Report - London Borough of Hillingdon

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WINTER SERVICE OPERATIONAL PLAN 74BPeriod Used to describe the length of cloud breaks or amounts of sunshine, generally of two hours or more duration. 75BPowder Snow The form of snow that occurs when air temperatures are well below freezing, (-2 o C or less). This form of snow is very fine (like sugar crystals), drifts very easily, but does not tend to stick to objects, (no accretion). It can be handled by snow blowers. Salt is usually less effective. 76BPrecipitation A general term that covers all water (or ice), which ‘falls’ from the skies. As well as rain, sleet, snow and hail it also includes dew, hoar frost and fog. 7BPrecipitation Type The individual type of precipitation. In winter maintenance activities, this will be one of rain, drizzle, sleet, wet snow, dry snow, hail, freezing rain and freezing drizzle, (see Precipitation). 78BProlonged Used to describe showers that merge together producing a spell or continuous precipitation, generally lasting more than one hour and covering a relatively large area. 79BRain Water droplets that fall from clouds. Rain takes many forms, and can be of many different intensities and duration’s. Within road weather forecasts there will often be differentiation between rain and showers, the former usually referring to longer-lived but light intensity precipitation, and the latter to short duration but heavy intensity. 80BRelative Humidity This is the amount of actual water vapour held in a sample of air at a given temperature, divided by the maximum amount of water that could be held in that sample of air at that temperature, expressed as a percentage. Within fog or heavy rain, humidities may reach 100%. On a sunny, warm afternoon in summer, humidities may fall to 30%. On an average night in winter, humidities rarely fall below 80%, (which is the minimum humidity at which salt crystals will start to absorb water). 81BRime Deposition of ice from freezing fog. It is a white form of ice, similar to hoar frost, but has a finer (at times feathery), structure. On roads, tends to be more of a problem at higher levels than lower levels. RST Common abbreviation for road surface temperature. Saturated Air is said to be saturated when, at a given temperature, it holds the maximum amount of water vapour possible. Any cooling below its current temperature will result in condensation. The relative humidity of saturated air is 100%. Saturated The rate at which air temperature falls with height within adiabatic lapse saturated air, e.g., within fog or cloud. It is less than the rate dry adiabatic lapse rate, 0.49 o C per 100 metres or around 1.5 o C per 1,000 feet. 68
WINTER SERVICE OPERATIONAL PLAN 82BScattered Used in conjunction with shower. Scattered showers imply that wide covering of showers across an area is expected. Most places will see a shower but one or two locations may stay dry, (see Frequent and Isolated). 83BSeepage Leakage of ground water from roadside verges. Can cause roads to become wet, when otherwise they would have stayed dry, possibly leading to ice formation later. 84BShower A short spell of precipitation, generally less than an hour, and covering a relatively small area. It can be assumed that a shower will be of rain unless qualified by the words snow, hail or wintry. 85BSleet Partially melted snow. If precipitation becomes heavy, sleet may readily turn to snow. Snow A form of precipitation where tiny ice crystals bond together into flakes. Snow can be either of Wet or Powder forms. 86BSpell Used to describe the length of cloud breaks or amount of sunshine, generally between one and two hours duration. 87BThermal The temperature trace along a road surface, (usually Fingerprint Recorded by an infrared thermometer during a thermal mapping run). Regardless of the mean temperature of the trace, it shows the thermal characteristics of the road surface (warm and cold spots). Thermal Map The representation of relative variations in road surface minimum temperature for each of three weather categories, presented in colour bands, (usually 1 o C). 8BThermal Map Type Defined as damped, or intermediate or extreme (see previous entries). When using thermal maps in the forecast mode, the weather forecast organisations will send the thermal map type with the ice prediction graph. 89BTrend The likely direction in which the weather is moving over the next two to five days, e.g., ‘turning much colder with night frosts’ or ‘remaining mild and windy’. 90BWash Off This occurs when rain is sufficiently heavy to remove salt solution from the road surface. 91BWater Vapour Water in its gaseous state. 92BWet Snow Snow, which falls with air temperatures close to freezing point. It melts easily and can be very sticky (see Accretion). It is more common in the UK than the other variant of powder snow. 69
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To: COUNCILLOR KEITH BURROWS CABINE
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Comments of Policy Overview Committ
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drafting the documents and that all
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2011/2012 (28 th Oct 2011 to 30th M
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Volume 2: - Appendices and Annexes
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1. INTRODUCTION 1.1 Winter Service
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Footways will only be treated once
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Can I clear the snow outside my hou
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2. SUMMARY OF REVISIONS Changes Fro
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and the salt spread rate. 17. Colle
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4.0 QUALITY 4.1 Document control pr
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5.0 ROUTE PLANNING FOR CARRIAGEWAYS
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The street-cleaning workforce are e
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5.9 Location and maintenance of sal
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7 ORGANISATIONAL ARRANGEMENTS AND P
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9 SALT AND DE-ICING MATERIALS 9.1 L
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11 OPERATIONAL COMMUNICATIONS 11.1
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WINTER SERVICE OPERATIONAL PLAN 0BW
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WINTER SERVICE OPERATIONAL PLAN 17B
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WINTER SERVICE OPERATIONAL PLAN 3BR
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Report - London Borough of Hillingdon

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