NWS Forecast Discussion
Area Forecast DiscussionIssued by NWS Reno, NV
000 FXUS65 KREV 090553 AFDREV AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RENO NV 1053 PM PDT WED SEP 8 2010 .UPDATE... WINDS AT LAKE TAHOE ARE DROPPING. SO WILL ALLOW THE ADVISORY TO EXPIRE. NO OTHER SIGNIFICANT UPDATES BUT THINK THE CHANCES OF PCPN RAPIDLY DIMINISHING. CURRENT FORECAST DOES SHOW A DECREASE IN POPS OVERNIGHT WITH NO DEEP CONVECTION. MLF && .PREVIOUS DISCUSSION... /ISSUED 816 PM PDT WED SEP 8 2010/ UPDATE... BUOYS AT LAKE TAHOE STILL SHOWING WINDS IN THE SUSTAINED 15 T0 25 MPH RANGE AND WINDS AT KTVL ARE STILL GUSTING TO NEAR 25 MPH. THIS LEADS ME TO BELIEVE THAT GRADIENT IS SUFFICIENT TO KEEP THE LAKE WIND ADVISORY CRITERIA WINDS GOING A BIT LONGER...SO WILL UPDATE THE WINDS TO REFLECT AND ADD HIGHER WAVES ALONG THE NORTHEAST SHORES...THEN EXTEND THE ADVISORY UNTIL 11 PM. ON PYRAMID LAKE THE ONE OBSERVATION SITE WE HAVE IS FAR FROM THE LAKE ONO THE WEST SHORE...BUT IS GUSTING INTO THE 30-35 MPH RANGE NOW. WITH SUNSET THE LAKE CLOSES AND WE DO NOT NORMALLY ISSUE ADVISORIES FOR THE NIGHTTIME HOURS. BUT WILL UPDATE TO INDICATE STRONGER NW WINDS AND HIGHER WAVES ON THE SOUTH END OF THE LAKE. THE UPPER TROF IS MOVING ACROSS CA NOW WITH A JET STREAK DROPPING SOUTH INTO THE BASE OF THE TROF. THIS JET STREAK COULD SLOW THE EASTWARD PROGRESSION OF THE TROF BUT RIGHT NOW APPEARS TO BE HAVING LITTLE AFFECT. EARLIER CONVECTION WAS A BIT MORE WIDESPREAD TO THE WEST OF THE CWA AND WOULD EXPECT SOME CONVECTION TO CONTINUE NEAR THE BASE OF THE TROF WHERE TEMPS ALOFT ARE COLDEST. BUT WITH LACK OF LOW LVL INSTABILITY OVERNIGHT AND WITH BEST JET DYNAMICS LIFTING OUT OF THE AREA TO THE EAST THINK ANY CONVECTION OVER OUR AREA WOULD BE SHORT LIVED AND ELEVATED. WILL LEAVE A MENTION OF ISOLATED CONVECTION OVER THE REGION THIS EVENING...BUT WILL TRIM POPS BACK SLIGHTLY. MLF PREVIOUS DISCUSSION... /ISSUED 323 PM PDT WED SEP 8 2010/ SHORT TERM... COLD POOL ALOFT HAS TRIGGERED SHOWERS AND A FEW TSTMS OVER NERN CA AND FAR NWRN NV WITH SOME RAWS SITES FROM EXTREME NWRN NV...SURPRISE VALLEY AND NRN LASSEN COUNTY REPORTING RAINFALL TOTALS BTWN 0.20 AND 0.40 INCH. FARTHER SOUTH AND EAST...LARGE BAND OF RADAR ECHOES ASSOCIATED WITH UPPER JET DIVERGENCE HAS NOT PRODUCED MUCH MEASURABLE PRECIP DUE TO INITIALLY DRY LOW LEVELS. FOR THIS EVENING...LATEST MODEL GUIDANCE STILL INDICATES SOME INSTBY ACROSS MUCH OF THE REGION WITH MODIFIED TOTALS IN THE LOWER 30S AS THE COLD POOL ALOFT EXPANDS TO INCLUDE MORE OF WRN NV. WHILE THE LIGHTNING POTENTIAL FOR MOST OF THE REGION IS SLIM...THIS CONTINUED DESTABILIZATION WITH SOME FAVORABLE JET DYNAMICS COULD SUPPORT SOME ELEVATED CONVECTION AFT 00Z. THE AREAS MOST FAVORABLE FOR RECEIVING MEASURABLE PRECIP WILL CONTINUE TO INCLUDE NERN CA-NWRN NV...AND ALSO W-CNTRL NV EAST OF HWY 95 AS LOW LEVELS SHOULD BECOME SUFFICIENTLY MOIST BEFORE THE MOISTURE BAND EXITS THE REGION. COOL CONDITIONS WILL PREVAIL TONIGHT ALTHOUGH PERSISTENT CLOUD COVERAGE WILL LIMIT THE TEMPERATURE DROP IN THE TYPICALLY COOLER VALLEYS OF ERN CA-WRN NV. BREEZY WEST WINDS WITH GUSTS IN THE 30-40 MPH RANGE WILL WIND DOWN THIS EVENING AS THE JET STREAM MOVES FARTHER SOUTH AND EAST...WITH THE LAKE WIND ADVISORY LIKELY TO RUN ITS COURSE THRU 03Z FOLLOWED BY IMPROVING LAKE CONDITIONS. ON THURSDAY...THE UPPER LOW WILL SLOWLY PULL OUT OF THE GREAT BASIN. LIGHT SHOWERS MAY LINGER ACROSS FAR NERN CA AND NWRN NV WITHIN THE AREA OF CYCLONIC 500 MB FLOW THRU THURS AFTN...OTHERWISE A GRADUAL DECREASE IN CLOUD COVER FROM WEST TO EAST WITH TEMPS WELL BELOW NORMAL. MOST LOWER ELEVATION SITES WILL REMAIN BELOW 70 DEGREES WITH A MODERATE NW WIND...BUT SPEEDS WILL BE LOWER THAN THE PAST COUPLE OF DAYS. THE COLDEST NIGHT OF THE WEEK WILL BE THURS NIGHT AS CLEARING SKIES AND LIGHT WINDS WILL ALLOW FOR GOOD RADIATIONAL COOLING. TEMPS IN SOME OF THE COOLER VALLEYS NEAR THE RENO-CARSON CITY VICINITY MAY BRIEFLY DROP CLOSE TO NEAR FREEZING JUST BEFORE DAYBREAK. TEMPS WILL REBOUND BY ABOUT 10 DEGREES ON FRIDAY...FOLLOWED BY ADDITIONAL WARMING OF 4-8 DEGREES ON SATURDAY AS RIDGE REBUILDS OFF THE WEST COAST. THIS WILL YIELD MAX TEMPS OF LOWER TO MID 80S IN THE WRN NV VALLEYS AND UPR 60S-LOWER 70S AT LAKE LEVEL AS THE WEEKEND BEGINS. DRY CONDITIONS WITH GENERALLY LIGHT WINDS WILL PREVAIL BOTH DAYS. MJD LONG TERM... ZONAL FLOW WILL PERSIST INTO MONDAY BEFORE A POSITIVELY TILTED LONGWAVE TROUGH BEGINS TO DEVELOP OVER THE BRITISH COLUMBIA COASTLINE. THE TROUGH WILL REMAIN MOSTLY STATIONARY AS IT CONTINUES TO BUILD THROUGH THE MIDDLE OF THE WEEK WITH SEVERAL ASSOCIATED SHORTWAVES PASSING OVER THE GREAT BASIN AS A RESULT. THIS WILL CONTINUE DRY SOUTHWEST FLOW THROUGH WEDNESDAY AND KEEP TEMPERATURES AROUND NORMAL SEASONAL VALUES. SEVERAL GEFS MEMBERS MOVE THE TROUGH SOUTHEAST OVER THE AREA BY THE END OF THE LONG TERM PERIOD...WHICH WOULD BRING A CHANGE TO THE ONGOING WEATHER PATTERN...WHILE THE REST REBUILD ZONAL FLOW OVER THE AREA. LITTLE CONFIDENCE IN THE TROUGH EVOLUTION AT THIS POINT AS OPERATIONAL MODELS DIFFER GREATLY WITH MINIMAL ENSEMBLE AGREEMENT. WILL HAVE TO WAIT AND SEE ON THIS ONE. LABELLE AVIATION... SW-W WINDS WITH GUSTS AROUND 25KTS TO CONTINUE THROUGH 03Z AT ALL TERMINALS. SCT SHOWERS WILL CAUSE OCCASIONAL MT TOP OBSCUREMENT AND POSSIBLE 5SM VIS IN HEAVIER RAINFALL AT KTRK AND KTVL. LIGHT VRB WIND WILL PERSIST OVERNIGHT WITH TYPICAL DIURNAL TRENDS FOR THURSDAY. VFR CONDITIONS EXPECTED THROUGH THE TAF PERIOD. LABELLE && .REV WATCHES/WARNINGS/ADVISORIES... NV...NONE. CA...NONE. && $$ HTTP://WEATHER.GOV/RENO