EXPLANATION OF THE 7-DAY SIGNIFICANT FIRE POTENTIAL PRODUCT
The purpose of this
document is to help clarify this Significant Fire Potential product and
hopefully answer some common questions about it.
It is very important that
the user understand that although weather is a major contributor to large fire
potential, this product is NOT a
weather forecast! It is an outlook summarizing the potential for Significant
The purpose of the
product is to estimate the daily large fire risk across northern
Daily probability for occurrence of a new large fire and/or,
Daily potential for significant new growth on an existing large fire
The product is based on a
statistical model which uses fuel moisture inputs from the NFDRS (WIMS) and
various gridded weather inputs from weather models. This data is processed
through a series of equations that yield forecasts of Fuel Dryness Level (DL)
as well as probabilities (some objective and some subjective) of certain
critical weather conditions for each of the next 7 days. When appropriate
combinations of DL and weather triggers are expected, a High Risk Day is designated on the Chart to warn of a
significantly higher than normal chance for a Large Fire.
A Large fire has been
defined for each Predictive Service Area based on a statistical analysis. These
Mid Coast 75 Acres
Bay Area 100 Acres
Northern Sierra 75
Information is portrayed
on the chart by a color code and, when appropriate, a symbol as follows:
Fuel Dryness (DL) is
represented on the chart for each day and for each Predictive Service Area as one
of three colors. DL is determined by combinations of ERC and F100.
Indicates a DL which historically has not resulted in any realistic
chance of large fires.
2. Yellow Indicates a rather
normal summertime dryness that typically will not result in large fires
unless accompanied by a critical trigger event (often weather related).
3. Brown Indicates very dry fuel
levels which result in a much higher than normal chance of large fires when accompanied
by a critical trigger event. A low to moderate threat for large fires exists in
the absence of a trigger.
High Risk Days are rare occasions when conditions (i.e. dry fuels
in conjunction with a critical trigger event) exist that historically have
yielded a significant chance for a large fire. They will be designated on the
chart in RED with a symbol designating the trigger as follows:
1. Red and a lightning
bolt An expected combination of dry fuels and a lightning trigger. It must be
remembered that this designation will only show on the chart when an
appropriate amount of lightning and an appropriate DL is expected. This is NOT
simply a lightning forecast.
2. Red and a HD An
expected critical combination of dry fuels and an unseasonably hot and dry air
mass. While this condition does not start fires, it often produces a favorable
environment for new starts to become large. Thus this trigger can result in
significant growth on existing fires but for most areas, it correlates poorly
with new large fires.
3. Red and a W
Represents dry and windy. Again as stated in number 2 above, wind does not
necessarily start fires (although in some extreme cases it could), it rather
produces a favorable environment for new start to become large.