Winter Storm Watch 7, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
410 AM PDT FRI MAR 18 2011

.SHORT TERM...
VERY ACTIVE WEATHER PATTERN TO PREVAIL THROUGH THIS WEEKEND WITH
STRONG AND COLD UPPER LOW PERSISTING OFF THE WEST COAST. THE
NUMEROUS LIGHTNING STRIKES NEAR THE NORTH CA COAST IS A PRECURSOR
TO CONVECTIVELY ENHANCED SNOWFALL RATES...2-3 INCHES PER HOUR AT
TIMES IN THE WARNING AREAS...AS ENERGY MOVES INTO THE SIERRA. WRN
LASSEN COUNTY HAS ALREADY RECEIVED PERIODS OF SNOW OVERNIGHT BUT
LITTLE EASTWARD PROGRESS IS EXPECTED UNTIL THIS AFTERNOON WHEN FIRST
WAVE OF SNOW SPREADS INTO THE TAHOE BASIN. CURRENT WINTER ADVISORIES
AND WARNINGS LOOK GOOD...ALTHOUGH LATEST GUIDANCE INDICATES SOME
HEAVIER SNOW TO REACH PARTS OF THE TAHOE BASIN BEFORE 00Z SO THE
ONSET TIME WAS CHANGED TO 21Z THIS AFTERNOON. OTHERWISE FOR
TODAY...WIND ADVISORIES WILL REMAIN IN PLACE FOR MUCH OF WRN NV FROM
I-80 SWD PLUS MONO COUNTY. THE LATEST NAM WAS ATTEMPTING TO ADD A
CRITICAL DRY AND STABLE LAYER BTWN 8500-11000 FT MSL AND INCREASED
30 MB AGL WINDS...BUT THIS MODEL TENDS TO OVERFORECAST WINDS WHEN
OTHER PARAMETERS ARE LESS THAN OPTIMAL FOR A DOWNSLOPE OR MOUNTAIN
WAVE EVENT.

FOR TONIGHT...SNOW WILL CONTINUE IN THE EXISTING ADVISORY AND
WARNING AREAS...BUT THE MAIN CHALLENGE WILL BE FOR THE RENO AND
CARSON ZONE AS MESOSCALE SNOW BANDS FORM NEAR AND BEHIND THE COLD
FRONT. THE NAM HIGHLIGHTS THE UNCERTAINTY AS THE 00Z RUN PLACED
THE HEAVIEST SNOW AMOUNTS OVER RENO BUT THE 06Z RUN FAVORED
CARSON-DOUGLAS. THE BOTTOM LINE IS THAT A PORTION OF THIS ZONE
UNDER THE MOST PERSISTENT SNOW BAND COULD RECEIVE 8 OR MORE INCHES
WHILE OTHER AREAS WILL ONLY RECEIVE AN INCH OR TWO. DUE TO THIS
MIXED DEGREE OF CONFIDENCE...HAVE GONE WITH A WINTER STORM WATCH
FOR NOW WITH A SLIGHTLY HIGHER POTENTIAL OF MORE SNOW FROM CARSON
SOUTHWARD. ANALYSIS OF SHORT TERM SATELLITE AND RADAR TRENDS LATER
TODAY WILL BE NECESSARY TO MORE ACCURATELY DETERMINE WHICH
PORTIONS OF THE RENO-CARSON ZONE WILL RECEIVE THE GREATER SNOW
IMPACTS TONIGHT. SNOW AMOUNTS MAY ALSO APPROACH ADVISORY CRITERIA
FOR ERN LASSEN COUNTY-SURPRISE VALLEY AND NWRN NV.

UNSETTLED WEATHER WILL CONTINUE INTO THE WEEKEND. ONGOING SNOW
BANDS COULD EXTEND INTO PARTS OF W-CNTRL NV BY SAT MORNING...WHILE
UNSTABLE CONDS ACROSS THE REST OF THE REGION WILL TRIGGER SCT-NMRS
SHOWERS BY MID MORNING. A FEW TSTMS WILL BE POSSIBLE ESPECIALLY
FROM HWY 50 NORTHWARD WHERE FORECAST LI VALUES OF 0 TO -2 AND CAPE
BETWEEN 250-500 J/KG ARE PROJECTED ON MODEL SOUNDINGS. FOR THE
SIERRA...SEVERAL MORE INCHES OF SNOW WILL BE POSSIBLE AS TSTM
ACTIVITY IN CNTRL CA LEADS TO MORE BANDS OF SNOW SPREADING OVER
THE CREST.

BY SAT NIGHT...COVERAGE OF SNOW WILL DECREASE ESPECIALLY AWAY FROM
THE SIERRA AS FORCING DECREASES BETWEEN WEATHER SYSTEMS. LIGHT
ACCUMULATIONS WILL STILL BE POSSIBLE NEAR THE SIERRA CREST AS
CONVECTIVE ACTIVITY DIMINISHES.

THE NEXT WAVE OF HEAVIER SNOW IS POISED TO REACH THE SIERRA BY SUN
AFTN AND CONTINUE THRU SUN NIGHT AS MAIN LOW DROPS TO THE CNTRL
CA COAST...WHILE ANOTHER SHORTWAVE PUSHES MOISTURE PLUME EAST
AHEAD OF THE LOW. FLOW ALOFT BECOMES S-SE OVER WRN NV WHICH WILL
INITIALLY DRAW SLIGHTLY WARMER AIR AND LIFT SNOW LEVELS ABOVE THE
VALLEYS SUN AFTN-EVE BEFORE COLDER AIR RETURNS LATE SUN NIGHT.
THE MONDAY MORNING COMMUTE FOR THE RENO AREA MAY INVOLVE SOME SNOW
ACCUMULATIONS AND SLICK ROAD CONDITIONS. MJD

.LONG TERM...MONDAY THROUGH THURSDAY...
COOL...WET AND ACTIVE WEATHER PATTERN SET TO CONTINUE THROUGH THE
LONG TERM...WITH SEVERAL SYSTEMS COMING INTO THE WEST COAST NEXT
WEEK.

UPPER TROUGH SWINGS THROUGH CA/NV ON MONDAY...WITH SOME CONTINUED
SHOWERS ACROSS THE REGION UNDERNEATH THE COLD POOL ALOFT. GFS HAS
BEEN SHOWING A DEEP OCCLUDED LOW COMING ONSHORE TO NORTHERN CA LATE
MONDAY. THIS COULD GIVE THE RENO-TAHOE AREA ANOTHER SHOT OF
ACCUMULATING SNOW...ESPECIALLY AS THE SURFACE LOW TRACKS THROUGH
WITH WINDS BACKING TO SE/E FLOW AND DEFORMATION ZONE BAND SETTING UP
OVER THE REGION. WILL HAVE TO KEEP A CLOSE EYE ON THIS FEATURE...AS
THIS TYPE OF WEATHER SYSTEM COULD LEAD TO MODERATE TO HEAVY SNOWS
PARTICULARLY FOR THE WESTERN NV VALLEYS.

SHOULD SEE SOME CONTINUED LIGHT SHOWERS ON TUESDAY...ALTHOUGH SOME
WEAK SHORTWAVE RIDGING WOULD HELP TO REDUCE THE AMOUNT OF SHOWERS.
THE NEXT STORM SYSTEM TO HIT THE WEST COAST WILL MOVE IN SOMETIME ON
WED-THU. THIS ONE HAS A BIT MORE UNCERTAINTY WITH THE TIMING...BUT
OVERALL WEATHER PATTERN AND TIMING OF THE SHORTWAVES SUGGEST THAT WE
COULD SEE MORE SNOW ON WED-THU FOR THE SIERRA ABOVE 6000 FEET. GFS
STILL HAS MUCH HIGHER QPF/SNOW AMOUNTS...WITH THE ECMWF CUTTING OFF
THE MOISTURE AS IT MOVES INLAND.

LONGWAVE TROUGH IS EXPECTED TO REMAIN OVER THE ERN PAC AND WRN CONUS
THROUGH THE REST OF NEXT WEEK WITH CONTINUED CHANCES OF SNOW AND
COOL TEMPERATURES INTO NEXT WEEKEND.  HOON

&&

.AVIATION...

WINTER STORM WILL MOVE INTO THE SIERRA TODAY...WITH INCREASING WINDS
AND CLOUDS ACROSS THE REGION. GUSTS AT KRNO WILL REACH UP TO
40-45KTS IN THE AFTERNOON. MOUNTAIN WAVE TURBULENCE WILL BE POSSIBLE
THROUGH THIS EVENING.

MODERATE TO HEAVY SNOW IS EXPECTED FOR THE SIERRA...INCLUDING KTRK
AND KTVL AFTER 21Z...WITH LIFR CIG/VIS AFTER 00Z AND THROUGH THE
ENTIRE NIGHT FOR THOSE TERMINALS. UP TO 12 INCHES EXPECTED AT THE
SIERRA TERMINALS BY SATURDAY MORNING.

FOR KRNO...SNOW WILL MOVE INTO THE RENO AREA FRIDAY EVENING AND
OVERNIGHT WITH IFR/LIFR AND SNOW ACCUMULATIONS ON THE RUNWAYS BEFORE
SATURDAY MORNING. A COUPLE INCHES OF NEW SNOW WILL BE LIKELY
OVERNIGHT...WITH AN OUTSIDE CHANCE OF UP TO 4 INCHES.  HOON

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...LAKE WIND ADVISORY UNTIL 5 PM PDT THIS AFTERNOON NVZ002.

     WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 8 AM PDT
     SATURDAY NVZ002.

     WIND ADVISORY FROM 2 PM THIS AFTERNOON TO 11 PM PDT THIS EVENING
     NVZ001-004.

     WIND ADVISORY FROM 11 AM THIS MORNING TO 8 PM PDT THIS EVENING
     NVZ003.

     WINTER STORM WATCH FROM THIS AFTERNOON THROUGH SATURDAY MORNING
     NVZ003.

CA...WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 5 AM PDT
     SATURDAY CAZ071.

     WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 8 AM PDT
     SATURDAY CAZ073.

     WIND ADVISORY FROM 11 AM THIS MORNING TO 11 PM PDT THIS EVENING
     CAZ073.

     LAKE WIND ADVISORY UNTIL 5 PM PDT THIS AFTERNOON CAZ072.

     WINTER STORM WARNING FROM 2 PM THIS AFTERNOON TO 8 AM PDT
     SATURDAY CAZ072.

&&

HTTP://WEATHER.GOV/RENO