The Smith Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Smith Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
28%
22938
12%
74973
8%
22894
34%
22894
14%
55185

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
10%
759
6%
2649
3%
757
14%
757
5%
2251
January11th to 20thNight
13%
760
5%
2627
3%
760
17%
760
5%
2251
January21st to endNight
13%
820
7%
2664
3%
820
18%
820
6%
2225
February1st to 10thNight
10%
720
8%
2340
1%
720
18%
720
7%
1907
February11th to 20thNight
11%
702
8%
2275
2%
700
18%
700
7%
1833
February21st to endNight
14%
592
10%
1784
4%
592
21%
592
10%
1409
March1st to 10thNight
19%
720
11%
2070
6%
720
24%
720
12%
1631
March11th to 20thNight
21%
720
14%
1980
7%
720
28%
720
14%
1503
March21st to endNight
22%
792
15%
2117
6%
792
29%
792
17%
1582
April1st to 10thNight
20%
720
12%
1800
3%
720
25%
720
17%
1382
April11th to 20thNight
26%
711
13%
1775
5%
711
29%
711
20%
1330
April21st to endNight
30%
662
16%
1742
7%
662
35%
662
21%
1251
May1st to 10thNight
36%
442
14%
1522
10%
442
42%
442
16%
1070
May11th to 20thNight
40%
354
19%
1416
17%
354
49%
354
20%
883
May21st to endNight
43%
388
16%
1551
15%
388
52%
388
23%
906
June1st to 10thNight
43%
360
14%
1440
14%
360
52%
360
18%
912
June11th to 20thNight
45%
360
14%
1440
16%
360
53%
360
20%
870
June21st to endNight
45%
360
15%
1440
16%
360
56%
360
21%
878
July1st to 10thNight
60%
350
15%
1400
19%
350
66%
350
25%
796
July11th to 20thNight
56%
348
17%
1392
22%
348
61%
348
26%
783
July21st to endNight
51%
430
17%
1520
17%
406
56%
406
25%
917
August1st to 10thNight
55%
537
17%
1600
12%
534
58%
534
31%
986
August11th to 20thNight
54%
538
17%
1602
12%
538
58%
538
26%
1062
August21st to endNight
53%
792
20%
1980
10%
792
55%
792
34%
1283
September1st to 10thNight
48%
720
16%
1800
8%
720
51%
720
30%
1215
September11th to 20thNight
50%
720
23%
1800
14%
720
54%
720
32%
1193
September21st to endNight
44%
720
19%
2058
15%
720
48%
720
25%
1381
October1st to 10thNight
33%
720
13%
2160
10%
720
37%
720
18%
1532
October11th to 20thNight
27%
720
13%
2160
8%
720
35%
720
18%
1528
October21st to endNight
19%
792
11%
2409
5%
792
27%
792
12%
1882
November1st to 10thNight
26%
740
15%
2407
11%
740
33%
740
15%
1715
November11th to 20thNight
20%
760
14%
2626
8%
760
27%
760
12%
1897
November21st to endNight
20%
760
9%
2660
5%
760
25%
760
9%
2057
December1st to 10thNight
12%
760
6%
2660
2%
760
16%
760
6%
2185
December11th to 20thNight
13%
759
6%
3251
2%
759
19%
759
5%
2604
December21st to endNight
10%
830
3%
4856
1%
817
14%
817
3%
4095

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%9%48%7%46%5%5%7%30%
74822
Night
16%10%48%6%45%5%5%7%30%
75212
TransparencyDay
52%8%12%18%9%1
74530
Night
53%8%12%17%8%1
75038
SeeingDay
22%16%30%20%9%3
13529
Night
22%15%29%24%9%1
22948

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
13%15%8%12%9%48%6%5%416%
1517
11th to 20thDay
16%17%7%13%11%5%5%445%14%
1550
21st to endDay
12%15%7%13%13%6%7%445%14%
1836
February1st to 10thDay
16%15%7%12%9%5%7%45%5%15%
1620
11th to 20thDay
13%14%9%13%10%5%7%5%45%16%
1573
21st to endDay
19%14%5%11%8%5%6%346%18%
1471
March1st to 10thDay
14%12%7%12%8%46%5%45%22%
1882
11th to 20thDay
14%14%6%9%8%45%446%27%
1980
21st to endDay
20%11%48%6%45%45%6%28%
2238
April1st to 10thDay
16%11%48%6%36%5%5%7%30%
2160
11th to 20thDay
19%8%36%6%35%447%36%
2134
21st to endDay
19%9%48%5%3445%7%32%
2234
May1st to 10thDay
16%8%46%8%46%45%7%33%
2436
11th to 20thDay
15%7%36%5%45%5%5%8%37%
2478
21st to endDay
13%5%26%6%45%5%6%8%41%
2725
June1st to 10thDay
17%7%35%5%345%6%8%36%
2520
11th to 20thDay
13%5%35%6%35%5%7%9%38%
2520
21st to endDay
11%6%26%6%46%5%7%8%38%
2520
July1st to 10thDay
9%5%36%6%35%5%7%10%42%
2520
11th to 20thDay
9%5%35%7%37%6%7%9%38%
2520
21st to endDay
11%5%26%7%47%7%7%8%36%
2704
August1st to 10thDay
10%5%25%6%47%7%8%9%37%
2327
11th to 20thDay
11%6%36%7%48%7%7%8%32%
2281
21st to endDay
13%6%36%6%5%5%6%6%9%35%
2376
September1st to 10thDay
15%6%25%5%45%6%5%8%39%
2160
11th to 20thDay
13%6%345%445%5%8%43%
2160
21st to endDay
15%7%35%7%45%6%6%7%36%
1897
October1st to 10thDay
17%8%27%6%45%5%6%6%34%
1800
11th to 20thDay
18%9%36%7%5%5%46%7%29%
1800
21st to endDay
24%10%48%8%4445%6%23%
1945
November1st to 10thDay
14%11%47%7%36%5%5%6%32%
1671
11th to 20thDay
13%13%410%7%46%46%8%26%
1549
21st to endDay
19%14%48%7%26%5%6%7%22%
1520
December1st to 10thDay
18%16%8%10%7%45%45%6%17%
1520
11th to 20thDay
19%14%7%12%7%45%45%5%19%
1906
21st to endDay
26%19%5%11%7%44445%12%
2772
January1st to 10thNight
15%16%6%12%8%46%6%5%5%16%
2649
11th to 20thNight
18%16%6%11%9%5%5%45%6%15%
2627
21st to endNight
13%14%7%11%10%6%7%5%5%6%17%
2664
February1st to 10thNight
17%14%7%12%7%35%45%5%21%
2340
11th to 20thNight
15%12%6%12%8%5%6%5%5%6%21%
2273
21st to endNight
18%10%5%12%7%45%6%5%6%23%
1784
March1st to 10thNight
14%13%6%8%8%46%6%5%6%24%
2060
11th to 20thNight
17%11%6%8%6%3445%5%30%
1979
21st to endNight
18%10%48%7%35%446%32%
2117
April1st to 10thNight
18%9%47%7%445%47%31%
1800
11th to 20thNight
19%7%36%6%45%5%46%35%
1775
21st to endNight
17%8%27%6%35%46%7%35%
1742
May1st to 10thNight
19%9%36%5%45%5%5%7%32%
1522
11th to 20thNight
12%5%25%6%45%6%6%9%40%
1415
21st to endNight
9%5%35%6%35%46%8%46%
1550
June1st to 10thNight
15%5%36%4446%5%9%38%
1440
11th to 20thNight
10%6%36%5%345%6%8%43%
1440
21st to endNight
10%5%25%6%5%5%5%6%8%43%
1440
July1st to 10thNight
6%426%5%46%5%6%10%46%
1440
11th to 20thNight
9%5%345%35%46%8%48%
1440
21st to endNight
12%5%345%25%5%6%10%42%
1610
August1st to 10thNight
9%5%25%5%25%5%7%8%47%
1611
11th to 20thNight
11%5%27%6%35%5%5%7%43%
1602
21st to endNight
10%426%43447%9%47%
1980
September1st to 10thNight
14%6%25%5%345%6%8%43%
1800
11th to 20thNight
14%5%3443445%8%46%
1800
21st to endNight
15%5%25%6%35%5%6%7%40%
2058
October1st to 10thNight
18%8%37%6%445%5%6%35%
2160
11th to 20thNight
19%9%36%5%35%5%5%7%33%
2160
21st to endNight
25%10%37%7%345%5%6%25%
2409
November1st to 10thNight
16%11%47%6%3445%7%34%
2407
11th to 20thNight
17%10%47%6%36%5%6%7%31%
2626
21st to endNight
16%14%5%7%6%45%5%6%7%25%
2660
December1st to 10thNight
19%15%6%8%6%46%5%6%6%19%
2660
11th to 20thNight
19%15%6%10%7%35%445%21%
3288
21st to endNight
30%14%5%8%6%45%5%5%5%13%
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
70%7%10%10%3
1518
11th to 20thDay
74%7%9%7%3
1550
21st to endDay
72%7%10%8%3
1836
February1st to 10thDay
71%9%9%8%3
1620
11th to 20thDay
71%7%7%12%3
1582
21st to endDay
66%7%10%11%5%1
1471
March1st to 10thDay
64%8%12%13%41
1885
11th to 20thDay
60%5%10%14%9%1
1980
21st to endDay
57%6%9%16%10%2
2238
April1st to 10thDay
54%7%11%18%10%2
2160
11th to 20thDay
49%6%11%19%13%2
2134
21st to endDay
51%7%8%18%13%2
2234
May1st to 10thDay
50%7%11%18%12%2
2436
11th to 20thDay
44%8%12%21%13%2
2482
21st to endDay
40%9%15%22%12%1
2725
June1st to 10thDay
45%9%11%19%16%1
2520
11th to 20thDay
40%9%14%23%12%1
2520
21st to endDay
40%11%15%21%13%1
2520
July1st to 10thDay
36%9%13%27%13%2
2450
11th to 20thDay
37%11%17%23%11%1
2445
21st to endDay
41%11%14%21%11%1
2553
August1st to 10thDay
39%11%16%22%12%1
2314
11th to 20thDay
44%11%15%22%8%
2281
21st to endDay
43%8%13%23%10%1
2376
September1st to 10thDay
41%8%13%25%12%1
2160
11th to 20thDay
39%7%12%24%16%1
2160
21st to endDay
46%9%11%23%11%1
1897
October1st to 10thDay
47%8%14%18%12%1
1800
11th to 20thDay
52%10%13%18%7%
1800
21st to endDay
61%8%12%13%5%1
1945
November1st to 10thDay
51%9%12%16%10%2
1671
11th to 20thDay
56%8%14%15%6%1
1549
21st to endDay
60%9%15%13%2
1520
December1st to 10thDay
69%8%10%11%2
1520
11th to 20thDay
67%8%12%8%4
1906
21st to endDay
75%8%8%8%1
2772
January1st to 10thNight
70%9%8%9%4
2649
11th to 20thNight
71%9%9%9%3
2627
21st to endNight
69%7%10%10%31
2664
February1st to 10thNight
66%8%10%11%6%
2340
11th to 20thNight
64%8%10%13%41
2275
21st to endNight
61%8%13%12%6%
1784
March1st to 10thNight
60%7%11%16%5%
2070
11th to 20thNight
56%6%10%18%8%1
1980
21st to endNight
54%6%9%17%12%2
2117
April1st to 10thNight
54%7%11%18%8%1
1800
11th to 20thNight
51%7%10%16%14%1
1775
21st to endNight
48%7%11%19%13%3
1742
May1st to 10thNight
50%8%10%16%13%3
1522
11th to 20thNight
40%9%12%24%14%2
1416
21st to endNight
36%8%17%22%15%3
1551
June1st to 10thNight
43%9%12%22%14%1
1440
11th to 20thNight
38%9%15%21%15%3
1440
21st to endNight
37%10%10%27%15%1
1440
July1st to 10thNight
33%10%15%22%17%4
1400
11th to 20thNight
33%8%13%29%16%1
1392
21st to endNight
36%9%15%24%14%2
1520
August1st to 10thNight
34%9%15%30%12%1
1600
11th to 20thNight
38%11%13%30%8%
1602
21st to endNight
33%9%16%27%13%2
1980
September1st to 10thNight
38%8%15%24%13%2
1800
11th to 20thNight
37%7%13%26%16%1
1800
21st to endNight
41%8%14%23%13%1
2058
October1st to 10thNight
49%7%13%18%12%
2160
11th to 20thNight
50%7%15%18%9%1
2160
21st to endNight
60%7%13%12%6%1
2409
November1st to 10thNight
50%8%12%19%9%2
2407
11th to 20thNight
52%9%14%16%7%2
2626
21st to endNight
58%10%15%14%4
2660
December1st to 10thNight
66%9%13%10%2
2660
11th to 20thNight
65%8%11%12%3
3288
21st to endNight
72%9%9%9%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
29%23%31%12%6%
180
11th to 20thDay
31%29%28%10%21
195
21st to endDay
24%25%35%12%4
282
February1st to 10thDay
37%27%30%7%
240
11th to 20thDay
35%24%37%4
240
21st to endDay
35%22%29%12%1
337
March1st to 10thDay
25%23%32%17%3
420
11th to 20thDay
29%23%29%15%4
420
21st to endDay
33%20%26%15%41
462
April1st to 10thDay
28%20%32%15%41
420
11th to 20thDay
30%20%25%14%7%4
412
21st to endDay
31%18%28%16%7%1
420
May1st to 10thDay
25%17%33%15%8%3
423
11th to 20thDay
19%14%32%23%9%2
447
21st to endDay
15%15%28%24%13%4
485
June1st to 10thDay
21%14%28%26%9%2
450
11th to 20thDay
16%13%32%26%11%3
450
21st to endDay
14%14%35%24%11%2
450
July1st to 10thDay
12%7%25%31%20%4
445
11th to 20thDay
12%8%26%31%20%4
444
21st to endDay
9%9%36%29%13%3
488
August1st to 10thDay
10%6%28%28%21%7%
446
11th to 20thDay
14%6%31%23%16%9%
439
21st to endDay
13%11%28%26%13%9%
495
September1st to 10thDay
18%9%24%23%16%9%
450
11th to 20thDay
13%10%25%24%18%10%
450
21st to endDay
17%13%28%22%14%6%
450
October1st to 10thDay
22%12%31%17%14%4
450
11th to 20thDay
24%16%34%17%8%2
450
21st to endDay
31%19%29%17%4
477
November1st to 10thDay
25%17%28%21%8%1
365
11th to 20thDay
29%21%31%14%4
209
21st to endDay
33%26%28%12%1
180
December1st to 10thDay
31%19%33%12%41
180
11th to 20thDay
32%25%28%13%2
180
21st to endDay
33%23%33%10%1
198
January1st to 10thNight
28%25%31%14%3
760
11th to 20thNight
29%22%28%18%21
760
21st to endNight
23%22%34%19%3
820
February1st to 10thNight
28%21%34%15%2
720
11th to 20thNight
25%22%35%15%3
703
21st to endNight
27%22%32%16%3
592
March1st to 10thNight
27%19%31%19%3
720
11th to 20thNight
27%20%28%21%4
720
21st to endNight
25%16%31%21%6%1
792
April1st to 10thNight
24%16%34%21%4
720
11th to 20thNight
23%16%31%23%6%1
711
21st to endNight
22%14%28%26%10%
662
May1st to 10thNight
26%7%24%32%10%1
442
11th to 20thNight
17%8%32%33%9%1
354
21st to endNight
11%8%32%31%18%
389
June1st to 10thNight
17%6%26%36%15%1
360
11th to 20thNight
13%9%26%37%15%1
360
21st to endNight
11%7%31%41%10%1
360
July1st to 10thNight
8%223%44%22%2
350
11th to 20thNight
11%322%41%22%1
348
21st to endNight
11%6%24%41%15%2
430
August1st to 10thNight
11%424%36%21%4
537
11th to 20thNight
12%419%37%24%3
538
21st to endNight
11%7%24%34%23%2
792
September1st to 10thNight
16%7%23%31%20%3
720
11th to 20thNight
16%7%21%30%23%5%
720
21st to endNight
15%13%23%26%21%3
720
October1st to 10thNight
23%11%27%19%19%2
720
11th to 20thNight
24%15%29%24%7%1
720
21st to endNight
31%14%31%21%3
792
November1st to 10thNight
24%15%30%23%7%1
740
11th to 20thNight
23%20%32%16%7%2
760
21st to endNight
26%22%27%18%6%
760
December1st to 10thNight
29%22%31%14%3
760
11th to 20thNight
28%22%30%17%3
760
21st to endNight
34%21%29%15%1
836
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Copyright 2024 Attilla Danko


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