Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 210342
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
1042 PM CDT SAT SEP 20 2014

UPDATED AVIATION PORTION FOR 06Z TAF ISSUANCE

.SHORT TERM...TONIGHT AND SUNDAY
ISSUED AT 308 PM CDT SAT SEP 20 2014

TONIGHT AND SUNDAY

RATHER COMPLEX EVOLUTION WILL EVOLVE OVER THE FORECAST AREA
OVERNIGHT AS VERY STRONG UPPER JET AND SHORTWAVE PLUNGE SOUTHEAST
INTO THE WESTERN GREAT LAKES.

WEAK COLD FRONT/SURFACE TROUGH CURRENTLY DRIFTING SOUTHEAST ACROSS
THE EASTERN PART OF THE FORECAST AREA. A WEAK SHORTWAVE IMPULSE IS
ALSO TRAVERSING EASTERN IOWA/NORTHERN ILLINOIS AND IS HELPING TO
GENERATE AREA OF SHOWERS AND THUNDERSTORMS OVER SOUTHEAST
WISCONSIN TO NORTHERN ILLINOIS ALONG AND AHEAD OF THE FRONT. A FEW
SHOWERS HAVE ALSO DEVELOPED AS FAR NORTH AS MANITOWOC COUNTY NEAR
THE FRONT BUT THESE SHOULD QUICKLY MOVE OFF TO THE EAST WITHIN THE
NEXT HOUR OR SO. MEANWHILE FURTHER NORTH...ANOTHER MORE
SUBSTANTIAL SHORT WAVE DISTURBANCE CONTINUES TO MOVE EASTWARD NORTH
OF LAKE SUPERIOR. THIS IMPULSE HAS ALSO HELPED TO GENERATE ANOTHER
AREA OF THUNDERSTORMS OVER EXTREME EASTERN UPPER MICHIGAN. IN THE
WAKE OF THIS DISTURBANCE VISIBLE SATELLITE IMAGERY AND SURFACE
OBSERVATIONS SUGGEST SOME ENHANCED CU/SC ALONG THE WISCONSIN
MICHIGAN BORDER WITH BOUNDARY LAYER WINDS SHIFTING MORE NORTHERLY
TO THE NORTH OF THIS FEATURE. WINDS HAVE BEEN QUITE GUSTY ACROSS
NORTHERN WISCONSIN REACHING 30 MPH AT IMT AT TIMES.

THE PRIMARY WEATHER FEATURE THIS EVENING AND OVERNIGHT WILL BE A
VERY STRONG UPPER-LEVEL JET MAX AND ASSOCIATED SHORTWAVE THAT IS
FORECAST TO DIVE SOUTHEAST INTO WISCONSIN. AS THIS FEATURE
CONTINUES TO APPROACH THE AREA...ORGANIZED AND RATHER STRONG
MESOSCALE LIFT WILL DEVELOP HELPING TO GENERATE SHOWER AND
THUNDERSTORM ACTIVITY. SHORT TERM MODEL GUIDANCE SUGGEST THAT A NW-
SE ORIENTATED SURFACE TROUGH WILL DEVELOP OVER NORTHCENTRAL TO
NORTHEAST WISCONSIN THIS EVENING IN RESPONSE TO PRESSURE FALLS
NEAR THE LFQ OF THE APPROACHING UPPER-LEVEL JET MAX. LATEST RADAR
DATA INDICATES WELL-ORGANIZED QUASILINEAR CONVECTIVE COMPLEX THAT
HAS ALREADY DEVELOPED NEAR THE LFQ OF THE JET AND HAS ALREADY
PRODUCED SOME SEVERE WEATHER OVER THE EASTERN DAKOTAS AND WESTERN
MINNESOTA. MODEL GUIDANCE RACES THIS FEATURE EASTWARD THIS
EVENING. BASED ON CURRENT OBSERVATIONS...THIS QUASILINEAR MCS
APPEARS TO BE PROPAGATING FASTER THAN MODEL GUIDANCE IS SUGGESTING.
THE LEADING EDGE OF THIS CONVECTIVE COMPLEX MAY MAKE IT TO THE
WESTERN PORTION OF THE FORECAST AREA BY 01 OR 02Z. IN
ADDITION...THE MAJORITY OF MODEL GUIDANCE ALSO SUGGEST SOME SHOWER
ACTIVITY MAY ALSO DEVELOP WITHIN INCREASING AREA OF BLYR
CONVERGENCE FURTHER EAST ALONG THE AFFORMENTIONED NW-SE ORIENTATED
SURFACE TROUGH THAT WILL BE DEVELOPING ACROSS NORTHEAST TO
NORTHCENTRAL WISCONSIN EARLY THIS EVENING. AS WE APPROACH THE LATE
EVENING...THE QUASILINEAR MCS AND SCATTERED UPSTREAM SHOWER
ACTIVITY WILL CONGEAL. THUS EXPECT FAIRLY WELL-ORGANIZED BAND OF
SHOWERS AND EMBEDDED THUNDERSTORMS TO PUSH SOUTHEAST ACROSS THE
FORECAST AREA AROUND AND AFTER MIDNIGHT. GIVEN THE STRENGTH OF THE
UPPER DYNAMICS AND FAIRLY STEEP MID-LEVEL LAPSE RATES...THERE IS
CERTAINLY SOME POTENTIAL FOR SOME OF THE STORMS TO PRODUCE
MARGINALLY SEVERE HAIL AND PERHAPS SOME STRONG WIND GUSTS. FEEL
BEST CHANCE OF THIS OCCURRING WILL BE OVER CENTRAL PORTIONS OF THE
FORECAST AREA LATER THIS EVENING WITH MODEL GUIDANCE WEAKENING THE
CONVECTION AFTER 09Z AS IT APPROACHES THE EASTERN PART OF THE
FORECAST AREA.

ALTHOUGH STRONG DYNAMICS SHOULD BE EAST OF THE FORECAST AREA
SHORTLY AFTER 12-14Z SUNDAY...LINGERED LOW POPS WELL INTO SUNDAY
AFTERNOON AS UPPER TROUGH AXIS WILL STILL BE OVER THE AREA WITH
ASSOCIATED SURFACE TROUGH MOVING SOUTHWARD ACROSS THE AREA DURING
THE EARLY AFTERNOON TO HELP FOCUS SCATTERED SHOWER ACTIVITY. BY
LATE AFTERNOON..DRIER AIR SHOULD BEGIN TO WORK ITS WAY SOUTHWARD
ACROSS THE FORECAST AREA ALLOWING SKIES TO CLEAR SOMEWHAT. TEMPS
WILL BE MARKEDLY COOLER THAN TODAY WITH DAYTIME HIGHS MAINLY IN
THE LOWER 60S.

.LONG TERM...SUNDAY NIGHT THROUGH SATURDAY
ISSUED AT 308 PM CDT SAT SEP 20 2014

EXTENDED MDLS ARE IN GENERAL AGREEMENT IN THE LARGE-SCALE WITH THE
MEAN FLOW TRANSITIONING FROM A ROCKIES UPR RDG/E-CNTRL CONUS UPR
TROF EARLY NEXT WEEK...TO A WRN CONUS UPR TROF/ERN CONUS UPR RDG
LATE NEXT WEEK. THE FCST ISSUES HAVE TO DEAL WITH SMALLER SCALE
FEATURES...ESPECIALLY A WEAK SHORTWAVE TROF MID-WEEK HEADED TOWARD
THE WRN GREAT LAKES. THIS PATTERN CHANGE WOULD SEND NE WI FROM
BELOW NORMAL TEMPS/ABOVE NORMAL PCPN...TO A WARMER/DRIER PATTERN.

THE CENTER OF AN AREA OF HI PRES IS FCST TO MOVE SE FROM THE NRN
PLAINS TOWARD THE MID-MS VALLEY SUNDAY NGT. THIS PLACES NE WI
UNDER THE NRN FRINGES OF THIS SFC HI...WITH MAINLY CLEAR SKIES AND
A LIGHT N-NW WIND. DEPENDING ON HOW MUCH PCPN FALLS TNGT/SUNDAY
MORNING...THERE COULD BE SOME PATCHY FOG DEVELOPING OVER MUCH OF
THE FCST AREA. ANOTHER CONCERN WOULD BR FROST POTENTIAL OVER THE
NORTH LATE SUNDAY NGT. BOUNDARY LAYER WINDS TO BE IN THE 10 TO 15
KT RANGE AND MAY NOT BE STRONG ENUF TO PREVENT TEMPS FROM REACHING
THE MID 30S OVER NRN WI. HAVE INCLUDED PATCHY FROST WORDING
GENERALLY NORTH OF A MERRILL-ANTIGO-WAUSAUKEE LINE.

THE SFC HI DRIFTS EAST INTO SRN SECTIONS OF THE GREAT LAKES/OHIO
RIVER VALLEY ON MON WITH MOSTLY SUNNY SKIES...WEST WINDS UNDER 10
MPH AND SEASONAL TEMPS FOR LATE SEPTEMBER. LOOK FOR MAX TEMPS TO
RANGE FROM THE LWR 60S LAKESIDE (DUE TO A LAKE BREEZE) TO THE MID
TO UPR 60S ELSEWHERE.

AS THE SFC HI HEADS FARTHER TO THE EAST MON NGT...MODEST WAA
BEGINS TO DEVELOP OVER WI...ESPECIALLY AFTER MIDNGT. 8H TEMPS ARE
ABOUT 4C DEGS WARMER COMPARED TO SUNDAY NGT...THUS DO NOT EXPECT
SFC TEMPS TO QUITE AS COOL. THE W-SW WINDS ALOFT WL ALSO BEGIN TO
BRING A TOUCH OF MOISTURE BACK INTO WI...THEREFORE CANNOT RULE OUT
ANOTHER BOUT OF PATCHY LATE NGT FOG OVER THE FCST AREA. MIN TEMPS
TO RANGE FROM THE LWR TO MID 40S NORTH...MID 40S TO AROUND 50 DEGS
SOUTH. RETURN FLOW IN FULL EFFECT BY TUE AS WINDS BACK TO THE
SOUTH (EXCEPT S-SE NEAR LAKE MI AS THE LAKE BREEZE MOVES INLAND)
AND WARMER/MORE MOIST AIR PUSHES INTO WI. THE FCST AREA TO RESIDE
ON THE WRN EDGE OF THE DEPARTED SFC HI...THUS EXPECT TO SEE
ANOTHER MOSTLY SUNNY DAY WITH MAX TEMPS IN THE MID TO UPR 60S
LAKESIDE...UPR 60S/LWR 70S ELSEWHERE.

HEADED INTO MID-WEEK...THE MAIN FOCUS TO BE ON THE MOVEMENT OF A
SHORTWAVE TROF (REMAINS OF A CA CLOSED UPR LOW) ACROSS THE CNTRL
CONUS. TUE NGT APPEARS TO REMAIN QUIET UNDER MOSTLY CLEAR SKIES
AND LIGHT S-SE WINDS. THIS SHORTWAVE TROF LIFTS NE INTO THE UPR MS
VALLEY/MIDWEST ON WED IN A WEAKENING STATE BETWEEN UPR RDGS OVER
THE ROCKIES AND ERN CONUS. CLOUDS WL GRADUALLY INCREASE OVER CNTRL
WI WITH THE LEADING EDGE OF LIGHT SHWRS IMPINGING ON N-CNTRL WI
LATE IN THE DAY. ERN WI SHOULD SEE ANOTHER DAY WITH MOSTLY SUNNY
SKIES AS TEMPS TO REACH INTO THE LWR 70S...SLIGHTLY COOLER N-CNTRL
AND LAKESHORE.

AN INTERESTING PHENOMENA THEN TAKES PLACE WED NGT INTO THU AS THE
ERN CONUS UPR RDG RETROGRADES WWD AND STARTS TO PINCH OFF THE
SHORTWAVE TROF STILL SITUATED OVER THE UPR MS VALLEY/MIDWEST. NRN
SECTIONS OF THE SHORTWAVE TROF WEAKENS AND EVENTUALLY DISSIPATES...
WHILE SRN SECTIONS OF THE TROF DRIFTS SW AND TRIES TO BECOME A WEAK
CLOSED UPR LOW OVER THE CNTRL PLAINS. IF THIS SCENARIO IS CORRECT...
CNTRL WI MAY HAVE A SMALL SHWR CHC WED NGT INTO THU MORNING...BUT
ERN WI MAY END UP NOT SEEING A DROP OF RAIN.

THE END OF THE WEEK WL FEATURE A DEEP UPR TROF HITTING THE WEST
COAST AND A LARGE UPR RDG OVER THE ERN HALF OF THE CONUS. THIS
SET-UP WOULD PROVIDE FOR DRY CONDITIONS WITH ABOVE NORMAL TEMPS.
IN FACT...CANNOT RULE OUT MAX TEMPS ON SAT REACHING 80 DEGS OVER
PARTS OF CNTRL WI.
&&

.AVIATION...FOR 06Z TAF ISSUANCE
ISSUED AT 1034 PM CDT SAT SEP 20 2014

A BAND OF THUNDERSTORMS WITH WIND GUSTS TO 3O TO 40 KTS AND BRIEF
HEAVY RAIN SHOULD MOVE OUT OVER LAKE MICHIGAN TOWARD THE BEGINNING
OF THE TAF PERIOD. WILL PROBABLY NEED TO INCLUDE A TEMPO GROUP
FOR TSTMS AT MTW FOR THE FIRST HOUR OF THE TAF PERIOD.

AFTER THE INITIAL BAND OF STORMS MOVES THROUGH...AN AREA OF STEADY
LIGHT TO MODERATE RAIN IS EXPECTED TO CONSOLIDATE OVER MUCH OF THE
FORECAST AREA OVERNIGHT INTO EARLY SUNDAY MORNING. MVFR/IFR
CONDITIONS ARE EXPECTED TO DEVELOP WITHIN THE RAIN BAND. CONDITIONS
WILL GRADUALLY IMPROVE AS THE RAIN TAPERS OFF SUNDAY MORNING...
WITH VFR CONDITIONS RETURNING BY MIDDAY OR EARLY AFTERNOON. GUSTY
NORTH WINDS ARE ANTICIPATED...ESPECIALLY NEAR LAKE MICHIGAN.

HIGH PRESSURE WILL BRING CLEAR SKIES AND LIGHT WINDS SUNDAY EVENING.
&&

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

$$

SHORT TERM.....ESB
LONG TERM......KALLAS
AVIATION.......KIECKBUSCH






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