Thursday, January 30, 2014

Alaska Winter Advisory / Warning Critera

As a follow-up to yesterday's post, here are maps depicting the winter warning and advisory criteria for all the Alaska forecast zones. The red dashed lines represent the boundaries between the Fairbanks, Anchorage, and Juneau offices. The differences is advisory numbers as shown in yesterday's post is largely attributable to the different criteria.

Winter Weather Advisory:

This is the snowfall criteria map for a Winter Weather Advisory. 

In addition, all zones have a blowing snow criteria as follows:

When one of the following combinations are forecast to occur for at least 3 hours: 

1. Sustained wind or frequent gusts 25 mph or greater and visibility less than or equal 1/2 mile (but greater than 1/4 mile)
2. Visibility is 1/4 mile or less, and winds are at least 25 mph but less than 35 mph 

There is also a multiple event criteria for all zones as follows:

Mixed precipitation or multiple winter weather events even if only one precipitation type meets or exceeds advisory criteria, but remains below warning criteria (this may include wind and/or wind chill).

Winter Storm Warning:

Just like the Winter Weather Advisory, there is a rule that applies across all zones. Namely:

Mixed precipitation or multiple winter events, even if only one precipitation type meets or exceeds warning criteria (this may include wind and wind chill) .

Freezing Rain Advisory:

This one is self-explanatory. Any ice amount greater than the amount defined for the Freezing Rain Advisory qualifies as an Ice Storm Warning.

Wind Chill Advisory / Warning:

These should be pretty self-explanatory. Remember that it is not just the wind chill alone but there has to be a sustained wind as well.

Blizzard Warning:

There is no map for the Blizzard Warning. It is standardized across not just Alaska but the entire U.S. The criteria is as follows:

When forecast to occur for at least 3 hours: Blowing snow (with or without falling snow) reducing visibility to < 1/4 mile when accompanied by sustained wind or frequent gusts > 35 mph. 

The text of all the criteria can be found at the following site:

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