(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 180833
SPC AC 180833
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0333 AM CDT TUE JUN 18 2013
VALID 211200Z - 261200Z
...DISCUSSION...
...NRN PLAINS TO THE UPPER GREAT LAKES...
A SEVERAL DAY PERIOD OF ORGANIZED SEVERE TSTMS MAY PERSIST INTO
EARLY NEXT WEEK. HOWEVER...SYNOPTIC/MESOSCALE PREDICTABILITY BREAKS
DOWN ON D3 AND LINGERS INTO THE MEDIUM-RANGE RENDERING LOW
CONFIDENCE FOR HIGHLIGHTING ANY INDIVIDUAL DAY WITH HIGH-END SEVERE
PROBABILITIES.
ON THE LARGE-SCALE...THERE IS BROAD CONSISTENCY AMONG ECMWF/GFS/CMC
DETERMINISTIC RUNS ALONG WITH ENSEMBLE MEANS THAT THE UPPER-LEVEL
TROUGH OVER THE NORTHWEST WILL EITHER DAMPEN OR EJECT NEWD INTO
S-CNTRL CANADA. IN THE WAKE OF THIS...A PRIMARILY ZONAL FLOW REGIME
SHOULD DEVELOP AROUND D6/SUN WITH A BELT OF MODERATE TO STRONG
MID-LEVEL WLYS PERSISTING ALONG THE NRN TIER OF STATES.
TIMING/EVOLUTION DIFFERENCES HAMPER THE HANDLING OF SHORTWAVE
IMPULSES AND HOW THEY MODULATE TSTM ACTIVITY ALONG THE LINGERING
PRESENCE OF A QUASI-STATIONARY FRONT. BUT WITH A STRONG TO EXTREMELY
UNSTABLE AIR MASS REMAINING S OF THE BOUNDARY OWING TO A PRONOUNCED
EML...DAILY BOUTS OF ORGANIZED MESOSCALE SEVERE EVENTS APPEAR
POSSIBLE.
..GRAMS.. 06/18/2013
CLICK TO GET WUUS48 PTSD48 PRODUCT
weather.gov 
@NWSSPC
