1. CLEARING THE AIR…..ON FOG FORECASTING FOG IN ONTARIO Bryan Tugwood Program Supervisor Ontario Storm Prediction Centre

2. FOG FOG Now-casting Tools Observations – Surface Observing Network (METAR’s) – Upper Air (00Z & 12Z) – Web-cams Satellite Imagery – Day: Visible Imagery – Night: Fog Imagery

3. FOG FOG 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

4. Nowcasting: Observations surface obs actual upper air webcams

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

6. Nowcasting: OSPC Fog Imagery

7. Forecasting: Climatology

10. Forecasting: H 1024 H 1020 Last Night Tonight Synoptic correlation Pattern recognition

11. Model Data: Inference from Prog Soundings

12. Model Data: SCRIBE Primary forecast generation tool. Does not have built in algorithm to forecast fog

13. Fog Formation Nomogram Tmax=25C Td = 18C Tmin = 15C TXover = 17C Fog formation ~ 07Z

14. Fog Nomogram Td Range ( o C)-2 to +22 - 55 – 99 - 1414 - 21 Cooling blo Td ( o C)54321 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.

15. Fog Dissipation Nomogram

16. BUFKIT FOG Nomogram RADIATION 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

17. 1.HYDROLAPSE HL HL ΔHL<0  As long as ΔHL<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 water vapor is an upward-directed humidity sink away from the surface.

18. 2. CROSSOVER TEMPERATURE (T XOver ) T XOver = the minimum dew point temperature observed during the warmest daytime hours (most representative airmass dewpoint). If T min ~ T Xover, generally forecast 1-3 miles visibilities in mist, with a risk for lower visibilities, especially in onshore/upslope. If T min <= (T Xover - 3 o F), generally forecast 1/2 mile visibility or lower, unless turbulent mixing will prevent fog or favour stratus (check mRi)

19. Tmin > TXover TXover>Tmin > TXover - 3 TXover >Tmin > TXover - 3 Tmin < TXover - 3 Tmin ~ TXover

20. "mixy". MRi <= 0.025 is "mixy". Turbulent boundary layer suppresses cooling and favours stratus rather than fog, if saturation occurs. "marginal". MRi between 0.025 and 0.040 is "marginal". For the turbulent dispersal of an existing fog, MRi must decrease to 0.008 or lower. "decoupled". MRi >= 0.040 is "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)