(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 a 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 highly unlikely during the entire period (e.g. less than a 30% probability for a regional severe storm area across the CONUS through the entire Day 4-8 period).
Forecast Discussion
ZCZC SPCSWOD48 ALL
ACUS48 KWNS 210848
SPC AC 210848
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0348 AM CDT TUE MAY 21 2013
VALID 241200Z - 291200Z
...DISCUSSION...
MEDIUM-RANGE MODELS IN DECENT AGREEMENT THROUGH ROUGHLY DAY 6 /SUN.
12-26/...IN TERMS OF THE LARGE-SCALE PATTERN.
DAY 4 /FRI. 12-24/...BOTH THE GFS AND ECMWF SHOW THE ERN U.S. TROUGH
CONTINUING TO PROGRESS...WITH THE SURFACE COLD FRONT MOVING OFFSHORE
EARLY IN THE PERIOD -- SUGGESTING ONLY LOW-END SEVERE THREAT AT BEST
PRIOR TO THE FRONT VACATING THE COAST.
MEANWHILE...A STRONG RIDGE OVER THE CENTRAL U.S. IS PROGGED TO
PERSIST...HINDERING EWD PROGRESSION OF THE WRN U.S. TROUGH. MODELS
AGREE OVERALL -- BUT DIFFER WITH DETAILS -- THAT THE RIDGE WILL
DEAMPLIFY/FLATTEN WITH TIME...AS SHORT-WAVE TROUGHS EJECT EWD FROM
THE MAIN WRN SYSTEM INTO THE MEAN RIDGING. WHILE THE DECREASE IN
RIDGING -- AND THUS LARGE-SCALE SUBSIDENCE -- WITH TIME COMBINED
WITH THE PASSAGE OF REPEATED VORTICITY MAXIMA WOULD RESULT IN SOME
SEVERE POTENTIAL LOCALLY...TIMING/LOCATION WOULD BE QUITE DIFFICULT
TO NARROW DOWN ATTM. EVEN SO...WITH NO WIDESPREAD/SIGNIFICANT
THREATS EVIDENT ATTM -- BUT MORE LIKELY SMALLER-SCALE/LOCAL
POTENTIAL...NO OUTLOOK AREAS WILL BE ISSUED THIS FORECAST.
..GOSS.. 05/21/2013
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