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“New Mesoscale Modeling by Raw Output Statistics (ROS) ”. How did the ROS model begin, and WHY do we need another model? Glad you asked.
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Glad you asked.
From there, others began to ask if the ROS could catch micro and mesoscale meteorological phenomenon…such as lake effect snowfall in Duluth, Minnesota and sea fog episodes in New Orleans. We put it to the test by inserting some local research and study material and the model began to show signs of working. After some fine tuning, the ROS was on its way.
NCEP would never be able to tackle such a tremendous project as running a mesoscale model for every single office. This is because each office has its own set of fire weather fields as well as mountains, hills, valleys, and lakes to input. Individual stations can also change modes when necessary…i.e. winter to summer equation useage.
And we come up with something that looks like this:
CWA = Coastal Warning Area
1 ETAROS7 TERICK KNEW 060545
2 GPT ETA ROS GUIDANCE 05/06/2002 0000UTC
3 WKDY MON TUE WED
3 DATE /MAY 6 /MAY 7 /MAY 8
3 HOUR 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12
2 TEMP 35 35 37 37 39 39 43 41 39 38 36 34 39 44 45 42 38 34 33 33
3 DWPT 34 35 35 35 35 33 33 36 35 35 33 32 30 30 29 29 26 27 27 26
1) Max Min temperature in F
2) Temperature on the hour in F
3) Dew Point temperature on the hour in F
2 CLHT 08 08 08 08 19 23 33 19 15 23 00 00 00 00 00 00 00 00 63 17
3 TMPO 05 05 05 05 15 19 28 15 11 19
4 TTSK OV OV OV OV OV OV OV OV OV OV CL CL CL CL CL CL CL CL PC PC
The CLDS field will tell if this number shows 100’s or 1000’s of feet. As an example, O< will first tell you the lowest prevailing cloud condition will be “O” overcast and the height of this deck will be “<“ less than 1000ft. Then the CLHT field would be read with two zeros. If a number is shown in the CLDS field then the CLHT field will be read also with two zeros. If a “>” or “^” sign is used then the CLHT field will be read with three zeros.
4) Total sky cover accumulates all cloud levels
Others who have worked with the TERICK equation are:
Dr. Eric Pani of the University of Louisiana at Monroe set thermodynamic theory and an integral explanation to the equation…Bob Rozumalski of COMET explained and found errors in the original equation…and Peter Parke of the National Weather Service in Duluth, Minnesota worked with verifying the units used in the equation.
Hl + [(Hc – Hl)/(Tc – Ts)] = LCH; Hl=LCL height in feet Tc=Conv temp in C
If (Tc – Ts) <= 0; then (Hc – Hl) = 0; Hc=CCL height in feet Ts=SFC temp in C
LCH=Lowest Cloud Height
2OBVS -S -S
1) The visibility is developed through local studies and research. There are many variables to this field.
2) The obstruction to visibility shows the weather phenomenon responsible for causing the reduction in visibility.
WSPD 13 10 11 10 10 08 07 05 06 04 06 08 08 08 09 06 08 10
Wind direction and wind speed in knots.
PP12 0 0 2 26 6
6 & 12 hour POP fields. These are derived from local studies and research as well.
ALWAYS CHECK FOR RH INITIALIZATION BEFORE USING POP’S FROM ANY MODEL.
PTYP RA RA RA RA RA RA RA RA
Total precipitation is straight from the raw grids. In other words, the amount of QPF you see on the raw grids is the amount shown here.
The total precip field is shown to the hundredths of an inch. They are also cumulative over each three hour period.
The Precipitation Type field is the only one computed through BUFKIT…it uses a thickness scheme.
2 SWEQ 01 01 01 01 01 02 02 03 03 03 05 05 05 05 05 04 04 04 03
WCHL 12 22 27 25 24 25 23 18 14 20 22 20 19 10 07 02-08-02 03-09
HINX 60 65 72 85 87 92 95 93 97 99 98 99 99 98 98 95 92 93 92 91
LE06 22 0 0 0 0 0 0 15 57 54
LE12 16 0 0 7 69
TEMP 12 23 28 27 27 28 24 19 19 29 31 28 27 22 16 12 09 14 15 06
These are test fields.
The wind chill and heat index are seasonal. They are shown here because they are not representative when temperatures fall outside the equations’ threshold.
The Lake effect pop field is currently in testing. It uses vectorization along with a few other predictors to determine the percentage of purely lake effect pops.
The temperature field here is a failed attempt to better the sfc temperature output without statistics.
Fields which are stripped and clipped straight from the ETA raw data
are as follows:
sections that MOS is run. In
other words, when looking
at FWC guidance, the header
information will show what
equations are run for that
guidance package. These are
split into climatologically
favored regions. An example
of the header info is shown
BRD C NGM MOS GUIDANCE 6/26/02 0000 UTC
DAY /JUNE 26 /JUNE 27 /JUNE 28
HOUR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12
DLH EC NGM MOS GUIDANCE 6/26/02 0000 UTC
DAY /JUNE 26 /JUNE 27 /JUNE 28
HOUR 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12
The future of ROS will be what individual offices want it to be. Offices using the ROS will break the large grids shown in the previous slide into very small grid sections relative to the offices’ CWA. This is very high resolution. Currently the ROS is run using data from the ETA, but it can be configured to run for any numerical model that NCEP produces. This is cutting edge technology, we here at the New Orleans WSO are doing our best to break new ground.
Each office will finally have the capability of introducing micro and mesoscale variables to their output. Studies and research can be sourced into the model to make an offices forecast extremely strong. All variables will benefit from the added data. Since no office can edit the NCEP models, this will make the ROS obsolete and interactive. Individual fields can be changed or removed depending on office needs.
An example would be the fire weather fields. These can be changed or “forced” to see what the offices’ users want to see for a particular site. MOS will never be able to do that as well as many other special features the ROS is able to provide.
NWP Models and Their Processes
This is a form of statistical equation. The future of probability diagnosis may begin to use these type of equations within 5 to 10 years or maybe sooner.
Bayesian equations are very efficient when compared to the current method of least squares linear regression. They use past, current and future data to derive a probability. They always use new information to “learn” from, and then possibly change an outcome based on the new information. In this way, MOS model data would be “learning” on two platforms. One would be climatology and the second would be the actual equations instead of a predictor coefficient constant.
You can easily find these equations at work today in new programs such as Microsoft Word or Excel. The funny character that pops up on the side in these software use these equations to try and find out what you are doing. Then it can give you hints or examples to use during your project.
The weekday is a simple algorithm that uses every fourth year as a leap year giving the model weekday from the model date.
The CLDS group is computed in conjunction with the CLHT…TMPO…and TTSK fields.
The model uses a top down approach. MOS uses a bottom up. First the model calculates the lowest possible level a prevailing cloud layer will be found.
A) LCL height in feet
B) Height of min RH between LCL and CCL
C) LCL height in feet + result of the TERICK equation
An algorithm run by the model determines which of these will be calculated and used. It then runs down the sounding profile keeping every level that meets a preset RH criteria for cloud layers. When it finds one it keeps it until another is found…then replaces that level with the current and so on...until it reaches the calculated lowest height. The height that is saved last will be set as the lowest ceiling height if it meets the RH value for a ceiling. The ROS always gives precedence to BKN or OVC. In other words…if it sees any BKN or OVC layer in the sounding, then no matter how low a SCT layer may be, it will still not be shown. The height is set in the CLHT field and the LCL is checked for high RH levels…if found then the TMPO group will receive this deck. All the layers are then counted and the model decides from the total layers, which category of clouds to use in the TTSK group, either CL…PC…MC…or OV. The clouds algorithm is extremely complicated but gives a strong answer to cloud heights.
Here is a set of RH values from the ROS:
Hl + [(Hc – Hl)/(Tc – Ts)] = LCH;
If (Tc – Ts) <= 0; then (Hc – Hl) = 0;
The way this equation works is quite simple. It uses the temperature difference between the Convective temp and the forecasted or ambient temp AND the height difference between the LCL and the CCL. This height is divided by the temp difference and the resulting height is added to the LCL to get the lowest cloud height. This process simply holds the latent heating within the parcel until it is cool enough to condense. The equation was created because textbooks only showed two processes. When a parcel is forced (LCL) and when the parcel is convectively driven (CCL). The only thing one will find in a textbook about when both of these processes are occurring at the same time is “…the cloud height will be found somewhere between the LCL and the CCL.” This simply wasn’t good enough and I knew I could at least get close to an actual height. Below is a pictorial explanation.
The Visibility section is calculated with studies and research. There are really no equations used, instead an enormous algorithm is used with generic low visibility producing variables or predictors. One visibility producing algorithm is shown below. This field will also show restrictions due to precipitation.
This is one set of equations used by NGM MOS for the cool season over the northern grid. It takes many more to make up an entire run. The ROS uses the same technique except these equations have been manipulated to fit the ETA data.
This field is a result of team effort involving local research. A research project was undertaken to find how deep snow would accumulate using temperature to water-equivalent ratios. I simply took this data and sourced it for use by the ROS model. Here are the ratios used:
0 - 9F30:1
SN:WE or .10” of water equivelant at 35F equals
.70” of snow accumulation.
Relative Humidity equation used:
Es = 6.11 * 10.0^(7.5 * Tc / (237.7 + Tc))
E = 6.11 * 10.0^(7.5 * TDc / (237.7 + TDc))
RH = (E/Es) * 100.0
The ROS computes the Haines index by national standards and uses the actual stations elevation. This is the most accurate method of getting the index, but local fire officials may want the data to show a generic view instead. This can be done when the ROS is used with the WS ETA. This field, and others, can be forced to show what fire officials currently use in their areas. No forcing can currently be done since other fields rely on elevation as well.
These are the generic
boundaries of the Haines
elevation determines the
level at which
temperature and dew
point data are drawn to
calulate the index. The
actual elevations range
Low < 1000ft
High > 3000ft
The mixing height is not an equation but an algorithm. The ROS simply moves up a dry adiabat until it crosses the ambient temperature line. This is normally at an inversion level.
Transport winds are defined as the average wind speed and direction of all winds within the layer between the surface and the mixing height. An explanation of how to equate average transport winds will be given over the next few tiles.
First, since wind is a vector, the averaging process begins with the calculation of the zonal (U-component) and the meridional (V-component) of the wind at each level.
The meridional component of the
wind,V, is considered positive
when the wind is blowing from
south to north. A south wind has a positive meridional component
while a north wind has a negative meridional component. The zonal component of the wind,U, is considered positive when the
wind is blowing from west to east. Thus, a west wind has a positive zonal component and an east
wind a negative zonal component.
If the speed of the wind is (ff) and the direction in degrees is (dd), then the formula for obtaining the meridional component, V, and the zonal component, U, are:
V = -ff * cos(dd)
U = -ff * sin(dd)
Given the U and V components of the average wind speed, the following equation is used to calculate the direction of the transport wind:
The ventilation rate is calculated nationally by multiplying the transport wind by the mixing height in feet and dividing the result by a constant 5280. Fire officials want the ventilation rate calculated another way which renders the result non-dimensional. Since the result is non-dimensional, it is not considered a rate…therefore it is only given as a ventilation number.
(Transport wind speed) x (Mixing height) / (5280) = vent rate
mph ft constant ft^2/hr
FIRE OFFICIALS EQUATION:
(Transport wind speed) x (Mixing height) = vent number
mph ft miles ft/hr
ROS calculates using the fire officials equation. It also has to divide the final number by 3600. This is done so the answer can fit into the field width provided. These can be changed for individual station preferences.
The category day is basically an index taken from the ventilation number. These are the values that drive the index.
The dispersion index is calculated by dividing the mixing height by 1000, then multiplying the result by the transport wind speed(mph).
(mixing height) / (1000) x (transport wind speed) = disp index #
ft constant mph
These are the values that drive the index.
0-7 Very Poor
This field is very simple. The ROS simply takes the first level above the two meter surface and converts the speed into mph and gives the direction.
This is an extremely complicated field. It looks all too easy but the computations and algorithms that are used to find a value are immense. All of the computations used can not be shown but the main emphasis can be conveyed.
The ROS first computes the total daylight hours using latitude longitude and date. It then strips the TTSK group for each hour and associates the sky cover with an amount of time. This time is added and the total is subtracted from the total daylight hours.
The ROS is the only model with this capability.
The LAL is taken directly from Jeanne Hoadley of the National Weather Service in Missoula, Montana and Don Latham of the Intermountain Fire Sciences Laboratory’s work. The LAL is a “CONDITIONAL” value. In other words, one must have everything in place for thunderstorms to form before this field can be used.
The numbers calculated are taken from the CAPE…LI…and 700mb thetaE. Below are the associations.
LAL CAPE LI THETA-E
1 <100 >2 no thetaE max
2 100-500 2to-2 310-320
3 >500 -2to-4 320-340
4 >1000 <-4 >330
5 >=1500 <-4 >=340
6 RH<=60% along with LAL #3 requirements only.
Lightning frequency was basically taken straight from the LAL and observed data. It works over a 1…5…and 15 minute interval. It gives the amount of strikes that should be produced by any single thunderstorm cell. This field is also “CONDITIONAL.” The numbers are rounded to the nearest whole number. More work may be done on a local level to make this a stronger field. The following associations are what the ROS uses.
LAL FREQUENCY #STRIKES INTERVAL
1 0 0 CG 1-5-15
2 1 1 . 1-5 . 1-8 CG 1-5-15
3 2 1-2 . 6-10 . 9-15 CG 1-5-15
4 4 2-3 . 11-15 . 16-25 CG 1-5-15
5 5 3 . 15-25 CG 1-5-15
6 3 SAME AS LAL#3 ABOVE
This number uses the ambient temperature and the calculated relative humidity to find the heat index temperature. This field is extremely useful. By simply scanning the heat index numbers, one can quickly determine if the forecast may need to be watched more carefully over the next few days for heat advisory criteria. It uses the equation implemented by the National Weather Service. It is a seasonal field and is replaced by the wind chill index during the Fall. The following is the equation used:
HI = -42.379 + 2.04901523*TempF + 10.14333127*RH
- 0.22475541*TempF*RH - .00683783*TempF^2
- .05481717*RH^2 + .00122874*TempF^2*RH
This number uses the ambient temperature and the wind speed to find the wind chill temperature. This field is extremely useful. By simply scanning the wind chill numbers, one can quickly determine if the forecast may need to be watched more carefully over the next few days for wind chill advisory criteria. It uses the newest equation implemented by the National Weather Service. It is a seasonal field and is replaced by the heat index during the Spring. This equation does not account for solar radiation to the skin. This is to be added in the coming years by NOAA. When it is, this equation will be updated to show that change. The following is the equation used:
WC = 35.74 + 0.6215*TempF -35.75*windSpkt^0.16 + 0.4275*TempF*windSpkt^0.16