Friday, December 26, 2014

Understanding Winter Weather Warnings


Meteorologist Jim Woodmencey
This past year, I became what is known as a “Weather Ready Nation (WRN) Ambassador” The WRN program started in 2011 and it partners private meteorologists, like myself, with NOAA and National Weather Service forecasters, to help spread the word and educate people about how to be prepared for hazardous weather conditions.

In this day and age of the Internet, Facebooking, Tweeting, NIXLE alerts, etc. there is virtually no reason we should not all be getting the message when extreme or hazardous weather is on the way.

For instance, on my website mountainweather.com on the Jackson Hole Forecast page, whenever the NWS in Riverton issues any kind of weather alert, advisory, watch or warning for Teton County Wyoming, a red box appears above the forecast.

This box works great for the big stuff, but it becomes a bit annoying when there is an “Alert!” issued for things like: colder temperatures, valley fog, or slick driving conditions. These are things that would be extreme weather events in L.A., but this is Wyoming, and I think we can handle that sort of stuff on a daily basis.

What is more important than an “Alert”, is an “Advisory” or most importantly, a “Watch” or “Warning”, of more severe weather. Weather that might cause a true Wyomingite to take heed.

Here are some links to the "Ready Weather Nation" websites:

Advisories

The National Weather Service will issue Winter Weather “Advisories” to alert the public to weather situations that may present a hazard. “Advisories” are for weather that may cause significant inconvenience or difficulty to travelers.  Although, these weather situations should not be life threatening.

The most common Advisories issued during the winter are:
1) Winter Weather Advisory:  Issued for snow events or when a combination of precipitation is expected, such as: snow, sleet, freezing rain, or blowing snow.

2) Snow Advisory: Issued when snowfall is expected to be between 3 and 6 inches in 24 hours in valley locations. For mountain locations the criteria is for 6 to 12 inches of accumulation within 24 hours.

3) Blowing Snow Advisory:  Issued when wind-driven snow intermittently reduces visibility to ¼ mile or less.


Watches and Warnings

“Watches” and “Warnings” are more serious business than advisories.

Winter Storm Watch means: Be Prepared! The NWS issues these when conditions are favorable for dangerous winter weather to occur. It does not mean it will occur, but you should start making preparations in case it does.

Watches are intended to provide enough lead-time so that people can adjust their schedules. They may be issued up to 48 hours in advance of the event and often will precede a “Warning”. 

Winter Storm Warning means: Take Action!  A warning is issued when a winter storm is imminent or occurring. If you hear a warning, immediately go home or seek shelter until it is safe to travel again. Blizzards, extreme cold and windchill can quickly become deadly outside.

Winter Storm Warnings are usually issued when heavy snow and/or strong wind are possible. Heavy snow means that snowfall is expected to exceed 6 inches per event in the valley. For mountain locations it is 12 inches or more per event.

Blizzard Warnings imply strong winds of 35 mph or greater, cold temperatures, and considerable falling and/or blowing snow that frequently drops visibility to ¼ mile or less. These conditions are expected to last for 3 hours or longer.

While a "Winter Storm Warning" may not necessarily translate into a “big dump” for skiers, it should at least prepare you to be cognizant of bad visibility, and some “western” driving conditions.

Unfortunately, there are times when I feel like we are being “over-warned”, and we run the risk of suffering from the “cry wolf syndrome”. That is, we stop paying attention to the warnings, because they come too often, in the form of alerts or advisories, that may seem like just everyday winter weather here in Jackson Hole. Hopefully this article helps to sort out the most important stuff, and explains some of the lesser weather events we may get alerted to during the winter.

 (This article was re-printed in part from the Mountain Weather Column in the Jackson Hole News & Guide)

Jim is the chief meteorologist at mountainweather.com and has been forecasting the weather in Jackson Hole and the Teton Mountains for over 20 years.

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