FXUS65 KREV 251133
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
333 AM PST WED NOV 25 2009

.SHORT TERM...
LOW PRESSURE OVER THE GULF OF ALASKA IS CURRENTLY AMPLIFYING THE
WEST COAST RIDGE. A VERY WEAK DISTURBANCE CAN BE SEEN ON MODIS
WATER VAPOR IMAGERY DROPPING SOUTH OVER CENTRAL CA. THIS
DISTURBANCE IS DOING VERY LITTLE BESIDES REINFORCING NORTHEAST
FLOW ALOFT OVER THE SIERRA RIDGES. RIDGE GUSTS TO 50 MPH OVERNIGHT
HAVE DECREASED SLIGHTLY IN THE LAST HOUR AND SHOULD CONTINUE TO
DROP THIS MORNING AS H7 WINDS DECREASE. THE NELY LOW LEVEL FLOW
WILL ONCE AGAIN PROMOTE INVERSIONS OVER VALLEY LOCATIONS WITH
ABOVE NORMAL TEMPS FOR MOUNTAIN LOCATIONS.

THE GULF OF ALASKA LOW SHIFTS CLOSER TO THE WEST COAST THURSDAY
PUSHING THE RIDGE AXIS EAST OF THE REGION. THIS WILL ALLOW FOR
INCREASING SOUTHWEST FLOW ALOFT HOWEVER LATEST MODEL RUNS ARE
SLOWER WITH THIS INCREASE. EVEN THOUGH SOUTHWEST FLOW MAY NOT
INCREASE FAST ENOUGH TO MIX ALL VALLEYS OUT THURSDAY...THE
SUBSIDENCE INVERSION SHOULD LOWER ENOUGH TO BRING WARMER AIR ALOFT
TO THE SURFACE.

THE LOW SWINGS A WEAK SHORTWAVE ACROSS NRN CALIFORNIA THURSDAY
NIGHT WITH AN ASSOCIATED SURFACE COLD FRONT SETTLING INTO THE
REGION FRIDAY. WINDS WILL NOT BE OVERLY STRONG WITH THE NOCTURNAL
FRONTAL PASSAGE...HOWEVER RIDGES AND WIND PRONE AREAS WILL SEE
BREEZY CONDITIONS OVERNIGHT THURSDAY. THERE IS ENOUGH SHALLOW
FORCING ALONG THE FRONT TO TRIGGER AT LEAST SOME LIGHT SHOWERS
NORTH OF LAKE TAHOE. MODELS DIFFER ON QPF WITH THE EURO AND NAM
HOLDING THE UPPER WAVE TOGETHER LONGER WITH HIGHER PRECIP
AMOUNTS...WHILE THE GFS IS FASTER AND WEAKER. CURRENTLY STICKING
WITH THE SHOWERY GFS SOLUTION ALTHOUGH POPS MAY NEED TO BE RAISED
IF THE ORGANIZED PRECIP BAND OF THE OTHER MODELS BECOMES THE
FAVORED SOLUTION. THE TROUGH QUICKLY EXITS THE AREA FRIDAY NIGHT
WITH SIGNIFICANT CLEARING AND GOOD RADIATIONAL COOLING MAKING FOR
A CHILLY NIGHT. JORDAN

.LONG TERM...SATURDAY THROUGH TUESDAY...

MODEL CONTINUE TO HAVE DIFFERING SOLUTIONS ON EVOLUTION OF SYSTEM 
PASSING THROUGH THE AREA FRIDAY AND HOW QUICKLY THE SYSTEM EXITS THE 
AREA SATURDAY.  THIS IS LARGELY IN RESPONSE TO MODELS EJECTING 
ENERGY FROM DEEP LOW OVER THE ALEUTIAN ISLANDS/BERING SEA.  SMALL 
DIFFERENCES NEAR THE PARENT LOW ARE MAGNIFIED INTO THE LARGER 
DIFFERENCES IN THE DOWNSTREAM HIGH AMPLITUDE PATTERN OVER WESTERN 
NORTH AMERICA.  WILL CONTINUE TO FOLLOW THE ECMWF WHICH HAS BEEN 
MORE CONSISTENT WITH RIDGE POSITION AND AMPLITUDE NEAR 130W EARLY IN 
THE PERIOD.  

ECMWF AND SEVERAL GFS ENSEMBLE MEMBERS HAVE A SLOWER TRACK WITH 
FRIDAY/S SYSTEM AND KEEPING IT OVER THE AREA THROUGH SATURDAY 
MORNING.  THIS KEEPS THE COLDER AIR OVER THE AREA WITH SOME 
LINGERING MOISTURE FOR A COLD DAY WITH A LOW CHANCE OF LIGHT SNOW 
SHOWERS.

BY SUNDAY THE RIDGE SHOULD START TO BUILD OVER THE WEST COAST...AS 
THERE IS NO BLOCKING TROUGH OVER EASTERN NORTH AMERICA AND SYSTEM 
MOVES INTO THE CANADIAN WEST COAST.  STILL THE LOW AND MID LEVEL 
FLOW IS FROM THE NORTH AND NORTHEAST...SO TEMPERATURES TO REMAIN 
IN THE 40S FOR THE NEVADA VALLEYS...WITH A FEW DEGREES WARMING IN 
THE SIERRA.

TEMPERATURES MAY MODERATE MONDAY AND TUESDAY WITH LIGHT 
WINDS...RIDGE MOVING OVERHEAD...AND STAGNANT VALLEY INVERSIONS.  
HIGHS IN THE SIERRA SHOULD BE WARMER OR CLOSE TO THE NEVADA VALLEYS. 
ENSEMBLE SPREAD REMAINS VERY HIGH...AS MODELS TRY TO DEAL WITH THE 
SYSTEM PASSING OVER THE RIDGE SUNDAY.  ECMWF RETROGRADES THE RIDGE 
BACK INTO THE PACIFIC...WHICH KEEPS THE AREA UNDER A COLD NORTH 
FLOW. GFS KEEPS THE RIDGE ALONG THE WEST COAST...BUT THIS GOES 
AGAINST MOST OF ITS ENSEMBLE MEMBERS...WHICH ARE CLOSER TO THE ECMWF 
SOLUTION. BRONG

&&

.AVIATION...

HIGH PRESSURE OVER THE WEST THROUGH THANKSGIVING...WITH LIGHT WINDS 
AND DRY CONDITIONS. FOG POSSIBLE AT TRUCKEE NEXT FEW NIGHTS...BUT 
DRY AIR MAY KEEP THE FOG SHALLOW. 

NO SIGNIFICANT IMPACTS FOR TRAVEL TO START OF THANKSGIVING WEEKEND. 
SYSTEM FORECAST TO MOVE INTO THE WEST COAST THURSDAY NIGHT AND 
THROUGH NEVADA FRIDAY AND FRIDAY NIGHT...SHOULD BRING AN INCREASE IN 
WINDS A CHANCE FOR SHOWERS. BRONG

&&

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

$$

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