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

Day 1 Outlook Convective Tornado
Hail Wind
Categorical Day1 1200Z Outlook
  
Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

  
000
ACUS01 KWNS 210556
SWODY1
SPC AC 210554

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1254 AM CDT Sat Oct 21 2017

Valid 211200Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
OKLAHOMA...NORTH TEXAS...SOUTHEAST KANSAS...SOUTHWEST
MISSOURI...EXTREME NORTHWEST ARKANSAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
PLAINS TO THE UPPER MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
SOUTHERN PLAINS TO THE UPPER MIDWEST SURROUNDING THE SLIGHT RISK...

...SUMMARY...
Scattered severe thunderstorms are expected especially across
portions of the south-central Plains late this afternoon and
evening, with very large hail, damaging winds, and a few tornadoes
possible.

...Synopsis...
An upper-level trough centered over the Great Basin and northern
Intermountain Region Friday evening will continue to dig/amplify
from the northern/central High Plains this morning toward the
central/southern Plains and Upper Midwest by early Sunday. An
east/southeastward-moving cold front will be a primary focus for
severe thunderstorm development later today, with a frontal wave and
dryline also factors across the southern Plains.

...Southern/Central Plains...
An active second-season severe-weather day is expected across the
region by late afternoon and evening. Ample moisture and moderate
buoyancy, especially by mid/late October standards, will support
intense thunderstorm development during the mid/late afternoon hours
into evening as upper trough-related forcing for ascent overspreads
the frontal zone. Low to middle 60s F surface dewpoints, as
currently found across much of OK/TX, will become increasingly
established by afternoon northward across eastern KS into far
eastern NE, IA, and southern MN. 

It seems likely that storms will initially develop and increase
during the mid/late afternoon (roughly 21Z-23Z) near the
east/southeastward-moving cold front spanning far eastern NE/western
IA and northeast/south-central KS into northern/western OK. While a
couple of initial supercells capable of hail could occur, a
relatively quick transition to a linear mode seems likely within
this corridor in vicinity of the advancing cold front with damaging
winds becoming the main concern.

Farther south, a somewhat greater spatiotemporal window for
semi-discrete supercells will likely exist across southern OK into
western north TX where deep-layer shear vectors will be somewhat
more line-normal oriented. Current thinking is the most probable
semi-discrete-supercell-related very large hail and potential for a
couple of tornadoes should be focused across
southwest/west-central/south-central OK in vicinity of the surface
low/dryline-related triple point between 22Z-02Z.

Quasi-linear bands of storms will be increasingly prevalent through
the mid/late evening hours with damaging winds being the primary
hazard, although a couple of tornadoes cannot ruled out across
central into eastern OK with any line-embedded circulations amid
adequate low-level shear/SRH. These linearly organized storms should
otherwise tend to gradually weaken during the overnight hours as
they move into south-central MO/west-central AR/southeast OK and the
Ark-La-Tex region.

...Upper Midwest...
Although low-level moisture and buoyancy will be considerably more
limited into the Upper Midwest including parts of IA into MN/western
WI, strong south-southwesterly deep-layer winds (850mb winds around
40 kt) will promote relatively shallow linear/bowing segments that
rapidly spread north-northeast. The strongest convection during the
evening hours may be capable of damaging gusts and perhaps a
tornado.

...West-central/southwest TX...
While the coverage/likelihood of storm development along the dryline
is not certain, a few supercells capable of large hail cannot be
ruled out during the late afternoon and early evening from the Low
Rolling Plains south-southwestward toward the Edwards Plateau and
Big Bend vicinity. A more likely scenario will be for increased
storm coverage later this evening into the overnight as the cold
front overtakes the dryline with some hail and wind being possible.

..Guyer/Cook.. 10/21/2017

$$