Alert archive / California / Mesoscale Discussions in 2021
Mesoscale Discussion 2055
The Storm Prediction Center issued this mesoscale discussion at Dec 23, 2021, 9:13 AM PST for Alpine County, Sierra County, California. It was in force for 6 hr.
The area
The outline as issued.
The facts
- Issued
- Dec 23, 2021, 9:13 AM PST (17:13 UTC)
- Expired
- Dec 23, 2021, 3:15 PM PST
- In force
- 6 hr
- Issued by
- the Storm Prediction Center
- Concerning
- Heavy snow
Counties Alpine County, CA, Sierra County, CA
The radar
The Reno radar (KRGX), 154 km from the middle of the area, began a volume at 17:14 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
Reno, NV (KREV), launched 12:00Z, 5.2 hours before the alert went out and 188 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
- 853 m above ground
- 0-6 km bulk shear
- 81 kt
- 0-1 km storm-relative helicity
- 97 m²/s²
- 0-3 km storm-relative helicity
- 276 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
786
ACUS11 KWNS 231713
SWOMCD
SPC MCD 231713
CAZ000-NVZ000-232315-
Mesoscale Discussion 2055
NWS Storm Prediction Center Norman OK
1113 AM CST Thu Dec 23 2021
Areas affected...high elevations of the Sierra Nevada
Concerning...Heavy snow
Valid 231713Z - 232315Z
SUMMARY...Snowfall rates in excess of 2 inches per hour are expected
this morning and afternoon above 7000 to 8000 feet within the
discussion area.
DISCUSSION...Latest water vapor image shows a long fetch of very
moist air aloft streaming northeastward into northern and central
California, on the southeast periphery of a sharp, positively
tilted, southward-moving upper trough over the eastern Pacific.
With this deep-layer, moist, west-southwesterly flow perpendicular
to, and impinging on, the Sierra Nevada, persistent, heavy
precipitation is ongoing.
Latest observations suggest that temperatures remain above freezing
-- and precipitation in the form of rainfall -- at the 6000 to 6500
foot level (TRK/TVL/BIH/BLU). However, with gradual cooling aloft
as the trough shifts southward, expect snowfall levels to gradually
decrease -- supporting heavy snowfall rates, at least above 7000
feet or so. The heavy snow will continue through the afternoon,
given the persistence of the upslope-induced ascent, shifting
gradually southward with time.
..Goss.. 12/23/2021
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...VEF...REV...HNX...STO...
LAT...LON 37601951 38031960 38221991 38371992 38552023 38872027
39252043 39612077 39782090 39952088 39812052 39532023
39142003 38781977 38231918 37791899 37311849 36791847
36781875 37091907 37471913 37601951Nearby
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.