680
ACUS01 KWNS 080539
SWODY1
SPC AC 080538
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1238 AM CDT TUE SEP 08 2026
VALID 081200Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
IOWA AND EASTERN NEBRASKA...
..SUMMARY
WIDELY SCATTERED SEVERE STORMS CAPABLE OF MAINLY SEVERE WIND GUSTS
APPEAR POSSIBLE ACROSS PORTIONS OF IOWA AND EASTERN NEBRASKA TUESDAY
AFTERNOON AND EVENING. MORE SPORADIC OCCURRENCES OF SEVERE WINDS AND
LARGE HAIL MAY OCCUR FROM PORTIONS OF THE UPPER MIDWEST INTO THE
CENTRAL PLAINS.
..SYNOPSIS
AN INTENSE UPPER LOW MOVING INTO SOUTHERN SK LATE THIS EVENING WILL
CONTINUE NORTHEAST THROUGH CENTRAL MB INTO NORTHERN ON AHEAD OF A
SECONDARY SHORT-WAVE TROUGH TRACKING FROM THE NORTHERN ROCKIES INTO
THE NORTHERN PLAINS. A BELT OF ENHANCED MID/UPPER-LEVEL WINDS WILL
BE MAINTAINED BETWEEN THOSE FEATURES FROM THE NORTHERN HIGH PLAINS
INTO THE UPPER GREAT LAKES. AT THE SURFACE, A COLD FRONT WILL
ADVANCE THROUGH THE EASTERN DAKOTAS AND UPPER MS VALLEY WITH THE
TRAILING EXTENSION OF THE BOUNDARY MOVING MORE SLOWLY SOUTHEAST
THROUGH THE MID-MO VALLEY AND CENTRAL HIGH PLAINS.
..CENTRAL PLAINS INTO THE UPPER MIDWEST
CLUSTERS OF THUNDERSTORMS ARE LIKELY TO BE ONGOING AT 12Z TUESDAY
FROM PORTIONS OF THE MID-MO VALLEY INTO THE UPPER MIDWEST WITHIN A
ZONE OF WARM ADVECTION AND MOISTURE TRANSPORT ALONG A NOCTURNAL
LOW-LEVEL JET (LLJ). SHOWERS AND STORMS MAY LINGER THROUGH THE
MORNING ACROSS PARTS OF WI AND THE U.P. OF MI, LIMITING THE DEGREE
OF AIR MASS DESTABILIZATION AND ASSOCIATED SEVERE WEATHER RISK
DURING THE AFTERNOON. FARTHER TO THE SOUTHWEST FROM IA THROUGH
EASTERN AND SOUTHERN NE INTO NORTHERN KS, STRONGER DAYTIME HEATING
ON THE SOUTHERN FRINGE OF LINGERING MID/HIGH-LEVEL CLOUDINESS WILL
CONTRIBUTE TO A WELL-MIXED BOUNDARY LAYER, FEATURING STEEP LOW-LEVEL
LAPSE RATES. WHEN COMBINED WITH BOUNDARY-LAYER DEWPOINTS IN THE 60S
TO LOW/MID 70S F, THE AIR MASS IS EXPECTED TO BECOME MODERATELY TO
STRONGLY UNSTABLE BY LATE AFTERNOON WITH MLCAPE OF 2000-3000 J/KG.
IN THE ABSENCE OF APPRECIABLE HEIGHT FALLS/LARGE-SCALE FORCING FOR
ASCENT, CONVERGENCE ALONG THE FRONT AND ANY PRECEDING CONFLUENCE
ZONES/OUTFLOW BOUNDARIES IS EXPECTED TO FOSTER A GRADUAL INCREASE IN
STORM COVERAGE AND INTENSITY BY MID TO LATE AFTERNOON AMIDST THE
DESTABILIZING AIR MASS. THE STRONGEST DEEP-LAYER SHEAR IS EXPECTED
TO BE DISPLACED TO THE NORTH OF THE EFFECTIVE WARM SECTOR WITH
AROUND 30-35 KT FORECAST ALONG THE FRONTAL ZONE. A LARGELY PARALLEL
SHEAR-VECTOR ORIENTATION WITH THE FRONT SUGGESTS THAT INITIAL STORMS
SHOULD GROW UPSCALE INTO LINE SEGMENTS OR A BROKEN BAND WITH AN
ASSOCIATED RISK FOR SEVERE WIND GUSTS FROM MID AFTERNOON THROUGH
EVENING. ISOLATED OCCURRENCES OF MARGINALLY SEVERE HAIL ARE
POSSIBLE; HOWEVER, POOR MID-LEVEL LAPSE ARE EXPECTED TO LIMIT THE
OVERALL THREAT. THE 00Z MODELS DO INDICATE SOME LLJ ENHANCEMENT OVER
CENTRAL IA BY LATE AFTERNOON INTO EVENING, RESULTING IN A CORRIDOR
OF STRONGER LOW-LEVEL SHEAR. WHILE A BRIEF TORNADO OR TWO ARE
POSSIBLE, A MORE ROBUST THREAT IS EXPECTED TO BE LIMITED BY LARGELY
OUTFLOW-DOMINANT STORMS.
..MEAD/CHALMERS.. 09/08/2026
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