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AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE RENO NV
938 PM PDT MON APR 20 2015

.UPDATE...

CURRENT FORECAST IS ON TRACK FOR TONIGHT, WITH ONLY A MINOR
CLEAN-UP PLANNED TO REMOVE CONVECTION AND REDUCE WIND SPEEDS THIS
EVENING.

THE LAST OF THE CONVECTIVE ACTIVITY OVER PLUMAS COUNTY HAS
DIMINISHED DURING THE PAST HOUR. THE GUST FRONT THAT PUSHED ACROSS
WESTERN NV EARLIER THIS EVENING LOST MUST OF ITS PUNCH AS IT MOVED
THROUGH FERNLEY AND PYRAMID LAKE, WITH GUSTS ONLY 15-20 MPH. THIS
PALES IN COMPARISON TO THE 30-40 MPH GUSTS THAT OCCURRED BETWEEN
RENO AND MINDEN A FEW HOURS AGO. THE OTHER EFFECT OF THE GUST
FRONT PASSAGE WAS A JUMP IN DEW POINTS INTO THE 20S AND 30S. EAST
OF THIS BOUNDARY INCLUDING LOVELOCK AND FALLON, DEW POINTS WERE
STILL IN THE SINGLE DIGITS.

ALTHOUGH MOST OF THE WINDS HAVE DROPPED OFF, SOME GUSTS TO 25 MPH
WERE STILL OCCURRING IN EASTERN LASSEN COUNTY FROM THE OUTFLOW
LEFT BY THE PLUMAS COUNTY ACTIVITY. THESE WINDS SHOULD DROP
FURTHER THROUGH THE REMAINDER OF THE EVENING.  

&&

.PREVIOUS DISCUSSION... /ISSUED 213 PM PDT MON APR 20 2015/ 

SYNOPSIS...
SCATTERED SHOWERS AND THUNDERSTORMS IN THE SIERRA WILL DIMINISH
THIS EVENING. LOW PRESSURE MOVING INLAND TUESDAY THROUGH THURSDAY
WILL BRING INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS AS
WELL AS COOLER TEMPERATURES AREA WIDE. A DRIER WESTERLY FLOW WILL
BRING A DECREASE IN SHOWERS THIS WEEKEND.

SHORT TERM...
CONVECTION INITIATED EARLIER THIS AFTERNOON COMPARED TO SUNDAY
SUGGESTING MID LEVEL COOLING AND A GRADUAL INCREASE IN MOISTURE
ALONG THE SIERRA. MOST OF THE ACTIVITY HAS BEEN WEST OF THE CREST
SO FAR THROUGH EARLY AFTERNOON, BUT WEAKER LOW LEVEL FLOW AND
OUTFLOW FROM CURRENT STORMS SHOULD BE SUFFICIENT FOR DEVELOPMENT
ON THE EAST SIDE. WE DO NOT EXPECT THEM TO PUSH INTO WESTERN NV
WHERE MOISTURE AND INSTABILITY IS MUCH LESS. HOWEVER, OUR LOCAL
HRRR INDICATES THAT OUTFLOW WILL PUSH OUT ACROSS THE SIERRA FRONT
INTO WESTERN NV LATE AFTERNOON AND EARLY EVENING WITH GUSTS AROUND
30 MPH FOR A COUPLE OF HOURS.

UPPER LOW OFF THE CA COAST WILL MOVE INLAND TUESDAY AND START AN
INFLUX OF MOISTURE ON SOUTHEASTERLY MID LEVEL FLOW. TIMING LOOKS
GOOD FOR SKIES TO BE CLEAR ENOUGH IN THE MORNING AND EARLY
AFTERNOON TO GET SOME DECENT HEATING WITH NAM MODEL SOUNDINGS
INDICATING LI/S -3C OR BETTER BY AFTERNOON ACROSS FAR WESTERN NV.
CONVECTION WILL ONCE AGAIN INITIATE OVER THE SIERRA AND THEN SHOW
MORE OF A TENDENCY TO PUSH OFF INTO WESTERN NV DURING THE LATE
AFTERNOON AND EVENING, ESPECIALLY WEST OF HIGHWAY 95. SHEAR WILL
BE WEAK, BUT SUB CLOUD LAYERS WILL BE DRY ENOUGH INITIALLY OVER
WESTERN NV FOR A POTENTIAL OF OUTFLOW GUSTS TO 50+ MPH. IN
ADDITION, STORMS WILL BE SLOW MOVING AS AREA WILL BE IN
DEFORMATION AND LIGHT WINDS ALOFT. THIS COULD PRODUCE LOCALLY
HEAVY RAINFALL.

UPPER LOW WILL MOVE ONLY VERY SLOWLY EASTWARD WED-THU WITH
ABUNDANT MID-HI LEVEL MOISTURE AND GENERAL LIFT IN DEFORMATION
REGION TO THE NORTH KEEPING SKIES MOSTLY CLOUDY. WHILE MODELS
CONTINUE TO SHOW WIDESPREAD QPF WITH LOCALLY DECENT QPF AMOUNTS
ALONG THE EASTERN SIERRA, THE CLOUD COVER WILL LIMIT THUNDERSTORM
POTENTIAL. WE MAINTAINED THE MENTION OF SHOWERS, EVEN AT NIGHT,
WITH A SLIGHT CHANCE OF DIURNALLY DRIVEN STORMS WHERE ENOUGH
BREAKS IN THE CLOUDS CAN PERSIST AND ALLOW FOR LOCALLY ENHANCED
INSTABILITY. SOME DRYING IS NOW NOTED IN THE MODELS ACROSS OUR
NORTHERN AREAS DURING THIS TIME FRAME, SO WE HAVE LOWERED OR
REMOVED POPS NORTH AND HIGHLIGHTED THE EASTERN SIERRA AND WESTERN
NV SOUTH OF I-80 FOR BEST CHANCES.

OTHERWISE, EXPECT TEMPERATURES TO REMAIN WARM THROUGH TUESDAY
BEFORE COOLING MIDWEEK. THE HAZE WILL DEPEND HEAVILY ON
PRECIPITATION AND COULD BE WITH US ANOTHER DAY OR SO. HOHMANN

LONG TERM (FRIDAY-MONDAY)...

TRENDS IN THE LONG RANGE GUIDANCE ARE FOR MORE SHOWERS FRIDAY, AND
DRIER/WARMER SATURDAY INTO MONDAY. WE'VE FOLLOWED THIS FOR THE MOST 
PART IN TODAYS FORECAST. 

FOR FRIDAY, BOTH THE GFS/EC ARE SHOWING A PRONOUNCED SHORTWAVE DIVING 
SE OUT OF THE NORTH PACIFIC JET. THIS FEATURE COUPLED WITH RESIDUAL 
MOISTURE ALOFT AND WEAK INSTABILITY SHOULD BE ENOUGH TO REGENERATE 
SHOWERS ACROSS MUCH OF THE AREA FRIDAY AFTERNOON. WHILE THUNDER 
RISKS APPEAR MINIMAL, THERE COULD BE SOME APPRECIABLE WETTING RAINS 
ACROSS MONO AND MINERAL COUNTIES INTO CENTRAL NV. FRIDAY MORNING 
SHOWERS AREN'T OUT OF THE QUESTION EITHER AS LIFT FROM APPROACHING 
WAVE OVERSPREADS THE REGION. 

GUIDANCE THEN SHOWS RIDGING MOVING OVER FOR SAT/SUN WITH PERIODS OF 
SCT-BKN HIGH CLOUDS, WARMING TEMPS, AND LOWER HUMIDITIES. SO A 
PLEASANT WEEKEND WEATHER-WISE IS LOOKING LIKELY. INTO EARLY NEXT 
WEEK, WHILE YESTERDAYS SIMULATIONS WERE SHOWING POTENTIAL FOR A LATE 
SEASON "WINTER" STORM MOVING INTO THE NORTHERN SIERRA, TODAY'S 
GUIDANCE IS MUCH FURTHER NORTH ON STORM TRACK. THIS WOULD LEAVE OUR 
CWA PRETTY MUCH DRY AND BREEZY MONDAY/TUESDAY. NOT TERRIBLY 
SURPRISING GIVEN THE WINTER WE HAD. ECMWF ENSEMBLE SPREADS ARE NOT 
OVERLY HIGH SO WE'VE FOLLOWED THIS TREND, REDUCED POPS, KEPT WINDS 
GUSTY, AND WARMED TEMPS FOR MONDAY. CS

AVIATION...

THUNDERSTORMS CONTINUE TO BE THE MAIN WEATHER CONCERN FOR AVIATION 
THROUGH AT LEAST TUESDAY. ISOLATED-SCATTERED TSTMS ARE EXPECTED 
AGAIN TODAY UP AND DOWN THE SIERRA 21Z-03Z, FOLLOWING THE LATEST HRRR 
AND SREF GUIDANCE. THE MAIN IMPACTS WOULD BE PERIODS OF MVFR 
CONDITIONS AND GUSTY OUTFLOW WINDS TO 30 KTS AT TVL/TRK (60% 
CHANCE). THE OUTFLOW WINDS FROM THE MOUNTAIN TSTMS MAY MAKE IT TO 
RNO/CXP LATE THIS AFTERNOON, WITH GUSTS 20-30 KTS AND POTENTIAL 
LLWS/TURBULENCE. TSTM RISK LATE TODAY AT MMH IS MORE NEBULOUS WITH 
MOST GUIDANCE SHOWING CELLS DEVELOPING OVER NEARBY HIGH TERRAIN AND 
THEN PUSHING OFF SLOWLY TO THE W/NW AWAY FROM THE TERMINAL. 

FOR TUESDAY GUIDANCE SHOWS MORE WIDESPREAD TSTMS 20Z-03Z, WITH A 
GREATER RISK FOR MVFR CONDITIONS, LIGHTNING, AND STRONG OUTFLOW 
WINDS. THIS COULD IMPACT NOT ONLY THE SIERRA AIRPORTS BUT ALSO 
RNO/CXP/MEV/SVE. FORECAST STORM MOTIONS ARE WESTERLY SOUTH OF I-80 
AND EASTERLY NORTH OF I-80, INTRODUCING SOME UNCERTAINTY IN STORM 
COVERAGE OVER WESTERN NEVADA. SUFFICIENT COVERAGE OF STORMS MAY 
EXIST OVER THE SIERRA TO IMPACT AIR ROUTES IN AND OUT OF THE BAY 
AREA AND CENTRAL CA AIRPORTS. CS

&&

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

$$

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