000
FXUS65 KREV 271128
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
328 AM PST MON DEC 27 2010
.SHORT TERM...
GRID CHANGES TO TWEAK PRECIP TIMING TUESDAY AND WEDNESDAY AND
ADJUST SNOW LEVELS...OTHERWISE NO SIGNIFICANT GRID CHANGES. DIRTY
RIDGE TO BUILD IN TODAY FOR NEAR AVERAGE TEMPS MONDAY AND TUESDAY
BEFORE MORE FUN ARRIVES FOR TUESDAY NIGHT AND WEDNESDAY WITH A
POTENT SHORT WAVE.
BEFORE THE MAIN FORCING AND MOISTURE TAP AFFECT THE REGION...A
PERIOD OF WARM AIR ADVECTION WILL AFFECT THE NORTHERN HALF OF THE
CWA LATE MONDAY NIGHT AND TUESDAY MORNING. EXPECT JUST SOME LIGHT
PRECIP IN THE NORTHERN SIERRA AND NORTH OF INTERSTATE 80 IN THE
BASIN.
TURNING TO THE MAIN EVENT...THE PWAT PLUME EXPECTED TO ARRIVE
TUESDAY EVENING HAS CURRENTLY MOVED NORTH OF 30 JUST EAST OF 150W
LONGITUDE. THIS IS IN AN EXCELLENT POSITION TO BE SCOOPED UP BY
THE UPPER LOW (CURRENTLY AT 40N/160W) PROGGED TO MOVE LATITUDINALLY
ALONG 40 DEGREES LATITUDE AND IMPACT THE NORTHERN CALIFORNIA COAST
LATE TUESDAY NIGHT. THE MOISTURE PLUME IS CURRENTLY SPORTING PWATS
OF 1.5 TO 1.75 INCHES WHICH WILL REDUCE TO AROUND 1.2 INCHES ONCE
IT ARRIVES AT THE CENTRAL AND NORTHERN CALIFORNIA COAST TUESDAY
NIGHT. THIS IS STILL A DECENT DEEP MOISTURE PLUME WHICH WHEN
COMBINED WITH WESTERLY WINDS OF 40-55 KTS AT 700 MB SHOULD ENSURE
SPILLOVER INTO WESTERN NEVADA.
QPF FOR TUESDAY NIGHT IS A BIT VARIABLE AND DEPENDS ON THE
ORGANIZATION OF THE LOW. HOWEVER...MODELS HAVE DECENTLY SIMILAR
NUMBERS WITH 12 HR PRECIP AMOUNTS OF 1 TO 1.5 INCHES NEAR THE
SIERRA CREST TO AROUND 0.25 TO 0.5 INCHES FOR WESTERN NEVADA. SNOW
LEVELS HAVE BEEN RAISED A BIT FOR TUESDAY NIGHT WITH THE EXPECTED
WITH THE SUBTROPICAL PLUME...HOWEVER THEY SHOULD NOT STAY UP FOR
TOO LONG AS A STRONG COLD FRONT ASSOCIATED WITH A NORTHERN BRANCH
LOW PUSHES THE PLUME SOUTH OF THE REGION EARLY WEDNESDAY. WINTER
STORM WATCHES WILL BE ISSUED WITH THE PACKAGE GIVEN THE HEAVY
SNOW EXPECTED TUESDAY NIGHT AND WEDNESDAY MORNING IN THE SIERRA.
WEDNESDAY...VERY COLD AIR WILL DIVE INTO THE REGION WITH 700 MB
TEMPS FALLING TO -16C TO -18C WEDNESDAY AFTERNOON AND EVENING.
THIS WILL DRIVE SNOW LEVELS TO BELOW ALL VALLEY FLOORS.
HOWEVER...MOST OF THE PRECIP IS EXPECTED AHEAD AND ALONG THE COLD
FRONT SO SNOWFALL ACCUMULATION IN THE LOWER VALLEYS SHOULD BE
LIMITED TO A FEW INCHES. ONE THING TO WATCH OUT FOR WILL BE WINDS
AS MODELS DEVELOP A STRONG PRESSURE GRADIENT ALONG THE COLD FRONT.
WITH A PERIOD OF SNOW POSSIBLE AND WINDS BEING QUITE GUSTY THERE
COULD BE A BRIEF PERIOD OF WHITEOUT CONDITIONS FOR SOME LOWER
VALLEYS WEDNESDAY NEAR FROPA. SNYDER
.LONG TERM...THURSDAY THROUGH SUNDAY...
AGAIN MADE FEW CHANGES TO FCST AS IT IS IN GOOD SHAPE FOR THU/FRI
OVERALL DURING PERIOD OF HIGHER CONFIDENCE. SAT/SUN...NEW YEARS
WEEKEND...CONFIDENCE IS EXTREMELY LOW WITH ANY POTENTIAL CUT-OFF LOW
IMPACTING THE AREA. SINCE FCST IS MIDDLE OF THE ROAD AND ALLOWS
MAXIMUM FLEXIBILITY AT THIS POINT...NO NEED TO CHANGE ANYTHING HERE
EITHER.
THU...IT WILL BE COLD WITH H7 TEMPS OF -16 TO -20C ACROSS THE AREA
KEEPING HIGHS BELOW FREEZING ALL AREAS. ALSO...MOST MODELS KEEP -35
OR BLO AT H5 FOR ENOUGH INSTABILTY FOR SOME SCT SNOW SHOWERS. WITH A
WEAK SHEAR LOBE DROPPING SWD AND JET IN POTENTIALLY A FAVORABLE
POSITION PER EC...COULD HAVE A WEAK INSIDE SLIDER TYPE SCENARIO.
THIS WOULD RESULT IN A LITTLE MORE OGRANIZED PRECIP ALONG SIERRA
FRONT INTO MONO COUNTY. STILL...NOTHING TOO BIG TO HAPPEN AND
PERHAPS UP TO AN ADDITIONAL 2 INCHES IN THE LOW PROBABILTY IT DOES
MATERIALIZE.
THU NIGHT/FRI...CONTINUED VERY COLD WITH TEMPS 15-20 DEGS BELOW
NORMAL. DEPENDING ON HOW QUICKLY SKIES CLEAR...AND HOW MUCH SNOW
FALLS IN LOWER VALLEYS TEMPS COULD BE COLDER THAN CURRENTLY FCST.
EVEN SO...BELIEVE MOST SIERRA VALLEYS WILL BE BELOW ZERO AND COLDER
AREAS LIKE THE MARTIS VALLEY/BOGARD BUTTES/CRESTVIEW LIKELY TO BE 10
BELOW. HAVE JUST NUGED TEMPS DOWN A BIT MOST AREAS. CONTINUED COLD
AND BLO FREEZING FRIDAY DESPITE WARMING TEMPS ALOFT. ALL THIS WILL
DO IS STRENGTHEN VALLEY INVERSIONS WHILE MTNS WARM.
FOR THE WEEKEND...MODELS ALL OVER THE PLACE WITH CUT-OFF LOW.
GFS/GEM TAKE THE LOW ALMOST OVERHEAD WITH SOME SNOW FOR SIERRA AND
PERHAPS WRN NV. EC KEEPS THE LOW WELL OFFSHORE. WHILE THE EC IS A
BIT MORE OF AN OUTLIER...WOULD NOT BE SURPRISED TO SEE IT VERIFY AS
CUT-OFFS OFTEN DO STAY OFFSHORE. TIMING ALSO AN ISSUE AS IT IS SPLIT
BETWEEN A SAT OR SUN SYSTEM. LEFT ALONE THE CHC POPS ALONG SIERRA
CREST TO A SLC CHC A BIT FURTHER EAST AND DRY CNTRL NV. TEMPS ALSO
KEPT BLO NORMAL AS H7 TEMPS ONLY WARM TO -6C OR SO AND IF THE EC IS
RIGHT IT WILL BE QUITE COOL FOR THE VALLEYS WITH STRONG
INVERSIONS...ESPECIALLY IF THERE IS SNOW COVER. WALLMANN
&&
.AVIATION...
EXPECT SOME OCNL BKN CIGS FOR KTVL/KTRK THRU 20Z...AROUND 4K. STILL
VFR EXPECTED ALL TERMINALS THRU 15Z TUE. NEXT STORM ON TRACK WITH
SOME IFR CIGS/VIS KTVL/KTRK IN -RASN AND OCNL MVFR CIGS FOR KRNO WED
MORNING IN -RA. WALLMANN
&&
.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
AFTERNOON NVZ002.
CA...WINTER STORM WATCH FROM TUESDAY AFTERNOON THROUGH WEDNESDAY
AFTERNOON CAZ072-073.
&&
$$
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