Area Forecast Discussion
FXUS66 KSTO [Sacramento/WFO CA] 022352 AFDSTO ∨
FXUS66 KSTO 022352 AFDSTO [HEAD]
National Weather Service Sacramento California 3:52pm PST Fri Dec 2 2016 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SACRAMENTO CA 352 PM PST FRI DEC 2 2016 [HEAD]
Synopsis. Breezy north winds will decrease Saturday. Morning low temperatures will be chilly, with warming daytime temperatures into the weekend. Light showers and cooling temperatures Sunday into Monday mainly north of Sacramento and over the northern Sierra. Turning much colder Tuesday through mid week. Valley minimum temperatures dropping to near freezing Tuesday through Thursday. A chance of rain or mountain snow again by the end of the week. ∨
.SYNOPSIS... BREEZY NORTH WINDS WILL DECREASE SATURDAY. MORNING LOW TEMPERATURES WILL BE CHILLY, WITH WARMING DAYTIME TEMPERATURES INTO THE WEEKEND. LIGHT SHOWERS AND COOLING TEMPERATURES SUNDAY INTO MONDAY MAINLY NORTH OF SACRAMENTO AND OVER THE NORTHERN SIERRA. TURNING MUCH COLDER TUESDAY THROUGH MID WEEK. VALLEY MINIMUM TEMPERATURES DROPPING TO NEAR FREEZING TUESDAY THROUGH THURSDAY. A CHANCE OF RAIN OR MOUNTAIN SNOW AGAIN BY THE END OF THE WEEK. [DISC]
Discussion. Gusty/breezy northerly winds continued over Northern California today due to increasing anticyclonic [clockwise] flow and subsidence in the wake of short wave energy that moved through Northern California earlier today and in conjunction with surface high pressure over the Great Basin. As the surface high sinks southward across the Great Basin tonight, the northerly gradients will slacken while the easterly gradients continue. This should allow winds to decouple in the valley while Katabatic/downslope winds continue over the Sierra. Decoupling of the winds in the valley along with clear skies and strong radiational cooling should lead to another chilly night. Although most of the valley will see drying from the northerly winds, the guidance suggests some return flow from the Great Basin high will shift winds lightly to the southeasterly which will slightly raise dewpoints by Saturday morning. Although fog is unlikely, we can't rule out the possibility of some frost in outlying areas mainly E side of the northern SJV Saturday morning and perhaps in southeastern SAC [Sacramento CA] Co. ∨
.DISCUSSION... GUSTY/BREEZY NLY WINDS CONTINUED OVER NORCAL TODAY DUE TO INCREASING ANTICYCLONIC FLOW AND SUBSIDENCE IN THE WAKE OF SHORT WAVE ENERGY THAT MOVED THROUGH NORCAL EARLIER TODAY AND IN CONJUNCTION WITH SURFACE HIGH PRESSURE OVER THE GREAT BASIN. AS THE SURFACE HIGH SINKS SWD ACROSS THE GREAT BASIN TONITE, THE NLY GRADIENTS WILL SLACKEN WHILE THE ELY GRADIENTS CONTINUE. THIS SHOULD ALLOW WINDS TO DECOUPLE IN THE VLY WHILE KATABATIC/DOWNSLOPE WINDS CONTINUE OVER THE SIERRA. DECOUPLING OF THE WINDS IN THE VALLEY ALONG WITH CLEAR SKIES AND STRONG RADIATIONAL COOLING SHOULD LEAD TO ANOTHER CHILLY NITE. ALTHOUGH MOST OF THE VALLEY WILL SEE DRYING FROM THE NLY WINDS, THE GUIDANCE SUGGESTS SOME RETURN FLOW FROM THE GREAT BASIN HIGH WILL SHIFT WINDS LIGHTLY TO THE SELY WHICH WILL SLIGHTLY RAISE DEWPOINTS BY SAT MORNING. ALTHOUGH FOG IS UNLIKELY, WE CAN`T RULE OUT THE POSSIBILITY OF SOME FROST IN OUTLYING AREAS MAINLY E SIDE OF THE NRN SJV SAT MORNING AND PERHAPS IN SERN SAC CO. [DISC]
Increased ridging over Northern California on Saturday will lead to a strong temp and subsidence inversion over the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map] and the formation of thermal belts roughly in the 1500–5000 ft level. The greatest warming will likely be in the northern SAC [Sacramento CA] Valley and in the thermal belt areas where maxes could be some 6–12° above normal. ∨
INCREASED RIDGING OVER NORCAL ON SAT WILL LEAD TO A STRONG TEMP AND SUBSIDENCE INVERSION OVER THE CWA AND THE FORMATION OF THERMAL BELTS ROUGHLY IN THE 1500-5000 FT LEVEL. THE GREATEST WARMING WILL LIKELY BE IN THE NRN SAC VLY AND IN THE THERMAL BELT AREAS WHERE MAXES COULD BE SOME 6-12 DEGREES ABOVE NORMAL. [DISC]
The upper ridge weakens on Sunday as a weak trough moves across the Pacific Northwest ahead of a low pressure system dropping southeastward from the goa. This will bring a chance of light precipitation to the northern mountains. Model guidance has been trending farther N and a bit slower with precipitation holding off until Sunday afternoon/Sunday night over our northern mountains. This trough moves through early in the day with most of Monday dry in our CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. This will be a precursor to the goa low dropping into the Great Basin bringing colder (wetter?) weather to our area early next week. (JHM [Lahaina/West Maui HI]) ∨
THE UPPER RIDGE WEAKENS ON SUNDAY AS A WEAK TROF MOVES ACROSS THE PAC NW AHEAD OF A LOW PRESSURE SYSTEM DROPPING SEWD FROM THE GOA. THIS WILL BRING A CHANCE OF LIGHT PRECIP TO THE NRN MOUNTAINS. MODEL GUIDANCE HAS BEEN TRENDING FARTHER N AND A BIT SLOWER WITH PRECIP HOLDING OFF UNTIL SUN AFTERNOON/SUN NITE OVER OUR NRN MTNS. THIS TROF MOVES THROUGH EARLY IN THE DAY WITH MOST OF MON DRY IN OUR CWA. THIS WILL BE A PRECURSOR TO THE GOA LOW DROPPING INTO THE GREAT BASIN BRINGING COLDER (WETTER?) WX TO OUR AREA EARLY NEXT WEEK. JHM [DISC]
Extended discussion (Tuesday through Friday) ∨
.EXTENDED DISCUSSION (TUESDAY THROUGH FRIDAY) [DISC]
A few showers may linger during the day Tuesday across the northern mountains as weak wave passes across the region. Colder air entrenched within system may drop snow levels to around 2000 feet but wave looks fairly moisture starved. Maybe an inch or two of snow accumulation but not expecting major impacts at this point. Wednesday looks dry as ridging briefly builds in across the region. Wednesday morning lows will hover near the freezing mark across most of the valley with teens to 20s across higher elevations. 12Z [4am PST] runs of the 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 ECMWF [European Center for Medium-Range Weather Forecasts model] have come into better agreement regarding the end of the week, but substantial timing differences still remain. Regardless, better confidence that wet system will move across the area sometime later Thursday into Friday. Associated moisture plume may allow for decent precipitation accumulations, especially across the mountains. Something to watch going forward as weekend travel may be impacted. (Ceo) ∨
A FEW SHOWERS MAY LINGER DURING THE DAY TUESDAY ACROSS THE NORTHERN MOUNTAINS AS WEAK WAVE PASSES ACROSS THE REGION. COLDER AIR ENTRENCHED WITHIN SYSTEM MAY DROP SNOW LEVELS TO AROUND 2000 FEET BUT WAVE LOOKS FAIRLY MOISTURE STARVED. MAYBE AN INCH OR TWO OF SNOW ACCUMULATION BUT NOT EXPECTING MAJOR IMPACTS AT THIS POINT. WEDNESDAY LOOKS DRY AS RIDGING BRIEFLY BUILDS IN ACROSS THE REGION. WEDNESDAY MORNING LOWS WILL HOVER NEAR THE FREEZING MARK ACROSS MOST OF THE VALLEY WITH TEENS TO 20S ACROSS HIGHER ELEVATIONS. 12Z RUNS OF THE GFS AND ECMWF HAVE COME INTO BETTER AGREEMENT REGARDING THE END OF THE WEEK, BUT SUBSTANTIAL TIMING DIFFERENCES STILL REMAIN. REGARDLESS, BETTER CONFIDENCE THAT WET SYSTEM WILL MOVE ACROSS THE AREA SOMETIME LATER THURSDAY INTO FRIDAY. ASSOCIATED MOISTURE PLUME MAY ALLOW FOR DECENT PRECIPITATION ACCUMULATIONS, ESPECIALLY ACROSS THE MOUNTAINS. SOMETHING TO WATCH GOING FORWARD AS WEEKEND TRAVEL MAY BE IMPACTED. CEO [DISC]
VFR [Visual Flight Rules] conditions for TAF [Terminal Aerodrome Forecast] sites next 24 hours. Gusty northerly winds for valley terminals will gradually subside this evening to less than 10 kts [12 mph] through remainder of period. ∨
VFR CONDITIONS FOR TAF SITES NEXT 24 HOURS. GUSTY NORTHERLY WINDS FOR VALLEY TERMINALS WILL GRADUALLY SUBSIDE THIS EVENING TO LESS THAN 10 KTS THROUGH REMAINDER OF PERIOD. [AVI2]
STO [Sacramento/WFO CA] Watches/Warnings/Advisories
.STO WATCHES/WARNINGS/ADVISORIES... NONE. [WARN]
03 Dec 1:02am PST
Overnight Mostly clear, with a low around 30°. Calm wind.
Saturday Sunny, with a high near 55°. East wind around 6 mph becoming calm in the morning.
Saturday Night Mostly clear, with a low around 36°. ENE wind around 7 mph.
Sunday Mostly sunny, with a high near 56°. East wind around 6 mph becoming calm in the morning.
Sunday Night Partly cloudy, with a low around 36°. Calm wind becoming east around 5 mph in the evening.
Monday Partly sunny, with a high near 48°.
Monday Night Mostly cloudy, with a low around 26°.
Tuesday Sunny, with a high near 42°.
Tuesday Night Mostly clear, with a low around 26°.
Wednesday Sunny, with a high near 46°.
Wednesday Night Partly cloudy, with a low around 28°.
Thursday Partly sunny, with a high near 51°.
Thursday Night A slight chance of rain. Mostly cloudy, with a low around 37°.
Friday A chance of rain. Mostly cloudy, with a high near 45°.
Mostly clear, with a low around 30. Calm wind.
Sunny, with a high near 55. East wind around 6 mph becoming calm in the morning.
Mostly clear, with a low around 36. East northeast wind around 7 mph.
Mostly sunny, with a high near 56. East wind around 6 mph becoming calm in the morning.
Partly cloudy, with a low around 36. Calm wind becoming east around 5 mph in the evening.
Partly sunny, with a high near 48.
Mostly cloudy, with a low around 26.
Sunny, with a high near 42.
Mostly clear, with a low around 26.
Sunny, with a high near 46.
Partly cloudy, with a low around 28.
Partly sunny, with a high near 51.
A slight chance of rain. Mostly cloudy, with a low around 37.
A chance of rain. Mostly cloudy, with a high near 45.