Shasta Dam
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shasta Dam clear sky chart from 2005-11-05 to 2019-06-10.

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
58%
17310
26%
53920
21%
17270
65%
17270
37%
29744

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
49%
840
18%
2887
15%
836
56%
836
23%
1806
January16th to endNight
47%
896
22%
2912
19%
896
53%
896
24%
1852
February1st to 15thNight
47%
818
22%
2678
19%
817
54%
817
24%
1712
February16th to endNight
44%
736
21%
2269
16%
736
53%
736
26%
1430
March1st to 15thNight
40%
840
16%
2356
10%
840
47%
840
21%
1686
March16th to endNight
44%
896
17%
2436
10%
896
49%
896
26%
1646
April1st to 15thNight
38%
839
18%
2099
6%
839
45%
839
27%
1440
April16th to endNight
54%
815
25%
2063
12%
815
59%
815
46%
1166
May1st to 15thNight
55%
562
28%
1822
19%
562
64%
562
47%
867
May16th to endNight
58%
438
21%
1752
20%
438
65%
438
28%
914
June1st to 15thNight
61%
408
26%
1632
26%
408
73%
408
39%
746
June16th to endNight
74%
390
32%
1560
40%
390
82%
390
60%
550
July1st to 15thNight
88%
370
33%
1480
45%
370
91%
370
68%
488
July16th to endNight
90%
539
37%
1665
39%
507
92%
507
75%
614
August1st to 15thNight
91%
574
39%
1719
33%
571
92%
571
75%
683
August16th to endNight
89%
785
44%
2027
29%
785
91%
785
84%
861
September1st to 15thNight
84%
780
45%
1950
28%
780
88%
780
84%
854
September16th to endNight
77%
776
39%
2135
32%
776
81%
776
63%
998
October1st to 15thNight
61%
780
32%
2340
25%
780
73%
780
50%
1136
October16th to endNight
66%
832
34%
2496
31%
832
73%
832
46%
1277
November1st to 15thNight
59%
820
26%
2626
23%
820
66%
820
32%
1497
November16th to endNight
53%
840
18%
2940
18%
840
57%
840
26%
1753
December1st to 15thNight
46%
840
21%
2940
16%
840
55%
840
26%
1757
December16th to endNight
39%
896
21%
3136
15%
896
48%
896
21%
2011

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
11%212212336%62%
54598
Night
14%312212346%57%
54103
TransparencyDay
25%49%19%22%19%
54280
Night
29%49%20%21%14%
53921
SeeingDay
14%10%25%30%16%3
8010
Night
16%317%35%25%1
17318

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
21%4132235%48%42%
1707
16th to endDay
23%6%12212236%45%
2016
February1st to 15thDay
23%41222345%6%43%
1846
16th to endDay
21%413313347%44%
1777
March1st to 15thDay
25%6%23423348%34%
2263
16th to endDay
23%413223348%42%
2492
April1st to 15thDay
22%5%2332335%7%41%
2509
16th to endDay
7%312322446%61%
2499
May1st to 15thDay
5%212212348%65%
2787
16th to endDay
10%313312348%56%
3063
June1st to 15thDay
7%211213346%66%
2857
16th to endDay
4111112380%
2730
July1st to 15thDay
11123383%
2730
16th to endDay
1112386%
2748
August1st to 15thDay
1111112485%
2484
16th to endDay
111388%
2525
September1st to 15thDay
11112483%
2340
16th to endDay
31122226%76%
2152
October1st to 15thDay
7%22211325%69%
1950
16th to endDay
12%32212245%61%
2080
November1st to 15thDay
13%412213446%53%
1891
16th to endDay
18%42322345%6%46%
1680
December1st to 15thDay
24%312222336%46%
1680
16th to endDay
27%313313337%42%
1792
January1st to 15thNight
21%41332245%6%44%
2887
16th to endNight
25%312313435%44%
2912
February1st to 15thNight
25%312423446%43%
2666
16th to endNight
22%413223347%44%
2269
March1st to 15thNight
26%5%24323338%35%
2356
16th to endNight
22%41332345%5%43%
2436
April1st to 15thNight
18%5%2442335%7%43%
2099
16th to endNight
9%312212246%62%
2063
May1st to 15thNight
6%212112337%66%
1822
16th to endNight
10%413323346%55%
1752
June1st to 15thNight
5%312313347%63%
1632
16th to endNight
2111122380%
1560
July1st to 15thNight
111223481%
1560
16th to endNight
1111111286%
1771
August1st to 15thNight
111122383%
1728
16th to endNight
111487%
2027
September1st to 15thNight
1112486%
1950
16th to endNight
311211235%76%
2135
October1st to 15thNight
7%21221233469%
2340
16th to endNight
10%212212236%64%
2496
November1st to 15thNight
12%41331345%7%53%
2626
16th to endNight
19%31332335%6%47%
2940
December1st to 15thNight
24%312212246%46%
2940
16th to endNight
27%412222346%41%
3136

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
40%7%11%20%13%5%
1707
16th to endDay
42%5%8%16%16%10%
2016
February1st to 15thDay
41%5%11%17%20%3
1846
16th to endDay
40%5%12%24%14%2
1777
March1st to 15thDay
48%7%10%15%13%4
2263
16th to endDay
41%7%13%19%14%3
2492
April1st to 15thDay
42%5%14%18%15%3
2509
16th to endDay
23%6%12%27%22%8%
2499
May1st to 15thDay
18%410%25%27%12%
2787
16th to endDay
26%6%12%23%23%7%
3067
June1st to 15thDay
19%5%9%20%24%20%
2857
16th to endDay
10%15%15%33%32%
2730
July1st to 15thDay
6%2412%30%43%
2581
16th to endDay
6%1411%26%49%
2591
August1st to 15thDay
6%1416%30%40%
2468
16th to endDay
5%1214%31%44%
2525
September1st to 15thDay
6%15%13%27%46%
2340
16th to endDay
11%27%20%32%25%
2152
October1st to 15thDay
18%48%19%28%20%
1950
16th to endDay
25%312%20%20%17%
2080
November1st to 15thDay
31%6%12%25%13%9%
1891
16th to endDay
39%7%10%19%15%8%
1680
December1st to 15thDay
41%5%8%16%21%6%
1680
16th to endDay
44%411%21%13%4
1792
January1st to 15thNight
40%7%13%18%14%6%
2887
16th to endNight
42%48%16%16%10%
2912
February1st to 15thNight
42%5%9%18%18%5%
2678
16th to endNight
40%5%11%22%16%3
2269
March1st to 15thNight
49%5%8%17%13%4
2356
16th to endNight
42%6%13%20%12%4
2436
April1st to 15thNight
41%6%15%19%13%4
2099
16th to endNight
23%5%13%30%21%5%
2063
May1st to 15thNight
18%5%11%26%27%10%
1823
16th to endNight
29%6%11%25%18%7%
1752
June1st to 15thNight
21%5%11%21%26%12%
1632
16th to endNight
10%2417%39%24%
1560
July1st to 15thNight
6%3413%31%39%
1480
16th to endNight
7%1314%25%47%
1665
August1st to 15thNight
8%1418%32%34%
1719
16th to endNight
5%1318%33%37%
2027
September1st to 15thNight
41413%30%45%
1950
16th to endNight
12%35%21%28%28%
2135
October1st to 15thNight
19%37%20%29%19%
2340
16th to endNight
22%38%25%20%18%
2496
November1st to 15thNight
30%6%14%26%13%8%
2626
16th to endNight
37%5%12%19%16%7%
2940
December1st to 15thNight
39%410%17%21%6%
2940
16th to endNight
45%49%18%17%4
3136

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
35%5%20%27%10%1
155
16th to endDay
32%6%21%22%13%3
352
February1st to 15thDay
28%10%21%26%12%1
326
16th to endDay
24%12%25%27%9%
324
March1st to 15thDay
36%13%22%17%8%1
390
16th to endDay
27%16%22%22%10%
416
April1st to 15thDay
28%17%25%21%5%
389
16th to endDay
12%17%30%22%14%3
378
May1st to 15thDay
6%17%31%29%12%2
408
16th to endDay
13%12%26%29%14%3
458
June1st to 15thDay
7%15%27%29%17%2
412
16th to endDay
48%32%32%18%2
375
July1st to 15thDay
2325%41%22%4
365
16th to endDay
420%47%22%5%
391
August1st to 15thDay
1327%37%23%5%
359
16th to endDay
1424%37%23%8%
396
September1st to 15thDay
15%24%40%25%3
375
16th to endDay
310%24%36%18%5%
375
October1st to 15thDay
9%15%27%30%15%2
375
16th to endDay
14%5%22%29%23%5%
400
November1st to 15thDay
21%421%27%21%2
223
16th to endDay
25%6%25%28%12%1
120
December1st to 15thDay
26%5%28%24%12%3
120
16th to endDay
16%332%31%14%
128
January1st to 15thNight
24%218%37%16%1
840
16th to endNight
27%218%32%17%1
896
February1st to 15thNight
25%417%35%15%
824
16th to endNight
25%5%20%35%11%1
736
March1st to 15thNight
28%5%20%27%16%1
840
16th to endNight
25%5%21%33%14%
896
April1st to 15thNight
20%9%26%27%14%1
839
16th to endNight
11%6%24%35%20%1
815
May1st to 15thNight
9%5%28%32%23%
563
16th to endNight
13%418%36%25%
439
June1st to 15thNight
7%423%42%21%
408
16th to endNight
4216%50%26%
390
July1st to 15thNight
17%40%49%1
370
16th to endNight
15%38%53%1
539
August1st to 15thNight
2433%56%3
574
16th to endNight
17%39%46%3
785
September1st to 15thNight
1111%34%47%3
780
16th to endNight
3313%35%40%3
776
October1st to 15thNight
9%5%21%34%26%3
780
16th to endNight
11%315%34%31%3
832
November1st to 15thNight
15%117%42%20%1
820
16th to endNight
21%317%36%19%1
840
December1st to 15thNight
26%320%32%14%2
840
16th to endNight
28%325%32%9%
896
Page generated at 2019-06-10 16:29:48. Version ac04

Copyright 2019 A. Danko


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