103
FXUS63 KARX 241735
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1135 AM CST TUE DEC 24 2024
KEY MESSAGES
- CLOUDY AND SEASONABLY MILD FOR MUCH OF THIS WEEK WITH HIGH
TEMPERATURES IN THE 30S AND 40S, LOW TEMPERATURES FRIDAY
THROUGH SUNDAY WILL BE WELL ABOVE NORMAL WITH MOST SPOTS NOT
FALLING BELOW THE FREEZING MARK.
- PRECIPITATION LIKELY (50-70% CHANCE) RETURNS BY LATE THURSDAY
AND FRIDAY WITH RAIN BEING THE PREDOMINANT PRECIPITATION TYPE.
ADDITIONAL PRECIPITATION CHANCES PERSIST THROUGH THE WEEKEND.
DISCUSSION
ISSUED AT 315 AM CST TUE DEC 24 2024
TODAY - CHRISTMAS: CLOUDY WITH MILDER TEMPERATURES
UPPER-LEVEL RIDGING AND SURFACE HIGH PRESSURE WILL BE THE NAME OF
THE GAME FOR TODAY ALLOWING FOR FAIRLY LIGHT SURFACE WINDS
THROUGHOUT THE DAY. HOWEVER, IN SPITE OF THE OVERALL SETUP, GUIDANCE
CONTINUES TO SUGGEST HOLDING ONTO LOW-LEVEL MOISTURE THROUGHOUT THE
DAY WHICH SHOULD KEEP THIS STRATUS DECK IN PLACE ACROSS MUCH OF THE
REGION, ALBEIT A VERY THIN STRATUS. INTERESTING TO NOTE THE VAST
DIFFERENCE IN THE 24.00Z GEFS AND EC FOR CLOUD COVER TODAY WHICH
PAINTS VERY DIFFERENT PICTURES FOR CLEARING WITH THE GEFS FAVORING A
VERY AGGRESSIVE SOLUTION FOR CLEARING OUT SKIES THIS AFTERNOON AS
THE SURFACE HIGH MOVES DIRECTLY OVERHEAD. REGARDLESS, IF ANY SUN
WERE TO PEAK THROUGH IT WOULD HAVE TO BE TODAY AS BOTH THE 24.00Z
GEFS AND EC ENSEMBLE HAVE EVERY SINGLE MEMBER SHOWING 100% SKY COVER
AFTER CHRISTMAS.
AS FAR AS CHRISTMAS DAY IS CONCERNED, BEHIND THIS SUBTLE RIDGING A
WEAK SHORTWAVE QUICKLY SWINGS THROUGH THE AREA WHICH COMBINED WITH
THE LOW-LEVEL MOISTURE ALREADY IN PLACE MAY BE ENOUGH TO BRING SOME
DRIZZLE TO PORTIONS OF THE AREA, PRIMARILY SOUTH OF I-90. THERMAL
PROFILES AT DECORAH IN THE 24.03Z RAP KEEPING SURFACE TEMPERATURES
RIGHT NEAR FREEZING WITH INCREASING LOW-LEVEL SATURATION FROM THE
SURFACE TO AROUND 3KFT DURING THE EVENING, SO IF SURFACE
TEMPERATURES TREND AT OR BELOW FREEZING CANNOT RULE OUT SOME
LOCALIZED FREEZING DRIZZLE DURING THE EVENING AND OVERNIGHT HOURS ON
CHRISTMAS. HOWEVER, THE JOINT PROBABILITIES FOR MEASURABLE QPF AND
FREEZING SURFACE TEMPERATURES IN THE RECENT GRAND ENSEMBLE
(GEFS/EC/CANADIAN ENSEMBLE) REMAIN LOW (0-20% CHANCE) DURING THE
OVERNIGHT. OTHERWISE, TEMPERATURES FOR CHRISTMAS WILL BE SLIGHTLY
ABOVE NORMAL IN THE BROADER UPPER-LEVEL RIDGING REGIME WITH HIGHS
GENERALLY IN THE UPPER 20S TO UPPER 30S AREAWIDE.
THURSDAY - SUNDAY: PRECIPITATION CHANCES RETURN
THE UPPER-LEVEL PATTERN BEGINS TO SHIFT MORE SUBSTANTIALLY HEADING
INTO THURSDAY WITH A SHORTWAVE TROUGH EJECTING FROM THE SOUTHERN
ROCKIES AND INTO THE TEXAS PANHANDLE. AS THIS OCCURS, THE
AFOREMENTIONED BROADER RIDGE WILL PUSH EASTWARD SUBJECTING OUR
REGION TO FAIRLY ROBUST SOUTHWESTERLY FLOW. ADDITIONALLY, WARM AIR
ADVECTION WILL NUDGE OUR TEMPERATURES FURTHER ABOVE NORMAL FROM
THURSDAY AND INTO THE WEEKEND WITH MEDIAN HIGH TEMPERATURES IN THE
24.00Z GRAND ENSEMBLE (GEFS/EC/CANADIAN ENSEMBLE) PUSHING HIGHS INTO
THE 40S AREAWIDE FROM FRIDAY THROUGH SUNDAY. WITH THE AFOREMENTIONED
PERSISTENT CLOUD COVER IN PLACE, OVERNIGHT LOW TEMPERATURES WILL NOT
FALL MUCH WITH THE 23.12Z EFI HAVING WARM LOWS ON SATURDAY IN THE
UPPER PERCENTILES OF MODEL CLIMATOLOGY WITH CURRENT FORECAST ONLY
HAVING OVERNIGHT LOWS IN THE MIDDLE TO UPPER 30S.
ADDITIONALLY, WITH UPPER-LEVEL SOUTHWESTERLY FLOW IN PLACE, SEVERAL
SHORTWAVE TROUGHS MEANDER THEIR WAY NORTHBOUND TOWARDS THE REGION.
THE FIRST OF THESE SHORTWAVES APPROACHES THE REGION FOR FRIDAY WITH
ANY PRECIPITATION LIKELY BEING IN THE FORM OF RAIN GIVEN THE
AFOREMENTIONED TEMPERATURES. STILL QUITE A LOT OF QUESTIONS WITH
HOW THIS WAVE WILL AMPLIFY AND IF IT WILL GET ABSORBED INTO THE
LARGER PARENT TROUGH TO ITS NORTHWEST. REGARDLESS, FAIRLY HIGH
PROBABILITIES (50-80%) IN THE 24.00Z GRAND ENSEMBLE REMAIN FOR AT
LEAST 0.1" OF QPF ACROSS THE AREA THROUGH SATURDAY MORNING WITH THE
90TH PERCENTILE SHOWING SOME LOCALIZED AREAS OF UP TO 0.5". AS WE
GET INTO THE WEEKEND, ADDITIONAL PRECIPITATION CHANCES REMAIN
(20-50%) WITH THE GLOBAL DETERMINISTIC MODELS (GFS/EC/CANADIAN)
SHOWING ADDITIONAL SHORTWAVES PIVOTING AROUND A BROADER UPPER-
LEVEL TROUGH DRAPED ACROSS THE CENTRAL CONUS. HOWEVER, THE
DETERMINISTIC MODELS AT THIS POINT BEGIN TO DEVIATE MORE
SIGNIFICANTLY WITH HOW THESE SHORTWAVES PROGRESS THROUGH SO WILL
KEEP PRECIPITATION CHANCES ON THE LOWER SIDE IN ACCORDANCE WITH
THE NBM AT THIS MOMENT, BUT WOULD EXPECT SOME LINGERING
PRECIPITATION THROUGH THE WEEKEND DEPENDING ON HOW THE OVERALL
UPPER-LEVEL PATTERN RESOLVES.
NEXT WEEK:
AS WE MOVE TOWARDS THE NEW YEAR, GLOBAL MODELS GENERALLY AGREE ON
MOVING THIS WEEKEND TROUGH MESS EASTWARD ALLOWING FOR ANOTHER TROUGH
TO EJECT OUT OF THE CENTRAL ROCKIES AND MOVE THROUGH QUASI-ZONAL
FLOW. THIS FAR OUT PREDICTABILITY IN GUIDANCE DECLINES SHARPLY.
HOWEVER, CLUSTER ANALYSIS GENERALLY AGREES ON THE PRESENCE OF THIS
SYSTEM FOR MONDAY/TUESDAY WITH THE INTENSITY AND EXACT POSITION
WILL HAVE LARGE IMPLICATIONS FOR ANY LOCAL IMPACTS. REGARDLESS,
THERE IS A FAIRLY STRONG CONSENSUS IN THE 24.00Z GRAND ENSEMBLE
THAT TEMPERATURES WILL COOL DOWN TO BRING IN THE NEW YEAR WITH
MEDIAN HIGH TEMPERATURES AT LA CROSSE FALLING BACK TO NEAR
AVERAGE AT THE VERY LEAST TO START 2025.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1130 AM CST TUE DEC 24 2024
A BROAD STRATUS DECK WILL REMAIN ACROSS MUCH OF THE REGION
THROUGH THIS TAF PERIOD WITH LOW-END MVFR TO IFR CONDITIONS
EXPECTED. THE MOST LIKELY PERIOD OF MVFR THROUGH THIS PERIOD
WILL BE DURING THE DAYLIGHT HOURS, WITH NOCTURNAL REDUCTIONS IN
FLIGHT CATEGORIES TO IFR/LIFR. THERE ARE LOW CHANCES (20 TO 40%)
FOR FOG DEVELOPMENT WEST OF THE MISSISSIPPI RIVER LATE TONIGHT,
WHICH COULD IMPACT RST BY CHRISTMAS MORNING (40%). HOWEVER, IF
FOG DOES NOT DEVELOP IFR TO LIFR CEILINGS ARE EXPECTED ACROSS
THE REGION, LINGERING THE LONGEST ON CHRISTMAS WEST OF THE
MISSISSIPPI. WINDS WILL REMAIN LIGHT FROM THE SOUTHEAST AROUND 5
TO 10KTS.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...NAYLOR
AVIATION...JAW
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