678
FXUS63 KARX 230317
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1017 PM CDT TUE APR 22 2025
KEY MESSAGES
- FREQUENT RAIN AND STORMS THROUGH FRIDAY AND AGAIN EARLY NEXT
WEEK.
- PRIMARY PRECIPITATION AND STORM IMPACTS EXPECTED IN LOCALLY
SOUTHERN COUNTIES OVER THE NEXT COUPLE OF DAYS.
- WIDESPREAD RAIN THURSDAY.
- SEVERE STORM POTENTIAL EARLY NEXT WEEK.
DISCUSSION
ISSUED AT 205 PM CDT TUE APR 22 2025
IN THE WAKE OF THIS MORNING'S STORMS, A WEAK QUASI-STATIONARY
SURFACE BOUNDARY REMAINS DRAPED THROUGH CENTRAL MINNESOTA. MORNING
GOES UPPER LEVEL WATER VAPOR IMAGERY SHOWED A ZONALLY ORIENTED
TRANSIENT THIN, DRY TROUGH AXIS RACING ACROSS THE NORTHERN
PLAINS CAUSING RAPID LIFTING TO THE LOW AND THE ATTACHED
FILAMENT OF MOISTURE. THE STRONGEST LOW LEVEL MOISTURE AXIS
EXTENDS WELL TO THE SOUTHWEST THROUGH THE CENTRAL INTO THE
SOUTHERN PLAINS WITH A 10 TO 20 DEGREE DEWPOINT GRADIENT,
SUBSIDING DRY AIR LEE OF THE ROCKY MOUNTAINS ABUTTING RICH GULF
MOISTURE. A QUASI-REGRESSIVE PATTERN WITH CONFLUENCE BETWEEN
TWO AREAS OF ANTICYCLONIC FLOW AMPLIFIES UPPER LEVEL HEIGHTS
FROM THE CENTRAL INTO THE NORTHERN PLAINS WHICH KEEPS THE
SURFACE BOUNDARY MOSTLY STATIONARY ACROSS THE SOUTHERN HALF OF
THE FORECAST AREA OVER THE NEXT COUPLE OF DAYS.
PRECIPITATION CHANCES TONIGHT:
INITIAL PRECIPITATION CHANCES WILL BE TIED TO THE ELONGATION OF
A CURVED LOW LEVEL MOISTURE AXIS BEING STRETCHED BY PRONOUNCED
SYNOPTIC EASTERLY FLOW. VWPS THROUGH THE CENTRAL PLAINS
COLLOCATE THE LOW LEVEL FRONT WITH EARLY AFTERNOON MRMS,
INCREASING AREAL EXTENT OF A NARROW CORRIDOR OF REFLECTIVITY
EARLY THIS AFTERNOON. MOSTLY WILL SKIRT TO OUR SOUTH TONIGHT
WITH THE AFOREMENTIONED EASTERLY FLOW.
PRECIPITATION & STORM CHANCES OVERNIGHT INTO WEDNESDAY:
SUBSEQUENT PRECIPITATION AND STORM CHANCES INCREASE IN LOCALLY
SOUTHERN COUNTIES FROM NORTHEAST IOWA INTO SOUTHWEST WISCONSIN
OVERNIGHT INTO EARLY WEDNESDAY MORNING. THE NOCTURNAL LOW LEVEL
JET REALLY RAMPS UP MOISTURE TRANSPORT, FLIRTING THE 60 DEGREE
ISODROSOTHERM ALONG OUR DOORSTEP. THE ANTICYCLONIC CURVATURE TO
THE LOW LEVEL JET AND OVERALL EASTERLY FLOW EXPECTED TO SHUNT
STRONGER STORMS AND HEAVIER RAIN ALONG OUR SOUTHERN MOST
COUNTIES AND THEN PARTS EAST. DUE TO HIGHER SHEAR VALUES
REMAINING POSTFRONTAL, A PUSH/PULL OF INSTABILITY OVER THE FRONT
LIMITS STRONG STORM CONCERNS. EXPECT WEAKENING STORMS AS THEY
PROGRESS NORTHEAST THEN EAST AS THEY POTENTIALLY REACH THE WEAK
FRONTAL BOUNDARY. A VERY SHORT, TRANSIENT WINDOW OF ISENTROPIC
UPGLIDE COULD ADVECT STORMS SLIGHTLY FARTHER NORTH BUT
CONFIDENCE IS LOW, SO HAVE KEPT HIGHEST POPS TO THE SOUTH.
NORTHERN EXTENT OF RAIN AND STORMS COULD END UP MORE OF AN IMMEDIATE
TERM FORECAST CONCERN. WHILE A STRONG TO SEVERE STORM CANNOT BE
RULED OUT, NOT OVERLY CONFIDENT AT THE CURRENT HOUR GIVEN AN
OVERALL LACK OF FORCING.
WEDNESDAY STORM POTENTIAL:
THE INSTABILITY AXIS BUILDS THROUGH CENTRAL WISCONSIN ON WEDNESDAY
AS DIURNAL HEATING HELPS ADVECT A NARROW AXIS OF SUFFICIENT
CAPE FROM SOUTHWEST TO NORTHEAST. SIMILAR TO WEDNESDAY MORNING,
FORCING LOOKS QUESTIONABLE AS OVERHEAD AGEOSTROPHIC DESCENT
DOWNSTREAM OF THE RIDGE AXIS IS COLLOCATED WITH ISENTROPIC
DESCENT. THEREFORE, A NARROW AXIS OF STORMS WILL BE POSSIBLE
THROUGH CENTRAL WISCONSIN. LREF CLUSTER ANALYSIS (22.00Z) HAS
HIGH AGREEMENT FOR INITIAL COLLOCATION OF MUCAPE, LIMITED
MUCIN, AND 30KTS OF BULK SHEAR ALONG OUR SOUTHERN HALF OF THE
FORECAST AREA, AGAIN.
ANY DIURNAL HEATING INFLUENCE HINGES ON MORNING STORM COVERAGE
AND TIMING ON EXIT CLOUD COVER. THE BEST LOW LEVEL STRETCHING
AND FORCING MAY BE OVERNIGHT WHICH WOULD LIMIT STORM CONCERNS.
HAVE INCREASED POPS GIVEN THE NARROW CORRIDOR OF STRETCHING. GFS
SUGGESTS SEVERE POSSIBILITY WITH SUFFICIENT 0-3KM SHEAR WHILE
THE ECMWF REMAINS NEAR NIL. WHILE OVERALL IMPACTS AND CONFIDENCE
IS LOW, WEDNESDAY STORMS COULD BE SOMETHING TO KEEP AN EYE ON
IN COMING FORECASTS AS THERE ARE A FEW THINGS TO COME TOGETHER
YET.
WIDESPREAD RAINFALL THURSDAY:
EVENTUALLY THE GLOBAL PATTERN GETS A LITTLE MORE PROGRESSIVE,
DRIVING A SURFACE LOW NORTHEAST ALONG THE LOW LEVEL BAROCLINIC
BOUNDARY THROUGH THURSDAY. THE QUASI-STATIONARY FRONT WON'T
BUDGE THOUGH, PERPETUATING PRECIPITATION THROUGH FRIDAY MORNING
WHEN IT EVENTUALLY SHOVES EAST.
THURSDAY WILL BE THE MOST WIDESPREAD RAIN WITH POTENTIAL STORMS
AS WELL. RAINFALL AMOUNTS WILL BE ABOVE AVERAGE BUT NOT EXTREME
ACCORDING TO 0.7 ECMWF EFI COLLECTED WITH A 1.25" PW THAT IS 2+
STANDARDIZED ANOMALIES ABOVE MODEL GUIDANCE. GLOBAL ENSEMBLE
SPREAD (25-75) SUGGESTS 0.5" TO 1.75" IN 24 HOURS. NOT OVERLY
CONCERNING REGARDING FLOODS. IMPACTS IN SOUTHERN MOST COUNTIES
MAY BE OF HIGHER CONCERN, DEPENDENT ON HOW THE NEXT COUPLE
STORMS SHAKE OUT.
SEVERE STORM POTENTIAL NEXT WEEK:
RAIN AND STORM CHANCES DON'T GO FAR HOWEVER AS A ROCKY MOUNTAIN LOW
QUICKLY FORMS THROUGH THE WEEKEND, SLOWLY LIFTING NORTHEAST THROUGH
THE CENTRAL PLAINS. WHILE CURRENT CONFIDENCE IN LOW PLACEMENT IS
MINUSCULE, EXTENDING FROM CANADA THROUGH THE TEXAS PANHANDLE
(EPS/GEFS), MOST LONG TERM GLOBAL ENSEMBLES SURGE 2000-4000 J/KG
OF CAPE SOMEWHERE FROM THE NORTHERN PLAINS THROUGH THE UPPER
MISSISSIPPI RIVER VALLEY. SPC CONVECTIVE OUTLOOK PLACES US IN A
DAY 7 FOR POTENTIAL SEVERE STORMS.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1015 PM CDT TUE APR 22 2025
VFR CONDITIONS TO CONTINUE FOR THE NEXT 24 HOURS. LIGHT WINDS AT
OR BELOW 10 KTS OUT OF THE SOUTH WILL CONTINUE FOR MUCH OF THE
OVERNIGHT PERIOD BEFORE VEERING TO THE WEST/NORTHWEST BY LATE IN
THE DAY. SHOWERS AND STORMS SHOULD REMAIN SOUTH OF THE
TERMINALS OVERNIGHT WITH ACTIVITY BUILDING NORTH THROUGH THE DAY
TOMORROW. CONFIDENCE ON THE NORTHWARD EXTENT HAS DECREASED SO
HAVE BACKED OFF ON SOME OF THE EARLIER PROB30S. HAVE UPDATED
TIMING WITH LATEST HI-RESOLUTION GUIDANCE BUT FURTHER
ADJUSTMENTS WILL LIKELY NEED TO BE MADE GOING FORWARD. CHANCES
FOR PRECIPITATION INCREASE AFTER 00Z, ESPECIALLY FOR THE LSE
TERMINAL SO CREATED A PREVAILING GROUP FOR THE SHOWERS AND
STORMS THERE.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...JAR
AVIATION...BARENDSE
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