Area Forecast Discussion
FXUS66 KSTO [Sacramento/WFO CA] 240541 AFDSTO ∨
FXUS66 KSTO 240541 AFDSTO [HEAD]
National Weather Service Sacramento California 10:40pm PDT Thu Mar 23 2017 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 1040 PM PDT THU MAR 23 2017 [HEAD]
Synopsis. Rain and mountain snow returns tonight and Friday. Sierra snow impacts likely late tonight into Saturday. Another system possible Sunday and Monday with mountain travel impacts. Brief break in precipitation mid weekend but more precipitation early next week. ∨
.SYNOPSIS... RAIN AND MOUNTAIN SNOW RETURNS TONIGHT AND FRIDAY. SIERRA SNOW IMPACTS LIKELY LATE TONIGHT INTO SATURDAY. ANOTHER SYSTEM POSSIBLE SUNDAY AND MONDAY WITH MOUNTAIN TRAVEL IMPACTS. BRIEF BREAK IN PRECIP MID WEEKEND BUT MORE PRECIPITATION EARLY NEXT WEEK. [DISC]
Discussion. IR [Infra-Red] imagery shows a fully occluded system off the Washington coast. The vertically stacked system indicates the surface low is off the Washington coast as well. This means the low is likely too far N of our area for the strongest of pressure gradients and the strongest of 925 mbs winds. These winds are forecast to be in the low 40s kts Friday morning with the NAM [North American Meso (formerly Eta) model] forecast BUFKIT [software tool used to examine the vertical profile and other aspects of the atmosphere] soundings forecasting very limited downward momentum transfer of these winds. There is a vast difference (one with wad criteria, the other without) in the MOS [Model Output Statistics] guidance from the models this evening. The strongest gradients and thickness solenoids occur during the 18Z [11am PDT] Friday time frame, so late morning into early afternoon looks to be the period of strongest valley winds. (JHM [Lahaina/West Maui HI]) ∨
.DISCUSSION... IR IMAGERY SHOWS A FULLY OCCLUDED SYSTEM OFF THE WA COAST. THE VERTICALLY STACKED SYSTEM INDICATES THE SURFACE LOW IS OFF THE WA COAST AS WELL. THIS MEANS THE LOW IS LIKELY TOO FAR N OF OUR AREA FOR THE STRONGEST OF PRESSURE GRADIENTS AND THE STRONGEST OF 925 MBS WINDS. THESE WINDS ARE FORECAST TO BE IN THE LOW 40S KTS FRI MORNING WITH THE NAM FORECAST BUFKIT SOUNDINGS FORECASTING VERY LIMITED DOWNWARD MOMENTUM TRANSFER OF THESE WINDS. THERE IS A VAST DIFFERENCE (ONE WITH WAD CRITERIA, THE OTHER WITHOUT) IN THE MOS GUIDANCE FROM THE MODELS THIS EVENING. THE STRONGEST GRADIENTS AND THICKNESS SOLENOIDS OCCUR DURING THE 18Z FRI TIME FRAME, SO LATE MORNING INTO EARLY AFTERNOON LOOKS TO BE THE PERIOD OF STRONGEST VALLEY WINDS. JHM [DISC]
Previous discussion. Pacific storm system now approaching the coast will move into Northern California late tonight bringing a return to precipitation. The heaviest amounts will fall during the day Friday. Valley rainfall amounts will range from 1–2 inches Redding area to 0.25–0.50 Stockton/ Modesto. Mountain precipitation amounts will be 1–2 inches liquid. Snowfall amounts 8–14 inches above 4500 feet with up to two feet highest elevations. Expect significant travel delays over the Sierra. Activity will turn more showery Friday afternoon with mesoscale [medium-scale (km to 10s of km)] models showing thunderstorms over the northern Sacramento Valley. Tightening pressure gradient will bring a few 40 mph south wind gusts up the Sacramento Valley… Stockton to Redding… strongest Central Valley around Red Bluff. ∨
.PREVIOUS DISCUSSION... PACIFIC STORM SYSTEM NOW APPROACHING THE COAST WILL MOVE INTO NORCAL LATE TONIGHT BRINGING A RETURN TO PRECIPITATION. THE HEAVIEST AMOUNTS WILL FALL DURING THE DAY FRIDAY. VALLEY RAINFALL AMOUNTS WILL RANGE FROM 1-2 INCHES REDDING AREA TO 0.25-0.50 STOCKTON/ MODESTO. MOUNTAIN PRECIP AMOUNTS WILL BE 1-2 INCHES LIQUID. SNOWFALL AMOUNTS 8-14 INCHES ABOVE 4500 FEET WITH UP TO TWO FEET HIGHEST ELEVATIONS. EXPECT SIGNIFICANT TRAVEL DELAYS OVER THE SIERRA. ACTIVITY WILL TURN MORE SHOWERY FRIDAY AFTERNOON WITH MESOSCALE MODELS SHOWING THUNDERSTORMS OVER THE NORTHERN SACRAMENTO VALLEY. TIGHTENING PRESSURE GRADIENT WILL BRING A FEW 40 MPH SOUTH WIND GUSTS UP THE SACRAMENTO VALLEY...STOCKTON TO REDDING...STRONGEST CENTRAL VALLEY AROUND RED BLUFF. [DISC]
Models continue the trend of drier weather Saturday with weak ridge northwest flow. Next system will drop through Northern California Sunday afternoon through Monday and looks to be slightly drier but colder than Friday system. Snow levels look to be 4000 feet or lower. ∨
MODELS CONTINUE THE TREND OF DRIER WEATHER SATURDAY WITH WEAK RIDGE NORTHWEST FLOW. NEXT SYSTEM WILL DROP THROUGH NORCAL SUNDAY AFTERNOON THROUGH MONDAY AND LOOKS TO BE SLIGHTLY DRIER BUT COLDER THAN FRIDAY SYSTEM. SNOW LEVELS LOOK TO BE 4000 FEET OR LOWER. [DISC]
Extended discussion (Monday through Thursday) ∨
.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY) [DISC]
Showers will linger on Monday as upper level wave moves through. Have boosted snow amounts a bit during the day with snow levels around 5000 feet. Modest additional accumulations likely but will probably be enough to cause a few travel delays. Have also introduced the possibility of thunderstorms during the afternoon/evening hours. This will hinge on the amount of clearing in the morning but models are indicating some decent instability. Ridging then builds in for Tuesday and Wednesday with warming temperatures. Models continue to show another system dropping into the area from the Gulf of Alaska on Thursday but disagree on the details. At this time, best chances for precipitation looks to lie across northern and eastern portions of the area. ∨
SHOWERS WILL LINGER ON MONDAY AS UPPER LEVEL WAVE MOVES THROUGH. HAVE BOOSTED SNOW AMOUNTS A BIT DURING THE DAY WITH SNOW LEVELS AROUND 5000 FEET. MODEST ADDITIONAL ACCUMULATIONS LIKELY BUT WILL PROBABLY BE ENOUGH TO CAUSE A FEW TRAVEL DELAYS. HAVE ALSO INTRODUCED THE POSSIBILITY OF THUNDERSTORMS DURING THE AFTERNOON/EVENING HOURS. THIS WILL HINGE ON THE AMOUNT OF CLEARING IN THE MORNING BUT MODELS ARE INDICATING SOME DECENT INSTABILITY. RIDGING THEN BUILDS IN FOR TUESDAY AND WEDNESDAY WITH WARMING TEMPERATURES. MODELS CONTINUE TO SHOW ANOTHER SYSTEM DROPPING INTO THE AREA FROM THE GULF OF ALASKA ON THURSDAY BUT DISAGREE ON THE DETAILS. AT THIS TIME, BEST CHANCES FOR PRECIPITATION LOOKS TO LIE ACROSS NORTHERN AND EASTERN PORTIONS OF THE AREA. [DISC]
Next system moves into Northern California tonight into Friday. VFR [Visual Flight Rules] conditions through this evening then local MVFR [Marginal Visual Flight Rules]/IFR [Instrument Flight Rules] conditions after 12Z [5am PDT] Friday with precipitation. Winds will increase on Friday with gusts to around 25 kts [29 mph] at TAF [Terminal Aerodrome Forecast] sites. ∨
NEXT SYSTEM MOVES INTO NORCAL TONIGHT INTO FRIDAY. VFR CONDITIONS THROUGH THIS EVENING THEN LOCAL MVFR/IFR CONDITIONS AFTER 12Z FRIDAY WITH PRECIPITATION. WINDS WILL INCREASE ON FRIDAY WITH GUSTS TO AROUND 25 KTS AT TAF SITES. [AVI2]
STO [Sacramento/WFO CA] Watches/Warnings/Advisories
.STO WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING FROM 11 PM THIS EVENING TO 5 AM PDT SATURDAY FOR WEST SLOPE NORTHERN SIERRA NEVADA-WESTERN PLUMAS COUNTY/LASSEN PARK. [WARN]
WIND ADVISORY FROM 9 AM TO 7 PM PDT FRIDAY FOR CARQUINEZ STRAIT AND DELTA-CENTRAL SACRAMENTO VALLEY-MOTHERLODE-NORTHEAST FOOTHILLS/SACRAMENTO VALLEY-NORTHERN SACRAMENTO VALLEY-NORTHERN SAN JOAQUIN VALLEY-SOUTHERN SACRAMENTO VALLEY. [WRN2]
WINTER STORM WARNING FROM 11 PM THIS EVENING TO 5 AM PDT SATURDAY FOR SHASTA LAKE AREA / NORTHERN SHASTA COUNTY. [WRN2]
23 Mar 11:30pm PDT
Overnight A 50% chance of rain. Cloudy, with a low around 48°. SE wind around 6 mph. New precipitation amounts of less than a tenth of an inch possible.
Friday Rain. High near 57°. Breezy, with a SSE wind 10 to 15 mph increasing to 18 to 23 mph in the afternoon. Winds could gust as high as 39 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.
Friday Night Rain likely before 11pm, then a chance of showers after 11pm. Cloudy, with a low around 46°. SSE wind 7 to 17 mph, with gusts as high as 30 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.
Saturday A 20% chance of showers before 11am. Partly sunny, with a high near 64°. SSE wind around 6 mph becoming light and variable in the morning.
Saturday Night Mostly cloudy, with a low around 44°. West wind around 5 mph becoming light and variable in the evening.
Sunday A 40% chance of rain, mainly after 11am. Mostly cloudy, with a high near 59°.
Sunday Night Rain before 11pm, then showers after 11pm. Low around 46°. Chance of precipitation is 80%.
Monday A chance of showers. Mostly cloudy, with a high near 64°.
Monday Night A slight chance of showers. Mostly cloudy, with a low around 43°.
Tuesday Mostly sunny, with a high near 71°.
Tuesday Night Partly cloudy, with a low around 46°.
Wednesday Mostly sunny, with a high near 74°.
Wednesday Night Partly cloudy, with a low around 49°.
Thursday Mostly sunny, with a high near 68°.
A 50 percent chance of rain. Cloudy, with a low around 48. Southeast wind around 6 mph. New precipitation amounts of less than a tenth of an inch possible.
Rain. High near 57. Breezy, with a south southeast wind 10 to 15 mph increasing to 18 to 23 mph in the afternoon. Winds could gust as high as 39 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.
Rain likely before 11pm, then a chance of showers after 11pm. Cloudy, with a low around 46. South southeast wind 7 to 17 mph, with gusts as high as 30 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.
A 20 percent chance of showers before 11am. Partly sunny, with a high near 64. South southeast wind around 6 mph becoming light and variable in the morning.
Mostly cloudy, with a low around 44. West wind around 5 mph becoming light and variable in the evening.
A 40 percent chance of rain, mainly after 11am. Mostly cloudy, with a high near 59.
Rain before 11pm, then showers after 11pm. Low around 46. Chance of precipitation is 80%.
A chance of showers. Mostly cloudy, with a high near 64.
A slight chance of showers. Mostly cloudy, with a low around 43.
Mostly sunny, with a high near 71.
Partly cloudy, with a low around 46.
Mostly sunny, with a high near 74.
Partly cloudy, with a low around 49.
Mostly sunny, with a high near 68.