What is the difference between all the products the National Weather Service (NWS) issues?
I found a list of all the products the NWS generates. I'm not going to itemize them all, but at last count there were about 330 separate identifiers! But I'm not here to talk about all those. Heck no!
I'm here to go over the difference between:
- WATCH, WARNING, and ADVISORY
Here are the NWS definitions if you are interested:
- WATCH: A watch is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so that those who need to set their plans in motion can do so.
- WARNING: A warning is issued when a hazardous weather or hydrologic event is occurring, is imminent, or has a very high probability of occurring. A warning is used for conditions posing a threat to life or property.
- ADVISORY: Highlights special weather conditions that are less serious than a warning. They are for events that may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may threaten life and/or property.
WHAT DOES IT ALL MEAN?
Basically this translates to degrees of certainty and impacts.
A WATCH is generally issued when meteorologists are forecasting a weather event with possible severe impacts. The weather event is not certain, but the possibility of severe impacts are worth informing the public about.
A WARNING is generally issued when there is high confidence that a weather event with severe impacts is occurring or is expected to occur in the near future.
An ADVISORY is generally issued when there is high confidence that a weather event will occur, BUT the impacts are expected to be less than severe.
Watches, warnings and/or advisories can be issued independently of each other.
- Basically the issuance of a WATCH means WARNING impacts are possible, but it is not certain.
- However, the issuance of a WATCH does NOT guarantee a later WARNING.
- A WATCH is NOT issued when only ADVISORY impacts are expected.
- However, it is possible for a meteorologist to forecast WARNING impacts, issue a WATCH, but later forecast models indicate of impacts will not be severe, resulting in "only" an ADVISORY being issued.
- Then again, it is possible for a forecaster to see possible "non-severe" impacts but later forecast models indicate impacts will be severe, resulting issuance of a WARNING without
CRITERIA
But what is a "significant/severe" impact? If you, as an individual, experience any weather event it may have significant or severe impacts on you.
The NWS generally has criteria to determine whether something constitutes a watch, warning or advisory. And the various types of weather variables begins to expand the list of possible watches, warnings or advisories.
The NWS monitors variables for cold and warm season.
COLD SEASON VARIABLES:
The NWS has different criteria for many of these variables, whether it be a WATCHES/WARNING/ADVISORIES for:
SNOW and/or HEAVY SNOW, FLOOD, COLD, FREEZING RAIN or ICE STORM, or BLIZZARD...etc.
WARM SEASON VARIABLES:
The NWS has different criteria for many of these variables, whether it be a WATCHES/WARNING/ADVISORIES for:
SEVERE THUNDERSTORM, TORNADO, HEAT, DUST, HURRICANES or TROPICAL STORMS...etc.
It would be too much to go into all of the critieria or thresholds in each Weather Forecast Office across the United States or wherever you may be. BUT if there is something specific you are looking for leave a comment or contact me.
Here is the description of the Snow Criteria from the website of National Weather Service in Spokane, Washington (USA):
"The NWS issues Snow Advisories for the Columbia Basin and the valleys for 2-3 inches of snow in 12 hours or 3-5 inches of snow in 24 hours. In the east slopes of the Cascades, snow advisories are issued for 6-11 inches of snow in 12 hours or 6-17 inches of snow in 24 hours.
The NWS has different criteria for heavy snow for different areas of the Inland Northwest. A Heavy Snow Warning is required if 4+ inches of snow in 12 hours or 6+ inches of snow in 24 are expected in the Columbia Basin and the valleys. For the Northeast Mountains, the Panhandle mountains and the Okanogan Highlands, 8+ inches of snow in 12 hours or 12+ inches of snow in 24 hours prompts a heavy snow warning. A heavy snow warning for the east slopes of the Cascades requires 12+ inches of snow in 12 hours or 18+ inches of snow in 24 hours. In the Blue Mountains, 12 + inches of snow in 24 hours is needed for a heavy snow warning.
Blizzard conditions exist when sustained winds of 50 mph or more with considerable falling and drifting snow, causing visibilities to drop to near 1/4 mile for at least 3 hours. Though there are no temperature requirement, temperatures that fall below 20 degrees F under these conditions can lead to life-threatening, sub-zero wind chill readings."
No comments:
Post a Comment