# Basic Guide to Calculating Atmospheric Dispersion Index (ADI, after Lavdas) - PowerPoint PPT Presentation

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## Basic Guide to Calculating Atmospheric Dispersion Index (ADI, after Lavdas)

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### FWF: Fire Weather Planning Forecast PFW: Point Fire Weather Matrix * * * Title: Basic Guide to Calculating Atmospheric Dispersion Index (ADI, after Lavdas) – PowerPoint PPT presentation

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Title: Basic Guide to Calculating Atmospheric Dispersion Index (ADI, after Lavdas)

1
Basic Guide to Calculating Atmospheric Dispersion
2
• ADI is derived from mixing height, transport
wind, and stability class.
• Many fields are already created in the Fire
Weather Forecast process (ex. sfc winds and
mixing height)
• Stability class is derived from the Net Radiation
Index (NRI)

3
• NRI can be obtained using a set of cloud and
ceiling rules.
• The rules are divided into a day and night class.
However, If the total opaque cloud cover is 10/10
and the ceiling height is lt7,000 ft, use net
radiation index equal to 0 (whether day or
night).

4
• For nighttime
•     A. If total opaque cloud cover lt 4/10, use
net radiation index equal to -2.
•
• B. If total opaque cloud cover gt4/10, use
net radiation index equal to -1.

5
• For daytime
•      A. Determine the insolation class number as
a function of solar elevation angle according to
the following table
• Solar Elevation Angle (d) Insolation
Class
60 lt d
4 35 lt d lt 60
3 15 lt d lt 35
2 d lt 15
1
• http//www.srrb.noaa.gov/highlights/sunrise/azel.h
tml.

6
• If the total opaque cloud cover lt 5/10, the net
radiation index is equal to the insolation class
number.
• If the opaque cloud cover is gt5/10, then follow
the set of rules on the next slide.

7
• If the total opaque cloud cover gt 5/10, modify
the insolation class number by following these
six steps
•       1. Ceiling height less than 7,000 ft,
subtract 2.
•       2. Ceiling height gt 7,000 ft but lt 16,000
ft, subtract 1.
•       3. Total opaque cloud cover equal to 10/10,
subtract 1.
•
• 4. If neither steps 1 and 2 nor 3
immediately above are applicable, assume the
modified insolation class number is equal to the
insolation class number.
•      5. If the modified insolation class number
is less than 1, let it equal 1.
•       6. Set the net radiation index equal to the
modified insolation class number.

8
STABILITY CLASS as a function of Net radiation
Index and Wind Speed
9
(No Transcript)
10
• You will need the following information to derive
the dispersion index (ADI) from the chart on the
next slide
• 1. modified stability index
• 2. forecast mixing height
• 3. forecast transport wind

11
(No Transcript)
12
(No Transcript)
13
Basic Guide to Calculating Low Visibility
Occurrence Risk Index (LVORI) after Lavdas and
Achtemeier
14
Low Visibility Occurrence Risk Index (LVORI)
• LVORI is calculated from the ADI and relative
humidity, both of which are obtained from the
forecast grids by the NWS LVORI software.

15
Low Visibility Occurrence Risk Index (LVORI)
16
(No Transcript)
17
Low Visibility Occurrence Risk Index (LVORI)
LVORI Category Interpretation
1 Lowest proportion of accidents with smoke and/or fog reported (130 of 127,604 accidents, or just over 0.0010 accidents)
2 Physical or statistical reasons for not including in category 1, but proportion of accidents not significantly higher.
3 Higher proportion of accidents than category 1, by about 30 to 50, marginal significance (1-5)
4 Significantly higher than category 1, by a factor of 2.
5 Significantly higher than category 1, by a factor of 3 to 10.
6 Significantly higher than category 1, by a factor of 10 to 20.
7 Significantly higher than category 1, by a factor of 20 to 40.
8 Significantly higher than category 1, by a factor of 40 to 75.
9 Significantly higher than category 1, by a factor of 75 to 125.
10 Significantly higher than category 1, by a factor of 150.
18
LVORI / Low Visibility
19
(No Transcript)
20
FWF Fire Weather Planning Forecast
TODAY
TONIGHT SAT CLOUD COVER
MCLDY MCLEAR
MCLEAR CHANCE PRECIP () 50
0 0 PRECIP
TYPE SLEET/RAIN
NONE NONE MAX/MIN TEMP
45 29
53 MIN/MAX RH 43
98
43 WND20FT2MIN/EARLY(MPH) SW 6 W
5 LGT/VAR WND20FT2MIN/LATE(MPH)
W 8 G17 LGT/VAR LGT/VAR PRECIP
DURATION 2
0 0 PRECIP AMOUNT
0.03 0.00
0.00 PRECIP BEGIN
6 AM PRECIP END
4 PM LAL
1 1
1 INVERSION(TEMP/TIME) 33/0900
2000 40/0900 HAINES INDEX
3 5
5 DSI
1
1 MIXING HGT(FT-AGL)
2700
2900 TRANSPORT WND (MPH) W 35
W 14 VENT RATE
(MPH-FT) 94500
42 49