Severe Storm Outlook Narrative (AC)
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000
ACUS02 KWNS 251723
SWODY2
SPC AC 251722

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1222 PM CDT Thu May 25 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
CENTRAL HIGH PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
ROCKIES EAST INTO THE MIDDLE MISSISSIPPI VALLEY AND OHIO VALLEY...

...SUMMARY...
Severe thunderstorms will be possible Friday across the central High
Plains eastward into the middle Mississippi and Ohio Valley region.
The greatest coverage of severe storms will be from northeastern
Colorado into western and central Kansas.

...Synopsis...
An upper-level low over the northeast states will lift northeast
while another upper low over Manitoba/Saskatchewan Provinces moves
little.  Within the relatively low-amplitude flow that will evolve
south of these features, a shortwave trough will move across the
central High Plains late in the day and across portions of the
middle MS and OH Valleys.  A cold front will extend south from the
upper Midwest across Kansas/eastern Colorado Friday afternoon, while
a second cold front extends from the southern High Plains across
Oklahoma to a weak surface low near the Missouri/Illinois border.  A
warm front will extend east from the low across the Ohio Valley.

...Central High Plains...
An increasingly moist southeasterly low-level flow (upper 40s/near
50 deg F surface dew points) will develop across the higher terrain
of northeast Colorado/southeast Wyoming on Friday, with dewpoints
near 60 degrees F farther east across central Kansas. This will
result in MLCAPE of 750-1500 j/kg by late afternoon, and mid-level
flow of 35 kts will contribute to deep-layer shear of around 40 kts.
Thunderstorms should develop across the high terrain as the upslope
flow is augmented by ascent with the approaching upper-level
impulse.  Initial storm mode will include a few supercells capable
of very large hail given steepening mid-level lapse rates.  Damaging
gusts will also be possible, and forecast soundings depict low-level
hodograph curvature (surface easterlies veering to 55-kt westerly
250-mb flow) and relatively modest surface temperature-dewpoint
spreads which suggests at least some risk for a tornado or two.  A
developing 30-35 kt low-level jet/warm advection regime should
result in one or two clusters eventually evolving and moving east
overnight across western/central Kansas.  A continued risk for large
hail and strong winds will exist with these storms.

...Eastern KS into the middle MS Valley and OH Valley...
Strong south to north low-level moisture advection over the lower
Rio Grande Valley midday Thursday will continue and increasingly
rich moisture will advect into the Ozarks by early Friday and into
portions of the OH Valley late Friday on the nose of a
strong/veering LLJ.  The eastward advection of an elevated mixed
layer will result in a substantial capping inversion across the
increasingly moist/unstable sector to the south of a frontal zone
draped across the region.  The accompanying plume of steep to very
steep 700-500 mb lapse rates (7-8.5 degrees C/km) coupled with
heating and low-level moisture (dewpoints in the 60s degrees F) will
yield moderate to strong buoyancy by late afternoon.  Deterministic
models vary considerably regarding the development of isolated
diurnal thunderstorm development during the late afternoon/early
evening when MLCINH is weakened.  Water-vapor imagery midday
Thursday indicates a weak shortwave trough over the Grand Canyon and
model guidance suggests this feature will move to the middle MS
Valley by noon Friday.  Adequate shear/instability profiles will
support organized severe thunderstorms should they develop with an
attendant hail/wind risk.  This disturbance is associated with
convective development in some model guidance over IL and quickly
moving east-southeast late in the day/evening as isentropic ascent
increases across the OH Valley and elevated thunderstorms may
develop on the eastern periphery of the central U.S. EML with a
wind/hail risk.

..Smith.. 05/25/2017

$$



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