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 2017-09-22.

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%
15080
26%
46938
21%
15040
65%
15040
37%
25759

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
50%
720
18%
2473
15%
716
58%
716
26%
1486
January16th to endNight
47%
768
25%
2496
21%
768
54%
768
26%
1540
February1st to 15thNight
46%
698
21%
2288
18%
697
53%
697
23%
1471
February16th to endNight
44%
632
21%
1948
15%
632
53%
632
25%
1246
March1st to 15thNight
42%
720
15%
2019
9%
720
48%
720
22%
1424
March16th to endNight
43%
768
18%
2088
11%
768
49%
768
27%
1387
April1st to 15thNight
39%
719
20%
1799
6%
719
46%
719
29%
1206
April16th to endNight
51%
705
25%
1785
12%
705
56%
705
45%
1016
May1st to 15thNight
51%
482
26%
1562
17%
482
60%
482
45%
759
May16th to endNight
59%
374
22%
1496
22%
374
67%
374
32%
739
June1st to 15thNight
59%
360
22%
1440
23%
360
71%
360
36%
683
June16th to endNight
73%
360
32%
1440
40%
360
82%
360
58%
514
July1st to 15thNight
88%
340
31%
1360
44%
340
91%
340
68%
451
July16th to endNight
90%
497
38%
1527
40%
465
91%
465
75%
560
August1st to 15thNight
90%
538
37%
1611
32%
535
92%
535
74%
645
August16th to endNight
88%
724
45%
1870
30%
724
90%
724
83%
800
September1st to 15thNight
84%
720
43%
1800
27%
720
88%
720
83%
791
September16th to endNight
75%
683
39%
1874
32%
683
81%
683
63%
876
October1st to 15thNight
63%
660
31%
1980
25%
660
74%
660
48%
978
October16th to endNight
63%
704
32%
2112
29%
704
70%
704
42%
1126
November1st to 15thNight
60%
700
24%
2242
22%
700
66%
700
33%
1277
November16th to endNight
53%
720
19%
2520
19%
720
58%
720
28%
1469
December1st to 15thNight
42%
720
19%
2520
13%
720
52%
720
23%
1559
December16th to endNight
37%
768
20%
2688
15%
768
46%
768
20%
1756

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%212212236%62%
47953
Night
14%312212336%58%
47121
TransparencyDay
24%49%19%22%19%
47635
Night
28%49%20%21%15%
46939
SeeingDay
13%10%26%30%15%2
5869
Night
15%318%35%24%1
15088

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
19%313213448%45%
1462
16th to endDay
23%5%12223235%47%
1728
February1st to 15thDay
23%41222345%6%42%
1576
16th to endDay
21%5%13323346%43%
1526
March1st to 15thDay
24%5%23323349%36%
1940
16th to endDay
22%413223248%43%
2136
April1st to 15thDay
19%5%2332335%8%43%
2149
16th to endDay
7%313322346%60%
2172
May1st to 15thDay
6%212213248%64%
2388
16th to endDay
9%313212348%59%
2615
June1st to 15thDay
7%211214346%64%
2520
16th to endDay
4111122379%
2520
July1st to 15thDay
11123484%
2520
16th to endDay
11111287%
2534
August1st to 15thDay
1111112484%
2340
16th to endDay
1111387%
2330
September1st to 15thDay
11112484%
2160
16th to endDay
31112226%75%
1895
October1st to 15thDay
8%22211326%67%
1650
16th to endDay
14%32212245%59%
1760
November1st to 15thDay
12%312223446%54%
1616
16th to endDay
17%42332335%6%48%
1440
December1st to 15thDay
26%322212436%43%
1440
16th to endDay
29%312212236%41%
1536
January1st to 15thNight
19%41232245%6%47%
2473
16th to endNight
25%3221333448%
2496
February1st to 15thNight
25%312423446%41%
2276
16th to endNight
23%413323347%42%
1948
March1st to 15thNight
25%5%24323348%36%
2019
16th to endNight
22%41322345%6%44%
2088
April1st to 15thNight
16%42442335%7%45%
1799
16th to endNight
9%313312246%62%
1785
May1st to 15thNight
8%212112237%65%
1562
16th to endNight
8%323323346%58%
1496
June1st to 15thNight
6%312313348%60%
1440
16th to endNight
3111122380%
1440
July1st to 15thNight
111222481%
1440
16th to endNight
1111111286%
1633
August1st to 15thNight
111122383%
1620
16th to endNight
1111486%
1870
September1st to 15thNight
1112486%
1800
16th to endNight
311211225%76%
1874
October1st to 15thNight
8%21221233468%
1980
16th to endNight
11%212212236%61%
2112
November1st to 15thNight
12%41331345%7%53%
2242
16th to endNight
18%21232335%7%49%
2520
December1st to 15thNight
27%312212246%44%
2520
16th to endNight
29%412222345%41%
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
37%7%12%20%14%6%
1462
16th to endDay
41%47%16%17%11%
1728
February1st to 15thDay
41%5%12%17%20%3
1576
16th to endDay
41%412%25%13%2
1526
March1st to 15thDay
46%7%11%16%14%5%
1940
16th to endDay
40%7%14%19%14%4
2136
April1st to 15thDay
39%5%14%20%16%3
2149
16th to endDay
24%6%11%26%22%8%
2172
May1st to 15thDay
19%410%25%27%13%
2388
16th to endDay
24%5%11%23%25%9%
2619
June1st to 15thDay
21%5%10%19%22%21%
2520
16th to endDay
11%16%15%32%32%
2520
July1st to 15thDay
6%2412%31%42%
2371
16th to endDay
6%139%24%53%
2377
August1st to 15thDay
6%1417%29%40%
2324
16th to endDay
5%1214%31%44%
2330
September1st to 15thDay
6%15%13%26%46%
2160
16th to endDay
11%37%20%32%24%
1895
October1st to 15thDay
20%48%20%29%17%
1650
16th to endDay
27%312%22%19%14%
1760
November1st to 15thDay
30%7%13%28%12%8%
1616
16th to endDay
38%7%9%19%16%9%
1440
December1st to 15thDay
43%5%8%16%19%5%
1440
16th to endDay
46%410%19%14%4
1536
January1st to 15thNight
36%6%13%18%15%7%
2473
16th to endNight
40%48%16%18%11%
2496
February1st to 15thNight
42%5%9%18%17%5%
2288
16th to endNight
41%5%12%22%15%3
1948
March1st to 15thNight
47%6%9%16%14%5%
2019
16th to endNight
40%6%14%20%12%4
2088
April1st to 15thNight
39%6%15%20%14%4
1799
16th to endNight
24%413%29%21%6%
1785
May1st to 15thNight
20%410%25%27%10%
1563
16th to endNight
26%6%11%26%20%8%
1496
June1st to 15thNight
23%5%11%21%24%13%
1440
16th to endNight
11%2418%38%24%
1440
July1st to 15thNight
7%3413%32%38%
1360
16th to endNight
7%1312%23%51%
1527
August1st to 15thNight
8%1419%31%33%
1611
16th to endNight
5%1317%34%37%
1870
September1st to 15thNight
5%1414%29%45%
1800
16th to endNight
12%35%21%28%27%
1874
October1st to 15thNight
19%47%22%29%16%
1980
16th to endNight
25%48%26%19%14%
2112
November1st to 15thNight
30%7%14%27%12%7%
2242
16th to endNight
35%5%11%20%18%8%
2520
December1st to 15thNight
41%410%16%23%3
2520
16th to endNight
46%48%17%18%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
34%7%30%22%5%
90
16th to endDay
30%7%23%19%14%3
256
February1st to 15thDay
27%8%23%26%12%
236
16th to endDay
23%11%24%28%12%
229
March1st to 15thDay
34%14%21%17%9%2
270
16th to endDay
23%21%22%22%9%
288
April1st to 15thDay
21%21%26%23%5%1
269
16th to endDay
13%22%34%19%8%1
270
May1st to 15thDay
7%19%35%25%10%1
288
16th to endDay
10%12%26%30%15%4
330
June1st to 15thDay
9%15%28%30%14%1
315
16th to endDay
5%7%32%33%19%2
315
July1st to 15thDay
1226%40%23%3
305
16th to endDay
421%49%18%4
327
August1st to 15thDay
1429%37%22%3
315
16th to endDay
25%26%37%21%7%
332
September1st to 15thDay
15%22%41%25%3
315
16th to endDay
412%22%35%21%4
280
October1st to 15thDay
11%11%24%30%17%3
255
16th to endDay
19%5%27%27%18%1
272
November1st to 15thDay
17%421%30%22%3
128
16th to endDay
18%13%33%28%5%1
60
December1st to 15thDay
41%10%31%15%1
60
16th to endDay
17%39%35%7%
64
January1st to 15thNight
21%220%39%15%1
720
16th to endNight
26%219%31%17%1
768
February1st to 15thNight
25%418%36%15%
704
16th to endNight
25%5%20%35%12%1
632
March1st to 15thNight
26%5%21%28%16%1
720
16th to endNight
24%6%23%32%13%
768
April1st to 15thNight
17%10%26%28%14%1
719
16th to endNight
11%7%25%36%16%1
705
May1st to 15thNight
10%5%31%33%19%
483
16th to endNight
8%5%20%37%27%
375
June1st to 15thNight
8%324%43%19%
360
16th to endNight
4216%49%26%
360
July1st to 15thNight
16%39%50%1
340
16th to endNight
15%39%52%1
497
August1st to 15thNight
2434%55%2
538
16th to endNight
18%40%45%2
724
September1st to 15thNight
1111%33%47%4
720
16th to endNight
4313%34%39%3
683
October1st to 15thNight
9%419%34%28%3
660
16th to endNight
13%316%34%28%2
704
November1st to 15thNight
15%118%43%19%2
700
16th to endNight
19%418%37%18%1
720
December1st to 15thNight
28%321%31%13%1
720
16th to endNight
29%326%30%9%
768
Page generated at 2017-09-23 03:43:43. Version ac04

Copyright 2017 A. Danko


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