Mesoscale Discussion 1839

Issued

Oct 12, 2021, 2:08 PM MDT (20:08 UTC)

Expired

Oct 12, 2021, 3:45 PM MDT

In force

97 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...tornado watch likely

Chance of a watch

95%

The Goodland radar (KGLD), 117 km from the middle of the area, began a volume at 20:09 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

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• Tornado Watch 522Oct 12, 2:45 PM MDT
• Tornado Watch 523Oct 12, 4:30 PM MDT

205 
ACUS11 KWNS 122008
SWOMCD
SPC MCD 122008 
OKZ000-KSZ000-TXZ000-NEZ000-COZ000-122145-

Mesoscale Discussion 1839
NWS Storm Prediction Center Norman OK
0308 PM CDT Tue Oct 12 2021

Areas affected...portions of the central High Plains

Concerning...Severe potential...Tornado Watch likely 

Valid 122008Z - 122145Z

Probability of Watch Issuance...95 percent

SUMMARY...Strong ascent ahead of an advancing upper low will support
rapid destabilization and storm development late this afternoon and
into this evening. Supercells with all hazards including tornadoes
are possible. A tornado watch is likely late this afternoon.

DISCUSSION...As of 1955 UTC, a well-defined upper low was located on
WV imagery near the Four Corners region moving east. To the south of
the low, an 80-100 kt mid-level speed max was observed rounding the
base and ejecting into southern CO. To the north and east of the
low, strong ascent (90-120 DM 12 hr H5 height falls) is supporting
widespread precipitation across the central and northern Rockies. In
response to the powerful dynamics aloft, already strong low-level
pressure gradients are forecast to strengthen rapidly allowing a
relatively warm/moist surface airmass to advect ahead of the
dryline/surface trough supporting destabilization late this
afternoon.

Mid and lower 50s F surface dewpoints at the nose of deeper surface
moisture, have already been observed across southwestern KS as far
north as TQK. Continued warm/moist advection beneath the cold-core
of the upper low will support rapid destabilization (MLCAPE values
of 500-1250 J/kg) by 23-01z given steep mid-level lapse rates near
8.5 C/km. Late afternoon/early evening model soundings also show
very strong and veering wind profiles developing beneath the
mid-level jet, with largely boundary-normal effective shear values
of 60-70 kt supportive of discrete supercells. Low-level shear is
also likely to be strong beneath a 50-60 kt low-level jet. Model
soundings show large looping hodographs (ESRH 300-400 M2/s2)
favorable for strong low-level mesocyclone development. Given the
overall parameter space and potential for strong supercells, a risk
for tornadoes (some significant), large hail, and damaging winds
appears likely to develop by 22-00z. 

Latest observational trends suggest hi-res guidance remains too cool
and dry across much of the High Plains where rapid
warming/moistening is occurring. This lends high confidence in
eventual destabilization of the airmass as the upper low approaches
late this afternoon. Deep convection should gradually evolve out of
the initial updrafts ongoing in the elevated cumulus field across
eastern CO. Weaker buoyancy and storm motions more parallel to the
northern sections of the dryline suggest initial storm mode may
remain linear, though a gradual transition to more isolated
convection is expected with southern extent. Fast-moving long-track
supercells capable of all hazards should evolve rapidly and
intensify as they move through the narrow, but unstable and strongly
sheared warm sector after dark. Given the potential for significant
severe weather, a tornado watch will likely be needed late this
afternoon.

..Lyons/Grams.. 10/12/2021

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

ATTN...WFO...LBF...DDC...GLD...AMA...PUB...BOU...

LAT...LON   36480181 36790197 37160211 37660219 38110231 38840240
            40060256 40510266 40770261 40960246 40970228 40900200
            40740169 40430136 39860108 39210076 38450049 37810030
            37370021 37220026 37010031 36760045 36610065 36540080
            36470097 36460128 36480153 36480181

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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.