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=20
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.
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