Heat IndexĪs an example, if the air temperature is 90☏ (found at the left side of the table) and the Relative Humidity (RH) is 70% (found at the top of the table), the Heat Index (HI)-or how hot it actually feels-is 106☏. The criteria for this advisory vary from state to state. Heat Advisory This product is issued by the National Weather Service when excessive heat may pose a hazard or is life threatening if action is not taken. All discharge of the river at this point is developed within the basin. Headwater Basin A basin at the headwaters of a river.
Headwater Advisory Table A table developed by a River Forecast Center for a Headwater Guidance Point a pre-computed matrix of values allows a forecaster to ascertain an anticipated crest or rise on a small river or stream for a variety of rainfall events and soil moisture conditions. Headwaters Streams at the source of a river.
Headward Erosion Erosion which occurs in the upstream end of the valley of a stream, causing it to lengthen its course in such a direction. Head Race A channel which directs water to a water wheel a forebay. Head Loss The decrease in total head caused by friction. Usually expressed in feet of head, or in lbs./sq. Head The difference between the pool height and tailwater height. However, the visibility in the haze layer can be very poor. Haze layers often have definite tops above which the visibilities are good. Occurs in stable air usually only a few thousand feet thick, but may extend as high as 15,000 feet (4,500 meters). Haze (HZ) A concentration of salt particles or other dry particles not readily classified as dust or other phenomenon. Hanging (Ice) Dam A mass of ice composed mainly of frazil or broken ice deposited underneath an ice cover in a region of low flow velocity. These are caused by refraction of light through ice crystals that make up cirrus clouds. Halos Rings or arcs that encircle the sun or moon. Very Low Potential (Moist Stable Lower Atmosphere) High Potential (Dry Unstable Lower Atmosphere)
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