Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 250238 AAA
AFDMKX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
938 PM CDT FRI APR 24 2015

.UPDATE...

RAIN SHOWERS DIMINISHING AS FORCING FROM 700 MB WARM ADVECTION AND
A WEAK VORTICITY MAXIMUM SHIFT EAST/NORTHEAST. HAD SOME BRIEF
PERIODS OF GRAUPEL...AND EVEN SNOW AS THE DENDRITE GROWTH ZONE
MOISTENED AND THE COLUMN COOLED TO 0C ALMOST DOWN TO THE
SURFACE...MIXED IN WITH THE MORE-DEEPLY CONVECTIVE SHOWERS
EARLIER.

LOOKS TO BE RELATIVELY QUIET FOR THE OVERNIGHT WITH A DRY
EASTERLY LOW-LEVEL FLOW...WITH ONLY SOME ISOLATED LIGHT
SHOWERS/SPRINKLES. BETTER CHANCES FOR SHOWERS LOOK TO STAY SOUTH
OVERNIGHT ACROSS NRN IL ALONG AND JUST TO THE NORTH OF THE
SURFACE BAROCLINIC ZONE PER THE LATEST HRRR AND RAP 13 MODEL
DEPICTIONS. NEW NAM 12 IS NOT BRINGING MEASURABLE RAIN INTO
SOUTHERN WISCONSIN SATURDAY...CONTINUING A TREND IN EARLIER MODEL
RUNS THAT WERE HINTING AT A SOUTHERLY SHIFT TO THE PRECIPITATION
SHIELD.

&&

.AVIATION/06Z TAFS/...

LOOKING FOR RELATIVELY DRY...VFR CONDITIONS INTO THE EARLY OVERNIGHT
WITH ONLY A PASSING SPRINKLE OR ISOLATED LIGHT RAIN SHOWER.
LOOKING FOR CIGS TO LOWER TO MVFR LEVELS AROUND 09Z AT KMSN...AND
BETWEEN 12Z AND 13Z AT EASTERN SITES WITH MOISTURE ADVECTING INTO
SOUTHERN WISCONSIN AHEAD OF APPROACHING LOW PRESSURE. NEW NAM 12
IS NOT BRINGING MEASURABLE RAIN INTO SOUTHERN WISCONSIN
SATURDAY...CONTINUING A TREND IN EARLIER MODEL RUNS THAT WERE
HINTING AT A SOUTHERLY SHIFT TO THE PRECIPITATION SHIELD. WILL
LOOK AT MORE OF THE 00Z DATA SET COMING IN PRIOR TO ISSUANCE TO
SEE IF VSBY REDUCING PCPN WILL OCCUR...THOUGH EXPECT AT LEAST MVFR
CIGS IF NOT LOWER. EAST WINDS WILL BE INCREASING IN THE EARLY TO
MID MORNING HOURS WITH GUSTS OF 20 TO 25 KNOTS.

&&

.MARINE...A SMALL CRAFT ADVISORY GOES INTO EFFECT AT 7 AM CDT
SATURDAY AS EAST WINDS WILL STEADILY INCREASE OVERNIGHT...REACHING
SMALL CRAFT ADVISORY LEVELS EARLY SATURDAY MORNING...THEN BECOMING
NORTHEAST BY SATURDAY NIGHT. GUSTS TO 25 KNOTS ARE EXPECTED
SATURDAY INTO SATURDAY EVENING...WITH A TIGHT PRESSURE GRADIENT
MOVING ACROSS THE WATERS OF SOUTHERN LAKE MICHIGAN FROM PASSING
LOW PRESSURE TO THE SOUTH.

ONSHORE FLOW WILL BUILD WAVE HEIGHTS INTO THE 2 TO 4 FOOT RANGE
BY MORNING...AND 3 TO 6 FEET BY LATE IN THE AFTERNOON AND EARLY
EVENING WITH THE LONGER NORTHEAST FETCH. WINDS DIMINISH FOR A
TIME LATE SATURDAY NIGHT...WITH WAVES DIMINISHING A BIT TOWARDS
MORNING. LATEST NAM HAS A NORTH FETCH SUNDAY...WHICH MAY KEEP
HIGHER WAVES JUST OFFSHORE. NEXT SHIFT WILL HAVE TO ASSESS NEED TO
EXTEND ADVISORY BEYOND SUNDAY MORNING EXPIRATION.

&&

.PREV DISCUSSION... /ISSUED 342 PM CDT FRI APR 24 2015/

TONIGHT AND SATURDAY...FORECAST CONFIDENCE IS MEDIUM.

AREA OF RAIN SHOWERS EXTENDS FROM NORTH CENTRAL IOWA AND SOUTHEAST
MINNESOTA INTO SOUTH CENTRAL WISCONSIN. THIS IS IN RESPONSE TO 700
MB WARM AIR ADVECTION AND FRONTOGENESIS RESPONSE...AS WELL AS FROM
AN ADVANCING 500 MB VORTICITY MAXIMUM. THESE FEATURES SHOULD
CONTINUE TO SLIDE EAST NORTHEAST ACROSS THE AREA INTO EARLY THIS
EVENING...SPREADING LIGHT TO MODERATE RAIN SHOWERS THROUGH THE AREA.

STRENGTH OF UPWARD VERTICAL MOTION SHOULD OVERCOME DRY LOW LEVELS
BELOW 5000 FEET ABOVE GROUND LEVEL DURING THIS TIME. RAP SOUNDINGS
SHOWING WEAK ELEVATED CAPE...LITTLE TO NONE ON OTHER MODELS...SO
WILL NOT INCLUDE THUNDER MENTION.

500 MB SHORTWAVE TROUGH SLIDES EAST SOUTHEAST FROM NORTHWEST
MISSOURI TO CENTRAL ILLINOIS SATURDAY. MODELS HAVE BEEN TRENDING
SLIGHTLY SOUTHWARD WITH THE BEST UPWARD VERTICAL MOTION ASSOCIATED
WITH THE SHORTWAVE AND LOW TO MID LEVEL FRONTOGENESIS/Q VECTOR
CONVERGENCE. THUS...THE QPF SHIELD IN THE MODELS HAS TRENDED A BIT
SOUTHWARD AS WELL.

AREA FORECAST SOUNDINGS STILL SHOWING A FAIR AMOUNT OF DEEP MOISTURE
IN THE SOUTH LATER TONIGHT INTO SATURDAY...LESS SO IN THE FAR
NORTHERN COUNTIES. LOOKS TO BE A NORTH TO SOUTH GRADIENT IN THE POPS
FOR THIS SYSTEM...WITH SOME UNCERTAINTY WITH THE SYSTEM TRACK.

CONTINUED HIGH POPS IN THE SOUTHERN 2/3 OF THE AREA SATURDAY...WITH
CHANCE POPS IN THE FAR NORTH. EAST NORTHEAST WINDS ARE EXPECTED TO
GRADUALLY INCREASE IN MAGNITUDE TONIGHT...WITH GUSTY EAST NORTHEAST
WINDS SATURDAY. THIS WILL MAKE FOR A RAW DAY WITH THE RAIN. LOWS
TONIGHT WILL DROP INTO THE UPPER 30S TO AROUND 40...WITH HIGHS ONLY
IN THE 40S SATURDAY WITH THE CLOUDS AND RAIN.

SATURDAY NIGHT THROUGH MONDAY...FORECAST CONFIDENCE HIGH.

ANY LINGERING PRECIPITATION WILL COME TO AN END SATURDAY EVENING AS
A SHORTWAVE IMPULSE AND ASSOCIATED SFC LOW TRACK EASTWARD THROUGH
THE OHIO VALLEY. UPSTREAM 500 MB HEIGHTS BEGIN RISING OVER MINNESOTA
ON SATURDAY NIGHT...WITH THE MID-LEVEL RIDGE AXIS BECOMING ORIENTED
FROM THE CENTRAL PLAINS NORTHEASTWARD INTO SOUTHERN ONTARIO BY
MONDAY. THIS WILL SUPPORT SFC RIDGING THAT BUILDS INTO THE WESTERN
GREAT LAKES AND UPPER MIDWEST REGIONS ON SUNDAY NIGHT INTO MONDAY.
LOW-LEVEL COLD ADVECTION AND NORTHEASTERLY FLOW OFF THE LAKE WILL
KEEP TEMPERATURES RELATIVELY COOL ON SUNDAY. 925 MB TEMPERATURES IN
THE 3 TO 8C RANGE SUPPORT HIGHS IN THE 50S TO NEAR 60 AWAY FROM THE
LAKESHORE. WITH NEAR NEUTRAL LOW-LEVEL THERMAL ADVECTION AND
NORTHERLY FLOW ON MONDAY EXPECT READINGS TO WARM A BIT MORE ACROSS
THE WEST. PERSISTENT EASTERLY WIND COMPONENT WILL ONCE AGAIN PREVAIL
FOR THE EASTERN CWA ON MONDAY...KEEPING THE LAKESHORE COMMUNITIES
COOLER.

TUESDAY THROUGH WEDNESDAY...FORECAST CONFIDENCE MEDIUM.

MID-LEVEL RIDGING INITIALLY OVER THE EASTERN GREAT LAKES REGION
SHIFTS EAST INTO NEW ENGLAND THROUGH WEDNESDAY AS SHORTWAVE ENERGY
ADVANCES FROM THE NORTHERN/CENTRAL PLAINS INTO THE EASTERN GREAT
LAKES AND MISSISSIPPI VALLEY REGIONS. SOME UNCERTAINTY REGARDING
SHORTWAVE EVOLUTION TUESDAY NIGHT...WITH DETERMINISTIC 00Z ECMWF
BRINGING A MORE PROGRESSIVE AND STRONGER WAVE THROUGH SOUTHERN
WISCONSIN THAN THE 06Z GFS. 12Z ECMWF RUN APPEARS SLOWER...AND
EVOLVES A CLOSED LOW OVER LAKE MICHIGAN ON WEDNESDAY. SOME LIGHT
PCPN IS POSSIBLE TUESDAY NIGHT OR WEDNESDAY...BUT OVERALL FORCING
FOR ASCENT APPEARS WEAK. WARMING 925 MB TEMPERATURES OF 9-12C
SUPPORT HIGHS POTENTIALLY REACHING WELL INTO THE 60S AWAY FROM THE
LAKE.

THURSDAY THROUGH FRIDAY...FORECAST CONFIDENCE MEDIUM.

MID-LEVEL RIDGE AXIS SETS UP OVER THE NORTHERN PLAINS WITH WEAK SFC
RIDGING KEEPING THINGS QUIET ACROSS THE CWA FOR THURSDAY INTO FRIDAY
AFTERNOON. THEREAFTER...MODEL DIFFERENCES IN THE TIMING/STRENGTH OF
A SHORTWAVE IMPULSE PASSING THROUGH SOUTHERN CANADA SUGGEST ADDING
SLIGHT CHANCE POPS FOR AREA FRIDAY NIGHT. SOME UNCERTAINTY REGARDING
TEMPERATURES DURING THE PERIOD...AND DID NOT DEVIATE FROM MODEL
BLENDED CONSENSUS VALUES.

AVIATION/00Z TAFS/...

LIGHT TO MODERATE BAND OF RAIN SHOWERS SHOULD
CONTINUE TO MOVE EAST NORTHEAST THROUGH THE AREA THROUGH EARLY THIS
EVENING. VFR CONDITIONS SHOULD REMAIN DURING THIS TIME.
EAST/SOUTHEAST WINDS WILL BECOME EAST NORTHEAST BY MIDDLE TO LATE
EVENING...GRADUALLY INCREASING IN STRENGTH LATER TONIGHT.

A LULL IN THE SHOWER ACTIVITY SHOULD OCCUR LATER THIS EVENING AND
INTO THE OVERNIGHT HOURS...UNTIL MAIN TROUGH OF LOW PRESSURE SLIDES
EAST SOUTHEAST FROM NORTHWEST MISSOURI INTO CENTRAL ILLINOIS
SATURDAY.

AREA OF LIGHT TO MODERATE RAIN SHOULD SPREAD ACROSS TAF SITES
BETWEEN 10Z AND 14Z SATURDAY...LINGERING THROUGH THE DAY. EAST TO
EAST NORTHEAST WINDS WILL REMAIN MODERATE IN STRENGTH
SATURDAY...WITH GUSTS TO AROUND 24 KNOTS. EXPECT MAINLY MVFR
CEILINGS AND VISIBILITIES WITH THE RAIN. SOME IFR VISIBILITIES AND
CEILINGS ARE POSSIBLE TOWARD KENOSHA...REMAINING ABOVE ALTERNATE
MINIMUMS.

MARINE...

EAST NORTHEAST WINDS ARE EXPECTED TO GATHER STRENGTH TONIGHT INTO
SATURDAY...BECOMING NORTHEAST SATURDAY NIGHT. GUSTS TO 25 KNOTS ARE
EXPECTED SATURDAY INTO SATURDAY NIGHT...WITH TIGHT PRESSURE GRADIENT
FROM PASSING LOW PRESSURE TO THE SOUTH.

ONSHORE FLOW WILL BUILD WAVE HEIGHTS INTO THE 3 TO 6 FOOT RANGE FOR
THE NEARSHORE WATERS. A SMALL CRAFT ADVISORY WILL BE NEEDED FOR
SATURDAY AND SATURDAY NIGHT.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...SMALL CRAFT ADVISORY FROM 7 AM SATURDAY TO 7 AM CDT SUNDAY FOR
     LMZ645-646.

     SMALL CRAFT ADVISORY FROM 10 AM SATURDAY TO 7 AM CDT SUNDAY FOR
     LMZ643-644.

&&

$$

UPDATE...REM
TONIGHT/SATURDAY AND AVIATION/MARINE...WOOD
SATURDAY NIGHT THROUGH FRIDAY...SPM



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