559
FXUS63 KARX 172339
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
539 PM CST SUN NOV 17 2024
KEY MESSAGES
- A STRONG WEATHER SYSTEM WILL BRING 1-1.5 INCHES OF RAIN MONDAY
AFTERNOON INTO TUESDAY MORNING TO THE AREA AND POTENTIALLY
WIND GUSTS OF 35 TO 40 MPH MONDAY NIGHT. WORST CASE SCENARIO
RAINFALL AMOUNTS SEEM TO BE IN THE 2-2.25" RANGE WITH A
PREFERENCE IN SOUTHWEST WI.
- COOLER TEMPERATURES MOVE IN MID WEEK, WITH CHANCES (40-60%)
FOR LIGHT RAIN/SNOW SHOWERS ACROSS THE AREA. COOLER (BUT SEASONAL)
CONDITIONS CONTINUE INTO THE WEEKEND.
DISCUSSION
ISSUED AT 256 PM CST SUN NOV 17 2024
MONDAY AND TUESDAY'S RAIN AND WIND FORECAST:
EARLY THIS AFTERNOON SKIES WERE CLEARING OVER MUCH OF MN/WI AS
CANADIAN LOW PRESSURE SHIFTS AWAY FROM THE AREA. A MORE MOIST
AIRMASS AND SOUTHWESTERLY FLOW REMAINS NEAR A SURFACE FRONTAL
BOUNDARY FROM OKLAHOMA INTO NORTHERN IL. SOME LINGERING MID-HIGH
CLOUD WILL SHIFT OUT OF THE AREA INTO THE EVENING MAKING FOR A
MAINLY CLEAR SKY TONIGHT. 19Z GOES WATER VAPOR DEPICTS THE DEEP AREA
OF LOW PRESSURE OVER THE GULF OF CALIFORNIA WITH THE SOUTHWEST FLOW
AHEAD OF IT ROOTED IN THE SUB-TROPICS. PRECIPITABLE WATER VALUES IN
THE MOIST AIRMASS OVER KS/OK/MO WERE IN THE 1" RANGE PER 17.12Z
UPPER AIR SOUNDINGS AND GOES ESTIMATES WERE CLOSER TO 1.25"...THUS
THE RAP FORECASTS ARE A BIT HIGH CURRENTLY. SURFACE LOW PRESSURE IS
FORMING NOW NEAR EL PASO TX.
GOES IMAGERY LOOPS SHOW THE TROUGH OVER MEXICO STARTING TO EJECT
NORTHEAST, SHIFTING INTO THE UPPER MISSISSIPPI RIVER VALLEY LATER
MONDAY. GOOD MODEL CONSENSUS REMAINS THAT THIS NEGATIVELY TILTED
TROUGH WILL BRING NEAR RECORD PRECIPITABLE WATER /1.25-1.50"/
NORTHWARD MONDAY, PEAKING IN THE LATE EVENING HOURS. THIS MOISTURE
STREAM IS CO-LOCATED WITH A STRONG 850MB MOISTURE TRANSPORT
CONVERGENT SURGE IN THE EVENING HOURS, WHEN PRECIPITATION RATES WILL
BE MAXIMIZED. THIS ALL IN CONCERT WITH INCREASING QG FORCING ALOFT.
THUS, CONFIDENCE IS HIGH IN RAIN SPREADING NORTH DURING THE DAY
MONDAY.
RAINFALL AMOUNTS THROUGH TUESDAY NOON HAVE REMAINED STABLE FOR THE
MOST PART WITH GOOD CONSENSUS ON 1-1.5", ALTHOUGH THE 17.12Z HREF
GUIDANCE SUGGESTS THERE MAY BE A PREFERENCE OF HIGHER AMOUNTS TOWARD
2" IN SOUTHWEST WI AND FAR NORTHEAST IA. THIS IS IN AN AREA OF RAP
FORECAST NON-ZERO MUCAPE AND TOWARD THE HIGHER INCOMING PRECIPITABLE
WATER SOURCE. THE 17.12Z HREF PMM SUGGESTS 1.5-1.75", WITH A MAX IN
THE 2-2.25" RANGE, IN THAT SAME AREA. THIS MATCHES THE NBM 90TH
PERCENTILE WELL WHICH SUGGESTED ~2". ONE LIMITING FACTOR TO AMOUNTS
MUCH OVER 2" IS THAT THE SYSTEM IS PROGRESSIVE. THE 17.00Z ECMWF
ENSEMBLE EFI/SOT SUGGESTS THE ANOMALOUS RAINFALL AMOUNTS HAVE
STRONGER SIGNAL WEST OF THE AREA. THUS, AMOUNTS OF 2-2.5" SEEM TO BE
A GOOD WORST CASE SCENARIO. WOULD EXPECT WITHIN BANK RIVER RISES,
WITH THE POTENTIAL FOR SLIGHTLY GREATER RIVER RISES IN SOUTHWEST WI
/KICKAPOO/. THE MORNING RIVER FORECASTS DID HAVE THE KICKAPOO IN
ACTION STAGE (PRE-FLOOD). WITH MINIMAL CAPE AND WHAT APPEARS TO BE
ALL WARM CONVECTIVELY UNSTABLE CLOUD, THUNDER IS NOT IN THE
FORECAST.
WITH THE LOW PRESSURE TRACKING INTO NORTHWEST IA MONDAY NIGHT, THE
SURFACE PRESSURE GRADIENT IS ENHANCED WITH THE LOW-LEVEL WIND FIELD
INCREASING AND GUSTING. THE 17.12Z HREF 925MB WIND FIELD SHOWS AN
AXIS SHIFTING THROUGH DURING THE EVENING AND OVERNIGHT FROM
SOUTHWEST TO NORTHEAST OF 30-50% PROBABILITIES OF GREATER THAN 45
KTS AT 925MB...HIGHEST NORTHEAST OF LA CROSSE. THE HREF ALSO HAS 60-
70% PROBABILITIES FOR OVER 45 MPH SURFACE WIND GUSTS IN THAT AXIS
SHIFTING THROUGH...WHICH SEEMS HIGH. THE SOUNDINGS FROM THE HREF
MEMBERS ARE BI-MODEL IN THEIR BOUNDARY LAYER STABILITY - SOME
UNSTABLE AND MIXED (GUSTY!) AND OTHERS STABLE IN THE RAIN. THERE IS
A MODERATE SURFACE PRESSURE RISE/FALL COUPLET, BUT HAVE SEEN
STRONGER. THUS, CONFIDENCE IN THE WIND GUST POTENTIAL MONDAY NIGHT
IS LOWER, BUT DID INCREASE THE GUSTS A BIT AND THINK THAT
NORTHCENTRAL WI SEEMS TO HAVE THE BETTER GUST >45 MPH POTENTIAL.
ADDITIONAL LIGHT RAIN/SNOW SHOWERS WEDNESDAY, COOLER MID TO
LATE WEEK:
RAIN WILL CONTINUE TO EXIT TO THE NORTH THROUGH EARLY TUESDAY, WITH
GUIDANCE SUGGESTING A LULL/DRIER CONDITION FOR LATE TUESDAY. WHILE
WINDS MIGHT WEAKEN SLIGHTLY, GUSTY CONDITIONS SHOULD CONTINUE FOR
TUESDAY. MODEL GUIDANCE SHOWS THE AFOREMENTIONED UPPER LEVEL LOW
MERGING WITH AN INCOMING TROUGH ON TUESDAY AND DEVELOPING INTO A
LARGE UPPER LEVEL LOW. THIS SYSTEM IS THEN FORECAST TO TRACK
ACROSS OUR AREA ON WEDNESDAY AND INTO THE OHIO RIVER VALLEY ON
THURSDAY. MUCH COOLER AIR FILTERS IN FOR WEDNESDAY, WITH
ADDITIONAL LIGHT PRECIPITATION WRAPPING AROUND AND KEEPING
CHANCES IN FOR RAIN/SNOW SHOWERS. WITH THE WARMER GROUND, TIME
OF DAY, AND LIGHT AMOUNTS THINKING IT MIGHT LIMIT ACCUMULATIONS
(PERHAPS A FEW COULD SEE LIGHT ACCUMS ON GRASSY SURFACES). THERE
STILL REMAIN SOME DIFFERENCES BETWEEN MEMBERS OF THE ECMWF AND
GEFS ON THE LOCATION OF SURFACE LOW PRESSURE TO THE EAST, WHICH
IN TURN IS SHOWING SOME IMPACT ON HOW MUCH IF ANY ADDITIONAL
PRECIPITATION CHANCES LINGER INTO THE DAY ON THURSDAY.
OTHERWISE, AS THAT SYSTEM CONTINUES TO PUSH FURTHER EASTWARD
ENSEMBLE SOLUTIONS HINT TOWARDS A RETURN OF DRIER CONDITIONS TO
START THE WEEKEND.
THE COOLER TEMPERATURES, ALBEIT MUCH CLOSER TO NORMAL THAN WE HAVE
BEEN SEEING, LOOK TO REMAIN THROUGH THE END OF THE WEEK AND INTO THE
WEEKEND. HIGHS IN THE MID 30S TO LOW 40S WITH LOWS IN THE 20S TO LOW
30S ARE CURRENTLY FORECAST. THE ADDITION OF CONTINUED GUSTY WINDS
THROUGH AT LEAST THURSDAY MIGHT ADD ON TO MAKE A MUCH COOLER
FEEL.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 534 PM CST SUN NOV 17 2024
PRIMARY AVIATION CONCERN OVER THE NEXT 24 HOURS IS THE
DEGRADATION OF FLYING CONDITIONS AFTER 18Z AS WIDESPREAD RAIN
OVERSPREADS THE AREA. EXPECT CONDITIONS TO DETERIORATE TO IFR
SOUTHWEST TO NORTHEAST DURING THE AFTERNOON, INCLUDING BOTH LSE
AND RST. GIVEN THE LONG LEAD TIME, HAVE TRIED TO BE OPTIMISTIC
ON TIMING BUT USERS SHOULD NOTE THIS WILL PROBABLY FLUCTUATE
OVER THE NEXT 2-3 ISSUANCES. ADDITIONALLY, WHILE LIFR IS
POSSIBLE, PARTICULARLY AFTER 21Z, HAVE ELECTED TO KEEP THINGS
IFR UNTIL CONFIDENCE IN OCCURRENCE AND TIMING INCREASES.
FINALLY, THERE WILL BE A VERY SMALL (5-10%) CHANCE FOR SPORADIC
THUNDER EMBEDDED WITHIN THE RAIN, TOO LOW A POTENTIAL FOR
INCLUSION IN THE TAFS.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...BAUMGARDT/EMS
AVIATION...FERGUSON
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