900
FXUS65 KREV 200931
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
131 AM PST WED NOV 20 2024
SYNOPSIS
A MULTI-DAY STORM ASSOCIATED WITH AN ATMOSPHERIC RIVER WILL BRING
SEVERAL ROUNDS OF GUSTY WINDS, HEAVY RAIN, AND MOUNTAIN SNOW TO
THE WESTERN U.S. THROUGH THE WEEKEND INTO EARLY NEXT WEEK.
* ROUND 1 TODAY-THU: SNOW WILL IMPACT AREAS IN LASSEN, E. PLUMAS,
E. SIERRA COUNTIES, BUT IT'S PRIMARILY A WIND IMPACTS DAY,
INCLUDING TURBULENCE, HAZARDOUS BOATING CONDITIONS, AND FIRE
WEATHER CONCERNS.
* ROUND 2 WARM, WET FRI-SAT: THE NEXT WAVE BRINGS HIGHER SNOW
LEVELS WITH HEAVY RAIN AND HIGH ELEVATION SNOW. PLAN ON
SIGNIFICANT RISES ON CREEKS AND STREAMS, BUT NO RIVER FLOODING
IS FORECAST.
* ROUND 3 COLDER, SUN-TUE: MORE GUSTY WINDS AND SIERRA TRAVEL
IMPACTS AS A COLDER STORM ARRIVES AHEAD OF THE BUSY TRAVEL WEEK.
DISCUSSION
IF YOU HAVE TRAVEL PLANS, BE SURE TO STAY UP-TO-DATE ON THE
ONGOING WEATHER, ESPECIALLY ACROSS NORTHERN CA, OR, AND WESTERN
NV. NO SIGNIFICANT CHANGES WERE MADE OVERNIGHT TO THE ONGOING
FORECAST.
* WINDS: A STRONG UPPER LEVEL JET ASSOCIATED WITH THE ATMOSPHERIC
RIVER (AR) PUSHING INTO NORTHERN CA WILL PRODUCE PERIODS OF
STRONG, GUSTY WINDS ACROSS THE SIERRA AND WESTERN NEVADA TODAY
INTO EARLY NEXT WEEK. SIERRA RIDGE WINDS WILL BE QUITE STRONG
TODAY AND PERSIST THROUGH MUCH OF THE WEEKEND. MOUNTAIN-TOP WIND
GUSTS 60-80 MPH WILL FEEL RATHER ROUTINE THIS WEEK WITH ONLY
BRIEF RESPITES BETWEEN STORMS. WIND AND LAKE WIND ADVISORIES ARE
IN EFFECT RESPECTIVELY FOR PORTIONS OF WESTERN NEVADA AND LAKE
TAHOE FOR TODAY. WIDESPREAD WIND GUSTS OF 30 TO 40 MPH ARE
POSSIBLE WITH LOCALLY STRONGER WIND GUSTS UP TO 50 MPH,
ESPECIALLY IN WESTERN NEVADA WHERE WINDS AND DRY CONDITIONS
ALIGN FOR FIRE WEATHER CONCERNS (SEE FIRE SECTION). PLAN ON
IMPACTS TO ROAD TRAVEL DUE TO CROSSWINDS AND AREAS OF BLOWING
DUST, TO AVIATION DUE TO WIND SHEAR AND TURBULENCE, AND
HAZARDOUS CONDITIONS FOR BACKCOUNTRY AND LAKE RECREATION.
BLENDED GUIDANCE SHOWS A 40-50% CHANCE OF WIND GUSTS EXCEEDING
50 MPH FOR FAR WESTERN NEVADA, WHICH MATCHES WITH SIGNALS FOR
DOWNSLOPE ENHANCEMENT SHOWING UP IN SOME MODEL SOUNDINGS THIS
MORNING. PLAN ON A COUPLE MORE BOUTS OF STRONGER WINDS AHEAD OF
THE NEXT TWO WAVES (1) FRIDAY AND (2) SUNDAY.
* RAIN/SNOW: RAIN AND SNOW ARE ONGOING ACROSS PORTIONS OF NORTHERN
CALIFORNIA THIS MORNING. THE HEAVY RAIN AND MOUNTAIN SNOW WILL
BE CONFINED TO AREAS ALONG AND WEST OF THE SIERRA WITH LIMITED
SPILLOVER INTO WESTERN NEVADA THROUGH MUCH OF TODAY AND A BIT OF
TAPERING IN PRECIPITATION CHANCES FOR THURSDAY. THE NEXT ROUND
OF PRECIPITATION PURPOSEFULLY PUSHES IN FRIDAY INTO SATURDAY
WITH INCREASED CHANCES AREAWIDE, INCLUDING FAR WESTERN NEVADA
AND THE EASTERN SIERRA TOO. BROADLY, UNTIL WE DIVE INTO THE SNOW
LEVELS IN THE NEXT SECTION, SNOW LEVELS WILL RISE UP
SIGNIFICANTLY (IN TRUE AR FASHION TO AROUND ~8500 FEET) TONIGHT
WHICH WILL LIMIT SNOW AMOUNTS FOR SOME FOOTHILL LOCATIONS.
BLENDED GUIDANCE SHOWS A 20-30% CHANCE OF AT LEAST AN 1" OF QPF
FOR FAR WESTERN NEVADA ON SATURDAY. HEAVY RAIN MAY EXACERBATE
RUNOFF AND RESULT IN PONDING OF WATER IN UNDESIRED AREAS. BE
SURE TO CLEAR OUT STORM DRAINS AND GUTTERS AHEAD OF THE WETTER
PART OF THIS STORM FOR FRIDAY INTO SATURDAY. ANOTHER ROUND OF
PRECIPITATION ARRIVES SUNDAY INTO MONDAY WHICH WILL RENEW
CHANCES FOR VALLEY RAIN AND MOUNTAIN SNOW. INITIAL PROJECTIONS
FOR THE NEXT STORM ARE QUITE COLD WITH SNOW LEVELS LOWERING BACK
TO NEAR 5500 FEET.
* SNOW LEVELS: THESE WILL MAKE OR BREAK WHETHER WE WILL SEE
FLOODING OR SNOW IMPACTS. INITIAL PROJECTIONS FOR SNOW LEVELS
TODAY WILL BE AROUND 5500 FEET BEFORE THE MEAT OF THE MILD, WET
AR DRIVES SNOW LEVELS UP ~10P TONIGHT TO NEAR 8500 FEET. THE
HIGHER THE SNOW LEVELS, THE HIGHER POTENTIAL FOR FLOOD IMPACTS,
PARTICULARLY ACROSS BURN AREAS AND FOR THE RIVERS AND STREAMS
(SEE HYDROLOGY SECTION). ONCE THE AR AND UPPER LEVEL JET BEGIN
TO SLIDE SOUTHWARD SATURDAY, THEN WE WILL SEE THE SNOW LEVELS
START TO DROP NEAR 6000 TO 7000 FEET. THIS IS WHERE SIERRA PASS
SNOW IMPACTS RETURN FOR LATE FRIDAY INTO EARLY SATURDAY.
FORECASTER CONFIDENCE ISN'T VERY HIGH CONCERNING THE SNOW
LEVELS, BUT PRECIPITATION IS EXPECTED TO PERSIST THROUGH MUCH
OF SATURDAY, EVEN IF IT WILL VARY FROM RAIN TO RAIN/SNOW TO
SNOW ACROSS THE REGION. SIMULATIONS DO APPEAR TO LOWER THE SNOW
LEVELS SIGNIFICANTLY FOR SUNDAY INTO MONDAY AND BLENDED
GUIDANCE SHOWS A 10% CHANCE OF AT LEAST 1" OF SNOW FOR THE RENO
AREA. BLENDED GUIDANCE ALSO SHOWS A 70-80% CHANCE OF AT 2 FEET
OF SNOW ALONG THE SIERRA CREST FROM SUNDAY - TUESDAY FOR NOW.
-EDAN
AVIATION
* VFR CONDITIONS CONTINUE FOR ALL TAF SITES THROUGH 18Z WEDNESDAY
WITH WIND GUSTS FROM THE S-SW 15-25 KTS FOR SIERRA AND FAR
WESTERN NV TERMINALS UP TO 35 KTS. FL100 35-45 KTS WINDS WILL
PRODUCE PERIODS OF MOUNTAIN WAVE TURBULENCE THIS EVENING. THE
AIRSPACE WILL BE IMPACTED BY TWO STORMS SYSTEMS THROUGH THE
WEEKEND.
* THE FIRST STORM SYSTEM WILL HIT SIERRA TERMINALS THIS MORNING
AROUND 18Z. PLAN ON PERIODS OF MVFR CONDITIONS WITH LIGHT TO
MODERATE RAIN SHOWERS TODAY. WINDS WILL BRING THE HIGHEST
IMPACTS WITH W-SW SURFACE WINDS 20-30 KTS AND FL100 WINDS
APPROACHING 50-60 KTS FOR KTRK, KTVL, KRTS, AND KRNO.
* BY FRIDAY INTO THE WEEKEND, WE'RE LOOKING AT A STRONGER, COLDER
AND WETTER STORM. LIQUID WATER STORM TOTALS ARE NEARING 1-3"
FOR ALONG THE SIERRA CREST, WITH A 50-60% CHANCE OF 2+ INCHES OF
SNOW FOR KTRK, KMMH, AND KTVL. IN ADDITION, LOOK FOR MOUNTAIN
OBSCURATIONS DURING PERIODS OF MVFR/IFR CONDITIONS IN RAIN/SNOW
FOR SIERRA AND FAR WESTERN NV TERMINALS.
-EDAN
FIRE WEATHER
WITH THE LACK OF A DECENT SEASON ENDING PRECIPITATION EVENT SO
FAR, WE'RE STILL IN A POSITION TO ISSUE RED FLAG WARNINGS FOR
THESE WINDY AND DRY DAYS IN NEVADA AND THE EASTERN SIERRA. STRONG
WINDS WILL COMBINE WITH MARGINAL RELATIVE HUMIDITY TO CREATE
CRITICAL FIRE WEATHER CONDITIONS FOR WESTERN NEVADA AREAS. PLAN ON
WIND GUSTS 35 TO 50 MPH ALONG WITH HUMIDITY VALUES IN THE 12-25%
RANGE TODAY. HIGHER HUMIDITY AND RAINFALL PUSHING IN LATE TODAY
INTO THURSDAY SHOULD HELP TO MITIGATE THE FIRE WEATHER CONCERNS
LATER THIS EVENING AND OVERNIGHT.
-EDAN
HYDROLOGY
AN ATMOSPHERIC RIVER IS STARTING TO BRING HEAVY RAINFALL ACROSS
NORTHERN CA TODAY. THIS WILL RESULT IN WATER PONDING IN POOR
DRAINAGE AREAS AND INCREASING FLOWS ALONG RIVERS AND STREAMS
THROUGHOUT THE AREA LATE TONIGHT THROUGH FRIDAY. IF THE STORM
TRENDS WETTER THAN FORECAST, THEN MINOR FLOODING WILL BE POSSIBLE
ALONG SMALL CREEKS AND STREAMS IN NORTHEASTERN CALIFORNIA AND THE
SUSAN RIVER. RECENT BURN AREAS ARE A CONCERN FOR MINOR FLOODING,
EXACERBATED BY THE TRANSPORT OF ASH, SEDIMENT, AND DEBRIS THAT MAY
OBSTRUCT DRAINAGE AREAS.
THERE IS CONSIDERABLE UNCERTAINTY IN THE HYDROLOGIC RESPONSE DUE
TO (1) RANGE IN THE PRECIPITATION FORECAST AND (2),SNOW LEVELS
WITH VARYING PRECIPITATION TYPE AND TRANSITIONS FROM SNOW TO RAIN
AND BACK TO SNOW AGAIN FROM WEDNESDAY INTO THE WEEKEND.
ADDITIONAL CONSIDERATION SHOULD BE GIVEN TO THE FACT THAT AT STORM
ONSET SOILS WILL BE DRY WITH GENERALLY LOW STREAMFLOWS, WHICH
WILL DELAY AND MUTE STREAMFLOW RESPONSES INITIALLY. KEEP AN EYE ON
RIVER FORECAST UPDATES AT CNRFC.NOAA.GOV.
-BARDSLEY
REV WATCHES/WARNINGS/ADVISORIES
NV...RED FLAG WARNING FROM 10 AM TO 7 PM PST WEDNESDAY
NVZ420-421-423-429.
LAKE WIND ADVISORY UNTIL 7 PM PST WEDNESDAY NVZ002.
WIND ADVISORY FROM 10 AM TO 7 PM PST WEDNESDAY NVZ001-003.
CA...WINTER WEATHER ADVISORY UNTIL 10 PM PST WEDNESDAY CAZ071.
RED FLAG WARNING FROM 10 AM TO 7 PM PST WEDNESDAY CAZ274.
LAKE WIND ADVISORY UNTIL 7 PM PST WEDNESDAY CAZ072.
WIND ADVISORY FROM 10 AM TO 7 PM PST WEDNESDAY CAZ073.
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