Using Historical Analogs as Medium-Range Guidance for Severe Weather Episodes

Using Historical Analogs as Medium-Range Guidance for

Severe Weather EpisodesChad M. Gravelle* and Charles E. Graves

Saint Louis University - Department of Earth and Atmospheric Sciences* Current affiliation: CIMSS-University of Wisconsin / NWS Operations Proving Ground

Jeffrey P. CravenNOAA/NWS Weather Forecast Office - Milwaukee/Sullivan, WI

Alan E. GerardNOAA/NWS Weather Forecast Office - Jackson, MS

John P. GaganNOAA/NWS Weather Forecast Office - Springfield, MO

2012 National Weather Association Annual Meeting – Madison, WI8 October 2012

• Began in 2008 after science meetings between SGF/LSX and SLU.

• Started with cold-season guidance and expanded to the warm season in 2011.

• Completely driven by a grassroots movement, no outside funding has ever been awarded.

CIPS Analog Guidance History

• Since November 2009, the CIPS analog guidance has been mentioned in over 250 AFDs by 38 WFOs across the CONUS.

• Early Analog Definition: If the current state of the atmosphere resembles a previous state then the two are termed analogs, and for a period of time the current state may evolve in a similar fashion as the past state (Lorenz 1969).

• Modern Analog Definition: Analogs are found using the perfect prognostic (“perfect prog”) approach. NWP forecast fields are used as a pattern-recognition tool in contrast to using analysis maps as a forecast tool (Root et al. 2007).

What are Historical Analogs?

GFS 30-h Forecast Analog – 19830212/0000

• Search the 31-yr North American Regional Reanalysis (NARR) dataset against the model forecast (NAM/GFS212-40km) for potential analogs.– 3 months (±45 days from current day)– 6 h temporal resolution– 11,160 potential analogs (31 years, 90 days, 4 per day)

• Remove duplicate times by choosing the “best” analog over a 24-h period. 1984011512, 1984011518, 1984011600, 1984011606

• Refine and rank (using the analog time and ±6h from analog time) the resulting analogs (prefect analog score is 21).

• Create “impact-based” guidance products.

Fields:

Field weights are in parenthesis.

CIPS Analog Guidance – “How Do We Do This?”

300HGHT300SPED500HGHT500SPED850HGHT

(3)

850SPED (2)PMSL (2)850TMPC850MIXR (3)2mTMP (2)2mDWP (2)

AVGRELHPWTR

6 CONUS Domains

• Impact Guidance– Precipitation and COOP Snow Mean and Exceedance Probabilities– Severe Thunderstorm Probabilities– Surface Temperature, Heat Index, and Wind Chill Exceedance Probabilities– Surface Wind Gusts Exceedance Probabilities– Surface Flight Rules Exceedance Probabilities (coming soon)

• Severe thunderstorm probabilities are developed from the mean of the individual analog Practically Perfect Forecasts (PPFs).

• Developed by SPC forecasters (Brooks et al. 1998), the approach of the PPF method is that it tries to “mimic” what a near-perfect forecast would look like.

CIPS Analog Guidance – Guidance Based on Most Similar Analogs

• Forecasters use deterministic and ensemble medium-range (days 4-7) NWP output to help formulate:

• Growing need for NWS partners to know the potential that a high-impact weather event may occur 4-8 days in advance.

• Identifying significant events is challenging.

• Historical analogs can be used as a “decision assistance tool”.

Historical Analogs – Why in the Medium Range of the Forecast?

CPC U.S. Hazards Outlook SPC Day 4-8 Outlook NWS Hazardous Weather Outlook

SPC Guidance – Valid on 14 April 2012

Day 4 Outlook

Day 5 OutlookDay 6 Outlook

SPC 24-h Storm Reports ending 20120415/1200

Day 2 Outlook

14 April 2012 – Severe Weather and Tornado Outbreak

L

L

GFS 120-h Forecast valid 20120415/0000PMSL, 2-m TMPF, and 2-m DWPF


L

L

GFS 120-h Forecast valid 20120415/0000850-mb Winds


L

L

GFS 120-h Forecast valid 20120415/0000300-mb Isotachs


L

L

GFS 120-h Forecast Synoptic-Scale Features valid 20120415/000024-h SPC Severe reports ending 20120415/1200


L

L

GFS 120-h Forecast Synoptic-Scale Features valid 20120415/000024-h SPC Severe reports ending 20120415/1200


Mean of Top 15 Analogs Based on GFS 120-h Forecast valid 20120415/0000PMSL, 2-m TMPF, and 2-m DWPF

L


L

Mean of Top 15 Analogs Based on GFS 120-h Forecast valid 20120415/0000850-mb Winds


L

Mean of Top 15 Analogs Based on GFS 120-h Forecast valid 20120415/0000300-mb Isotachs


Mean of Top 15 Analog Features Based on GFS 120-h Forecast valid 20120415/0000Probability of Severe Weather Within 40km Grid Point (8 most severe analogs)

L



L

Synoptic-Scale Features Based on GFS 120-h Forecast

24-h SPC Severe Reports ending 20120415/1200

Analog Guidance (F144-F072) – 14 April 2012

Based on 3-day ForecastBased on 4-day Forecast


SPC Guidance – Valid on 29 June 2012

Day 4 Outlook

Day 5 OutlookDay 6 Outlook

SPC 24-h Storm Reports ending 20120630/1200


29-30 June 2012 – Great Lakes/Ohio Valley Derecho

L

L



L

L


L

L



L

L



L

L

GFS 108-h Forecast valid 20120629/1200300-mb Isotachs


GFS 108-h Forecast Synoptic-Scale Features valid 20120629/1200GFS 48-h QPF ending 20120701/0000V144

L

L


GFS 108-h Forecast Synoptic-Scale Features valid 20120629/120024-h SPC Severe Reports ending 20120630/1200

L

L


GFS 108-h Forecast Synoptic-Scale Features valid 20120629/120024-h SPC Severe Reports ending 20120630/1200

L

L


L

L

Mean of Top 15 Analogs Based on GFS 108-h Forecast valid 20120629/1200PMSL, 2-m TMPF, and 2-m DWPF


L

L



L

L



L

L

Mean of Top 15 Analogs Based on GFS 108-h Forecast valid 20120629/1200300-mb Isotachs



L

L



L

L

Surface Features Based on GFS 108-h Forecast24-h SPC Severe Reports ending 20120630/1200

Analog Guidance (F144-F072) – 29 June 2012



Analog Guidance Individual Events (F144-F072) – 29 June 2012

20 July 1998 22 July 1998 09 August 2000

08 July 1991 08 July 2000 05 July 1980

F096 – The Day Before

Analog Guidance 20120625/0000 F096 and F144

F144 – The Day After

• Analog guidance has qualitative skill to provide situational awareness in the medium range of the forecast.

• Meteorological patterns are not created equal…some are more “predictable” and easier to identify than others.

• In the medium range, the analog guidance should be used with deterministic and ensemble model output to assist in identifying patterns that are historically associated with a weather impact.

• A “perfect” analog does not exist.

• Only a few, good quality analogs may exist for anomalous and record breaking events.

Conclusions and Takeaways

Questions or comments?

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Questions

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Using Historical Analogs as Medium-Range Guidance for Severe Weather Episodes