FXUS65 KVEF 091735 AAA
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
935 AM PST WED DEC 9 2009

SYNOPSIS...A DRY NORTHWEST FLOW OVER THE REGION TODAY WILL GIVE WAY 
TO INCREASING MOISTURE THURSDAY AND A WEAK PACIFIC SYSTEM MOVING 
INLAND EARLY FRIDAY. A STRONGER STORM AND ADDITIONAL MOISTURE WILL 
BRING PRECIPITATION TO MUCH OF THE REGION SATURDAY AND SUNDAY...WITH 
SNOW MAINLY CONFINED TO ELEVATIONS ABOVE 5000 FEET.
&&

.UPDATE...TEMPERATURES ARE STARTING TO RISE ACROSS THE CWA AFTER A 
FEW LOCATIONS SAW THEIR COLDEST TEMPERATURES IN YEARS. SPRING VALLEY 
STATE PARK IN EASTERN LINCOLN COUNTY RECORDED A LOW OF -27 DEGREES 
THIS MORNING. EXPECT ANOTHER COLD NIGHT TONIGHT...BUT WITH HIGH 
CLOUDS MOVING IN...TEMPERATURES ARE NOT EXPECTED TO BE QUITE AS 
COLD. CURRENT FORECAST IN GOOD SHAPE AND NO UPDATES PLANNED. 
-GORELOW-
&&

.PREVIOUS DISCUSSION.../400 AM PST WED DEC 9/

.SHORT TERM...TODAY WILL BE A TRANSITION DAY WITH CONDITIONS SIMILAR 
TO TUESDAY. COLD AND DRY NORTHWEST FLOW THEN GIVES WAY TO INCREASING 
MID AND HIGH LEVEL PACIFIC MOISTURE CURRENTLY BEING HELD AT BAY OFF 
THE CALIFORNIA COAST. SOME WEAK DISTURBANCES EMBEDDED IN THE ZONAL 
FLOW THURSDAY WILL ACCOMPANY THIS BUT THE CHANCE FOR PRECIPITATION 
HAS BEEN TRIMMED BACK UNTIL FRIDAY. A LITTLE MORE ORGANIZED TROUGH 
MOVING INTO THE WEST COAST THURSDAY NIGHT WILL MOVE ACROSS THE 
REGION FRIDAY WITH ADDITIONAL LOW TO MID LEVEL MOISTURE. MOUNTAINS 
WILL SEE A BETTER CHANCE OF SOME LIGHT PRECIPITATION WHILE THE 
VALLEYS STAND ONLY A SLIGHT CHANCE OF SEEING MEASURABLE PRECIP. THIS 
WILL PRIME THE PUMP A LITTLE AHEAD OF A MORE SIGNIFICANT PACIFIC 
SYSTEM QUICKLY FOLLOWING IT SATURDAY AND SUNDAY. INCREASED CLOUD 
COVER TONIGHT SHOULD BRING TEMPERATURES UP A FEW DEGREES FROM THE 
COLD TEMPS THIS MORNING. THE LATEST NAM MOS GUIDANCE INDICATES HIGH 
TEMPERATURES WILL NOT INCREASE MUCH IN THE VALLEYS AS INVERSIONS 
HOLD DUE TO LACK OF MIXING AND LIMITED SUNSHINE.
&&

.LONG TERM...THE LAST STORM SYSTEM OF THE WEEK WILL MOVE ACROSS THE 
AREA SATURDAY AFTERNOON INTO SATURDAY NIGHT. DESPITE THEIR STRUGGLES 
WITH THIS SYSTEM SEVERAL DAYS AGO THE ECMWF...GFS AND GEM HAVE ALL 
COME INTO BETTER AGREEMENT WITH THE TIMING OF THIS SYSTEM. ALTHOUGH 
THE INITIAL PACIFIC LOW WILL HEAD TOWARDS SOUTHERN OREGON/NORCAL ON 
SATURDAY AFTERNOON...A PLUME OF MOISTURE WILL PUSH ACROSS OUR AREA 
THEN. GIVEN THE PLUME OF MOISTURE AIMED AT OUR AREA...SPILLOVER 
SHOULD OCCUR AND THUS HAVE POPS RAMPING UP BIG TIME FOR THE LATER 
HALF OF SATURDAY. MODEL TIME HEIGHTS FROM THE GFS SHOW SATURATED 
LOW-LEVELS AND THIS IS 'DRIER' THAN THE ECMWF WITH RESPECT TO 
FORECASTED PRECIPITATION AMOUNTS. OVERALL THE MAIN ISSUE IS HOW FAR 
SOUTH THIS PLUME OF MOISTURE GETS AS THE MODELS AGREE THAT SOUTH OF 
I-40 NOT MUCH PRECIPITATION MAY FALL AND AS A RESULT HAVE A TIGHT 
GRADIENT IN POPS ACROSS THE FAR SOUTHERN CWFA. PRECIP CHANCES LOOK 
BEST ESPECIALLY FROM I-15 NORTHWARD AND HAVE BUMPED UP POPS FOR 
THEN. UNLIKE THE LAST SYSTEM WARMER AIR WILL WORK INTO THE AREA DUE 
TO THE TRAJECTORY OF THIS SYSTEM AND THE FLOW ALOFT BEING WEST TO 
SOUTHWEST AS IT APPROACHES. SNOW LEVELS REMAIN PROBLEMATIC THOUGH AS 
WET BULB ZERO HEIGHTS IN THE SOUTHERN GREAT BASIN VALLEYS ARE AROUND 
4000 FEET SATURDAY BUT RISE BY SATURDAY NIGHT AS WARMER AIR MOVES 
IN. THUS EXPECT THAT WE WILL SEE SNOW TO START IN THESE AREAS BUT IT 
WILL ULTIMATELY MIX WITH OR CHANGE TO RAIN AT TIMES. HIGHER 
ELEVATIONS SUCH AS THE SIERRA AND SPRING MOUNTAINS WILL GET ANOTHER 
ROUND OF SNOW...AT THIS TIME IT LOOKS LIKE MORE SO TO BE AN ISSUE OF 
HOW MUCH. IN LAS VEGAS THE MOST LIKELY TIME FOR RAIN WILL BE 
SATURDAY AFTERNOON INTO EARLY SUNDAY MORNING. THE SYSTEM PULLS OFF 
TO THE EAST ON SUNDAY AND PRECIP WILL TAPER OFF ACROSS THE AREA BY 
THE AFTERNOON. WINDS WILL BE GUSTY AND THERE IS DECENT UPPER SUPPORT 
FOR THE PERIOD AROUND SATURDAY NIGHT TO SEE AT LEAST 25 MPH GUSTS IN 
SPOTS THAT NORMALLY FAVOR BLOWING IN WEST AND SOUTHWEST DIRECTIONS.

DRY NORTHWEST FLOW TAKES HOLD SUNDAY NIGHT AS AN UPPER RIDGE BUILDS 
TOWARDS THE SOUTHWEST U.S.. THIS RIDGE THEN SHIFTS EASTWARD 
GRADUALLY NEXT WEEK KEEPING US IN A DRY PATTERN THOUGH SOME CLOUDS 
MAY SKIM NORTHERN COUNTIES AT TIMES AS SYSTEMS PASS BY WELL TO THE 
NORTH. TEMPERATURES WILL REBOUND BACK CLOSER TO NORMAL AND LIKELY BY 
MID-WEEK EVEN BE A FEW DEGREES ABOVE NORMAL. GIVEN MODELS SHOWING 
WEAK MIXING...UNDERCUT GUIDANCE SOME BUT IT STILL LOOKS POSSIBLE LAS 
VEGAS MAY CRACK 60 DEGREES - YES BY THEN THIS IS A MARK THAT WILL 
NOT HAVE BEEN REACHED IN NEARLY TWO WEEKS. 
&&

.AVIATION...FOR MCCARRAN...LIGHT AND VARIABLE WINDS THROUGH TONIGHT 
WITH INCREASING CLOUDS AOA 25K FEET THIS AFTERNOON. SCT-BKN AOA 25K 
FEET TONIGHT. THE NEXT STORM SYSTEM TO BRING THE POSSIBILITY OF LOW 
CEILINGS AND RAIN TO THE AIRPORT WILL ARRIVE FRIDAY NIGHT INTO 
SATURDAY MORNING AND EXIT BY SUNDAY AFTERNOON. THE MOST LIKELY TIME 
FOR RAIN IN THE VALLEY RIGHT NOW LOOKS TO BE SATURDAY AFTERNOON AND 
NIGHT.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST 
CALIFORNIA...LIGHT WINDS MAINLY FOLLOWING NORMAL DIURNAL DIRECTIONAL 
TRENDS THROUGH TONIGHT. INCREASING CLOUDS AOA 25K FEET THIS 
AFTERNOON. SCT-BKN AOA 25K FEET TONIGHT. THE NEXT SYSTEM TO IMPACT 
THE AREA WILL ARRIVE ON FRIDAY AFTERNOON. HOWEVER MOST OF THE AREA 
WILL PROBABLY NOT SEE PRECIPITATION AND LOWER CEILINGS UNTIL 
SATURDAY AFTERNOON INTO SATURDAY EVENING. THIS SYSTEM WILL MOVE OUT 
ON SUNDAY.
&&

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

$$

ADAIR/STACHELSKI

HTTP://WEATHER.GOV/LASVEGAS