Alert archive / Nevada / Mesoscale Discussions in 2012
Mesoscale Discussion 1799
The Storm Prediction Center issued this mesoscale discussion at Aug 22, 2012, 10:43 AM MST for 4 states. It was in force for 2 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 22, 2012, 10:43 AM MST (17:43 UTC)
- Expired
- Aug 22, 2012, 12:45 PM MST
- In force
- 2 hr
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 20%
Counties Mohave County, AZ, Riverside County, CA, Clark County, NV, Lincoln County, NV, Washington County, UT
The radar
The Las Vegas radar (KESX), 21 km from the middle of the area, began a volume at 17:44 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
Las Vegas, NV (KVEF), launched 12:00Z, 5.7 hours before the alert went out and 114 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
- 296 J/kg
- Mixed-layer CIN
- -130 J/kg
- Mixed-layer LCL
- 1290 m above ground
- 0-6 km bulk shear
- 28 kt
- 0-1 km storm-relative helicity
- 103 m²/s²
- 0-3 km storm-relative helicity
- 176 m²/s²
- Significant tornado parameter
- 0.1
- Supercell composite
- 3.4
The text
As transmitted, in the capitals the NWS used until 2016.
261
ACUS11 KWNS 221743
SWOMCD
SPC MCD 221743
AZZ000-UTZ000-NVZ000-CAZ000-221945-
MESOSCALE DISCUSSION 1799
NWS STORM PREDICTION CENTER NORMAN OK
1243 PM CDT WED AUG 22 2012
AREAS AFFECTED...SOUTHEAST CA/SOUTHERN NV TO NORTHWEST AZ/FAR
SOUTHWEST UT
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 221743Z - 221945Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...LOCALLY VERY HEAVY/PERSISTENT RAINFALL WILL LIKELY BE THE
PRIMARY CONCERN...BUT ISOLATED DAMAGING WINDS/MAINLY SUB-SEVERE HAIL
WILL BE POSSIBLE ACROSS PORTIONS OF SOUTHEAST CA/SOUTHERN NV INTO
NORTHWEST AZ/FAR SOUTHWEST UT THROUGH THIS AFTERNOON.
DISCUSSION...A SOUTHERN STREAM UPPER LOW CONTINUES TO SHIFT SLOWLY
EAST-SOUTHEASTWARD OVER SOUTH-CENTRAL CA AT MIDDAY PER WATER VAPOR
IMAGERY...WITH AN ASSOCIATED DIFFLUENT/UPPER JET EXIT REGION
OVERSPREADING MUCH OF NV TO NEAR THE UT/AZ BORDERS. A VERY MOIST
AIRMASS IS IN PLACE ACROSS THE REGION...ESPECIALLY EVIDENT BY AN
EXTREMELY HIGH CLIMO-RELATIVE PRECIPITABLE WATER VALUE OF 1.69
INCHES PER THE 12Z LAS VEGAS OBSERVED SOUNDING...IN ADDITION TO
RECENT GPS-DERIVED PW VALUES AROUND 2-INCHES ACROSS SOUTHEAST CA.
THE DEGREE OF MOISTURE/PW...ALONG WITH INCREASING LARGE
SCALE/OROGRAPHIC ASCENT AND DIURNAL HEATING WILL CONTRIBUTE TO
INCREASING NUMBER/VIGOR OF TSTMS THROUGH THIS AFTERNOON. LOCALLY
VERY HEAVY/PERSISTENT RAINFALL WILL LIKELY BE THE PRIMARY
IMPACT...ALTHOUGH SUFFICIENT VERTICAL SHEAR AND THERMODYNAMIC
CHARACTERISTICS WILL EXIST FOR SOME SEMI-SUSTAINED STORMS/MULTICELLS
CAPABLE OF WIND DAMAGE AND MAINLY SUB-SEVERE HAIL. SAMPLING THE
RELATIVELY STRONG SOUTHWESTERLY MID-HIGH LEVEL WINDS AHEAD OF THE
ADVANCING UPPER LOW...THE 12Z OBSERVED SOUNDING AND MORE RECENT
WSR-88D VWP DATA FROM LAS VEGAS ARE INDICATIVE OF AROUND 25 KT OF
0-6 KM SHEAR...WHILE THERMODYNAMIC ADJUSTMENTS TO THE 12Z VEF
SOUNDING SUGGEST AS MUCH AS 1000-1500 J/KG MLCAPE EXISTS ACROSS THE
LOWER CO RIVER VALLEY WHERE MORE AGGRESSIVE HEATING IS OCCURRING.
..GUYER/MEAD.. 08/22/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...FGZ...SLC...PSR...VEF...LKN...SGX...
LAT...LON 33371647 35131580 37001592 38151500 37911361 37321304
35751243 34801351 33271469 33371647Nearby
Mesoscale Discussions in Nevada, 2012Mesoscale Discussions in Arizona, 2012Mesoscale 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.