Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 251836
SPC MCD 251835

Mesoscale Discussion 0840
NWS Storm Prediction Center Norman OK
0135 PM CDT Thu May 25 2017

Areas affected...Portions of northeastern CO...western/central
NE...and northwestern KS

Concerning...Severe potential...Watch possible

Valid 251835Z - 252030Z

Probability of Watch Issuance...40 percent

SUMMARY...An isolated large hail and damaging wind threat may
develop over the next several hours. Watch issuance is possible
depending on convective trends.

DISCUSSION...18Z surface analysis depicts a cold front arcing from a
low over north-central SD across parts of central/western NE and
into northeastern CO. A small cluster of thunderstorms ongoing as of
1830Z across northeastern CO is probably associated with a minor
shortwave trough embedded within larger upper troughing extending
from Saskatchewan into the northern Plains/Rockies and Great Basin.
Additional thunderstorms will likely form over the next several
hours across parts of northern/central CO as broad large-scale
ascent attendant to the upper trough overspreads this region. The
boundary layer downstream of ongoing convection across the central
High Plains is becoming well-mixed this afternoon with plentiful
diurnal heating occurring. Although low-level moisture remains
somewhat modest with surface dewpoints generally in the mid 40s to
lower 50s, steep mid-level lapse rates and cool mid-level
temperatures are contributing to MLCAPE up to 1000 J/kg per latest
RAP Mesoanalysis. Additional heating may encourage instability to
increase up to 1500 J/kg along and south of the front by peak
heating this afternoon.

Strengthening mid-level west-southwesterly winds associated with the
mid/upper-level trough will support effective bulk shear values of
35-45 kt across this region through this evening, which should be
sufficient for supercell structures. Recent short-term
convection-allowing model guidance remains unclear regarding the
coverage and intensity of thunderstorms this afternoon. But, the
overall parameter space will be favorable for organized updrafts
with an isolated large hail and damaging wind risk, with at least
some chance at upscale growth into one or more line segments
potentially focused along/near the front. If radar/satellite trends
indicate an increase in convective strength/coverage this afternoon,
then watch issuance may be needed.

..Gleason/Kerr.. 05/25/2017

...Please see for graphic product...


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