Dust Storm and Strong Wind in Nevada, September 29, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
1015 PM PDT MON SEP 28 2009

.FIRE WEATHER UPDATE...
WINDS ARE DECOUPLING ACROSS MUCH OF THE FORECAST AREA THIS EVENING
AND RH VALUES ARE STARTING TO SLOWLY INCREASE. HOWEVER...LATEST
MODEL GUIDANCE STILL INDICATES AN INCREASE IN WINDS JUST ABOVE THE
BOUNDARY LAYER BEFORE 12 UTC TUESDAY MORNING. THIS IS IN RESPONSE
TO THE APPROACH OF A 110 KT JET STREAK AND A STRENGTHENING LOW LVL
PRESSURE GRADIENT AHEAD OF A COLD FRONT THAT WILL MOVE THROUGH THE
FORECAST AREA ON TUESDAY. AS WINDS INCREASE LATE TONIGHT FROM I-80
SOUTHWARD MIXING WILL INCREASE. THIS WILL KEEP RH VALUES FROM
RISING MUCH AND...IN FACT...SHOULD CAUSE RH VALUES TO FALL A BIT
ON THE MID SLOPES AND RIDGES BEFORE DAYBREAK. WHILE RED FLAG
CRITERIA IS NOT CURRENTLY BEING SEEN OVER THE FORECAST AREA THE
CONTINUED LOW RH VALUES AND LIKELIHOOD THAT WINDS WILL INCREASE
LATE TONIGHT WARRANT MAINTAINING RED FLAG WARNING FOR ZONE 450
THROUGH THE NIGHT. WARNING STARTS FOR ZONE 273 LATER THIS EVENING
AND WARNINGS START FOR ZONES 453 AND 459 TUESDAY MORNING.

CONDITIONS ACROSS THE NORTHERN HALF OF THE FORECAST AREAS SHOULD
IMPROVE OVERNIGHT WITH RH VALUES RECOVERING ENOUGH TO LIMIT THE
LIKELIHOOD OF CRITICAL CONDITIONS REDEVELOPING. MLF

&&

.PREVIOUS DISCUSSION... /ISSUED 808 PM PDT MON SEP 28 2009/

UPDATE...
WINDS HAVE STARTED TO DECREASE SLOWLY ACROSS MUCH OF THE AREA THIS
EVENING. WINDS AT PYRAMID LAKE HAVE DROPPED BELOW 20 MPH AND THE
LAKE WIND ADVISORY HAS BEEN ALLOWED TO EXPIRE. MID SLOPE AND RIDGE WINDS
CONTINUE RATHER GUSTY IN SOME LOCATIONS AND RH VALUES REMAIN QUITE
LOW. WILL ADDRESS RED FLAG WARNINGS THAT EXPIRE AT 10 PM SHORTLY...BUT
FOR NOW THEY ARE STILL ON TRACK. NEW NAM MODEL GUIDANCE CONTINUES
TO INDICATE RATHER STRONG 30MB AGL WINDS THIS EVENING...AROUND 30
KTS OVER NRN PORTIONS OF THE FORECAST AREA. THIS SHIFTS SOUTH BY
MORNING INTO MONO COUNTY ALONG WITH 700MB WINDS AROUND 45 KTS AND
INCREASING JET LEVEL WINDS. STILL THE STRONGEST JET SUPPORT DOES
NOT IMPACT THE AREA UNTIL TUESDAY AFTN. SO WIND ADVISORIES AND RED
FLAG WARNINGS FOR TOMORROW STILL LOOK GOOD. UPDATES OUT SOON. MLF

PREVIOUS DISCUSSION... /ISSUED 406 PM PDT MON SEP 28 2009/

SHORT TERM...
COLD UPPER LOW WAS DROPPING SWD OFF THE WA AND OR COASTLINE
THIS AFTN. MODELS TRACK VORT CENTER TO NEAR THE NORTHERN CA COAST
BY 12Z TUE AND THEN TO NORTHEAST NV BY 06Z WED. MODELS HAVE BEEN
FAIRLY CONSISTENT WITH THIS TRACK AND SHOW COLD FRONT OVR NERN CA
AROUND DAYBREAK TUE AND PUSHING SEWD TO MONO/MINERAL COUNTIES BY
LATE AFTN.

FOR TONIGHT...MAINLY SOME HIGH CLOUDINESS STREAMING NORTHEAST FROM
PAC IN ADVANCE OF SYSTEM. VERY DRY LOW LEVELS WL PRECLUDE ANY
PRECIPITATION. HOWEVER THE CLOUDS AND INCREASING WIND TONIGHT
SHOULD KEEP TEMPS UP ONE MORE NIGHT. READINGS WERE HELD ABOVE MOS
GUIDANCE ESPECIALLY ALONG THE SIERRA FRONT AND HIGHER SIERRA
VALLEYS WHERE WINDS AND MIXING WL KEEP READINGS UP OVER LAST
NIGHTS VALUES.

FOR TUESDAY AND TUESDAY NIGHT...INCREASING MT TOP WINDS AND
FRONTAL SYSTEM WL BRING A VERY WINDY DAY TO THE REGION. THE 18Z
GFS RUN BACKED OFF SLIGHTLY ON 700MB WIND SPEEDS TUE MORNING BUT
WERE STILL NEAR 50KT AT 12Z AND LOCAL RUN OF THE 8KM WRF SHOWS 30
AGL WINDS NEAR 50KT ALONG CREST EARLY TUE MORNING SPREADING OFF
THE CREST BETWEEN 14-18Z SUGGESTING WIDESPREAD WIND GUSTS TO 50-55
MPH DEVELOPING ALONG THE SIERRA FRONT AND EXPANDING INTO PORTIONS
OF SWRN CHURCHILL...SOUTHERN LYON AND WESTERN MINERAL COUNTIES BY
MIDDAY. SOUNDING PROFILES DO NOT CURRENTLY SHOW INGREDIENTS
NECESSARY FOR HIGH WINDS. HOWEVER...MODELS CAN MISS THESE SMALL
SCALE FEATURES AND THIS WILL HAVE TO BE MONITORED CLOSELY TONIGHT.
AT THIS TIME WINDS ARE EXPECTED TO BE CLOSE TO ADVISORY LEVELS
OVER A WIDESPREAD AREA FROM THE HIGHWAY 395 CORRIDOR TO HIGHWAY
95...ESPECIALLY FROM RENO SOUTHWARD THROUGH CARSON CITY TO MAMMOTH
LAKES. THE ATMOSPHERE WILL BE WELL MIXED EARLY TUE AND ALLOW WINDS
TO MATERIALIZE EARLY ALONG THE SIERRA FRONT. THUS ADVISORIES WERE
STARTED EARLY IN THESE AREAS AND IT WOULD NOT BE OUT OF THE
QUESTION TO SEE GUSTS TO 65 MPH IN THE MORE WIND PRONE AREAS.
FURTHER EAST...STRONGER WINDS WILL LIKELY HOLD OFF UNTIL LATE
MORNING AS FRONT APROACHES AND MIXING TAKES FULL AFFECT. WHILE
LOCALIZED AREAS OF BLOWING DUST WILL BE POSSIBLE ALONG THE SIERRA
FRONT...THE BASIN AND RANGE WILL BE OPTIMAL FOR MORE WIDESPREAD
REDUCED VISIBILITY IN BLOWING DUST WHICH WILL BE THE PRIMARY
HAZARD TUE AFTN AND EVENING. OTHERWISE LAKE WATERS ARE EXPECTED TO
REMAIN ROUGH AND HAZARDOUS WITH LITTLE DECOUPLING TONIGHT ON LAKE
TAHOE WHERE WINDS WILL CONT OVERNIGHT INTO TUE.

MODEL QPF REMAINS LIGHT IF NOT NON EXISTENT. THE NAM12 SHOWED
SCT AREAS OF QPF GENERALLY LESS THAN 1/10 INCH ACROSS MANY AREAS
LATE TUE AFTN INTO TUE NGT AS VORT CENTER PASSES OVERHEAD.
IMPRESSIVE FRONTOGENESIS ALONG FRONT AND SUBSEQUENT COOLING ALOFT
SHOULD PRIME THE ATMOSPHERE FOR VORT MAXIMA/ASSOCD PVA TO PRODUCE
SCATTERED LIGHT SHOWERS. POPS WERE INCREASED TO CHC CATEGORY FOR THE
TAHOE BASIN NORTHWARD INTO LASSEN AND OVER NRN/ERN ZONES TUE
EVENING. DESPITE THE EXPECTED INCREASE IN COVERAGE...QPF WILL AMOUNT
TO ONLY A FEW HUNDREDTHS OF AN INCH. SNOW LEVELS WILL FALL SHARPLY
WITH A DUSTING OF NEW SNOW ON SOME AREA PEAKS.

SYSTEM WILL QUICKLY MOVE EAST WED WITH MUCH COOLER TEMPS AND
DECREASING CLOUDS. AFTER NEAR RECORD HIGH TEMPS IN THE 80S AND 90S
OVER THE WEEKEND...READINGS WILL BE AS MUCH AS 35 DEGREES COLDER
WED. LOCALIZED FREEZING TEMPS WILL BE LIKELY WED MORNING IN THE
TYPICAL COLD VALLEYS WITH A MORE WIDESPREAD FREEZE LIKELY BY THU
MORNING UNDER CLEAR SKIES AND LIGHT WINDS. WEAK UPPER S/W RDG AND
LGT NELY SFC FLOW WILL ALLOW FOR A SLOW WARMUP THU. HOHMANN

LONG TERM...FRIDAY THROUGH MONDAY...
SHORTWAVE RIDGING SHIFTS EAST OF THE AREA FRIDAY AS THE NEXT SYSTEM
TO AFFECT THE WEST COAST STARTS DROPPING SOUTH OUT OF CANADA. MODELS
CONTINUE TO SHOW AN INITIAL WAVE OF WEAK ENERGY PASSING OVER THE NRN
ZONES LATE FRIDAY...HOWEVER THE AMOUNT OF MOISTURE ASSOCIATED WITH
THE WAVE NOW LOOKS LESS FAVORABLE FOR ANY PRECIP. KEPT WITH THE DRY
FORECAST THROUGH FRIDAY NIGHT HOWEVER CLOUDS WILL BEGIN SPREADING
OVER THE REGION WITH INCREASING WEST FLOW.

SATURDAY IS WHEN THE PATTERN REALLY BREAKS DOWN AGAIN WITH THE LOW
STRENGTHENING AS IT DROPS SOUTH THROUGH THE PACNW AND REACHES NRN
CA/NV BY SATURDAY EVENING. LATEST MODEL RUNS HAVE A SLIGHTLY
DIFFERENT SOLUTION THAN THEY PREVIOUSLY DID HOWEVER MODEL TO MODEL
CONSISTENCY IS STILL GOOD. MODELS HAVE GONE BACK TO THE OLDER
SOLUTION OF A TRACK SLIGHTLY FURTHER EAST CREATING A COLDER AND
DRIER LOW. THE DEEPENING LOW SPINS UP A 120+ KT JET MAX OVER THE
CENTRAL SIERRA LATE SATURDAY WITH A FAIR AMOUNT OF OVERWATER
TRAJECTORY HELPING TO OVERCOME THE LACK OF MOISTURE. CONTINUED THE
TREND TO RAISE POPS WITH THE BEST CHANCE FOR PRECIP MAINLY NORTH OF
RENO SATURDAY NIGHT UNDER THE COLD POOL ALOFT. MODEL QPF AMOUNTS ARE
RATHER HIGH AND FAIRLY LOCALIZED INDICATING THE CONVECTIVE NATURE OF
THE PRECIP UNDER THE COLD POOL. FORCING LOOKS SUFFICIENT FOR STEADY
AND WIDESPREAD FRONTAL PRECIP LATE SATURDAY BECOMING MORE CONVECTIVE
SUNDAY.

THE LOW BECOMES STATIONARY OVER NEVADA SUNDAY BEFORE SLOWLY SHIFTING
EAST MONDAY. H7 TEMPS AROUND -6C WILL BE SUFFICIENTLY COLD TO RAISE
THE POSSIBILITY FOR LAKE ENHANCED SHOWERS SUNDAY IF A FAVORABLE WIND
PROFILE DEVELOPS. THE BEST CHANCE WOULD BE OVER PYRAMID LAKE BUT
WILL HAVE TO MONITOR. OTHERWISE CANT RULE OUT SHOWERS ANYWHERE IN
THE CWA WITH COOL...MOIST...AND UNSTABLE AIRMASS IN PLACE. EMBEDDED
VORT MAXIMA ROTATING AROUND THE LOW WILL ENHANCE SHOWER ACTIVITY BUT
IT IS FAR TOO EARLY TO TIME ANY OF THOSE FEATURES. TEMPERATURES WILL
FALL MUCH BELOW NORMAL FOR THE WEEKEND AND EARLY NEXT WEEK WITH THE
CONTINUED POSSIBILITY FOR FREEZING CONDITIONS AT NIGHT. JORDAN

FIRE WEATHER...
EARLIER THIS AFTERNOON...ADDED ZONE 453 TO THE RFW FOR
TODAY...MAINLY FOR AREAS NORTH OF INTERSTATE 80. SO FAR LOOKS TO BE
RIGHT ON TRACK. SHOULD SEE SEVERAL MORE HOURS OF CRITICAL WINDS AND
LOW HUMIDITY NORTH OF I-80 UNTIL 10PM.

ALSO EARLIER TODAY...UPGRADED TOMORROWS WATCHES TO RED FLAG
WARNINGS. AS FAR AS THE TIMING...ALL AREAS SOUTH OF INTERSTATE 80
ARE EXPECTED TO HIT CRITICAL CONDITIONS ON TUESDAY. GUSTY AND
ERRATIC WIND SHIFTS ARE EXPECTED ALONG THE COLD FRONT...WHICH ARE
EXPECTED TO MAKE CONDITIONS EVEN TOUGHER FOR ANY FIRE SUPPRESSION.
RH VALUES WILL RISE BEHIND THE COLD FRONT...BUT GUSTY AND ERRATIC
WINDS WILL CONTINUE UNTIL THE FRONT HAS COMPLETELY MOVED OUT OF THE
AREA.

CONCERNING THE SIERRA FRONT ZONES...450 AND 273...DOWNSLOPING WINDS
WILL KEEP HUMIDITY IN THE TEENS TONIGHT... ESPECIALLY AREAS NORTH OF
BRIDGEPORT...INCLUDING WALKER...MARKLEEVILLE...GALENA...LITTLE
VALLEY...WASHOE VALLEY... AND OTHER WIND PRONE MIDSLOPES AND RIDGES.
WINDS ARE EXPECTED TO GUST UP TO 35 MPH EVEN IN THE OVERNIGHT HOURS.

WITH THE COLD FRONT EXPECTING TO MOVE IN EARLY TUESDAY
MORNING...WINDS WILL BECOME WIDESPREAD BY 6AM IN ZONES 450-273.
STRONG THERMAL AND PRESSURE GRADIENTS ARE SUGGESTING WIND GUSTS
BETWEEN 45-50 MPH AND SUSTAINED WINDS AT 25 MPH THROUGH TUESDAY
AFTERNOON. RFW GOES THROUGH THE OVERNIGHT PERIOD TONIGHT AND THROUGH
TUESDAY AFTERNOON. ZONES 453 AND 458 RFWS DO NOT BEGIN UNTIL
9AM...WHEN DAYTIME MIXING BRINGS IN THE STRONGER WINDS.

SOME RH VALUES WILL BE MARGINAL TUESDAY...ONLY IN THE 15-20% IN SOME
AREAS BETWEEN I-80 AND HWY 50...BUT WITH THESE STRONG ADVISORY LEVEL
WINDS AND ERRATIC SHIFTS CAUSED BY THE COLD FRONT...PLUS THE
ABNORMALLY HOT AND DRY PERIOD THAT WE JUST CAME OFF...FEEL THAT THIS
FRONT WILL CAUSE SOME MAJOR FIRE WEATHER ISSUES. BEHIND THE COLD
FRONT WINDS WILL SHIFT TO THE NORTHWEST WITH RH VALUES INCREASING TO
AT LEAST 30%. WINDS WILL REMAIN BREEZY ON WEDNESDAY...ALTHOUGH MUCH
LESS THAN TUESDAY...WITH MUCH COOLER TEMPS AND HIGHER HUMIDITY.  HOON

AVIATION...
SOUTHWEST FLOW CONTINUES TO INCREASE AHEAD OF A STRONG COLD FRONT.
SURFACE GUSTS AROUND 30 KTS WILL CONTINUE THROUGH 03Z THIS EVENING
WITH LOCALIZED BLOWING DUST. GUSTS OVER THE SIERRA CREST DURING THIS
TIME WILL BE AROUND 50 KTS CREATING TURBULENCE NEAR THE SIERRA.

SOUTHWEST FLOW ALOFT FURTHER INCREASES TONIGHT WHILE LOW-LYING
VALLEYS DECOUPLE AND WINDS DECREASE. THIS WILL RAISE THE CONCERN FOR
LLWS AS THE WINDS ALOFT PEAK AROUND SUNRISE...12-15Z TUESDAY. THE
BIGGEST CONCERN FOR LLWS WILL BE AT KRNO AND THE NEARBY AIRPORTS IN
THE LEE OF THE SIERRA...WHILE KTRK AND KTVL MAY STAY WINDY ALL NIGHT
NEGATING THE CONCERN. WILL CONTINUE TO CARRY LLWS IN THE TAFS AND
FINETUNE LEVELS AND SPEEDS AS OBSERVATIONS COME IN.

GUSTY WINDS BECOME WIDESPREAD IN ALL LOCATIONS AGAIN TUESDAY MORNING
AS THE LOWER VALLEYS MIX OUT. WINDS TUESDAY APPEAR TO BE ROUGHLY 10
KTS STRONGER THAN MONDAY WITH GUSTS AS HIGH AS 40-45 KTS. THIS WILL
CREATE IFR VISIBILITY IN BLOWING DUST OVER MANY LOCATIONS IN WRN
NEVADA INCLUDING NEAR KLOL AND KNFL. THE MOST GUSTY AND ERRATIC
WINDS WILL OCCUR ALONG THE COLD FRONT WHICH IS EXPECTED TO BE NEAR
KSVE AROUND 18Z...KRNO-KLOL AROUND 21Z...AND KMMH-KHTH BY 00Z.
ISOLATED-SCATTERED SHOWERS OCCUR BEHIND THE COLD FRONT TUESDAY
EVENING MAINLY NORTH OF RENO...WITH PERIODS OF MVFR CIGS POSSIBLE.
JORDAN

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...BLOWING DUST ADVISORY FROM 11 AM TO 8 PM PDT TUESDAY FOR NVZ001-
     004.

     RED FLAG WARNING FROM 9 AM TO 5 PM PDT TUESDAY FOR NVZ453-459.

     RED FLAG WARNING UNTIL 5 PM PDT TUESDAY FOR NVZ450.

     WIND ADVISORY FROM 6 AM TO 8 PM PDT TUESDAY FOR NVZ003.

     LAKE WIND ADVISORY UNTIL 8 PM PDT TUESDAY FOR NVZ002.

CA...RED FLAG WARNING UNTIL 5 PM PDT TUESDAY FOR CAZ273.

     WIND ADVISORY FROM 6 AM TO 8 PM PDT TUESDAY FOR CAZ073.

     LAKE WIND ADVISORY UNTIL 8 PM PDT TUESDAY FOR CAZ072.

&&

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