SPC AC 260601
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0101 AM CDT Sat May 26 2018
Valid 271200Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE CENTRAL AND NORTHERN HIGH PLAINS...AND EASTWARD ACROSS PARTS OF
THE DAKOTAS TO NORTHERN MINNESOTA...
Strong/severe storms will be possible across portions of the
northern and central High Plains and into the Dakotas and northern
Minnesota. A couple of brief tornadoes may also be possible in
conjunction with Alberto as it crosses the eastern Gulf.
An upper low centered in the vicinity of the Great Basin will remain
quasi-stationary on Sunday, though several satellite disturbances
moving through eastern portions of the low will affect convective
potential across portions of the High Plains/northern Plains.
Otherwise, weak troughing will shift across the Great
Lakes/Northeast, with ridging largely prevailing elsewhere with the
exception of the Gulf of Mexico vicinity.
Over the Gulf, Subtropical Storm Alberto is forecast to be moving
slowly northward across the eastern Gulf as a Tropical Storm (please
refer to the latest forecasts from the NHC regarding this system).
Elsewhere, the surface pattern will feature persistent lee troughing
over the High Plains, with a weak surface low possibly moving east
across the North Dakota vicinity overnight, as hints that a
convectively enhanced vort max may crest the central U.S. upper
ridge and shift toward the Upper Great Lakes region can be gleaned
from the latest model runs.
...Central and northern High Plains northeast across northern
Continued northward advection of low-level moisture is expected
across the High Plains, in conjunction with southerly winds near and
ahead of the lee trough. This combined with daytime heating will
result in moderate destabilization from central and eastern Wyoming
east/northeast across the Dakotas, and southward across the High
Plains near/ahead of the lee trough.
As short-wave energy aloft rotates north-northeastward across the
High Plains in cyclonic southerly flow ahead of the Great Basin
system, large-scale ascent should increase through the day. By
afternoon, storm development is expected in upslope-favored areas of
Wyoming, and southward along the lee trough, with clustering/upscale
growth possible into the evening as a low-level jet increases.
With moderate south-southwest flow aloft atop a low-level
south/southeast component, shear supportive of organized/rotating
storms is expected. Initial convective development thus may include
a few supercells, with associated potential for large hail and
damaging winds, along with possibly a tornado or two. With time, as
upscale growth of convection is expected, a
north-northeastward-moving band or bands of storms may spread across
portions of the western Dakotas, with continued severe risk.
Overnight, a cluster of storms may acquire a more eastward
progression -- cresting the upper ridge and shifting into/across
northern Minnesota, possibly including wind and hail risk through
the end of the period.
...Florida/far southern Georgia...
Per latest NHC forecasts, Alberto is expected to have become a
Tropical Storm, and should be moving slowly northward across the
eastern Gulf Sunday. Variability amongst the models with respect to
track and intensity of Alberto remains evident, which has direct
influence on the spatial region within which low-level shear would
be more likely to support enhanced risk for more strongly rotating
cells. As such, specificity regarding the risk area remains
difficult to define, and therefore will introduce a large 5%/MRGL
risk area across a large portion of Florida, and into far southern
Georgia. Expect future adjustments to the forecast as Alberto's
track becomes more certain over time.
...MAXIMUM RISK BY HAZARD...
Tornado: 5% - Slight
Wind: 15% - Slight
Hail: 15% - Slight
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z