Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 210410
AFDMKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1110 PM CDT MON APR 20 2015

.UPDATE...

&&

.AVIATION/06Z TAFS/...

ISOLATED LIGHT SHOWERS THIS EVENING. MAINLY VFR CIGS AROUND LARGE
LOW CENTERED JUST NORTHEAST OF LAKE SUPERIOR.

CIGS SHOULD MAY FALL BACK TO MVFR LATE TONIGHT INTO TUESDAY
MORNING AS ANOTHER SURGE OF COLD AIR WRAPS AROUND THE LOW.
THERE IS A CHANCE OF RAIN/SNOW SHOWERS MAINLY NORTH OF MILWAUKEE AND
MADISON TONIGHT. ISOLATED SHOWERS POSSIBLE AGAIN TUESDAY AFTERNOON.

&&

.PREV DISCUSSION... /ISSUED 336 PM CDT MON APR 20 2015/

SHORT TERM...

TONIGHT AND TUESDAY... FORECAST CONFIDENCE MEDIUM.

DRIER AIR IS WORKING INTO SOUTH CENTRAL AND SOUTHEAST WI THIS
AFTERNOON. THE DEEPER MIXING IS ALLOWING FOR PERSISTENT GUSTS UP TO
30 MPH IN MANY LOCATIONS. WINDS WILL GRADUALLY DIMINISH THIS EVENING.

A CLOSED UPPER LOW PARKED ITSELF OVER THE UPPER GREAT LAKES TODAY AND
WILL LINGER THROUGH TUESDAY. SHORTWAVES ROTATING AROUND THIS UPPER
LOW WILL BRING PERIODS OF LIGHT SHOWERS TO SOUTHERN WI. IT IS
DIFFICULT TO TIME THESE SHORTWAVES... BUT THE MODELS ARE IN FAIR
AGREEMENT THAT ONE WOULD ARRIVE EARLY TUE MORNING AND PRODUCE CLOUDS
AND POSSIBLE LIGHT SHOWERS. A PUSH OF COLDER AIR WILL ACCOMPANY THE
WAVE... SO SNOW SHOWERS WILL BE POSSIBLE. NO ACCUMULATION.

STEEP LOW LEVEL LAPSE RATES WILL CAUSE DEEP MIXING ALL DAY TUESDAY.
THEY WILL ALSO LEAD TO PERSISTENT CLOUDS AND POSSIBLY SOME RAIN
SHOWERS THROUGH THE DAY. WE WILL BE MIXING A LITTLE DEEPER THAN
TODAY... SO EXPECT A LITTLE HIGHER WIND GUSTS FOR TUESDAY. WIND
ADVISORY CRITERIA IS SUSTAINED WINDS OF 30 MPH OR GREATER OR WIND
GUSTS OF 45 MPH OR HIGHER. AT THIS TIME... IT LOOKS LIKE SOUTHERN WI
SHOULD BE JUST SHY OF MEETING CRITERIA SO NO HEADLINE. WE WILL
CONTINUE TO ASSESS ON LATER SHIFTS.

TUESDAY NIGHT THROUGH THURSDAY...FORECAST CONFIDENCE...MEDIUM

A BROAD CUTOFF UPPER LOW WILL SLOWLY MOVE FROM NORTHERN LAKE
SUPERIOR TO SOUTHEASTERN ONTARIO IN THIS PERIOD. THE LOW WILL
KEEP THE UPPER MIDWEST IN CYCLONIC FLOW WITH A SHEAR VORTICITY MAX
ENTRENCHED ACROSS SOUTHERN WISCONSIN THROUGH THURSDAY. IN
ADDITION TO THIS FORCING ALOFT...WE WILL STILL HAVE SOME SURFACE TROUGHING
ASSOCIATED WITH A DEEP LOW OVER FAR SOUTHERN HUDSON BAY. THROUGH
THE DAY ON WEDNESDAY...PORTIONS OF THE LOWER ATMOSPHERE IN CENTRAL
AND NORTHERN WISCONSIN WILL REMAIN NEARLY SATURATED. THEREFORE
KEPT SMALL PRECIP CHANCES IN THE FAR NORTHERN CWA BOTH TUESDAY
NIGHT AND THROUGH THE DAY WEDNESDAY. ADDITIONALLY...WILL KEEP A
SLIGHT CHANCE FOR SNOW WEDNESDAY MORNING WHEN SURFACE TEMPS FALL
JUST BELOW FREEZING. ON THURSDAY...THE LOWER ATMOSPHERE DRIES OUT
AS SURFACE RIDGING BEGINS TO BUILD INTO THE REGION..SO WILL BE
GOING DRY. FINALLY...STEEP LAPSE RATES DUE TO VERY COOL
TEMPERATURES ALOFT WILL ALLOW FOR BLUSTERY WINDS TO MIX DOWN TO
THE SURFACE BOTH ON WEDNESDAY AND THURSDAY AFTERNOONS.

LONG TERM...

FRIDAY...FORECAST CONFIDENCE...MEDIUM

THE UPPER LEVEL CUTOFF LOW WILL CONTINUE ITS SLOW TREK EAST
ACROSS THE NORTHEASTERN US/SOUTHEASTERN CANADA...DRAGGING THE
VORTICIY MAX OUT OF WISCONSIN AS RIDGING BUILDS INTO THE REGION.
AT THE SURFACE...AN INVERTED RIDGE WILL BUILD INTO WISCONSIN
WHILE A CYCLONE DEVELOPS IN THE CENTRAL PLAINS BEFORE TRACKING TO
THE SOUTH OF THE STATE. PREVIOUS RUNS OF THE GFS HAD THE PRECIP
SHIELD OF THIS SOUTHERLY CYCLONE ENCROACHING ON SOUTHERN
WISCONSIN...BUT RECENT RUNS HAVE BROUGHT GFS IN LINE WITH OTHER
GUIDANCE...KEEPING THE FORECAST AREA DRY ON FRIDAY. BLENDED
GUIDANCE TRIES TO BRING SOME PRECIP INTO THE SOUTHWEST FORECAST
AREA ON FRIDAY NIGHT...BUT THERE APPEARS TO BE LITTLE EVIDENCE OF
PRECIP IN THE GFS...ECMWF...OR CANADIAN MODEL...SO WILL BE LEAVING
PRECIP OUT FOR NOW.

SATURDAY AND SUNDAY...FORECAST CONFIDENCE...LOW

MODELS BEGIN TO SIGNIFICANTLY DIVERGE AT THIS POINT. THE GFS KEEPS
THE CUTOFF UPPER LOW OVER SOUTHEASTERN CANADA THROUGH THE
WEEKEND...KEEPING WISCONSIN IN NW FLOW ALOFT. MEANWHILE...THE ECMWF
FINALLY MOVES THE UPPER LOW OUT TO THE ATLANTIC...ALLOWING AN UPPER
RIDGE TO BUILD INTO WISCONSIN. HOWEVER...THE DEPTH OF THE ATMOSPHERE
WILL BE RELATIVELY DRY THROUGH THIS PERIOD...SO THE IMPACT OF THE
DIFFERENCE IN THE GUIDANCE WILL BE MINIMAL. KEEPING PRECIP OUT OF
THE FORECAST.

SUNDAY NIGHT AND MONDAY...FORECAST CONFIDENCE...LOW

DRASTIC DIFFERENCES IN THE GUIDANCE REMAIN PREVALENT THROUGH THE
REST OF THE FORECAST PERIOD. IN THE GFS...THE UPPER LEVEL CUTOFF LOW
REMAINS OVER SOUTHEASTERN CANADA AND SWINGS ANOTHER SHEARED
VORTICITY MAX SOUTH THROUGH THE STATE ON MONDAY. MEANWHILE THE ECMWF
HAS A SHORTWAVE DIVING SOUTHEAST OUT OF SASKATCHEWAN AND MOVING JUST
TO THE WEST OF THE STATE. THE ATMOSPHERE DOES MOISTEN UP IN THIS
PERIOD...SO HAVE PRECIPITATION CHANCES IN SW PORTION OF THE FORECAST
AREA ON SUNDAY NIGHT/MONDAY MORNING.

AVIATION/12Z TAFS/...
DRIER AIR IS WORKING INTO SOUTH CENTRAL AND SOUTHEAST WI THIS
AFTERNOON. THE DEEPER MIXING IS ALLOWING FOR PERSISTENT GUSTS UP TO
30 MPH IN MANY LOCATIONS. CEILINGS ARE RISING TO MVFR AND EXPECT A
PERIOD OF VFR LATE THIS AFTERNOON THROUGH MOST OF THE NIGHT. WINDS
WILL GRADUALLY DIMINISH THIS EVENING.

CIGS SHOULD FALL BACK TO MVFR LATE TONIGHT INTO TUESDAY MORNING AS
ANOTHER SURGE OF COLD AIR WRAPS AROUND THE GREAT LAKES UPPER LOW.
HIGHER WINDS ALOFT WILL ACCOMPANY THIS COLDER AIR LATE TONIGHT...
BUT WINDS AT THE SURFACE WILL BE IN THE 7 TO 11 KNOT RANGE UNTIL TUE
MORNING. THUS... LOW LEVEL WIND SHEAR IS LIKELY.

MARINE...

SMALL CRAFT ADVY CONDITIONS WILL PERSIST THROUGH THIS EVENING DUE TO
A TIGHT PRESSURE GRADIENT IN THE WAKE OF LOW PRESSURE PARKED OVER
ONTARIO.

ANOTHER BREEZY DAY IS EXPECTED TUESDAY WITH THE LINGERING STRONG
PRESSURE GRADIENT. WEST WINDS AND GUSTS WILL REACH SMALL CRAFT ADVY
LEVELS. FREQUENT GALE FORCE GUSTS TO 35 KNOTS ARE ALSO LOOKING MORE
LIKELY MIDDAY TUESDAY. WINDS WILL BE HIGHEST NEAR THE SHORELINE DUE
TO A DEEPER MIXING POTENTIAL. A GALE WATCH IS IN EFFECT.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...GALE WATCH FROM 9 AM CDT TUESDAY THROUGH TUESDAY EVENING FOR
     LMZ645-646.

     SMALL CRAFT ADVISORY UNTIL 9 AM CDT TUESDAY FOR LMZ645-646.

     SMALL CRAFT ADVISORY UNTIL 10 PM CDT TUESDAY FOR LMZ643-644.

&&

$$

UPDATE...HENTZ
TONIGHT/TUESDAY AND AVIATION/MARINE...MRC
TUESDAY NIGHT THROUGH MONDAY...BSH



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