONT SINKS SOUTH IT WILL HAVE INSTABILITY TO WORK
WITH AS MLCAPE VALUES RISE TO AROUND 300 J/KG...LIFTED INDEX
VALUES FALL TO 0 TO -1 AND MID LEVEL LAPSE RATES RISE TO 6 TO 8
CELSIUS/KM. THE MARGINAL INSTABILITY AND LIFT FROM THE COLD FRONT
ITSELF WILL LEND ITSELF TO THE POSSIBILITY FOR A SHOWERS AND A FEW
RUMBLES OF THUNDER AS IT TRACKS THROUGH THE AREA THROUGH THIS
EVENING. OVERALL THE BEST INSTABILITY APPEARS TO BE OUT TO THE
WEST ACROSS CENTRAL WISCONSIN...HOWEVER MODEL SOUNDINGS SHOW THE
BEST MOISTURE IS ACROSS EAST CENTRAL WISCONSIN. DESPITE THE BETTER
INSTABILITY THE BEST CHANCES FOR RAIN APPEAR TO BE ACROSS THE EAST
GIVEN THE DEEPER MOISTURE. THEREFORE WILL CONTINUE THE CHANCY POPS
ACROSS EAST CENTRAL AND STICK WITH THE SLIGHT CHANCES FURTHER TO
THE WEST. HIGHS TODAY WILL RANGE FROM THE LOWER TO MIDDLE 60S
ACROSS THE NORTH WITH THE EARLIER COLD FROPA...WITH HIGHS AROUND
70 FURTHER SOUTH WITH A LATER FROPA ANTICIPATED.

LATER TONIGHT HIGH PRESSURE WILL BUILD BACK IN...WITH CLEARING
SKIES...LIGHT WINDS AND COLD AIR ADVECTION. THIS WILL PROVIDE
IDEAL RADIATIVE COOLING CONDITIONS...ESPECIALLY ACROSS THE NORTH
WHERE CLEARING WILL OCCUR QUICKER AND COLD AIR WILL FILTER IN
SOONER THAN THE REST OF THE CWA. TEMPERATURES ACROSS CENTRAL AND
EAST CENTRAL WISCONSIN ARE EXPECTED TO FALL TO AROUND 40
TONIGHT...HOWEVER LOWS AROUND 30 ARE EXPECTED ACROSS MUCH OF NORTH
CENTRAL WISCONSIN...WITH A FEW 20S NOT OUT OF THE QUESTION. IT IS
POSSIBLE NORTH CENTRAL WISCONSIN WILL SEE ANOTHER ROUND OF FROST
TONIGHT...HOWEVER UNLIKE THE OTHER NIGHT THE SETUP IS NOT AS
CERTAIN AS THERE IS A HUGE DIFFERENCE BETWEEN PARTICULAR MOS
GUIDANCE VALUES. GIVEN THE UNCERTAINTY WILL HOLD OFF ON ANY
HEADLINES FOR FROST AT THIS TIME.

HIGH PRESSURE WILL THEN BUILD IN OVER THE WESTERN GREAT LAKES ON
FRIDAY...PROVIDING COOL DRY CONDITIONS ACROSS THE CWA. DESPITE
ABUNDANT SUNSHINE THE COOL TEMPERATURES IN PLACE WILL LIMIT HIGH
TEMPERATURES TO THE 60S ACROSS THE AREA FRIDAY AFTERNOON.

.LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY
ISSUED AT 322 AM CDT THU MAY 21 2015

GENERALLY MINOR CHANGES MADE TO THE PREVIOUS LONG TERM FORECAST.

SURFACE HIGH PRESSURE OVER THE REGION AND AN APPROACHING UPPER
RIDGE SHOULD KEEP THE AREA DRY THROUGH AT LEAST MIDDAY ON
SATURDAY. THE 00Z ECMWF CONTINUED TO BE THE SLOWEST WITH THE
APPROACHING RAIN ASSOCIATED WITH THE SOUTHERN STREAM UPPER SYSTEM.
THE 00Z GFS WAS FASTEST WITH QPF ALREADY INTO THE AREA ON
SATURDAY. HAVE GONE A BIT SLOWER THAN THE GFS...WITH ONLY SLIGHT
CHANCE POPS FOR SATURDAY. POPS THEN GRADUALLY INCREASE TO LIKELY
BY SUNDAY NIGHT. STILL NOT THE GREATEST OF CONFIDENCE IN THIS
SOLUTION DUE TO THE VARIABILITY OF THE MODELS. POPS REMAIN IN THE
FORECAST THROUGH WEDNESDAY AS SHORT WAVES MOVING INTO THE REGION
FROM THE SOUTHWEST BRING CHANCES FOR MORE RAIN. DAYTIME HIGHS
SHOULD BE NEAR OR ABOVE NORMAL.
&&

.AVIATION...FOR 18Z TAF ISSUANCE
ISSUED AT 1238 PM CDT THU MAY 21 2015

CDFNT TO GRADUALLY DROP SOUTH THRU CNTRL/E-CNTRL WI LATE THIS
AFTERNOON INTO THE EARLY EVENING. THIS FNT IS HAVING MOISTURE
ISSUES IN TRYING TO DEVELOP PCPN...BUT ANTICIPATE A NARROW BAND OF
MAINLY SHWRS TO ACCOMPANY THE FROPA...ESPECIALLY OVER E-CNTRL WI
WHERE CONVERGENCE IS BETTER. EVEN WITH THE ISOLATED/SCATTERED
SHWRS...CIGS/VSBYS ARE FCST TO REMAIN IN THE VFR CATEGORY AS MOST
OF THE CLOUDS ARE OF THE MID-VARIETY. ONCE THIS CDFNT CLEARS THE
AREA...HI PRES WL BUILD OVER THE GREAT LAKES OVRNGT INTO FRI.
ANOTHER SURGE OF DRY AIR SHOULD BRING CLEARING SKIES TNGT AND A
SUNNY DAY ON FRI.
&&

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

$$

SHORT TERM.....KURIMSKI
LONG TERM......MG
AVIATION.......AK



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