832  
FXUS65 KREV 191112  
AFDREV  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RENO NV  
312 AM PST SUN FEB 19 2017  
   
SYNOPSIS
 
 
LIGHT SNOW AND RAIN SHOWERS WILL LINGER TODAY, THEN A POWERFUL  
ATMOSPHERIC RIVER STORM WILL BRING GUSTY WINDS AND VERY HEAVY  
PRECIPITATION WITH HIGHER SNOW LEVELS TONIGHT THROUGH MONDAY  
NIGHT. KEEP FLOOD MITIGATION IN PLACE OR READILY AVAILABLE. WEAKER  
BUT COLDER STORM SYSTEMS MAY BRING SNOW TO LOWER ELEVATIONS AT  
TIMES FROM TUESDAY THROUGH NEXT WEEKEND.  
 

 
   
SHORT TERM
 
 
WEAK SHORTWAVE PASSAGE ACROSS THE PACIFIC NORTHWEST HAS KICKED UP  
WINDS EARLY THIS MORNING WITH SIERRA RIDGE GUSTS AROUND 70 MPH,  
AND SOME GUSTS 40-50 MPH FROM NORTH RENO TO COLD SPRINGS. THESE  
BREEZY CONDITIONS WILL CONTINUE TODAY, MIXING DOWN MORE  
EFFICIENTLY TO MOST VALLEY LOCATIONS BY THIS AFTERNOON.  
 
AS FOR PRECIPITATION TODAY, BANDS OF LIGHT SNOW AND RAIN WEST OF  
THE SIERRA WILL SPREAD TO NEAR THE CREST DURING THE DAY, WITH  
LIMITED MOISTURE PUSHING VERY FAR BEYOND THE CREST. ALSO, AREAS OF  
LIGHT SNOW REMAIN POSSIBLE FROM FAR NORTHERN LASSEN COUNTY TO THE  
OREGON BORDER INCLUDING THE SURPRISE VALLEY, WITH ACCUMULATIONS  
GENERALLY 1 INCH OR LESS.  
 
THEN FROM TONIGHT THROUGH MONDAY NIGHT, A STRONG ATMOSPHERIC  
RIVER STORM REMAINS ON TRACK TO MAKE A DIRECT HIT TO THE SIERRA,  
NORTHEAST CA AND MOST OF WESTERN NV, BRINGING EXTREME AMOUNTS OF  
RAIN AND HIGHER ELEVATION SNOW, SIMILAR TO SOME OF THE STRONGEST  
AR SYSTEMS ALREADY EXPERIENCED SO FAR THIS SEASON. THE PROGRESSION  
OF THIS SYSTEM IS A LITTLE FASTER, WITH THE LEADING EDGE OF THE  
MORE INTENSE PRECIP RATES ARRIVING BY EARLY MONDAY MORNING. ANYONE  
PLANNING TRAVEL IN THE SIERRA IS STRONGLY URGED TO ARRIVE AT  
THEIR DESTINATIONS TODAY, AS MAIN HIGHWAYS ARE LIKELY TO BECOME  
IMPASSIBLE DUE TO VERY HEAVY SNOW IN HIGHER ELEVATIONS AND HEAVY  
RAIN CAPABLE OF PRODUCING LARGE MUD AND ROCK SLIDES IN LOWER  
ELEVATIONS. EXPECT A MYRIAD OF MAJOR WEATHER IMPACTS WITH THIS  
STORM.  
 
HEAVY PRECIPITATION...MODEL GUIDANCE REMAINS CONSISTENT WITH VERY  
LARGE AMOUNTS OF PRECIP FOR ALL OF EASTERN CA AND MOST OF WESTERN  
NV. THE HEAVIEST PRECIP RATES ARE PROJECTED TO TARGET THE TAHOE  
BASIN FOR MOST OF THIS EVENT, WITH ONLY SLIGHTLY LESS INTENSE  
PRECIP RATES SOUTHWARD ACROSS ALPINE AND MONO COUNTIES. BY MONDAY  
EVENING, MOST GUIDANCE SOURCES LIFT THE HEAVIEST PRECIP RATES  
NORTHWARD INTO NORTHEAST CA, THEN RETURNING SOUTH ACROSS TAHOE  
AGAIN LATE MONDAY NIGHT ALTHOUGH PRECIP RATES WILL FINALLY BEGIN  
TO DECREASE BY THAT TIME. IMPRESSIVE 700 MB FLOW WILL PEAK OUT  
AROUND 60-80 KTS MONDAY-MONDAY NIGHT, BRINGING VERY EFFICIENT  
SPILLOVER INTO WESTERN NV MAINLY FROM US-50 NORTHWARD. OVERALL, WE  
EXPECT TO SEE AROUND 3-6 INCHES WITH LOCALLY HIGHER AMOUNTS OF  
PRECIP IN THE SIERRA AND NORTHEAST CA WEST OF SUSANVILLE, WITH  
1.0-2.5 INCHES INTO THE VALLEYS OF WESTERN NEVADA, LOWER VALLEYS  
OF NORTHEAST CA, AND MONO COUNTY NEAR US-395. HIGHER RAINFALL  
AMOUNTS GREATER THEN 3 INCHES ARE EXPECTED IN THE FOOTHILLS WEST  
OF US-395, INCLUDING AREAS WEST OF RENO-CARSON CITY AND AROUND  
WASHOE VALLEY. THIS STORM WILL ALSO BRING MODERATE TO HEAVY  
AMOUNTS OF RAINFALL BETWEEN 0.50 TO 1 INCH INTO NORTHWEST AND WEST  
CENTRAL NEVADA, EXCEPT LESSER AMOUNTS SOUTH OF US-50 INTO MINERAL  
COUNTY. FLOOD WATCHES REMAIN IN EFFECT FOR THE SIERRA ZONES AND  
THE WESTERN NEVADA SIERRA FRONT, AS HEAVY RAINFALL WILL CAUSE  
FLOODING, MUDSLIDES, ROCK SLIDES, AND INCREASES TO THE MAINSTEM  
RIVERS AND SMALLER CREEKS AND STEAMS. SEE OUR HYDROLOGY SECTION  
BELOW FOR MORE DETAILS ON FLOODING.  
 
SNOW LEVELS/AMOUNTS...WE STILL EXPECT SNOW LEVELS RISING TO  
AROUND 7000-7500 FEET FROM TAHOE NORTHWARD AND 7500-8000 FEET  
SOUTH OF TAHOE TO MONO COUNTY MONDAY MORNING THROUGH MONDAY  
EVENING. THIS WILL LEAD TO INCREASED FLOODING CONCERNS IN THE  
SIERRA BELOW 7000 FEET. SNOW LEVELS COULD GET PUSHED DOWN BY AS  
MUCH AS 500-1000 FEET LOWER DURING PERIODS OF HEAVIEST PRECIP. ALL  
WINTER RELATED HEADLINES REMAIN INTACT AS THIS HEAVY SNOWFALL  
WILL CAUSE MANY PROBLEMS. ELEVATIONS ABOVE 7500 FEET CAN EXPECT  
2-5 FEET OF SNOWFALL WITH HIGHEST AMOUNTS LIKELY ALONG THE SIERRA  
CREST WEST OF TAHOE, WHICH WILL LIKELY HAVE AN IMPACT ON  
AVALANCHE POTENTIAL AS WELL. FINDING PLACES TO PUT ALL OF THIS  
EXCESSIVE SNOW WILL CONTINUE TO BE A CHALLENGE ESPECIALLY AROUND  
MAMMOTH LAKES AND OTHER LOCATIONS IN THE SIERRA ABOVE 7000 FEET.  
SNOW AMOUNTS BETWEEN 6500-7500 FEET WILL VARY WIDELY, RANGING  
ANYWHERE FROM ABOUT 6 INCHES TO AT LEAST 2 FEET DEPENDING ON HOW  
MUCH RAIN MIXES IN DURING THE PEAK PRECIP RATES, WHILE MOST AREAS  
BELOW 6500 FEET RECEIVE LIMITED SNOWFALL AMOUNTS. SNOW LEVELS  
WILL LOWER BY EARLY TUESDAY MORNING NORTH OF US-50 TO NEAR  
5000-5500 FEET AROUND LASSEN PLUMAS, AND 6000-6500 FEET AROUND THE  
RENO-CARSON-TAHOE AREAS.  
 
STRONG WINDS...AS THE STRONGER WINDS ALOFT PUSH IN BY MONDAY, WE  
CAN EXPECT TO SEE STRONG WINDS GUSTING AROUND 55-60 MPH TO THE  
VALLEYS, ESPECIALLY FOR AREAS SOUTH OF HIGHWAY 50 IN MONO, MINERAL  
AND SOUTHERN LYON COUNTIES. AS FOR THE SIERRA RIDGES, WE COULD  
SEE EXTREME GUSTS OVER 140 MPH DURING THE MAIN STORM ON MONDAY.  
FARTHER NORTH AROUND THE RENO-CARSON-TAHOE AREAS, WE COULD ALSO  
SEE STRONG WINDS ON MONDAY, ALTHOUGH THE HEAVY RAINFALL WILL  
LIKELY DAMPEN THE WINDS DOWN SLIGHTLY WITH GUSTS UP TO 45 MPH.  
MJD  
   
LONG TERM...TUESDAY THROUGH SATURDAY
 
 
PRIMARY CHANGES TO THE LONG TERM FORECAST THIS MORNING INVOLVE  
INCREASING SNOW LEVELS SLIGHTLY FOR EARLY TUESDAY AND BUMPING UP  
QPF A LITTLE FOR TUESDAY...THEN LOWERING QPF SLIGHTLY FOR  
WEDNESDAY.  
 
OVERALL...THE OPERATIONAL MODELS ARE A LITTLE SLOWER WITH LOWERING  
SNOW LEVELS TUESDAY. WHILE THIS MAY NOT MAKE A GREAT DEAL OF  
DIFFERENCE TO SNOW AMOUNTS IN THE SIERRA AND NORTHEAST  
CALIFORNIA...IT COULD INCREASE THE FLOODING POSSIBILITIES SLIGHTLY  
IN THE LOWER ELEVATIONS EAST OF THE SIERRA AND THE LOWER PORTIONS OF  
THE RIVER BASINS IN NORTHEAST CALIFORNIA. QPF NUMBERS ARE A LITTLE  
HIGHER FOR EARLY TUESDAY...BUT THEN THE AMOUNT OF PRECIPITATION  
SHOULD DECREASE THROUGH THE DAY AS THE MOISTURE TAP BECOMES CUT  
OFF AND SLIDES SOUTH. THE BIGGEST INCREASE IN QPF WAS FOR MONO  
COUNTY WHERE ADDITIONAL SNOW IS EXPECTED AT THE HIGHER ELEVATIONS.  
 
BEYOND TUESDAY THE MODELS HAVE TRENDED A LITTLE DRIER TUESDAY NIGHT  
INTO WEDNESDAY NIGHT. THE MAIN UPPER TROUGH BEGINS TO SLIDE OVER THE  
REGION WEDNESDAY. THIS WILL LOWER SNOW LEVELS TO ALL VALLEY FLOORS  
AND COULD RESULT IN A FEW INCHES OF ACCUMULATION IN THE WESTERN  
NEVADA AND NORTHEAST CALIFORNIA VALLEYS. THERE MAY EVEN BE AN INCH  
OR TWO IN THE BASIN AND RANGE. WITH THE SLIGHT DECREASE IN EXPECTED  
QPF FOR WEDNESDAY THE AMOUNT OF SNOW FOR THE TAHOE BASIN AND MONO  
COUNTY FOR WEDNESDAY AND WEDNESDAY NIGHT WAS LOWERED  
SLIGHTLY...GENERALLY LESS THAN A FOOT AT LAKE LEVEL AND AROUND  
MAMMOTH LAKES WITH IN EXCESS OF A FOOT AT THE HIGHER ELEVATIONS.  
 
SNOW SHOWERS LINGER INTO EARLY THURSDAY AFTERNOON BEFORE WEAK  
RIDGING TEMPORARILY DEVELOPS AND BRINGS AN END TO THE PRECIPITATION  
FOR A SHORT TIME. OPERATIONAL MODELS AND ENSEMBLE MEMBERS ARE STILL  
STRUGGLING WITH FORECAST AGREEMENT BEYOND THURSDAY. SOME WANT TO  
DROP A LONG WAVE TROUGH SOUTH OVER THE REGION WITH PRECIPITATION  
REDEVELOPING FRIDAY AFTERNOON/EVENING AND EXTENDING INTO SATURDAY.  
OTHERS SHOW A SLOWER DEVELOPMENT OF A CLOSED LOW DROPPING SOUTH  
ALONG THE COAST. THIS WOULD BE A SLIGHTLY DRIER SOLUTION ALTHOUGH  
SOME SNOW WOULD BE POSSIBLE IN THE SIERRA AND NORTHEAST CALIFORNIA.  
WHATEVER SOLUTION PREVAILS WE SHOULD BE COLD ENOUGH FOR MAINLY SNOW.  
 
GIVEN THE DISAGREEMENTS AMONG THE MODEL SOLUTIONS BEYOND THURSDAY WE  
HAVE LEFT SMALL POPS IN THE FORECAST FROM FRIDAY NIGHT THROUGH  
SATURDAY NIGHT.  
 

 
   
AVIATION
 
 
INCREASING WINDS TODAY AHEAD OF AN APPROACHING STORM SYSTEM WILL  
LEAD TO TURBULENCE ALOFT AND NEAR THE SURFACE ALONG WITH LOW LEVEL  
WIND SHEAR POSSIBILITIES.  
 
MAINLY VFR CONDITIONS EAST OF THE SIERRA THIS MORNING WITH FOG IN  
SOME SIERRA VALLEYS PRODUCING IFR/MVFR CONDITIONS GIVE WAY TO ALL  
VFR INTO THE LATE AFTERNOON HOURS. BY THIS EVENING CONDITIONS BEGIN  
TO DETERIORATE AGAIN AS MOISTURE AND LOWER CIGS/VSBYS PUSH INTO THE  
REGION FROM THE WEST. SNOW LEVELS RISE THROUGH THE NIGHT INTO  
MONDAY. THE HEAVIEST PRECIPITATION IS LIKELY DURING THE DAY MONDAY.  
ALL RAIN AT THE TERMINALS BY THEN. GUSTY WINDS REMAIN A POSSIBILITY  
EAST OF THE SIERRA LATE MONDAY AFTERNOON INTO MONDAY EVENING WHEN  
PRECIPITATION STARTS TO DECREASE.  
 
LOWER CIGS AND VSBYS RETURN MONDAY NIGHT AND SNOW LEVELS START TO  
LOWER. THIS WILL PRODUCE IFR CONDITIONS AND ACCUMULATING SNOWS FOR  
THE SIERRA TERMINALS. BY LATE TUESDAY SNOW LEVELS ARE LIKELY TO THE  
LOWER VALLEY FLOORS WITH MINOR ACCUMULATIONS EAST OF THE SIERRA. BUT  
THE AMOUNT OF PRECIPITATION WILL BE MUCH LOWER BY THEN.  
 

 
 
HYDROLOGY...  
 
* MODERATE FLOODING EXPECTED FOR THE MIDDLE FORK OF THE FEATHER  
RIVER NEAR PORTOLA.  
* TRUCKEE RIVER AT RENO AND VISTA ALONG WITH THE CARSON RIVER NEAR  
CARSON CITY FORECAST TO BE NEAR MONITOR STAGE.  
* FLOODING POSSIBLE FOR CREEKS, STREAMS, URBAN AREAS AND DRAINAGE  
BASINS IN THE TAHOE BASIN, EASTERN SIERRA, NORTHEAST CALIFORNIA  
AND WESTERN NEVADA EARLY MONDAY THROUGH EARLY TUESDAY.  
 
A STRONG ATMOSPHERIC RIVER WILL PUSH INTO THE REGION LATE SUNDAY  
NIGHT THROUGH TUESDAY MORNING BRINGING HEAVY RAIN AND RISING SNOW  
LEVELS ON MONDAY. CURRENTLY, SNOW LEVELS ARE EXPECTED TO BE AROUND  
6500 FEET IN NORTHEAST CALIFORNIA AND AROUND 7500 FEET FOR MUCH  
OF THE SIERRA AND WESTERN NEVADA. PRECIPITATION TOTALS IN THE  
SIERRA COULD REACH 3 TO 6 INCHES, WITH 2 TO 3 INCHES IN THE  
CARSON RANGE AND MUCH OF THE SUSAN, PIT, AND MIDDLE FORK OF THE  
FEATHER RIVER BASINS. 1 TO 2 INCHES OF RAIN IS LIKELY THROUGH MUCH  
OF THE GREATER RENO/SPARKS/CARSON CITY METRO AREAS AND ALONG THE  
HIGHWAY 395 CORRIDOR INTO MONO COUNTY.  
 
UNPRECEDENTED AMOUNTS OF RAIN AND SNOW HAVE ALREADY FALLEN THIS  
WINTER AND THE GROUND IS AT RECORD SATURATION LEVELS. IT WILL NOT  
TAKE MUCH TO BRING RENEWED FLOOD CONCERNS THROUGHOUT THE SIERRA,  
NORTHEAST CALIFORNIA, AND IN WESTERN NEVADA. AROUND THE TAHOE BASIN,  
THE EASTERN SIERRA, AND WESTERN NEVADA, MAIN THREAT FOR FLOODING  
WILL BE ALONG CREEKS, STREAMS, AND DRAINAGE BASINS/FARMLAND WHERE  
WATER COLLECTS FROM CREEKS RUNNING OUT OF THE MOUNTAINS. FLOODING IS  
ALSO POSSIBLE THROUGH BOTH THE CARSON VALLEY AND WASHOE VALLEY ALONG  
WITH HARDSCRABBLE CREEK IN THE VIRGINIA RANGE. URBAN FLOODING IS  
PROBABLE IN THE TAHOE BASIN AS SNOW BERMS WON'T ALLOW FOR WATER TO  
PROPERLY DRAIN FROM THE REGION. THE OTHER CONCERN WILL BE THE  
INCREASED POTENTIAL FOR ROCK AND MUDSLIDES IN AREAS OF STEEP  
TERRAIN, WITH ROAD CLOSURES POSSIBLE.  
 
THE RIVER BASINS TO WATCH AT THIS TIME WILL BE THE MIDDLE FORK OF  
THE FEATHER, THE SUSAN, AND THE PIT IN NORTHEAST CALIFORNIA. SNOW  
LEVELS MAY BE JUST LOW ENOUGH FOR KEEP THE SUSAN AND PIT RIVERS FROM  
FLOODING, BUT WITH COPIOUS AMOUNTS OF ADDITIONAL RAINFALL EXPECTED,  
THESE WILL NEED TO BE CLOSELY MONITORED. THE MIDDLE FORK OF THE  
FEATHER IS CURRENTLY FORECAST TO REACH MODERATE FLOOD STAGE, WITH  
ONLY AN ADDITIONAL 500 CFS/0.3 FEET NEEDED TO REACH MAJOR FLOOD  
STAGE.  
 
SNOW LEVELS BELOW 8000 FEET USUALLY PREVENT FLOODING ALONG THE  
CARSON, TRUCKEE AND WALKER RIVERS. HOWEVER WITH SIGNIFICANT RUNOFF  
ANTICIPATED, THE DRAINAGES WHICH FLOW INTO THE MAINSTEM RIVERS MAY  
OVERCOME THE SLIGHTLY LOWER SNOW LEVELS. THIS INCLUDES, BUT IS NOT  
LIMITED TO, STEAMBOAT CREEK AND THE NORTH TRUCKEE DRAINAGE. THE  
CURRENT FORECAST TAKES THE CARSON RIVER NEAR CARSON CITY AND THE  
TRUCKEE RIVER AT RENO AND VISTA TO NEAR MONITOR STAGE. SMALL CHANGES  
TO PRECIPITATION TOTALS AND/OR SNOW LEVELS MAY RESULT IN MINOR  
FLOODING.  
 
SNOW LEVELS ARE ANTICIPATED TO FALL BY TUESDAY MORNING OR AFTERNOON,  
WHICH ALSO COINCIDES WITH WEAKENING MOISTURE TRANSPORT. THIS WILL  
HELP LESSEN NEW FLOOD RISKS, BUT IT MAY TAKE A DAY OR TWO FOR  
ONGOING FLOOD WATERS TO SUBSIDE. -DAWN  
 

 
   
REV WATCHES/WARNINGS/ADVISORIES
 
 
NV...LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 10 PM PST THIS  
EVENING FOR LAKE TAHOE IN NVZ002.  
 
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST TUESDAY  
ABOVE 6500 FEET IN NVZ002.  
 
FLOOD WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING NVZ002.  
 
FLOOD WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING NVZ003.  
 
LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 10 PM PST THIS  
EVENING FOR PYRAMID LAKE IN NVZ004.  
 
CA...FLOOD WATCH FROM LATE TONIGHT THROUGH TUESDAY AFTERNOON CAZ071.  
 
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 4 AM PST  
TUESDAY ABOVE 5500 FEET IN CAZ071.  
 
FLOOD WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING CAZ073.  
 
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST TUESDAY  
ABOVE 7000 FEET IN CAZ073.  
 
LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 10 PM PST THIS  
EVENING FOR LAKE TAHOE IN CAZ072.  
 
WINTER STORM WARNING FROM 10 PM THIS EVENING TO 4 AM PST TUESDAY  
ABOVE 6500 FEET IN CAZ072.  
 
FLOOD WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING CAZ072.  
 

 
 

 
 
FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...  
HTTP://WEATHER.GOV/RENO  
 
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