The Friedman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Friedman Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
32%
15369
16%
48064
9%
15335
40%
15335
19%
32803

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
18%
720
13%
2506
5%
716
28%
716
11%
1813
January16th to endNight
16%
768
13%
2529
4%
768
27%
768
12%
1800
February1st to 15thNight
12%
704
11%
2287
2%
701
23%
701
11%
1664
February16th to endNight
16%
631
16%
1906
5%
631
29%
631
13%
1383
March1st to 15thNight
18%
720
15%
2070
6%
720
29%
720
16%
1478
March16th to endNight
21%
768
18%
2047
7%
768
31%
768
19%
1419
April1st to 15thNight
19%
718
13%
1796
3%
718
25%
718
18%
1336
April16th to endNight
30%
720
17%
1800
5%
720
35%
720
26%
1221
May1st to 15thNight
34%
450
17%
1530
10%
450
43%
450
18%
1042
May16th to endNight
43%
374
15%
1497
14%
374
49%
374
17%
958
June1st to 15thNight
43%
360
14%
1440
13%
360
52%
360
18%
917
June16th to endNight
55%
360
14%
1440
16%
360
62%
360
25%
826
July1st to 15thNight
56%
340
13%
1360
17%
340
60%
340
22%
829
July16th to endNight
59%
403
15%
1443
16%
379
63%
379
25%
838
August1st to 15thNight
61%
539
16%
1609
13%
536
63%
536
28%
1016
August16th to endNight
57%
761
19%
1907
11%
761
59%
761
33%
1257
September1st to 15thNight
48%
720
21%
1800
10%
720
52%
720
30%
1210
September16th to endNight
51%
717
25%
1955
19%
717
56%
717
32%
1231
October1st to 15thNight
41%
720
20%
2160
16%
720
48%
720
23%
1409
October16th to endNight
30%
768
17%
2337
10%
768
40%
768
20%
1583
November1st to 15thNight
29%
760
16%
2472
9%
760
39%
760
20%
1643
November16th to endNight
24%
780
17%
2688
10%
780
36%
780
15%
1831
December1st to 15thNight
19%
780
10%
2730
4%
780
27%
780
10%
2023
December16th to endNight
16%
788
11%
2755
3%
788
26%
788
10%
2076

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%7%36%6%35%45%7%34%
48780
Night
14%7%35%5%3445%7%37%
48237
Cloud CoverDay
15%7%36%5%35%45%7%34%
48790
Night
14%7%35%5%3445%7%37%
48242
TransparencyDay
48%7%12%19%11%1
48471
Night
45%7%13%20%11%1
48064
SeeingDay
20%16%26%20%12%4
5931
Night
19%15%28%25%10%
15370

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%10%5%9%7%4445%5%28%
1432
16th to endDay
11%10%5%9%9%45%45%7%27%
1692
February1st to 15thDay
15%11%5%8%6%45%46%6%25%
1575
16th to endDay
14%9%5%8%7%34446%30%
1566
March1st to 15thDay
15%9%47%7%3436%7%29%
1876
16th to endDay
16%9%46%5%34446%34%
2175
April1st to 15thDay
18%9%445%24445%35%
2152
16th to endDay
15%6%26%42445%6%40%
2160
May1st to 15thDay
20%6%36%6%34447%33%
2432
16th to endDay
16%5%26%6%36%5%5%7%33%
2618
June1st to 15thDay
16%5%26%6%36%6%6%9%31%
2520
16th to endDay
14%6%35%5%35%6%6%7%35%
2520
July1st to 15thDay
11%5%37%6%36%5%7%8%33%
2520
16th to endDay
10%415%6%36%7%7%9%36%
2625
August1st to 15thDay
14%5%35%6%47%5%7%7%31%
2331
16th to endDay
14%5%35%5%45%5%6%8%37%
2292
September1st to 15thDay
16%5%25%5%35%45%6%39%
2160
16th to endDay
13%5%25%434337%45%
2004
October1st to 15thDay
17%6%36%42445%7%37%
1800
16th to endDay
19%7%25%6%3445%6%33%
1887
November1st to 15thDay
15%8%35%5%2335%6%38%
1716
16th to endDay
17%8%36%5%34347%37%
1599
December1st to 15thDay
17%11%5%7%5%35%45%5%29%
1560
16th to endDay
17%12%5%7%6%35%5%5%6%25%
1568
January1st to 15thNight
15%8%48%6%35%45%6%30%
2506
16th to endNight
12%9%46%6%346%5%7%31%
2529
February1st to 15thNight
13%9%37%6%36%5%5%6%32%
2285
16th to endNight
11%10%36%8%45%5%5%5%32%
1906
March1st to 15thNight
16%7%36%5%3446%6%34%
2058
16th to endNight
15%6%35%42445%6%39%
2047
April1st to 15thNight
16%9%46%4345%5%6%34%
1796
16th to endNight
15%6%25%423445%45%
1800
May1st to 15thNight
16%6%27%425%45%6%38%
1530
16th to endNight
14%5%26%425%46%6%40%
1495
June1st to 15thNight
16%435%5%2445%8%38%
1440
16th to endNight
11%3143245%6%12%43%
1440
July1st to 15thNight
10%5%25%435%5%7%9%40%
1440
16th to endNight
9%4144345%6%10%43%
1541
August1st to 15thNight
10%424435%5%7%9%42%
1620
16th to endNight
11%4245%25%45%7%46%
1907
September1st to 15thNight
14%5%2443445%6%45%
1800
16th to endNight
13%5%25%42335%7%47%
1955
October1st to 15thNight
18%5%25%334236%44%
2160
16th to endNight
18%6%24435%446%39%
2337
November1st to 15thNight
13%7%26%5%2445%6%40%
2472
16th to endNight
15%7%36%5%35%45%6%36%
2688
December1st to 15thNight
18%9%47%6%34446%28%
2730
16th to endNight
17%9%37%7%45%5%5%7%26%
2755

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
13%10%5%8%8%35%35%5%28%
1432
16th to endDay
11%10%5%9%8%45%45%6%27%
1692
February1st to 15thDay
15%11%5%7%6%46%5%5%6%25%
1575
16th to endDay
15%9%5%8%6%35%447%30%
1566
March1st to 15thDay
16%9%5%7%6%3346%7%29%
1887
16th to endDay
17%9%36%5%24346%34%
2174
April1st to 15thDay
19%8%45%424345%35%
2152
16th to endDay
15%6%35%42345%7%40%
2160
May1st to 15thDay
20%7%25%6%34446%34%
2432
16th to endDay
15%7%35%5%35%5%6%7%33%
2618
June1st to 15thDay
16%5%35%5%35%5%6%9%32%
2520
16th to endDay
14%6%35%5%35%6%6%8%35%
2520
July1st to 15thDay
12%5%36%6%45%5%6%9%34%
2520
16th to endDay
9%5%245%36%6%7%9%37%
2625
August1st to 15thDay
15%5%25%6%47%6%6%8%30%
2331
16th to endDay
14%5%345%345%6%8%38%
2292
September1st to 15thDay
16%5%25%6%335%5%5%40%
2160
16th to endDay
13%6%25%424347%45%
2004
October1st to 15thDay
17%6%25%424448%38%
1800
16th to endDay
19%8%26%5%2445%6%34%
1887
November1st to 15thDay
15%10%35%42335%6%39%
1716
16th to endDay
17%8%35%43435%7%37%
1599
December1st to 15thDay
18%11%47%5%34445%29%
1560
16th to endDay
17%13%6%7%5%25%45%6%24%
1568
January1st to 15thNight
15%9%48%6%35%5%5%6%29%
2506
16th to endNight
12%10%5%6%5%45%47%6%31%
2529
February1st to 15thNight
14%9%48%6%35%45%5%32%
2278
16th to endNight
13%9%37%8%45%446%32%
1906
March1st to 15thNight
16%8%46%43435%6%35%
2070
16th to endNight
16%7%35%5%24446%39%
2047
April1st to 15thNight
17%8%35%5%25%45%6%34%
1796
16th to endNight
16%6%245%24345%45%
1800
May1st to 15thNight
17%6%25%435%35%7%37%
1530
16th to endNight
12%6%35%5%35%45%7%39%
1495
June1st to 15thNight
16%435%5%2436%7%39%
1440
16th to endNight
11%3244335%5%12%43%
1440
July1st to 15thNight
10%4245%345%7%8%42%
1440
16th to endNight
10%3135%3447%10%44%
1541
August1st to 15thNight
11%4234346%7%10%42%
1620
16th to endNight
11%425%326%45%7%45%
1907
September1st to 15thNight
13%6%24334446%46%
1800
16th to endNight
12%5%24423346%48%
1955
October1st to 15thNight
17%5%25%423346%44%
2160
16th to endNight
18%6%25%424446%39%
2337
November1st to 15thNight
13%8%35%5%24346%40%
2472
16th to endNight
14%8%36%5%35%45%6%36%
2688
December1st to 15thNight
19%10%46%5%3446%6%27%
2730
16th to endNight
17%9%47%6%45%5%5%7%26%
2755

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%6%11%17%6%1
1433
16th to endDay
57%6%12%16%7%
1692
February1st to 15thDay
59%6%10%14%9%
1577
16th to endDay
54%5%12%20%6%
1566
March1st to 15thDay
54%5%13%16%8%
1887
16th to endDay
50%5%9%19%12%1
2175
April1st to 15thDay
50%5%9%19%11%2
2152
16th to endDay
42%6%8%21%17%3
2160
May1st to 15thDay
51%5%10%20%10%1
2432
16th to endDay
47%9%13%15%12%1
2622
June1st to 15thDay
47%9%13%19%9%
2520
16th to endDay
44%9%14%22%9%
2520
July1st to 15thDay
45%9%13%18%12%
2371
16th to endDay
38%9%17%21%12%
2460
August1st to 15thDay
48%9%12%17%10%
2318
16th to endDay
42%7%12%22%13%1
2292
September1st to 15thDay
44%7%10%19%16%1
2160
16th to endDay
38%6%10%22%19%2
2004
October1st to 15thDay
43%7%14%19%14%1
1800
16th to endDay
49%6%12%21%9%
1887
November1st to 15thDay
45%6%13%19%11%3
1716
16th to endDay
47%6%13%22%10%
1599
December1st to 15thDay
56%6%15%14%6%
1560
16th to endDay
59%7%13%13%5%
1568
January1st to 15thNight
54%6%13%16%7%1
2506
16th to endNight
51%7%14%19%7%
2529
February1st to 15thNight
53%7%13%17%7%1
2287
16th to endNight
52%6%11%19%10%
1906
March1st to 15thNight
50%5%14%19%9%1
2070
16th to endNight
44%6%14%19%12%2
2047
April1st to 15thNight
49%7%10%18%12%1
1796
16th to endNight
40%5%10%22%18%1
1800
May1st to 15thNight
46%7%11%20%12%1
1530
16th to endNight
43%8%13%19%13%2
1497
June1st to 15thNight
43%7%12%24%11%
1440
16th to endNight
32%9%17%28%11%
1440
July1st to 15thNight
36%10%13%24%13%1
1360
16th to endNight
34%8%17%24%13%2
1443
August1st to 15thNight
34%10%15%25%13%
1609
16th to endNight
35%7%12%23%18%1
1907
September1st to 15thNight
38%7%12%24%15%1
1800
16th to endNight
36%49%25%21%1
1955
October1st to 15thNight
41%6%11%23%15%1
2160
16th to endNight
45%6%14%23%9%
2337
November1st to 15thNight
44%5%15%19%11%3
2472
16th to endNight
47%6%12%21%10%
2688
December1st to 15thNight
56%7%13%15%6%
2730
16th to endNight
56%7%15%15%4
2755

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
26%36%25%8%3
60
16th to endDay
25%34%23%14%2
90
February1st to 15thDay
31%38%25%4
90
16th to endDay
20%29%34%11%3
225
March1st to 15thDay
24%22%31%16%4
270
16th to endDay
23%26%26%14%6%3
288
April1st to 15thDay
27%20%26%15%8%1
270
16th to endDay
17%18%29%18%9%5%
270
May1st to 15thDay
30%20%24%10%11%3
288
16th to endDay
17%12%30%21%14%3
331
June1st to 15thDay
19%15%22%26%12%2
315
16th to endDay
20%13%27%24%12%1
315
July1st to 15thDay
13%11%30%22%17%4
305
16th to endDay
12%7%25%30%19%5%
326
August1st to 15thDay
16%6%23%24%19%9%
313
16th to endDay
13%5%21%25%18%15%
332
September1st to 15thDay
15%11%22%20%20%9%
315
16th to endDay
15%6%21%21%20%14%
314
October1st to 15thDay
21%9%20%24%18%5%
315
16th to endDay
23%17%28%21%8%
328
November1st to 15thDay
21%17%25%24%10%1
280
16th to endDay
20%27%29%17%3
129
December1st to 15thDay
25%30%24%10%7%2
90
16th to endDay
30%29%36%4
72
January1st to 15thNight
21%21%33%19%3
720
16th to endNight
19%24%34%19%1
768
February1st to 15thNight
23%24%36%15%
704
16th to endNight
23%24%33%15%2
631
March1st to 15thNight
26%22%30%18%2
720
16th to endNight
20%23%31%17%6%
768
April1st to 15thNight
22%21%33%18%3
718
16th to endNight
21%14%30%24%9%
720
May1st to 15thNight
18%13%28%29%9%
450
16th to endNight
14%8%25%36%14%
375
June1st to 15thNight
18%7%23%33%17%
360
16th to endNight
10%425%48%11%
360
July1st to 15thNight
12%324%40%18%
340
16th to endNight
10%220%42%20%3
403
August1st to 15thNight
13%215%42%23%2
539
16th to endNight
12%417%33%30%2
761
September1st to 15thNight
17%6%22%30%21%2
720
16th to endNight
15%7%19%26%26%5%
717
October1st to 15thNight
19%10%22%28%16%1
720
16th to endNight
24%15%26%27%5%
768
November1st to 15thNight
18%16%30%23%9%1
760
16th to endNight
21%20%29%21%6%1
780
December1st to 15thNight
25%20%31%18%4
780
16th to endNight
24%22%33%16%2
788
Page generated at 2017-12-21 07:04:46. Version ac04

Copyright 2017 A. Danko


The Friedman Observatory Clear Sky Chart |Charts Home