Writing-on-Stone Provincial Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Writing-on-Stone Provincial Park clear sky chart from 2005-11-06 to 2024-03-06.

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
38%
23905
16%
80636
9%
23833
45%
23833
23%
49552

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
27%
939
16%
4663
6%
926
34%
926
14%
2777
January11th to 20thNight
29%
943
18%
4672
9%
930
37%
930
13%
3037
January21st to endNight
27%
837
12%
4619
8%
824
40%
824
13%
2563
February1st to 10thNight
31%
760
13%
2494
9%
760
37%
760
17%
1732
February11th to 20thNight
29%
740
12%
2403
7%
740
36%
740
17%
1662
February21st to endNight
33%
628
14%
1994
8%
628
42%
628
20%
1348
March1st to 10thNight
33%
742
13%
2158
8%
742
39%
742
21%
1489
March11th to 20thNight
36%
720
16%
1980
9%
720
42%
720
23%
1341
March21st to endNight
33%
792
11%
2178
4%
792
39%
792
21%
1544
April1st to 10thNight
34%
611
14%
1786
6%
611
40%
611
22%
1210
April11th to 20thNight
30%
533
17%
1601
9%
533
37%
533
22%
1063
April21st to endNight
36%
540
14%
1620
10%
540
41%
540
21%
1086
May1st to 10thNight
45%
540
13%
1548
10%
540
49%
540
29%
985
May11th to 20thNight
53%
470
18%
1355
14%
470
58%
470
33%
820
May21st to endNight
43%
389
9%
1358
8%
388
47%
388
17%
934
June1st to 10thNight
45%
360
8%
1260
6%
360
49%
360
26%
745
June11th to 20thNight
37%
360
7%
1260
3%
360
41%
360
22%
771
June21st to endNight
59%
360
10%
1260
7%
360
63%
360
38%
617
July1st to 10thNight
61%
350
12%
1225
10%
350
65%
350
44%
565
July11th to 20thNight
57%
348
17%
1218
16%
348
64%
348
42%
591
July21st to endNight
65%
394
25%
1335
26%
372
75%
372
48%
570
August1st to 10thNight
60%
493
20%
1559
19%
491
65%
491
40%
817
August11th to 20thNight
60%
534
23%
1602
16%
534
67%
534
43%
862
August21st to endNight
57%
594
28%
1782
20%
594
62%
594
40%
963
September1st to 10thNight
53%
540
24%
1729
19%
540
59%
540
37%
937
September11th to 20thNight
54%
720
23%
1980
16%
720
59%
720
38%
1176
September21st to endNight
46%
720
24%
1980
15%
720
53%
720
36%
1195
October1st to 10thNight
45%
720
21%
2123
12%
720
53%
720
29%
1311
October11th to 20thNight
36%
720
22%
2160
9%
720
48%
720
28%
1323
October21st to endNight
31%
792
17%
2568
7%
792
42%
792
23%
1607
November1st to 10thNight
25%
883
15%
2548
6%
883
33%
883
21%
1763
November11th to 20thNight
28%
950
19%
2660
7%
950
39%
950
25%
1732
November21st to endNight
30%
950
14%
2705
6%
950
36%
950
28%
1733
December1st to 10thNight
34%
950
15%
2850
8%
950
40%
950
21%
1923
December11th to 20thNight
27%
949
14%
3433
5%
949
34%
949
18%
2193
December21st to endNight
27%
1034
11%
4970
6%
1026
36%
1026
15%
2567

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
9%8%36%6%35%5%6%8%43%
78019
Night
7%8%47%5%35%5%6%8%42%
81512
TransparencyDay
39%5%15%25%13%3
77702
Night
39%6%16%24%12%3
81352
SeeingDay
13%10%28%28%17%5%
14455
Night
12%10%33%32%13%1
23948

By Month

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 10thDay
415%5%7%8%45%5%7%8%32%
2219
11th to 20thDay
49%49%7%5%9%8%6%6%32%
2229
21st to endDay
37%47%5%45%5%5%8%47%
2794
February1st to 10thDay
6%13%5%9%8%46%5%5%8%30%
1685
11th to 20thDay
7%15%48%8%5%5%6%7%6%29%
1665
21st to endDay
410%6%11%8%45%447%35%
1458
March1st to 10thDay
5%11%5%11%7%5%35%5%8%36%
1917
11th to 20thDay
7%10%5%6%6%35%5%6%8%38%
1980
21st to endDay
7%12%5%8%6%46%5%6%9%31%
2178
April1st to 10thDay
9%9%47%8%46%6%6%8%33%
2168
11th to 20thDay
12%13%48%6%345%5%8%32%
2307
21st to endDay
14%8%38%6%45%45%8%35%
2340
May1st to 10thDay
13%9%35%6%46%5%6%7%35%
2412
11th to 20thDay
13%6%25%5%35%6%6%9%39%
2535
21st to endDay
23%8%35%6%35%5%5%7%31%
2917
June1st to 10thDay
15%6%35%5%45%5%6%8%38%
2700
11th to 20thDay
17%5%35%6%45%6%6%8%35%
2700
21st to endDay
7%413435%5%7%9%51%
2700
July1st to 10thDay
6%3135%245%6%9%55%
2700
11th to 20thDay
6%323335%5%6%8%58%
2700
21st to endDay
421232446%9%64%
2902
August1st to 10thDay
6%31332446%10%59%
2370
11th to 20thDay
8%313425%45%8%56%
2299
21st to endDay
9%3235%3445%7%55%
2574
September1st to 10thDay
11%42432445%6%54%
2226
11th to 20thDay
12%5%24425%45%7%51%
1980
21st to endDay
12%5%2442445%7%51%
1980
October1st to 10thDay
11%9%36%4245%47%44%
1836
11th to 20thDay
7%9%47%6%35%45%7%42%
1800
21st to endDay
9%9%36%6%345%6%9%40%
1787
November1st to 10thDay
14%13%46%6%3445%6%35%
1511
11th to 20thDay
5%9%38%6%36%6%6%8%39%
1520
21st to endDay
411%48%6%36%45%8%39%
1473
December1st to 10thDay
5%12%49%7%47%45%7%36%
1330
11th to 20thDay
5%10%49%6%45%5%8%9%34%
1685
21st to endDay
47%26%5%345%5%8%49%
2442
January1st to 10thNight
412%5%8%6%346%7%9%36%
4726
11th to 20thNight
412%5%8%6%48%6%5%8%34%
4740
21st to endNight
48%47%5%35%5%6%8%45%
4885
February1st to 10thNight
7%12%5%10%6%45%5%5%7%33%
2494
11th to 20thNight
6%13%48%7%5%6%5%7%7%32%
2402
21st to endNight
6%11%5%9%7%5%6%5%5%7%34%
1994
March1st to 10thNight
5%9%5%10%7%46%6%6%9%33%
2158
11th to 20thNight
5%9%5%7%6%46%5%7%9%37%
1980
21st to endNight
8%12%47%7%35%6%7%9%33%
2178
April1st to 10thNight
9%10%5%7%6%45%5%6%7%37%
1786
11th to 20thNight
11%11%48%5%345%6%7%35%
1601
21st to endNight
13%9%35%6%36%5%5%7%37%
1620
May1st to 10thNight
10%7%35%5%35%5%6%8%42%
1548
11th to 20thNight
10%425%5%35%46%8%47%
1355
21st to endNight
20%7%26%5%45%5%46%35%
1358
June1st to 10thNight
11%5%335%35%6%6%10%43%
1260
11th to 20thNight
16%425%5%36%5%48%42%
1260
21st to endNight
7%4133235%7%9%56%
1260
July1st to 10thNight
7%21232435%6%63%
1260
11th to 20thNight
7%31332346%8%60%
1260
21st to endNight
4213423348%65%
1413
August1st to 10thNight
7%3144345%5%8%56%
1567
11th to 20thNight
7%42342345%10%55%
1602
21st to endNight
8%5%2443445%7%55%
1782
September1st to 10thNight
11%42343336%7%53%
1729
11th to 20thNight
11%6%245%2345%6%52%
1980
21st to endNight
9%6%344235%5%7%51%
1980
October1st to 10thNight
12%6%35%43445%7%47%
2123
11th to 20thNight
10%6%36%5%35%5%6%8%44%
2160
21st to endNight
8%7%46%6%46%6%6%8%40%
2568
November1st to 10thNight
12%12%48%6%3446%7%35%
2548
11th to 20thNight
5%9%37%6%36%5%6%8%41%
2660
21st to endNight
411%5%7%6%345%6%10%41%
2705
December1st to 10thNight
5%11%5%8%7%45%6%6%8%36%
2850
11th to 20thNight
48%410%7%45%5%7%9%38%
3506
21st to endNight
48%36%5%45%5%6%7%48%
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
48%6%16%23%5%1
2219
11th to 20thDay
50%8%13%13%14%2
2229
21st to endDay
36%7%22%30%5%
2794
February1st to 10thDay
53%6%15%19%7%1
1685
11th to 20thDay
52%6%15%18%7%1
1674
21st to endDay
49%414%23%9%1
1458
March1st to 10thDay
47%6%17%23%7%
1917
11th to 20thDay
42%6%16%26%8%2
1980
21st to endDay
49%6%16%19%9%
2178
April1st to 10thDay
48%5%14%23%9%
2168
11th to 20thDay
51%5%11%23%9%1
2310
21st to endDay
47%5%14%25%8%1
2340
May1st to 10thDay
45%6%15%24%10%1
2412
11th to 20thDay
40%5%16%26%12%1
2539
21st to endDay
51%5%13%22%8%
2918
June1st to 10thDay
42%5%17%23%12%1
2700
11th to 20thDay
45%5%14%20%14%2
2700
21st to endDay
27%5%17%33%14%3
2700
July1st to 10thDay
23%5%16%30%21%5%
2626
11th to 20thDay
24%5%13%27%25%7%
2619
21st to endDay
18%411%29%30%8%
2741
August1st to 10thDay
22%414%31%24%6%
2353
11th to 20thDay
26%414%32%21%3
2299
21st to endDay
27%5%10%29%23%6%
2574
September1st to 10thDay
29%413%26%18%10%
2226
11th to 20thDay
33%5%13%29%17%4
1980
21st to endDay
33%413%31%16%4
1980
October1st to 10thDay
40%6%17%25%10%2
1836
11th to 20thDay
41%5%15%25%12%2
1800
21st to endDay
40%6%17%26%10%1
1787
November1st to 10thDay
50%5%14%20%8%3
1511
11th to 20thDay
40%6%21%23%8%1
1520
21st to endDay
42%6%20%21%8%2
1473
December1st to 10thDay
47%5%16%22%7%3
1330
11th to 20thDay
44%7%19%26%31
1684
21st to endDay
33%5%18%25%16%3
2442
January1st to 10thNight
42%7%19%24%7%1
4726
11th to 20thNight
48%6%14%16%13%2
4740
21st to endNight
36%8%19%28%8%
4885
February1st to 10thNight
51%5%15%17%10%2
2494
11th to 20thNight
49%6%15%19%9%1
2403
21st to endNight
49%414%22%9%2
1994
March1st to 10thNight
46%6%19%21%7%
2158
11th to 20thNight
43%7%18%22%10%
1980
21st to endNight
46%7%19%20%6%1
2178
April1st to 10thNight
46%6%15%25%8%
1786
11th to 20thNight
45%6%12%23%13%1
1601
21st to endNight
45%6%14%26%8%1
1620
May1st to 10thNight
40%416%28%11%1
1548
11th to 20thNight
33%6%14%28%17%2
1356
21st to endNight
50%6%12%23%9%
1358
June1st to 10thNight
36%6%17%28%12%1
1260
11th to 20thNight
39%6%15%25%13%1
1260
21st to endNight
23%6%18%31%19%4
1260
July1st to 10thNight
21%411%35%21%8%
1225
11th to 20thNight
23%5%11%28%25%9%
1218
21st to endNight
18%49%26%32%13%
1335
August1st to 10thNight
25%6%11%29%22%7%
1559
11th to 20thNight
25%5%12%28%23%6%
1602
21st to endNight
28%49%23%28%8%
1782
September1st to 10thNight
30%39%30%18%10%
1729
11th to 20thNight
32%412%30%16%6%
1980
21st to endNight
33%413%30%17%3
1980
October1st to 10thNight
38%5%15%25%14%2
2123
11th to 20thNight
37%5%15%27%13%3
2160
21st to endNight
40%7%16%26%10%1
2568
November1st to 10thNight
48%5%15%20%9%2
2548
11th to 20thNight
40%6%19%24%11%
2660
21st to endNight
39%5%24%20%10%2
2705
December1st to 10thNight
45%6%15%22%11%1
2850
11th to 20thNight
41%8%23%22%41
3507
21st to endNight
35%6%13%26%15%6%
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
10%12%36%19%14%9%
180
11th to 20thDay
10%12%33%31%11%3
180
21st to endDay
12%13%44%21%8%3
198
February1st to 10thDay
16%17%35%24%6%2
258
11th to 20thDay
10%14%38%27%8%3
270
21st to endDay
12%13%33%27%13%2
270
March1st to 10thDay
11%16%37%22%12%2
441
11th to 20thDay
11%15%32%26%11%5%
420
21st to endDay
12%14%35%24%13%2
462
April1st to 10thDay
14%15%34%29%8%
420
11th to 20thDay
17%15%32%25%11%2
412
21st to endDay
18%13%22%26%19%1
420
May1st to 10thDay
16%11%22%26%19%5%
495
11th to 20thDay
18%8%20%27%21%6%
625
21st to endDay
21%6%18%29%20%7%
679
June1st to 10thDay
15%13%24%26%17%5%
630
11th to 20thDay
19%11%33%24%10%3
630
21st to endDay
8%7%25%32%23%6%
630
July1st to 10thDay
8%420%34%28%7%
621
11th to 20thDay
8%5%24%38%22%3
618
21st to endDay
3421%37%27%8%
648
August1st to 10thDay
6%6%19%34%28%6%
447
11th to 20thDay
8%416%33%28%11%
437
21st to endDay
8%5%25%31%23%8%
495
September1st to 10thDay
12%9%26%28%20%5%
450
11th to 20thDay
14%8%24%32%17%6%
450
21st to endDay
16%11%27%27%14%5%
450
October1st to 10thDay
15%8%26%26%18%7%
306
11th to 20thDay
14%10%31%23%16%5%
270
21st to endDay
20%14%32%22%10%2
297
November1st to 10thDay
25%10%34%23%8%
270
11th to 20thDay
9%14%44%24%8%1
270
21st to endDay
9%17%38%22%9%4
248
December1st to 10thDay
11%18%43%14%12%2
180
11th to 20thDay
13%16%41%16%13%1
180
21st to endDay
13%11%28%29%13%7%
198
January1st to 10thNight
11%13%40%26%9%1
950
11th to 20thNight
10%13%40%26%11%1
950
21st to endNight
9%14%39%27%8%2
846
February1st to 10thNight
13%14%32%28%11%2
760
11th to 20thNight
12%14%35%28%11%1
744
21st to endNight
10%10%32%31%14%2
628
March1st to 10thNight
7%11%36%31%14%1
742
11th to 20thNight
10%13%34%32%10%1
720
21st to endNight
13%12%34%29%11%2
792
April1st to 10thNight
12%10%35%31%11%1
611
11th to 20thNight
14%10%37%27%11%1
533
21st to endNight
18%10%29%31%13%
540
May1st to 10thNight
13%8%28%31%19%1
540
11th to 20thNight
11%6%23%40%19%1
470
21st to endNight
24%5%16%35%15%3
389
June1st to 10thNight
13%8%28%33%16%1
360
11th to 20thNight
18%11%33%28%11%
360
21st to endNight
9%5%22%44%20%
360
July1st to 10thNight
7%323%46%20%1
350
11th to 20thNight
9%325%46%16%1
348
21st to endNight
5%322%47%22%1
394
August1st to 10thNight
8%322%42%24%2
493
11th to 20thNight
7%422%43%24%1
534
21st to endNight
10%424%42%20%1
594
September1st to 10thNight
12%226%41%16%2
540
11th to 20thNight
13%423%37%23%2
720
21st to endNight
13%7%29%33%16%2
720
October1st to 10thNight
16%7%24%35%18%1
720
11th to 20thNight
13%9%35%28%12%3
720
21st to endNight
12%13%36%28%9%1
792
November1st to 10thNight
17%12%40%25%6%
883
11th to 20thNight
10%15%42%24%8%1
950
21st to endNight
9%11%42%29%8%1
950
December1st to 10thNight
10%12%34%32%9%2
950
11th to 20thNight
10%11%41%27%9%2
950
21st to endNight
12%12%39%27%9%2
1045
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