Cascade
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cascade clear sky chart from 2005-11-05 to

2017-09-12
.

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
54%
14693
17%
46768
16%
14665
56%
14665
24%
30285

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
39%
716
11%
2506
9%
716
42%
716
12%
1899
January16th to endNight
48%
768
14%
2688
15%
768
50%
768
17%
1870
February1st to 15thNight
40%
700
8%
2285
7%
696
43%
696
14%
1723
February16th to endNight
37%
632
10%
1895
9%
632
40%
632
14%
1486
March1st to 15thNight
39%
720
8%
2151
7%
720
42%
720
15%
1645
March16th to endNight
40%
768
10%
2046
6%
768
42%
768
18%
1554
April1st to 15thNight
45%
719
14%
1799
8%
719
47%
719
24%
1297
April16th to endNight
50%
557
20%
1637
14%
557
53%
557
28%
1027
May1st to 15thNight
58%
527
18%
1607
15%
527
61%
527
32%
947
May16th to endNight
59%
374
14%
1496
21%
374
61%
374
22%
896
June1st to 15thNight
63%
360
12%
1440
17%
360
66%
360
25%
829
June16th to endNight
76%
360
22%
1440
34%
360
80%
360
39%
664
July1st to 15thNight
86%
340
22%
1360
36%
340
89%
340
52%
525
July16th to endNight
86%
376
33%
1416
48%
354
87%
354
59%
511
August1st to 15thNight
80%
470
30%
1543
32%
468
82%
468
52%
700
August16th to endNight
82%
672
35%
1818
26%
672
83%
672
62%
863
September1st to 15thNight
81%
706
32%
1813
22%
706
83%
706
59%
935
September16th to endNight
70%
656
32%
1815
27%
656
73%
656
43%
1015
October1st to 15thNight
60%
660
23%
1863
21%
660
63%
660
34%
1135
October16th to endNight
56%
704
17%
2288
18%
704
59%
704
24%
1479
November1st to 15thNight
47%
700
17%
2275
17%
700
50%
700
19%
1581
November16th to endNight
43%
720
11%
2379
10%
720
45%
720
16%
1719
December1st to 15thNight
40%
720
8%
2520
5%
720
44%
720
13%
1896
December16th to endNight
32%
768
10%
2688
9%
768
35%
768
11%
2089

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
10%10%36%423445%42%
47906
Night
12%10%35%423345%42%
46938
Cloud CoverDay
10%10%36%424345%43%
47907
Night
10%10%35%424446%43%
46941
TransparencyDay
42%5%10%18%15%7%
47578
Night
42%5%12%19%13%5%
46769
SeeingDay
13%16%32%25%10%1
5317
Night
15%6%17%33%24%3
14703

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
13%16%5%8%6%2445%5%28%
1432
16th to endDay
15%15%48%43325%5%30%
1536
February1st to 15thDay
14%17%5%8%5%3335%426%
1574
16th to endDay
11%21%10%11%5%2335%5%19%
1579
March1st to 15thDay
17%19%7%8%6%35%44320%
1809
16th to endDay
16%19%6%8%5%25%345%20%
2174
April1st to 15thDay
12%17%6%8%5%34445%26%
2149
16th to endDay
12%13%36%423446%38%
2322
May1st to 15thDay
7%8%36%5%35%5%5%7%41%
2340
16th to endDay
12%10%5%8%7%35%45%6%30%
2615
June1st to 15thDay
14%7%46%5%35%5%5%6%33%
2520
16th to endDay
7%42432333458%
2520
July1st to 15thDay
3313313445%66%
2520
16th to endDay
2112213345%72%
2657
August1st to 15thDay
321331335%5%65%
2408
16th to endDay
321321233470%
2381
September1st to 15thDay
4213322335%67%
2066
16th to endDay
8%6%13423345%55%
1815
October1st to 15thDay
11%6%36%424345%47%
1766
16th to endDay
14%11%37%5%33346%35%
1584
November1st to 15thDay
15%14%5%7%5%33436%30%
1584
16th to endDay
16%14%5%7%6%2433331%
1579
December1st to 15thDay
17%16%5%7%5%3335%6%26%
1440
16th to endDay
20%17%5%7%423445%24%
1536
January1st to 15thNight
16%18%5%7%423345%29%
2506
16th to endNight
13%16%46%423245%35%
2688
February1st to 15thNight
16%16%47%6%3334428%
2274
16th to endNight
13%17%7%9%5%3425%424%
1895
March1st to 15thNight
17%16%5%7%6%2333427%
2151
16th to endNight
16%14%46%5%3446%6%27%
2043
April1st to 15thNight
11%11%36%6%3445%5%36%
1799
16th to endNight
12%7%34423346%45%
1637
May1st to 15thNight
7%5%3433445%6%50%
1607
16th to endNight
8%7%45%5%345%6%8%39%
1496
June1st to 15thNight
15%42332445%7%44%
1440
16th to endNight
6%32242445%5%60%
1440
July1st to 15thNight
11222345%6%68%
1440
16th to endNight
12123223474%
1512
August1st to 15thNight
321321345%5%66%
1551
16th to endNight
121221334471%
1818
September1st to 15thNight
231222233470%
1813
16th to endNight
9%41332323460%
1815
October1st to 15thNight
10%425%424436%51%
1863
16th to endNight
13%9%25%5%3445%6%39%
2288
November1st to 15thNight
18%11%35%42335%6%33%
2275
16th to endNight
17%13%47%5%2433433%
2379
December1st to 15thNight
14%15%5%8%7%24445%27%
2520
16th to endNight
17%20%6%8%42333425%
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
11%15%5%8%6%35%345%30%
1432
16th to endDay
13%14%5%7%433346%33%
1536
February1st to 15thDay
11%17%5%10%6%2434428%
1574
16th to endDay
9%19%10%12%6%23345%21%
1579
March1st to 15thDay
13%19%7%8%6%36%44421%
1809
16th to endDay
14%20%5%8%6%34335%22%
2175
April1st to 15thDay
12%17%48%6%34446%26%
2149
16th to endDay
11%13%36%423436%39%
2322
May1st to 15thDay
7%8%37%5%35%346%42%
2340
16th to endDay
13%10%38%7%35%5%47%30%
2615
June1st to 15thDay
14%6%36%6%46%5%5%7%33%
2520
16th to endDay
7%415%423335%58%
2520
July1st to 15thDay
332312346%67%
2520
16th to endDay
211213335%72%
2657
August1st to 15thDay
32331345%6%65%
2408
16th to endDay
31232333470%
2381
September1st to 15thDay
421321334468%
2066
16th to endDay
9%414234445%56%
1815
October1st to 15thDay
12%6%15%43434448%
1766
16th to endDay
11%11%27%435%446%36%
1584
November1st to 15thDay
15%14%5%5%5%3335%7%31%
1584
16th to endDay
15%14%6%6%5%34335%32%
1579
December1st to 15thDay
14%17%5%8%5%22346%27%
1440
16th to endDay
15%19%5%9%433345%25%
1536
January1st to 15thNight
14%16%5%8%5%2334429%
2506
16th to endNight
10%17%46%423335%37%
2688
February1st to 15thNight
12%16%6%6%5%3445%5%29%
2274
16th to endNight
11%16%7%10%5%3435%5%26%
1895
March1st to 15thNight
11%17%5%7%5%35%345%29%
2151
16th to endNight
13%14%45%5%26%46%7%29%
2046
April1st to 15thNight
10%10%47%5%35%45%6%36%
1799
16th to endNight
11%7%25%423346%47%
1637
May1st to 15thNight
6%5%25%4245%47%50%
1607
16th to endNight
9%6%45%5%35%46%9%40%
1496
June1st to 15thNight
14%4234245%47%46%
1440
16th to endNight
6%113424346%61%
1440
July1st to 15thNight
2111235%5%7%69%
1440
16th to endNight
22221233475%
1512
August1st to 15thNight
3212312346%66%
1551
16th to endNight
1112222335%72%
1818
September1st to 15thNight
221222334470%
1813
16th to endNight
9%213223335%60%
1815
October1st to 15thNight
10%42442435%6%50%
1863
16th to endNight
12%8%25%42445%7%40%
2288
November1st to 15thNight
16%11%25%5%33446%35%
2275
16th to endNight
14%14%35%6%34445%33%
2379
December1st to 15thNight
13%14%47%6%45%45%5%28%
2520
16th to endNight
14%20%6%10%5%2334425%
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
56%8%14%15%3
1432
16th to endDay
54%6%15%16%6%
1536
February1st to 15thDay
59%8%12%16%3
1574
16th to endDay
65%5%11%13%2
1579
March1st to 15thDay
65%6%10%12%4
1809
16th to endDay
64%411%14%4
2175
April1st to 15thDay
58%6%13%16%4
2149
16th to endDay
47%6%12%23%9%
2322
May1st to 15thDay
41%5%12%29%10%
2340
16th to endDay
53%6%12%17%8%1
2619
June1st to 15thDay
48%6%11%18%12%3
2520
16th to endDay
27%47%22%29%8%
2520
July1st to 15thDay
18%38%16%29%23%
2371
16th to endDay
13%25%11%28%37%
2490
August1st to 15thDay
18%5%7%17%29%21%
2391
16th to endDay
17%27%20%33%18%
2381
September1st to 15thDay
18%37%19%33%17%
2066
16th to endDay
29%38%28%22%6%
1815
October1st to 15thDay
38%5%12%23%16%2
1766
16th to endDay
48%6%10%17%15%
1584
November1st to 15thDay
53%6%13%18%7%
1584
16th to endDay
56%6%13%14%7%1
1579
December1st to 15thDay
58%7%17%13%3
1440
16th to endDay
61%7%11%14%4
1536
January1st to 15thNight
58%7%12%14%5%1
2506
16th to endNight
50%6%13%18%9%1
2688
February1st to 15thNight
57%7%13%15%5%
2285
16th to endNight
60%6%12%14%31
1895
March1st to 15thNight
58%6%12%16%5%
2151
16th to endNight
53%7%16%16%5%
2046
April1st to 15thNight
47%6%16%21%8%
1799
16th to endNight
37%6%15%27%12%1
1637
May1st to 15thNight
32%6%12%31%16%
1608
16th to endNight
39%6%15%26%9%1
1496
June1st to 15thNight
36%6%15%25%12%3
1440
16th to endNight
23%39%27%26%9%
1440
July1st to 15thNight
13%49%18%31%22%
1360
16th to endNight
11%2413%30%36%
1416
August1st to 15thNight
17%37%18%30%22%
1543
16th to endNight
13%37%20%33%20%
1818
September1st to 15thNight
17%37%22%30%18%
1813
16th to endNight
27%48%26%23%10%
1815
October1st to 15thNight
33%6%12%26%18%3
1863
16th to endNight
42%5%15%18%17%
2288
November1st to 15thNight
50%5%12%21%9%
2275
16th to endNight
53%6%12%16%8%2
2379
December1st to 15thNight
56%8%14%14%5%
2520
16th to endNight
63%5%11%13%5%
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
16%5%20%28%20%10%
60
16th to endDay
20%15%28%18%12%4
64
February1st to 15thDay
22%15%25%17%16%3
147
16th to endDay
23%23%33%13%6%
238
March1st to 15thDay
28%21%32%14%2
270
16th to endDay
23%28%29%16%2
288
April1st to 15thDay
17%24%30%15%9%3
269
16th to endDay
21%24%29%18%5%
270
May1st to 15thDay
11%20%38%23%5%
288
16th to endDay
17%13%23%30%12%3
330
June1st to 15thDay
12%20%33%22%9%1
315
16th to endDay
8%15%33%29%12%1
315
July1st to 15thDay
49%37%35%13%
305
16th to endDay
211%42%31%10%1
327
August1st to 15thDay
5%11%37%32%11%1
315
16th to endDay
38%32%36%14%3
332
September1st to 15thDay
6%11%33%32%13%3
300
16th to endDay
10%10%35%30%11%
255
October1st to 15thDay
17%13%33%27%7%
236
16th to endDay
23%8%28%26%10%3
96
November1st to 15thDay
13%13%24%26%22%
90
16th to endDay
15%22%32%20%6%2
83
December1st to 15thDay
36%18%35%6%3
60
16th to endDay
21%15%20%29%10%1
64
January1st to 15thNight
25%5%17%28%20%2
720
16th to endNight
20%6%16%27%24%4
768
February1st to 15thNight
23%6%20%30%15%3
704
16th to endNight
19%11%22%27%15%3
632
March1st to 15thNight
21%10%21%29%14%2
720
16th to endNight
20%10%23%29%13%1
768
April1st to 15thNight
15%10%21%27%21%3
719
16th to endNight
14%9%21%33%18%2
557
May1st to 15thNight
8%6%21%38%23%2
528
16th to endNight
10%217%36%28%4
375
June1st to 15thNight
16%212%38%27%2
360
16th to endNight
6%111%43%36%1
360
July1st to 15thNight
26%47%39%3
340
16th to endNight
27%50%36%1
376
August1st to 15thNight
48%41%41%2
470
16th to endNight
219%39%39%7%
672
September1st to 15thNight
319%38%40%6%
706
16th to endNight
10%212%30%34%9%
656
October1st to 15thNight
12%5%15%36%25%5%
660
16th to endNight
16%415%35%22%5%
704
November1st to 15thNight
22%5%17%31%21%2
700
16th to endNight
21%7%22%25%17%4
720
December1st to 15thNight
20%9%20%30%16%1
720
16th to endNight
25%9%22%27%14%1
768
Page generated at 2017-09-13 05:39:12. Version ac04

Copyright 2017 A. Danko


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