River Flood Watch 1, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
848 AM PST WED NOV 28 2012

.UPDATE...
PRECIPITATION ASSOCIATED WITH A QUICK MOVING SHORTWAVE IS IMPACTING
THE WEST COAST THIS MORNING. WINDS ARE BEGINNING TO INCREASE AHEAD
OF THE SHORTWAVE AS WELL. MODEL SOUNDINGS SHOW STRONGER WINDS
ALOFT WITH 50 TO 60 KNOTS AT 700MB. WHEN THE WINDS MIX DOWN INTO
THE LOWER VALLEYS, WINDS ARE EXPECTED TO BE STRONGER THAN
INITIALLY FORECAST FOR THIS AFTERNOON. DECIDED TO ISSUE A WIND
ADVISORY FOR RENO-CARSON CITY-MINDEN AREAS WHICH WILL BE IN EFFECT
FROM 10 AM THROUGH 7 PM TONIGHT. SOUTHWEST WINDS 15 TO 25 MPH WITH
GUSTS TO 50 MPH ARE EXPECTED. WIND GUSTS UP TO 60 MPH ARE POSSIBLE
IN WIND PRONE AREAS. EL

&&

.PREVIOUS DISCUSSION... /ISSUED 335 AM PST WED NOV 28 2012/

SHORT TERM...

FORECASTER CONFIDENCE REMAINS HIGH THAT THERE WILL BE A
SIGNIFICANT SERIES OF STORM SYSTEMS TO IMPACT NORTHERN
CALIFORNIA/WESTERN NEVADA STARTING TODAY AND CONTINUING THROUGH
THE WEEKEND. THE JET STREAM BECOMES DIRECTED TOWARDS THE FORECAST
REGION WHILE TAPPING INTO A TROPICAL MOISTURE FEED. THIS SERIES OF
SYSTEMS WILL BRING SUBSTANTIAL PRECIPITATION TO THE WESTERN
SLOPES OF THE SIERRA, PERIODS OF STRONG WINDS, AND RISES ALONG
SIERRA AND LOWER ELEVATION STREAMS.

THE FIRST SYSTEM WILL REACH THE FORECAST REGION TODAY AND QUICKLY
EXIT TONIGHT. WITH ENERGY ORIENTED MAINLY NORTH TO SOUTH AS THE
SUPPORTING TROUGH BECOMES NEGATIVELY TILTED, SPILLOVER INTO
WESTERN NEVADA WILL BE MINIMAL. SNOW LEVELS REMAIN ABOVE 6500 FEET
AND SNOW RATIOS WILL TEND TO BE RELATIVELY LOW. THIS SUGGESTS THAT
OVERALL IMPACTS OF THIS SYSTEM WILL BE LOW WITH THE HIGHEST SIERRA
PASSES RECEIVING TOKEN ACCUMULATIONS OF SLUSHY SNOW. THE MOST
SIGNIFICANT IMPACTS WILL BE FROM WINDS ESPECIALLY ALONG THE HWY
395 CORRIDOR AS GUSTS EXCEED 35 MPH. AS IMPLIED BY THE NAM, THERE
MAY BE A BRIEF PERIOD THIS AFTERNOON WHERE ISOLATED WIND GUSTS
COULD REACH UP TO 45 MPH ALONG THE SIERRA FRONT.

A BREAK IN PRECIPITATION WILL OCCUR THURSDAY BETWEEN SYSTEMS.
HOWEVER, WINDS INCREASE THURSDAY AFTERNOON WITH SUBSTANTIAL WINDS
OCCURRING OVERNIGHT THURSDAY INTO FRIDAY. 700MB FLOW INCREASES
ABOVE 60 KNOTS WITH MOISTURE PILING UP ALONG THE WESTERN SLOPES OF
THE SIERRA. WINDS WILL BECOME DIRECTED TO THE VALLEY SURFACES ON
THE LEE OF THE SIERRA; A HIGH WIND WATCH HAS BEEN ISSUED. HAVE
INCREASED PRECIPITATION CHANCES FOR THE RENO/CARSON CITY AREAS IN
THE 12-18Z TIMEFRAME FRIDAY AS STRONG WINDS PUSH PRECIPITATION
OVER THE CREST. THIS SCENARIO IS ANALOGOUS TO OTHER EVENTS WHERE
THE FOOTHILLS RECEIVED AROUND AN INCH OF PRECIPITATION AND
RENO/CARSON CITY RECEIVED 0.25-0.33 INCHES.

INITIAL RISES ALONG STREAMS WILL BE SMALL FROM TODAY'S SYSTEM
WHILE MODEST RISES CAN BE ANTICIPATED FRIDAY INTO SATURDAY. HOWEVER,
PRECIPITATION FROM TODAY AND FRIDAY WILL LEAVE SOILS SATURATED. WITH
ANOTHER VERY WET SYSTEM MOVING INTO THE REGION LATE IN THE
WEEKEND, HYDRO RELATED CONCERNS INCREASE. FOR MORE INFORMATION,
CONSULT OUR HYDRO OUTLOOK. BOYD

LONG TERM...SATURDAY THROUGH TUESDAY...
MODELS STILL IN GOOD AGREEMENT WITH POSSIBLY THE STRONGEST STORM OF
THE SERIES LATE SATURDAY INTO SUNDAY MORNING. THEY ALSO AGREE ON THE
HIGH SNOW LEVELS THROUGH THE EVENT BEFORE CRASHING WITH THE FRONT
SUNDAY AFTERNOON. MAIN DIFFERENCE IS THAT EC CONTINUES TO BE A
LITTLE FURTHER NORTH, BUT GEM/GFS/GEFS AGREE ON A SLIGHTLY FURTHER
SOUTH PLACEMENT. RIGHT NOW, LEANING A BIT MORE TO THE GFS WITH
BETTER OVERALL AGREEMENT. THIS SYSTEM ALSO APPEARS TO BE THE MOST
DYNAMIC OF THE THREE SYSTEMS WITH A RAPIDLY DEEPENING SURFACE LOW
INTO NORTHWEST NEVADA SUNDAY MORNING.

MOIST UPSLOPE FLOW WILL KEEP PRECIP GOING ALONG THE SIERRA CREST
SATURDAY FROM THE TAHOE BASIN NORTH WITH SOME LIMITED SPILLOVER.
THIS IS AHEAD OF THE MAIN SYSTEM WHICH ARRIVES SUNDAY MORNING. AS
MENTIONED BEFORE IT IS VERY DYNAMIC, WITH AN INTENSE JET AND STRONG
COLD FRONT. IN ADDITION, IT HAS THE MOST IMPRESSIVE MOISTURE PLUME
WITH PRECIP WATER ABOVE 1.5 INCHES APPROACHING THE COAST. EXPECT
HEAVY RAIN TO SPREAD ACROSS MUCH OF THE SIERRA AND WESTERN NEVADA
AFTER MIDNIGHT SATURDAY NIGHT WITH SNOW LEVELS 8-9000 FEET FROM
NORTH TO SOUTH. SPILLOVER WILL ALSO BE HEAVY, ESPECIALLY FOR A 6
HOUR PERIOD NEAR AND AHEAD OF THE COLD FRONT SUNDAY MORNING AS
PARAMETERS ARE IDEAL. IN ADDITION TO THE RAINFALL, STRONG PRESSURE
GRADIENTS WILL ALSO CREATE WINDY CONDITIONS AREAWIDE WITH GUSTS TO
50 MPH POSSIBLE ALL AREAS AND OVER 100 MPH LIKELY ALONG THE SIERRA
CREST.

LEANING TOWARD A GFS/GEM SOLUTION WHICH PUTS THE MOISTURE PLUME
SQUARE ON TAHOE WOULD LEAD TO SOME LARGE AMOUNTS IN A 12 HOURS
PERIOD IF THEY VERIFY. EC WOULD FOCUS THE PRECIPITATION MORE ON THE
FEATHER BASIN TO LASSEN COUNTY WITH AMOUNTS FOR TAHOE/RENO LIGHTER.
FOR A 36 HOUR PERIOD SATURDAY MORNING THROUGH SUNDAY AFTERNOON
POTENTIAL RAINFALL AMOUNTS ARE IMPRESSIVE WITH 6 INCHES OR MORE
POSSIBLE ALONG THE SIERRA CREST AND 3 OR MORE POSSIBLE IN THE TAHOE
BASIN TO THE WESTERN NEVADA FOOTHILLS. EVEN THE SIERRA FRONT ALONG
HIGHWAY 395 COULD SEE AN INCH OR MORE. THERE MAY BE POTENTIAL
FLOODING ISSUES, MORE IN THE HYDRO DISCUSSION BELOW.

AFTER THE FRONT MOVES THROUGH SUNDAY AFTERNOON, SNOW LEVELS WILL
RAPIDLY FALL TO NEAR 5000 FEET BY EVENING. HOWEVER, ONLY EXPECT
LIGHT ACCUMULATIONS AS THE PRECIPITATION RAPIDLY DIMINISHES BEHIND
THE FRONT. MODELS THEN AGREE ON SOME MODERATE AMPLITUDE RIDGING WITH
NEAR OR SLIGHTLY ABOVE NORMAL TEMPS FOR MONDAY AND TUESDAY. WINDS
WILL ALSO BE MUCH LIGHTER UNDER THE RIDGE. SYSTEM FOR THE MIDDLE OF
NEXT WEEK LOOKS TO BE MORE DIRECTED NOW TOWARDS THE PACIFIC
NORTHWEST AND DOES NOT LOOK AS STRONG. WALLMANN

AVIATION...
NEXT SYSTEM IS MOVING ONSHORE WITH WINDS BEGINNING TO INCREASE.
EXPECT LOCALLY GUSTY S-SW WINDS TODAY WITH PEAK GUSTS 30-35 KTS
FOR ALL VALLEYS. PRECIP WILL MOVE INTO THE SIERRA AROUND 18Z WITH
SOME LIGHT TO MODERATE -SHRASN WITH SNOW LEVELS HOVERING NEAR 6500
FEET. EXPECT MVFR CONDS KTRK/KTVL/KMMH UNTIL AROUND 02Z BEFORE
RETURNING TO VFR. FOR KRNO, SCT -SHRA AROUND BUT EXPECT CIGS TO
REMAIN AOA 4000 FEET.

WINDS WILL REMAIN GUSTY OVERNIGHT WITH PEAK GUSTS TO 35 KTS IN
VALLEYS NEAR AND IN THE SIERRA BUT CONDITIONS WILL REMAIN VFR INTO
THURSDAY.

TWO MAJOR SYSTEMS TO AFFECT THE AREA AFTERWARD, ONE THURSDAY NIGHT
AND FRIDAY WITH THE SECOND SATURDAY AFTERNOON INTO SUNDAY AFTERNOON.
THE FIRST WILL BE MORE OF A WIND MAKER FOR MOST AREAS WITH VALLEY
GUSTS OF 50+ KTS POSSIBLE NEAR AND SOUTH OF I-80. HEAVY RAIN WILL
ALSO OCCUR IN THE SIERRA FROM TAHOE NORTH WITH WITH IFR CONDS
EXPECTED. EXPECT STRONG MTN WAVES IN AREAS OF STRONGEST WINDS WITH
STRONG WIND SHEAR AND TURBULENCE.

SECOND SYSTEM FOR THE WEEKEND HAS BETTER POTENTIAL FOR HEAVY RAIN
BUT WIND GUSTS TO 45 KTS STILL POSSIBLE. IFR CONDS LIKELY ALL ALONG
SIERRA INTO WRN NV 06-18Z SUN. DUE TO HEAVY RAIN, MTN WAVES WILL NOT
BE AS DEVELOPED, BUT STILL MAY CAUSE ISSUES. WALLMANN

HYDROLOGY...
TWO INTENSE SYSTEMS WITH HIGH SNOW LEVELS ARE BEGINNING TO CREATE
MORE OF A CONCERN THIS MORNING. THE ANTECEDENT DRY CONDITIONS WILL
HELP, AND ONE STORM ALONE WOULD NOT BE AS MUCH OF A CONCERN. THE
FIRST STORM WILL JUST MOISTEN THE GROUND WITH BETTER RUNOFF
POTENTIAL FOR THE SECOND STORM OVER THE WEEKEND. IN ADDITION, SNOW
LEVELS WILL BE QUITE HIGH, AVERAGING 8-8500 FEET FOR THE EVENT.

WITH THE TWO STORM TOTALS OF OVER 10 INCHES POSSIBLE ALONG THE
SIERRA CREST AND NEAR 5 INCHES FOR THE TAHOE BASIN, RUNOFF WILL
SURELY INCREASE. EVEN WESTERN NEVADA VALLEYS COULD SEE AN INCH OR
MORE OF RAINFALL, MOST OF IT FALLING OVER THE WEEKEND.

WITH THE PERIODS OF HEAVY PRECIPITATION, THERE COULD BE SOME URBAN
AND SMALL STREAM FLOODING, MOST LIKELY OVER THE WEEKEND. IN
ADDITION, THERE WILL BE RISES ON THE MAINSTEM RIVERS, WITH THE SUSAN
RIVER POSSIBLY REACHING WITHIN A FOOT OF FLOOD STAGE. NO CONCERNS
WITH THE OTHER MAINSTEM RIVERS SUCH AS THE TRUCKEE AT THIS TIME, BUT
IF RAINFALL AMOUNTS ARE HEAVIER (AND THEY COULD BE IF THE GFS IS
CORRECT) THERE MAY BE MINOR ISSUES. SEE THE FLOOD POTENTIAL
STATEMENT FOR THE LATEST DETAILS. WALLMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...LAKE WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR PYRAMID LAKE
     IN NVZ004.

     HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY EVENING
     NVZ002-003.

     LAKE WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR LAKE TAHOE IN
     NVZ002.

     WIND ADVISORY UNTIL 7 PM PST THIS EVENING NVZ003.

CA...HIGH WIND WATCH FROM THURSDAY EVENING THROUGH FRIDAY EVENING
     CAZ072-073.

     LAKE WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR LAKE TAHOE IN
     CAZ072.

&&

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