Alert archive / Michigan / Mesoscale Discussions in 2021

Mesoscale Discussion 1737

September 13, 20218 counties in Michigan

The Storm Prediction Center issued this mesoscale discussion at Sep 13, 2021, 10:52 AM EDT for 8 counties in Michigan. It was in force for 83 min.

The area

The outline as issued.

The facts

Issued: Sep 13, 2021, 10:52 AM EDT (14:52 UTC)
Expired: Sep 13, 2021, 12:15 PM EDT
In force: 83 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Barry County, MI, Clinton County, MI, Gratiot County, MI, Ionia County, MI, Kent County, MI, Montcalm County, MI, Muskegon County, MI, Ottawa County, MI

The radar

The Grand Rapids radar (KGRR), 44 km from the middle of the area, began a volume at 14:56 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.

The nearest sounding before it

Detroit, MI (KDTX), launched 12:00Z, 2.9 hours before the alert went out and 217 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 947 m above ground
0-6 km bulk shear: 54 kt
0-1 km storm-relative helicity: 12 m²/s²
0-3 km storm-relative helicity: 50 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

373 
ACUS11 KWNS 131452
SWOMCD
SPC MCD 131452 
MIZ000-131615-

Mesoscale Discussion 1737
NWS Storm Prediction Center Norman OK
0952 AM CDT Mon Sep 13 2021

Areas affected...portions of west-central and southwestern Lower
Michigan

Concerning...Severe potential...Watch unlikely 

Valid 131452Z - 131615Z

Probability of Watch Issuance...20 percent

SUMMARY...Gusty winds -- possibly nearing severe levels locally --
will move onshore over the next half hour, across Muskegon and
Ottawa Counties.  However, storms should remain elevated/north of
the front, which will limit any severe risk.

DISCUSSION...A cluster of storms moving across southern Lake
Michigan has organized a bit over the past half hour -- aided by
fairly steep lapse rates aloft and strong mid-level westerlies --
with hints of bowing as a favored zone of updraft redevelopment is
indicated along leading outflow.  This suggests to at least some
degree that downdrafts are penetrating the stable boundary layer
north of the cold front over southern Lower Michigan/southern Lake
Michigan. 

This convection will move onshore over the next half hour or so,
with gusty winds expected.  However, given the aforementioned stable
layer, gusts should remain largely -- if not entirely -- below
severe levels -- likely in the 40 to 50 MPH range.  As such, WW is
not currently anticipated, but we will continue to monitor
convective evolution as storms approach/reach coastal counties.

..Goss/Thompson.. 09/13/2021

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

ATTN...WFO...GRR...

LAT...LON   43448678 43468586 43288449 42698467 42478538 42628709
            42668750 43448678

Nearby

Mesoscale Discussions in Michigan, 2021 Every mesoscale discussion in 2021

Sources

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.