Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 220157 AAA
AFDMKX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MILWAUKEE/SULLIVAN WI
857 PM CDT SAT MAR 21 2015

.UPDATE...

MADE A FEW MINOR ADJUSTMENTS TO SKY AND TEMPS DUE TO TREND OF
WARM ADVECTION MID-CLOUD DECK. WILL CONTINUE TO MONITOR
TEMPERATURES IN THE NEAR TERM AS LEADING EDGE OF MID DECK IS
ERODING AND IS SLOWER TO OVERSPREAD SRN WI. OTHERWISE CURRENT
FORECAST GENERALLY ON TRACK. TOP NEWS STORY ON OUR WEB PAGE HAS
THE LATEST ON THE UPCOMING SNOW EVENT FOR MAINLY SW WISCONSIN
SUNDAY AFTERNOON/NIGHT AND WILL BE UPDATED AS NEW INFORMATION
BECOMES AVAILABLE.

&&

.AVIATION/06Z TAFS/...

UNLESS THERE IS AN UNEXPECTED SURPRISE IN THE 00Z MODEL GUIDANCE
DO NOT EXPECT MUCH CHANGE TO THE 06Z TAF ISSUANCE WITH RESPECT TO
UPCOMING SNOW EVENT. LOOKING FOR A MID DECK TO OVERSPREAD THE
REGION OVERNIGHT...BUT DRY AIR WRAPPING AROUND RETREATING HIGH
PRESSURE MEANS VFR CONDITIONS THROUGH THE FIRST PART OF SUNDAY.
EVEN THE START OF PRECIPITATION...AROUND 18Z AT KMSN AND TOWARD
00Z AT KMKE AND KENW...WILL SEE CLOUD BASES IN THE 3500 TO 5K FT
RANGE INITIALLY AND 6 MILE VSBYS BEFORE DIPPING TO MVFR WITH THE
STEADIER SNOW.

THE HEAVIEST SNOW WILL BE STAYING TO THE SOUTHWEST OF THE TAF
SITES. CHECK OUR WEB PAGE FOR THE LATEST INFORMATION ON THE
EXPECTED SNOW AMOUNTS. CURRENTLY SNOW AMOUNTS BY 12Z MONDAY LOOK
TO TOTAL AROUND 2 INCHES AT KMSN...1 INCH AT KUES...AND BETWEEN
3/4 INCH AND 1 INCH AT KMKE AND KENW. THE MAJORITY OF THE SNOW
WILL FALL SUNDAY NIGHT. THERE COULD BE A A PERIOD OF FREEZING
DRIZZLE AS THE PRECIPITATION COMES TO AN END EARLY MONDAY MORNING.

&&

.PREV DISCUSSION... /ISSUED 328 PM CDT SAT MAR 21 2015/

TONIGHT... FORECAST CONFIDENCE HIGH.

MID LEVEL CLOUDS WILL SPREAD INTO SOUTHERN WI THIS EVENING...
ASSOCIATED WITH WEAK 700MB FRONTOGENESIS AND THE ENTRANCE REGION OF
AN UPPER JET. THERE IS NOT ENOUGH UPWARD MOTION OR LOW LEVEL
MOISTURE TO SUPPORT ANY PRECIPITATION. LOW TEMPERATURES WILL DROP
INTO THE MID/UPPER 20S TONIGHT WITH LOW LEVEL COLD AIR ADVECTION AND
DRY LOW LEVEL AIR DESPITE THE CLOUD COVER.

SUNDAY... FORECAST CONFIDENCE MEDIUM.

MID CLOUDS WILL LINGER THROUGH THE DAY. LOOK FOR DRY AIR AND A
STEADY EASTERLY BREEZE AT THE SURFACE.

A BAND OF 850-700MB WARM AIR ADVECTION AND FRONTOGENESIS AND ALSO
500MB VORTICITY ADVECTION WILL ALLOW FOR STRONG OMEGA IN PORTIONS OF
SOUTH CENTRAL WI BEGINNING MID SUNDAY AFTERNOON. THIS MID LEVEL
FORCING AND MOISTURE SHOULD BE ENOUGH TO OVERCOME THE DRY AIR AT THE
GROUND AND BEGIN PRODUCING PRECIP MAINLY WEST OF MADISON THROUGH 7
PM. SURFACE TEMPERATURES IN THE UPPER 30S AT THIS TIME WOULD SUGGEST
RAIN... BUT GIVEN THE STRONG FORCING WITHIN THE DENDRITIC GROWTH
ZONE... IT COULD STILL REACH THE GROUND AS SNOW. THUS KEPT THE
RAIN/SNOW MIX IN THE FORECAST.

TIMING OF THE PRECIP IS A LITTLE UNCERTAIN. SOME MODELS ARE QUICKER
TO BRING IT ALL THE WAY INTO SOUTHEAST WI BY 00Z. I WAS CONSERVATIVE
WITH THE START TIME IN THE FORECAST.

SUNDAY NIGHT AND MONDAY...CONFIDENCE - MEDIUM.

MUCH BETTER AGREEMENT AND RECENT CONSISTENCY IN SHORT TERM GUIDANCE
VS 24 HOURS AGO...SO ABLE TO INCREASE CONFIDENCE FOR THIS PERIOD.
TIGHTENING BAROCLINIC ZONE ACROSS SRN WI AND ADJOINING STATES SETS
THE STAGE FOR PERIOD OF ISENTROPIC LIFT AND OMEGA THAT CROSSES SRN
WI SUN NGT. CONDENSATION PRESSURE DEFICITS ON 295 THETA SFC QUICKLY
DROP TO LESS THAN 5MB SUN EVENING OVER SRN WI.  STRONGEST LIFT AS
DEPICTED BY LAYER Q-VECTOR CONVERGENCE GRAZES SOUTHWEST WI...CLOSER
TO PASSING 850H LOW PRESSURE CIRCULATION.  850-700 FRONTOGENETICAL
FORCING ALSO PASSES ACROSS SOUTHWEST WI.  ENOUGH LIFT IN PLACE AND
MODEL CONSENSUS TO CONTINUE HIGH POPS SUN NGT FOR A PERIOD OF
ACCUMULATING SNOW OVR MUCH OF SRN WI.  SNOW-LIQUID RATIOS WILL
AVERAGE AROUND 10 TO 1 SO LOOKING FOR SNOWFALL UP TO 3 INCHES IN THE
DODGEVILLE AND DARLINGTON AREAS DIMINISHING TO A TENTH IN THE
NORTHEAST CWA AROUND SHEBOYGAN. LACKING DEEP LAYER OF MOISTURE
COLUMN IN DENDRITIC GROWTH ZONE SO ATMOSPHERE WILL NOT BE QUITE AS
EFFICIENT PRODUCING FLAKES. AS LIFT SLIDES SOUTH OF THE AREA LATER
SUNDAY NIGHT INTO EARLY MORNING...LOSE SOME ICE CRYSTALS FALLING
INTO CLOUD LAYER SO WL CONTINUE TO MENTION CHANCE FOR -ZR TOWARDS
END OF EVENT.

SINCE THE SNOW AND LIGHT GLAZE MAY AFFECT THE MONDAY MORNING
COMMUTE...NEXT SHIFT MAY DECIDE TO ISSUE WEATHER ADVY FOR PARTS OF
THE WEST.

LINGERING LIGHT PRECIP WILL END QUICKLY ON MONDAY AS UPSTREAM SHORT
WAVE RIDGING PUSHES INTO THE WRN GTLAKES.

MONDAY NIGHT THROUGH TUESDAY...CONFIDENCE - HIGH.

SHORT WAVE RIDGE AHEAD OF AMPLIFYING LOW PRESSURE IN THE PLAINS WILL
RESULT IN QUIET CONDITIONS MONDAY NIGHT.  WL DELAY PRECIP RETURN ON
TUESDAY AND CONFINE TO THE SOUTH.  WITH TEMPS WARMING INTO THE
40S...THIS WILL ELIMINATE NEED FOR MENTIONING MIXED PRECIP IN THE
MRNG. AS LOW PRESSURE UNDERGOES CYCLOGENESIS TO THE SOUTHWEST OF WI
ON TUESDAY...STRONG SOUTH WINDS WILL FINALLY TAP INTO DEEPER GULF
MOISTURE.  THIS MOISTURE ADVECTION WILL CONTRIBUTE TO THE INCREASING
CHANCE FOR RAIN LATER IN THE DAY...HOWEVER THE MAIN PERIOD FOR
RAINFALL WILL REMAIN TUE NGT.

TUESDAY NIGHT THROUGH SATURDAY...CONFIDENCE - MEDIUM.

NO SIGNIFICANT CHANGES FROM EARLIER THINKING.  STILL LOOKS LIKE MORE
AMPLIFIED PATTERN SHAPES UP EARLY IN THE PERIOD.  WEAKENING PIECE OF
ENERGY FROM ERN PAC LONG WAVE TROF CROSSES NW CONUS INTO THE NRN
PLAINS ON TUE.  SYSTEM UNDERGOES AMPLIFICATION TUE INTO TUE NIGHT AS
STRONG PIECE OF MID-LEVEL ENERGY UNDERGOES CYCLOGENESIS AS IT
ROTATES THROUGH BASE OF DEEPENING LONG WAVE TROF.  STRONG SOUTHERLY
WINDS AHEAD OF THIS SYSTEM WILL TRANSPORT DEEP MOISTURE RAPIDLY
NORTHWARD.  HENCE MOISTURE WILL BE IN PLACE AS STRONG SHORT WAVE
MOVES NORTHEAST ACROSS SRN WI TUE NGT.  HENCE PERIOD OF RAIN STILL
EXPECTED TUE NGT AND BUMPED UP POPS TO CATEGORICAL.  WL CONTINUE TO
HOLD BACK ON THUNDER MENTION DUE TO LITTLE ELEVATED INSTABILITY.

WARMER AIR SURGES INTO SRN WI ON TUE WITH DAYTIME TEMPS RISING INTO
THE 40S.  CLOUDS AND BREEZY SOUTH WINDS WL NOT ALLOW MUCH OF A TEMP
FALL TUE EVE SO PRECIP WL REMAIN LIQUID.  MOST AREAS SHOULD
RECEIVE BENEFICIAL RAINFALL OF 0.10 TO 0.40 INCH.

DRIER...COOLER AIR QUICKLY RETURNS FOR WED...WRAPPING AROUND SECOND
LOW PRESSURE SYSTEM MOVING ACROSS NRN GTLAKES.  NEED TO KEEP LOWER
CHANCE FOR -RA IN ON WED AS LINGERING UPPER TROF AND EMBEDDED SHORT
WAVES MOVE ACROSS WRN GTLAKES.  COOL AIR GETS REINFORCED WED/WED NGT
AS COLD FRONT MOVES THROUGH THE AREA.  COLDER AIR WILL REMAIN IN
PLACE ON FRIDAY BUT WARMER AIR WL BEGIN TO RETURN OVER THE WEEKEND
AS UPSTREAM LONG WAVE RIDGE BEGINS TO BREAK DOWN.  SOME LIGHT PRECIP
MAY ACCOMPANY THE RETURN OF THE WARMER AIR LATER IN THE WEEKEND.

5 DAY 500H ANOMOLIES BASED ON THE GFS LOOK MORE ENCOURAGING AS LARGE
NEGATIVE ANOMOLY OVER ERN NOAM BEGINS TO BREAK DOWN ALLOWING MORE
ZONAL FLOW OVER THE NRN TIER OF CONUS AROUND APR1.

AVIATION/00Z TAFS/...

PLAN ON LIGHT EASTERLY WINDS TONIGHT WITH MID LEVEL CLOUDS SPREADING
INTO SOUTHERN WI DURING THE EVENING AND LINGERING THROUGH SUNDAY.

RAIN OR SNOW IS EXPECTED TO BEGIN WEST OF MADISON LATE SUNDAY
AFTERNOON AND SPREAD ACROSS ALL OF SOUTHERN WI AS SNOW SUNDAY
EVENING. SNOW WILL TAPER OFF TO FREEZING DRIZZLE EARLY MONDAY
MORNING. MOST OF THE SNOW WILL BE FROM MADISON AND WEST. CHECK OUT
OUR WEBPAGE FOR LATEST EXPECTED SNOWFALL AMOUNTS.

&&

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

$$

UPDATE...REM
TONIGHT/SUNDAY AND AVIATION/MARINE...MRC
SUNDAY NIGHT THROUGH SATURDAY...MBK


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