545  
FXUS65 KREV 231006  
AFDREV  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RENO NV  
306 AM PDT WED MAY 23 2018  
   
SYNOPSIS
 
 
LOW PRESSURE SYSTEMS WILL CONTINUE TO AFFECT THE SIERRA AND  
WESTERN NEVADA THIS WEEK AND THE FIRST PART OF THE MEMORIAL DAY  
WEEKEND. LOCALLY HEAVY RAIN, SMALL HAIL AND GUSTY WINDS WILL  
ACCOMPANY STRONGER STORMS. TEMPERATURES WILL GENERALLY BE NEAR  
SEASONAL LEVELS EXCEPT FOR FRIDAY AND SATURDAY WHEN EXTENSIVE  
SHOWERS AND CLOUDS WILL KEEP READINGS BELOW NORMAL.  
 

 
   
SHORT TERM
 
 
ONE UPPER LOW EXITS WHILE ANOTHER APPROACHES THE WEST COAST TODAY.  
THE FLOW ALOFT WILL TURN BACK TO THE SOUTHWEST BY THIS AFTERNOON.  
AS A RESULT, IT IS GOING TO BE A BIT MORE ACTIVE ALONG AND JUST  
EAST OF THE SIERRA AS ABUNDANT MOISTURE AND INSTABILITY WILL BE  
IN PLACE FOR THUNDERSTORMS. WHILE SHEAR WILL BE WEAK, WESTERLY  
WINDS WILL DEVELOP FROM CONVECTIVE OUTFLOW OVER THE HIGHER TERRAIN  
AND ACT TO INCREASE LOW LEVEL CONVERGENCE AS STORMS PUSH OFF INTO  
THE LOWER VALLEYS. BEST COVERAGE WILL BE ALONG THE HIGHWAY 395  
CORRIDOR FROM RENO-CARSON CITY NORTHWARD WITH MORE ISOLATED  
COVERAGE ELSEWHERE. A FEW STRONGER STORMS WILL PRODUCE SMALL HAIL  
AND HEAVY RAINFALL. ANY STORMS THAT CAN WORK A LITTLE FARTHER EAST  
TOWARD HIGHWAY 95 WILL HAVE A BETTER CHANCE FOR STRONG OUTFLOW  
GUSTS TO 50 MPH AS LOWER LEVELS ARE DRIER ACROSS THE BASIN AND  
RANGE.  
 
AS THE UPPER TROUGH APPROACHES, A LOW WILL CLOSE OFF THE CENTRAL  
CA COAST AND MOVE INLAND FRIDAY ALONG A TRACK THAT WILL TAKE IT TO  
THE SOUTHERN SIERRA. THIS TRACK IS A BIT FARTHER SOUTH AND BRINGS  
THE POTENTIAL FOR MORE WIDESPREAD SHOWERS AND THUNDERSTORMS TO  
THE SIERRA AND WESTERN NV. LOCALLY HEAVY RAIN AND ACCUMULATING  
HAIL WILL ACCOMPANY STRONGER STORMS WITH A FEW VERY INTENSE STORMS  
POSSIBLE ON THE LEADING EDGE OF THE COOLER AIRMASS THAT DEVELOPS  
ALONG THE EAST SLOPES OF THE SIERRA AND FAR WESTERN NV. SUFFICIENT  
LOW-MID LEVEL SHEAR WILL EXIST FOR THESE STORMS TO SUSTAIN STRONG  
UPDRAFTS CAPABLE OF PRODUCING LARGER HAIL (AROUND 1 INCH) AND  
STRONGER OUTFLOW WINDS (GUSTS 50-60 MPH). AFTER HIGH TEMPERATURES  
NEAR SEASONAL LEVELS TODAY AND THURSDAY, MUCH COOLER CONDITIONS  
WILL PREVAIL FRIDAY, ESPECIALLY FOR THE SIERRA AND EXTENDING  
INTO THE HIGHWAY 395 CORRIDOR. HOHMANN  
   
LONG TERM...FRIDAY NIGHT THROUGH TUESDAY
 
 
THE REASONING FOR MUCH OF THE EXTENDED PORTION OF THE FORECAST HAS  
CHANGED LITTLE IN THE PAST 12-24 HOURS...BUT THERE WERE SOME CHANGES  
MADE TO THE FORECAST THIS MORNING TO REFLECT SUBTLE CHANGES IN THE  
MODEL GUIDANCE.  
 
FIRST...BOTH THE ECMWF AND GFS ARE BRINGING THE UPPER LOW FOR THE  
WEEKEND INTO CALIFORNIA AND NEVADA A LITTLE FARTHER SOUTH THAN  
PREVIOUS RUNS INDICATED. THIS HAS SOME SUPPORT FROM THE GEFS  
ENSEMBLE MEMBERS AS WELL. THIS WOULD MEAN A BETTER CHANCE FOR RAIN  
WITH EMBEDDED THUNDERSTORMS NORTH OF THE LOW COVERING MORE OF THE  
FORECAST AREA THAN PREVIOUSLY THOUGHT AND SLIGHTLY COOLER  
TEMPERATURES FOR SATURDAY. TO TREND TOWARD A WETTER SCENARIO WE HAVE  
INCREASED POPS AND QPF FOR FRIDAY NIGHT INTO SATURDAY EVENING.  
TEMPERATURES HAD ALREADY BEEN LOWERED FOR SATURDAY...SO FEW CHANGES  
WERE MADE THERE. WITH THE INCREASE IN QPF IT IS POSSIBLE THAT AREAS  
ABOVE 8000 FEET COULD SEE UP TO 3 INCHES OF SNOW BY SATURDAY  
EVENING. ACCUMULATING SNOWS ARE EVEN POSSIBLE ON THE PASSES ABOVE  
7500 FEET BY LATE SATURDAY EVENING.  
 
SECOND...THE FORECAST MODELS ARE A LITTLE SLOWER AT MOVING THE UPPER  
LOW AWAY THE REGION SUNDAY AND MONDAY. THE PRESENCE OF THE LOW TO  
THE EAST MAY BE JUST ENOUGH TO INDUCE SHOWERS AND A FEW  
THUNDERSTORMS SUNDAY AFTERNOON...WITH THE BEST CHANCES IN FAR  
EASTERN CHURCHILL AND PERSHING COUNTIES AND ALSO ALONG THE SIERRA  
FROM ALPINE COUNTY SOUTH INTO MONO COUNTY WHERE NORTHEAST UPSLOPE  
FLOW WILL BE MAXIMIZED. WHILE LESS LIKELY...IT IS NOT OUTSIDE THE  
REALM OF POSSIBILITY FOR CONVECTION TO REDEVELOP MONDAY. THUS WE  
HAVE INCLUDED VERY LOW END POPS FOR MONDAY AFTERNOON AND EVENING  
IN THE CENTRAL SIERRA WHERE DIFFERENTIAL HEATING AND UPSLOPE FLOW  
WILL BE MAXIMIZED.  
 
LASTLY...TUESDAY IS BECOMING MORE UNCERTAIN. THE GFS IS NOW MORE  
AGGRESSIVE IN TRYING TO PUSH ANOTHER TROUGH INTO THE COAST BY LATE  
TUESDAY WHILE THE ECMWF BUILDS A SHORT WAVE RIDGE. THERE IS SUPPORT  
FOR BOTH OF THESE SOLUTIONS...AND OTHERS...IN THE CURRENT CROP OF  
GEFS ENSEMBLE MEMBERS. WHILE THERE IS QUITE A BIT OF UNCERTAINTY...  
AND CONFIDENCE IN ANY SOLUTION IS LOW...WE WILL ERR ON THE SIDE OF  
CAUTION AND INTRODUCE SLIGHT CHANCE POPS FOR PARTS OF THE SIERRA FOR  
LATE TUESDAY. THERE IS LITTLE FLOW IN THE MID AND UPPER LEVELS AND  
THAT GENERALLY TRANSLATES TO SHORT LIVED CONVECTION CAUSED MORE BY  
LOW LEVEL HEATING ACTING ON RESIDUAL MOISTURE WITH SOME BOOST FROM  
DIFFERENTIAL HEATING IN THE TERRAIN.  
 

 
   
AVIATION
 
 
MID CLOUDS ROTATING AROUND UPPER LOW HAVE BEEN IN AND OUT OF KTRK  
THIS MORNING WITH FOG TRYING TO DEVELOP. PROBABLY BEST TO COUNT ON  
IT BEING THERE MORE THAN NOT THROUGH ABOUT 16Z. OTHERWISE VFR  
CONDITIONS WILL PREVAIL TODAY OUTSIDE OF SHOWER/STORM ACTIVITY.  
 
SHOWERS AND THUNDERSTORMS WILL LIKELY FIRE ALONG THE SIERRA EARLY  
TO MID AFTERNOON AND THEN PUSH OFF INTO THE LOWER VALLEYS OF  
NORTHEAST CA AND WESTERN NV BY EVENING AS THE FLOW ALOFT TURNS  
SOUTHWEST AND A LOW LEVEL WESTERLY ZEPHYR/OUTFLOW DEVELOPS JUST TO  
THE LEE OF THE SIERRA. STORM COVERAGE WILL BE BEST FROM THE TAHOE  
BASIN AND SIERRA FRONT NORTHWARD WITH MORE ISOLATED COVERAGE  
ELSEWHERE.  
 
IT WILL BE MOSTLY QUIET LATE TONIGHT INTO THURSDAY MORNING EXCEPT  
FOR FOG AROUND KTRK. ANOTHER LOW PRESSURE AREA APPROACHING THE  
WEST COAST WILL ONCE AGAIN INCREASE SHOWER AND STORM CHANCES  
THURSDAY AFTERNOON THROUGH SATURDAY WITH ACTIVITY NOT JUST  
CONFINED TO THE DAYTIME PERIOD BUT ALSO LIKELY TO PERSIST  
OVERNIGHT. HOHMANN  
 

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

 
 

 
 
FOR MORE INFORMATION FROM THE NATIONAL WEATHER SERVICE VISIT...  
HTTP://WEATHER.GOV/RENO  
 
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