Alert archive / Michigan / Mesoscale Discussions in 2021
Mesoscale Discussion 1496
The Storm Prediction Center issued this mesoscale discussion at Aug 12, 2021, 6:38 AM EDT for 7 counties in Michigan. It was in force for 97 min.
The area
The outline as issued.
The facts
- Issued
- Aug 12, 2021, 6:38 AM EDT (10:38 UTC)
- Expired
- Aug 12, 2021, 8:15 AM EDT
- In force
- 97 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 20%
Counties Hillsdale County, MI, Jackson County, MI, Lenawee County, MI, Monroe County, MI, Oakland County, MI, Washtenaw County, MI, Wayne County, MI
The radar
The Detroit radar (KDTX), 76 km from the middle of the area, began a volume at 10:40 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 00:00Z, 10.6 hours before the alert went out and 80 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.
- Mixed-layer CAPE
- 12 J/kg
- Mixed-layer CIN
- -458 J/kg
- Mixed-layer LCL
- 1474 m above ground
- 0-6 km bulk shear
- 39 kt
- 0-1 km storm-relative helicity
- 243 m²/s²
- 0-3 km storm-relative helicity
- 373 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
861
ACUS11 KWNS 121039
SWOMCD
SPC MCD 121038
MIZ000-OHZ000-INZ000-121215-
Mesoscale Discussion 1496
NWS Storm Prediction Center Norman OK
0538 AM CDT Thu Aug 12 2021
Areas affected...Southern Lower MI
Concerning...Severe potential...Watch unlikely
Valid 121038Z - 121215Z
Probability of Watch Issuance...20 percent
SUMMARY...Damaging wind gusts are possible across south-central and
southeast Lower MI over the next hour or so.
DISCUSSION...Convective cluster moving northeastward across southern
Lower MI recently produced a severe gust of 51 kt at Coldwater MI
(OEB). Velocity signatures from IWX and DTX show this an area of
enhanced outbounds well at around 5 and 6 kft, respectively. The
cluster itself has also surged forward, with recent storm motion
estimated at around 55 kt. The downstream air mass is very moist,
with relatively minimal temperature-dewpoint spreads, suggesting
these gusts are not driven by negative buoyancy but likely the
manifestation of a strong downdraft reaching the surface and/or
downward momentum transfer from the low-level jet. Given the
reduction in buoyancy with northeastward extent, it is likely that
this downburst will eventually surge ahead as the storm gusts out.
However, low-level vertical shear is strong enough for localized
downdraft/vertical shear balance to persist for an hour or so. As a
result, damaging wind gusts are possible across south-central and
southeast Lower MI for the next hour. Limited spatial and temporal
extent of the threat will likely preclude the need for watch.
..Mosier/Edwards.. 08/12/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CLE...DTX...IWX...GRR...
LAT...LON 42208489 42518436 42778302 42378279 41788319 41668412
41678486 42208489SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 11, 8:35 PM EDT | Mesoscale Discussion | SPC | Berrien, Cass, Van Buren | 85 min |
| Aug 11, 9:22 PM EDT | Severe Thunderstorm Watch | SPC | Allegan, Barry, Berrien, Branch, Calhoun, Cass and 9 more | 8 hr |
| Aug 11, 10:17 PM EDT | Mesoscale Discussion | SPC | Genesee, Lapeer, Livingston, Macomb, Oakland, Saint Clair and 3 more | 88 min |
| Aug 12, 12:06 AM EDT | Mesoscale Discussion | SPC | Allegan, Barry, Berrien, Branch, Calhoun, Cass and 7 more | 84 min |
Nearby
Mesoscale Discussions in Michigan, 2021Every 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.