Weather Condition Codes

Weather stations in the NWS/FAA network (and some RWIS stations) report a weather condition code. For legacy reasons we refer to this variable as WNUM or “weather number.” The WNUM is an integer value that can be converted into a weather condition description.

The weather condition code is requested as weather_cond_code, and the weather condition string derived from this code is requested as weather_condition. Note that this variable is only reported when there is present weather.

The derived weather condition is also included in the derived weather_summary variable. This variable is intended to provide a single string for each observation timestamp summarizing the current weather. If a weather condition is present it is returned; if there is not a current weather condition the cloud layer with greatest sky coverage is returned. Read more about cloud layer codes here.

Many automated stations can report up to three “present weather” types which will be returned in a single string (e.g. "light snow,blowing snow,freezing fog"). The three conditions are represented by A, B, and C in the following formula:

NONE

WNUM = A × 80 × 80 + B × 80 + C

If the coded value is < 80, only one condition is being reported, and the condition is easily found using the descriptions given below.

If the coded value is between 80 and 80 × 80, two conditions are reported, and using algebra it is possible to determine the two codes B and C which both will have numbers between 0-79.

If the coded value is >= 80 × 80, three conditions are reported (A, B, and C). So, using the example above (light snow, blowing snow, and freezing fog) those would correspond to values of A=20, B=32, C=30, therefore:

NONE

WNUM = 20 × 80 × 80 + 32 × 80 + 30 = 128000 + 2560 + 30 = 130590

The following are the steps involved to unravel the values working backwards:

Begin with the value of 130590
Find A: floor(130590/6400) = 20
Subtract 130590 - (6400*20) to get the remainder: 130590 - (6400*20) = 2590
Find B: floor(2590/80) = 32
C will then be 2590 - (80*32), so 2590 - (80*32) = 30

WNUM Values

The following table outlines the code values which can fill in for A, B or C in the examples above.

Code	Description
0	(no value)
1	R (mod rain)
2	L (mod drizzle)
3	S (mod snow)
4	A (mod hail)
5	T (thunder)
6	H (haze)
7	K (smoke)
8	D (dust)
9	F (fog)
10	Q (squalls)
11	V volcanic ash)
12
13	R- (lt rain)
14	R+ (hvy rain)
15	ZR (mod frz rain)
16	RW (mod rain shwr)
17	L- (lt drizzle)
18	L+ (hvy drizzle)
19	ZL (frz drizzle)
20	S- (lt snow)
21	S+ (hvy snow)
22	SW (mod snow shwr)
23	IP (mod ice pellet)
24	SG (mod snow grain)
25	SP (mod snow pellet)
26	A- (lt hail)
27	A+ (hvy hail)
28	T- (lt thunder)
29	T+ (hvy thunder)
30	IF (ice fog)
31	GF (ground fog)
32	BS (blowing snow)
33	BD (blowing dust)
34	BY (blowing spray)
35	BN (blowing sand)
36	IC (mod ice crystals)
37	IN (ice needles)
38	AP (small hail)
39	KH (smoke, haze)
40	PO (dust whirls)
41	UP (unknown prcp)
42
43
44
45
46
47
48
49	ZR- (lt frz rain)
50	ZR+ (hvy frz rain)
51	RW- (lt rain shwr)
52	RW+ (hvy rain shwr)
53	ZL- (lt freezing drizzle)
54	ZL+ (hvy freezing drizzle)
55	SW- (lt snow shwr)
56	SW+ (hvy snow shwr)
57	IP- (lt ice pellets)
58	IP+ (hvy ice pellets)
59	SG- (lt snow grains)
60	SG+ (hvy snow grains)
61	SP- (lt snow pellets)
62	SP+ (hvy snow pellets)
63	IPW (mod ice pellet shwr)
64	IC- (lt ice crystals)
65	IC+ (hvy ice crystals)
66	TRW (mod thunder shwr)
67	SPW (snow pellet shwr)
68	BD+ (hvy blowing dust)
69	BN+ (hvy blowing sand)
70	BS+ (hvy blowing snow)
71
72
73
74
75	IPW- (lt ice pellet shwr)
76	IPW+ (hvy ice pellet shwr)
77	TRW- (lt rain thunder shwr)
78	TRW+ (hvy rain thunder shwr)
79

And there are 3 Manual character codes which will only be sent on their own:

Code	Description
-1	Tornado
-2	Funnel Cloud
-3	Water Spout

For more information on the origin and interpretation of Weather Condition Codes, please review the Gempak Parameter guides.