Stone Trail Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stone Trail Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
43%
16291
20%
47379
12%
16251
49%
16251
31%
29190

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
32%
897
17%
2506
10%
895
38%
895
24%
1710
January16th to endNight
30%
903
19%
2631
8%
903
41%
903
26%
1688
February1st to 15thNight
32%
699
11%
2288
9%
699
38%
699
20%
1567
February16th to endNight
35%
632
15%
1929
9%
632
42%
632
23%
1260
March1st to 15thNight
42%
720
19%
2113
10%
720
49%
720
30%
1311
March16th to endNight
37%
686
16%
2030
9%
686
44%
686
26%
1335
April1st to 15thNight
40%
539
16%
1798
13%
539
48%
539
22%
1154
April16th to endNight
37%
540
15%
1767
12%
540
43%
540
22%
1165
May1st to 15thNight
48%
539
18%
1440
12%
539
52%
539
33%
910
May16th to endNight
40%
563
13%
1498
7%
561
44%
561
27%
1031
June1st to 15thNight
44%
540
11%
1440
5%
540
47%
540
31%
943
June16th to endNight
50%
540
18%
1440
9%
540
55%
540
49%
782
July1st to 15thNight
60%
510
17%
1360
10%
510
63%
510
48%
741
July16th to endNight
61%
564
27%
1416
19%
531
65%
531
56%
719
August1st to 15thNight
61%
539
24%
1536
16%
536
68%
536
50%
793
August16th to endNight
61%
573
28%
1878
27%
573
67%
573
44%
927
September1st to 15thNight
58%
540
24%
1800
22%
540
66%
540
37%
953
September16th to endNight
55%
566
30%
1943
26%
566
63%
566
41%
971
October1st to 15thNight
40%
720
22%
2160
15%
720
46%
720
28%
1365
October16th to endNight
47%
846
28%
2382
15%
846
56%
846
36%
1416
November1st to 15thNight
42%
875
23%
2296
12%
875
48%
875
37%
1402
November16th to endNight
39%
900
23%
2520
12%
900
48%
900
33%
1546
December1st to 15thNight
33%
900
14%
2520
6%
900
41%
900
23%
1744
December16th to endNight
33%
960
19%
2688
7%
960
45%
960
27%
1757

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%6%25%42445%8%47%
48393
Night
6%7%35%42445%8%46%
47548
Cloud CoverDay
7%6%2442445%8%47%
48393
Night
6%6%35%43445%8%46%
47550
TransparencyDay
33%6%14%24%15%5%
48066
Night
34%6%15%24%14%4
47379
SeeingDay
10%7%28%31%18%4
6188
Night
10%7%34%35%11%
16300

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
5%9%5%7%5%35%5%5%7%39%
1433
16th to endDay
38%47%43347%8%41%
1602
February1st to 15thDay
6%12%6%6%6%345%5%8%34%
1575
16th to endDay
411%47%5%5%6%5%48%36%
1544
March1st to 15thDay
38%35%5%345%6%8%45%
1845
16th to endDay
8%9%37%5%345%6%8%37%
2192
April1st to 15thDay
9%8%345%25%5%6%8%40%
2150
16th to endDay
15%11%35%4245%5%6%35%
2190
May1st to 15thDay
11%9%36%5%3445%6%40%
2511
16th to endDay
13%7%35%5%3446%9%36%
2616
June1st to 15thDay
8%42443446%9%46%
2520
16th to endDay
32123235%5%9%61%
2520
July1st to 15thDay
321332448%10%57%
2520
16th to endDay
3232245%6%10%59%
2656
August1st to 15thDay
4213425%5%7%10%51%
2415
16th to endDay
3213323446%63%
2324
September1st to 15thDay
7%313223346%60%
2160
16th to endDay
7%312222346%61%
2016
October1st to 15thDay
12%7%24223337%48%
1800
16th to endDay
8%6%2432345%8%50%
1829
November1st to 15thDay
7%5%344245%6%8%48%
1559
16th to endDay
48%25%425%6%5%8%46%
1440
December1st to 15thDay
5%6%48%6%45%5%5%8%39%
1440
16th to endDay
5%8%37%6%35%46%8%38%
1536
January1st to 15thNight
5%9%47%6%36%46%8%38%
2506
16th to endNight
48%47%5%245%5%9%42%
2631
February1st to 15thNight
411%5%9%6%35%36%7%33%
2277
16th to endNight
410%47%6%35%447%40%
1929
March1st to 15thNight
46%25%6%35%45%8%47%
2113
16th to endNight
9%8%35%6%2446%9%38%
2027
April1st to 15thNight
9%8%35%4245%5%7%41%
1798
16th to endNight
14%10%2442435%7%38%
1767
May1st to 15thNight
10%8%2431435%5%48%
1439
16th to endNight
13%5%245%336%5%10%37%
1498
June1st to 15thNight
10%415%435%5%7%8%43%
1440
16th to endNight
331422345%7%60%
1440
July1st to 15thNight
3224245%6%11%54%
1440
16th to endNight
22221436%9%62%
1512
August1st to 15thNight
33232346%10%57%
1544
16th to endNight
422232336%7%60%
1878
September1st to 15thNight
7%41432345%6%55%
1800
16th to endNight
8%412213346%60%
1943
October1st to 15thNight
14%7%3432324447%
2160
16th to endNight
7%6%2442345%7%51%
2382
November1st to 15thNight
5%6%25%42446%8%48%
2296
16th to endNight
7%7%35%4345%5%7%46%
2520
December1st to 15thNight
47%49%7%46%6%5%7%36%
2520
16th to endNight
39%36%6%35%447%43%
2688

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
5%8%5%6%7%35%5%5%7%39%
1432
16th to endDay
38%5%7%5%2447%8%42%
1602
February1st to 15thDay
6%11%6%7%5%345%5%7%34%
1575
16th to endDay
410%47%5%45%5%5%7%37%
1544
March1st to 15thDay
48%35%5%345%6%8%45%
1845
16th to endDay
8%9%36%5%25%5%6%9%37%
2193
April1st to 15thDay
9%8%35%4245%6%8%41%
2150
16th to endDay
15%11%345%2445%6%35%
2190
May1st to 15thDay
11%7%36%5%3445%7%40%
2511
16th to endDay
13%6%25%5%25%45%10%36%
2616
June1st to 15thDay
8%41443446%9%46%
2520
16th to endDay
32232345%8%62%
2520
July1st to 15thDay
32123245%6%10%57%
2520
16th to endDay
321221346%10%60%
2656
August1st to 15thDay
42144245%6%10%52%
2415
16th to endDay
321332345%7%63%
2324
September1st to 15thDay
8%313313346%61%
2160
16th to endDay
8%312222346%61%
2016
October1st to 15thDay
13%8%24323437%48%
1800
16th to endDay
8%6%2442345%8%50%
1829
November1st to 15thDay
7%5%244246%5%8%48%
1559
16th to endDay
47%25%425%5%6%8%46%
1440
December1st to 15thDay
5%7%48%7%46%5%47%40%
1440
16th to endDay
5%8%47%6%35%5%6%9%38%
1536
January1st to 15thNight
5%9%47%5%45%5%5%8%38%
2506
16th to endNight
48%47%5%35%5%5%8%42%
2631
February1st to 15thNight
5%10%5%9%7%35%46%7%33%
2277
16th to endNight
410%5%6%6%35%447%41%
1929
March1st to 15thNight
46%35%5%45%45%8%46%
2113
16th to endNight
9%7%35%6%245%6%9%38%
2030
April1st to 15thNight
10%7%25%4245%5%8%41%
1798
16th to endNight
15%10%3442445%6%39%
1767
May1st to 15thNight
9%8%2432435%6%48%
1439
16th to endNight
13%5%25%4345%6%10%38%
1497
June1st to 15thNight
10%425%5%246%6%9%43%
1440
16th to endNight
4214322448%60%
1440
July1st to 15thNight
32133245%7%10%56%
1440
16th to endNight
12232445%10%62%
1512
August1st to 15thNight
321242346%10%57%
1544
16th to endNight
421332345%7%60%
1878
September1st to 15thNight
7%42432345%6%56%
1800
16th to endNight
8%313213346%60%
1943
October1st to 15thNight
14%7%34413335%46%
2160
16th to endNight
7%5%2442445%8%50%
2382
November1st to 15thNight
5%6%25%42446%7%49%
2296
16th to endNight
6%7%35%4345%5%7%47%
2520
December1st to 15thNight
37%410%7%45%6%6%7%36%
2520
16th to endNight
39%36%6%35%447%43%
2688

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
42%7%19%20%7%2
1433
16th to endDay
37%7%18%25%8%2
1602
February1st to 15thDay
46%8%16%20%7%1
1575
16th to endDay
44%6%17%20%6%3
1544
March1st to 15thDay
34%6%17%27%13%
1845
16th to endDay
42%6%14%25%10%
2193
April1st to 15thDay
39%7%17%25%8%1
2150
16th to endDay
47%6%14%19%11%
2190
May1st to 15thDay
42%6%15%25%8%1
2511
16th to endDay
42%9%18%19%9%
2620
June1st to 15thDay
32%8%17%25%13%3
2520
16th to endDay
17%6%13%30%21%10%
2520
July1st to 15thDay
19%7%14%25%23%11%
2371
16th to endDay
17%5%11%24%24%16%
2489
August1st to 15thDay
22%7%12%26%19%11%
2399
16th to endDay
19%49%24%26%14%
2324
September1st to 15thDay
24%5%8%22%27%12%
2160
16th to endDay
23%411%29%24%5%
2016
October1st to 15thDay
37%411%25%16%4
1800
16th to endDay
31%416%25%16%5%
1829
November1st to 15thDay
30%7%16%21%18%5%
1559
16th to endDay
34%7%16%27%13%2
1440
December1st to 15thDay
42%6%18%23%8%
1440
16th to endDay
40%7%17%21%10%2
1536
January1st to 15thNight
42%8%16%22%7%3
2506
16th to endNight
38%6%17%22%12%2
2631
February1st to 15thNight
47%6%17%18%7%1
2288
16th to endNight
42%6%15%22%10%3
1929
March1st to 15thNight
35%7%16%26%12%2
2113
16th to endNight
40%7%19%23%9%
2030
April1st to 15thNight
39%9%14%26%9%1
1798
16th to endNight
43%6%14%23%10%
1767
May1st to 15thNight
35%6%16%27%12%1
1440
16th to endNight
39%10%18%22%8%
1498
June1st to 15thNight
34%9%21%22%11%1
1440
16th to endNight
20%5%15%30%21%6%
1440
July1st to 15thNight
21%6%16%31%17%7%
1360
16th to endNight
16%5%11%28%26%11%
1416
August1st to 15thNight
20%415%28%19%11%
1536
16th to endNight
21%5%9%26%24%12%
1878
September1st to 15thNight
27%49%22%25%11%
1800
16th to endNight
24%410%27%26%6%
1943
October1st to 15thNight
39%411%23%15%4
2160
16th to endNight
30%6%13%26%17%5%
2382
November1st to 15thNight
31%5%18%21%17%5%
2296
16th to endNight
34%5%16%25%15%2
2520
December1st to 15thNight
43%8%15%21%8%1
2520
16th to endNight
39%6%16%24%10%2
2688

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
11%427%26%18%11%
90
16th to endDay
15%243%21%12%4
96
February1st to 15thDay
8%14%53%20%3
90
16th to endDay
6%13%37%28%13%1
81
March1st to 15thDay
7%11%40%28%9%2
135
16th to endDay
15%13%30%25%11%2
288
April1st to 15thDay
13%14%34%28%7%1
269
16th to endDay
27%11%24%19%13%2
291
May1st to 15thDay
16%9%24%28%15%5%
468
16th to endDay
17%8%27%24%17%4
517
June1st to 15thDay
8%7%29%31%18%4
495
16th to endDay
45%32%35%19%2
495
July1st to 15thDay
4320%36%30%3
475
16th to endDay
4323%36%28%3
515
August1st to 15thDay
4227%39%24%1
390
16th to endDay
5%324%32%23%10%
332
September1st to 15thDay
11%428%34%15%6%
315
16th to endDay
10%5%26%28%22%5%
201
October1st to 15thDay
14%8%24%34%14%4
135
16th to endDay
10%13%22%34%14%4
144
November1st to 15thDay
6%226%35%15%13%
90
16th to endDay
16%10%40%28%31
90
December1st to 15thDay
6%8%40%37%6%
90
16th to endDay
8%5%40%31%14%
96
January1st to 15thNight
10%14%35%28%10%1
900
16th to endNight
8%12%42%28%7%
903
February1st to 15thNight
8%9%39%30%11%
704
16th to endNight
9%8%39%31%9%1
632
March1st to 15thNight
7%6%39%36%9%
720
16th to endNight
12%7%36%36%6%
686
April1st to 15thNight
14%8%32%36%8%
539
16th to endNight
20%7%28%31%11%
540
May1st to 15thNight
13%8%25%38%13%
540
16th to endNight
18%431%30%14%1
563
June1st to 15thNight
11%7%31%40%8%
540
16th to endNight
5%5%36%40%11%
540
July1st to 15thNight
5%228%46%17%
510
16th to endNight
2229%49%15%
564
August1st to 15thNight
4226%49%16%
539
16th to endNight
5%324%44%20%1
573
September1st to 15thNight
9%422%41%20%1
540
16th to endNight
10%328%37%17%2
566
October1st to 15thNight
17%7%30%33%10%1
720
16th to endNight
10%7%29%37%12%2
846
November1st to 15thNight
8%8%36%34%10%1
875
16th to endNight
10%8%38%33%9%
900
December1st to 15thNight
7%9%42%33%7%
900
16th to endNight
9%8%40%31%9%
960
Page generated at 2017-11-01 15:23:39. Version ac04

Copyright 2017 A. Danko


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