Winter Storm Warning 8, NWS Reno, NV

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
1111 AM PST THU NOV 18 2010

UPDATED FOR AVIATION SECTION ONLY

.UPDATE...
SEE AVIATION SECTION FOR UPDATED THOUGHTS FOR TODAY THROUGH FRIDAY.
&&

.PREVIOUS DISCUSSION... /ISSUED 227 AM PST THU NOV 18 2010/

SHORT TERM...

..FIRST SIGNIFICANT WINTER STORM OF THE SEASON THIS WEEKEND...

TROUGH WILL PUSH INTO THE PAC NW TODAY...WITH THE JET DIPPING DOWN
TO OREGON BY THIS AFTERNOON. WINDS ALOFT HAVE INCREASED OVERNIGHT
AND WILL CONTINUE TO INCREASE THROUGHOUT THE DAY AS 700MB WINDS NEAR
60KTS. A WIND ADVISORY IS IN EFFECT FOR THE SIERRA AND SIERRA FRONT
FROM RENO-TAHOE NORTHWARD FOR TODAY. STRONGEST WINDS ARE EXPECTED
NORTH OF US-50 WITH GUSTS UP TO 50 MPH. WIND PRONE AREAS ALONG
HIGHWAY 395 WILL GUST UP TO 60 MPH...WHILE SIERRA RIDGE GUSTS WILL
REACH OVER 90 MPH AT TIMES TODAY.

BY FRIDAY...THE TROUGH MOVES FURTHER SOUTH BRINGING ANOTHER ROUND OF
WINDY CONDITIONS...MAINLY SOUTH OF RENO-TAHOE. IT IS POSSIBLE THAT
ANOTHER WIND ADVISORY MAY BE NECESSARY FOR FRIDAY...BUT DECIDED TO
LEAVE THAT UP TO THE NEXT SHIFT SINCE MAIN FOCUS FOR THIS FORECAST
PACKAGE WAS ON SNOW AMOUNTS AND QPF FOR THE WEEKEND. LATEST NAM
BEGINS TO PUSH THE COLD FRONT DOWN INTO NORTHERN CA/NV LATE FRIDAY
EVENING...WHILE THE GFS IS A BIT MORE PROGRESSIVE BRINGING THE FRONT
THROUGH IN THE AFTERNOON. TRENDED FORECAST TOWARDS THE GFS... WITH
SOME SHOWERS BEGINNING TO AFFECT THE NORTHWESTERN PORTION OF THE
REGION DURING THE DAY ON FRIDAY.

BEGAN TO INCREASE QPF WITH THIS TROUGH AND ITS ASSOCIATED
SHORTWAVES...SINCE GFS HAS TRENDED WITH HIGHER AMOUNTS. MODEL
PRECIPITABLE WATER AMOUNTS APPEAR TO HAVE INCREASED AS WELL WITH
ABOUT 0.5 INCH TO 1.00 INCH EDGING INTO NORTHERN CA AND WESTERN
NEVADA BY THE FRI-SAT TIME PERIOD. SIGNIFICANTLY COLDER TEMPERATURES
WITH THIS TROUGH WILL ESTABLISH HIGH SNOW RATIOS AND ALLOW FOR SNOW
ACCUMULATIONS ACROSS THE REGION...SO CONTINUED THE WINTER STORM
WATCH FOR THE SIERRA ZONES.

BY SATURDAY NIGHT...A SECOND WAVE WILL MOVE ACROSS THE REGION
FURTHER LOWERING SNOW LEVELS TO ALL VALLEY FLOORS AND BRINGING
ANOTHER ROUND OF HEAVY SNOW TO THE SIERRA. VERY COLD AIR ASSOCIATED
WITH THE TROUGH WILL DECREASE 700MB TEMPS AROUND -12C TO -14C. SNOW
RATIOS WILL INCREASE TO NEAR 20:1 IN THE SIERRA ALLOWING FOR SNOW
ACCUMULATIONS TO BUILD UP QUICKLY. BY EARLY SUNDAY MORNING SNOW
TOTALS IN THE HIGH SIERRA ABOVE TAHOE WILL BE BETWEEN 2 TO 4 FEET
WITH AROUND 1 TO 2 FEET NEAR LAKE LEVEL. ALSO EXPECTING MONO COUNTY
TO HAVE 1 TO 2 FEET OF SNOW ABOVE 8000 FEET.

THERE IS STILL SOME UNCERTAINTY WITH SNOW AMOUNTS IN THE LOWER
WESTERN NV VALLEYS...BUT SEVERAL INCHES OF SNOW REMAINS LIKELY.
THERE IS HIGHER CONFIDENCE IN SPILLOVER OCCURRING SAT-SUN...WHICH IS
SUPPORTED BY THE GFS...SO WINTER STORM WATCH WILL LIKELY NEED TO BE
EXPANDED INTO THE NV VALLEYS FOR SATURDAY NIGHT. MOST OF THE SNOW IN
THE WESTERN NV VALLEYS WILL OCCUR ON SATURDAY NIGHT AND SUNDAY
MORNING...SO WILL HOLD OFF ON A WATCH FOR THE RENO AREA FOR NOW. LINDAMAN

LONG TERM...SUNDAY THROUGH WEDNESDAY...
A COUPLE OF MAIN ISSUES DURING PERIOD INCLUDE SHORTWAVE FEATURES
DROPPING DOWN BACK SIDE OF TROUGH AND PROGRESSION OF THE LARGE
SCALE TROUGH. OVERALL THE MODELS LOOK QUITE A BIT DIFFERENT THAN
THEY DID 24 HOURS AGO AND THUS CONFIDENCE IS NOT PARTICULARLY HIGH.
POSITIVE TILT LONGWAVE TROUGH SHOULD EXTEND FROM THE NORTHERN
ROCKIES TO CA AT BEGINNING OF PERIOD WITH MODELS GENERALLY SHOWING
TROUGH PASSAGE SUN NIGHT. THE GFS IS QUITE WET SUN-SUN NIGHT AS IT
SHOWS ANOTHER WAVE AND FRONTAL LOBE ALOFT ACCOMPANYING TROUGH. THE
ECMWF IS SOMEWHAT SIMILAR ALTHOUGH ITS QPF IS LOWER. A NUMBER OF GFS
ENSEMBLE MEMBERS ALSO SHOW THIS FEATURE. SO BUMPED POPS UP SUN NIGHT
AND INCREASED THE QPF A BIT. IF THE WETTER GFS IS CORRECT...THERE
WILL LIKELY BE ANOTHER FOOT OR SO IN THE SIERRA AND SEVERAL INCHES
OR MORE FOR WESTERN NV VALLEY FLOORS.

BEYOND THE WEEKEND...MODELS HAVE BECOME MORE PROGRESSIVE ALTHOUGH
THE GEM/UKMET MAINTAIN SOLUTIONS OF THE GFS/ECMWF 24 HOURS AGO WHICH
SHOWED ONE MORE SHORTWAVE DROPPING INTO THE WESTERN GREAT BASIN MON
NIGHT AND EARLY TUE. LOW POPS WERE MAINTAINED FOR THIS PERIOD TO
ACCOUNT FOR THIS POSSIBILITY AND WE WILL JUST HAVE TO WAIT A COUPLE
MORE MODEL RUNS TO DETERMINE THE MORE LIKELY OUTCOME. SUCH AN INSIDE
SLIDER COULD BRING SEVERAL MORE INCHES OF SNOW...ESPECIALLY TO THE
LOWER VALLEYS.

TEMPERATURES WILL REMAIN ON THE DOWNRIGHT FRIGID SIDE...ESPECIALLY
WITH THE ANTICIPATED SNOW COVER. OVERNIGHT LOW TEMPERATURES WERE
LOWERED A FEW DEGREES BEGINNING TUE MORNING AND MAY NEED TO BE
LOWERED MORE AS MOS GUIDANCE DOES NOT YET KNOW ABOUT THE IMPENDING
SNOW COVER. READINGS WILL DROP BELOW ZERO IN SOME OF THE COLDER
VALLEYS WITH SINGLE DIGITS AND TEENS PREVALENT TUE AND WED MORNINGS.
HOHMANN

AVIATION...
RECEIVED A PIREP AT 1822Z INDICATING +20 KTS OF LLWS AT 055 MSL 10
SM NORTH OF KRNO. OBS ARE LIMITED AS TO OTHER EVIDENCE FOR LLWS...
HOWEVER JUDGING FROM SURFACE OBS NORTH OF RENO AND EXPECTED WINDS
ALOFT...WE LIKELY HAVE SOME WIND CHANNELING FROM SOUTH TO NORTH
THROUGH VALLEY/AT KRNO WITH MORE SW-W WINDS NORTH OF KRNO. THIS
WOULD EXPLAIN THE INCREASE IN HEADWINDS AND PROBABLY SOME DIRECTIONAL
SHEAR ON DESCENT INTO KRNO. LLWS SHOULD CONTINUE TODAY ALTHOUGH IT
MAY EASE SOME AS WINDS INCREASE AT KRNO THIS AFTERNOON.

THE STRONGEST WINDS AT KRNO ARE EXPECTED THIS EVENING THROUGH FRIDAY
AFTERNOON AS A STRONG COLD FRONT BEGINS TO APPROACH FROM NORTHERN
CALIFORNIA AND SOUTHERN OREGON.

A SIGNIFICANT WINTER STORM SYSTEM WILL AFFECT THE SIERRA AND WESTERN
NV THIS WEEKEND. IT WILL LIKELY SNOW AT ALL TERMINALS SATURDAY AND
SUNDAY WITH PERIODS OF IFR CONDITIONS POSSIBLE IN HEAVIER SNOW.
GROUND MAINTENANCE SHOULD PREPARE FOR ACCUMULATING SNOW ON RUNWAYS.

FOR KRNO...AN INCH OR TWO SAT MORNING AND SEVERAL INCHES FOR SAT
NIGHT/SUN MORNING AND POSSIBLY AGAIN FOR SUN NIGHT/MON MORNING.

FOR KTVL/KTRK...FRI NIGHT THROUGH MONDAY...1 TO 2 FEET.

HOHMANN/SNYDER
&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WIND ADVISORY UNTIL 7 PM PST THIS EVENING NVZ002-003-005.

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SUNDAY
     AFTERNOON NVZ002.

     LAKE WIND ADVISORY UNTIL 7 PM PST THIS EVENING FOR PYRAMID LAKE
     IN NVZ004.

CA...WIND ADVISORY UNTIL 7 PM PST THIS EVENING CAZ070>073.

     WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SUNDAY
     AFTERNOON CAZ071-072.

     WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SUNDAY AFTERNOON
     CAZ073.

&&

HTTP://WEATHER.GOV/RENO