(ABOVE) Hawaii Island Weather Alert map plots the area under a National Weather Service Blizzard Watch

There is still some uncertainty as to whether or not the deep moisture will extend over the Big Island or remain just to the east. Even if the heavy snow does not materialize, very strong winds are expected. National Weather Service on Dec. 22

Here is the discussion posted to the Mauna Kea Weather Center webpage:

The airmasses above the islands is destabilizing rather quickly. The inversion over the Big Island is expected to vanish throughout today. This is allowing the mid and low level moisture to reach the summit already. Expect fog tonight. Precipitation is likely in the form of ice, snow and flurries tonight, and it possible Tuesday night as well. The atmosphere will remain unstable throughout at least the next three days while it will start slowly stabilizing on Christams day.

Mid-high clouds will start approaching the summit today. As the atmosphere destabilizes and the inversion lifts and vanishes, low-mid clouds will continue to raise up to the summit level throughout this evening/night. The summit skies will be therefore occluded tonight and through the following two nights. They might start open up a bit on Thursday and through Friday.

Precipitable water will exceed the 4 mm threshold tonight and Tuesday night. It is likely to linger close to 4 mm on Wednesday night, and decrease and be close to 2 mm on Thursday. The models project a further decrease, between 1 and 1.5 mm, on Friday nigth.

Observing conditions will be unoperable/very poor at least throughout Wednesday night. An improvement is possible for the following two days.