This is a message from the Dean, College of Natural Science and Mathematics
at Cal State Fullerton.


Subject: Rainfall coming

In some parts of Southern California, a whole season's worth of rain could
fall over the course of 5-10 days.

This is what the emergency response community is saying (by way of our
county emergency response group):
Currently, the strong El Nino is reaching its peak in the Eastern Pacific,
and now finally appears to be exerting an influence on our weather. The
strong jet has been apparent for quite some time out over the open water,
but the persistent block had prevented it from reaching the coast. Now that
the block has dissolved completely, a 200+ kt jet is barreling towards us.
Multiple large and powerful storm systems are expected to slam into CA from
the west and northwest over the coming two weeks, all riding this extremely
powerful jet stream directly into the state. The jet will itself provide
tremendous dynamic lift, in addition to directing numerous disturbances
right at the state and supplying them with an ample oceanic moisture source.

The jet will be at quite a low latitude over much of the Pacific, so these
storms will be quite cold, at least initially. Very heavy rainfall and
strong to potentially very strong winds will impact the lower elevations
beginning late Sunday and continuing through at least the following Sunday.
This will be the case for the entire state, from (and south of) the Mexican
border all the way up to Oregon. Above 3000-4000 feet, precipitation will be

all snow, and since temperatures will be unusually cold for a precipitation
event of this magnitude, a truly prodigious amount of snowfall is likely to
occur in the mountains, possibly measured in the tens of feet in the Sierra
after it's all said and done. But there's a big and rather threatening
caveat to that (discussed below).Individual storm events are going to be
hard to time for at least few more days, since this jet is just about as
powerful as they come (on this planet, anyway). Between this Sunday and the
following Sunday, I expect categorical statewide rainfall totals in excess
of 3-4 inches. That is likely to be a huge underestimate for most areas.
Much of NorCal is likely to see 5-10 inches in the lowlands, with 10-20
inches in orographically-favored areas. Most of SoCal will see 3-6 inches at

lower elevations, with perhaps triple that amount in favored areas.

This is where things get even more interesting, though. The models are
virtually unanimous in "reloading" the powerful jet stream and forming an
additional persistent kink 2000-3000 miles to our southwest after next
Sunday. This is a truly ominous pattern, because it implies the potential
for a strong Pineapple-type connection to develop. Indeed, the 12z GFS now
shows copious warm rains falling between days 12 and 16 across the entire
state. Normally, such as scenario out beyond day seven would be dubious at
best. Since the models are in such truly remarkable agreement, however, and
because of the extremely high potential impact of such an event, it's worth
mentioning now. Since there will be a massive volume of freshly-fallen snow
(even at relatively low elevations between 3000-5000 feet), even a
moderately warm storm event would cause very serious flooding. This
situation will have to monitored closely. Even if the tropical connection
does not develop, expected rains in the coming 7-10 days will likely be
sufficient to cause flooding in and of themselves (even in spite of dry
antecedent conditions).

In addition to very heavy precipitation, powerful winds may result from very

steep pressure gradients associated with the large and deep low pressure
centers expect ed to begin approaching the coast by early next week. Though
it's not clear at the moment just how powerful these winds may be, there is
certainly the potential for a widespread damaging wind event at some point,
and the high Sierra peaks are likely to see gusts in the 100-200 mph range
(since the 200kt jet at 200-300 mb will essentially run directly into the
mountains at some point). The details of this will have to be hashed out as
the event(s) draw closer.

In short, the next 2-3 weeks (at least) are likely to be more active across
California than any other 2-3 week period in recent memory. The potential
exists for a dangerous flood scenario to arise at some point during this
interval, especially with the possibility of a heavy rain-on-snow event
during late week 2. In some parts of Southern California, a whole season's
worth of rain could fall over the course of 5-10 days. This is likely to be
a rather memorable event. Stay tuned.

Steve Murray
Dean, College of Natural Sciences and Mathematics
California State University, Fullerton
Phone: 657-278-2638; FAX: 657-278-5390