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 2017-09-16.

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%
15151
29%
46872
24%
15110
70%
15110
43%
24059

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
54%
719
20%
2452
16%
716
62%
716
30%
1401
January16th to endNight
51%
768
26%
2496
22%
768
60%
768
28%
1501
February1st to 15thNight
50%
698
24%
2283
21%
697
58%
697
28%
1372
February16th to endNight
51%
632
25%
1927
19%
632
60%
632
31%
1136
March1st to 15thNight
54%
720
17%
2020
13%
720
59%
720
30%
1288
March16th to endNight
50%
768
23%
2085
13%
768
57%
768
34%
1252
April1st to 15thNight
51%
719
24%
1799
9%
719
59%
719
37%
1101
April16th to endNight
60%
720
28%
1800
14%
720
65%
720
52%
973
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%
660
43%
1811
37%
660
86%
660
72%
784
October1st to 15thNight
69%
660
34%
1980
31%
660
78%
660
55%
911
October16th to endNight
66%
704
35%
2112
31%
704
74%
704
50%
1040
November1st to 15thNight
65%
700
27%
2225
24%
700
72%
700
40%
1171
November16th to endNight
58%
720
23%
2490
23%
720
63%
720
32%
1363
December1st to 15thNight
46%
720
21%
2520
15%
720
56%
720
24%
1519
December16th to endNight
44%
768
22%
2688
16%
768
53%
768
23%
1654

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
7%212212235%66%
47883
Night
9%312213346%61%
47061
TransparencyDay
20%38%19%25%21%
47566
Night
23%49%20%23%18%
46878
SeeingDay
9%5%15%24%27%18%
5886
Night
9%416%35%29%4
15159

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
16%4233235%47%46%
1483
16th to endDay
18%6%13314336%47%
1728
February1st to 15thDay
16%5%23223248%48%
1576
16th to endDay
15%5%2332345%8%47%
1546
March1st to 15thDay
16%42432445%7%43%
1938
16th to endDay
12%5%234233410%48%
2139
April1st to 15thDay
11%32442336%9%47%
2149
16th to endDay
5%312222446%64%
2160
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%
1835
October1st to 15thDay
6%22212335%69%
1650
16th to endDay
9%313312236%62%
1760
November1st to 15thDay
9%21332445%7%54%
1631
16th to endDay
13%414224346%52%
1467
December1st to 15thDay
20%5%2321434447%
1440
16th to endDay
21%5%23324336%42%
1536
January1st to 15thNight
14%5%1331335%8%48%
2452
16th to endNight
17%5%2432333449%
2496
February1st to 15thNight
16%423424448%44%
2276
16th to endNight
14%32332445%7%48%
1927
March1st to 15thNight
15%32442446%8%42%
2020
16th to endNight
12%42332345%7%50%
2085
April1st to 15thNight
7%2244345%6%9%49%
1799
16th to endNight
5%213213346%65%
1800
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%
1811
October1st to 15thNight
4111212245%71%
1980
16th to endNight
7%112212346%64%
2112
November1st to 15thNight
9%31232346%8%55%
2225
16th to endNight
13%41231335%7%51%
2490
December1st to 15thNight
21%423323346%44%
2520
16th to endNight
21%5%22324446%43%
2688

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
36%5%14%19%17%7%
1483
16th to endDay
38%49%16%18%12%
1728
February1st to 15thDay
35%313%19%21%5%
1576
16th to endDay
33%5%10%29%16%4
1546
March1st to 15thDay
37%6%13%20%13%8%
1938
16th to endDay
32%6%14%20%19%6%
2139
April1st to 15thDay
32%5%13%21%20%5%
2149
16th to endDay
20%5%12%24%26%11%
2160
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%32%26%
1835
October1st to 15thDay
18%37%21%29%19%
1650
16th to endDay
24%37%25%26%12%
1760
November1st to 15thDay
26%5%14%29%16%8%
1631
16th to endDay
32%6%10%22%19%9%
1467
December1st to 15thDay
40%5%8%18%21%5%
1440
16th to endDay
42%5%9%18%17%6%
1536
January1st to 15thNight
33%5%13%22%16%8%
2452
16th to endNight
38%37%16%19%14%
2496
February1st to 15thNight
37%410%20%18%8%
2288
16th to endNight
33%6%11%23%20%5%
1927
March1st to 15thNight
36%6%13%18%16%7%
2020
16th to endNight
32%5%13%23%18%6%
2085
April1st to 15thNight
28%7%14%24%16%8%
1799
16th to endNight
18%5%11%26%28%9%
1800
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
8%25%17%33%32%
1811
October1st to 15thNight
15%37%18%32%21%
1980
16th to endNight
19%48%23%26%17%
2112
November1st to 15thNight
24%6%14%28%16%9%
2225
16th to endNight
31%49%23%21%10%
2490
December1st to 15thNight
39%410%16%22%6%
2520
16th to endNight
39%5%9%16%20%6%
2688

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
27%9%23%21%17%1
111
16th to endDay
20%6%20%21%14%16%
256
February1st to 15thDay
18%9%19%22%19%10%
236
16th to endDay
18%9%22%24%14%11%
233
March1st to 15thDay
20%10%23%19%15%10%
270
16th to endDay
16%18%18%28%14%4
288
April1st to 15thDay
13%14%25%23%13%9%
269
16th to endDay
8%15%21%30%14%9%
270
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
3210%26%28%28%
258
October1st to 15thDay
7%5%14%26%24%21%
255
16th to endDay
13%6%15%26%27%11%
272
November1st to 15thDay
13%318%12%39%11%
137
16th to endDay
10%7%26%33%21%
65
December1st to 15thDay
40%8%18%20%13%
60
16th to endDay
17%26%31%20%4
64
January1st to 15thNight
16%419%35%20%4
720
16th to endNight
18%318%31%20%5%
768
February1st to 15thNight
16%8%18%36%18%1
704
16th to endNight
15%5%22%36%17%3
632
March1st to 15thNight
15%418%35%22%3
720
16th to endNight
13%7%22%34%20%1
768
April1st to 15thNight
8%7%25%37%17%2
719
16th to endNight
6%7%21%37%23%3
720
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%32%41%10%
660
October1st to 15thNight
6%6%15%33%31%6%
660
16th to endNight
8%218%31%32%7%
704
November1st to 15thNight
9%316%35%32%3
700
16th to endNight
13%416%39%22%3
720
December1st to 15thNight
22%418%32%17%4
720
16th to endNight
21%6%20%31%17%1
768
Page generated at 2017-09-17 09:05:47. Version ac04

Copyright 2017 A. Danko


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