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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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Roll or Arcus Cloud

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Roll or arcus cloud

Roll or Arcus Cloud


Roll or arcus cloud

Supercell Thunderstorms


Roll or arcus cloud

Storm split 1

Storm Split 2

Storm split 3


Roll or arcus cloud

Squall Lines


Roll or arcus cloud

Bow Echoes and Derechos


Dc derecho june 10 2013

DC Derecho: June 10, 2013


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


Climatology events over 1980 2001

Climatology (Events over 1980-2001


Major derecho on june 2012

Major Derecho on June 2012


June 2012 derecho

June 2012 Derecho

  • 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

  • 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

  • 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

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

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


High resolution numerical prediction of convection

High Resolution Numerical Prediction of Convection


Explicit convective prediction

Explicit Convective Prediction

  • 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.


Roll or arcus cloud

10 km WRF forecast domain

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


Roll or arcus cloud

Real-time WRF 4 km BAMEX Forecast

Initialized 00 UTC 9 June 03

Reflectivity forecast

Composite NEXRAD Radar


Roll or arcus cloud

Real-time WRF 4 km BAMEX Forecast

Valid 6/10/03 12Z

4 km BAMEX forecast 36 h Reflectivity

4 km BAMEX forecast 12 h Reflectivity

Composite NEXRAD Radar


Roll or arcus cloud

Real-time WRF 4 km BAMEX Forecast

Initialized 00 UTC 10 June 03

Reflectivity forecast

Composite NEXRAD Radar


Roll or arcus cloud

Real-time 12 h WRF Reflectivity Forecast

Valid 6/10/03 12Z

4 km BAMEX forecast

10 km BAMEX forecast

22 km CONUS forecast

Composite NEXRAD Radar


Roll or arcus cloud

Real-time WRF 4 km BAMEX Forecast

Initialized 00 UTC 30 May 03

Reflectivity forecast

Composite NEXRAD Radar


Roll or arcus cloud

Real-time WRF 4 km BAMEX Forecast

Valid 5/30/03 23Z

23 h Reflectivity Forecast

Composite NEXRAD Radar

Line of

Supercells


Roll or arcus cloud

Realtime WRF 4 km BAMEX Forecast

Valid 6/23/03 06Z

30 h Reflectivity Forecast

Composite NEXRAD Radar

6” hail 00Z

Squall line


Roll or arcus cloud

Realtime WRF 4 km BAMEX Forecast

Initialized 5/24/03 00Z

Reflectivity Forecast

Composite NEXRAD Radar

12 h

Squall line

24 h

Persists

Dissipates


Roll or arcus cloud

Preliminary BAMEX Forecast Verification

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)


Roll or arcus cloud

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(Loop time: 17UTC – 22 UTC)


Surface analysis satellite images

Surface analysis + satellite images

From Wakimoto et al.

(2006 MWR).

2000

1900

2200

2100


Roll or arcus cloud

18 UTC May 24, 2002 I.C.

3 km / 1km grid


Model configurations

Model Configurations

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


Roll or arcus cloud

t=3h, 2100 UTC

sfc. winds, qv, and composite reflectivity


Roll or arcus cloud

t=4h, 2200 UTC


Roll or arcus cloud

t=5h, 2300 UTC


Roll or arcus cloud

t=3h, 2100 UTC


Roll or arcus cloud

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

  • 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

  • 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.)


Roll or arcus cloud

  • http://www.spc.noaa.gov/exper/sseo/


Storm prediction center ensemble of opportunity

Storm Prediction Center Ensemble of Opportunity

  • 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


Storm prediction center

Storm Prediction Center

  • 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 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

  • 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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