The ARB should be dry today. For the short term forecast we have a secondary
push of cold air riding down the east side of the ridge that could give some
light snow showers over the Sierra on Sunday afternoon and evening. WRF-NMM
cross-sections show predominatly NE winds so the ARB will be on the downslope
side of things, similar to the past system.
In the medium term The GFS dprog/dt shows the 12z run has changed in the
position of the system for Thursday 18 Jan actually bringing a more respectable
trough onshore over CA. This is the system currently located near the eastern
end of the PACJET at about 170W longitude. The ECMWF concurs, so it now looks
like yesterday's GFS ensemble outliers may have a greater likelihood of
verifying. The deterministic GFS has a closed low sliding SEWD over SFO about
15Z Jan 17. The wave then opens up a bit into a positively tilted trough.
Heaviest precip should be near the coast with light/moderate amounts over
the ARB. We'll want to watch this in case it could reach minimum IOP criteria.
The possibility of some downslope wind component could be an inhibiting factor.
The GFS ensemble spread shows this event could happen anytime Wednesday or
A weak to moderate PW plume is associated with the mid-week system in the
GFS although it is connected to the tropics via a rather narrow feed.
Longer term around 23 Jan there is some model divergence with the ECMWF having
a ridge just off the west coast and the GFS developing a cutoff low WSW of
San Diego with the ridge farther west. Subtropical jet action now looks a bit
less pronounced and farther east over northern and central Mexico at this time.