468
ACUS02 KWNS 201732
SWODY2
SPC AC 201731

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1231 PM CDT Thu Jun 20 2024

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS BLACK HILLS
VICINITY EAST INTO THE UPPER MISSISSIPPI VALLEY...

...SUMMARY...
Scattered strong to severe storms will be possible from the northern
High Plains into the upper Mississippi Valley on Friday, with a few
strong storms over parts of the Northeast. A few severe gusts are
also possible over parts of the eastern Great Basin.

...North-Central High Plains to the upper MS Valley...
An organized cluster of showers/thunderstorms will likely be ongoing
early Friday morning in the vicinity of southern MN along a
west-east oriented frontal zone.  It is possible a rejuvenation of
this activity or additional storms on the leading edge of the
outflow will continue to develop east along the warm front during
the late morning into the early afternoon east of the MS River.
Some model data suggest appreciable destabilization will occur ahead
of this thunderstorm cluster, supporting storm intensification and
severe risk.  Farther west, diurnal storms likely develop over the
high terrain of eastern WY into north-central CO, and likely produce
hail and wind as they move across western and into central NE. Ample
instability will remain overnight ahead of High Plains activity to
support a hail and wind risk as it persists all night across SD and
into MN.

...MT...
A weak mid-level trough over the southern Canadian Rockies will
pivot east and glance the MT/Canadian border.  Weak easterly
low-level flow will advect increasing moisture with upper 40s to
lower 50s dewpoints beneath steep 700-500 mb lapse rates (7.5 to 8
deg C/km).  Model forecast soundings show 1500-2000 J/kg MLCAPE
developing by mid afternoon as isolated storms begin to develop over
terrain-favored locales.  Ample mid to high-level westerly flow will
favor storm organization, including the possibility for a couple of
supercells.  Large hail and severe gusts will be the primary hazards
with the stronger storms.  A thunderstorm cluster or two will
probably evolve by evening and eventually move downstream into
eastern MT by the late evening.

...Lower Great Lakes into the Northeast...
Models agree in showing a moist air mass and heating contributing to
destabilization and renewed thunderstorm activity developing from
eastern OH into southern New England.  Forecast soundings indicate
perhaps poorer midlevel lapse rates overall compared to the previous
day, with more of a subsidence inversion around 700 mb. However,
heating will easily support at least isolated development by early
afternoon along the weak front. Isolated to scattered strong to
damaging gusts (50-65 mph) will be the primary concern.

...UT...northern AZ...western CO into WY...
Early Thursday morning observed upper-air raobs and surface data
showed a very moist airmass has advected westward into the Four
Corners.  A mid-level trough initially over CA/NV will weaken as it
moves eastward into the central Rockies by early Saturday morning.
However, ample moisture and diurnally steepening lapse rates coupled
with weak ascent associated with the disturbance, will support
scattered to numerous thunderstorms during the period.  Severe gusts
(60-75 mph) are possible with the stronger downdrafts.

...Southeast AZ...
Isolated to widely scattered thunderstorms are forecast to develop
during the afternoon as temperatures warm into the 90s to the lower
100s.  An appreciably moist airmass (1.25 inch PW; observed on the
12 UTC El Paso, TX observed upper-air sounding) and the development
of 9.5 deg C/km 0-3 km lapse rates will favor isolated microbursts
capable of severe gusts (60-70 mph) with the stronger evaporatively
cooled cores.

..Smith.. 06/20/2024

$$