Matthew Vaughan, Brian Tang, and Lance Bosart
Department of Atmospheric and Environmental Sciences
University at Albany/SUNY
Albany, NY 12222
NROW XV
Nano-scale College South Auditorium
Albany, New York
Thursday 13 November 2014
Supported by the NOAA Collaborative Science,
Technology and Applied Research Program
 CSTAR
initiative to investigate severe
convection with low predictive skill

Cooperation between SUNY-Albany and NWS
offices at ALB, BGM, and PIT
 Improve
forecasting skill of severe
convection by focusing study on
environments with poor predictive skill
 Identify
and evaluate poor forecast
performance
 Use
forecasting performance as a proxy for
predictability

Underlying assumption: If forecasters had trouble, the
event had low predictability.

Create Northeast domain to evaluate forecast
skill

Plot SPC convective outlook contours over the
domains.

Verify SLIGHT contours with storm reports

Sound familiar?


Hitchens and Brooks (2012) evaluated SLIGHT contours
over CONUS domain
MOD and HIGH contours were treated the same as SLIGHT

Algorithm details




40-km grid spacing
Use 0600 UTC SLIGHT risk valid 1200-1200 UTC
Plot all valid storm reports for forecast period
Every grid point <40km from report is designated: “hit”
Legend:
= False Alarm (grid)
= Correct Hit (grid)
= Missed report
 Analysis
grid over the Northeast
=
=
=
=
=
Legend:
False Alarm (grid)
Correct Hit (grid)
Missed report
Correct Hit (report)
Incorrect Hit (grid)
 For
inclusion in the 1980-2013 dataset, an
event must meet 1 of 2 criteria:

Have a SLIGHT risk contour within the NE domain

Contain at least 20 reports within the domain

Given a SLIGHT in NE, 20 reports = 55th percentile
 Event
days = 1508
 SLIGHT
 Events
days = 1331
>20 reports without SLIGHT = 177
Probability of Detection (Yearly Median)
100
90
80
70
POD
60
50
40
30
20
10
0
Northeast
Median Reports per Event
120
100
Northeast
Reports
80
60
40
20
0
False Alarm Ratio (Yearly Median)
100
90
80
70
FAR
60
50
40
Northeast
30
20
Linear
(Northeast)
10
0
Year
Cumulative Annual SLIGHT Area
14000
Northeast Gridpoints
12000
10000
8000
6000
4000
2000
0
Northeast
Critical Success Index (Yearly Median)
0.4
Northeast
0.35
0.3
Linear
(Northeast)
CSI
0.25
0.2
0.15
0.1
0.05
0
Year
 Type
Type 3


Low
POD
High
FAR

Type 1

Type 2
20+ reports;
Lowest 25th
percentile POD
 Type

1
2
Highest 75th
percentile FA area
Lowest 25th
percentile severe
report area
No events meet Type 3 requirements as defined here

N = 189 events

N = 66 events

25th POD percentile =
2.15%

All but 4 events have
FAR > 95%
Median: 2.5 reports
per event
Average: 3 reports
per event

All but 3 events have POD
=0

Median: 37 reports per
event


Average: 50 reports per
event

Type 1
Type 2
Type 1 (Low POD) Occurrence
18
16
Annual Occurrences
14
12
10
8
6
4
2
0
Type 1 Monthly Climatology
60
48
50
Occurences
42
40
35
30
22
20
10
15
9
4
2
4
3
0
Jan
Feb Mar
Apr May Jun
Jul
Month
Aug Sep
4
1
Oct Nov Dec
Type 2 (High FAR) Occurrence
7
Annual Occurrences
6
5
4
3
2
1
0
Type 2 Monthly Climatology
25
20
Occurences
20
15
13
13
9
10
5
0
3
0
Jan
0
3
1
Feb Mar
3
1
Apr May Jun
Jul
Month
Aug Sep
0
Oct Nov Dec
 0.5°

Climate Forecast System Reanalysis (CFSR)
Chose morning (1200 UTC) for following analysis.
 Type
1 centered on maximum report density
 Type
2 centered at centroid of SLIGHT risk
region

Chose largest of SLIGHT risk contours for composite
center
Percentage of 20+ report
events that are Type 1
other N
4% 4%
100%
90%
80%
NW
10%
70%
60%
Type 1 500 hPa Flow
Distribution
N=7
SW
32%
50%
N=5
40%
N=60
30%
N=95
N=20
20%
W
50%
10%
0%
N
S
SW
W
NW
500 hPa wind direction
Geopotential
height (meters;
contoured every
100 m), wind speed
(knots; fill), and
wind vector (knots;
barbed) on the 250
hPa pressure
surface. The red
dot indicates
event-composite
center and the
median location of
the maximum
report density.
250 hPa
N=60
Geopotential
height (meters;
contoured every 40
m) and total
wind(knots;
barbed) on the 500
hPa pressure
surface. The red
dot indicates
event-composite
center and the
median location of
the maximum
report density.
500 hPa
N=60
Geopotential
height (meters;
contoured every 25
m), relative
humidity (%; fill
contoured every
5%) on the 700 hPa
pressure surface.
The red dot
indicates eventcomposite center
and the median
location of the
maximum report
density.
700 hPa
N=60
Geopotential
height (meters;
solid contour every
20 m),
temperature
(Celsius; dashed),
and wind vector
(knots; barbed) on
the 850 hPa
pressure surface.
The red dot
indicates eventcomposite center
and the median
location of the
maximum report
density.
850 hPa
N=60
MSLP (hPa;
contoured every 2
hPa), precipitable
water (mm; fill),
and total surface
wind (knots;
barbed). The red
dot indicates
event-composite
center and the
median location of
the maximum
report density.
Surface
N=60
700-500 hPa lapse
rates (°C/km;
contoured every .5
°C/km), MUCAPE
(J/kg; fill), and
1000-500 hPa shear
vector (knots;
barbed). The red
dot indicates
event-composite
center and the
median location of
the maximum
report density.
CAPE & Shear
N=60
N Type 2 500 hPa Flow Distribution
2%
N=1
NW
9%
N=6
SW
41%
N=27
W
48%
N=32
Geopotential
height (meters;
contoured every
100 m), wind speed
(knots; fill), and
wind vector (knots;
barbed) on the 250
hPa pressure
surface. The red
dot indicates
event-composite
center and the
median location of
the centroid of the
NE SLIGHT risk
areas.
250 hPa
N=32
Geopotential
height (meters;
contoured every 40
m) and total
wind(knots;
barbed) on the 500
hPa pressure
surface. The red
dot indicates
event-composite
center and the
median location of
the centroid of the
NE SLIGHT risk
areas.
500 hPa
N=32
Geopotential
height (meters;
contoured every 25
m), relative
humidity (%; fill
contoured every
5%) on the 700 hPa
pressure surface.
The red dot
indicates eventcomposite center
and the median
location of the
centroid of the NE
SLIGHT risk areas.
700 hPa
N=32
Geopotential
height (meters;
solid contour every
20 m),
temperature
(Celsius; dashed),
and wind vector
(knots; barbed) on
the 850 hPa
pressure surface.
The red dot
indicates eventcomposite center
and the median
location of the
centroid of the NE
SLIGHT risk areas.
850 hPa
N=32
MSLP (hPa;
contoured every 2
hPa), precipitable
water (mm; fill),
and total surface
wind (knots;
barbed). The red
dot indicates
event-composite
center and the
median location of
the centroid of the
NE SLIGHT risk
areas.
Surface
N=32
700-500 hPa lapse
rates (°C/km;
contoured every .5
°C/km), MUCAPE
(J/kg; fill), and
1000-500 hPa shear
vector (knots;
barbed). The red
dot indicates
event-composite
center and the
median location of
the centroid of the
NE SLIGHT risk
areas.
CAPE & Shear
N=32
 Assess

variability in composites
Analyze deviation among cases and reassess
compositing method
 Compare
Type 1 & Type 2 flow regimes to
cases with good predictive skill scores

May extend comparison to events of similar scale
 Expand

composites
Investigate variables identified in Hurlbut and
Cohen (2014)
 NE


Flat POD, decreasing FAR, increasing CSI
Number of reports per event increasing
 NE



predictive skill
low predictive skill event climatology
Type 1: 5 median events per year (Trending up)
Type 2: 2 median events per year (Trending down)
Peak in warm season
 Most
cases with low predictive skill follow
climatology except rare N-ly, S-ly flow
 Type

Westerly

Anticyclonic side of jet, relatively low humidity at 700
hPa, higher mid-level lapse rates
 Type

1 (Low POD)
2 (High FAR)
Westerly

Anticyclonic side of jet, higher 700 hPa humidity, higher
precipitable water values, more confluent 850 hPa flow