(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 190845
SPC AC 190845
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0345 AM CDT SUN MAY 19 2013
VALID 221200Z - 271200Z
...DISCUSSION...
MEDIUM-RANGE MODELS ARE IN FAIRLY POOR AGREEMENT THROUGH THE DAY 4-8
PERIOD...FIRST WITH THE TROUGH CROSSING THE MS VALLEY INTO THE OH
VALLEY/MIDWEST DAY 4 /WED. 5-22/ AND LATER WITH A SECOND TROUGH
CROSSING THE WRN CONUS.
SOME SEVERE POTENTIAL WILL LIKELY ACCOMPANY THE INITIAL/ERN TROUGH
AS IT CROSSES THE MS VALLEY WEDNESDAY -- PERHAPS MOST CONCENTRATED
ACROSS THE MID OH/TN VALLEYS...BUT ATTM DEGREE OF THREAT DOES NOT
APPEAR TO WARRANT INCLUSION OF A 30% EQUIVALENT THREAT AREA. MODEL
DIFFERENCES BECOME MUCH MORE DRASTIC DAY 5...AS THE SYSTEM SHIFTS
EWD. WITH THE ECMWF SHOWING THE TROUGH DEEPENING SIGNIFICANTLY DUE
TO PHASING WITH ERN CANADA UPPER TROUGHING...WHILE THE GFS MAINTAINS
TWO DISTINCT SYSTEMS...CONVECTIVE POTENTIAL ACROSS THE ERN/NERN U.S.
REMAINS ENTIRELY UNCERTAIN.
MEANWHILE...MODELS ARE IN DECENT AGREEMENT THROUGH DAY 6 /FRI. 3-24/
FARTHER W...MOVING THE WRN U.S. TROUGH SLOWLY EWD -- ITS PROGRESS
BEING HINDERED BY A DOWNSTREAM CENTRAL U.S. RIDGE. WITH THIS RIDGE
RESIDING OVER THE CENTRAL U.S. THROUGH DAY 6...ANY SEVERE POTENTIAL
ACROSS THE PLAINS WILL BE RELATIVELY LIMITED/ISOLATED.
AFTERWARD...WITH THE MODEL DISAGREEMENT INCREASING DAYS 7-8 WITH
RESPECT TO EVOLUTION OF THIS TROUGH AND THE DOWNSTREAM RIDGE...NO
THREAT AREAS WILL BE INTRODUCED THIS FORECAST.
..GOSS.. 05/19/2013
CLICK TO GET WUUS48 PTSD48 PRODUCT
weather.gov 
@NWSSPC
