Winter Weather in Nevada, December 20 to 21, 2013

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
925 PM PST FRI DEC 20 2013

.UPDATE...

JUST SPOKE TO A COUPLE OF WEATHER SPOTTERS IN SURPRISE VALLEY WITH
GOOD REPORTS OF INCREASING TEMPERATURES AND LIGHT RAIN SHOWERS.
SHOWERS ARE VERY SHALLOW AND ALMOST TOTALLY INVISIBLE ON RADAR DUE
TO OVERSHOOTING BEAMS.

IT LOOKS LIKE THE VALLEY IS MIXING AS THE SHOWERS MOVE INTO THE
AREA. TEMPERATURES ARE PUSHING UP ABOVE FREEZING IN SURPRISE
VALLEY, BUT SINCE TEMPERATURES HAVE BEEN BELOW FREEZING FOR MOST
OF THE DAY. PATCHES OF ICE ARE STILL POSSIBLE, ALTHOUGH THE
RISING TEMPERATURES WILL HELP TO KEEP THINGS WET INSTEAD OF ICY.

ANOTHER THING, THE LATEST NAM AND GFS MODEL SOUNDINGS ARE
DEFINITELY TOO COLD ALOFT OVER CEDARVILLE. THERE IS DEFINITELY
LIGHT RAIN FALLING ACCORDING TO THE SPOTTER REPORTS, BUT THE
MODEL SOUNDINGS INDICATE ALL SNOW.

LIGHT SHOWERS WILL CONTINUE INTO PERSHING AND CHURCHILL COUNTIES
OVERNIGHT, WHERE A MIX OF FREEZING AND FROZEN PRECIPITATION WILL
BE POSSIBLE. THE VALLEYS ARE QUITE A BIT LOWER THERE, SO TRAPPED
COLD AIR MAY HAVE A BETTER CHANCE OF REMAINING IN PLACE. HOON

&&

.PREVIOUS DISCUSSION... /ISSUED 201 PM PST FRI DEC 20 2013/

SYNOPSIS...
LOW PRESSURE PASSING ACROSS OREGON AND IDAHO TONIGHT COULD PRODUCE
A MIX OF RAIN, SNOW, SLEET AND FREEZING RAIN FROM CEDARVILLE TO
FALLON TONIGHT. DRY CONDITIONS WILL OCCUR SATURDAY THROUGH MOST
OF NEXT WEEK WITH HIGH PRESSURE REMAINING NEAR THE WEST COAST.

SHORT TERM...

HIGH CLOUDS STARTING TO INCREASE OVER THE EASTERN SIERRA AND
WESTERN NEVADA AHEAD OF THE SYSTEM PASSING THROUGH OREGON AND
IDAHO. LIGHT PRECIPITATION IS POSSIBLE THIS EVENING AND TONIGHT
AS WEAK WARM AIR ADVECTION PASSES OVER NORTHERN NEVADA. BEST
CHANCE FOR PRECIPITATION IS FROM THE SURPRISE VALLEY TO PERSHING
AND CHURCHILL COUNTIES. THE LIFT WITHIN THE WARM AIR ADVECTION IS
FAIRLY WEAK WITH WHICH WILL KEEP PRECIPITATION AMOUNTS LESS THAN
0.05 INCH. NO RAIN OR SNOW WILL REACH THE RENO-TAHOE AREA TONIGHT.

PRECIPITATION TYPE IS THE MAIN FORECAST CHALLENGE TONIGHT WITH
MODELS VARYING ON THE DEPTH OF AN ABOVE FREEZING LATER SOMEWHERE
BETWEEN 4500 TO 7500 FEET. THIS WOULD ALLOW SNOW TO MELT, THEN
REFREEZE TO EITHER SLEET OR FREEZING RAIN IN VALLEY LOCATIONS.
HOWEVER MODELS ARE SLIGHTLY COLDER THAN YESTERDAY WHICH COULD
GREATLY LIMIT THE DEPTH OF THE ABOVE FREEZING LAYER AND ALLOW MOST
PRECIPITATION TO FALL AS EITHER SNOW AND/OR ICE PELLETS.

DESPITE THE LIGHT PRECIPITATION AMOUNTS AND UNCERTAINTY IN
PRECIPITATION TYPE, IF ANY FREEZING RAIN OCCURS IT WOULD LEAD TO
DIFFICULT TRAVEL CONDITIONS. BEST CHANCE FOR FREEZING RAIN EXISTS
IN THE SURPRISE VALLEY, ALONG HIGHWAY 447 BETWEEN NIXON AND
GERLACH AND INTERSTATE 80 IN PERSHING COUNTY. THOSE TRAVELING
ALONG THESE ROADS TONIGHT SHOULD USE CAUTION FOR AREAS OF BLACK
ICE ON ROADS.

ONCE THIS SYSTEM PASSES THE RIDGE IN THE EASTERN PACIFIC WILL MOVE
TOWARD THE COAST WITH DRY CONDITIONS SATURDAY AFTERNOON THROUGH
MONDAY. SURFACE INVERSIONS WILL REDEVELOP IN THE NEVADA VALLEYS,
WHICH WILL LIMIT WARMING AND MAY CAUSE A DECREASE IN AIR QUALITY.
HIGHS IN THE SIERRA WILL WARM INTO THE MID TO UPPER 40S THIS
WEEKEND AND INTO THE LOW 50S BY MONDAY. BRONG

LONG TERM...TUESDAY THROUGH FRIDAY...

FEW CHANGES WERE MADE TO THE ONGOING FORECAST. MODELS HAVE TRENDED
NORTHEAST WITH THE SYSTEM FOR TUESDAY, WHICH NO LONGER BRINGS A WEAK
BACK DOOR COLD FRONT THROUGH NORTHERN NEVADA. THIS MEANS VALLEY
INVERSIONS THAT DO DEVELOP ARE UNLIKELY TO FULLY MIX OUT DUE TO LESS
WIND AND NOT MUCH COOLING ALOFT. THEREFORE HAVE MAINTAINED INVERSION
CONDITIONS IN THE TEMPERATURE FORECAST, BUT IT WILL NOT BE AS COLD
IN THE VALLEYS AS IT WAS EARLIER THIS MONTH DUE TO LESS SNOW ON THE
GROUND. THIS SYSTEM WILL TRACK ACROSS THE NORTHERN ROCKIES, KEEPING
THE SIERRA AND NORTHWEST NEVADA UNDER DRY NORTHERLY FLOW. SURFACE
WINDS WILL GENERALLY BE LIGHT WITH AN EASTERLY GRADIENT IN PLACE. A
WEAK SYSTEM IS POSSIBLE HEADING INTO THE WEEKEND, BUT AT THIS TIME
APPEARS MAIN ENERGY WILL BE IN THE PACIFIC NORTHWEST AND THE
GREATEST IMPACT ACROSS THE SIERRA AND NORTHWEST NEVADA WILL BE A FEW
DEGREES OF COOLING. DJ

AVIATION...

A SYSTEM WILL BRUSH ACROSS NORTHERN NEVADA THIS EVENING INTO
SATURDAY MORNING BRINGING A MIX OF WINTER WEATHER TO AREAS NORTH AND
EAST OF A KAAT-KNFL LINE. THERE IS A 20 PERCENT CHANCE FOR SNOW
AND/OR ICE PELLETS THROUGH THIS REGION WITH A 10 PERCENT CHANCE OF
FREEZING RAIN. ICING WILL BE A CONCERN FOR THOSE FLYING ACROSS
NORTHERN NEVADA WITH TERRAIN OBSCURATION LIKELY. ELSEWHERE, THE MAIN
IMPACT WILL JUST BE AN INCREASE IN CIGS BETWEEN 040-070 AGL WITH NO
PRECIPITATION EXPECTED FOR KRNO, KCXP, KTVL, KTRK, OR KMMH.

NORTHERLY RIDGE WINDS WILL REMAIN GUSTY INTO SATURDAY WITH DOWNWIND
TURBULENCE LIKELY. VALLEY WINDS TO REMAIN LIGHT. DJ

&&

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

FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/RENO (ALL LOWER CASE)