DaltonSkyGazer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DaltonSkyGazer Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
26%
14896
16%
46884
7%
14865
36%
14865
16%
31945

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
12%
720
15%
2506
5%
716
25%
716
9%
1778
January16th to endNight
12%
768
15%
2668
4%
768
28%
768
10%
1881
February1st to 15thNight
8%
704
12%
2219
1%
701
21%
701
9%
1640
February16th to endNight
14%
631
18%
1893
5%
631
30%
631
10%
1341
March1st to 15thNight
16%
720
14%
2160
5%
720
27%
720
11%
1570
March16th to endNight
21%
768
22%
2002
7%
768
33%
768
17%
1397
April1st to 15thNight
18%
718
14%
1796
3%
718
25%
718
17%
1338
April16th to endNight
23%
648
17%
1728
4%
648
32%
648
20%
1188
May1st to 15thNight
24%
498
16%
1578
7%
498
34%
498
16%
1078
May16th to endNight
33%
374
12%
1497
9%
374
42%
374
15%
988
June1st to 15thNight
33%
360
12%
1440
10%
360
43%
360
15%
951
June16th to endNight
44%
360
11%
1440
12%
360
52%
360
22%
863
July1st to 15thNight
46%
340
13%
1360
15%
340
52%
340
23%
789
July16th to endNight
53%
376
15%
1418
16%
354
59%
354
24%
809
August1st to 15thNight
49%
474
16%
1545
10%
472
55%
472
29%
916
August16th to endNight
50%
764
19%
1910
10%
764
53%
764
33%
1248
September1st to 15thNight
40%
720
20%
1812
8%
720
45%
720
30%
1186
September16th to endNight
47%
681
25%
1880
17%
681
52%
681
32%
1161
October1st to 15thNight
31%
660
20%
1903
11%
660
40%
660
20%
1290
October16th to endNight
19%
704
13%
2244
4%
704
30%
704
14%
1560
November1st to 15thNight
25%
700
19%
2277
10%
700
39%
700
17%
1491
November16th to endNight
22%
720
17%
2400
8%
720
35%
720
13%
1647
December1st to 15thNight
16%
720
12%
2520
3%
720
27%
720
9%
1819
December16th to endNight
13%
768
13%
2688
4%
768
25%
768
7%
2016

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
16%8%36%6%35%5%5%6%32%
47991
Night
15%8%36%5%35%45%6%34%
47054
Cloud CoverDay
16%7%36%6%35%5%5%7%32%
48001
Night
15%7%36%5%25%5%5%6%35%
47059
TransparencyDay
50%411%20%11%1
47679
Night
47%5%12%21%11%1
46884
SeeingDay
23%17%26%18%10%3
5778
Night
23%18%25%22%8%1
14897

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%9%5%7%8%37%6%6%6%25%
1432
16th to endDay
13%10%48%9%47%5%47%25%
1554
February1st to 15thDay
12%11%6%9%8%46%5%5%6%22%
1641
16th to endDay
15%10%49%7%35%43429%
1580
March1st to 15thDay
16%10%39%5%3445%6%28%
1790
16th to endDay
16%8%46%6%24445%35%
2221
April1st to 15thDay
17%10%47%6%34335%31%
2152
16th to endDay
14%7%37%6%345%5%5%36%
2232
May1st to 15thDay
24%8%35%5%345%46%29%
2385
16th to endDay
18%6%25%6%345%5%7%34%
2618
June1st to 15thDay
22%6%36%5%45%45%8%28%
2520
16th to endDay
17%6%35%6%45%5%6%8%28%
2520
July1st to 15thDay
13%6%25%6%36%7%6%7%32%
2520
16th to endDay
13%5%25%6%45%6%6%8%34%
2654
August1st to 15thDay
14%6%26%6%35%6%6%9%31%
2391
16th to endDay
12%5%25%6%45%46%8%37%
2292
September1st to 15thDay
14%6%26%6%35%437%38%
2147
16th to endDay
14%5%24423347%45%
1873
October1st to 15thDay
21%9%37%5%2334434%
1724
16th to endDay
19%11%46%6%2445%5%29%
1628
November1st to 15thDay
14%9%45%5%1345%7%37%
1581
16th to endDay
18%7%35%6%35%45%5%33%
1560
December1st to 15thDay
18%12%48%6%34346%27%
1440
16th to endDay
17%13%6%9%8%345%45%22%
1536
January1st to 15thNight
15%9%48%7%35%5%5%6%26%
2506
16th to endNight
12%11%48%7%47%5%5%6%26%
2668
February1st to 15thNight
13%8%49%7%48%6%6%6%23%
2218
16th to endNight
13%12%46%6%345%6%5%30%
1893
March1st to 15thNight
17%9%36%6%36%5%4430%
2147
16th to endNight
14%8%47%423446%37%
2002
April1st to 15thNight
17%10%36%7%34445%32%
1796
16th to endNight
18%8%25%414446%38%
1728
May1st to 15thNight
19%8%36%5%235%5%5%34%
1578
16th to endNight
15%8%35%5%2446%8%33%
1495
June1st to 15thNight
21%7%25%423446%35%
1440
16th to endNight
14%424425%45%9%41%
1440
July1st to 15thNight
12%5%15%5%35%5%5%8%41%
1440
16th to endNight
11%5%244245%5%8%43%
1514
August1st to 15thNight
10%415%435%46%7%45%
1555
16th to endNight
12%5%245%2445%8%44%
1910
September1st to 15thNight
15%5%245%33346%45%
1812
16th to endNight
13%424323447%49%
1880
October1st to 15thNight
19%6%35%5%2434439%
1903
16th to endNight
18%9%37%5%2345%6%32%
2244
November1st to 15thNight
14%9%26%42445%5%40%
2277
16th to endNight
15%8%46%6%35%46%5%33%
2400
December1st to 15thNight
20%10%37%7%25%446%25%
2520
16th to endNight
19%10%47%7%46%5%5%5%23%
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
12%9%46%7%5%7%6%5%7%27%
1432
16th to endDay
12%9%38%8%46%5%6%6%27%
1554
February1st to 15thDay
13%9%5%9%7%47%5%6%6%24%
1641
16th to endDay
15%9%410%7%25%436%30%
1580
March1st to 15thDay
17%9%48%5%35%46%6%28%
1800
16th to endDay
16%8%46%5%34446%35%
2221
April1st to 15thDay
17%9%47%6%34335%33%
2152
16th to endDay
14%7%36%6%345%5%6%36%
2232
May1st to 15thDay
24%8%35%5%34445%29%
2385
16th to endDay
18%6%25%5%345%6%8%33%
2618
June1st to 15thDay
22%6%35%5%35%45%8%28%
2520
16th to endDay
17%7%26%5%46%5%6%8%29%
2520
July1st to 15thDay
13%6%26%6%5%6%6%6%8%32%
2520
16th to endDay
13%5%26%5%45%6%6%8%34%
2654
August1st to 15thDay
14%6%36%6%35%5%7%8%32%
2391
16th to endDay
12%6%25%6%35%5%6%8%37%
2292
September1st to 15thDay
13%7%26%6%44437%38%
2147
16th to endDay
14%5%24434447%45%
1873
October1st to 15thDay
19%10%37%424435%34%
1724
16th to endDay
18%11%36%6%345%5%5%30%
1628
November1st to 15thDay
14%8%37%4235%5%6%38%
1581
16th to endDay
17%7%35%5%25%45%6%35%
1560
December1st to 15thDay
17%10%37%6%45%347%28%
1440
16th to endDay
16%11%5%9%7%4445%5%24%
1536
January1st to 15thNight
15%8%36%7%35%6%5%7%28%
2506
16th to endNight
12%9%47%7%36%6%6%7%29%
2668
February1st to 15thNight
13%7%48%8%37%7%6%7%26%
2211
16th to endNight
14%10%38%5%245%5%6%32%
1893
March1st to 15thNight
16%9%36%5%37%5%6%5%30%
2160
16th to endNight
14%7%37%5%2445%5%38%
2001
April1st to 15thNight
16%10%36%6%245%5%5%32%
1796
16th to endNight
18%6%36%323445%39%
1728
May1st to 15thNight
19%8%46%42346%5%34%
1578
16th to endNight
16%8%36%5%25%5%6%7%33%
1495
June1st to 15thNight
21%6%25%5%23447%35%
1440
16th to endNight
15%425%3245%5%8%43%
1440
July1st to 15thNight
12%5%25%5%2445%9%42%
1440
16th to endNight
10%6%25%4245%5%8%43%
1514
August1st to 15thNight
10%5%245%2445%7%46%
1555
16th to endNight
12%5%15%5%245%47%45%
1910
September1st to 15thNight
13%6%25%424446%44%
1812
16th to endNight
13%5%24323446%49%
1880
October1st to 15thNight
18%7%35%414345%40%
1903
16th to endNight
17%8%36%5%3345%6%34%
2244
November1st to 15thNight
14%8%35%5%24446%40%
2277
16th to endNight
15%8%36%6%36%45%6%34%
2400
December1st to 15thNight
19%8%36%6%35%6%5%6%28%
2520
16th to endNight
17%10%36%6%36%7%6%6%24%
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
54%5%9%20%8%1
1433
16th to endDay
55%5%12%17%8%1
1554
February1st to 15thDay
57%6%11%14%8%
1644
16th to endDay
56%38%18%11%1
1580
March1st to 15thDay
54%412%17%10%1
1800
16th to endDay
50%39%18%15%3
2221
April1st to 15thDay
54%37%21%11%1
2152
16th to endDay
47%48%21%15%3
2232
May1st to 15thDay
56%36%20%10%1
2385
16th to endDay
47%6%13%19%11%1
2622
June1st to 15thDay
53%5%13%19%8%
2520
16th to endDay
50%5%13%17%11%
2520
July1st to 15thDay
46%6%11%23%10%
2371
16th to endDay
44%5%16%20%12%
2487
August1st to 15thDay
46%6%14%22%9%
2377
16th to endDay
42%5%10%27%13%
2292
September1st to 15thDay
46%410%22%14%1
2147
16th to endDay
39%48%26%19%1
1873
October1st to 15thDay
52%38%21%10%2
1724
16th to endDay
54%413%16%9%1
1628
November1st to 15thDay
45%414%20%12%1
1581
16th to endDay
50%311%20%11%1
1560
December1st to 15thDay
56%313%17%8%
1440
16th to endDay
61%411%14%7%
1536
January1st to 15thNight
54%411%16%10%1
2506
16th to endNight
52%5%10%19%10%1
2668
February1st to 15thNight
55%6%12%15%8%
2219
16th to endNight
51%5%10%21%10%1
1893
March1st to 15thNight
53%5%11%18%9%1
2160
16th to endNight
46%49%20%14%5%
2002
April1st to 15thNight
52%410%19%12%1
1796
16th to endNight
45%49%21%16%2
1728
May1st to 15thNight
50%310%19%14%1
1578
16th to endNight
47%7%15%18%10%1
1497
June1st to 15thNight
49%5%13%21%9%
1440
16th to endNight
37%7%16%25%12%
1440
July1st to 15thNight
37%5%13%31%11%
1360
16th to endNight
35%6%16%26%12%1
1418
August1st to 15thNight
36%5%18%27%10%1
1545
16th to endNight
37%5%13%30%13%
1910
September1st to 15thNight
39%313%25%17%1
1812
16th to endNight
35%49%28%21%1
1880
October1st to 15thNight
47%311%20%14%3
1903
16th to endNight
51%414%21%8%
2244
November1st to 15thNight
45%411%20%15%2
2277
16th to endNight
50%412%19%10%1
2400
December1st to 15thNight
55%5%14%16%7%
2520
16th to endNight
58%6%10%17%7%
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
33%30%23%6%5%1
60
16th to endDay
29%29%28%11%
67
February1st to 15thDay
28%31%29%8%1
157
16th to endDay
23%29%28%15%2
239
March1st to 15thDay
31%24%25%14%3
270
16th to endDay
29%25%22%11%7%3
288
April1st to 15thDay
30%21%24%13%8%
270
16th to endDay
19%19%30%17%7%5%
270
May1st to 15thDay
35%17%22%12%6%4
288
16th to endDay
21%15%30%23%8%
331
June1st to 15thDay
25%11%28%20%13%
315
16th to endDay
20%15%28%20%12%2
315
July1st to 15thDay
18%8%37%22%12%1
305
16th to endDay
15%7%32%27%12%3
326
August1st to 15thDay
14%13%23%25%14%7%
313
16th to endDay
13%7%23%27%15%12%
332
September1st to 15thDay
19%12%23%20%16%8%
315
16th to endDay
18%8%22%16%18%15%
275
October1st to 15thDay
24%13%23%19%14%4
255
16th to endDay
25%22%26%17%7%
248
November1st to 15thDay
23%20%23%22%8%
235
16th to endDay
27%23%22%16%7%2
180
December1st to 15thDay
26%38%21%8%5%
60
16th to endDay
35%31%23%9%
64
January1st to 15thNight
26%25%31%13%2
720
16th to endNight
24%27%28%17%1
768
February1st to 15thNight
24%28%31%12%1
704
16th to endNight
27%30%23%15%2
631
March1st to 15thNight
30%24%24%18%2
720
16th to endNight
26%23%23%19%6%
768
April1st to 15thNight
27%19%30%19%4
718
16th to endNight
26%18%28%17%7%1
648
May1st to 15thNight
26%15%28%21%7%
498
16th to endNight
20%8%30%26%13%
375
June1st to 15thNight
23%10%24%29%11%
360
16th to endNight
16%5%26%40%10%
360
July1st to 15thNight
15%5%26%38%14%
340
16th to endNight
11%421%41%19%
376
August1st to 15thNight
14%425%36%17%1
474
16th to endNight
15%6%20%32%21%3
764
September1st to 15thNight
18%8%26%26%17%1
720
16th to endNight
17%8%21%26%18%6%
681
October1st to 15thNight
24%14%23%25%10%1
660
16th to endNight
27%21%26%20%4
704
November1st to 15thNight
23%20%25%22%8%1
700
16th to endNight
25%20%26%17%7%1
720
December1st to 15thNight
29%26%24%15%4
720
16th to endNight
32%27%24%12%2
768
Page generated at 2017-09-22 07:35:31. Version ac04

Copyright 2017 A. Danko


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