Revisiting the freezing spray forecast algorithms used in Canada

Une revisite des algorithmes de prévision d’embruns verglaçants utilisés au Canada

par Serge Desjardins

Mark Pilon Ted Mcildoon*

National Lab for Marine and Coastal Meteorology (aka MAC Lab) *Atlantic Storm Prediction Centre

Halifax, Nova Scotia

CMOS 2012 Montréal, Québec

Page 2 –

- PART 1 : Taking the responsibility of the freezing spray program - a) Generates the YQB_FRZSP maps (Golfe, Hudson) – Modified Stallabrass - b) Duplication of the YQB_FRZSP on various domains (NAtl, Artic)

- PART 2 : Collaboration with USA (Seattle-Marine Workshop) : Matt Glazewski, Aimee Fish

- Adding the Alaska domain - Adding the Overland algorithm (used by USA) - Verifying various Stallabrass algorithm code

- i) Original Stallabrass (from Ross Brown’s code) - ii) Modified Stallabrass (from Ross Brown’s code) = YQB_Modified_Stallabrass - iii) Modified Stallabrass (from SCRIBE [interface&matrices] = mixture of i) & ii) = not pure

- PART 3 : Operimental script to generate 1PAN & 4PAN charts on various domain and with different

flavors - Overland

- Original, Fetch Factor (wave,wind) - Stallabrass

- Modified (sig wave, wind wave), original, YQB, SCRIBE, rel. Vessel speed = 5 m/sOriginal - PART 4 : Subjective Evaluation

- Collaboration USA & Canada - With Various SPCs (discussion on this)

FREEZING SPRAY PROJECT

Page 3 –

N. Atlantic

Labrador

Gulf of St-Lawrence Baffin Beaufort

Hudson East- Arctic Kane

Alaska

Products de-activated

Domains Activity by June 2012

?

? Until August

Products activated in coming summer months

? in July

? in July

Until June

? Until August

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ATMO/WAVE INPUTS to compute Freezing Spray rate

Domain ATMO WAVE Comments

Dom Res. Dom Res.

Alaska GLB 35 km PAC 0.5 deg

Arctic GLB 35 km ARC 0.5 deg < 0.5 deg Wave

Hudson REG 15km ARC 0.5 deg Prob. 0.15 deg Wv

N. Atl. REG 15km NAT 0.55 deg

0.15 deg

Gulf Coupled-REG 15km GSL 0.05 deg Ice timely-

depend.

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Freezing Spray – Overland Algorithm FREEZING SPRAY TABLE

WIND SPEED (KTS)

20 25 30 35 40 45 50 55 60 65- 4 NIL NIL F F F F F F F SF

T - 5 NIL F F F F F F F SF SFE - 6 F F F F F F F SF SF SFM - 7 F F F F F F F SF SF SFP - 8 F F F F F F SF SF SF SFE - 9 F F F F F SF SF SF SF SFR - 10 F F F F F SF SF SF SF SFA - 11 F F F F SF SF SF SF SF SFT - 12 F F F F SF SF SF SF SF SFU - 13 F F F F SF SF SF SF SF SFR - 14 F F F F SF SF SF SF SF SFE - 15 F F F SF SF SF SF SF SF SF

F = COMAR CODE FOR MODERATE FREEZING SPRAYSF = COMAR CODE FOR SEVERE FREEZING SPRAY

SAWADA (from COMAR)

Mod

ified

PPR = Icing Predictor (moCs-1) Va = Wind Speed (m s-1) Tf = Freezing point of seawater (usually -1.7 oC or -1.8 oC) Ta = Air Temperature (oC) Tw = Sea Temperature (oC)

Sawada condition

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Overland Algorithm (calm down please !)

Over most of Canadian Waters (Golfe, Hudson, Arctic)

( ) ( ) ( )TVTVTTV aaaaafaFPPR ,8.1 =--=-=

Fetch Factor or % Spray Flux availability

( )PPRPPR

SprayFluxMaxSprayFluxAvaiPPRFETCH

UV

Wave Sig

Wind **___

132=÷÷

ø

öççè

æ=

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Freezing Spray – Stallabrass Algorithm q Considers air temperature, water temperature, wind speed, and wave

height

q Assume 20 knots for relative to the wave vessel speed (SCRIBE)

q Predicts the average icing rate

o 1200 Events from 138

different vessels. Data collected by Jim Stallabrass 1968 to 1980

o Each event described by 67 fields

o Icing categorized by severity: Trace, Lights, Moderate, Heavy

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Summary of the Algorithms

SAWADA Wind Speed

Cat

egor

y

Light

Moderate

Severe

Extreme

FREEZING SPRAY TABLE

WIND SPEED (KTS)

20 25 30 35 40 45 50 55 60 65- 4 NIL NIL F F F F F F F SF

T - 5 NIL F F F F F F F SF SFE - 6 F F F F F F F SF SF SFM - 7 F F F F F F F SF SF SFP - 8 F F F F F F SF SF SF SFE - 9 F F F F F SF SF SF SF SFR - 10 F F F F F SF SF SF SF SFA - 11 F F F F SF SF SF SF SF SFT - 12 F F F F SF SF SF SF SF SFU - 13 F F F F SF SF SF SF SF SFR - 14 F F F F SF SF SF SF SF SFE - 15 F F F SF SF SF SF SF SF SF

F = COMAR CODE FOR MODERATE FREEZING SPRAYSF = COMAR CODE FOR SEVERE FREEZING SPRAY

SAWADA : F (Wind Speed, Temperature) OVERLAND : F (Wind Speed, Temperature, Sea Surface Temperature) STALLABRASS : F (Wind Speed, Temperature, Sea Surface Temperature, Wave, RH)

Cloud of possibility generated by the other variables

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Why Numerical Model Outputs are still a forecast guidance

• Cold frontal passage Jan 18/19, 2012

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Model Output Temperatures

Matrix Points

St. Paul Island OBS

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January 19/00Z (24HR) to 20/00z (48HR) OVERLAND

F(T,UV,TM) STALLABRASS F(T,UV,TM,WV,HR)

SAWADA F(T,UV)

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3:00 am Fcst Jan. 18/2012

CABOT STRAIT. GALE WARNING IN EFFECT. WIND SOUTHEAST 15 TO 20 KNOTS INCREASING TO 30 LATE THIS MORNING WITH GUSTS TO 50 IN THE WRECKHOUSE AREA. WIND BECOMING SOUTHWEST 35 LATE THIS AFTERNOON THEN DIMINISHING TO NORTHWEST 25 THURSDAY MORNING. WIND DIMINISHING TO NORTHWEST 15 THURSDAY EVENING. SNOW CHANGING TO RAIN EARLY THIS MORNING AND ENDING LATE THIS AFTERNOON. FLURRIES BEGINNING NEAR MIDNIGHT. FOG PATCHES FORMING EARLY THIS MORNING AND DISSIPATING EARLY THIS EVENING. TEMPERATURES MINUS 1 RISING TO PLUS 5 THIS AFTERNOON THEN FALLING TO MINUS 3 THURSDAY AFTERNOON.

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3:00 am Fcst Jan. 19/2012

CABOT STRAIT. GALE WARNING IN EFFECT. FREEZING SPRAY WARNING IN EFFECT. WIND WEST 35 TO 45 KNOTS DIMINISHING TO NORTHWEST 30 THIS MORNING AND TO 15 EARLY THIS EVENING. WIND VEERING TO NORTHEAST 15 NEAR MIDNIGHT THEN DIMINISHING TO LIGHT FRIDAY MORNING. WIND BECOMING SOUTHEAST 15 FRIDAY EVENING. FLURRIES ENDING NEAR NOON. FREEZING SPRAY ENDING THIS MORNING. TEMPERATURES NEAR MINUS 3.

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Conclusions : Freezing Spray - findings

ØGraphics are very helpful ØBetter than nomogram (point by point) ØGives forecaster the whole picture

Ø Provides a variety of algorithms ØUse/evaluation hampered by lack of

reports ØBased on biased model temperatures

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Conclusions : Next Steps v More Validation work needs to be done vBig Problem : Lack of observations

v Developing a global product to get more ship obs ? v Canada/USA Collaboration continue

v Probably a joint Operational Validation next year vAn evolving file with METAREA.. To be

continued v The SPRAY GENERATION (spray which could

eventually freeze) comes from the ship’s movement. v How can we take this into account in our guidance products ?

v Stallabrass has it but …