Area Forecast Discussion
FXUS66 KSTO [Sacramento/WFO CA] 292200 AFDSTO ∨
FXUS66 KSTO 292200 AFDSTO [HEAD]
National Weather Service Sacramento California 3:00pm PDT Thu Sep 29 2016 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 300 PM PDT THU SEP 29 2016 [HEAD]
Synopsis. Significant cooling trend through the weekend with daytime highs 15–25° below normal Sunday. Chance of showers and isolated thunderstorms Sunday into Monday. Drier Tuesday into Thursday with a warming trend. ∨
.SYNOPSIS... SIGNIFICANT COOLING TREND THROUGH THE WEEKEND WITH DAYTIME HIGHS 15 TO 25 DEGREES BELOW NORMAL SUNDAY. CHANCE OF SHOWERS AND ISOLATED THUNDERSTORMS SUNDAY INTO MONDAY. DRIER TUESDAY INTO THURSDAY WITH A WARMING TREND. [DISC]
Discussion. Afternoon temperatures running upwards of 12° cooler than 24 hours ago as large upper low west of BC digs and approaches the West Coast. LAV [GFS-LAMP Text Bulletin] MOS [Model Output Statistics] guidance has trended a little weaker with the Delta breeze tonight but still expecting a moderately strong flow overnight with the potential for some patchy stratus in the Sacramento area Friday morning. ∨
.DISCUSSION... AFTERNOON TEMPERATURES RUNNING UPWARDS OF 12 DEGREES COOLER THAN 24 HOURS AGO AS LARGE UPPER LOW WEST OF B.C. DIGS AND APPROACHES THE WEST COAST. LAV MOS GUIDANCE HAS TRENDED A LITTLE WEAKER WITH THE DELTA BREEZE TONIGHT BUT STILL EXPECTING A MODERATELY STRONG FLOW OVERNIGHT WITH THE POTENTIAL FOR SOME PATCHY STRATUS IN THE SACRAMENTO AREA FRIDAY MORNING. [DISC]
Moisture starved surface front pushes into northwest California tonight into Friday with main impact being some breezy to windy conditions ahead of boundary over interior Northern California. Additional cooling will result, with Max temps tomorrow forecast mostly in the upper 70s to around 80 with upper 50s to mid 70s for the mountains and foothills. ∨
MOISTURE STARVED SURFACE FRONT PUSHES INTO NORTHWEST CA TONIGHT INTO FRIDAY WITH MAIN IMPACT BEING SOME BREEZY TO WINDY CONDITIONS AHEAD OF BOUNDARY OVER INTERIOR NORCAL. ADDITIONAL COOLING WILL RESULT, WITH MAX TEMPS TOMORROW FORECAST MOSTLY IN THE UPPER 70S TO AROUND 80 WITH UPPER 50S TO MID 70S FOR THE MOUNTAINS AND FOOTHILLS. [DISC]
Frontolysis occurs along baroclinic zone as it slides south Friday night, while associated upper low weakens to trough and swings inland Saturday. Cooling trend continues Saturday with some breezy conditions. Secondary colder, more dynamic, low is forecast to drop down the base of long wave and track into Northern California Sunday. Models continue to show widespread precipitation with this feature over interior Northern California. GFS [Global Forecast System: global spectral model used primarily for aviation weather forecasts; provides guidance out to 384 hours at 00, 06, 12 and 18UTC.] maintains some increased afternoon CAPE [Convective Available Potential Energy. A measure of the amount of energy available for convection. Related to the maximum potential vertical speed within an updraft; thus, higher values indicate greater potential for severe weather. Observed values in thunderstorm environments often may exceed 1000 joules per kilogram (J/kg), and in extreme cases may exceed 5000 J/kg.] over the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map] to support deep moist convection. Best instability currently depicted over the northern and central Sacramento Valley and along the eastern foothills and motherlode. 700 mb temps cool to around –5 to –6°C Sunday afternoon with 1000–500 mb thicknesses from around 541–544 dm [decameters] over the Shasta and coastal mountains to 545–550 dm [decameters] over the Sierra Nevada. This suggest snow levels could lower to around 5500 feet in the north to 6500 feet over the Sierra later Sunday. Although precipitation is expected to be scattered and highly variable amounts given the showery pattern, potential exists for several inches of accumulation at pass levels. Sunday's high temperatures forecast to be 15–25° below normal with mid 60s to lower 70s for the Central Valley. Potential exists for some new record lowest maximum temperatures to be set Sunday. ∨
FRONTOLYSIS OCCURS ALONG BAROCLINIC ZONE AS IT SLIDES SOUTH FRIDAY NIGHT, WHILE ASSOCIATED UPPER LOW WEAKENS TO TROUGH AND SWINGS INLAND SATURDAY. COOLING TREND CONTINUES SATURDAY WITH SOME BREEZY CONDITIONS. SECONDARY COLDER, MORE DYNAMIC, LOW IS PROGGED TO DROP DOWN THE BASE OF LONG WAVE AND TRACK INTO NORCAL SUNDAY. MODELS CONTINUE TO SHOW WIDESPREAD PRECIP WITH THIS FEATURE OVER INTERIOR NORCAL. GFS MAINTAINS SOME INCREASED AFTERNOON CAPE OVER THE CWA TO SUPPORT DEEP MOIST CONVECTION. BEST INSTABILITY CURRENTLY DEPICTED OVER THE NORTHERN AND CENTRAL SACRAMENTO VALLEY AND ALONG THE EASTERN FOOTHILLS AND MOTHERLODE. 700 MB TEMPS COOL TO AROUND -5 TO -6 DEG C SUNDAY AFTERNOON WITH 1000-500 MB THICKNESSES FROM AROUND 541-544 DM OVER THE SHASTA AND COASTAL MOUNTAINS TO 545-550 DM OVER THE SIERRA NEVADA. THIS SUGGEST SNOW LEVELS COULD LOWER TO AROUND 5500 FEET IN THE NORTH TO 6500 FEET OVER THE SIERRA LATER SUNDAY. ALTHOUGH PRECIPITATION IS EXPECTED TO BE SCATTERED AND HIGHLY VARIABLE AMOUNTS GIVEN THE SHOWERY PATTERN, POTENTIAL EXISTS FOR SEVERAL INCHES OF ACCUMULATION AT PASS LEVELS. SUNDAY`S HIGH TEMPERATURES FORECAST TO BE 15 TO 25 DEGREES BELOW NORMAL WITH MID 60S TO LOWER 70S FOR THE CENTRAL VALLEY. POTENTIAL EXISTS FOR SOME NEW RECORD LOWEST MAXIMUM TEMPERATURES TO BE SET SUNDAY. [DISC]
Extended discussion (Monday through Thursday) the upper level low quickly shifts east into the Great Basin by Monday. Cool northerly flow aloft takes hold across the region on Monday, but there still may be enough residual moisture for a few showers. Overnight temperatures will likely be on the cool side for a few nights, with 40s across the Central Valley and 20s possible over higher terrain. ∨
.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY) THE UPPER LEVEL LOW QUICKLY SHIFTS EAST INTO THE GREAT BASIN BY MONDAY. COOL NORTHERLY FLOW ALOFT TAKES HOLD ACROSS THE REGION ON MONDAY, BUT THERE STILL MAY BE ENOUGH RESIDUAL MOISTURE FOR A FEW SHOWERS. OVERNIGHT TEMPERATURES WILL LIKELY BE ON THE COOL SIDE FOR A FEW NIGHTS, WITH 40S ACROSS THE CENTRAL VALLEY AND 20S POSSIBLE OVER HIGHER TERRAIN. [DISC]
Drier weather is expected by the middle of next week as the eastern Pacific ridge rebuilds into California. High temperatures are expected to warm back to near normal levels, though overnight lows may remain on the cooler side. ∨
DRIER WEATHER IS EXPECTED BY THE MIDDLE OF NEXT WEEK AS THE EASTERN PACIFIC RIDGE REBUILDS INTO CALIFORNIA. HIGH TEMPERATURES ARE EXPECTED TO WARM BACK TO NEAR NORMAL LEVELS, THOUGH OVERNIGHT LOWS MAY REMAIN ON THE COOLER SIDE. [DISC]
VFR [Visual Flight Rules] conditions across valley terminals the next 24 hours. Southerly onshore wind continue across the valley through Friday, with local gusts up to 25 kt [29 mph] during the afternoon. Near the Delta and over higher terrain… higher gusts are possible. ∨
VFR CONDITIONS ACROSS VALLEY TERMINALS THE NEXT 24 HOURS. SOUTHERLY ONSHORE WIND CONTINUE ACROSS THE VALLEY THROUGH FRIDAY, WITH LOCAL GUSTS UP TO 25 KT DURING THE AFTERNOON. NEAR THE DELTA AND OVER HIGHER TERRAIN...HIGHER GUSTS ARE POSSIBLE. [AVI2]
STO [Sacramento/WFO CA] Watches/Warnings/Advisories
.STO WATCHES/WARNINGS/ADVISORIES... NONE. [WARN]
29 Sep 4:02pm PDT
Tonight Mostly clear, with a low around 55°. SSW wind 7 to 9 mph becoming east in the evening.
Friday Sunny, with a high near 71°. East wind 8 to 10 mph becoming SSW in the afternoon.
Friday Night Mostly clear, with a low around 48°. SW wind 5 to 8 mph becoming calm.
Saturday Sunny, with a high near 64°. ESE wind 6 to 8 mph becoming SW in the morning.
Saturday Night Mostly clear, with a low around 43°. West wind around 6 mph becoming east in the evening.
Sunday A 30% chance of showers after 11am. Mostly sunny, with a high near 56°.
Sunday Night A chance of showers and thunderstorms. Mostly cloudy, with a low around 37°. Chance of precipitation is 50%.
Monday A chance of showers before 11am. Mostly sunny, with a high near 52°.
Monday Night Partly cloudy, with a low around 37°.
Tuesday Mostly sunny, with a high near 59°.
Tuesday Night Partly cloudy, with a low around 42°.
Wednesday Mostly sunny, with a high near 67°.
Wednesday Night Partly cloudy, with a low around 47°.
Thursday Mostly sunny, with a high near 73°.
Mostly clear, with a low around 55. South southwest wind 7 to 9 mph becoming east in the evening.
Sunny, with a high near 71. East wind 8 to 10 mph becoming south southwest in the afternoon.
Mostly clear, with a low around 48. Southwest wind 5 to 8 mph becoming calm.
Sunny, with a high near 64. East southeast wind 6 to 8 mph becoming southwest in the morning.
Mostly clear, with a low around 43. West wind around 6 mph becoming east in the evening.
A 30 percent chance of showers after 11am. Mostly sunny, with a high near 56.
A chance of showers and thunderstorms. Mostly cloudy, with a low around 37. Chance of precipitation is 50%.
A chance of showers before 11am. Mostly sunny, with a high near 52.
Partly cloudy, with a low around 37.
Mostly sunny, with a high near 59.
Partly cloudy, with a low around 42.
Mostly sunny, with a high near 67.
Partly cloudy, with a low around 47.
Mostly sunny, with a high near 73.