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HMT forecast made 1930Z Sun 30 Dec 07

Still looks like the new year will start with great IOP potential! Conditions remain on track for a major event (could well be the best of this La Nina year) coming up Th 3 thru Sun 6 Jan 08! Models continue to be consistent in calling for this event coming in 4 parts, the first one to affect mainly the Northwest and coast ranges of northern CA on W, and the remaining 3 to affect all of CA. Total pcpn amounts for the Th thru Sunday period are virtually guaranteed to exceed 5" melted at Blue Canyon in my opinion, and could well approach twice that. This is due to a combination of adequate moisture, good "balanced dynamics" (e.g., quasi-geostrophic forcing of upward motion) and very strong orographic forcing due to the overall strength of the onshore flow. There could well be periods of good warm advection, not only in the earlier stages of the Th 3 Jan event, but also in the 2 to follow. Consensus of ensembles is that there will be no American River Basin pcpn before sundown Wednesday 2 Jan; the first batch of heavier pcpn will occur mainly during the day Th (although could well commence before daybreak Th 3 Jan), followed closely by another on Friday, and then perhaps a slight break before the last batch late Saturday and ending daytime Sunday. As indicated yesterday, snow levels are likely to vary between 4,000 and 5,500ft, with Blue Canyon getting mostly snow Th 3 Jan and F 4 Jan, with snow levels coming down on Saturday to between 3,000 and 4,000ft, so Blue Canyon will get all snow in the last event.

Be advised that strong winds (combination strong synoptic pressure gradient and barrier jet) will also accompany this event, particularly Th and F 3 and 4 Jan, with gusts of up to 50kt possible KSCK and KSAC, so tippable equipment should be well secured.

Beware of dense fog potential for New Years Eve.

Beyond Sunday, the liklihood of further multi-inch (melted) events at Blue Canyon goes down substantially.
Ensembles begin to diverge markedly on Sunday, some (as the operational GFS initialized 12Z this morning) showing a trough digging into AZ and others keeping conditions more zonal. So, although the potential for events after Sunday 6 Jan isn't zero, it certainly reduces to be closer to climatology.

John B.