Area Forecast Discussion
Issued by NWS Las Vegas, NV

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FXUS65 KVEF 191643
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
943 AM PDT SUN APR 19 2015

.SYNOPSIS...AN AREA OF LOW PRESSURE WILL SINK SOUTH OFF THE
CALIFORNIA COAST TODAY THROUGH TUESDAY. THIS WILL HELP TO TRIGGER
SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS
EACH DAY MAINLY OVER THE HIGHER ELEVATIONS WITH THE GREATEST CHANCE
OVER THE SOUTHERN SIERRA NEVADA. THIS LOW WILL MOVE INLAND TUESDAY
AFTERNOON. TWO ADDITIONAL SYSTEMS ARE EXPECTED TO PASS NEAR OR
ACROSS THE AREA BETWEEN TUESDAY NIGHT AND SATURDAY BRINGING
ADDITIONAL CHANCES FOR SHOWERS ALONG WITH A DROP IN TEMPERATURES.
&&

.UPDATE...

OVERALL THE FORECAST IS IN GOOD SHAPE. ONLY MADE MINOR EDITS TO THE
NEAR-TERM FORECAST TO ACCOUNT FOR CURRENT OBSERVATIONS AND TRENDS.
STILL EXPECT THE BEST CHANCE OF ANY SHOWERS /THUNDERSTORM/ TO BE
ALONG THE SOUTHERN SIERRA. OUTSIDE CHANCES EXIST FOR THE HIGHER
TERRAIN OF SOUTHERN NEVADA. LATEST SOUNDING DATA SHOW THE LOWER
ATMOSPHERE IS QUITE DRY...LEADING TO THE POTENTIAL FOR DRY
LIGHTNING. WILL CONTINUE TO MONITOR FOR DEVELOPMENT THROUGH THE DAY.
&&

.PREV DISCUSSION...
324 AM PDT SUN APR 19 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT.

AN AREA OF LOW PRESSURE SWIRLING OFF THE COAST OF NORCAL THIS
MORNING NEAR 40N/130W WILL CONTINUE TO DROP SOUTH OFF THE COAST OF
CALIFORNIA THROUGH TUESDAY. THE PROXIMITY OF THIS LOW AND THE COLD
AND UNSTABLE AIR ALOFT ASSOCIATED WITH IT PLUS WHATEVER MOISTURE IT
IS ABLE TO TAP INTO WILL BRING THE PROSPECTS FOR SOME ACTIVE
AFTERNOONS AND EARLY EVENINGS ACROSS THE AREA. ALTHOUGH MOISTURE
WILL INITIALLY LACK WITH THIS LOW THE LONGER IT SITS OFF THE COAST
OF CALIFORNIA, IT SHOULD BE ABLE TO TAP A BETTER SUPPLY OF MOISTURE
AND PUSH IT INLAND. ADDITIONALLY, ALTHOUGH WE HAVE AN EXCEPTIONALLY
MEAGER SNOWPACK SOME OF THIS WILL SUBLIMATE WITH THE HEATING OF THE
DAY AND PROVIDE AN ALTERNATIVE MOISTURE SOURCE. THE COMBINATION OF
THE MOISTURE AND INSTABILITY IN THE ATMOSPHERE WILL HELP TO SET OFF
SHOWERS AND THUNDERSTORMS EACH AND EVERY AFTERNOON THAT WILL LAST
INTO THE EARLY EVENING OVER THE HIGHER ELEVATIONS OF THE AREA WITH
THE GREATEST CHANCE OVER THE SOUTHERN SIERRA ESPECIALLY NEAR THE
CREST. THE BEST INSTABILITY AND MOISTURE WILL EXIST IN THIS AREA AND
THUS WE KEPT THE BEST POPS HERE. FURTHER EAST OVER THE REMAINDER OF
THE AREA, INSTABILITY IS NOT AS IMPRESSIVE TODAY, HOWEVER, GIVEN
THAT WE GOT ACTIVITY TO GO YESTERDAY, WHAT WAS THOUGHT TO BE THE
OVERDONE WRF WAS ACTUALLY PRETTY GOOD. SO, THAT AND THE GFS WERE
LEANED TOWARD FOR TODAY`S POPS. THIS RESULTS IN A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS FOR THE HIGHER TERRAIN OF CLARK, LINCOLN
AND CENTRAL NYE COUNTY ONCE AGAIN AS WELL AS THE PLATEAU AREA OF
NORTHERN MOHAVE. DRY LOW-LEVELS WILL MAKE FOR A THREAT OF DRY
LIGHTNING AS MOST OF THE MOISTURE REMAINS ABOVE 700 MB AND ANY
PRECIPITATION WILL STRUGGLE TO REACH THE GROUND. THE STEERING FLOW
TODAY IS LIGHT WHICH SHOULD CONFINE ACTIVITY OVER THE SIERRA AND
WHITES TO THOSE RANGES. HOWEVER, A LIGHT NORTHWEST STEERING FLOW
COULD PUSH SOME ACTIVITY OFF THE SPRINGS TOWARD RED ROCK CANYON IN
THE LATE AFTERNOON/EVENING AS WELL AS WHATEVER WE SEE GO LINCOLN
COUNTY TOWARD THE UTAH BORDER. TEMPS SHOULD BE A LITTLE WARMER THAN
YESTERDAY AND HIGHS WERE BUMPED UP A TOUCH IN SPOTS.

AS THE LOW MOVES SOUTH TOWARD A POSITION WEST OF POINT CONCEPTION BY
TOMORROW MORNING AND INTO THE COASTAL WATERS OFF OF SOCAL BY THE
AFTERNOON WE SHOULD SEE AN EVEN BETTER CHANCE FOR SHOWERS AND
THUNDERSTORMS IN THE AFTERNOON AND EVENING OVER THE SOUTHERN SIERRA
AND WE CARRIED SLIGHTLY HIGHER POPS. A WESTERLY STEERING FLOW IS
NOTED WHICH MAY BE ENOUGH TO DRIVE SOME ACTIVITY TOWARD THE OWENS
VALLEY OR SOME OUTFLOW SO A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS WAS ADDED IN HERE. OTHERWISE ISOLATED SHOWERS AND
THUNDERSTORMS COULD BLOSSOM IN THE AFTERNOON OVER THE HIGHER TERRAIN
OF CLARK, LINCOLN AND CENTRAL NYE COUNTIES ONCE AGAIN. ELSEWHERE IT
REMAINS DRY AND A LITTLE ABOVE NORMAL FOR TEMPS.

THE AFOREMENTIONED LOW SHOULD MOVE INLAND ON TUESDAY OVER THE COAST
OF SOCAL OR THE NORTHERN BAJA. THIS WILL HELP TO PUSH MOISTURE
FURTHER INLAND AND ALSO RESULT IN BETTER INSTABILITY OVER MORE OF
THE AREA SO A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS EXISTS IN
THE AFTERNOON AND EVENING OVER THE HIGHEST ELEVATIONS OF EACH
COUNTY. I KEPT THE HIGHEST POPS OVER THE SOUTHERN SIERRA, WHITE MTS,
INYO RANGE AND THE PANAMINTS. AGAIN A WESTERLY STEERING FLOW IS
PRESENT SO SOMETHING COULD DRIFT INTO THE OWENS VALLEY AND WE KEPT
IN A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS THERE. IT IS ALSO
POSSIBLE SOMETHING COULD DRIFT OFF THE SPRINGS TOWARD RED ROCK OR
THE FAR WEST SIDE OF THE LAS VEGAS VALLEY AS WELL. TEMPS AGAIN
REMAIN A FEW DEGREES ABOVE NORMAL.

.LONG TERM...WEDNESDAY MORNING THROUGH SUNDAY.

THE STORY OF THE LONG TERM PERIOD CONTINUES TO BE UNSETTLED WEATHER
SHAPING UP FOR THE CWA AS A SERIES OF SHORTWAVES IS SLATED TO
TRAVERSE THE AREA FROM MID-WEEK THROUGH THE WEEKEND. THE FIRST OF
THESE SHORTWAVES WILL IMPACT THE REGION WEDNESDAY BEFORE ANOTHER
ROUND OF SHORTWAVES MOVE OVER THE AREA THURSDAY-SATURDAY.
OPERATIONAL GUIDANCE CONTINUES TO GENERALLY HAVE GOOD AGREEMENT ON
THE STRENGTH AND TIMING OF THE INITIAL SHORTWAVE...KEEPING IT A
WEAKER/LESS AMPLIFIED OPEN WAVE. GUIDANCE SEEMS TO HAVE THE JIST OF
THE EVOLUTION OF THE NEXT ROUND OF SHORTWAVES FOR THURSDAY-FRIDAY AS
WELL...WITH THE ONLY NOTABLE DIFFERENCES IN MODEL SOLUTIONS BEING
STRENGTH AND TIMING. THE OPERATIONAL GFS CONTINUES TO CLOSE OFF THE
LOW WHILE EMITTING A SEPARATE VIGOROUS SHORTWAVE OUT AHEAD OF THE
AFOREMENTIONED LOW AS IT SWINGS INTO THE AREA EARLY THURSDAY. THE
OPERATIONAL ECMWF HAS THE SAME IDEA...BUT MUCH WEAKER IN TERMS OF
STRENGTH AS IT CONTINUES TO DEPICT A FLATTER OPEN TROUGH QUICKLY
TRAVERSING THROUGH AND OUT OF THE AREA BY EARLY FRIDAY. THERE
CONTINUES TO BE SUFFICIENT INSTABILITY AND MOISTURE...AS WELL AS THE
UPPER LEVEL SUPPORT TO POTENTLY GENERATE SHOWERS ACROSS MUCH OF
THE CWA WEDNESDAY-FRIDAY. THEREFORE...CONTINUE THE RECENT TREND OF
KEEPING SHOWER CHANCES IN THE FORECAST THROUGH THIS PERIOD. IF THE
STRONGER/MORE AMPLIFIED GFS VERIFIES...SHOWERS WILL LINGER IN THE
AREA THROUGH THE MAJORITY OF THE DAY FRIDAY.

THE LATEST OPERATIONAL MODEL RUNS HAVE BEGUN TO GET ON THE SAME PAGE
REGARDING THE SHORTWAVE THIS WEEKEND...WITH THE GFS/ECMWF DEPICTING
A MORE PROGRESSIVE WAVE SLIDING ACROSS THE AREA ON SATURDAY. AT THIS
TIME...STRENGTH AND TIMING DIFFERENCES EXIST FROM MODEL TO
MODEL...DUE TO THE ECMWF BEING STRONGER/MORE AMPLIFIED THAN THE GFS
SOLUTION. DESPITE THIS...GUIDANCE CONTINUES TO HINT AT ENOUGH
MOISTURE/INSTABILITY LEFT OVER THE AREA TO GENERATE SHOWERS WITH
THIS SHORTWAVE AS WELL. THEREFORE...KEPT POPS UP ACROSS THE
AREA...AND THE MENTION OF SHOWERS ACROSS THE NORTHERN ZONES THROUGH
SATURDAY AFTERNOON. IT APPEARS THAT THIS SHORTWAVE WILL CLEAR THE
AREA BY SUNDAY...GIVING WAY TO A SHORTWAVE RIDGE AHEAD OF THE NEXT
POTENTIAL SYSTEM THAT WILL BE LOOMING OFF OF THE COAST OF THE
PACIFIC NORTHWEST.

TEMPERATURE WISE...DIFFERENCES IN THE AMPLITUDE OF EACH SHORTWAVE
CONTINUES TO KEEP THINGS TRICKY ON THURSDAY AND FRIDAY...AS THERE
CONTINUES TO BE A FAIRLY SUBSTANTIAL SPREAD AMONGST GUIDANCE
REGARDING FORECAST HIGHS. FOR NOW...CONTINUED TO FAVOR THE LOWER END
OF GUIDANCE GIVEN THE OVERALL PATTERN THAT IS SETTING UP FOR THE
COMING WEEK. THE BOTTOM LINE IS THAT TEMPERATURES LOOK TO DROP BELOW
WHAT WE HAVE BEEN EXPERIENCING LATELY ON THURSDAY AND FRIDAY...WITH
THE QUESTION OF "HOW LOW WILL WE GO" DEPENDING ON WHICH MODEL
SOLUTION VERIFIES. TEMPERATURES LOOK TO REBOUND BY LATE WEEKEND IN
RESPONSE TO THE POTENTIAL SHORTWAVE RIDGE THAT MAY TRAVERSE THE AREA
AHEAD OF THE NEXT SYSTEM.
&&

.AVIATION...FOR MCCARRAN...LIGHT AND VARIABLE WINDS ARE EXPECTED
THROUGH MID-MORNING BEFORE WINDS FAVOR A LIGHT EASTERLY DIRECTION IN
THE AFTERNOON AND EARLY EVENING AT SPEEDS OF 8 KTS OR LESS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...EXPECT DIURNAL WIND TRENDS AT ALL TAF SITES THROUGH THE
TAF PERIOD...WITH SLIGHTLY ENHANCED WEST WINDS AT KDAG. SKIES WILL
BE CLEAR AT ALL TAF SITES WITH THE EXCEPTION OF KBIH WHERE SCT-BKN
250 CAN BE EXPECTED THROUGH SUNDAY WITH A FEW CLOUD BASES AS LOW AS
8K-12K FEET IN THE LATE AFTERNOON AND EARLY EVENING HOURS. ISOLATED
SHRA AND TSRA ARE POSSIBLE OVER THE SOUTHERN SIERRA NEVADA, WHITE
MOUNTAINS AND THE SPRING MOUNTAINS AND SHEEP RANGE BETWEEN 21Z TODAY
AND 03Z MONDAY.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTERS SHOULD REPORT ACCORDING TO
STANDARD OPERATING PROCEDURES.
&&

$$

UPDATE...PADDOCK
SHORT TERM/AVIATION...STACHELSKI
LONG TERM...PULLIN

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