Alert archive / Arizona / Mesoscale Discussions in 2020

Mesoscale Discussion 1521

August 17, 20208 counties in Arizona

The Storm Prediction Center issued this mesoscale discussion at Aug 17, 2020, 4:48 PM MST for 8 counties in Arizona. It was in force for 87 min.

The area

The outline as issued.

The facts

Issued
Aug 17, 2020, 4:48 PM MST (23:48 UTC)
Expired
Aug 17, 2020, 6:15 PM MST
In force
87 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
20%

Counties Cochise County, AZ, Gila County, AZ, Graham County, AZ, Maricopa County, AZ, Pima County, AZ, Pinal County, AZ, Santa Cruz County, AZ, Yavapai County, AZ

The radar

The Phoenix radar (KIWA), 71 km from the middle of the area, began a volume at 23:52 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

Tuscon, AZ (KTUS), launched 12:00Z, 11.8 hours before the alert went out and 86 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-pSkew-T log-p diagram, Tuscon, AZ at 12:00Z on 2020-08-17Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 21 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Tuscon, AZ at 12:00Z on 2020-08-17The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -9 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
21 J/kg
Mixed-layer CIN
-508 J/kg
Mixed-layer LCL
3015 m above ground
0-6 km bulk shear
27 kt
0-1 km storm-relative helicity
-9 m²/s²
0-3 km storm-relative helicity
-18 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.1

Open this sounding in Storm Lab

The text

As transmitted.

051 
ACUS11 KWNS 172349
SWOMCD
SPC MCD 172348 
AZZ000-180115-

Mesoscale Discussion 1521
NWS Storm Prediction Center Norman OK
0648 PM CDT Mon Aug 17 2020

Areas affected...Central and southern Arizona

Concerning...Severe potential...Watch unlikely 

Valid 172348Z - 180115Z

Probability of Watch Issuance...20 percent

SUMMARY...A few storms may move off the higher terrain and produce a
few severe wind gusts this evening.

DISCUSSION...Storms have started to form along the Mogollon Rim and
are slowly drifting southeastward. These storms will be moving into
a very hot airmass with temperatures of 110 to 115 F and dewpoints
around 50F. This yields MLCAPE around 250 to 500 J/kg. The KIWA VWP
shows effective shear around 30 to 35 kts which should be plenty
sufficient for storm organization. However, the limited instability
will likely preclude a greater severe-weather threat. Nonetheless, a
few strong to severe storms are possible through the evening, and
given the very steep low to mid-level lapse rates and DCAPE values
over 2000 J/kg, a few severe wind gusts may be possible through the
evening, especially if any storms congeal into clusters and create
an enhanced cold pool.

..Bentley/Edwards.. 08/17/2020

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

ATTN...WFO...TWC...FGZ...PSR...

LAT...LON   31290942 32770957 33730997 34471095 34891187 34781261
            33081275 31771268 31281107 31290942

Nearby

Mesoscale Discussions in Arizona, 2020Every mesoscale discussion in 2020

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.