SPC MD 1498


MD 1498 Image

Mesoscale Discussion 1498
NWS Storm Prediction Center Norman OK
0242 PM CDT Sat Aug 15 2020

Areas affected...Parts of northeastern Colorado and western Nebraska

Concerning...Severe potential...Watch unlikely 

Valid 151942Z - 152215Z

Probability of Watch Issuance...20 percent

SUMMARY...Isolated to widely scattered strong thunderstorms may
continue to develop into the 4-6 PM MDT time frame.  It still seems
unlikely that a severe weather watch will be needed, but trends will
be monitored.

DISCUSSION...Initiation of isolated strong storm development appears
underway to the southeast of Chadron NE, near the dryline.  This
might be aided by lift associated with weak mid-level warm
advection, but forcing for large-scale ascent otherwise appears
weak, to the south of a seasonably strong northwesterly mid/upper
jet digging into the northern Great Plains.  Northwesterly mid-level
flow is much more modest closer to the northern periphery of
prominent mid-level subtropical ridging, across and to the lee of
the Wyoming/Colorado Rockies, but veering of weak to modest wind
fields with height does appear to be contributing sufficient shear
for supercell structures along the dryline.  

In the presence of steep/steepening lower through mid-tropospheric
lapse rates, inhibition is becoming increasingly negligible along
the dryline, where mixed-layer CAPE is becoming moderately large (on
the order of 1500-2500+ J/kg) within a narrow corridor.  

Further intensification of the ongoing storms seems probable, with
isolated to widely scattered additional storm development possible
through 22-00Z.  While the vertical shear is moderately strong,
deep-layer mean ambient westerly/northwesterly flow is rather weak
(around 15 kt or less).  As a result, any developing supercell
structures likely will be slow moving, with a tendency to drift
south-southwestward.  These probably will be accompanied by a risk
for severe hail and locally strong surface gusts.  A short-lived,
weak tornado/land spout or two may not be out of the question.

..Kerr/Grams.. 08/15/2020

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


LAT...LON   42660298 42640233 42220221 41080267 40170279 39750332
            40160363 42660298 

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