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 2018-04-23.

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%
15911
18%
49649
16%
15883
53%
15883
26%
31603

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
39%
776
14%
2716
11%
776
44%
776
16%
1914
January16th to endNight
43%
832
16%
2912
15%
832
48%
832
20%
1940
February1st to 15thNight
35%
760
11%
2460
10%
756
38%
756
16%
1776
February16th to endNight
33%
684
10%
2051
10%
684
36%
684
14%
1585
March1st to 15thNight
36%
780
10%
2298
9%
780
39%
780
17%
1691
March16th to endNight
37%
832
12%
2265
7%
832
40%
832
19%
1651
April1st to 15thNight
41%
766
12%
1936
7%
766
43%
766
20%
1430
April16th to endNight
44%
558
17%
1674
13%
558
47%
558
26%
1072
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
67%
716
30%
1980
24%
716
70%
716
44%
1103
October1st to 15thNight
57%
720
23%
2028
18%
720
62%
720
36%
1214
October16th to endNight
53%
768
23%
2483
19%
768
60%
768
29%
1492
November1st to 15thNight
43%
760
18%
2470
16%
760
48%
760
21%
1661
November16th to endNight
38%
807
14%
2562
11%
807
42%
807
19%
1776
December1st to 15thNight
38%
975
10%
2906
8%
975
39%
975
18%
2086
December16th to endNight
31%
916
12%
2996
9%
916
36%
916
14%
2239

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%3445%6%41%
49865
Night
38%46%5%345%5%7%43%
49821
TransparencyDay
43%5%11%18%14%6%
49536
Night
39%7%13%20%14%5%
49650
SeeingDay
14%20%33%21%8%1
6109
Night
9%9%24%33%19%3
15921

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
12%6%9%8%345%6%6%36%
1552
16th to endDay
113%7%9%7%3445%6%35%
1664
February1st to 15thDay
214%6%12%7%25%45%6%31%
1732
16th to endDay
214%9%17%9%4445%6%21%
1709
March1st to 15thDay
115%8%11%7%35%5%6%7%27%
1992
16th to endDay
419%7%11%7%44447%23%
2307
April1st to 15thDay
419%8%10%7%34446%24%
2342
16th to endDay
6%13%5%9%6%34446%35%
2400
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%8%23323346%53%
1980
October1st to 15thDay
7%10%25%5%24446%46%
1931
16th to endDay
5%9%36%5%3445%8%42%
1740
November1st to 15thDay
5%12%5%8%6%35%35%6%36%
1719
16th to endDay
111%6%10%7%3446%7%35%
1712
December1st to 15thDay
211%7%13%8%45%435%32%
1381
16th to endDay
212%7%13%10%45%5%5%5%26%
1589
January1st to 15thNight
214%6%7%7%445%48%32%
2716
16th to endNight
29%6%7%6%3445%7%38%
2912
February1st to 15thNight
212%7%10%6%35%5%6%7%30%
2449
16th to endNight
110%7%12%9%5%6%5%6%7%26%
2051
March1st to 15thNight
211%6%10%7%45%5%7%8%31%
2298
16th to endNight
312%48%6%35%6%7%8%34%
2265
April1st to 15thNight
312%7%8%5%35%6%6%7%32%
1936
16th to endNight
411%45%5%24447%44%
1674
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%5%13312345%60%
1980
October1st to 15thNight
5%8%2331445%7%53%
2028
16th to endNight
5%8%344345%5%7%48%
2483
November1st to 15thNight
5%12%5%7%4245%6%9%35%
2470
16th to endNight
38%47%7%47%6%5%7%36%
2562
December1st to 15thNight
211%6%10%8%35%5%5%8%33%
2906
16th to endNight
212%6%13%10%4445%5%28%
2996

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
47%9%15%16%8%2
1552
16th to endDay
50%6%10%18%9%3
1664
February1st to 15thDay
53%8%14%15%6%2
1732
16th to endDay
65%6%9%12%4
1709
March1st to 15thDay
56%7%15%14%5%
1992
16th to endDay
62%6%13%13%4
2307
April1st to 15thDay
60%7%13%14%3
2342
16th to endDay
49%6%15%19%9%
2400
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
32%410%26%20%5%
1980
October1st to 15thDay
40%5%12%24%14%2
1931
16th to endDay
40%7%12%23%14%1
1740
November1st to 15thDay
48%7%14%18%7%2
1719
16th to endDay
47%7%13%19%8%3
1712
December1st to 15thDay
54%6%14%15%7%1
1381
16th to endDay
59%7%11%13%6%1
1589
January1st to 15thNight
50%7%12%16%9%2
2716
16th to endNight
44%8%13%18%10%4
2912
February1st to 15thNight
51%8%15%16%7%1
2460
16th to endNight
56%8%12%15%41
2051
March1st to 15thNight
51%9%13%17%8%
2298
16th to endNight
45%11%17%17%7%
2265
April1st to 15thNight
49%8%14%20%6%
1936
16th to endNight
40%6%18%24%10%
1674
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
26%411%30%21%6%
1980
October1st to 15thNight
30%7%14%29%15%3
2028
16th to endNight
34%6%13%25%17%1
2483
November1st to 15thNight
44%8%14%19%10%2
2470
16th to endNight
45%9%13%17%10%3
2562
December1st to 15thNight
49%7%18%15%7%1
2906
16th to endNight
56%7%11%15%7%1
2996

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
411%31%27%16%8%
90
16th to endDay
10%26%31%18%11%2
96
February1st to 15thDay
17%24%30%16%10%1
173
16th to endDay
17%25%35%17%21
290
March1st to 15thDay
15%35%32%12%2
330
16th to endDay
20%30%36%12%
352
April1st to 15thDay
22%25%30%12%6%1
329
16th to endDay
21%21%35%18%3
288
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
16%12%33%25%11%1
315
October1st to 15thDay
19%20%29%20%7%1
266
16th to endDay
13%17%27%29%6%5%
144
November1st to 15thDay
15%14%32%21%15%
135
16th to endDay
8%22%41%20%5%1
135
December1st to 15thDay
18%15%30%18%13%3
94
16th to endDay
15%25%32%14%12%
96
January1st to 15thNight
10%12%29%31%14%2
780
16th to endNight
7%10%30%32%15%3
832
February1st to 15thNight
9%14%32%28%13%1
764
16th to endNight
8%14%34%29%10%2
684
March1st to 15thNight
10%15%30%30%11%2
780
16th to endNight
11%14%31%32%10%
832
April1st to 15thNight
10%12%28%29%14%3
766
16th to endNight
10%12%27%32%14%2
558
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%31%31%9%
716
October1st to 15thNight
10%7%21%35%20%4
720
16th to endNight
9%7%24%36%15%5%
768
November1st to 15thNight
14%10%26%33%14%
760
16th to endNight
11%14%31%27%9%4
807
December1st to 15thNight
9%14%29%33%10%1
975
16th to endNight
11%14%34%28%10%1
916
Page generated at 2018-04-24 08:03:04. Version ac04

Copyright 2018 A. Danko


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