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Depicting LAMP probabilities and uncertainty in best category forecast N ew LAMP web page product Judy E. Ghirardelli Scott Scallion National Weather Service Meteorological Development Laboratory. How we make our “best category” selection in LAMP. Development: - PowerPoint PPT Presentation
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Depicting LAMP probabilities and uncertainty in best category forecast
New LAMP web page product
Judy E. GhirardelliScott Scallion
National Weather ServiceMeteorological Development Laboratory
How we make our “best category” selection in LAMP
• Development:– Thresholds are statistically developed by one of two techniques,
either:♦ Targeting unit bias (forecast the event as often as it occurs),
or♦ Maximizing the threat score within a bias range
– Thresholds vary by region, start time, projection, element, category, etc.
• Implementation:– LAMP compares the probability of the category to the threshold
for the category– LAMP starts with the rarest category and goes to the most
common category– The first category whose probability exceeds its threshold is the
chosen category
0
20
40
60
80
Clear Few Scattered Broken Overcast
Forecast Probability
Threshold Value
LAMP Categorical Forecast Selection Process
Pro
bab
ility
(%
)
Does the probability
equal or exceed the threshold?
The probability of “few” exceeds the threshold value for “few” – therefore LAMP categorical forecast is “few”
Category 1 Category 4Category 3Category 2 Category 5
Does the probability
equal or exceed the threshold?
Does the probability
equal or exceed the threshold?
Does the probability equal
or exceed the threshold?
Depicting Probabilistic Information
Take the “simple” example of Probability of Precipitation, which is a yes/no decision. If the probability exceeds the threshold, then the category chosen is “yes.” If not, the category chosen is “no.”
Depicting Probabilistic Information
Purpose: indicate to user the uncertainty associated with the Best Category forecasts given the probabilistic information
Threshold = dashed black line
Probability < thres = green line
Probability ≥ thres = red line
San Francisco – very small chance
of precip
St. Louis – slight chance of precip
Chicago – slight chance yes and slight
chance no precip
St. Cloud – high chance of precip
Depicting Probabilistic Information
Now take the more complicated example of visibility, which has multiple categories to choose.
The probability of vis < 1 mile (solid line) does not exceed the threshold (dashed line). Look to next
rarest category.
LAMP Probabilities and Thresholds for Flight CategoriesThreshold Plot Tab
Look at rarest of these categories
first.
LAMP Probabilities and Thresholds for Flight CategoriesThreshold Plot Tab
Look at next rarest of these
categories.
The probability of vis < 3 miles (solid line) exceeds the threshold (dashed line) only for the last hour;
therefore this condition is indicated for only that hour. Look to next rarest category to determine the
conditions for other hours.
LAMP Probabilities and Thresholds for Flight CategoriesThreshold Plot Tab
Look at next rarest of these
categories.
The probability of vis ≤ 5 miles (solid line) DOES exceed the threshold (dashed line) at times; therefore
this condition is indicated for those times.
Note that vis ≤ 5 is not chosen for the last hour, because a rarer condition (vis < 3 miles) was already
indicated.
LAMP Probabilities and Thresholds for Flight CategoriesThreshold Plot Tab
Show all together.
Looking at these categories, look at the rarest first, then the next rarest, etc. The condition indicated is the rarest probability which exceeds its threshold.
This is indicated by the red probability line.
Depicting Probabilistic Information
In addition to the previous kinds of plots, we are also offering a web page that shows one category’s probability and threshold at a time, and color codes the confidence in choosing that category by indicating how close the probability was to the threshold. One would have more confidence in a chosen category if the probability exceeded the threshold by a large amount, compared to the probability just barely exceeding the threshold.
Red=YesProbability exceeds threshold by more
than 10%
Orange=LikelyProbability exceeds
threshold but NOT by more than 10%
Yellow = ChanceProbability is less than threshold but
within 10%
Cyan = NoProbability is less than threshold by more than 10%
LAMP Probabilities and Thresholds for Flight CategoriesUncertainty Plot Tab – looking at vis ≤ 5 miles
Note that this shows you one condition (e.g., vis ≤ 5 miles). To determine the most likely condition, you
should consider the rarest conditions first.
Depicting Probabilistic Information
• New LAMP web pages coming soon:– Uncertainty plots - station selection page:
♦ http://weather.gov/mdl/gfslamp/uncertform.php♦ Accessible from the main GFS-LAMP Realtime Products
page:■ http://weather.gov/mdl/gfslamp/gfslamp.shtml
– Uncertainty plots - direct access:♦ http://weather.gov/mdl/gfslamp/uncertplots.php
– Threshold plots - direct access:♦ http://weather.gov/mdl/gfslamp/threshplots.php
Depicting Probabilistic Information
• Documentation on the new page:– http://weather.gov/mdl/gfslamp/docs/uncertplots_info.shtml
• For questions or comments, contact:– Judy.Ghirardelli@noaa.gov (LAMP Task Leader)– Scott.Scallion@noaa.gov (LAMP Developer and
Web Master)
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