Alert archive / California / Mesoscale Discussions in 2012

Mesoscale Discussion 2197

December 20, 2012Siskiyou County, Trinity County, California

The Storm Prediction Center issued this mesoscale discussion at Dec 20, 2012, 1:17 PM PST for Siskiyou County, Trinity County, California. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued
Dec 20, 2012, 1:17 PM PST (21:17 UTC)
Expired
Dec 20, 2012, 6:15 PM PST
In force
5 hr
Issued by
the Storm Prediction Center

Counties Siskiyou County, CA, Trinity County, CA

The radar

The Medford radar (KMAX), 127 km from the middle of the area, began a volume at 21:20 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

Medford/Jackson, OR (KMFR), launched 12:00Z, 9.3 hours before the alert went out and 159 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.

Skew-T log-pSkew-T log-p diagram, Medford/Jackson, OR at 12:00Z on 2012-12-20Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Medford/Jackson, OR at 12:00Z on 2012-12-20The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 276 square meters per square second.1939587897117136Sfc1 km3 km6 km9 kmRMLM
The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.
Mixed-layer CAPE
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
1768 m above ground
0-6 km bulk shear
75 kt
0-1 km storm-relative helicity
276 m²/s²
0-3 km storm-relative helicity
578 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted, in the capitals the NWS used until 2016.

610 
ACUS11 KWNS 202117
SWOMCD
SPC MCD 202117 
CAZ000-210215-

MESOSCALE DISCUSSION 2197
NWS STORM PREDICTION CENTER NORMAN OK
0317 PM CST THU DEC 20 2012

AREAS AFFECTED...PARTS OF NRN CA

CONCERNING...HEAVY SNOW 

VALID 202117Z - 210215Z

SUMMARY...HEAVY SNOW WITH RATES INCREASING TO 1-2 IN/HR IS EXPECTED
TO OCCUR AFTER 2200Z AND CONTINUE INTO THIS EVENING.

DISCUSSION...RECENT WATER VAPOR LOOPS DEPICT A RIBBON OF ASCENT
LEADING A DEEP TROUGH THAT IS AMPLIFYING OVER THE E PACIFIC. THE
ASCENT WILL REMAIN JUXTAPOSED WITH A PLUME OF ENHANCED PACIFIC
MOISTURE FEATURING PW VALUES AROUND 0.6-0.75 INCH THAT EXTENDS NEWD
ACROSS THE E PACIFIC. THIS WILL SUPPORT AN INCREASE IN PRECIPITATION
RATES DURING THE NEXT COUPLE OF HOURS. SNOW WILL BE THE PRIMARY
PRECIPITATION TYPE FOR ELEVATIONS ABOVE 2000-3000 FT. THE ASCENT
WILL BE AUGMENTED BY UPSLOPE FLOW OVER S-FACING MOUNTAIN
SLOPES...WHILE MID-LEVEL COOLING ACCOMPANYING THE AMPLIFYING TROUGH
MAY PROVIDE A WEAK CONVECTIVE ENHANCEMENT TO PRECIPITATION. AS
SUCH...SNOWFALL RATES WILL LIKELY INCREASE TO 1-2 IN/HR OVER THE
MOUNTAINS OF NRN CA AFTER 2200Z...INCLUDING THE KLAMATH AND SISKYOU
MOUNTAINS. THESE SNOWFALL RATES WILL LIKELY CONTINUE INTO THE
EVENING HOURS.

..COHEN.. 12/20/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MFR...STO...EKA...

LAT...LON   41512182 41132194 40892225 40572250 40392281 40042272
            39932289 39962319 40342356 41212374 41822361 41972309
            41912211 41512182

Nearby

Mesoscale Discussions in California, 2012Every mesoscale discussion in 2012

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.