Transcript Evan Lowery Dr. Eric Hoffman Northeast Regional Operational Workshop IX - Northern New England thunderstorms pose a forecasting challenge - Large-scale flow has often been.

Evan Lowery
Dr. Eric Hoffman
Northeast Regional Operational Workshop IX
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Northern New England thunderstorms pose a forecasting challenge
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Large-scale flow has often been used as a forecasting tool
Few thunderstorm climatologies have been completed across
northern New England
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How does large-scale flow affect the development and intensity of
northern New England thunderstorms during the warm-season months
April – September (2003 – 2007)?
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Questions
1. How can thunderstorms be identified and monitored?
2. How can the pre-convective environment be analyzed?
3. How can large-scale flow be identified for each thunderstorm cell?
4. How can results be objectively analyzed?
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
“Vertically integrated liquid (VIL) water content of thunderstorms has been
shown to be a good indicator for the potential of severe weather.” Winston and
Ruthi (1986) Grasso and Hilgendorf (2001)
a. cell-based or gridded VIL?
b. VIL limitations
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
FIG 1: Miller (2007)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL?
(VIL: cell-based)
b. Limitations of VIL
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
25 km
25 km
125km
km
125
FIG 2: FMiller
IG 3: and
Brown
Sirvakta
(2000)(2007)
How does large-scale flow affect the development
and intensity of northern New England
thunderstorms?
25 km from RDA
125 km from RDA
FIG 4: VIL sampling region (25 – 125 km from KGYX)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL?
(VIL: cell-based)
b. VIL limitations?
(Range: 25 – 125 km)
c. VIL threshold for thunderstorms?
d. Which radar product will be used?
“VIL values in organized convective cells usually exceeded 10 kg m-2.”
Kitzmiller et al. (1995) Brimelow (2006)
“A VIL threshold of 25-30 kg m-2 was effective at correctly identifying
those storms associated with the severe hail over central Alberta.”
Brimelow (2006)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL?
(VIL: cell-based)
b. VIL limitations?
(Range: 25 – 125 km)
c. VIL threshold for thunderstorms?
(Threshold: 10 kg m-2)
d. Which radar product will be used?
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
FIG
FIG
4:
5:
6:7:
NCDC
NCDC
Java
Java
NEXRAD
NEXRAD
Viewer
Viewer
(Short
(Storm
(Storm
range
structure
structure
reflectivity
product
product
06/19/2006)
06/19/2006)
06/19/2006)
FIG 9:
8: NCDC Java NEXRAD Viewer (Storm structure alphanumeric table 06/19/2006)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
a. cell-based or gridded VIL?
(VIL: cell-based)
b. VIL limitations?
(Range: 25 – 125 km)
c. VIL threshold for thunderstorms?
(Threshold: 10 kg m-2)
d. Which radar product will be used?
(Storm Structure)
WSR-88D Level III Storm Structure Product (Gray/Portland, ME)
How accurately can the storm structure product track storms?
“The results show that cells above 40 dBz have a 68% of being detected and
that cells with reflectivities above 50 dBz have a 96% chance of being
detected.” Johnson et al. 1998
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
CRITERIA
VIL:
cell-based
Range:
25 – 125 km from GYX
Min VIL:
10 kg m-2
Min Reflectivity:
50 dBz
Min Duration:
> 1 Volume scan
WSR-88D Product:
Storm Structure
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
1. How can thunderstorms be identified and monitored?
NLDN Lightning strikes Vs. VIL values June – August (2005)
Radar Identified Storms With CG Lightning (%)
% (Lightning Count / Total Count)
100
95
90
89.8
85
80
75
70
65
60
55
50
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
VIL
FIG 10: VIL (kg m-2) Vs. Lightning Count (%)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
2. How can the pre-convective environment be analyzed?
Proximity Soundings
a. Def. proximity sounding?
“Proximity refers to events which are required to occur within 3 h of
the sounding time and within 100 nautical miles (185 km) in space.
Craven (2001), Craven et al. (2002a,b), and Brooks (2003)
b. Which Reanalysis dataset should be used?
“It is expected that the NARR data set will show the mesoscale detail
in weather systems, particularly severe weather, that the coarser
NCEP/NCAR GR would miss.” Grumm (2005)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
3. How can large-scale flow be identified for each thunderstorm?
700 hPa is “the first mandatory pressure level that is clearly above the
underlying terrain.” Wasula and Bosart (2002)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
4. How can results be objectively analyzed?
Radar Data Objective Analysis
Interpolation Method:
Isotropic Barnes Analysis
wq = exp(-r’2/k)
k = k*[(2Δaz)2max]
Trapp and Doswell (2000)
k
32.8
k*
0.5
2Δaz
232km [1o (π/180)]
grid spacing
4 km
radius of influence
3 * grid spacing
min. # obs
3
R = 232 km
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Monitoring Storm Cell Intensity
- Find radar indicated start time
- Find location of Max intensification (ΔVIL/Δt)
- Find location of Max intensity (VIL)
- Find location of Max Weakening (ΔVIL/Δt)
- Find radar indicated end time
- Download relevant NARR data
- Identify large-scale flow (925, 700 hPa) per storm
- Stratify results by large-scale flow
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
-
231 events
-
3238 thunderstorm cells meet criteria
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700 hPa Flow: (SW=1921, W=651, NW=599, SE=45, NE=22)
Total Storm Cells Per Flow (700 hPa)
2500
1921
# Storm cells
2000
1500
1000
651
599
W
NW
500
0
22
0
45
NE
E
SE
SW
Flow
FIG 11: Thunderstorm cells per flow regime (700 hPa)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Yearly, Monthly, and Diurnal distribution
Total
Storm
Cells
PerHour
Month
(700hPa
hPaFlow)
Flow)
Total
Storm
Total
Storm
Cells
Per
Cells
Per (700
Year
800
900 300
792
800 700
730
250
749
700 600
500
400
300
200
593
200
# Storm Cells
cells
## Storm
Storm cells
600
500
NE NE
400
150
374
300
E
SE
SE
SW SW
100
W
200
W
NW NW
50
100 100
0
E
00
0
2003
1 42
3
4
5
5620047
8
9
10
6 112005
12 13 14
7 15 16 2006
17 188 19 20 21 2007
22 9 23
HourYear
Month
(UTC)
FFFIG
IG
IG12:
13:
14:Yearly
Monthly
Diurnaldistribution
distribution
distribution
ofof
of
thunderstorm
thunderstorm
thunderstorm
cells
cells
cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Focus on 4 Flow Regimes
Level, Flow
# Events
# Thunderstorm cells
925 hPa, SE
49
274
700 hPa, SW
150
1921
700 hPa, W
79
651
700 hPa, NW
73
599
Northern New England Terrain Map
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
925 hPa SE Flow
49 events
Storm Density [count / area * 100]
274 thunderstorm cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa SW Flow
Storm Density [count / area * 100]
High
Storm Density
150 events
1921 thunderstorm cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa W Flow
Storm Density [count / area * 100]
High
Storm Density
79 events
651 thunderstorm cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
700 hPa NW Flow
Storm Density [count / area * 100]
High
Storm Density
73 events
599 thunderstorm cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Stability Assessment
700 hPa Flow
CAPE [ J / kg ]
CAPE(J/kg)
0
Stable
0-1000
Marginally unstable
1000-2500
Moderately unstable
Highest CAPE values
south of
2500-3500
Very unstable
mountains and away
from coast
≥3500
Extremely
unstable
Avg MU CAPE (700 hPa Flow): All Storms
1600
CAPE [ J / kg ]
1400
1200
NE
1000
E
800
SE
600
SW
400
W
200
NW
0
79
73
150events
events
Flow
FIG 15: Avg CAPE per 700 hPa Flow Regime
651
599
1921thunderstorm
thunderstormcells
cells
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
Thunderstorm cells (VIL ≥ 23 kg m-2, Ref ≥ 50 dBz, Range ≥ 25 km and ≤ 125 km, > 1 Volume scan)
Stability Assessment
Total Totals Index
43
Total Totals [-]
53
TT = (T850 + Td850) - (2 * T500)
Thunderstorms
Severe thunderstorms possible
Severe thunderstorms likely,
tornadoes possible
Avg TT (700 hPa Flow): All Storms
50
45
40
Total Totals [-]
44
50
≥ 55
700 hPa Flow
35
NE
30
E
25
SE
20
SW
15
W
10
NW
5
0
Flow
FIG 15: Avg. TT per 700 hPa Flow
FIG 26: Total Totals Histogram (700 hPa SW Flow)
How does large-scale flow affect the development and intensity of northern New England thunderstorms?
SW Flow
has the largest number of thunderstorm cells
925 hPa SE Flow
thunderstorm cells develop along mountains
700 hPa SW, W, NW Flow localized concentrations of thunderstorm cells
Total Totals
low variability across all flow regimes
Ongoing Research
- Compare:
Severe Vs. non-severe days
Short, medium, long duration storms
- Generate soundings
Severe Vs. non-severe days
Short, medium, long duration storms
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http://amsglossary.allenpress.com/glossary/search?id=vertically-integrated-liquid1
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208-220.
2,
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