Basic Guide to Basic Guide to Calculating Calculating Atmospheric Atmospheric

Dispersion Index Dispersion Index (ADI, after Lavdas) (ADI, after Lavdas)

ADI is derived from mixing height, ADI is derived from mixing height, transport wind, and stability class.transport wind, and stability class.

Many fields are already created in Many fields are already created in the Fire Weather Forecast process the Fire Weather Forecast process (ex. sfc winds and mixing height)(ex. sfc winds and mixing height)

Stability class is derived from the Stability class is derived from the Net Radiation Index (NRI)Net Radiation Index (NRI)

NRI can be obtained using a set of NRI can be obtained using a set of cloud and ceiling rules.cloud and ceiling rules.

The rules are divided into a day and The rules are divided into a day and night class. However, If the total night class. However, If the total opaque cloud cover is 10/10 and the opaque cloud cover is 10/10 and the ceiling height is <7,000 ft, use net ceiling height is <7,000 ft, use net radiation index equal to 0 (whether radiation index equal to 0 (whether day or night). day or night).

Net Radiation Index (NRI)

Net Radiation Index (NRI)

For nighttime :For nighttime :

        A.A. If total opaque cloud cover =< If total opaque cloud cover =< 4/10, use net radiation index equal to -4/10, use net radiation index equal to -2.2.

                            

B.B. If total opaque cloud cover >4/10, If total opaque cloud cover >4/10, use net radiation index equal to -1.use net radiation index equal to -1.

Net Radiation Index (NRI)

For daytime:For daytime:

          A.A. Determine the insolation class number as a Determine the insolation class number as a function of solar elevation angle according to the function of solar elevation angle according to the following table:following table:

Solar Elevation Angle (d) Insolation Class Solar Elevation Angle (d) Insolation Class 60 < d 60 < d 4 435 < d =< 60 335 < d =< 60 315 < d =< 35 215 < d =< 35 2 d =< 15 1 d =< 15 1

http://www.srrb.noaa.gov/highlights/sunrise/azel.hthttp://www.srrb.noaa.gov/highlights/sunrise/azel.htmlml

. .

Net Radiation Index (NRI)

If the total opaque cloud cover <= If the total opaque cloud cover <= 5/10, the net radiation index is equal 5/10, the net radiation index is equal to the insolation class number. to the insolation class number.

If the opaque cloud cover is >5/10, If the opaque cloud cover is >5/10, then follow the set of rules on the then follow the set of rules on the next slide.next slide.

Net Radiation Index (NRI)If the total opaque cloud cover > 5/10, modify the insolation If the total opaque cloud cover > 5/10, modify the insolation

class number by following these six steps:class number by following these six steps:

            1.1. Ceiling height less than 7,000 ft, subtract 2. Ceiling height less than 7,000 ft, subtract 2.

            2.2. Ceiling height >= 7,000 ft but < 16,000 ft, subtract 1. Ceiling height >= 7,000 ft but < 16,000 ft, subtract 1.

            3.3. Total opaque cloud cover equal to 10/10, subtract 1. Total opaque cloud cover equal to 10/10, subtract 1.                 4.4. If neither steps 1 and 2 nor 3 immediately above are If neither steps 1 and 2 nor 3 immediately above are

applicable, assume the modified insolation class number is applicable, assume the modified insolation class number is equal to the insolation class number.equal to the insolation class number.

          5.5. If the modified insolation class number is less than 1, If the modified insolation class number is less than 1, let it equal 1.let it equal 1.

            6.6. Set the net radiation index equal to the modified Set the net radiation index equal to the modified insolation class number.insolation class number.

STABILITY CLASS

as a function of Net radiation Index and Wind Speed

Deriving the ADIDeriving the ADI

You will need the following You will need the following information to derive the dispersion information to derive the dispersion index (ADI) from the chart on the index (ADI) from the chart on the next slidenext slide

1. modified stability index 1. modified stability index

2. forecast mixing height2. forecast mixing height

3. forecast transport wind 3. forecast transport wind

Basic Guide to Basic Guide to Calculating Low Calculating Low

Visibility Visibility Occurrence Risk Occurrence Risk Index (LVORI)Index (LVORI)

after Lavdas and Achtemeierafter Lavdas and Achtemeier

Low Visibility Occurrence Low Visibility Occurrence Risk Index (LVORI)Risk Index (LVORI)

LVORI is calculated from the ADI LVORI is calculated from the ADI and relative humidity, both of which and relative humidity, both of which are obtained from the forecast grids are obtained from the forecast grids by the NWS LVORI software. by the NWS LVORI software.

Low Visibility Occurrence Low Visibility Occurrence Risk Index (LVORI)Risk Index (LVORI)

LVORI CategoryLVORI Category InterpretationInterpretation

11Lowest proportion of accidents Lowest proportion of accidents with smoke and/or fog reported with smoke and/or fog reported (130 of 127,604 accidents, or (130 of 127,604 accidents, or just over 0.0010 accidents)just over 0.0010 accidents)

22Physical or statistical reasons for Physical or statistical reasons for not including in category 1, but not including in category 1, but proportion of accidents not proportion of accidents not significantly higher.significantly higher.

33Higher proportion of accidents Higher proportion of accidents than category 1, by about 30% to than category 1, by about 30% to 50%, marginal significance (1%-50%, marginal significance (1%-5%)5%)

44Significantly higher than Significantly higher than category 1, by a factor of 2.category 1, by a factor of 2.

55Significantly higher than Significantly higher than category 1, by a factor of 3 to 10.category 1, by a factor of 3 to 10.

66Significantly higher than Significantly higher than category 1, by a factor of 10 to category 1, by a factor of 10 to 20.20.

77Significantly higher than Significantly higher than category 1, by a factor of 20 to category 1, by a factor of 20 to 40.40.

88Significantly higher than Significantly higher than category 1, by a factor of 40 to category 1, by a factor of 40 to 75.75.

99Significantly higher than Significantly higher than category 1, by a factor of 75 to category 1, by a factor of 75 to 125.125.

1010 Significantly higher than Significantly higher than category 1, by a factor of 150.category 1, by a factor of 150.

Low Visibility Occurrence Risk Index (LVORI)

LVORI / Low VisibilityLVORI / Low Visibility

TODAY TONIGHT SAT

CLOUD COVER MCLDY MCLEAR MCLEARCHANCE PRECIP (%) 50 0 0PRECIP TYPE SLEET/RAIN NONE NONEMAX/MIN TEMP 45 29 53MIN/MAX RH % 43 98 43WND20FT2MIN/EARLY(MPH) SW 6 W 5 LGT/VARWND20FT2MIN/LATE(MPH) W 8 G17 LGT/VAR LGT/VARPRECIP DURATION 2 0 0PRECIP AMOUNT 0.03 0.00 0.00PRECIP BEGIN 6 AMPRECIP END 4 PMLAL 1 1 1INVERSION(TEMP/TIME) 33/0900 2000 40/0900HAINES INDEX 3 5 5DSI 1 1MIXING HGT(FT-AGL) 2700 2900TRANSPORT WND (MPH) W 35 W 14VENT RATE (MPH-FT) 94500 40600ADI EARLY 42 49 24ADI LATE 75 10 35MAX LVORI EARLY 4 4 5MAX LVORI LATE 1 6 1

REMARKS...ADI IS ATMOSPHERIC DISPERSION INDEX BY LAVDAS.LVORI IS LOW VISIBILITY OCCURRENCE RISK INDEX.

FWF: Fire Weather Planning Forecast

PFW: Point Fire Weather Matrix

Questions?Questions?