642
FXUS63 KARX 182327
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
527 PM CST FRI JAN 18 2019
SHORT TERM
(THIS EVENING THROUGH SATURDAY)
ISSUED AT 213 PM CST FRI JAN 18 2019
AN IMPRESSIVE MID-LEVEL FRONTOGENETIC SNOW BAND HAS SET UP THIS
AFTERNOON ALONG THE MN/IA BORDER INTO SOUTHWEST WI PRODUCING
SNOWFALL RATES IN EXCESS OF AN INCH AN HOUR. THIS BAND WILL CONTINUE
TO PIVOT NORTH AND EAST THROUGH THE AFTERNOON. IN ADDITION, BROAD
SYNOPTIC LIFT INCREASING INTO THE EVENING AS THE UPPER TROUGH
EJECTING FROM SD INTERACTS WITH ANOTHER TROUGH COMING OUT OF THE
CENTRAL PLAINS WILL LEAD TO ADDITIONAL SNOW ACROSS MUCH OF THE AREA,
ESPECIALLY SOUTH AND WEST OF INTERSTATE 94. MUCH OF THE HEAVIER
ACCUMULATING SNOW SHOULD END BY AROUND MIDNIGHT. HOWEVER, AS THE
THERMAL PROFILES COOL THIS EVENING, THE DENDRITIC SNOW GROWTH REGION
WILL INCREASE AND EXTEND FROM NEAR THE SURFACE TO 600 MB. THIS MAY
BOOST SNOW RATIOS UP TO 25:1 TONIGHT, WHICH COULD HELP BUMP UP SNOW
TOTALS IN SPOTS A BIT MORE IF REALIZED. LIFT WILL WANE LATER ON
OVERNIGHT AS THE SURFACE WAVE PASSES TO THE SOUTHEAST WITH LIGHT
SNOW GRADUALLY DIMINISHING. THE HEADLINES LOOK TO BE IN GOOD SHAPE
FOR NOW BUT WILL HAVE TO WATCH THE SNOW GRADIENT IN WEST-CENTRAL WI.
A QUIET START TO THE WEEKEND IS ON TAP WITH CLEARING SKIES FROM THE
NORTHWEST AS HIGH PRESSURE NOSES SOUTHEASTWARD FROM CANADA. HIGHS
WILL BE MAINLY IN THE TEENS.
LONG TERM
(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 213 PM CST FRI JAN 18 2019
THERE WILL BE A COUPLE OF SYSTEMS TO WATCH THROUGH THE MIDDLE OF
NEXT WEEK. THE FIRST WILL COME OVER THE WEEKEND WHEN A SHORT WAVE
TROUGH DROPS ACROSS THE REGION IN THE NORTHWEST FLOW ALOFT. THE
GENERAL MODEL CONSENSUS IS THAT THIS SHORT WAVE TROUGH WILL BRING
A ROUND OF WEAK TO POSSIBLY SOME MODERATE PV ADVECTION IN THE 500
TO 300 MB LAYER TO THE AREA ALONG AND WEST OF THE MISSISSIPPI
RIVER LATE SATURDAY NIGHT INTO SUNDAY MORNING. THERE LOOKS TO BE A
BAND OF MODERATE MID-LEVEL FRONTOGENESIS IN THE 750-500 MB LAYER
THAT MOVES ACROSS CENTRAL MINNESOTA INTO EASTERN IOWA. THE CONCERN
WITH THIS SYSTEM IS HOW FAR EAST WILL IT AND THE RESULTING LIGHT
SNOW MAKE IT. IN THE LOW LEVELS, A STRONG AREA OF HIGH PRESSURE
LOOKS TO BE CENTERED OVER ONTARIO JUST TO THE NORTH LAKE SUPERIOR
THAT WILL BE FEEDING DRY AIR IN THE LOW LEVELS INTO THE REGION.
IT LOOKS LIKE THE BULK OF THE LIGHT SNOW FROM THIS SYSTEM SHOULD
MISS THE AREA, WITH THE WESTERN SECTIONS GETTING GRAZED AND WILL
HAVE A SHORT PERIOD OF UP TO 50 PERCENT SNOW CHANCES SUNDAY
MORNING FOR THIS SYSTEM.
THE SECOND AND MORE INTERESTING SYSTEM, LOOKS TO SWING IN FROM THE
SOUTHWEST FOR MONDAY NIGHT AND TUESDAY. A STRONG SHORT WAVE TROUGH
LOOKS TO COME IN FROM THE PACIFIC OCEAN LATE THIS WEEKEND BEFORE
DROPPING INTO THE DESERT SOUTHWEST. THIS WAVE WILL THEN TURN THE
CORNER AND MOVE NORTHEAST WITH A POSITIVE TILT INTO THE MIDDLE OF
NEXT WEEK. DESPITE THE POSITIVE TILT, EARLY INDICATIONS FROM THE
MODELS SUGGEST IT WILL STILL HAVE THE POTENTIAL TO PRODUCE UP TO
SOME MODERATE PV ADVECTION IN THE 500-300 MB LAYER. THE SURFACE
REFLECTION WITH THIS SYSTEM DOES NOT LOOK TO BE ALL THAT STRONG
BECAUSE OF THE POSITIVE TILT OF THE UPPER LEVEL SUPPORT, BUT IT
SHOULD TAKE A TRACK FROM KANSAS TOWARD THE CHICAGO AREA, WHICH
WOULD BE FAVORABLE FOR PLACING THE LOCAL AREA IN THE DEFORMATION
ZONE OF THIS SYSTEM. TOO EARLY FOR SNOW FALL AMOUNTS WITH THIS
SYSTEM BUT WILL BE GOING WITH 80 PERCENT OR HIGHER SNOW CHANCES
WITH THIS SYSTEM FOR MUCH OF TUESDAY.
WIND CHILLS WILL ALSO BE MAKING AN UNWELCOME APPEARANCE FOR THE
NEXT FEW NIGHTS. VALUES OF 10 TO 20 BELOW SATURDAY NIGHT WILL BE
COMMON AND 5 TO 15 BELOW FOR SUNDAY NIGHT. NOT LOW ENOUGH FOR WIND
CHILL HEADLINES, BUT DEFINITELY SOMETHING THAT WILL BE NOTICED
AND NEED TO BE MESSAGED.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 527 PM CST FRI JAN 18 2019
A BROAD AREA OF SNOW CONTINUES TO WORK ACROSS THE REGION,
IMPACTING BOTH LSE AND RST. A NARROW BAND OF HEAVIER SNOW HAS BEEN
AFFECTING THE RST TERMINAL FOR A WHILE NOW, BUT THAT AXIS IS
WEAKENING AND INSTEAD BEING REPLACED BY A LARGER AREA OF MODERATE
TO OCCASIONALLY HEAVY SNOW THAT WILL WORK NORTH TOWARD LSE AS WELL
THE NEXT FEW HOURS. AS SUCH, EXPECT IFR TO LIFR VISIBILITY TO
CONTINUE FOR BOTH LOCATIONS UNTIL SNOW GRADUALLY ABATES IN
INTENSITY THROUGH LATE EVENING. HOWEVER, SOME LIGHT SNOW IS LIKELY
TO LINGER RIGHT ON THROUGH THE NIGHT, THOUGH WITH VISIBILITY AND
CEILINGS EXPECTED TO IMPROVE TO MVFR LEVELS FOR MOST LOCATIONS BY
OR JUST AFTER 06Z BEFORE ENDING TOWARD OR AFTER SUNRISE AS SKIES
CLEAR OUT WITH MUCH DRIER AIR ARRIVING IN THE WAKE OF OUR
DEPARTING STORM. LOOK FOR WINDS FROM THE NORTH TO NORTHEAST 10
KNOTS OR LESS SHIFTING NORTHERLY 10-15 KNOTS THROUGH THE DAY ON
SATURDAY.
ARX WATCHES/WARNINGS/ADVISORIES
WI...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR WIZ053>055-061.
WINTER WEATHER ADVISORY UNTIL 6 AM CST SATURDAY FOR WIZ041>044.
MN...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR MNZ086-087-
094>096.
WINTER WEATHER ADVISORY UNTIL 6 AM CST SATURDAY FOR MNZ079-088.
IA...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR IAZ008>011-018-
019-029-030.
SHORT TERM...JM
LONG TERM...04
AVIATION...LAWRENCE
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