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SPC Convective Outlook

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Day 1 Outlook Convective Tornado
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Images courtesy of the NWS Storm Prediction Center
 Forecast Discussion

ACUS01 KWNS 200411
SPC AC 200409

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1109 PM CDT Thu Oct 19 2017

Valid 201200Z - 211200Z


Scattered thunderstorms are possible during the day on Friday over
eastern Texas, with more isolated activity overnight into eastern
Nebraska and Iowa.

An amplified upper trough will move across the Rockies during the
day, approaching the High Plains into Saturday morning. A surface
low will deepen over south-central Canada, with a cold front
extending southward across the central Plains Friday night. A broad
area of southerly low-level flow will allow dewpoints to rise into
the low to mid 60s from the middle MO Valley into KS and OK, and
into the lower 70s along the TX coast. This northward flux of
moisture will be aided by a broad 850 mb jet, in excess of 50 kt and
extending from TX to MN.

Ahead of the primary upper trough will be a lead wave that will move
from TX and OK northeastward across the lower MO Valley during the
day. This wave will be responsible for the bulk of the storm
activity over eastern TX.

...East Texas...
Aforementioned leading shortwave trough combined with moist return
flow will lead to a zone of thunderstorm activity mainly east of
I-35 in TX. This zone of lift will be on the western periphery of
the larger scale surface high centered over the Appalachians.
Activity is likely to be ongoing Friday morning, and will likely
dissipate after 00Z as wind fields re-adjust with the approach of
the larger upper system. Forecast soundings show some low-level
veering of the winds with height, but with weak magnitude.  Given
this, and relatively cool surface temperatures, it appears any
low-end tornado threat is too minimal even for a 2 percent area,
though storms may exhibit weak/transient rotation at times.

...Eastern NE into IA overnight...
Persistent warm advection via a 50+ kt low-level jet and height
falls into Saturday morning may be enough for isolated thunderstorm
activity, though capping will remain a concern across much of the
Plains. Conditionally, any storm could be capable of marginally
severe hail as temperatures aloft will be cool, but, even effective
shear values at that time will not be particularly favorable. As
such, potential looks to remain sub-marginal.

..Jewell/Cook.. 10/20/2017