Transcript Weather Briefing

NWCC Lightning Prediction
Oregon AMS
Feb 28 2012
John Saltenberger
NWCC Predictive Services Decision Support
Fire Workload
–Mobilization
–Logistic Planning
–GMAC support
• Prioritizing
• Pre-positioning
3-5 day planning
window is crucial!
2004-5-6
2011
2005
2007
2003
2002
2002
2008-9
2006
Synoptic
Number
of
Does
analysis
of
the
Wind Index
Reported Fires
Observed
historical
record
reveal
Fire
Lapse
Danger
Rates
relationships between
Number of
Large Fires
lightning and wildfire
frequency and/or size?
Observed
Lightning
Level
Map
Type
Lightning Ignition facts
• Roughly half of Oregon & Washington
wildfires result from lightning.
• However, up to 75% of large wildfires are
from lightning in some areas.
• …but only 7% of thunderstorm outbreaks
result in large fires (3 to 4% west side).
NWCC strives to identify those
few critical lightning events.
Lightning Forecasting
Phase 1
Map typing
Clustering 500mb map types
500mb hgt grid GFS 500mb init
Clustering to identify map types
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500mb hgt grid
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500mb hgt grid
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Create
a column
for each
daily
500mb hgt
grid
Clustering to identify map types
500mb hgt grid 13 500 mb maps
N
N
Y
NN
Y
Y
Y
Y
NY Y
Record 500mb
map type for
every day in fire
season.
Record if any
lightning
occurred in each
PSA during those
same days.
PSA E4:
Total days with map type 1:
36
Total days with map type 1
and any lightning:
Historical probability:
6
16%
E4
Lightning
More frequent
lightning
Most
problematic
Lightning Forecasting
Phase 2
GIS support
0
0
2
0 0
3
5
7
1
01 1
Use GIS to count
how many strikes
in each PSA on
every day of fire
season.
(categorized into
10 decile bins
based on strike
count history)
PSA E4:
Total days with map type 1:
36
Total days with map type 1
and Lightning Level 5:
Historical probability:
3
8%
E4
E4
Lightning Forecasting
Phase 3
Logistic Regression
Fine tuning
the forecast
Smaller 20 pt grid
Archive daily 00Z
and 12Z initialized
GFS variables at
each gridpoint
DAILY ARCHIVES OF INITIALZED GFS DATA
• 850, 700, 500mb heights and thickness
• 850-700mb and 700-500mb Lapse Rates
• 500 mb Temperature, Dew Pt & RH
• 700 mb Temperature,
Dew Ptmethod!
& RH
Perfect
Prog
• Column Precipitable Water
• U and V components of 700 mb and 500 mb wind
• CAPE, LI, Totals, 700mb Theta-e
Historical PSA lightning prob for each map type
2000-2011
Logistic regression
Best predictors
occurrence & amount
• Map Type probability
• 700-500 mb Lapse Rt
• 500 mb Temperature
• Precipitable Water
• 700 mb Rel Hum
• quadratic/cubic bias
2011 PSA
Probability
and Amount
0% 45%
25% 30%
Each PSA was
assigned a value
of probability
and LL weighted
from nearby grid
boxes known to
be significant
E4
E4
Lightning Forecasting
Phase 4
Logistic Regression
applied to forecasting
Probability Forecasts of a
Binary (Yes or No) Event
At what confidence of probability
percentage do I commit to
saying an binary event is going
to happen?
40%? 50%? 60%?
POD
Probability of Detection
(how many cases correctly forecast?)
FAR
False Alarm Rate
(how many cases forecast
…but did not occur?)
As POD increases,
so does FAR
…or…
As FAR decreases, so
does POD
40%? 50%? 60%?
GOAL:
Define the confidence
percentage to maximize
POD until FAR
becomes unacceptable
40%? 50%? 60%?
POD:
FAR:
NWCC’s GOAL:
Experiment with defining
the (Y/N) confidence
percentage until…
POD rises to 67%
…or…
FAR falls to 49%...
Lightning
• Best predictors at each
gridpoint are populated
from the 00Z or 06Z
GFS via a perfect prog
type scheme to
objectively forecast:
– Lightning YES/NO
– Mostly likely LL
(percentile rank bin)
Large Fire Probability
• Significant fire probability during lightning
events (for each PSA) is determined by:
– The forecasted lightning amount (decile)
– A pro-rated likely number of ignitions
– The fraction of those ignitions that become
historically have become “large”
– Forecasted fluctuation in the Fire Danger
Historical Large Fire Probability
From Multiple Ignitions
47 ignitions
21 ignitions
19 ignitions
5 ignitions
3 ignitions
Historical Large Fire Probability
From Multiple Ignitions
LOW FIRE DANGER
Historical Large Fire Probability
From Multiple Ignitions
HIGH FIRE DANGER
Fire Activity Forecast 2012
5-Day Forecasted Fire Activity
High Risk
Event
Forecasted
Activity
PSA
C2
Large Fire
Probability
Forecasted
Ignitions
Lightning
Today
Wed
Lightning
Thu
Unstable
Fri
Sat
0%
1%
52%
1%
10%
5-Day
Total
1
4
15
4
8
32
6 to 10 Day Outlook based on Historical Fire Occurrence
Climatology
PSA
C2
Large Fire
Probability
Climo
Ignitions
Sun
Mon
Tue
Wed
Thu
0%
0%
0%
1%
2%
5-Day
Total
1
1
2
4
6
14
Initial Attack Overwhelmed by:
Sheer number of ignitions
R
U
W
Severity of atmosphere
Thank You!