Area Forecast Discussion
Issued by NWS Reno, NV

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FXUS65 KREV 210158 AAA
AFDREV

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
558 PM PST SAT DEC 20 2014

.UPDATE...
QUICK UPDATE TO RAISE A WIND ADVISORY FOR AREAS NEAR THE OREGON
BORDER. STRONG WARM ADVECTION WILL BE ONGOING WITH SOME LIGHT RAIN
TONIGHT AND EARLY SUNDAY ACROSS THE FAR NORTH. IMPRESSIVE SURFACE
GRADIENT IS FORECAST TO DEVELOP WITH 30AGL WINDS INCREASING TO
40-55KT IN THE 18Z NAM OVERNIGHT AND EARLY SUNDAY MORNING. STRONG
DOWNSLOPING AND HIGH WINDS WILL BE LOCALIZED DUE TO THE MOIST
ENVIRONMENT. HOWEVER WIDESPREAD GUSTS BETWEEN 45 AND 55 MPH ARE
LIKELY, ESPECIALLY LATE TONIGHT, ACROSS THE SURPRISE VALLEY AND
FAR NORTHERN WASHOE COUNTY. WINDS WILL BACK OFF LATE SUNDAY
MORNING INTO SUNDAY AFTERNOON BUT COULD STILL GUST AS HIGH AS 45
MPH. SO WE RAN THE ADVISORY UNTIL MID AFTERNOON. HOHMANN

&&

.PREVIOUS DISCUSSION... /ISSUED 212 PM PST SAT DEC 20 2014/

SYNOPSIS...

CHANCES FOR RAIN AND SNOW WILL GRADUALLY DIMINISH FROM SOUTH TO
NORTH THROUGH EARLY MONDAY. DRY CONDITIONS AND MILD TEMPERATURES
ARE ANTICIPATED MONDAY THROUGH WEDNESDAY AS HIGH PRESSURE BUILDS
INTO THE REGION. A STRONG COLD FRONT IS POSSIBLE LATE WEDNESDAY
INTO CHRISTMAS DAY WITH GUSTY WINDS, RAIN AND SNOW.

SHORT TERM...

UPPER LEVEL RIDGE WILL BUILD INTO THE WEST THE NEXT SEVERAL DAYS
WITH MILD TEMPERATURES AND RISING SNOW LEVELS. LINGERING MOIST
WESTERLY FLOW OVER THE TOP OF THE RIDGE WILL KEEP CHANCES FOR RAIN
AND HIGH ELEVATION SNOW IN THE FORECAST, THOUGH PRECIPITATION
WILL GRADUALLY LIFT NORTH OVER THE NEXT 36 HOURS. DUE TO DEEP
MOISTURE AND ISENTROPIC LIFT PRESENT HAVE RAISED CHANCES FOR
PRECIPITATION MAINLY NORTH OF A PORTOLA-LOVELOCK LINE THROUGH
TOMORROW, LIFTING IT FARTHER NORTH BY SUNDAY NIGHT. THIS IS A
WEAKLY FORCED SITUATION WITH THE MAIN MOISTURE PLUME AND JET
DIRECTED AT THE PACIFIC NORTHWEST, SO AM NOT ANTICIPATING MUCH
ACCUMULATION. LIQUID TOTALS WILL LIKELY BE A FEW HUNDREDTHS UP TO
A COUPLE TENTHS OF AN INCH FOR MOST AREAS. SNOW LEVELS ARE
EXPECTED TO RISE TO AROUND 8.5-10K FOR THE REMAINDER OF THE EVENT
WITH LITTLE IMPACT TO SIERRA PASSES.

WINDS WILL INCREASE THIS EVENING, ESPECIALLY FOR NORTHERN WASHOE
COUNTY, AS THE SURFACE GRADIENT INCREASES IN RESPONSE TO BUILDING
HIGH PRESSURE. WINDS WILL GENERALLY BE GUSTING 30 TO 35 MPH IN THE
SIERRA AND FOR MUCH OF WESTERN NEVADA, BUT SPEEDS MAY APPROACH 45
MPH IN NORTHERN WASHOE COUNTY WHERE THE GRADIENT AND 700 MB WINDS
ARE THE STRONGEST. WINDS WILL DECREASE SUNDAY NIGHT INTO MONDAY
AS THE RIDGE AXIS BECOMES POSITIVELY TILTED AND SHIFTS INLAND.
THIS WILL ALSO CUT OFF THE MOISTURE TAP TO THE REGION WITH DRY
CONDITIONS MONDAY THROUGH TUESDAY.

AFTER A FEW DAYS OF WARMING CONDITIONS, TUESDAY MORNING WILL BE
SEASONABLY COOL DUE TO CLEARING SKIES AND WITHOUT WIND PRESENT,
INVERSIONS ARE LIKELY TO STRENGTHEN DURING THE DAY. THEREFORE,
VALLEY HIGH TEMPERATURES TUESDAY ARE LIKELY TO COOL AS COMPARED TO
SUNDAY AND MONDAY WITH DIMINISHED AIR QUALITY. DJ

LONG TERM...WEDNESDAY THROUGH SATURDAY...

MAIN WEATHER FEATURE FOR THE EXTENDED PERIOD CONTINUES TO BE THE
FAST MOVING TROUGH AND STRONG COLD FRONT PASSAGE WHICH IS ON TRACK
TO MOVE THROUGH THE REGION ON CHRISTMAS EVE. THE MAIN TREND IS
HOLDING OFF MOST PRECIPITATION UNTIL LATE WEDNESDAY AFTERNOON OR
EARLY EVENING NORTH OF SUSANVILLE-GERLACH, BUT STILL PUSHING QUICKLY
SOUTH ACROSS MUCH OF WESTERN NV AND THE TAHOE BASIN OVERNIGHT.

BECAUSE OF THE LATER ARRIVAL OF THE COLD FRONT AND ASSOCIATED
PRECIPITATION, TEMPERATURES ON WEDNESDAY HAVE A HIGHER POSSIBILITY
OF SURPASSING 60 DEGREES IN SOME WESTERN NV VALLEYS. BREEZY
SOUTHWEST-WEST WINDS WITH 40-45 MPH GUSTS ARE POSSIBLE AHEAD OF THE
FRONT, WITH SIERRA RIDGE GUSTS 60-70 MPH.

CONFIDENCE REMAINS AT MEDIUM FOR A WHITE CHRISTMAS FROM SOUTH
TAHOE-MINDEN-FALLON NORTHWARD AS FORCING SHOULD BE SUFFICIENT TO
GENERATE A BAND OF PRECIPITATION, MAINLY SNOW, BEHIND THE COLD
FRONT. SNOW AMOUNTS WOULD BE GENERALLY LIGHT, PROBABLY 2 INCHES OR
LESS DUE TO THE SHORT DURATION OF THIS EVENT. THE MAIN UNCERTAINTY
IS THE SOUTHERN EXTENT OF THIS SNOW BAND. THE ECMWF HOLDS IT
TOGETHER INTO THE TAHOE BASIN AND MUCH OF WESTERN NV FROM HIGHWAY 50
NORTHWARD, WHILE THE GFS PUSHES THE STRONGER FORCING INTO CENTRAL
AND EASTERN NV WITH ONLY SPARSE PRECIP AMOUNTS AROUND RENO-TAHOE.
HOWEVER, THE 12Z GFS WAS NOTABLY FARTHER SOUTH WITH THE PRECIP AREAS
COMPARED TO ITS OPERATIONAL 00Z/06Z RUNS. THE ECMWF HAS GENERALLY
BEEN MORE CONSISTENT WITH BRINGING PRECIP IN WESTERN NV AROUND
CHRISTMAS EVE, EVEN SHOWING UP ON ITS MODEL RUNS SEVERAL DAYS AGO.

OTHER THAN A FEW LINGERING SNOW SHOWERS ON CHRISTMAS DAY, A DRY
PATTERN WILL THEN RETURN AS HIGH PRESSURE REBUILDS NEAR THE WEST
COAST. THIS WILL BRING INVERSION CONDITIONS THROUGH FRIDAY WITH
DAYTIME TEMPERATURES IN WESTERN NV VALLEYS NEAR OR SLIGHTLY COOLER
THAN THE TAHOE BASIN AND OTHER SIERRA VALLEYS. THURSDAY NIGHT LOOKS
TO BE QUITE CHILLY AS A PERIOD OF CLEARING SKIES WILL ALLOW FOR
RADIATIONAL COOLING. WIDESPREAD LOWS IN THE TEENS AND SINGLE DIGITS
ARE LIKELY ESPECIALLY IF SNOW COVER IS PRESENT.

BY NEXT WEEKEND, THE RIDGE BEGINS TO WEAKEN WITH ANOTHER TROUGH
APPROACHING THE NORTHWEST U.S.. THE LATEST ECMWF BRINGS ANOTHER
SHORTWAVE AND COLD FRONT SOUTH ACROSS WESTERN NV NEXT SATURDAY
NIGHT, IN A SIMILAR MANNER TO THE CHRISTMAS EVE EVENT. THIS IS A NEW
DEVELOPMENT AND WILL BE WORTH WATCHING, BUT FOR NOW WE WILL KEEP THE
FORECAST DRY THROUGH SATURDAY. MJD

AVIATION...

SOME BREEZY CONDITIONS HAVE DEVELOPED IN WESTERN NV THIS AFTERNOON
WITH SOME GUSTS OVER 30 KT AROUND KCXP AND IN THE NORTH RENO HILLS.
THESE WINDS COULD ALSO AFFECT KRNO BEFORE DIMINISHING BY 03Z. SOME
25-30 KT GUSTS ARE AGAIN POSSIBLE SUNDAY AFTERNOON. CIGS SHOULD
REMAIN VFR AT THE WESTERN NV TERMINALS THRU SUNDAY, BUT HIGHER
MTNS WILL REMAIN OBSCD AT TIMES THRU TONIGHT.

PERIODS OF LIGHT RAIN COULD BRING MVFR CIGS AT TIMES TO KTVL/KTRK
TONIGHT, WITH PRECIP DIMINISHING AND RETREATING FARTHER NORTH ON
SUNDAY. MJD

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...WIND ADVISORY UNTIL 3 PM PST SUNDAY NVZ005.

CA...WIND ADVISORY UNTIL 3 PM PST SUNDAY CAZ070.

&&

$$

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





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