Diamond Trailhead
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Diamond Trailhead clear sky chart from 2005-11-05 to 2017-09-23.

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
28%
14483
8%
46795
5%
14452
31%
14452
11%
36729

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
22%
750
10%
2686
7%
746
27%
746
8%
2220
January16th to endNight
19%
783
7%
2777
4%
783
24%
783
7%
2266
February1st to 15thNight
18%
701
5%
2288
3%
699
22%
699
8%
1914
February16th to endNight
19%
632
9%
2050
4%
632
25%
632
10%
1632
March1st to 15thNight
14%
720
4%
2061
2%
720
16%
720
6%
1823
March16th to endNight
16%
768
4%
2074
2%
768
18%
768
7%
1833
April1st to 15thNight
24%
707
4%
1787
2%
707
25%
707
10%
1527
April16th to endNight
23%
498
5%
1578
4%
498
25%
498
10%
1309
May1st to 15thNight
43%
360
9%
1440
12%
360
45%
360
13%
1038
May16th to endNight
37%
375
5%
1433
7%
374
38%
374
12%
1088
June1st to 15thNight
32%
360
1%
1260
0%
360
32%
360
13%
961
June16th to endNight
36%
360
3%
1260
1%
360
36%
360
11%
964
July1st to 15thNight
62%
340
7%
1190
5%
340
63%
340
29%
679
July16th to endNight
67%
376
12%
1307
17%
354
69%
354
31%
700
August1st to 15thNight
71%
421
13%
1493
17%
419
73%
419
32%
807
August16th to endNight
60%
603
15%
1749
13%
603
61%
603
28%
1122
September1st to 15thNight
57%
720
19%
1800
10%
720
60%
720
37%
1137
September16th to endNight
38%
688
14%
1896
9%
688
40%
688
17%
1427
October1st to 15thNight
30%
660
10%
1980
8%
660
32%
660
15%
1490
October16th to endNight
20%
704
5%
2216
2%
704
24%
704
7%
1872
November1st to 15thNight
10%
700
5%
2450
2%
700
13%
700
4%
2189
November16th to endNight
16%
720
5%
2520
3%
720
20%
720
7%
2086
December1st to 15thNight
13%
737
7%
2620
2%
737
19%
737
7%
2146
December16th to endNight
8%
800
6%
2880
1%
800
13%
800
5%
2499

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
27%14%35%42333425%
48146
Night
27%15%35%42333425%
46946
Cloud CoverDay
28%16%35%42333424%
48146
Night
27%16%3442333425%
46949
TransparencyDay
64%5%9%13%5%1
47801
Night
62%5%10%12%6%1
46795
SeeingDay
34%12%25%19%5%1
6194
Night
36%6%22%20%11%1
14486

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
36%19%3431233417%
1253
16th to endDay
30%20%36%42223419%
1443
February1st to 15thDay
31%20%44313235%18%
1576
16th to endDay
18%25%5%7%5%2334418%
1424
March1st to 15thDay
34%25%46%41222311%
1899
16th to endDay
30%27%5%6%42322211%
2149
April1st to 15thDay
27%25%5%7%5%2332312%
2159
16th to endDay
30%22%5%8%42333212%
2382
May1st to 15thDay
22%15%5%7%5%2345%5%22%
2511
16th to endDay
31%12%45%5%34445%17%
2676
June1st to 15thDay
35%12%36%424345%16%
2700
16th to endDay
33%11%46%5%3333421%
2700
July1st to 15thDay
15%6%25%424345%44%
2700
16th to endDay
17%5%24413446%45%
2772
August1st to 15thDay
15%5%2441335%6%47%
2457
16th to endDay
16%6%15%43345%6%41%
2453
September1st to 15thDay
14%5%3431445%5%46%
2160
16th to endDay
32%9%3432334428%
1899
October1st to 15thDay
33%9%2441333428%
1650
16th to endDay
41%12%25%412225%18%
1653
November1st to 15thDay
47%17%2432231212%
1408
16th to endDay
32%19%3442322319%
1440
December1st to 15thDay
27%19%5%6%31322224%
1338
16th to endDay
31%28%5%6%31121214%
1344
January1st to 15thNight
35%17%25%21234319%
2686
16th to endNight
30%19%35%322337%17%
2777
February1st to 15thNight
29%20%44422346%16%
2276
16th to endNight
20%25%46%5%2233323%
2050
March1st to 15thNight
33%24%36%32332214%
2061
16th to endNight
31%23%45%42333314%
2070
April1st to 15thNight
24%21%45%6%3344418%
1787
16th to endNight
27%16%47%433335%20%
1578
May1st to 15thNight
19%10%25%435%5%47%31%
1439
16th to endNight
23%10%46%5%2445%6%25%
1433
June1st to 15thNight
27%10%46%5%1344427%
1260
16th to endNight
25%7%36%6%43445%27%
1260
July1st to 15thNight
11%314423346%53%
1260
16th to endNight
12%5%22212346%55%
1397
August1st to 15thNight
12%3132135%46%55%
1501
16th to endNight
13%6%143335%5%7%45%
1749
September1st to 15thNight
12%41322335%6%53%
1800
16th to endNight
28%9%34323346%30%
1896
October1st to 15thNight
28%9%25%31344431%
1980
16th to endNight
38%11%35%5%2343317%
2216
November1st to 15thNight
46%17%3441223311%
2450
16th to endNight
31%19%35%42322320%
2520
December1st to 15thNight
28%19%45%42333420%
2620
16th to endNight
32%27%45%31222215%
2880

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
36%20%25%21232418%
1253
16th to endDay
28%22%46%42213419%
1443
February1st to 15thDay
29%23%4432223418%
1576
16th to endDay
17%26%6%6%5%3334418%
1424
March1st to 15thDay
31%29%45%42222311%
1899
16th to endDay
29%30%5%6%42222210%
2149
April1st to 15thDay
26%29%5%5%43333311%
2159
16th to endDay
30%26%46%5%2332312%
2382
May1st to 15thDay
23%18%46%5%2434421%
2511
16th to endDay
33%13%36%5%33445%17%
2676
June1st to 15thDay
38%11%36%334335%15%
2700
16th to endDay
36%10%36%42333421%
2700
July1st to 15thDay
18%5%34424345%42%
2700
16th to endDay
20%423313345%45%
2772
August1st to 15thDay
16%423313347%46%
2457
16th to endDay
17%6%25%4335%46%39%
2453
September1st to 15thDay
16%6%14323345%47%
2160
16th to endDay
32%10%25%32333428%
1899
October1st to 15thDay
34%9%2432332428%
1650
16th to endDay
40%13%35%312225%19%
1653
November1st to 15thDay
45%19%3431222212%
1408
16th to endDay
32%20%45%41332318%
1440
December1st to 15thDay
26%20%6%5%32321224%
1338
16th to endDay
28%28%7%6%31221214%
1344
January1st to 15thNight
34%18%3432323320%
2685
16th to endNight
29%20%35%312345%19%
2777
February1st to 15thNight
28%22%34323346%17%
2276
16th to endNight
18%27%46%42332323%
2050
March1st to 15thNight
31%26%45%42322214%
2061
16th to endNight
28%26%46%42323214%
2074
April1st to 15thNight
22%25%35%425%33418%
1787
16th to endNight
26%20%45%5%23335%19%
1578
May1st to 15thNight
19%13%34424446%31%
1439
16th to endNight
27%11%25%42445%6%24%
1433
June1st to 15thNight
29%10%36%5%2343326%
1260
16th to endNight
29%7%26%6%34445%26%
1260
July1st to 15thNight
12%3235%23346%52%
1260
16th to endNight
14%413213345%54%
1397
August1st to 15thNight
12%412223437%54%
1501
16th to endNight
14%5%224345%5%7%44%
1749
September1st to 15thNight
13%412324346%53%
1800
16th to endNight
29%9%25%423246%29%
1896
October1st to 15thNight
29%8%25%41334432%
1980
16th to endNight
38%12%35%42333318%
2216
November1st to 15thNight
45%19%2431222311%
2450
16th to endNight
30%21%4442222320%
2520
December1st to 15thNight
26%20%45%41332322%
2620
16th to endNight
29%28%5%5%31222217%
2880

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
71%36%10%5%2
1253
16th to endDay
70%47%9%32
1443
February1st to 15thDay
71%49%7%5%1
1576
16th to endDay
69%5%8%11%4
1424
March1st to 15thDay
80%46%6%1
1899
16th to endDay
81%37%7%
2149
April1st to 15thDay
78%5%6%7%1
2159
16th to endDay
78%5%6%6%2
2382
May1st to 15thDay
65%7%10%12%4
2511
16th to endDay
70%7%9%10%2
2680
June1st to 15thDay
70%6%11%7%2
2700
16th to endDay
67%410%12%4
2700
July1st to 15thDay
43%6%13%21%12%1
2541
16th to endDay
38%7%14%24%12%1
2599
August1st to 15thDay
37%8%14%26%10%1
2440
16th to endDay
43%7%17%22%7%1
2453
September1st to 15thDay
39%6%11%21%16%3
2160
16th to endDay
61%5%8%14%7%2
1899
October1st to 15thDay
60%6%11%12%8%
1650
16th to endDay
72%310%9%4
1653
November1st to 15thDay
79%45%421
1408
16th to endDay
72%5%5%8%6%2
1440
December1st to 15thDay
68%46%10%7%2
1338
16th to endDay
79%347%21
1344
January1st to 15thNight
70%5%5%11%5%2
2686
16th to endNight
68%6%7%10%43
2777
February1st to 15thNight
70%5%8%8%41
2288
16th to endNight
66%410%12%5%1
2050
March1st to 15thNight
77%46%9%2
2061
16th to endNight
76%5%9%7%
2074
April1st to 15thNight
70%6%10%10%2
1787
16th to endNight
67%7%11%10%2
1578
May1st to 15thNight
52%9%16%16%4
1440
16th to endNight
58%7%15%14%3
1433
June1st to 15thNight
61%5%19%8%31
1260
16th to endNight
58%9%11%16%31
1260
July1st to 15thNight
33%6%20%23%14%1
1190
16th to endNight
29%7%17%30%13%2
1307
August1st to 15thNight
29%7%21%26%12%2
1493
16th to endNight
37%7%20%21%8%3
1749
September1st to 15thNight
30%8%15%24%17%3
1800
16th to endNight
56%5%11%16%6%3
1896
October1st to 15thNight
56%6%11%15%10%
1980
16th to endNight
71%5%8%9%4
2216
November1st to 15thNight
80%45%5%21
2450
16th to endNight
71%47%7%8%1
2520
December1st to 15thNight
69%5%8%9%6%1
2620
16th to endNight
77%446%5%1
2880

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
18%6%30%23%16%5%
60
16th to endDay
52%7%13%19%7%
67
February1st to 15thDay
44%11%24%13%6%
236
16th to endDay
37%15%21%20%4
212
March1st to 15thDay
54%19%17%7%1
270
16th to endDay
51%15%20%7%4
288
April1st to 15thDay
49%15%16%12%5%
269
16th to endDay
42%17%20%17%11
270
May1st to 15thDay
35%15%27%16%4
288
16th to endDay
36%7%24%20%8%1
391
June1st to 15thDay
40%13%23%16%5%1
495
16th to endDay
33%14%26%20%41
495
July1st to 15thDay
20%10%31%30%5%1
475
16th to endDay
18%10%32%30%5%2
441
August1st to 15thDay
15%8%25%33%12%5%
315
16th to endDay
15%13%32%26%8%2
332
September1st to 15thDay
22%13%30%25%6%1
315
16th to endDay
33%11%26%18%8%2
284
October1st to 15thDay
41%9%27%15%41
255
16th to endDay
50%5%21%14%6%1
192
November1st to 15thDay
63%6%16%11%1
60
16th to endDay
38%8%18%11%11%11%
60
December1st to 15thDay
51%325%15%5%
60
16th to endDay
39%6%32%12%9%
64
January1st to 15thNight
43%7%21%20%5%1
750
16th to endNight
40%10%24%18%5%
783
February1st to 15thNight
40%6%29%20%2
704
16th to endNight
34%11%28%17%7%
632
March1st to 15thNight
48%10%21%13%5%
720
16th to endNight
45%8%24%15%5%
768
April1st to 15thNight
38%7%22%24%7%
707
16th to endNight
37%426%21%8%1
498
May1st to 15thNight
25%321%30%17%1
360
16th to endNight
32%120%29%15%
375
June1st to 15thNight
32%423%18%19%1
360
16th to endNight
28%5%19%30%16%1
360
July1st to 15thNight
11%214%38%31%1
340
16th to endNight
13%211%29%38%4
376
August1st to 15thNight
14%7%32%40%3
421
16th to endNight
19%213%30%33%2
603
September1st to 15thNight
16%220%28%29%3
720
16th to endNight
33%418%25%15%1
688
October1st to 15thNight
33%5%26%20%13%
660
16th to endNight
45%5%24%17%5%1
704
November1st to 15thNight
59%7%20%11%1
700
16th to endNight
41%12%23%15%5%1
720
December1st to 15thNight
40%10%30%16%2
737
16th to endNight
49%10%29%10%
800
Page generated at 2017-09-24 06:15:47. Version ac04

Copyright 2017 A. Danko


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