DeJoVu Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the DeJoVu Observatory clear sky chart from 2005-11-05 to 2017-10-31.

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%
16395
12%
47182
6%
16348
34%
16348
19%
33886

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
21%
900
10%
2638
6%
895
25%
895
12%
2079
January16th to endNight
16%
960
10%
2649
3%
960
22%
960
12%
2117
February1st to 15thNight
25%
879
12%
2288
2%
875
31%
875
17%
1684
February16th to endNight
26%
753
13%
2015
4%
753
33%
753
16%
1514
March1st to 15thNight
26%
630
14%
2070
9%
630
32%
630
16%
1460
March16th to endNight
30%
576
16%
2065
11%
576
41%
576
17%
1382
April1st to 15thNight
29%
539
15%
1797
11%
539
37%
539
18%
1229
April16th to endNight
30%
540
13%
1629
8%
540
35%
540
17%
1171
May1st to 15thNight
26%
540
12%
1440
4%
540
31%
540
19%
1057
May16th to endNight
37%
563
10%
1498
4%
561
40%
561
25%
1020
June1st to 15thNight
37%
540
8%
1329
4%
540
41%
540
29%
924
June16th to endNight
43%
540
8%
1260
4%
540
45%
540
31%
868
July1st to 15thNight
48%
510
11%
1190
6%
510
50%
510
41%
754
July16th to endNight
50%
564
15%
1414
7%
531
51%
531
37%
848
August1st to 15thNight
56%
539
19%
1512
12%
536
60%
536
39%
885
August16th to endNight
44%
573
21%
1785
16%
573
53%
573
33%
1017
September1st to 15thNight
49%
540
17%
1800
14%
540
57%
540
30%
1037
September16th to endNight
34%
606
15%
1968
12%
606
40%
606
23%
1251
October1st to 15thNight
28%
720
17%
2160
9%
720
35%
720
21%
1461
October16th to endNight
20%
768
11%
2387
5%
768
27%
768
14%
1794
November1st to 15thNight
20%
855
12%
2431
5%
855
25%
855
15%
1811
November16th to endNight
19%
900
10%
2520
5%
900
24%
900
11%
2047
December1st to 15thNight
14%
900
6%
2520
3%
900
18%
900
9%
2083
December16th to endNight
14%
960
8%
2817
3%
960
19%
960
7%
2393

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
15%9%47%6%35%5%5%6%31%
48578
Night
13%10%47%6%35%5%5%6%31%
47339
Cloud CoverDay
15%9%47%6%35%5%5%6%31%
48589
Night
13%10%47%6%35%5%5%6%31%
47343
Cloud CoverDay
15%9%46%6%35%45%6%31%
48587
Night
14%10%47%6%3445%6%31%
47343
TransparencyDay
52%413%21%8%
48253
Night
52%412%21%8%
47182
SeeingDay
21%13%31%20%10%3
6359
Night
19%12%31%25%9%1
16396

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
10%12%8%10%7%5%6%7%6%6%18%
1297
16th to endDay
11%13%5%13%9%47%9%6%5%14%
1574
February1st to 15thDay
8%13%6%7%6%47%6%6%5%25%
1575
16th to endDay
10%11%7%8%9%36%446%26%
1457
March1st to 15thDay
10%11%5%8%6%33446%33%
1888
16th to endDay
16%11%47%5%24345%31%
2158
April1st to 15thDay
13%10%36%6%35%5%5%6%33%
2151
16th to endDay
20%10%36%5%2345%6%30%
2330
May1st to 15thDay
19%10%47%6%34435%29%
2511
16th to endDay
18%7%35%5%35%45%7%33%
2617
June1st to 15thDay
16%6%36%5%35%6%5%8%32%
2628
16th to endDay
18%6%35%435%5%6%9%31%
2700
July1st to 15thDay
12%5%24425%5%5%8%42%
2700
16th to endDay
10%5%25%5%35%5%6%8%41%
2658
August1st to 15thDay
8%6%25%5%35%6%7%8%39%
2436
16th to endDay
14%5%145%345%5%7%42%
2417
September1st to 15thDay
13%7%245%345%5%7%40%
2160
16th to endDay
20%7%35%433446%36%
1978
October1st to 15thDay
18%10%35%43435%7%32%
1800
16th to endDay
22%16%5%6%42433426%
1835
November1st to 15thDay
16%14%6%7%5%24445%27%
1426
16th to endDay
18%13%5%14%10%45%43416%
1440
December1st to 15thDay
12%15%7%11%11%45%7%5%414%
1440
16th to endDay
15%19%10%13%7%4443411%
1402
January1st to 15thNight
11%12%6%10%9%5%5%7%6%5%19%
2638
16th to endNight
11%12%7%12%8%45%6%7%5%17%
2649
February1st to 15thNight
8%10%5%8%6%47%6%5%7%28%
2285
16th to endNight
9%10%5%9%8%46%5%5%6%27%
2015
March1st to 15thNight
11%10%5%8%6%35%5%5%6%31%
2058
16th to endNight
14%9%37%5%2445%6%35%
2065
April1st to 15thNight
15%11%46%5%23336%34%
1797
16th to endNight
19%10%35%5%36%446%30%
1629
May1st to 15thNight
20%8%35%5%335%5%5%32%
1440
16th to endNight
14%7%344245%5%8%38%
1496
June1st to 15thNight
16%5%35%5%345%5%6%39%
1329
16th to endNight
14%5%24425%6%7%8%38%
1260
July1st to 15thNight
9%4233235%5%9%49%
1260
16th to endNight
7%425%325%45%9%50%
1509
August1st to 15thNight
9%31322446%8%53%
1521
16th to endNight
12%5%23323347%52%
1785
September1st to 15thNight
10%5%25%424447%49%
1800
16th to endNight
16%7%35%42345%6%40%
1968
October1st to 15thNight
17%11%24434346%38%
2160
16th to endNight
20%15%45%5%24446%26%
2387
November1st to 15thNight
15%15%49%5%3345%6%27%
2431
16th to endNight
16%12%6%12%10%44435%20%
2520
December1st to 15thNight
12%14%6%12%10%47%7%6%5%13%
2520
16th to endNight
15%19%8%12%9%4444313%
2817

Percentage Cloud Cover SW (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
9%12%8%10%7%5%6%7%6%6%18%
1297
16th to endDay
11%13%5%13%8%47%9%6%5%14%
1574
February1st to 15thDay
8%13%6%7%6%47%7%6%5%25%
1575
16th to endDay
10%11%6%8%9%36%446%26%
1457
March1st to 15thDay
10%12%5%8%6%34446%33%
1899
16th to endDay
16%11%47%5%24345%31%
2158
April1st to 15thDay
13%10%36%6%35%45%7%33%
2151
16th to endDay
20%10%36%5%2445%6%30%
2330
May1st to 15thDay
20%10%47%6%34435%29%
2511
16th to endDay
18%7%35%5%35%447%33%
2617
June1st to 15thDay
16%6%36%5%35%6%5%8%32%
2628
16th to endDay
18%6%35%435%5%6%9%31%
2700
July1st to 15thDay
12%5%24426%5%5%8%42%
2700
16th to endDay
9%5%25%5%35%5%6%8%41%
2658
August1st to 15thDay
8%6%25%5%35%6%6%8%39%
2436
16th to endDay
13%5%245%345%6%7%42%
2417
September1st to 15thDay
13%7%244345%5%7%40%
2160
16th to endDay
20%7%25%434446%36%
1978
October1st to 15thDay
19%10%35%43435%7%32%
1800
16th to endDay
23%15%5%6%42433426%
1835
November1st to 15thDay
16%14%6%7%5%25%445%27%
1426
16th to endDay
17%13%5%14%10%45%43416%
1440
December1st to 15thDay
11%15%7%11%11%45%7%5%5%14%
1440
16th to endDay
15%19%9%13%7%4443411%
1402
January1st to 15thNight
12%12%6%10%9%5%5%7%6%5%19%
2638
16th to endNight
11%13%7%12%7%45%6%7%5%17%
2649
February1st to 15thNight
8%10%5%8%7%48%6%5%7%27%
2278
16th to endNight
9%11%5%9%9%46%5%5%6%27%
2015
March1st to 15thNight
11%10%5%8%6%35%5%5%6%31%
2070
16th to endNight
14%9%37%5%2445%6%35%
2065
April1st to 15thNight
15%11%5%6%5%23436%34%
1797
16th to endNight
19%10%35%6%36%446%30%
1629
May1st to 15thNight
20%8%35%43445%5%32%
1439
16th to endNight
14%6%344345%5%8%38%
1496
June1st to 15thNight
16%5%25%5%345%5%6%39%
1329
16th to endNight
13%5%24425%5%7%8%38%
1260
July1st to 15thNight
9%4233235%6%9%49%
1260
16th to endNight
7%424325%45%9%50%
1509
August1st to 15thNight
9%3132245%5%8%53%
1521
16th to endNight
12%5%23223347%52%
1785
September1st to 15thNight
10%5%25%424347%48%
1800
16th to endNight
16%7%24423447%40%
1968
October1st to 15thNight
17%11%24334346%37%
2160
16th to endNight
20%14%45%5%24446%26%
2387
November1st to 15thNight
15%15%5%9%6%3335%6%26%
2431
16th to endNight
16%12%6%11%10%44435%20%
2520
December1st to 15thNight
12%14%6%12%10%47%7%5%5%13%
2520
16th to endNight
15%19%8%12%9%4444313%
2817

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
10%13%7%10%6%5%7%7%6%6%18%
1297
16th to endDay
11%13%5%12%8%47%8%7%414%
1574
February1st to 15thDay
8%13%6%7%7%47%6%6%6%25%
1575
16th to endDay
11%12%6%9%8%45%5%46%26%
1457
March1st to 15thDay
10%12%6%8%6%34446%33%
1899
16th to endDay
17%11%47%5%24336%32%
2156
April1st to 15thDay
13%10%35%5%45%45%6%34%
2151
16th to endDay
20%10%46%434446%30%
2330
May1st to 15thDay
21%9%45%7%34445%29%
2511
16th to endDay
19%7%35%5%3445%7%33%
2617
June1st to 15thDay
16%6%35%435%5%5%8%32%
2628
16th to endDay
19%5%35%435%5%6%7%32%
2700
July1st to 15thDay
13%424435%5%5%7%43%
2700
16th to endDay
11%425%5%35%5%5%9%42%
2658
August1st to 15thDay
9%6%25%6%25%5%6%8%39%
2436
16th to endDay
14%5%24425%46%7%42%
2417
September1st to 15thDay
13%6%345%245%47%40%
2160
16th to endDay
21%7%245%23346%36%
1978
October1st to 15thDay
18%12%35%423347%33%
1800
16th to endDay
22%17%5%5%423335%26%
1835
November1st to 15thDay
16%14%6%8%5%24445%27%
1426
16th to endDay
17%13%5%14%10%4433416%
1440
December1st to 15thDay
11%16%7%10%12%46%6%5%414%
1440
16th to endDay
15%18%10%13%8%3443412%
1402
January1st to 15thNight
12%12%6%11%9%5%5%6%6%5%19%
2638
16th to endNight
11%13%7%12%8%45%6%6%5%17%
2649
February1st to 15thNight
8%10%5%9%6%47%6%5%6%27%
2278
16th to endNight
9%11%5%9%8%45%5%5%6%27%
2015
March1st to 15thNight
11%11%48%6%35%45%6%32%
2070
16th to endNight
14%10%37%5%3445%6%34%
2065
April1st to 15thNight
15%11%5%6%5%24346%35%
1797
16th to endNight
19%11%346%35%445%31%
1629
May1st to 15thNight
21%8%35%5%25%45%5%32%
1439
16th to endNight
15%6%34435%46%7%39%
1496
June1st to 15thNight
16%435%5%335%6%5%39%
1329
16th to endNight
15%4245%245%8%7%39%
1260
July1st to 15thNight
9%32432446%10%48%
1260
16th to endNight
7%424325%45%10%49%
1509
August1st to 15thNight
9%31322437%7%53%
1521
16th to endNight
12%5%23223347%52%
1785
September1st to 15thNight
10%5%25%423346%49%
1800
16th to endNight
17%7%2442345%6%40%
1968
October1st to 15thNight
18%10%24424346%37%
2160
16th to endNight
20%15%45%423446%27%
2387
November1st to 15thNight
15%15%5%8%6%23345%27%
2431
16th to endNight
16%12%6%12%10%44425%20%
2520
December1st to 15thNight
12%14%7%11%11%47%7%5%5%13%
2520
16th to endNight
15%19%7%13%8%4444313%
2817

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
64%48%16%6%
1298
16th to endDay
67%5%8%14%4
1574
February1st to 15thDay
56%413%15%9%
1576
16th to endDay
58%311%19%5%
1457
March1st to 15thDay
52%314%18%10%
1899
16th to endDay
55%312%19%6%1
2158
April1st to 15thDay
50%310%19%13%1
2151
16th to endDay
54%210%19%11%1
2330
May1st to 15thDay
57%310%20%6%
2511
16th to endDay
49%411%22%10%
2621
June1st to 15thDay
48%5%14%24%7%
2628
16th to endDay
48%416%22%7%
2700
July1st to 15thDay
37%414%29%12%
2541
16th to endDay
39%5%16%27%10%
2490
August1st to 15thDay
40%5%15%28%9%1
2421
16th to endDay
39%417%26%11%
2417
September1st to 15thDay
41%415%30%8%
2160
16th to endDay
49%418%23%4
1978
October1st to 15thDay
51%415%20%8%
1800
16th to endDay
62%410%16%5%
1835
November1st to 15thDay
57%414%15%7%
1426
16th to endDay
70%48%9%6%
1440
December1st to 15thDay
68%410%14%2
1440
16th to endDay
76%17%11%3
1402
January1st to 15thNight
64%38%18%4
2638
16th to endNight
64%310%16%4
2649
February1st to 15thNight
54%314%17%8%1
2288
16th to endNight
57%310%21%7%
2015
March1st to 15thNight
52%5%12%17%11%1
2070
16th to endNight
49%413%21%8%2
2065
April1st to 15thNight
50%38%21%13%1
1797
16th to endNight
55%39%19%11%1
1629
May1st to 15thNight
52%411%21%9%
1440
16th to endNight
42%6%11%25%12%1
1498
June1st to 15thNight
44%412%26%10%1
1329
16th to endNight
39%6%18%25%8%1
1260
July1st to 15thNight
31%415%34%12%
1190
16th to endNight
31%417%29%14%1
1414
August1st to 15thNight
27%6%17%33%12%1
1512
16th to endNight
32%317%30%14%
1785
September1st to 15thNight
34%417%33%9%
1800
16th to endNight
42%418%27%6%
1968
October1st to 15thNight
47%312%27%8%
2160
16th to endNight
57%5%13%19%5%
2387
November1st to 15thNight
57%312%19%6%
2431
16th to endNight
66%411%11%5%
2520
December1st to 15thNight
68%411%12%2
2520
16th to endNight
74%27%11%3
2817

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
26%21%28%16%6%
90
16th to endDay
25%11%37%21%4
96
February1st to 15thDay
17%25%41%12%3
90
16th to endDay
29%23%32%7%7%
81
March1st to 15thDay
12%21%33%23%8%1
90
16th to endDay
24%14%28%18%11%3
142
April1st to 15thDay
18%14%33%22%9%1
270
16th to endDay
31%15%26%17%7%1
411
May1st to 15thDay
26%17%32%15%6%2
468
16th to endDay
26%12%27%19%9%3
517
June1st to 15thDay
18%17%33%19%7%3
495
16th to endDay
22%12%30%20%10%3
495
July1st to 15thDay
16%9%31%25%11%5%
475
16th to endDay
12%11%31%22%15%6%
515
August1st to 15thDay
14%7%27%29%17%3
493
16th to endDay
19%9%29%23%14%3
457
September1st to 15thDay
17%6%31%26%14%3
315
16th to endDay
29%15%28%17%7%
214
October1st to 15thDay
19%21%35%11%8%3
135
16th to endDay
36%15%31%11%4
144
November1st to 15thDay
22%16%42%13%41
90
16th to endDay
38%13%24%18%31
90
December1st to 15thDay
26%5%48%17%1
90
16th to endDay
28%17%38%12%12
96
January1st to 15thNight
18%16%35%21%7%1
900
16th to endNight
18%16%39%20%4
960
February1st to 15thNight
15%15%34%24%9%1
880
16th to endNight
15%14%33%23%10%1
753
March1st to 15thNight
17%15%32%25%9%
630
16th to endNight
20%11%29%24%11%2
576
April1st to 15thNight
21%11%32%26%8%
539
16th to endNight
25%10%28%26%7%1
540
May1st to 15thNight
23%12%31%23%6%1
540
16th to endNight
18%10%29%30%10%
563
June1st to 15thNight
18%5%32%33%8%
540
16th to endNight
16%8%26%34%13%
540
July1st to 15thNight
11%6%29%33%17%
510
16th to endNight
10%6%28%35%17%1
564
August1st to 15thNight
10%425%36%21%2
539
16th to endNight
14%8%29%30%15%1
573
September1st to 15thNight
13%6%27%31%19%1
540
16th to endNight
19%10%32%24%10%1
606
October1st to 15thNight
26%12%28%22%9%
720
16th to endNight
28%12%31%21%5%
768
November1st to 15thNight
23%15%33%22%41
855
16th to endNight
24%17%33%18%6%
900
December1st to 15thNight
20%16%36%19%6%
900
16th to endNight
25%14%30%21%6%1
960
Page generated at 2017-11-01 16:23:34. Version ac04

Copyright 2017 A. Danko


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