Area Forecast Discussion
Issued by NWS Reno, NV

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000
FXUS65 KREV 041541
AFDREV

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
841 AM PDT SAT JUL 4 2015

.UPDATE...
SHOWERS ARE DEVELOPING OVER NORTHERN LYON CHURCHILL AND MINERAL
COUNTIES AS A WAVE MOVES INTO THE AREA. ABUNDANT MOISTURE WITH THE
WAVE HAS ALSO ALLOWED A LARGE CLOUD SHIELD TO DEVELOP OVER THE
REGION. THIS WILL LIMIT SURFACE BASED INSTABILITY AND MAY HELP TO
INHIBIT STRONG CONVECTION THIS AFTERNOON. A FLASH FLOOD WATCH IS
IN PLACE FOR TODAY ALONG AND SOUTH OF I-80 WITH HIGH SURFACE DEW
POINTS, ABUNDANT MOISTURE AND LOW STORM MOTIONS. HOWEVER NOT ALL
LOCATIONS WILL BE IMPACTED BY A THUNDERSTORM AND/OR HEAVY
RAINFALL.

WITH THE MANY LARGE OUTDOOR ACTIVITIES TAKING PLACE TODAY AROUND
THE REGION, THUNDERSTORMS ARE A CONCERN EVEN IF THEY DO NOT LEAD
TO FLASH FLOODING. GUSTY WINDS AND DANGEROUS LIGHTNING ARE ALSO
POSSIBLE. HAVE A PLAN TO RETURN TO SHELTER IF A THUNDERSTORM
APPROACHES YOUR LOCATION, ESPECIALLY IF YOU ARE NEAR A LAKE. HEAVY
RAINFALL CAN ALSO LEAD TO HYPOTHERMIA, CARRY RAIN GEAR IF YOU ARE
GOING ON A HIKE TODAY. BRONG

&&

.SYNOPSIS...

VERY MOIST AND UNSTABLE CONDITIONS WILL ALLOW SHOWERS AND
THUNDERSTORMS TO DEVELOP TODAY. A FEW STRONG THUNDERSTORMS THIS
AFTERNOON MAY PRODUCE TORRENTIAL RAINFALL AND FLASH FLOODING. LOW
PRESSURE NEAR THE CALIFORNIA COAST WILL KEEP THE THREAT FOR
SHOWERS AND THUNDERSTORMS THE NEXT SEVERAL DAYS.

&&

.PREVIOUS DISCUSSION... /ISSUED 313 AM PDT SAT JUL 4 2015/

SHORT TERM...

FOR TODAY, WE HAVE ISSUED A FLASH FLOOD WATCH FOR MUCH OF THE
REGION GENERALLY FROM I-80 SOUTHWARD. THERE ARE SEVERAL FACTORS
FAVORING THE POTENTIAL FOR HEAVY RAINFALL CAPABLE OF PRODUCING
FLASH FLOODING. THE AIR MASS REMAINS UNUSUALLY MOIST WITH DEW
POINTS MAINLY IN THE 50S AND PRECIPITABLE WATER VALUES BETWEEN 1
AND 1.25 INCH THIS AFTERNOON AND EVENING, WITH PLENTY OF
INSTABILITY AS LIFTED INDEX RANGES FROM -2 TO -4 C IN MOST AREAS.
MODEL GUIDANCE HAS BEEN RELATIVELY CONSISTENT WITH PUSHING AN
UPPER LEVEL DISTURBANCE NORTHWARD INTO THE SIERRA AND WESTERN NV
THIS AFTERNOON, WHICH WOULD PROVIDE ADDITIONAL FORCING FOR
GENERATING THUNDERSTORMS. MODEL SOUNDINGS ALSO INDICATE LIGHT MID
LEVEL FLOW WHICH WOULD RESULT IN GENERALLY SLOW CELL MOVEMENT,
WITH POSSIBLE CELL TRAINING OR REDEVELOPMENT OVER THE SAME AREAS.
RECENT RAINFALL HAS PRODUCED SATURATED GROUND IN SOME LOCATIONS,
AND WE HAVE ALREADY RECEIVED SOME FLOODING IN THE PAST FEW DAYS,
INCLUDING THE HIGHLY SENSITIVE WASHINGTON FIRE SCAR IN ALPINE
COUNTY. THE MAIN LIMITING FACTOR IS IF CLOUD COVER BECOMES TOO
THICK TO ALLOW THE FULL INSTABILITY TO BE REALIZED AND REDUCING
THUNDERSTORM INTENSITY. HOWEVER, WITH SO MANY FAVORABLE FACTORS
IN PLAY DURING THE MIDDLE OF THIS VERY BUSY HOLIDAY WEEKEND, THE
DECISION WAS MADE TO ISSUE THE WATCH FOR TODAY`S THUNDERSTORM
EVENT WHICH BEEN WIDELY ADVERTISED THE PAST SEVERAL DAYS. FARTHER
NORTH INTO NORTHEAST CA-NORTHWEST NV, LOCALLY HEAVY RAIN IS
POSSIBLE, BUT COVERAGE IS NOT EXPECTED TO BE WIDESPREAD WITH CELL
MOVEMENT A LITTLE FASTER SO THEY WERE NOT INCLUDED IN THE FLASH
FLOOD WATCH.

IN ADDITION TO THE FLASH FLOOD POTENTIAL, SOME HAIL OR STRONG
OUTFLOW GUSTS WILL BE POSSIBLE WITH STRONGER STORMS, WITH FREQUENT
LIGHTNING STRIKES ALSO IMPACTING OUTDOOR ACTIVITIES THIS AFTERNOON
AND EARLY EVENING.

AS THE DISTURBANCE MOVES FARTHER NORTH THIS EVENING, MOST OF THE
CONVECTION WILL ALSO DECREASE. THERE MAY BE A FEW LEFTOVER
SHOWERS OR THUNDERSTORMS AFTER 9 PM, BUT FOR MOST AREAS THE WORST
WEATHER CONDITIONS SHOULD HAVE PASSED THROUGH.

FOR SUNDAY, LINGERING MOISTURE AND INSTABILITY WILL CONTINUE BUT
FORCING IS LIKELY TO BE WEAKER, RESULTING IN LESS THUNDERSTORM
COVERAGE COMPARED TO TODAY. THE AREAS MORE LIKELY TO RECEIVE
CONVECTION INCLUDE AREAS SOUTH OF HIGHWAY 50 AND NORTH OF
SUSANVILLE-GERLACH.

BY MONDAY, UPPER LOW OVER THE EASTERN PACIFIC MOVES SLOWLY TOWARD
THE CALIFORNIA COAST, WITH SOUTH TO SOUTHEAST FLOW ALOFT DRAWING
IN MORE MOISTURE AND INSTABILITY DURING THE AFTERNOON. THERE
APPEARS TO BE ANOTHER DISTURBANCE ROTATING INTO THE SIERRA, WHICH
WOULD LEAD TO INCREASED THUNDERSTORM CHANCES AGAIN. INITIAL CELLS
ARE MOST LIKELY TO FORM NEAR THE SIERRA, WITH ACTIVITY THEN
SPREADING SLOWLY EAST. IF TODAY REACHES ITS POTENTIAL FOR
PRODUCING HEAVY RAIN AND FLOODING, WE MAY BE DEALING WITH
ADDITIONAL FLOOD POTENTIAL FOR MONDAY. MJD

LONG TERM...TUESDAY THROUGH FRIDAY...

MEDIUM RANGE OPERATIONAL MODELS HAVE COME MORE IN LINE WITH THE
EVOLUTION OF A CLOSED UPPER LOW THAT MOVES INTO CALIFORNIA DURING
THE EXTENDED PERIOD BEFORE STARTING TO OPEN INTO A WAVE AND LIFT OUT
OF THE AREA BY LATE FRIDAY. THE GEFS ENSEMBLE MEMBERS ALL GENERALLY
SUPPORT THE TIMING OF THIS FEATURE WITH ONLY A FEW EXCEPTIONS THAT
LIFT THE LOW OUT A LITTLE QUICKER EARLY FRIDAY.

WHAT DOES ALL THIS MEAN FOR THE FORECAST? THE CONTINUED PRESENCE OF
THE LOW TO THE WEST THROUGH MOST OF THE FORECAST PERIOD ALONG WITH A
HIGH WELL EAST OF THE AREA WILL DRAW MOISTURE NORTH INTO THE REGION
AND PRODUCE ENOUGH INSTABILITY TO DEVELOP THUNDERSTORMS EACH DAY.
UPPER DIFFLUENCE TO THE NORTH AND NORTHEAST OF THE LOW SHOULD CAUSE
NORTHEAST CALIFORNIA AND NORTHWEST NEVADA TO HAVE THE BEST CHANCE OF
CONVECTION AND POSSIBLY INTO THE OVERNIGHT HOURS. SO POPS WERE
INCREASED A LITTLE EACH DAY NORTH OF INTERSTATE 80 AND POPS WERE
INCLUDED FOR THE OVERNIGHT HOURS THROUGH WEDNESDAY NIGHT. AFTER THAT
THERE IS A BIT TOO MUCH UNCERTAINTY IN INSTABILITY DURING THE
OVERNIGHT HOURS.

WITH THE UPPER LOW GETTING CLOSER AND AN INCREASE IN CLOUD COVER...
DAYTIME HIGHS SHOULD BE AT OR POSSIBLY BELOW AVERAGE DURING THE
EXTENDED PERIOD. OVERNIGHT LOWS SHOULD REMAIN ABOVE AVERAGE DUE TO
INCREASED CLOUD COVER. 20


AVIATION...

THUNDERSTORMS ARE EXPECTED OVER WRN NV AND ERN CA EACH DAY THROUGH
NEXT FRIDAY. TODAY COULD HAVE MORE COVERAGE THAN ANY OTHER DAY...BUT
ALL DAYS HAVE THE POSSIBILITY OF GUSTY SURFACE WINDS...SMALL HAIL...
TURBULENCE NEAR STORMS AND REDUCED VISIBILITY DUE TO THICK CLOUDS
AND HEAVY RAIN.

WHILE VFR CONDITIONS ARE EXPECTED OUTSIDE OF STORMS EACH DAY...IN
AND NEAR THE STORMS VSBY COULD BE QUITE LOW. ALSO AN ISSUE COULD BE
OBSCURED MOUNTAIN TOPS DUE TO RAIN AND CLOUDS. AVIATION INTERESTS
ARE ADVISED TO USE EXTREME CAUTION IN AND NEAR THUNDERSTORMS. 20

&&

.REV WATCHES/WARNINGS/ADVISORIES...
NV...FLASH FLOOD WATCH UNTIL 8 PM PDT THIS EVENING NVZ001>004.

CA...FLASH FLOOD WATCH UNTIL 8 PM PDT THIS EVENING CAZ072-073.

&&

$$

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


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