High Wind in California, September 29, 2009

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
925 AM PDT TUE SEP 29 2009

.UPDATE...
MOVED BLOWING DUST ADVISORY UP. STRONG COLD FRONT WAS CONTINUING
TO MOVE SOUTH AND WAS LOCATED NEAR SUSANVILLE AT MID MORNING.
TEMPERATURE CONTRAST ACROSS THE FRONT WAS IMPRESSIVE WITH 30S AND
LOWER 40S TO THE NORTH OF BOUNDARY AND 60S TO THE SOUTH. COLD
FRONT WILL CONTINUE TO MAKE SLOW PROGRESS THIS MORNING AND THEN
ACCELERATE THIS AFTERNOON AS SFC LOW DEVELOPS OVER CNTRL-ERN NV IN
RESPONSE TO INCOMING TROF/UPR LVL JET. WINDS ACROSS THE REGION
HAVE BEEN INCREASING WITH GUSTS TO 55 MPH REPORTED AT A NUMBER OF
LOCATIONS INCLUDING PYRAMID LAKE WHERE WEB CAMS INDICATED BLOWING
DUST. SO THE BLOWING DUST ADVISORY WAS MOVED UP TO START
IMMEDIATELY ALTHOUGH THE WORST CONDITIONS FOR ZONES 1 AND 4 WILL
BE THIS AFTN. REMAINDER OF FCST IS ON TRACK. RADAR SHOWED SOME
LIGHT RETURNS BUT AIRMASS REMAINS TOO DRY FOR ANY PRECIPITATION.
LATEST NAM12 CONTINUES TO INDICATE SCT LGT SHOWERS TNGT AS CORE OF
TROF OPENS AND MOVES ACROSS THE AREA. UPDATES ALREADY ISSUED. HOHMANN

&&

.PREVIOUS DISCUSSION... /ISSUED 653 AM PDT TUE SEP 29 2009/

FIRE WEATHER...
WINDS BEGINNING TO INCREASE AS EXPECTED THIS MORNING. SO FAR IT
HAS BEEN JUST A FEW OF THE WIND PRONE AREAS IN THE TAHOE
BASIN/SIERRA FRONT. RH IS STILL 15-20% ACROSS MUCH OF THE
AREA...BUT DO NOT EXPECT IT TO DROP ANYMORE...AND WILL PROBABLY
RISE NORTH OF I-80 BY THIS AFTERNOON AS THE FRONT PASSES.
CURRENTLY THE FRONT IS ALONG A RAVENDALE TO DENIO LINE AND IS
SLOWLY PUSHING SOUTHWARD.

WITH RIDGE GUSTS TO 85 MPH ALREADY AND THE THERMAL AND PRESSURE
GRADIENTS INCREASING...STRONG WINDS LOOK ON TRACK WITH GUSTS TO 55
MPH IN THE WARNING AREA ALTHOUGH SOME WIND PRONE AREAS COULD GUST
AS HIGH AS 60 MPH. HAVE ADDED THE TAHOE BASIN TO THE WARNING AS
WINDS THERE WILL GUST TO 45-50 MPH AND RH WILL HOVER NEAR 20%
UNTIL AT LEAST 2 PM. AFTER THE FRONT PASSES THIS AFTERNOON WINDS
WILL SHIFT TO NORTHWEST AND GRADUALLY WEAKEN. RH WILL ALSO BE ON
THE RISE WITH MUCH COOLER TEMPERATURES. WALLMANN

PREVIOUS DISCUSSION... /ISSUED 409 AM PDT TUE SEP 29 2009/

SHORT TERM...
WINDS CONTINUE TO INCREASE IN THE SIERRA WITH GUSTS OVER 60 MPH ON
SLIDE MTN DURING THE PAST HOUR. SOME GUSTS OF 20-30 MPH HAVE MIXED
DOWN TO THE TAHOE BASIN AND RENO AIRPORT...WITH SUSTAINED WINDS
GENERALLY 10-20 MPH AT THE LAKE TAHOE BUOYS. AFTER SUNRISE...THE
WINDS WILL BECOME MUCH STRONGER OVER THE REGION WITH GUSTS
STARTING TO REACH ADVISORY CRITERIA BETWEEN 8 AND 10 AM IN MOST
AREAS...EXCEPT MAYBE ANOTHER HOUR OR TWO LATER IN W-CNTRL NV.
RIDGE GUSTS ARE EXPECTED TO REACH PEAK SPEEDS NEAR 100 MPH FROM
MID TO LATE MORNING.

COLD FRONT PASSAGE WILL OCCUR QUICKLY OVER NERN CA AND NWRN NV
DURING THE MID OR LATE MORNING...THEN SLOW DOWN A BIT BEFORE
PUSHING ACROSS THE I-80 AND HWY 50 CORRIDORS DURING THE AFTERNOON.
THE FRONT SHOULD THEN CLEAR SRN MINERAL COUNTY TOWARD SUNSET. THIS
MAY ALLOW FOR SOME AREAS OF WRN NV TO BRIEFLY REACH THE 70S
BEFORE COLDER AIR ADVECTS IN. THE STRONGEST WINDS WILL OCCUR UP
UNTIL THE FRONT PASSES THROUGH...THEN BEGIN TO DIMINISH.

LIGHT MEASURABLE PRECIP WILL REMAIN POSSIBLE MAINLY OVER NERN CA
AND NWRN NV IN THE POST FRONTAL AIR MASS THIS AFTN THRU EARLY
EVE...THEN SHIFT TO ERN PERSHING AND CHURCHILL COUNTIES LATER THIS
EVENING. BRIEF SHOWERS MAY OCCUR IN OTHER PARTS OF THE REGION THIS
EVENING DUE TO FORCING FROM STRONG FRONTOGENESIS AFTER THE FRONT
PASSES THROUGH...BUT THE DURATION OF THIS STRONG FORCING WILL BE
QUITE SHORT SO THE POTENTIAL FOR MEASURABLE PRECIP IS SLIM. SNOW
LEVELS WILL PLUMMET TONIGHT WITH THE FIRST SNOWFLAKES OF THE
SEASON IN PORTIONS OF THE NRN SIERRA...ALTHOUGH ACCUMULATIONS ARE
UNLIKELY.

BY WEDNESDAY...TEMPS WILL BE MUCH BELOW NORMAL IN ALL AREAS EVEN
AS CLOUDS DECREASE FROM WEST TO EAST WITH THE ARRIVAL OF DRIER
AIR. MOST LOWER ELEVATIONS WILL FAIL TO SURPASS 60 DEGREES...WHILE
BRISK NORTH WINDS WITH GUSTS 20-30 MPH WILL ADD TO THE COOLING
EFFECT. DRY NORTHWEST FLOW ALOFT AND FURTHER RELAXING OF PRESSURE
GRADIENTS WILL CONTINUE TO DIMINISH THE WINDS FOR WED NIGHT AND
THURSDAY...SETTING THE STAGE FOR A POTENTIAL WIDESPREAD FREEZE IN
MANY AREAS WED NIGHT BEFORE TEMPS REBOUND INTO THE 60S BY
THURSDAY. MJD

LONG TERM...FRIDAY THROUGH MONDAY...
SHORTWAVE RIDGE ON FRIDAY AHEAD OF NEXT SYSTEM ARRIVING SATURDAY.
DEEP TROUGH THEN TO STAY OVER THE AREA SUN AND MON. GFS/EC/GEM IN
GOOD AGREEMENT WITH THE PATTERN AND AS PREV SHIFT MENTIONED...
SOLUTIONS HAVE TRENDED MORE INLAND LAST 24 HRS. DID NOT CHG FORECAST
MUCH EXCEPT TO COOL SUN-MON A BIT. GFS/EC/GEM ALL SPIN LOW BACK WWD
MON IN A WEAKENED FORM. A FEW GFS ENSEMBLE MEMBERS HINT AT IT A BIT
BUT THE 12Z EC ENSEMBLE IS MUCH FURTHER EAST. GIVEN ALL THE HIGH RES
OPERATIONAL RUNS SHOW IT...WILL LEAN TOWARD THEM AND STEER AWAY FROM
ENSEMBLE MEANS WITH SOMEWHAT REDUCED CONFIDENCE.

OVERALL...EXPECT A MILD DAY FRI THEN TURNING A LITTLE COOLER AND
BREEZY SAT. PRETTY GOOD FRONT ARRIVES SAT WITH H7 WINDS OF 30 KTS OR
SO ALTHOUGH THERMAL GRADIENT IS NOT AS STRONG AS TODAYS. GFS IS
HINTING AT A POSSIBLE TROP FOLD EVENT NEAR THE FRONT SAT AFTERNOON
WHICH COULD ACT TO SIGNIFICANTLY ENHANCE WINDS. HAVE TRENDED WINDS
UP A BIT FOR THE SOUTHERN 2/3 OF THE AREA BUT STILL ONLY NR 20 MPH
OR SO SUSTAINED.

THIS SYSTEM STILL LOOKS TO HAVE A BIT MORE MOISTURE AND MOST IF NOT
ALL PRECIP WILL BE POST-FRONTAL. A DECENT BAND OF RAIN/SNOW TO FORM
JUST BEHIND FRONT THAT SHOULD PROGRESS SOUTH FROM NEAR OREGON BORDER
SAT AFTERNOON TO MONO-MINERAL SUNDAY MORNING. IT WILL WEAKEN AS IT
PROGRESSES SWD AND EXPECT MAINLY ISOLD-SCT SHOWERS FOR SUN. SNOW
LEVELS WILL DROP RAPIDLY BEHIND THE FRONT AND COULD DROP AS LOW AS
4500 FEET TOWARD HWY 50. RIGHT NOW DO NOT HAVE THEM THAT LOW...IN
CASE THE SYSTEM AND COLD AIR CONTINUES TO TREND FURTHER EAST.

FOR MON...HIGH RES RUNS SUPPORT KEEPING SOME MENTION OF SHOWERS WITH
SNOW LEVELS SLIGHTLY HIGHER AS COLD AIR IS MODIFIED AND LOW FILLS
SLOWLY. HOWEVER...TEMPS WILL BE SLOW TO RISE WITH NOW A NORTH TO
NORTHEAST LOW LEVEL FLOW EXPECTED. TEMPS BOTH SUN-MON TO BE 15
DEGREES BELOW NORMAL FOR HIGHS...IF NOT MORE SO WITH OVERNIGHT LOWS
MODIFIED DUE TO SOME LLVL MOISTURE. WALLMANN

AVIATION...
WINDS PICKING UP OVER SIERRA WITH SOME MIXING DOWN TO LAKE LEVEL
WHILE WRN NV WINDS ARE LIGHT. EXPECT SOME LLVL WIND SHEAR THIS
MORNING THRU 16Z FOR KTVL/KTRK/KRNO. CHANNELING EFFECTS WILL RESULT
IN NEAR SURFACE WINDS NEAR A 200 DIRECTION WHILE WINDS ALOFT ARE
ABOUT 20 KTS STRONGER AND FROM 250 OR SO. HGHT APPEARS TO BE ABOUT
1500 FEET AGL AROUND TAHOE AND MORE LIKE 2 KFT RENO. WILL CONTINUE
TO MONITOR FOR HGHT ADJUSTMENTS AS NECESSARY THIS MORNING.

AFT 16-18Z...WINDS AT THERE TERMINALS WILL INCREASE SIGNIFICANTLY
WHICH SHOULD ALLEVIATE MOST LLWS. PEAK GUSTS STILL LOOK TO BE NR
40-45 KTS AT KRNO AND ABT 5 KTS LIGHTER KTVL/KTRK. COLD FRONT TO
PUSH THROUGH AROUND 21Z AND WINDS WILL BECOME MORE WNW WHICH LIKELY
WILL CREATE ANOTHER PERIOD OF LLWS AT KTVL DUE TO TERRAIN CHANNELING
A MORE SFC SOUTH WIND DIRECTION. 75 PCT CONFIDENCE IN FRONTAL TIMING
WITHIN 2 HRS OF 21Z AND ALSO IN WIND SPEEDS/DIRECTION. KLOL
SIMILAR...BUT DO NOT EXPECT LLWS IMPACTS. OTHER DIFFERENCE IS
POTENTIAL 1-3SM VIS AT TIMES IN BLDU THIS AFTERNOON.

EXPECT GRADUAL DIMINISHING WIND OVERNIGHT WITH A FEW -SHRA/-SHSN
NORTH OF HWY 50. LOCALIZED CIGS TO MVFR IN ANY SHOWERS. WALLMANN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...BLOWING DUST ADVISORY UNTIL 8 PM PDT THIS EVENING FOR NVZ001-004.

     RED FLAG WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR NVZ450-453-
     459.

     WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR NVZ003.

     LAKE WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR NVZ002.

CA...RED FLAG WARNING UNTIL 5 PM PDT THIS AFTERNOON FOR CAZ272-273.

     WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR CAZ073.

     LAKE WIND ADVISORY UNTIL 8 PM PDT THIS EVENING FOR CAZ072.

&&

HTTP://WEATHER.GOV/RENO