Area Forecast Discussion
Issued by NWS Sacramento, CA
FXUS66 KSTO 132344
Area Forecast Discussion
National Weather Service Sacramento CA
344 PM PST Fri Jan 13 2017
Dry conditions through Monday except a slight chance of light
showers over the coastal mountains on Sunday. Next chance of
precipitation begins late next Tuesday and continues through the
end of the week. Heavy precipitation is possible during the middle
of next week with renewed flooding concerns.
Ten to 30 mile wide strip of stratus from Latrobe Swd into SErn
Stanislaus Co eroding and will likely be clear in time for
sunset. Drier Nly flow has eroded the cloud cover and developed
north of the upper level low along the Socal coast. The low will
continue to drift Swd to W of Baja tonite, and then across Baja
and the Desert SW Sat through Sun. The stratus/fog should make a
return Sat morning as upper ridging increases over the region. The
higher resolution HRRRX Sfc Vis prog has a smaller area of
coverage of lower VSBYS Sat morning than this morning given the
drier Nly flow today and continuing overnight. Generally, the Nly
flow will continue through the weekend likely keeping areal
coverage of fog to a minimum and towards the E side of the Valley
and Mother Lode.
Models have been trending a little more consistent in forecasting
a weak low to drop Swd along the CA coast late Sat nite and Sunday.
This is not expected to be a progressive wave and given the
"westerly track" the chances of any light precip look to be confined
to our Coastal range. The ECMWF does bring the precip farther
inland, while yesterday it kept our area dry. Given the amount of
uncertainty, we have kept the PoPs low over the coastal range Sat
nite and Sun morning.
Cloud cover associated with this weak system might hinder fog
formation a bit Sun morning, but can`t rule it out entirely.
After this weak system drops Swd, a positively-tilted ridge will
build into Norcal and higher cloud cover should spill over the
ridge and into Norcal on Mon. These positively-tilted ridges are
not "storm blockers" for Norcal and are susceptible to isentropic
processes/ WAA precip from incoming trofs, especially those
tapping anomalous TPW plumes, as will be the case in the EFP.
Strong radiational cooling under a strengthening inversion this
weekend will result in cold/chilly mornings, especially over the
cold Sierra mtn basins due to cold NEly flow from the Great Basin.
Otherwise, a warming air mass will result in slightly above
normal highs in areas benefiting from the warming katabatic winds,
and near normal highs elsewhere. Some foothill locations will be
warmer than some locations in the Srn portion of the Valley. JHM
.EXTENDED DISCUSSION (Tuesday THROUGH Friday)
Models still showing that another atmospheric river could be
aimed for the West Coast next week. Both the GFS and ECMWF
indicate that the moisture plume should start impacting NorCal
sometime Tuesday. Heavier and more widespread precipitation is
forecast to begin by Wednesday morning and continue through
Thursday. Looks like weather will become more showery on Friday,
but another wave of widespread precipitation would arrive Friday
night into Saturday. Snow levels would initially be high, above
7000 ft, then lower on Thursday and Friday ranging 3000-4000 ft.
Given the already high river/creek stream levels, flooding will
continue to be a concern.
Mainly VFR conditions the next 24 hours. Areas of dense fog may
develop from the Sutter Buttes southward early Saturday morning.
North winds up to 15 kt will decrease below 10 kt tonight.
Flash Flood Watch through Saturday afternoon for the Glanville
Tract in the Sacramento Delta.