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AREA FORECAST DISCUSSION

 
 FXUS65 KREV 241127
 AFDREV
 
 AREA FORECAST DISCUSSION
 NATIONAL WEATHER SERVICE RENO NV
 327 AM PST TUE NOV 24 2009
 
 .SHORT TERM...
 LOW PRESSURE OVER THE GULF OF ALASKA IS BRINGING RISING HEIGHTS
 OVER THE WEST COAST WITH GRADUALLY WARMING TEMPS ALOFT. AT THE
 SAME TIME...SURFACE HIGH PRESSURE OVER THE INTERMOUNTAIN WEST WILL
 CONTINUE TO BRING NELY LOW LEVEL FLOW PREVENTING SURFACE TEMPS
 FROM WARMING MUCH. MAIN FORECAST CONCERN THROUGH WEDNESDAY IS
 TRICKY TEMPERATURE FORECAST WITH SOME VALLEYS MIXING OUT TO THEIR
 FULL POTENTIAL WHILE LOWER VALLEYS STAY UNDER INVERSIONS. NELY
 WINDS WILL ALSO BE BREEZY AT TIMES OVER HIGH SIERRA RIDGES...
 ESPECIALLY AT NIGHT WHEN DIURNAL EFFECTS TIGHTEN LOW LEVEL
 GRADIENTS. 
 
 THE GULF OF ALASKA LOW SHIFTS TOWARD THE PAC NW COAST THURSDAY
 SHIFTING THE RIDGE AXIS EAST AND ALLOWING FOR INCREASED SWLY FLOW
 ALOFT. THE MAIN FRONTAL BOUNDARY ASSOCIATED WITH THE LOW IS STILL
 OFF THE COAST THURSDAY AFTERNOON...HOWEVER AN INITIAL SURFACE
 FRONT MOVES ACROSS NRN CA TO THE WRN NV BORDER. H7 WINDS INCREASE
 TO NEAR 40 KTS BY 00Z THURSDAY AFTERNOON HOWEVER SOME MODEL RUNS
 ARE A LITTLE SLOWER AND DON`T HAVE A SIGNIFICANT INCREASE IN WINDS
 ALOFT UNTIL THURSDAY EVENING. THIS IS IMPORTANT IN FORECASTING
 HIGH TEMPS THURSDAY AS ALL VALLEYS SHOULD MIX OUT ONCE THE H7
 WINDS REACH 30 KTS. GOING WITH THE FASTER SOLUTION MIXING OUT ANY
 INVERSIONS THURSDAY AFTERNOON WITH VALLEY HIGHS CLOSE TO 60
 DEGREES.
 
 THE MAIN FRONTAL BOUNDARY AND SHORTWAVE TROUGH QUICKLY MOVE OVER
 NRN CA THURSDAY NIGHT WITH A SHORT PERIOD OF PRECIP FORCING.
 LIMITED MOISTURE AND SHALLOW FORCING ALONG THE FRONT WILL HAVE A
 HARD TIME PRODUCING MUCH MORE THAN SHOWERS. THE SHOWERS SHOULD
 REMAIN NORTH AND WEST OF SUSANVILLE. JORDAN
 
 .LONG TERM...FRIDAY THROUGH MONDAY...
 
 TROUGH MOVING THROUGH THE AREA FRIDAY WILL BRING COOLER CONDITIONS 
 TO THE AREA FOR THE REST OF THE THANKSGIVING WEEKEND.  COLD FRONT 
 SHOULD BE OVER AREAS NORTH OF I-80 EARLY IN THE MORNING...WITH A 
 CHANCE OF SHOWERS FOR AREAS NORTH OF HIGHWAY 50.
 
 MAIN ISSUE FOR SATURDAY-MONDAY IS POSITION OF RIDGE FORECAST TO 
 REDEVELOP IN THE EASTERN PACIFIC IN RESPONSE TO SYSTEM ENTERING THE 
 GULF OF ALASKA.  LOCATION OF THE RIDGE WILL FACTOR IN ON THE TRACK 
 OF COLD CANADIAN AIR DROPPING SOUTH INTO THE GREAT BASIN OR THE  
 ROCKIES.  00Z ECMWF/CANADIAN AND A FEW GFS ENSEMBLE MEMBERS HAVE A 
 MORE WESTERLY TRACK...ALLOWING THE COLD AIR TO MOVE OVER WESTERN 
 NEVADA.  THE GFS AND MOST OF ITS ENSEMBLE MEMBERS ARE MUCH FARTHER 
 EAST...WITH THE COLDEST AIR OVER THE UTAH AND THE ROCKIES.  
 
 BOTH SOLUTIONS WOULD BRING A COLD NORTH-NORTHEAST SURFACE 
 FLOW AND DROP TEMPERATURES BELOW NORMAL.  IF THE ECMWF/CANADIAN 
 VERIFY HIGHS SATURDAY-SUNDAY MAY STRUGGLE TO REACH 40 DEGREES FOR 
 MOST LOCATIONS...WITH A CHANCE OF SNOW SHOWERS. HAVE TRENDED THE 
 FORECAST COOLER AND ADDED A SLIGHT CHANCE OF SHOWERS FOR SATURDAY TO 
 ACCOUNT FOR THE MORE RELIABLE ECMWF.
 
 BY MONDAY CONFIDENCE IN THE FORECAST IS LOW...WITH LARGE ENSEMBLE 
 SPREADS DUE TO THE HIGH AMPLITUDE PATTERN THAT DEVELOPS ACROSS THE 
 PACIFIC.  MODELS SEEM TO AGREE THAT RIDGE SHOULD BE OVER THE WEST 
 FOR DRY CONDITIONS...BUT THE COOL NORTH FLOW WOULD REMAIN.  BRONG
 
 &&
 
 .AVIATION...
 
 HIGH PRESSURE OVER THE WEST THROUGH THANKSGIVING...WITH LIGHT WINDS 
 AND DRY CONDITIONS. FOG POSSIBLE AT TRUCKEE NEXT FEW LIGHTS...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 INTO 
 FRIDAY...SHOULD BRING AN INCREASE IN WINDS A CHANCE FOR RAIN/SNOW 
 SHOWERS NORTH OF KTVL-KRNO-KNFL. BRONG
 
 &&
 
 
 .REV WATCHES/WARNINGS/ADVISORIES...
 NV...NONE.
 CA...NONE.
 &&
 
 

 
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