Mesoscale Discussion 43
The Storm Prediction Center issued this mesoscale discussion at Jan 28, 2021, 3:33 PM CST. It was in force for 4 hr.
The area
The outline as issued.
The facts
- Issued
- Jan 28, 2021, 3:33 PM CST (21:33 UTC)
- Expired
- Jan 28, 2021, 7:30 PM CST
- In force
- 4 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Heavy snow
The radar
The Los Angeles radar (KVTX), 23 km from the middle of the area, began a volume at 21:36 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
Vandenberg AFB, CA (KVBG), launched 12:00Z, 9.6 hours before the alert went out and 117 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
- 612 m above ground
- 0-6 km bulk shear
- 81 kt
- 0-1 km storm-relative helicity
- 599 m²/s²
- 0-3 km storm-relative helicity
- 596 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
720 ACUS11 KWNS 282134 SWOMCD SPC MCD 282133 CAZ000-290130- Mesoscale Discussion 0043 NWS Storm Prediction Center Norman OK 0333 PM CST Thu Jan 28 2021 Areas affected...Transverse Ranges of Santa Barbara...Ventura and adjacent portions of Los Angeles Counties Concerning...Heavy snow Valid 282133Z - 290130Z SUMMARY...Heavy precipitation appears likely to develop across the Transverse Ranges of Santa Barbara, Ventura and adjacent portions of Los Angeles County through 4-7 PM PST. This probably will include snow rates in excess of 2 inches per hour, at heights perhaps lowering below 5500 feet. DISCUSSION...As an initial short wave impulse within amplified mid-level troughing gradually approaches the southern California coast late this afternoon, an associated frontal precipitation band will continue advancing inland of coastal areas. Through 20/00-03Z, models suggest that lift will maximize across the Transverse Ranges of Santa Barbara, Ventura, and perhaps adjacent portions of Los Angeles counties, aided by strengthening orographic forcing for ascent. It appears that this will increasingly include the favorably cold mid-level layers supportive of large dendritic ice crystal growth. Although ambient freezing levels may not lower much, if at all, through this period, strong lift and melting precipitation may contribute to snow levels lowering below 5500 feet. Within a narrow plume of precipitable water on the order of .75-.90+ inches, models suggest that peak snow rates will exceed 2 inches/hour. ..Kerr.. 01/28/2021 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...LOX... LAT...LON 34771968 34731890 34481852 34401904 34511958 34771968
Nearby
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.