Redwood Loop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Redwood Loop 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
44%
14963
12%
47413
11%
14928
46%
14928
16%
34775

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
28%
718
7%
2506
7%
716
30%
716
9%
2046
January16th to endNight
37%
768
11%
2497
12%
768
39%
768
13%
1924
February1st to 15thNight
35%
696
6%
2288
6%
696
36%
696
10%
1887
February16th to endNight
32%
632
8%
2032
6%
632
34%
632
9%
1673
March1st to 15thNight
29%
720
4%
1982
3%
720
30%
720
10%
1691
March16th to endNight
26%
768
5%
2112
4%
768
26%
768
8%
1840
April1st to 15thNight
33%
719
6%
1808
3%
719
33%
719
11%
1545
April16th to endNight
45%
573
11%
1653
7%
573
47%
573
15%
1270
May1st to 15thNight
42%
467
10%
1547
9%
467
44%
467
17%
1087
May16th to endNight
45%
375
7%
1496
9%
374
46%
374
11%
1099
June1st to 15thNight
50%
360
7%
1440
11%
360
52%
360
16%
972
June16th to endNight
60%
360
11%
1440
17%
360
61%
360
21%
871
July1st to 15thNight
72%
340
17%
1360
26%
340
74%
340
33%
676
July16th to endNight
78%
463
22%
1496
27%
434
80%
434
42%
733
August1st to 15thNight
73%
538
20%
1611
18%
535
74%
535
35%
899
August16th to endNight
71%
634
27%
1780
21%
634
72%
634
41%
990
September1st to 15thNight
74%
720
26%
1800
17%
720
75%
720
51%
1024
September16th to endNight
60%
716
23%
1998
19%
716
61%
716
30%
1290
October1st to 15thNight
53%
720
17%
2160
17%
720
56%
720
26%
1411
October16th to endNight
40%
768
14%
2304
14%
768
42%
768
16%
1729
November1st to 15thNight
35%
700
8%
2375
8%
700
37%
700
10%
1944
November16th to endNight
35%
720
7%
2520
7%
720
36%
720
11%
1976
December1st to 15thNight
37%
720
10%
2520
10%
720
39%
720
12%
1930
December16th to endNight
26%
768
7%
2688
6%
768
28%
768
7%
2268

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
23%7%35%423347%32%
48349
Night
26%8%35%423346%31%
47589
Cloud CoverDay
25%7%35%423346%32%
48349
Night
26%8%35%423345%32%
47593
TransparencyDay
52%7%12%15%8%2
48028
Night
54%6%11%15%9%3
47414
SeeingDay
26%5%23%28%13%2
5958
Night
30%413%25%22%3
14974

By Month

Percentage Cloud Cover NW (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
39%9%3432332421%
1432
16th to endDay
32%7%34323435%28%
1725
February1st to 15thDay
37%8%36%5%45%245%15%
1576
16th to endDay
34%10%46%42443420%
1442
March1st to 15thDay
42%9%35%5%3335%411%
1977
16th to endDay
37%10%46%6%34335%14%
2112
April1st to 15thDay
31%10%47%5%33345%17%
2140
16th to endDay
26%9%35%42445%8%23%
2304
May1st to 15thDay
20%9%46%423347%31%
2403
16th to endDay
24%8%36%43346%10%25%
2615
June1st to 15thDay
23%7%45%5%24446%32%
2520
16th to endDay
16%6%35%42335%8%40%
2520
July1st to 15thDay
8%5%13313237%59%
2520
16th to endDay
9%423213248%56%
2568
August1st to 15thDay
6%7%25%422349%49%
2340
16th to endDay
8%5%23322448%54%
2420
September1st to 15thDay
6%323213348%60%
2160
16th to endDay
17%6%35%424346%41%
1961
October1st to 15thDay
20%7%25%433447%34%
1800
16th to endDay
27%8%245%2345%5%29%
1918
November1st to 15thDay
37%8%36%5%23445%18%
1480
16th to endDay
33%8%35%425%35%5%20%
1440
December1st to 15thDay
32%7%36%6%25%34421%
1440
16th to endDay
41%11%36%32433416%
1536
January1st to 15thNight
38%10%36%42332420%
2506
16th to endNight
30%10%45%423335%26%
2497
February1st to 15thNight
34%8%36%5%24445%18%
2276
16th to endNight
32%11%36%42444420%
2032
March1st to 15thNight
39%10%36%41333418%
1982
16th to endNight
38%10%47%6%2334414%
2108
April1st to 15thNight
31%11%45%5%3443420%
1808
16th to endNight
24%8%35%5%34447%29%
1653
May1st to 15thNight
19%10%35%6%23435%35%
1547
16th to endNight
25%9%45%42345%8%26%
1496
June1st to 15thNight
19%8%36%42335%7%35%
1440
16th to endNight
15%8%133235%5%7%43%
1440
July1st to 15thNight
7%41331335%6%57%
1440
16th to endNight
6%5%1321235%9%57%
1599
August1st to 15thNight
5%7%2332345%10%51%
1620
16th to endNight
8%6%23212349%54%
1780
September1st to 15thNight
7%313212336%62%
1800
16th to endNight
15%7%24323446%45%
1998
October1st to 15thNight
19%6%25%312346%44%
2160
16th to endNight
27%8%36%5%2333431%
2304
November1st to 15thNight
36%7%35%43445%5%19%
2375
16th to endNight
31%7%36%6%2434425%
2520
December1st to 15thNight
31%9%35%423335%26%
2520
16th to endNight
41%9%36%42434417%
2688

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
41%8%3432333421%
1432
16th to endDay
34%8%24422345%26%
1725
February1st to 15thDay
38%7%37%6%35%34415%
1576
16th to endDay
36%11%46%41433319%
1442
March1st to 15thDay
44%10%35%5%2333411%
1977
16th to endDay
41%10%37%6%2323413%
2112
April1st to 15thDay
34%10%47%6%34345%14%
2140
16th to endDay
28%9%36%5%2435%7%22%
2304
May1st to 15thDay
22%9%36%5%23446%31%
2403
16th to endDay
27%7%36%43345%9%24%
2615
June1st to 15thDay
25%7%36%42335%6%31%
2520
16th to endDay
17%6%35%423348%39%
2520
July1st to 15thDay
9%423213236%60%
2520
16th to endDay
10%423213236%59%
2568
August1st to 15thDay
6%7%24423447%52%
2340
16th to endDay
8%413323346%56%
2420
September1st to 15thDay
6%312313346%62%
2160
16th to endDay
17%5%25%334346%41%
1961
October1st to 15thDay
21%6%25%5%33445%35%
1800
16th to endDay
27%9%25%5%23445%29%
1918
November1st to 15thDay
39%8%35%5%34445%17%
1480
16th to endDay
34%7%45%42445%5%19%
1440
December1st to 15thDay
33%8%27%6%2434421%
1440
16th to endDay
42%11%3442333415%
1536
January1st to 15thNight
40%9%25%5%2322420%
2506
16th to endNight
31%9%35%413335%26%
2497
February1st to 15thNight
34%9%46%5%34336%18%
2276
16th to endNight
33%10%36%5%2344420%
2032
March1st to 15thNight
40%9%35%42333418%
1982
16th to endNight
39%10%36%5%2433415%
2112
April1st to 15thNight
32%11%46%5%3333420%
1808
16th to endNight
24%7%35%435%446%30%
1653
May1st to 15thNight
19%10%36%424435%35%
1547
16th to endNight
24%10%344235%49%27%
1496
June1st to 15thNight
19%7%35%42435%7%36%
1440
16th to endNight
16%6%14312348%45%
1440
July1st to 15thNight
7%314223245%61%
1440
16th to endNight
6%323212238%63%
1599
August1st to 15thNight
45%24324348%55%
1620
16th to endNight
8%5%23222438%57%
1780
September1st to 15thNight
7%312312236%64%
1800
16th to endNight
15%6%24423347%46%
1998
October1st to 15thNight
19%5%24413335%45%
2160
16th to endNight
28%8%35%5%1333430%
2304
November1st to 15thNight
37%6%35%5%2445%5%18%
2375
16th to endNight
32%7%37%42433425%
2520
December1st to 15thNight
32%8%34423335%26%
2520
16th to endNight
42%9%25%42433417%
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
68%39%5%9%3
1432
16th to endDay
59%6%9%10%8%6%
1725
February1st to 15thDay
72%5%9%8%21
1576
16th to endDay
69%6%8%9%5%1
1442
March1st to 15thDay
75%6%7%7%3
1977
16th to endDay
75%6%7%8%2
2112
April1st to 15thDay
70%7%11%8%2
2140
16th to endDay
60%9%13%11%41
2304
May1st to 15thDay
53%6%15%14%8%1
2403
16th to endDay
56%10%15%13%2
2619
June1st to 15thDay
52%9%15%17%4
2520
16th to endDay
42%9%19%20%5%2
2520
July1st to 15thDay
27%6%17%24%19%4
2371
16th to endDay
26%5%14%29%19%5%
2408
August1st to 15thDay
32%9%18%27%9%3
2324
16th to endDay
28%8%16%25%18%3
2420
September1st to 15thDay
23%6%16%26%19%8%
2160
16th to endDay
43%7%13%20%12%1
1961
October1st to 15thDay
48%7%12%15%13%2
1800
16th to endDay
54%9%10%14%9%1
1918
November1st to 15thDay
67%9%10%10%2
1480
16th to endDay
65%7%8%6%7%4
1440
December1st to 15thDay
65%6%10%9%8%
1440
16th to endDay
73%48%8%41
1536
January1st to 15thNight
69%47%7%7%3
2506
16th to endNight
61%47%9%9%6%
2497
February1st to 15thNight
67%6%9%10%41
2288
16th to endNight
67%6%8%9%6%1
2032
March1st to 15thNight
70%6%8%10%4
1982
16th to endNight
73%5%9%8%2
2112
April1st to 15thNight
67%8%11%8%3
1808
16th to endNight
55%9%12%15%5%1
1653
May1st to 15thNight
50%7%14%17%7%1
1548
16th to endNight
54%10%16%12%41
1496
June1st to 15thNight
48%8%18%20%3
1440
16th to endNight
37%9%20%24%5%2
1440
July1st to 15thNight
26%6%14%26%19%6%
1360
16th to endNight
23%415%25%23%7%
1496
August1st to 15thNight
27%8%16%30%11%5%
1611
16th to endNight
26%6%13%29%18%6%
1780
September1st to 15thNight
22%5%13%25%21%11%
1800
16th to endNight
38%5%14%21%15%4
1998
October1st to 15thNight
41%6%11%20%14%5%
2160
16th to endNight
57%49%14%10%3
2304
November1st to 15thNight
65%7%10%10%4
2375
16th to endNight
62%6%8%8%8%5%
2520
December1st to 15thNight
61%5%10%13%9%
2520
16th to endNight
71%6%8%7%41
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
36%5%30%18%10%
60
16th to endDay
38%5%15%15%18%6%
253
February1st to 15thDay
42%6%16%22%11%
236
16th to endDay
40%8%21%23%4
215
March1st to 15thDay
51%10%17%15%4
270
16th to endDay
44%6%26%17%4
288
April1st to 15thDay
37%9%23%17%9%1
269
16th to endDay
34%7%25%22%7%1
270
May1st to 15thDay
27%9%27%24%10%
288
16th to endDay
22%7%26%26%15%3
330
June1st to 15thDay
25%130%28%12%1
315
16th to endDay
14%327%40%12%
315
July1st to 15thDay
12%224%42%14%3
305
16th to endDay
8%126%42%18%1
327
August1st to 15thDay
9%119%44%22%3
315
16th to endDay
7%319%41%22%5%
332
September1st to 15thDay
7%324%35%24%4
315
16th to endDay
19%6%24%32%16%
315
October1st to 15thDay
25%7%26%26%12%2
315
16th to endDay
35%418%23%13%4
336
November1st to 15thDay
36%8%24%25%21
105
16th to endDay
36%10%18%21%13%
60
December1st to 15thDay
60%6%21%11%
60
16th to endDay
34%15%18%25%41
64
January1st to 15thNight
42%6%14%20%15%1
720
16th to endNight
34%414%24%18%3
768
February1st to 15thNight
39%312%24%18%2
704
16th to endNight
39%7%15%18%18%1
632
March1st to 15thNight
42%8%12%20%14%1
720
16th to endNight
41%7%14%21%13%1
768
April1st to 15thNight
37%5%15%20%17%2
719
16th to endNight
28%415%27%21%3
573
May1st to 15thNight
25%421%26%19%2
468
16th to endNight
29%312%25%25%3
375
June1st to 15thNight
23%115%33%23%3
360
16th to endNight
20%112%32%30%2
360
July1st to 15thNight
9%10%37%39%2
340
16th to endNight
8%6%42%37%4
463
August1st to 15thNight
10%6%30%43%9%
538
16th to endNight
12%19%29%38%8%
634
September1st to 15thNight
9%9%28%41%10%
720
16th to endNight
19%111%29%31%5%
716
October1st to 15thNight
22%215%29%24%5%
720
16th to endNight
33%314%20%21%6%
768
November1st to 15thNight
38%415%24%15%1
700
16th to endNight
33%7%15%24%15%2
720
December1st to 15thNight
35%6%13%25%16%1
720
16th to endNight
45%7%13%20%12%
768
Page generated at 2017-11-01 14:23:38. Version ac04

Copyright 2017 A. Danko


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