ACUS01 KWNS 181254
SWODY1
SPC AC 181253

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0753 AM CDT Sun Aug 18 2024

Valid 181300Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR KANSAS INTO
THE WESTERN OZARKS...AND FROM THE MID-ATLANTIC STATES INTO THE DEEP SOUTH...

...SUMMARY...
Scattered severe gusts are possible from northern Kansas to the
western part of the Ozark Plateau, and in a separate area from the
Mid-Atlantic States to the Deep South this afternoon to early
evening.

...Rockies/Central Plains...
Water-vapor imagery this morning indicates a short-wave trough
cresting the Rockies mid-level ridge.  This feature is forecast to
move southeast with an enhanced belt of 500-mb flow (40-50 kt)
moving into the Ozarks late.  The 00z MPAS-HT-NSSL model seemed to
reasonably depict elevated convection and a small severe cluster
this morning over SD and northern NE.  Other model guidance varies
considerably on the handling of this early day storm activity.  A
risk for large hail will continue across east-central NE through the
late morning in association with WAA-related storms favoring the
eastern gradient of moisture/instability where isentropic lift will
be maximized.  Based on several factors 1) the aforementioned MPAS
guidance, 2) enhanced mid to upper-level northwesterly flow per OAX,
TOP, and SGF 12 UTC raobs, and a reservoir of higher theta-e across
northern OK into KS, it seems possible a forward-propagating
cluster/MCS may evolve this afternoon from KS into the western
Ozarks.  Have increased severe probabilities to account for this
forecast evolution.

...Middle Atlantic to Deep South...
Not much change in thinking from the prior forecast in that a Great
Lakes/OH Valley upper trough will shift east and reach the spine of
the Appalachians by early evening.  Modest 500mb flow should extend
within the base of the trough into the Mid-Atlantic states where
shear profiles will be most supportive of organized storm structures
(including multicells and transient supercells). Damaging gusts
(50-65 mph) will likely be the primary risk, but some risk for hail
and perhaps a brief tornado can be expected.

The trailing portion of the front across the Deep South will not be
particularly convergent as it surges into GA-AL-MS.  However, a
seasonably moist airmass (15-16 g/kg lowest 100-mb mean mixing
ratios) sampled by the 12 UTC Jackson, MS east to the coastal
Carolinas raob sites, will undergo strong heating through mid
afternoon.  Several clusters of strong to severe/damaging
thunderstorm clusters are forecast to evolve by mid to late
afternoon and push towards the coastal areas by early evening.

...Interior West...
Scattered to numerous diurnal thunderstorms are forecast to develop
on the western/northern periphery of a mid-level anticyclone
centered over northeast NM.  An ongoing thunderstorm cluster over
central AZ will continue to move northward through the midday.  This
convection appears to be partly influenced by a weak disturbance of
convective origin and is partly evident some augmenting of mid-level
flow in the KIWA (Phoenix WSR-88D) VAD data.  As a result, greater
storm coverage will likely be associated with this feature as it
moves into a destabilizing airmass across southern UT by early to
mid afternoon.  Severe gusts (60-75 mph) are possible with this
diurnally enhanced activity from the UT/AZ border northward into MT.

..Smith/Mosier.. 08/18/2024

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