- Day Three
acus02 kwns 250556
Storm Prediction Center ac 250555
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1255 am CDT Fri may 25 2018
Valid 261200z - 271200z
..there is a marginal risk of severe thunderstorms across portions
of Montana and the adjacent High Plains...as well as over portions
Isolated severe storms are possible across Montana into the western
Dakotas. A tornado or two may also occur with Gulf-low-associated
convection over portions of the Florida Peninsula.
Gradual eastward progression of the upper pattern is progged for
Saturday, as a closed low shifts across the Great Basin vicinity and
a weaker trough moves slowly across the Great Lakes/Ohio Valley
At the surface, a weak/remnant front is progged to extend westward
from southern New England across the Midwest and into the northern
plains, while a Lee trough persists over the High Plains. Finally,
a low of tropical/sub-tropical origin is progged to shift northward
across the central/eastern Gulf of Mexico. For additional
information on this low, please see the latest tropical weather
outlook from the NHC.
..Montana vicinity into the northern High Plains...
Despite rather modest moist advection across the northern High
Plains and into Montana, steep mid-level lapse rates northeast of
the upper low center in the vicinity of the Great Basin will support
moderate afternoon destabilization across the Montana vicinity.
Expect storms to develop across this region during the afternoon,
within an environment of moderate/veering flow with height. The
anticipated cape/shear combination should be sufficient to support a
few stronger multicell clusters or even a couple of storms with
mid-level updraft rotation -- and thus attendant/limited risk for
locally damaging winds and hail remains apparent.
As a southerly low-level jet develops across the High Plains during
the evening, some potential for a cluster of storms to shift out of
Montana and into the Dakotas is apparent, with limited risk for
severe weather possibly accompanying any cluster of storms into the
..southern and western portions of Florida, and the Keys...
While the track of the evolving low -- now centered near the Yucatan
Peninsula -- remains variable per different forecast models, general
consensus is that a slowly deepening low will drift north across the
western/central Gulf of Mexico Saturday, with the low-level wind
field gradually increasing across portions of Florida as a result.
Most models suggest that by afternoon/evening, the low-level wind
field surrounding the system will likely have increased sufficiently
such that enhanced low-level updraft rotation will be possible. As
such -- stronger cells evolving within bands of convection streaming
northwestward may pose some risk for brief tornadic spin-ups as a
result. Greatest risk at this time would appear to be over South
Florida and then Keys, and then northward along a West-Coast
sea-breeze boundary through the Tampa vicinity. Risk may continue
through the overnight hours.
..maximum risk by hazard...
Tornado: 2% - marginal
wind: 5% - marginal
hail: 5% - marginal