(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 180859
SPC AC 180859
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT SAT MAY 18 2013
VALID 211200Z - 261200Z
...DISCUSSION...
THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH AN
UPPER-LEVEL TROUGH OVER THE CNTRL HIGH PLAINS AND SRN ROCKIES WITH
SOUTHWEST FLOW LOCATED FROM THE SCNTRL STATES NEWD INTO THE GREAT
LAKES REGION. STRONG TO POSSIBLY SEVERE THUNDERSTORM DEVELOPMENT
WILL BE POSSIBLE ON TUESDAY/DAY 4 ALONG A CORRIDOR OF MODERATE
INSTABILITY FROM THE SRN PLAINS EXTENDING NEWD INTO THE MID MS
VALLEY. ON WEDNESDAY/DAY 5...THE MODELS MOVE THE UPPER-LEVEL TROUGH
EWD INTO THE OZARKS WITH A COLD FRONT LOCATED FROM THE OH VALLEY
SWWD INTO THE ARKLATEX. STRONG THUNDERSTORM DEVELOPMENT WILL BE
POSSIBLE WEDNESDAY AND WEDNESDAY NIGHT ALONG AND AHEAD OF THE FRONT.
ON THURSDAY/DAY 6...THE MODELS MAINTAIN REASONABLE AGREEMENT WITH AN
UPPER-LEVEL RIDGE BUILDING ACROSS THE GREAT PLAINS AND AN
UPPER-LEVEL TROUGH LOCATED IN THE ERN STATES. THUNDERSTORMS WILL BE
POSSIBLE ALONG THE ERN SEABOARD THURSDAY AFTERNOON AND EVENING WITH
MORE ISOLATED DEVELOPMENT POSSIBLE IN THE SRN PLAINS. MODEL
SOLUTIONS DIVERGE ON FRIDAY/DAY 7 SUGGESTING UNCERTAINTY IS
SUBSTANTIAL AT THAT RANGE.
AT THIS POINT...TUESDAY/DAY 4 AND WEDNESDAY/DAY 5 APPEAR TO HAVE THE
GREATEST CHANCE FOR AN ENHANCED SEVERE THREAT AREA. ON THOSE
DAYS...A POTENTIAL FOR SEVERE STORMS WILL EXIST ACROSS A BROAD
CORRIDOR. MESOSCALE INTERACTIONS WILL PROBABLY BE IMPORTANT AS TO
WHERE THE SEVERE THREAT ENDS UP BECOMING ENHANCED. FOR THAT
REASON...WILL GO PREDICTABILITY TOO LOW FOR THIS OUTLOOK.
..BROYLES.. 05/18/2013
CLICK TO GET WUUS48 PTSD48 PRODUCT
weather.gov 
@NWSSPC
