Lake Wind Advisory 49, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
215 PM PDT SUN SEP 27 2009

.SHORT TERM...

HAVE MADE ONLY SLIGHT CHANGES TO THE ONGOING FORECAST...PRIMARILY
INCREASING POPS AND WINDS A BIT WITH INCOMING FRONTAL SYSTEM FOR
TUES.

CONSENSUS BLEND OF GFS/EC/UKMET/SREF (NAM A BIG OUTLIER) CONTINUES
TO SHOW STRONG FRONT PLOWING THROUGH THE REGION TUESDAY ASSOCIATED
WITH SIGNIFICANT TROF (2-2.5 SD BELOW NORMAL HEIGHT ANOMALIES).
CONFIDENCE WITH THIS FORECAST IS HIGH (E.G. 4 OUT OF 5) GIVEN SREFS
RELATIVELY LOW SPREADS WITH THE SYNOPTIC FEATURES. SOME VARIATIONS
IN FRONTAL SPEED DO EXIST, WHICH IS SOMETHING TO WATCH IN LATER
FORECASTS.

TIGHT THERMAL/PRESSURE GRADIENTS COUPLED WITH +2 SD 700MB WIND
ANOMALIES WILL CREATE STRONG WINDS FROM LATE MON THROUGH TUES. FOR
MORE DETAILED INFORMATION ABOUT THE WINDS, SEE THE FIRE WEATHER
DISCUSSION. WE WILL POST A LAKE WIND ADVISORY FOR PYRAMID LAKE FOR
MONDAY...AND IT IS CERTAINLY POSSIBLE THAT WE WILL END UP ISSUING
WIND ADVISORIES FOR TUESDAY GIVEN PATTERN AND STRENGTH OF THE
FRONT.

INTENSE FRONTOGENESIS ALOFT WILL YIELD SCT SHRA MAINLY NORTH OF HWY
50 TUES/TUES NGT...EVEN IN THE PRESENCE OF RELATIVELY LOW PW VALUES.
AS IS NORMAL, SURFACE FRONT REDEVELOPS TO THE EAST OF THE CWA, SO
LOCATIONS ALONG AND IMMEDIATELY EAST OF THE SIERRA FRONT WILL HAVE A
RELATIVE MIN IN PRECIP COVERAGE. COULD SEE A FEW THUNDERSTORMS AS
EC SHOWING SFC BASED LI VALUES TO NEAR ZERO TUES AFTN. A FEW SNOW
SHOWERS LIKELY ABOVE 6000FT BASED ON PROJECTED SNOW LEVELS.
TEMPERATURES BEHIND THE FRONT WILL BE DRAMATICALLY COOLER. WERE
FORECASTING HIGHS AROUND 60 IN WRN NV ON WEDNESDAY...IF WE STAY
CLOUDIER THEN TEMPS WILL BE CLOSER TO RAW GFS NUMBERS (E.G.
LOW/MID 50S).

WE WILL CONTINUE THE SPECIAL WEATHER STATEMENT FOR WINDS/TEMPS, AND
WE HAVE ALSO POSTED AN ONLINE WEATHER BRIEFING ON OUR WEBSITE
DETAILING THE PATTERN CHANGE.

CS

.LONG TERM...

ACTIVE WEATHER PATTERN WILL CONTINUE DURING THE EXTENDED PERIOD
WITH HIGH PRESSURE CENTER REMAINING WELL OFF THE WEST COAST AROUND
150W. AFTER A VERY COLD START THURSDAY MORNING...BRIEF SHORTWAVE
RIDGING OVER THE WEST COAST WILL BRING WARMING TEMPERATURES ALOFT.
SEVERAL DEGREES OF WARMING IS EXPECTED THURSDAY WITH INCREASING
WEST FLOW ALOFT BRINGING TEMPS BACK UP TO NORMAL FRIDAY.

THE INCREASE IN WEST FLOW FRIDAY IS IN RESPONSE TO THE NEXT UPPER
TROUGH WHICH SETTLES INTO THE WEST COAST NEXT WEEKEND. MODELS
GENERALLY AGREE ON INITIAL SHORTWAVE ENERGY BRUSHING NRN CA/NV
LATE FRIDAY WITH THE MAIN LOW DROPPING THROUGH THE PACNW SATURDAY.
THERE IS A DECENT MOISTURE TAP WITH THE INITIAL SHORTWAVE WHICH IS
EXPECTED TO GENERATE LIGHT TO MODERATE QPF AMOUNTS...HOWEVER IT
SHOULD ALL REMAIN NORTH OF THE CWA. THE LATEST EURO SPLITS THE
INITIAL ENERGY OFF AND DIVES IT SOUTH OVER CALIFORNIA WHERE THERE
IS MUCH LESS MOISTURE TO WORK WITH. EITHER WAY...FRIDAY AND MOST
OF FRIDAY NIGHT SHOULD REMAIN DRY.

THE STRONG LOW PRESSURE ANOMALY DROPS OVER OREGON SATURDAY
PUSHING A SURFACE FRONTAL BOUNDARY INTO NRN CA/NV. THE BROAD UPPER
LOW THEN STALLS OUT SOMEWHERE OVER OREGON OR NRN CA/NV AND
PERSISTS THROUGH THE WEEKEND. MOST MODEL RUNS HAVE A COLDER AND
STRONGER SYSTEM WHICH MAKES SENSE WITH THE CONTINENTAL ORIGINS OF
THE LOW...HOWEVER THE LATEST EURO IS TRENDING TOWARD A WARMER AND
WETTER SYSTEM. BOTH SOLUTIONS INDICATE A DECENT CHANCE FOR PRECIP
SO STARTED TRENDING POPS UPWARD SATURDAY AND SUNDAY MAINLY OVER
THE NRN ZONES. THE MAIN QUESTION WILL BE THE AMOUNT OF PRECIP AND
THE AMOUNT OF COLD AIR ASSOCIATED WITH THE LOW. THE BEST CHANCE
FOR PRECIP WILL BE SATURDAY AS THE UPPER JET DYNAMICS AND SURFACE
FRONTAL FORCING SAG INTO THE AREA...WHILE SUNDAY IS EXPECTED TO BE
INSTABILITY DRIVEN SHOWERS. JORDAN

&&

.AVIATION...

LIGHT WINDS...CLEAR SKIES...AND HOT TEMPERATURES TODAY WILL BEGIN
TO CHANGE MONDAY MORNING AS HIGH PRESSURE OVER THE WEST COAST
BREAKS DOWN. SOUTHWEST FLOW ALOFT INCREASES MONDAY MORNING WITH
GUSTS OVER SIERRA RIDGES APPROACHING 50 KTS BY 00Z MONDAY
AFTERNOON. SURFACE GUSTS SHOULD PICK UP AROUND 20Z WITH GUSTS AT
AREA TERMINALS GENERALLY 25-30 KTS.

WINDS ALOFT CONTINUE TO INCREASE MONDAY NIGHT WHILE SURFACE WINDS
ARE EXPECTED TO PERIODICALLY DROP OFF. THIS WILL CAUSE INCREASING
CONCERN FOR TURBULENCE OVER THE SIERRA AND POSSIBLY LOW LEVEL WIND
SHEAR AT KRNO. SURFACE WIND GUSTS WILL INCREASE ONCE AGAIN TUESDAY
MORNING AS A COLD FRONT APPROACHES THE AREA. GUSTS 30-35 KTS ARE
EXPECTED AFTER 18Z WITH GUSTS CLOSE TO 45 KTS POSSIBLE ALONG THE
COLD FRONT AROUND 00Z TUESDAY AFTERNOON. NO SIGNIFICANT PRECIP IS
EXPECTED WITH THE COLD FRONT HOWEVER BLOWING DUST WILL LIKELY
LOWER VISIBILITY...ESPECIALLY NEAR LOVELOCK AND FALLON. JORDAN

&&

.FIRE WEATHER...

A STRONG COLD FRONT WILL APPROACH THE PAC NW/NRN CA ON MONDAY AND
MOVE THROUGH OUR AREA ON TUESDAY. CURRENT MODELS HAVE SLOWED DOWN
THE FRONT JUST A BIT AND IN TURN 700 MB TEMPS AND THE GRADIENTS
ARE NOT AS IMPRESSIVE. HOWEVER...AHEAD OF THIS FRONT A DECENT
GRADIENT STILL DEVELOPS AND 700 MB WINDS INCREASE TO 25-30 KTS
FROM RENO NORTH LATE MONDAY AFTERNOON. WIND GUSTS OVER THE RIDGES
WILL INCREASE TO 40-50 MPH MONDAY AFTERNOON AND TO AROUND 60 MPH
DURING THE EVENING. VALLEY WIND GUSTS WILL LIKELY INCREASE TO
30-35 MPH ESPECIALLY OVER NRN AREAS AND ALONG HIGHWAY 395. THE
FIRE WEATHER WATCH WAS UPGRADED TO A RED FLAG WARNING...BUT THE
START TIME FOR THE RENO AREA WAS PUSHED BACK TO 2P. HUMIDITY HAS
BEEN DOWN IN THE SINGLE DIGITS FOR SEVERAL DAYS WITH POOR
OVERNIGHT RECOVERIES TO ONLY AROUND 15% IN MANY AREAS. HUMIDITY
MAY IMPROVE SLIGHTLY ON MONDAY...BUT ONLY TO 10-15% IN AREAS EAST
OF THE SIERRA. HUMIDITY WILL INCREASE MONDAY NIGHT...HOWEVER
CONTINUED GUSTY WINDS MAY CAUSE CRITICAL FIRE WEATHER CONDITIONS
TO PERSIST PAST SUNSET. DURING THE OVERNIGHT HOURS AS THE FRONT
APPROACHES NRN AREAS...SOME AREAS MAY HAVE PERIODS OF STRONGER
WINDS...BUT THIS WOULD LIKELY BE LESS WIDESPREAD AND ALSO HUMIDITY
WILL BE ON THE RISE TO AT LEAST 25% IN MOST AREAS.

WINDS WILL INCREASE ON TUESDAY AS THE FRONT NEARS. WINDS AHEAD OF
THE FRONT SOUTH OF INTERSTATE 80 WILL INCREASE DURING THE MORNING
WITH GUSTS UP TO 40 MPH OR HIGHER THROUGH THE AFTERNOON. DRY
CONDITIONS WILL REMAIN IN PLACE FURTHER SOUTH WITH HUMIDITY AROUND
15%. EVEN IF RH COMES UP TO 20% IN SOME AREAS CRITICAL FIRE
WEATHER CONDITIONS CAN STILL BE EXPECTED DUE TO THE STRENGTH OF
THE WINDS...ESPECIALLY IN THE FEW HOURS JUST BEFORE FRONTAL
PASSAGE. THEREFORE THE FIRE WEATHER WATCH WILL REMAIN FOR ZONES
273 AND 459. WILL LEAVE ZONE 450 OUT OF THE WATCH FOR NOW BUT
LATER SHIFTS WILL HAVE TO MONITOR IF FRONTAL PASSAGE IS SLOWER.
WINDS WILL SHIFT TO THE NORTHWEST AND REMAIN GUSTY BEHIND THE
FRONT...BUT HUMIDITY WILL BE ON THE RISE. MINIMUM HUMIDITIES NORTH
OF HIGHWAY 50 WILL LIKELY INCREASE TO AROUND 20% OR HIGHER.
GMCGUIRE

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...RED FLAG WARNING FROM NOON TO 10 PM PDT MONDAY FOR NVZ458.

     FIRE WEATHER WATCH FROM TUESDAY MORNING THROUGH TUESDAY
     AFTERNOON FOR NVZ459.

     RED FLAG WARNING FROM 2 PM TO 10 PM PDT MONDAY FOR NVZ450.

     LAKE WIND ADVISORY FROM 2 PM TO 8 PM PDT MONDAY FOR NVZ004.

CA...RED FLAG WARNING FROM NOON TO 10 PM PDT MONDAY FOR CAZ270-271-
     278.

     FIRE WEATHER WATCH FROM TUESDAY MORNING THROUGH TUESDAY
     AFTERNOON FOR CAZ273.

&&

HTTP://WEATHER.GOV/RENO