Sawyer Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sawyer Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
27%
23230
9%
74844
4%
23175
33%
23175
9%
59860

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
16%
819
7%
2772
1%
816
24%
816
6%
2291
January11th to 20thNight
17%
741
7%
2591
1%
741
23%
741
5%
2175
January21st to endNight
15%
792
11%
2642
3%
792
25%
792
9%
2059
February1st to 10thNight
16%
720
7%
2340
1%
720
23%
720
8%
1874
February11th to 20thNight
14%
703
8%
2266
1%
700
23%
700
6%
1853
February21st to endNight
19%
592
12%
1776
2%
592
30%
592
9%
1420
March1st to 10thNight
16%
720
10%
2086
4%
720
24%
720
9%
1732
March11th to 20thNight
24%
720
8%
1980
4%
720
28%
720
9%
1639
March21st to endNight
22%
792
13%
2178
4%
792
30%
792
11%
1737
April1st to 10thNight
19%
672
9%
1860
3%
672
23%
672
10%
1543
April11th to 20thNight
24%
534
13%
1598
6%
534
30%
534
11%
1271
April21st to endNight
23%
540
10%
1620
4%
540
29%
540
11%
1326
May1st to 10thNight
30%
540
11%
1620
5%
540
35%
540
11%
1308
May11th to 20thNight
29%
532
9%
1552
6%
532
33%
532
10%
1273
May21st to endNight
32%
525
9%
1493
6%
524
37%
524
12%
1213
June1st to 10thNight
34%
360
6%
1260
4%
360
37%
360
7%
1059
June11th to 20thNight
38%
360
10%
1260
7%
360
43%
360
9%
1016
June21st to endNight
37%
360
5%
1260
6%
360
39%
360
6%
1086
July1st to 10thNight
43%
350
5%
1225
5%
350
46%
350
8%
1005
July11th to 20thNight
47%
348
7%
1319
6%
348
50%
348
8%
1052
July21st to endNight
46%
502
6%
1588
7%
474
47%
474
9%
1315
August1st to 10thNight
51%
538
6%
1600
5%
534
52%
534
11%
1293
August11th to 20thNight
48%
532
11%
1596
8%
532
50%
532
12%
1277
August21st to endNight
49%
594
12%
1782
7%
594
51%
594
13%
1367
September1st to 10thNight
49%
617
10%
1845
7%
617
52%
617
15%
1425
September11th to 20thNight
44%
720
14%
1980
9%
720
49%
720
17%
1500
September21st to endNight
40%
720
15%
1980
8%
720
45%
720
15%
1537
October1st to 10thNight
39%
720
14%
2096
8%
720
44%
720
15%
1605
October11th to 20thNight
32%
720
13%
2160
5%
720
38%
720
12%
1687
October21st to endNight
24%
792
10%
2503
4%
792
31%
792
9%
2014
November1st to 10thNight
28%
740
10%
2407
7%
740
33%
740
10%
1895
November11th to 20thNight
24%
843
14%
2644
7%
843
32%
843
9%
2089
November21st to endNight
21%
850
9%
2660
2%
850
28%
850
8%
2125
December1st to 10thNight
15%
850
8%
2660
1%
850
22%
850
7%
2223
December11th to 20thNight
13%
850
9%
3473
1%
849
22%
849
5%
2805
December21st to endNight
13%
922
6%
5172
1%
907
20%
907
3%
3771

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
19%8%35%5%3445%7%37%
74655
Night
20%8%35%5%3445%7%35%
75135
TransparencyDay
31%38%9%13%8%1
74358
Night
33%38%8%13%7%1
74967
SeeingDay
23%12%28%25%10%1
15060
Night
24%12%29%25%8%1
23243

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
16%12%46%5%25%5%5%6%34%
1388
11th to 20thDay
22%11%47%5%23445%33%
1480
21st to endDay
14%8%46%6%35%45%6%38%
1711
February1st to 10thDay
18%10%47%5%36%5%47%31%
1620
11th to 20thDay
15%10%38%5%36%5%37%34%
1582
21st to endDay
13%10%36%5%35%447%38%
1480
March1st to 10thDay
17%11%36%5%345%5%6%34%
1869
11th to 20thDay
18%8%35%5%35%45%6%38%
1980
21st to endDay
19%10%47%5%34446%36%
2178
April1st to 10thDay
21%9%47%6%35%446%31%
2097
11th to 20thDay
21%8%25%434447%38%
2312
21st to endDay
24%9%25%5%34446%35%
2340
May1st to 10thDay
23%9%47%5%34446%31%
2340
11th to 20thDay
23%6%25%434446%38%
2340
21st to endDay
19%7%26%5%35%5%5%8%34%
2796
June1st to 10thDay
24%8%36%6%4435%7%30%
2700
11th to 20thDay
21%7%35%5%34447%37%
2700
21st to endDay
25%7%36%6%45%447%30%
2700
July1st to 10thDay
17%5%345%35%5%5%9%38%
2700
11th to 20thDay
16%6%35%5%446%5%9%38%
2594
21st to endDay
16%7%36%5%45%6%6%8%35%
2617
August1st to 10thDay
16%6%25%6%35%47%9%38%
2327
11th to 20thDay
17%6%36%5%46%47%8%36%
2304
21st to endDay
14%4245%35%5%5%8%46%
2574
September1st to 10thDay
13%425%4245%47%50%
2111
11th to 20thDay
17%5%2443435%5%50%
1980
21st to endDay
19%5%34423347%46%
1980
October1st to 10thDay
16%7%35%43446%6%42%
1864
11th to 20thDay
20%6%245%25%5%5%7%40%
1800
21st to endDay
22%7%26%5%34446%36%
1850
November1st to 10thDay
22%7%25%4245%45%39%
1671
11th to 20thDay
21%6%24325%45%9%40%
1535
21st to endDay
20%9%35%5%2435%7%36%
1520
December1st to 10thDay
24%9%35%4345%6%7%30%
1516
11th to 20thDay
25%11%46%5%34436%29%
1668
21st to endDay
24%9%25%435%446%34%
2431
January1st to 10thNight
17%12%46%5%35%45%6%32%
2772
11th to 20thNight
18%12%47%5%35%45%6%30%
2591
21st to endNight
12%10%48%6%35%6%6%7%35%
2642
February1st to 10thNight
18%11%35%5%46%5%5%7%32%
2340
11th to 20thNight
17%10%38%6%35%5%5%5%33%
2263
21st to endNight
16%11%36%5%34445%39%
1776
March1st to 10thNight
16%10%5%6%6%35%446%34%
2077
11th to 20thNight
19%8%36%6%35%5%6%7%32%
1979
21st to endNight
19%10%36%5%25%446%36%
2178
April1st to 10thNight
24%10%36%5%3445%5%32%
1860
11th to 20thNight
22%9%35%42446%5%36%
1598
21st to endNight
28%7%36%5%2435%7%30%
1620
May1st to 10thNight
24%7%35%5%34447%34%
1620
11th to 20thNight
25%7%35%5%35%5%5%5%32%
1551
21st to endNight
20%8%36%6%2446%7%34%
1492
June1st to 10thNight
26%6%36%5%35%45%8%28%
1260
11th to 20thNight
22%6%46%4345%6%7%34%
1260
21st to endNight
28%8%35%6%35%436%31%
1260
July1st to 10thNight
17%8%36%5%35%5%7%10%32%
1260
11th to 20thNight
20%7%345%25%5%5%9%34%
1362
21st to endNight
19%8%36%5%46%6%6%6%32%
1682
August1st to 10thNight
16%7%35%5%35%5%6%9%37%
1612
11th to 20thNight
17%8%35%5%35%46%8%35%
1596
21st to endNight
16%7%244245%5%8%43%
1782
September1st to 10thNight
16%6%245%2446%7%45%
1845
11th to 20thNight
18%5%24423346%48%
1980
21st to endNight
19%6%23324447%46%
1980
October1st to 10thNight
20%5%15%42446%7%41%
2096
11th to 20thNight
19%6%25%5%3445%7%41%
2160
21st to endNight
23%9%25%5%3445%5%36%
2503
November1st to 10thNight
20%6%246%345%47%38%
2407
11th to 20thNight
20%6%25%5%35%45%6%39%
2644
21st to endNight
20%6%26%5%25%5%5%7%36%
2660
December1st to 10thNight
26%10%46%5%23447%29%
2660
11th to 20thNight
25%9%35%43445%6%32%
3531
21st to endNight
24%8%36%424446%34%
5236

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
32%42%9%11%5%1
1389
11th to 20thDay
35%42%8%11%31
1480
21st to endDay
30%39%9%13%9%1
1711
February1st to 10thDay
35%37%8%11%8%1
1620
11th to 20thDay
34%38%9%11%6%1
1590
21st to endDay
33%36%8%16%5%2
1480
March1st to 10thDay
34%37%8%13%8%1
1873
11th to 20thDay
30%39%8%12%9%2
1980
21st to endDay
31%37%8%13%9%2
2178
April1st to 10thDay
36%37%7%9%10%1
2097
11th to 20thDay
30%37%7%15%10%2
2312
21st to endDay
31%36%7%13%9%3
2340
May1st to 10thDay
36%38%6%10%8%2
2340
11th to 20thDay
30%37%8%14%9%1
2344
21st to endDay
30%39%8%14%7%1
2796
June1st to 10thDay
37%37%9%10%6%1
2700
11th to 20thDay
32%38%7%12%9%2
2700
21st to endDay
40%40%7%8%41
2700
July1st to 10thDay
31%40%11%12%5%1
2625
11th to 20thDay
29%42%11%12%7%
2514
21st to endDay
30%41%10%14%6%
2471
August1st to 10thDay
30%40%9%14%6%1
2314
11th to 20thDay
29%39%10%14%8%
2304
21st to endDay
24%38%9%18%10%1
2574
September1st to 10thDay
24%38%8%19%11%1
2111
11th to 20thDay
23%37%8%16%13%3
1980
21st to endDay
29%37%6%19%8%1
1980
October1st to 10thDay
27%38%9%17%9%
1864
11th to 20thDay
29%39%10%17%6%
1800
21st to endDay
29%39%8%15%9%
1850
November1st to 10thDay
28%41%8%13%10%1
1671
11th to 20thDay
24%41%9%15%10%1
1535
21st to endDay
30%41%10%14%41
1520
December1st to 10thDay
35%42%8%9%5%
1516
11th to 20thDay
42%33%9%11%5%
1668
21st to endDay
41%28%12%12%6%2
2431
January1st to 10thNight
34%41%8%11%5%
2772
11th to 20thNight
34%43%7%10%5%1
2591
21st to endNight
29%39%9%14%7%1
2642
February1st to 10thNight
34%38%11%10%6%1
2340
11th to 20thNight
35%39%9%10%6%2
2266
21st to endNight
33%37%8%13%7%1
1776
March1st to 10thNight
36%38%6%11%9%1
2086
11th to 20thNight
35%38%10%10%6%1
1980
21st to endNight
30%38%7%15%9%1
2178
April1st to 10thNight
36%37%7%11%8%1
1860
11th to 20thNight
33%37%6%13%10%1
1598
21st to endNight
35%37%6%11%10%1
1620
May1st to 10thNight
35%36%6%12%9%1
1620
11th to 20thNight
34%39%7%12%7%2
1552
21st to endNight
32%39%8%14%7%1
1493
June1st to 10thNight
39%39%8%11%31
1260
11th to 20thNight
34%39%7%12%7%1
1260
21st to endNight
43%37%5%9%32
1260
July1st to 10thNight
32%43%10%9%6%
1225
11th to 20thNight
33%40%9%11%7%
1319
21st to endNight
34%42%9%10%6%1
1588
August1st to 10thNight
31%41%9%14%6%
1600
11th to 20thNight
31%39%9%15%6%
1596
21st to endNight
26%39%8%17%10%
1782
September1st to 10thNight
27%38%7%17%9%1
1845
11th to 20thNight
25%36%8%16%14%1
1980
21st to endNight
28%37%6%17%10%1
1980
October1st to 10thNight
27%38%8%17%9%
2096
11th to 20thNight
29%38%10%14%8%
2160
21st to endNight
32%39%7%13%8%
2503
November1st to 10thNight
26%43%7%14%9%
2407
11th to 20thNight
29%41%8%13%8%1
2644
21st to endNight
29%41%10%13%5%1
2660
December1st to 10thNight
36%41%7%12%5%
2660
11th to 20thNight
39%34%9%12%6%
3532
21st to endNight
40%28%11%13%5%3
5236

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
28%17%32%18%5%
180
11th to 20thDay
28%24%34%11%31
170
21st to endDay
21%18%34%22%5%
303
February1st to 10thDay
26%20%33%18%3
340
11th to 20thDay
23%23%35%15%4
340
21st to endDay
18%21%34%23%4
346
March1st to 10thDay
20%20%37%19%3
420
11th to 20thDay
20%20%32%20%7%
420
21st to endDay
23%19%31%19%6%2
462
April1st to 10thDay
28%18%30%19%41
420
11th to 20thDay
23%14%34%23%5%1
412
21st to endDay
26%13%30%22%8%1
420
May1st to 10thDay
26%13%32%20%9%
423
11th to 20thDay
22%10%31%26%9%1
486
21st to endDay
24%8%30%25%11%1
680
June1st to 10thDay
27%7%29%27%9%2
630
11th to 20thDay
23%7%25%29%13%2
630
21st to endDay
29%5%23%27%12%3
630
July1st to 10thDay
22%424%33%15%1
620
11th to 20thDay
21%423%34%16%3
513
21st to endDay
18%423%39%15%1
488
August1st to 10thDay
15%425%35%18%2
446
11th to 20thDay
20%5%20%36%17%2
439
21st to endDay
19%5%22%32%20%2
495
September1st to 10thDay
14%326%40%16%2
450
11th to 20thDay
23%8%24%26%16%4
450
21st to endDay
19%7%30%26%15%4
450
October1st to 10thDay
18%14%23%26%17%3
392
11th to 20thDay
21%9%29%28%10%4
360
21st to endDay
25%13%31%23%7%1
396
November1st to 10thDay
24%16%29%21%9%2
365
11th to 20thDay
24%20%30%18%7%1
370
21st to endDay
25%22%29%20%41
370
December1st to 10thDay
28%17%34%17%4
366
11th to 20thDay
31%26%28%12%3
180
21st to endDay
24%27%30%13%5%2
198
January1st to 10thNight
24%19%31%21%3
819
11th to 20thNight
27%18%32%19%4
741
21st to endNight
18%22%37%19%4
792
February1st to 10thNight
25%19%36%18%3
720
11th to 20thNight
25%23%31%17%31
703
21st to endNight
23%17%36%19%41
592
March1st to 10thNight
23%15%38%22%2
720
11th to 20thNight
23%16%31%24%5%
720
21st to endNight
23%14%33%22%6%1
792
April1st to 10thNight
29%14%34%19%4
672
11th to 20thNight
25%9%36%25%6%
534
21st to endNight
32%6%32%21%9%1
540
May1st to 10thNight
25%6%31%29%9%1
540
11th to 20thNight
27%5%30%30%7%1
532
21st to endNight
22%7%32%29%9%2
525
June1st to 10thNight
29%5%23%33%8%1
360
11th to 20thNight
23%5%26%31%13%1
360
21st to endNight
32%418%34%11%1
360
July1st to 10thNight
23%419%41%13%
350
11th to 20thNight
24%416%39%16%1
348
21st to endNight
23%217%42%14%1
502
August1st to 10thNight
17%418%46%14%1
538
11th to 20thNight
23%417%39%18%1
532
21st to endNight
18%421%36%21%2
594
September1st to 10thNight
19%322%37%18%1
617
11th to 20thNight
20%6%24%29%19%2
720
21st to endNight
21%427%30%15%2
720
October1st to 10thNight
23%5%26%29%15%2
720
11th to 20thNight
21%10%31%24%12%2
720
21st to endNight
27%15%29%22%7%
792
November1st to 10thNight
23%13%30%24%8%1
740
11th to 20thNight
25%16%31%19%9%1
843
21st to endNight
26%20%30%18%6%
850
December1st to 10thNight
33%13%33%16%4
850
11th to 20thNight
27%22%32%15%21
850
21st to endNight
29%20%31%16%4
935
Page generated at 2024-01-13 01:38:14. Version ac07

Copyright 2024 Attilla Danko


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