Mesoscale Discussion 1560

Issued

Aug 19, 2021, 12:00 PM MDT (18:00 UTC)

Expired

Aug 19, 2021, 2:00 PM MDT

In force

2 hr

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch likely

Chance of a watch

80%

The Goodland radar (KGLD), 135 km from the middle of the area, began a volume at 18:05 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Severe Thunderstorm Watch 449Aug 19, 12:40 PM MDT

211 
ACUS11 KWNS 191801
SWOMCD
SPC MCD 191800 
NEZ000-KSZ000-COZ000-192000-

Mesoscale Discussion 1560
NWS Storm Prediction Center Norman OK
0100 PM CDT Thu Aug 19 2021

Areas affected...Northeast Colorado...southwest Nebraska...and far
northwest Kansas

Concerning...Severe potential...Watch likely 

Valid 191800Z - 192000Z

Probability of Watch Issuance...80 percent

SUMMARY...Thunderstorms are expected to initiate by the mid
afternoon hours (around 20z) across northeast Colorado. A watch is
likely in the coming hours to address this concern.

DISCUSSION...Latest GOES visible imagery shows a shallow, but
growing, field of cumulus north of a surface low and along a
strongly confluent stationary boundary. The lack of vertical
development within this field suggests that the environment remains
capped, which is supported by the latest RAP forecast soundings and
mesoanalysis estimates. However, a modest moisture flux to the east
of the low/surface boundary is allowing MLCAPE to increase into the
1000-1500 J/kg range. Furthermore, inhibition is forecast to
continue to weaken through the mid afternoon hours as broad scale
ascent associated with the approach of the main synoptic wave to the
west overspreads the region and continued diurnal heating/mixing
erode the cap. Latest guidance suggests storms may initiate around
20z across northeast CO roughly within this zone. Effective bulk
shear values between 30-40 knots will be favorable for storm
organization and may support a few supercells capable of posing a
severe wind/hail threat. Initially discrete modes will likely grow
upscale through the late afternoon due to a strong meridional wind
component above the boundary layer that is in line with the main
axis of forcing for ascent. Backed flow in the lowest 1 km is
supporting effective SRH values on the order of 50-150 m2/s2, which
suggests a tornado or two is possible - especially with any
initially discrete cells. An increase in the nocturnal jet this
evening will boost low-level SRH, but storm mode may hinder the
tornado threat to a degree. Regardless, severe wind/hail appear
probable this afternoon, and a watch is likely in the next 1-2 hours
to address this concern.

..Moore/Dial.. 08/19/2021

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

ATTN...WFO...LBF...GLD...PUB...BOU...CYS...

LAT...LON   38820357 40470366 41610355 41950356 42210328 42320274
            42170206 41760117 41050060 40200039 39510073 39070144
            38620213 38440295 38820357

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The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.