Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sacramento California
850 am PST Fri Jan 30 2015
mainly dry weather expected into the weekend with local night and
morning valley fog and above normal temperatures. Some breezy north
wind today into Saturday. A slight chance of showers northern areas
Monday and Tuesday...otherwise mostly dry weather likely to continue
through mid week. A chance of precipitation over much of northern
California is possible towards the end of next week.
Short term discussion (today through monday)...
areas of fog developed again this morning in the northern San
Joaquin Valley with patchy fog in the southern Sacramento Valley.
The fog is not as dense as yesterday morning and is expected to
dissipate later this morning. Upper low off the socal coast attm
with short wave, currently over the Bay area, dropping south towards
the low will help deepen it over the next 24 hours. Lingering
cloudiness near the Sierra Nevada crest today but any light shower
activity expected to remain outside of the forecast area. Meanwhile
upper ridging beginning to nose into the pacnw while surface ridging
extends into the Great Basin. Kmfr-krdd surface pressure gradient is
trending up which will result in some breezy north to east wind
today. Wind speeds already in the teens in the northern Sacramento
Valley with speeds expected to trend up farther southward in the
Central Valley by the afternoon. High temperatures today expected
to be similar to Thursday.
Upper ridging continues to build over norcal tonight into Saturday
as upper low to the south digs. Low level pressure gradient
strengthens further tonight into early Saturday as it becomes more
east-west oriented over norcal. This will favor stronger winds over the
eastern foothills/mountains and along the west side of the
Sacramento Valley into the Delta. Any fog that develops Saturday
morning will be limited to the San Joaquin Valley. Air mass undergoes
synoptic warming Saturday with increasing heights/thicknesses. Highs
tomorrow approach near records in the northern Sacramento Valley
with readings in the mid 70s, with upper 60s to lower 70s throughout
the remainder of the Central Valley.
Upper ridging flattens some Sunday as impulses ride over the top of
it into the pacnw. Greater area of morning valley fog possible in
the San Joaquin and possibly into the southern Sacramento Valley and
Delta Sunday under lighter surface wind and increased subsidence.
Some associated overrunning cloudiness Sunday will result in slight
cooling over interior norcal. Models depict potential for some light
overrunning precip over mainly Shasta County Sunday night into
Extended discussion (tuesday through friday)
The ridge is flattened enough Tuesday to potentially allow the
southern periphery of a trough to bring a slight chance of light
rain to Shasta County. But that's as far south as the rain
extends. The dominant ridge builds back up over the West Coast
Wednesday, keeping the area dry.
However, a broad, deep upper trough is taking shape over the
eastern Pacific. The models show promising signs of the upper ridge
shifting into inter-mountain west, allowing the trough to creep
closer to the coast with increased chances of much needed
precipitation late Thursday through Friday. This system is
looking like an atmospheric river (ar) event, but the main swath of
moisture still looks to remain just north of our forecast area on
Friday, across northwest California and western Oregon. We need
the ridge to continue to shift east to allow the Arkansas to settle over
Genly VFR ovr intr norcal nxt 24 hrs exc LCL IFR/LIFR in fog til
arnd 19z this mrng in ptns of srn SAC/nrn San Joaquin vlys. Nly sfc
wnd gsts to 25 kts poss in cntrl Vly this aftn.