Walnut Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walnut Hill Observatory clear sky chart from 2005-11-06 to 2024-02-15.

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
39%
24776
22%
79783
12%
24679
48%
24679
29%
48023

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
31%
939
17%
4066
8%
926
42%
926
15%
2837
January11th to 20thNight
28%
949
23%
3992
9%
930
38%
930
18%
2358
January21st to endNight
26%
1032
15%
4469
7%
1023
36%
1023
17%
2858
February1st to 10thNight
24%
950
16%
2470
5%
950
32%
950
24%
1722
February11th to 20thNight
28%
846
18%
2277
7%
842
35%
842
28%
1492
February21st to endNight
28%
592
26%
1776
7%
592
43%
592
29%
1070
March1st to 10thNight
31%
602
23%
2042
11%
602
43%
602
26%
1202
March11th to 20thNight
29%
540
21%
1980
14%
540
39%
540
24%
1178
March21st to endNight
26%
594
14%
2178
8%
594
35%
594
17%
1456
April1st to 10thNight
26%
540
19%
1958
11%
540
39%
540
24%
1134
April11th to 20thNight
28%
533
24%
1624
13%
533
42%
533
26%
996
April21st to endNight
32%
540
21%
1620
15%
540
43%
540
26%
1024
May1st to 10thNight
36%
540
16%
1620
12%
540
44%
540
26%
1061
May11th to 20thNight
38%
531
18%
1594
11%
531
45%
531
29%
989
May21st to endNight
40%
582
12%
1746
7%
582
45%
582
27%
1124
June1st to 10thNight
59%
540
21%
1472
11%
540
63%
540
42%
838
June11th to 20thNight
50%
540
22%
1440
8%
540
55%
540
40%
841
June21st to endNight
53%
540
24%
1363
9%
540
58%
540
47%
778
July1st to 10thNight
67%
525
17%
1516
12%
525
68%
525
40%
857
July11th to 20thNight
70%
522
21%
1566
15%
522
73%
522
47%
818
July21st to endNight
72%
591
25%
1673
21%
558
75%
558
48%
855
August1st to 10thNight
66%
537
20%
1601
21%
534
69%
534
38%
915
August11th to 20thNight
65%
534
26%
1600
28%
534
71%
534
44%
853
August21st to endNight
60%
594
28%
1790
27%
594
66%
594
41%
982
September1st to 10thNight
57%
540
26%
1916
25%
540
65%
540
40%
945
September11th to 20thNight
52%
540
30%
1980
26%
540
63%
540
39%
967
September21st to endNight
46%
540
30%
1980
23%
540
59%
540
36%
985
October1st to 10thNight
42%
628
27%
2068
18%
628
50%
628
31%
1193
October11th to 20thNight
34%
720
27%
2160
12%
720
45%
720
35%
1204
October21st to endNight
39%
810
27%
2394
14%
810
48%
810
33%
1391
November1st to 10thNight
41%
925
29%
2405
11%
925
52%
925
43%
1362
November11th to 20thNight
30%
950
29%
2470
10%
950
44%
950
36%
1488
November21st to endNight
34%
950
24%
2640
12%
950
43%
950
34%
1577
December1st to 10thNight
31%
950
21%
2660
8%
950
41%
950
29%
1642
December11th to 20thNight
31%
949
25%
3097
10%
948
42%
948
27%
1776
December21st to endNight
28%
1041
15%
4580
8%
1026
41%
1026
14%
3255

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
11%7%36%5%345%5%7%45%
78616
Night
10%6%36%5%3445%7%48%
80478
TransparencyDay
39%6%13%25%15%2
78339
Night
36%6%13%26%17%3
80275
SeeingDay
14%9%31%29%14%2
14724
Night
12%9%34%33%10%1
24808

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
9%12%411%9%5%6%5%5%6%29%
2847
11th to 20thDay
8%11%5%8%5%28%6%46%37%
2850
21st to endDay
8%10%5%12%7%34446%37%
3135
February1st to 10thDay
10%10%5%7%7%35%5%5%8%34%
1710
11th to 20thDay
9%9%36%6%35%45%8%41%
1682
21st to endDay
10%9%36%434448%44%
1480
March1st to 10thDay
9%8%46%5%24446%46%
1916
11th to 20thDay
15%8%36%5%24447%41%
1980
21st to endDay
18%11%47%5%35%46%6%32%
2178
April1st to 10thDay
14%7%35%6%34446%44%
2001
11th to 20thDay
16%8%45%5%35%45%6%40%
2284
21st to endDay
19%7%36%5%24447%39%
2340
May1st to 10thDay
16%7%37%5%35%5%5%6%37%
2340
11th to 20thDay
15%7%35%5%445%5%8%41%
2302
21st to endDay
15%7%45%5%35%6%6%8%35%
2531
June1st to 10thDay
7%4245%35%46%9%50%
2484
11th to 20thDay
11%4245%3446%9%48%
2520
21st to endDay
7%4245%35%5%5%9%51%
2573
July1st to 10thDay
9%424435%5%5%10%51%
2386
11th to 20thDay
6%4134245%6%8%56%
2340
21st to endDay
6%423435%6%8%9%49%
2546
August1st to 10thDay
8%5%26%6%35%7%8%9%42%
2328
11th to 20thDay
8%3245%345%6%9%52%
2301
21st to endDay
9%425%42345%7%54%
2566
September1st to 10thDay
12%5%245%23446%53%
2040
11th to 20thDay
10%5%24434446%54%
1980
21st to endDay
9%413424447%58%
1980
October1st to 10thDay
12%7%25%4235%47%50%
1872
11th to 20thDay
11%5%24434335%56%
1800
21st to endDay
13%6%35%5%23445%49%
1958
November1st to 10thDay
8%5%3432435%7%56%
1673
11th to 20thDay
9%6%35%6%3435%8%50%
1710
21st to endDay
13%7%35%43435%6%46%
1538
December1st to 10thDay
9%7%25%5%345%5%7%47%
1520
11th to 20thDay
8%8%37%6%35%5%7%7%41%
1918
21st to endDay
14%9%412%7%35%5%5%6%29%
3007
January1st to 10thNight
7%10%412%9%45%5%5%7%32%
4108
11th to 20thNight
8%9%36%5%37%6%6%8%40%
4120
21st to endNight
10%11%6%10%5%23446%41%
4532
February1st to 10thNight
11%9%47%6%45%45%6%40%
2470
11th to 20thNight
8%7%46%6%45%5%6%5%44%
2276
21st to endNight
10%7%26%42445%6%50%
1776
March1st to 10thNight
10%7%36%5%23446%50%
2042
11th to 20thNight
16%8%34313346%48%
1980
21st to endNight
16%9%47%5%345%7%8%34%
2178
April1st to 10thNight
12%6%35%5%3445%7%47%
1958
11th to 20thNight
12%7%25%5%34448%46%
1624
21st to endNight
14%7%25%5%2435%7%45%
1620
May1st to 10thNight
16%6%35%5%3446%7%41%
1620
11th to 20thNight
13%6%25%5%34448%47%
1593
21st to endNight
14%6%26%5%3346%9%43%
1745
June1st to 10thNight
5%3244345%5%10%55%
1472
11th to 20thNight
7%42343445%10%53%
1440
21st to endNight
33134246%5%9%59%
1363
July1st to 10thNight
6%425%5%3345%8%55%
1561
11th to 20thNight
3214425%5%6%9%61%
1620
21st to endNight
32134245%6%10%58%
1772
August1st to 10thNight
5%315%5%35%6%6%9%53%
1611
11th to 20thNight
6%32343446%8%57%
1600
21st to endNight
7%423434346%58%
1790
September1st to 10thNight
9%423223436%61%
1916
11th to 20thNight
9%31342345%7%59%
1980
21st to endNight
8%414423345%60%
1980
October1st to 10thNight
13%5%234245%5%7%50%
2068
11th to 20thNight
12%5%24423235%58%
2160
21st to endNight
13%5%2432345%5%54%
2394
November1st to 10thNight
5%42433445%7%59%
2405
11th to 20thNight
9%5%25%5%33446%54%
2470
21st to endNight
11%6%35%423447%52%
2640
December1st to 10thNight
8%7%25%5%345%47%49%
2660
11th to 20thNight
8%6%36%434448%51%
3279
21st to endNight
16%11%49%6%33445%34%
4655

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
55%7%12%18%8%1
2848
11th to 20thDay
48%6%16%20%10%1
2850
21st to endDay
49%6%12%20%12%
3135
February1st to 10thDay
48%6%15%19%11%1
1710
11th to 20thDay
42%5%13%23%14%3
1691
21st to endDay
40%5%14%24%15%3
1480
March1st to 10thDay
40%5%13%26%14%2
1916
11th to 20thDay
44%6%9%24%15%2
1980
21st to endDay
52%6%16%19%7%1
2178
April1st to 10thDay
41%5%13%25%15%1
2001
11th to 20thDay
44%5%12%23%13%3
2284
21st to endDay
46%5%11%25%13%
2340
May1st to 10thDay
47%7%11%20%14%1
2340
11th to 20thDay
41%7%14%25%13%
2306
21st to endDay
46%8%16%19%10%1
2531
June1st to 10thDay
29%7%16%32%14%2
2484
11th to 20thDay
33%7%13%30%16%2
2520
21st to endDay
29%9%15%28%15%4
2573
July1st to 10thDay
29%7%16%30%17%2
2322
11th to 20thDay
26%6%13%29%20%6%
2271
21st to endDay
27%8%18%31%16%1
2405
August1st to 10thDay
34%11%18%26%10%2
2314
11th to 20thDay
28%7%14%32%18%1
2301
21st to endDay
30%6%12%26%20%6%
2566
September1st to 10thDay
32%5%9%30%18%6%
2040
11th to 20thDay
31%6%11%32%19%2
1980
21st to endDay
28%410%33%25%1
1980
October1st to 10thDay
36%410%26%22%2
1872
11th to 20thDay
32%38%27%23%7%
1800
21st to endDay
37%413%21%20%4
1958
November1st to 10thDay
28%415%29%21%3
1673
11th to 20thDay
34%5%12%27%20%1
1710
21st to endDay
40%310%30%14%2
1538
December1st to 10thDay
35%7%14%28%14%2
1520
11th to 20thDay
40%6%16%30%7%
1915
21st to endDay
55%6%10%19%9%1
3007
January1st to 10thNight
50%7%11%19%12%1
4108
11th to 20thNight
40%5%15%27%11%1
4120
21st to endNight
46%5%14%20%14%1
4532
February1st to 10thNight
45%6%13%20%13%3
2470
11th to 20thNight
40%5%14%24%14%3
2277
21st to endNight
35%5%11%25%19%4
1776
March1st to 10thNight
35%6%10%29%16%3
2042
11th to 20thNight
40%310%26%18%3
1980
21st to endNight
48%6%15%20%10%1
2178
April1st to 10thNight
37%5%12%26%18%2
1958
11th to 20thNight
38%5%12%26%17%2
1624
21st to endNight
39%5%12%24%19%1
1620
May1st to 10thNight
41%6%14%23%15%2
1620
11th to 20thNight
36%6%15%26%16%
1594
21st to endNight
39%7%18%20%14%2
1746
June1st to 10thNight
24%8%16%33%17%2
1472
11th to 20thNight
27%7%14%27%20%5%
1440
21st to endNight
21%8%14%34%20%4
1363
July1st to 10thNight
27%7%13%29%19%5%
1516
11th to 20thNight
20%7%16%31%21%5%
1566
21st to endNight
19%7%17%35%19%2
1673
August1st to 10thNight
26%9%18%31%15%1
1601
11th to 20thNight
24%5%16%31%21%2
1600
21st to endNight
26%5%12%26%21%9%
1790
September1st to 10thNight
25%412%29%22%8%
1916
11th to 20thNight
24%5%12%34%21%4
1980
21st to endNight
27%48%30%27%4
1980
October1st to 10thNight
33%6%10%25%24%2
2068
11th to 20thNight
31%48%25%26%7%
2160
21st to endNight
32%411%24%26%3
2394
November1st to 10thNight
24%6%14%27%25%5%
2405
11th to 20thNight
32%411%30%20%3
2470
21st to endNight
33%412%28%20%3
2640
December1st to 10thNight
35%6%13%30%15%1
2660
11th to 20thNight
33%413%36%12%1
3281
21st to endNight
53%5%9%23%8%1
4655

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
16%17%37%20%9%1
270
11th to 20thDay
19%13%36%26%5%1
270
21st to endDay
14%11%44%22%8%1
297
February1st to 10thDay
15%17%43%21%3
270
11th to 20thDay
14%15%38%23%10%
252
21st to endDay
17%20%41%18%41
198
March1st to 10thDay
16%13%44%21%5%1
240
11th to 20thDay
25%10%36%21%8%
240
21st to endDay
31%15%35%15%3
264
April1st to 10thDay
18%16%45%17%3
261
11th to 20thDay
20%15%38%19%8%
562
21st to endDay
22%15%34%19%9%1
600
May1st to 10thDay
19%13%33%25%9%1
603
11th to 20thDay
18%11%31%26%12%2
625
21st to endDay
17%8%30%31%13%2
679
June1st to 10thDay
6%6%24%38%21%5%
630
11th to 20thDay
10%5%32%35%16%3
630
21st to endDay
7%8%30%36%17%3
630
July1st to 10thDay
7%316%38%28%7%
621
11th to 20thDay
6%324%38%22%6%
618
21st to endDay
7%221%41%25%4
684
August1st to 10thDay
7%222%42%23%4
626
11th to 20thDay
8%319%43%24%3
615
21st to endDay
10%322%37%24%3
685
September1st to 10thDay
14%428%34%17%3
330
11th to 20thDay
7%331%37%18%4
270
21st to endDay
14%9%33%31%11%3
270
October1st to 10thDay
19%7%31%26%13%6%
270
11th to 20thDay
14%15%39%22%9%1
270
21st to endDay
20%13%40%17%9%1
297
November1st to 10thDay
18%12%38%21%7%3
270
11th to 20thDay
12%15%47%19%7%1
270
21st to endDay
20%14%33%23%9%1
270
December1st to 10thDay
11%12%44%26%6%1
270
11th to 20thDay
14%12%37%27%9%
270
21st to endDay
20%16%41%20%3
297
January1st to 10thNight
11%14%37%31%7%1
950
11th to 20thNight
13%14%38%28%7%1
950
21st to endNight
14%11%40%29%5%
1045
February1st to 10thNight
15%11%43%27%4
950
11th to 20thNight
13%12%42%29%4
846
21st to endNight
14%14%41%27%5%
592
March1st to 10thNight
15%13%37%28%7%
602
11th to 20thNight
21%8%38%28%6%
540
21st to endNight
20%11%38%25%5%
594
April1st to 10thNight
15%15%40%24%6%
540
11th to 20thNight
16%14%38%28%4
533
21st to endNight
17%11%36%27%8%1
540
May1st to 10thNight
16%8%35%31%9%
540
11th to 20thNight
14%9%33%32%11%
531
21st to endNight
16%7%31%33%12%1
584
June1st to 10thNight
7%5%25%46%17%1
540
11th to 20thNight
8%6%31%42%12%1
540
21st to endNight
45%34%41%16%
540
July1st to 10thNight
7%219%45%27%1
525
11th to 20thNight
3122%49%23%2
522
21st to endNight
3117%54%24%
591
August1st to 10thNight
6%219%48%23%2
537
11th to 20thNight
6%220%48%23%1
534
21st to endNight
9%224%42%22%2
594
September1st to 10thNight
9%427%39%20%1
540
11th to 20thNight
11%331%39%16%1
540
21st to endNight
10%6%34%34%15%1
540
October1st to 10thNight
17%7%31%32%11%2
628
11th to 20thNight
14%12%36%29%7%
720
21st to endNight
17%11%30%33%9%
810
November1st to 10thNight
9%10%38%36%7%1
925
11th to 20thNight
13%11%41%27%6%1
950
21st to endNight
13%12%37%29%8%1
950
December1st to 10thNight
12%13%40%29%6%
950
11th to 20thNight
15%11%36%32%6%
950
21st to endNight
17%15%35%28%5%
1045
Page generated at 2024-02-12 05:35:35. Version ac07

Copyright 2024 Attilla Danko


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