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

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

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

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: H 1024 H 1020 Last 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 ( o C)-2 to – 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.

Fog Dissipation Nomogram

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

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.

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)

Tmin > TXover TXover>Tmin > TXover - 3 TXover >Tmin > TXover - 3 Tmin < TXover - 3 Tmin ~ TXover

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