Waterton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waterton clear sky chart from 2005-11-06 to 2024-03-08.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.
Observation TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(no limit)Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
27%
23679
11%
81016
7%
23585
33%
23585
18%
51674

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
14%
944
6%
4707
3%
926
19%
926
8%
3014
January11th to 20thNight
15%
836
15%
4464
5%
820
22%
820
8%
2918
January21st to endNight
15%
834
7%
4849
5%
814
26%
814
8%
3136
February1st to 10thNight
18%
760
9%
2608
5%
760
26%
760
10%
1862
February11th to 20thNight
14%
742
7%
2403
3%
740
20%
740
12%
1688
February21st to endNight
21%
628
11%
1886
6%
628
27%
628
14%
1337
March1st to 10thNight
22%
750
8%
2249
3%
750
28%
750
14%
1597
March11th to 20thNight
25%
720
13%
1994
5%
720
32%
720
18%
1368
March21st to endNight
26%
792
7%
2165
2%
792
29%
792
17%
1530
April1st to 10thNight
26%
691
9%
1771
3%
691
30%
691
21%
1204
April11th to 20thNight
25%
533
13%
1601
6%
533
31%
533
18%
1088
April21st to endNight
27%
540
11%
1620
7%
540
32%
540
19%
1105
May1st to 10thNight
32%
537
8%
1617
6%
537
35%
537
20%
1094
May11th to 20thNight
43%
354
13%
1280
15%
354
46%
354
22%
786
May21st to endNight
36%
388
7%
1358
6%
388
38%
388
17%
923
June1st to 10thNight
35%
360
6%
1260
3%
360
39%
360
19%
810
June11th to 20thNight
31%
360
5%
1260
1%
360
34%
360
18%
813
June21st to endNight
45%
360
8%
1260
3%
360
49%
360
34%
647
July1st to 10thNight
60%
350
11%
1225
8%
350
64%
350
43%
572
July11th to 20thNight
49%
348
17%
1218
15%
348
58%
348
41%
579
July21st to endNight
61%
394
23%
1459
26%
372
74%
372
46%
595
August1st to 10thNight
59%
390
22%
1456
24%
388
67%
388
38%
689
August11th to 20thNight
59%
534
24%
1602
18%
534
65%
534
46%
805
August21st to endNight
49%
594
28%
1782
17%
594
57%
594
39%
944
September1st to 10thNight
43%
656
19%
1767
11%
656
47%
656
36%
1036
September11th to 20thNight
48%
720
20%
1980
13%
720
53%
720
36%
1170
September21st to endNight
35%
720
20%
1980
11%
720
42%
720
33%
1177
October1st to 10thNight
38%
720
17%
2042
10%
720
45%
720
25%
1307
October11th to 20thNight
32%
720
15%
2258
8%
720
41%
720
24%
1344
October21st to endNight
20%
792
11%
2574
5%
792
27%
792
15%
1706
November1st to 10thNight
16%
773
9%
2438
4%
773
22%
773
13%
1702
November11th to 20thNight
12%
950
10%
2660
3%
950
20%
950
14%
1808
November21st to endNight
15%
950
8%
2826
2%
950
20%
950
15%
1949
December1st to 10thNight
18%
950
10%
2850
5%
950
23%
950
15%
1984
December11th to 20thNight
14%
950
7%
3472
2%
949
18%
949
11%
2507
December21st to endNight
14%
1039
5%
5075
2%
1026
20%
1026
9%
2880

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

Occurrence of each ForecastData
Points
Cloud CoverDay
6%8%48%8%6%7%7%7%8%31%
78062
Night
48%48%8%6%8%7%7%9%30%
81445
TransparencyDay
39%11%21%18%10%2
77777
Night
36%12%23%18%9%2
81310
SeeingDay
17%21%29%21%11%3
14295
Night
13%21%31%24%10%1
23700

By Month

Percentage Cloud Cover NW (2006-)
Color Meanings:
Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
16%5%12%14%8%10%11%9%11%15%
2219
11th to 20thDay
16%413%13%6%8%11%8%7%23%
2402
21st to endDay
27%6%9%13%10%10%8%7%8%20%
2794
February1st to 10thDay
311%5%12%12%6%9%8%8%9%17%
1572
11th to 20thDay
211%6%12%11%7%10%7%6%7%19%
1665
21st to endDay
29%6%12%14%8%11%7%7%7%19%
1565
March1st to 10thDay
17%6%12%11%9%9%10%8%7%19%
1871
11th to 20thDay
38%6%10%11%9%11%7%6%8%22%
1965
21st to endDay
412%6%13%12%8%9%6%6%6%17%
2189
April1st to 10thDay
5%12%7%12%12%7%8%7%6%7%18%
2188
11th to 20thDay
6%15%7%11%9%5%7%7%6%7%21%
2310
21st to endDay
8%15%6%9%8%5%6%5%6%8%24%
2340
May1st to 10thDay
7%15%5%9%8%5%6%6%6%7%26%
2340
11th to 20thDay
12%13%38%7%46%5%6%7%28%
2612
21st to endDay
21%12%47%6%5%7%5%6%7%20%
2917
June1st to 10thDay
14%9%48%8%5%7%7%5%7%25%
2700
11th to 20thDay
16%9%48%8%7%8%8%6%7%20%
2700
21st to endDay
7%5%26%6%47%6%7%7%41%
2700
July1st to 10thDay
5%5%25%7%46%6%7%8%46%
2700
11th to 20thDay
44245%46%6%6%8%51%
2700
21st to endDay
33233345%6%7%61%
2770
August1st to 10thDay
5%5%25%5%35%5%6%8%51%
2473
11th to 20thDay
6%4245%36%46%9%51%
2299
21st to endDay
8%425%5%35%6%6%8%47%
2574
September1st to 10thDay
10%8%25%5%35%45%7%46%
2189
11th to 20thDay
8%6%26%6%45%6%6%9%42%
1980
21st to endDay
9%8%25%5%5%5%45%10%41%
1980
October1st to 10thDay
10%10%47%6%46%6%6%6%34%
1918
11th to 20thDay
48%410%10%6%7%6%6%8%31%
1699
21st to endDay
5%10%410%8%6%7%6%6%9%29%
1782
November1st to 10thDay
5%10%5%8%11%7%10%7%7%10%21%
1622
11th to 20thDay
18%5%7%7%7%9%9%7%12%28%
1520
21st to endDay
28%411%10%7%7%8%6%11%26%
1353
December1st to 10thDay
17%5%8%9%7%8%9%10%11%24%
1330
11th to 20thDay
26%410%13%9%8%9%9%11%18%
1682
21st to endDay
17%49%9%7%11%8%9%9%26%
2442
January1st to 10thNight
17%5%12%11%9%13%11%9%8%14%
4726
11th to 20thNight
18%411%12%7%9%9%7%9%25%
4514
21st to endNight
29%49%11%12%12%7%7%8%18%
4862
February1st to 10thNight
311%7%11%10%6%9%9%7%8%19%
2608
11th to 20thNight
210%6%11%11%7%10%9%8%8%20%
2402
21st to endNight
27%5%13%11%7%12%8%9%7%19%
1886
March1st to 10thNight
17%5%10%10%8%11%10%9%10%20%
2249
11th to 20thNight
26%5%8%8%8%9%8%8%10%27%
1994
21st to endNight
49%49%9%8%10%8%8%9%22%
2165
April1st to 10thNight
49%6%7%8%5%8%7%9%11%26%
1771
11th to 20thNight
412%5%8%7%5%7%7%7%9%28%
1601
21st to endNight
6%12%47%10%5%8%45%7%33%
1620
May1st to 10thNight
7%12%48%9%6%5%6%6%7%31%
1617
11th to 20thNight
9%8%38%6%5%8%7%6%8%34%
1280
21st to endNight
19%10%35%7%45%6%6%6%28%
1358
June1st to 10thNight
12%8%46%8%7%6%5%6%7%32%
1260
11th to 20thNight
15%6%36%6%6%7%6%7%7%30%
1260
21st to endNight
5%425%6%35%7%6%7%52%
1260
July1st to 10thNight
5%31342346%7%61%
1260
11th to 20thNight
431443435%8%61%
1260
21st to endNight
4212224446%68%
1545
August1st to 10thNight
6%5%15%324447%58%
1464
11th to 20thNight
6%3134245%6%8%58%
1602
21st to endNight
6%6%2433345%8%57%
1782
September1st to 10thNight
10%5%25%5%2445%8%50%
1767
11th to 20thNight
6%7%26%6%35%46%9%46%
1980
21st to endNight
8%8%24445%5%7%9%45%
1980
October1st to 10thNight
9%10%37%5%35%5%5%8%41%
2042
11th to 20thNight
47%37%7%6%7%6%6%9%38%
2258
21st to endNight
49%48%7%7%9%7%7%10%27%
2574
November1st to 10thNight
410%5%9%9%7%9%7%7%9%23%
2438
11th to 20thNight
16%39%9%7%11%10%7%10%26%
2660
21st to endNight
28%5%9%8%6%8%8%9%11%26%
2826
December1st to 10thNight
18%5%10%8%6%9%10%9%13%21%
2850
11th to 20thNight
17%411%12%7%11%9%9%8%20%
3510
21st to endNight
17%5%10%10%6%10%7%8%9%26%
5214

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
40%12%35%9%31
2219
11th to 20thDay
46%14%17%9%9%6%
2426
21st to endDay
35%18%31%13%3
2794
February1st to 10thDay
48%16%20%11%41
1572
11th to 20thDay
46%11%25%12%5%1
1674
21st to endDay
45%14%21%13%6%1
1565
March1st to 10thDay
38%16%24%17%4
1871
11th to 20thDay
39%16%22%17%5%1
1966
21st to endDay
48%13%24%10%41
2189
April1st to 10thDay
48%9%26%15%2
2188
11th to 20thDay
50%9%20%16%41
2310
21st to endDay
48%9%20%17%5%1
2340
May1st to 10thDay
47%8%21%17%6%
2340
11th to 20thDay
47%9%18%20%7%
2616
21st to endDay
55%8%20%13%4
2918
June1st to 10thDay
48%9%19%18%6%
2700
11th to 20thDay
50%9%18%17%6%1
2700
21st to endDay
31%8%23%24%12%2
2700
July1st to 10thDay
29%8%15%27%17%4
2626
11th to 20thDay
25%7%13%25%23%7%
2619
21st to endDay
18%5%12%28%29%8%
2616
August1st to 10thDay
27%7%15%24%20%8%
2456
11th to 20thDay
26%6%16%30%18%4
2299
21st to endDay
28%6%15%27%21%4
2574
September1st to 10thDay
33%5%15%25%16%7%
2189
11th to 20thDay
30%8%18%26%15%3
1980
21st to endDay
32%8%23%25%10%2
1980
October1st to 10thDay
40%9%20%22%8%2
1918
11th to 20thDay
37%10%24%19%8%2
1699
21st to endDay
39%11%23%20%7%1
1782
November1st to 10thDay
40%15%26%12%5%1
1622
11th to 20thDay
33%18%29%13%6%1
1520
21st to endDay
40%15%25%11%8%2
1353
December1st to 10thDay
38%20%22%13%5%3
1330
11th to 20thDay
38%21%27%11%31
1684
21st to endDay
34%14%22%14%12%3
2442
January1st to 10thNight
41%15%31%9%41
4726
11th to 20thNight
45%12%19%12%6%6%
4552
21st to endNight
35%21%26%14%4
4862
February1st to 10thNight
47%13%18%12%7%2
2608
11th to 20thNight
42%15%25%12%6%1
2403
21st to endNight
45%12%22%15%5%1
1886
March1st to 10thNight
40%17%25%15%4
2249
11th to 20thNight
33%18%24%18%6%1
1994
21st to endNight
39%15%28%13%41
2165
April1st to 10thNight
38%10%27%19%6%
1771
11th to 20thNight
42%10%20%21%6%
1601
21st to endNight
43%9%18%22%7%1
1620
May1st to 10thNight
43%8%21%20%8%
1617
11th to 20thNight
38%9%23%21%10%
1280
21st to endNight
46%8%22%17%6%
1358
June1st to 10thNight
41%8%22%20%8%
1260
11th to 20thNight
42%8%20%19%10%1
1260
21st to endNight
24%8%24%27%14%2
1260
July1st to 10thNight
19%5%19%32%19%5%
1225
11th to 20thNight
20%6%15%26%24%9%
1218
21st to endNight
15%6%11%28%30%10%
1459
August1st to 10thNight
23%5%14%31%19%8%
1456
11th to 20thNight
20%6%16%34%20%4
1602
21st to endNight
24%5%12%31%24%4
1782
September1st to 10thNight
29%6%17%26%17%6%
1767
11th to 20thNight
30%7%18%28%14%4
1980
21st to endNight
29%7%24%23%14%2
1980
October1st to 10thNight
34%10%19%24%11%2
2042
11th to 20thNight
30%10%26%22%9%2
2258
21st to endNight
38%13%23%18%8%
2574
November1st to 10thNight
42%14%24%12%6%2
2438
11th to 20thNight
33%17%29%15%6%
2660
21st to endNight
37%16%26%12%8%2
2826
December1st to 10thNight
37%18%24%13%6%2
2850
11th to 20thNight
42%18%25%12%31
3507
21st to endNight
35%12%25%15%9%4
5214

Seeing (when cloud cover <= 80%)
Color Meanings:
Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
13%31%29%15%7%4
180
11th to 20thDay
12%28%29%24%32
180
21st to endDay
20%30%32%12%5%3
198
February1st to 10thDay
20%22%36%16%5%
204
11th to 20thDay
13%29%36%16%7%
270
21st to endDay
18%29%33%15%5%
377
March1st to 10thDay
15%29%33%16%5%2
449
11th to 20thDay
16%25%30%17%10%2
420
21st to endDay
19%28%31%15%5%2
462
April1st to 10thDay
18%26%36%14%6%
420
11th to 20thDay
18%31%26%17%7%1
412
21st to endDay
21%22%29%18%7%3
420
May1st to 10thDay
18%22%25%21%11%3
423
11th to 20thDay
26%13%23%18%16%4
583
21st to endDay
27%11%19%22%17%4
679
June1st to 10thDay
18%21%23%23%13%3
630
11th to 20thDay
23%22%25%18%10%2
630
21st to endDay
10%14%26%29%16%5%
630
July1st to 10thDay
8%14%27%29%18%4
621
11th to 20thDay
8%12%32%31%14%2
618
21st to endDay
6%11%32%31%15%4
516
August1st to 10thDay
12%12%28%28%15%5%
447
11th to 20thDay
8%8%33%32%15%4
437
21st to endDay
13%14%31%28%11%3
495
September1st to 10thDay
18%20%27%21%11%3
450
11th to 20thDay
12%19%31%23%12%2
450
21st to endDay
22%23%28%18%7%2
450
October1st to 10thDay
18%21%30%18%13%1
388
11th to 20thDay
18%22%30%18%9%3
270
21st to endDay
22%26%30%13%7%2
297
November1st to 10thDay
21%30%30%15%4
270
11th to 20thDay
22%34%30%12%1
270
21st to endDay
19%38%18%13%8%4
191
December1st to 10thDay
18%34%29%13%6%1
180
11th to 20thDay
23%26%29%20%21
180
21st to endDay
12%28%30%19%9%3
198
January1st to 10thNight
15%31%33%15%41
950
11th to 20thNight
12%28%36%17%5%1
840
21st to endNight
11%31%37%15%5%2
836
February1st to 10thNight
13%21%36%21%8%1
760
11th to 20thNight
11%25%36%21%6%
744
21st to endNight
11%25%32%23%8%
628
March1st to 10thNight
8%23%37%24%7%1
750
11th to 20thNight
11%25%31%23%8%2
720
21st to endNight
12%21%29%27%10%2
792
April1st to 10thNight
10%22%32%25%10%1
691
11th to 20thNight
12%20%35%22%8%1
533
21st to endNight
13%17%34%26%10%1
540
May1st to 10thNight
16%16%26%27%14%2
537
11th to 20thNight
14%8%23%35%18%2
354
21st to endNight
27%9%19%26%18%2
389
June1st to 10thNight
16%14%26%29%15%1
360
11th to 20thNight
19%16%28%26%10%1
360
21st to endNight
7%7%32%33%20%1
360
July1st to 10thNight
7%9%19%40%23%1
350
11th to 20thNight
8%5%31%39%16%1
348
21st to endNight
7%6%22%43%20%2
394
August1st to 10thNight
9%421%40%25%2
390
11th to 20thNight
7%425%37%25%3
534
21st to endNight
11%10%25%37%15%2
594
September1st to 10thNight
15%9%26%28%17%5%
656
11th to 20thNight
11%11%25%31%17%5%
720
21st to endNight
15%15%30%24%13%3
720
October1st to 10thNight
17%18%22%29%13%2
720
11th to 20thNight
12%21%28%28%10%1
720
21st to endNight
17%25%32%19%6%1
792
November1st to 10thNight
17%29%33%17%4
773
11th to 20thNight
16%33%35%13%21
950
21st to endNight
15%30%33%17%5%1
950
December1st to 10thNight
12%25%37%19%5%1
950
11th to 20thNight
11%29%39%17%4
950
21st to endNight
13%25%38%18%5%
1045
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