Special Weather Statement, NWS Reno, NV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
210 PM PDT THU AUG 7 2014

.SYNOPSIS...

ISOLATED SHOWERS AND THUNDERSTORMS ARE POSSIBLE MAINLY NEAR THE
SIERRA AND IN NORTHEAST CALIFORNIA THROUGH THIS EVENING. ANOTHER
LOW PRESSURE APPROACHING THE WEST COAST WILL BRING INCREASED
CHANCES OF THUNDERSTORMS FROM FRIDAY THROUGH EARLY NEXT WEEK. SOME
STORMS MAY PRODUCE LOCALLY HEAVY RAINFALL. TEMPERATURES WILL
REMAIN NEAR NORMAL FOR THE UPCOMING WEEK.

&&

.SHORT TERM...

CUMULUS BUILDUPS HAVE FORMED ACROSS MUCH OF THE REGION, WITH
BEST DEVELOPMENT SO FAR IN THE CONVERGENCE ZONE OF NORTHERN LASSEN
COUNTY, PARTS OF NORTHWEST NV NORTH OF INTERSTATE 80, AND NEAR THE
SIERRA CREST. INSTABILITY IS NOT AS STRONG TODAY AND NO
SIGNIFICANT UPPER FORCING IS EXPECTED, SO CONVECTION SHOULD BE
MORE SPARSE BEFORE WINDING DOWN LATER THIS EVENING. MOISTURE WILL
REMAIN PLENTIFUL WITH LITTLE CELL MOTION EXPECTED ESPECIALLY SOUTH
OF I-80, SO AS STORMS PULSE UP THEY COULD PRODUCE BRIEF HEAVY
RAINFALL. STEERING FLOW IN THE SIERRA IS GENERALLY NORTHEAST TO
EAST SO MOST CELLS THAT FORM NEAR THE CREST SHOULD PROPAGATE
PRIMARILY TO THE WEST.

FOR FRIDAY, THE POTENTIAL FOR AFTERNOON AND EVENING CONVECTION
WILL INCREASE AS LOW PRESSURE APPROACHES THE NORTHERN CALIFORNIA
COAST, WITH SOME COOLING ALOFT PRODUCING INCREASED INSTABILITY
OVER THE REGION. 700-500 MB FLOW BECOMES SOUTHWEST-WEST WITH A
MODEST ZEPHYR BREEZE EAST OF THE CREST DEVELOPING BY MID
AFTERNOON, SO THIS WOULD FAVOR AN EAST TO NORTHEAST STORM MOTION
GENERALLY AROUND 10 KNOTS. MOISTURE WILL REMAIN PLENTIFUL, AND
PROPAGATION AIDED BY OUTFLOWS COULD INCREASE RAIN DURATION IN
SOME LOCATIONS, SO THE POTENTIAL FOR LOCALLY HEAVY RAIN WILL
CONTINUE DESPITE THIS INCREASE IN CELL MOTION.

FOR SATURDAY, MOST GUIDANCE DATA IS INDICATING A CLOSED LOW
CENTER REACHING THE SAN FRANCISCO BAY. FLOW ALOFT OVER EASTERN
CA-WESTERN NV BECOMES SOUTHEAST-SOUTH WHICH WILL LEAD TO MORE
MOISTURE AND CONTINUED INSTABILITY FOR PRODUCING SHOWERS AND
THUNDERSTORMS. THE MORE FAVORED AREAS FOR THUNDERSTORM ACTIVITY
WILL DEPEND ON HOW CLOSE THE LOW TRACKS TO THE COAST, AND TIMING
OF SHORTWAVE ENERGY ROTATING AROUND THE MAIN LOW. FOR NOW WE HAVE
INCREASED POPS MAINLY SOUTH OF HIGHWAY 50, BUT DEFORMATION ZONE
COULD SET UP OVER THE SIERRA AND NORTHEAST CA SATURDAY EVENING AND
OVERNIGHT AND SUSTAIN DEVELOPMENT LONGER THAN USUAL. AS A RESULT,
WE CARRIED POPS THROUGH SUNDAY MORNING GENERALLY WEST OF A
GERLACH-FERNLEY-MAMMOTH LAKES LINE. MJD

.LONG TERM...SUNDAY THROUGH THURSDAY...

MODELS ARE IN GOOD AGREEMENT WITH A TROUGH ALONG THE CALIFORNIA
COAST SUNDAY-MONDAY AND A SERIES OF WEAK VORTICITY LOBES SWINGING
ACROSS THE SIERRA AND NORTHWEST NV. THIS PROVIDES POTENTIAL FOR
AFTERNOON/EVENING THUNDERSTORMS ACROSS THE SIERRA AND ACROSS
WESTERN NV WEST OF A GERLACH TO HAWTHORNE LINE. THERE IS ALSO
POTENTIAL FOR NOCTURNAL THUNDERSTORMS SUNDAY NIGHT MAINLY FROM THE
TAHOE BASIN NORTHWARD INTO LASSEN AND MODOC COUNTIES. FORECAST
CONFIDENCE IS QUITE LOW TUESDAY-THURSDAY WITH THE GFS ENSEMBLE
SYSTEM SUPPORTING RIDGING OVER THE EASTERN SIERRA AND WESTERN NV,
WHILE OTHER MODELS SHOW A LOW PRESSURE SYSTEM IN VARIOUS POSITIONS
ACROSS THE WEST. THE CURRENT FORECAST FOLLOWS THE GFS WITH DRY
CONDITIONS AND NEAR NORMAL TEMPERATURES WED-THU. JCM

&&

.AVIATION...

SMALL ISOLATED SHOWERS HAVE DEVELOPED ACROSS THE WESTERN NV DESERT
THIS AFTERNOON. LATER THIS AFTERNOON AND EVENING, THUNDERSTORMS WILL
DEVELOP NEAR THE SIERRA CREST AND ACROSS PLUMAS, LASSEN AND NORTHERN
WASHOE COUNTIES. HEAVY RAIN AND OUTFLOW WINDS TO 40 KTS ARE THE
BIGGEST THREAT WITH ANY STRONGER STORMS. LOW PRESSURE ALONG THE
CALIFORNIA COAST WILL ALLOW SHOWERS AND THUNDERSTORMS TO DEVELOP
EACH DAY THROUGH MONDAY. JCM

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...NONE.
CA...NONE.
&&

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

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RENO NV
442 PM PDT THU AUG 7 2014

CAZ072-080030-
GREATER LAKE TAHOE AREA-
442 PM PDT THU AUG 7 2014

...STRONG THUNDERSTORM OVER BARKER PASS AND BLACKWOOD CREEK...

AT 434 PM PDT...NATIONAL WEATHER SERVICE METEOROLOGISTS WERE TRACKING
A STRONG THUNDERSTORM 4 MILES SOUTHWEST OF TAHOE CITY...AND MOVING
EAST AT 5 MPH.

OCCASIONAL LIGHTNING...HEAVY RAIN WITH AMOUNTS NEAR ONE INCH PER
HOUR...AND PENNY SIZE HAIL...WILL OCCUR WITH THIS STORM.

* LOCATIONS AFFECTED THROUGH 515 PM PDT INCLUDE...HOMEWOOD...
  SUNNYSIDE-TAHOE CITY...TAHOE CITY...SUGAR PINE POINT STATE PARK.

IF ON THE WEST SHORE OF LAKE TAHOE...PREPARE TO HEAD FOR SHORE NOW.
DON'T BE CAUGHT ON THE WATER IN A THUNDERSTORM. STRONG WIND GUSTS
AND LIGHTNING POSE AN IMMEDIATE DANGER TO BOATERS. GUSTY WINDS WILL
CAUSE A RAPID INCREASE IN WAVE HEIGHTS WHICH MAY CAPSIZE SMALL BOATS.

&&

LAT...LON 3920 12010 3903 12010 3903 12022 3916 12026
      3920 12025
TIME...MOT...LOC 2340Z 270DEG 4KT 3912 12024

JHW