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FXUS66 KSTO [Sacramento/WFO CA] 062237 AFDSTO 

FXUS66 KSTO 062237
AFDSTO [HEAD]

National Weather Service Sacramento California 2:37pm PST Mon Dec 6 2021 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
237 PM PST MON DEC 6 2021 [HEAD]

Synopsis. A few light showers this afternoon and overnight as a weak system moves through. A colder weather system could bring mountain snow, light valley showers, and colder temperatures mid to late week. Cold overnight lows Thursday night into the weekend. Unsettled weather late weekend into next week. 

.SYNOPSIS...
A FEW LIGHT SHOWERS THIS AFTERNOON AND OVERNIGHT AS A WEAK SYSTEM
MOVES THROUGH. A COLDER WEATHER SYSTEM COULD BRING MOUNTAIN SNOW,
LIGHT VALLEY SHOWERS, AND COLDER TEMPERATURES MID TO LATE WEEK.
COLD OVERNIGHT LOWS THURSDAY NIGHT INTO THE WEEKEND. UNSETTLED
WEATHER LATE WEEKEND INTO NEXT WEEK. [DISC]

Discussion. Water vapor shows a trough ~600 miles off the coast of the California/Oregon border. This trough will dig down the California coast tonight into tomorrow morning. We are seeing a few light showers ahead of this trough across the area but soundings indicate dry mid-levels, this has limited precipitation that is making it to the ground. Mid levels will continue to saturate as the trough pushes closer and we will continue to see scattered shower chances across the area into the overnight. The best shower chances and forcing over our area will be in southern areas mainly from I-80 south. Rain totals will remain light with most areas seeing only a few hundredths but we could see up to 0.25" near the Sierra Crest south of I-80. Short wave ridging then builds in for Tuesday bringing clearing skies and quiet conditions. Valley fog will be likely Wednesday morning and could be dense in some locations. 

.DISCUSSION...
WATER VAPOR SHOWS A TROUGH ~600 MILES OFF THE COAST OF THE CA/OR
BORDER. THIS TROUGH WILL DIG DOWN THE CA COAST TONIGHT INTO
TOMORROW MORNING. WE ARE SEEING A FEW LIGHT SHOWERS AHEAD OF THIS
TROUGH ACROSS THE AREA BUT SOUNDINGS INDICATE DRY MID-LEVELS,
THIS HAS LIMITED PRECIP THAT IS MAKING IT TO THE GROUND. MID
LEVELS WILL CONTINUE TO SATURATE AS THE TROUGH PUSHES CLOSER AND
WE WILL CONTINUE TO SEE SCATTERED SHOWER CHANCES ACROSS THE AREA
INTO THE OVERNIGHT. THE BEST SHOWER CHANCES AND FORCING OVER OUR
AREA WILL BE IN SOUTHERN AREAS MAINLY FROM I-80 SOUTH. RAIN TOTALS
WILL REMAIN LIGHT WITH MOST AREAS SEEING ONLY A FEW HUNDREDTHS BUT
WE COULD SEE UP TO 0.25" NEAR THE SIERRA CREST SOUTH OF I-80.
SHORT WAVE RIDGING THEN BUILDS IN FOR TUESDAY BRINGING CLEARING
SKIES AND QUIET CONDITIONS. VALLEY FOG WILL BE LIKELY WEDNESDAY
MORNING AND COULD BE DENSE IN SOME LOCATIONS. [DISC]

A deeper trough will be tracking out of the Gulf of Alaska into BC on Wednesday. A short wave will dig on the back side of this trough into Northern California. The wave will be pretty flat and unimpressive until it reaches Northern California when it will start to strengthen as it digs down the coast. This will bring another chance for showers across the area later Wednesday into Thursday and they will once again favor southern areas. The forcing does look a bit better with this system and it will have some moisture with it and the showers should be more widespread than what we will see with today's system. It will also have colder air along with it and we will see snow levels start out 6000–7000 feet falling to 4500–5500 feet Thursday morning. Snow totals are looking to be 3–10 inches above 5500 feet with a dusting to 3 inches between 4500 and 5500 feet. Rain totals will be light over the valley with less than 0.15", generally 0.20–0.60" over the foothills and up to an inch over the mountains. There is quite a bit of uncertainty with this system given that it is strengthening over us and we are seeing a wide spread in possible QPF [Quantitative Precipitation Forecast] outcomes in the ensembles, right now low to moderate confidence in rain and snow totals. With this being the first potential impactful snow in over a month went ahead and issued a Winter Storm Watch above 5500 feet Wednesday evening into Thursday. 

A DEEPER TROUGH WILL BE TRACKING OUT OF THE GULF OF ALASKA INTO
BC ON WEDNESDAY. A SHORT WAVE WILL DIG ON THE BACK SIDE OF THIS
TROUGH INTO NORCAL. THE WAVE WILL BE PRETTY FLAT AND UNIMPRESSIVE
UNTIL IT REACHES NORCAL WHEN IT WILL START TO STRENGTHEN AS IT
DIGS DOWN THE COAST. THIS WILL BRING ANOTHER CHANCE FOR SHOWERS
ACROSS THE AREA LATER WEDNESDAY INTO THURSDAY AND THEY WILL ONCE
AGAIN FAVOR SOUTHERN AREAS. THE FORCING DOES LOOK A BIT BETTER
WITH THIS SYSTEM AND IT WILL HAVE SOME MOISTURE WITH IT AND THE
SHOWERS SHOULD BE MORE WIDESPREAD THAN WHAT WE WILL SEE WITH
TODAY`S SYSTEM. IT WILL ALSO HAVE COLDER AIR ALONG WITH IT AND WE
WILL SEE SNOW LEVELS START OUT 6000 TO 7000 FEET FALLING TO 4500
TO 5500 FEET THURSDAY MORNING. SNOW TOTALS ARE LOOKING TO BE 3 TO
10 INCHES ABOVE 5500 FEET WITH A DUSTING TO 3 INCHES BETWEEN 4500
AND 5500 FEET. RAIN TOTALS WILL BE LIGHT OVER THE VALLEY WITH
LESS THAN 0.15", GENERALLY 0.20 TO 0.60" OVER THE FOOTHILLS AND UP
TO AN INCH OVER THE MOUNTAINS. THERE IS QUITE A BIT OF
UNCERTAINTY WITH THIS SYSTEM GIVEN THAT IT IS STRENGTHENING OVER
US AND WE ARE SEEING A WIDE SPREAD IN POSSIBLE QPF OUTCOMES IN THE
ENSEMBLES, RIGHT NOW LOW TO MODERATE CONFIDENCE IN RAIN AND SNOW
TOTALS. WITH THIS BEING THE FIRST POTENTIAL IMPACTFUL SNOW IN OVER
A MONTH WENT AHEAD AND ISSUED A WINTER STORM WATCH ABOVE 5500
FEET WEDNESDAY EVENING INTO THURSDAY. [DISC]

Showers diminish during the afternoon and early evening Thursday as upper level ridging builds in. Cold air will be in place behind this system and we will see clear skies develop Thursday night, this will lead to cold overnight lows. Valley and foothill lows will fall into the upper 20s to mid 30s with single digits to teens over the mountains. This will likely be our first widespread frost of the season. 

SHOWERS DIMINISH DURING THE AFTERNOON AND EARLY EVENING THURSDAY
AS UPPER LEVEL RIDGING BUILDS IN. COLD AIR WILL BE IN PLACE BEHIND
THIS SYSTEM AND WE WILL SEE CLEAR SKIES DEVELOP THURSDAY NIGHT,
THIS WILL LEAD TO COLD OVERNIGHT LOWS. VALLEY AND FOOTHILL LOWS
WILL FALL INTO THE UPPER 20S TO MID 30S WITH SINGLE DIGITS TO
TEENS OVER THE MOUNTAINS. THIS WILL LIKELY BE OUR FIRST WIDESPREAD
FROST OF THE SEASON. [DISC]

-CJM 

-CJM [CRED]

Extended discussion (Friday through Monday). We will be under an upper level ridge for the start of the extended period with cold air in place. This will bring cooler temperatures especially for the overnight Friday, widespread frost is likely as lows fall into the upper 20s to mid 30s at lower elevations and single digits to teens over the mountains. The upper level ridge will then be replaced by long wave troughing over the west Sunday into next week. This will bring an extended period of unsettled weather and likely our wettest period of weather since October. Confidence in high with long wave troughing over the west but there is quite a bit of spread in the ensembles when it comes to timing and placement of the trough. Cold air is also expected with this troughing and this will result in low snow levels in the 4000–5000 range, locally lower over Shasta County. If you have mountain travel plans Sunday into early next week be sure to keep up with the forecast as winter driving conditions will be likely. 

.EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)...
WE WILL BE UNDER AN UPPER LEVEL RIDGE FOR THE START OF THE
EXTENDED PERIOD WITH COLD AIR IN PLACE. THIS WILL BRING COOLER
TEMPERATURES ESPECIALLY FOR THE OVERNIGHT FRIDAY, WIDESPREAD FROST
IS LIKELY AS LOWS FALL INTO THE UPPER 20S TO MID 30S AT LOWER
ELEVATIONS AND SINGLE DIGITS TO TEENS OVER THE MOUNTAINS. THE
UPPER LEVEL RIDGE WILL THEN BE REPLACED BY LONG WAVE TROUGHING
OVER THE WEST SUNDAY INTO NEXT WEEK. THIS WILL BRING AN EXTENDED
PERIOD OF UNSETTLED WEATHER AND LIKELY OUR WETTEST PERIOD OF
WEATHER SINCE OCTOBER. CONFIDENCE IN HIGH WITH LONG WAVE TROUGHING
OVER THE WEST BUT THERE IS QUITE A BIT OF SPREAD IN THE ENSEMBLES
WHEN IT COMES TO TIMING AND PLACEMENT OF THE TROUGH. COLD AIR IS
ALSO EXPECTED WITH THIS TROUGHING AND THIS WILL RESULT IN LOW SNOW
LEVELS IN THE 4000 TO 5000 RANGE, LOCALLY LOWER OVER SHASTA
COUNTY. IF YOU HAVE MOUNTAIN TRAVEL PLANS SUNDAY INTO EARLY NEXT
WEEK BE SURE TO KEEP UP WITH THE FORECAST AS WINTER DRIVING
CONDITIONS WILL BE LIKELY. [DISC]

-CJM 

-CJM [CRED]

Aviation. MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules]/LIFR [Low Instrument Flight Rules] conditions at sites due to low ceilings across Northern California and varying visibilities as a system passes over the area. Shower chances continue through 08–12Z [12–4am PST] at Sacramento terminals and southward. Clearing from N to S after 09Z [1am PST] with a chance of fog/mist redevelopment as skies clear. Winds generally under 10 knots [12 mph]

.AVIATION...
MVFR/IFR/LIFR CONDITIONS AT SITES DUE TO LOW CIGS ACROSS NORCAL
AND VARYING VISBYS AS A SYSTEM PASSES OVER THE AREA. SHOWER
CHANCES CONTINUE THROUGH 08-12Z AT SACRAMENTO TERMINALS AND
SOUTHWARD. CLEARING FROM N TO S AFTER 09Z WITH A CHANCE OF FG/BR
REDEVELOPMENT AS SKIES CLEAR. WINDS GENERALLY UNDER 10 KNOTS. [AVIA]

STO [Sacramento/WFO CA] Watches/Warnings/Advisories

  • Winter Storm Watch from Wednesday afternoon through Thursday afternoon for west slope northern Sierra Nevada-western Plumas County/Lassen Park. 
.STO WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH THURSDAY
AFTERNOON FOR WEST SLOPE NORTHERN SIERRA NEVADA-WESTERN PLUMAS
COUNTY/LASSEN PARK. [WARN]

Point Forecast

Mather CA

06 Dec 07:02pm PST

Tonight Showers likely, mainly before 10pm. Cloudy, with a low around 32°. ENE wind around 6 mph becoming calm in the evening. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.
Tuesday Sunny, with a high near 59°. Calm wind becoming west around 5 mph in the afternoon.
Tuesday Night Mostly clear, with a low around 31°. ENE wind 3 to 6 mph.
Wednesday Mostly sunny, with a high near 57°. Calm wind becoming SW 5 to 7 mph in the afternoon.
Wednesday Night Rain showers likely between 10pm and 4am, then rain and snow showers. Low around 29°. Calm wind becoming SSW 5 to 7 mph. Chance of precipitation is 80%. New snow accumulation of less than a half inch possible.
Thursday Rain and snow showers before 10am, then a chance of rain showers between 10am and 4pm, then a chance of rain and snow showers after 4pm. High near 44°. Chance of precipitation is 80%. New snow accumulation of less than a half inch possible.
Thursday Night A 20% chance of snow showers before 10pm. Partly cloudy, with a low around 13°.
Friday Sunny, with a high near 46°.
Friday Night Mostly clear, with a low around 19°.
Saturday Sunny, with a high near 52°.
Saturday Night Mostly clear, with a low around 21°.
Sunday A slight chance of showers. Mostly sunny, with a high near 52°.
Sunday Night A chance of rain and snow showers. Mostly cloudy, with a low around 26°.
Monday A chance of rain and snow showers. Mostly cloudy, with a high near 49°.
Tonight
Showers likely, mainly before 10pm. Cloudy, with a low around 32. East northeast wind around 6 mph becoming calm in the evening. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.
Tuesday
Sunny, with a high near 59. Calm wind becoming west around 5 mph in the afternoon.
Tuesday Night
Mostly clear, with a low around 31. East northeast wind 3 to 6 mph.
Wednesday
Mostly sunny, with a high near 57. Calm wind becoming southwest 5 to 7 mph in the afternoon.
Wednesday Night
Rain showers likely between 10pm and 4am, then rain and snow showers. Low around 29. Calm wind becoming south southwest 5 to 7 mph. Chance of precipitation is 80%. New snow accumulation of less than a half inch possible.
Thursday
Rain and snow showers before 10am, then a chance of rain showers between 10am and 4pm, then a chance of rain and snow showers after 4pm. High near 44. Chance of precipitation is 80%. New snow accumulation of less than a half inch possible.
Thursday Night
A 20 percent chance of snow showers before 10pm. Partly cloudy, with a low around 13.
Friday
Sunny, with a high near 46.
Friday Night
Mostly clear, with a low around 19.
Saturday
Sunny, with a high near 52.
Saturday Night
Mostly clear, with a low around 21.
Sunday
A slight chance of showers. Mostly sunny, with a high near 52.
Sunday Night
A chance of rain and snow showers. Mostly cloudy, with a low around 26.
Monday
A chance of rain and snow showers. Mostly cloudy, with a high near 49.

This page is generated dynamically from the National Weather Service's NWS point forecast and Area Forecast Discussion, reformatted for readability. NWS glossary; about point forecasts. For more information, visit the Lobitos Weather Project home page. Comments and corrections are welcome: