Day 1 Severe Weather Outlook

Valid 141200Z – 151200Z


Scattered severe thunderstorms with very large hail and damaging
winds are expected across the central High Plains this afternoon and
evening. A few strong storms may be noted across the Gulf Coast to
the southern Middle Atlantic.

…Central High Plains…

Large-scale pattern is forecast to change little across the western
US through the day1 period. Broad upper ridging will hold across the
Great Basin with seasonally strong mid-level flow extending from
WA/OR, across the northern Rockies into the central Plains. It’s not
entirely clear whether a weak disturbance will affect the High
Plains later today, however steep mid-level lapse rates persist
across this region within broad northwesterly flow regime. Strong
diurnal heating will once again contribute to significant buoyancy
in the lee of the Rockies prior to convective initiation. In the
absence of a meaningful short-wave trough, it appears surface
heating will prove instrumental in thunderstorm development. It
appears thunderstorms should develop by 21-22z as convective
temperatures are breached. Latest CAMs support this scenario with
scattered convection developing by late afternoon from southeast
MT-eastern WY/CO. Forecast soundings across this region strongly
favor supercells and steep lapse rates/bulk shear appear supportive
of very large hail. Local hail algorithm generates hail in excess of
2″ with robust convection across the High Plains again this
afternoon. Given the stronger shear expected later today, compared
to Tuesday, there is reason to believe supercells may maintain their
character a bit longer than yesterday. For these reasons have
increased severe probabilities to account for a potentially more
widespread severe event from eastern WY into eastern CO/northwest
KS. While initial activity should prove productive in generating
hail, damaging winds will become more common if an MCS evolves later
in the evening along nose of LLJ.

…Gulf States/Southeast-Middle Atlantic Coast…

Weak surface boundary will sag southeast during the day, extending
from VA-Carolinas-central Gulf States by 18z. This boundary will
serve as the focus for convection within a high-PW air mass
characterized by generally weak shear. While lapse rates are not
particularly steep, Isolated damaging winds could be noted with
short-lived wet micro bursts.

..Darrow/Cook.. 08/14/2019


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