Wildfire in Nevada, May 22 to 26, 2012

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
200 AM PDT TUE MAY 22 2012

.SHORT TERM...

FEW CHANGES WERE MADE TO THE ONGOING FORECAST. A COUPLE OF FAST
MOVING SHORTWAVES WILL BE DRIVEN THROUGH THE SIERRA AND WESTERN
NEVADA BACKED BY A STRONG JET, WHICH WILL BRING GUSTY WINDS AND
GRADUALLY COOLING TEMPERATURES. THE FLOW AMPLIFIES THURSDAY INTO
FRIDAY AS A TROUGH DIGS INTO THE WEST WITH A SIGNIFICANT CHANGE IN
THE WEATHER PATTERN BY THE END OF THE WEEK.

A WEAK COLD FRONT BRUSHING ACROSS NORTHERN CA/NV EARLY THIS
MORNING WILL ALLOW AREAS NORTH OF HIGHWAY 50 TO COOL BY 5 TO 10
DEGREES, WHILE AREAS SOUTH WILL ONLY COOL 2 TO 5 DEGREES. THE MAIN
CONCERN WILL BE THE STRONG PRESSURE GRADIENT WITH ANOTHER ROUND OF
GUSTY AFTERNOON WINDS TODAY. THESE WINDS WILL COMBINE WITH A DRY
AIR MASS, MAKING FOR CRITICAL FIRE WEATHER CONDITIONS. PLEASE SEE
THE FIRE WEATHER SECTION OF THE DISCUSSION BELOW FOR MORE DETAILS.

A TROUGH WILL DIG INTO THE WEST BY MIDWEEK, CLOSING OFF INTO AN
UPPER LEVEL LOW ACROSS NORTHEASTERN CA/WESTERN NV THURSDAY INTO
FRIDAY. THERE IS A 15 TO 20 PERCENT CHANCE FOR SHOWERS NORTH OF
GERLACH THURSDAY MORNING, WITH INCREASING CHANCES FOR
PRECIPITATION AS FAR SOUTH AS HIGHWAY 50 BY EARLY FRIDAY MORNING.
THIS LOW WILL USHER IN A COLDER AIR MASS WITH HIGH TEMPERATURES ON
THURSDAY 3 TO 5 DEGREES BELOW AVERAGE. DF

.LONG TERM...FRIDAY THROUGH MONDAY...

NO SIGNIFICANT CHANGE IN THE MODEL DATA FOR FRIDAY WITH A COLD
TROUGH DROPPING SOUTH INTO NORTHERN CALIFORNIA/NORTHWEST NEVADA.
MAIN IMPACTS FROM THIS SYSTEM CONTINUE TO BE RAIN, SNOW AND
AFTERNOON HIGHS AS MUCH AS 20 DEGREES BELOW NORMAL FRIDAY. THE LOW
SHOULD MOVE EAST OF THE AREA BY LATE SATURDAY WITH DRIER AND WARMER
CONDITIONS FOR THE END OF THE MEMORIAL DAY WEEKEND. THOSE PLANNING
OUTDOOR ACTIVITIES SHOULD PREPARE FOR THE POTENTIAL OF SNOW IN THE
SIERRA/NORTHEAST CALIFORNIA AND WELL BELOW NORMAL TEMPERATURES
FRIDAY AND SATURDAY.

MODELS HAVE BEEN CONSISTENT WITH THE LOW MOVING INTO NORTHERN
CALIFORNIA/NORTHWEST NEVADA BY EARLY FRIDAY MORNING.  LATEST 00Z
ECMWF FORECAST HAS A TRACK SLIGHTLY FATHER WEST, BUT THE SHIFT IN
TRACK DOESN'T HAVE MUCH IMPACT ON THE LOCATION OF THE DEFORMATION
ZONE ON THE NORTH SIDE OF THE LOW.

DEFORMATION ZONES CONTINUES TO BE THE MAIN FOCUS FOR RAIN/SNOW NORTH
OF US-50, WITH A DRY SLOT ACROSS AREAS SOUTH OF US-50. PRECIPITATION
BAND SHOULD START TO IMPACT AREAS NORTH OF SUSANVILLE-GERLACH AROUND
MIDNIGHT FRIDAY, THEN SPREAD SOUTH TO I-80/US-50 FRIDAY MORNING.
UNDER THE COLD CORE OF THE LOW, SNOW LEVELS MAY DROP AS LOW AS
5000-6000 FEET EARLY FRIDAY MORNING THEN REMAIN NEAR 6000 FEET
FRIDAY AFTERNOON WITH DAYTIME HEATING. AFTERNOON HIGHS FRIDAY ACROSS
WESTERN NEVADA MAY BE STUCK IN THE 50S TO LOW 60S WITH 40S TO LOW
50S IN THE SIERRA.

RAINFALL AMOUNTS OF 0.50 INCHES OR MORE ARE POSSIBLE IN THE MAIN
PRECIPITATION BAND, EVEN ON WESTERN NEVADA VALLEY FLOORS.  FOR SNOW
ACCUMULATIONS, POTENTIAL IS THERE FOR A FEW INCHES ON NON-PAVED
SURFACES ABOVE 5500 FEET, WITH ACCUMULATIONS POSSIBLE ON ROADS ABOVE
7000 FEET.

MODEL DIFFERENCES INCREASE ON SATURDAY IN HOW QUICKLY THE SYSTEM
WILL MOVE INTO IDAHO AND UTAH.  LATEST GFS IS MUCH FASTER, PERHAPS
TOO FAST IN KICKING THE SYSTEM INTO EASTERN NEVADA FRIDAY EVENING.
THE ECMWF IS SLOWER AND LEAVES THE DEFORMATION BAND OVER NORTHWEST
NEVADA THROUGH SATURDAY AFTERNOON.  IF THIS OCCURS HIGHER RAINFALL
AMOUNTS ARE POSSIBLE, WITH MUCH COOLER AFTERNOON HIGHS SATURDAY.

FOR SUNDAY AND MEMORIAL DAY,  A DRIER AND WARMER WEST-NORTHWEST FLOW
DEVELOPS OVER THE WEST. THE RESULT SHOULD BE WARM AND DRY CONDITIONS
WITH AFTERNOON HIGHS RETURNING TO NORMAL, UPPER 70S-LOW 80S FOR
WESTERN NEVADA, AND 60S-LOW 70S FOR THE SIERRA. BRONG

&&

.AVIATION...

VFR CONDITIONS CONTINUE THROUGH THURSDAY. INCREASED WINDS WILL
CONTINUE TODAY WITH PEAK GUSTS TO 35 KTS AT KRNO-KMMH AND ACROSS
WESTERN NEVADA.  MAIN DIFFERENCE TODAY IS THE POTENTIAL FOR
SUSTAINED WINDS OVER 20 KTS ACROSS WESTERN NEVADA. FOR KTVL AND
KTRK GUSTS SHOULD REMAIN AT 25 KTS OR LESS. SIERRA RIDGE WINDS
40-60 KTS WILL PRODUCE TURBULENT APPROACHES AT ALL TERMINALS.

COLDER SYSTEM SHOULD REACH NORTHERN CALIFORNIA/NORTHWEST NEVADA
AFTER 00Z FRIDAY WITH POTENTIAL FOR MFR CONDITIONS ACROSS WESTERN
NEVADA AND MVFR/IFR AT KTVL AND KTRK DUE TO RAIN AND HIGH ELEVATION
SNOW.  BRONG

&&

.FIRE WEATHER...

RED FLAG WARNING IS IN EFFECT TODAY FOR PERSHING, CHURCHILL, MINERAL
AND SOUTHERN LYON COUNTIES DUE TO GUSTY WINDS AND LOW HUMIDITY. AS
A LARGE TROUGH STARTS TO DEVELOP OVER THE WEST, SEVERAL DEGREES OF
COOLING WILL OCCUR TODAY WITH INCREASED HUMIDITY NORTH OF US-50
AND WEST OF US-95. AFTERNOON HUMIDITY SHOULD DROP TO NEAR AND
BELOW 15% ACROSS MINERAL AND CHURCHILL COUNTIES, AND REMAIN CLOSER
TO 15-20% FOR SOUTHERN LYON AND PERSHING COUNTIES.

GUSTS TODAY WILL REMAIN AT 30-40 MPH, HIGHER GUSTS TO 45 MPH ARE
POSSIBLE ALONG US-95 BETWEEN FALLON AND HAWTHORNE. THE BIGGER IMPACT
WILL BE A LENGTHY PERIOD OF SUSTAINED WINDS OF 20-30 MPH ACROSS
THE RED FLAG WARNING AREA. THIS IS DUE TO A 35-40 DEGREE THERMAL
GRADIENT BETWEEN SOUTHERN NEVADA (AFTERNOON HIGHS NEAR 100) AND
NORTHERN WASHOE COUNTY (AFTERNOON HIGHS IN THE LOW 60S).

BREEZY WINDS MAY CONTINUE WEDNESDAY, THOUGH GUSTS SHOULD REMAIN NEAR
AND BELOW 30 MPH.  ADDITIONAL COOLING WILL OCCUR WITH AFTERNOON
HUMIDITY NEAR AND ABOVE 20% AS THE TROUGH PUSHES SOUTH OVER THE
GREAT BASIN.

WETTING RAINS AND HIGH ELEVATION SNOW ARE BECOMING MORE LIKELY
FRIDAY NORTH OF US-50 AS A COLD LOW REACHES NORTHERN CALIFORNIA AND
NORTHWEST NEVADA. HIGH END RAINFALL AMOUNTS COULD EXCEED 0.50 INCHES
EVEN ON NEVADA VALLEY FLOORS. BRONG

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...RED FLAG WARNING FROM 1 PM THIS AFTERNOON TO 9 PM PDT THIS
     EVENING NVZ453-459.

     LAKE WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 9 PM PDT THIS
     EVENING FOR PYRAMID LAKE IN NVZ004.

     LAKE WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM PDT
     WEDNESDAY FOR LAKE TAHOE IN NVZ002.

CA...LAKE WIND ADVISORY FROM 1 PM THIS AFTERNOON TO 5 AM PDT
     WEDNESDAY FOR LAKE TAHOE IN CAZ072.

&&

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