Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Tornado Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
2 %
41,200
3,052,164
Omaha, NE...Des Moines, IA...Cedar Rapids, IA...Waterloo, IA...Iowa City, IA...
Probabilistic Damaging Wind Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 081252
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0752 AM CDT MON SEP 08 2014
VALID 081300Z - 091200Z
...NO SVR TSTM AREAS FORECAST...
...SUMMARY...
AT LEAST ISOLATED SEVERE THUNDERSTORMS WILL BE POSSIBLE FROM EASTERN
NEBRASKA EASTWARD ACROSS IOWA TO NORTHWESTERN ILLINOIS. HAIL AND
STRONG WIND GUSTS ARE EXPECTED TO BE THE PRIMARY WEATHER HAZARDS.
...SYNOPSIS...
FAIRLY LOW AMPLITUDE WILL CHARACTERIZE SYNOPTIC-SALE UPPER-AIR
PATTERN OVER CONUS THIS PERIOD. IN NRN STREAM...SHORTWAVE TROUGHS
NOW OVER SRN IL AND SWRN MN EACH ARE FCST TO MOVE ENEWD AND
WEAKEN...LATTER REACHING WI BY 00Z AND LM/WRN LOWER MI AREA BY 12Z.
TRAILING AND LOOSELY ATTACHED VORTICITY LOBE IS EVIDENT OVER WRN
SD...AND SHOULD MOVE TO FSD/SUX REGION BY 00Z...THEN ACROSS NRN IA
OVERNIGHT.
HEIGHTS ALOFT WILL FALL ACROSS MUCH OF NRN ROCKIES AND INTERIOR NWRN
CONUS...ESPECIALLY AFTER 00Z...IN RESPONSE TO SERIES OF SHORTWAVE
TROUGHS PIVOTING SEWD AND EWD OVER WRN CANADA. AS THAT
OCCURS...MID/UPPER-LEVEL CYCLONE -- NOW EVIDENT IN MOISTURE-CHANNEL
IMAGERY OVER CAPE MENDOCINO AREA -- SHOULD MOVE INLAND AND DEVOLVE
TO OPEN-WAVE TROUGH...REACHING FROM NRN NV TO CENTRAL CA BY 12Z.
AHEAD OF AFOREMENTIONED HEIGHT FALLS...SFC COLD FRONT ANALYZED AT
11Z FROM SERN SK ACROSS N-CENTRAL MT IS FCST TO MOVE SEWD OVER NRN
PLAINS. BY 12Z THIS BOUNDARY SHOULD EXTEND FROM LS LAKEHEAD REGION
OF ONT SWWD ACROSS NRN MN...THROUGH FRONTAL-WAVE LOW INVOF BLACK
HILLS...TO EXTREME NRN WY OR SRN MT. RESIDUAL/QUASISTATIONARY FRONT
WILL REMAIN NEAR PRESENT LOCATION FROM SC TO SRN LA AND S-CENTRAL
TX...WHILE CONTINUING GRADUAL FRONTOLYSIS.
...MID MO VALLEY/MID TO UPPER MS VALLEY...
ONGOING CLUSTER OF STG TSTMS ACROSS FSD/SUX REGION IS LOCATED WITHIN
JUXTAPOSITION OF TWO REGIMES OF LARGE-SCALE ASCENT--LOW-LEVEL WAA
AND ISENTROPIC ASCENT TO LFC NEAR NOSE OF 30-40-KT LLJ...AND COMPACT
PLUME OF DCVA RELATED TO SWRN MN SHORTWAVE TROUGH. THIS ACTIVITY IS
EXPECTED TO CONTINUE SHIFTING SEWD TO ESEWD OVER NWRN IA THROUGH
MID-LATE MORNING. EXPECT CONVECTION TO BECOME MORE DISORGANIZED AND
PERHAPS DISSIPATE DURING FORENOON HOURS AS LLJ WEAKENS AND
PRIMARY/LEADING VORTICITY LOBE EJECTS AWAY FROM AREA.
MEANWHILE...HOWEVER...EMBEDDED CELLS MAY FLARE UP TO PRODUCE HAIL OR
GUSTS NEAR SVR LEVELS...WHERE DOWNDRAFTS ACCELERATE THROUGH
RELATIVELY DRY SUBCLOUD LAYER ENOUGH TO PENETRATE NEAR-SFC LAYER OF
STG STATIC STABILITY.
OUTFLOW/DIFFERENTIAL-HEATING BOUNDARY FROM ONGOING MCS SHOULD
CONTRIBUTE TO RENEWED POTENTIAL FOR STG/ISOLATED SVR TSTM
DEVELOPMENT THIS AFTN -- WHETHER FROM REMAINS OF MORNING CONVECTION
MOVING INTO DESTABILIZING AIR MASS OR DEVELOPMENT ANEW INVOF
BOUNDARY. RICHEST PW PLUME CONTAINING GULF-ORIGIN MOISTURE WILL
REMAIN S OF THIS AREA THROUGH PERIOD. HOWEVER...LEADING PHASE OF
MOIST ADVECTION THROUGH WEAKENING SRN-CONUS BAROCLINIC ZONE WILL
COMBINE WITH EVAPOTRANSPIRATION TO BOOST NEAR-SFC MOISTURE OVER THIS
REGION THROUGHOUT TODAY. BY LATE AFTN...60S F SFC DEW POINTS SHOULD
APPEAR...COMBINING WITH DIURNAL HEATING ALONG AND SE OF BOUNDARY TO
YIELD MLCAPE RANGING FROM AROUND 1000 J/KG NEAR MS RIVER TO OVER
2000 J/KG IN ERN NEB...CONCURRENT WITH WWD STEEPENING OF MIDLEVEL
LAPSE RATES THAT IS RELATED TO PROGRESSIVELY STRONGER EML WITH WWD
EXTENT. LOW-LEVEL SHEAR AND VORTICITY SHOULD BE LOCALLY MAXIMIZED
NEAR THAT BOUNDARY ALSO...OFFERING POTENTIAL LOCALIZED FOCUS FOR
SUPERCELL EVOLUTION.
GIVEN CAPPING CONCERNS AND MESOSCALE BOUNDARY UNCERTAINTIES...TIMING
AND POSITION OF STRONGEST AFTN/EVENING DEVELOPMENT IS STILL UNCLEAR.
RATHER FOCUSED AREA OF HIGHER UNCONDITIONAL SVR PROBABILITIES MAY
DEVELOP WITHIN BROADER 5% SWATH ONCE THOSE SPATIAL/TIMING
UNCERTAINTIES ARE BETTER-RESOLVED. SHORT-LIVED MCS ALSO MAY EVOLVE
FROM AFTN/EVENING CONVECTION AND PROCEED SEWD OVER PORTIONS
IA...NWRN IL AND/OR NRN MO TONIGHT.
..EDWARDS/JIRAK.. 09/08/2014
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z