(All days are valid from 12 UTC - 12 UTC the following day)
Note: A severe weather area depicted in the Day 4-8 period indicates 15%, 30% or higher probability for severe thunderstorms within 25 miles of any point.
PREDICTABILITY TOO LOW is used to indicate severe storms may be possible based on some model scenarios. However, the location or occurrence of severe storms are in doubt due to: 1) large differences in the deterministic model solutions, 2) large spread in the ensemble guidance, and/or 3) minimal run-to-run continuity.
POTENTIAL TOO LOW means the threat for a regional area of organized severe storms appears unlikely (i.e., less than 15%) for the forecast day.
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 050858
SPC AC 050858
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT SUN APR 05 2015
VALID 081200Z - 131200Z
...DISCUSSION...
APPRECIABLE SPREAD -- EVEN MORE THAN 24 HOURS PRIOR -- IS EVIDENT
AMONGST THE MEDIUM-RANGE MODELS THIS FORECAST...WITH THE GFS
SHIFTING THE WRN TROUGH INTO THE PLAINS FASTER AND WITH MORE OF A
POSITIVE TILT...WHILE THE UKMET AND PARTICULARLY THE ECMWF DEPICT A
SLOWER AND MORE NEUTRAL TO NEGATIVE TILT PROGRESSION. AS A RESULT
OF THESE DIFFERENCES -- AND THE ASSOCIATED VARIANCES IN SURFACE
FEATURE LOCATIONS IN THE DAY 4-5 TIME FRAME...SPECIFICS OF THE
SEVERE WEATHER FORECAST WITH RESPECT TO TIMING/LOCATION REMAIN
DIFFICULT TO ASCERTAIN.
DESPITE TIMING DIFFERENCES WITH RESPECT TO THE MAIN UPPER
LOW/TROUGH...CONFIDENCE HAS INCREASED THIS FORECAST WITH RESPECT TO
SEVERE RISK FOR DAY 4 /WED 4-8/ ACROSS CENTRAL AND ERN OK/ERN KS/MO.
ALL MODELS INDICATE MID-LEVEL HEIGHT FALLS ACROSS THIS AREA...AND
AT LEAST HINTS OF A SUBTLE/EMBEDDED WAVE CROSSING THE REGION NEAR
PEAK HEATING. ATTM...EXPECT RESULTING UVV TO BE SUFFICIENT ATOP THE
EWD-MIXING DRYLINE TO PERMIT CAP WEAKENING SUFFICIENT TO YIELD
ISOLATED TO SCATTERED STORM DEVELOPMENT BY LATE AFTERNOON. WITH A
VERY MOIST BOUNDARY LAYER AHEAD OF THE DRYLINE TOPPED BY STEEP LAPSE
RATES...AND A KINEMATIC ENVIRONMENT FEATURING FLOW THAT VEERS
SUBSTANTIALLY AND INCREASES STEADILY WITH HEIGHT...SHEAR WILL FAVOR
LONG-LIVED SUPERCELLS AND ATTENDANT RISK FOR VERY LARGE
HAIL...DAMAGING WINDS...AND TORNADOES. GIVEN UNCERTAINTY DUE TO
STORM COVERAGE...WILL MAINTAIN ONLY 15% PROBABILITY AREA ATTM --
DESPITE SIGNIFICANT SEVERE WEATHER POTENTIAL WITH ANY STORM THAT
DOES DEVELOP.
THE LIKELIHOOD FOR MORE WIDESPREAD STORMS -- BUT WITH GREATER
UNCERTAINTY IN TERMS OF TIMING AND AREA -- EXISTS DAY 5 /THU 4-9/.
DEEPENING OF THE SURFACE LOW IN THE KS/NEB/IA VICINITY AND ADVANCE
OF A TRAILING COLD FRONT INTO THE CENTRAL/SRN PLAINS WILL FACILITATE
A BROAD ZONE OF STORM INITIATION...GIVEN THE MOIST/FAVORABLY
UNSTABLE AIRMASS EXPECTED. WITH STRONGER FLOW ALOFT AS COMPARED TO
DAY 4 GIVEN PROGRESSION OF THE MAIN MID-LEVEL JET STREAK INTO THE
CENTRAL STATES...SUPERCELL STORMS AND ASSOCIATED RISK FOR VERY LARGE
HAIL...DAMAGING WINDS...AND TORNADOES CAN BE EXPECTED.
MODELS CONTINUE TO DIVERGE DAY 6 AND BEYOND...AND GIVEN THE
INCREASING SPREAD IN SOLUTIONS BETWEEN THEM...LOW CONFIDENCE EXISTS
WITH RESPECT TO EVOLUTION OF SEVERE RISK THROUGH THE SECOND HALF OF
THE PERIOD. THUS...LOW PREDICTABILITY PRECLUDES ATTEMPTS TO
HIGHLIGHT THREAT AREAS BEYOND DAY 5.
..GOSS.. 04/05/2015
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