Fred G. Dale Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fred G. Dale Planetarium clear sky chart from 2005-11-05 to 2017-10-16.

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%
16131
21%
47036
11%
16085
46%
16085
30%
28874

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
27%
900
17%
2422
7%
895
36%
895
25%
1608
January16th to endNight
24%
960
22%
2496
7%
960
34%
960
26%
1682
February1st to 15thNight
25%
879
11%
2288
3%
875
30%
875
21%
1647
February16th to endNight
31%
663
23%
1925
7%
663
43%
663
30%
1178
March1st to 15thNight
31%
591
19%
2031
11%
591
41%
591
24%
1237
March16th to endNight
28%
576
15%
2112
10%
576
36%
576
20%
1352
April1st to 15thNight
29%
539
18%
1837
12%
539
41%
539
23%
1138
April16th to endNight
31%
540
18%
1620
12%
540
41%
540
23%
1094
May1st to 15thNight
39%
540
20%
1620
12%
540
48%
540
30%
984
May16th to endNight
39%
562
15%
1640
6%
561
47%
561
29%
1029
June1st to 15thNight
49%
540
17%
1380
7%
540
52%
540
35%
883
June16th to endNight
58%
540
25%
1260
9%
540
61%
540
55%
714
July1st to 15thNight
63%
510
17%
1347
7%
510
66%
510
48%
755
July16th to endNight
72%
564
23%
1594
18%
531
73%
531
48%
815
August1st to 15thNight
66%
539
22%
1610
22%
536
70%
536
39%
900
August16th to endNight
58%
573
25%
1719
24%
573
64%
573
40%
953
September1st to 15thNight
57%
540
24%
1929
21%
540
66%
540
35%
995
September16th to endNight
46%
537
29%
1980
22%
537
59%
537
36%
978
October1st to 15thNight
34%
660
27%
2100
16%
660
44%
660
27%
1260
October16th to endNight
39%
743
24%
2159
12%
743
47%
743
34%
1261
November1st to 15thNight
37%
875
28%
2275
11%
875
48%
875
40%
1324
November16th to endNight
32%
900
23%
2487
11%
900
41%
900
32%
1522
December1st to 15thNight
25%
900
16%
2520
6%
900
34%
900
24%
1686
December16th to endNight
28%
960
18%
2685
7%
960
38%
960
22%
1879

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
11%6%25%42445%7%44%
48357
Night
10%6%2442435%7%48%
47218
Cloud CoverDay
11%6%25%42445%7%44%
48368
Night
10%6%24424347%48%
47222
Cloud CoverDay
11%6%25%42445%7%43%
48366
Night
9%6%24424447%48%
47222
TransparencyDay
39%6%14%24%13%1
48057
Night
35%5%14%26%16%2
47036
SeeingDay
14%7%31%29%14%2
6123
Night
12%9%34%31%10%
16133

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
6%8%47%6%4445%7%39%
1508
16th to endDay
9%12%49%6%2445%6%33%
1728
February1st to 15thDay
13%9%46%7%4435%5%35%
1575
16th to endDay
10%8%47%43345%6%39%
1560
March1st to 15thDay
11%8%26%5%3335%7%42%
1917
16th to endDay
17%9%46%5%2445%6%34%
2112
April1st to 15thDay
15%8%45%423347%40%
2110
16th to endDay
24%8%25%42335%6%33%
2340
May1st to 15thDay
14%6%25%43435%7%39%
2331
16th to endDay
16%7%25%3345%5%7%38%
2472
June1st to 15thDay
12%5%25%5%335%5%7%42%
2576
16th to endDay
5%4243245%6%8%52%
2700
July1st to 15thDay
7%31442446%9%51%
2525
16th to endDay
5%2133245%7%9%55%
2466
August1st to 15thDay
9%425%5%35%6%5%7%43%
2340
16th to endDay
9%424324447%51%
2483
September1st to 15thDay
13%5%245%24347%46%
2030
16th to endDay
10%213313346%57%
1980
October1st to 15thDay
14%6%2441325%5%50%
1848
16th to endDay
14%7%23312336%50%
1733
November1st to 15thDay
7%5%15%423446%53%
1583
16th to endDay
11%8%35%423337%45%
1473
December1st to 15thDay
10%11%47%5%2435%6%36%
1440
16th to endDay
13%10%5%8%6%25%45%7%30%
1527
January1st to 15thNight
6%6%25%6%47%46%8%41%
2422
16th to endNight
9%9%36%5%24448%41%
2496
February1st to 15thNight
12%10%47%5%34345%37%
2285
16th to endNight
8%6%3343445%6%47%
1925
March1st to 15thNight
11%7%24424446%46%
2019
16th to endNight
13%8%36%5%23347%41%
2112
April1st to 15thNight
13%7%35%42345%6%43%
1837
16th to endNight
17%5%25%434345%42%
1620
May1st to 15thNight
13%5%1332345%8%48%
1620
16th to endNight
13%415%5%1435%8%46%
1638
June1st to 15thNight
10%42341446%7%49%
1380
16th to endNight
221331346%7%64%
1260
July1st to 15thNight
5%22232335%8%59%
1428
16th to endNight
311342445%8%61%
1702
August1st to 15thNight
5%2134235%6%9%53%
1620
16th to endNight
7%414324447%56%
1719
September1st to 15thNight
8%313223447%57%
1929
16th to endNight
8%423313336%59%
1980
October1st to 15thNight
14%5%23424235%51%
2100
16th to endNight
14%5%13323245%54%
2159
November1st to 15thNight
7%42431345%6%56%
2275
16th to endNight
8%5%25%32335%7%50%
2487
December1st to 15thNight
10%9%36%5%2335%6%41%
2520
16th to endNight
12%10%5%6%5%33336%38%
2685

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
6%8%38%6%44447%39%
1508
16th to endDay
9%11%49%5%2445%6%34%
1728
February1st to 15thDay
13%9%46%7%44346%34%
1575
16th to endDay
10%8%48%4235%5%6%40%
1560
March1st to 15thDay
10%8%26%5%2335%7%42%
1928
16th to endDay
17%9%45%42445%6%34%
2112
April1st to 15thDay
15%8%45%423346%40%
2110
16th to endDay
24%8%24423346%33%
2340
May1st to 15thDay
14%7%25%5%3445%8%39%
2331
16th to endDay
16%7%25%33445%7%38%
2472
June1st to 15thDay
12%5%25%5%335%5%7%42%
2576
16th to endDay
5%3234245%6%8%52%
2700
July1st to 15thDay
8%22442345%9%51%
2525
16th to endDay
5%21332447%9%55%
2466
August1st to 15thDay
9%5%145%35%5%5%8%43%
2340
16th to endDay
9%5%23424448%51%
2483
September1st to 15thDay
12%5%24434346%47%
2030
16th to endDay
10%213313346%57%
1980
October1st to 15thDay
14%5%1442235%5%49%
1848
16th to endDay
13%7%24212336%51%
1733
November1st to 15thDay
7%5%24423446%53%
1583
16th to endDay
12%8%35%423347%45%
1473
December1st to 15thDay
11%10%47%5%34446%37%
1440
16th to endDay
12%10%5%8%6%25%46%6%30%
1527
January1st to 15thNight
6%6%25%6%47%5%5%8%41%
2422
16th to endNight
9%9%36%5%24448%42%
2496
February1st to 15thNight
13%10%46%6%34345%37%
2278
16th to endNight
8%6%34435%45%6%48%
1925
March1st to 15thNight
11%7%25%424346%45%
2031
16th to endNight
14%8%26%5%2435%6%40%
2112
April1st to 15thNight
13%7%25%42345%6%44%
1837
16th to endNight
17%5%25%434445%42%
1620
May1st to 15thNight
12%5%1332445%8%48%
1619
16th to endNight
13%425%42345%8%46%
1638
June1st to 15thNight
10%4234235%6%8%48%
1380
16th to endNight
211331335%7%65%
1260
July1st to 15thNight
5%22232335%9%58%
1428
16th to endNight
311332345%7%61%
1702
August1st to 15thNight
5%31342347%8%54%
1620
16th to endNight
8%413323447%56%
1719
September1st to 15thNight
8%313323446%58%
1929
16th to endNight
8%422313336%59%
1980
October1st to 15thNight
15%423424235%51%
2100
16th to endNight
14%5%13323335%54%
2159
November1st to 15thNight
6%42331345%6%56%
2275
16th to endNight
8%5%2442335%7%50%
2487
December1st to 15thNight
10%9%36%5%2335%6%41%
2520
16th to endNight
12%10%5%6%5%33236%38%
2685

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
6%8%47%7%45%447%39%
1508
16th to endDay
8%12%49%6%2345%7%33%
1728
February1st to 15thDay
13%9%46%7%44445%34%
1575
16th to endDay
10%8%47%4335%5%7%39%
1560
March1st to 15thDay
11%8%27%5%2435%7%42%
1928
16th to endDay
17%9%36%42445%7%33%
2110
April1st to 15thDay
15%8%35%413348%39%
2110
16th to endDay
23%8%25%424346%32%
2340
May1st to 15thDay
13%7%35%435%45%7%39%
2331
16th to endDay
15%7%25%43445%7%38%
2472
June1st to 15thDay
12%6%25%5%2445%7%42%
2576
16th to endDay
5%3244245%6%9%51%
2700
July1st to 15thDay
7%32342446%9%51%
2525
16th to endDay
42133245%6%9%55%
2466
August1st to 15thDay
8%425%5%36%5%6%6%43%
2340
16th to endDay
8%5%14334348%51%
2483
September1st to 15thDay
12%5%25%434346%47%
2030
16th to endDay
9%313323346%57%
1980
October1st to 15thDay
14%6%1442234450%
1848
16th to endDay
14%6%23322346%50%
1733
November1st to 15thDay
7%5%245%23447%52%
1583
16th to endDay
11%8%35%324347%45%
1473
December1st to 15thDay
10%11%38%5%35%347%35%
1440
16th to endDay
12%10%5%8%6%35%448%29%
1527
January1st to 15thNight
6%5%26%6%47%5%5%7%41%
2422
16th to endNight
8%9%36%5%2445%8%41%
2496
February1st to 15thNight
12%11%47%5%34345%37%
2278
16th to endNight
7%6%34435%45%6%47%
1925
March1st to 15thNight
11%7%345%24446%46%
2031
16th to endNight
13%9%35%5%23446%41%
2112
April1st to 15thNight
13%7%35%33335%6%44%
1837
16th to endNight
16%6%25%424346%42%
1620
May1st to 15thNight
12%5%2332445%8%47%
1619
16th to endNight
13%415%42345%8%46%
1638
June1st to 15thNight
10%42442346%8%48%
1380
16th to endNight
221332245%7%64%
1260
July1st to 15thNight
4223323449%58%
1428
16th to endNight
221332445%8%61%
1702
August1st to 15thNight
5%2234245%7%9%53%
1620
16th to endNight
7%414323447%56%
1719
September1st to 15thNight
8%313323447%57%
1929
16th to endNight
8%423222336%59%
1980
October1st to 15thNight
14%5%23424345%51%
2100
16th to endNight
14%41332324454%
2159
November1st to 15thNight
6%424323446%56%
2275
16th to endNight
8%5%25%42445%7%49%
2487
December1st to 15thNight
10%9%46%5%23446%41%
2520
16th to endNight
12%10%5%6%6%24346%38%
2685

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
43%6%16%22%9%
1509
16th to endDay
49%6%15%17%10%
1728
February1st to 15thDay
51%5%15%19%7%
1576
16th to endDay
43%6%14%23%9%2
1560
March1st to 15thDay
41%6%16%22%11%2
1928
16th to endDay
49%7%13%21%5%1
2112
April1st to 15thDay
43%5%15%25%9%
2110
16th to endDay
51%5%11%20%9%
2340
May1st to 15thDay
43%7%13%22%12%
2331
16th to endDay
44%7%14%22%10%
2476
June1st to 15thDay
39%7%16%23%11%1
2576
16th to endDay
26%8%16%31%13%3
2700
July1st to 15thDay
30%7%17%27%13%3
2377
16th to endDay
23%8%16%29%20%2
2311
August1st to 15thDay
36%8%14%24%14%1
2326
16th to endDay
31%6%11%28%17%4
2483
September1st to 15thDay
36%6%11%24%17%2
2030
16th to endDay
28%411%35%18%1
1980
October1st to 15thDay
36%410%26%18%3
1848
16th to endDay
36%412%28%16%2
1733
November1st to 15thDay
31%5%15%24%22%1
1583
16th to endDay
39%415%26%11%1
1473
December1st to 15thDay
47%5%16%20%7%2
1440
16th to endDay
52%6%14%17%8%1
1527
January1st to 15thNight
39%6%16%23%12%
2422
16th to endNight
41%5%17%23%10%
2496
February1st to 15thNight
50%414%21%7%1
2288
16th to endNight
35%416%26%13%3
1925
March1st to 15thNight
39%5%13%26%13%1
2031
16th to endNight
43%6%14%24%8%1
2112
April1st to 15thNight
40%5%11%27%14%1
1837
16th to endNight
43%7%11%22%13%1
1620
May1st to 15thNight
34%6%12%27%18%
1620
16th to endNight
36%6%16%24%14%1
1640
June1st to 15thNight
32%8%13%28%14%2
1380
16th to endNight
18%5%15%34%20%4
1260
July1st to 15thNight
22%5%18%27%18%6%
1347
16th to endNight
19%6%15%31%22%4
1594
August1st to 15thNight
25%8%15%29%19%2
1610
16th to endNight
28%413%27%20%6%
1719
September1st to 15thNight
26%6%10%29%22%4
1929
16th to endNight
26%411%34%20%3
1980
October1st to 15thNight
36%47%22%25%3
2100
16th to endNight
33%314%27%19%2
2159
November1st to 15thNight
27%413%24%25%3
2275
16th to endNight
33%6%15%27%15%1
2487
December1st to 15thNight
43%5%17%24%9%
2520
16th to endNight
48%413%20%11%1
2685

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
16%10%38%27%6%
90
16th to endDay
21%441%28%31
96
February1st to 15thDay
17%11%47%18%4
90
16th to endDay
11%18%34%19%16%
81
March1st to 15thDay
17%13%47%16%31
90
16th to endDay
31%7%32%12%16%
96
April1st to 15thDay
18%12%41%22%5%
229
16th to endDay
28%13%27%19%8%1
450
May1st to 15thDay
17%11%35%22%11%1
468
16th to endDay
19%9%33%24%10%2
517
June1st to 15thDay
12%6%31%32%15%2
495
16th to endDay
5%6%36%31%16%2
495
July1st to 15thDay
9%224%38%20%5%
475
16th to endDay
4124%45%21%1
515
August1st to 15thDay
8%221%41%23%2
493
16th to endDay
10%425%33%22%3
523
September1st to 15thDay
12%431%33%14%3
185
16th to endDay
14%237%25%16%3
135
October1st to 15thDay
21%6%31%25%10%3
135
16th to endDay
15%441%27%9%3
99
November1st to 15thDay
46%28%42%11%6%
90
16th to endDay
40%7%28%20%3
90
December1st to 15thDay
25%21%35%12%23
90
16th to endDay
27%20%38%9%4
96
January1st to 15thNight
11%14%40%27%5%
900
16th to endNight
13%12%40%26%5%
960
February1st to 15thNight
17%12%38%26%5%
880
16th to endNight
11%10%42%24%9%1
663
March1st to 15thNight
13%9%40%29%6%
591
16th to endNight
18%9%38%26%6%
576
April1st to 15thNight
18%10%37%29%3
539
16th to endNight
19%11%33%25%10%
540
May1st to 15thNight
13%9%34%31%10%
540
16th to endNight
16%5%34%31%11%
563
June1st to 15thNight
12%5%27%41%12%
540
16th to endNight
3330%46%15%
540
July1st to 15thNight
5%224%40%26%
510
16th to endNight
219%53%23%
564
August1st to 15thNight
4121%49%22%
539
16th to endNight
8%423%39%21%2
573
September1st to 15thNight
9%327%38%18%2
540
16th to endNight
10%7%33%30%17%1
537
October1st to 15thNight
18%10%33%28%7%1
660
16th to endNight
17%6%32%31%10%
743
November1st to 15thNight
9%10%39%32%6%1
875
16th to endNight
10%13%41%25%9%
900
December1st to 15thNight
16%12%40%26%4
900
16th to endNight
17%11%35%27%6%
960
Page generated at 2017-10-17 15:35:28. Version ac04

Copyright 2017 A. Danko


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