Area Forecast Discussion
Issued by NWS Las Vegas, NV

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000
FXUS65 KVEF 201008
AFDVEF

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
208 AM PST SAT DEC 20 2014

.SYNOPSIS...A WEAK SYSTEM WILL PASS ACROSS THE AREA TODAY INTO
TONIGHT BRINGING ABUNDANT CLOUDS WITH IT. A FEW SHOWERS ARE POSSIBLE
IN THE HIGHER ELEVATIONS OF THE SOUTHERN GREAT BASIN. AN AREA OF
HIGH PRESSURE IS EXPECTED TO BUILD OFF OF CALIFORNIA SUNDAY THROUGH
TUESDAY KEEPING THE AREA DRY AND MILD. A STORM SYSTEM SHOULD PASS IN
OR NEAR THE AREA BETWEEN CHRISTMAS EVE AND CHRISTMAS DAY USHERING IN
A DROP IN TEMPERATURES FOR THE END OF NEXT WEEK.
&&

.SHORT TERM...TODAY THROUGH MONDAY NIGHT.

THERE IS AN EXTENSIVE AREA OF ENHANCED CLOUD TOPS SHOWING UP ON
INFRARED SATELLITE IMAGERY EARLY THIS MORNING ACROSS OREGON, NORCAL
AND NORTHERN NEVADA IN ASSOCIATION WITH THE JET STREAM PASSING OVER
THIS AREA. THIS SHIELD OF MAINLY HIGH LEVEL CLOUDS WILL ADVANCE ON
SOUTH AND EAST TODAY AND AS A RESULT SUNSHINE WILL BE EVEN MORE
LIMITED TODAY THAN WHAT WE SAW YESTERDAY. TEMPS FELL SHORT OF
PREDICTED HIGHS YESTERDAY AND GIVEN THAT WE SHOULD SEE EVEN MORE
EXTENSIVE CLOUD COVER TODAY, SOME OF THE BIAS CORRECTED AND CONS
MODEL GUIDANCE LOOKS TO WARM FOR TEMPS. THUS I SIDED WITH
PERSISTENCE AND STATISCAL MOS FOR A BLEND AS A STARTING POINT. MOST
OF THE MOISTURE WITH THIS SYSTEM WILL BE ABOVE 15000 FEET AND VERY
LITTLE IN THE WAY OF ENERGY IS SHOWN TO CROSS THE AREA THIS EVENING
INTO TONIGHT IN THE MID-LEVELS. AS A RESULT THERE IS NOT ALL THAT
MUCH GOING TO SUPPORT A LOT OF PRECIPITATION BUT A FEW LIGHT SHOWERS
MAY BE YIELDED ACROSS THE HIGHER TERRAIN OF THE SOUTHERN GREAT BASIN
THROUGH SUNDAY MORNING. THE BEST CHANCES WILL BE OVER THE SOUTHERN
SIERRA CREST AND IN THE PANHANDLE OF LINCOLN COUNTY.

THERE MAY BE SOME LOW STRATUS CLOUDS OR PATCHY FOG THIS MORNING IN
AND AROUND COLORADO CITY AS THE TEMP-DEWPOINT SPREAD REMAINS SMALL
AND WINDS ARE VERY LIGHT TO CALM. HOWEVER, THE AMOUNT OF CIRRUS
AROUND WOULD SEEM TO FAVOR A LOW STRATUS DECK FORMING VERSUS
RADIATION FOG.

ON SUNDAY, A LARGE AREA OF HIGH PRESSURE IN THE MID AND UPPER LEVELS
IS EXPECTED TO SET UP OFF OF CALIFORNIA. THIS WILL HELP TO PUSH
TEMPS UP SEVERAL DEGREES AND ALL AREAS WILL BE 4-8 DEGREES ABOVE
NORMAL, ESPECIALLY IN THOSE AREAS ABOVE THE INVERSION HEIGHT.
FURTHER WARMING SHOULD TAKE PLACE ON MONDAY AS THE RIDGE STAYS
OFFSHORE. WHILE THE DAY SHOULD START WITH AN INVERSION, THERE ARE
SIGNS, ESPECIALLY PER THE GFS, THAT IT MAY BREAK BY THE AFTERNOON AS
A MID/UPPER LEVEL TROUGH SWINGS ACROSS THE EASTERN GREAT BASIN. IF
THIS TROUGH CAN BREAK THE INVERSION AND WE MIX JUST ENOUGH, THE
CURRENT FORECAST HIGHS ARE TOO COOL, ESPECIALLY IN THE LOWER MOJAVE
DESERT VALLEYS. EITHER WAY IF YOU LIKE IT MILD, THIS WILL BE A NICE
STRETCH OF WEATHER FOR LATE DECEMBER.

.LONG TERM...TUESDAY THROUGH FRIDAY.

BEGINNING TUESDAY MORNING THE MODELS AGREE ON HIGH PRESSURE TO THE
WEST BEING THE DOMINANT FEATURE...WITH NORTHERLY FLOW OVER OUR AREA
PRODUCING LOCALLY BREEZY CONDITIONS PARTICULARLY DOWN THE COLORADO
RIVER VALLEY. THE MODEL AGREEMENT QUICKLY DETERIORATES BY
WEDNESDAY...AS THE OPERATIONAL MODELS DISAGREE ON WHETHER TO AMPLIFY
/ECMWF/ OR NOT AMPLIFY /GFS/ A SHORTWAVE TROUGH PASSING THROUGH 135W
WEDNESDAY MORNING. BOTH OPERATIONAL SOLUTIONS ARE REPRESENTED IN THE
ENSEMBLE PERTURBATIONS SO CONFIDENCE IS NEARLY NIL. BY WEDNESDAY
AFTERNOON THE GFS SUGGESTS FLAT RIDGING OVERHEAD AS THE WEAK TROUGH
PASSES THROUGH THE PACIFIC NORTHWEST...WHILE THE ECMWF SUGGESTS A
DEEPENING TROUGH MOVING INTO NORTHERN CALIFORNIA AND NEVADA WITH
INCREASING WINDS AREAWIDE....FOLLOWED BY A SHOT OF PRECIP WEDNESDAY
NIGHT AND STRONG NORTHWESTERLY WINDS ON CHRISTMAS DAY. MEANWHILE THE
GFS ZIPS ITS WEAK TROUGH INTO THE PLAINS WITH MINIMAL EFFECT ON OUR
AREA. TEMPERATURE FORECASTS ARE ALSO WILDLY DIFFERENT WITH THE GFS
MOS ONLY KNOCKING KLAS DOWN TO 60F FOR A HIGH ON FRIDAY...WHILE THE
ECMWF WITH ITS MUCH STRONGER TROUGH SHOWS 47F. OFFICIAL FORECAST
WILL TAKE A MIDDLE OF THE ROAD APPROACH FOR NOW AND WAIT FOR BETTER
CONFIDENCE.
&&

.AVIATION...FOR MCCARRAN...WINDS SHOULD BE 6 KTS OR LESS AND FAVOR
TYPICAL DIURNAL DIRECTIONAL TRENDS THROUGH TONIGHT. MAINLY BKN-OVC
CLOUDS AOA 20K FEET WITH FEW-SCT CLOUDS AS LOW AS 10K FEET.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...WINDS WILL BE 6 KTS OR LESS AND TREND TOWARD TYPICAL
DIURNAL DIRECTIONS THROUGH TONIGHT. A FEW SHOWERS WILL BE POSSIBLE
ACROSS THE HIGHER ELEVATIONS OF INYO, ESMERALDA, CENTRAL NYE AND
NORTHERN LINCOLN COUNTIES. CIGS AS LOW AS 6K-8K FEET IN AND NEAR ANY
SHOWERS OTHERWISE EXPECT MAINLY BKN CLOUDS AOA 20K FEET WITH A FEW
CLOUDS AS LOW AS 10K-12K FEET.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION IS NOT EXPECTED.
&&

$$

SHORT TERM/AVIATION...STACHELSKI
LONG TERM...MORGAN

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