Snobie Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Snobie Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
39%
15179
20%
46936
11%
15143
49%
15143
25%
29656

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
26%
719
22%
2506
10%
716
42%
716
19%
1557
January16th to endNight
21%
768
22%
2496
8%
768
40%
768
22%
1572
February1st to 15thNight
20%
704
18%
2266
6%
701
34%
701
21%
1434
February16th to endNight
21%
631
25%
1893
9%
631
41%
631
24%
1182
March1st to 15thNight
28%
720
21%
2076
9%
720
41%
720
26%
1322
March16th to endNight
28%
768
21%
2041
9%
768
38%
768
27%
1363
April1st to 15thNight
28%
718
19%
1796
5%
718
36%
718
30%
1201
April16th to endNight
39%
720
19%
1800
7%
720
44%
720
30%
1207
May1st to 15thNight
36%
534
16%
1614
8%
534
43%
534
21%
1113
May16th to endNight
51%
374
16%
1497
15%
374
56%
374
20%
914
June1st to 15thNight
55%
360
17%
1440
18%
360
62%
360
23%
860
June16th to endNight
59%
360
16%
1440
20%
360
63%
360
26%
830
July1st to 15thNight
58%
340
12%
1360
14%
340
60%
340
18%
865
July16th to endNight
68%
441
16%
1478
16%
414
71%
414
27%
871
August1st to 15thNight
66%
577
17%
1647
13%
574
67%
574
31%
1045
August16th to endNight
63%
764
18%
1910
11%
764
64%
764
33%
1254
September1st to 15thNight
57%
720
25%
1800
14%
720
61%
720
34%
1184
September16th to endNight
56%
689
25%
1862
20%
689
59%
689
33%
1193
October1st to 15thNight
48%
660
22%
1980
18%
660
55%
660
27%
1253
October16th to endNight
37%
704
27%
2128
15%
704
52%
704
32%
1246
November1st to 15thNight
37%
700
23%
2277
14%
700
50%
700
26%
1383
November16th to endNight
32%
720
21%
2421
12%
720
45%
720
22%
1496
December1st to 15thNight
26%
720
18%
2520
8%
720
40%
720
19%
1624
December16th to endNight
23%
768
21%
2688
8%
768
40%
768
19%
1687

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%5%244345%5%7%42%
47970
Night
14%5%2442445%7%43%
47113
Cloud CoverDay
13%5%244345%5%8%42%
47980
Night
14%5%2442445%7%43%
47118
TransparencyDay
39%6%12%23%16%2
47665
Night
40%5%11%22%17%2
46936
SeeingDay
17%6%23%26%17%7%
5769
Night
17%7%29%30%13%1
15181

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
13%6%245%33437%42%
1432
16th to endDay
14%6%24435%346%44%
1728
February1st to 15thDay
15%6%243346%45%42%
1594
16th to endDay
12%7%35%43447%5%40%
1580
March1st to 15thDay
15%5%245%24446%43%
1870
16th to endDay
17%5%24334445%42%
2181
April1st to 15thDay
15%5%25%324446%44%
2152
16th to endDay
15%335%42445%7%44%
2160
May1st to 15thDay
16%6%245%25%46%7%38%
2346
16th to endDay
14%4244345%7%9%39%
2618
June1st to 15thDay
11%5%25%435%6%7%9%38%
2520
16th to endDay
9%424425%6%6%9%42%
2520
July1st to 15thDay
9%425%5%35%5%7%10%40%
2520
16th to endDay
5%3246%37%7%8%11%38%
2586
August1st to 15thDay
10%5%25%5%345%7%8%40%
2289
16th to endDay
9%5%144345%6%9%43%
2292
September1st to 15thDay
12%42443445%7%46%
2160
16th to endDay
14%5%245%3445%7%41%
1932
October1st to 15thDay
16%5%13423447%45%
1650
16th to endDay
16%423433345%47%
1744
November1st to 15thDay
15%5%14323445%46%
1581
16th to endDay
16%5%23423446%46%
1539
December1st to 15thDay
16%425%4245%6%6%41%
1440
16th to endDay
18%5%25%4145%5%6%39%
1536
January1st to 15thNight
17%5%24424446%42%
2506
16th to endNight
16%7%2442335%6%43%
2496
February1st to 15thNight
14%7%35%415%446%41%
2265
16th to endNight
16%6%23324446%46%
1893
March1st to 15thNight
16%5%1442435%6%45%
2064
16th to endNight
17%6%34424435%43%
2041
April1st to 15thNight
15%6%1442445%7%44%
1796
16th to endNight
17%5%2432445%7%43%
1800
May1st to 15thNight
17%6%36%6%2335%6%38%
1614
16th to endNight
14%5%25%5%3445%8%40%
1495
June1st to 15thNight
13%4245%3445%8%43%
1440
16th to endNight
9%425%4345%6%10%42%
1440
July1st to 15thNight
8%5%35%7%46%6%6%9%36%
1440
16th to endNight
6%425%5%35%6%8%10%41%
1579
August1st to 15thNight
8%5%136%345%6%7%45%
1658
16th to endNight
11%4244245%48%46%
1910
September1st to 15thNight
12%5%25%42335%7%47%
1800
16th to endNight
13%6%145%23447%45%
1862
October1st to 15thNight
17%5%2342335%6%44%
1980
16th to endNight
16%413323336%51%
2128
November1st to 15thNight
13%6%35%423235%49%
2277
16th to endNight
16%6%2343446%6%41%
2421
December1st to 15thNight
18%5%25%5%34345%39%
2520
16th to endNight
18%5%2442445%7%40%
2688

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
14%6%25%6%245%46%42%
1432
16th to endDay
14%7%24435%346%44%
1728
February1st to 15thDay
15%7%24335%5%45%43%
1594
16th to endDay
13%7%25%5%2445%6%40%
1580
March1st to 15thDay
15%5%25%5%34347%43%
1881
16th to endDay
17%5%234245%45%42%
2180
April1st to 15thDay
15%5%24324447%44%
2152
16th to endDay
15%425%424447%44%
2160
May1st to 15thDay
16%6%25%435%5%5%8%37%
2346
16th to endDay
14%424425%5%6%9%39%
2618
June1st to 15thDay
10%4245%35%6%6%10%38%
2520
16th to endDay
10%424435%6%6%10%43%
2520
July1st to 15thDay
8%415%5%35%6%6%11%39%
2520
16th to endDay
4325%6%46%6%9%11%38%
2586
August1st to 15thDay
10%5%26%5%345%7%9%40%
2289
16th to endDay
9%5%245%345%6%9%43%
2292
September1st to 15thDay
11%5%2443445%7%45%
2160
16th to endDay
15%425%5%345%47%40%
1932
October1st to 15thDay
16%5%23423447%45%
1650
16th to endDay
16%414424345%47%
1744
November1st to 15thDay
15%5%2342335%5%46%
1581
16th to endDay
16%5%23423445%46%
1539
December1st to 15thDay
16%425%5%245%6%6%41%
1440
16th to endDay
18%5%34425%45%6%38%
1536
January1st to 15thNight
17%5%25%424446%42%
2506
16th to endNight
16%7%24423346%43%
2496
February1st to 15thNight
14%6%345%2445%6%42%
2258
16th to endNight
15%6%23324446%46%
1893
March1st to 15thNight
16%5%2442335%6%44%
2076
16th to endNight
16%6%24423436%43%
2041
April1st to 15thNight
15%6%24424447%43%
1796
16th to endNight
18%5%24323447%43%
1800
May1st to 15thNight
17%7%36%5%2345%6%37%
1614
16th to endNight
14%5%346%3445%8%40%
1495
June1st to 15thNight
13%5%245%3445%7%43%
1440
16th to endNight
8%4345%25%5%6%11%42%
1440
July1st to 15thNight
8%5%25%7%5%5%7%6%9%36%
1440
16th to endNight
6%426%5%35%6%8%10%41%
1579
August1st to 15thNight
8%4146%35%5%6%8%45%
1658
16th to endNight
11%5%244245%5%8%46%
1910
September1st to 15thNight
13%425%33345%7%47%
1800
16th to endNight
13%6%15%423447%44%
1862
October1st to 15thNight
18%42432235%6%44%
1980
16th to endNight
16%413323336%51%
2128
November1st to 15thNight
14%6%35%422335%49%
2277
16th to endNight
16%6%1443446%6%41%
2421
December1st to 15thNight
18%5%25%5%34446%38%
2520
16th to endNight
18%5%2442445%7%40%
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%414%21%13%4
1433
16th to endDay
41%311%25%14%3
1728
February1st to 15thDay
42%412%26%12%2
1597
16th to endDay
41%411%27%12%2
1580
March1st to 15thDay
41%412%24%15%1
1881
16th to endDay
42%5%9%21%18%3
2181
April1st to 15thDay
40%410%23%16%4
2152
16th to endDay
38%5%10%17%22%5%
2160
May1st to 15thDay
42%7%12%19%15%2
2346
16th to endDay
38%8%15%23%13%1
2622
June1st to 15thDay
38%8%13%26%11%1
2520
16th to endDay
34%8%14%22%18%1
2520
July1st to 15thDay
36%8%13%22%15%3
2371
16th to endDay
33%9%16%25%14%2
2424
August1st to 15thDay
36%7%14%23%16%1
2276
16th to endDay
35%7%12%22%17%3
2292
September1st to 15thDay
36%6%11%21%21%2
2160
16th to endDay
41%49%18%23%1
1932
October1st to 15thDay
37%412%24%17%2
1650
16th to endDay
38%39%28%18%1
1744
November1st to 15thDay
39%411%22%18%3
1581
16th to endDay
39%310%28%15%2
1539
December1st to 15thDay
40%6%15%24%11%2
1440
16th to endDay
44%5%13%22%13%
1536
January1st to 15thNight
42%411%20%16%3
2506
16th to endNight
42%310%26%15%1
2496
February1st to 15thNight
42%412%23%14%2
2266
16th to endNight
39%310%23%19%3
1893
March1st to 15thNight
39%5%12%25%15%2
2076
16th to endNight
42%411%20%17%3
2041
April1st to 15thNight
40%411%20%18%4
1796
16th to endNight
39%5%10%18%20%5%
1800
May1st to 15thNight
46%7%9%17%16%2
1614
16th to endNight
41%7%14%17%16%2
1497
June1st to 15thNight
39%6%12%23%17%
1440
16th to endNight
34%8%13%25%16%2
1440
July1st to 15thNight
41%9%15%18%12%3
1360
16th to endNight
34%8%17%23%14%1
1478
August1st to 15thNight
34%8%15%20%19%1
1647
16th to endNight
36%7%12%21%20%2
1910
September1st to 15thNight
36%6%10%21%21%3
1800
16th to endNight
38%48%22%23%3
1862
October1st to 15thNight
39%5%10%23%18%2
1980
16th to endNight
34%310%28%19%3
2128
November1st to 15thNight
39%49%21%17%7%
2277
16th to endNight
40%411%23%16%2
2421
December1st to 15thNight
45%412%22%13%1
2520
16th to endNight
42%5%13%23%12%1
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
20%18%40%15%5%1
60
16th to endDay
25%16%37%16%4
96
February1st to 15thDay
21%18%38%18%1
111
16th to endDay
16%14%43%23%2
239
March1st to 15thDay
17%16%29%28%7%
270
16th to endDay
21%10%34%22%7%2
288
April1st to 15thDay
19%10%34%23%7%4
270
16th to endDay
22%6%22%25%16%5%
270
May1st to 15thDay
30%11%22%20%12%2
288
16th to endDay
18%416%28%22%9%
331
June1st to 15thDay
14%421%27%22%8%
315
16th to endDay
12%324%32%21%6%
315
July1st to 15thDay
12%117%33%25%9%
305
16th to endDay
5%113%30%34%13%
326
August1st to 15thDay
15%13%26%29%15%
313
16th to endDay
10%18%30%28%19%
332
September1st to 15thDay
14%221%21%21%17%
315
16th to endDay
20%114%28%20%15%
283
October1st to 15thDay
23%217%30%16%9%
255
16th to endDay
15%6%33%28%14%1
269
November1st to 15thDay
18%7%29%24%16%2
235
16th to endDay
19%11%32%21%15%
159
December1st to 15thDay
18%21%25%18%13%3
60
16th to endDay
35%7%34%17%4
64
January1st to 15thNight
19%12%37%24%5%
720
16th to endNight
20%11%41%24%1
768
February1st to 15thNight
18%13%43%23%1
704
16th to endNight
19%15%40%21%2
631
March1st to 15thNight
20%11%36%25%5%
720
16th to endNight
19%7%39%24%7%
768
April1st to 15thNight
18%9%38%26%6%
718
16th to endNight
21%6%28%32%11%
720
May1st to 15thNight
21%5%30%32%9%
534
16th to endNight
17%319%37%20%
375
June1st to 15thNight
13%120%41%21%
360
16th to endNight
10%120%47%20%
360
July1st to 15thNight
11%118%45%23%
340
16th to endNight
9%111%43%31%2
441
August1st to 15thNight
11%10%45%30%2
577
16th to endNight
13%114%36%31%3
764
September1st to 15thNight
15%217%36%26%2
720
16th to endNight
17%216%33%26%4
689
October1st to 15thNight
22%319%34%16%3
660
16th to endNight
18%7%33%28%11%
704
November1st to 15thNight
16%7%33%27%13%1
700
16th to endNight
18%11%30%28%9%
720
December1st to 15thNight
20%10%34%23%9%1
720
16th to endNight
19%11%39%25%3
768
Page generated at 2017-09-24 09:15:45. Version ac04

Copyright 2017 A. Danko


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