Alert archive / California / Mesoscale Discussions in 2021
Mesoscale Discussion 1784
The Storm Prediction Center issued this mesoscale discussion at Sep 24, 2021, 3:30 PM PDT for San Diego County, California. It was in force for 90 min.
The area
The outline as issued.
The facts
- Issued
- Sep 24, 2021, 3:30 PM PDT (22:30 UTC)
- Expired
- Sep 24, 2021, 5:00 PM PDT
- In force
- 90 min
- Issued by
- the Storm Prediction Center
- Concerning
- Severe potential...watch unlikely
- Chance of a watch
- 5%
County San Diego County, CA
The radar
The San Diego radar (KNKX), 23 km from the middle of the area, began a volume at 22:34 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
San Diego, CA (KNKX), launched 12:00Z, 10.5 hours before the alert went out and 41 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
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 1990 m above ground
- 0-6 km bulk shear
- 4 kt
- 0-1 km storm-relative helicity
- -36 m²/s²
- 0-3 km storm-relative helicity
- 15 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
904
ACUS11 KWNS 242230
SWOMCD
SPC MCD 242230
CAZ000-250000-
Mesoscale Discussion 1784
NWS Storm Prediction Center Norman OK
0530 PM CDT Fri Sep 24 2021
Areas affected...portions of southern California
Concerning...Severe potential...Watch unlikely
Valid 242230Z - 250000Z
Probability of Watch Issuance...5 percent
SUMMARY...Scattered thunderstorms across far southern California may
pose an isolated severe risk for damaging gusts or small hail into
this evening. Storm coverage and intensity are not expected to be
great enough for a watch.
DISCUSSION...As of 2220 UTC, scattered thunderstorms were observed
across far southern California in the vicinity of San Diego.
Enhanced by steeper lapse rates from cold temperatures aloft beneath
a weak upper low centered over the eastern Pacific, weak to moderate
buoyancy (1000-1500 J/kg of MLCAPE) should continue to support
convection this afternoon and into the early evening. Easterly flow
along the southern half of the upper low is weak, supporting only
modest deep-layer shear profiles below 25 kts. The combination of
marginal buoyancy and shear will continue to favor poorly organized
multicell storms. The lack of broader scale forcing and limited
shear should limit overall convective organization of these storms
to occasional bouts of damaging outflow winds and or small hail.
Storms should gradually weaken with westward extent as they
encounter a cooler and more stable boundary layer near the Pacific
coast. Given the limited storm coverage and spatial extent, a watch
is unlikely.
..Lyons/Grams.. 09/24/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...SGX...
LAT...LON 32531654 32471705 32581719 32911723 33271742 33641731
33861698 33381652 33041634 32821631 32611626 32531654Nearby
Mesoscale Discussions in California, 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.