Drought in California, February 1 to 28, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
212 PM PST SAT JAN 31 2009

.SHORT TERM...
NORTHWEST FLOW ALOFT INCREASES TONIGHT AS A TROUGH DIGS INTO THE
GREAT PLAINS AND A RIDGE BUILDS ALONG 130W. SURFACE HIGH SETTLES
BACK INTO THE EASTERN GREAT BASIN AND MAINTAINS A MODERATE TO
STRONG EAST-NORTHEAST WIND OVER THE RIDGES THROUGH SUNDAY
NIGHT/MONDAY MORNING. TEMPERATURES WILL DROP OFF A FEW DEGREES ON
SUNDAY...BUT REMAIN ABOVE NORMAL.

WINDS DECREASE MONDAY AS THE PACIFIC RIDGE MOVES OVERHEAD AND THE
SURFACE GRADIENTS RELAX. TEMPERATURES WILL INCREASE...BUT WARMING
MAY BE LIMITED IN THE NEVADA VALLEYS WITH SURFACE INVERSIONS.
HIGHS MOST AREAS SHOULD EASILY REACH 50 DEGREES.

A SYSTEM CURRENTLY SOUTH OF ALEUTIANS WILL SPLIT...WITH THE
SOUTHERN PIECE DEVELOPING INTO A CUT OF LOW. THIS LOW WILL
APPROACH THE CALIFORNIA COAST TUESDAY. THE FLOW ALOFT WILL TURN TO
THE SOUTH AND BRING ADDITIONAL WARM AIR INTO THE REGION. HIGHS WILL
BE IN THE 50S... WITH LOW 60S POSSIBLE. BRONG

.LONG TERM...WEDNESDAY THROUGH SATURDAY...

WETTER PATTERN TO RETURN TO THE AREA NEAR THE MIDDLE OF NEXT WEEK.
THE MODELS ARE CONSISTENT WITH A CENTRAL PAC TROUGH MOVING EAST AND
BECOMING A CLOSED LOW OFF THE WEST COAST BY WEDNESDAY AND AN
UPSTREAM TROUGH OVER THE GULF OF ALASKA THAT WILL HAVE SOME
INFLUENCE ON THE CUT OFF LOW. AMSU PW VALUES AHEAD OF THE CENTRAL
PAC TROUGH ARE OVER ONE INCH AND MUCH OF THE MOISTURE SHOULD AT
LEAST MAKE ITS WAY TOWARD THE SIERRA BY MID WEEK. HOWEVER...THERE
ARE STILL MODEL DIFFERENCES WITH RESPECT TO HOW MUCH INFLUENCE THIS
UPSTREAM TROUGH WITH HAVE AS WE GET INTO LATE THURSDAY AND FRIDAY.
THE EUROPEAN AND CANADIAN DROP THE TROUGH FURTHER SOUTH AND PUSH THE
FIRST CUT OFF THROUGH THE AREA ON THURSDAY WITH ANOTHER LOW TAKING
SHAPE ALONG THE COAST. THE GFS KEEPS THE TROUGH SLIGHTLY FURTHER
NORTH AND ONLY ALLOWS A WEAKER SHORT WAVE TO PASS OVER THE AREA ON
THURSDAY AND IS ALSO ABOUT 6 HOURS SLOWER THAN THE EURO/CANADIAN.
ENSEMBLES ARE STILL SHOWING VARIABILITY WITH SPEED OF CUT OFF
THROUGH THURSDAY AND SCENARIO INTO THE WEEKEND. HOWEVER ALL MODELS
STILL POINT TO A DECENT SLUG OF MOISTURE MOVING INTO THE SIERRA
DURING THIS TIME PERIOD...WITH LESSER PRECIPITATION FURTHER EAST
INTO NV. MODELS INDICATE AROUND 0.75 OR MORE INCH OF LIQUID
PRECIPITATION IN THE SIERRA FROM THURSDAY THROUGH FRIDAY
MORNING...WITH PRECIP TAPERING TO ONLY A FEW HUNDREDTHS INTO THE NV
BASIN AND RANGE. THIS LOOKS GOOD AS SPILLOVER SHOULD HOLD OFF INTO
WRN NV UNTIL THURSDAY EVENING INTO FRIDAY MORNING...DEPENDING ON
TIMING OF THE FIRST WAVE.

SNOW LEVELS WILL BE FAIRLY HIGH INITIALLY AS WARM SOUTHWEST FLOW
PRECEDES THE LOW AND WILL GRADUALLY LOWER THROUGH FRIDAY. THEY
WILL START OUT ABOVE 8000 FEET ON WEDNESDAY NIGHT AND GRADUALLY
LOWER TO 5000-5500 FEET BY FRIDAY AS COOLER AIR FILTERS DOWN.
SOUTHWEST WINDS WILL PICK UP ESPECIALLY IN THE HIGHER ELEVATIONS
WEDNESDAY AND THURSDAY AS 700 MB FLOW INCREASES TO 25-30 KTS.

BEYOND THURSDAY A POSITIVE TILT TROUGH REMAINS ALONG THE WEST COAST
AND OVER CA/NV WITH CONTINUED UNSETTLED WEATHER. QPF AMOUNTS ARE
UNCERTAIN...BUT MORE SPILLOVER SHOULD BE OCCURRING AS SHOWERS INTO
NV ON FRIDAY AS INSTABILITY INCREASES IN DEFORMATION AXIS OVER THE
AREA. THE TROUGH WILL GRADUALLY SLIDE SOUTH THROUGH THE WEEKEND WITH
DRIER AIR MOVING INTO AT LEAST THE NRN HALF OF THE CWA BY SATURDAY
NIGHT. SNOW LEVELS DO NOT LOOK TO DROP MUCH BELOW 5500 FEET THROUGH
THE EVENT. TEMPERATURES IN THE UPPER 50S ON WEDNESDAY WILL DROP BACK
DOWN TO NEAR NORMAL VALUES IN THE UPPER 30S TO MID 40S BY FRIDAY AS
COOLER AIR MOVES IN AND SHOWERS CONTINUE. GMCGUIRE
&&

.AVIATION...

VFR THRU SUN. ONLY EXCEPTION WILL BE KTRK...WHERE PERIODIC IFR
CIGS/VSBYS EXPECTED EARLY SUNDAY MORNING THROUGH ABOUT 15Z. GMCGUIRE
&&

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

HTTP://WEATHER.GOV/RENO