Transit Dreams Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Transit Dreams Observatory 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
49%
16171
22%
48467
15%
16130
56%
16130
27%
30681

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%
779
23%
2522
12%
776
47%
776
25%
1502
January16th to endNight
31%
788
26%
2560
14%
788
47%
788
26%
1534
February1st to 15thNight
32%
702
25%
2187
11%
700
47%
700
29%
1292
February16th to endNight
27%
631
26%
1893
11%
631
43%
631
28%
1171
March1st to 15thNight
36%
720
26%
1992
16%
720
45%
720
30%
1250
March16th to endNight
35%
768
19%
2112
10%
768
43%
768
27%
1383
April1st to 15thNight
41%
718
23%
1964
12%
718
50%
718
34%
1200
April16th to endNight
47%
570
24%
1650
15%
570
53%
570
31%
1022
May1st to 15thNight
47%
540
16%
1620
8%
540
53%
540
25%
1075
May16th to endNight
60%
561
16%
1684
12%
561
62%
561
25%
1115
June1st to 15thNight
65%
540
12%
1620
10%
540
66%
540
23%
1114
June16th to endNight
71%
540
15%
1620
13%
540
71%
540
27%
1077
July1st to 15thNight
70%
510
9%
1530
8%
510
70%
510
22%
1071
July16th to endNight
72%
564
12%
1595
10%
531
73%
531
23%
1114
August1st to 15thNight
66%
539
12%
1609
11%
536
67%
536
23%
1128
August16th to endNight
66%
624
16%
1830
14%
624
66%
624
22%
1286
September1st to 15thNight
64%
720
17%
1980
15%
720
65%
720
27%
1345
September16th to endNight
55%
717
20%
1980
17%
717
59%
717
26%
1335
October1st to 15thNight
54%
720
28%
2071
24%
720
60%
720
33%
1265
October16th to endNight
54%
768
35%
2304
27%
768
67%
768
39%
1265
November1st to 15thNight
53%
760
27%
2370
22%
760
62%
760
34%
1356
November16th to endNight
46%
780
27%
2535
20%
780
56%
780
30%
1453
December1st to 15thNight
41%
780
24%
2535
14%
780
53%
780
25%
1556
December16th to endNight
36%
832
23%
2704
14%
832
47%
832
21%
1772

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
13%424435%5%5%7%43%
49055
Night
13%42442445%7%45%
48664
TransparencyDay
38%7%12%19%17%4
48756
Night
37%6%11%18%19%5%
48467
SeeingDay
16%417%23%22%14%
5952
Night
16%5%21%30%22%3
16176

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
17%5%34413345%47%
1746
16th to endDay
16%5%14314345%49%
1768
February1st to 15thDay
15%42432345%6%48%
1672
16th to endDay
15%5%23424337%47%
1580
March1st to 15thDay
15%423324446%48%
1966
16th to endDay
19%423324447%43%
2111
April1st to 15thDay
13%41442345%7%48%
1984
16th to endDay
12%4245%25%45%7%45%
2319
May1st to 15thDay
12%426%5%35%5%47%41%
2331
16th to endDay
11%424435%6%7%11%38%
2431
June1st to 15thDay
8%4246%47%8%8%9%33%
2340
16th to endDay
6%4145%47%8%9%10%38%
2340
July1st to 15thDay
9%5%36%7%46%6%7%10%32%
2340
16th to endDay
7%325%6%5%7%8%8%12%32%
2465
August1st to 15thDay
12%6%26%6%48%6%7%9%29%
2340
16th to endDay
12%426%6%45%6%7%11%33%
2357
September1st to 15thDay
9%5%25%6%35%5%6%7%42%
1980
16th to endDay
15%6%25%43445%8%41%
1980
October1st to 15thDay
16%4321223456%
1887
16th to endDay
11%31331223361%
1920
November1st to 15thDay
13%313312346%55%
1816
16th to endDay
15%313313335%52%
1755
December1st to 15thDay
17%5%245%23346%45%
1755
16th to endDay
22%6%15%413245%40%
1872
January1st to 15thNight
17%42332344450%
2522
16th to endNight
17%423324346%48%
2560
February1st to 15thNight
14%413323435%52%
2178
16th to endNight
13%4235%2345%6%48%
1893
March1st to 15thNight
14%5%2432335%6%47%
1992
16th to endNight
16%5%2442335%6%45%
2112
April1st to 15thNight
14%414314347%50%
1964
16th to endNight
12%5%2443345%450%
1650
May1st to 15thNight
12%425%6%4445%7%40%
1619
16th to endNight
9%426%5%36%5%6%8%40%
1682
June1st to 15thNight
10%4145%46%7%9%11%33%
1620
16th to endNight
7%414436%6%7%11%40%
1620
July1st to 15thNight
7%5%26%6%46%8%8%11%31%
1620
16th to endNight
6%425%6%46%7%10%13%31%
1703
August1st to 15thNight
12%6%245%35%6%7%11%33%
1620
16th to endNight
11%6%26%6%45%47%10%33%
1830
September1st to 15thNight
10%6%246%35%5%7%9%38%
1980
16th to endNight
17%6%24423447%41%
1980
October1st to 15thNight
15%413323335%52%
2071
16th to endNight
11%31332323459%
2304
November1st to 15thNight
13%412323335%55%
2370
16th to endNight
15%423323445%52%
2535
December1st to 15thNight
17%5%13413445%46%
2535
16th to endNight
21%5%235%23336%40%
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
40%5%8%18%22%5%
1747
16th to endDay
38%27%20%21%9%
1768
February1st to 15thDay
36%311%19%23%5%
1674
16th to endDay
38%49%22%18%5%
1580
March1st to 15thDay
37%48%23%19%6%
1966
16th to endDay
39%6%13%20%17%2
2112
April1st to 15thDay
34%411%22%21%5%
1984
16th to endDay
37%6%11%20%17%7%
2319
May1st to 15thDay
40%6%14%18%16%2
2331
16th to endDay
36%10%17%21%13%1
2435
June1st to 15thDay
39%11%19%21%7%1
2340
16th to endDay
33%13%17%20%12%2
2340
July1st to 15thDay
41%12%17%17%7%3
2201
16th to endDay
37%13%20%17%8%1
2310
August1st to 15thDay
46%11%15%16%8%
2327
16th to endDay
42%12%16%17%9%1
2357
September1st to 15thDay
38%9%13%18%16%4
1980
16th to endDay
41%6%12%17%17%4
1980
October1st to 15thDay
31%5%9%21%25%6%
1887
16th to endDay
28%36%20%29%10%
1920
November1st to 15thDay
31%48%18%27%9%
1816
16th to endDay
35%47%19%24%8%
1755
December1st to 15thDay
40%49%20%18%6%
1755
16th to endDay
45%49%18%16%5%
1872
January1st to 15thNight
38%39%16%24%7%
2522
16th to endNight
38%37%19%23%8%
2560
February1st to 15thNight
35%38%21%24%6%
2187
16th to endNight
36%5%9%21%23%3
1893
March1st to 15thNight
36%410%18%21%7%
1992
16th to endNight
40%5%10%20%18%4
2112
April1st to 15thNight
35%39%23%23%6%
1964
16th to endNight
36%410%19%20%7%
1650
May1st to 15thNight
41%8%12%19%16%2
1620
16th to endNight
38%10%12%23%12%2
1684
June1st to 15thNight
39%13%19%18%7%1
1620
16th to endNight
35%12%16%19%12%3
1620
July1st to 15thNight
40%13%18%17%6%2
1530
16th to endNight
38%15%20%16%6%2
1595
August1st to 15thNight
42%11%20%14%10%
1609
16th to endNight
42%11%17%17%9%1
1830
September1st to 15thNight
39%9%16%17%13%3
1980
16th to endNight
41%7%11%16%17%4
1980
October1st to 15thNight
35%49%20%23%6%
2071
16th to endNight
28%36%20%28%12%
2304
November1st to 15thNight
32%46%18%26%11%
2370
16th to endNight
34%46%18%27%8%
2535
December1st to 15thNight
39%410%18%19%7%
2535
16th to endNight
45%410%16%17%5%
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
18%14%34%22%9%
135
16th to endDay
16%13%45%16%7%
109
February1st to 15thDay
17%20%40%20%2
90
16th to endDay
18%11%40%19%9%
81
March1st to 15thDay
17%11%31%30%8%
256
16th to endDay
20%8%29%27%13%1
288
April1st to 15thDay
15%9%23%28%20%2
270
16th to endDay
18%218%30%18%10%
270
May1st to 15thDay
15%5%28%22%17%10%
288
16th to endDay
16%310%23%27%18%
331
June1st to 15thDay
13%110%25%23%25%
315
16th to endDay
9%110%25%24%28%
315
July1st to 15thDay
11%17%17%31%30%
305
16th to endDay
5%5%19%35%33%
326
August1st to 15thDay
23%17%17%23%26%
313
16th to endDay
16%7%17%28%29%
332
September1st to 15thDay
15%112%16%30%24%
315
16th to endDay
20%111%21%29%15%
314
October1st to 15thDay
22%116%25%26%7%
315
16th to endDay
13%5%15%34%23%8%
336
November1st to 15thDay
25%420%23%18%7%
234
16th to endDay
11%421%37%20%5%
135
December1st to 15thDay
25%7%33%22%11%
135
16th to endDay
32%8%36%18%4
144
January1st to 15thNight
19%11%31%29%7%
780
16th to endNight
20%11%33%31%3
788
February1st to 15thNight
16%12%35%32%2
704
16th to endNight
15%11%42%27%3
631
March1st to 15thNight
18%10%30%35%5%
720
16th to endNight
19%8%29%30%11%
768
April1st to 15thNight
16%9%28%30%14%
718
16th to endNight
15%427%31%20%
570
May1st to 15thNight
16%423%33%20%1
540
16th to endNight
12%213%27%37%5%
563
June1st to 15thNight
12%111%29%35%9%
540
16th to endNight
10%8%28%39%12%
540
July1st to 15thNight
11%7%25%45%9%
510
16th to endNight
7%16%23%48%11%
564
August1st to 15thNight
17%5%23%44%9%
539
16th to endNight
13%6%26%42%9%
624
September1st to 15thNight
13%110%26%40%8%
720
16th to endNight
20%113%26%32%5%
717
October1st to 15thNight
18%220%25%29%4
720
16th to endNight
13%422%33%23%2
768
November1st to 15thNight
16%321%35%18%3
760
16th to endNight
16%8%25%31%17%
780
December1st to 15thNight
20%7%24%33%12%
780
16th to endNight
25%6%26%33%8%
832
Page generated at 2018-01-21 12:19:30. Version ac04

Copyright 2018 A. Danko


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