Phil's Observatory at Sanctuary
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Phil's Observatory at Sanctuary clear sky chart from 2005-11-05 to 2018-01-20.

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
58%
16402
21%
48473
16%
16363
63%
16363
30%
30389

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
42%
778
21%
2522
14%
776
52%
776
25%
1576
January16th to endNight
41%
788
25%
2515
18%
788
52%
788
28%
1499
February1st to 15thNight
42%
701
24%
2106
15%
700
52%
700
30%
1277
February16th to endNight
41%
631
24%
1845
13%
631
52%
631
31%
1138
March1st to 15thNight
49%
720
29%
1980
16%
720
60%
720
40%
1125
March16th to endNight
53%
768
26%
2112
18%
768
60%
768
41%
1208
April1st to 15thNight
53%
718
25%
1976
17%
718
60%
718
42%
1118
April16th to endNight
59%
720
27%
1842
17%
720
63%
720
43%
1080
May1st to 15thNight
70%
542
25%
1622
19%
542
75%
542
43%
886
May16th to endNight
74%
561
23%
1682
19%
561
75%
561
35%
1016
June1st to 15thNight
69%
540
13%
1620
10%
540
69%
540
24%
1123
June16th to endNight
72%
540
8%
1620
8%
540
73%
540
21%
1171
July1st to 15thNight
72%
510
8%
1530
8%
510
72%
510
21%
1108
July16th to endNight
76%
564
6%
1595
6%
531
77%
531
21%
1149
August1st to 15thNight
75%
539
6%
1609
7%
536
75%
536
21%
1155
August16th to endNight
67%
705
10%
2028
10%
705
67%
705
21%
1451
September1st to 15thNight
65%
720
9%
1980
8%
720
66%
720
20%
1440
September16th to endNight
61%
717
14%
1980
14%
717
62%
717
20%
1441
October1st to 15thNight
67%
720
24%
2044
25%
720
68%
720
33%
1265
October16th to endNight
61%
768
29%
2304
27%
768
67%
768
34%
1358
November1st to 15thNight
59%
760
27%
2281
23%
760
66%
760
37%
1282
November16th to endNight
51%
780
29%
2441
21%
780
61%
780
33%
1418
December1st to 15thNight
50%
780
27%
2535
24%
780
58%
780
30%
1507
December16th to endNight
54%
832
24%
2704
22%
832
60%
832
30%
1598

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
8%5%26%6%46%6%6%8%38%
49037
Night
7%425%5%35%5%6%8%45%
48679
TransparencyDay
40%9%14%16%13%6%
48738
Night
34%8%15%19%14%6%
48482
SeeingDay
9%314%22%26%23%
6196
Night
10%319%32%26%7%
16410

By Month

Percentage Cloud Cover SE (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
11%6%26%5%345%5%7%41%
1746
16th to endDay
10%434425%46%7%46%
1810
February1st to 15thDay
12%5%25%5%35%35%5%45%
1750
16th to endDay
9%5%3443445%7%48%
1628
March1st to 15thDay
6%4245%3445%8%50%
1980
16th to endDay
6%5%26%5%2445%6%49%
2111
April1st to 15thDay
5%325%5%25%45%9%49%
1972
16th to endDay
5%3244345%7%8%50%
2121
May1st to 15thDay
5%314436%5%5%8%50%
2331
16th to endDay
6%425%6%46%7%7%9%38%
2431
June1st to 15thDay
9%5%37%8%5%8%7%7%9%27%
2340
16th to endDay
8%5%46%9%5%9%8%7%9%25%
2340
July1st to 15thDay
9%6%37%8%5%8%7%8%9%22%
2340
16th to endDay
9%6%5%8%9%5%8%8%8%9%19%
2465
August1st to 15thDay
6%7%38%9%6%8%8%7%10%21%
2340
16th to endDay
11%6%48%8%5%8%7%8%8%22%
2158
September1st to 15thDay
8%5%38%10%5%7%7%8%9%23%
1980
16th to endDay
10%7%38%9%5%7%7%7%7%25%
1980
October1st to 15thDay
8%5%27%8%45%5%5%8%37%
1914
16th to endDay
8%5%15%5%25%446%48%
1920
November1st to 15thDay
6%4235%2445%7%51%
1907
16th to endDay
8%5%25%5%35%447%47%
1846
December1st to 15thDay
10%6%25%425%5%5%8%43%
1755
16th to endDay
6%5%25%5%25%46%9%45%
1872
January1st to 15thNight
10%7%35%5%3445%9%41%
2522
16th to endNight
13%425%41345%7%46%
2515
February1st to 15thNight
11%5%2443345%5%50%
2103
16th to endNight
8%5%245%245%5%7%47%
1845
March1st to 15thNight
6%32332446%6%56%
1980
16th to endNight
7%42432335%7%56%
2112
April1st to 15thNight
6%41332435%9%55%
1976
16th to endNight
6%323424447%55%
1842
May1st to 15thNight
42143235%6%9%55%
1622
16th to endNight
5%3245%246%6%7%50%
1682
June1st to 15thNight
9%425%5%46%8%7%9%35%
1620
16th to endNight
7%6%35%5%5%6%6%9%12%30%
1620
July1st to 15thNight
6%436%7%47%7%8%12%32%
1620
16th to endNight
45%25%7%5%8%9%8%10%32%
1703
August1st to 15thNight
4326%8%5%6%7%9%13%31%
1620
16th to endNight
8%5%36%6%36%7%8%11%33%
2028
September1st to 15thNight
8%6%26%6%36%5%7%12%33%
1980
16th to endNight
8%7%37%6%47%7%6%10%29%
1980
October1st to 15thNight
7%4245%3447%8%46%
2044
16th to endNight
8%5%25%32435%6%51%
2304
November1st to 15thNight
5%425%42346%7%54%
2281
16th to endNight
6%434425%45%7%49%
2441
December1st to 15thNight
9%5%245%24447%47%
2535
16th to endNight
8%5%25%4345%5%8%46%
2704

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%6%8%18%17%7%
1747
16th to endDay
34%6%8%17%21%10%
1810
February1st to 15thDay
39%5%6%13%19%14%
1752
16th to endDay
35%5%10%16%20%12%
1628
March1st to 15thDay
30%6%11%22%20%8%
1980
16th to endDay
34%6%12%18%18%9%
2112
April1st to 15thDay
30%7%11%20%21%7%
1972
16th to endDay
28%6%14%21%19%8%
2121
May1st to 15thDay
29%7%13%21%18%9%
2331
16th to endDay
36%10%15%20%13%3
2435
June1st to 15thDay
48%12%16%17%4
2340
16th to endDay
49%13%20%12%2
2340
July1st to 15thDay
50%14%22%11%1
2201
16th to endDay
53%14%19%11%1
2310
August1st to 15thDay
50%15%23%8%1
2327
16th to endDay
53%15%16%13%1
2158
September1st to 15thDay
51%15%18%10%4
1980
16th to endDay
52%11%13%13%6%2
1980
October1st to 15thDay
43%7%9%15%13%10%
1914
16th to endDay
35%5%8%13%23%13%
1920
November1st to 15thDay
30%411%22%21%9%
1907
16th to endDay
36%5%9%17%20%10%
1846
December1st to 15thDay
37%6%13%18%15%7%
1755
16th to endDay
34%5%15%21%15%8%
1872
January1st to 15thNight
39%5%10%19%15%8%
2522
16th to endNight
36%49%16%22%9%
2515
February1st to 15thNight
35%5%7%16%19%16%
2112
16th to endNight
35%6%11%16%21%9%
1845
March1st to 15thNight
26%5%13%24%20%8%
1980
16th to endNight
27%5%12%23%20%10%
2112
April1st to 15thNight
26%6%13%25%20%8%
1976
16th to endNight
27%5%13%25%21%7%
1842
May1st to 15thNight
24%6%18%24%18%7%
1623
16th to endNight
29%9%15%24%19%2
1684
June1st to 15thNight
40%11%19%22%5%
1620
16th to endNight
41%14%22%16%3
1620
July1st to 15thNight
42%14%27%13%2
1530
16th to endNight
39%17%28%12%2
1595
August1st to 15thNight
37%18%31%11%
1609
16th to endNight
40%15%24%17%2
2028
September1st to 15thNight
41%16%22%14%5%
1980
16th to endNight
44%13%17%17%5%2
1980
October1st to 15thNight
33%8%12%20%17%8%
2044
16th to endNight
32%5%9%14%25%11%
2304
November1st to 15thNight
28%5%11%23%22%8%
2281
16th to endNight
32%5%9%20%19%12%
2441
December1st to 15thNight
34%6%11%25%14%7%
2535
16th to endNight
33%6%14%23%13%8%
2704

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
15%11%40%18%11%2
135
16th to endDay
13%16%30%26%10%2
109
February1st to 15thDay
6%22%25%23%17%4
90
16th to endDay
14%8%34%29%11%
129
March1st to 15thDay
9%8%28%32%17%2
270
16th to endDay
9%426%24%29%5%
288
April1st to 15thDay
6%7%22%32%23%7%
270
16th to endDay
6%220%22%30%16%
270
May1st to 15thDay
5%314%29%27%19%
288
16th to endDay
6%16%21%35%28%
331
June1st to 15thDay
14%6%15%28%34%
315
16th to endDay
6%313%26%48%
315
July1st to 15thDay
6%7%23%60%
305
16th to endDay
12%49%24%47%
326
August1st to 15thDay
9%410%28%46%
313
16th to endDay
12%312%21%49%
332
September1st to 15thDay
13%1314%31%35%
315
16th to endDay
12%5%14%35%31%
314
October1st to 15thDay
10%212%29%31%12%
315
16th to endDay
8%422%30%27%7%
336
November1st to 15thDay
8%216%32%32%7%
325
16th to endDay
9%225%35%22%4
226
December1st to 15thDay
7%9%34%34%12%2
135
16th to endDay
6%218%44%23%4
144
January1st to 15thNight
13%7%32%30%14%
780
16th to endNight
16%8%29%34%11%
788
February1st to 15thNight
13%6%32%34%11%
704
16th to endNight
12%7%33%40%6%
631
March1st to 15thNight
8%8%30%39%12%
720
16th to endNight
9%428%40%16%1
768
April1st to 15thNight
8%329%41%16%1
718
16th to endNight
8%323%43%20%1
720
May1st to 15thNight
6%114%48%26%2
543
16th to endNight
7%9%36%39%7%
563
June1st to 15thNight
11%16%31%36%13%
540
16th to endNight
10%1317%42%24%
540
July1st to 15thNight
9%212%43%31%
510
16th to endNight
4213%53%24%
564
August1st to 15thNight
5%215%49%26%
539
16th to endNight
12%5%16%39%24%
705
September1st to 15thNight
11%6%22%38%19%
720
16th to endNight
13%9%26%38%11%
717
October1st to 15thNight
9%111%37%35%4
720
16th to endNight
12%216%36%29%3
768
November1st to 15thNight
6%322%38%25%2
760
16th to endNight
9%328%37%19%1
780
December1st to 15thNight
11%426%34%21%1
780
16th to endNight
9%5%23%38%21%1
832
Page generated at 2018-01-21 12:19:21. Version ac04

Copyright 2018 A. Danko


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