Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 251612
AFDMKX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
1012 AM CST WED FEB 25 2015

.AVIATION/18Z TAFS/...RADAR MOSAIC SHOWS SNOW SPREADING INTO SW WI
WITH IFR VSBYS WEST OF KMSN. WATER VAPOR SHOWS SHORTWAVE RIDING
EAST FROM MN/IA. MEANWHILE SURFACE LOW IS DROPPING SE FROM ERN NE.
MODELS IN GOOD AGREEMENT IN SPREADING SNOW ACROSS REMAINDER OF SRN
WI THIS AFTN AND EVE WITH ONSHORE COMPONENT LEADING TO SOME LAKE
EFFECT SNOWS AS WELL...HOWEVER ICE COVERAGE LIKELY TO HAVE A SAY
ON EXTENT OF THIS. SO EXPECTING IFR CIGS AND SOME LIFR VSBYS
SPREADING ACRS SRN WI THIS AFTN WITH COMBO OF LAKE EFFECT AND SYS
THIS EVENING BEFORE ANY LINGERING LAKE EFFECT WRAPS UP THURSDAY
MORNING. SO OVERALL 1-2 OF SYSTEM SNOW FOR MAINLY SRN HALF OF THE
CWA WITH SOME ISOLD 3 INCH AMOUNTS NEAR LAKE MI DUE TO ADDED
INFLUENCE OF LAKE EFFECT.

PC

&&

.PREV DISCUSSION... /ISSUED 336 AM CST WED FEB 25 2015/

TODAY...FORECAST CONFIDENCE IS MEDIUM.

MID-LEVEL CIRCULATION SHOWING UP ON THE VWP NETWORK IN NODAK AT 850H
TAKES A SOUTHEAST TRACK ACROSS ERN SODAK AND WRN IA TO NEAR IA/MO
BORDER BY 00Z. ALL 00Z GUIDANCE HAS BEEN NUDGING THIS SYSTEM FARTHER
NORTHEAST AND 06Z NAM EVEN FARTHER NORTHEAST WITH MID-LEVEL
CIRCULATION. THIS CIRCULATION IS TRAVELING SOUTHEAST ALONG A TIGHT
BAROCLINIC RIBBON. THIS NORTHEAST NUDGE IS BRINGING A MUCH BETTER
THREAT FOR -SN AFFECTING PORTIONS OF SOUTHWEST WI FROM LATE MRNG
INTO THE EVE. 285 ISENTROPIC OMEGA SHOWS BRIEF PERIOD OF HIGHER LIFT
IN THE AFTN AFFECTING SOUTHWEST CWA WHICH TIES INTO WHERE BETTER
LAYER Q-VECTOR CONVERGENCE IS LOCATED. MODERATE LOW LEVEL
FRONTOGENETICAL FORCING ALSO BRUSHES SOUTHWEST DURING THE AFTN.

THICKNESSES FAVOR SLR AROUND 20 TO 1 WITH QPF BETWEEN 0.05 TO 0.1.
AT THIS TIME THINKING A COUPLE INCHES COULD OCCUR IN THE DARLINGTON
AREA INTO THE EARLY EVENING...TRAILING OFF TO AROUND AN INCH IN THE
MADISON AREA. BUMPED UP POPS TO CATEGORICAL IN THE SOUTHWEST DURING
THE AFTN. WL ADD MENTION TO THE HWO AS -SN WILL BE OCCURING DURING
EVE RUSH.

TONIGHT...FORECAST CONFIDENCE IS MEDIUM.

HUNG ONTO SOME LIKELY POPS IN THE SOUTH DURING THE EARLY EVENING AS
MID-LEVEL DEFORMATION AND LIFT WITH PASSING 850MB LOW SINKS TO THE
SOUTH. ATTENTION QUICKLY TURNS TO THE SOUTHEAST WHERE LOW LEVEL WIND
FLOW MORE LIKELY TO TURN TO THE NORTHEAST DUE TO STRONGER SFC LOW
PRESSURE SYSTEM PASSING THRU THE MID-MISSISSIPPI VALLEY REGION.
COLD AIR SINKING ACROSS LAKE MI WILL RESULT IN THE DELTA-T
INCREASING OVERNIGHT TO AROUND 20C. EXPECT DEEP RH UP TO 10K FEET
FOR A TIME ACROSS THE SOUTHERN LAKESHORE COUNTIES...WITH MUCH OF THE
COLUMN IN FAVORABLE DENDRITIC GROWTH ZONE DURING THE LATE EVE TO AFT
MIDNIGHT. LOW LEVEL WINDS INCREASE TO OVER 20KTS RESULTING IN
SEVERAL PERIODS OF FAVORABLE OMEGA ALONG THE LAKESHORE.

HIGH RES MODIS IMAGE FROM TUE AFTN SHOWED ICE COVER REMAINING OVER
MUCH OF THE NEARSHORE WATERS...BUT LAKE WATERS BEYOND 10 MILES
REMAINED ICE FREE. HARD TO SAY WHAT AFFECT THE ICE COVER WILL
HAVE...BUT ENOUGH FORCING AND MOISTURE TO WARRANT INCREASING POPS TO
LIKELYS FROM SRN MKE COUNTY SOUTH TO IL BORDER WITH SCT WORDING
FARTHER NORTH. LAKE EFFECT SNOW FLOW CHART RESULTS IN MODERATE SNOW
ACCUMULATIONS OVERNIGHT BUT WITH ICE COVER AND GRADUALLY BACKING
WINDS...WL LIMIT SNOWFALL TO 1 TO 3 INCHES FOR NOW.

SHORT TERM...THURSDAY THROUGH FRIDAY NIGHT...FORECAST CONFIDENCE
IS MEDIUM.

MODELS LINGER LIGHT LAKE EFFECT QPF ACROSS THE FAR SOUTHEAST
COUNTIES THURSDAY MORNING...AS 1000/850 MB CONVERGENCE SLOWLY
SHIFTS TO THE EAST. VERY FAVORABLE DELTA T VALUES REMAIN...THOUGH
AIR COLUMN ABOVE INVERSION DRIES OUT. THUS...CONTINUED TO MENTION
MODEST POPS IN THIS AREA THURSDAY MORNING.

OTHERWISE...COLD AIR ADVECTION CONTINUES THURSDAY...AS ARCTIC HIGH
PRESSURE BUILDS INTO THE NORTHERN PLAINS. THE HIGH WILL SLOWLY
SHIFT SOUTHEAST INTO CENTRAL ILLINOIS BY 00Z SATURDAY...THEN TO
THE EAST BY 12Z SATURDAY. THIS WILL BRING ANOTHER SHOT OF WELL
BELOW NORMAL TEMPERATURES THURSDAY INTO FRIDAY NIGHT.

DRY AIRMASS/MOSTLY CLEAR SKIES AND STRONG NEAR SURFACE INVERSION
THURSDAY NIGHT INTO FRIDAY NIGHT SHOULD LEAD TO LOWS WELL INTO THE
SINGLE DIGITS BELOW ZERO. LOWS MAY GET SEVERAL DEGREES COLDER IF
WINDS FULLY DECOUPLE...WHICH IS POSSIBLE EACH NIGHT. LATER SHIFTS
WILL HAVE TO WATCH FOR THIS POSSIBILITY. HIGHS THURSDAY IN THE
SINGLE DIGITS ABOVE ZERO...AND FRIDAY INTO THE MID TEENS...ARE
EXPECTED.

LONG TERM...SATURDAY THROUGH TUESDAY...FORECAST CONFIDENCE IS
MEDIUM.

GFS/ECMWF MODELS SHOW 500 MB FLOW BECOMING MORE ZONAL BY 12Z
SATURDAY...AND GENERALLY LINGERING INTO EARLY NEXT WEEK. THEY
CONTINUE TO DIFFER WITH TRENDS FOR THE SYSTEM FOR SATURDAY NIGHT
AND SUNDAY. ECMWF IS ABOUT 6 TO 9 HOURS QUICKER WITH BRINGING
INITIAL WARM AIR ADVECTION QPF INTO THE AREA SATURDAY NIGHT. THEY
BOTH BRING THE COLD FRONT SOUTHEAST THROUGH THE AREA LATER SUNDAY
INTO SUNDAY EVENING.

BEST UPWARD VERTICAL MOTION REMAINS TO THE SOUTH AND SOUTHEAST
WITH THIS SYSTEM...WITH MORE MODEST UPWARD VERTICAL MOTION IN
SOUTHERN WISCONSIN. KEPT MAINLY CHANCE POPS GOING FOR THIS
PERIOD...THOUGH MAY NEED ADJUSTMENT IN LATER FORECASTS IF QPF
CONTINUES TO LINGER ACROSS THE AREA.

HIGH PRESSURE SLIDES EAST ACROSS THE REGION MONDAY...BEFORE
RELATIVELY STRONG LOW PRESSURE SLIDES NORTHEAST FROM THE SOUTHERN
PLAINS INTO THE CENTRAL GREAT LAKES REGION TUESDAY INTO WEDNESDAY.
GFS IS ABOUT 12 HOURS QUICKER THAN THE ECMWF WITH THE LOW TRACK
TIMING...THOUGH BOTH DO BRING A FAIR AMOUNT OF QPF AND UPWARD
VERTICAL MOTION THROUGH THE AREA. THIS WILL NEED TO BE WATCHED
CLOSELY IN LATER FORECASTS...AS THIS TRACK COULD BRING A DECENT
AMOUNT OF SNOW AND/OR MIXED PRECIPITATION TO THE AREA. STAY
TUNED...

AVIATION/12Z TAFS/...

BETTER THREAT FOR -SN TO SPREAD INTO KMSN THIS AFTN WITH CIGS AND
VSBYS BRIEFLY LOWERING TO MVFR. LAKE EFFECT -SHSN LIKELY TO AFFECT
KMKE AND KENW TNGT WITH POTENTIAL FOR CIGS AND VSBYS DROPPING AS LOW
AS IFR.

MARINE...

HIGH RESOLUTION MODIS IMAGE FROM TUE AFTN HAD PARTIAL CLEARING OVER
THE NEARSHORE WATERS WHICH REVEALED ICE COVER PERSISTING IN THOSE
VSBL AREAS. WITH COLD AIR RETURNING AND SETTLING IN FOR THE REST OF
THE WEEK...EXPECT WIDESPREAD ICE COVER TO CONTINUE. WIND GUSTS WL
GET CLOSE TO SMALL CRAFT ADVY FOR A TIME TONIGHT AS PRESSURE
GRADIENT TIGHTENS DUE TO LOW PRESSURE PASSING WELL SOUTH OF THE
AREA.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
LM...NONE.
&&

$$
TODAY/TONIGHT AND AVIATION/MARINE...MBK
THURSDAY THROUGH TUESDAY...WOOD



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