NWS TERMINOLOGY PRECIPITATION TERMINOLOGY

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 (seldom used) Isolated or few 20% Slight Chance Widely Scattered 30-50% Chance Scattered 60-70% Likely Numerous 80-100% None Used 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, light, heavy, very heavy. VERY LIGHT <.01 inches LIGHT .01 to .10 inch per hour MODERATE .10 to .30 inch per hour HEAVY .30 inch per hour





WIND TERMINOLOGY

WIND DIRECTION and SPEED A forecast wind (direction and speed) is included in the first two periods of the forecast. The wind is included in the third and/or 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.
Speed range		Terms
0-5 mph Light or Light and Variable 5-15 mph None used 15-25 mph Breezy (usually for mild weather) Brisk (usually for cold weather) 20-30 mph Windy 30-40 mph Very Windy 40 mph or greater Strong, Damaging, Dangerous, High
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.
2. A general range where the terms are defined by the following:
		LOWER 50's	(50 - 54)
		MID 50's	(53 - 57)
		UPPER 50's	(56 - 59)
		50's		(50 - 59)
3. A specific range rounded to the nearest five or zero (except ranges below 10°F or above 100°F, any number may be used). For example, 70 to 75 or 102 to 108.

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






SKY COVER TERMINOLOGY
Term				Opaque Coverage			Aviation
Clear or Sunny < 1/10 Clear Mostly Clear/Mostly Sunny 1/10 to 2/10 Scattered Partly Cloudy/Partly Sunny 3/10 to 6/10 Scattered Mostly Cloudy 7/10 to 8/10 Broken Cloudy 9/10 to 10/10 opaque clouds Overcast





WIND CHILL INDEX
The wind chill index provided below shows the effective cooling on exposed skin.  When the wind blows across the skin, 
it removes the insulating layer of warm air adjacent to the skin.  When all factors are the same, the faster the wind blows, 
the greater the heat loss, which results in a colder feeling.

	                          Temperature (° F)
		35     30      25     20     15     10      5      0     -5     -10    -15    -20    -25     -30    -35    -40
mph
W  	 5	32	27	 22	 16	 11	  6	  0	 -5	-10	-15	-21	-26	-31	 -36	 -42	 -47
I 	10	22	16	 10	  3	 -3	 -9	-15	-22	-27	-34	-40	-46	-52	 -58	 -65	 -71
N	15	16	 9	  2	 -5	-11	-18	-25	-31	-38	-45	-51	-58	-65	 -72	 -78	 -85
D	20	12	 4	 -3	-10	-17	-24	-31	-39	-46	-53	-60	-67	-74	 -81	 -88	 -95
	25	 8	 1	 -7	-15	-22	-29	-36	-44	-51	-59	-66	-74	-81	 -88	 -96	-103
S  	30	 6	-2	-10	-18	-25	-33	-41	-49	-56	-64	-71	-79	-86	 -93	-101	-109
P  	35	 4	-4	-12	-20	-27	-35	-43	-52	-58	-67	-74	-82	-89	 -97	-105	-113
E  	40	 3	-5	-13	-21	-29	-37	-45	-53	-60	-69	-76	-84	-92	-100	-107	-115
E  	45	 2	-6	-14	-22	-30	-38	-46	-54	-62	-70	-78	-85	-93	-102	-109	-117
D





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.  The table below is the Heat Index Chart. (Note: This chart is based upon shady, 
light wind conditions.  Exposure to full sunshine can increase HI values by up to 15° F.)

				Relative Humidity (%)
                  0      5     10     15     20     25     30     35     40     45      50     55     60     65     70      75    80     85     90     95    100
	120	107	111	116	123	130	139	148				
	115	103	107	111	115	120	127	135	143	151
	110	 99	102	105	108	112	117	123	130	137	143	150
T	105	 95	 97	100	102	105	109	113	118	123	129	135	142	149
E	100	 91	 93	 95	 97	 99	101	104	107	110	115	120	126	132	138	144
M	 95	 87	 88	 90	 91	 93	 94	 96	 98	101	104	107	110	114	119	124	130	136
P	 90	 83	 84	 85	 86	 87	 88	 90	 91	 93	 95	 96	 98	100	102	106	109	113	117	122
	 85	 78	 79	 80	 81	 82	 83	 84	 85	 86	 87	 88	 89	 90	 91	 93	 95	 97	 99	102	105	108
	 80	 73	 74	 75	 76	 77	 77	 78	 79	 79	 80	 81	 81	 82	 83	 85	 86	 86	 87	 88	 89	 91
	 75	 69	 69	 70	 71	 72	 72	 73	 73	 74	 74	 75	 75	 76	 76	 77	 77	 78	 78	 79	 79	 80
	 70	 64	 64	 65	 65	 66	 66	 67	 67	 68	 68	 69	 69	 70	 70	 70	 70	 71	 71	 71	 71	 72

Heat Index      Possible Heat Disorder
 80°F to  90°F        Fatigue possible with prolonged exposure and/or physical activity.
 90°F to 105°F        Sunstroke, heat cramps and heat exhaustion possible with prolonged exposure and/or physical activity.
105°F to 130°F        Sunstroke, heat cramps, or heat exhaustion likely, and heatstroke possible with prolonged 			exposure and/or physical activity.
130°F or greater    Heat stroke/sunstroke highly likely with continued exposure.