Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 061502 AAA
AFDMKX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1002 AM CDT WED MAY 6 2015

.UPDATE...

THE DENSE FOG IN THE EASTERN LAKESHORE COUNTIES IS GRADUALLY
THINNING AND LIFTING THIS MORNING PER WEB CAMS AND SURFACE
OBSERVATIONS. I ISSUED A NEW SPECIAL WEATHER STATEMENT TO HANDLE
IT. THE DENSE FOG OVER THE SOUTHWEST FORECAST AREA IS ALSO
DISSIPATING... SO THE DENSE FOG ADVISORY WILL BE ALLOWED TO
EXPIRE AT 10 AM.

SCATTERED SHOWERS AND THUNDERSTORMS DEVELOPED THIS MORNING IN A
REGION OF 925MB WARM AIR ADVECTION. THESE ARE JUST ABOVE THE
SURFACE INVERSION. IT LOOKS LIKE THIS AREA OF THUNDERSTORMS WILL
CONTINUE TO LIFT NORTH THROUGH THE MORNING. THE CHANCE OF SHOWERS
AND THUNDERSTORMS WILL CONTINUE THROUGH THE AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 426 AM CDT WED MAY 6 2015/

UPDATE...SURFACE OBSERVATIONS...CALLS TO LOCAL LAW ENFORCEMENT AND
WEB CAMS SHOW DENSE FOG EXPANDING ACROSS SOUTHWEST CWA. BOUNDARY
LAYER WINDS SUPPORT DENSE FOG PERSISTING THROUGH THE EARLY
MORNING. HENCE POSTED DENSE FOG ADVY FOR ROCK...GREEN....LAFAYETTE
AND IOWA COUNTIES. MAY NEED TO EXPAND INTO DANE AND SAUK COUNTIES
AS FOG MAY SPREAD NWD.

PREV DISCUSSION... /ISSUED 328 AM CDT WED MAY 6 2015/

TODAY AND TONIGHT...FORECAST CONFIDENCE - MEDIUM.

SHOWERS CONTINUE TO DIMINISH ACROSS NORTHEAST CWA AS WEAK MID-LEVEL
WAVE OVER CENTRAL WI PROGRESSES EWD.  SMALL BAND OF SHOWERS HAS
RECENTLY DEVELOPED WEST OF THE BARABOO AREA...AND IS PROGRESSING
NNE.  THINK THESE SHOWERS MORE A RESULT OF NORTHWARD MOVING LOW
LEVEL WARM FRONT AS WINDS JUST OFF THE SURFACE...ABOVE SHALLOW
INVERSION TURN MORE SOUTH AND INCREASE.  SPC MESOANALYSIS HAS
WIDESPREAD DEEP LAYER MOISTURE FLUX CONVERGENCE OVER NRN HALF OF CWA
INTO WEST CENTRAL WI.  HENCE WL CONTINUE LOW POPS EARLY THIS MRNG
ACROSS NORTH.  SURGE OF LOW LEVEL WARM AIR ALSO CONTRIBUTING TO FOG
OVER SOUTHWEST CWA WHICH WILL LIKELY SPREAD NORTH TOWARD REST OF
WESTERN CWA.  DRIER AIR OVER EASTERN CWA LIKELY TO KEEP FOG MORE
PATCHY THIS MRNG.  CALL TO GREEN COUNTY SHERIFF HAD WIDESPREAD
MODERATE FOG OVER THE COUNTY...BUT KEFT HAS BEEN 1/4SM FOR AN HOUR.
FOR NOW WL ISSUE SPS FOR DENSE FOG BUT MAY NEED TO UPGRADE TO DENSE
FOG ADVY THRU 15Z OR SO IF IT CONTINUES TO THICKEN.

UPSTREAM SHORT WAVE OVER NORTHWEST MO/SWRN IA MAY BRING A FEW
THUNDERSTORMS TO SRN WI LATE THIS MRNG THRU THE AFTN AS WARMER MORE
HUMID AIR SETTLES OVER SRN WI.  MUCAPE EXPECTED TO REACH SEVERAL
HUNDRED JOULES THIS AFTN...BUT FORCING AT THIS TIME LOOKS WEAK.  FOR
NOW WL GO WITH LOW POPS AND CARRY INTO THE EARLY EVENING.  AS
UPSTREAM LOW LEVEL JET PIVOTS EAST LATER TONIGHT AHEAD OF SLOWLY
MOVING PLAINS TROF...FEW SHOWERS OR STORMS COULD SKIM THE FAR WEST
LATER TONIGHT.

THURSDAY - CONFIDENCE...MEDIUM
MID LEVEL RIDGE AXIS PROGGD TO THE EASTERN GREAT LAKES. 500
MILLIBAR FLOW TURNS MORE SOUTHWEST. PRIMARY SHORTWAVE WILL LIFT
NORTHEAST THROUGH MN. MUCH WEAKER RIPPLES IN THE FLOW FURTHER EAST
ACROSS IA/IL/WI. LOW LEVEL FLOW WILL BE SOUTHERLY WITH A WARMER
AND MORE MOIST REGIME. 925 MILLIBAR SOUTH FLOW SENDS TEMPS TO NEAR
20C...SO WARM DAY TAKING SHAPE WITH MANY LOCALES LIKELY TO HIT THE
80 DEGREE MARK. MODELS CONTINUE TO SHOW POTENTIAL FOR SHRA/TSRA
ESP DURG THE AFTN ACROSS SC WI. THIS DUE TO APPCH SFC/850
FRONT...WEAK MID LEVEL WAVES AND DIURNALLY DRIVEN
INSTABILITY...ALTHOUGH NAM BUFKIT SOUNDINGS NOT OVERLY UNSTABLE.

FRIDAY AND FRIDAY NIGHT - CONFIDENCE...MEDIUM
500 MILLIBAR FLOW REMAINS SOUTHWEST WITH SURFACE/850 FRONTS
ENHANCING LOW LEVEL CONVERGENCE THIS PERIOD. IN ADDITION...BETTER
CONSENSUS FOR SECONDARY LOW RIDING NORTHEAST ALONG THE
FRONT...RAISING CONFIDENCE A BIT FOR SHRA/TSRA INTO AT LEAST
FRIDAY EVENING. AS IT STANDS THE GEM TAKES THE LOW ACROSS CNTRL WI
WITH THE ECMWF IN SRN WI AND THE GFS ACRS NRN IL. IN ALL CASES
DECENT SHOT AT SHRA/TSRA SO WILL GO WITH LIKELY POPS FOR THE CNTRL
AND ERN CWA FRI NGT.

SATURDAY - CONFIDENCE...MEDIUM
850/925 FRONT SAGS SOUTH THOUGH BAROCLINIC ZONE LINGERS FOR A
BIT...SO THE ECMWF IDEA OF KEEPING SOME SHRA AROUND SEEMS
REASONABLE...SO WILL KEEP THE SUPERBLEND POPS GOING. SURFACE
BOUNDARY DOES SHIFT SOUTH OF WI THOUGH SOME TIMING DIFFERENCES IN
THIS REGARD. EXPECT WINDS TO SHIFT NE. GFS A BIT QUICKER THAN THE
ECMWF.

SUNDAY - CONFIDENCE...MEDIUM
ISENTROPIC LIFT PROGGD TO INCREASE INTO THE AREA. THE GEM AND GFS
ARE QUICKER ON THIS WITH SURFACE LOW LIFTING INTO WRN IA/ERN NE.
THE GFS KEEPS THE LOW FURTHER SOUTHWEST AND SHOWS ONLY SPOTTY
PRECIP. WILL GO WITH SUPERBLEND POPS AT THIS TIME.

SUNDAY NIGHT THROUGH MONDAY NIGHT - CONFIDENCE...MEDIUM
500 MILLIBAR UPPER LOW PROGGD TO MOVE FROM THE CENTRAL PLAINS
THROUGH WI THIS PERIOD. SURFACE REFLECTION OF THIS FEATURE SHOWS
VARYING SOLUTIONS WITH THE GFS KEEPING LOW SOUTH AND A LARGE DEF
ZONE SHIELD OF RAIN/THUNDER SETTING UP ACROSS THE CWA. MEANWHILE
THE ECMWF HAS BEEN THE SURFACE LOW MOVING THROUGH SRN WI WITH THE
GEM FAVORING THE SOUTHERN GFS SOLUTION. DESPITE THE MODEL
DIFFERENCES LOOKS LIKE A WET AND UNSETTLED PERIOD.

TUESDAY - CONFIDENCE...MEDIUM
DECENT COOLING IN THE WAKE OF THE LOW WITH A DROP IN THICKNESSES
AND 850 TEMPS. LINGERING SHRA POTENTIAL WITHIN THIS REGIME.
LINGERING CYCLONIC FLOW MORE AMPLIFIED ON THE GFS WITH CLOSED LOW
SLOWER AND JUST EAST OF WI.

AVIATION/12Z TAFS/...EXPECT AREAS OF FOG THIS MORNING TO THIN LATER
THIS MRNG INTO THE AFTN...HOWEVER WL LIKELY HANG ON BY LAKE MI...OR
ELSE REDEVELOP. WARMER...MORE HUMID AIR MOVING ACROSS THE COOL LAKE
WATERS WILL RESULT IN FOG THAT MAY BE DENSE FOR A TIME BY THE LAKE
THRU TNGT.

OTHERWISE...THE SURGE OF WARMER AIR WILL LIKELY SET OFF ISOLD TO SCT
SHOWERS AND THUNDERSTORMS LATER TODAY INTO THIS EVENING.  IFR CIGS
THIS MRNG SHOULD THIN AND LIFT INLAND...BUT MAY HANG ON BY THE LAKE
INTO TNGT.

MARINE...SHIFTING LOW LEVEL WINDS MORE TO THE SOUTHEAST WILL ALLOW
WARMER AIR WITH HIGHER DEWPTS TO PUSH NORTHWARD ACROSS COOL LAKE MI
TODAY INTO TNGT. UPSTREAM SFC OBS OVER SOUTHWEST LOWER MI INTO NRN
INDIANA SHOWING SFC DEWPTS IN THE LOWER 50S. WITH LAKE SURFACE TEMPS
AROUND 38...DENSE FOG WILL LIKELY DEVELOP OVER THE NEAR SHORE WATERS
TODAY AND LINGER INTO TONIGHT. WL POST MARINE DENSE FOG ADVY FOR VSBYS
OF 1NM OR LESS BEGINNING THIS MRNG.

INCREASING SOUTHWEST WINDS IN THE BOUNDARY LAYER ON THURSDAY SHOULD
THIN ANY LINGERING FOG.  SOUTHWEST WIND GUSTS WILL APPROACH SMALL
CRAFT ADVY LEVELS ON THU AS WELL.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR WIZ062-
     067>069.

LM...DENSE FOG ADVISORY UNTIL 1 AM CDT THURSDAY FOR LMZ643>646.

&&

$$

UPDATE...MRC
TODAY/TONIGHT AND AVIATION/MARINE...COLLAR
THURSDAY THROUGH TUESDAY...MBK


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