177
FXUS63 KARX 182008
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
208 PM CST MON NOV 18 2024
KEY MESSAGES
- WIDESPREAD RAIN THROUGH TONIGHT WILL BRING A GENERAL 1-1.5
INCHES, WITH LOCALLY HIGHER AMOUNTS. IT WILL TURN WINDY AS
WELL WITH PEAK GUSTS IN THE 40 TO 45 MPH RANGE POSSIBLE..
- SNOW CHANCES ON WEDNESDAY INTO WEDNESDAY NIGHT, WITH A 50 TO
80% CHANCE OF 0.1 INCHES OR MORE TO OCCUR, WILL BE
ACCOMPANIED BY BREEZY WESTERLY WINDS.
- COOLER TEMPERATURES FROM WEDNESDAY THROUGH THE WEEKEND WITH
HIGHS IN THE MID 30S TO LOW 40S.
DISCUSSION
ISSUED AT 208 PM CST MON NOV 18 2024
WELL ADVERTISED AND DYNAMIC WAVE CONTINUES TO APPROACH THIS
AFTERNOON AS STRONG FORCING AND ANOMALOUSLY STRONG MOISTURE
ADVECTION HAVE LED TO A LARGE PRECIPITATION SWATH. MOST UNSTABLE
CAPE VALUES VIA ENSEMBLE MEANS REALLY GET PINCHED OFF THE FURTHER
NORTH YOU GO SO JUST NOT SEEING MUCH SIGNAL FOR THUNDER.
FORECAST DETAILS APPEAR ON TRACK WITH THIS WARM SECTOR SCENARIO AND
EXPECTED RAINFALL TOTALS HAVE REMAINED SURPRISINGLY CONSISTENT,
GENERALLY IN THE 1 TO 1.5" RANGE. ENSEMBLE PROBABILITIES DROP OFF
OVER THIS RANGE BUT AN OUTLIER SCENARIO /10-20%/ COULD LEAD TO
ISOLATED AMOUNTS CLOSER TO 2 INCHES ACROSS PARTS OF NORTHEAST IOWA
INTO SOUTHERN WISCONSIN. FORWARD PROGRESSION OF PRECIPITATION SHOULD
KEEP IMPACTS TO A MINIMUM, EVEN WITH A FEW RIVER FORECAST MODELS
BRINGING TRIBUTARIES SOUTH OF INTERSTATE 90 INTO ACTION STAGE.
ANOTHER ITEM TO WATCH TONIGHT WILL BE INCREASE IN WIND FIELD AS
PREVIOUSLY MENTIONED WAVE BECOMES MORE NEGATIVELY TILTED. ALREADY
NOTING IMPRESSIVE INCREASES IN LOW LEVEL VAD WIND FIELDS ON WSR88DS
TO THE SOUTH BUT UNSURE HOW MUCH TRUE MIXING WILL ACCOMPANY THIS LOW
LEVEL JET, EVEN WITH IMPRESSIVE WIND SPEEDS /40-60KTS/ A FEW
THOUSAND FEET OFF THE SURFACE. SOME ENSEMBLE MEMBERS HIGHLIGHT THESE
STRONGER WINDS BUT CONFIDENCE IS NOT STRONG ENOUGH FOR WIND RELATED
HEADLINES. COULD CERTAINLY SEE SOME GUSTS IN EXCESS OF 40 MPH SO
WILL HAVE TO BE WATCH THIS TREND AND MIGHT NEED SOME ADDITIONAL
MESSAGING TO CONVEY A POTENTIAL THREAT.
BY TUESDAY MORNING, WAVE WILL BE PASSING BUT ALSO BECOME PHASED WITH
ANOTHER SHORT WAVE DROPPING INTO THE NORTHERN PLAINS FROM SOUTHERN
CANADA. AREA WILL LIKELY BE MORE INTO THE DRY SECTOR WITH CHANCE FOR
SOME DRY TIME AND LIGHTER WINDS. FRONT WILL ALSO BE APPROACHING FROM
THE WEST AND PROVIDE A WIND SHIFT AND CHANGE TO A COLD AIR ADVECTION
REGIME BY LATE DAY.
WEDNESDAY - THURSDAY: NEXT PRECIPITATION CHANCE, SNOW?
THE STORM SYSTEM THAT IS CURRENTLY PRODUCING RAIN AND WIND WILL
WEAKEN AND GET ABSORBED BY THE BIGGER LONGWAVE TROUGH. AS THIS
LONGWAVE TROUGH SHIFTS EASTWARD, IT WILL DEEPEN OVER THE UPPER
MIDWEST. THIS WILL BRING COOLER TEMPERATURES AND GUSTY WEST TO
NORTHWEST WINDS ON WEDNESDAY. WIND GUSTS ON WEDNESDAY ARE FORECASTED
TO BE 20 TO 30 MPH. TEMPERATURES WILL BE COLD ENOUGH THAT ANY
PRECIPITATION THAT DOES FALL WOULD BE SNOW. ACCUMULATIONS WILL BE
POSSIBLE ON GRASSY SURFACES AND HIGHER ELEVATION. WHEN LOOKING AT
HOW MUCH SNOW WE WILL GET, THERE CONTINUES TO BE A GOOD SIGNAL (50
TO 80%) THAT MEASURABLE SNOW (>0.1") WILL BE POSSIBLE ACROSS THE
FORECAST AREA. TOTAL ACCUMULATIONS LOOK TO BE BETWEEN A TRACE TO
AROUND 0.5", HOWEVER THERE IS A LOW CHANCE (10 TO 30%) THAT OVER AN
INCH WILL BE POSSIBLE, MAINLY FOR AREAS NORTH OF I-90. COMPARED TO
THE PREVIOUS FORECAST, THE SNOW SQUALL PARAMETER FROM THE NAM STILL
SHOWS VALUES BETWEEN 1 AND 4 WEDNESDAY AFTERNOON AND EVENING. THERE
CONTINUES TO BE SOME INSTABILITY, UP TO 100 J/KG OF SBCAPE, STEEP
LAPSE RATES, AND GUSTY WINDS. EVEN WITH THE LIGHT SNOW SHOWERS THAT
ARE EXPECTED, THERE REMAINS A GOOD CHANCE THAT REDUCED VISIBILITIES
COULD OCCUR GIVEN THESE CONDITIONS.
FRIDAY - THE WEEKEND: NEAR NORMAL TEMPERATURES, DRIER
AFTER THIS SYSTEM EXITS, RIDGING BUILDS IN, HOWEVER OUR AREA IS
FORECASTED TO BE ON THE EDGE OF THE RIDGE AND MAINTAIN A NORTHWEST
FLOW. WITH THIS FLOW PATTERN, HIGH TEMPERATURES WILL BE IN THE MID
30S TO LOW 40S. HEADING INTO SUNDAY, ENSEMBLE AND DETERMINISTIC
GUIDANCE BEGINS TO SPLIT ON WHAT WILL HAPPEN. THE GEFS FAVORS A
BREAKDOWN OF THE RIDGE AND HAS A SHORTWAVE TROUGH PASS THROUGH THE
AREA. ABOUT 70% OF GEFS MEMBERS FAVOR THIS SOLUTION. OF THOSE 70%,
ABOUT HALF SHOW MEASURABLE PRECIPITATION. THE EPS REMAINS MOSTLY DRY
FOR SUNDAY. BOTH GEFS AND EPS SHOW POTENTIAL FOR AN UNSETTLED
PATTERN NEXT WEEK WITH SCATTERED PRECIPITATION CHANCES.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1143 AM CST MON NOV 18 2024
AS PRECIPITATION SHIELD ADVANCES INTO THE AREA, ALONG WITH
INFLUX OF BOUNDARY LAYER MOISTURE, AVIATION WEATHER CONDITIONS
WILL DETERIORATE THIS AFTERNOON. IN ADDITION, EXPECT SOUTHEAST
WINDS TO INCREASE AS THIS STRONGER WAVE ADVECTS OUR AREA. VFR
CONDITIONS WILL DROP TO FAIRLY WIDESPREAD LIFR WHICH COULD LAST WELL
INTO TUESDAY MORNING. WHILE ENSEMBLE GUIDANCE IS A BIT MORE LEAN
ON LIFR CHANCES (25-40%), UPSTREAM OBSERVATIONS SUGGEST
DIFFERENTLY.
WILL REMAIN RELATIVELY OPTIMISTIC, AS DRY SECTOR WORKS IN
TUESDAY MORNING, THAT CEILINGS WILL IMPROVE SOMEWHAT. HARD TO
PROVIDE DETAIL THAT FAR OUT GIVEN SUCH A DYNAMIC SYSTEM BUT
TRIED TO TREND A DRIER PERIOD WITH SLIGHTLY BETTER CONDITIONS,
EVEN AS WINDS REMAIN RELATIVELY STRONG.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...CECAVA/SHEA
AVIATION...SHEA
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