709
FXUS63 KARX 011710
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1110 AM CST SAT MAR 1 2025
KEY MESSAGES
- MORE SEASONABLE TODAY WITH DAYTIME HIGH TEMPERATURES IN THE
20S.
- LOW PRECIPITATION CHANCES MONDAY.
- HEAVY RAIN AND SNOW LIKELY TUESDAY AND WEDNESDAY. VERY MOIST
AIR WILL BRING SIGNIFICANT RAINFALL WITH A NARROW HEAVY SNOW
BAND TO FOLLOW THROUGH WEDNESDAY MORNING. LOCATION AND AMOUNTS
REMAIN UNCERTAIN AT THE LONGER FORECAST HOUR.
DISCUSSION
ISSUED AT 339 AM CST SAT MAR 1 2025
SEASONABLE TODAY, WARMING INTO EARLY NEXT WEEK:
THE LOW LEVEL COLD AIR RESPONSIBLE FOR YESTERDAY'S STRONG WINDS
HAS SETTLED INTO THE UPPER MISSISSIPPI RIVER VALLEY THIS
MORNING. EXPECT THE COLD TO STAY PUT THROUGH TODAY RESULTING IN
THE RETURN OF MORE SEASONABLE TEMPERATURES WITH DAYTIME HIGHS IN
THE 20S. WILL BE NOTICEABLE AS IT'S BEEN ABNORMALLY WARM SINCE
LAST SUNDAY.
LOW LEVEL WARM AIR ADVECTION MOVES WEST TO EAST LATE TONIGHT
FROM AN AMPLIFIED UPPER LEVEL RIDGE EXTENDING FROM CALIFORNIA'S
CENTRAL VALLEY THROUGH THE CANADIAN ROCKIES ON GOES WATER VAPOR
IMAGERY EARLY THIS MORNING. THE WARMEST TEMPERATURES REMAIN JUST
OFF TO OUR WEST THROUGH SUNDAY AS THE UPPER LEVEL RIDGE AXIS FLATTENS
AS IT PROGRESSES SOUTHEAST THROUGH THE UPPER MISSISSIPPI RIVER
VALLEY (EPS/GEFS/CMC). THE UPSTREAM LOW LEVEL WARM AIR ADVECTION
WILL BE ENHANCED BY A STUNTED ATMOSPHERIC RIVER IN THE CENTRAL
PLAINS.
EVENTUALLY, THE EASTERLY PROPAGATING WARM AIRMASS REACHES
WESTERN PERIPHERAL COUNTIES IN SOUTHEAST MINNESOTA AND NORTHEAST
IOWA THROUGH MONDAY MORNING AND THE MISSISSIPPI RIVER VALLEY
THROUGH THE AFTERNOON. AS A RESULT, DAYTIME HIGH TEMPERATURES
EXPECTED TO NEAR 50 DEGREES IN OUR WESTERN COUNTIES TO NEAR 40
IN OUR NORTHERN COUNTIES.
INITIAL PRECIPITATION CHANCES MONDAY:
A LOW PRESSURE SYSTEM OFF THE SOUTH CALIFORNIA COAST ON GOES
WATER VAPOR IMAGERY EARLY THIS MORNING PROGRESSES THROUGH THE
DESERT SOUTHWEST TODAY AND THE CENTRAL PLAINS SUNDAY. GLOBAL
FLOW PUSHING THE RIDGE AXIS SOUTHEAST MOSTLY SHUNTS AND WEAKENS
THIS LOW OFF TO THE SOUTHEAST THROUGH MONDAY. LONG TERM ENSEMBLE
PROBABILISTIC TRENDS WITHIN/BETWEEN MODELS HAVE MORE RAPIDLY
WEAKENED THIS WAVE, DECREASING CONFIDENCE FOR PRECIPITATION
LOCALLY COMPARED TO PREVIOUS FORECASTS.
LONG TERM GLOBAL ENSEMBLE MEMBER SOUNDINGS AND ASSOCIATED
DETERMINISTIC MODELS SUGGEST LOW LEVEL DRY AIR LIMITING OVERALL
SATURATION. THE RESPONSIBLE DRY AIR PLUME CAN BE SEEN ON POES
DERIVED LOW LEVEL DEWPOINT DEPRESSIONS IN A NOSE OF 20 DEGREES
PUSHING INTO NORTHWEST MINNESOTA EARLY THIS MORNING. THIS PLUME
OF DRY AIR WILL BECOME ENTRAINED BETWEEN THE DOWNSTREAM, WRAPPING
LOW AND THE UPSTREAM PROGRESSIVE RIDGE. FURTHERMORE, A LACK OF
OVERALL FORCING WITH TRANSIENT ISENTROPIC MID-LOW LEVEL UPGLIDE
NOT EXPECTED TO BE ENOUGH FORCING INITIALLY UNTIL FRONTOGENESIS
LOBES PASS BY.
HAVE KEPT NBM FOR PROBABILITY OF PRECIPITATION GRIDS WHICH
ADVECT SLIGHT CHANCES FROM SOUTHWEST TO NORTHEAST THROUGH THE
DAY. THE MORE SOUTHERN LOCATION TO THE WEAKENING MID LEVEL WAVE
MEANS HIGHEST PROBABILITY LOCALLY FOR PRECIPITATION LIES ALONG
OUR SOUTHERN PERIPHERY FROM NORTHEAST IOWA INTO SOUTHWEST
WISCONSIN.
MIDWEEK PRECIPITATION CHANCES:
SHORTLY THEREAFTER, A DEEPENING AND WELL AMPLIFIED UPPER LEVEL
TROUGH REJOINS MEAN UPPER LEVEL FLOW OVER THE UPPER MISSISSIPPI
RIVER VALLEY. THE UPPER LEVEL TROUGH CAN BE SEEN ON GOES 18
UPPER LEVEL WATER VAPOR IMAGERY EARLY THIS MORNING, CHURNING IN
THE NORTHEASTERN PACIFIC, CAUSING A NARROW ATMOSPHERIC RIVER
ALONG THE PACIFIC NORTHWEST. THE TROUGH UNDERGOES A FEW CHANGES
AS IT PROGRESSES THROUGH THE WESTERN CONUS AS A NORTHERN AND
SOUTHERN JET STREAK ON GOES 18 DERIVED WINDS CAUSE CLOSING OF
THE LOW OVER THE DESERT SOUTHWEST AND EVENTUALLY REUNIFICATION
WITH THE MEAN UPPER LEVEL FLOW THROUGH MIDWEEK. DUE TO THE
CHANGING NATURE OF THE LOW, MANY SOLUTIONS REMAIN POSSIBLE WITH
ANY VARIABLE CHANGE.
THE LOW UNDERGOES RAPID PHASING OVER THE UPPER MISSISSIPPI RIVER
VALLEY WITH WIDESPREAD, STRONG AGEOSTROPHIC ASCENT OVER THE
FORECAST AREA WEDNESDAY. CURRENT PROGRESSION AND LOCATION OF
THE LOW LIFTING FROM THE MISSOURI RIVER VALLEY THROUGH THE
UPPER MISSISSIPPI RIVER VALLEY MEANS THE TIGHTENING WARM SECTOR
WILL INITIALLY CAUSE RAIN AS PRECIPITATION TYPE BEFORE THE
FREEZING ISOTHERM AND POTENTIAL DEFORMATION BAND MOVES
NORTHWEST TO SOUTHEAST. WILL BE VERY MOIST WITH MORE THE 90TH
PERCENTILE (SPC CLIMATOLOGY) PRECIPITABLE WATER VALUES NEAR
0.5" (GEFS/EPS) FUELED BY A MIDWEST ATMOSPHERIC RIVER.
GIVEN THE HIGH MOISTURE AND FROZEN GROUND, FLOODING MAY BE A
CONCERN. THE GEFS AND EPS VARY BETWEEN RAINFALL AMOUNTS AND
LOCATION. THE EPS HAS A MORE RAPID, NORTHERN LIFT TO THE
STRENGTHENING LOW, BRINGING 100% CONFIDENCE FOR 0.5" 24 HOUR QPF
ACROSS THE SOUTHEASTERN HALF OF THE FORECAST AREA. THE GEFS ON
THE OTHER HAND KEEPS A MORE ZONAL ROUTE OF THE SYNOPTIC LOW,
LEAVING 60% CONFIDENCE FOR THE SAME. ALTHOUGH, BOTH ENSEMBLES
HAVE BEEN TRENDING NORTHWEST FOR THE INCREASED MOISTURE OVER THE
LAST COUPLE RUNS.
THE SUBSEQUENT CHANGE IN PRECIPITATION TYPE AS THE FREEZING ISOTHERM
ADVECTS FROM NORTHWEST TO SOUTHEAST BRINGS A HEAVY SNOWFALL CONCERN
WITHIN A POTENTIAL SOUTHWEST TO NORTHEAST ORIENTED DEFORMATION BAND.
A SIGNIFICANT SHIFT FOR POTENTIAL LOCAL IMPACTS HAS OCCURRED
OVER THE LAST COUPLE OF ENSEMBLE RUNS. A QUICKER PROGRESSION OF
THE STRONG LOW HAS BROUGHT THE HEAVIEST BAND, 25TH-75TH OF
4"-10" FARTHER SOUTHWEST INTO THE FORECAST AREA. THE ENS HAS
BEEN LOCKED IN ON THIS SOLUTION WITH 0.5" PER HOUR (10:1 SLR)
OVER LA CROSSE COUNTY WHILE THE GEFS AND GEPS ARE STARTING TO
COME IN LINE WITH THIS SOLUTION. CURRENT TIMING WOULD BE EARLY
WEDNESDAY MORNING.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1108 AM CST SAT MAR 1 2025
VFR CONDITIONS EXPECTED ACROSS THE TERMINALS FOR THE NEXT 24 HOURS.
GUSTS OUT OF THE NORTH/NORTHWEST WILL CONTINUE TO FALL OFF OVER THE
NEXT HOUR OR TWO WITH SUSTAINED WINDS AROUND 10 KTS EXPECTED THROUGH
THE AFTERNOON BEFORE DECREASING AFTER SUNSET. WINDS WILL QUICKLY
BACK TO THE SOUTH OVERNIGHT AROUND 06Z BUT SPEEDS SHOULD REMAIN
LIGHT AT AROUND 5 KTS. WINDS MAY PICK UP AGAIN TO NEAR 10 KTS
OUT OF THE SOUTH FOR THE KRST TERMINAL BY MID TOMORROW MORNING.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...JAR
AVIATION...BARENDSE
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