Uh Oh
.This information is from the U S Geological Survey
====================================================================
Get ready. This is what the emergency response community is saying:
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.
*******************************************************************
Charles N. Alpers, Ph.D.
U.S. Geological Survey, California Water Science Center
Placer Hall
6000 J Street
Sacramento, CA 95819-6129
tel. 916-278-3134
fax. 916-278-3013
e-mail
cnalpers@usgs.gov<;mailto:cnalpers@usgs.gov>
<http://profile.usgs.gov/cnalpers>
, thanks don for posting
