Severe Storm Outlook Narrative (AC)
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000
ACUS03 KWNS 180441
SWODY3
SPC AC 180440

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
1140 PM CDT Tue Oct 17 2017

Valid 201200Z - 211200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Thunderstorm potential will increase across the south-central US and
over the upper Mississippi Valley.

...Discussion...

Strong short-wave trough will spread across the northern
intermountain region Friday into the northern High Plains by 21/12z.
Height falls ahead of this feature should encourage short-wave
trough over the southern Plains to eject into the Arklatex region.
Thunder probabilities will increase ahead of these features from the
lower Sabine River into the upper MS Valley.

1) South-central US - Southern-stream short-wave trough will eject
across NM into the TX South Plains early in the period. This feature
is expected to aid northward transport of low-level moisture and a
notable increase in PW from the upper TX coast into central OK where
values should be on the order of 1.5". Forecast lapse rates are not
particularly steep ahead of this feature but buoyancy should be more
than adequate for convection in advance of the trough. Some
consideration has been given to introduce 5% severe probs due to the
marked increase in moisture as deep-layer shear will increase ahead
of the trough such that convection could become sustained in nature.
If later guidance is more aggressive with buoyancy then severe probs
may be warranted.

2) Upper MS Valley - Low-level warm advection will increase across
the upper MS Valley during the day3 period as LLJ strengthens from
KS into the Arrowhead of MN. Air mass is initially quite dry across
this region but sustained moistening should lead to adequate
instability for weak elevated convection after dark well ahead of a
sharp cold front that will surge into this region by the end of the
period.

..Darrow.. 10/18/2017

$$


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