- Day Three
acus03 kwns 250730
Storm Prediction Center ac 250729
Day 3 convective outlook corr 1
National Weather Service Storm Prediction Center Norman OK
0229 am CDT Sat may 25 2019
Valid 271200z - 281200z
..there is a slight risk of severe thunderstorms from portions of
the Central Plains eastward to the Midwest...
Corrected for 5% label
Strong to severe storms are possible from Nebraska eastward to the
Midwest. Isolated severe storms are possible from northern Kansas
southward through West Texas.
Severe potential on d3/Monday will be tied to an approaching
mid-level cutoff low that should reach the central rockies by the
end of the period. A belt of strong mid-level flow will exist on
the southeastern periphery of the mid-level low, but this jet should
remain mostly west of a surface dryline that will extend from
southwestern Nebraska southward through West Texas through much of
the day. Downstream, shortwave ridging will exist across the
Missouri River valley during the afternoon, while shifting eastward
overnight. At the surface, a low will organize in eastern Colorado
throughout the period, while a warm front extends across central
Nebraska northeastward to southern Wisconsin. A buoyant airmass
will reside south of this boundary throughout the forecast period.
Primary indications are that convection will be tied to the warm
front through most of the forecast period, with strong capping and
subsidence evident across the open warm sector through late in the
period. Steep lapse rates aloft (especially over nebraska) will
Foster hail with mostly elevated cells that form near the front,
though any cells that can ingest surface-based parcels and reside
near the warm front will have a risk of damaging wind and tornadoes.
Guidance suggests that multiple rounds of convection may traverse
this boundary through the forecast period.
The greatest chance of warm-sector convection will exist across
southern Nebraska and northwestern Kansas along and ahead of a Stout
dryline. This risk should be greatest after 00z when forcing for
ascent finally reaches the northwestern extent of the warm sector
and weakens the cap. Supercellular shear profiles will Foster storm
organization, while strong instability and steep mid-level lapse
rates will Foster hail and damaging wind gusts. The tornado threat
is a bit conditional in this area and will depend on timing of
convective development - if storms develop too late in the forecast
period they will likely be slightly elevated. Storms that can form
earlier in the day will pose a threat of all severe hazards.
Across western Nebraska, easterly low-level flow just north of the
front may bring 50s f dewpoints up against higher terrain in
Wyoming. A few thunderstorms may result, with shear profiles
supportive of updraft rotation along with an attendant threat for
hail, wind and perhaps an isolated tornado. Some uncertainty exists
with this scenario, however, with some models suggesting more of a
northerly component to low-level flow and stable low-levels.
..southern Wisconsin, Illinois, Indiana...
Early-day convection may alter the position of a surface warm front,
which models inconsistently depict across the area. By late
afternoon, however, models hint at the potential for a few
surface-based storms to develop south of the warm front, which seems
plausible as models also indicate the passage of a mid-level
shortwave trough just north of the region during peak heating hours.
Should these storms materialize, they will reside in a strongly
buoyant airmass, with vertical shear profiles favoring supercellular
storms. Model inconsistencies lend greater-than-usual uncertainty,
although the warm-sector environmental parameter space suggests that
conditional marginal/slight risks are appropriate.
..northern Kansas southward to Texas...
Models generally depict only isolated storm development along the
dryline - most likely after 03z. This seems plausible given the
late arrival of forcing and eastward shift of the dryline beginning
after dark. Any storms that can develop along this boundary will
have a threat for large hail and damaging wind gusts, but will also
struggle against mid-level inhibition. Thus, the severe threat in
this area is conditional.