FXUS65 KREV 100505
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
905 PM PST WED DEC 9 2009

.UPDATE...
FREEZING FOG CAME IN EARLY IN THE FALLON AREA THIS EVENING AND
HAVE MOVED TIMING OF THE FREEZING FOG ADVISORY UP AS A RESULT.
WILL LEAVE IT IN PLACE TIL 10AM. FOG HAS ALSO DEVELOPED AT TRUCKEE
SO ADDED THAT TO THE WEATHER GRIDS AND ZONE FORECASTS. ALL UPDATED
PRODUCTS HAVE BEEN ISSUED. NO OTHER CHANGES TO PREVIOUS FORECAST. RC

&&

.PREVIOUS DISCUSSION... /ISSUED 318 PM PST WED DEC 9 2009/ 

SHORT TERM...
MAIN CONCERN THIS EVENING IS HOW QUICKLY FOG WILL REDEVELOP ACROSS
WESTERN NEVADA. AREAS NEAR PYRAMID LAKE...FALLON AND THE WALKER
RIVER VALLEY BETWEEN YERINGTON AND WALKER LAKE HAVE YET TO CLEAR
OUT. SO THINKING THOSE AREAS WILL FOG IN AS EARLY AS 6-8 PM...WITH
THE FOG EXPANDING TO A LARGER AREA BY 10 PM. THUS REISSUED THE
FREEZING FOG ADVISORY FOR TONIGHT FOR THE PYRAMID LAKE
AREA...PORTIONS OF LYON...MINERAL...PERSHING...AND CHURCHILL
COUNTIES. HIGH CLOUDS ARE NEARING THE SIERRA AHEAD OF A WEAK
SYSTEM...BUT LIKELY WILL HAVE LITTLE AFFECT ON FOG POTENTIAL
ACROSS WEST CENTRAL NEVADA.

TEMPERATURES MAY BE A FEW DEGREES HIGHER THAN LAST NIGHT DUE TO
SOME CLOUD COVER...BUT STILL GOING TO BE ANOTHER VERY COLD NIGHT
FOR THE AREA.

LIGHT SHOWERS COULD REACH THE SIERRA EARLY THURSDAY MORNING AS THE
WEAK SYSTEM MOVES ONSHORE. BETTER CHANCE FOR SHOWERS WILL BE
THURSDAY AFTERNOON IN THE SIERRA WITH LIGHT ACCUMULATIONS...AS
THE MOISTURE DEEPENS IN A SLIGHT WARM AIR ADVECTION FLOW.

THE MOIST ONSHORE FLOW INCREASES THURSDAY NIGHT AND FRIDAY...ALONG
WITH WARM AIR ADVECTION. THIS WILL BEGIN A PERIOD OF SNOW IN THE
SIERRA THAT MAY LAST INTO SUNDAY. SINCE THE PRIMARY LIFTING
MECHANISM WILL BE WARM AIR ADVECTION...AMOUNTS SHOULD BE LIGHT
AND SLOW TO ACCUMULATE WITH SEVERAL INCHES IN THE SIERRA. MODELS
DO BRING A WAVE INTO NORTHERN CALIFORNIA ON FRIDAY...WHICH COULD
HELP BOOST AMOUNTS IN PLUMAS AND LASSEN COUNTY.

LIGHT SNOW IS POSSIBLE ACROSS WESTERN NEVADA ON LATE THURSDAY
NIGHT AND FRIDAY...BUT AMOUNTS SHOULD REMAIN BELOW AN INCH...THOUGH
HIGHER AMOUNTS ARE IN THE REALM OF POSSIBILITY. WITH THE COLD AIR
IN PLACE...SLICK ROADS MAY IMPACT TRAVEL FOR THE FRIDAY MORNING
COMMUTE.

SYSTEM IS FORECAST TO REACH THE AREA SATURDAY WITH A BOOST FROM
THE JET TO PRODUCE A PERIOD OF HEAVY SNOW TO THE SIERRA. CERTAINLY
A GOOD CHANCE AT SIGNIFICANT ACCUMULATIONS BASED ON PRECIPITATION
AMOUNTS...BUT MAIN CONCERN IS MODEL TRENDING A BIT FARTHER SOUTH
WITH THE JET. THIS WOULD FAVOR AREAS FROM US-50 SOUTHWARD FOR THE
HIGHEST SNOW AMOUNTS.

SYSTEM COULD ALSO BRING ADDITIONAL SNOW TO WESTERN NEVADA. SNOW
LEVELS REMAIN THE BIGGEST UNCERTAINTY AS MODELS DON'T BRING MUCH
MIXING TO RAISE TEMPERATURES. HIGHS SATURDAY COULD CLIMB INTO THE
LOW 40S...OR REMAIN IN THE LOW 30S DEPENDING ON THE AMOUNT OF
MIXING. IF SNOW LEVELS REMAINED AT VALLEY FLOORS SEVERAL INCHES
ARE POSSIBLE. IF SNOW LEVELS RISE TO 5000 FEET OR SO...ACCUMULATIONS
WOULD BE LIGHT. BRONG

LONG TERM...SUNDAY THROUGH WEDNESDAY...
UPPER LEVEL TROUGH WILL BE OVER THE GREAT BASIN ON SUNDAY...WITH 
SOME LINGERING LIGHT SNOW SHOWERS FROM INSTABILITY ALOFT. SNOW 
LEVELS SHOULD BE DOWN TO PRETTY MUCH ALL VALLEY FLOORS...WITH 
SHOWERS TAPERING OFF THROUGH THE DAY SUNDAY AS THE TROUGH DEPARTS TO 
THE EAST. 

RIDGE IS EXPECTED TO BUILD INTO THE WESTERN STATES FOR NEXT 
WEEK...ALTHOUGH NOT STRONG THIS WILL MOVE THE JET STREAM INTO THE 
PAC NW. WE WILL SEE SOME WARMER TEMPERATURES ALOFT AS WELL...SNOW 
LEVELS COMING UP BY TUESDAY. A FEW WEAKER SYSTEMS WILL PASS TO THE 
NORTH OF THE AREA INTO WA/OR...WITH THE NORTHERN HALF OF THE 
FORECAST AREA HAVING A CHANCE TO GET GRAZED BY A PASSING STORM. KEPT 
A CHANCE FOR LIGHT RAIN/SNOW FOR AREAS NORTH OF RENO-TAHOE THROUGH 
WEDNESDAY.  HOON

AVIATION...
PATCHY FREEZING FOG EXPECTED TO DEVELOP AGAIN IN THE VALLEYS
EARLY THURSDAY MORNING...INCLUDING KRNO...KLOL...KTRK. MID AND
HIGH CLOUDS EXPECTED TO ROLL IN LATE TONIGHT...WHICH COULD LIMIT
FREEZING FOG DEVELOPMENT TO ONLY THE COLDEST VALLEYS. BEST CHANCE
WILL BE VIS BELOW 1SM...WITH LESS THAN 25 PERCENT CHANCE OF LIFR
1/4SM AT KRNO...KLOL...KTRK. HOON

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...FREEZING FOG ADVISORY UNTIL 10 AM PST THURSDAY FOR NVZ001-004.

CA...NONE.
&&

$$

HTTP://WEATHER.GOV/RENO