898
FXUS63 KARX 180351
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1051 PM CDT THU APR 17 2025
KEY MESSAGES
- PERIODS OF SHOWERS AND A FEW STORMS WITH STORMS RE-DEVELOPING
OVER SOUTHERN MINNESOTA THIS AFTERNOON (75-95%).
- SHOWERS AND STORMS LIKELY AREAWIDE TONIGHT (70-100%) WITH A
SEVERE THREAT THIS EVENING (ESPECIALLY WEST OF THE MISSISSIPPI
RIVER). SEVERE WEATHER RISK LEVEL 2 OF 5.
- SHOWERS AND A FEW STORMS INCREASING SUNDAY (30-60% SUNDAY
AFTERNOON/60-90% SUNDAY NIGHT)
DISCUSSION
ISSUED AT 153 PM CDT THU APR 17 2025
OVERVIEW:
AT MIDDAY, WATER VAPOR SATELLITE IMAGERY AND HEIGHTS SHOWED A 500MB
RIDGE THE GREAT LAKES TOWARD THE TENNESSEE/LOWER MISSISSIPPI RIVER
VALLEY. THE LONG WAVE MID-TROPOSPHERIC TROUGH STRETCHED FROM
ALBERTA/SASKATCHEWAN SOUTHWEST TOWARD THE SIERRA AND SOUTHERN
CALIFORNIA. THE 15Z SUBJECTIVE SURFACE ANALYSIS HAD A WARM FRONT
OVER CENTRAL IOWA WITH SURFACE LOW PRESSURE OVER SOUTHEAST SOUTH
DAKOTA INTO SOUTHWEST MINNESOTA WITH A TRAILING COLD FRONT INTO
PARTS OF EASTERN NEBRASKA.
SPORADIC MORNING STORMS HAVE FILLED THROUGH THE EARLY THE
AFTERNOON. HASN'T BEEN HIGH CONFIDENCE IMMEDIATE TERM FORECAST
AS THE MAIN AXIS OF INCREASED MOISTURE REMAINS SITUATED
UPSTREAM ORIENTED FROM SOUTHWEST TO NORTHEAST THROUGH THE
MISSOURI RIVER VALLEY. A WEAKER SMEAR OF MOISTURE WITH MID 40
ISODROSOTHERMS ALONG AN AREA OF LOW LEVEL SPEED CONVERGENCE HAS
BEEN MOSTLY RESPONSIBLE FOR THE ONGOING PRECIPITATION AND
STORMS. AN ELEVATED MIXED LAYER WITH AND OFF DECK INVERSION HAS
BEEN LIMITING EXTENT AND INTENSITY OF STORMS LOCALLY. THE
RESULTANT INCREASED CLOUD COVER HAS LIMITED LIFTING OF SURFACE
PARCELS THROUGH DIURNAL HEATING. THEREFORE, VERY LOW CONFIDENCE
FOR BREAKING THROUGH THE EML AND SEVERE STORMS.
AT 18Z...SHOWERS AND A FEW STRONGER STORMS HAD DEVELOPED BY
WABASHA AND LIFTED NORTHEAST INTO NORTHERN WISCONSIN. THE WARM
FRONT AT 18Z WAS LOCATED NEAR WATERLOO TO WEST OF CHARLES CITY.
THE AXIS OF MID TO UPPER 50S WAS JUST TO THE WEST IN WESTERN
MN/WESTERN IA.
THROUGH FRIDAY:
THE 500MB TROUGH WILL CONTINUE TO SHIFT EASTWARD INTO THE PLAINS
THROUGH FRIDAY. MEANWHILE, THE SURFACE COLD FRONT WILL SLOWLY MOVE
TO THE EAST. BY 12Z FRIDAY, THE COLD FRONT WILL MAKE IT TO
NORTHEAST IOWA AND WESTERN WISCONSIN, AND BY 00Z SATURDAY SHOULD BE
NEAR MKE, EAST OF THE AREA. AT THE BEGINNING OF THE FORECAST
PERIOD, THE AXIS OF MUCAPE (1000-1500 J/KG) WILL BE MOVING THROUGH
PARTS OF WISCONSIN WITH THE MAIN AXIS OF MUCAPE/MLCAPE FROM JUST TO
THE WEST OF THE FORECAST AREA TOWARD SOUTHWEST MN/NORTHWEST IOWA
INTO EASTERN AND CENTRAL NEBRASKA.
THE SHOWERS AND THUNDERSTORMS WILL CONTINUE TO LIFT NORTHEAST ON THE
GRADIENT OF THE DEEP MOISTURE AND THE ELEVATED CAPE THIS AFTERNOON.
ADDITIONAL STORMS WILL FORM DURING THE AFTERNOON CLOSER TO THE COLD
FRONT AND ALSO IN THE VICINITY OF THE WARM FRONT. THE STORMS WILL
CONSOLIDATE IN A SOUTHWEST TO NORTHEAST LINE OVER PARTS OF SOUTHERN
MINNESOTA DURING THE AFTERNOON AND SHIFT SOUTHEAST THIS EVENING.
SOME OF THE CONVECTIVE ALLOWING MODELS CONTINUE TO SHOW THAT HAIL
AND DAMAGING WINDS ARE THE PRIMARY THREATS. SOME BOWING
SEGMENTS WILL BE POSSIBLE. THE SPC MESO-ANALYSIS GRAPHICS SHOW
DOWNDRAFT CAPE AROUND 1000J/KG FOR OVER SOUTHWEST MN AND
NORTHWEST IA. STRENGTHENING MOISTURE TRANSPORT IS FORECAST WITH
FORECAST SOUNDINGS SHOWING LIMITED INSTABILITY (SKINNY CAPE),
HOWEVER 0-6KM SHEAR INCREASES TO 50 TO 60KTS WITH STEEP LAPSE
RATES (7.5 DEG C/KM) AND EFFECTIVE SHEAR AROUND 40KTS. WE WILL
CONTINUE TO MONITOR STORMS NEAR THE WARM FRONT AND NEAR THE
HIGHER INSTABILITY/DEWPOINTS/TEMPERATURES FOR THE ISOLATED
TORNADO THREAT. WE REMAIN IN A LEVEL 2 OF 5 SEVERE WEATHER RISK
TODAY WEST OF THE MISSISSIPPI RIVER WITH A LEVEL 1 FARTHER
EAST. THE CAMS HAVE WIDESPREAD SHOWERS AND THUNDERSTORMS ALONG
THE LINE THIS EVENING ACROSS THE WEST, SPREADING EAST ACROSS THE
FORECAST AREA THROUGH THE EVENING HOURS. BY 06Z THE BULK OF THE
SHOWERS AND STORMS ARE EXITING PARTS OF WISCONSIN, HOWEVER AN
ADDITIONAL CLUSTER OF STORMS IS MOVING THROUGH PARTS OF CENTRAL
IOWA AND THESE COULD CLIP PARTS OF THE SOUTHERN PART OF THE
FORECAST AREA INTO THE EARLY MORNING HOURS. LATEST TRENDS HAVE
WEAKENED THIS AREA, BUT HAVE A DIFFERENT AREAS SOMEWHAT FARTHER
NORTH MOVING IN AT 09Z.
ADDITIONAL SHOWERS AND THUNDERSTORMS ARE FORECAST TO DEVELOP FRIDAY
AS THE UPPER LEVEL TROUGH IS STILL MOVING THROUGH AND THE 850MB
CENTER AND FRONTAL SYSTEM ARE STILL IN THE AREA. FORECAST SOUNDINGS
SHOW VERY STEEP LAPSE RATES OF 8+ DEG C/KM WITH HIGH EFFECTIVE
SHEAR, ALTHOUGH THE INSTABILITY VARIES ON THE MODEL. THUS THE
POTENTIAL FOR ELEVATED HAIL FRIDAY WILL BE DEPENDENT ON WHERE THE
FRONT IS AND THE DEGREE OF INSTABILITY/FORCING. AS THE FRONT MOVES
SOUTHEAST, THE SHOWERS AND STORMS WILL BE ENDING. THERE IS A HINT
THAT SOME SNOW COULD MIX IN NORTH I94 BEFORE THE PRECIPITATION ENDS
FRIDAY EVENING, BUT HAVE KEPT IT ALL LIQUID FOR NOW.
THE WEEKEND/EARLY NEXT WEEK.
FOR SATURDAY THROUGH MONDAY, A 500MB TROUGH OVER NORTHERN PLAINS AND
UPPER MISSISSIPPI VALLEY WILL CONTINUE TO SWING THROUGH THE GREAT
LAKES SATURDAY. SURFACE HIGH PRESSURE BUILDS IN WITH COOLER
TEMPERATURES. HIGHS SATURDAY SHOULD TOP OUT IN THE UPPER 40S AND
50S WITH NORTH THEN NORTHEAST WINDS 5 TO 15 MPH. ALTHOUGH THE
NORTHERN BRANCH OF THE TROUGH IS SWINGING THROUGH, THE SOUTHERN
BRANCH CLOSES OFF OVER THE FOUR CORNERS AREA. THIS AREA OF
CLOSED LOW PRESSURE WILL TRACK ACROSS THE PLAINS SUNDAY AND
TOWARD IOWA. THE DETERMINISTIC 17.12Z GFS IS NOW TAKING A MORE
NORTHERN TRACK AND THIS IS MORE SIMILAR TO THE EC. THERE REMAINS
SOME TIMING DIFFERENCES AS THE GFS IS DRIER IN THE MORNING,
WITH THE PRECIPITATION ALREADY INTO NORTHEAST IOWA AND SOUTHERN
WI BY 18Z SUNDAY. THE SURFACE LOW IS FORECAST TO TRACK FROM
NORTHERN MISSOURI INTO EASTERN IOWA SUNDAY EVENING AND LIFT
NORTHEAST ACROSS WESTERN/CENTRAL WISCONSIN SUNDAY NIGHT AND
MONDAY MORNING. AGAIN, PRECIPITATION OF .4 TO 1.10" COULD OCCUR.
THE GEFS/GEPS/ENS HAVE PROBABILITY OF 60 TO 70% CHANCE OF .5"
OR MORE OF PRECIPITATION FOR THE 24HRS ENDING MONDAY AT 1PM WITH
THE GEFS ON THE LOWER SIDE AND THE GEPS/ENS OF THE HIGHER SIDE.
THE GRAND ENSEMBLE PROBABILITIES FOR ONE INCH OR MORE OF
PRECIPITATION IS 20 TO 30%. WITH THE TRACK OF THE SURFACE LOW,
HIGHS SUNDAY AND MONDAY ARE FORECAST TO BE SIMILAR TO SATURDAY;
IN THE 50S.
MORE SPRING-LIKE TEMPERATURES TUESDAY THROUGH THURSDAY:
A WEAK RIDGE DEVELOPS IN THE 500MB FLOW MONDAY NIGHT INTO
TUESDAY WITH TEMPERATURES WARMING INTO THE 60S AND 70S, HOWEVER,
THE NEXT TROUGH IS ALREADY LOWERING HEIGHTS. SCATTERED SHOWERS
WILL BE POSSIBLE TUESDAY WITH THE WARM FRONT AND ADDITIONAL
SHOWERS WITH THE COLD FRONT. THERE CONTINUES TO BE DIFFERENCES
IN TIMING, SO UNSURE WITH THE COLD FRONT WILL BE THROUGH BY
WEDNESDAY, OR STILL MORNING THROUGH WEDNESDAY.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 1050 PM CDT THU APR 17 2025
THE CURRENT CLUSTER OF SHOWERS AND STORMS MOVES OUT OF THE AREA
SHORTLY AFTER 06Z. A SECOND CLUSTER OF STORMS MAY MOVE THROUGH
BETWEEN 08-14Z, MAINLY SOUTH OF AN RST TO KY50 LINE. IFR TO
LIFR STRATUS IS EXPECTED TO BUILD IN AFTER 06-09Z BEHIND THE
FIRST LINE OF STORMS AND PERSISTS FOR THE REMAINDER OF THE TAF
PERIOD, LIFTING TO IFR/MVFR DURING THE DAY. OVERNIGHT SSE WINDS
OF 5-10 KTS VEER TO THE NORTHWEST AT 10-15G20-25KTS FOR THE DAY
ON FRIDAY.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
DISCUSSION...JAR/ZAPOTOCNY
AVIATION...SKOW
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