Salewsky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Salewsky Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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
38%
16250
17%
47368
10%
16205
44%
16205
24%
31559

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%
900
13%
2506
6%
895
33%
895
17%
1855
January16th to endNight
21%
960
12%
2640
4%
960
29%
960
16%
2008
February1st to 15thNight
27%
877
15%
2288
4%
875
33%
875
22%
1617
February16th to endNight
26%
642
17%
1904
7%
642
35%
642
18%
1331
March1st to 15thNight
32%
699
16%
2139
11%
699
38%
699
22%
1415
March16th to endNight
36%
576
18%
2012
16%
576
43%
576
21%
1314
April1st to 15thNight
28%
539
17%
1797
11%
539
39%
539
19%
1228
April16th to endNight
36%
540
19%
1759
13%
540
45%
540
23%
1168
May1st to 15thNight
33%
540
17%
1461
8%
540
40%
540
23%
1030
May16th to endNight
47%
563
16%
1498
7%
561
53%
561
33%
953
June1st to 15thNight
49%
540
14%
1440
8%
540
51%
540
33%
921
June16th to endNight
53%
540
16%
1440
8%
540
57%
540
37%
882
July1st to 15thNight
65%
510
17%
1360
9%
510
68%
510
45%
771
July16th to endNight
70%
564
22%
1417
15%
531
73%
531
48%
783
August1st to 15thNight
67%
539
24%
1509
20%
536
71%
536
40%
875
August16th to endNight
60%
573
22%
1901
23%
573
64%
573
33%
1081
September1st to 15thNight
59%
540
26%
1800
25%
540
65%
540
36%
982
September16th to endNight
52%
669
25%
1932
17%
669
59%
669
33%
1155
October1st to 15thNight
41%
720
22%
2159
14%
720
48%
720
30%
1297
October16th to endNight
35%
768
18%
2411
11%
768
44%
768
22%
1579
November1st to 15thNight
32%
700
21%
2276
15%
700
41%
700
24%
1436
November16th to endNight
26%
891
15%
2511
8%
891
33%
891
18%
1805
December1st to 15thNight
21%
900
10%
2520
3%
900
27%
900
15%
1911
December16th to endNight
19%
960
11%
2688
3%
960
25%
960
12%
2162

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
14%8%36%5%3445%7%36%
48391
Night
14%8%36%5%24446%39%
47535
Cloud CoverDay
26%6%25%5%23446%32%
48401
Night
26%7%25%423345%34%
47540
Cloud CoverDay
14%8%36%5%35%45%7%36%
48399
Night
14%8%36%5%24446%38%
47540
TransparencyDay
47%312%24%11%1
48076
Night
45%312%24%12%1
47368
SeeingDay
17%6%26%27%16%5%
6231
Night
18%6%28%32%12%1
16253

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
11%11%8%9%7%35%45%7%26%
1432
16th to endDay
12%14%6%12%8%345%5%6%20%
1581
February1st to 15thDay
11%12%5%8%5%35%45%6%31%
1575
16th to endDay
12%12%37%7%36%446%30%
1568
March1st to 15thDay
14%10%45%5%3445%5%36%
1820
16th to endDay
17%9%36%4345%48%33%
2211
April1st to 15thDay
17%10%47%6%35%345%32%
2151
16th to endDay
22%10%36%423336%34%
2199
May1st to 15thDay
18%7%37%6%35%5%5%6%31%
2487
16th to endDay
14%5%25%5%35%5%5%8%37%
2617
June1st to 15thDay
15%3246%35%5%6%8%39%
2520
16th to endDay
10%5%25%5%35%5%6%9%39%
2520
July1st to 15thDay
7%314435%5%8%9%45%
2520
16th to endDay
9%424435%5%6%9%44%
2655
August1st to 15thDay
8%425%6%35%5%6%8%41%
2441
16th to endDay
14%5%24424348%43%
2301
September1st to 15thDay
13%424424446%47%
2160
16th to endDay
12%5%25%5%25%45%7%43%
2016
October1st to 15thDay
18%7%245%24436%41%
1800
16th to endDay
17%10%25%5%23346%37%
1812
November1st to 15thDay
14%9%36%5%23345%39%
1582
16th to endDay
17%8%46%6%34336%34%
1447
December1st to 15thDay
17%12%5%8%6%35%435%27%
1440
16th to endDay
20%16%5%9%8%46%42418%
1536
January1st to 15thNight
15%9%5%8%6%36%345%30%
2506
16th to endNight
13%12%5%10%7%35%446%25%
2640
February1st to 15thNight
10%12%47%5%24445%37%
2285
16th to endNight
14%10%46%6%34436%34%
1904
March1st to 15thNight
13%8%35%5%345%46%39%
2126
16th to endNight
17%8%35%424446%37%
2012
April1st to 15thNight
21%8%35%42435%5%34%
1797
16th to endNight
21%7%23423447%36%
1759
May1st to 15thNight
21%7%234245%46%35%
1461
16th to endNight
10%5%24435%45%8%44%
1496
June1st to 15thNight
11%5%25%5%3435%7%44%
1440
16th to endNight
8%4245%245%5%8%46%
1440
July1st to 15thNight
6%32331445%7%56%
1440
16th to endNight
6%2133245%5%10%54%
1513
August1st to 15thNight
5%325%425%45%9%49%
1518
16th to endNight
11%5%13423447%50%
1901
September1st to 15thNight
12%42232345%7%53%
1800
16th to endNight
10%424434346%50%
1932
October1st to 15thNight
16%6%24413246%47%
2159
16th to endNight
16%8%16%4345%5%6%37%
2411
November1st to 15thNight
14%9%35%423346%42%
2276
16th to endNight
17%10%37%6%23346%32%
2511
December1st to 15thNight
17%11%5%8%6%44446%26%
2520
16th to endNight
20%15%6%9%6%34335%21%
2688

Percentage Cloud Cover SW (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
25%9%5%8%7%24345%24%
1432
16th to endDay
26%12%411%6%33445%16%
1581
February1st to 15thDay
25%10%36%423346%28%
1575
16th to endDay
24%10%36%6%25%43427%
1568
March1st to 15thDay
27%8%3433333433%
1830
16th to endDay
31%8%24333436%27%
2211
April1st to 15thDay
30%9%26%42333328%
2151
16th to endDay
36%9%25%41223427%
2199
May1st to 15thDay
31%6%26%5%34445%25%
2487
16th to endDay
29%415%42345%6%31%
2617
June1st to 15thDay
29%4145%2445%6%31%
2520
16th to endDay
25%41442445%7%33%
2520
July1st to 15thDay
22%3135%3446%7%37%
2520
16th to endDay
25%3134335%6%6%37%
2655
August1st to 15thDay
16%415%6%3446%7%38%
2441
16th to endDay
20%5%2432345%7%41%
2301
September1st to 15thDay
18%424423346%44%
2160
16th to endDay
18%5%1442445%7%40%
2016
October1st to 15thDay
25%5%14423335%38%
1800
16th to endDay
24%9%245%23235%35%
1812
November1st to 15thDay
26%7%26%42333436%
1582
16th to endDay
30%6%35%5%33335%29%
1447
December1st to 15thDay
31%11%37%5%2343324%
1440
16th to endDay
32%14%48%6%3432316%
1536
January1st to 15thNight
26%7%47%5%35%23428%
2506
16th to endNight
27%10%39%6%34345%21%
2640
February1st to 15thNight
25%11%36%42233432%
2278
16th to endNight
26%9%35%5%23435%29%
1904
March1st to 15thNight
25%7%24423435%35%
2139
16th to endNight
30%7%24423346%31%
2012
April1st to 15thNight
33%7%2442324429%
1797
16th to endNight
34%7%23323336%29%
1759
May1st to 15thNight
34%6%13323445%30%
1460
16th to endNight
26%413424347%37%
1496
June1st to 15thNight
26%5%15%42325%6%35%
1440
16th to endNight
24%32341345%7%40%
1440
July1st to 15thNight
22%313313445%47%
1440
16th to endNight
22%2231235%8%47%
1513
August1st to 15thNight
14%3244245%48%46%
1518
16th to endNight
18%413323337%47%
1901
September1st to 15thNight
17%413313346%49%
1800
16th to endNight
17%324424336%48%
1932
October1st to 15thNight
23%5%14313235%44%
2159
16th to endNight
23%7%15%4235%5%6%34%
2411
November1st to 15thNight
26%8%2431233438%
2276
16th to endNight
29%8%36%5%22345%28%
2511
December1st to 15thNight
31%10%37%6%33335%21%
2520
16th to endNight
31%13%5%8%5%2323419%
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
11%12%7%9%7%35%35%7%25%
1432
16th to endDay
11%13%6%13%8%345%5%6%20%
1581
February1st to 15thDay
10%14%48%5%35%446%30%
1575
16th to endDay
12%11%47%7%26%5%37%30%
1568
March1st to 15thDay
14%10%5%6%5%25%445%36%
1830
16th to endDay
17%9%36%4345%48%32%
2209
April1st to 15thDay
17%10%46%6%34345%31%
2151
16th to endDay
21%11%45%413346%33%
2199
May1st to 15thDay
18%7%37%6%35%5%5%6%30%
2487
16th to endDay
13%5%25%6%345%6%8%37%
2617
June1st to 15thDay
14%425%5%25%5%5%8%38%
2520
16th to endDay
10%5%36%5%35%5%6%9%39%
2520
July1st to 15thDay
6%415%5%25%5%8%8%45%
2520
16th to endDay
9%424435%6%6%9%43%
2655
August1st to 15thDay
8%425%6%36%6%6%9%41%
2441
16th to endDay
13%5%25%424448%42%
2301
September1st to 15thDay
13%5%15%423446%47%
2160
16th to endDay
12%5%25%5%345%47%43%
2016
October1st to 15thDay
18%6%25%424346%40%
1800
16th to endDay
17%10%26%423346%37%
1812
November1st to 15thDay
14%9%37%424446%39%
1582
16th to endDay
17%8%47%6%34336%34%
1447
December1st to 15thDay
17%13%48%6%45%435%27%
1440
16th to endDay
19%16%6%9%8%36%33418%
1536
January1st to 15thNight
15%10%5%8%6%36%345%30%
2506
16th to endNight
12%11%5%10%7%45%445%26%
2640
February1st to 15thNight
11%11%5%7%5%24446%36%
2278
16th to endNight
14%10%46%7%24446%34%
1904
March1st to 15thNight
13%8%35%4345%46%39%
2139
16th to endNight
17%9%35%424446%37%
2012
April1st to 15thNight
21%9%35%42335%5%35%
1797
16th to endNight
20%7%24423347%36%
1759
May1st to 15thNight
20%7%244245%46%35%
1460
16th to endNight
9%5%245%35%45%9%43%
1496
June1st to 15thNight
11%5%15%6%25%35%8%44%
1440
16th to endNight
8%4344245%5%9%46%
1440
July1st to 15thNight
6%32331446%6%56%
1440
16th to endNight
6%21233446%10%54%
1513
August1st to 15thNight
5%425%425%5%6%9%49%
1518
16th to endNight
11%5%13414437%50%
1901
September1st to 15thNight
11%42232345%7%52%
1800
16th to endNight
10%424434447%49%
1932
October1st to 15thNight
15%6%23313346%47%
2159
16th to endNight
16%7%25%4245%5%6%37%
2411
November1st to 15thNight
14%9%25%5%23336%43%
2276
16th to endNight
16%10%47%6%23346%32%
2511
December1st to 15thNight
16%11%5%8%6%45%446%26%
2520
16th to endNight
19%15%6%9%6%3334421%
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
57%412%16%8%
1433
16th to endDay
63%313%13%6%
1581
February1st to 15thDay
53%314%20%8%1
1576
16th to endDay
54%311%22%7%
1568
March1st to 15thDay
50%314%21%9%1
1830
16th to endDay
50%414%23%6%
2211
April1st to 15thDay
55%29%21%10%
2151
16th to endDay
53%210%20%11%1
2199
May1st to 15thDay
52%311%22%8%
2487
16th to endDay
42%410%24%15%2
2621
June1st to 15thDay
42%313%27%12%
2520
16th to endDay
39%315%25%14%1
2520
July1st to 15thDay
33%413%30%15%2
2371
16th to endDay
35%414%26%16%2
2488
August1st to 15thDay
37%412%30%13%1
2426
16th to endDay
39%214%27%14%1
2301
September1st to 15thDay
36%311%32%15%
2160
16th to endDay
39%214%30%11%
2016
October1st to 15thDay
44%211%28%12%
1800
16th to endDay
49%114%25%8%
1812
November1st to 15thDay
46%211%24%12%1
1582
16th to endDay
52%316%20%6%
1447
December1st to 15thDay
60%312%18%4
1440
16th to endDay
71%29%10%5%
1536
January1st to 15thNight
56%310%20%8%
2506
16th to endNight
59%212%17%7%
2640
February1st to 15thNight
49%212%25%8%1
2288
16th to endNight
51%312%22%8%1
1904
March1st to 15thNight
46%312%24%11%2
2139
16th to endNight
48%212%27%7%1
2012
April1st to 15thNight
51%36%22%14%2
1797
16th to endNight
47%210%21%15%2
1759
May1st to 15thNight
48%311%21%14%
1461
16th to endNight
37%413%27%15%1
1498
June1st to 15thNight
38%312%30%14%
1440
16th to endNight
34%312%28%17%2
1440
July1st to 15thNight
26%312%32%20%3
1360
16th to endNight
23%416%34%17%3
1417
August1st to 15thNight
30%413%29%20%2
1509
16th to endNight
34%313%30%15%3
1901
September1st to 15thNight
30%310%29%23%1
1800
16th to endNight
35%210%35%14%
1932
October1st to 15thNight
38%210%28%17%1
2159
16th to endNight
46%314%22%12%
2411
November1st to 15thNight
43%212%24%14%1
2276
16th to endNight
53%214%21%6%
2511
December1st to 15thNight
58%311%20%4
2520
16th to endNight
67%210%14%4
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
27%8%35%21%5%1
90
16th to endDay
28%9%28%27%7%
96
February1st to 15thDay
17%17%42%13%8%
90
16th to endDay
28%13%28%20%8%
81
March1st to 15thDay
26%8%32%23%7%1
90
16th to endDay
30%5%24%25%11%3
195
April1st to 15thDay
24%7%31%27%9%
270
16th to endDay
25%7%27%22%13%3
270
May1st to 15thDay
22%10%32%24%7%3
444
16th to endDay
18%8%26%29%11%5%
517
June1st to 15thDay
16%6%27%28%16%4
495
16th to endDay
11%6%29%30%16%5%
495
July1st to 15thDay
8%324%30%22%10%
475
16th to endDay
9%226%28%24%8%
515
August1st to 15thDay
9%217%36%25%8%
493
16th to endDay
17%5%13%29%24%9%
341
September1st to 15thDay
12%319%30%21%12%
315
16th to endDay
13%422%34%21%2
314
October1st to 15thDay
21%10%28%25%10%2
135
16th to endDay
24%6%34%27%7%
144
November1st to 15thDay
8%7%33%31%13%5%
90
16th to endDay
34%6%40%12%6%
90
December1st to 15thDay
24%15%38%16%31
90
16th to endDay
38%10%39%8%3
96
January1st to 15thNight
20%8%33%29%6%1
900
16th to endNight
18%7%36%31%5%
960
February1st to 15thNight
18%9%34%29%8%
880
16th to endNight
20%11%32%28%8%
642
March1st to 15thNight
19%9%30%28%10%1
699
16th to endNight
21%6%29%30%9%2
576
April1st to 15thNight
25%7%34%26%5%
539
16th to endNight
25%6%29%31%6%
540
May1st to 15thNight
25%5%31%30%6%1
540
16th to endNight
12%427%40%14%
563
June1st to 15thNight
14%324%42%15%
540
16th to endNight
10%225%42%16%1
540
July1st to 15thNight
8%117%45%24%2
510
16th to endNight
7%115%47%27%2
564
August1st to 15thNight
7%113%47%26%2
539
16th to endNight
13%216%41%22%3
573
September1st to 15thNight
12%219%36%20%7%
540
16th to endNight
12%424%33%21%2
669
October1st to 15thNight
18%6%28%28%16%1
720
16th to endNight
21%8%28%30%10%
768
November1st to 15thNight
19%7%35%24%11%1
700
16th to endNight
23%13%29%25%7%
891
December1st to 15thNight
24%11%32%24%6%
900
16th to endNight
28%9%28%27%5%1
960
Page generated at 2017-11-01 16:23:41. Version ac04

Copyright 2017 A. Danko


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