MCCC Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the MCCC Observatory clear sky chart from 2005-11-06 to 2024-02-20.

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
33%
23369
20%
80203
10%
23271
45%
23271
21%
50298

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 10thNight
18%
755
24%
4337
9%
737
39%
737
12%
2407
January11th to 20thNight
22%
760
24%
4267
8%
740
40%
740
11%
2453
January21st to endNight
20%
833
15%
4471
7%
814
41%
814
11%
2879
February1st to 10thNight
20%
760
19%
2470
7%
760
35%
760
19%
1604
February11th to 20thNight
14%
742
19%
2262
4%
739
33%
739
17%
1492
February21st to endNight
15%
592
26%
1776
7%
592
37%
592
18%
1164
March1st to 10thNight
23%
720
23%
2156
9%
720
40%
720
23%
1316
March11th to 20thNight
21%
720
21%
1980
8%
720
35%
720
21%
1331
March21st to endNight
23%
792
22%
2052
7%
792
35%
792
26%
1383
April1st to 10thNight
19%
720
19%
1800
3%
720
29%
720
23%
1233
April11th to 20thNight
28%
711
20%
1775
7%
711
33%
711
27%
1211
April21st to endNight
30%
720
20%
1800
5%
720
38%
720
26%
1212
May1st to 10thNight
29%
582
15%
1662
7%
582
35%
582
19%
1173
May11th to 20thNight
29%
354
18%
1416
10%
354
41%
354
17%
886
May21st to endNight
48%
388
14%
1551
14%
388
53%
388
19%
954
June1st to 10thNight
42%
360
18%
1440
16%
360
53%
360
22%
859
June11th to 20thNight
45%
360
15%
1440
15%
360
53%
360
21%
887
June21st to endNight
55%
360
16%
1440
17%
360
63%
360
24%
828
July1st to 10thNight
53%
350
13%
1400
15%
350
58%
350
18%
903
July11th to 20thNight
59%
348
16%
1392
18%
348
63%
348
25%
784
July21st to endNight
54%
430
18%
1520
17%
406
61%
406
27%
874
August1st to 10thNight
60%
537
17%
1600
12%
534
62%
534
28%
1023
August11th to 20thNight
54%
684
16%
1748
10%
684
56%
684
26%
1223
August21st to endNight
54%
792
16%
1980
7%
792
56%
792
30%
1355
September1st to 10thNight
47%
720
21%
1800
10%
720
52%
720
32%
1213
September11th to 20thNight
53%
720
29%
1826
19%
720
57%
720
38%
1135
September21st to endNight
45%
720
24%
1980
17%
720
52%
720
27%
1317
October1st to 10thNight
40%
720
16%
2157
13%
720
46%
720
25%
1409
October11th to 20thNight
41%
720
24%
2160
16%
720
52%
720
30%
1310
October21st to endNight
30%
792
25%
2438
14%
792
45%
792
25%
1525
November1st to 10thNight
36%
740
25%
2407
13%
740
53%
740
30%
1364
November11th to 20thNight
30%
760
25%
2470
13%
760
45%
760
22%
1518
November21st to endNight
28%
760
22%
2598
10%
760
45%
760
23%
1539
December1st to 10thNight
22%
760
18%
2660
7%
760
37%
760
17%
1710
December11th to 20thNight
23%
760
20%
3192
7%
759
39%
759
16%
1925
December21st to endNight
23%
827
14%
4780
9%
817
39%
817
11%
2899

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
15%6%35%5%35%5%6%7%40%
78345
Night
16%6%35%5%3445%7%43%
80836
TransparencyDay
41%6%12%23%16%2
78053
Night
41%6%11%23%16%3
80662
SeeingDay
22%14%28%22%11%3
13956
Night
20%11%31%28%10%1
23387

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 10thDay
15%7%245%34446%45%
2517
11th to 20thDay
14%10%47%7%35%45%6%36%
2584
21st to endDay
21%8%36%5%34346%35%
3124
February1st to 10thDay
17%6%35%6%345%5%7%39%
1710
11th to 20thDay
16%8%36%5%35%5%46%40%
1789
21st to endDay
20%7%35%6%245%46%38%
1480
March1st to 10thDay
13%6%35%6%345%47%45%
1797
11th to 20thDay
16%7%35%5%45%5%5%7%39%
1980
21st to endDay
21%6%25%5%34347%39%
2303
April1st to 10thDay
15%7%36%43445%8%41%
2160
11th to 20thDay
15%6%35%4345%5%7%42%
2134
21st to endDay
17%436%6%35%5%6%7%39%
2160
May1st to 10thDay
18%7%36%6%35%5%5%7%35%
2312
11th to 20thDay
20%6%35%6%36%5%5%8%35%
2478
21st to endDay
14%6%35%5%35%5%6%9%39%
2725
June1st to 10thDay
13%5%35%5%36%6%7%10%38%
2520
11th to 20thDay
13%6%36%6%46%5%7%8%37%
2520
21st to endDay
12%425%5%35%6%6%11%41%
2520
July1st to 10thDay
10%6%26%5%36%6%7%10%39%
2520
11th to 20thDay
8%424436%7%8%10%43%
2520
21st to endDay
10%6%36%5%46%6%7%10%37%
2704
August1st to 10thDay
9%5%26%5%46%6%8%9%40%
2327
11th to 20thDay
11%5%25%6%35%5%8%8%40%
2135
21st to endDay
13%6%35%5%246%6%8%42%
2376
September1st to 10thDay
15%6%345%35%5%5%6%44%
2160
11th to 20thDay
13%5%24324447%52%
2134
21st to endDay
16%7%36%6%345%6%6%39%
1980
October1st to 10thDay
19%6%23425%5%5%7%43%
1800
11th to 20thDay
16%5%2443446%6%46%
1800
21st to endDay
19%6%25%42445%5%44%
1917
November1st to 10thDay
13%7%24423345%52%
1671
11th to 20thDay
16%5%25%42446%6%48%
1710
21st to endDay
16%5%344345%6%7%44%
1580
December1st to 10thDay
18%8%26%4245%5%6%39%
1520
11th to 20thDay
20%7%34423447%41%
1906
21st to endDay
17%6%36%6%46%6%5%6%35%
2772
January1st to 10thNight
16%6%245%34445%45%
4429
11th to 20thNight
18%8%35%424346%43%
4372
21st to endNight
24%8%25%424446%37%
4532
February1st to 10thNight
17%8%35%4345%46%41%
2470
11th to 20thNight
18%8%25%6%34446%40%
2261
21st to endNight
18%8%35%33445%5%42%
1776
March1st to 10thNight
16%5%244345%5%8%45%
2146
11th to 20thNight
17%7%36%434445%44%
1979
21st to endNight
17%8%345%34347%43%
2052
April1st to 10thNight
17%6%25%5%35%5%5%7%41%
1800
11th to 20thNight
14%6%36%5%3445%7%42%
1775
21st to endNight
20%5%2443345%8%42%
1800
May1st to 10thNight
18%7%47%5%35%5%5%6%35%
1662
11th to 20thNight
17%7%26%5%35%5%5%7%38%
1415
21st to endNight
15%6%35%5%3445%8%41%
1550
June1st to 10thNight
15%6%36%42445%8%43%
1440
11th to 20thNight
12%6%25%6%35%5%8%9%40%
1440
21st to endNight
11%4245%35%7%7%9%43%
1440
July1st to 10thNight
10%5%27%7%45%6%8%8%38%
1440
11th to 20thNight
8%435%5%35%5%8%11%43%
1440
21st to endNight
9%5%35%6%345%7%11%43%
1610
August1st to 10thNight
9%6%25%5%36%6%8%9%41%
1611
11th to 20thNight
11%7%36%5%45%6%7%8%39%
1748
21st to endNight
13%5%25%5%35%5%6%9%41%
1980
September1st to 10thNight
14%7%35%5%34446%46%
1800
11th to 20thNight
12%6%24423446%53%
1826
21st to endNight
16%6%345%3445%7%42%
1980
October1st to 10thNight
18%8%25%5%33445%43%
2157
11th to 20thNight
15%5%15%33445%6%49%
2160
21st to endNight
18%7%24323345%47%
2438
November1st to 10thNight
12%5%2432345%6%53%
2407
11th to 20thNight
17%7%25%324445%48%
2470
21st to endNight
14%4245%35%5%5%8%45%
2598
December1st to 10thNight
20%7%35%5%3445%6%39%
2660
11th to 20thNight
18%6%25%4345%5%7%41%
3288
21st to endNight
18%8%36%5%3445%7%38%
4884

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 10thDay
39%314%27%14%3
2518
11th to 20thDay
46%5%13%20%14%2
2584
21st to endDay
49%6%12%22%10%1
3124
February1st to 10thDay
43%6%14%24%12%2
1710
11th to 20thDay
44%410%23%16%2
1798
21st to endDay
47%5%10%22%13%4
1480
March1st to 10thDay
39%5%12%27%15%3
1800
11th to 20thDay
44%5%11%21%16%3
1980
21st to endDay
47%5%8%20%17%3
2303
April1st to 10thDay
42%5%11%22%16%5%
2160
11th to 20thDay
40%5%13%22%17%4
2134
21st to endDay
43%6%12%19%17%4
2160
May1st to 10thDay
47%6%10%19%16%3
2312
11th to 20thDay
47%7%10%21%14%2
2482
21st to endDay
41%8%13%22%14%2
2725
June1st to 10thDay
40%8%13%24%14%1
2520
11th to 20thDay
43%8%14%23%11%2
2520
21st to endDay
37%9%12%25%16%1
2520
July1st to 10thDay
39%9%13%21%14%3
2450
11th to 20thDay
34%9%13%25%15%3
2445
21st to endDay
40%8%12%21%17%2
2553
August1st to 10thDay
38%9%14%23%15%1
2314
11th to 20thDay
37%9%14%23%16%2
2135
21st to endDay
39%8%11%21%18%3
2376
September1st to 10thDay
40%6%11%19%21%3
2160
11th to 20thDay
33%5%9%25%24%4
2134
21st to endDay
45%6%8%18%21%2
1980
October1st to 10thDay
41%5%11%23%18%1
1800
11th to 20thDay
36%6%11%24%21%2
1800
21st to endDay
41%5%10%24%18%2
1917
November1st to 10thDay
35%412%25%21%3
1671
11th to 20thDay
37%5%10%25%20%3
1710
21st to endDay
37%414%31%12%2
1580
December1st to 10thDay
45%5%16%21%13%1
1520
11th to 20thDay
42%414%26%11%2
1906
21st to endDay
45%6%14%22%12%1
2772
January1st to 10thNight
41%5%9%29%13%3
4429
11th to 20thNight
44%411%25%13%3
4372
21st to endNight
49%48%25%12%2
4532
February1st to 10thNight
44%5%12%25%12%2
2470
11th to 20thNight
46%49%19%18%4
2263
21st to endNight
44%5%6%23%18%4
1776
March1st to 10thNight
37%5%12%24%18%4
2156
11th to 20thNight
44%5%9%21%17%4
1980
21st to endNight
43%410%18%19%6%
2052
April1st to 10thNight
42%6%10%20%17%5%
1800
11th to 20thNight
42%5%10%19%21%3
1775
21st to endNight
41%5%10%20%19%5%
1800
May1st to 10thNight
48%6%9%16%17%2
1662
11th to 20thNight
44%7%13%16%18%3
1416
21st to endNight
41%8%16%18%15%2
1551
June1st to 10thNight
40%6%12%21%19%2
1440
11th to 20thNight
40%8%13%24%14%1
1440
21st to endNight
33%10%15%26%15%2
1440
July1st to 10thNight
40%12%14%18%14%2
1400
11th to 20thNight
32%10%16%25%14%3
1392
21st to endNight
33%8%17%23%16%2
1520
August1st to 10thNight
36%10%15%23%16%2
1600
11th to 20thNight
41%10%13%20%15%2
1748
21st to endNight
39%9%12%19%19%3
1980
September1st to 10thNight
39%7%11%20%20%3
1800
11th to 20thNight
33%5%9%22%27%4
1826
21st to endNight
41%6%7%21%22%2
1980
October1st to 10thNight
43%5%12%22%16%2
2157
11th to 20thNight
35%5%12%27%18%3
2160
21st to endNight
40%48%27%18%2
2438
November1st to 10thNight
32%5%12%25%20%5%
2407
11th to 20thNight
40%49%22%20%5%
2470
21st to endNight
37%5%13%27%16%2
2598
December1st to 10thNight
45%5%12%22%14%1
2660
11th to 20thNight
41%5%13%20%17%4
3288
21st to endNight
45%6%13%24%11%1
4884

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 10thDay
25%28%31%11%32
180
11th to 20thDay
36%25%27%10%3
198
21st to endDay
27%28%28%12%5%1
297
February1st to 10thDay
31%24%31%10%4
270
11th to 20thDay
31%22%36%10%1
403
21st to endDay
30%22%32%14%2
346
March1st to 10thDay
26%20%32%19%3
420
11th to 20thDay
25%23%33%15%32
420
21st to endDay
30%22%28%14%6%1
462
April1st to 10thDay
26%22%31%14%6%1
420
11th to 20thDay
22%23%29%17%7%2
412
21st to endDay
28%19%31%17%42
420
May1st to 10thDay
29%18%28%16%8%2
423
11th to 20thDay
24%12%30%23%9%2
447
21st to endDay
22%7%24%25%17%5%
485
June1st to 10thDay
14%13%28%27%14%4
450
11th to 20thDay
17%11%27%29%14%3
450
21st to endDay
14%9%29%29%14%5%
450
July1st to 10thDay
13%422%31%24%8%
445
11th to 20thDay
9%225%32%27%5%
444
21st to endDay
13%6%25%34%17%5%
488
August1st to 10thDay
10%424%33%21%7%
446
11th to 20thDay
14%418%36%22%7%
439
21st to endDay
13%8%24%28%17%9%
495
September1st to 10thDay
19%10%21%25%17%8%
450
11th to 20thDay
16%6%25%27%16%10%
450
21st to endDay
25%13%19%25%12%5%
450
October1st to 10thDay
26%6%25%21%14%8%
450
11th to 20thDay
18%14%28%25%12%2
450
21st to endDay
24%14%33%17%10%3
463
November1st to 10thDay
21%12%29%24%13%2
365
11th to 20thDay
22%17%32%23%5%1
370
21st to endDay
21%18%37%18%5%1
240
December1st to 10thDay
29%23%33%8%7%
180
11th to 20thDay
35%19%31%11%4
180
21st to endDay
29%19%33%12%7%1
198
January1st to 10thNight
21%17%37%20%4
760
11th to 20thNight
26%16%30%25%3
760
21st to endNight
19%18%37%23%2
836
February1st to 10thNight
22%15%37%24%1
760
11th to 20thNight
25%20%36%17%1
742
21st to endNight
24%18%38%17%2
592
March1st to 10thNight
23%17%34%23%3
720
11th to 20thNight
24%17%35%19%5%1
720
21st to endNight
21%11%41%20%6%
792
April1st to 10thNight
22%18%37%17%6%
720
11th to 20thNight
18%13%38%26%6%
711
21st to endNight
22%11%33%28%6%
720
May1st to 10thNight
24%11%32%27%6%
582
11th to 20thNight
23%7%36%29%6%
354
21st to endNight
17%6%22%40%14%2
389
June1st to 10thNight
18%428%38%11%1
360
11th to 20thNight
12%5%32%40%11%1
360
21st to endNight
11%227%49%12%
360
July1st to 10thNight
14%322%41%18%2
350
11th to 20thNight
8%322%44%21%2
348
21st to endNight
10%425%40%21%1
430
August1st to 10thNight
12%217%44%23%2
537
11th to 20thNight
14%218%38%25%2
684
21st to endNight
14%418%39%23%2
792
September1st to 10thNight
18%325%34%17%3
720
11th to 20thNight
15%421%34%21%4
720
21st to endNight
22%422%33%18%1
720
October1st to 10thNight
23%6%24%25%18%4
720
11th to 20thNight
17%10%27%33%12%
720
21st to endNight
22%12%31%25%9%
792
November1st to 10thNight
16%8%36%28%12%1
740
11th to 20thNight
21%15%29%26%8%1
760
21st to endNight
17%14%34%27%7%1
760
December1st to 10thNight
25%15%32%21%6%1
760
11th to 20thNight
21%13%36%23%6%
760
21st to endNight
22%14%34%27%2
836
Page generated at 2024-02-17 06:28:39. Version ac07

Copyright 2024 Attilla Danko


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