Scientific Forecaster Discussion
fxus66 ksto 171248
Area forecast discussion
National Weather Service Sacramento California
448 am PST Sat Nov 17 2018
dry with near to above normal daytime temperatures and cool
nights through early next week with smoke in the valley due to
the Camp wildfire. Breezy northeasterly winds over the Sierra
Nevada tonight into Sunday bringing critical fire conditions.
Cooler temperatures next week with a series of wet systems the
middle to end of next week.
conditions this morning fairly similar to 24 hours ago with
similar temperatures, light winds and smoke in the Central Valley.
High amplitude high pressure ridge now over the eastern Pacific
will keep conditions dry through the weekend and early next week.
A weak trough dropping southward into the Great Basin will bring
a slight cooling to the airmass today. Temperatures may cool
slightly some areas but bigger influence on temperatures will be
the wildfire smoke still over much of the region. Conditions
remain stable under the high pressure ridge with continued light
northerly winds expected over most of the cwa. Therefore,
wildfire smoke will continue to be an issue reducing visibilities
and keeping daytime highs down in areas of heavier smoke.
Radiational cooling has allowed temperatures in the Sacramento and
San Joaquin valleys and the Delta to drop back down into the lower
30s. Surface high pressure dropping into the Great Basin behind
the weak trough will create a fairly tight surface gradient across
the Sierra tonight and Sunday. This will bring breezy northeast
winds tonight and Sunday. Winds will be the strongest through the
Sierra canyons and over ridges and unfortunately over the Camp
fire in Butte County. Therefore the red flag warning will remain
in place. The surface gradient is expected to decrease by Sunday
afternoon but then tighten back up again Sunday night although not
quite as strong as it is forecast for tonight. Winds outside of
the Sierra will be elevated a bit on Sunday. Increased mixing from
the winds may mix out the smoke in the valley a bit so daytime
highs Saturday in the Sacramento Valley may nudge up a bit.
Upper ridge axis shifts east of the forecast area on Monday
bringing just a slight cooling. Lighter surface gradients should
bring lighter winds all areas. An upper low off the socal coast
will spread high clouds over the forecast area during the day.
Models still on track in bringing a significant Pacific frontal
system towards the coast on Tuesday. Most areas will see cooler
temperatures with increasing clouds and a shift to more onshore
winds. By Tuesday night, the forecast area could begin to see the
beginning of a prolonged period of much needed precipitation.
Extended discussion (wednesday through saturday)
Confidence is increasing that the first widespread precipitation
event of the season will affect the region later next week. Models
continue to indicate that the persistent ridge will be displaced
eastward allowing a series of disturbances to move through norcal
Wednesday thru Friday as the upper trough moves onto the West
Coast. More zonal pattern possible by next weekend potentially
allowing additional systems to bring precipitation to mainly the
northern portion of the forecast area. Details on quantitative precipitation forecast and mountain
snow amounts are uncertain at this time, but the systems should be
strong enough to remove the stagnant smoky airmass from the region.
Widespread MVFR with local IFR likely to continue in the Central
Valley the next 24 hours as smoke from the Camp fire persists. VFR
conditions elsewhere. Generally light winds at taf sites.
red flag warning from 10 PM this evening to 4 PM PST Sunday for
northern motherlode from 1000 to 3000 ft. Includes portions of
Nevada-Yuba-Placer-Amador and Eldorado units-northern Sierra
foothills from 1000 to 3000 ft. Includes portions of Shasta-
Trinity and Butte units-northern Sierra including Lassen np and
Plumas and Lassen nf/S west of the Sierra crest (west of Evans
Peak-Grizzly Peak-beckworth peak)-northern Sierra including the
Tahoe and Eldorado nf/S west of the Sierra crest.