Wednesday, January 29, 2014

Winter Storm Warning...and other Weather Alerts

Meteorologist Jim Woodmencey


Good timing on the weather!
In last week's Jackson Hole News & Guide I primed you with an article about NWS
Winter Weather Advisories, Watches, and Warnings….what they mean to you.......and here we go, with a "Winter Storm Warning" for Jackson Hole issued Wednesday mroning, which was upgraded from a "Watch" that was issued on Tuesday morning.




Mountain Weather Column
Jackson Hole News & Guide
January 22, 2014 Issue
During the course of the winter season we will see a number of different weather alerts issued by the National Weather Service Office in Riverton, which is responsible for issuing weather warnings for all of western Wyoming.

In this week’s column I will delineate for you the different types of Advisories, Watches, and Warnings you may come across during the winter season, what the criteria is for issuing them, and what they really mean to you.

Advisories
 
The National Weather Service will issue Winter Weather “Advisories” to alert the public to weather situations that may present a hazard, but do not meet the “Warning” category criteria. “Advisories” are for weather that may cause significant inconvenience or difficulty to travelers. 

The earliest type of advisory you may see is a “Hazardous Weather Outlook”, which may be issued several days ahead of time if a large storm system is expected, which might affect travel. Other wintertime advisories and their criteria are listed below.

Winter Weather Advisory:  Most commonly issued for snow events or when a combination of precipitation is expected; such as: snow, sleet, freezing rain, or blowing snow, is in the forecast.

A Snow Advisory would be a more specific type of Winter Weather Advisory that would be issued when snowfall is expected to be between 3 and 6 inches in 24 hours in valley locations. Mountain locations have snow advisories issued when between 6 and12 inches of accumulation is expected in 24 hours.

Blowing Snow Advisory:  Issued when wind-driven snow intermittently reduces visibility to ¼ mile or less. Travel may be hampered.  Strong winds can create blowing snow by picking up old or new snow.

Other winter advisories you might see are: Wind-Chill Advisory (-20F) or a Dense Fog Advisory (¼ mile visibility).


Watches and Warnings

“Watches” and “Warnings” are more serious than “Advisories”.

A “Watch” is issued when conditions are favorable for the development of a particular weather event that meets certain threshold criteria.  A “Warning” is issued when a particular severe weather condition is imminent or actually occurring. “Watches” & “Warnings” are usually reserved for weather situations that will make travel impossible, or could pose a threat to life and property.

Note: Be aware that the criteria used for Advisories and Warnings is different for different locations across the country.

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

When a Watch is upgraded to a Warning, you should take it very seriously. Listed below are the most common Warnings you may see issued in western Wyoming.

Winter Storm Warning: Issued when heavy snow and/or strong wind are possible.

Winter Storm Warning for Heavy Snow: Issued when snowfall is expected to exceed 6 inches per event in the valley. For mountain locations it is 12 inches or more per event.

Blizzard Warning: 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. And these conditions are expected to last for 3 hours or longer.

Other Warnings might include: Wind-Chill Warning (-30F) or an Avalanche Warning (High to Extreme Avalanche danger rating).

Winter Weather Advisory & Warning Criteria for Heavy Snow in Western Wyoming
Per Event or Time Period

Advisory
Warning
Valley
3 to 6 inches
6 inches or more
Mountains
5 to 12 inches
12 inches or more
From NWS Central Region


While a "Winter Storm Warning" may not necessarily translate to copious powder for skiers, it should at least mean that we are in for some nasty weather involving snow, wind, bad visibility, and sporty driving conditions.

Blizzard, Winter storm, and Avalanche Warnings are serious enough to be sent out on the Emergency Alert System (EAS), and if you subscribe to NIXLE alerts, you should see them show up there, as well.

On the MountainWeather.com website on the Jackson Hole Forecast page, a flashing box will appear at the top of that page above the forecast content whenever the National Weather Service in Riverton has issued any sort of weather alert specifically for Teton County. Read these carefully, and don’t just assume the flashing box means a big dump is on the way!



Post by Meteorologist Jim Woodmencey
Republished with permission from JH N&G

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