480
FXUS63 KARX 012026
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
226 PM CST SAT FEB 1 2025
KEY MESSAGES
- LIGHT WINTRY MIX POSSIBLE TONIGHT
- TEMPERATURES POTENTIALLY CLIMBING TO NEAR RECORD HIGHS ALONG
AND SOUTH OF INTERSTATE 90 ON SUNDAY
- SNOW BAND LOOKING LIKELY NORTH OF INTERSTATE 90 ON SUNDAY
NIGHT AND MONDAY MORNING
DISCUSSION
ISSUED AT 225 PM CST SAT FEB 1 2025
TONIGHT
A WEAK, BROAD UPPER SHORTWAVE TROUGH IS SHOWING UP ON WATER VAPOR
SATELLITE IMAGERY CUTTING ACROSS SOUTH DAKOTA INTO CENTRAL
MINNESOTA. VORTICITY ADVECTION OUT AHEAD OF THIS FEATURE IS CO-
LOCATED WITH A STRONG LOW LEVEL JET AND ISENTROPIC LIFT, INTERACTING
WITH A FAVORABLE FEED OF INCREASING MOISTURE TO PRODUCE WIDESPREAD
CLOUD COVER ACROSS THE REGION. PWATS WILL CONTINUE TO INCREASE INTO
THIS EVENING, REACHING AROUND 200 PERCENT OF NORMAL OVER OUR
FORECAST AREA TONIGHT. DESPITE THIS, OUR MAIN FORECAST CONUNDRUM
INTO TONIGHT WILL BE SATURATION ISSUES AS THIS SYSTEM MOVES THROUGH,
DICTATING HOW MUCH OF THE AREA ACTUALLY SEES LIGHT PRECIPITATION
AS WELL AS PRECIPITATION TYPES/AMOUNTS.
THE LOW LEVELS ARE QUITE DRY TODAY, ESPECIALLY NORTH OF I-94 WHERE
DEWPOINTS ARE STILL IN THE SINGLE DIGITS. THIS SHALLOW DRY LAYER
SHOULD MOISTEN UP PRETTY QUICKLY BY THIS EVENING PER FORECAST
SOUNDINGS, BUT BY THE TIME THE LOWEST LEVELS FINALLY SATURATE, THE
COLUMN BEGINS TO DRY OUT ABOVE 800MB. THIS WILL LEAD TO ICE
NUCLEATION AND PTYPE FORECAST CHALLENGES. DEPENDING ON THE LOCATION,
RAP/HRRR FORECAST SOUNDINGS SHOW ONLY MAYBE A 2-3 HOUR WINDOW THIS
EVENING WITH SUFFICIENT ICE NUCLEATION TO SUPPORT LIGHT SNOW
REACHING THE SURFACE. THEREAFTER, THE SATURATED LAYER BECOMES TOO
SHALLOW FOR SNOW TO FALL ACROSS MUCH OF THE AREA WHICH WOULD FAVOR
DRIZZLE OR FREEZING DRIZZLE (DEPENDING ON SURFACE TEMPS), UNLESS
TRANSIENT SEEDER-FEEDER PROCESSES WOULD COME INTO PLAY. EVEN NORTH
OF I-94, WHICH WAS LOOKING TO BE THE MOST SLAM-DUNK AREA FOR SNOW
ACCUMULATION, NOW LOOKS TO EVENTUALLY BE IMPACTED BY ICE NUCLEATION
LIMITATIONS AND POTENTIALLY SOME A BRIEF WINDOW OF FREEZING DRIZZLE
AS PRECIPITATION DIMINISHES THROUGH THE PRE-DAWN HOURS.
OVERALL SNOW AMOUNTS LOOK LIGHT, GENERALLY AROUND 1/2 TO 1 INCH
NORTH OF I-94 WITH TRACE AMOUNTS POSSIBLE ELSEWHERE. WARM ADVECTION
OVERNIGHT WILL LEAD TO A GRADUAL RISE IN SURFACE TEMPERATURES FROM
SOUTHWEST TO NORTHEAST. THIS WILL HELP TO LIMIT THE FREEZING DRIZZLE
THREAT, BUT INITIAL WET BULB EFFECTS MAY ALLOW FOR A LIGHT GLAZE OF
ICE TO DEVELOP IN SOME AREAS (MAINLY SOUTH OF I-94) BEFORE SWITCHING
OVER TO JUST AREAS OF DRIZZLE. THESE LIGHT SNOW AND ICE AMOUNTS MAY
LEAD TO SLIPPERY TRAVEL IN SOME AREAS, BUT THE THREAT DOES NOT LOOK
SIGNIFICANT ENOUGH TO WARRANT A WINTER WEATHER ADVISORY AT THIS
TIME. FOR NOW WILL ADVERTISE THE POTENTIAL SLIPPERY IMPACTS VIA AN
SPS AND WILL LET NEXT SHIFT MONITOR NEAR-TERM FORECAST TRENDS AND
OBSERVATIONS THIS EVENING.
SUNDAY
A LOW PRESSURE SYSTEM WILL TRACK ACROSS THE US/CANADIAN
BORDER. A WARM FRONT WILL MOVE THROUGH THE AREA DRY ON SUNDAY
MORNING. WARM AIR ADVECTION WILL CAUSE 925 MB TEMPERATURES TO
WARM INTO THE 0 TO 2C NORTH OF INTERSTATE 94 AND 2 TO 6C
ELSEWHERE. MIXING DOWN THESE TEMPERATURES WOULD RESULT IN
HIGHS IN THE LOWER AND MID-40S NORTH OF INTERSTATE 94 AND FROM
THE MID-40S TO LOWER 50S ELSEWHERE. THESE TEMPERATURES WILL BE
WARM ENOUGH THAT WE COULD APPROACH SOME RECORDS HIGHS ALONG AND
SOUTH OF INTERSTATE 90.
SUNDAY NIGHT INTO MONDAY MORNING
A COLD FRONT WILL MOVE SOUTH ACROSS THE AREA ON SUNDAY EVENING
AS A LOW PRESSURE AREA MOVES ACROSS THE NORTHERN GREAT LAKES
INTO SOUTHERN ONTARIO. AS THE NIGHT PROGRESSES, THE CONVERGENCE
AND FRONTOGENESIS WILL INCREASE ALONG THE 850-700 MB FRONT
NORTH OF INTERSTATE 94. INITIALLY THERE WILL BE VERY DRY AIR
OVER THE AREA, SO MUCH OF THIS INITIAL FORCING WILL GO INTO
SATURATING THE AIRMASS. DURING THE OVERNIGHT AND ON MONDAY
MORNING, THE MODELS ARE IN GENERAL AGREEMENT THAT A SNOW BAND
WILL DEVELOP MAINLY NORTH OF INTERSTATE 90. OVER THE PAST
24-HOURS, THE QPF HAS INCREASED AND BEEN SHIFTING NORTH. THE
01.12Z HREF HAS A NARROW CORRIDOR OF 2 TO 4 INCHES INCHES
(PROBABILITIES OF 15 TO 30 PERCENT) ACROSS NORTH-CENTRAL
WISCONSIN. ELSEWHERE, NORTH OF INTERSTATE SNOW TOTALS RANGE FROM
JUST A DUSTING TO 2 INCHES.
WEDNESDAY NIGHT INTO THURSDAY
THERE CONTINUE TO BE MUCH UNCERTAINTY ON WHETHER THE NORTHERN
AND SOUTHERN STREAMS WILL PHASE OR NOT. IN THE ENSEMBLE MEMBERS
WHICH DO NOT PHASE, WE STAY DRY. THE PRECIPITATION REMAINS NORTH
AND SOUTH OF THE FORECAST AREA. MEANWHILE, IN THE ENSEMBLE
MEMBERS THAT PHASE THE 2 STREAMS, THIS RESULT IN MORE
PRECIPITATION (LIKELY SNOW) FOR THE AREA. DUE TO THESE
UNCERTAINTIES, CONFIDENCE IS LOW ON PRECIPITATION CHANCES AND
AMOUNTS.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1145 AM CST SAT FEB 1 2025
GUSTY SOUTHEAST WINDS AND SOME TRANSIENT MVFR CIGS WILL
CONTINUE THIS AFTERNOON AHEAD OF THE NEXT APPROACHING SYSTEM.
INCREASING LOW LEVEL MOISTURE WILL CAUSE CIGS TO DETERIORATE TO
IFR BY LATE EVENING AND LIKELY TO LIFR AT RST IN THE EARLY
MORNING HOURS. THIS SIGNAL FOR LOW CIGS HAS BEEN CONSISTENT IN
RECENT MODEL RUNS, LENDING HIGHER CONFIDENCE IN IFR TO LIFR
LIKELIHOOD (>60%). THERE IS LOWER CONFIDENCE IN PRECIPITATION
POTENTIAL AS A SYSTEM QUICKLY SWINGS THROUGH THE REGION
TONIGHT. LIFT IS FAVORABLE, BUT THERE ARE QUESTIONS ON HOW
SATURATED THE LOWER ATMOSPHERE WILL BECOME, IMPACTING
PRECIPITATION LIKELIHOOD AT THE TAF SITES AS WELL AS PRECIP
TYPES/AMOUNTS. HIGHEST PRECIP CHANCES (40 TO 70%) LOOK TO
DEVELOP ALONG/EAST OF THE MISSISSIPPI RIVER, SO HAVE INCLUDED
SMALL CHANCES AT LSE. MAY START OUT AS A BRIEF PERIOD OF LIGHT
SNOW BEFORE TRANSITIONING TO DRIZZLE OR FREEZING DRIZZLE,
DEPENDING ON WARMING SURFACE TEMPERATURES. REGARDLESS, PRECIP
AMOUNTS WILL BE VERY MINOR. RST STANDS A RATHER LOW CHANCE OF
ANY PRECIP (<20%) AND DUE TO LOW CONFIDENCE HAVE LEFT MENTION
OUT OF THIS TAF ISSUANCE BUT WILL MONITOR UPSTREAM CONDITIONS
THIS AFTERNOON.
AS THE SYSTEM EXITS EARLY SUNDAY MORNING, WINDS WILL BECOME
LIGHTER OUT OF THE SOUTH TO SOUTHWEST. RESIDUAL LOW LEVEL
MOISTURE MAY ALLOW FOR AREAS OF FOG TO DEVELOP, ESPECIALLY WEST
OF THE MISSISSIPPI RIVER. QUESTIONS ON HOW THICK THIS FOG MAY
DEVELOP OR IF IT MAY JUST MANIFEST AS VERY LOW STRATUS, BUT
HAVE INTRODUCED IFR VSBY AT RST. CIGS AND VSBY SHOULD BEGIN TO
IMPROVE ACROSS THE AREA BY LATE MORNING.
CLIMATE
ISSUED AT 225 PM CST SAT FEB 1 2025
ON SUNDAY, 925 MB TEMPERATURES WILL WARM INTO THE 0 TO 2C RANGE
NORTH OF INTERSTATE 94 AND FROM 2 TO 6C RANGE FOR THE REMAINDER
OF THE AREA. MIXING DOWN THESE TEMPERATURES WOULD RESULT IN
HIGHS IN THE LOWER AND MID-40S NORTH OF INTERSTATE 94 AND FROM
THE MID-40S TO LOWER 50S ELSEWHERE. THESE TEMPERATURES WILL BE
WARM ENOUGH THAT WE COULD APPROACH APPROACH SOME RECORDS HIGHS
ALONG AND SOUTH OF INTERSTATE 90. THE RECORD HIGH TEMPERATURE
FOR LA CROSSE IS 51F IN 2006 AND FOR ROCHESTER IS 48F IN 2012.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...BOYNE/KURZ
AVIATION...KURZ
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