Godfrey Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Godfrey Road Observatory 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
29%
22752
13%
74728
8%
22708
36%
22708
15%
53920

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%
760
11%
2649
5%
757
26%
757
8%
2059
January11th to 20thNight
17%
737
9%
2577
4%
737
24%
737
7%
2018
January21st to endNight
17%
792
12%
2772
4%
792
28%
792
10%
2062
February1st to 10thNight
15%
720
11%
2369
4%
720
24%
720
9%
1828
February11th to 20thNight
17%
703
13%
2100
4%
700
28%
700
10%
1628
February21st to endNight
19%
592
15%
1776
6%
592
30%
592
12%
1317
March1st to 10thNight
20%
720
15%
2160
8%
720
30%
720
12%
1618
March11th to 20thNight
22%
720
13%
2102
6%
720
31%
720
13%
1579
March21st to endNight
24%
792
19%
1998
6%
792
33%
792
18%
1459
April1st to 10thNight
22%
720
16%
1800
4%
720
28%
720
17%
1366
April11th to 20thNight
26%
711
14%
1775
5%
711
31%
711
18%
1306
April21st to endNight
22%
540
16%
1620
6%
540
30%
540
15%
1153
May1st to 10thNight
24%
540
13%
1620
7%
540
30%
540
15%
1190
May11th to 20thNight
29%
385
17%
1447
13%
385
40%
385
15%
968
May21st to endNight
40%
389
12%
1551
12%
388
47%
388
17%
992
June1st to 10thNight
39%
360
11%
1440
10%
360
47%
360
13%
1000
June11th to 20thNight
41%
360
11%
1440
12%
360
49%
360
16%
952
June21st to endNight
46%
360
11%
1440
14%
360
52%
360
18%
937
July1st to 10thNight
53%
350
12%
1400
16%
350
58%
350
21%
863
July11th to 20thNight
51%
348
13%
1392
17%
348
55%
348
22%
836
July21st to endNight
54%
394
17%
1486
20%
372
60%
372
23%
879
August1st to 10thNight
57%
393
17%
1457
18%
391
60%
391
23%
879
August11th to 20thNight
48%
573
16%
1637
11%
573
49%
573
26%
1097
August21st to endNight
51%
792
18%
1980
9%
792
53%
792
31%
1323
September1st to 10thNight
47%
720
16%
1800
7%
720
51%
720
31%
1194
September11th to 20thNight
47%
720
22%
1939
13%
720
52%
720
29%
1263
September21st to endNight
43%
720
22%
1980
15%
720
49%
720
27%
1303
October1st to 10thNight
37%
720
15%
1993
9%
720
42%
720
18%
1432
October11th to 20thNight
34%
720
14%
2237
9%
720
41%
720
17%
1588
October21st to endNight
22%
792
12%
2574
7%
792
30%
792
12%
1956
November1st to 10thNight
31%
740
16%
2407
12%
740
38%
740
16%
1695
November11th to 20thNight
27%
760
19%
2470
12%
760
37%
760
15%
1761
November21st to endNight
22%
760
13%
2569
7%
760
30%
760
12%
1899
December1st to 10thNight
15%
760
9%
2660
3%
760
22%
760
7%
2156
December11th to 20thNight
18%
760
9%
3258
4%
759
24%
759
7%
2476
December21st to endNight
13%
829
6%
4853
2%
817
21%
817
4%
3888

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
17%9%47%6%35%5%5%7%33%
74803
Night
17%9%47%6%35%5%5%7%33%
74960
TransparencyDay
51%7%11%19%11%1
74508
Night
52%7%11%19%10%1
74789
SeeingDay
25%17%28%18%9%2
13715
Night
23%15%25%26%10%1
22759

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
12%12%5%11%7%35%6%6%7%26%
1517
11th to 20thDay
16%11%48%7%5%5%6%6%7%26%
1472
21st to endDay
11%11%6%9%7%45%5%6%8%29%
1584
February1st to 10thDay
14%12%5%9%6%47%5%46%27%
1589
11th to 20thDay
10%11%6%10%8%45%6%6%6%28%
1748
21st to endDay
16%10%6%9%7%445%5%6%29%
1480
March1st to 10thDay
13%11%410%7%46%5%45%31%
1797
11th to 20thDay
16%12%5%7%6%2445%5%32%
1856
21st to endDay
16%11%5%7%6%34446%33%
2353
April1st to 10thDay
19%11%47%5%34346%34%
2160
11th to 20thDay
17%9%46%5%35%5%5%6%35%
2134
21st to endDay
23%10%47%6%34447%28%
2338
May1st to 10thDay
23%9%46%6%35%345%32%
2340
11th to 20thDay
19%7%35%6%345%5%6%38%
2462
21st to endDay
15%7%36%6%35%5%5%7%38%
2725
June1st to 10thDay
19%7%47%6%47%6%6%6%29%
2520
11th to 20thDay
18%7%35%5%35%5%49%36%
2520
21st to endDay
19%7%27%7%5%6%5%6%8%28%
2520
July1st to 10thDay
16%7%35%6%36%5%5%8%37%
2520
11th to 20thDay
13%6%46%7%46%6%7%9%35%
2520
21st to endDay
14%5%36%6%46%6%7%9%35%
2744
August1st to 10thDay
13%6%36%6%46%6%7%9%35%
2453
11th to 20thDay
13%7%36%6%46%6%6%8%34%
2260
21st to endDay
12%5%26%7%35%5%6%8%42%
2376
September1st to 10thDay
13%5%26%5%25%5%5%9%43%
2160
11th to 20thDay
14%5%25%5%23446%48%
2020
21st to endDay
15%7%25%5%335%6%7%43%
1980
October1st to 10thDay
23%8%37%6%35%346%33%
1963
11th to 20thDay
15%8%37%6%445%5%6%37%
1721
21st to endDay
25%11%46%6%345%46%27%
1782
November1st to 10thDay
13%8%46%5%345%6%7%38%
1671
11th to 20thDay
18%9%47%5%35%6%5%6%33%
1710
21st to endDay
19%9%5%7%6%35%45%6%30%
1610
December1st to 10thDay
20%12%49%8%36%437%23%
1520
11th to 20thDay
22%13%37%435%346%30%
1906
21st to endDay
24%13%5%11%6%35%43322%
2772
January1st to 10thNight
13%10%5%9%8%46%6%6%7%27%
2649
11th to 20thNight
14%14%5%9%7%5%6%6%5%6%23%
2577
21st to endNight
11%8%6%9%7%5%7%5%6%6%31%
2772
February1st to 10thNight
13%11%48%9%45%6%7%7%25%
2369
11th to 20thNight
11%8%6%9%8%5%6%5%7%6%28%
2098
21st to endNight
13%9%5%9%7%46%5%5%6%30%
1776
March1st to 10thNight
13%10%49%8%35%5%5%6%31%
2150
11th to 20thNight
17%9%48%8%45%6%45%31%
2101
21st to endNight
17%9%37%5%35%5%5%6%38%
1998
April1st to 10thNight
20%8%37%6%35%45%6%33%
1800
11th to 20thNight
19%9%37%5%445%5%5%35%
1775
21st to endNight
21%10%35%5%35%447%33%
1620
May1st to 10thNight
21%11%37%6%245%36%31%
1620
11th to 20thNight
19%7%37%5%35%45%6%37%
1446
21st to endNight
16%6%36%5%35%5%6%8%38%
1550
June1st to 10thNight
20%5%26%7%45%5%6%8%32%
1440
11th to 20thNight
20%6%34425%5%5%6%38%
1440
21st to endNight
16%6%37%5%445%6%7%36%
1440
July1st to 10thNight
15%5%245%36%5%6%8%41%
1440
11th to 20thNight
13%5%25%5%335%6%9%42%
1440
21st to endNight
12%5%35%5%445%5%8%44%
1574
August1st to 10thNight
13%5%26%5%345%5%8%45%
1467
11th to 20thNight
12%7%26%6%35%46%10%39%
1637
21st to endNight
15%6%2442445%7%44%
1980
September1st to 10thNight
13%5%244245%6%7%47%
1800
11th to 20thNight
14%5%25%33335%7%49%
1939
21st to endNight
15%5%245%3446%6%46%
1980
October1st to 10thNight
22%7%36%6%3345%7%35%
1993
11th to 20thNight
16%9%36%6%36%5%47%35%
2237
21st to endNight
23%9%36%6%345%6%6%29%
2574
November1st to 10thNight
15%8%37%7%35%5%6%6%36%
2407
11th to 20thNight
17%7%45%6%45%5%6%8%35%
2470
21st to endNight
17%10%47%6%3446%7%31%
2569
December1st to 10thNight
19%13%6%10%7%45%5%5%7%21%
2660
11th to 20thNight
21%10%48%6%44447%27%
3288
21st to endNight
24%13%6%10%6%3444421%
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
59%8%8%18%8%
1518
11th to 20thDay
58%8%11%14%8%1
1472
21st to endDay
55%7%9%17%11%2
1584
February1st to 10thDay
59%6%9%16%7%2
1589
11th to 20thDay
58%7%9%15%9%1
1757
21st to endDay
58%6%9%14%12%1
1480
March1st to 10thDay
56%6%11%14%10%3
1800
11th to 20thDay
54%5%10%14%14%3
1856
21st to endDay
54%5%6%16%14%3
2353
April1st to 10thDay
54%5%7%19%11%3
2160
11th to 20thDay
50%7%9%19%14%2
2134
21st to endDay
57%6%8%16%11%2
2338
May1st to 10thDay
56%47%20%11%2
2340
11th to 20thDay
48%5%9%20%15%2
2466
21st to endDay
46%6%13%22%11%2
2725
June1st to 10thDay
54%8%12%17%9%1
2520
11th to 20thDay
47%7%10%21%14%2
2520
21st to endDay
54%7%11%18%9%1
2520
July1st to 10thDay
44%8%11%22%15%1
2450
11th to 20thDay
44%8%14%24%9%
2445
21st to endDay
42%8%14%24%11%1
2591
August1st to 10thDay
45%9%14%23%9%
2439
11th to 20thDay
46%8%15%22%9%
2260
21st to endDay
40%8%14%24%14%1
2376
September1st to 10thDay
39%6%12%29%13%1
2160
11th to 20thDay
38%5%8%30%17%2
2020
21st to endDay
39%7%13%26%13%2
1980
October1st to 10thDay
54%6%9%20%10%2
1963
11th to 20thDay
48%6%13%25%7%1
1721
21st to endDay
61%5%10%14%8%2
1782
November1st to 10thDay
47%6%13%21%14%1
1671
11th to 20thDay
53%7%12%14%13%2
1710
21st to endDay
57%6%16%15%5%
1610
December1st to 10thDay
64%7%10%13%5%
1520
11th to 20thDay
59%6%9%16%10%1
1906
21st to endDay
68%5%7%11%8%
2772
January1st to 10thNight
59%10%9%13%8%
2649
11th to 20thNight
62%8%10%13%6%1
2577
21st to endNight
56%9%9%15%10%2
2772
February1st to 10thNight
60%7%9%13%9%1
2369
11th to 20thNight
58%8%7%16%10%1
2100
21st to endNight
54%8%11%17%8%2
1776
March1st to 10thNight
57%6%9%17%10%2
2160
11th to 20thNight
56%5%9%16%10%3
2102
21st to endNight
48%7%10%17%15%3
1998
April1st to 10thNight
55%48%18%12%2
1800
11th to 20thNight
50%6%9%22%13%1
1775
21st to endNight
52%5%10%17%12%3
1620
May1st to 10thNight
55%48%17%14%2
1620
11th to 20thNight
49%6%9%19%15%2
1447
21st to endNight
44%8%15%21%10%1
1551
June1st to 10thNight
51%8%11%18%10%1
1440
11th to 20thNight
46%8%13%20%11%2
1440
21st to endNight
45%7%14%23%10%
1440
July1st to 10thNight
40%8%16%22%14%1
1400
11th to 20thNight
38%9%17%25%12%
1392
21st to endNight
37%7%15%28%11%1
1486
August1st to 10thNight
37%8%14%29%11%1
1457
11th to 20thNight
41%8%16%23%12%
1637
21st to endNight
39%6%14%27%14%
1980
September1st to 10thNight
37%8%15%28%13%
1800
11th to 20thNight
37%7%10%29%16%1
1939
21st to endNight
40%7%11%26%14%2
1980
October1st to 10thNight
49%7%11%21%10%2
1993
11th to 20thNight
50%7%13%22%7%1
2237
21st to endNight
57%7%10%16%9%1
2574
November1st to 10thNight
50%7%11%19%11%2
2407
11th to 20thNight
50%9%10%19%11%2
2470
21st to endNight
56%7%12%18%6%
2569
December1st to 10thNight
66%8%9%14%4
2660
11th to 20thNight
61%7%11%13%8%
3288
21st to endNight
68%7%7%15%3
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
31%18%33%13%41
180
11th to 20thDay
38%24%24%10%31
168
21st to endDay
23%27%32%12%6%1
176
February1st to 10thDay
36%30%26%5%3
244
11th to 20thDay
30%25%30%12%2
416
21st to endDay
31%25%25%16%4
346
March1st to 10thDay
27%19%35%15%4
420
11th to 20thDay
34%23%27%11%41
420
21st to endDay
30%22%25%13%8%3
462
April1st to 10thDay
37%19%23%13%6%2
420
11th to 20thDay
33%24%20%14%8%1
412
21st to endDay
34%20%26%11%6%2
420
May1st to 10thDay
34%22%24%12%6%2
423
11th to 20thDay
23%19%31%17%7%2
447
21st to endDay
21%16%31%22%9%2
485
June1st to 10thDay
23%16%33%19%8%1
450
11th to 20thDay
21%16%31%19%10%2
450
21st to endDay
20%17%30%20%10%2
450
July1st to 10thDay
18%11%31%24%13%3
445
11th to 20thDay
14%9%36%25%14%2
444
21st to endDay
14%10%35%27%12%2
488
August1st to 10thDay
13%12%28%26%18%2
446
11th to 20thDay
17%10%25%26%15%7%
439
21st to endDay
15%13%27%25%14%6%
495
September1st to 10thDay
16%10%27%24%16%7%
450
11th to 20thDay
19%12%26%18%16%8%
450
21st to endDay
20%12%29%22%11%7%
450
October1st to 10thDay
27%13%23%19%14%3
450
11th to 20thDay
24%16%26%20%12%2
410
21st to endDay
40%14%23%15%7%
396
November1st to 10thDay
25%16%23%22%12%1
365
11th to 20thDay
29%21%23%19%7%1
370
21st to endDay
33%18%26%17%5%
270
December1st to 10thDay
32%21%29%12%6%1
180
11th to 20thDay
36%22%28%11%3
180
21st to endDay
35%19%30%13%31
198
January1st to 10thNight
23%21%31%22%4
760
11th to 20thNight
26%20%28%22%3
737
21st to endNight
19%21%35%20%4
792
February1st to 10thNight
25%18%33%22%3
720
11th to 20thNight
23%22%31%20%3
703
21st to endNight
25%19%29%23%4
592
March1st to 10thNight
28%16%30%23%3
720
11th to 20thNight
27%21%24%22%6%
720
21st to endNight
27%17%27%20%8%1
792
April1st to 10thNight
28%19%25%23%5%
720
11th to 20thNight
24%20%25%22%7%1
711
21st to endNight
26%18%28%23%5%
540
May1st to 10thNight
31%14%26%22%7%
540
11th to 20thNight
19%13%29%30%8%1
385
21st to endNight
19%8%28%32%12%1
389
June1st to 10thNight
23%8%23%35%11%1
360
11th to 20thNight
21%8%22%36%13%
360
21st to endNight
19%6%21%41%13%
360
July1st to 10thNight
17%5%19%43%17%1
350
11th to 20thNight
16%322%37%21%2
348
21st to endNight
13%5%19%43%19%1
394
August1st to 10thNight
16%413%45%22%1
393
11th to 20thNight
16%6%22%35%20%2
573
21st to endNight
18%6%15%35%23%2
792
September1st to 10thNight
16%6%24%32%20%2
720
11th to 20thNight
18%9%21%27%22%3
720
21st to endNight
19%10%22%29%17%2
720
October1st to 10thNight
25%11%18%28%15%2
720
11th to 20thNight
23%13%23%28%12%1
720
21st to endNight
31%13%26%23%7%
792
November1st to 10thNight
22%17%24%28%9%
740
11th to 20thNight
25%17%26%23%8%1
760
21st to endNight
27%18%26%22%7%1
760
December1st to 10thNight
27%21%29%20%4
760
11th to 20thNight
29%18%30%20%3
760
21st to endNight
30%20%28%18%3
836
Page generated at 2024-01-11 22:33:48. Version ac07

Copyright 2024 Attilla Danko


Godfrey Road Observatory Clear Sky Chart |Charts Home