Snow only moves once the wind is strong enough to lift it. Above that threshold the flow of snow grows with the cube of the wind, and the cloud of blowing snow near the ground can cut visibility to a few metres. Change the wind, the snow and the fence and watch drifts build.
-state of the snow surface
-visibility at eye height (1.8 m)
-friction velocity u* / threshold u*t
-wind at 10 m needed to lift snow
-snow transport (saltation + suspension)
-snow in the air at 1.8 m (grams per m3)
-snow moved in the storm (tonnes per metre of width)
-fence: trapped / passes through (t/m)
-drift depth on the road behind the fence
-settling speed of one grain / Rouse exponent
The science
Wind near the ground. A turbulent boundary layer has a logarithmic profile, U(z) = (u*/k) ln(z/z0), with k = 0.4 and a snow roughness z0 = 0.2 mm. The friction velocity u* is what the surface feels.
Threshold. Snow starts to move when u* exceeds a threshold u*t. We take the 10 m threshold wind from the fit of Li and Pomeroy (1997), Ut = 9.43 + 0.18 T + 0.0033 T^2 (T in degrees C), and multiply it by a hardness factor for wind-packed or wet snow. Colder snow is looser and moves earlier.
Saltation. Bouncing grains in the lowest few centimetres carry a flux of Owen/Bagnold type, Q = Cq (rho_air/g) u*^3 (1 - (u*t/u*)^2), so doubling the wind multiplies the transport by about eight. The layer is about 0.084 u*^1.27 metres thick.
Suspension. Above it, turbulence keeps grains aloft with a Rouse profile c(z) = c_a (z/h)^(-Z) and Z = w / (k u*), where w is the grain settling speed (Schiller-Naumann drag for an ice sphere, about 0.3 m/s for 100 micrometre grains). The transport above the saltation layer is the integral of c(z) U(z) up to 5 m.
Visibility. For particles much larger than the wavelength of light the extinction coefficient is beta = 1.5 c / (rho_ice r_eff), with r_eff of a log-normal size distribution. Falling snow adds its own extinction. The Koschmieder rule, V = 3.912 / beta, gives the distance at which a dark object keeps only 2 % contrast; the scene fog is calibrated to exactly that.
Snow fence. A fence slows the wind and makes the snow settle in a drift on its lee side. Its storage capacity follows a Tabler-type law, Qc = 8.5 H^2.2 tonnes per metre (H in metres). Snow beyond that passes the fence; here it is spread over a 12 m wide road, which is only illustrative.
Honest limits. Equilibrium transport on an unlimited fetch (real storms are often fetch- and supply-limited, so this overestimates large fluxes); one grain size plus a width; no sublimation, no snow-surface hardening or erosion; the drift shape is a stylised sketch, and a visibility under about 100 m is our label for a whiteout, which in reality is also a lack of contrast. Coefficients (Cq, z0, 8.5 and 2.2) are typical values: check them against the literature before quoting any single number.