FXUS65 KREV 150003
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
403 PM PST MON DEC 14 2009

.UPDATE...
TIMING OF ALL FREEZING FOG ADVISORIES WAS MOVED UP AND WILL BEGIN
IMMEDIATELY RATHER THAN 6 PM THIS EVENING. NO OTHER CHANGES. RC

&&

.PREVIOUS DISCUSSION... /ISSUED 239 PM PST MON DEC 14 2009/ 

SHORT TERM...THE PRIMARY CONCERN FOR THE IMMEDIATE SHORT TERM WILL 
BE AREAS OF FREEZING FOG THAT WILL SETTLE INTO WESTERN NEVADA VALLEY 
AREAS TONIGHT. THE FOG WAS SLOW TO LIFT MONDAY AND WILL SETTLE RIGHT 
BACK IN AFTER SUNSET AS WINDS WILL WINDS REMAIN LIGHT THROUGH THE 
EVENING. STRONGER WINDS ALOFT IN MOST OF EASTERN CALIFORNIA WILL 
KEEP THE AIR MIXED TONIGHT AND PREVENT ANY FOG FORMATION. 

A WARM FRONTAL SYSTEM IS APPROACHING THE WEST COAST AND WILL BRING 
CHANCES OF PRECIPITATION AND AT THE VERY LEAST CONSIDERABLE MOISTURE 
TO THE REGION. THE FRONT IS PULLING FROM A DECENT MOISTURE TAP IN 
THE PACIFIC WHICH WILL PUSH MID AND UPPER LEVEL MOISTURE IN FROM THE 
WEST UP TO THE SIERRA CREST BY TUESDAY MORNING. MODELS AGREE THAT 
THERE ISN'T MUCH DYNAMIC SUPPORT REGARDING MUCH PRECIPITATION MAKING 
IT OVER THE CREST...WITH THE EXCEPTION BEING NORTHERN LASSEN AND 
MODOC COUNTIES. AREAS NORTHWEST OF TRUCKEE HAVE THE BEST CHANCE AT 
SEEING PRECIPITATION THROUGH WEDNESDAY MORNING. PW VALUES DO NOT GET 
ABOVE A HALF INCH THROUGH THE WHOLE EVENT MEANING WHAT DOES FALL 
WILL BE LESS THAN THE PREVIOUS STORMS IN THE AREA. SNOW LEVELS WILL 
BE A BIT SQUIRRELY AS THE ASSOCIATED WARM FRONT PASSES THROUGH. DID 
NOT HAVE MUCH CONFIDENCE IN THICKNESS OR H700 SNOW LEVEL PROGS SO 
TRENDED ALONG WITH THE NAM BUFR SOUNDINGS. NORTHERN LASSEN...EASTERN 
MODOC AND NORTHERN WASHOE SNOW LEVELS WILL BE AROUND 4500 FEET AND 
ARE MOST LIKELY TO SEE SNOW OUT OF THIS SYSTEM. BROUGHT SNOW LEVELS 
UP 1000 FEET ACROSS THE BOARD BY WEDNESDAY MORNING.

WINDS REMAIN UNIMPRESSIVE WITH THE FRONTAL PASSAGE AS THE ASSOCIATED 
JET REMAINS WELL TO OUR NORTH. HOWEVER...GUSTY WINDS WILL INTRODUCE 
A WARMING TREND THROUGH THE WEEK. MINIMUM TEMPERATURES WILL RISE 3 
OR 4 DEGREES FROM LAST NIGHT DUE TO THE CLOUD COVER MOVING IN THIS 
EVENING. THE WARMING TREND WILL CONTINUE UNTIL THURSDAY WHEN THE LOW 
AND MID LEVEL MOISTURE MOVE OFF TO THE EAST. - LABELLE - 

LONG TERM...FRIDAY THROUGH MONDAY...
WEAK SHORTWAVE RIDGING OVER THE AREA FRIDAY AND SATURDAY WILL KEEP A 
MOISTURE STREAM AND POPS JUST ALONG THE NORTHERN TIER OF THE CWA. 
HAVE KEPT SLIGHT CHANCE POPS THROUGH LASSEN COUNTY AND EXTREME 
NORTHERN WASHOE COUNTY WITH THE MOISTURE TAP RIGHT ALONG THE BORDER. 

CONFIDENCE BECOMES LOW SUNDAY AND MONDAY AS THE ECMWF BUILDS A RIDGE 
OVER THE AREA AND KEEPS THE STORM TRACK JUST TO THE NORTH OF THE CWA 
AND THE GFS BREAKS DOWN THE RIDGE AND BRINGS A TROUGH INTO THE 
REGION. TAKING AN ENSEMBLE APPROACH...HAVE SLIGHTLY INCREASED POPS 
THROUGH THE SIERRA AND LOWERED TEMPERATURES FROM PREVIOUS FORECAST. 
HOWEVER...IF WE DO END UP WITH A RIDGE OVER US...IT WILL BE DRIER 
AND AN INVERSION WILL BE IN PLACE. THIS WILL KEEP VALLEY 
TEMPERATURES DOWN WITH MID SLOPES SIGNIFICANTLY WARMER. IN 
ADDITION...IF THIS SOLUTION COMES TRUE...WITH ALL THE LOW LEVEL 
MOISTURE IN PLACE AND AN INVERSION... POOR AIR QUALITY AND AREAS OF 
FOG MAY OCCUR THROUGHOUT THE WEEKEND. DF

AVIATION...
AREAS OF FOG CONTINUE THROUGH THE RENO METRO AREA AND ACROSS 
PORTIONS OF CHURCHILL...PERSHING...AND NORTHERN WASHOE COUNTIES. 
CLOUDS WILL BE INCREASING AND LOWERING OVERNIGHT WITH THE APPROACH 
OF THE NEXT SYSTEM WITH PRECIPITATION STARTING THROUGH NRN CA AND 
NRN NV TOMORROW MORNING. 

FOR KRNO...THE WIDESPREAD FOG HAS BEGUN TO BREAK UP THIS AFTERNOON 
AND VISIBILITY WILL BE ABOUT A MILE WITH 200-400 FT CIGS THROUGH 02Z 
THIS EVENING. AM CONFIDENT THAT THE DENSE FOG WILL RETURN AGAIN 
TONIGHT WITH A 70 PERCENT CHANCE THE AIRPORT WILL BE BELOW LANDING 
MINIMUMS BY 07Z. THE FOG WILL NOT LAST AS LONG AS IT HAD THIS 
MORNING AND WILL LIKELY START TO DISSIPATE AROUND 18Z TUESDAY 
MORNING.  

FOR KTVL AND KTRK...PATCHY FOG IS POSSIBLE IN THE VICINITY OF THE 
AIRPORTS...BUT CONDITIONS WILL LIKELY STAY VFR DUE TO THE INCREASING 
CLOUDS. THERE IS A 50 PERCENT CHANCE OF LIGHT SNOW BY TUESDAY 
AFTERNOON IN BOTH LOCATIONS.

FOR KLOL...DENSE FOG WILL REMAIN OVERNIGHT WITH THE AIRPORT STAYING 
BELOW LANDING MINIMUMS. DF

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...FREEZING FOG ADVISORY UNTIL 6 AM PST TUESDAY FOR NVZ003-004.

CA...FREEZING FOG ADVISORY UNTIL 6 AM PST TUESDAY FOR CAZ071.

&&

$$

HTTP://WEATHER.GOV/RENO