High Wind Watch 4, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
445 PM PDT SAT MAY 2 2009

UPDATED TO ADD HIGH WIND WATCH FOR SUNDAY NV003 AND
CA073...RENO-CARSON AREAS AND MONO COUNTY.

.SHORT TERM...
AMSU IMAGERY SHOWS THAT A PLUME OF AROUND 1.4 OF PWAT AHEAD OF
THE NEXT FAST-MOVING IMPULSE HAS MOVED TO NEAR 36N/134W...OR ABOUT
580 MILES WEST OF SAN FRANCISCO...THIS AFTERNOON. THIS PLUME IS
EXPECTED TO RAM INTO NORTHERN CALIFORNIA WITH LITTLE LOSS IN PWAT
VALUES TONIGHT. THIS COULD BE DUE TO A FLATTER TRAJECTORY THAN THE
LAST SYSTEM...ALLOWING THE PLUME TO HOLD ONTO ITS SOURCE OVER THE
CENTRAL PACIFIC LONGER (THE LAST SYSTEM WAS NEGATIVE TILT AND THE
PWAT PLUME BROKE OFF). IN ADDITION TO THE GOOD SUBTROPICAL
PLUME...THE INCOMING SYSTEM IS SHOWING INCREASING LIFT IN THE
WATER VAPOR SATELLITE AS EVIDENCED BY THE EXPANDING MOISTURE
SHIELD ALOFT NOW APPROACHING THE NORTHERN CALIFORNIA COAST.

I HAVE INCREASED QPF NUMBERS FOR THE LAKE TAHOE REGION AND NORTH
INTO PLUMAS AND WESTERN LASSEN COUNTIES...ESPECIALLY 12Z-18Z
SUNDAY. THIS IS IN RESPONSE TO INCREASED AND REASONABLE-LOOKING QPF
IN THE GFS AND GOOD AGREEMENT FROM THE NAM. MEANWHILE...THE ECMWF
WAS MUCH DRIER IN ITS QPF WITH THIS STORM SO IT WAS IGNORED. WITH
SUCH A GOOD PWAT PLUME ALONG WITH EXCELLENT OROGRAPHIC FLOW...I
CANNOT SEE THE DRIER ECMWF PANNING OUT. FOR DETAILS OF THE
EXPECTED EFFECTS OF THE INCREASED QPF ON STREAMS AND RIVERS...SEE
THE HYDROLOGY DISCUSSION BELOW.

AS FAR AS SNOW LEVELS WITH THIS STORM...THEY ARE A BIT LOWER THAN
WITH THE LAST ONE TO START WITH MORE WESTERLY FLOW TO LIMIT MAJOR
WARM AIR ADVECTION. THEY ARE CURRENTLY RUNNING BETWEEN 7000-8500
FEET FROM LASSEN TO MONO COUNTY...RESPECTIVELY...AND SHOULD RISE
TO 8000-9000 FEET OVERNIGHT UNDER SLIGHT WARM AIR ADVECTION THIS
EVENING. THIS MEANS THAT ONCE AGAIN ONLY THE HIGHEST PASSES (MT
ROSE AND MAYBE CARSON PASS) WITH HAVE ANY ISSUES WITH SIGNIFICANT
SNOWFALL ACCUMULATIONS.

THE CURRENT SYSTEM WILL DRIVE THROUGH BY LATE MORNING SUNDAY...WITH
PRECIP MOSTLY SHUTTING OFF EAST OF THE SIERRA AT THAT TIME. MOIST
WESTERLY FLOW SHOULD KEEP SCATTERED SHOWERS GOING IN THE SIERRA
THROUGH THE DAY. MONDAY NIGHT...THE ATTENTION TURNS TO THE NEXT
SYSTEM WHICH COULD BRING SIGNIFICANT PRECIPITATION TO THE NORTHERN
SIERRA AND UP INTO LASSEN COUNTY. AS THIS TIME...THE BEST FOCUS IS
A BIT NORTH OF TAHOE...BUT A SLIGHT JOG SOUTH (POSSIBLE WITH FAST
FLOW IN A TIGHT GRADIENT) WOULD BRING BETTER PRECIP INTO TAHOE.
STAY TUNED FOR MORE DETAILS ONCE WE GET PAST THIS CURRENT STORM.
SNYDER

.LONG TERM...WEDNESDAY THROUGH SATURDAY...
MEDIUM RANGE MODELS SHOW A BROAD UPPER TROUGH APPROACHING THE
PACIFIC NW COAST ON WEDNESDAY.  ZONAL FLOW SHOULD KEEP THE MAIN
DYNAMICS ASSOCIATED WITH THIS SYSTEM NORTH OF THE KREV CWFA.
HOWEVER A COLD FRONT STRETCHING SOUTH FROM THE UPPER LOW SHOULD
BRUSH THE NRN SIERRA AND NWRN NEVADA SO HAVE KEPT A MENTION OF SHRA
OVER THE NWRN ZONES FOR WEDNESDAY AND WEDNESDAY NIGHT.

ON THURSDAY THE GFS AND ECMWF TAKE THE UPPER LOW ACROSS THE NRN TIER
WITH DRY WLY FLOW SETTING UP ACROSS THE NRN SIERRA AND WRN GREAT
BASIN.  THIS REGIME CONTINUES INTO FRIDAY WITH DRY CONDITIONS AND
DAYTIME TEMPERATURES AROUND 5 DEGREES ABOVE NORMAL.  THE MODELS
START TO DIVERGE ON FRIDAY WITH THE GFS BRINGING A DEEPENING UPPER
TROUGH INTO THE WEST COAST WHILE THE EURO KEEPS ZONAL FLOW OVER THE
REGION.  BY SATURDAY THE EURO HAS A WEAK SHORTWAVE MOVING INTO THE
PACIFIC NW WHILE THE GFS SHOWS A TROUGH EXTENDING FROM SRN BRITISH
COLUMBIA TO BAJA CALIFORNIA.  TIMING AND INTENSITY OF THE TROUGH IS
A QUESTION THIS FAR OUT WITH THE GFS AND EURO OUT OF PHASE AND THE
GFS ENSEMBLE MEMBERS ALSO NOT SHOWING MUCH AGREEMENT.  WILL KEEP
FRIDAY AND SATURDAY DRY BUT MAY NEED TO ADD PRECIP TO THE FAR NRN
ZONES FOR SUNDAY IF THE MODELS START COMING MORE INTO LINE. OHARA
&&

.AVIATION...
VFR CONDITIONS WILL GRADUALLY DECREASE TO MVFR CONDITIONS...MAINLY
AT KTVL AND KTRK...AFTER 03/06Z.  LCL IFR CONDITIONS POSSIBLE IN
HEAVIER BANDS OF SHRA FROM 09Z THRU 15Z.  WIND SPEEDS WILL INCREASE
ON SUNDAY WITH GUSTS TO 45 KTS POSSIBLE AT THE TAF SITES. OHARA
&&

.HYDROLOGY...
A STRONG 140KT+ JET WILL PROPEL A DEEP SUBTROPICAL MOISTURE TAP INTO
NORTHERN CA TONIGHT BRINGING A PERIOD OF HEAVY PRECIPITATION TO THE
SIERRA FROM ALPINE COUNTY NORTH INTO WESTERN PLUMAS INCLUDING THE
TAHOE BASIN. LAST NIGHT THERE WERE WIDESPREAD PRECIPITATION AMOUNTS
OF 1-2 INCHES ALONG THE SIERRA CREST AND WEST SLOPES SO THE GROUND
IS WELL SATURATED. WE ALSO SAW SOME DECENT RISES ON SOME SMALLER
CREEKS IN THE TAHOE BASIN. OROGRAPHICS WILL BE VERY GOOD WITH THIS
NEXT WARM PRECIPITATION EVENT AND EXPECT TO SEE SIMILAR AMOUNTS OF
PRECIPITATION LATE TONIGHT INTO EARLY SUNDAY...ROUGHLY AFTER
MIDNIGHT THROUGH NOON. EXPECT SMALLER CREEKS TO RISE RAPIDLY DURING
A PERIOD OF MODERATE TO HEAVY RAINFALL DURING THE EARLY TO LATE
MORNING HOURS. THEREFORE ISSUED A SMALL STREAM ADVISORY FOR THE
TAHOE BASIN INTO EASTERN PLUMAS COUNTY. IF THE QPF BULLSEYE MIGRATES
FURTHER NORTH THE SUSAN RIVER AT SUSANVILLE MAY REACH MONITOR...IF
IT MIGRATES FURTHERN SOUTH THE WEST FORK OF THE CARSON AT WOODFORDS
MAY SEE PROBLEMS AS WELL. FOR NOW THINK THAT THE MAIN CONCERN WILL
BE SMALL STREAM RISES IN THE TAHOE BASIN AND EASTERN PLUMAS
COUNTIES. JAH
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...SMALL STREAM FLOOD ADVISORY FROM 1 AM TO 1 PM SUNDAY FOR NV002.
     HIGH WIND WATCH SUNDAY FROM 8 AM TO 8 PM NV003.

CA...SMALL STREAM FLOOD ADVISORY FROM 1 AM TO 1 PM SUNDAY FOR
     CA072-071.
     HIGH WIND WATCH SUNDAY FROM 8 AM TO 8 PM CA073.
&&

HTTP://WEATHER.GOV/RENO

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