Blizzard and Heavy Snow in California, January 27 to 28, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
330 PM PST SAT JAN 26 2008

.SHORT TERM...
DEEP CLOSED LOW PRESSURE CIRCULATION STILL LOCATED OFF THE WEST
COAST NEAR 32N 133W. THIS LOW WILL ONLY DRIFT EAST THROUGH THIS
EVENING BEFORE INCREASING IN FORWARD SPEED AS A MUCH COLDER LOW
DROPS SOUTH FROM THE GULF OF ALASKA AND ABSORBS THE SRN BRANCH
TONIGHT AND SUNDAY. VERY FEW SNOW SHOWERS AROUND TODAY...HOWEVER
THAT WILL CHANGE TONIGHT AS WARM ADVECTION INCREASES AHEAD OF LOW
AND MOISTURE SURGES NORTH ACROSS THE AREA. PRECIPITATION WILL MOVE
INTO MONO COUNTY LATER THIS EVENING...THEN SPREAD NORTH THROUGH
SUNDAY MORNING. SNOW LEVELS WILL BE TRICKY AS QUESTIONS STILL LINGER
AS TO HOW FAST THE WARM ADVECTION WILL WORK ITS MAGIC. SIERRA
LOCATIONS HAVE DRIED OUT CONSIDERABLY TODAY...WITH DEWPOINTS
DROPPING INTO THE TEENS AND SINGLE DIGITS IN MANY LOCATIONS IN THE
TAHOE BASIN AND MONO COUNTY. THEREFORE SNOW LEVELS MAY START OUT AT
VALLEY FLOORS ACROSS THE AREA FOR A SHORT PERIOD OF TIME BEFORE
LIFTING ABOVE 5000-5500 FEET DURING THE MORNING. VALLEY AREAS IN THE
SIERRA AND FAR WRN NV MAY SEE A RAIN/SNOW MIX OR EVEN A BRIEF PERIOD
OF SNOW BEFORE SNOW LEVELS LIFT. AMOUNTS DO NOT LOOK THAT IMPRESSIVE
BEFORE A CHANGEOVER TO RAIN IN WRN NV VALLEYS. HOWEVER FOOTHILLS
AND AREAS ABOVE 5000 FEET MAY PICK UP AN INCH OR TWO OF SNOW BY NOON
BEFORE MELTING. ROADS WILL STILL BE SLICK DURING THE MORNING.

SNOW WILL BE HEAVY AT TIMES IN SIERRA LOCATIONS STARTING LATE
TONIGHT AND CONTINUING STEADILY THROUGH SUNDAY MORNING WITH THE PUSH
OF WARM ADVECTION. SNOW WILL LIGHTEN UP FOR A PERIOD OF TIME AT
LOWER ELEVATIONS AND TAPER TO SHOWERS IN WRN NV SUNDAY AFTERNOON
BEFORE A STRONG ARCTIC COLD FRONT DROPS SOUTH ACROSS THE AREA.
HIGHER ELEVATIONS WILL NOT SEE ANY BREAKS IN SNOWFALL ON
SUNDAY...BUT MAY SEE PERIODS OF LIGHTER SNOW. EXACT TIMING OF THE
COLD FRONT MAY NEED TO BE TWEAKED IN THE NEXT 24 HOURS...HOWEVER
RIGHT NOW IT LOOKS LIKE IT WILL MOVE OVER ERN MODOC AND NRN WASHOE
COUNTIES BETWEEN 8P-10P SUNDAY...TAHOE AND RENO AREAS BY 3AM-6AM
MONDAY AND OVER MONO/MINERAL COUNTIES 10AM-NOON. ANOTHER SIGNIFICANT
SNOW BAND WILL LIKELY DEVELOP NEAR THE FRONT DUE TO STRONG
FRONTOGENESIS...INSTABILITY AND COLD AIR ALOFT. WITHIN THIS
BAND...SEVERAL INCHES OF SNOW MAY FALL IN A SHORT PERIOD OF TIME.
SNOW/BLOWING SNOW ADVISORIES OR WINTER STORM WARNINGS MAY BE NEEDED
FOR THE RENO AREA EASTWARD INTO PERSHING/CHURCHILL COUNTIES AND
POSSIBLY SOUTH INTO MINERAL COUNTIES FOR THE SUNDAY NIGHT/MONDAY
MORNING PERIOD...ESPECIALLY SINCE THE MONDAY MORNING COMMUTE WILL
LIKELY BE AFFECTED IN SOME AREAS. THE MIDNIGHT SHIFT CAN LOOK AT
THIS ONCE AMOUNTS ARE MORE CERTAIN. FOR NRN WASHOE COUNTY/ERN MODOC
COUNTY AMOUNTS ARE EXPECTED TO BE HIGHER WHEN COMBINING THE SNOW
BAND ALONG THE FRONT AND SNOW THAT IS EXPECTED TO FALL SUNDAY
AFTERNOON. THEREFORE A WINTER STORM WATCH WAS ISSUED FOR THESE
COUNTIES SINCE CONFIDENCE IS HIGHER.

ANOTHER CONCERN WILL BE THE WINDS. BREEZY CONDITIONS WITH GUSTS UP
TO 30 MPH TODAY WILL INCREASE ON SUNDAY. BREEZY TO WINDY CONDITIONS
ARE EXPECTED WITH GUSTS UP TO 40 AND POSSIBLY 45 MPH IN MANY
AREAS...ESPECIALLY DURING THE AFTERNOON. BREEZY WINDS WILL BE
COVERED IN THE WINTER STORM WARNINGS...HOWEVER AREAS IN NV WILL BE
ADDRESSED IN THE SPECIAL WEATHER STATEMENT. WIND PROFILES AND MODEL
SOUNDINGS DO NOT SUPPORT MUCH MORE WIND THAN GUSTS TO 45 MPH IN THE
WARM ADVECTION...THEREFORE A WIND ADVISORY WAS NOT ISSUED. A LAKE
WIND ADVISORY WAS ISSUED FOR PYRAMID LAKE AS WINDS WILL BE GUSTING
ABOVE 30 MPH MOST OF THE AFTERNOON AND EVENING. THE MID SHIFT CAN
REEVALUATE TONIGHT. ANOTHER WIND CONCERN WILL BE SUNDAY NIGHT INTO
MONDAY MORNING AHEAD OF THE COLD FRONT. STRONG THERMAL GRADIENT
ALONG THE FRONT MAY BE SUFFICIENT ENOUGH TO PRODUCE WIND GUSTS ABOVE
ADVISORY LEVEL...EVEN THOUGH IT DOES NOT LOOK LIKE A TRADITIONAL
HIGH WIND CASE. BELIEVE THESE STRONGER WINDS WOULD ONLY LAST A
COUPLE OF HOURS AS THE FRONT APPROACHES AND MOVES THROUGH...AND
THEREFORE NO WATCHES OR ADVISORIES HAVE BEEN ISSUED. MID SHIFT CAN
TAKE ANOTHER LOOK AT THIS AS WELL.

OTHERWISE THE HEAVIER PRECIPITATION WILL END AS THE FRONT MOVES
THROUGH...WITH LOOKS TO BE EARLY MONDAY MORNING OVER NRN ZONES...MID
MORNING OVER CENTRAL ZONES...AND LATE MORNING OVER SRN ZONES. PLENTY
OF COLD AIR ALOFT AND REMAINING MOISTURE WILL STILL ALLOW LIGHTER
SNOW SHOWERS TO LINGER THROUGH THE DAY ON MONDAY...THEN TAPER OFF
MONDAY NIGHT. MUCH COLDER AIR WILL FILTER OVER THE AREA WITH HIGHS
ON MONDAY ONLY REACHING THE LOW 30S IN WARMER LOCATIONS...AND LOWS
ON MONDAY NIGHT DIPPING INTO THE SINGLE DIGITS AND TEENS. A MORE
PROGRESSIVE PATTERN BEGINS ON TUESDAY AS A FAST MOVING JET STREAM
SETS UP OVER THE NORTH PACIFIC. ANOTHER SYSTEM APPROACHES WITH WARM
ADVECTION SPREADING SNOW OVER NRN ZONES TUESDAY MORNING...WITH SNOW
SPREADING SOUTH THROUGH THE DAY. SNOW WILL BE MORE SHOWERY IN WRN NV
WITH ONLY MODEST AMOUNTS. MCGUIRE

.LONG TERM...WEDNESDAY THROUGH SATURDAY...
PROGRESSIVE PATTERN CONTINUES INTO NEXT WEEKEND WITH SEVERAL
SHORTWAVES MOVING ACROSS THE REGION. NONE ARE EXPECTED TO BE VERY
STRONG OR CONTAIN AS MUCH MOISTURE AS THE STORM AFFECTING THE REGION
THIS WEEKEND...BUT WITH COLD AIR REMAINING IN PLACE THE POTENTIAL
FOR OCCASIONAL LIGHT SNOW ACCUMULATIONS IN THE LOWER VALLEYS...WITH
MODERATE AMOUNTS IN AND NEAR THE SIERRA...EXISTS WITH EACH SYSTEM.
THE 12Z ECMWF AND SEVERAL MEMBERS OF THE LATEST GFS ENSEMBLE DATA
SEEM IN BETTER AGREEMENT THAN THE 12Z GFS FOR TIMING THE SHORTWAVE
PASSAGES ESPECIALLY TOWARD NEXT WEEKEND. THIS FORECAST WILL TREND
MORE TOWARD THE ECMWF...ALTHOUGH WITH THIS AMOUNT OF UNCERTAINTY THE
CONFIDENCE IN THIS SOLUTION IS NOT VERY HIGH AT THIS TIME.

FOR WEDNESDAY...REGION WILL BE BACK IN A COOLER POST FRONTAL AIR
MASS WITH ISOLD-SCT SNOW SHOWERS MAINLY IN THE SIERRA. A SHORT BREAK
BETWEEN SYSTEMS WED NIGHT WITH POSSIBLE THINNING OF CLOUD DECK MAY
ALLOW TEMPS TO DROP SEVERAL MORE DEGREES TO THE TEENS OR SINGLE
DIGITS IN MOST AREAS.

BY THURSDAY...NEXT SYSTEM IS EXPECTED TO ARRIVE AS A SPLIT TROUGH BY
THE AFTERNOON IN THE NORTH ZONES AND THE TAHOE BASIN WITH A FEW
SHOWERS POSSIBLE AT TIMES IN PARTS OF WRN NV THRU MOST OF THURS
NIGHT. COLD FRONT BRUSHING ACROSS THE REGION LATE THURS NIGHT OR
EARLY FRIDAY MAY PRODUCE A SHORT PERIOD OF SNOW OR SNOW SHOWERS IN
THE BEFORE THE SYSTEM WASHES OUT AND EXITS THE REGION.

YET ANOTHER SHORTWAVE TROF MAY AFFECT THE REGION BY LATE SAT-SAT
NIGHT. THE ECMWF/ENSEMBLE CONSENSUS TRIES TO PULL MORE MOISTURE INTO
THIS SYSTEM BUT AT THIS TIME IT IS MUCH TOO EARLY TO DETERMINE
WHETHER THIS SYSTEM WILL PRODUCE SIGNIFICANT SNOW.

MAX TEMPS WILL REMAIN BELOW NORMAL THRU NEXT WEEKEND WITH LITTLE OR
NO OPPORTUNITY FOR MUCH WARMING BETWEEN THESE FAST MOVING SYSTEMS.
TEMPS ARE UNLIKELY TO REACH 40 DEGREES IN MOST VALLEYS FROM WED
THRU SAT. MJD
&&

.AVIATION...
AIR TRAVEL IN THE SIERRA AND WRN NV WILL BECOME DIFFICULT OR
HAZARDOUS LATER TONIGHT THRU SUNDAY NIGHT. CURRENT VFR CONDS RAPIDLY
WORSEN TO IFR/LIFR IN THE SIERRA AND TAHOE BASIN AS SNOW BEGINS AFT
06Z TONIGHT AND CONTINUES THRU 12Z MONDAY. PRECIP MAY DIMINISH FOR A
PORTION OF SUNDAY AFTERNOON BUT ANY IMPROVEMENTS IN CIGS/VSBY WILL
BE SHORT LIVED. FOR LOWER ELEVATIONS...CIGS AND/OR VSBY WILL WORSEN
AFT 08Z TO MVFR IF RAINING OR IFR IF SNOWING. MOST PRECIP IN FORM OF
RAIN AT KRNO AND KLOL THRU 06Z SUN EVENING...BUT MAY MIX WITH SNOW
AT TIMES DURING BANDS OF HEAVIER PRECIP. LEVEL FOR ACCUMULATING SNOW
500-1500 FT ABOVE THE VALLEY FLOOR IN WRN NV...BEFORE LOWERING TO
VALLEY FLOOR BY LATE SUN EVENING WITH 2-4 HR PERIOD OF IFR CONDS IN
SNOW AND WIND. TEMPORARY IMPROVEMENT TO VFR POSSIBLE BETWEEN 18Z-06Z
AT KRNO AND KLOL BUT WINDS WILL INCREASE DURING THIS TIME WITH GUSTS
ABOVE 35 KT AND POTENTIAL LLWS. MJD
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY NIGHT
     FOR NVZ005.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST MONDAY
     FOR NVZ002.

     LAKE WIND ADVISORY FROM 10 AM TO 10 PM PST SUNDAY FOR NVZ004.

CA...WINTER STORM WARNING FROM 4 AM SUNDAY TO 4 AM PST MONDAY FOR
     CAZ071.

     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY NIGHT
     FOR CAZ070.

     WINTER STORM WARNING FROM 10 PM THIS EVENING TO 10 AM PST MONDAY
     FOR CAZ072-073.

&&

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