Day 1 Severe Weather Outlook

Valid 141300Z – 151200Z

…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
ACROSS PARTS OF THE CENTRAL PLAINS TO THE UPPER MS VALLEY…AND THIS
AFTERNOON/EVENING ACROSS PARTS OF AZ…

…SUMMARY…
Isolated severe storms with damaging gusts and large hail will be
possible from the upper Mississippi Valley into the central Plains.
Isolated damaging gusts will be possible this afternoon/evening in
the lower desert regions of Arizona.

…Upper MS Valley to the central Plains through tonight…
Elevated thunderstorms are ongoing over northeast NE in a zone of
low-level warm advection on the nose of a 45 kt southwesterly
low-level jet. This zone of ascent and storms will spread
east-northeastward across northern IA/southern MN through the day,
immediately in advance of a low-amplitude shortwave trough moving
from the Dakotas to the upper MS Valley. In the wake of the warm
advection, storm initiation will depend on weak low-level ascent
along a surface trough that extends southwestward across NE/KS.
Stronger surface heating and deeper mixing is expected along the
trough in KS, with lesser mixing depths and a greater probability of
maintaining convective inhibition through the afternoon in the warm
sector farther northeast. Thus, surface-based thunderstorm
development is uncertain this afternoon/evening.

The elevated convection could pose a threat for isolated large hail
as far east as western WI later today into tonight. If
surface-based storms form as far northeast as southern MN this
afternoon, vertical shear profiles will be sufficient for
supercells. Somewhat weaker vertical shear is expected with
southwestward extent into southwest KS, where high-based storms
would pose a threat for isolated damaging gusts and large hail.

…Southern AZ this afternoon/evening…
An MCV over northwest Mexico will drift north-northwestward toward
southeast AZ through tonight. A substantial increase in
low-midlevel moisture/PW has occurred across southeast and south
central AZ the past 12-24 hours, and the moisture will continue to
spread westward today. Stronger surface heating west of the thicker
clouds, as well as 10-20 kt east-northeasterly midlevel flow around
the north side of the MCV, will provide an environment favorable for
storms to form and spread westward into the lower deserts this
afternoon/evening. Typical inverted-v profiles and MLCAPE of
500-1000 J/kg will support a threat for hybrid microbursts capable
of producing isolated damaging winds.

…Central/southern Appalachians this afternoon…
A narrow corridor of weak-moderate buoyancy is expected this
afternoon across the central/southern Appalachians, and a few storms
are expected along a cold front and over the higher terrain this
afternoon. Very isolated strong downburst winds cannot be ruled
out, though the threat is too marginal to warrant damaging wind
probabilities.

..Thompson/Gleason.. 09/14/2019

$$

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