Area Forecast Discussion
FXUS66 KSTO [Sacramento/WFO CA] 211127 AFDSTO ∨
FXUS66 KSTO 211127 AFDSTO [HEAD]
National Weather Service Sacramento California 4:27am PDT Sun Sep 21 2014 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 427 AM PDT SUN SEP 21 2014 [HEAD]
Synopsis. Lingering Sierra showers/thunderstorms are possible through this evening. Otherwise, dry and warmer temperatures into early next week. Cooler and possibly wetter weather for the middle to end of next week. ∨
.SYNOPSIS... LINGERING SIERRA SHOWERS/T-STORMS ARE POSSIBLE THROUGH THIS EVENING. OTHERWISE, DRY AND WARMER TEMPERATURES INTO EARLY NEXT WEEK. COOLER AND POSSIBLY WETTER WEATHER FOR THE MIDDLE TO END OF NEXT WEEK. [DISC]
Discussion. Upper level closed low center now appears from satellite imagery to be somewhere over the northern San Joaquin Valley. IR [Infra-Red] image shows abundant cloudiness in the deformation zone [change in shape by variations in wind, specifically by stretching and/or shearing] in the northeast section of the low. A short wave trough rotating out of this zone and westward across north central California brought light showers and isolated thunderstorms over the northern Sierra and westward into the southern Sacramento Valley overnight. This disturbance has moved westward and weakened and the showers have ended most areas. The upper low is forecast to move rapidly to the northeast today with the center moving into Nevada by 18Z [11am PDT] today. Instability forecasts show some minor instability still over the eastern portion of Northern California today near the back side of the low so left a slight threat of showers and thunderstorms over the east side mountains through this evening. The remainder of the forecast area should see clearing skies as the low continues eastward. Slightly cooler airmass today should bring slightly cooler daytime high temperatures. Upper level high pressure ridge sliding over the north state will bring fair skies and warmer temperatures on Monday. The high will shift quickly eastward on Tuesday as a low pressure system in the Pacific moves towards the coast. Daytime temperatures Tuesday will be similar to Monday before a bigger cooling trend expected to begin Wednesday. Mid range models in fair agreement in bringing a Pacific frontal system onto the north coast sometime early Wednesday. If current models hold… parts of the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map] will be seeing light precipitation as early as mid day Wednesday. ∨
.DISCUSSION... UPPER LEVEL CLOSED LOW CENTER NOW APPEARS FROM SATELLITE IMAGERY TO BE SOMEWHERE OVER THE NORTHERN SAN JOAQUIN VALLEY. IR IMAGE SHOWS ABUNDANT CLOUDINESS IN THE DEFORMATION ZONE IN THE NORTHEAST SECTION OF THE LOW. A SHORT WAVE TROUGH ROTATING OUT OF THIS ZONE AND WESTWARD ACROSS NORTH CENTRAL CALIFORNIA BROUGHT LIGHT SHOWERS AND ISOLATED THUNDERSTORMS OVER THE NORTHERN SIERRA AND WESTWARD INTO THE SOUTHERN SACRAMENTO VALLEY OVERNIGHT. THIS DISTURBANCE HAS MOVED WESTWARD AND WEAKENED AND THE SHOWERS HAVE ENDED MOST AREAS. THE UPPER LOW IS FORECAST TO MOVE RAPIDLY TO THE NORTHEAST TODAY WITH THE CENTER MOVING INTO NEVADA BY 18Z TODAY. INSTABILITY PROGS SHOW SOME MINOR INSTABILITY STILL OVER THE EASTERN PORTION OF NORTHERN CALIFORNIA TODAY NEAR THE BACK SIDE OF THE LOW SO LEFT A SLIGHT THREAT OF SHOWERS AND THUNDERSTORMS OVER THE EAST SIDE MOUNTAINS THROUGH THIS EVENING. THE REMAINDER OF THE FORECAST AREA SHOULD SEE CLEARING SKIES AS THE LOW CONTINUES EASTWARD. SLIGHTLY COOLER AIRMASS TODAY SHOULD BRING SLIGHTLY COOLER DAYTIME HIGH TEMPERATURES. UPPER LEVEL HIGH PRESSURE RIDGE SLIDING OVER THE NORTH STATE WILL BRING FAIR SKIES AND WARMER TEMPERATURES ON MONDAY. THE HIGH WILL SHIFT QUICKLY EASTWARD ON TUESDAY AS A LOW PRESSURE SYSTEM IN THE PACIFIC MOVES TOWARDS THE COAST. DAYTIME TEMPERATURES TUESDAY WILL BE SIMILAR TO MONDAY BEFORE A BIGGER COOLING TREND EXPECTED TO BEGIN WEDNESDAY. MID RANGE MODELS IN FAIR AGREEMENT IN BRINGING A PACIFIC FRONTAL SYSTEM ONTO THE NORTH COAST SOMETIME EARLY WEDNESDAY. IF CURRENT MODELS HOLD...PARTS OF THE CWA WILL BE SEEING LIGHT PRECIPITATION AS EARLY AS MID DAY WEDNESDAY. [DISC]
Extended discussion (Thursday through Sunday) ∨
.EXTENDED DISCUSSION (THURSDAY THROUGH SUNDAY) [DISC]
Extended models in fairly good agreement in moving a Pacific frontal system across the Pacific Northwest and Northern California Thursday. Nearly all of the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map] will see at least a chance of precipitation. With cloud cover and cooler airmass… daytime highs will drop to well below normal. Extended models begin to diverge a bit by next Friday. 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.] model progresses the upper trough axis east of the forecast area by 00Z [5pm PDT] Friday while the ECMWF [European Center for Medium-Range Weather Forecasts model] lingers it offshore. GEM [Global Environmental Multiscale model] model takes a middle of the road approach to the other two. Regardless of the solution… next Friday looks to be a mainly cloudy day with at least a threat of precipitation most areas. Significance of model variance grows by next Saturday as 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.] would bring clearing and warming under a ridge pattern while a less progressive ECMWF [European Center for Medium-Range Weather Forecasts model] would keep showers in the region. Have kept with the more middle of the road GEM [Global Environmental Multiscale model] and kept precipitation threat mainly over the eastern portions of the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. Rap around moisture could still be an issue for the Sierra next Sunday if ECMWF [European Center for Medium-Range Weather Forecasts model] solution is correct. 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.] and GEM [Global Environmental Multiscale model] models show drying under a ridge of high pressure. ∨
EXTENDED MODELS IN FAIRLY GOOD AGREEMENT IN MOVING A PACIFIC FRONTAL SYSTEM ACROSS THE PACIFIC NORTHWEST AND NORCAL THURSDAY. NEARLY ALL OF THE CWA WILL SEE AT LEAST A CHANCE OF PRECIPITATION. WITH CLOUD COVER AND COOLER AIRMASS...DAYTIME HIGHS WILL DROP TO WELL BELOW NORMAL. EXTENDED MODELS BEGIN TO DIVERGE A BIT BY NEXT FRIDAY. GFS MODEL PROGRESSES THE UPPER TROUGH AXIS EAST OF THE FORECAST AREA BY 00Z FRIDAY WHILE THE ECMWF LINGERS IT OFFSHORE. GEM MODEL TAKES A MIDDLE OF THE ROAD APPROACH TO THE OTHER TWO. REGARDLESS OF THE SOLUTION...NEXT FRIDAY LOOKS TO BE A MAINLY CLOUDY DAY WITH AT LEAST A THREAT OF PRECIPITATION MOST AREAS. SIGNIFICANCE OF MODEL VARIANCE GROWS BY NEXT SATURDAY AS GFS WOULD BRING CLEARING AND WARMING UNDER A RIDGE PATTERN WHILE A LESS PROGRESSIVE ECMWF WOULD KEEP SHOWERS IN THE REGION. HAVE KEPT WITH THE MORE MIDDLE OF THE ROAD GEM AND KEPT PRECIP THREAT MAINLY OVER THE EASTERN PORTIONS OF THE CWA. RAP AROUND MOISTURE COULD STILL BE AN ISSUE FOR THE SIERRA NEXT SUNDAY IF ECMWF SOLUTION IS CORRECT. GFS AND GEM MODELS SHOW DRYING UNDER A RIDGE OF HIGH PRESSURE. [DISC]
VFR [Visual Flight Rules] conditions next 24 hours. Local MVFR [Marginal Visual Flight Rules] visibilities vicinity King fire near KPVF. Isolated light rain showers mainly over northern Sierra Nevada with scattered thunderstorms with rain PSB [Philipsburg PA] HYR [Hayward WI] elevations northern Sierra Nevada after 21Z [2pm PDT] til about 02Z [7pm PDT] Monday. ∨
VFR CONDS NXT 24 HRS. LCL MVFR VSBYS VCNTY KING FIRE NEAR KPVF. ISOLD -SHRA MAINLY OVR NRN SIERNEV WITH SCT TSRA PSB HYR ELEVS NRN SIERNEV AFT 21Z TIL ABT 02Z MON. [AVI2]
STO [Sacramento/WFO CA] Watches/Warnings/Advisories
.STO WATCHES/WARNINGS/ADVISORIES... NONE. [WARN]
18 Miles E Groveland CA
2:40am PDT Sep 21 2014
Today. A 20% chance of showers and thunderstorms before 11am. Mostly sunny, with a high near 84°. Light and variable wind becoming west 5 to 8 mph in the afternoon.
Tonight. Partly cloudy, with a low around 60°. West wind 5 to 8 mph becoming calm.
Monday. Sunny, with a high near 84°. ENE wind 5 to 8 mph becoming WSW in the morning.
Monday Night. Mostly clear, with a low around 60°. West wind 5 to 8 mph becoming ENE in the evening.
Tuesday. Sunny, with a high near 85°. ENE wind 6 to 8 mph becoming SSW in the morning.
Tuesday Night. Mostly clear, with a low around 60°.
Wednesday. Mostly sunny, with a high near 87°.
Wednesday Night. Partly cloudy, with a low around 60°.
Thursday. A slight chance of showers. Mostly sunny, with a high near 79°.
Thursday Night. A slight chance of showers. Partly cloudy, with a low around 56°.
Friday. A slight chance of showers. Mostly sunny, with a high near 80°.
Friday Night. A slight chance of showers. Partly cloudy, with a low around 56°.
Saturday. Mostly sunny, with a high near 68°.