ACUS01 KWNS 141231
SWODY1
SPC AC 141229

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0729 AM CDT Wed Aug 14 2024

Valid 141300Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR EASTERN
NEBRASKA...SOUTHWEST IOWA...NORTHEAST KANSAS...AND NORTHWEST MISSOURI...

...SUMMARY...
Scattered severe thunderstorms capable of all hazards are possible
late this afternoon through the evening across adjacent portions of
the mid and lower Missouri Valley.

...Synopsis...
Water-vapor imagery this morning shows a mid- to upper-level
shortwave trough over WY/CO moving east-northeast.  This upper
feature is forecast to rotate through the base of a larger-scale
trough and move into the eastern ND/northern MN vicinity by daybreak
Thursday.  In its wake, an upstream perturbation will move from
southeast OR/southern ID into NE by late tonight.  Consequently, an
upper ridge will shift eastward from the lower-mid MO Valley through
the mid MS Valley during the period.

At the surface, weak/broad low pressure initially over the High
Plains is forecast to gradually consolidate as it shifts eastward
across the central Plains, in tandem with the advance of the upper
trough.  As this occurs, a cool front will shift southeastward
across the central Plains through the afternoon and evening.
Overnight, further consolidation of the surface low is expected as
it moves slowly northeastward into southern Minnesota, while the
trailing front sharpens, extending from the low southwestward across
Kansas and into New Mexico by the end of the period.

...Mid to lower Missouri Valley...
Mid morning radar/IR satellite mosaic shows an MCS over northern
MO/IA with a well-developed MCV moving east-northeast over northeast
NE.  This activity will continue to weaken this morning and become
increasingly displaced from KS/NE where a renewed focus for
thunderstorm development will occur later today.  The remnant
outflow boundary will likely persist into the afternoon across
the southeastern Nebraska/northwestern Missouri/southwestern Iowa
area and modify as heating occurs to the west edge of the MCS cirrus
canopy.  Rich low-level moisture was sampled this morning on the
Topeka, KS 12 UTC raob (16.7 g/kg lowest 100-mb mean mixing ratio).
Southerly low-level flow will aid in moistening the airmass as
insolation contributes to moderate to strong buoyancy (2000-4000
J/kg  MLCAPE) by peak heating.

By late afternoon as low pressure and the cold front shifts
eastward into this area, the low/front and remnant outflow should
all provide low-level foci for storm initiation.  With enhanced
southerly low-level flow ahead of the advancing mid-level trough
beneath moderate (30 to 40 kt) mid-level westerlies, resulting shear
suggests that initial storms will likely be supercells capable of
producing large hail (1 to 2.5 inches in diameter).  Enlarged
hodographs along and north of the modified outflow boundary suggest
a tornado risk will probably accompany a couple of the more intense
supercells, where surface to 0.5 km flow remains relatively backed
beneath a belt of 30-40 700-mb flow.  Given modest flow above 300
mb, upscale growth into a cluster is forecast to occur relatively
quickly during the early evening with a band further consolidating
into a eastward-moving line by mid to late evening.  Coincident with
the transition to upscale growth, the tornado risk will gradually
wane and severe gusts capable of wind damage will become the primary
concern.  This activity will likely persist as a linear MCS but the
severe threat should lessen with east extent towards the MS River
late.

...Wyoming and vicinity eastward across the northern and central
Plains...
As the upper trough -- comprised of several vorticity maxima
embedded in the broader cyclonic flow field -- shifts across the
Rockies toward/into the Plains, daytime heating beneath cooler air
at mid levels will support modest destabilization across a broad
area.  Ascent -- focused near favored higher terrain areas and near
various weak surface boundaries -- will contribute to widely
scattered thunderstorm development during the afternoon.  Moderate
mid-level westerlies will contribute to shear sufficient for a few
stronger storms -- and attendant risks for hail and locally
strong/severe wind gusts into the evening hours.

..Smith.. 08/14/2024

$$
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