808
FXUS63 KARX 030312
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1010 PM CDT WED APR 2 2025
KEY MESSAGES
- SHOWERS AND STORMS POSSIBLE (40-60% CHANCE) THIS AFTERNOON
ACROSS PORTIONS OF NORTHEAST IOWA AND SOUTHWESTERN WISCONSIN.
AN ISOLATED STRONG TO SEVERE STORM CANNOT BE RULED OUT WITH
WIND GUSTS OF 40 TO 60 MPH.
- GUSTY WINDS DEVELOP BEHIND A PASSING COLD FRONT THIS AFTERNOON
AND INTO THE EVENING. A WIND ADVISORY IS IN EFFECT FOR
PORTIONS OF NORTHEAST IA FROM 1 PM TO 7 PM FOR WIND GUSTS UP
TO 45 MPH.
- SEASONABLE TO SLIGHTLY BELOW NORMAL TEMPERATURES FOR THURSDAY
AND ONWARD WITH SOME PRECIPITATION CHANCES (20-60%) LATE
FRIDAY AND EARLY SATURDAY.
DISCUSSION
ISSUED AT 117 PM CDT WED APR 2 2025
REST OF TODAY: STORMS THIS AFTERNOON, GUSTY WINDS INTO THIS EVENING
THE OVERALL THREAT FOR ANY STRONG TO SEVERE STORMS ACROSS NORTHEAST
IA AND SOUTHWEST WI HAS BEEN DIMINISHING IN RECENT MODEL RUNS WHICH
HAVE SOME SUBSIDENCE PRESENT THROUGHOUT THE MID-LEVELS THIS
AFTERNOON AND SUGGEST LOW-TOPPED CONVECTION. AS WE HEAD TOWARDS
NOON, A PRE-FRONTAL MID-LEVEL TROUGH WILL SWING NORTHEAST OF THE
REGION, WITH A PRESENT TROWAL WARMING THE 500-700MB LAYER AND THUS
CAPPING THIS LAYER AS WELL. IN ADDITION TO THIS, A STRONG LOW-LEVEL
CAP IS ALREADY PRESENT THIS MORNING AS WARM ADVECTION BEGINS TO PUSH
INTO THE REGION PRIOR TO WARMING SURFACE TEMPERATURES. AS SURFACE
WARMING TAKES PLACE AHEAD OF AN INCOMING COLD FRONT, SEVERAL OF THE
CAMS HAVE THE CAP BREAKING AND ALLOWING FOR CONVECTION TO THE TOP OF
THE SECONDARY CAP AT 500-600MB WHERE OUR EQUILIBRIUM LAYER IS
ROUGHLY 14KFT AS SHOWN IN THE 02.15Z RAP/HRRR. A COUPLE POINTS OF
CONSIDERATION NEED TO BE REALIZED IN ORDER FOR CONVECTION TO
MANIFEST THOUGH. THE FIRST OF THESE IS THAT SURFACE TEMPERATURES
NEED TO WARM QUICKLY OVER THE NEXT COUPLE OF HOURS FROM THE LOW-
LEVEL WARM ADVECTION. IF CLOUD COVER MITIGATES THIS OR THE WARM
ADVECTION IS NOT ROBUST ENOUGH, THE LOW-LEVEL CAP WILL REMAIN IN
PLACE AND CONVECTION SIMPLY WILL NOT OCCUR. SECOND, WITH THE MID-
LEVEL SUBSIDENCE AND STABLE LAYER PRESENT, THE QUESTION IS IF THIS
WOULD SUPPRESS ANY CONVECTION IF THE LIFT IN THE LOW-LEVEL IS NOT
SUFFICIENT.
ASSUMING THAT CONVECTION IS ABLE TO TAKE PLACE, GUSTY TO POTENTIALLY
DAMAGING WIND GUSTS WOULD BE THE PRIMARY THREAT WITH THE 02.15Z
RAP/HRRR HAVING A LOW-LEVEL JET OF 45 TO 65 KTS AND WINDS ATOP THE
EQUILIBRIUM LAYER REACHING 80 TO 100 KTS. AS A RESULT, ANY
SUBSIDENCE WITH THIS CONVECTION COULD MOMENTUM TRANSFER A STRAY 40-60
MPH GUST OR TWO. THIS IS SECONDED BY THE HRRR MACHINE LEARNING
PROBABILITIES (5-10% CHANCE) WHICH ONLY HAVE SEVERE PROBABILITIES
FOR WIND GUSTS IN EXCESS OF 58 MPH. GIVEN THE EQUILIBRIUM LEVELS TOP
OUT AT AROUND 14KFT, THE TOP OF THE CONVECTIVE LAYER WOULD ONLY GET
TO AROUND -5C, AS A RESULT HAIL SEEMS TO BE VERY UNLIKELY AND LIKELY
YOU WOULD NOT SEE ANY LIGHTNING WITH THESE CONVECTIVE CELLS.
THIS MAY CHANGE AS YOU HEAD FURTHER WEST INTO NORTH-CENTRAL IA
WHERE THE DEPTH OF THE CONVECTIVE LAYER IN 02.15Z HRRR/RAP
SOUNDINGS IS SLIGHTLY DEEPER AND MAY BE CONDUCIVE FOR HAIL AND
LIGHTNING PRODUCTION. CANNOT COMPLETELY RULE OUT A WEAK TORNADO
WITH THESE AS 0-3KM CAPE RANGES FROM 100-150 J/KG WITH RESIDUAL
0-1KM SRH AS HIGH AS 200 M2/S2 THAT RAPIDLY DIMINISHES AS THE
COLD FRONT APPROACHES. AS THE COLD FRONT PROGRESSES THROUGH THE
REGION, WE STABILIZE THE LOW-LEVELS QUICKLY AND THUS ENDING ANY
POTENTIAL FOR CONVECTION.
LATER INTO THE AFTERNOON AND EVENING, LOW-LEVEL COLD AIR ADVECTION
WILL AID IN MOMENTUM TRANSFER OF STRONGER LOW-LEVEL WINDS DOWN TO
THE SURFACE AS THEY MIX INTO A 35 TO 50 KT LOW-LEVEL JET. THE
STRONGEST OF THESE WIND GUSTS GENERALLY WILL BE OVER UNSHELTERED
AREAS OF NORTHEAST IA WHERE THE 02.12Z HREF HAS FAIRLY HIGH
PROBABILITIES (40-70%) FOR WIND GUSTS OVER 40 MPH. CONSEQUENTLY,
HAVE CONTINUED THE WIND ADVISORY FOR PORTIONS OF NORTHEAST IA
THROUGH 7PM THIS EVENING.
THURSDAY AND BEYOND: CALMER CONDITIONS WITH COOLER TEMPERATURES
LOOKING TO THE END OF THE WORK WEEK, WIND ADVISORY UNTIL 7 PM CDT
THIS EVENING FOR IAZ008-018-019- 029.THE OVERALL UPPER-LEVEL
FLOW PATTERN FEATURES A BROAD TROUGH SITUATED OVER THE WESTERN CONUS
WITH UPPER-LEVEL RIDGING IN THE EAST AND OUR AREA SQUARELY IN
SOUTHWESTERLY FLOW. SOME WEAK UPPER-LEVEL RIDGING SNEAKS ITS WAY IN
FOR LATE THURSDAY AND FRIDAY ALLOWING IN TEMPERATURES WITH THE
NATIONAL BLEND KEEPING HIGHS ON FRIDAY IN THE LOWER TO MIDDLE 50S
FOR THE AREA, PERHAPS SOME UPPER 50S. AS WE HEAD INTO FRIDAY NIGHT
AND SATURDAY, A NORTHERN STREAM TROUGH PHASES WITH THE
AFOREMENTIONED BROADER WESTERN TROUGH AS A DEVELOPING SURFACE LOW
PROGRESSES NORTHEAST THROUGH THE MID-MISSISSIPPI VALLEY. DEPENDING
ON HOW THESE TWO UPPER-LEVEL FEATURES INTERACT, DETERMINISTIC MODELS
PUSH THE NORTHERN EXTENT OF THE ASSOCIATED DEFORMATION ZONE OF THIS
LOW INTO THE SOUTHERN HALF OF OUR AREA. THE GRAND ENSEMBLE
(GEFS/CANADIAN/EC ENS) DEPICT FAIRLY HIGH PROBABILITIES (50-80%
CHANCE) FOR MEASURABLE PRECIPITATION SOUTH OF I-90 BUT UNLIKELY (10-
40% CHANCE) SEEING MORE THAN 0.1" LATE FRIDAY AND INTO SATURDAY.
OVERALL, DOES NOT LOOK IMPACTFUL BUT IS LIKELY OUR NEXT REALISTIC
SHOT AT ANY PRECIPITATION. AFTER THIS SYSTEM MOVES EAST OF OUR
REGION, A DESCENDING UPSTREAM TROUGH WILL PROVIDE SOME COLD AIR
ADVECTION WHICH WILL PUSH TEMPERATURES BELOW NORMAL FOR SUNDAY AND
INTO MONDAY WITH HIGHS IN THE 40S TO LOWER 50S SOUTH OF I-94 WITH
SOME UPPER 30S FOR HIGHS ON MONDAY IN NORTH-CENTRAL WI. CANNOT RULE
OUT SOME SNOW SHOWERS (15-25% CHANCE) AS IT PASSES OVERNIGHT SUNDAY
AND ON MONDAY MORNING BUT STILL QUITE A BIT OF UNCERTAINTY AMONGST
DETERMINISTIC AND ENSEMBLE GUIDANCE AS TO HOW MUCH MOISTURE WILL BE
PRESENT, SO HAVE OPTED TO HOLD WITH THE NATIONAL BLEND FOR
PRECIPITATION CHANCES FOR NOW.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1010 PM CDT WED APR 2 2025
CIGS: MVFR CIGS EXPECTED THROUGH THE NIGHT AND THE BETTER PART OF
THE DAY THURSDAY. SHORT TERM MODELS SCATTER IT OUT THU EVENING AS
WEAK HIGH PRESSURE MOVES OVERHEAD...AND FAVORED THROUGH THU NIGHT.
THAT SAID, A FEW MODELS SUGGEST SOME LOW LEVEL RH COULD LINGER, AND
PERHAPS RE-MANIFEST AS LOW STRATUS THU NIGHT. GOING TO STAY THE
SKC/SCT FOR NOW AND MONITOR.
WX/VSBY: NO IMPACTS EXPECTED.
WINDS: WEST STAYING FAIRLY BREEZY/GUSTY THROUGH THU MORNING. WINDS
WILL BE DIMINISHING BY MID/LATE AFTERNOON THU AS HIGH PRESSURE
STARTS TO INFLUENCE THE REGION. LIGHT NORTH/NORTHEAST THU NIGHT.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...NAYLOR
AVIATION.....RIECK
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