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Roll or Arcus Cloud. Supercell Thunderstorms. Storm split 1. Storm Split 2. Storm split 3. Squall Lines. Bow Echoes and Derechos. DC Derecho: June 10, 2013. Often Associated with Strong Straight Line Winds Known as “Derechos”.

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Storm split 1

Storm Split 2

Storm split 3





Often associated with strong straight line winds known as derechos
Often Associated with Strong Straight Line Winds Known as “Derechos”

  • These straight-line winds may exceed 100 miles per hour, reaching 130 miles per hour in past eventshttp://www.youtube.com/watch?v=EGJmOeDEBtw

  • Great Derecho Website:

    http://www.spc.noaa.gov/misc/AbtDerechos/derechofacts.htm




June 2012 derecho
June 2012 Derecho “Derechos”

  • Wind gusts increased substantially, peaking as high as 91 mph (147 km/h) in Fort Wayne, Indiana

  • Extremely hot and highly unstable atmosphere with CAPE values in excess of 5,000 J/kg. Temperatures on the south side of a stationary front were in excess of 100F.


Derecho prediction
Derecho Prediction “Derechos”

  • Warm season derechos in the Northern Hemisphere form in west to northwesterly flow at mid levels with moderate to high levels of instability (CAPE).

  • Derechos form within environments of low-level warm air advection and significant low-level moisture


Numerical simulation of convection
Numerical Simulation of Convection “Derechos”

  • High resolution simulates cable of explicitly resolving convection have been run in research mode.

  • It appears that such numerical model can provide great insights into the conditions necessary for convection and how varying environments influence convective evolution.


Meted convective storm matrix
METED Convective Storm Matrix “Derechos”

  • http://www.meted.ucar.edu/convectn/csmatrix/

  • Allows you to experiment with instability and shear and view how the storms evolve.



Explicit convective prediction
Explicit Convective Prediction “Derechos”

  • Requires high resolution (4km or less grid spacing)

  • Requires high-resolution analysis of current situation, using radar, surface observations and all other assets.

  • NCAR (WRF model) and CAPS (Oklahoma, ARPS model) are two leading efforts.


10 km WRF forecast domain “Derechos”

4 km WRF forecast domain

Bow Echo and Mesoscale Convective Vortex Experiment (BAMEX)

Using the WRF Model

Goal: Study the lifecycles of mesoscale convective vortices and bow echoes in and around the St. Louis MO area

Field program conducted 20 May – 6 July 2003


Real-time WRF 4 km BAMEX Forecast “Derechos”

Initialized 00 UTC 9 June 03

Reflectivity forecast

Composite NEXRAD Radar


Real-time WRF 4 km BAMEX Forecast “Derechos”

Valid 6/10/03 12Z

4 km BAMEX forecast 36 h Reflectivity

4 km BAMEX forecast 12 h Reflectivity

Composite NEXRAD Radar


Real-time WRF 4 km BAMEX Forecast “Derechos”

Initialized 00 UTC 10 June 03

Reflectivity forecast

Composite NEXRAD Radar


Real-time 12 h WRF Reflectivity Forecast “Derechos”

Valid 6/10/03 12Z

4 km BAMEX forecast

10 km BAMEX forecast

22 km CONUS forecast

Composite NEXRAD Radar


Real-time WRF 4 km BAMEX Forecast “Derechos”

Initialized 00 UTC 30 May 03

Reflectivity forecast

Composite NEXRAD Radar


Real-time WRF 4 km BAMEX Forecast “Derechos”

Valid 5/30/03 23Z

23 h Reflectivity Forecast

Composite NEXRAD Radar

Line of

Supercells


Realtime WRF 4 km BAMEX Forecast “Derechos”

Valid 6/23/03 06Z

30 h Reflectivity Forecast

Composite NEXRAD Radar

6” hail 00Z

Squall line


Realtime WRF 4 km BAMEX Forecast “Derechos”

Initialized 5/24/03 00Z

Reflectivity Forecast

Composite NEXRAD Radar

12 h

Squall line

24 h

Persists

Dissipates


Preliminary BAMEX Forecast Verification “Derechos”

Mode for corresponding convective systems

For Convective Mode 2 or 3

Yes

No

Probability of detection (POD) = 79%

False alarm rate (FAR) = 29%

(Done, Davis, and Weisman)


A High-Resolution Modeling Study of the 24 May 2002 Dryline Case during IHOP(Xue and Martin 2006a,b MWR)Goal: Understand exactly WHEN, WHERE, HOW convection is initiated


Time and location of initiation loop time 17utc 22 utc
Time and Location of Initiation Case during IHOP(Loop time: 17UTC – 22 UTC)


Surface analysis satellite images
Surface Case during IHOPanalysis + satellite images

From Wakimoto et al.

(2006 MWR).

2000

1900

2200

2100


18 UTC May 24, 2002 I.C. Case during IHOP

3 km / 1km grid


Model configurations
Model Configurations Case during IHOP

CI ~ 2000UTC

  • ARPS model with full physics, including ice microphysics + soil model + PBL and TKE-SGS turbulence

1800 UTC

0000 UTC

1200 UTC

0006 UTC

3km

1km

ADAS

ADAS


t=3h, 2100 UTC Case during IHOP

sfc. winds, qv, and composite reflectivity


t=4h, 2200 UTC Case during IHOP


t=5h, 2300 UTC Case during IHOP


t=3h, 2100 UTC Case during IHOP


2000 UTC 2015 UTC 2030 UTC 2045 UTC

t=2h t=2h 15min t=2h 30min t=2h 45min

C

C

B

B

B

A

A

A

C

B

A


Bottom line
Bottom Line 2045 UTC

  • High resolution NWP can often predict the mode of the convection correctly, even a day ahead (supercell, bow echo, scattered convection).

  • Skill in predicting the magnitude and location of convection fades out quickly after only a few hours.

  • Predictability is lengthened when there is strong, large scale forcing (e.g,. front or dry line)


The future of convective forecasting
The Future of Convective Forecasting 2045 UTC

  • Clearly, there is substantial uncertainty that must be considered.

  • A major requirement is for there to be large convection-resolving ensembles run operationally (25-100 members), with varying initializations and physics.

  • Need for better initializations to describe the detailed 3D configuration of the lower atmosphere (using all assets: commuter aircraft, mesosnets, satellite data, etc.)



Storm prediction center ensemble of opportunity
Storm Prediction Center Ensemble of Opportunity 2045 UTC

  • Based on 7 high-resolution deterministic forecasts run by a variety of groups.


Another major advancing tool high resolution rapid refresh particularly for next few hours
Another Major Advancing Tool: High Resolution Rapid Refresh: Particularly for Next Few Hours.


The u s storm prediction center
The U.S Storm Prediction Center Refresh: Particularly for Next Few Hours.


Storm prediction center
Storm Prediction Center Refresh: Particularly for Next Few Hours.

  • Main U.S. entity responsible for severe weather forecasting.

  • Coordinates between NWS forecast offices, who also important players for their areas.


Forecasting of convection summary
Forecasting of Convection Refresh: Particularly for Next Few Hours.Summary

  • The big challenge is to predict the environment in which convection will develop.

  • Parameters such as vertical instability (CAPE), wind shear and helicity, low-level thermal and moisture structures, CIN, etc.

  • These can change rapidly with large mesoscale variations.


Major ingredients for general convection
Major Ingredients for General Convection Refresh: Particularly for Next Few Hours.

  • Convective or conditional instability

    • Lifting turns convectively unstable sounding to a conditionally unstable sounding

    • Negative LI

    • High CAPE

    • Low LFC

    • CAPE is more useful than LI

  • Moist layer near the surface

    • Generally Td > 53F needed.

  • An initiator

    • Source of upward motion (front, dry line, sea breeze front)

  • Low or moderate CIN


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