Waterton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Waterton clear sky chart from 2005-11-05 to 2017-09-16.

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
26%
15205
11%
46789
6%
15174
32%
15174
17%
31016

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 15thNight
14%
891
5%
2676
3%
886
17%
886
9%
2056
January16th to endNight
18%
768
12%
2688
7%
768
26%
768
12%
1811
February1st to 15thNight
21%
702
8%
2375
3%
700
26%
700
10%
1690
February16th to endNight
18%
632
9%
1955
4%
632
24%
632
13%
1414
March1st to 15thNight
15%
720
8%
2109
1%
720
21%
720
12%
1507
March16th to endNight
22%
768
6%
2103
1%
768
26%
768
12%
1551
April1st to 15thNight
25%
639
8%
1719
2%
639
28%
639
17%
1207
April16th to endNight
26%
540
13%
1620
8%
540
31%
540
16%
1112
May1st to 15thNight
34%
476
10%
1524
8%
476
37%
476
20%
959
May16th to endNight
35%
374
7%
1309
5%
374
39%
374
14%
905
June1st to 15thNight
34%
360
4%
1260
2%
360
36%
360
18%
799
June16th to endNight
33%
360
6%
1260
1%
360
38%
360
23%
711
July1st to 15thNight
53%
340
10%
1190
6%
340
57%
340
37%
559
July16th to endNight
51%
376
19%
1340
16%
354
67%
354
36%
589
August1st to 15thNight
58%
443
20%
1515
20%
441
65%
441
36%
746
August16th to endNight
49%
573
28%
1719
17%
573
57%
573
39%
877
September1st to 15thNight
45%
678
18%
1839
11%
678
49%
678
34%
1065
September16th to endNight
41%
660
21%
1826
12%
660
48%
660
33%
1066
October1st to 15thNight
30%
660
14%
1913
8%
660
37%
660
19%
1283
October16th to endNight
28%
704
13%
2288
7%
704
36%
704
19%
1441
November1st to 15thNight
14%
781
11%
2356
3%
781
22%
781
12%
1648
November16th to endNight
14%
900
8%
2625
2%
900
19%
900
12%
1890
December1st to 15thNight
18%
900
8%
2700
4%
900
21%
900
11%
2014
December16th to endNight
12%
960
7%
2880
2%
960
17%
960
9%
2116

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
7%9%47%7%5%7%6%6%7%30%
48004
Night
47%47%6%5%7%7%7%8%31%
46945
Cloud CoverDay
7%7%36%5%35%6%7%10%35%
48005
Night
5%7%36%5%35%5%7%12%38%
46948
TransparencyDay
41%10%19%17%8%1
47664
Night
37%12%21%18%8%1
46789
SeeingDay
15%26%25%19%10%2
5944
Night
11%31%25%20%9%1
15209

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 15thDay
26%6%10%9%6%10%11%10%8%18%
1274
16th to endDay
29%7%11%8%6%9%7%5%8%22%
1536
February1st to 15thDay
39%49%9%6%9%8%7%9%20%
1488
16th to endDay
213%5%12%10%6%10%8%6%6%17%
1518
March1st to 15thDay
6%6%10%10%9%9%10%9%7%19%
1851
16th to endDay
5%13%6%13%11%7%9%6%5%6%12%
2120
April1st to 15thDay
6%15%7%9%10%5%8%8%5%6%16%
2228
16th to endDay
8%16%5%9%8%46%5%5%6%22%
2340
May1st to 15thDay
8%14%48%7%5%5%5%5%6%29%
2424
16th to endDay
21%12%37%6%46%46%6%20%
2802
June1st to 15thDay
16%9%47%6%5%7%6%5%6%23%
2700
16th to endDay
10%6%36%7%5%8%6%6%6%32%
2700
July1st to 15thDay
45%25%7%46%5%6%8%43%
2700
16th to endDay
43134345%5%7%55%
2734
August1st to 15thDay
6%5%25%5%35%5%5%8%46%
2436
16th to endDay
7%314435%46%8%49%
2483
September1st to 15thDay
10%7%245%35%447%44%
2118
16th to endDay
10%5%144344410%44%
1823
October1st to 15thDay
10%10%49%8%5%7%6%5%5%27%
1715
16th to endDay
6%8%37%7%7%7%7%7%10%26%
1584
November1st to 15thDay
36%46%8%6%12%9%7%11%22%
1491
16th to endDay
212%5%9%8%6%5%7%6%8%26%
1335
December1st to 15thDay
28%48%9%7%7%9%10%11%21%
1260
16th to endDay
19%49%8%6%9%9%9%9%20%
1344
January1st to 15thNight
19%49%10%8%10%10%9%8%16%
2676
16th to endNight
29%48%8%6%8%9%9%9%24%
2688
February1st to 15thNight
310%5%9%9%6%8%10%8%8%19%
2364
16th to endNight
29%6%12%8%5%9%9%8%8%18%
1955
March1st to 15thNight
7%48%8%7%11%11%10%10%20%
2109
16th to endNight
49%5%8%8%7%9%8%7%9%20%
2100
April1st to 15thNight
5%10%6%6%5%49%8%9%9%24%
1719
16th to endNight
7%11%46%8%5%5%45%7%33%
1620
May1st to 15thNight
6%10%36%5%5%5%5%6%6%36%
1523
16th to endNight
18%8%27%6%35%5%5%7%27%
1309
June1st to 15thNight
12%6%46%5%5%446%7%36%
1260
16th to endNight
8%425%5%35%6%6%7%43%
1260
July1st to 15thNight
5%2332235%7%60%
1260
16th to endNight
321222435%7%64%
1433
August1st to 15thNight
6%333145%48%56%
1523
16th to endNight
5%41332335%8%59%
1719
September1st to 15thNight
9%5%1442435%7%51%
1839
16th to endNight
8%5%143245%7%9%48%
1826
October1st to 15thNight
9%9%46%5%45%5%5%8%34%
1913
16th to endNight
46%26%6%6%8%8%7%10%30%
2288
November1st to 15thNight
36%47%7%6%11%10%7%8%27%
2356
16th to endNight
27%48%8%6%8%8%9%9%24%
2625
December1st to 15thNight
110%5%10%6%5%9%10%9%12%18%
2700
16th to endNight
17%6%10%8%6%10%10%10%7%20%
2880

Percentage Cloud Cover SW (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 15thDay
16%48%6%36%6%9%19%26%
1274
16th to endDay
28%48%7%46%7%7%12%29%
1536
February1st to 15thDay
28%5%6%6%45%8%8%14%28%
1488
16th to endDay
211%410%6%37%6%8%12%25%
1518
March1st to 15thDay
15%6%8%6%46%7%9%15%29%
1851
16th to endDay
5%12%5%7%7%47%9%9%12%18%
2121
April1st to 15thDay
6%13%5%7%6%47%8%7%12%21%
2228
16th to endDay
8%14%5%7%6%446%6%9%26%
2340
May1st to 15thDay
9%11%45%6%35%5%6%9%32%
2424
16th to endDay
22%9%36%5%35%5%6%7%23%
2802
June1st to 15thDay
15%8%26%7%36%5%7%8%27%
2700
16th to endDay
9%4247%36%6%8%9%36%
2700
July1st to 15thDay
44245%35%6%8%8%46%
2700
16th to endDay
43133245%5%8%58%
2734
August1st to 15thDay
8%4144245%7%7%48%
2436
16th to endDay
7%3133245%6%8%52%
2483
September1st to 15thDay
12%5%14425%447%47%
2118
16th to endDay
10%412224449%50%
1823
October1st to 15thDay
10%9%26%7%35%5%7%8%33%
1715
16th to endDay
5%8%26%435%7%9%11%34%
1584
November1st to 15thDay
36%34426%5%8%18%34%
1491
16th to endDay
211%5%6%6%345%7%12%33%
1335
December1st to 15thDay
17%48%7%36%7%9%12%30%
1260
16th to endDay
17%47%6%45%7%9%15%29%
1344
January1st to 15thNight
27%48%5%37%8%9%17%25%
2676
16th to endNight
18%37%5%26%6%8%14%33%
2688
February1st to 15thNight
210%5%7%7%26%6%8%15%27%
2364
16th to endNight
110%49%7%36%5%7%13%28%
1955
March1st to 15thNight
6%47%5%35%6%10%17%32%
2109
16th to endNight
48%5%7%6%347%8%15%28%
2103
April1st to 15thNight
5%11%443345%9%15%31%
1719
16th to endNight
8%10%45%5%35%45%9%37%
1620
May1st to 15thNight
7%8%26%5%3446%9%40%
1523
16th to endNight
19%7%24426%5%6%8%31%
1309
June1st to 15thNight
12%5%245%35%47%8%40%
1260
16th to endNight
8%4145%3445%9%47%
1260
July1st to 15thNight
6%21122245%8%62%
1260
16th to endNight
311331335%6%66%
1433
August1st to 15thNight
7%3322345%7%58%
1523
16th to endNight
6%31321335%7%61%
1719
September1st to 15thNight
10%5%13323346%55%
1839
16th to endNight
9%31332445%9%52%
1826
October1st to 15thNight
9%8%25%4245%7%10%39%
1913
16th to endNight
45%25%4345%8%13%39%
2288
November1st to 15thNight
35%26%446%5%7%16%36%
2356
16th to endNight
27%48%6%35%5%7%17%32%
2625
December1st to 15thNight
18%5%9%5%26%7%8%14%29%
2700
16th to endNight
17%5%9%7%46%6%8%14%29%
2880

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 15thDay
41%18%26%9%21
1274
16th to endDay
45%12%23%12%42
1536
February1st to 15thDay
42%17%23%11%4
1488
16th to endDay
49%12%20%12%3
1518
March1st to 15thDay
39%20%22%15%1
1851
16th to endDay
52%14%22%8%2
2121
April1st to 15thDay
52%9%22%13%2
2228
16th to endDay
51%8%19%15%4
2340
May1st to 15thDay
46%7%19%16%8%
2424
16th to endDay
57%8%18%12%3
2807
June1st to 15thDay
50%10%16%16%6%
2700
16th to endDay
38%8%21%21%8%1
2700
July1st to 15thDay
31%6%15%26%16%3
2541
16th to endDay
22%5%14%27%24%5%
2564
August1st to 15thDay
30%6%16%27%14%3
2419
16th to endDay
26%415%29%20%2
2483
September1st to 15thDay
33%415%24%16%4
2118
16th to endDay
30%7%19%25%12%3
1823
October1st to 15thDay
45%10%21%15%5%
1715
16th to endDay
38%13%25%18%4
1584
November1st to 15thDay
34%19%28%12%4
1491
16th to endDay
42%14%24%10%6%1
1335
December1st to 15thDay
42%21%20%11%3
1260
16th to endDay
41%19%19%13%6%
1344
January1st to 15thNight
42%22%21%8%31
2676
16th to endNight
39%14%22%16%5%2
2688
February1st to 15thNight
43%15%21%12%5%1
2375
16th to endNight
46%12%20%14%4
1955
March1st to 15thNight
35%20%26%15%1
2109
16th to endNight
43%15%24%13%2
2103
April1st to 15thNight
41%11%24%17%4
1719
16th to endNight
43%9%17%22%5%
1620
May1st to 15thNight
38%7%22%20%10%
1524
16th to endNight
47%9%20%16%6%
1309
June1st to 15thNight
39%9%18%22%10%
1260
16th to endNight
32%6%23%24%12%
1260
July1st to 15thNight
20%418%33%16%5%
1190
16th to endNight
18%5%12%29%27%6%
1340
August1st to 15thNight
23%5%16%36%15%3
1515
16th to endNight
22%412%33%23%3
1719
September1st to 15thNight
29%415%27%17%5%
1839
16th to endNight
26%6%21%25%15%3
1826
October1st to 15thNight
37%12%22%20%7%
1913
16th to endNight
34%12%25%20%6%
2288
November1st to 15thNight
36%17%23%14%5%
2356
16th to endNight
40%16%24%11%5%1
2625
December1st to 15thNight
43%19%21%12%3
2700
16th to endNight
43%16%24%11%3
2880

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 15thDay
310%36%20%21%8%
60
16th to endDay
12%31%29%14%6%6%
64
February1st to 15thDay
12%28%36%18%5%
75
16th to endDay
13%33%30%15%6%
177
March1st to 15thDay
16%45%30%7%
270
16th to endDay
18%39%28%12%1
288
April1st to 15thDay
17%39%27%11%3
269
16th to endDay
18%30%26%14%7%2
270
May1st to 15thDay
20%28%22%18%9%1
321
16th to endDay
25%20%16%16%14%5%
517
June1st to 15thDay
16%28%20%19%12%2
495
16th to endDay
12%25%24%22%12%3
495
July1st to 15thDay
8%16%25%28%17%4
475
16th to endDay
7%20%31%25%12%2
403
August1st to 15thDay
11%15%24%27%16%4
315
16th to endDay
12%15%27%29%10%4
332
September1st to 15thDay
20%23%25%17%9%3
315
16th to endDay
13%32%25%19%8%
258
October1st to 15thDay
25%21%29%12%9%
162
16th to endDay
17%20%25%20%10%5%
96
November1st to 15thDay
21%28%31%16%2
90
16th to endDay
17%21%27%20%6%5%
73
December1st to 15thDay
15%25%13%36%6%3
60
16th to endDay
10%34%18%21%10%3
64
January1st to 15thNight
12%39%29%13%41
891
16th to endNight
10%38%27%16%41
768
February1st to 15thNight
9%35%25%18%9%
704
16th to endNight
7%33%29%21%6%
632
March1st to 15thNight
7%39%32%15%4
720
16th to endNight
11%35%21%23%6%1
768
April1st to 15thNight
10%36%24%18%8%1
639
16th to endNight
12%28%26%20%9%2
540
May1st to 15thNight
12%26%20%25%12%2
477
16th to endNight
21%22%13%23%17%1
375
June1st to 15thNight
13%27%20%23%14%1
360
16th to endNight
11%24%23%24%15%1
360
July1st to 15thNight
9%17%16%33%21%1
340
16th to endNight
6%21%16%35%18%1
376
August1st to 15thNight
7%12%16%31%29%2
443
16th to endNight
8%16%21%32%17%2
573
September1st to 15thNight
15%15%18%25%17%6%
678
16th to endNight
10%21%22%24%15%4
660
October1st to 15thNight
17%25%20%22%11%2
660
16th to endNight
11%26%27%24%7%1
704
November1st to 15thNight
13%42%27%12%3
781
16th to endNight
11%40%29%14%31
900
December1st to 15thNight
9%36%29%18%5%1
900
16th to endNight
8%39%31%14%5%
960
Page generated at 2017-09-17 10:05:41. Version ac04

Copyright 2017 A. Danko


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