141
FXUS63 KARX 230435
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1035 PM CST SUN DEC 22 2024
KEY MESSAGES
- FREEZING DRIZZLE AND LIGHT SNOW WILL LIKELY OCCUR LATE TONIGHT
INTO EARLY MONDAY AFTERNOON. WHILE AMOUNTS WILL BE LIGHT,
CONFIDENCE HAS INCREASED (60%) THAT FREEZING DRIZZLE WILL
AFFECT THE MORNING COMMUTE ALONG AND NORTHEAST OF I-94 AND
ALONG I-90 EAST OF THE MISSISSIPPI RIVER.
- WARMER TEMPERATURES IN THE 30S AND POTENTIALLY EVEN THE 40S
RETURN OVER THE NEXT 7 DAYS.
UPDATE
ISSUED AT 927 PM CST SUN DEC 22 2024
TRICKY FORECAST CONTINUES FOR OVERNIGHT AND EARLY MONDAY. WHILE
NO HEADLINE CHANGES ARE PLANNED AT THE MOMENT, CONFIDENCE IS
STILL WAVERING ON HOW POSSIBLE FREEZING DRIZZLE MAY WORK OUT
OVERNIGHT INTO MONDAY MORNING. OFTEN A TOUGH FORECAST TO
DETERMINE, BUT WE ARE CERTAINLY TAKING INTO ACCOUNT POTENTIAL
FOR IMPACTS MONDAY MORNING WITH HOLIDAY TRAVELERS AND SUCH. GOOD
THING IS MOST SCHOOLS ARE CLOSED.
TEMPERATURES CONTINUE TO WARM THIS EVENING WITH READINGS ABOVE
FREEZING UP TO I-90 ALREADY. WITH CONTINUED WARM AIR ADVECTION
OVERNIGHT, SHOULD NOT SEE ANY DROP, ESPECIALLY AS WET BULBS
CONTINUE TO CLIMB TOO. STILL FIGHTING SOME DRY MID LAYERS WITH
PASSING RADAR ECHOES RARELY REACHING THE GROUND.
00Z MODEL GUIDANCE IS DELAYING ADDITIONAL PRECIPITATION A BIT,
AND QUICK LOOK AT ENSEMBLES SUGGEST MAYBE LOWER SIGNALS FOR
FREEZING PRECIPITATION, OR AT LEAST LOWER CONFIDENCE. TRICKY
PART IS IT DOES NOT TAKE MUCH TO CAUSE IMPACTS. LATEST RAP DATA
SUGGESTS THERE IS SOME LOSS OF ICE ADVECTING IN OVERNIGHT WHICH
MIGHT FAVOR DRIZZLE AND CERTAINLY THE ISENTROPIC LIFT FAVORS
EVENTUAL SATURATION. SO, WE WILL SEE HOW IT ALL COMES TOGETHER.
COULD STILL SEE A BRIEF, LIGHT SNOW ACCUMULATION AS SYSTEM MOVES
THROUGH DURING THE DAY MONDAY BUT NOT SURE THERE WILL BE MUCH
IMPACT.
DISCUSSION
ISSUED AT 302 PM CST SUN DEC 22 2024
WINTRY PRECIP OVERNIGHT INTO MONDAY
OVERNIGHT INTO MONDAY, UPPER WAVE, LOCATED OVER MT AS OF 19Z, WILL
ADVANCE EAST-SOUTHEAST TO THE GREAT LAKES, PASSING OVER THE CWA.
AHEAD OF THIS FEATURE, EXPECT LOW LEVEL WAA, CURRENTLY ONGOING, TO
CONTINUE WIT THIS ALSO BRINGING SOME MOISTURE TO THE AREA IN THE
LOW TO MID-LEVELS. WITH QG FORCING HELPING TO GENERATE LIFT AND LOW-
LEVEL UPGLIDE SEEN ON THE 280 AND 285K SURFACES, PRECIP WOULD
SEEMINGLY BE A GOOD BET ACROSS MUCH OF THE AREA. HOWEVER, ISSUE WITH
THE PRECIP EVENT CONTINUES TO BE TROUBLE WITH A DRY AIR INTRUSION
AROUND 700MB, GIVING PROGGED SOUNDINGS, INCLUDING MUCH OF THE 22.12Z
HREF, A BIT OF AN ONION SHAPE WITH A SATURATED DGZ ATOP A DRY LAYER
ATOP SATURATED LOW LEVELS. IN NORTHEAST IOWA AND ADJACENT AREAS OF
MN AND WI, THIS DRY AIR WILL LIKELY EAT INTO BOTH THE ICE
INTRODUCTION ZONE ALOFT AND THE NEAR-SURFACE MOIST LAYER TO PREVENT
MUCH PRECIP FROM OCCURRING, THOUGH IF IT WERE TO OCCUR, IT WOULD
MAINLY BE FREEZING DRIZZLE. FOR AREAS TO THE NORTHEAST - ROUGHLY
BETWEEN A ROCHESTER TO BOSCOBEL LINE AND I-94 - ICE CRYSTALS WILL
STRUGGLE TO SURVIVE THE FALL WHILE LOW LEVEL MOISTURE DEPTH MAY BE
SUFFICIENT FOR FREEZING DRIZZLE TO OCCUR MORE OFTEN COMPARED TO
AREAS TO THE SOUTHWEST, WITH SURFACE TEMPS RISING ABOVE FREEZING
DURING THE DAY LEADING TO A CHANGEOVER TO STRAIGHT DRIZZLE. FOR
AREAS IN OUR FAR NORTHEAST, THIS INTRUSION WILL BE WEAKER BUT STILL
STRONG ENOUGH TO LEAD TO AN INITIAL PERIOD WITH FREEZING DRIZZLE
BEFORE SNOW BECOMES DOMINANT AFTER SUNRISE AS ICE SLOWLY SATURATED
THE MID-LEVEL DRY LAYER.
UNFORTUNATELY, THE TIMING OF THIS FREEZING DRIZZLE, IF IT OCCURS,
WOULD AFFECT THE MORNING COMMUTE AND AREAS ALONG I-90 EAST OF THE
RIVER AND ALONG I-94. THUS, WHILE CONFIDENCE IN IMPACTFUL FREEZING
DRIZZLE IS LOWER THAN WOULD BE COMFORTABLE, HAVE ISSUED A WINTER
WEATHER ADVISORY COVERING NORTH CENTRAL WI, THE I-94 CORRIDOR, AND
VERNON AND RICHLAND COUNTIES. BUFFALO AND TREMPEALEAU MAY NEED TO BE
ADDED BUT CONFIDENCE IN IMPACTS THERE WAS TOO LOW TO OVERRIDE
COLLABORATION CONCERNS WITH THIS UPDATE. THIS MAY CHANGE THIS
EVENING OR OVERNIGHT AS THE SITUATION EVOLVES.
WARMING UP NEXT WEEK
NEXT WEEK BRINGS A GENERAL TREND TOWARD RISING HEIGHTS ALOFT AND
WARMER TEMPERATURES WITH HIGHS IN THE 40S AND 50S. CHRISTMAS UPPER
TROUGH CONTINUES TO FOCUS POTENTIAL IMPACTS TO OUR SOUTHEAST, SO THE
FORECAST REMAINS FREE OF PRECIP FOR THE 24TH AND 25TH. BEYOND
CHRISTMAS, CONFIDENCE IN DETAILS OF THE UPPER PATTERN BECOMES LOW,
PARTICULARLY WITH A SERIES OF THREE UPPER DISTURBANCES DURING THE
LATTER PART OF THE WEEK, WHERE GUIDANCE SPREAD REMAINS LARGE WITH
BOTH TIMING AND POSITION, WHICH WILL HAVE IMPLICATIONS FOR ANY
PRECIP WITH THESE WAVES. THAT SAID, TEMPERATURES ARE WARM ENOUGH
THAT LREF PROBS FOR SNOW ARE UNDER 5 PERCENT, SO HAVE GONE WITH AN
ALL RAIN FORECAST WHILE STICKING WITH NBM POPS.
AVIATION /06Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 1035 PM CST SUN DEC 22 2024
SEEMINGLY A TOUGH AVIATION FORECAST BUT GIVEN ISENTROPIC LIFT
AHEAD OF APPROACHING WAVE AND GRADUAL SATURATION, EXPECTING VFR
CONDITIONS TO ERODE OVERNIGHT INTO IFR WITH SOME LIFR POSSIBLE,
ESPECIALLY IF PRECIPITATION DEVELOPS. LOWER CONFIDENCE IN HOW
MUCH SATURATION WILL OCCUR, ESPECIALLY AT TAF SITES, BUT
GUIDANCE IS PERSISTENT WITH FAR LOWER CEILINGS FORMING AND THEN
LASTING WELL INTO MONDAY.
NOT SURE HOW WIDESPREAD LIGHT PRECIPITATION WILL BE EITHER SO
USED PROB30 FOR A MORE FAVORED MORNING TIME WINDOW. COULD SEE
SOME WRAP AROUND SNOW AS COLDER AIR RETURNS SO MIGHT SEE A SHORT
WINDOW OF LIGHT ACCUMULATION, AND HENCE LOWER
CEILINGS/VISIBILITIES. BUT THOSE DETAILS WILL HAVE TO BE FINE
TUNED AS IT DRAWS CLOSER.
ARX WATCHES/WARNINGS/ADVISORIES
WI...WINTER WEATHER ADVISORY UNTIL 3 PM CST MONDAY FOR WIZ017-029.
WINTER WEATHER ADVISORY FROM 3 AM TO 3 PM CST MONDAY FOR
WIZ034-041>044-053-055.
MN...NONE.
IA...NONE.
UPDATE...SHEA
DISCUSSION...FERGUSON
AVIATION...SHEA
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