Day 1 Outlook Day 2 Outlook Day 3 Outlook Days 4-8 Outlook

Day 4-8 Outlook
Day 4 - 8 Outlook
Day 4-8 Severe Weather Outlook. A depicted severe weather area indicates a 30% or higher probability for severe thunderstorms within 25 miles of a point.
D4Fri, Sep 22, 2017 - Sat, Sep 23, 2017 D7Mon, Sep 25, 2017 - Tue, Sep 26, 2017
D5Sat, Sep 23, 2017 - Sun, Sep 24, 2017 D8Tue, Sep 26, 2017 - Wed, Sep 27, 2017
D6Sun, Sep 24, 2017 - Mon, Sep 25, 2017 (All days are valid from 12 UTC - 12 UTC)
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. 1) large differences in the deterministic model solutions,
  2. 2) large spread in the ensemble guidance, and/or
  3. 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).

Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

ACUS48 KWNS 190841
SPC AC 190839

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0339 AM CDT Tue Sep 19 2017

Valid 221200Z - 271200Z

A persistent longwave trough over the West will be key to most
severe weather concerns for the extended forecast period.  This
trough will spread south-southwesterly mid/upper flow across the
Plains and into the Upper Mississippi Valley for much of the
forecast period, with a slowly moving surface boundary separating
cooler continental air to its north from modified tropical airmass
to its south.  Some severe risk will be likely on D4/Friday
afternoon and evening, where models focus convective potential in
portions of Minnesota and vicinity within a strongly sheared,
moderately unstable airmass.  Some difference in depiction of key
synoptic features preclude Slight/15% probabilities for this
outlook, although the region will be monitored.

From D5/Saturday and beyond, the aforementioned surface boundary
will migrate slowly southward across portions of the High Plains and
likely provide a focus for deep convection.  At least a Marginal
severe risk is likely with this activity, although subtle
differences in guidance continue at this time range and widespread
clouds/precipitation may limit the degree of destabilization in some
areas.  These factors preclude 15% or higher severe probabilities at
this time.

..Cook.. 09/19/2017