Monday, November 28, 2011

The Big Snows Will Come....

With the ridge off the West Coast blocking storms the next couple of weeks the good news is that there will be some shots of cold and light snow. The first being Wednesday night into Thursday and another one to start the following week.

This will be more cold than snow right now but there are signs that the pattern will flip in December. This Winter is still on track to bring big snows. Once the Snow starts it should come in earnest and last a while.

Looking at the temperatures in the Pacific they are not helping with the current pattern of the ridge in the Northeast Pacific. Earlier this Fall we saw warmer than average temperatures along and just off of the CA coast. The ocean temps between here and Hawaii are now colder than this time last year.

With the current pattern it means the water is too cold to support a Southern branch of the jetstream to come underneath of the ridge. But as we go into the Winter the sinking air over the cold water along the subtropical waters will favor troughing off the West Coast. That combined with warmer than average water temps in the Western Pacific strengthening the jetstream should mean the perfect ingredients for lots of snow in the Winter months.

First, we need to get the ridge to retrograde back away from the West Coast. Right now the positive PNA pattern is supporting the ridge off the coast blocking the storms. We need the PNA to go back negative which supports trough along the West Coast. During La Nina conditions the negative phase of the PNA is supported so we should see it more than not going into the Winter. The current forecasts show it possibly going negative around mid-December.

The other thing that can pull the ridge back and bring a period of enhance precip to the West Coast is the MJO when it enters the Western Pacific. The MJO is actually getting pretty strong in the Indian Ocean as it progresses towards the Maritime Continent. As it moves into the Western Pacfic over the next couple of weeks it should begin to help pull back the ridge.

So although we have quiet weather for the next couple of weeks things are definitely lining up for Winter to possibly begin for real later in the month.

Stay tuned...BA

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