Mesoscale Discussion 1339

Issued

Jul 18, 2017, 2:19 PM CDT (19:19 UTC)

Expired

Jul 18, 2017, 4:15 PM CDT

In force

116 min

Issued by

the Storm Prediction Center

Chance of a watch

40%

The Green Bay radar (KGRB), 148 km from the middle of the area, began a volume at 19:18 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.

338 
ACUS11 KWNS 181919
SWOMCD
SPC MCD 181919 
MIZ000-WIZ000-IAZ000-MNZ000-182115-

Mesoscale Discussion 1339
NWS Storm Prediction Center Norman OK
0219 PM CDT Tue Jul 18 2017

Areas affected...Far northern Iowa...southeastern Minnesota...much
of Wisconsin...and the Upper Peninsula of Michigan

Concerning...Severe potential...Watch possible 

Valid 181919Z - 182115Z

Probability of Watch Issuance...40 percent

SUMMARY...Convective coverage is increasing across the region, and
is expected to continue to do so over the next two to three hours. 
At least an isolated severe hail/wind threat will exist with this
activity.  A WW may be considered for parts of the area pending
convective trends.

DISCUSSION...Convection continues to increase across the region, and
this increase is likely aided by forcing for ascent associated with
a mid-level shortwave approaching northern portions of the
discussion area in conjunction with an approaching surface cold
front.  Ahead of the front, surface temperatures have reached the
upper 80s in a few areas amidst a broken mid-level cloud deck from
Iowa into western Wisconsin - with a moderately unstable airmass in
place (MUCAPE around 2000 J/kg).  Storms so far have been sub-severe
and have struggled to organize especially across southeastern
Minnesota where surface heating has been stunted some by the
aforementioned cloud deck.  Storms in the U.P. of Michigan (west of
Marquette) will pose a near-term threat for hail and gusty winds,
although this activity is somewhat displaced from stronger
instability to the southwest.

Latest thinking is that storms will continue to gradually increase
in intensity and coverage - especially across northern Wisconsin as
that area resides nearer to mid/upper forcing attendant to the
shortwave trough.  At least an isolated threat for severe wind and
hail will exist with this activity, although there is considerable
uncertainty regarding the extent of the severe threat and whether a
severe thunderstorm watch will be needed.  Convective trends will
continue to be monitored.

..Cook/Hart.. 07/18/2017

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

ATTN...WFO...APX...MQT...GRB...MKX...DLH...ARX...MPX...DMX...

LAT...LON   46199023 46538960 46818859 46798746 46768683 46588576
            46248550 45728597 44988690 44898697 44308803 43628991
            43069213 42829417 42879460 43309456 43719384 44269256
            45079150 45779057 46199023

Mesoscale Discussions in Wisconsin, 2017Mesoscale Discussions in Iowa, 2017Mesoscale Discussions in Michigan, 2017Every mesoscale discussion in 2017

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.