FXUS65 KREV 012340
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
340 PM PST TUE DEC 1 2009

.SHORT TERM...
WEDNESDAY AND THURSDAY WILL FEATURE HIGHS AROUND SEASONAL NORMS WITH
NORTHERLY FLOW ALOFT HOLDING DOWN HIGHS/MIXING. MOST AREAS WILL
COME DOWN A FEW DEGREES FROM TUESDAY TO WEDNESDAY AS A REINFORCING
SURFACE HIGH BACKDOORS IN FROM THE NORTHEAST.

BY FRIDAY...AN UPPER LOW IS PROGGED BY MANY ENSEMBLES AND MODELS TO
BEGIN DIGGING SOUTH THROUGH WASHINGTON AND OREGON AND SWITCH WINDS
ALOFT TO WEST AND NORTHWEST. THIS IS EXPECTED TO BUMP UP FRIDAY'S
HIGHS AS THE FLOW ALOFT ALLOWS FOR BETTER MIXING. HOWEVER...THE
18Z RUNS OF THE GFS AND NAM ARE SLOWING DOWN THE PROGRESSION OF
THE UPPER LOW. THIS COULD HAVE THE EFFECT OF LIMITING MIXING AND KEEPING
COOLER HIGHS OVER THE REGION FOR FRIDAY THAN WE HAVE CURRENTLY
FORECAST (THE GFS ENSEMBLE TEMP GUIDANCE HAS A RANGE OF 45 TO 55
FOR RENO'S HIGHS FRIDAY). IT WOULD ALSO MEAN COLDER LOWS FRIDAY
NIGHT NORTH OF PYRAMID LAKE AS I AM CURRENTLY PINNING ON A STRONG
COLD FRONT APPROACHING WITH THE UPPER LOW TO KEEP LOWS UP. WITH
VERY DRY AIR EXPECTED TO BE IN PLACE FRIDAY...A SLOWER COLD FRONT
WOULD CERTAINLY MEAN MORE DECOUPLING/COLDER TEMPS ACROSS THE
NORTHERN CWA FRIDAY NIGHT. SNYDER

.LONG TERM...SATURDAY THROUGH TUESDAY...
MEDIUM RANGE MODELS ARE GRADUALLY COMING INTO BETTER AGREEMENT IN 
THE HANDLING OF THE LONG TERM...HOWEVER MUCH UNCERTAINTY STILL 
EXISTS BEYOND THIS WEEKEND. A VERY COLD UPPER LOW DIGS SOUTH OUT OF 
WRN CANADA SATURDAY WITH A REINFORCING SHOT OF ENERGY DROPPING INTO 
THE LOW SUNDAY. THE LAST FEW GFS RUNS HAVE BEEN STEADY WITH HOW FAR 
WEST THE COLD CORE TRACKS AND THE 12Z EURO FINALLY JOINED THE GFS 
SOLUTION...WHICH SEEMS TO BE A MORE LIKELY SCENARIO WITH 
RETROGRADING HIGHS THIS TIME OF YEAR. A STRONG AND DRY COLD FRONT 
SLOWLY SAGS OVER NRN NEVADA SATURDAY MORNING WITH TEMPERATURES 
DROPPING 10-15 DEGREES BELOW NORMAL BY SUNDAY. ALTHOUGH THE INITIAL 
FRONT SEEMS DRY...SHALLOW INSTABILITY UNDER THE COLD CORE AND 
DEFORMATION SOUTH OF THE LOW SHOULD GENERATE FAIRLY STEADY LIGHT 
SNOW LATE SATURDAY THROUGH SUNDAY. THE MOST FAVORABLE LOCATION FOR 
THIS SNOW BAND WILL BE OVER THE CENTRAL SIERRA AND WRN NEVADA. THIS 
INITIAL PUSH SHOULD BRING ACCUMULATING SNOW TO THE AREA BUT NOTHING 
TOO SIGNIFICANT.

THE UNCERTAINTY REALLY BEGINS STARTING MONDAY. MODELS GENERALLY 
AGREE ON THE LOW ONLY SLOWLY SHIFTING EAST OF THE AREA 
MONDAY...HOWEVER THE QUESTION THAT REMAINS IS IF SUBTROPICAL 
MOISTURE GETS ENTRAINED INTO THE LOW AND REALLY BOOSTS QPF AMOUNTS 
OVER THE REGION. THE UNCERTAINTY REALLY STEMS ON HOW FAST THE GULF 
OF ALASKA HIGH CENTER RETROGRADES NORTHWEST OVER ALASKA. A FASTER 
RETROGRESSION WILL ALLOW ABUNDANT MOISTURE IN THE PACIFIC TO CREEP 
NORTH TO THE WEST COAST AS EARLY AS MONDAY...WHILE A SLOWER SOLUTION 
KEEPS THE UNDERCUTTING MOISTURE SOUTH OF THE REGION UNTIL THE MIDDLE 
OF NEXT WEEK. CONVECTIVE ACTIVITY OVER THE WRN PACIFIC ASSOCIATED 
WITH THE ACTIVE MJO INDICATES GOOD POTENTIAL FOR A SIGNIFICANT 
PRECIP EVENT OVER THE WEST COAST...BUT AGAIN THE UNCERTAINTY IS IN 
THE TIMING. ANALYZING CURRENT SATELLITE IMAGERY OVER THE PACIFIC AND 
CONSIDERING THE TYPICAL EVOLUTION OF THESE UNDERCUTTING 
SCENARIOS...THINK THAT A SLOWER SOLUTION IS MORE FITTING AND THE 
MOST SIGNIFICANT PRECIP SHOULD HOLD OFF UNTIL BEYOND THE FORECAST 
PERIOD. ALTHOUGH TYPHOON NIDA HAS DISPERSED BITS OF MOISTURE AND 
ENERGY INTO THE FLOW OVER THE LAST FEW DAYS...THE BULK OF THE ENERGY 
IS STILL EAST OF 150E WHICH MEANS IT WILL TAKE ROUGHLY 7 DAYS TO 
REACH THE WEST COAST.

SO FOR THE FORECAST...KEPT WITH MODEST POPS MAINLY SOUTH OF 
INTERSTATE 80 THROUGH MONDAY NIGHT. THERE DOES APPEAR TO BE A BRIEF 
BREAK SOMETIME AROUND TUESDAY BEFORE THE BIGGER SURGE OF MOISTURE 
REACHES THE REGION IN THE MIDDLE OF NEXT WEEK.  TIMING THIS 
SHORTWAVE BREAK 7 DAYS IN ADVANCE IN THIS UNCERTAIN PATTERN IS 
HIGHLY UNLIKELY...SO KEPT AT LEAST SLIGHT CHANCE POPS EVERYWHERE AS 
PRECIP REALLY CAN'T BE RULED OUT. FEEL THAT THE DETAILS OF THIS 
SIGNIFICANT PATTERN CHANGE SHOULD BECOME MORE CLEAR BY THE END OF 
THE WEEK. JORDAN
&&

.AVIATION...
HIGH PRESSURE OVER THE WEST COAST WILL CONTINUE TO BRING VFR 
CONDITIONS AND LIGHT WINDS. SHALLOW FOG WILL LIKELY GENERATE ONCE 
AGAIN OVER COLD SIERRA LAKES MAINLY IN MONO COUNTY. MOST WIDESPREAD 
FOG WILL BE OVER MONO LAKE IF IT FORMS AND TIMING WOULD BE ROUGHLY 
10Z-18Z...SIMILAR TO PREVIOUS NIGHTS. FOR KTRK AND TVL...EAST FLOW 
ALOFT WILL LIKELY PREVENT FOG FORMATION THERE SO KEEPING IT OUT OF 
THE TAFS. JORDAN
&&

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

$$

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