Severe Thunderstorm Warning 12, NWS Las Vegas, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
355 PM PDT SAT AUG 14 2004

.SYNOPSIS...MOIST UNSTABLE AIR WILL CONTINUE TO SUPPORT SCATTERED
THUNDERSTORM DEVELOPMENT OVER THE SOUTHERN HALF OF THE DISTRICT
AGAIN TODAY AND TOMORROW. CLOUD COVER AND RELATIVELY HIGH HUMIDITY
WILL KEEP MAXIMUM TEMPERATURES SLIGHTLY BELOW NORMAL.
&&

.SHORT TERM...SEVERAL IMPRESSIVE CLUSTERS OF STORMS ACROSS THE AREA
THIS AFTERNOON. AIRMASS IN EXTREMELY MOIST AND UNSTABLE. SHEAR
PROFILES ARE WEAK BUT INTERACTION OF NUMEROUS BOUNDARIES WILL
CONTINUE TO PROVIDE LOCAL TRIGGERS AND SOME OF THE MERGED COLD POOLS
MAY BECOME STRONG ENOUGH TO ENHANCE STORM RELATIVE SHEAR AS WELL AS
PROVIDING ORGANIZED LIFT. AS EXPECTED...MOVEMENT IS SLOW AND THE
PRIMARY THREAT IS FOR FLASH FLOODING BUT CANNOT RULE OUT AN ISOLATED
OCCURENCE OF MODERATE HAIL AND/OR DAMAGING WIND. HAVE ADDED LV
VALLEY TO FLASH FLOOD WATCH FOR TONIGHT. UNCERTAIN ABOUT WHETHER
STORMS WILL BE TRIGGERED IN THE VALLEY BUT WITH ALL THESE BOUNDARIES
TRAIPSING AROUND THERE IS HOPE FOR ONE TO WORK ITS WAY INTO THE
LOWER DESERTS WITH SUFFICIENT LIFT TO REACH THE LFC. SHOULD THAT
HAPPEN THE POTENTIAL IS QUITE GOOD FOR LOCALLY HEAVY RAIN...SO OPTED
TO INCLUDE THE ENTIRE COUNTY IN THE UPDATED WATCH.

MODEL GUIDANCE STILL SUGGESTING AN INCURSION OF DRIER WESTERLIES
ALOFT BUT THE FLOW IS EXPECTED TO BE TOO WEAK TO SCOUR OUT THE LOW
LEVEL MOISTURE TOO QUICKLY. THEREFORE DO NOT BELIEVE THIS AIRMASS IS
GOING TO CHANGE MUCH IN THE NEXT 3 DAYS OR SO. ETA AND GFS LOOK
REASONABLE ON THE LARGE SCALE EVOLUTION BUT THE DAILY FORECAST
CHALLENGES TOMORROW AND MONDAY WILL BE FOCUSED ON MESOSCALE
BOUNDARIES AND CIRCULATIONS LEFT OVER FROM OVERNIGHT CONVECTION...
AND ON AMOUNT OF CLOUD COVER THAT LINGERS THROUGH THE NIGHT FROM
CONVECTIVE DEBRIS. THESE ARE TRICKY PROBLEMS THAT WILL AFFECT
EVERYTHING FROM TEMPERATURES TO PRECIP PROBABILITIES...AND THE MODEL
GUIDANCE WILL BE OF LITTLE VALUE ON SUCH FEATURES.

&&

.LONG TERM...DUE TO EXPECTATION OF AFTERNOON THUNDERSTORMS WE
FOCUSED ON THE SHORT TERM AND LEFT THE EXTENDED PERIODS UNCHANGED.
SEE PREVIOUS DISCUSSION FOR REASONING ASSOCIATED WITH THE LONG TERM
FORECASTS.

&&

.AVIATION...TAF ADEQUATELY COVERS ALL SIGNIFICANT WEATHER EXPECTED
AT KLAS.
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
.NV...FLOOD WATCH NOON TO 9 PM NVZ016-022.
.AZ...FLOOD WATCH NOON TO 9 PM AZZ002-003-036.
.CA...FLOOD WATCH NOON TO 9 PM CAZ028-029.
&&

RUNK/MORGAN

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LAS VEGAS NV
1026 AM PDT SAT AUG 14 2004

AZZ001>003-036-CAZ026>029-NVZ014>022-151700-
DEATH VALLEY NATIONAL PARK-ESMERALDA AND CENTRAL NYE COUNTY-
LAKE HAVASU AND FORT MOJAVE-LAKE MEAD NATIONAL RECREATION AREA-
LAS VEGAS VALLEY-LINCOLN COUNTY-NORTHEAST CLARK COUNTY-
NORTHWEST DESERTS-NORTHWEST PLATEAU-
OWENS VALLEY AND ADJACENT EASTERN SIERRA SLOPES-
SAN BERNARDINO COUNTY DESERTS-SAN BERNARDINO COUNTY-
UPPER COLORADO RIVER VALLEY-SHEEP RANGE-SOUTHERN CLARK COUNTY-
SPRING MOUNTAINS-RED ROCK CANYON-
WESTERN CLARK AND SOUTHERN NYE COUNTY-
1026 AM PDT (1026 AM MST) SAT AUG 14 2004

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHEAST
CALIFORNIA/SOUTHERN NEVADA AND NORTHWEST ARIZONA.

.DAY ONE...TODAY.

SCATTERED THUNDERSTORMS WILL CONTINUE THIS AFTERNOON AND EVENING.
SOME STORMS ARE EXPECTED TO PRODUCE HEAVY RAIN AND FLASH FLOODING.
THE GREATEST THREAT WILL BE OVER SAN BERNARDINO...MOHAVE...AND
SOUTHERN CLARK COUNTIES.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY.

SCATTERED AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS CAN BE
EXPECTED THROUGH AT LEAST WEDNESDAY WITH ISOLATED FLASH FLOODING AND
SEVERE STORMS POSSIBLE EACH DAY.

RUNK