Alert archive / Arizona / Mesoscale Discussions in 2021
Mesoscale Discussion 1541
The Storm Prediction Center issued this mesoscale discussion at Aug 16, 2021, 11:39 PM MST for Maricopa County, Arizona. It was in force for 96 min.
The area
The outline as issued.
The facts
- Issued
- Aug 16, 2021, 11:39 PM MST (06:39 UTC)
- Expired
- Aug 17, 2021, 1:15 AM MST
- In force
- 96 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 442
County Maricopa County, AZ
The radar
The Phoenix radar (KIWA), 95 km from the middle of the area, began a volume at 06:41 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
Phoenix, AZ (KPSR), launched 00:00Z, 6.7 hours before the alert went out and 74 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
- 2667 J/kg
- Mixed-layer CIN
- -7 J/kg
- Mixed-layer LCL
- 1942 m above ground
- 0-6 km bulk shear
- 18 kt
- 0-1 km storm-relative helicity
- 24 m²/s²
- 0-3 km storm-relative helicity
- 44 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
596
ACUS11 KWNS 170639
SWOMCD
SPC MCD 170639
AZZ000-170815-
Mesoscale Discussion 1541
NWS Storm Prediction Center Norman OK
0139 AM CDT Tue Aug 17 2021
Areas affected...Parts of central into southern/southwestern Arizona
Concerning...Severe Thunderstorm Watch 442...
Valid 170639Z - 170815Z
The severe weather threat for Severe Thunderstorm Watch 442
continues.
SUMMARY...Strong thunderstorm development posing a risk for strong
to locally severe wind gusts may continue into areas between
Interstate 8 and 10, near and northwest of Gila Bend, through
midnight-2 AM MST.
DISCUSSION...A strong to locally severe downburst producing cluster
of storms across the Greater Phoenix metropolitan area is embedded
within an environment characterized by generally weak shear. Light
northerly deep-layer mean flow is tending to advect stronger
convection slowly southward, but associated outflow is surging
southwestward into/toward the lingering very warm and deeply mixed
boundary layer across the lower deserts. New convection is
continuing to develop above the cold pool, and contributing to a
southwest propagation of convection, but latest objective
instability analysis suggests that this may only be able to continue
another hour or two. It appears possible that convection capable of
producing an additional strong downburst or two may continue
along/in between the Interstate 8 and 10 corridors, at least into
areas near/northwest of Gila Bend through 07-09Z, before activity
begins to diminish.
..Kerr.. 08/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...TWC...PSR...
LAT...LON 33551303 33541216 32571149 32531255 32771310 33301334
33551303SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 16, 6:21 PM MST | Mesoscale Discussion | SPC | Cochise, Gila, Graham, Greenlee, Maricopa, Pima and 2 more | 84 min |
| Aug 16, 9:23 PM MST | Mesoscale Discussion | SPC | Pinal | 97 min |
Nearby
Mesoscale Discussions in Arizona, 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.