......NWS TERMINOLOGY

PRECIPITATION

PROBABILITY of PRECIPITATION (POP) is the likelihood of occurrence (expressed as a percent) of a precipitation event at any given point in the forecast area. The NWS uses two different methods to indicate the chance of precipitation for a specific area: numerical or in non- numerical terms. The "Expression of Uncertainty" category is used for widespread precipitation and the "Equivalent Areal Coverage" for convective (i.e., showery) events. Below is a table of these two methods with the corresponding POP.

POP	Expression of Uncertainty	Equivalent Areal Coverage
0%	None used	None Used
10%	Slight Chance	Isolated or none used
20%	Slight Chance	Isolated
30-40%	Chance	Scattered
60-70%	Likely	Numerous or none used
80-100%	None	None used

There are other qualifying terms which are used with the above non-numerical expressions. For example:
For duration - brief, occasional, intermittent, frequent.
For intensity:

Very Light	< .01 inch per hour
Light	.01 to .10 inch per hour
Moderate	.10 to .30 inch per hour
Heavy	greater than .30 inch per hour

WIND DIRECTION and SPEED A forecast wind (direction and speed) is included in the first three periods of the forecast. The wind is included in the fourth period if considered significant.

1. Wind direction is the direction where the wind is coming FROM and is based on an 8-point compass (NE, E, SE, etc.). Light wind (usually 5 mph or less) will be handled in the following ways:

	LIGHT SOUTH WINDS (if direction is known),
	LIGHT AND VARIABLE WINDS , or
	LIGHT WINDS (where "light" implies a variable wind direction).

2. Wind speed will be given in miles per hour. Following is a list of terms sometimes used to describe the wind speed.

Note: A forecast can contain a peak wind speed in gusty situations. For example, "NORTHWEST WIND 20 TO 30 MPH WITH OCCASIONAL GUSTS TO 40 MPH.")

TEMPERATURE TERMINOLOGY
Numerical temperature values are represented in NWS forecasts in four ways:

1. "Near," "around," or "about" a specific value rounded to the nearest five zero. Above 100°F or below 10°F, any number will be used. For example:

		NEAR 40, AROUND 15, ABOUT 85, or NEAR 106.

		LOWER 50's	(50 - 54)
		MID 50's	(53 - 57)
		UPPER 50's	(56 - 59)
		50's		(50 - 59)

4. Specific numbers for site-specific locations: TRI-CITIES 70/50/72

SKY COVER TERMINOLOGY

Predominate Sky Condition	Daytime Terminology	Day or Night Terminology
0/8 Opaque Clouds	Sunny	Clear
1/8 - 2/8 Opaque Clouds	Mostly Sunny	Mostly Clear
3/8 - 5/8 Opaque Clouds	Partly Sunny	Partly Cloudy
6/8 - 7/8 Opaque Clouds	Mostly Cloudy	Mostly Cloudy
8/8 Opaque Clouds	Cloudy	Cloudy

HEAT INDEX

The NWS has devised the "HEAT INDEX" (HI), sometimes called the "apparent temperature." The HI is the temperature the body feels when the heat and humidity are combined.