Alert archive / Arizona / Mesoscale Discussions in 2021
Mesoscale Discussion 1539
The Storm Prediction Center issued this mesoscale discussion at Aug 16, 2021, 6:21 PM MST for 8 counties in Arizona. It was in force for 84 min.
The area
The outline as issued.
The facts
- Issued
- Aug 16, 2021, 6:21 PM MST (01:21 UTC)
- Expired
- Aug 16, 2021, 7:45 PM MST
- In force
- 84 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe thunderstorm watch 442
Counties Cochise County, AZ, Gila County, AZ, Graham County, AZ, Greenlee County, AZ, Maricopa County, AZ, Pima County, AZ, Pinal County, AZ, Santa Cruz County, AZ
The radar
The Phoenix radar (KIWA), 85 km from the middle of the area, began a volume at 01:21 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, 1.4 hours before the alert went out and 111 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.
353
ACUS11 KWNS 170121
SWOMCD
SPC MCD 170121
AZZ000-170245-
Mesoscale Discussion 1539
NWS Storm Prediction Center Norman OK
0821 PM CDT Mon Aug 16 2021
Areas affected...Central Arizona
Concerning...Severe Thunderstorm Watch 442...
Valid 170121Z - 170245Z
The severe weather threat for Severe Thunderstorm Watch 442
continues.
SUMMARY...The risk for damaging wind gusts and isolated hail remains
across WW442. A favored corridor for damaging wind gusts may be
evolving with a cluster of storms across northeastern Arizona.
DISCUSSION...Across WW442, isolated reports of strong wind gusts and
large hail have been received overt the last several hours.
Strong/severe storms continue across the region with several
clusters developing as surface cold pools have strengthened. The
largest of these clusters, observed via regional radar in the
vicinity of Flagstaff, AZ, has shown signs of organization and
intensification as outflow has coalesced. Observational trends and
hi-res cam guidance suggest that this cluster may begin to
accelerate to the south-southwest over the next few hours. The
downstream environment remains favorable for additional convective
development/strengthening with around 3000 J/kg of MLCAPE observed
via the PHX 00z sounding. While observed vertical shear remains less
than 15 kts, convective enhancement from the cold pool motion and
the approach of a back-door shortwave trough to the east will likely
continue to support a loosely organized cluster of multicell storms
capable of damaging wind gusts as they approach the Phoenix, AZ area
this evening.
..Lyons.. 08/17/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...TWC...FGZ...PSR...
LAT...LON 35301063 35401005 35140939 34530913 33920908 33470910
32730920 32000931 31500963 31431034 31521125 31841248
32261377 32941381 34231291 34671239 35301063SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 16, 9:23 PM MST | Mesoscale Discussion | SPC | Pinal | 97 min |
| Aug 16, 11:39 PM MST | Mesoscale Discussion | SPC | Maricopa | 96 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.