Creston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Creston 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
48%
15032
11%
46891
10%
15004
50%
15004
20%
32630

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
23%
795
5%
2583
4%
793
24%
793
7%
2212
January16th to endNight
27%
768
4%
2688
3%
768
29%
768
6%
2280
February1st to 15thNight
35%
701
6%
2439
5%
699
38%
699
11%
1909
February16th to endNight
43%
632
9%
1895
9%
632
46%
632
17%
1423
March1st to 15thNight
42%
720
6%
2160
4%
720
44%
720
16%
1622
March16th to endNight
41%
768
8%
2028
4%
768
43%
768
18%
1541
April1st to 15thNight
54%
701
10%
1781
6%
701
55%
701
27%
1247
April16th to endNight
51%
540
13%
1620
11%
540
53%
540
25%
1064
May1st to 15thNight
63%
389
15%
1470
19%
389
66%
389
29%
799
May16th to endNight
55%
374
10%
1371
13%
374
57%
374
21%
876
June1st to 15thNight
59%
360
5%
1260
4%
360
59%
360
26%
778
June16th to endNight
67%
360
9%
1260
4%
360
68%
360
34%
676
July1st to 15thNight
85%
340
12%
1218
11%
340
86%
340
56%
496
July16th to endNight
86%
376
21%
1416
34%
354
88%
354
55%
534
August1st to 15thNight
84%
369
27%
1441
37%
367
87%
367
53%
570
August16th to endNight
81%
619
32%
1765
26%
619
82%
619
62%
807
September1st to 15thNight
77%
720
26%
1822
16%
720
78%
720
55%
976
September16th to endNight
67%
688
22%
1903
18%
688
69%
688
38%
1140
October1st to 15thNight
56%
660
16%
1934
15%
660
58%
660
28%
1255
October16th to endNight
46%
704
13%
2288
11%
704
50%
704
20%
1573
November1st to 15thNight
34%
700
8%
2281
7%
700
36%
700
12%
1786
November16th to endNight
31%
888
4%
2688
2%
888
33%
888
10%
2223
December1st to 15thNight
27%
900
6%
2700
5%
900
28%
900
8%
2327
December16th to endNight
25%
960
5%
2880
2%
960
28%
960
7%
2516

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
9%9%47%6%45%5%5%6%33%
48046
Night
8%11%47%6%35%5%5%7%33%
47051
Cloud CoverDay
10%10%48%6%35%5%5%6%32%
48047
Night
10%12%5%7%6%3445%6%32%
47054
TransparencyDay
50%314%20%9%1
47710
Night
51%415%19%8%1
46891
SeeingDay
14%9%24%28%17%5%
5870
Night
17%215%39%21%2
15040

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
12%18%7%10%8%35%6%46%16%
1367
16th to endDay
7%15%7%12%10%47%6%5%6%15%
1536
February1st to 15thDay
6%14%6%12%8%47%6%5%6%19%
1425
16th to endDay
6%13%6%11%9%37%7%5%6%22%
1579
March1st to 15thDay
10%16%7%10%8%46%6%5%6%18%
1800
16th to endDay
13%16%7%10%8%46%5%5%6%15%
2192
April1st to 15thDay
9%13%5%10%7%5%6%6%5%6%22%
2167
16th to endDay
11%10%5%9%7%46%5%5%5%27%
2340
May1st to 15thDay
8%9%46%6%35%45%6%38%
2481
16th to endDay
14%7%48%7%5%6%46%7%26%
2740
June1st to 15thDay
15%7%47%7%46%6%46%27%
2700
16th to endDay
12%5%26%6%45%6%6%7%34%
2700
July1st to 15thDay
42135%245%6%7%55%
2669
16th to endDay
2113425%45%7%60%
2657
August1st to 15thDay
221342446%9%56%
2511
16th to endDay
5%21333446%7%58%
2435
September1st to 15thDay
43245%35%346%56%
2137
16th to endDay
10%6%35%5%345%5%7%43%
1893
October1st to 15thDay
13%6%27%7%45%45%6%36%
1695
16th to endDay
13%10%38%5%47%6%5%5%27%
1584
November1st to 15thDay
15%13%5%8%6%46%5%5%7%20%
1574
16th to endDay
9%16%6%11%8%47%5%45%20%
1260
December1st to 15thDay
10%14%8%9%9%5%6%5%5%6%18%
1260
16th to endDay
10%18%7%13%8%46%5%5%414%
1344
January1st to 15thNight
12%21%8%11%8%46%45%413%
2583
16th to endNight
9%20%7%12%9%5%7%436%13%
2688
February1st to 15thNight
9%18%49%7%36%447%23%
2427
16th to endNight
6%13%5%10%8%45%5%5%7%27%
1895
March1st to 15thNight
10%13%5%8%6%37%5%5%7%25%
2160
16th to endNight
10%12%48%7%35%5%5%8%27%
2025
April1st to 15thNight
9%7%35%5%37%7%7%8%34%
1781
16th to endNight
6%7%47%6%45%5%6%6%39%
1620
May1st to 15thNight
5%5%25%425%5%7%8%46%
1469
16th to endNight
11%7%38%435%5%5%8%35%
1371
June1st to 15thNight
11%327%5%45%6%6%8%38%
1260
16th to endNight
6%315%5%345%7%9%46%
1260
July1st to 15thNight
11122345%9%67%
1290
16th to endNight
11111435%6%71%
1512
August1st to 15thNight
2122123410%66%
1449
16th to endNight
112113347%70%
1765
September1st to 15thNight
4112324347%64%
1822
16th to endNight
8%4144245%5%7%50%
1903
October1st to 15thNight
10%6%36%5%345%5%6%42%
1934
16th to endNight
12%9%37%6%35%5%5%7%32%
2288
November1st to 15thNight
14%12%48%7%36%5%5%8%21%
2281
16th to endNight
12%19%8%9%7%35%445%18%
2688
December1st to 15thNight
10%18%8%14%9%45%5%4414%
2700
16th to endNight
9%22%8%11%8%47%5%5%5%11%
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
15%19%7%10%8%4445%5%13%
1367
16th to endDay
8%18%7%14%7%48%5%45%12%
1536
February1st to 15thDay
8%15%7%11%11%5%5%6%45%17%
1425
16th to endDay
7%15%7%12%8%46%6%5%5%20%
1579
March1st to 15thDay
12%17%6%11%8%35%5%5%6%16%
1800
16th to endDay
15%18%6%11%9%45%45%5%14%
2193
April1st to 15thDay
11%14%6%10%8%36%6%5%6%20%
2167
16th to endDay
12%11%410%8%45%45%5%26%
2340
May1st to 15thDay
9%9%46%5%35%5%47%36%
2481
16th to endDay
14%8%48%7%46%5%6%6%26%
2740
June1st to 15thDay
17%8%48%7%46%6%5%6%26%
2700
16th to endDay
13%6%36%7%35%6%5%6%34%
2700
July1st to 15thDay
43134345%5%7%55%
2669
16th to endDay
221343446%7%59%
2657
August1st to 15thDay
32133245%6%10%55%
2511
16th to endDay
5%2144235%5%7%56%
2435
September1st to 15thDay
4425%42445%7%53%
2137
16th to endDay
12%6%26%5%3445%7%42%
1893
October1st to 15thDay
14%7%37%6%445%46%35%
1695
16th to endDay
15%10%5%9%6%36%6%5%5%25%
1584
November1st to 15thDay
18%15%6%8%6%46%5%47%17%
1574
16th to endDay
11%19%6%10%8%45%45%5%18%
1260
December1st to 15thDay
11%15%8%13%9%36%45%5%16%
1260
16th to endDay
10%22%8%12%9%3444413%
1344
January1st to 15thNight
15%23%8%11%8%3435%412%
2583
16th to endNight
11%22%7%11%9%46%5%4411%
2688
February1st to 15thNight
10%18%7%11%8%35%346%20%
2427
16th to endNight
7%16%6%10%7%35%5%5%7%24%
1895
March1st to 15thNight
12%15%5%8%6%46%46%7%21%
2160
16th to endNight
12%13%5%8%7%35%5%5%8%24%
2028
April1st to 15thNight
9%9%36%6%46%6%6%8%32%
1781
16th to endNight
7%8%47%8%3445%7%37%
1620
May1st to 15thNight
5%6%245%35%5%6%8%44%
1469
16th to endNight
10%8%38%6%35%5%6%8%34%
1371
June1st to 15thNight
11%437%5%35%5%7%8%36%
1260
16th to endNight
7%425%5%25%6%7%8%44%
1260
July1st to 15thNight
21121247%8%66%
1290
16th to endNight
111112335%8%69%
1512
August1st to 15thNight
31221235%9%66%
1449
16th to endNight
1212123347%69%
1765
September1st to 15thNight
331332335%6%63%
1822
16th to endNight
9%4244335%5%8%48%
1903
October1st to 15thNight
11%7%35%5%45%45%7%40%
1934
16th to endNight
13%11%37%5%35%5%5%7%30%
2288
November1st to 15thNight
16%16%6%8%7%345%5%7%19%
2281
16th to endNight
14%21%8%8%7%345%4417%
2688
December1st to 15thNight
12%19%9%14%8%35%33413%
2700
16th to endNight
11%25%8%11%8%45%45%49%
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
69%6%11%9%3
1367
16th to endDay
71%411%9%3
1536
February1st to 15thDay
65%5%14%9%4
1425
16th to endDay
62%315%13%4
1579
March1st to 15thDay
66%417%10%1
1800
16th to endDay
70%213%10%2
2193
April1st to 15thDay
62%315%14%3
2167
16th to endDay
58%315%18%2
2340
May1st to 15thDay
45%216%23%10%
2481
16th to endDay
56%317%18%4
2744
June1st to 15thDay
56%211%18%8%1
2700
16th to endDay
47%214%25%10%
2700
July1st to 15thDay
27%213%28%21%5%
2512
16th to endDay
23%311%28%27%6%
2490
August1st to 15thDay
22%315%36%17%4
2494
16th to endDay
24%215%33%21%2
2435
September1st to 15thDay
30%112%32%19%2
2137
16th to endDay
40%317%25%10%1
1893
October1st to 15thDay
48%415%24%6%
1695
16th to endDay
58%5%17%15%3
1584
November1st to 15thDay
64%6%11%12%4
1574
16th to endDay
66%6%14%9%2
1260
December1st to 15thDay
68%5%11%12%1
1260
16th to endDay
73%49%9%3
1344
January1st to 15thNight
74%49%8%2
2583
16th to endNight
74%410%8%2
2688
February1st to 15thNight
63%5%14%10%5%
2439
16th to endNight
57%417%15%4
1895
March1st to 15thNight
58%320%15%1
2160
16th to endNight
57%417%15%4
2028
April1st to 15thNight
45%5%21%20%6%
1781
16th to endNight
45%219%24%6%
1620
May1st to 15thNight
35%319%26%14%
1470
16th to endNight
46%319%23%6%
1371
June1st to 15thNight
43%217%25%8%3
1260
16th to endNight
33%218%28%16%1
1260
July1st to 15thNight
14%216%32%26%7%
1218
16th to endNight
14%110%33%29%9%
1416
August1st to 15thNight
16%214%39%22%4
1441
16th to endNight
14%115%35%27%4
1765
September1st to 15thNight
21%211%38%21%4
1822
16th to endNight
32%419%28%12%3
1903
October1st to 15thNight
42%320%24%8%
1934
16th to endNight
50%419%20%4
2288
November1st to 15thNight
62%5%12%13%4
2281
16th to endNight
67%6%12%10%2
2688
December1st to 15thNight
75%38%11%1
2700
16th to endNight
76%48%8%2
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
8%18%35%35%11%
60
16th to endDay
26%112%31%15%12%
64
February1st to 15thDay
10%130%36%19%1
73
16th to endDay
18%7%25%28%16%2
238
March1st to 15thDay
21%14%38%21%4
270
16th to endDay
22%13%33%22%7%1
288
April1st to 15thDay
21%14%30%20%10%3
269
16th to endDay
22%17%25%20%9%5%
270
May1st to 15thDay
16%14%27%27%9%4
288
16th to endDay
18%7%18%25%21%9%
455
June1st to 15thDay
17%9%18%29%20%4
495
16th to endDay
12%8%22%30%19%6%
495
July1st to 15thDay
5%5%22%32%29%5%
446
16th to endDay
49%37%25%15%6%
327
August1st to 15thDay
5%6%22%34%20%10%
315
16th to endDay
6%9%25%28%21%9%
332
September1st to 15thDay
10%9%23%28%20%6%
315
16th to endDay
14%5%27%29%16%6%
284
October1st to 15thDay
20%9%24%29%12%3
217
16th to endDay
30%318%22%17%7%
96
November1st to 15thDay
29%316%31%16%2
89
16th to endDay
18%118%33%13%15%
60
December1st to 15thDay
26%16%36%16%11%
60
16th to endDay
9%312%50%17%7%
64
January1st to 15thNight
28%218%33%14%2
798
16th to endNight
23%316%38%15%2
768
February1st to 15thNight
21%317%38%15%3
704
16th to endNight
16%215%43%18%3
632
March1st to 15thNight
20%219%39%15%1
720
16th to endNight
20%220%39%15%1
768
April1st to 15thNight
14%116%43%21%2
701
16th to endNight
12%419%40%20%
540
May1st to 15thNight
9%416%45%21%2
390
16th to endNight
15%110%35%34%3
375
June1st to 15thNight
14%15%39%26%2
360
16th to endNight
10%11%46%29%2
360
July1st to 15thNight
316%44%41%2
340
16th to endNight
37%46%40%2
376
August1st to 15thNight
35%33%51%5%
369
16th to endNight
319%40%42%3
619
September1st to 15thNight
5%110%38%34%10%
720
16th to endNight
12%110%40%29%6%
688
October1st to 15thNight
16%214%40%22%3
660
16th to endNight
19%217%39%18%3
704
November1st to 15thNight
25%219%40%11%
700
16th to endNight
26%318%34%14%2
888
December1st to 15thNight
22%318%41%13%1
900
16th to endNight
24%318%40%12%
960
Page generated at 2017-09-24 06:15:44. Version ac04

Copyright 2017 A. Danko


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