Area Forecast Discussion
FXUS66 KSTO [Sacramento/WFO CA] 231158 AFDSTO ∨
FXUS66 KSTO 231158 AFDSTO [HEAD]
National Weather Service Sacramento California 4:58am PDT Thu Oct 23 2014 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 458 AM PDT THU OCT 23 2014 [HEAD]
Synopsis. A weak Pacific cold front will drag slowly across Northern California bringing light precipitation north of about I-80 today and tonight. A brief break Friday will be followed by another frontal passage on Saturday with thunderstorms possible north of the Sacramento area. Drying and warming most areas early next week then another frontal system moving in around Tuesday. Weather model confidence decreases by mid week but more light precipitation possible next Wednesday and Thursday mainly north of Sacramento. ∨
.SYNOPSIS... A WEAK PACIFIC COLD FRONT WILL DRAG SLOWLY ACROSS NORCAL BRINGING LIGHT PRECIPITATION NORTH OF ABOUT I-80 TODAY AND TONIGHT. A BRIEF BREAK FRIDAY WILL BE FOLLOWED BY ANOTHER FRONTAL PASSAGE ON SATURDAY WITH THUNDERSTORMS POSSIBLE NORTH OF THE SACRAMENTO AREA. DRYING AND WARMING MOST AREAS EARLY NEXT WEEK THEN ANOTHER FRONTAL SYSTEM MOVING IN AROUND TUESDAY. WEATHER MODEL CONFIDENCE DECREASES BY MID WEEK BUT MORE LIGHT PRECIP POSSIBLE NEXT WEDNESDAY AND THURSDAY MAINLY NORTH OF SACRAMENTO. [DISC]
A weak Pacific cold front dragging across the northwest corner of the state is bringing light precipitation from about chico northward. The precipitation is forecast to continue moving very slowly to the southeast with light precipitation reaching southward to about the Sacramento area by 00Z [5pm PDT] this afternoon. Cloud cover and a slightly cooler airmass will bring slightly cooler temperatures today. High pressure is forecast to rebound northward over the Western US on Friday limiting any precipitation to the far northwest corner of the state. Clearing skies and a warming airmass under the ridge will bring daytime highs to near or a little above normal Friday. A Pacific low pressure system approaching the coast will bring a threat of precipitation inland Friday night with a chance of rain and high elevation snow across the entire forecast area by Saturday afternoon and evening. Precipitable water proggs show a moderate amount of moisture associated with this system with moderate dynamics but it will take mountain orograhics to squeeze out more than light precipitation. 500 mb winds associated with the main frontal passage early Saturday are forecast to top 60 mph so ridgetops may see some fairly gusty winds. Stability proggs show enough instability behind the cold front for a threat of thunderstorms Saturday afternoon and evening across the northern CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. As the upper trough passes through the Pacific Northwest Saturday night and Sunday, winds will decrease and precipitation will shift to the northeast. Daytime highs over the weekend will remain well below normal under the cool airmass behind the front. ∨
A WEAK PACIFIC COLD FRONT DRAGGING ACROSS THE NORTHWEST CORNER OF THE STATE IS BRINGING LIGHT PRECIPITATION FROM ABOUT CHICO NORTHWARD. THE PRECIPITATION IS FORECAST TO CONTINUE MOVING VERY SLOWLY TO THE SOUTHEAST WITH LIGHT PRECIPITATION REACHING SOUTHWARD TO ABOUT THE SACRAMENTO AREA BY 00Z THIS AFTERNOON. CLOUD COVER AND A SLIGHTLY COOLER AIRMASS WILL BRING SLIGHTLY COOLER TEMPERATURES TODAY. HIGH PRESSURE IS FORECAST TO REBOUND NORTHWARD OVER THE WESTERN U.S ON FRIDAY LIMITING ANY PRECIPITATION TO THE FAR NORTHWEST CORNER OF THE STATE. CLEARING SKIES AND A WARMING AIRMASS UNDER THE RIDGE WILL BRING DAYTIME HIGHS TO NEAR OR A LITTLE ABOVE NORMAL FRIDAY. A PACIFIC LOW PRESSURE SYSTEM APPROACHING THE COAST WILL BRING A THREAT OF PRECIPITATION INLAND FRIDAY NIGHT WITH A CHANCE OF RAIN AND HIGH ELEVATION SNOW ACROSS THE ENTIRE FORECAST AREA BY SATURDAY AFTERNOON AND EVENING. PRECIPITABLE WATER PROGGS SHOW A MODERATE AMOUNT OF MOISTURE ASSOCIATED WITH THIS SYSTEM WITH MODERATE DYNAMICS BUT IT WILL TAKE MOUNTAIN OROGRAHICS TO SQUEEZE OUT MORE THAN LIGHT PRECIPITATION. 500 MB WINDS ASSOCIATED WITH THE MAIN FRONTAL PASSAGE EARLY SATURDAY ARE PROGGED TO TOP 60 MPH SO RIDGETOPS MAY SEE SOME FAIRLY GUSTY WINDS. STABILITY PROGGS SHOW ENOUGH INSTABILITY BEHIND THE COLD FRONT FOR A THREAT OF THUNDERSTORMS SATURDAY AFTERNOON AND EVENING ACROSS THE NORTHERN CWA. AS THE UPPER TROUGH PASSES THROUGH THE PACIFIC NORTHWEST SATURDAY NIGHT AND SUNDAY, WINDS WILL DECREASE AND PRECIPITATION WILL SHIFT TO THE NORTHEAST. DAYTIME HIGHS OVER THE WEEKEND WILL REMAIN WELL BELOW NORMAL UNDER THE COOL AIRMASS BEHIND THE FRONT. [DISC]
Extended discussion (Monday through Thursday) ∨
.EXTENDED DISCUSSION (MONDAY THROUGH THURSDAY) [DISC]
Monday looks like a dry day with models rebuilding a ridge over the eastern Pacific and West Coast. Daytime highs may push back up to near normal. A shortwave trough moving through the Paciiic northwest will flatten the West Coast ridge on Tuesday bringing clouds and cooler temperatures with a chance of precipitaton across the northern mountains. After Tuesday… models really begin to diverge so confidense in the day 6 plus forecast not real high. 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.] rebuilds a fairly strong ridge over the West Coast Wednesday and Thursday and has been doing so over the last couple of runs. ECMWF [European Center for Medium-Range Weather Forecasts model] and GEM [Global Environmental Multiscale model] dig the next upper trough into the eastern Pacific Wednesday and Thursday bringing cooler temperatures and a continued threat of precipitation especially across the northern portions of the forecast area. Have leaned towards the more stable ECMWF [European Center for Medium-Range Weather Forecasts model] and GEM [Global Environmental Multiscale model] for now but will continue to watch model developments in this time frame. ∨
MONDAY LOOKS LIKE A DRY DAY WITH MODELS REBUILDING A RIDGE OVER THE EASTERN PACIFIC AND WEST COAST. DAYTIME HIGHS MAY PUSH BACK UP TO NEAR NORMAL. A SHORTWAVE TROUGH MOVING THROUGH THE PACIIIC NORTHWEST WILL FLATTEN THE WEST COAST RIDGE ON TUESDAY BRINGING CLOUDS AND COOLER TEMPERATURES WITH A CHANCE OF PRECIPITATON ACROSS THE NORTHERN MOUNTAINS. AFTER TUESDAY...MODELS REALLY BEGIN TO DIVERGE SO CONFIDENSE IN THE DAY 6 PLUS FORECAST NOT REAL HIGH. GFS REBUILDS A FAIRLY STRONG RIDGE OVER THE WEST COAST WEDNESDAY AND THURSDAY AND HAS BEEN DOING SO OVER THE LAST COUPLE OF RUNS. ECMWF AND GEM DIG THE NEXT UPPER TROUGH INTO THE EASTERN PACIFIC WEDNESDAY AND THURSDAY BRINGING COOLER TEMPERATURES AND A CONTINUED THREAT OF PRECIPITATION ESPECIALLY ACROSS THE NORTHERN PORTIONS OF THE FORECAST AREA. HAVE LEANED TOWARDS THE MORE STABLE ECMWF AND GEM FOR NOW BUT WILL CONTINUE TO WATCH MODEL DEVELOPMENTS IN THIS TIME FRAME. [DISC]
Cold front moving on shore today with increasing rain spreading into the northern Sacramento Valley, peaking around 15Z [8am PDT]-21Z [2pm PDT]. This will bring some local visibilities reduced to MVFR [Marginal Visual Flight Rules] levels, IFR [Instrument Flight Rules] in the mountains. Local precipitation will stay mainly north of I-80 today, and will decrease in intensity by 00Z [5pm PDT]. Mid level cloud cover will increase over the rest of the area. Winds around 10 kt [12 mph] or less expected today for TAF [Terminal Aerodrome Forecast] sites. (Ek) ∨
COLD FRONT MOVING ON SHORE TODAY WITH INCREASING RAIN SPREADING INTO THE NORTHERN SACRAMENTO VALLEY, PEAKING AROUND 15Z-21Z. THIS WILL BRING SOME LCL VISIBILITIES REDUCED TO MVFR LEVELS, IFR IN THE MOUNTAINS. LOCAL PRECIPITATION WILL STAY MAINLY NORTH OF I80 TODAY, AND WILL DECREASE IN INTENSITY BY 00Z. MID LEVEL CLOUD COVER WILL INCREASE OVER THE REST OF THE AREA. WINDS AROUND 10 KT OR LESS EXPECTED TODAY FOR TAF SITES. EK [AVI2]
STO [Sacramento/WFO CA] Watches/Warnings/Advisories
.STO WATCHES/WARNINGS/ADVISORIES... NONE. [WARN]
18 Miles E Groveland CA
9:50am PDT Oct 23 2014
This Afternoon. Mostly sunny, with a high near 70°. SSW wind around 10 mph.
Tonight. Mostly clear, with a low around 54°. SSW wind 6 to 8 mph becoming ENE in the evening.
Friday. Sunny, with a high near 74°. East wind 8 to 11 mph becoming south in the afternoon.
Friday Night. Partly cloudy, with a low around 52°. SE wind 7 to 9 mph.
Saturday. A 20% chance of showers after 11am. Partly sunny, with a high near 61°. South wind 10 to 18 mph, with gusts as high as 28 mph.
Saturday Night. A 30% chance of showers. Mostly cloudy, with a low around 45°.
Sunday. Mostly sunny, with a high near 55°.
Sunday Night. Mostly clear, with a low around 42°.
Monday. Sunny, with a high near 59°.
Monday Night. Mostly clear, with a low around 45°.
Tuesday. Mostly sunny, with a high near 62°.
Tuesday Night. Partly cloudy, with a low around 46°.
Wednesday. Mostly sunny, with a high near 64°.