The HomCav Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The HomCav Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
30%
15770
13%
49551
8%
15739
36%
15739
16%
35674

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 15thNight
15%
780
9%
2716
4%
776
21%
776
8%
2145
January16th to endNight
14%
832
9%
2768
4%
832
21%
832
9%
2156
February1st to 15thNight
12%
764
8%
2482
2%
761
19%
761
8%
2009
February16th to endNight
16%
683
12%
2077
5%
683
25%
683
11%
1620
March1st to 15thNight
17%
780
12%
2249
5%
780
24%
780
12%
1742
March16th to endNight
23%
832
17%
2217
7%
832
31%
832
17%
1623
April1st to 15thNight
20%
778
14%
1946
4%
778
24%
778
18%
1458
April16th to endNight
30%
743
17%
1857
6%
743
35%
743
25%
1276
May1st to 15thNight
33%
407
17%
1487
11%
407
42%
407
15%
1018
May16th to endNight
43%
374
17%
1497
18%
374
51%
374
20%
944
June1st to 15thNight
38%
360
14%
1440
15%
360
47%
360
17%
936
June16th to endNight
52%
360
12%
1440
15%
360
59%
360
24%
845
July1st to 15thNight
58%
340
13%
1360
17%
340
61%
340
24%
799
July16th to endNight
57%
376
15%
1418
17%
354
61%
354
24%
833
August1st to 15thNight
57%
537
14%
1608
10%
535
60%
535
28%
1023
August16th to endNight
60%
747
20%
1893
12%
747
61%
747
33%
1228
September1st to 15thNight
47%
720
17%
1800
9%
720
50%
720
29%
1244
September16th to endNight
49%
717
24%
1956
18%
717
54%
717
31%
1261
October1st to 15thNight
38%
720
18%
2160
14%
720
44%
720
20%
1487
October16th to endNight
23%
768
13%
2349
7%
768
32%
768
15%
1748
November1st to 15thNight
27%
760
15%
2472
10%
760
35%
760
17%
1733
November16th to endNight
23%
780
14%
2717
9%
780
32%
780
13%
1959
December1st to 15thNight
16%
780
6%
2730
3%
780
20%
780
8%
2159
December16th to endNight
12%
832
6%
2912
3%
832
18%
832
6%
2428

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
16%9%47%6%35%45%6%29%
49978
Night
16%9%37%6%35%45%6%31%
49721
Cloud CoverDay
16%9%47%6%35%45%6%29%
49988
Night
16%9%37%6%35%45%6%31%
49726
TransparencyDay
53%6%10%17%9%
49667
Night
51%6%11%18%10%
49551
SeeingDay
24%13%26%19%11%4
6277
Night
22%14%28%24%10%
15771

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 15thDay
15%12%6%14%7%45%45%5%18%
1552
16th to endDay
12%12%7%13%10%45%45%5%18%
1807
February1st to 15thDay
16%13%8%12%10%35%44316%
1710
16th to endDay
19%12%5%9%8%34445%21%
1682
March1st to 15thDay
18%15%6%9%6%33445%23%
2030
16th to endDay
17%11%48%5%34445%29%
2359
April1st to 15thDay
20%11%5%6%434445%29%
2332
16th to endDay
16%10%37%424346%37%
2218
May1st to 15thDay
18%8%36%435%447%31%
2473
16th to endDay
15%7%36%5%45%45%7%33%
2618
June1st to 15thDay
20%6%35%5%35%5%5%7%31%
2520
16th to endDay
15%7%26%6%35%5%6%9%31%
2520
July1st to 15thDay
11%5%36%6%36%7%6%9%32%
2520
16th to endDay
11%5%36%6%46%5%7%9%33%
2654
August1st to 15thDay
14%5%26%6%45%6%6%8%31%
2340
16th to endDay
13%6%36%5%36%5%6%8%33%
2297
September1st to 15thDay
18%6%36%5%3435%7%35%
2160
16th to endDay
15%6%25%5%24445%43%
2003
October1st to 15thDay
20%8%36%424347%33%
1800
16th to endDay
21%11%37%6%35%5%45%26%
1873
November1st to 15thDay
15%11%37%6%2445%7%31%
1716
16th to endDay
18%12%38%7%24446%26%
1570
December1st to 15thDay
17%18%5%11%5%3445%5%19%
1560
16th to endDay
19%16%10%11%6%3443414%
1664
January1st to 15thNight
18%11%410%8%46%5%5%6%17%
2716
16th to endNight
14%12%5%9%10%45%5%5%6%20%
2768
February1st to 15thNight
14%11%6%11%9%47%5%45%19%
2480
16th to endNight
15%11%411%7%36%5%5%5%22%
2077
March1st to 15thNight
18%10%5%9%7%34345%26%
2237
16th to endNight
16%9%37%6%35%446%32%
2217
April1st to 15thNight
21%11%35%5%23445%32%
1946
16th to endNight
19%7%2442335%6%41%
1857
May1st to 15thNight
17%7%26%5%35%5%5%6%34%
1487
16th to endNight
12%6%246%25%5%6%7%39%
1495
June1st to 15thNight
19%7%25%423448%37%
1440
16th to endNight
10%3245%446%6%8%43%
1440
July1st to 15thNight
8%425%436%5%6%10%43%
1440
16th to endNight
10%4235%445%6%8%43%
1514
August1st to 15thNight
9%5%245%346%7%8%42%
1618
16th to endNight
11%4245%3345%8%45%
1893
September1st to 15thNight
13%5%25%5%3445%6%43%
1800
16th to endNight
13%4145%34448%45%
1956
October1st to 15thNight
20%7%26%5%23346%38%
2160
16th to endNight
22%9%37%5%24347%28%
2349
November1st to 15thNight
15%9%37%5%35%45%6%32%
2472
16th to endNight
17%11%45%5%3445%6%29%
2717
December1st to 15thNight
21%12%5%9%7%44446%19%
2730
16th to endNight
21%12%7%11%7%35%5%45%15%
2912

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 15thDay
16%12%5%13%7%35%45%5%19%
1552
16th to endDay
11%13%7%12%9%45%5%5%5%19%
1807
February1st to 15thDay
16%13%7%12%10%3443417%
1710
16th to endDay
18%13%410%8%4444423%
1682
March1st to 15thDay
18%14%6%9%6%235%35%24%
2041
16th to endDay
17%11%5%7%5%34345%29%
2358
April1st to 15thDay
19%11%5%7%424445%30%
2332
16th to endDay
17%9%36%5%24345%38%
2218
May1st to 15thDay
19%8%36%425%5%46%32%
2473
16th to endDay
16%7%35%6%35%5%5%7%34%
2618
June1st to 15thDay
21%6%36%5%345%5%8%30%
2520
16th to endDay
15%6%36%6%35%5%5%9%31%
2520
July1st to 15thDay
11%5%37%6%46%6%7%8%33%
2520
16th to endDay
11%5%36%6%46%6%7%8%34%
2654
August1st to 15thDay
15%6%26%6%46%6%6%8%31%
2340
16th to endDay
13%6%25%6%46%6%6%8%32%
2297
September1st to 15thDay
18%7%35%5%3445%6%36%
2160
16th to endDay
15%5%35%5%24446%42%
2003
October1st to 15thDay
19%9%36%443347%33%
1800
16th to endDay
21%11%26%7%35%445%26%
1873
November1st to 15thDay
15%12%36%5%245%46%32%
1716
16th to endDay
18%12%47%6%24446%27%
1570
December1st to 15thDay
17%17%6%9%6%24345%21%
1560
16th to endDay
20%17%9%10%6%24445%14%
1664
January1st to 15thNight
18%11%310%8%46%45%6%18%
2716
16th to endNight
14%12%410%9%46%45%6%21%
2768
February1st to 15thNight
14%11%6%11%9%5%6%5%5%420%
2473
16th to endNight
15%12%411%7%36%446%23%
2077
March1st to 15thNight
19%11%5%8%7%34345%26%
2249
16th to endNight
17%9%47%5%24446%33%
2217
April1st to 15thNight
21%11%35%423445%32%
1946
16th to endNight
20%6%24423346%42%
1857
May1st to 15thNight
16%7%25%6%35%5%47%34%
1487
16th to endNight
12%6%35%5%35%5%6%7%40%
1495
June1st to 15thNight
18%7%35%42345%8%37%
1440
16th to endNight
9%3245%45%6%5%7%44%
1440
July1st to 15thNight
8%5%245%36%5%5%9%43%
1440
16th to endNight
11%424435%5%6%8%43%
1514
August1st to 15thNight
9%5%25%5%346%7%8%42%
1618
16th to endNight
11%415%5%25%349%46%
1893
September1st to 15thNight
14%5%15%5%3445%6%42%
1800
16th to endNight
13%41442435%8%45%
1956
October1st to 15thNight
20%6%35%5%24337%38%
2160
16th to endNight
22%9%37%5%24446%29%
2349
November1st to 15thNight
15%10%37%5%25%45%6%33%
2472
16th to endNight
17%11%46%5%345%5%6%30%
2717
December1st to 15thNight
21%12%6%8%6%35%5%46%20%
2730
16th to endNight
20%13%7%10%7%35%5%45%16%
2912

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 15thDay
66%49%12%6%1
1553
16th to endDay
64%6%12%10%4
1807
February1st to 15thDay
70%5%6%11%5%
1712
16th to endDay
64%49%14%6%
1682
March1st to 15thDay
63%5%11%12%6%
2041
16th to endDay
56%48%17%11%1
2359
April1st to 15thDay
55%5%8%19%9%1
2332
16th to endDay
48%48%18%16%2
2218
May1st to 15thDay
51%6%9%21%9%1
2473
16th to endDay
48%8%12%17%12%
2622
June1st to 15thDay
51%7%11%20%9%
2520
16th to endDay
47%7%13%20%9%
2520
July1st to 15thDay
45%9%11%21%10%1
2371
16th to endDay
43%9%14%20%10%
2487
August1st to 15thDay
47%9%13%18%10%
2327
16th to endDay
45%8%11%22%11%
2297
September1st to 15thDay
48%5%10%21%13%
2160
16th to endDay
41%6%9%23%16%1
2003
October1st to 15thDay
50%5%8%20%12%1
1800
16th to endDay
58%7%11%16%6%
1873
November1st to 15thDay
51%5%14%17%9%2
1716
16th to endDay
57%5%12%16%7%
1570
December1st to 15thDay
65%6%10%12%4
1560
16th to endDay
72%5%9%9%2
1664
January1st to 15thNight
63%6%11%11%6%
2716
16th to endNight
62%5%11%14%5%
2768
February1st to 15thNight
66%6%9%12%5%
2482
16th to endNight
60%5%11%13%7%
2077
March1st to 15thNight
60%5%11%16%6%
2249
16th to endNight
52%410%19%11%1
2217
April1st to 15thNight
53%410%18%11%1
1946
16th to endNight
43%5%10%20%17%2
1857
May1st to 15thNight
48%8%9%18%14%1
1487
16th to endNight
40%8%12%23%12%2
1497
June1st to 15thNight
46%6%10%25%10%
1440
16th to endNight
35%8%16%25%12%1
1440
July1st to 15thNight
36%7%14%25%15%1
1360
16th to endNight
35%9%15%23%14%2
1418
August1st to 15thNight
35%9%17%25%10%
1608
16th to endNight
35%6%13%27%15%
1893
September1st to 15thNight
40%7%11%23%14%1
1800
16th to endNight
37%5%10%26%18%1
1956
October1st to 15thNight
46%6%10%21%14%1
2160
16th to endNight
55%5%13%17%7%
2349
November1st to 15thNight
50%5%12%17%11%2
2472
16th to endNight
53%6%12%19%7%
2717
December1st to 15thNight
64%6%12%11%4
2730
16th to endNight
69%6%10%10%2
2912

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 15thDay
31%26%28%8%22
90
16th to endDay
26%27%33%10%3
129
February1st to 15thDay
30%31%33%3
135
16th to endDay
31%26%28%10%3
263
March1st to 15thDay
32%20%28%13%5%
330
16th to endDay
28%20%28%14%5%2
352
April1st to 15thDay
34%16%26%14%5%1
330
16th to endDay
24%15%27%16%9%5%
289
May1st to 15thDay
31%13%23%16%10%4
288
16th to endDay
18%13%29%20%13%4
331
June1st to 15thDay
25%9%26%23%12%2
315
16th to endDay
22%7%33%21%12%2
315
July1st to 15thDay
16%432%25%15%5%
305
16th to endDay
14%326%30%19%4
326
August1st to 15thDay
17%5%26%21%19%9%
313
16th to endDay
15%6%18%25%17%16%
332
September1st to 15thDay
20%8%20%21%21%8%
315
16th to endDay
15%7%21%22%18%14%
314
October1st to 15thDay
24%5%25%21%16%5%
315
16th to endDay
29%15%29%17%8%
324
November1st to 15thDay
26%11%22%25%12%1
280
16th to endDay
25%22%33%16%4
100
December1st to 15thDay
28%21%28%15%41
90
16th to endDay
45%20%25%8%
96
January1st to 15thNight
25%21%33%16%3
780
16th to endNight
24%18%35%19%1
832
February1st to 15thNight
24%21%35%17%1
764
16th to endNight
26%19%32%18%2
683
March1st to 15thNight
28%20%29%18%3
780
16th to endNight
23%18%30%18%7%
832
April1st to 15thNight
30%16%28%21%2
778
16th to endNight
25%13%29%21%9%
743
May1st to 15thNight
21%9%28%29%10%
407
16th to endNight
12%8%29%34%13%
375
June1st to 15thNight
21%9%25%31%11%
360
16th to endNight
11%5%25%40%15%
360
July1st to 15thNight
9%322%43%19%1
340
16th to endNight
13%119%44%19%1
376
August1st to 15thNight
11%222%36%24%3
537
16th to endNight
13%317%32%30%2
747
September1st to 15thNight
16%5%24%30%21%1
720
16th to endNight
15%7%22%24%24%5%
717
October1st to 15thNight
24%10%21%26%15%1
720
16th to endNight
29%13%28%23%5%
768
November1st to 15thNight
21%13%32%24%8%
760
16th to endNight
25%18%29%20%6%
780
December1st to 15thNight
28%21%28%18%3
780
16th to endNight
29%21%32%14%2
832
Page generated at 2018-04-24 10:03:04. Version ac04

Copyright 2018 A. Danko


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