095
FXUS63 KARX 020027
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
627 PM CST SAT FEB 1 2025
KEY MESSAGES
- LIGHT WINTRY MIX POSSIBLE TONIGHT IS STILL POSSIBLE. CHANCES
ARE ABOUT THE SAME AS THIS AFTERNOON (20-30% CHANCE) AND WE
ARE CURRENTLY MONITORING FOR CONDITIONS THAT PROMOTE FREEZING
DRIZZLE FOR LATE EVENING (SERN MN/NERN IA) AND OVERNIGHT (WI).
SEE UPDATE SECTION BELOW.
- WIDESPREAD FOG IS EXPECTED TO DEVELOP OVER SOUTHEAST MN AND
NORTHEAST IA OVERNIGHT WITH SOME DENSE POCKETS AS WELL. A
DENSE FOG ADVISORY CANNOT BE RULED OUT FOR THE SUNRISE HOURS
AND MORNING.
- 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
UPDATE
ISSUED AT 627 PM CST SAT FEB 1 2025
WHILE THE RADAR IS SOMEWHAT ACTIVE AT 6PM/00Z, LOW-LEVEL DRY
AIR HAS BEEN THE WINNER THUS FAR TODAY WITH THE LIFT AND
DYNAMICS WITH THIS WINTER SYSTEM GENERALLY WEAK. FOR THE
OVERNIGHT, WE WILL BE MONITORING FOR THE LOW-LEVELS TO SATURATE
AND DEEPEN, WITH PREDOMINATELY SUPERCOOLED LIQUID DROPS IN THE
0-2KM LAYER AND DRY/NO CLOUD ALOFT. GOES RGB MICROPHYSICS
IMAGERY IS REALLY HELPFUL DEPICTING THE BACK EDGE OF THE HIGHER
LEVEL CLOUD FROM NORTHWEST WI TO NORTHWEST IA AND SLOWLY MOVING
EAST. ONCE THIS LAYER WORKS EAST, THE ICE SOURCE FOR
PRECIPITATION IS MOSTLY GONE. THE GOES IMAGERY ALSO "REVEALS"
THE LOWER CLOUD DECK WELL IN CENTRAL MN INTO NORTHEAST IA...AND
OBSERVATIONS SUGGEST THE CEILINGS ARE ABOUT 2-3KFT. THIS LAYER
IS FORECAST TO DEEPEN AND CEILINGS LOWER AND SHIFT EAST THROUGH
THE EVENING, INCREASING DRIZZLE OR FREEZING DRIZZLE
PROBABILITIES (DEPENDING ON SURFACE TEMPS). CLIMATOLOGY FOR
DRIZZLE SUGGESTS CEILINGS ARE TYPICALLY NEAR OR BELOW 1KFT OR
VISIBILITIES <3MI. THAT HAPPENS OVER SOUTHEAST MN LATER THIS
EVENING FOR A PEAK FREEZING DRIZZLE PROBABILITY PERIOD OF
10PM-3AM ACCORDING TO THE LATEST HRRR/RAP MODELS. THIS SHIFTS
EAST INTO WI OVERNIGHT WITH A PEAK WINDOW OF 12-6 AM.
CONFIDENCE ISNT INCREASING QUITE YET, AND WANT TO SEE LOWERING
CEILINGS IN THE OBSERVATIONS AND PRECIPITATION REPORTS SOMEWHERE
AS THE EVENING WEARS ON. SOME SNOW MAY OCCASIONALLY MIX IN AS
ANOTHER UPSTREAM SHORTWAVE TROUGH IS OVER ABERDEEN SD AND
MOVING IN, WHICH WILL ADD TO THE LIFT BUT ALSO INITIATE
SCATTERED ICE ABOVE THE LOW-LEVEL LAYER.
THIS MOIST LOW-LEVEL LAYER WILL PROMOTE WIDESPREAD FOG OVER
SOUTHEAST MN AND NORTHEAST IA BY SUNRISE WITH POSSIBLY DENSE FOG
POCKETS. A DENSE FOG ADVISORY FOR SOME AREAS THERE CANNOT BE
RULED OUT.
WE HAVE TRIED TO RAISE AWARENESS OF THE FREEZING DRIZZLE THREAT
MUCH LIKE PREVIOUS SHIFTS AND IF WE SEE SOME OF THOSE CONFIDENCE
BUILDERS, WE WILL STEP UP OUR COMMUNICATION OF THE THREAT. WOULD
NOT EXPECT MUCH ICE GLAZING BUT MAYBE ENOUGH TO CAUSE SOME
MINOR TRAVEL PAINS IF IT HAPPENS.
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 /00Z TAFS THROUGH 00Z MONDAY/
ISSUED AT 627 PM CST SAT FEB 1 2025
A CHALLENGING FORECAST ACROSS THE AREA FOR THIS PERIOD WITH DRY
LOW-LEVELS NOW AND VFR, TRANSITIONING TO IFR/LIFR OVERNIGHT AND
THE POSSIBILITY OF SOME LIGHT FREEZING DRIZZLE. OBSERVATIONS
SHOW A 2-3KFT CLOUD DECK FROM SOUTHCENTRAL MN INTO NORTHEAST IA
AND SHIFTING EAST AHEAD OF A LOW-LEVEL TROUGH IN SOUTHERLY FLOW.
OVERNIGHT, AS THE TROUGH APPROACHES, THE LOW-LEVELS WILL
MOISTEN AND DEEPEN BRINGING A TRANSITION TO IFR OR LIFR. THE
LOWEST CEILINGS AND VISIBILITIES WILL BE OVER NORTHEAST IA AND
SOUTHEAST MN TONIGHT WHERE SOME DENSE FOG AND LIFR IS EXPECTED.
THE SIGNALS FOR THIS LIFR/IFR HAS BEEN CONSISTENT IN THE MODEL
FORECASTS AND NBM PROBABILITIES.
WINDS WILL BE ON THE DECREASE OVERNIGHT WITH THE MAX GUSTS
HAVING BEEN REACHED THIS AFTERNOON.
AS THE LOW-LEVELS MOISTEN, AN AREA OF POSSIBLE FREEZING DRIZZLE
WILL TRANSITION ACROSS THE AREA, AT TIMES MIXED WITH LIGHT
SNOW (30% CHANCE AT THIS TIME). ANY ICE ACCUMULATIONS SHOULD BE
MINOR. FOR MORE ON THE FREEZING DRIZZLE CHANCES, SEE THE
UPDATE SECTION ABOVE.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
UPDATE...BAUMGARDT
DISCUSSION...BOYNE/KURZ
AVIATION...BAUMGARDT
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