985  
FXUS65 KREV 240413 AAA  
AFDREV  
 
AREA FORECAST DISCUSSION...UPDATED  
NATIONAL WEATHER SERVICE RENO NV  
813 PM PST THU JAN 23 2020  
   
UPDATE
 
 
INITIAL SHOWERS WITH THE WEAK INCOMING SYSTEM HAVE JUST PRODUCED  
TRACE AMOUNTS. HOWEVER, RADAR TRENDS AND HI RES MODELS SUGGEST A  
BETTER CHANCE OVERNIGHT. BEST CHANCES WILL BE ALONG THE SIERRA  
CREST TO NEAR THE OREGON BORDER AS WELL AS EASTERN PERSHING  
COUNTY. AMOUNTS STILL LOOK TO BE LIGHT AND GENERALLY LESS THAN A  
TENTH OF AN INCH, BUT ISOLATED SPOTS COULD SEE UP TO A QUARTER  
INCH. SNOW LEVELS REMAIN HIGH, NEAR 8000 FEET SO ONLY THE HIGHEST  
PEAKS AND RIDGES WILL SEE SNOW LEAVING THE PASSES JUST WET. X  
 

 
   
PREVIOUS DISCUSSION
 
/ISSUED 127 PM PST THU JAN 23 2020/  
 
SYNOPSIS...  
 
MAINLY LIGHT WINDS WITH ABOVE AVERAGE TEMPERATURES WILL PREVAIL  
THROUGH WEEK'S END WITH SOME VERY LIGHT RAIN OR SNOW LATE THURSDAY  
NIGHT INTO EARLY FRIDAY. THIS WEEKEND ANOTHER SYSTEM WILL BRING  
CHANCES OF VALLEY RAIN AND MOUNTAIN SNOW ALONG WITH GUSTY WINDS.  
EXTENSIVE CLOUD COVER AND A COUPLE OF WEAK STORMS ARE POSSIBLE  
INTO NEXT WEEK.  
 
SHORT TERM...  
 
THERE ARE TWO MAIN FEATURES OF NOTE IN THE SHORT TERM PART OF THE  
FORECAST TODAY. EACH...WHILE NOT STRONG AS FAR AS WINTER STORMS  
GO...PRESENTS ITS OWN SET OF PROBLEMS.  
 
THE FIRST IS A WAVE THAT MOVES THROUGH THE REGION TONIGHT. THE  
MAIN PART OF THE WAVE CAN CURRENTLY BE SEEN ON WATER VAPOR  
SATELLITE IMAGERY NEAR 130W. AHEAD OF THE THE MAIN WAVE IS A WEAK  
AREA OF WARM AIR ADVECTION NOTED BY ENHANCED MOISTURE AND SLIGHTLY  
COOLER CLOUD TOPS IN THE SATELLITE IMAGERY. THE WARM AIR  
ADVECTION PORTION OF THIS FEATURE SHOULD BEGIN IMPACTING NORTHEAST  
CALIFORNIA AND THE NORTHERN SIERRA BY EARLY EVENING WHILE THE  
MAIN PART OF THE WAVE MOVES THROUGH JUST AFTER DAYBREAK FRIDAY.  
 
LOW CLOUDS AND FOG KEPT SOME OF THE COLDER VALLEYS IN THE SIERRA  
FROM COMPLETELY MIXING OUT TODAY. THE PRESENCE OF CLOUD COVER AND  
THE WARM AIR ADVECTION ALOFT CREATING AN INVERSION MAY RESULT IN  
A FEW POCKETS OF TEMPERATURES NEAR FREEZING IN THESE COLDER  
VALLEYS THIS EVENING. SO WHILE OVERALL SNOW LEVELS SHOULD BE  
RISING THIS EVENING THERE IS THE POSSIBILITY THAT A FEW VERY  
REMOTE LOCATIONS COULD SEE A BRIEF PERIOD OF VERY LIGHT FREEZING  
RAIN BELOW 7500 FEET BEFORE EVERYTHING CHANGES TO RAIN. THE SNOW  
LEVELS RISE TO NEAR 8000-8500 FEET BRIEFLY THIS EVENING AS MIXING  
INCREASES THEN FALL WELL BELOW 7000 FEET WITH THE PASSAGE OF THE  
MAIN WAVE BY EARLY FRIDAY.  
 
MOISTURE IS NOT OVERLY ABUNDANT WITH THIS SYSTEM AND THE HIGHER  
SNOW LEVELS WILL LIMIT ACCUMULATIONS ON THE PASSES...BUT THERE  
COULD BE A PERIOD OF SLICK/SNOW COVERED ROADS FOR THE TRANS-  
SIERRA PASSES LATE THIS EVENING AND EARLY FRIDAY.  
 
A BRIEF BREAK BRINGS DRY WEATHER FRIDAY AFTERNOON INTO EARLY  
SATURDAY MORNING BEFORE THE NEXT WAVE AFFECTS THE AREA. THE MODEL  
SOLUTIONS HAVE BEEN HAVING A DIFFICULT TIME WITH THIS SYSTEM...AND  
TODAY WAS NO EXCEPTION.  
 
THE PREVIOUS FORECAST CYCLE SAW A FASTER SYSTEM WITH LESS DWELL  
TIME OVER THE REGION AND LESS QPF. WELL...NOW SOME OF THE MODEL  
SOLUTIONS HAVE SLOWED THE INITIAL ONSET OF PRECIPITATION FROM LATE  
SATURDAY AFTERNOON TO SATURDAY EVENING (SATURDAY NIGHT FOR MOST  
AREAS EAST OF THE SIERRA). BUT THE SYSTEM STILL MOVES THROUGH  
RATHER QUICKLY WITH STEADY PRECIPITATION OUT OF THE AREA BY MID-  
TO LATE-MORNING SUNDAY. THIS SLOWER ENTRY INTO THE REGION RESULTS  
IN HIGHER SNOW LEVELS AT THE ONSET OF PRECIPITATION. THAT MEANS  
LESS TOTAL SNOW ACCUMULATION IN THE HIGHER ELEVATIONS. WHILE THE  
HEAVIEST BURST OF PRECIPITATION IS STILL IN THE MIDNIGHT TO 6 AM  
TIME FRAME SATURDAY NIGHT INTO SUNDAY MORNING...THERE IS SLIGHTLY  
LESS PRECIPITATION OVERALL. SNOW TOTALS BELOW 8000 FEET AT THE  
CURRENT TIME DO NOT REACH THE LEVEL OF AN ADVISORY...BUT THERE  
COULD BE HAZARDOUS DRIVING CONDITIONS BY SUNDAY MORNING OVER THE  
HIGHER PASSES OF THE SIERRA AS A FEW INCHES PILE UP.  
 
WINDS DO NOT LOOK OVERLY STRONG WITH THIS SYSTEM EITHER. GUSTS  
AHEAD OF THE MAIN WAVE COULD REACH 30-35 MPH SUNDAY MORNING. THEN  
AFTER THE PRECIPITATION HAS ENDED WINDS COULD GUST 30-40 MPH  
SUNDAY AFTERNOON IN THE LEE OF THE SIERRA. WE MAY NEED A LAKE WIND  
ADVISORY FOR LAKE TAHOE.  
 
SHOWERS LINGER IN THE SIERRA AND THE FAR EASTERN PART OF THE  
FORECAST AREA SUNDAY AFTERNOON AND EVENING. THEN ANOTHER WEAK WAVE  
BRINGS VERY LIGHT RAIN/SNOW TO AREAS NEAR THE OREGON BORDER BEFORE  
DAYBREAK MONDAY MORNING.  
 
AS STATED...NONE OF THESE INDIVIDUAL SYSTEMS RISE TO THE LEVEL OF  
EVEN A WINTER WEATHER ADVISORY...BUT THEY ALL HAVE THE POTENTIAL  
TO CAUSE SOME TRAFFIC DELAYS DUE TO JUST A SMALL AMOUNT OF SNOW ON  
THE HIGHER ELEVATION ROADS.  
 
LONG TERM...MONDAY THROUGH THE END OF JANUARY...  
 
FOR THE EARLY AND MIDDLE PART OF NEXT WEEK, A FEW WEAK  
DISTURBANCES WILL MOVE THROUGH THE NORTHWEST US. CURRENTLY THE  
BEST OVERALL CHANCES FOR LIGHT RAIN AND SNOW ARE ANTICIPATED FOR  
TUESDAY, BUT A FEW LIGHTER SHOWERS ARE ALSO POSSIBLE MAINLY FOR  
FAR NORTHEAST CA-NORTHWEST NV AT TIMES FROM MONDAY THROUGH  
WEDNESDAY. DAYTIME TEMPERATURES ARE EXPECTED TO BE ABOUT 4-8  
DEGREES ABOVE AVERAGE THROUGH MIDWEEK.  
 
FOR TUESDAY WHEN THE MAIN DISTURBANCE MOVES THROUGH, PRECIP  
AMOUNTS STILL LOOK RATHER MODEST, WITH THE WETTER SCENARIOS  
SHOWING AROUND 0.50" FOR WESTERN LASSEN AND PLUMAS COUNTIES AND  
0.25" NORTHWARD TO SURPRISE VALLEY, WHILE DRIER SCENARIOS SHOW  
LESS THAN HALF THESE VALUES. SNOW LEVELS ARE PROJECTED TO START  
NEAR 4500-5000 FEET, SO THE HIGHER ELEVATION ROADS AND PASSES OF  
NORTHEAST CA COULD HAVE SOME SNOW ACCUMULATIONS IN THE MORNING,  
BEFORE SNOW LEVELS RISE TO NEAR 6000 FEET DURING THE DAY. FROM  
I-80 SOUTHWARD, THESE PRECIP VALUES DROP OFF SO THE SIERRA/TAHOE  
AREAS MAY ONLY SEE A SMALL AMOUNT OF SNOW WHILE MUCH OF WESTERN NV  
LIKELY GETS SHADOWED OUT WITH ONLY A FEW SPRINKLES OR FLURRIES.  
 
LATER NEXT WEEK, THE MAJORITY OF MODEL/ENSEMBLE GUIDANCE FAVORS A  
STRONGER RIDGE OF HIGH PRESSURE BUILDING INTO CA-NV. THIS WOULD  
SHUT DOWN PRECIP CHANCES FOR ALL OF EASTERN CA-WESTERN NV,  
ALTHOUGH CIRRUS COVERAGE LOOKS WIDESPREAD AT LEAST FOR THURSDAY.  
TEMPERATURES WILL BE ON THE RISE WITH HIGHS WELL ABOVE AVERAGE  
(60+ DEGREES FOR LOWER ELEVATIONS AND 50+ DEGREES FOR SIERRA  
VALLEYS) AS JANUARY COMES TO A CLOSE. MJD  
 
AVIATION...  
 
HIGH RESOLUTION MODEL GUIDANCE BRINGS AN AREA OF MOISTURE WITH  
LIGHT RAIN SHOWERS THROUGH EASTERN CA-WESTERN NV MAINLY NORTH OF  
US-50 TONIGHT INTO EARLY FRIDAY. HIGH SNOW LEVELS NEAR 8000 FEET  
AND LIGHT INTENSITY WILL LIMIT IMPACTS TO MAINLY PERIODIC  
OBSCURATION OF TERRAIN IN MVFR CIGS/VSBY FOR THE TAHOE TERMINALS  
AND INTO KRNO-KCXP-KMEV, MAINLY BETWEEN 01-06Z, THEN PUSHING  
ACROSS WEST CENTRAL NV FROM 04-09Z. MORE ISOLATED SHOWER ACTIVITY  
IS POSSIBLE OVERNIGHT. IF SUFFICIENT RAIN FALLS AT KTVL/KTRK THIS  
EVENING, PATCHY FOG COULD PRODUCE IFR/LIFR CONDITIONS OVERNIGHT  
INTO FRIDAY MORNING IF CLOUD COVER DIMINISHES. KMMH IS EXPECTED TO  
REMAIN DRY WITH VFR CONDITIONS TONIGHT. LIGHT SURFACE WINDS WILL  
PREVAIL AT ALL TERMINALS THROUGH SATURDAY, ALTHOUGH SIERRA RIDGE  
GUSTS MAY INCREASE TO NEAR 45 KT LATE TONIGHT AND FRIDAY.  
 
ANOTHER STORM SYSTEM WILL MOVE THROUGH THE REGION LATE SATURDAY  
EVENING THROUGH SUNDAY MORNING. PERIODS OF MVFR/IFR CIG/VIS,  
MOUNTAIN OBSCURATION, LIGHT SNOW AT THE SIERRA TERMINALS AND LIGHT  
RAIN FOR WESTERN NV TERMINALS ARE EXPECTED, ALONG WITH GUSTY  
WINDS, TURBULENCE AND POSSIBLE LLWS. MJD  
 

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

 
 

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