Flash Flood Watch 10, NWS Las Vegas, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
1045 AM PST TUE DEC 16 2008

.SYNOPSIS...A COLD PACIFIC STORM CENTERED OVER NORTHERN CALIFORNIA
WILL AFFECT THE AREA THROUGH THE MIDDLE OF THE WEEK. A BRIEF BREAK
IN THE WEATHER WILL OCCUR TODAY BEFORE THE CORE OF THE STORM SWINGS
DOWN THROUGH SOUTHERN CALIFORNIA INTO ARIZONA WEDNESDAY AND EARLY
THURSDAY. THIS WILL BRING ANOTHER GOOD CHANCE OF RAIN AND SNOW TO
THE SOUTHERN HALF OF THE REGION WEDNESDAY BEFORE A DRYING TREND
DEVELOPS FOR THE END OF THE WEEK. TEMPERATURES WILL REMAIN CHILLY
THROUGH THE END OF THE WEEK.
&&

.UPDATE...MORE SNOW ON THE WAY. THE MAIN FORECAST PROBLEM IS THE
POTENTIAL FOR ANOTHER SIGNIFICANT SNOW EVENT WITH THE INCOMING
SYSTEM FOR SOUTHERN NEVADA AND SOUTHEAST CALIFORNIA WEDNESDAY.
FORECASTING SNOW LEVELS IS GOING TO BE TRICKY BECAUSE THE LOW
PRESSURE SYSTEM INDUCES A STRONG SURFACE PRESSURE GRADIENTS BETWEEN
THE SOUTHERN CALIFORNIA COAST AND THE NORTHERN GREAT
BASIN...BRINGING COLD DRY NORTH WINDS DOWN INTO SOUTHERN NEVADA
TONIGHT AND WEDNESDAY MORNING. THE GFS SOLUTION CLOSES THE LOW
SOONER THAN THE NAM AND BRINGS ABUNDANT MOISTURE UP INTO CLARK
COUNTY BY 18Z WEDNESDAY. WE ARE GOING TO ISSUE A WINTER STORM WATCH
FOR CLARK...SOUTHERN NYE AND SAN BERNARDINO COUNTIES ABOVE 3000 FEET
WEDNESDAY MORNING THROUGH WEDNESDAY EVENING. IT APPEARS THERE WILL
BE ENOUGH WARM AIR PULLED INTO SOUTHERN MOHAVE COUNTY THAT WILL
RAISE SNOW LEVELS POSSIBLY ABOVE 6000 FEET WHILE UP TO AN INCH OF
RAIN COULD FALL WEDNESDAY AFTERNOON. WE ARE CONSIDERING A FLASH
FLOOD WATCH FOR SOUTHERN MOHAVE COUNTY WEDNESDAY AFTERNOON AND
EVENING. -ADAIR- &&

.AVIATION...FOR MCCARRAN...SCT TO BRIEFLY BROKEN CONDITIONS BETWEEN
6000 AND 10000 FEET FOR THE REST OF THE DAY. WINDS WILL REMAIN
SOUTHWEST THROUGH MOST OF TUESDAY BEFORE TURNING TO THE NORTH THIS
EVENING. LATE IN THE EVENING THE EFFECTS OF THE NEXT SYSTEM WILL BE
FELT AS A LOW MOVES IN FROM CALIFORNIA. CLOUD COVER WILL INCREASE
TUESDAY EVENING AND SO WILL A CHANCE FOR RAIN IN THE LATE EVENING.
CHANCES INCREASE TO ABOUT 50 PERCENT FOR KLAS FOR LIGHT RAIN OR SNOW
WEDNESDAY. THOUGH THE BULK OF THE PRECIPITATION WILL BE SOUTHWEST
THROUGH THE SOUTHEAST OF KLAS THERE IS STILL A GOOD LIKELIHOOD OF
CIGS GETTING BELOW 2000 FEET WEDNESDAY AND HAVE PUT THIS IN THE LAST
PART OF THE 12Z TAFS.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...MOHAVE COUNTY ARIZONA WILL SEE CONTINUED LINGERING RAIN
AND SNOW SHOWERS THIS MORNING AND MVFR CONDITIONS THROUGH MID
MORNING. LIGHT WINDS AREAWIDE TODAY AND SCT TO FEW LOW AND MID
CLOUDS. THE NEXT STORM SYSTEM IS POISED TO START MAKING ITS EFFECTS
FELT LATE TUESDAY EVENING AND EARLY WEDNESDAY MORNING. RAIN AND SNOW
WILL MAKE ITS WAY WEST TO EAST WEDNESDAY WITH THE MOST PRECIPITATION
AND LOW CIGS/VSBY SOUTH OF INTERSTATE 15.
&&

.PREV DISCUSSION.../350 AM PST TUE DEC 16 2008/

.SHORT TERM...SATELLITE SHOWS MAIN CIRCULATION CENTER NEAR THE COAST
OF FAR NORTHERN CALIFORNIA. SHOWERS AND A FEW THUNDERSTORMS WERE
OCCURRING UNDER THE ASSOCIATED COLD POOL ALOFT. IN OUR AREA...RADAR
INDICATED ONLY A FEW BANDS OF LIGHT PRECIP REMAINING OVER MOHAVE
COUNTY...AND SURFACE OBS SHOWED RISING SNOW LEVELS AND LOWERING
PRECIP RATES AT MOST STATIONS. THUS...WILL LET THE WINTER STORM
WARNING EXPIRE AT 12Z. MODELS STILL SUGGEST A BREAK IN THE ACTION
TODAY...WITH THE POSSIBLE EXCEPTION OF A BAND OF PRECIP DEVELOPING
OVER THE NORTHERN ZONES /ESPECIALLY LINCOLN COUNTY/ IN A LOW LEVEL
CONVERGENCE ZONE DEPICTED BY THE GFS. LEFT CHANCE POPS IN THAT AREA
WITH LESSER POPS IN MOST OTHER AREAS. AS THE MAIN LOW CENTER SLOWLY
SLIDES SOUTH DOWN THE CALIFORNIA COAST...IT WILL EVENTUALLY TAP INTO
THE SLUG OF SUBTROPICAL MOISTURE CLEARLY SEEN BETWEEN 20N AND 26N
EAST OF 127W. THIS WILL LEAD TO OUR NEXT CONCERN ON WEDNESDAY AS THE
MOISTURE GETS PULLED UP INTO OUR SOUTHERN ZONES. RAISED POPS AND QPF
SIGNIFICANTLY IN THIS AREA. SNOW AMOUNTS AND POSSIBLE WINTER WEATHER
PRODUCTS WILL BE TRICKY...AS SNOW LEVELS WILL RISE RAPIDLY DURING
THE STORM THANKS TO THE SUBTROPICAL INFLUENCE. WILL LET THE DAY CREW
SEE ONE MORE RUN AND CHECK FOR CONSISTENCY BEFORE MAKING THAT
DECISION. ALSO CANNOT RULE OUT FLASH FLOODING CONCERNS...ESPECIALLY
IN MOHAVE AND SAN BERNARDINO COUNTIES...DUE TO THE SUBTROPICAL
CONNECTION AND CHILLY TEMPERATURES INCREASING PRECIPITATION
EFFICIENCY. SPEAKING OF CHILLY TEMPERATURES...THE STORM SHOULD STILL
HAVE VERY COLD AIR ON ITS BACK SIDE...WHICH COULD LEAD TO PRECIP
CHANGING BACK OVER TO SNOW WEDNESDAY NIGHT. PLENTY OF UNCERTAINTY
REMAINING IN THE DETAILS...BUT SOMETHING TO WATCH.

.LONG TERM...FRIDAY THROUGH MONDAY...FRIDAY STARTS OUT WITH ZONAL
FLOW OVER THE AREA AS A LOW...THE NEXT SYSTEM TO CONTEND
WITH...DROPS INTO THE PACNW. TREND OF MODELS HAS BEEN TO KEEP THE
MOISTURE WITH THIS NEXT LOW TO OUR NORTH AND EAST. STILL LOOK FOR A
FRONT TO DROP THROUGH THE AREA SATURDAY AND BRING ABOUT A CHANCE FOR
BREEZY CONDITIONS DOWN THE COLORADO RIVER VALLEY. CONFIDENCE IS NOT
AS HIGH AS LAST NIGHT AS IT LOOKS LIKE THE SUPPORTING UPPER LEVEL
TROUGH WILL BE HITTING OUR AREA HARDER. REST OF THE EXTENDED LOOKS
TO BE FAIRLY DRY UNDER WEST TO NORTHWEST FLOW. NEXT SYSTEM APPEARS
ON THE HORIZON MONDAY AS IT PLOWS INTO THE PACNW AND MOISTURE
INCREASES OVER THE ENTIRE WEST. FOR NOW HAVE KEPT PREVIOUS FORECAST
OF POPS IN WHICH WILL HAVE RAIN/SNOW SHOWERS IN THE NORTH AND
SOUTHERN IN SOUTHERN AREA MOUNTAIN MONDAY. BEYOND THE EXTENDED
TOWARDS WEDNESDAY OR SO IT LOOKS LIKE ANOTHER ACTIVE PERIOD COMING.
&&

.VEF WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
AZ...NONE.
CA...NONE.
&&

MORGAN/JACQUES

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