Climatology and Environments of Derecho-Producing Convective Systems

Climatology and Environments Climatology and Environments of Derecho-Producing of Derecho-Producing Convective SystemsConvective Systems

Mike Coniglio

CIMMS/OU

BAMEX Forecasters Workshop

March 18-19, 2003

OutlineOutline

• Derecho definitions & climatology of 15 May - 15 July events

• 500-mb flow patterns• Parameter distributions

– wind speeds derived from NCEP/NCAR Reanalysis

– proximity soundings

• progressive or swaths of wind gusts 26 ms-1 with a major axis length 400 km.

3 reports, separated by 64 km or more, of either F1 damage, or gusts 33 ms-1

• no more than 3 h can elapse between successive wind gust reports.

• multiple swaths of wind gusts must be a part of the same MCS and show linear/bowed radar signature

““Mid-End” Derechos (Johns and Mid-End” Derechos (Johns and Hirt, 1987)Hirt, 1987)





““Low-End” DerechosLow-End” Derechos





3 reports of F2 damage or gusts 40 ms-1 during the initial and mature stages

““High-End” DerechosHigh-End” Derechos

Distribution of all Derechos Distribution of all Derechos (131)(131)

Distribution “Low-End” Distribution “Low-End” Derechos (46)Derechos (46)

Distribution of “Mid-End” Distribution of “Mid-End” Derechos (54)Derechos (54)

Distribution of “High-End” Distribution of “High-End” Derechos (31)Derechos (31)

Temporal Distribution of all Temporal Distribution of all Derechos within BAMEX (99)Derechos within BAMEX (99)

0

2

4

6

8

10

12

14

16

18

20

00-02 02-04 04-06 06-08 08-10 10-12 12-14 14-16 16-18 18-20 20-22 22-00

TIME (UTC)

FR

EQ

UE

NC

Y

First Report

Midpoint

Last Report

Patterns associated with Patterns associated with Derechos (Johns, 1993)Derechos (Johns, 1993)

“Warm Season” Pattern “Dynamic” Pattern

Variability of 500-mb patterns Variability of 500-mb patterns among BAMEX events (99)among BAMEX events (99)

• Dominant synoptic-scale influence:– Ridge (39%)– Upstream trough (35%)

• Broad, long-wave trough (16%)

• Upstream trough/ridge couplet (12%)

• Upstream trough/zonal flow (8%)

– Zonal (13%)– Others (13%)

Ridge example:Ridge example:

Broad, Upstream Trough Broad, Upstream Trough example: example:

Upstream Trough/Ridge Couplet Upstream Trough/Ridge Couplet example: example:

Upstream Trough/Zonal Flow Upstream Trough/Zonal Flow example: example:

Zonal Flow example: Zonal Flow example:

Other example: Other example:

925-mb Wind Speeds Derived 925-mb Wind Speeds Derived from Large-Scale Analyses (99): from Large-Scale Analyses (99):

0

1

2

3

4

5

6

7

8

9

10

LOW-END (31) MID-END (40) HIGH-END (28)

925-

mb

WIN

D S

PE

ED

(m

/s)

0

5

10

15

20

25

30


500-

mb

WIN

D S

PE

ED

(m

/s)


0

5

10

15

20

25

30

35

40

45

50


200-

mb

WIN

D S

PE

ED

(m

/s)


CAPE/0-2.5 km shear Derived CAPE/0-2.5 km shear Derived from Proximity Soundings (38): from Proximity Soundings (38):

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30

0-2.5-km BULK SHEAR (m/s)

CA

PE

(J/

kg

)

LOW-END (11)

MID-END (17)

HIGH-END (10)

Median: 12.2 m/sIQR: 10.0-15.1 m/s

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30

0-5-km BULK SHEAR (m/s)

CA

PE

(J/

kg

)

LOW-END (11)

MID-END (17)

HIGH-END (10)

Median: 20.1 m/sIQR: 15.9-22.6 m/s

CAPE/0-5 km shear Derived CAPE/0-5 km shear Derived from Proximity Soundings (38): from Proximity Soundings (38):

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 5 10 15 20 25 30

5-10-km BULK SHEAR (m/s)

CA

PE

(J/

kg

)

LOW-END (11)

MID-END (17)

HIGH-END (10)

Median: 11.8 m/sIQR: 7.5-18.3 m/s

CAPE/5-10 km shear Derived CAPE/5-10 km shear Derived from Proximity Soundings (38): from Proximity Soundings (38):

Vertical RH Distribution Derived Vertical RH Distribution Derived from Proximity Soundings (38):from Proximity Soundings (38):

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

0 10 20 30 40 50 60 70 80 90 100

RELATIVE HUMIDITY (%)

HE

IGH

T (

km A

GL

)

10th90th

25th75thMedian

90 % of cases have RH < 58% at ~3 km

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

315 320 325 330 335 340 345 350 355 360 365 370

EQUIVALENT POTENTIAL TEMP (K)

HE

IGH

T (

km A

GL

)

10th 90th25th 75thMedian

90 % of cases have e < 331 at ~4-5 km

Medain e drops~27 K in 0-5 km

Vertical Vertical ee Distribution Derived Distribution Derived

from Proximity Soundings (38):from Proximity Soundings (38):

SummarySummary• Climatological distributions

– “Low-End” events favored in southern & eastern portions of BAMEX domain

– “High-end” events favored in northern corridor– Temporally, peak in midpoints spread between 2000-0800

UTC

• 500-mb large-scale patterns– Upstream trough occurs with nearly equal frequency to

“classic” warm-season derecho pattern– Remaining events (26%) occur under zonal flow and mixture

of the three regimes

Summary (cont.)Summary (cont.)• Parameter distributions

– 500 and 200-mb wind speeds (derived from NCEP/NCAR Reanalysis) are significantly larger for “high-end” events

– 0-2.5 km shear is mostly weak to moderate; 0-5 km usually shear moderate to strong

– Shear above 5 km is usually non-zero mid-upper-level environment is usually baroclinic

– 3-4 km AGL is often relatively dry

– Vertical decrease in e relatively large large convective instability

Climatology and Environments of Derecho-Producing Convective Systems

Documents

multiple swaths of wind

successive wind gust

mb wind speeds

upstream trough example

distribution lowend

ridge example

reports of f2 damage

f1 damage