SPC MD 1466


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Mesoscale Discussion 1466
NWS Storm Prediction Center Norman OK
0217 PM CDT Tue Aug 11 2020

Areas affected...extreme southeast WY...northeast CO and the NE

Concerning...Severe potential...Watch possible 

Valid 111917Z - 112115Z

Probability of Watch Issuance...40 percent

SUMMARY...Showers and thunderstorms will gradually increase in
coverage and intensity through late afternoon. Isolated strong gusts
and hail are possible. A severe thunderstorm watch may be needed
later this afternoon, but exact timing is uncertain as convection
may initially remain rather isolated.

DISCUSSION...Isolated thunderstorms have developed near the CO/WY
border in the vicinity of CYS over the last hour or so. Additional
showers have also been noted further south across northeast CO in
the vicinity of a surface trough. This activity should gradually
increase in coverage and intensity over the next couple of hours as
boundary layer inhibition continues to erode. In the meantime,
transient showers and storm could produce isolated strong gusts,
generally east of the I-25 corridor. 

Once capping has sufficiently eroded and low level flow begins to
increase late this afternoon, better organized and longer-lived
cells are expected. This will occur in a zone of moderate
instability along/just east of a surface trough extending southward
from eastern WY into eastern CO. MLCAPE values around 1000-2000 J/kg
have already been noted in 18z mesoanalysis, and some additional
destabilization is possible as southeasterly low level flow
continues to transport upper 50s to low 60s dewpoints westward to
the surface trough/dryline. Strong heating is resulting in very
steep low level lapse rates, which will aid in downburst potential.
With time, effective shear is forecast to increase, and large hail
will be possible with strongest cells.

..Leitman/Grams.. 08/11/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   42980307 42930236 42590192 41850189 40070198 39490217
            39150254 39150362 39230418 39800449 41270442 41980440
            42310429 42840391 42980307 

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