Weather Forecast Interpretation for Boaters. Cindy Yu Feb 14 th, 2018 Meteorological Service of Canada

Transcription

1 Weather Forecast Interpretation for Boaters Cindy Yu Feb 14 th, 2018 Meteorological Service of Canada

2 Environment Canada s Forecast Regions & Offices PSPC CMC NFSPC PASPC (Edmonton) & CMAC-W PASPC (Winnipeg) OSPC QSPC&CMAC-E ASPC&CHC

3 Where do your marine forecasts come from? Pacific Storm Prediction Centre Downtown Vancouver

4 Integrated Forecaster Workstation NinJo is installed on the new workstation 3 monitors / 1 tablet New adjustable desks

5 History of the PSPC Created in 2003 as a result of a restructuring of the weather offices (aim was for one office per region) Merger of the Pacific Weather Centre already in Vancouver (PWC) and the Mountain Weather Centre (MWC) in Kelowna.

6 Present Day 32 forecasters work in the PSPC 2 desks staffed 24hrs - Supervisor (Public Yukon), Marine 1.5 desks staffed 20.5hrs Public Coast, Public Interior Consultation desk staffed 20.5 hours

7 Public Forecast Regions 3 Forecasters Yukon Interior Coast

8 Marine Forecast Regions

9 Today s talk will cover: What causes wind? How do we measure wind? Effects of terrain on wind Waves Wind Warnings Interpreting the forecast

10 WHAT CAUSES WIND?

11 What Causes Wind? Coriolis Force Pressure Gradient

12 Air movement L Coriolis force deflects the air to the right (in Northern Hemisphere) H

13 Wind = pressure differences Air flows toward low pressure

14 Pressure Gradient Isobars are lines of equal pressure Closer the lines = great the change in pressure = greater the Pressure Gradient = stronger the winds

15 Geostrophic Wind Pressure Gradient Coriolis Force

16 1 The Strait of Georgia Winds are heavily channelled by terrain

17 Variability..! Unlike any other body of water in Canada

18 HOW DO WE MEASURE WIND?

19 19 Measuring The Wind

20 Which wind are you measuring? Measurement heights are WMO standards

21 Land-based Automatic Weather Stations Anemometer height: 10 metres above ground 21

22 Lightkeeper Marine Weather Reports lightstations report every 3 hours during daytime Some lightkeepers estimate the wind

23 Moored Buoys 3-metre Discus ~ 5 metres above the water 23

24 Ship vs Buoy Anemometers

25 Which wind are you talking about?

26 A Marine Wind Observation SE20G30 southeast 20 gusting 30 knots 20 is the sustained wind 26

27 Land-based Weather Stations the sustained wind is a 2-minute averaged wind

28 Land-based Weather Stations the gust is the highest 5-second average

29 Wind measurements/averaging

30 Buoys the sustained wind is the 10-minute average wind 30 1-sec wind max = Wind Speed (knots) Time (seconds)

31 A Rule for Buoy Winds Warning thresholds are lower for buoys

32 Wind Measurement Realities Wind is measured at different heights, over different surfaces (land and water) at different times. Using different instruments, and averaged over different periods. Some stations are favoured over others because the forecast is for the strongest wind expected in that marine region. The bottom-line: meteorologists use the observations available to them to assist in forecasting.

33 Actual Wind Observations EFFECTS OF TERRAIN, & SIZE OF FORECAST AREA ON WIND

34 Peak Winds Wind Speed (knots) Time (seconds)

35 Peak Winds!!! Douglas Channel Buoy = Nanakwa Shoal Sustained 34KT 48KT 64KT Strait of Georgia Buoys = Sentry Shoal = Halibut Bank 20KT 34KT 48KT 64KT

36 Qualicum Winds High-resolution models may capture

37 Synthetic Aperture Radar Winds (SAR Winds) High-resolution satellite image of ocean surface winds

38 Waves Peaks and Periods

39 Wave Height

40 Buoys Significant wave heights, maximum wave, wave period

41 Wave terms Hsignificant, Hpeak For any sufficient sample of waves Wave Forecast

42 A Wave Forecast

43 Peak Wave Frequency How often to expect the Peak Wave? Given Hsig = 5m 1 wave in 10 may be ~ 5m 1 wave in 1000 may be ~ 10m

44 Wave Period

45 Significant Wave Period If a buoy measures a Wave Period of 6 seconds, Then on the water: - 10 waves pass every minute waves pass every hour (1200 in 2 hours) If a Peak Wave occurs every 1000 waves, then given a wave period of 6 seconds, you may encounter one about every 2 hours.

46 WIND WARNINGS

47 Poll for Marine Wind Warnings

48 Poll for Marine Wind Warnings

49 Strong Wind Warning Previously known as Small Craft Advisory Sustained Winds of: knots US: ONLY ISSUED March 20 th to Remembrance Day

50 Gale Force Wind Warning Sustained Winds of: knots

51 Storm Force Wind Warning Sustained Winds of: knots

52 Hurricane Force Wind Warning Sustained Winds of: 64+ knots

53 Know your Wind Warnings!! Warning Level Wind Strength (knots) Strong Gale Storm Hurricane 64+

54 INTERPRETING THE FORECAST Where will the strongest winds be observed and can I avoid them?

55 Marginal Gales:

56 Marginal Gales.

57 Interpreting the Forecast Getting the most out of: Use both public & marine forecasts!

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66 66 Forecast Time References

67 Weather information by telephone Speak with marine forecaster anytime <FREE & 24/7> o Speak with a public forecaster (6am to 9pm weekdays, 10am to 6pm weekends & holidays) <FREE * 3am 9pm> o Recorded marine weather o o Howe Sound, Strait of Georgia/Juan De Fuca 67

68 Weather Rules of Thumb How to forecast your own weather

69 Weather Forecasting Hints Deteriorating weather : Barometer is falling Temperature change & humidity increase Cirrus clouds increasing Clouds darken and develop multiple layers Strong winds in morning with a shift to SE Red sky at morning

70 Weather Forecasting Hints Improving weather : Barometer is rising Winds steady or shifting to W or NW Steady temperature Early morning clouds or fog burn off Shallow cumulus or thin high clouds Red sky at night

71 Avalanche Blog Created daily, 365 days a year Synopsis Day 1-7 Forecast /weather/forecast

72 PSPC Alerts Dissemination /warnings EC Alert Me ECCC Weather BC

73 Free Online Resources Guide to marine weather forecasts canada.ca

74 For further information Cindy Yu