Cahall Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cahall Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
26%
22969
19%
74539
8%
22925
39%
22925
20%
48092

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
13%
760
21%
2649
5%
757
33%
757
18%
1609
January11th to 20thNight
14%
729
16%
2549
3%
729
31%
729
13%
1742
January21st to endNight
17%
792
20%
2772
6%
792
36%
792
16%
1745
February1st to 10thNight
14%
720
17%
2260
4%
720
30%
720
16%
1521
February11th to 20thNight
13%
703
20%
2100
4%
700
31%
700
16%
1431
February21st to endNight
16%
592
25%
1776
7%
592
39%
592
18%
1169
March1st to 10thNight
18%
720
22%
2160
7%
720
37%
720
19%
1427
March11th to 20thNight
16%
720
19%
2049
4%
720
31%
720
18%
1396
March21st to endNight
19%
792
23%
2080
6%
792
33%
792
21%
1437
April1st to 10thNight
21%
720
20%
1800
5%
720
31%
720
22%
1276
April11th to 20thNight
22%
685
18%
1749
4%
685
30%
685
24%
1213
April21st to endNight
21%
540
20%
1620
6%
540
32%
540
19%
1101
May1st to 10thNight
21%
540
13%
1620
6%
540
27%
540
17%
1154
May11th to 20thNight
22%
532
15%
1594
6%
532
31%
532
20%
1085
May21st to endNight
32%
402
13%
1564
11%
401
40%
401
20%
992
June1st to 10thNight
33%
360
13%
1440
10%
360
44%
360
17%
923
June11th to 20thNight
34%
360
13%
1440
13%
360
43%
360
18%
920
June21st to endNight
40%
360
12%
1440
10%
360
49%
360
22%
855
July1st to 10thNight
45%
350
13%
1400
14%
350
53%
350
23%
829
July11th to 20thNight
47%
348
15%
1392
15%
348
53%
348
21%
845
July21st to endNight
46%
394
20%
1486
20%
372
53%
372
23%
880
August1st to 10thNight
44%
519
16%
1583
11%
517
49%
517
31%
948
August11th to 20thNight
48%
539
18%
1603
13%
539
51%
539
25%
1047
August21st to endNight
52%
792
22%
1980
11%
792
56%
792
36%
1268
September1st to 10thNight
45%
720
19%
1818
8%
720
50%
720
33%
1204
September11th to 20thNight
45%
720
25%
1980
14%
720
53%
720
35%
1188
September21st to endNight
40%
720
24%
1980
14%
720
49%
720
29%
1276
October1st to 10thNight
35%
720
18%
1980
10%
720
42%
720
25%
1337
October11th to 20thNight
31%
720
22%
2186
10%
720
45%
720
27%
1342
October21st to endNight
22%
792
16%
2574
7%
792
35%
792
19%
1723
November1st to 10thNight
30%
740
22%
2407
10%
740
45%
740
25%
1443
November11th to 20thNight
22%
760
23%
2470
8%
760
41%
760
20%
1529
November21st to endNight
20%
760
23%
2470
6%
760
39%
760
19%
1507
December1st to 10thNight
17%
760
20%
2588
6%
760
34%
760
16%
1688
December11th to 20thNight
18%
760
19%
3194
4%
758
35%
758
13%
1966
December21st to endNight
14%
828
15%
4786
4%
817
34%
817
10%
3076

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%7%35%5%345%5%7%40%
74820
Night
17%7%35%5%3445%6%40%
74903
TransparencyDay
43%411%23%16%2
74526
Night
45%411%23%15%2
74732
SeeingDay
21%15%33%22%8%2
13983
Night
21%13%33%25%7%1
22977

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
15%9%446%24445%44%
1517
11th to 20thDay
19%8%35%32446%6%39%
1456
21st to endDay
14%7%25%5%3445%7%43%
1584
February1st to 10thDay
21%8%345%35%6%45%36%
1697
11th to 20thDay
15%7%36%435%45%6%42%
1748
21st to endDay
19%9%36%5%245%45%38%
1480
March1st to 10thDay
16%8%345%345%5%8%39%
1797
11th to 20thDay
17%7%36%4345%48%39%
1909
21st to endDay
18%9%35%5%23446%41%
2272
April1st to 10thDay
19%8%35%435%35%6%38%
2160
11th to 20thDay
17%7%345%3446%6%40%
2158
21st to endDay
21%6%25%5%3445%7%37%
2340
May1st to 10thDay
24%10%35%5%24437%33%
2340
11th to 20thDay
18%7%35%5%335%5%6%41%
2302
21st to endDay
15%6%2443445%8%44%
2725
June1st to 10thDay
20%6%35%5%35%5%7%10%32%
2520
11th to 20thDay
17%5%25%6%35%6%6%8%37%
2520
21st to endDay
16%6%25%6%46%5%6%8%36%
2520
July1st to 10thDay
13%5%346%35%6%7%9%39%
2520
11th to 20thDay
12%6%35%5%36%6%7%9%38%
2520
21st to endDay
11%5%25%6%46%6%7%9%39%
2744
August1st to 10thDay
10%6%25%6%46%7%6%10%38%
2327
11th to 20thDay
13%6%26%5%36%5%6%9%38%
2295
21st to endDay
13%5%25%5%35%5%6%8%43%
2376
September1st to 10thDay
14%5%245%3446%7%46%
2142
11th to 20thDay
15%6%2332435%6%51%
1980
21st to endDay
18%6%24424446%45%
1980
October1st to 10thDay
24%6%24423345%42%
1980
11th to 20thDay
15%6%34433447%46%
1770
21st to endDay
20%6%35%43445%5%40%
1782
November1st to 10thDay
18%6%25%423345%48%
1671
11th to 20thDay
18%7%34424346%45%
1710
21st to endDay
18%7%24435%5%5%6%43%
1710
December1st to 10thDay
17%9%35%5%35%446%40%
1590
11th to 20thDay
21%7%25%423345%44%
1906
21st to endDay
22%11%35%5%34345%35%
2772
January1st to 10thNight
16%9%35%424346%45%
2649
11th to 20thNight
19%10%46%5%3445%6%35%
2549
21st to endNight
14%9%45%5%4445%6%41%
2772
February1st to 10thNight
17%10%36%5%3445%6%38%
2260
11th to 20thNight
16%8%36%6%35%5%45%39%
2098
21st to endNight
18%8%25%5%345%5%5%41%
1776
March1st to 10thNight
16%8%35%5%45%5%46%41%
2150
11th to 20thNight
16%9%46%5%3445%6%38%
2049
21st to endNight
17%9%36%5%34345%41%
2080
April1st to 10thNight
18%7%47%5%3445%6%38%
1800
11th to 20thNight
18%7%25%5%3445%7%39%
1749
21st to endNight
21%7%35%5%25%446%38%
1620
May1st to 10thNight
23%10%37%5%3445%6%32%
1620
11th to 20thNight
18%6%26%6%35%5%7%7%36%
1593
21st to endNight
18%6%36%5%3446%8%38%
1563
June1st to 10thNight
18%7%35%5%35%5%6%7%36%
1440
11th to 20thNight
17%7%37%4345%6%8%35%
1440
21st to endNight
16%5%24445%47%9%40%
1440
July1st to 10thNight
12%6%27%5%35%5%7%9%40%
1440
11th to 20thNight
12%7%36%6%35%5%7%10%35%
1440
21st to endNight
13%5%36%5%36%5%5%8%40%
1574
August1st to 10thNight
8%6%26%6%45%5%8%8%44%
1593
11th to 20thNight
10%6%36%6%45%8%6%8%38%
1603
21st to endNight
13%5%245%2446%7%47%
1980
September1st to 10thNight
13%5%26%5%35%5%6%7%44%
1818
11th to 20thNight
14%5%24423347%52%
1980
21st to endNight
17%5%25%4235%5%7%44%
1980
October1st to 10thNight
22%5%34433336%42%
1980
11th to 20thNight
15%5%35%5%345%46%46%
2186
21st to endNight
21%8%25%5%34446%38%
2574
November1st to 10thNight
15%5%25%5%34446%47%
2407
11th to 20thNight
17%8%3432445%5%45%
2470
21st to endNight
16%6%344335%5%6%45%
2470
December1st to 10thNight
20%7%35%5%235%45%39%
2588
11th to 20thNight
19%8%25%43445%6%41%
3288
21st to endNight
20%11%36%5%24346%36%
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
43%38%28%16%2
1518
11th to 20thDay
47%6%12%21%11%3
1456
21st to endDay
42%311%27%15%2
1584
February1st to 10thDay
50%312%19%14%2
1697
11th to 20thDay
43%413%23%15%2
1757
21st to endDay
48%410%21%14%3
1480
March1st to 10thDay
45%412%22%13%4
1800
11th to 20thDay
44%410%22%16%4
1909
21st to endDay
45%49%20%17%5%
2272
April1st to 10thDay
47%38%19%18%4
2160
11th to 20thDay
44%39%23%17%3
2158
21st to endDay
46%39%22%16%4
2340
May1st to 10thDay
53%38%20%14%2
2340
11th to 20thDay
44%5%9%20%19%4
2306
21st to endDay
38%5%15%25%14%2
2725
June1st to 10thDay
46%6%12%24%11%1
2520
11th to 20thDay
43%5%13%22%15%2
2520
21st to endDay
44%6%13%24%13%1
2520
July1st to 10thDay
39%7%11%25%16%3
2450
11th to 20thDay
40%5%13%26%13%2
2445
21st to endDay
39%6%13%25%13%4
2591
August1st to 10thDay
39%5%14%26%13%1
2314
11th to 20thDay
42%6%13%24%15%1
2295
21st to endDay
37%5%11%26%19%2
2376
September1st to 10thDay
38%5%10%25%21%1
2142
11th to 20thDay
35%48%28%23%2
1980
21st to endDay
41%48%23%23%2
1980
October1st to 10thDay
45%48%23%15%4
1980
11th to 20thDay
38%311%30%16%2
1770
21st to endDay
45%412%20%15%4
1782
November1st to 10thDay
40%312%26%16%2
1671
11th to 20thDay
42%38%25%20%2
1710
21st to endDay
43%5%13%25%13%2
1710
December1st to 10thDay
47%314%18%17%1
1590
11th to 20thDay
45%214%18%16%5%
1906
21st to endDay
53%310%22%11%1
2772
January1st to 10thNight
43%312%24%17%2
2649
11th to 20thNight
52%412%20%10%2
2549
21st to endNight
45%49%21%19%2
2772
February1st to 10thNight
48%312%20%13%2
2260
11th to 20thNight
48%48%21%15%3
2100
21st to endNight
45%37%24%17%4
1776
March1st to 10thNight
46%38%23%16%5%
2160
11th to 20thNight
47%410%18%17%4
2050
21st to endNight
48%36%19%19%5%
2080
April1st to 10thNight
48%48%20%17%4
1800
11th to 20thNight
46%38%22%18%3
1749
21st to endNight
48%49%20%15%4
1620
May1st to 10thNight
54%310%17%13%3
1620
11th to 20thNight
47%5%11%19%13%4
1594
21st to endNight
46%415%21%12%1
1564
June1st to 10thNight
47%5%14%22%11%1
1440
11th to 20thNight
48%412%21%15%1
1440
21st to endNight
40%6%15%25%13%1
1440
July1st to 10thNight
39%6%14%23%17%1
1400
11th to 20thNight
42%5%13%29%9%1
1392
21st to endNight
40%6%12%29%12%2
1486
August1st to 10thNight
35%6%17%26%13%2
1583
11th to 20thNight
40%8%16%22%13%
1603
21st to endNight
36%5%10%28%20%1
1980
September1st to 10thNight
39%5%12%25%18%2
1818
11th to 20thNight
35%310%24%25%2
1980
21st to endNight
40%47%25%21%3
1980
October1st to 10thNight
45%411%22%14%4
1980
11th to 20thNight
39%413%29%14%1
2186
21st to endNight
49%311%21%15%2
2574
November1st to 10thNight
39%412%24%18%3
2407
11th to 20thNight
42%310%22%20%3
2470
21st to endNight
41%313%27%13%2
2470
December1st to 10thNight
48%312%22%14%1
2588
11th to 20thNight
44%414%18%18%1
3288
21st to endNight
51%47%27%11%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
28%23%29%16%4
180
11th to 20thDay
21%26%41%10%21
164
21st to endDay
23%23%41%10%31
176
February1st to 10thDay
30%20%36%13%1
362
11th to 20thDay
25%27%38%10%1
416
21st to endDay
23%24%38%12%2
346
March1st to 10thDay
23%23%36%15%3
420
11th to 20thDay
25%24%36%11%41
420
21st to endDay
25%22%34%11%7%1
462
April1st to 10thDay
27%21%30%14%7%1
420
11th to 20thDay
24%20%34%18%3
412
21st to endDay
27%15%37%18%21
420
May1st to 10thDay
32%20%31%13%31
423
11th to 20thDay
20%13%41%19%41
447
21st to endDay
17%11%34%29%7%2
485
June1st to 10thDay
20%11%33%27%8%2
450
11th to 20thDay
16%11%41%23%7%2
450
21st to endDay
14%8%38%29%10%1
450
July1st to 10thDay
18%6%28%31%15%2
445
11th to 20thDay
14%5%27%38%13%2
444
21st to endDay
10%7%31%39%12%1
488
August1st to 10thDay
12%5%31%38%12%2
446
11th to 20thDay
16%7%28%31%16%3
439
21st to endDay
15%7%28%31%15%4
495
September1st to 10thDay
18%8%26%30%14%4
450
11th to 20thDay
19%11%25%23%14%7%
450
21st to endDay
22%11%29%23%10%5%
450
October1st to 10thDay
26%10%27%23%10%4
450
11th to 20thDay
16%16%31%24%11%2
394
21st to endDay
25%15%33%18%7%2
396
November1st to 10thDay
19%17%32%18%14%1
365
11th to 20thDay
22%22%35%16%41
370
21st to endDay
22%21%34%16%6%1
370
December1st to 10thDay
24%22%36%13%4
250
11th to 20thDay
30%24%37%7%2
180
21st to endDay
25%19%37%15%32
198
January1st to 10thNight
23%19%39%15%3
760
11th to 20thNight
26%19%37%16%2
729
21st to endNight
19%20%36%20%4
792
February1st to 10thNight
24%18%37%19%1
720
11th to 20thNight
26%18%39%15%2
703
21st to endNight
23%21%35%17%3
592
March1st to 10thNight
23%19%36%18%3
720
11th to 20thNight
23%18%38%16%41
720
21st to endNight
24%16%35%20%5%
792
April1st to 10thNight
23%16%35%21%4
720
11th to 20thNight
22%14%38%20%5%
685
21st to endNight
25%12%36%24%3
540
May1st to 10thNight
29%11%34%20%6%1
540
11th to 20thNight
20%12%39%22%6%1
532
21st to endNight
20%7%36%30%8%
402
June1st to 10thNight
21%6%31%34%8%1
360
11th to 20thNight
19%7%33%34%7%1
360
21st to endNight
17%334%38%8%
360
July1st to 10thNight
13%230%44%9%1
350
11th to 20thNight
15%326%46%9%1
348
21st to endNight
13%230%44%11%
394
August1st to 10thNight
10%431%42%12%
519
11th to 20thNight
13%426%45%12%1
539
21st to endNight
15%421%39%18%3
792
September1st to 10thNight
14%328%39%14%2
720
11th to 20thNight
16%6%28%30%18%3
720
21st to endNight
21%6%27%32%13%3
720
October1st to 10thNight
24%8%27%25%13%2
720
11th to 20thNight
18%11%34%24%11%2
720
21st to endNight
25%13%34%21%7%
792
November1st to 10thNight
19%12%34%25%9%1
740
11th to 20thNight
21%21%31%20%6%1
760
21st to endNight
21%21%34%19%5%1
760
December1st to 10thNight
25%17%36%17%4
760
11th to 20thNight
23%21%33%20%3
760
21st to endNight
24%16%39%18%2
836
Page generated at 2024-01-10 01:25:04. Version ac07

Copyright 2024 Attilla Danko


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