Severe Storm Outlook Narrative (AC)
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ACUS48 KWNS 220803
SPC AC 220801

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0301 AM CDT Thu Mar 22 2018

Valid 251200Z - 301200Z

On Sunday/D4, an upper ridge will shift east of the MS river, with a
broad area of cyclonic flow aloft across the West. Upper jets across
the Great Basin and northern Mexico will merge into an intense speed
max nosing into the southern High Plains by Monday morning. At the
surface, high pressure will stretch from Quebec across the eastern
states, with low pressure over the central High Plains. A warm front
will lift north from the Red River at 12Z Sunday into KS by 12Z
Monday. Southerly surface winds will maintain 60s F dewpoints south
of the warm front resulting in MUCAPE around 1000-1500 J/kg.
Scattered storms are expected during the day along the warm front
from OK into KS, elevated above a cool boundary layer. Steep lapse
rates aloft will favor hail in some of these storms, and severe
probabilities may be issued in future outlooks. By late afternoon, a
dryline is forecast across western OK into northwest TX. While
heating will occur which would ordinarily help initiate storms, this
dryline will retreat westward during the evening, and forecast
soundings indicate warm 700 mb temperatures and midlevel subsidence.
An isolated storm along the dryline cannot be ruled out, but
coverage appears to be low.

On Monday/D5, flow aloft will increase markedly over the southern
Plains as an upper low drops south across the CO river valley. Low
pressure will remain over the central High Plains with the dryline
from central KS across western OK and into western TX. Storms should
form by late afternoon and continue into the night along the length
of the dryline, which will be oriented parallel to the upper flow.
The possibility exists for numerous storms, and favorable deep-layer
shear suggests some severe weather is likely. Wind and hail appear
most probable, as storm mode may become complex. Sufficient
low-level shear with about 30 kt 850 mb flow may support a tornado
risk before storms become too numerous and merge during the evening.

Models continue to be in good agreement through the D6-D8 period,
showing the upper low slowly moving east across NM, maintaining a
strong southwesterly flow regime across the southern Plains.
Numerous rounds of heavy thunderstorms are expected across OK and TX
on D6-D7, and shifting toward the lower MS Valley by D8. While
low-predictability severe weather may occur during this time frame,
heavy rain is most likely.

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