Mesoscale Discussion 1617

Issued

Aug 27, 2021, 1:53 PM CDT (18:53 UTC)

Expired

Aug 27, 2021, 3:30 PM CDT

In force

97 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch possible

Chance of a watch

40%

The Des Moines radar (KDMX), 148 km from the middle of the area, began a volume at 18:54 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

• Tornado Watch 465Aug 27, 5:15 PM CDT

532 
ACUS11 KWNS 271853
SWOMCD
SPC MCD 271853 
IAZ000-MNZ000-272030-

Mesoscale Discussion 1617
NWS Storm Prediction Center Norman OK
0153 PM CDT Fri Aug 27 2021

Areas affected...North Central Iowa and Southern Minnesota

Concerning...Severe potential...Watch possible 

Valid 271853Z - 272030Z

Probability of Watch Issuance...40 percent

SUMMARY...Ongoing storms may become surface based in the next 1-3
hours and increase the severe threat. Area is being monitored for
possible watch issuance.

DISCUSSION...Visible satellite shows widespread cloud cover over
parts of northern Iowa and southern Minnesota associated with
renewed convective development. This is in response to ascent from
an approaching mid-level shortwave trough and low-level warm/moist
air advection. Peripheral/adjacent areas of this activity have
warmed into the mid 80s F to low 90s F where strong insolation has
been occurring this morning and early afternoon. With rich low-level
moisture in place (70+ F surface dew point temperatures), a corridor
of moderate instability (MLCAPE near 2500 J/kg) has developed across
west-central and central Iowa amid ample deep-layer shear (effective
bulk shear 35-45 kt).

The short-term evolution of the ongoing convective activity and any
new development remains unclear. With the aforementioned downstream
heating and destabilization that is occurring, it seems plausible
for the activity over north-central Iowa to become surface-based in
the next couple of hours. This scenario is supported by
high-resolution satellite imagery showing boundary-layer cumulus
developing along the southeastern flank of this activity along an
apparent surface trough. Should this occur, storms may quickly
acquire supercell characteristics. Surface winds remain backed
across north-central Iowa, supporting a favorable low-level shear
environment (e.g., 0-3 km SRH 300 m^2/s^2) for a tornado risk, in
addition to large hail and damaging winds.

Although cloud cover remains expansive farther north, over parts of
southern Minnesota, continued low-level warm/moist advection and
possible clearing along with ascent from the advancing mid-level
trough may allow for additional convective development later this
afternoon. These areas continue to be monitored for potential watch
issuance.

..Karstens/Dial.. 08/27/2021

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

ATTN...WFO...DVN...ARX...MPX...DMX...

LAT...LON   42139334 42319471 43119490 44029407 44169290 43709155
            42929141 42469215 42139334

Mesoscale Discussions in Iowa, 2021Mesoscale Discussions in Minnesota, 2021Every mesoscale discussion in 2021

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.