Shawn M. Milrad and John R. Gyakum Department of Atmospheric and Oceanic Sciences McGill University Montreal, QC, Canada

Transcription

1 Shawn M. Milrad and John R. Gyakum Department of Atmospheric and Oceanic Sciences McGill University Montreal, QC, Canada

2 Motivation Outline 6-8 December 2010 surprise snow Meteorological Issues Case overview Model forecasts Forecasting and Communication Issues Conclusions and Discussion

3 Surprise snowstorm: 6-8 December 2010

4 I left work at 3:15 p.m. on Monday and I walked into my house at 5:50 p.m.! Roads were not salted, sidewalks unplowed so pedestrians walking in the street and people blocking intersections (like they were going to get home any faster!) There is blame to go around here - forecasters: really, you couldn't foresee 20 centimeters vs. the announced 4cms? Doubtful! The city - we pay higher taxes every year and yet our services are deplorable! Surprise Snow: The Mess

5 We use tools like numerical guidance that simulates weather patterns, but the guidance had a problem to really pick up the fine details of this weather pattern, so we underforecasted the snow amount. By that, I mean that the precipitation was coming from the east towards the west while usually it s the other way around, -Rene Heroux, Environment Canada Quebec Region warning and preparedness meteorologist Surprise Snow : The Response

6 Surprise Snow: The Response

7 Sources: Iowa State University Climate Data Archive Case Overview Meteograms for Trudeau International Airport (CYUL) Upper panel: Temperature (C) in red, dewpoint (C) in green Lower panel: 10 m wind (barbs), present weather (bottom) and visibility (sm, blue) Tuesday 7 December 2010 Wednesday 8 December 2010

8 Case Overview Total snow accumulation: 31.2 cm Source: Environment Canada Climate Data Archive

9 Case Overview KCXX (Burlington, VT) base reflectivity images every hour from 12 UTC Monday 6 December to 12 UTC Tuesday 7 December CYUL Source: NCDC Radar Archive

10 500 hpa height (dam, contours) and absolute vorticity (s -1, shaded) The Dynamics hpa layer-averaged Q-vector divergence (shaded, cool colors for convergence/ascent) Sea-level pressure(hpa, solid), and hpa thickness (dam, dashed) 0000 UTC Monday 6 December 1200 UTC Wednesday 8 December, every 3 hours Source: NCEP North American Regional Reanalysis (NARR)

11 The Dynamics 30 m total frontogenesis (K/100 km/3 hours, shaded), mb thickness (dam, dashed) and 30 m winds (barbs) 925 hpa geostrophic frontogenesis (K/100 km/3 hours, shaded), mb thickness (dam, dashed) and 925 hpa geostrophic winds (barbs) 0000 UTC Monday 6 December 1200 UTC Wednesday 8 December, every 3 hours Source: NCEP North American Regional Reanalysis (NARR)

12 The Moisture 120-hour backward trajectories ending at 0000 UTC 7 December Ending at ~500 hpa Ending at ~700 hpa Ending at ~850 hpa Source: NOAA Hysplit Model (GFS data)

13 Meteorology: Recap Strong quasi-geostrophic forcing for ascent at CYUL Cyclonic vorticity advection (CVA) and warm air advection (WAA) from the north and east Rapidly ascending warm moist Atlantic air over cold continental air Frontogenesis: ascent-focusing mechanism Enhanced due to the effects of the St. Lawrence valley? Helped to prolong event?

14 Model Forecasts NAM, GFS, UKMET Focus verification time: 0000 UTC 7 December 2010 Afternoon/evening commute Time of best dynamics according to the NARR

15 Models: 500 hpa Height/Vorticity 00 UTC 6 December, 24 hour forecasts, verifying at 00 UTC 7 December 500 hpa height (dam, contours) and absolute vorticity (s -1, shaded) NAM GFS UKMET NARR

16 Models: Q-vector Divergence 00 UTC 6 December, 24 hour forecasts, verifying at 00 UTC 7 December Sea-level pressure(hpa, solid), hpa thickness (dam, dashed) and hpa layer-averaged Q-vector divergence (shaded, cool colors for convergence/ascent) NAM GFS UKMET NARR

17 00 UTC 6 December, 24 hour forecasts, verifying at 00 UTC 7 December 925 hpa (850 hpa UKMET) frontogenesis (K/100 km/3 hours, shaded), mb thickness (dam, dashed) and 925 hpa (850 hpa UKMET) winds (barbs) NAM Models: Frontogenesis GFS UKMET NARR

18 Models: Precipitation Total 48-hour accumulated precipitation shaded (mm), SLP (hpa, contours) Initialized: 12 UTC Sunday 5 December Precipitation time period: 48 hours: 12 UTC Monday 6 Dec-12 UTC Wednesday 8 Dec SLP: 00 UTC Tuesday 7 December NAM GFS mm liquid equivalent mm liquid equivalent

19 Models: Precipitation Total 48-hour accumulated precipitation shaded (mm), SLP (hpa, contours) Initialized: 00 UTC Monday 6 December Precipitation time period: 12 UTC Monday 6 Dec-12 UTC Wednesday 8 Dec SLP: 00 UTC Tuesday 7 December NAM GFS mm liquid equivalent mm liquid equivalent

20 The signs were evident amongst various models for a significant snow event (24-48 hour lead time) CVA WAA Model Forecasts: Recap Frontogenesis Both the GFS and NAM showed at minimum 14 cm of total snow accumulation Observations show a 12:1 snow:liquid ratio General run-to-run consistency The NAM and GFS underforecasted the event by cm Prolonged frontogenesis in the St. Lawrence valley?

21 FPCN11 CWUL FORECASTS FOR WESTERN QUEBEC ISSUED BY ENVIRONMENT CANADA AT11.30 AM EST MONDAY 6 DECEMBER 2010 FOR TODAY AND TUESDAY. METRO MONTREAL - LAVAL. TODAY..SNOW. LOCAL BLOWING SNOW LATE THIS AFTERNOON. WIND WEST 20 KM/H GUSTING TO 40 BECOMING SOUTHWEST 40 GUSTING TO 60 THIS AFTERNOON. HIGH MINUS 2. TONIGHT..SNOW AND LOCAL BLOWING SNOW. AMOUNT 2 TO 4 CM. WIND SOUTHWEST 40 KM/H GUSTING TO 60. LOW MINUS 4. TUESDAY..SNOW ENDING NEAR NOON THEN CLOUDY WITH 60 PERCENT CHANCE OF FLURRIES. WIND SOUTHWEST 30 KM/H GUSTING TO 60. HIGH MINUS 1. Forecasts: Environment Canada Issued: Monday 6 December (11 am EST, 16 UTC)

22 Forecasts: Environment Canada By 5 am Tuesday morning, at least 15 cm had already been RECORDED at CYUL A snowfall warning was not issued until *after* the 5 am Tuesday forecast (when about 20 cm was already on the ground) Snowfall warning criterion: 15 cm

23 What went wrong? The operational forecast The response to the media Most importantly: The system

24 The Operational Problem Clearly, the GEM forecast underforecasted the precipitation with this event Models are wrong all the time This does not mean the model is bad or not worth using But would you write a research paper only relying on one source?

25 The Operational Problem Environment Canada s public forecast desk workstations: Only show Canada s GEM model output (regional, global, LAM 2.5) If you want to look at other models, you have to use what is publicly available on the internet NinJo visualization software Collaborative project (Europe)

26 The Operational Problem So what does the forecaster do if they think the GEM is the outlier? To manually change the forecast grids is time-consuming and tedious

27 From the Forecasters By most accounts, EC forecasters have been frustrated by the limitations of the system for years Thank you for breaking through the wall Kudos for your quotes in the Montreal Gazette re: early Dec 2010 Quebec winter storm. (It s) just one example of many where our meteorological services are being dumbed down or blatant issues are being sugar coated. Those of us in the service have to wait for knowledgeable people like yourself, on the outside of the civil service, to ask the hard questions. -Environment Canada forecaster

28 Possible Solutions Like most nations/organizations that run a forecast model, Environment Canada spends a large portion of their budget on model operations U.S., UK, ECMWF, etc. The Canadian GEM model certainly performs well enough on average to justify its existence CMC/public forecast desk disconnect

29 Possible Solutions Enable access to other nations models within the workstation NAM, GFS, UKMET, RAP, ECMWF Allow those grids to be used as automated forecast output if the forecaster so chooses Evolution of a chaotic fluid cannot always be characterized by one possible solution The forecaster needs a way out if he/she judges the GEM to be the outlier

30 Bottom Line Bottom line: The current operational forecast procedures put Canada at a competitive disadvantage David Grimes: International collaboration is important to Canada's future science and technology strategy