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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
Index (ADI, after Lavdas)
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
Net Radiation Index (NRI)
  • 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
Net Radiation Index (NRI)
  • 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
Net Radiation Index (NRI)
  • 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
Net Radiation Index (NRI)
  • 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
Net Radiation Index (NRI)
  • 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
Deriving the ADI
  • 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
40600 ADI EARLY
42 49
24 ADI LATE
75 10
35 MAX LVORI EARLY 4
4 5 MAX LVORI
LATE 1
6 1 REMARKS...ADI IS
ATMOSPHERIC DISPERSION INDEX BY LAVDAS. LVORI IS
LOW VISIBILITY OCCURRENCE RISK INDEX.
21
PFW Point Fire Weather Matrix
22
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