Smith Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smith Observing Site clear sky chart from 2005-11-06 to 2024-01-15.

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
35%
24648
17%
74683
10%
24591
42%
24591
22%
50405

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
19%
950
15%
2648
3%
946
29%
946
18%
1888
January11th to 20thNight
18%
925
12%
2589
4%
925
25%
925
14%
1985
January21st to endNight
18%
990
11%
2740
3%
990
25%
990
15%
2088
February1st to 10thNight
17%
873
12%
2313
2%
873
23%
873
17%
1740
February11th to 20thNight
22%
700
18%
2099
7%
700
32%
700
17%
1449
February21st to endNight
19%
592
19%
1776
6%
592
31%
592
17%
1262
March1st to 10thNight
23%
720
13%
2160
7%
720
29%
720
18%
1531
March11th to 20thNight
30%
706
19%
2122
9%
706
40%
706
24%
1385
March21st to endNight
31%
594
15%
1980
10%
594
38%
594
17%
1400
April1st to 10thNight
28%
540
14%
1800
8%
540
37%
540
19%
1213
April11th to 20thNight
31%
533
19%
1775
12%
533
42%
533
18%
1196
April21st to endNight
34%
540
17%
1690
9%
540
43%
540
21%
1146
May1st to 10thNight
35%
540
14%
1620
8%
540
40%
540
21%
1134
May11th to 20thNight
41%
531
19%
1452
11%
531
48%
531
26%
975
May21st to endNight
47%
582
16%
1552
9%
582
52%
582
28%
1045
June1st to 10thNight
55%
540
16%
1440
10%
540
60%
540
35%
900
June11th to 20thNight
50%
540
20%
1440
13%
540
55%
540
34%
913
June21st to endNight
52%
540
17%
1440
11%
540
56%
540
33%
933
July1st to 10thNight
68%
525
16%
1400
12%
525
70%
525
39%
847
July11th to 20thNight
60%
522
20%
1392
14%
522
64%
522
40%
830
July21st to endNight
68%
591
23%
1487
17%
558
71%
558
42%
877
August1st to 10thNight
70%
537
22%
1455
19%
534
72%
534
41%
863
August11th to 20thNight
67%
534
22%
1744
22%
534
71%
534
35%
958
August21st to endNight
64%
594
23%
1980
23%
594
69%
594
36%
1078
September1st to 10thNight
57%
540
24%
1800
23%
540
62%
540
30%
1049
September11th to 20thNight
57%
634
32%
1894
26%
634
65%
634
37%
1089
September21st to endNight
47%
720
25%
1980
16%
720
53%
720
31%
1263
October1st to 10thNight
47%
720
23%
2029
17%
720
52%
720
31%
1258
October11th to 20thNight
30%
720
21%
2179
10%
720
42%
720
24%
1410
October21st to endNight
28%
792
16%
2574
10%
792
37%
792
19%
1754
November1st to 10thNight
31%
740
25%
2406
16%
740
44%
740
25%
1460
November11th to 20thNight
24%
760
18%
2470
9%
760
36%
760
16%
1669
November21st to endNight
23%
842
18%
2552
7%
842
35%
842
19%
1744
December1st to 10thNight
18%
950
13%
2660
4%
950
26%
950
16%
1940
December11th to 20thNight
21%
950
14%
3215
5%
948
30%
948
15%
2298
December21st to endNight
12%
1041
6%
4830
2%
1026
20%
1026
7%
3835

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
13%9%46%6%35%5%5%7%37%
74823
Night
14%9%46%5%3445%6%39%
74984
TransparencyDay
45%7%12%22%12%2
74524
Night
45%6%11%22%14%2
74804
SeeingDay
16%12%30%25%12%4
14669
Night
18%10%30%28%12%1
24657

By Month

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 10thDay
14%11%5%7%6%4445%6%34%
1517
11th to 20thDay
13%16%7%9%7%3445%7%25%
1477
21st to endDay
13%16%8%11%7%3445%5%24%
1611
February1st to 10thDay
13%16%6%7%6%35%5%6%7%27%
1645
11th to 20thDay
15%11%48%6%35%45%5%36%
1748
21st to endDay
14%14%5%9%7%44346%30%
1480
March1st to 10thDay
14%13%6%8%6%35%45%6%31%
1800
11th to 20thDay
13%8%46%6%4445%8%37%
1852
21st to endDay
18%12%5%8%6%45%45%6%27%
2376
April1st to 10thDay
17%11%47%6%4445%6%31%
2160
11th to 20thDay
17%9%35%7%35%46%7%33%
2134
21st to endDay
20%8%36%6%445%5%6%33%
2268
May1st to 10thDay
17%7%37%6%45%46%8%32%
2340
11th to 20thDay
17%8%37%6%25%5%5%8%34%
2439
21st to endDay
12%7%36%6%45%5%6%9%38%
2725
June1st to 10thDay
9%6%26%5%35%5%5%8%46%
2520
11th to 20thDay
10%6%25%435%5%6%9%45%
2520
21st to endDay
11%6%26%6%35%5%7%10%39%
2520
July1st to 10thDay
8%424436%7%7%10%47%
2520
11th to 20thDay
9%5%245%345%6%9%48%
2520
21st to endDay
7%435%5%36%5%7%9%46%
2743
August1st to 10thDay
8%5%35%5%35%6%7%11%43%
2472
11th to 20thDay
10%7%25%6%35%5%6%9%42%
2155
21st to endDay
8%425%5%35%5%7%9%46%
2376
September1st to 10thDay
13%5%25%5%35%5%5%8%45%
2160
11th to 20thDay
13%4144245%5%7%51%
2047
21st to endDay
11%6%25%5%35%5%6%9%42%
1980
October1st to 10thDay
13%8%36%5%24446%46%
1928
11th to 20thDay
19%8%37%7%44447%34%
1780
21st to endDay
20%10%35%5%34445%36%
1782
November1st to 10thDay
12%8%46%43435%7%44%
1672
11th to 20thDay
15%10%48%7%345%46%33%
1710
21st to endDay
18%11%46%5%35%346%37%
1625
December1st to 10thDay
15%12%48%7%35%35%6%30%
1520
11th to 20thDay
12%14%48%6%46%5%6%7%29%
1918
21st to endDay
19%21%9%10%6%3434416%
2783
January1st to 10thNight
15%11%6%8%7%3333437%
2648
11th to 20thNight
16%13%6%9%6%25%445%28%
2589
21st to endNight
14%14%7%9%6%345%5%6%26%
2740
February1st to 10thNight
14%15%5%8%7%34445%31%
2313
11th to 20thNight
14%11%47%6%345%46%36%
2098
21st to endNight
19%11%46%6%24345%35%
1776
March1st to 10thNight
15%10%48%7%3445%6%34%
2160
11th to 20thNight
12%7%36%5%45%46%7%41%
2122
21st to endNight
19%10%47%5%3445%5%34%
1980
April1st to 10thNight
16%8%37%5%35%5%5%6%37%
1800
11th to 20thNight
20%8%45%44445%5%38%
1775
21st to endNight
19%7%36%6%235%5%5%39%
1690
May1st to 10thNight
14%8%46%6%47%5%6%7%34%
1620
11th to 20thNight
18%7%35%42435%9%39%
1452
21st to endNight
12%6%36%6%44447%43%
1551
June1st to 10thNight
10%4245%36%5%6%8%48%
1440
11th to 20thNight
11%6%236%345%6%8%46%
1440
21st to endNight
9%5%35%5%26%5%7%10%43%
1440
July1st to 10thNight
8%323436%5%7%10%50%
1440
11th to 20thNight
6%5%14426%6%6%8%51%
1440
21st to endNight
5%424435%6%8%8%51%
1575
August1st to 10thNight
5%4135%35%6%8%9%51%
1464
11th to 20thNight
8%325%42346%9%53%
1744
21st to endNight
7%4245%3445%7%54%
1980
September1st to 10thNight
10%6%245%2435%6%52%
1800
11th to 20thNight
10%5%24423347%55%
1894
21st to endNight
13%6%2443445%7%48%
1980
October1st to 10thNight
12%5%35%5%2345%6%50%
2029
11th to 20thNight
18%7%25%5%24445%43%
2179
21st to endNight
20%8%36%43445%6%37%
2574
November1st to 10thNight
11%8%36%43335%6%47%
2406
11th to 20thNight
14%11%37%7%34447%36%
2470
21st to endNight
17%8%47%5%335%5%6%37%
2552
December1st to 10thNight
16%11%5%8%6%45%5%5%6%31%
2660
11th to 20thNight
15%13%5%7%6%4445%6%32%
3279
21st to endNight
22%18%6%9%7%34445%19%
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
53%5%13%18%11%1
1518
11th to 20thDay
60%6%12%16%6%
1477
21st to endDay
63%410%13%9%
1611
February1st to 10thDay
57%5%12%16%9%1
1645
11th to 20thDay
51%410%22%11%2
1758
21st to endDay
56%6%8%18%11%1
1480
March1st to 10thDay
55%5%11%19%8%1
1800
11th to 20thDay
45%7%12%22%12%2
1852
21st to endDay
58%6%12%17%6%1
2376
April1st to 10thDay
53%6%11%18%11%
2160
11th to 20thDay
49%6%9%21%12%3
2134
21st to endDay
50%8%12%16%12%2
2268
May1st to 10thDay
50%7%13%23%7%
2340
11th to 20thDay
47%8%12%21%11%1
2443
21st to endDay
42%8%14%21%14%1
2725
June1st to 10thDay
36%7%12%26%17%2
2520
11th to 20thDay
35%7%13%22%20%3
2520
21st to endDay
39%9%13%22%14%2
2520
July1st to 10thDay
30%9%15%29%14%4
2451
11th to 20thDay
32%7%16%26%17%2
2445
21st to endDay
31%9%16%26%15%3
2591
August1st to 10thDay
33%8%17%29%12%2
2457
11th to 20thDay
38%7%15%26%13%1
2155
21st to endDay
31%9%13%25%19%3
2376
September1st to 10thDay
36%8%12%23%17%3
2160
11th to 20thDay
31%7%13%30%17%2
2047
21st to endDay
38%6%11%28%16%1
1980
October1st to 10thDay
40%6%10%27%15%1
1928
11th to 20thDay
51%412%19%13%1
1780
21st to endDay
51%6%9%23%10%2
1782
November1st to 10thDay
41%5%13%22%17%1
1672
11th to 20thDay
51%5%11%22%10%1
1710
21st to endDay
51%5%12%24%9%
1625
December1st to 10thDay
54%5%14%19%7%1
1520
11th to 20thDay
53%6%15%17%7%2
1915
21st to endDay
74%48%10%4
2783
January1st to 10thNight
52%310%20%13%1
2648
11th to 20thNight
58%5%13%15%9%
2589
21st to endNight
57%5%11%15%10%1
2740
February1st to 10thNight
56%5%9%18%12%1
2313
11th to 20thNight
48%6%11%20%13%2
2099
21st to endNight
51%5%8%21%10%4
1776
March1st to 10thNight
52%5%13%20%9%2
2160
11th to 20thNight
42%6%13%21%15%3
2122
21st to endNight
53%5%12%20%10%1
1980
April1st to 10thNight
47%6%11%21%14%1
1800
11th to 20thNight
49%5%7%18%17%4
1775
21st to endNight
47%6%11%20%15%2
1690
May1st to 10thNight
47%7%12%22%11%
1620
11th to 20thNight
43%6%10%25%15%2
1453
21st to endNight
43%5%11%23%17%2
1552
June1st to 10thNight
32%8%12%27%18%3
1440
11th to 20thNight
35%6%10%26%21%2
1440
21st to endNight
35%8%16%23%16%2
1440
July1st to 10thNight
27%10%14%28%17%4
1400
11th to 20thNight
28%7%14%29%18%4
1392
21st to endNight
26%8%15%28%18%5%
1487
August1st to 10thNight
26%8%17%30%16%2
1455
11th to 20thNight
28%8%15%31%17%1
1744
21st to endNight
28%7%12%29%20%4
1980
September1st to 10thNight
33%7%10%26%22%3
1800
11th to 20thNight
30%5%8%33%21%2
1894
21st to endNight
36%7%9%32%15%1
1980
October1st to 10thNight
36%5%10%28%19%2
2029
11th to 20thNight
42%5%11%22%18%2
2179
21st to endNight
48%6%11%23%11%1
2574
November1st to 10thNight
38%5%9%27%18%3
2406
11th to 20thNight
49%5%11%22%12%2
2470
21st to endNight
48%5%12%23%11%1
2552
December1st to 10thNight
53%5%12%19%9%1
2660
11th to 20thNight
53%5%13%19%10%1
3281
21st to endNight
68%49%13%5%
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
21%16%35%23%5%1
270
11th to 20thDay
23%19%33%22%31
254
21st to endDay
20%16%40%17%5%1
264
February1st to 10thDay
18%24%40%16%3
240
11th to 20thDay
25%22%35%15%3
240
21st to endDay
24%23%40%10%21
198
March1st to 10thDay
20%26%39%13%2
240
11th to 20thDay
24%15%38%16%6%1
262
21st to endDay
27%14%28%22%8%2
462
April1st to 10thDay
24%15%34%23%5%
420
11th to 20thDay
20%22%26%19%9%2
412
21st to endDay
22%16%30%19%11%2
420
May1st to 10thDay
22%13%33%21%9%2
423
11th to 20thDay
21%11%31%24%9%3
585
21st to endDay
17%8%30%24%16%5%
679
June1st to 10thDay
9%9%32%30%16%4
630
11th to 20thDay
13%8%28%33%13%5%
630
21st to endDay
12%8%29%34%14%4
630
July1st to 10thDay
6%324%31%24%12%
621
11th to 20thDay
9%5%30%32%16%8%
618
21st to endDay
7%429%38%17%6%
684
August1st to 10thDay
8%5%22%34%22%10%
591
11th to 20thDay
11%5%20%29%24%11%
439
21st to endDay
7%425%31%25%8%
495
September1st to 10thDay
15%6%25%27%22%6%
450
11th to 20thDay
11%421%31%21%12%
450
21st to endDay
14%12%24%25%15%8%
450
October1st to 10thDay
16%12%26%28%14%5%
398
11th to 20thDay
24%21%32%18%5%
270
21st to endDay
33%16%31%14%5%
297
November1st to 10thDay
16%16%34%24%9%2
270
11th to 20thDay
21%19%38%16%7%
270
21st to endDay
24%10%44%19%3
270
December1st to 10thDay
16%23%41%14%5%1
270
11th to 20thDay
19%18%39%19%6%
270
21st to endDay
26%24%34%14%1
297
January1st to 10thNight
18%17%38%23%4
950
11th to 20thNight
23%15%36%20%5%1
925
21st to endNight
20%13%38%24%4
990
February1st to 10thNight
22%14%38%22%4
873
11th to 20thNight
22%15%35%25%3
703
21st to endNight
26%15%36%20%31
592
March1st to 10thNight
20%13%36%22%8%
720
11th to 20thNight
16%11%38%27%8%
706
21st to endNight
23%10%30%28%8%1
594
April1st to 10thNight
20%12%36%26%6%1
540
11th to 20thNight
24%12%31%23%8%1
533
21st to endNight
24%8%27%30%10%1
540
May1st to 10thNight
17%9%34%31%9%1
540
11th to 20thNight
21%5%27%30%16%1
531
21st to endNight
14%5%25%34%20%2
584
June1st to 10thNight
10%325%42%19%1
540
11th to 20thNight
14%426%38%16%1
540
21st to endNight
11%426%39%20%2
540
July1st to 10thNight
8%215%39%32%3
525
11th to 20thNight
9%221%37%26%4
522
21st to endNight
6%218%47%26%1
591
August1st to 10thNight
6%115%45%28%4
537
11th to 20thNight
7%315%35%33%6%
534
21st to endNight
8%319%37%31%3
594
September1st to 10thNight
10%419%35%26%5%
540
11th to 20thNight
12%420%32%26%5%
634
21st to endNight
13%9%25%27%22%4
720
October1st to 10thNight
15%8%25%31%20%3
720
11th to 20thNight
22%13%31%26%9%
720
21st to endNight
25%11%32%24%8%1
792
November1st to 10thNight
16%14%35%24%10%1
740
11th to 20thNight
20%19%32%23%5%1
760
21st to endNight
21%14%36%23%6%
842
December1st to 10thNight
21%16%38%20%5%
950
11th to 20thNight
22%14%37%22%4
950
21st to endNight
29%16%36%18%2
1045
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