storm warnings

[Oolie]

someone passed this along to me, i don't know if the source is credible, but they sound at least somewhat educated.



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 be 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 expected 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...