Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 260549
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
1049 PM PDT SAT OCT 25 2014

.UPDATE...
WINDS CONTINUE TO SLOWLY SUBSIDE AROUND THE FORECAST AREA TONIGHT.
THE LATEST CHECK OF THE LAKE TAHOE BUOYS SHOWED WINDS IN THE 10 TO
15 MPH RANGE. GIVEN THESE DECREASING WINDS WE WILL ALLOW THE LAKE
WIND ADVISORY TO EXPIRE AT 11 PM. ELSEWHERE GUSTY WINDS TO NEAR 35
MPH ARE STILL POSSIBLE IN THE MORE WIND PRONE LOCATIONS EAST OF
THE SIERRA LATE THIS EVENING. THESE WILL WILL DECREASE AS THE
UPPER LEVEL TROUGH PASSES THROUGH THE FORECAST AREA LATE TONIGHT.
20

&&

.PREVIOUS DISCUSSION... /ISSUED 755 PM PDT SAT OCT 25 2014/

UPDATE...
UPPER LEVEL TROUGH IS MOVING INTO CA NOW. THE SFC FRONT HAS PASSED
THROUGH MOST OF THE REGION AND WE HAVE GOTTEN INTO THE COLDER AIR.
WITH THE FRONT TO EAST MOST OF OUR STRONGEST WINDS HAVE DECREASED
BELOW ADVISORY CRITERIA. A PLUME OF MOISTURE AHEAD OF THE UPPER
TROUGH IS STILL CREATING SHOWERS AND EVEN A FEW THUNDERSTORMS OVER
NRN CA. UPSLOPE FLOW ALONG THE WESTERN SLOPES FROM THE TAHOE BASIN
NORTHWARD IS HELPING DEVELOP HEAVIER PCPN IN SOME SPOTS BUT IT IS
NOT WIDESPREAD. UNDER THE HEAVIEST PCPN SNOW LEVELS ARE LIKELY TO
DROP TO AROUND 6500 FEET LATER TONIGHT WITH AN INCH OR TWO OF
ACCUMULATION POSSIBLE AT THE HIGHER PASSES FROM ECHO SUMMIT
NORTH.

WITH THE DECREASE IN WINDS HAVE OPTED TO CANCEL THE WIND
ADVISORIES EARLY...EXCEPT THE LAKE WIND ADVISORY FOR TAHOE. THERE
THE BUOYS ARE STARTING TO INCREASE AGAIN. THIS WILL RUN THROUGH 11
PM. FOR PYRAMID LAKE THE OBSERVATION AT ANAHO ISLAND STILL SHOWS
GUSTS CLOSE TO 50 MPH...BUT THE LAKE IS CLOSED AFTER SUNSET SO
WILL NOT ISSUE A LAKE WIND ADVISORY FOR THIS. THERE WILL LIKELY BE
A FEW WIND PRONE AREAS WITH GUSTS TOPPING 45 MPH FOR THE NEXT FEW
HOURS...BUT THESE WILL BE VERY ISOLATED IN NATURE.

RH VALUES ARE INCREASING BEHIND THE COLD FRONT AS WELL. ALTHOUGH
WIND GUSTS IN SOME AREAS MAY CONTINUE ABOVE 30 MPH...THE STRONGEST
GUSTS HAVE PASSED AND THE INCREASE IN HUMIDITY WILL SPELL AN END
TO CRITICAL FIRE WEATHER CONDITIONS. THEREFORE...THE RED FLAG WILL
BE ALLOWED TO EXPIRE AT 8 PM. 20

PREVIOUS DISCUSSION... /ISSUED 309 PM PDT SAT OCT 25 2014/

SYNOPSIS...
LOW PRESSURE WILL MOVE INLAND TONIGHT, BRINGING GUSTY WINDS ALONG
WITH LIGHT RAIN AND MOUNTAIN SNOW. COOLER CONDITIONS WITH A FEW
LINGERING SHOWERS ARE EXPECTED EARLY SUNDAY NORTH OF INTERSTATE 80.
MILD AND DRIER CONDITIONS WILL RETURN NEXT WEEK, WITH A CHANCE OF
RAIN AND SNOW WITH COOLER TEMPERATURES BY NEXT WEEKEND.

SHORT TERM...
COLD FRONTAL PRECIPITATION BAND HAS MOVED INTO WESTERN NEVADA AND
THE EASTERN SIERRA AROUND LAKE TAHOE AND ALPINE COUNTY. THE
PRECIPITATION HAS FALLEN APART AS PROGGED BY MODELS NORTH OF RENO.
HOWEVER, PRECIPITATION HELD TOGETHER BETTER THAN EXPECTED FOR RENO
SOUTH TO MINDEN MAINLY ALONG AND WEST OF HIGHWAY 395. NEAR THE
CREST WEST OF LAKE TAHOE THE PRECIPITATION WAS HEAVY ENOUGH TO
BRIEFLY DRIVE SNOW LEVELS DOWN TO BETWEEN 6500 AND 7000 FEET AND
CAUSE SLUSHY ACCUMULATIONS ON INTERSTATE 80 (THAT HAS SINCE MELTED).
OUTSIDE OF THE BRIEF LOWERING, SNOW LEVELS ARE RUNNING BETWEEN
ABOUT 7500 AND 8500 FEET. AS SLIGHTLY COLDER AIR ALOFT FILTERS IN
WITH THIS SYSTEM`S TROUGH AXIS TONIGHT AND PRECIPITATION TURNS
SHOWERY SNOW LEVELS WILL SLOWLY FALL TO AS LOW AS 6000-6500 FEET
ALTHOUGH MOST PRECIPITATION WILL TAPER OFF BY THEN. IN ANY CASE,
BURSTS OF SNOW SHOWERS COULD CERTAINLY CAUSE LIGHT ACCUMULATIONS
AND SLICK ROADS AT THE HIGHER ELEVATIONS FROM TAHOE NORTH OVERNIGHT.

WIND-WISE, SUSTAINED WINDS OF 20-35 MPH WITH GUSTS TO BETWEEN 40
AND 60 MPH WERE WIDESPREAD TODAY. WINDS HAVE BEGUN TO FALL OFF
BEHIND THE COLD FRONT BUT ARE STILL HOWLING OUT IN THE BASIN AND
RANGE WITH STRONG WEST WINDS DRIVING A LARGE AREA OF DUST OFF THE
CARSON SINK (EASTERN PERSHING/CHURCHILL COUNTIES).

FOR TONIGHT, THERE IS ONE MORE DISTURBANCE ROUNDING THE BASE OF
THE MAIN UPPER TROUGH. AT THIS TIME, IT IS FIRING UP NUMEROUS
SHOWERS AND EVEN ISOLATED THUNDERSTORMS OVER NORTHWEST CALIFORNIA.
THIS IMPULSE WILL MOVE THROUGH FAR NORTHERN CALIFORNIA THIS
EVENING AND FIRE UP ANOTHER ROUND OF SHOWERS FOR NORTHEAST CALIFORNIA
AND WESTERN NEVADA, MAINLY NORTH OF INTERSTATE 80. THIS COULD
BRING LIGHT SNOWFALL ACCUMULATIONS ABOVE 6500-7000 FEET. ELSEWHERE,
RAIN AND HIGHER ELEVATION SNOW SHOWERS SHOULD REMAIN LIGHT. WINDS
WILL REMAIN A BIT GUSTY FOR MANY AREAS THIS EVENING BEFORE DYING
OFF CONSIDERABLY FOR VALLEYS AS A WEAK SURFACE HIGH BUILD IN.

SUNDAY MORNING A FEW VERY LIGHT SHOWERS MAY LINGER WELL NORTH OF
I-80 BEFORE AN UPPER RIDGE BEGINS TO SLOWLY BUILD OVERHEAD THROUGH
MONDAY. AFTERNOON TEMPERATURES WILL REMAIN A BIT BELOW AVERAGE AS
A COOL SURFACE HIGH BUILDS INTO THE GREAT BASIN. SNYDER

LONG TERM...TUESDAY THROUGH SATURDAY...
RIDGING WILL BUILD OVER THE REGION AT THE BEGINNING ON THE LONG TERM
ON TUESDAY. RATHER QUIET WEATHER OVERALL TUESDAY-THURSDAY. ONE
EXCEPTION IS POSSIBILITY OF LIGHT WARM ADVECTION PRECIP NORTH OF
SUSANVILLE TUESDAY NIGHT INTO WEDNESDAY. THIS IS ASSOCIATED WITH A
FILAMENT OF MOISTURE BREAKING OFF A MORE SIGNIFICANT ATMOSPHERIC
RIVER OVER THE EASTERN PACIFIC OCEAN. FORECAST CONFIDENCE IN THIS
PRECIP IS ONLY MEDIUM - MAINLY DUE TO UNCERTAINTIES IN HOW FAR
SOUTH THE MOISTURE PLUME WILL GET.

MAIN INTEREST IN THE LONG TERM IS INCREASING LIKELIHOOD OF AN
APPRECIABLE TROF MOVING INTO CA/NV FRIDAY-SATURDAY. THERE ARE
DIFFERENCES BETWEEN THE ECMWF/GFS BUT OVERALL THE BIG PICTURE
PATTERN IS SIMILAR, LEADING TO MEDIUM FORECAST CONFIDENCE WHICH AT
THIS LEAD TIME ISN`T BAD. NAEFS ANOMALY CHARTS ALSO PICKING UP ON
THIS TROUGH WHICH HELPS INCREASE CONFIDENCE IN THE PATTERN
VERIFYING. OVERALL CHANGES TO THE FORECAST WERE MINIMAL. CHANCE OF
RAIN FRIDAY-SATURDAY WITH SNOW LEVELS FALLING FROM 10KFT TO 6-7KFT.
QPF/TIMING ARE THE MAIN UNCERTAINTIES: ECMWF LIGHTER QPF BUT FASTER
WHILE GFS HAS SOME PERIODS OF HEAVY PRECIP IN THE SIERRA BUT IT`S
SLOWER. NO REASON TO FAVOR ONE OUTCOME OVER THE OTHER RIGHT NOW.
STRONG GUSTY WINDS ARE ALSO POSSIBLE LATE FRIDAY INTO SATURDAY GIVEN
SFC GRADIENT AND 700MB FLOW 40-55 KTS DEPICTED IN THE GFS; TO A
LESSER EXTENT IN THE ECMWF. CS

AVIATION...
NOT EXACTLY THE MOST PLEASANT DAY FOR FLYING WITH STRONG WINDS AND
SHOWERS CONTINUING THROUGH MID-EVENING. FORECAST CONFIDENCE IN THE
TAFS IS MEDIUM.

WINDS HAVE BEEN SOMEWHAT ERRATIC AROUND RNO/CXP WITH PRECIP SPILLING
OVER AND SWITCHING WIND DIRECTION AT SFC TO W/NW. S/SW WINDS IN
FOOTHILLS YIELDING LLWS WHICH HAS BEEN REPORTED BY RECENT ARRIVALS
INTO RNO. NOT SURE HOW LONG THIS WESTERLY WIND WILL LAST SO HAVE
USED TEMPO IN TAF. THE NEXT UNCERTAINTY IS POTENTIAL FOR MOUNTAIN
WAVE AND DOWNSLOPE WIND ENHANCEMENTS AT RNO/CXP FROM 23Z-03Z AS
WINDS ALOFT TURN MORE W/SW. IF THIS HAPPENS WINDS AT THE SURFACE
WOULD TURN MORE SSE BUT JUST OFF THE SURFACE STRONG SW WINDS OF
50KTS WOULD RESULT IN APPRECIABLE LLWS CONTINUING AT RNO/CXP. HRRR
SHOWING THIS SIGNATURE CLEARLY IN LATEST RUNS. OVERALL THE
PROBABILITY OF THIS SCENARIO PANNING OUT IS ABOUT 50-60% SO HAVE
INCLUDED IN THE 18Z TAFS.

OTHERWISE MAIN ISSUE IS PRECIP IN THE SIERRA AND IN FAR WESTERN
NEVADA WEST OF HWY 395. BASED ON RADAR TRENDS AND HRRR GUIDANCE -
BETWEEN NOW AND 03Z IS OPTIMAL TIME FOR COLD FRONTAL RAIN TO IMPACT
AIRFIELDS INCLUDING TRK/TVL/BRIDGEPORT. MOUNTAIN OBSCURATION IS A
GIVEN IN THE SIERRA AND WILL CONTINUE THROUGH ABOUT DAYBREAK SUNDAY
IN THE COOLER POST FRONTAL AIRMASS. IF SKIES CLEAR ENOUGH FOG IS
POSSIBLE AT TRK LATE TONIGHT SINCE THEY DID GET A BURST OF RAIN THIS
AFTERNOON. CS

FIRE WEATHER...
STRONG WINDS CONTINUE OVER THE REGION THROUGH THIS EVENING AS A COLD
FRONT PUSHES IN. INCREASING MOISTURE OVER THE SIERRA AND ALONG THE
SIERRA FRONT HAVE HELPED TO INCREASE THE HUMIDITY IN THE RENO-CARSON
CITY-MINDEN AREAS. THE RED FLAG WARNING FOR THE WESTERN NEVADA
SIERRA FRONT WILL BE ALLOWED TO EXPIRE AT 3PM THIS AFTERNOON.

FURTHER EAST, DRIER CONDITIONS AND STRONG WINDS WILL KEEP THE RED
FLAG WARNING IN PLACE THROUGH 8PM THIS EVENING. THE FRONT WILL
CONTINUE TO PUSH THROUGH WESTERN NEVADA THIS EVENING WITH
DIMINISHING WINDS, GOOD RECOVERY AND COOLER TEMPERATURES TONIGHT.
HOON

&&

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

$$

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






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