Mesoscale Discussion 652

Issued

Jun 6, 2018, 2:22 PM CDT (19:22 UTC)

Expired

Jun 6, 2018, 4:15 PM CDT

In force

113 min

Issued by

the Storm Prediction Center

Chance of a watch

60%

The Omaha radar (KOAX), 30 km from the middle of the area, began a volume at 19:25 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.

• Severe Thunderstorm Watch 157Jun 6, 3:20 PM CDT

494 
ACUS11 KWNS 061923
SWOMCD
SPC MCD 061922 
IAZ000-MOZ000-NEZ000-SDZ000-062115-

Mesoscale Discussion 0652
NWS Storm Prediction Center Norman OK
0222 PM CDT Wed Jun 06 2018

Areas affected...Portions of the mid Missouri Valley

Concerning...Severe potential...Watch possible 

Valid 061922Z - 062115Z

Probability of Watch Issuance...60 percent

SUMMARY...Scattered thunderstorms are expected to develop by late
afternoon, with an attendant threat of damaging winds and large
hail. A watch may be needed within the next 1-2 hours.

DISCUSSION...Visible satellite and surface analysis data indicate a
somewhat complex pattern across the region this afternoon. A
well-defined surface trough stretches from northeastern Colorado to
a weak low over northeastern Nebraska, and then onward to northern
Iowa. To the south of this trough, observations indicate a prior
outflow boundary has mixed out across Iowa, yielding a quickly
destabilizing boundary layer from western Iowa into south-central
and eastern Nebraska. Along with temperatures rising into the lower
90s, dew points in the upper 60s/lower 70s are yielding MLCAPE
values upwards of 4000 J/kg (based on meso-analysis data) south of
the trough. The 12Z OAX sounding, adjusted for current surface
conditions, confirms this level of strong instability.

Although forcing for ascent aloft remains nebulous, radar/satellite
data highlight an MCV over north-central Kansas, and this could
support convective initiation across parts of southern Nebraska, as
it continues to slide east/northeast. More probable, however, is the
development of organized convection over eastern Nebraska into Iowa,
as weak mid-level ascent northeast of the MCV overspreads a
low-level theta-e/instability maximum near the Missouri Valley.

Although effective shear and flow through 500mb remain modest at
best (i.e., no more than 20-25 kt), very unstable profiles will
favor strong downdraft momentum and a damaging wind threat. Large
hail will also be possible, but aforementioned modest flow may
temper the threat for very large hail growth. Into early evening,
cells will likely propagate southward into the instability axis,
with some upscale growth maintaining a damaging wind threat. To
account for this threat, a watch may be needed within the next 1-2
hours.

..Picca/Weiss.. 06/06/2018

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

ATTN...WFO...DMX...EAX...FSD...OAX...GID...LBF...

LAT...LON   40399837 40849857 41349855 42039817 42549686 42769598
            42749506 42119364 41609264 41349251 40819271 40399441
            40169542 40099618 40129775 40219809 40399837

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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.