Heavy Snow in Nevada, December 6 to 7, 2013

AREA FORECAST DISCUSSION...UPDATE
NATIONAL WEATHER SERVICE RENO NV
500 PM PST FRI DEC 6 2013

.UPDATE...

SNOW HAS INCREASED RAPIDLY IN THE SIERRA OVER THE LAST 1-2 HOURS
WITH SNOW COVERED ROADS SEEN ON CALTRANS WEBCAMS. WEVE ACCELERATED
THE START TIME OF THE WINTER STORM WARNING FOR TRUCKEE/TAHOE TO
START NOW. REST OF FORECAST REMAINS UNCHANGED. HOWEVER WELL HAVE TO
MONITOR THE RENO/CARSON CITY ZONE FOR POSSIBLE UPGRADE AS
INGREDIENTS FOR A BURST OF +SN APPEAR IN LATEST GUIDANCE: UPPER AND
LOWER LEVEL FORCING PHASE AROUND 6Z PLUS A TOUCH OF INSTABILITY
EXISTS. WELL KEEP AN EYE ON IT.

CS

&&

.SYNOPSIS...
A WINTER STORM WILL BRING SNOW TO THE SIERRA AND WESTERN NEVADA
TONIGHT INTO SATURDAY. WINTER STORM WARNINGS AND WINTER WEATHER
ADVISORIES ARE IN EFFECT. EXPECT OVERNIGHT TEMPERATURES BELOW ZERO
SATURDAY AND SUNDAY NIGHTS FOR COLDER VALLEYS. TEMPERATURES WILL
REMAIN WELL BELOW NORMAL THROUGH EARLY NEXT WEEK.
&&

.SHORT TERM...
MAIN CHANGES TO THE SHORT TERM INCLUDE UPGRADING THE WINTER
WEATHER ADVISORY TO A WINTER STORM WARNING FOR PERSHING AND
NORTHERN WASHOE COUNTIES AND BUMPING UP WINDS SLIGHTLY THROUGH
SATURDAY, ESPECIALLY FOR RIDGES AND IN THE IMMEDIATE LEE OF THE
SIERRA.

MODELS SHOW THE COLD AND DYNAMIC SYSTEM DUE IN TONIGHT SIMILARLY
AS COMPARED WITH RECENT RUNS SO ONLY MINOR TWEAKS WERE MADE TO
THE SHORT TERM FORECAST. CURRENTLY, THE INFRARED INDICATES COOLING
CLOUD TOPS OVER SOUTHERN OREGON AND EXTREME NORTHERN CALIFORNIA
WITH RADAR SHOWING PRECIPITATION OVER NORTHERN CALIFORNIA SO
TIMING IS STILL ON TRACK FOR SNOW TO MOVE INTO THE NORTHERN SIERRA
BY MID EVENING AND INTO WESTERN NEVADA OVERNIGHT.

THE SREF, NAM AND GFS HAVE BEEN CONSISTENTLY SHOWING A BULLSEYE
OF HIGHER PRECIPITATION OVER PERSHING AND HUMBOLDT COUNTIES LATE
TONIGHT WITH A STRONG AREA OF FRONTOGENESIS AS THE NOSE OF A
100-120 KT JET STREAK MOVES INTO THE REGION. IN ADDITION, THE SREF
PLUME FOR KAAT INDICATED WIDESPREAD SUPPORT FOR 4 TO 7 INCHES SO
THE WINTER WEATHER ADVISORY FOR PERSHING AND NORTHERN WASHOE
COUNTIES WAS UPGRADED TO A WINTER STORM WARNING. ELSEWHERE, THE
STATEMENTS LOOK ON TRACK SO THEY REMAIN LARGELY THE SAME.

AS FAR AS WINDS, THEY DO NOT LOOK OVERLY STRONG BELOW RIDGES
THROUGH SATURDAY MORNING. HOWEVER, THEY WILL PICK UP TONIGHT AHEAD
OF THE STRONG COLD FRONT CURRENTLY NEAR AND WEST OF THE OREGON AND
CALIFORNIA BORDER. THERE COULD BE A SEVERAL-HOUR PERIOD OF
MODERATELY GUSTY WINDS JUST AHEAD OF THE FRONT WITH WINDS DROPPING
OFF AS SNOW INTENSIFIES NEAR FROPA. THIS COULD LEAD TO A SHORT PERIOD
OF LOW VISIBILITY AS THE WINDS COMBINE WITH AN INITIAL BURST OF
THE LIGHT, FLUFFY SNOW. THIS IS MENTIONED IN THE WINTER WEATHER
STATEMENTS.

SATURDAY, THE FRONT WILL BLAST TO NEAR A LINE FROM BISHOP TO
TONOPAH BY MID TO LATE MORNING. THIS WILL TAPER PRECIPITATION TO
ISOLATED TO SCATTERED SNOW SHOWERS FOR MOST AREAS ALTHOUGH
COVERAGE MAY REMAIN NUMEROUS IN THE SIERRA AS RESIDUAL UPSLOPE
(WESTERLY) FLOW CONTINUES INTO THE AFTERNOON. BEHIND THE FRONT,
700 MB TEMPERATURES OF -16C TO -20C FILTER IN WITH VALLEY
TEMPERATURES HOLDING IN THE 20S. IN ADDITION, THERE WILL BE A
NOTICEABLE WIND CHILL WITH NORTHWEST WINDS GENERALLY IN THE 10-20
MPH RANGE.

SATURDAY NIGHT THROUGH SUNDAY NIGHT, VERY COLD AND DRY CANADIAN AIR
SETTLES INTO NORTHEAST CALIFORNIA AND WESTERN NEVADA. HIGHS ON
SUNDAY WILL REMAIN IN THE HIGH TEENS TO MID 20S FOR VALLEYS WITH
SNOW COVER ENHANCING THE COLD AIR FOR VERY COLD NIGHTTIME
TEMPERATURES. IN FACT, BY SUNDAY NIGHT LOWS COULD DROP TO -10 TO
-20 FOR COLDER VALLEYS WITH WARMEST LOCATIONS FALLING INTO THE
SINGLE DIGITS. SNYDER

.LONG TERM...MONDAY THROUGH FRIDAY...
MONDAY AND TUESDAY, DRY NORTHWEST FLOW WILL BE IN PLACE TO START
NEXT WEEK. THIS WILL CONTINUE OUR COLD TEMPERATURES MONDAY WITH
LIGHT EASTERLY WINDS IN PLACE. BY TUESDAY, AN AMPLIFIED EASTERN
PACIFIC RIDGE BEGINS TO NUDGE ITS WAY ONSHORE ALLOWING
TEMPERATURES TO WARM ALOFT. LIGHT WINDS WILL SHIFT MORE SOUTHERLY
AND WILL ENABLE HIGH TEMPERATURES ON TUESDAY TO CREEP BACK UP
TOWARDS THE FREEZING MARK ACROSS WESTERN NEVADA AND THE SIERRA.
VALLEY AREAS WILL BE SLOWER TO WARM WHICH WILL MAINTAIN VALLEY
INVERSIONS. THIS ALONG WITH CLEAR SKIES SHOULD ALLOW OVERNIGHT LOW
TEMPERATURES TO REMAIN IN THE TEENS AND SINGLE DIGITS ACROSS
COLDER VALLEYS THROUGH TUESDAY NIGHT. TF

WEDNESDAY THROUGH FRIDAY, SUFFICE IT TO SAY THIS WILL BE A LOW
CONFIDENCE PERIOD IN THE FORECAST. OVERALL PATTERN OF RIDGE
PRESSING EASTWARD WITH TROF MOVING INTO WEST SEEMS REASONABLE
BASED ON ENSEMBLE GUIDANCE - BUT POSITION OF THE TROF IS HIGHLY
UNCERTAIN. GFS WOULD GIVE US A BURST OF SNOW LATE THURS INTO FRI
WHILE EC SHOWS THE DREADED SPLIT PATTERN WITH LOW TRACKING INTO
SOCAL. ILL CONTINUE LOW CHANCE POPS FOR THURS INTO FRI WITH
MINIMAL CHANGES TO THE FORECAST. THERES A SMALL CHANCE SOME OF
OUR COLDER VALLEYS COULD END UP WITH A PERIOD OF -FZRA DEPENDING
ON TIMING OF STORM AND AMOUNT OF WARM AIR ALOFT LEFTOVER FROM THE
RIDGE.

LOOKING INTO THE D8-14 RANGE - ENSEMBLE GUIDANCE DOES SHOW AN
ATMOSPHERIC RIVER SETTING UP OVER THE PACIFIC OCEAN NORTHEAST OF
HAWAII AROUND MID/LATE NEXT WEEK. OF COURSE TONS OF UNCERTAINTY
WHERE THIS WOULD IMPACT THE WEST COAST - LATEST ANALOG GUIDANCE
SUGGESTS THE PACIFIC NW WITH FLOW ALOFT BECOMING WSW. EVEN JUST A
SLIGHT SHIFT IN THE FLOW WOULD PUT US IN THE AR TRAJECTORY -
SOMETHING TO WATCH. CS
&&

.AVIATION...
PERIODS OF SNOW AND GUSTY WINDS WILL IMPACT ALL TAF SITES OVER THE
NEXT 24 HOURS. HIGH CONFIDENCE IN IFR (OR WORSE) VSBY/CIGS FOR A
3-6 HOUR PERIOD OVERNIGHT DUE TO +SN. ACCUMULATIONS ON RUNWAYS
LIKELY WITH 2-4 INCHES AT RNO/CXP, 6-9 INCHES AT TRK/TVL, 4-8 AT
MMH. CONFIDENCE IN TIMING OF THE SNOW IS MEDIUM-HIGH - THERE COULD
BE FLUCTUATIONS OF AN HOUR OR TWO FROM WHAT WE HAVE IN THE TAFS.

WINDS MAY BE ANOTHER ISSUE. GUIDANCE IS INDICATING A PERIOD OF
STRONG WINDS AT 700MB AFTER 3Z/SAT JUST AHEAD OF AND WITHIN THE MAIN
PRECIP BAND. THE WIND FORECAST FOR THE TAFS IS ADMITTEDLY LOW
CONFIDENCE - WHETHER OR NOT THESE STRONG WINDS WILL HIT THE SURFACE
IS UNCERTAIN. WE HAVE INCLUDED LLWS IN THE OVERNIGHT PERIOD TO
ACCOUNT FOR STRONG WINDS ALOFT. TURBULENCE ON APPROACH/DEPARTURE IS
LIKELY IN ANY CASE.

IMPORTANT NOTE: THE VISIBILITY SENSOR AT TVL IS OUT OF SERVICE UNTIL
FURTHER NOTICE. TECHNICIANS VISITED THE SITE TODAY BUT COULD NOT
REPAIR THE SENSOR. WE WILL CONTINUE TO ISSUE A TAF FOR TVL AT THE
REGULAR 6-HOURLY INTERVALS BASED ON REMAINING ASOS OBSERVATION AND
NEARBY WEBCAMS - BUT WE WILL NOT ISSUE AMENDMENTS FOR CHANGING
CONDITIONS DURING THE UPCOMING STORM.

STORM MOVES OUT QUICKLY ON SATURDAY LEAVING BEHIND A VERY COLD
AIRMASS THROUGH MONDAY. LIGHT WINDS WILL PROMOTE VALLEY INVERSIONS
WITH SLIGHTLY REDUCED VISIBILITY IN HAZE AT RNO MONDAY-WEDNESDAY.
DRY AIR ALOFT WOULD LIMIT FZFG POTENTIAL AT RNO/TRK SUNDAY BUT ONCE
WE START MELTING SNOW - SOME MORNING FZFG IS POSSIBLE EARLY NEXT
WEEK. CS
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WARNING UNTIL 4 AM PST SATURDAY NVZ005.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST
     SATURDAY NVZ001.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     SATURDAY NVZ002.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 10 AM PST
     SATURDAY NVZ003.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     SATURDAY NVZ004.

CA...WINTER STORM WARNING UNTIL 4 AM PST SATURDAY CAZ071.

     WINTER STORM WARNING UNTIL 4 AM PST SATURDAY CAZ070.

     WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 PM PST
     SATURDAY CAZ073.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST
     SATURDAY CAZ072.

&&

FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/RENO (ALL LOWER CASE)