Mesoscale Discussion 1224
NWS Storm Prediction Center Norman OK
1154 PM CDT Sat Jun 20 2026
Areas affected...portions of northeast Colorado
Concerning...Severe potential...Watch unlikely
Valid 210454Z - 210700Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated thunderstorms capable of producing large hail
will be possible this evening into the early morning hours. The
overall limited space and time of this threat should preclude a
watch. The area will continue to be monitored.
DISCUSSION...Despite the cool nocturnal boundary layer, isolated
supercell thunderstorms have developed across portions of northeast
Colorado this evening. These storms are developing on the nose of an
objective analyzed 70-knot upper-level jet moving across the central
Rockies, and appear to be rooted around 700 millibars per RAP
forecast soundings. One of these supercells produced 2.5" hail
across portions of Logan County, CO, within the last hour before
weakening and eventually dissipating as it moved east. A second
supercell has developed to its southwest across Weld County, CO.
This secondary supercell appears to have undergone a split, with the
left mover remaining nearly stationary over Greeley, CO.
Multi-radar, multi-sensor objective analysis of these storms
suggests hail around 1.5" is possible.
Although there is a lack of well defined low-level forcing
mechanisms, general large-scale ascent of a moist unstable
environment will support an ongoing threat of thunderstorm
development this evening into the early morning hours. Steep lapse
rates in the 700-500 millibar layer (around 9 C/km) will support
large hail potential with any of these storms, perhaps even
significant (2-2.5") hail. The overall space/time of this potential
should remain fairly limited and a watch is currently not
anticipated. However, should it become apparently that additional
thunderstorm development is likely, a watch may be considered late
this evening/overnight.
..Marsh/Smith.. 06/21/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GLD...BOU...
LAT...LON 40250504 40810482 40880382 40700274 40700254 40080260
39820297 40000452 40250504
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
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