Useful weather information depends upon the generation
of accurate forecasts and their timely distribution.
It is then the responsibility of the person on the ground
to take the time to listen to and have the knowledge
and skills to comprehend the information.
This information, along with personal observations
and local knowledge can then be applied.
So how do you interpret the information
in a fire weather forecast?
How is it different when you read it versus listening to it
over the radio, and how do you give it
or receive it in a briefing?
Rick Ochoa works for predictive Services
at the National Interagency Fire Center.
He has written many fire weather forecasts.
We hope he can help you to interpret the content
of the forecasts you see, hear and deliver every day.
The main components of a Fire Weather Forecast are first:
THE HEADLINES.
The headlines could be a Red Flag Warning,
a Fire Weather Watch; something real critical
for the firefighters.
And if I can explain what a Red Flag Warning is,
a Red Flag Warning is a combination
of critical fire weather, such as winds, dry lightning,
in combination with dry fuels.
These warnings and watches are provided for firefighter safety.
A warning, a Red Flag Warning means those conditions are
either occurring or eminent.
A Fire Weather Watch means that those conditions may occur
in the near future; in the next 12 to 48 hours.
The good warning or good watch has both a geographic location,
such as the Boise National Forest,
in addition to a particular fire weather zone number.
The WEATHER DISCUSSION will talk about the synoptic features
such as: cold fronts, high pressure ridges,
low pressure troughs, and so, that's producing the weather.
A lot of times these forecasts are very detailed and very long
and it's important for the listener to try and pull
out what are the important things like:
cold fronts are very important, any kind of wind shifts,
thunderstorms, turning hotter, turning drier, things like that.
So you should really be listening
for those weather features that are really going
to affect the conditions on your fire.
The first element in a Fire Weather Forecast is the SKY
WEATHER: and that'll be the sky conditions, whether it's cloudy
or clear or partly cloudy, and a weather element like,
thunderstorms, rain showers, fog, things like that.
So pay particular attention to those things that are critical
such as thunderstorms.
The next element is TEMPERATURE: and it'll give you a range
of temperatures for your particular fire weather area.
And it'll often times give you a trend, whether it's going
to be five degrees warmer, five degrees cooler, and so on.
The next one is HUMIDITY: it'll give you again,
a range of humidity values, along with a trend.
And after that is the WIND: with the winds you'll get a variety,
you'll get slope valley winds,
ridge top winds, twenty-foot winds.
And twenty-foot winds are those winds twenty feet
above the affected vegetation.
So, if you're dealing with an area with just grass,
it's going to be twenty feet.
If you're dealing in timber,
it's twenty above the average tops of those trees there.
Obviously, if you're on a ridge top you want
to listen for those winds.
If you're down in the valley, pay particular attention
to those slope and valley winds.
The HAINES INDEX is a index that combines stability and moisture.
And the values range from 2 to 6, 6 being High.
And so this index does not include things like wind
or other factors like that; it's strictly a moisture
and stability of that atmosphere close to the ground.
So again, what I'd be listening for there is if there's a Haines
of 5 or 6, Moderate or High,
those are the times I'd really be concerned about.
If it's a 2, 3 or 4, typically those are the lower ranges
and typically there's not going to be an issue
with stability or moisture.
LAL, LIGHTNING ACTIVITY LEVEL talk about the number
of lightning strikes you're going to have over a given area.
They range from 1, which is no thunder storms to a 6,
which is numerous thunderstorms, typically dry.
So again, I'd be listening for, you know, values like 3, 4, 5,
6; those are the ones that are going
to contain more thunderstorms.
In addition to the thunderstorms,
listen very closely as to whether they're going
to be wet thunderstorms / dry thunderstorms or a mixture.
The MIXING HEIGHT basically tells the firefighter
that lower atmosphere.
What is the depth of that atmosphere that's going
to be well mixed?
Typically, in the afternoons it'll be quite high;
it could be several thousand feet.
And at night, typically those mixing layers,
mixing levels come down quite a bit;
they might just be few hundred feet.
That's important because the higher the mixing height,
the greater the instability, and so with that you're going
to probably see more fire activity, fire behavior
with the greater mixing heights.
TRANSPORT WINDS are important because you want to know
where that smoke's going to be going.
So that'll, the average winds within that mixed layer
as to whether their going to be coming out of the south
or north, and they'll give you a wind speed there.
So, if you have high mixing heights
and high transport winds, you're going
to have pretty good smoke dispersion.
Low mixing height and low winds are typically going
to be smoke problems.
The EXTENDED FORECAST: There what I'd be looking
for is anything out of the ordinary:
Are there going to be thunderstorms?
Are there going to be strong winds?
Get an idea about whether it's going
to be turning warmer or drier.
A lot of times the most interesting
and most significant weather is going to be occurring
in the extended period so pay close attention to that.
Fire weather forecasts are full of useful information
and are readily available throughout the fire season.
The next exercise is intended to provide an opportunity
to translate a fire weather forecast
into the form of a briefing.
Your facilitator will now set up the exercise.