CLEARING THE AIR…..ON FOGCLEARING THE AIR…..ON FOG

FORECASTING FOG FORECASTING FOG IN IN

ONTARIOONTARIO

Bryan TugwoodProgram Supervisor Ontario Storm Prediction Centre

FOGFOG Now-casting Tools

•Observations – Surface Observing Network (METAR’s)– Upper Air (00Z & 12Z) – Web-cams

•Satellite Imagery– Day: Visible Imagery– Night: Fog Imagery

FOGFOG Prognostic Tools

• Numerical Model Data: – Inference from Sounding data

BUFKIT Fog algorithm GEM BUFR profiles

• Fog Nomograms • Forecaster Experience

– Synoptic correlation (persistence)– Pattern recognition– Climatology

Nowcasting: Observations

surface obs

actual upper air

webcams

Nowcasting: Fog Imagery• The "Fog Image" IR (10.7 um) – NIR (3.9 um)

Nowcasting: OSPC Fog Imagery

Forecasting: Climatology

Forecasting: Climatology

Forecasting: Climatology

Forecasting:

H

1024

H

1020Last Night

Tonight

• Synoptic correlation• Pattern recognition

Model Data: Inference from Prog Soundings

Model Data: SCRIBE Primary forecast generation tool.

Does not have built in algorithm to forecast fog

Fog Formation Nomogram

Tmax=25C

Td = 18C

Tmin = 15C

TXover = 17C

Fog formation ~ 07Z

Fog Nomogram

Td Range (oC) -2 to +2 2 - 5 5 – 9 9 - 14 14 - 21

Cooling blo Td (oC) 5 4 3 2 1

Cooling blo Td required for Fog formation (Td at Tmax)

TXover = Td (at Tmax) – Cooling Blo Td Note: (BUFKIT TXover does not use “cooling blo Td” adjustment. ex. If Td at Tmax = 5, TXover = 1 meanwhile if Td (at Tmax) = 21, TXover = 20.

Fog Dissipation Nomogram

BUFKIT FOG NomogramRADIATION FOG: UPS AIRLINES CONCEPTUAL MODELS AND FORECAST METHODS Randy Baker UPS Airlines, Louisville, KY., Jim Cramer, and Jeff Peters. 10th Conference on Aviation, Range, and Aerospace Meteorology

1.1. HYDROLAPSEHYDROLAPSE

HLHL

As long as ΔΔHL<0HL<0, Fog usually does not form (except in still air) and often results in only dew or rime on the ground. This likely explains many of the situations involving surface saturation with no fog development.

If HL decreases with height (ΔHL<0), then the transport of watervapor is an upward-directed humidity sink away from the surface.

2. CROSSOVER TEMPERATURE (T2. CROSSOVER TEMPERATURE (TXOverXOver))

TXOver = the minimum dew point temperature observed during the warmest daytime hours (most representative airmass dewpoint).

If Tmin ~ TXover, generally forecast 1-3 miles visibilities in mist, with a risk for lower visibilities, especially in onshore/upslope. If Tmin <= (TXover- 3oF), generally forecast 1/2 mile visibility or lower, unless turbulent mixing will prevent fog or favour stratus (check mRi)

Tmin > TXoverTmin > TXover

TXoverTXover >Tmin > TXover - 3>Tmin > TXover - 3Tmin < TXover - 3Tmin < TXover - 3

Tmin ~ TXoverTmin ~ TXover

MRi <= 0.025 is "mixy""mixy".. Turbulent boundary layer suppresses cooling and favours stratus rather than fog, if saturation occurs.

MRi between 0.025 and 0.040 is "marginal""marginal"..

For the turbulent dispersal of an existing fog, MRi must decrease to 0.008 or lower.

MRi >= 0.040 is "decoupled""decoupled".. Low-level winds decoupled from winds aloft. Unmixed boundary layer supports strong cooling and favours fog rather than stratus, if saturation occurs.

3. BOUNDARY LAYER TURBULENCE (mRi)3. BOUNDARY LAYER TURBULENCE (mRi)