Alert archive / California / Mesoscale Discussions in 2012

Mesoscale Discussion 497

April 12, 201213 counties in California

The Storm Prediction Center issued this mesoscale discussion at Apr 12, 2012, 11:11 AM PDT for 13 counties in California. It was in force for 64 min.

The area

The outline as issued.

The facts

Issued
Apr 12, 2012, 11:11 AM PDT (18:11 UTC)
Expired
Apr 12, 2012, 12:15 PM PDT
In force
64 min
Issued by
the Storm Prediction Center

Counties Amador County, CA, Calaveras County, CA, Colusa County, CA, Glenn County, CA, Humboldt County, CA, Sacramento County, CA, San Joaquin County, CA, Stanislaus County, CA, Sutter County, CA, Tehama County, CA, Trinity County, CA, Yolo County, CA, Yuba County, CA

The radar

The Beale AFB radar (KBBX), 71 km from the middle of the area, began a volume at 18:13 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

Oakland, CA (KOAK), launched 12:00Z, 6.2 hours before the alert went out and 183 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, Oakland, CA at 12:00Z on 2012-04-12Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 4 joules per kilogram.LCLEL10008507005003002001001 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, Oakland, CA at 12:00Z on 2012-04-12The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 221 square meters per square second.19395878Sfc1 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
4 J/kg
Mixed-layer CIN
-2 J/kg
Mixed-layer LCL
657 m above ground
0-6 km bulk shear
37 kt
0-1 km storm-relative helicity
221 m²/s²
0-3 km storm-relative helicity
308 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.

696 
ACUS11 KWNS 121811
SWOMCD
SPC MCD 121811 
CAZ000-121915-

MESOSCALE DISCUSSION 0497
NWS STORM PREDICTION CENTER NORMAN OK
0111 PM CDT THU APR 12 2012

AREAS AFFECTED...COASTAL RANGES INTO THE SACRAMENTO VALLEY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

VALID 121811Z - 121915Z

A THREAT OF ISOLATED TORNADOES AND MARGINALLY SEVERE HAIL WILL
INCREASE THIS AFTERNOON. AREA IS BEING MONITORED FOR A POSSIBLE WW.

18Z WV IMAGERY REFLECTS AN AREA OF IMPLIED FORCING FOR ASCENT
APPROACHING THE NRN CA COAST. ISOLATED LIGHTNING STRIKES HAVE BEEN
OBSERVED...ASSOCIATED WITH INCREASING CONVECTIVE DEVELOPMENT AHEAD
OF THE UPPER FEATURE. THESE STORMS HAVE BEEN SHOWING WEAK LOW-MID
LEVEL ROTATION PER EUREKA RADAR...IN PART DUE TO STEEPENING LOW-MID
LEVEL LAPSE RATES AND STRENGTHENING DEEP LAYER WINDS WITH THE WRN
TROUGH. ALTHOUGH THESE STORMS MAY PRODUCE MARGINALLY SEVERE HAIL AS
THEY IMPACT THE COAST...A TEMPORARY WEAKENING MAY BE NOTED AS THE
STORMS TRAVERSE INTO A DRIER AND RELATIVELY MORE STABLE AIR MASS.
HOWEVER...VERY LITTLE CLOUD COVER AND COOLING TEMPERATURES ALOFT
WILL CONTRIBUTE TO WEAK INSTABILITY THIS AFTERNOON. THUNDERSTORMS
ARE EXPECTED TO INITIATE/INCREASE IN COVERAGE OVER THE SACRAMENTO
VALLEY WHERE TERRAIN INFLUENCES WILL SUPPORT SURFACE CONVERGENCE FOR
CUMULUS DEVELOPMENT. FAVORABLE MID/UPPER JET DYNAMICS WITH AN
APPROACHING SPEED MAX WILL FURTHER SUPPORT VERTICAL
DEVELOPMENT...WITH ROTATING STORMS BECOMING INCREASINGLY POSSIBLE
LATER THIS AFTERNOON. HOWEVER...ONLY MODEST MOISTURE CHARACTERIZED
BY DEW POINTS LARGELY IN THE MID 40S AND PWAT VALUES NEAR 0.50 INCH
MAY POTENTIALLY LIMIT A MORE WIDESPREAD SEVERE THREAT. CONVECTIVE
TRENDS WILL CONTINUE TO BE MONITORED.

..HURLBUT.. 04/12/2012

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

ATTN...WFO...HNX...STO...MTR...EKA...

LAT...LON   40182210 38292051 37442039 37292082 38202177 39022240
            40052315 39972404 40142465 40762449 40812285 40182210

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Apr 12, 3:08 PM PDTMesoscale DiscussionSPCColusa, Glenn, Merced, Sacramento, San Joaquin, Stanislaus and 3 more97 min

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.