Stanley
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stanley 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
50%
15023
18%
46927
16%
14995
54%
14995
26%
29760

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
37%
716
14%
2506
11%
716
42%
716
16%
1778
January16th to endNight
44%
768
17%
2688
16%
768
48%
768
20%
1775
February1st to 15thNight
36%
700
10%
2268
10%
696
39%
696
16%
1634
February16th to endNight
32%
632
10%
1895
9%
632
35%
632
14%
1462
March1st to 15thNight
36%
720
9%
2121
8%
720
38%
720
17%
1565
March16th to endNight
37%
768
12%
2091
7%
768
40%
768
19%
1523
April1st to 15thNight
42%
707
13%
1787
8%
707
43%
707
21%
1308
April16th to endNight
44%
540
17%
1620
12%
540
47%
540
26%
1040
May1st to 15thNight
56%
539
16%
1619
13%
539
59%
539
31%
963
May16th to endNight
57%
418
12%
1541
15%
418
59%
418
21%
978
June1st to 15thNight
61%
360
12%
1356
14%
360
65%
360
24%
809
June16th to endNight
73%
360
23%
1372
34%
360
78%
360
42%
612
July1st to 15thNight
85%
340
21%
1360
34%
340
87%
340
53%
529
July16th to endNight
82%
376
32%
1416
44%
354
85%
354
56%
523
August1st to 15thNight
77%
518
29%
1591
27%
516
79%
516
52%
762
August16th to endNight
76%
630
35%
1776
26%
630
78%
630
58%
837
September1st to 15thNight
76%
720
32%
1881
23%
720
79%
720
59%
960
September16th to endNight
69%
656
30%
1816
24%
656
72%
656
47%
988
October1st to 15thNight
58%
660
24%
1859
19%
660
63%
660
37%
1112
October16th to endNight
52%
704
20%
2276
16%
704
58%
704
28%
1399
November1st to 15thNight
44%
700
19%
2275
17%
700
49%
700
22%
1514
November16th to endNight
39%
745
14%
2365
11%
745
43%
745
19%
1637
December1st to 15thNight
35%
900
8%
2682
6%
900
36%
900
17%
1978
December16th to endNight
32%
846
12%
2766
9%
846
37%
846
14%
2074

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
5%10%47%6%34446%42%
47814
Night
38%46%5%3445%7%44%
47099
TransparencyDay
43%5%11%18%14%6%
47485
Night
39%7%13%20%14%5%
46928
SeeingDay
13%20%34%21%8%2
5429
Night
9%9%24%33%20%3
15033

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 15thDay
13%6%9%8%3445%6%36%
1432
16th to endDay
113%7%9%8%3445%5%36%
1536
February1st to 15thDay
214%6%11%7%25%5%5%6%32%
1594
16th to endDay
215%9%16%8%4445%6%22%
1579
March1st to 15thDay
115%8%11%7%35%5%6%7%27%
1839
16th to endDay
5%20%6%11%7%44447%24%
2130
April1st to 15thDay
418%8%10%7%3445%6%25%
2161
16th to endDay
6%13%5%9%6%24446%35%
2340
May1st to 15thDay
6%10%47%6%45%45%6%38%
2331
16th to endDay
11%14%5%8%7%45%446%27%
2570
June1st to 15thDay
12%9%26%6%35%5%6%6%34%
2595
16th to endDay
5%4135%23435%59%
2579
July1st to 15thDay
321442435%7%60%
2520
16th to endDay
321333433465%
2657
August1st to 15thDay
33245%25%45%6%55%
2361
16th to endDay
2213323345%65%
2423
September1st to 15thDay
5%313323345%63%
2079
16th to endDay
7%7%23323346%54%
1816
October1st to 15thDay
7%10%25%5%24445%46%
1770
16th to endDay
5%10%46%5%4445%8%40%
1595
November1st to 15thDay
6%12%5%8%6%3435%6%36%
1584
16th to endDay
112%6%10%7%3346%7%36%
1581
December1st to 15thDay
212%7%14%9%45%435%29%
1275
16th to endDay
313%7%13%10%45%45%5%26%
1467
January1st to 15thNight
214%7%8%7%345%48%32%
2506
16th to endNight
210%7%8%6%3445%6%39%
2688
February1st to 15thNight
212%7%10%6%35%5%6%7%30%
2257
16th to endNight
111%7%11%8%5%6%5%6%7%27%
1895
March1st to 15thNight
212%6%10%6%45%5%7%8%30%
2121
16th to endNight
312%48%6%35%5%7%8%34%
2091
April1st to 15thNight
311%6%8%5%35%6%6%7%33%
1787
16th to endNight
411%45%5%24447%43%
1620
May1st to 15thNight
38%25%4245%49%48%
1619
16th to endNight
6%10%25%6%35%6%5%10%37%
1540
June1st to 15thNight
9%5%25%425%47%9%43%
1356
16th to endNight
231232345%7%62%
1372
July1st to 15thNight
11121346%7%69%
1440
16th to endNight
11221323475%
1512
August1st to 15thNight
22322345%7%65%
1599
16th to endNight
212213346%70%
1776
September1st to 15thNight
3212212345%70%
1881
16th to endNight
6%413312346%61%
1816
October1st to 15thNight
5%8%2331445%6%53%
1859
16th to endNight
5%8%35%4345%5%7%45%
2276
November1st to 15thNight
5%12%5%7%4245%6%9%37%
2275
16th to endNight
37%47%7%47%5%5%7%37%
2365
December1st to 15thNight
211%6%11%8%45%5%5%8%30%
2682
16th to endNight
212%6%13%10%4445%6%28%
2766

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
48%9%14%16%8%2
1432
16th to endDay
50%5%11%19%10%3
1536
February1st to 15thDay
52%8%14%15%6%2
1594
16th to endDay
65%6%10%13%3
1579
March1st to 15thDay
55%7%15%14%5%
1839
16th to endDay
61%6%13%14%4
2130
April1st to 15thDay
59%7%12%15%4
2161
16th to endDay
49%6%15%18%9%
2340
May1st to 15thDay
45%5%16%23%8%
2331
16th to endDay
58%413%16%5%1
2574
June1st to 15thDay
48%6%10%21%11%2
2595
16th to endDay
27%37%23%29%6%
2579
July1st to 15thDay
23%36%21%26%17%
2371
16th to endDay
22%2412%28%30%
2490
August1st to 15thDay
28%48%17%25%16%
2344
16th to endDay
21%36%23%30%15%
2423
September1st to 15thDay
24%46%21%29%12%
2079
16th to endDay
31%411%27%20%5%
1816
October1st to 15thDay
40%5%12%23%14%2
1770
16th to endDay
42%7%12%22%13%
1595
November1st to 15thDay
48%7%15%19%7%2
1584
16th to endDay
47%6%13%19%8%4
1581
December1st to 15thDay
57%6%15%14%5%
1275
16th to endDay
60%7%11%14%5%1
1467
January1st to 15thNight
51%7%12%16%9%2
2506
16th to endNight
44%7%12%18%11%4
2688
February1st to 15thNight
51%7%15%16%7%1
2268
16th to endNight
57%8%13%15%31
1895
March1st to 15thNight
51%9%13%16%8%
2121
16th to endNight
46%11%16%18%7%
2091
April1st to 15thNight
47%8%15%20%6%
1787
16th to endNight
40%6%18%23%10%
1620
May1st to 15thNight
31%8%17%33%8%
1620
16th to endNight
42%7%18%24%7%
1541
June1st to 15thNight
36%7%15%26%10%2
1356
16th to endNight
19%5%7%26%31%8%
1372
July1st to 15thNight
13%48%21%32%19%
1360
16th to endNight
13%2413%33%32%
1416
August1st to 15thNight
18%37%21%28%19%
1591
16th to endNight
14%37%21%33%18%
1776
September1st to 15thNight
17%38%25%31%13%
1881
16th to endNight
23%411%30%21%7%
1816
October1st to 15thNight
30%6%15%29%14%3
1859
16th to endNight
36%7%14%24%16%1
2276
November1st to 15thNight
43%8%14%20%10%2
2275
16th to endNight
45%9%13%17%10%3
2365
December1st to 15thNight
52%7%18%14%5%
2682
16th to endNight
56%6%11%16%7%1
2766

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
5%11%30%30%15%8%
60
16th to endDay
10%20%31%18%15%3
64
February1st to 15thDay
17%21%29%16%12%1
125
16th to endDay
19%27%32%17%21
238
March1st to 15thDay
16%37%34%10%1
270
16th to endDay
22%28%35%12%1
288
April1st to 15thDay
20%23%31%14%8%2
269
16th to endDay
20%22%35%17%3
270
May1st to 15thDay
12%22%35%21%6%1
288
16th to endDay
21%16%26%23%10%3
330
June1st to 15thDay
16%18%29%23%9%1
390
16th to endDay
10%16%36%21%12%1
374
July1st to 15thDay
7%13%39%29%8%2
305
16th to endDay
7%19%38%25%7%1
327
August1st to 15thDay
6%16%43%22%9%2
315
16th to endDay
417%33%29%10%4
332
September1st to 15thDay
11%15%31%25%13%3
315
16th to endDay
14%12%35%24%10%1
256
October1st to 15thDay
19%21%30%20%7%
210
16th to endDay
17%15%30%25%6%5%
96
November1st to 15thDay
12%10%32%23%21%1
90
16th to endDay
326%41%21%5%2
90
December1st to 15thDay
22%20%38%12%41
63
16th to endDay
14%20%29%17%18%
64
January1st to 15thNight
10%12%30%29%13%2
720
16th to endNight
7%10%29%32%16%3
768
February1st to 15thNight
9%13%30%29%14%1
704
16th to endNight
8%14%34%28%10%2
632
March1st to 15thNight
10%16%30%29%11%2
720
16th to endNight
11%14%31%30%11%
768
April1st to 15thNight
10%11%29%28%15%4
707
16th to endNight
11%12%27%31%14%2
540
May1st to 15thNight
8%8%22%32%24%3
540
16th to endNight
13%416%31%30%4
419
June1st to 15thNight
12%5%15%40%23%2
360
16th to endNight
4217%40%32%2
360
July1st to 15thNight
17%42%43%4
340
16th to endNight
110%45%37%4
376
August1st to 15thNight
4111%42%38%2
518
16th to endNight
3212%39%36%5%
630
September1st to 15thNight
4112%35%38%7%
720
16th to endNight
9%314%32%31%9%
656
October1st to 15thNight
11%7%20%35%20%4
660
16th to endNight
10%7%25%35%15%5%
704
November1st to 15thNight
13%10%25%34%15%
700
16th to endNight
10%14%32%28%10%4
745
December1st to 15thNight
10%15%31%32%9%1
900
16th to endNight
11%13%33%28%10%1
846
Page generated at 2017-09-16 15:07:00. Version ac04

Copyright 2017 A. Danko


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