Tuesday, December 18, 2012

Winter Storm Post

Someone from the NWS posted the following comment on my earlier post: 

"Actually, we *can* depict watches/warnings/advisories ("Hazards") with more precision. All of these text products are created in the Graphical Forecast Editor from 2.5km-resolution grids.

Unfortunately, the map display only paints by zone or county. It also has trouble when there are overlapping hazards (which gets precedence?) However, the map can handle polygon based warnings.

Why not just display the gridded hazards? Why indeed. I and others have wondered about that for years."

All of the above sounds like steps could be taken to produce more precise graphics that would show the casual user exactly where the products are valid. But, it also seems that there are a variety of problems that continue to result in some broad brush graphics. Given the high resolution grids, defining Forecast Zones may well be an antiquated concept.

"It's one of the biggest reasons many offices switched to topography-based zones over the past few years, but even then you can only slice and dice so much. Keep in mind Tucson used to get painted over for Winter Hazards affecting just Mount Lemmon. (Zone 514 is presumably not in the Watch because the snowfall will be less than criteria for that zone since it is higher elevation. Zone 504 has "lower standards" being mostly lowlands). How much of zone 504 is even above 4000'? Any populated areas?"

The comments above bring up a couple of key questions - since criteria for many NWS watches and warnings, e.g., strong winds, snow accumulations, etc., vary regionally and even locally, how does one learn precisely what are the criteria the NWS uses. I know that these criteria vary locally across the Tucson CWA, but I'll be damned if I know where to locate a precise statement quantifying these criteria for different locations in southeast Arizona. I have looked and looked and can not find a link to such information. Does one exist?

How much of Zone 504 is above 4000 ft ? - a small part, since the dividing line between the mountain and lower zones is 5000 ft MSL. People do live above 4000 ft in Zone 504, for example the town of Oracle is at about 4500 ft. Also of interest is that a number of highways and roads cross above 4,000 ft. 

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