Winter Storm in Nevada, January 18 to 19, 2010

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
936 AM PST MON JAN 18 2010

.UPDATE...
UPDATING TO SPEED UP TMIING OF ADVISORY FOR ZONES 3/5 AS PRECIP
SHOULD START MOVING INT SHORTLY AFTER NOON. WITH GOOD INSTABILITY
AND FORCING...DO NOT SEE MUCH SHADOWING TAKIGN PLACE OUSIDE OF THE
FIRST 2 HRS OR SO. ALSO LOWERED SNOW LEVELS FOR THE AFTERNOONA FEW
HUNDRED FEET AS THEY SHOULD DROP WITH THE CONVECTIVE PRECIP AND
THE FRONT. KEPT THEM A LITTLE ABOVE 5000 FEET...TO KEEP ANY
ACCUMULATIONS CONFINED TO THE FOOTHILLS FOR THE AFTERNOON.
EVERYTHING ELSE LOOKS ON TRACK...ALTHOUGH EVENING SHIFT MAY BE
ABLE KILL WARNINGS/ADVISORIES EARLY. SYSTEM LOOKS TO MOVE THROUGH
BY 06Z THIS EVENING WITH SOME SHOWERS AFTERWARD. NOT SURE ABOUT
VALLEY FLOOR ACCUMULATIONS AROUND RENO...BUT CUODL SEE A QUICK
INCH OR TWO AROUND EVENING RUSH SO WILL LET CURRENT AMTS RIDE AS
CONVECTINO COUDL BRING LOWER SNOW LEVELS IN THE HEAVIER PRECIP.

OUTSIDE OF THIS...ALSO HOISTED LAKE WIND ADVY FOR PYRAMID AS WINDS
ALREADY GUSTING TO 30 MPH AND WILL GET A BIT STRONGER. FCST WAS
ALREADY PRETTY MUCH ALONG THE LINE OF A LWA SO THIS SHOULD MATCH
BETTER. WALLMANN

&&

.PREVIOUS DISCUSSION... /ISSUED 400 AM PST MON JAN 18 2010/

SHORT TERM...

FAIRLY IMPRESSIVE NORTH PAC LOW CONTINUES TO MOVE TOWARD THE WEST
COAST THIS MORNING. STRONG DIFFLUENCE ALOFT...AS EVIDENCED BY CLOUD
TOPS COOLING OFF NICELY ON IR IMAGERY...WILL MOVE OVER NORTHERN
CA/NV LATER TODAY...BRINGING MODERATE TO HEAVY SNOW AND RAIN ACROSS
THE FORECAST AREA. THE SHORTWAVE TROUGH WILL SWING ACROSS THE AREA
TODAY AND TONIGHT...BEFORE LEAVING A SHORT BREAK IN THE ACTION FOR
TUESDAY MORNING.

SOME OROGRAPHICALLY ENHANCED PRECIP DEVELOPED OVER THE WEST SIDE OF
THE CREST LATE LAST NIGHT AND PUSHED OVER INTO EASTERN LASSEN AND
PLUMAS COUNTIES EARLY THIS MORNING. THIS INCLUDES THE AREAS FROM
PORTOLA-GRAEAGLE TO SUSANVILLE WITH PRECIP TOTALS ALREADY AT ABOUT
0.4" SO FAR. SNOW LEVELS BRIEFLY DROPPED TO BELOW 5000 FEET IN THE
HEAVIEST SHOWERS...WITH SOME LIGHT SNOW SEEN ON WEBCAMS AROUND
PORTOLA. SNOW LEVELS HAVE COME UP SINCE THEN...WITH PLUMAS SO
REPORTING PRECIP CHANGING BACK TO RAIN. CURRENTLY SNOW LEVELS ARE
BETWEEN 5500 FEET IN THE NORTHERN ZONES...TO BETWEEN 6000-6500 SOUTH
OF LAKE TAHOE.

WINTER STORM WARNINGS REMAIN ON TRACK FOR TODAY. INCREASED QPF
AMOUNTS FOR THIS MORNING FOR THE TAHOE AND LASSEN ZONES...MAINLY IN
THE ERN SIERRA NORTH OF INTERSTATE 80. GFS HAS BEEN TRENDING A
FASTER ONSET OF THE HEAVIER PRECIP IN THE SIERRA THIS
MORNING...TRENDED FORECAST TO REFLECT THIS. SNOW AMOUNTS STILL LOOK
GOOD OVERALL...WITH STORM TOTAL SNOW ACCUMULATIONS OF 20-30" ABOVE
7000 FEET AND 10-18" IN THE LOWER SIERRA VALLEYS AROUND
TAHOE-TRUCKEE.

MOST DIFFICULT PART OF THE FORECAST THIS MORNING WAS THE SNOW LEVELS
FOR WESTERN NV...AND TRYING TO SEE WHEN/IF THE SNOW LEVELS WOULD
COME DOWN TO VALLEY FLOORS. MODELS ARE INDICATING A GOOD AMOUNT OF
SPILLOVER THIS AFTERNOON INTO THE WESTERN NV VALLEYS...WITH SNOW
SNOW LEVELS COMING DOWN TO AROUND 5000-5500 FEET BY MIDDAY. BY LATE
AFTERNOON...AROUND 4 PM...SNOW LEVELS WILL LOWER TO NEAR VALLEYS
FLOORS AT 4000-4500 FEET. GFS CONTINUES TO COME IN A BIT COLDER WITH
EACH RUN...AND WITH A WIDE FIELD OF COLD AIR STATOCU JUST OFF SHORE
NORTHERN CA..AS NOTED BY THE DAY SHIFT YESTERDAY...FEELING MORE AND
MORE CONFIDENT THAT WE WILL SEE THE LOWER SNOW LEVELS AND SNOW
ACCUMULATIONS DOWN TO VALLEY FLOORS THIS EVENING.

PRECIP WILL BEGIN TO WIND DOWN AS WE GO INTO THE EVENING...BUT NOT
BEFORE WE SEE 1-3" ON THE WESTERN NV FLOORS ALONG THE US-395
CORRIDOR FROM RENO TO CARSON CITY...AND ABOUT 3-6" IN THE WESTERN
FOOTHILLS ABOVE 5000 FEET MSL. 1-3" INCHES OF SNOWFALL CAN ALSO BE
EXPECTED MONDAY EVENING FOR NORTHERN WASHOE COUNTY AND SURPRISE
VALLEY...INCLUDING CEDARVILLE AND GERLACH. WINTER WEATHER ADVISORIES
HAVE BEEN ISSUED THIS MORNING FOR THESE AREAS...AS LATE AFTERNOON
AND EVENING SNOW ACCUMULATIONS WILL CAUSE SOME PROBLEMS AROUND THE
LOCAL AREA FOR EVENING COMMUTES. SNOW LEVELS WILL BE DOWN TO ALL
VALLEY FLOORS BY ABOUT 10PM...BUT PRECIP WILL SERIOUSLY BEGIN TO
TAPER OFF BY THIS POINT AS SHORTWAVE RIDGING MOVES IN OVERHEAD FOR
TUESDAY MORNING.

AS WE GO INTO TUESDAY EVENING...PRECIP WILL INCREASE AGAIN FOR THE
EASTERN SIERRA NORTH OF LAKE TAHOE. THIS WILL BE A FAST MOVING
SYSTEM...WITH LESS MOISTURE AND DYNAMICS...BUT WILL STILL HAVE A
QUICK 6-10 HOUR BURST OF MODERATE SNOWFALL TUESDAY AFTERNOON AND
EVENING...POSSIBLY WITH ADVISORY LEVEL SNOW AMOUNTS IN THIS SHORT
PERIOD OF TIME. THIS INCREASE IN PRECIP TUESDAY WILL LIKELY BE
ADDRESSED WITH LATER TODAY OR TONIGHT.  HOON

LONG TERM...WEDNESDAY THROUGH SUNDAY...

ONLY SIGNIFICANT CHANGE TO MEDIUM RANGE MODELS THIS FORECAST CYCLE
CAME FROM THE OPERATIONAL ECMWF. IT IS STARTING TO TREND MORE
CLOSELY TO THE OPERATIONAL GFS AND GEFS ENSEMBLE MEMBERS STARTING
FRIDAY AS IT TRIES TO BECOME MORE PROGRESSIVE WITH THE MAIN UPPER
TROF AND THEN BUILDS A SHORT WAVE RIDGE INTO THE RGN LATE SATURDAY.
IT IS STILL A BIT SLOWER THAN THE GFS...BUT THIS TREND GIVES ME A
BIT MORE CONFIDENCE IN THE DAY 5 AND 6 FORECAST.

FOR WEDNESDAY AND THURSDAY...MODELS REMAIN ON TRACK WITH LAST OF TWO
OF THE SIGNIFICANT SHORT WAVES EJECTING OVER THE RGN. LIKE THE MOST
PREVIOUS MODEL RUNS BOTH SHORT WAVES ARE TRENDING COLDER THAN THE
ONES IN THE SHORT TERM AND THE THURSDAY SHORT WAVE IS TRENDING A BIT
FARTHER SOUTH WITH THE BULK OF ITS PCPN IN RESPONSE TO PRIMARY JET
BEING PULLED FARTHER SOUTH INTO SRN CA AND NRN MEXICO. GEFS MEAN
ENSEMBLE ANOMALIES ARE STILL QUITE IMPRESSIVE FOR THE WED/THURS
TIME FRAME WITH SIGNIFICANT NEGATIVE ANOMALY CENTERS IN THE H500
HEIGHT FIELD AND SLP FIELD OFF THE WEST COAST...AND POSITIVE H250
WIND U COMPONENT JUST SOUTH OF THE FORECAST AREA.

WILL START TO SHOW A BREAK IN THE QPF AND POP FIELDS EARLY WEDNESDAY
BEFORE THE SHORT WAVE AFFECTS THE AREA AND RAMP UP THE POPS AND QPF
FOR WED AFTN/EVNG. SNOW LEVELS DROP TO ALL BUT THE LOWEST VALLEY
FLOORS WITH THIS SHORT WAVE AND TRENDED THE DAYTIME HIGH TEMPS TO
THE COOL SIDE OF THE GUIDANCE ENVELOPE. MUCH THE SAME HOLDS TRUE FOR
THURSDAY...WITH A BREAK IN THE PCPN LATE WED NIGHT INTO THURS MRNG
AND HIGHER POPS/QPF THURS AFTN. WILL THEN DECREASE POPS/QPF THURS
NIGHT. TRENDED QPF HIGHER SOUTH FOR THE DAYTIME HOURS THURS AS
STATED ABOVE. SNOW LEVELS NEAR ALL VALLEY FLOORS. SUBSEQUENT SHIFTS
WILL NEED TO START LOOKING AT WATCHES FOR AT LEAST THE SIERRA...IF
NOT PORTIONS OF WRN NV...FOR THE WED TIME FRAME...BUT WILL HOLD OFF
FOR NOW.

BEYOND THURS MODELS DO START TO DIVERGE A BIT BUT AS STATED ECMWF IS
STARTING TO TREND TOWARD THE GFS. OPERATIONAL GFS AND GEFS ENSEMBLE
MEMBERS ARE STILL A BIT FASTER IN MOVING THE MAIN UPPER TROF EAST.
WHERE CANADIAN YESTERDAY WAS TRENDING TOWARD GFS...IT IS NOW MORE
LIKE THE SLOWER ECMWF. GIVEN DIFFERENCES IN MODELS WILL HOLD ON TO
POPS IN MOST OF THE CWA THROUGH FRIDAY NIGHT...BUT HIGHEST IN THE
SIERRA. WITH OPERATIONAL ECMWF NOW STARTING TO BUILD A SHORT WAVE
RIDGE OVER THE RGN LATE SAT HAVE OPTED TO LOWER SAT POPS A BIT AND
WILL NOT MENTION ANY PCPN EARLY SUN FOR SOME PARTS OF THE ERN CWA.
ALSO OPTED TO BUMP UP TEMPS A FEW DEGREES SAT/SUN TIME FRAME...MORE
SUN THAN SAT. OPERATIONAL GFS AND ITS ENSEMBLES BRING ANOTHER LOW
CLOSE TO THE COAST LATE SUN WHILE ECMWF IS SLOWER WITH THIS FEATURE.
WILL START TO BUMP POPS A BIT SUN NIGHT...BUT WILL NOT GO TOO HIGH
MOST OF THE CWA. MLF

AVIATION...
RAIN/SNOW SHOULD MOVE INTO THE NRN/CNTRL SIERRA THROUGH THE DAY WITH
PCPN BECOMING HEAVY AND CHANGING TO ALL SNOW INTO THE LATE
MRNG/AFTN. CIGS/VSYBS DOWN TO LIFR THROUGH THE AFTN INTO THE EARLY
EVNG. FOR KTRK/KTVL WILL SHOW WORST CONDITIONS AFTER 18/18 UTC WITH
CIGS/VSBYS IN THE 200/1/2 RANGE OR LOWER BY 19/00 UTC. THIS WILL
CONTINUE INTO THE OVERNIGHT HOURS...BUT START TO EASE SOMEWHAT AFTER
19/09 UTC. STILL THINK CIGS/VSBYS WILL BE NO BETTER THAN IFR THROUGH
19/15 UTC. AFTER THAT THERE WILL BE A BRIEF BREAK THEN CONDITIONS
WILL BEGIN TO DETERIORATE AGAIN AFTER 20/00 UTC.

EAST OF THE SIERRA WILL SEE RAIN/SNOW BEGIN TO SPILL OVER THIS MRNG
NORTH OF I-80...WITH LESSER CHANCE OF SPILL OVER SOUTH OF THE
INTERSTATE UNTIL THIS EVNG. CIGS WILL BEGIN TO LOWER AFTER 18/20
UTC. FOR KRNO WILL MENTION VCSH AFTER ABOUT 18/16 UTC THEN BEGIN -RA
AFTER 18/19UTC. CIGS/VSBYS LOWER LATER TODAY...GOING TO MVFR BY EARLY
AFTN THEN TO IFR BY 19/00 UTC AS RAIN CHANGES TO A MIX THEN ALL SNOW
BY 19/02 UTC. SNOWS SHOULD ACCUMULATE ON RUNWAY THIS EVNG...BUT WILL
TAPER OFF AFTER 19/08 UTC. AFTER THAT CONDITIONS SHOULD IMPROVE TO
AT LEAST MVFR THEN TO VFR BY 19/15 UTC. MLF

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 4 AM PST
     TUESDAY FOR NVZ003-005.

     WINTER STORM WARNING UNTIL 4 AM PST TUESDAY FOR NVZ002.

     LAKE WIND ADVISORY UNTIL 6 PM PST THIS EVENING FOR NVZ004.

CA...WINTER STORM WARNING UNTIL 4 AM PST TUESDAY FOR CAZ071.

     WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 4 AM PST
     TUESDAY FOR CAZ070.

     WINTER STORM WARNING UNTIL 4 AM PST TUESDAY FOR CAZ072-073.

&&

HTTP://WEATHER.GOV/RENO

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE RENO NV
950 AM PST MON JAN 18 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0806 AM     HEAVY RAIN       1 E SLOAT               39.87N 120.72W
01/18/2010  M0.90 INCH       PLUMAS             CA   TRAINED SPOTTER

            STORM TOTAL RAINFALL

0809 AM     HEAVY SNOW       5 ENE CISCO             39.32N 120.45W
01/18/2010  M7.0 INCH        NEVADA             CA   TRAINED SPOTTER

            24 HOUR STORM TOTAL SNOWFALL. WATER EQUIVALENT OF 1.07
            INCHES.

&&

JKIELHOR