045
FXUS65 KREV 302111
AFDREV
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RENO NV
111 PM PST TUE DEC 30 2025
KEY MESSAGES
* STRONG VALLEY INVERSIONS AND AIR STAGNATION REMAIN INTO
WEDNESDAY.
* QUICK MOVING STORM BRINGS RAIN SHOWERS WITH HIGH ELEVATION SNOW
LATE WEDNESDAY INTO NEW YEAR'S DAY, WITH A RISK OF FREEZING
RAIN IN COLDER VALLEYS.
* STRONGER STORM BRINGS HEAVY MOUNTAIN SNOW, STRONG RIDGE WINDS,
AND RAIN SHOWERS TO VALLEYS FRIDAY EVENING INTO SATURDAY AND
POSSIBLY SUNDAY. SOME FLOODING CONCERNS FOR THE SUSAN AND
FEATHER RIVERS
DISCUSSION
* RATHER IMPRESSIVE INVERSIONS TODAY WILL REMAIN IN PLACE THROUGH
TONIGHT AND WEDNESDAY MORNING WITH CONTINUED LIGHT WINDS.
EXAMPLE: NOON TEMPS HOLDING NEAR 10F IN THE LONG VALLEY CALDERA
NEAR MAMMOTH MEANWHILE IT'S NEAR 40F AT THE SUMMIT OF MAMMOTH
MOUNTAIN.
* FIRST OF A PAIR OF SYSTEMS WILL LIFT NORTH LATE WEDNESDAY
THROUGH NEW YEAR'S DAY. MOISTURE TRANSPORT (IVT) IS SOUTHERLY
WHICH TYPICALLY IS NOT GREAT FOR EFFICIENT SPILLOVER EAST OF THE
SIERRA CREST. THAT BEING SAID, MOST MODELS INCLUDING RRFS BRING
LIGHT TO MODERATE RAIN SHOWERS WITH HIGH ELEVATION (8-9000'+)
SNOW TO OUR AREA. WITH ANTECEDENT INVERSIONS, THE SETUP IS
DECENT FOR POCKETS OF FREEZING RAIN WEDNESDAY EVENING INTO
THURSDAY MORNING IN THE EASTERN SIERRA AND LASSEN COUNTY (E.G.
20-40% CHANCES OF FZRA PRECIP TYPE AT BRIDGEPORT AND MAMMOTH
AIRPORT IN NBM). DETERMINISTIC NAM3 AND RRFS SHOW FREEZING RAIN
SOUNDINGS IN THESE AREAS TOO.
* SECOND WAVE IS MORE IMPACTFUL FOR TRAVEL, FRIDAY EVENING INTO
SATURDAY WITH MORE TRADITIONAL FRONTAL TRAJECTORY AND LOWER
RAIN- SNOW LINES (7500' LOWERING TO 5500'). RRFS SHOWING A NCFR
HEADING INTO CA BY SUNDOWN FRIDAY WHICH WOULD MOVE INTO THE
SIERRA FRIDAY EVENING WITH RAPID DROPS IN RAIN-SNOW LINES,
STRONG WINDS, AND HEAVY SNOW RATES FOR TRAVELERS ON A BUSY
EVENING. WINTER STORM WATCHES ISSUED AS A RESULT. NBM GUIDANCE
SHOWS CONTINUED RISK FOR HEAVY SNOW SHOWERS FOR THE MOUNTAINS
SATURDAY INTO SUNDAY IN THE COLD AND UNSTABLE POST-FRONTAL
AIRMASS, BUT CONFIDENCE IS MORE MIXED ON SUNDAY WHERE SOME
DETERMINISTIC MODELS SHOW A PRONOUNCED DRY PERIOD.
* FOR THE W NEVADA & NE CALIFORNIA VALLEYS, PERIODS OF LIGHT TO
MODERATE RAIN ARE EXPECTED FRIDAY NIGHT INTO SATURDAY. WITH SOME
SNOW COVER AND WET SOILS, WE MAY SEE RUNOFF RATHER QUICKLY SO
EXPECT TO SEE RISES ON CREEKS AND RIVERS. MAINSTEM RIVER
FLOODING CONCERNS ARE FOCUSED ON THE SUSAN RIVER AND FEATHER,
WHERE THE RFC HAS UPWARD TRAJECTORIES INTO ACTION STAGES LATE
FRIDAY INTO SATURDAY. WINDS DO NOT LOOK OVERLY STRONG IN THE
VALLEYS, WITH NBM SHOWING ONLY 20-30% ODDS OF 40 MPH GUSTS, BUT
THE SIERRA RIDGES WILL BE RATHER BRISK WITH S/SW 700MB FLOW
40-50 KNOTS.
* ADDITIONAL STORMS POSSIBLE EARLY NEXT WEEK BUT LARGE SPREAD AND
NOISINESS IN THE NBM GUIDANCE KEEPS CONFIDENCE LOW IN TERMS OF
POTENTIAL AMOUNTS AND IMPACTS.
-CHRIS
AVIATION
* VFR CONDITIONS WITH VALLEY HAZE DUE TO INVERSIONS EXPECTED THE
REST OF TODAY INTO TONIGHT. FZFG POSSIBLE (20% CHANCE) AT TRK,
MONO LAKE, AND OTHER VALLEYS BUT PROBABILITIES ARE LOWER THAN
PREVIOUS NIGHTS DUE TO INCREASING CLOUD COVER AHEAD OF NEXT
STORM SYSTEM.
* SHOWERS DEVELOP FROM SOUTH TO NORTH TOMORROW EVENING INTO
TOMORROW NIGHT. MAINLY MVFR CONDITIONS DUE TO SUB-OPTIMAL
SOUTHERLY FLOW PATTERN FOR EFFICIENT SPILLOVER EAST OF THE
SIERRA CREST. RAIN-SNOW LINES HIGH ENOUGH THAT MOST TAF SITES
WOULD BE RAIN SHOWERS, EXCEPT MMH AND SVE WHERE SNOW (20%
CHANCE) OR EVEN LIGHT FREEZING RAIN (20%) IS POSSIBLE.
ADDITIONAL RAIN SHOWERS CONTINUE THROUGH NEW YEAR'S DAY BUT
MAINLY OF THE MVFR VARIETY.
* WINDS ARE NOT A MAJOR ISSUE THROUGH WEDNESDAY. THURSDAY SEES AN
INCREASE IN 700MB FLOW AND RIDGE WINDS AHEAD OF A DEEPENING
TROUGH OFF-SHORE. MOUNTAIN WAVES AND SOME WIND SHEAR IS POSSIBLE
NEW YEAR'S DAY.
-CHRIS
AVALANCHE
* STRONG INVERSIONS WITH MOUNTAIN TOP TEMPS INTO THE 40S AND LOW
50S TODAY WILL PERSIST INTO TONIGHT. TOMORROW THE INVERSION
INTENSITY SHOULD GRADUALLY WANE AS TEMPS ALOFT COOL AHEAD OF
INCOMING STORM, THOUGH LIMITED WINDS COULD COUNTER THAT EFFECT.
* QUICK MOVING AND WARM SYSTEM FOR WEDNESDAY LATE AFTERNOON
THROUGH THURSDAY BRINGS MAINLY RAIN TO THE MOUNTAINS, WITH SNOW
LINES 8000- 9000' FOR THE MOST PART. NBM 50TH PERCENTILE PRECIP
AMOUNTS 0.5 TO 1.0" WITH SLR'S BELOW 6:1.
* HEAVIER PRECIP AND MORE SNOWFALL EXPECTED FRIDAY EVENING
THROUGH SATURDAY WITH LOWER RAIN-SNOW LINES (7000' LOWERING TO
5500'). SWE PICKUPS GENERALLY 1 TO 1.75" AT THE 50TH PERCENTILE
OF THE NBM GUIDANCE WITH SLRS ON THE WET SIDE, 8-11:1 ON
AVERAGE. HEAVY SNOW SHOWERS IN A COLD, UNSTABLE AIRMASS WILL
CONTINUE SATURDAY AND POSSIBLY SUNDAY.
* MOUNTAIN WINDS WITH FIRST STORM ARE NOT TOO SIGNIFICANT, BUT
BECOME STRONGER WITH THE SECOND ONE FRIDAY INTO SATURDAY. 700MB
FLOW PROJECTED S/SW AT 40-60 KNOTS WHICH CAN TRANSLATE TO RIDGE
GUSTS IN THE 70-90 MPH RANGE.
-CHRIS
REV WATCHES/WARNINGS/ADVISORIES
NV...WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SUNDAY MORNING
NVZ002.
CA...WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SUNDAY MORNING
CAZ072-073.
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