Alert archive / Arizona / Mesoscale Discussions in 2021
Mesoscale Discussion 1537
The Storm Prediction Center issued this mesoscale discussion at Aug 16, 2021, 3:01 PM MST for 5 counties in Arizona. It was in force for 59 min.
The area
The outline as issued.
The facts
- Issued
- Aug 16, 2021, 3:01 PM MST (22:01 UTC)
- Expired
- Aug 16, 2021, 4:00 PM MST
- In force
- 59 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch possible
- Chance of a watch
- 40%
Counties Gila County, AZ, Graham County, AZ, Maricopa County, AZ, Pinal County, AZ, Yavapai County, AZ
The radar
The Flagstaff radar (KFSX), 89 km from the middle of the area, began a volume at 22:05 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 watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Phoenix, AZ (KPSR), launched 12:00Z, 10.0 hours before the alert went out and 76 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
- 509 J/kg
- Mixed-layer CIN
- -264 J/kg
- Mixed-layer LCL
- 1804 m above ground
- 0-6 km bulk shear
- 15 kt
- 0-1 km storm-relative helicity
- -13 m²/s²
- 0-3 km storm-relative helicity
- 80 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
196
ACUS11 KWNS 162201
SWOMCD
SPC MCD 162201
AZZ000-162300-
Mesoscale Discussion 1537
NWS Storm Prediction Center Norman OK
0501 PM CDT Mon Aug 16 2021
Areas affected...North-central Arizona
Concerning...Severe potential...Watch possible
Valid 162201Z - 162300Z
Probability of Watch Issuance...40 percent
SUMMARY...A few high-based storms may pose a risk for damaging wind
gusts or hail as they develop and move south into this evening.
Conditions are being monitored for a possible weather watch.
DISCUSSION...As of 2145 UTC, regional radar and visible imagery
shows a few strong/severe thunderstorms developing across the
Mogollon Rim and Grand Canyon areas of north-central Arizona. As
lift from a back-door trough on the southeastern flank of the strong
mid-level ridge continues to move into the area, additional storm
development is likely into this evening. Diurnal warming and
monsoonal moisture have destabilized the atmosphere as 1500 to 3000
J/kg of MLCAPE is present from SPC mesoanalyis. Enhanced northerly
flow on the backside of the ridge will support organized multicell
storms with between 20 and 30 kts of effective shear.
As additional storms develop and surface cold pools strengthen late
this afternoon and into the evening, several clusters of storms may
evolve as they drift south-southwest away from the higher terrain
towards central Arizona. DCAPE around 1000-1300 J/kg and T/TD
spreads of 25-35 degrees F will favor strong downdrafts and outflow
conducive to strong/severe wind gusts. The magnitude of available
instability may also support a risk for severe hail with the
strongest cores. While uncertainty on the coverage of storms and any
cluster development remains high, conditions are being monitored for
a possible weather watch.
..Lyons/Thompson.. 08/16/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...TWC...FGZ...PSR...VEF...
LAT...LON 34611392 35391310 35731243 35581121 35001031 34430978
33740943 32860953 32491065 32671240 33001316 33451397
33981410 34611392SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 15, 8:50 PM MST | Mesoscale Discussion | SPC | Pinal | 55 min |
| Aug 16, 3:54 PM MST | Severe Thunderstorm Watch | SPC | Cochise, Gila, Graham, Maricopa, Pima, Pinal and 2 more | 10 hr |
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.