Winter Storm Watch 3, NWS Las Vegas, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAS VEGAS NV
856 PM PST WED JAN 27 2016

.SYNOPSIS...DRY CONDITIONS AND WARMING TEMPERATURES WILL OCCUR
THROUGH THE END OF THE WORK WEEK IN ADVANCE OF A POTENT PACIFIC
STORM SYSTEM THAT WILL MOVE THROUGH THE REGION THIS WEEKEND. THIS
STORM WILL LIKELY BRING SIGNIFICANT SNOW TO THE SOUTHERN SIERRA AND
CHANCES OF PRECIPITATION AND WINDY CONDITIONS TO MUCH OF THE AREA.
MUCH COOLER TEMPERATURES ARE EXPECTED EARLY NEXT WEEK AS THE SYSTEM
MOVES OFF TO THE EAST.
&&

.UPDATE...A WEAK UPPER DISTURBANCE SPINNING OFF THE SOUTHERN CAL
COAST THIS EVENING CONTINUES TO SPREAD HIGH CLOUDS ACROSS THE AREA.
MODEL FORECASTS TRACK THIS FEATURE SOUTH ALONG THE COAST OVERNIGHT
WITH LESS CLOUDINESS OVER THE NORTHERN REGIONS OF THE FORECAST AREA
AND CONTINUED PARTLY TO MOSTLY CLOUDY CONDITIONS ACROSS THE SOUTH.
ADJUSTED SKY COVER TO TAKE IN ACCOUNT THE LATEST TRENDS OTHERWISE,
THE FORECAST IS IN GOOD SHAPE.
&&

.PREVIOUS DISCUSSION...244 PM PST...

.SHORT TERM...THROUGH FRIDAY NIGHT.

RIDGING CONTINUES IN THE WEST TODAY, BUT A WEAK VORT MAX NEAR
34N/124W IS ADVANCING ESE TOWARD THE CALIFORNIA/MEXICO BORDER THIS
AFTERNOON. THIS SHORTWAVE TROUGH IS BRINGING INCREASED CLOUD COVER
TO THE DESERT SOUTHWEST, WHICH HAS ACTED TO IMPEDE WARMING SOMEWHAT
IN WESTERN PORTIONS OF THE CWA THIS AFTERNOON. VORT MAX WILL
CONTINUE ESE TO FAR SOUTHERN ARIZONA AND ADJACENT NORTHWEST MEXICO
BY 00Z FRIDAY WITH INCREASED CLOUD COVER (ESPECIALLY FOR THE
SOUTHERN CWA) OVERNIGHT AND DECREASING CLOUD COVER FROM NORTHWEST TO
SOUTHEAST TOMORROW. MODELS HAVE NOT HANDLED THIS SYSTEM PARTICULARLY
WELL, AND GUIDANCE IS STRUGGLING A TAD WITH TEMPERATURES OWING TO
THE VARIATIONS IN CLOUD COVER. GIVEN THE ABOVE...WAS INCLINED TO
KEEP MIN TEMPS A BIT WARMER THAN GUIDANCE IN MUCH OF THE CWA TONIGHT
GIVEN THE UPTICK IN CLOUD COVER, BUT KEPT MAX TEMPS TOMORROW QUITE
CLOSE TO GUIDANCE GIVEN THE DECREASING TREND IN CLOUDS EXPECTED.
NEVERTHELESS, CONFIDENCE IS SOMEWHAT LOWER THAN AVERAGE WITH TEMPS
FOR THE FIRST 24 HOURS OF THE FORECAST GIVEN THE UNCERTAINTY WITH
EXTENT/SPATIAL DISTRIBUTION OF CLOUDS. CURRENT FORECAST FOR THE NEXT
24 HOURS HAS BOTH MAX AND MIN TEMPS ABOUT 3-5 DEGREES WARMER THAN
WHAT WAS OBSERVED TODAY.

AS THE WEAK VORT MAX ADVANCES INTO THE RIDGE, THE RIDGE PROGRESSES
EAST AND WEAKENS SUFFICIENTLY TO ALLOW FOR THE EAST PACIFIC JET TO
SINK SOUTHWARD WITH TIME FRIDAY INTO THE WEEKEND. ONE SYSTEM QUICKLY
REACHES THE PACIFIC NORTHWEST BY 00Z FRIDAY WITH SENSIBLE WEATHER
EFFECTS WELL TO THE NORTH OF THE AREA. HOWEVER, THE SUBSEQUENT
SYSTEM REACHES THE COAST FRIDAY AFTERNOON. BY THIS TIME, ASCENT AND
MOIST ADVECTION WILL ALLOW FOR PRECIPITATION TO DEVELOP GRADUALLY
INTO THE SOUTHERN SIERRA BY FRIDAY NIGHT. GFS IS A BIT QUICKER TO
DEVELOP THIS PRECIP (12Z-18Z FRIDAY) AND REMAINS SOMEWHAT MORE
AGGRESSIVE IN BRINGING PRECIP TO THE SOUTHERN GREAT BASIN (THOUGH
LESS SO THAN YESTERDAY). AS SUCH...SLIGHT-TO-CHANCE POPS CONTINUE
FOR THE SOUTHERN SIERRA BEGINNING 12Z FRIDAY WITH VALUES INCREASING
THROUGH FRIDAY NIGHT. GIVEN THE ORIENTATION OF THE FLOW (SUBSTANTIAL
SHADOWING DOWNSTREAM OF THE SIERRA) AND THE JET ONLY SLOWLY
ADVANCING SOUTHWARD, KEPT POPS RELATIVELY LOW FOR ESMERALDA, NYE,
AND LINCOLN COUNTIES THROUGH FRIDAY NIGHT. SNOW LEVELS LOOK HIGH TO
BEGIN WITH (8000+ FEET), SO ACCUMULATIONS WILL BE CONFINED MOSTLY TO
THE RIDGETOPS THROUGH FRIDAY NIGHT.

THE OTHER MAIN STORY WITH THE INITIAL STAGES OF THE WEEKEND STORM IS
THE INCREASING WINDS IN THE SIERRA AND WESTERN MOJAVE DESERT. MODEL
SOUNDINGS SHOW 600-500 MB WINDS 50+ KTS BY 06Z SATURDAY WITH HI-RES
GUIDANCE SUGGESTING RIDGETOP WINDS EXCEEDING HIGH WIND WARNING
CRITERIA FRIDAY NIGHT. SOME UNCERTAINTY REMAINS HOWEVER GIVEN THE
TIMING OF PRECIPITATION AND RESULTANT EFFECTS ON SURFACE WINDS AS
WELL AS SPATIOTEMPORAL VARIATIONS REGARDING THE STRENGTH/ORIENTATION
OF THE ASSOCIATED MIDLEVEL JET. HELD OFF ON ISSUING WATCH PRODUCTS
AT THIS TIME GIVEN THESE UNCERTAINTIES, BUT FULLY EXPECT SOME
COMBINATION OF WINTER WEATHER/WIND PRODUCTS WILL BE REQUIRED FOR THE
SIERRA NEAR OR SUBSEQUENT TO THIS TIME. MEANWHILE, WEST-SOUTHWEST
WINDS WILL BEGIN TO APPROACH WIND ADVISORY CRITERIA IN THE WESTERN
MOJAVE DESERT BY FRIDAY NIGHT.

TEMPERATURES FRIDAY AND FRIDAY NIGHT WILL BE ABOUT 5-10 DEGREES
ABOVE NORMAL.

.LONG TERM...SATURDAY THROUGH WEDNESDAY.

NO MAJOR CHANGES IN THE MODEL TRENDS TODAY. STILL LOOKING AT A
STRONG MOIST WESTERLY FLOW SATURDAY WITH A WEAK EMBEDDED SHORTWAVE
MOVING ACROSS NORTHERN NEVADA. THIS WILL LEAD TO PRECIPITATION
CHANCES INCREASING A BIT OVER THE SIERRA AND THE FAR NORTHERN PART
OF OUR FORECAST AREA. THE SIERRA COULD START TO SEE SIGNIFICANT
SNOWFALL ALONG WITH STRONG WESTERLY WINDS AND IF MODELS REMAIN
CONSISTENT A WINTER STORM WATCH/WARNING WILL LIKELY BE NEEDED. NOT
QUITE READY TO PULL THE TRIGGER AT THIS STAGE. ANY PRECIPITATION
SHOULD STILL BE FAIRLY LIGHT ACROSS THE SOUTHERN GREAT BASIN WHILE
THE CENTRAL AND SOUTHERN PORTIONS OF THE CWA REMAIN DRY WITH MILD
TEMPERATURES. HOWEVER...TEMPERATURES MAY BE TEMPERED A BIT BY
SIGNIFICANT HIGH CLOUD COVER. WINDS WILL ALSO BE INCREASING SATURDAY
AFTERNOON ACROSS MUCH OF THE MOJAVE DESERT AND THERE IS A GOOD
CHANCE OF WINDS HITTING ADVISORY LEVELS IN SAN BERNARDINO COUNTY.

THE MOISTURE BAND WILL CONTINUE TO SAG SLOWLY SOUTH ACROSS THE AREA
SATURDAY NIGHT AS A TROUGH DROPS SOUTH ALONG THE NORTHERN CALIFORNIA
COAST. MUCH OF THE AREA NORTH OF LAS VEGAS WILL SEE A CHANCE OF
PRECIPITATION WITH THE POSSIBILITY OF SOME MORE HEAVY SNOW
CONTINUING IN THE SIERRA. OVERALL...OTHER THAN IN THE
SIERRA...PRECIPITATION AMOUNTS SHOULD REMAIN FAIRLY LIGHT. WINDS
LOOK TO ABATE SOMEWHAT SATURDAY NIGHT BUT THERE COULD STILL BE
BREEZY TO WINDY AREAS ACROSS THE DESERT.

PRECIPITATION CHANCES WILL INCREASE ACROSS THE REST OF THE AREA
SUNDAY AND SUNDAY NIGHT AS THE UPPER TROUGH MOVES EAST OUT OF
CALIFORNIA AND ACROSS NEVADA. THE GFS CONTINUES TO BE QUITE A BIT
MORE MOIST THAN THE ECMWF WITH MORE WIDESPREAD SIGNIFICANT
PRECIPITATION. ALL THE MODELS SEEM TO PLACE THE BEST QPF IN SOMEWHAT
DIFFERENT LOCATIONS AND CONFIDENCE IS STILL NOT VERY HIGH REGARDING
THAT ASPECT OF THE FORECAST. TEMPERATURES WILL START TO COOL SUNDAY
WITH BREEZY TO WINDY CONDITIONS ACROSS THE MOJAVE DESERT AND SIERRA
AND SPRING MOUNTAINS CONTINUING SUNDAY NIGHT. GUSTY NORTHERLY WINDS
WILL START TO SPREAD INTO THE NORTHERN CWA SUNDAY NIGHT.

A DRIER NORTHWEST FLOW ALOFT WILL PUSH INTO THE AREA BEHIND THE
TROUGH MONDAY WITH SOME LINGERING SHOWERS POSSIBLE ACROSS MAINLY
LINCOLN AND MOHAVE COUNTIES. GUSTY NORTH/NORTHWEST WINDS APPEAR
LIKELY ACROSS THE ENTIRE FORECAST AREA WITH TEMPERATURES EVEN COOLER
THAN SUNDAY. MANY AREAS WILL HAVE HIGH TEMPERATURES AROUND 15
DEGREES COOLER THAN WHAT IS EXPECTED SATURDAY WITH LAS VEGAS ONLY
AROUND 50 DEGREES FOR A HIGH...WITH 60 BEING THE NORMAL HIGH FOR
FEBRUARY 1ST.

A MAINLY DRY NORTHWEST FLOW WILL CONTINUE TUESDAY INTO WEDNESDAY
WITH SIGNS OF A RIDGE STARTING TO BUILD IN FROM THE WEST WEDNESDAY
AFTERNOON. TEMPERATURES WILL REMAIN BELOW NORMAL BUT SHOULD START TO
WARM A BIT WEDNESDAY.
&&

.AVIATION...FOR MCCARRAN...LIGHT AND VARIABLE WINDS THROUGH THE
PERIOD WITH SOME PREFERENCE TO NOCTURNAL DRAINAGE SOUTHWEST FLOW
OVERNIGHT. SCT-BKN HIGH CLOUDS THROUGH TONIGHT WITH PERHAPS A SLOW
DECREASING TREND EXPECTED TOMORROW.

FOR THE REST OF SOUTHERN NEVADA...NORTHWEST ARIZONA...AND SOUTHEAST
CALIFORNIA...WINDS LIGHT AND DIURNALLY DRIVEN AT MOST TAF SITES
THROUGH THE PERIOD. THE COLORADO RIVER VALLEY WILL CONTINUE TO SEE
NORTHERLY BREEZES (5-15 KTS AT KEED AND 10-20 KTS AT KIFP DURING THE
DAY) WITH OCCASIONAL GUSTS. WINDS SHOULD BE LIGHTER AT NIGHT. SCT-
BKN HIGH CLOUDS EXPECTED FOR MUCH OF THE REGION AT LEAST THROUGH
TONIGHT AND TO A LESSER EXTENT TOMORROW. CLOUDS WILL BEGIN TO
INCREASE IN THE SIERRA BY TOMORROW NIGHT IN ADVANCE OF A POTENT
STORM SYSTEM TO AFFECT THE REGION THIS WEEKEND.
&&

.SPOTTER INFORMATION STATEMENT...SPOTTER ACTIVATION IS NOT
ANTICIPATED. PLEASE REPORT ANY SIGNIFICANT WEATHER ACCORDING TO
STANDARD OPERATING PROCEDURES.
&&

UPDATE...SALMEN

PREVIOUS DISCUSSION...

SHORT TERM/AVIATION...SHAFER
LONG TERM.............HARRISON

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