1st UNSTABLE Science Workshop18-19 April 2007

Science Question 3:Science Question 3:

Numerical Weather PredictionAspects of Forecasting Alberta Thunderstorms

Jason Milbrandt

Recherche en Prévision Numérique [RPN](Numerical Weather Prediction Research Section),Meteorological Research Division, Environment Canada

1st UNSTABLE Science Workshop18-19 April 2007

OUTLINE of PRESENTATION

1. ISSUES related to high-resolution NWP

2. DEMONSTRATION of high-resolution simulations

3. SUB-QUESTIONS

4. CONCLUSION

Premise:

• NWP part of UNSTABLE should focus on maximizing and improving the usefulness of high-resolution Canadian models as forecasting tools for severe convection

(with emphasis on storms that originate along the foothills)

Science Question 3Science Question 3

Science Question 3:Science Question 3:To what extent can high-resolution NWP models contribute to forecasting the initiation and development of severe convective storms that originate in the Alberta foothills?

That is:

1. How can the usefulness of the current GEM-LAM (2.5 km) forecasts be maximized?

2. How can the forecasts from the GEM-LAM be improved?

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ISSUESPertaining to

Science Question 3

Issues Pertaining to Science Question 3:(and high-resolution NWP in general)

• DATA

- initial conditions of model are crucial

high-resolution data assimilation is a complex topic

research on development of high-resolution analyses is possible in context of UNSTABLE

- IOP data useful for verification (examination of sub-questions)

Science Question 3Science Question 3

Issues Pertaining to Science Question 3:(and high-resolution NWP in general)

• DATA

• COMPUTATIONAL RESOURCES

- high-resolution NWP is very expensive

- resources are increasing

This is a logical time to examine Science Question 3

Science Question 3Science Question 3

Issues Pertaining to Science Question 3:(and high-resolution NWP in general)

• DATA

• COMPUTATIONAL RESOURCES

• MODEL DETAILS

- GEM is an appropriate tool for this job

non-hydrostatic, limited-area model (LAM), sophisticated physics

- To be learned:

1. modelling strategies

2. improvements to physics parameterizations

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Issues Pertaining to Science Question 3:(and high-resolution NWP in general)

• DATA

• COMPUTATIONAL RESOURCES

• MODEL DETAILS

• DETERMINISTIC vs. PROBABILISTIC

- Use of any single model run is inherently deterministic

- Analysis errors mean that a single high-resolution NWP run is doomed

Ensembles of runs will ultimately need to be considered for high-resolution NWP

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EXAMPLESof simulated thunderstorms

Estimated from WMI radar:

4-km GEM simulation:*

* Source: Erfani et al. (2003), Meteorol. Atmos. Phy.

14 July 2000 Pine Lake Storm

Accumulated Precipitation

RADAR

mm40

30

25

20

16

13

10

8

6

4

RADAR

33 mm

1-km CNTR

8:00 pm

1-km MC2 simulation:*

50 km

N

Estimated from WMI radar:

8:00 pm

50 km

N

30

25

20

15

10

5

mm

14 July 2000 Pine Lake Storm

Accumulated Precipitation

* Source: Milbrandt and Yau (2006a), J. Atmos. Sci.

dBZdBZ

1-km MC2 Simulation*using detailed microphysics

40 km

16 km

40 km

16 km

Maximum: 60–65 dBZ

COMPOSITE

Maximum: 63.6 dBZ

750 hPa

RADAR: 0030 UTC [6:30 pm]

SIMULATION: 4:30 h [6:30 pm]

NN

65

60

57

54

51

48

45

42

39

36

33

30

* Source: Milbrandt and Yau (2006a), J. Atmos. Sci.

Reflectivity CAPPI (2 km)

10 km

Equivalent Reflectivity (750 hPa)

10 km

RADAR: 0030 UTC [6:30 pm]

1-km SIMULATION: 4:15 h [6:15 pm]

N N

Source: Milbrandt and Yau (2006a), J. Atmos. Sci.

1-km MC2 Simulation*using detailed microphysics

Local time: 6:30 pm(Simulation time: 4:30 h)

SENSITIVITY EXPERIMENTS: Variations in microphysics scheme

TRIPLE-MOMENT

SINGLE-MOMENT-A

DOUBLE-MOMENTDiagnosed

DOUBLE-MOMENTFixed

700 hPa: Zeh [dBZ]

Source: Milbrandt and Yau (2006b), J. Atmos. Sci.

10 99

6-h ACCUMLATED SOLID PRECIPITATION (Hail) [mm]

132535

3414

23

TRIPLE-MOMENT DOUBLE-MOMENTDiagnosed

SINGLE-MOMENT DOUBLE-MOMENTFixed

Source: Milbrandt and Yau (2006b), J. Atmos. Sci.

SENSITIVITY EXPERIMENTS: Variations in microphysics scheme

SENSITIVITY OF MICROPHYSICS SCHEME4-category SINGLE-moment vs. 6-cateogory DOUBLE-moment:

MC2_2.5 km: Milbrandt-Yau scheme(nested from GEM15 output)

MC2_2.5 km: Kong-Yau scheme(nested from GEM15 output)

429 mm h-1

112 mm h-1

[g kg-1]

[g kg-1]

RAIN

“GRAUPEL”

GRAUPELHAIL

RAIN

SUB-QUESTIONSfor Science Question 3

SUB-QUESTION A:

What defines a “success” for a high-resolution simulation in terms providing useful numerical guidance from the current GEM-LAM-2.5 configuration?

• The simulated storm structure may be realistic,

but its track displaced;

• The location of CI may be incorrect, but the type

of storm that is forecast may be similar to the

observed

Success or a bust?

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SUB-QUESTION B:

How can the model’s ability to accurately simulate the general nature of the observed convection be quantified?

• Once a “success” is defined, how can the

general skill of the model be measured?

• Important for evaluating the effects of changes

to the model configuration

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SUB-QUESTION C:

Can the atmospheric state be classified a priori as “predictable” or “non-predictable” in terms of recommended use of the GEM-LAM-2.5 run to guide the forecast?

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SUB-QUESTION D:

How realistic are the simulated storm structures and microphysical fields?

• Comparison to radar observations

• (related to definition of “success”?)

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SUB-QUESTION E:

How realistic is the evolution of the boundary layer and surface processes in the foothill regions for the high-resolution model simulations?

• Comparison to IOP observations

• Sensitivity tests for hind-cast simulations

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SUB-QUESTION F:

Can deficiencies in the current physical parameterizations be identified?

• Comparison to IOP observations

• Sensitivity tests for hind-cast simulations

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SUB-QUESTION G:

What would be the effect of performing a subsequent nest to a higher-resolution (e.g. 1-km) grid, driven from the 2.5-km run?

• dx = 2.5 km is INSUFFICIENT to fully resolve

individual storms

• Would the value added by a 1-km grid be worth

the cost?

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SUB-QUESTION H:

Can an ensemble of high-resolution runs improve the prediction of convective initiation?

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• Modified ICs (different members from different

15-km driving runs)

• Modified physical parameterizations/settings for

2-5 km runs

SUB-QUESTION I:

Can a high-resolution analysis, created using the additional observations, improve the numerical prediction of convective initiation and subsequent storm development?

Science Question 3Science Question 3

1st UNSTABLE Science Workshop18-19 April 2007

CONCLUSION

1. Emphasis of NWP component of UNSTABLE is on maximizing and improving the utility of high-resolution NWP output as a forecast tool

2. Real-time 2.5-km runs will be done (and archived) by CMC for summers of 2007 and 2008 (and hopefully beyond…)

3. Investigation of several sub-questions can begin any time