Alert archive / California / Mesoscale Discussions in 2017
Mesoscale Discussion 72
The Storm Prediction Center issued this mesoscale discussion at Jan 18, 2017, 4:16 PM PST for 5 counties in California. It was in force for 5 hr.
The area
The outline as issued.
The facts
- Issued
- Jan 18, 2017, 4:16 PM PST (00:16 UTC)
- Expired
- Jan 18, 2017, 9:15 PM PST
- In force
- 5 hr
- Issued by
- the Storm Prediction Center
Counties Alpine County, CA, Nevada County, CA, Plumas County, CA, Sierra County, CA, Tuolumne County, CA
The radar
The Sacramento radar (KDAX), 147 km from the middle of the area, began a volume at 00:19 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 00:00Z, 0.3 hours before the alert went out and 199 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
- 913 m above ground
- 0-6 km bulk shear
- 55 kt
- 0-1 km storm-relative helicity
- 181 m²/s²
- 0-3 km storm-relative helicity
- 179 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
345
ACUS11 KWNS 190016
SWOMCD
SPC MCD 190016
CAZ000-NVZ000-190515-
Mesoscale Discussion 0072
NWS Storm Prediction Center Norman OK
0616 PM CST Wed Jan 18 2017
Areas affected...Portions of the Sierra Nevada in central/northern
California
Concerning...Heavy snow
Valid 190016Z - 190515Z
SUMMARY...Heavy snowfall (generally above 3500-4500 ft) will
continue and develop southward across the northern/central Sierra
Nevada this evening into tonight. Snowfall rates upwards of 2+
inches per hour will be possible across higher elevations.
DISCUSSION...An expansive area of precipitation exists across much
of central/northern California late this afternoon, in response to a
mid-level jet streak progressing southeast along the CA coast and a
related plume of enhanced tropospheric moisture (e.g., PW values
near 1 inch). Near-term guidance and regional radar data depict
increasing southwesterly 700-mb flow approaching portions of the
western Sierra slopes, which will enhance upslope flow and
precipitation rates. Heavier rates will expand down the Sierra range
as this stronger flow evolves southward this evening into the
overnight. Moreover, KBBX velocity data illustrate strong veering
with height, indicating ample warm-air advection which is also
contributing to higher rates. Recent KDAX data show pockets of
higher specific differential phase (KDP) around 15000 ft, likely
suggesting efficient crystal growth supporting higher snowfall rates
(upwards of 1-2+ inches per hour) at higher elevations. Strong wind
gusts will also combine with this snowfall to occasionally restrict
visibility across higher passes.
KBBX correlation coefficient (CC) data indicate snow levels
currently around 3500-4000 ft across parts of the northern Sierra
range, while KDAX CC data indicate these levels rising to around
5000-6000 ft farther south. These levels will fluctuate slightly
through the evening (with diabatic effects in heavier bands
periodically lowering levels) before they more consistently descend
overnight with the arrival of mid-level cooling.
..Picca.. 01/19/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...REV...HNX...STO...
LAT...LON 36511883 38502036 38782043 39422090 39942150 40322170
40552136 40442101 39932036 37881917 36731841 36391840
36211858 36511883Nearby
Mesoscale Discussions in California, 2017Every mesoscale discussion in 2017
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.