High Wind Watch 5, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
445 AM PDT MON OCT 12 2009

.SHORT TERM...

THE RETURN TO WET WEATHER IS TAKING SHAPE WITH STRONG JET STREAK
AND MOISTURE PLUME BEARING DOWN ON THE WEST COAST. LATEST WATER
VAPOR IMAGERY SHOWS THE MAIN FEATURES WELL WITH INITIAL SHORTWAVE
ENERGY AROUND 33N 128W...AND THE MAIN JET STREAK EXTENDING ACROSS
THE PACIFIC BETWEEN 40 & 50N WITH THE EXIT REGION NOW APPROACHING
140W. LATEST SATELLITE DERIVED PWAT ESTIMATES SHOW A GOOD PLUME OF
NEARLY 2 INCH VALUES INTERACTING WITH THE JET STREAK. THESE ARE
ALL VERY IMPRESSIVE FEATURES FOR THIS TIME OF YEAR. MODEL
SOLUTIONS CONTINUE TO BE STABLE FURTHER INCREASING FORECAST
CONFIDENCE.

THE INITIAL SHORTWAVE ENERGY WILL SPREAD MID AND HIGH CLOUDS OVER
THE AREA THIS MORNING. THE SHORTWAVE AXIS SWINGS INTO THE CA COAST
THIS AFTERNOON BRINGING INCREASINGLY MOIST AND UNSTABLE
CONDITIONS. SHOWERS ARE POSSIBLE OVER THE SIERRA CREST BY LATE
THIS AFTERNOON HOWEVER THE MAJORITY OF THE PRECIP WILL NOT MOVE
INTO THE AREA UNTIL LATE TONIGHT. SNOW LEVELS WILL INITIALLY BE
7500-8000 FEET WITH THE RELATIVELY COOL INITIAL SHORTWAVE.

THE MAIN JET STREAK AND HIGHER PWATS START PUSHING INTO THE WEST
COAST AROUND 12Z TUE BRINGING A DRAMATIC INCREASE IN PRECIP OVER
CA. GOOD ISENTROPIC UPGLIDE AND DECENT OROGRAPHIC FLOW DURING THE
DAY TUE WILL INITIALLY BRING MODERATE RAINFALL RATES IN THE SIERRA
OF AROUND 2 TENTHS AN HOUR. SNOW LEVELS WILL STEADILY RISE IN THE
WARM CONVEYOR BELT GETTING CLOSE TO 10,000 FEET AROUND TAHOE BY
TUE EVENING.

THE PEAK OF THE EVENT CONTINUES TO BE EXPECTED TUE EVENING AS THE
FORCING IS FURTHER INCREASED BY THE MAIN TROUGH AXIS AND UPPER
LEVEL FRONT. DURING THIS PERIOD...PRECIP RATES COULD BE AS HIGH
AS 4 TENTHS PER HOUR IN THE SIERRA WITH MODERATE RAINFALL IN THE
LEE OF THE SIERRA. A WEAK SURFACE COLD FRONT WILL BRING SNOW
LEVELS BACK DOWN CLOSER TO 8000 FEET OVERNIGHT TUE RAISING THE
CONCERN FOR SNOW ACCUMULATIONS ON THE HIGHER MOUNTAIN PASSES. WARM
ROAD SURFACES WILL LIMIT MUCH OF THE CONCERN WITH THE BEST
POTENTIAL FOR SNOW BUILDUP ON PASSES ABOVE 8500 FEET SUCH AS MT
ROSE.

THE BEST UPPER FORCING SWINGS NORTH AND EAST OF THE AREA WEDNESDAY
BRINGING A DRAMATIC DECREASE IN THE RAIN AND SNOW. MODELS CONTINUE
TO GENERATE STEADY QPF OVER THE LASSEN COUNTY SIERRA WED WITH
ONLY SHOWERY PRECIP ELSEWHERE. FEEL THAT THE QPF NUMBERS OVER
LASSEN COUNTY WED ARE OVERDONE IN RESPONSE TO SHORTWAVE RIDGING
AND WAA...HOWEVER STILL KEPT THE HIGHEST POPS AND QPF VALUES IN
THAT AREA. TOTAL PRECIP AMOUNTS FROM LATE TONIGHT THROUGH MOST OF
WED CONTINUE AS PREVIOUSLY FORECAST...AROUND 5 INCHES ON THE
SIERRA CREST WITH 2-3 INCHES FOR LAKE TAHOE AND THE ERN SIERRA
AND CLOSER TO 1 INCH ALONG THE SIERRA FRONT. THE HIGHEST QPF
AMOUNTS ARE STILL EXPECTED ALONG THE SIERRA CREST JUST SOUTH OF
LAKE TAHOE. THESE QPF VALUES WILL LEAD TO SIGNIFICANT SNOWFALL
AMOUNTS MEASURED IN FEET ON THE HIGHEST SIERRA RIDGES. NO WINTER
STORM WARNINGS WILL BE POSTED SIMPLY BECAUSE THE SNOWFALL WILL BE
WELL ABOVE ANY POPULATION CENTERS.

REGARDING THE WIND POTENTIAL ASSOCIATED WITH THIS STORM...THE
STRONG WINDS ARE STILL EXPECTED TO REMAIN IN THE HIGH SIERRA. WITH
140+ KT JET MAX AND 700 MB WINDS MAXING OUT AROUND 70 KTS...GUSTS
IN THE SIERRA WILL EASILY TOP 100 MPH. DEEP MOISTURE AND
UNFAVORABLE TEMPERATURE PROFILE WILL LIMIT THE AMOUNT OF WIND
THAT MIXES DOWN TO THE LOWER ELEVATIONS. THE HIGHEST VALLEY GUSTS
ARE EXPECTED TO BE IN THE 45-50 MPH RANGE TUESDAY AND TUESDAY
NIGHT. THE BEST WIND POTENTIAL LOOKS TO BE TUESDAY NIGHT WHEN THE
SUPPRESSED TROPOPAUSE AND DRY SLOT ALOFT MOVE INTO THE WEST COAST
POSSIBLY DUCTING THE HIGH WINDS ALOFT DOWN TO THE SURFACE. THIS
ALSO COINCIDES WITH THE SURFACE TROUGH PASSAGE. THE POTENTIAL IS
THERE FOR A HIGH WIND EVENT IF THESE INGREDIENTS COME
TOGETHER...HOWEVER CURRENT THINKING IS THAT IT IS UNLIKELY. LATER
SHIFTS MAY ISSUE WIND ADVISORIES. JORDAN

.LONG TERM...THURSDAY THROUGH SUNDAY...

THE UPPER RIDGE BUILDS IN QUICKLY ON THURSDAY WITH WARMER AND DRIER
CONDITIONS THAT LAST INTO THE WEEKEND. SHOWERS WERE REMOVED FROM
LASSEN COUNTY AND THE SURPRISE VALLEY THURSDAY ALTHOUGH CLOUDS WILL
LINGER INTO THE AFTERNOON. SHOWERS WERE REINTRODUCED IN WESTERN
LASSEN COUNTY SATURDAY AFTERNOON AND CONTINUED THROUGH SUNDAY AS A
WEAK SHORT WAVE MOVES THROUGH NORTHERN CA. AN UPPER LOW APPROACHES
THE PAC NW COAST ON SUNDAY AND BRINGS A CHANCE OF PRECIP TO NORTHERN
WASHOE COUNTY INTO NORTHEAST CA BY SUNDAY NIGHT WITH SNOW LEVELS
REMAINING NEAR OR ABOVE 8000 FEET THROUGH THAT PERIOD. TEMPERATURES
ACROSS THE AREA WILL RISE TO NEAR OR ABOVE NORMAL READINGS FOR
FRIDAY AND SATURDAY THEN DIP A FEW DEGREES SUNDAY WITH INCREASED
CLOUD COVER AND LOWERING HEIGHTS/THICKNESS AHEAD OF THE APPROACHING
LOW PRESSURE. RC

&&

.AVIATION...

VFR CONDITIONS EXPECTED THROUGH 12Z TUE FOR KRNO/KLOL. FOR THE
SIERRA TAF SITES...KTVL/KTRK...VFR CONDITIONS THROUGH 06Z THEN MVFR
CIGS AND VIS IN RAIN BETWEEN 06Z-12Z AS A MAJOR STORM SYS MOVES
INTO CA. GUSTY S TO SW WINDS WILL DEVELOP AFTER 21Z AND LIKELY
REMAIN GUSTY MON NGT AS THE SYS GETS CLOSER. MUCH STRONGER WINDS ARE
EXPECTED TUE INTO WED.

ANTICIPATED AVIATION IMPACTS WITH THE UPCOMING STORM BETWEEN 12Z TUE
AND 12Z WED INCLUDE WIDESPREAD MOUNTAIN OBSCUREMENT...STRONG S TO SW
WINDS GUSTING 35-45 KTS AT TIMES AND WELL OVER 100 KTS ON SIERRA
RIDGES...HEAVY RAIN PRODUCING IFR CIGS/VIS AT KTVL/KTRK AND LCL MVFR
CONDITIONS AT KRNO...AND LLWS. RC

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
CA...NONE.
&&

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