SPC AC 250608
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0108 AM CDT Fri Aug 25 2017
Valid 261200Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ALONG AND INLAND
OF THE MIDDLE TO UPPER TX COAST INTO SOUTHWEST LA...PRIMARILY FOR A
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK FROM THE TX COAST TO SOUTHWEST LA...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WESTERN AND CENTRAL SD THROUGH NE TO WESTERN IA...
A tornado threat will exist near and to the north to northeast of
the inland track of Hurricane Harvey on Saturday, primarily along
and inland of the middle to upper Texas coast. Meanwhile, a couple
of severe storms may develop near and southeast of the Black Hills
late Saturday afternoon, before spreading into parts of west-central
Nebraska Saturday evening. Isolated severe storms could also
develop into eastern Nebraska to western Iowa Saturday afternoon and
Latest National Hurricane Center guidance as of 25/06Z indicated
Hurricane Harvey will be near the TX coast between CRP and VCT at
26/12Z, with some continued inland movement toward the northwest.
Meanwhile across the rest of the contiguous U.S., 500-mb heights are
expected to rise across the Great Basin, with a ridge building from
the Pacific Northwest into the southern portions of the western
Canadian Provinces. Northwesterly winds are expected to strengthen
across the northern Plains into NE within the northeast periphery of
the western ridge and a shortwave trough tracking into the Upper
Midwest. At the surface, a weakening area of low pressure will
track east across southern MN with a trailing cold front advancing
southeast and south across IA and NE.
...TX Coastal Plain to southwest LA...
Given the presence of Hurricane Harvey moving inland some across the
northern portion of the lower TX to middle TX coast, enlarged
clockwise hodograph curvature and some instability suggest a
potential tornado threat will exist this forecast period.
...Southern MN/IA/eastern NE...
A cluster of storms, possibly an MCS, should be ongoing at 12Z
Saturday across parts of southern MN and northwest to northern IA.
This activity will be associated with a weak mid-level impulse
tracking across MN and northern IA late day 1 into early day 2.
This impulse is expected to move into WI and the Upper Great Lakes
Saturday, while models suggest warming 500-mb temperatures in its
wake. Although convection may continue to form along and ahead of
the ongoing MCS into Saturday afternoon, weak instability/shear
suggest the severe threat should be too low to introduce severe
probabilities across northern IA into MN.
Greater destabilization will be possible across parts of western IA
and eastern NE near the cold front, as greater potential will exist
for surface heating to the south of the cloudiness and early day
convection/thunderstorms farther north. Despite this factor, weak
effective bulk shear may limit the overall severe threat.
...Parts of western and central SD and NE...
Despite weak low-level winds, strengthening northwesterly 500-mb
winds of 30-35+ kt and vertically veering wind profiles suggest the
potential for organized convective development, including an
isolated supercell or two, and perhaps the evolution of a small
convective system. Late Saturday afternoon CAPE should be modest
with MLCAPE up to 1000 J/kg. These factors and steep mid-level
lapse rates suggest some severe potential. Given weak forcing
aloft, orographic forcing near the Black Hills may support
initiation of activity Saturday afternoon, with some potential for
upscale growth into western NE within an area of increasing
low-level warm-air advection. Isolated hail and strong/damaging wind
gusts will be the primary threats.
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z