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2006-03-02 WX Discussion and Forecast - Ed Szoke

The first wave of rain and snow currently pounding the area with
freezing level around 3500 to 4000 feet or so and heavy snows at Blue
Canyon where about an inch of precipitation has fallen thusfar. The
precipitation will become more spotty especially at lower elevations
today and much of tonight before increasing again friday morning
ahead of the trough axis. the forecast soundings for this afternoon are
pretty unstable so would expect some good convection and possible
thunderstorms as well. Latest 12z models are in good agreement that the
trough axis at 500 mb pushing across the HMT area between 18z/Friday and
00z/Sat. the 700 mb trough axis will precede this by 6-9 hours with
winds shifting to southwest by about 18z/friday then more westerly by
00z/Sat. the precipitation by friday night then should become much
more spotty and pretty much be over by saturday morning except for some
lingering mountain snow showers. As the trough axis approaches the
precipitation will increase in coverage and intensity then diminish to
showery after passage but persist at higher elevations well into friday
night at least in showery form. The heaviest precipitation is expected
from about 10z through 21z on Friday. By 00z/Sat the eta generates an
additional 1.5 inches of melted over the higher terrain for storm total
and the gfs about this or a little more. The 12z 3 km LAPS HMT run
generates about 3" max amounts for the 24-h ending 12z Friday, but at
that time still has the heavy second round of precipitation approaching
the HMT area, which may be a bit slow. Not as wet as the last system but
should be good for 2 to 3 feet or more of snow in the mountains. The
snow levels should drop quite low as the trough axis approaches and
passes as thicknesses go down to 528 dm, so would think down to at least
2000 feet or so, maybe lower in some areas.

The active pattern will continue as the mean trough position remains
just off the West Coast. Another strong wave deepens off the West
Coast by Saturday/4 March and will set up what looks like a fairly long
duration event beginning by Sunday/5 March. There is quite a mass of
tropical moisture lurking in the Pacific extending from southwest to
northwest of Hawaii in association with a broad and rather deep
trough near 175 W. Currently this connects northward all the way north
to the Aleutians...at least in the IR imagery...ahead of the next wave
that will be diving southeast and deeping off California. These two
systems don't end up phasing as the sourthern one is left behind...but
it seems apparent that some of this tropical moisture will get caught
up in this next wave and so would expect this next system to be wetter
than the current one. Best guess right now is that this next event
would begin as early as later Sunday afternoon (5 March), with higher
terrain precipitation perhaps as early as 18z but certainly by 00z/6 Mar,
and not end until later tuesday or tuesday night. During this period the
00z GFS generates between 4-5 inches of melted precipitation over
portions of the area and the 12z GFS is just a little less. Initially
snow levels should be rather high on Sunday night but lower to around
4000-5000 feet or so on monday and then possibly quite low by tuesday
when the trough moves inland...although it should be noted the 00z ECMWF
is slower with the end of the event although the latest 12z run has
similar timing to the GFS.

Looking farther ahead yet another wave could be heading down the coast
towards the end of the week for a potentially colder system though the
ECMWF is farther north than the 00z GFS with this one so obviously
uncertainty exists that far out. Nonetheless, the GFS ensembles
generally support a potential late week system, beginning as early as
late Wednesday, and beyond this a pattern that would remain very active.