Observatoire Obaska
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Obaska clear sky chart from 2005-11-05 to 2017-03-22.

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
24%
14302
9%
45173
6%
14270
28%
14270
11%
35493

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
14%
881
5%
2666
3%
876
16%
876
4%
2367
January16th to endNight
21%
768
6%
2658
4%
768
24%
768
6%
2259
February1st to 15thNight
23%
703
8%
2287
5%
701
28%
701
9%
1880
February16th to endNight
16%
631
7%
2019
3%
631
22%
631
8%
1691
March1st to 15thNight
22%
720
10%
2061
7%
720
27%
720
12%
1652
March16th to endNight
28%
732
16%
1969
8%
732
33%
732
19%
1461
April1st to 15thNight
24%
658
13%
1646
5%
658
27%
658
17%
1271
April16th to endNight
27%
493
16%
1483
9%
493
34%
493
19%
1039
May1st to 15thNight
33%
330
15%
1320
16%
330
42%
330
16%
879
May16th to endNight
28%
343
9%
1369
7%
342
38%
342
15%
950
June1st to 15thNight
30%
330
7%
1201
5%
330
33%
330
12%
870
June16th to endNight
41%
330
6%
1155
4%
330
43%
330
20%
756
July1st to 15thNight
36%
310
8%
1085
7%
310
38%
310
20%
713
July16th to endNight
48%
348
8%
1286
11%
326
48%
326
17%
857
August1st to 15thNight
39%
395
10%
1376
9%
393
44%
393
15%
992
August16th to endNight
40%
582
13%
1632
8%
582
43%
582
23%
1120
September1st to 15thNight
32%
660
11%
1650
4%
660
34%
660
21%
1225
September16th to endNight
34%
657
15%
1814
8%
657
38%
657
22%
1274
October1st to 15thNight
23%
660
12%
1980
8%
660
28%
660
14%
1522
October16th to endNight
18%
704
7%
2194
5%
704
20%
704
8%
1846
November1st to 15thNight
15%
700
8%
2435
5%
700
19%
700
8%
1963
November16th to endNight
13%
720
6%
2520
4%
720
16%
720
5%
2164
December1st to 15thNight
11%
720
4%
2520
1%
720
14%
720
5%
2191
December16th to endNight
13%
927
5%
2847
4%
927
15%
927
4%
2551

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
21%12%47%6%34445%23%
45720
Night
20%13%5%8%6%35%445%22%
45332
TransparencyDay
62%49%15%6%
45397
Night
64%49%14%6%
45173
SeeingDay
29%11%29%19%8%2
5046
Night
28%10%28%22%8%
14303

By Month

Percentage Cloud Cover NE (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
21%17%7%13%9%16%5%438%
1271
16th to endDay
15%18%6%11%9%46%6%5%411%
1565
February1st to 15thDay
10%13%6%14%11%6%7%45%7%12%
1575
16th to endDay
15%18%7%11%8%45%33317%
1453
March1st to 15thDay
16%14%5%8%6%35%445%25%
1885
16th to endDay
14%15%46%4445%45%31%
2052
April1st to 15thDay
23%15%6%6%42434325%
1972
16th to endDay
21%10%46%5%33345%32%
2153
May1st to 15thDay
20%10%35%435%46%6%30%
2301
16th to endDay
25%8%35%323335%33%
2394
June1st to 15thDay
23%8%25%435%5%5%8%25%
2427
16th to endDay
19%6%36%6%35%5%5%7%30%
2475
July1st to 15thDay
21%7%27%6%35%6%5%8%26%
2475
16th to endDay
21%7%36%5%35%5%5%6%27%
2477
August1st to 15thDay
25%8%37%5%35%45%6%25%
2242
16th to endDay
21%7%37%6%445%5%7%25%
2206
September1st to 15thDay
25%7%35%5%34446%29%
1980
16th to endDay
26%7%25%424337%30%
1815
October1st to 15thDay
25%15%37%5%33246%22%
1650
16th to endDay
34%21%36%43232312%
1678
November1st to 15thDay
25%20%6%8%41322320%
1420
16th to endDay
26%20%9%11%6%3332310%
1440
December1st to 15thDay
20%24%8%11%7%343249%
1440
16th to endDay
20%19%8%12%8%34435%9%
1374
January1st to 15thNight
22%17%8%12%7%36%4329%
2666
16th to endNight
13%16%8%12%8%5%8%6%4411%
2658
February1st to 15thNight
11%13%6%12%10%5%8%6%5%5%14%
2285
16th to endNight
15%16%7%11%8%46%6%5%315%
2019
March1st to 15thNight
17%16%5%6%7%46%5%5%5%19%
2049
16th to endNight
16%11%47%435%44432%
1969
April1st to 15thNight
23%11%5%8%32343430%
1646
16th to endNight
20%8%45%42434436%
1483
May1st to 15thNight
15%9%5%6%5%2445%6%34%
1320
16th to endNight
22%8%35%435%448%29%
1367
June1st to 15thNight
22%7%37%5%345%45%28%
1201
16th to endNight
15%5%27%6%3445%7%36%
1155
July1st to 15thNight
18%6%245%2447%8%34%
1155
16th to endNight
15%5%35%7%35%5%5%7%35%
1381
August1st to 15thNight
21%7%27%5%445%6%6%28%
1386
16th to endNight
14%8%36%434447%37%
1632
September1st to 15thNight
23%7%35%5%24345%34%
1650
16th to endNight
25%7%2442234438%
1814
October1st to 15thNight
24%11%47%5%34345%26%
1980
16th to endNight
34%18%45%42334416%
2194
November1st to 15thNight
23%17%7%8%5%2333420%
2435
16th to endNight
28%20%6%8%42422314%
2520
December1st to 15thNight
21%22%7%12%7%2432311%
2520
16th to endNight
20%21%8%12%8%35%4229%
2847

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
79%38%7%1
1272
16th to endDay
74%35%11%5%
1565
February1st to 15thDay
71%47%11%4
1577
16th to endDay
71%26%15%4
1453
March1st to 15thDay
61%46%15%10%
1896
16th to endDay
54%47%20%10%2
2052
April1st to 15thDay
63%27%13%10%2
1972
16th to endDay
55%29%16%13%1
2153
May1st to 15thDay
53%49%18%12%1
2301
16th to endDay
54%48%21%10%
2398
June1st to 15thDay
56%5%10%18%9%
2427
16th to endDay
52%5%11%20%8%1
2475
July1st to 15thDay
53%6%13%18%7%
2316
16th to endDay
58%6%11%18%5%
2309
August1st to 15thDay
58%6%12%17%3
2228
16th to endDay
56%5%15%16%6%
2206
September1st to 15thDay
56%5%13%17%5%1
1980
16th to endDay
55%412%22%4
1815
October1st to 15thDay
64%312%12%6%
1650
16th to endDay
77%37%7%3
1678
November1st to 15thDay
70%311%9%4
1420
16th to endDay
81%26%7%2
1440
December1st to 15thDay
80%35%9%1
1440
16th to endDay
78%37%7%2
1374
January1st to 15thNight
80%26%8%1
2666
16th to endNight
75%36%9%4
2658
February1st to 15thNight
69%48%10%6%
2287
16th to endNight
71%46%12%4
2019
March1st to 15thNight
65%48%12%9%
2061
16th to endNight
54%38%20%10%1
1969
April1st to 15thNight
57%47%16%11%2
1646
16th to endNight
50%47%20%15%1
1483
May1st to 15thNight
50%49%19%13%2
1320
16th to endNight
53%5%9%20%11%
1369
June1st to 15thNight
57%5%7%16%10%1
1201
16th to endNight
45%6%13%23%10%1
1155
July1st to 15thNight
45%6%15%24%8%
1085
16th to endNight
48%6%16%22%6%
1286
August1st to 15thNight
54%6%14%20%4
1376
16th to endNight
45%6%20%22%5%
1632
September1st to 15thNight
53%416%18%7%
1650
16th to endNight
49%415%24%6%
1814
October1st to 15thNight
60%413%13%6%1
1980
16th to endNight
71%49%10%3
2194
November1st to 15thNight
69%312%11%3
2435
16th to endNight
76%47%8%3
2520
December1st to 15thNight
79%27%8%1
2520
16th to endNight
81%35%6%3
2847

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
31%18%33%11%5%
60
16th to endDay
39%7%30%14%8%
69
February1st to 15thDay
24%14%44%13%21
90
16th to endDay
25%16%38%17%1
112
March1st to 15thDay
26%16%32%18%6%
270
16th to endDay
22%12%34%19%8%2
250
April1st to 15thDay
31%12%25%20%5%4
210
16th to endDay
23%16%27%20%9%3
210
May1st to 15thDay
25%12%29%20%10%
228
16th to endDay
30%12%25%23%5%2
267
June1st to 15thDay
34%11%28%16%8%1
372
16th to endDay
18%11%32%27%8%1
420
July1st to 15thDay
25%9%32%23%8%1
400
16th to endDay
24%6%31%22%10%3
288
August1st to 15thDay
32%329%18%12%4
253
16th to endDay
30%7%26%20%10%2
268
September1st to 15thDay
28%8%25%22%9%5%
255
16th to endDay
27%8%30%20%9%2
254
October1st to 15thDay
32%11%28%18%8%
255
16th to endDay
43%14%17%16%7%1
257
November1st to 15thDay
41%13%29%10%4
74
16th to endDay
45%15%26%11%1
60
December1st to 15thDay
35%13%33%13%31
60
16th to endDay
42%14%32%7%3
64
January1st to 15thNight
33%11%30%20%4
881
16th to endNight
21%12%31%22%12%
768
February1st to 15thNight
18%12%35%26%7%
704
16th to endNight
24%13%34%22%5%
631
March1st to 15thNight
28%17%25%21%5%
720
16th to endNight
23%12%31%23%8%1
732
April1st to 15thNight
28%14%27%23%6%
658
16th to endNight
25%11%31%23%6%1
493
May1st to 15thNight
21%6%33%28%10%
330
16th to endNight
27%6%31%25%6%
343
June1st to 15thNight
27%7%29%24%10%
330
16th to endNight
15%6%28%34%14%
330
July1st to 15thNight
20%433%31%10%
310
16th to endNight
16%322%40%15%1
348
August1st to 15thNight
23%423%29%16%2
395
16th to endNight
19%6%27%28%16%1
582
September1st to 15thNight
30%7%24%21%14%1
660
16th to endNight
28%7%24%26%11%
657
October1st to 15thNight
30%11%28%19%8%
660
16th to endNight
45%8%22%16%5%1
704
November1st to 15thNight
34%12%30%14%6%1
700
16th to endNight
41%11%26%15%4
720
December1st to 15thNight
36%12%26%17%5%1
720
16th to endNight
33%13%25%19%5%2
927
Page generated at 2017-03-23 07:36:17. Version ac04

Copyright 2017 A. Danko


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