Method For Improved Fire Weather Forecast
Deb Ross and Jeanette Comstock
Department of Physics and Astronomy, University of Montana
Introduction
Analysis – Weather Forecast
Analysis – Surface Wind Forecast
It has been agreed upon by the meteorological community that
the current radiosonde network being the “backbone” for upper
air observations has limited temporal and spatial samples. An
increase in either temporal or spatial resolution would be
exceedingly helpful (Kaiser, Pevear 2009). Additionally, it is well
known that accurate weather observations improve spot
weather forecasts, a special forecast issued to fit the time,
topography, and weather of each specific fire. Radiosonde data
is used to initialize numerical models for weather forecasting.
The current spatial resolution of radiosonde data in Montana is
500km and the data is retrieved two times daily. We will
establish and test a methodology to assess the degree of
improvement provided by short-term weather forecasts issued
for a particular location using input parameters from a mobile
radiosonde sounding system at the same location hence
increasing spatial resolution to approximately 8km from the
forecast site.
RAOB: The Universal Rawinsonde Observation Program: The
GRAW data has been formatted to be ingested into the RAOB
software for detailed analysis of the sounding ascent and to produce a
short term forecast (see figure 3). In addition to a typical sounding
analysis, RAOB will be able to use the GRAW data to forecast a
maximum surface temperature that can be used to adjust the
sounding profile and associated index displays. Inversion layers (both
nocturnal and subsidence) will be measured, as well as the vertical
wind profile, and various stability indices including: Showalter Index,
K-Index, Lifted Index, Total Totals Index, Sweatt Index, CAPE Index,
and the CINH index.
WindNinja: WindNInja is a computer program that computes
spatially varying wind fields for wildland fire application. Inputs
include a domain-mean initial wind speed and direction, and
specification of the dominant vegetation in the area. A diurnal
slope flow model can be optionally turned on or off
(http://firemodels.org/index.php/research-systems/windninja).
It may be possible to enhance the current network of sounding
stations through improvements regarding spatial resolution of
data from sounding balloons. To this end, the program used in
Canada’s East Fire Region will be applied to soundings taken in
Western Montana and its effectiveness then evaluated against
other numerical weather models initialized with this data.
Radiosondes are still considered the most effective means for
obtaining a detailed analysis of vertical composition in the
atmosphere. Radiosondes provide outstanding vertical
resolution in their soundings and are able to directly measure
simultaneously temperature, wind, moisture and pressure
measurements.
Data Collection - Sounding
The output can provide predicted wind variations among terrain
changes (see figure 4).
Figure 4. WindNinja output on Google earth initialized with GRAW radiosonde data
from 8/17/11 launch.
Discussion and Conclusions
Figure 3. RAOB analysis of GRAW radiosonde data from 8/17/11 launch.
GRAW system: The ground station is the GRAW mobile
station, GS-H communicating with a DFM-06 radiosonde. A
skew-T plot is made in real-time as data is transmitted for quick
analysis to identify low level jets and inversion cap layers (see
figures 1 and 2).
The overall purpose is to identify any weather issues that could
affect fires in the area of concern. How to actively pursue this
end can involve a number of methods. Since balloon soundings
get a high resolution picture of the vertical structure of the
atmosphere, We propose starting with the process outlined
here. The main use of the ascent on site is to capture any
inversions and identify any low level jets that were not picked
up by initial scans. Using our morning on site data also allows
us to have RAOB prepare an afternoon “forecasted” sounding
in an effort again to pick up weather issues not resolved by
other models.
Literature Cited
Jason Kaiser and Brian Pevear. (2009). A Report on the Current Radiosonde
Temporal and Spatial Resolution in the Continguous United States (Internal NOAA
and NWS Report).
WindNinja. Fire Behavior and Fire Danger Software.Retrieved 10 April 2012.
http://www.firemodels.org/
Acknowledgments
Figure 1. GRAW
radiosonde launch
8/17/11, Missoula, MT
Jennifer Fowler, University of Montana, Flight Director UM-BOREALIS
Roger DesJardins, Canadian East Fire Region, Incident Meteorologist
Figure 2. GRAW Skew-t plot from 8/17/11 launch, Missoula, MT