Orland
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orland 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
64%
16019
29%
49550
24%
15978
70%
15978
43%
25513

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
53%
779
19%
2657
16%
776
61%
776
29%
1559
January16th to endNight
51%
832
25%
2704
21%
832
59%
832
27%
1653
February1st to 15thNight
50%
758
27%
2478
22%
757
61%
757
30%
1439
February16th to endNight
52%
684
26%
2086
20%
684
61%
684
33%
1209
March1st to 15thNight
53%
780
18%
2188
13%
780
58%
780
30%
1407
March16th to endNight
50%
832
23%
2259
13%
832
57%
832
35%
1356
April1st to 15thNight
51%
779
25%
1949
10%
779
58%
779
37%
1198
April16th to endNight
61%
744
29%
1860
14%
744
66%
744
52%
1000
May1st to 15thNight
59%
515
30%
1595
21%
515
66%
515
54%
732
May16th to endNight
70%
375
26%
1496
28%
374
77%
374
46%
612
June1st to 15thNight
68%
360
27%
1440
28%
360
78%
360
46%
592
June16th to endNight
78%
360
35%
1440
43%
360
87%
360
68%
468
July1st to 15thNight
87%
340
34%
1360
45%
340
90%
340
74%
417
July16th to endNight
91%
520
41%
1549
40%
487
93%
487
86%
535
August1st to 15thNight
89%
538
39%
1611
33%
535
91%
535
76%
633
August16th to endNight
93%
747
46%
1893
30%
747
94%
747
87%
804
September1st to 15thNight
90%
720
43%
1800
29%
720
92%
720
82%
800
September16th to endNight
82%
716
45%
1965
38%
716
86%
716
73%
843
October1st to 15thNight
68%
720
33%
2160
30%
720
77%
720
56%
972
October16th to endNight
69%
768
38%
2304
35%
768
76%
768
52%
1116
November1st to 15thNight
63%
760
26%
2416
23%
760
70%
760
38%
1294
November16th to endNight
57%
780
24%
2698
23%
780
63%
780
31%
1502
December1st to 15thNight
49%
780
22%
2730
17%
780
58%
780
27%
1591
December16th to endNight
45%
832
23%
2912
17%
832
55%
832
24%
1781

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
8%312212236%65%
49962
Night
9%312213346%61%
49739
TransparencyDay
21%38%19%25%20%
49645
Night
23%49%20%23%18%
49556
SeeingDay
9%6%15%24%26%17%
6588
Night
10%416%35%29%4
16027

By Month

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
17%42342345%6%43%
1607
16th to endDay
18%6%14314336%45%
1872
February1st to 15thDay
15%423223248%50%
1711
16th to endDay
14%5%2332245%8%47%
1673
March1st to 15thDay
16%5%2432445%7%42%
2099
16th to endDay
12%5%134234410%48%
2317
April1st to 15thDay
12%32442336%9%47%
2329
16th to endDay
5%312222446%64%
2214
May1st to 15thDay
2212212247%70%
2351
16th to endDay
4212312347%65%
2615
June1st to 15thDay
4212213336%68%
2520
16th to endDay
2112383%
2520
July1st to 15thDay
1112288%
2520
16th to endDay
111190%
2510
August1st to 15thDay
1112386%
2340
16th to endDay
112389%
2309
September1st to 15thDay
1112484%
2160
16th to endDay
21112125%79%
1992
October1st to 15thDay
5%2211223472%
1800
16th to endDay
8%313311236%64%
1920
November1st to 15thDay
11%31332445%7%53%
1770
16th to endDay
13%5%14224346%50%
1589
December1st to 15thDay
18%5%1321434449%
1560
16th to endDay
20%5%24324337%42%
1664
January1st to 15thNight
15%5%1331335%8%46%
2657
16th to endNight
17%5%24323335%47%
2704
February1st to 15thNight
15%423424447%47%
2471
16th to endNight
13%32332445%6%49%
2086
March1st to 15thNight
15%425%42445%8%42%
2188
16th to endNight
12%42332445%7%50%
2259
April1st to 15thNight
8%21443446%9%49%
1949
16th to endNight
5%213213346%65%
1860
May1st to 15thNight
3212212345%69%
1595
16th to endNight
311222346%7%63%
1496
June1st to 15thNight
3212223345%69%
1440
16th to endNight
11111222381%
1440
July1st to 15thNight
1111112384%
1440
16th to endNight
12289%
1656
August1st to 15thNight
1111112285%
1620
16th to endNight
112388%
1893
September1st to 15thNight
11111487%
1800
16th to endNight
1111123481%
1965
October1st to 15thNight
411212245%73%
2160
16th to endNight
7%111212346%66%
2304
November1st to 15thNight
9%31232446%8%54%
2416
16th to endNight
14%41331335%7%50%
2698
December1st to 15thNight
20%423323346%47%
2730
16th to endNight
20%5%23324447%42%
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
38%5%13%19%15%6%
1607
16th to endDay
39%49%16%18%11%
1872
February1st to 15thDay
33%312%19%24%6%
1711
16th to endDay
33%5%10%28%17%4
1673
March1st to 15thDay
38%6%12%20%13%8%
2099
16th to endDay
32%6%14%20%19%5%
2317
April1st to 15thDay
33%5%13%22%20%5%
2329
16th to endDay
20%5%11%24%27%11%
2214
May1st to 15thDay
14%39%23%32%16%
2351
16th to endDay
18%412%25%25%12%
2619
June1st to 15thDay
17%5%9%21%24%22%
2520
16th to endDay
7%1415%35%34%
2520
July1st to 15thDay
41311%31%47%
2371
16th to endDay
5%1211%23%56%
2354
August1st to 15thDay
6%1314%31%43%
2324
16th to endDay
41214%35%41%
2309
September1st to 15thDay
6%1312%34%40%
2160
16th to endDay
8%26%24%33%24%
1992
October1st to 15thDay
16%37%20%29%23%
1800
16th to endDay
22%37%25%27%13%
1920
November1st to 15thDay
27%5%14%29%15%7%
1770
16th to endDay
33%6%10%21%19%8%
1589
December1st to 15thDay
37%5%8%17%23%7%
1560
16th to endDay
41%5%9%19%17%6%
1664
January1st to 15thNight
35%5%13%22%15%8%
2657
16th to endNight
39%47%16%18%13%
2704
February1st to 15thNight
34%49%20%20%10%
2483
16th to endNight
32%5%11%23%21%5%
2086
March1st to 15thNight
37%6%13%19%16%7%
2188
16th to endNight
32%5%12%24%18%6%
2259
April1st to 15thNight
28%6%14%25%15%8%
1949
16th to endNight
18%5%10%26%29%9%
1860
May1st to 15thNight
14%49%24%30%16%
1596
16th to endNight
15%415%28%22%12%
1496
June1st to 15thNight
16%5%11%24%23%19%
1440
16th to endNight
9%5%15%31%37%
1440
July1st to 15thNight
6%1210%29%49%
1360
16th to endNight
3212%23%56%
1549
August1st to 15thNight
7%1215%29%42%
1611
16th to endNight
41314%35%40%
1893
September1st to 15thNight
5%1211%31%46%
1800
16th to endNight
7%25%18%33%31%
1965
October1st to 15thNight
14%37%17%30%26%
2160
16th to endNight
18%38%22%26%20%
2304
November1st to 15thNight
25%6%14%28%15%8%
2416
16th to endNight
32%48%23%20%9%
2698
December1st to 15thNight
37%49%16%22%9%
2730
16th to endNight
39%5%9%17%21%6%
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
26%8%20%20%18%4
145
16th to endDay
21%6%19%22%15%14%
304
February1st to 15thDay
16%9%20%23%19%9%
281
16th to endDay
15%10%22%26%14%10%
282
March1st to 15thDay
21%10%23%18%15%10%
330
16th to endDay
16%16%17%29%15%4
352
April1st to 15thDay
16%13%23%24%15%7%
329
16th to endDay
9%14%20%29%16%9%
288
May1st to 15thDay
5%6%25%29%22%9%
288
16th to endDay
6%5%15%21%27%23%
330
June1st to 15thDay
45%16%27%29%16%
315
16th to endDay
2111%28%35%20%
315
July1st to 15thDay
1421%42%29%
305
16th to endDay
423%43%27%
327
August1st to 15thDay
27%20%40%28%
315
16th to endDay
15%18%37%36%
332
September1st to 15thDay
26%21%37%32%
315
16th to endDay
4112%28%27%24%
315
October1st to 15thDay
6%9%16%24%23%19%
315
16th to endDay
10%5%13%24%27%17%
336
November1st to 15thDay
19%219%15%33%9%
186
16th to endDay
14%7%18%38%20%1
97
December1st to 15thDay
28%7%12%21%18%11%
90
16th to endDay
14%123%29%21%9%
96
January1st to 15thNight
18%418%34%20%3
780
16th to endNight
18%318%32%21%5%
832
February1st to 15thNight
14%8%19%36%18%2
764
16th to endNight
14%5%22%36%17%3
684
March1st to 15thNight
15%5%17%35%22%3
780
16th to endNight
13%7%22%35%20%1
832
April1st to 15thNight
9%7%25%37%17%2
779
16th to endNight
6%6%21%38%24%3
744
May1st to 15thNight
4427%35%25%2
516
16th to endNight
35%15%36%36%2
375
June1st to 15thNight
3319%47%24%1
360
16th to endNight
1116%43%36%1
360
July1st to 15thNight
27%40%48%2
340
16th to endNight
6%35%51%5%
520
August1st to 15thNight
15%33%51%6%
538
16th to endNight
1432%57%5%
747
September1st to 15thNight
11433%51%7%
720
16th to endNight
2210%34%39%10%
716
October1st to 15thNight
5%6%16%33%30%6%
720
16th to endNight
7%216%31%32%8%
768
November1st to 15thNight
10%316%34%31%3
760
16th to endNight
13%416%38%22%3
780
December1st to 15thNight
21%318%31%18%5%
780
16th to endNight
20%6%20%30%19%1
832
Page generated at 2018-04-24 07:03:00. Version ac04

Copyright 2018 A. Danko


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