Mount Shasta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Shasta clear sky chart from 2005-11-05 to 2017-08-12.

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
48%
14859
21%
46522
17%
14826
54%
14826
31%
27300

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
41%
717
15%
2497
13%
716
47%
716
20%
1641
January16th to endNight
43%
768
21%
2496
20%
768
47%
768
23%
1626
February1st to 15thNight
39%
699
14%
2288
12%
699
44%
699
19%
1550
February16th to endNight
36%
632
17%
1951
13%
632
42%
632
20%
1328
March1st to 15thNight
33%
720
11%
2028
8%
720
37%
720
18%
1486
March16th to endNight
32%
768
12%
2082
7%
768
36%
768
19%
1512
April1st to 15thNight
31%
719
12%
1799
4%
719
35%
719
21%
1290
April16th to endNight
39%
698
19%
1778
8%
698
44%
698
35%
1079
May1st to 15thNight
42%
461
20%
1541
11%
461
51%
461
36%
784
May16th to endNight
45%
374
18%
1496
17%
374
53%
374
26%
803
June1st to 15thNight
46%
360
18%
1440
16%
360
59%
360
29%
747
June16th to endNight
59%
360
29%
1440
32%
360
72%
360
52%
544
July1st to 15thNight
76%
340
30%
1360
37%
340
84%
340
60%
475
July16th to endNight
81%
469
36%
1502
35%
440
87%
440
66%
584
August1st to 15thNight
84%
526
37%
1575
30%
523
87%
523
70%
660
August16th to endNight
73%
660
41%
1710
25%
660
77%
660
76%
756
September1st to 15thNight
76%
660
44%
1650
25%
660
82%
660
83%
715
September16th to endNight
67%
656
34%
1804
28%
656
71%
656
56%
871
October1st to 15thNight
55%
660
26%
1980
22%
660
64%
660
44%
1017
October16th to endNight
55%
704
24%
2112
23%
704
60%
704
33%
1252
November1st to 15thNight
43%
700
16%
2265
15%
700
47%
700
24%
1445
November16th to endNight
42%
720
15%
2520
13%
720
48%
720
21%
1611
December1st to 15thNight
38%
720
15%
2520
12%
720
44%
720
20%
1657
December16th to endNight
31%
768
16%
2688
13%
768
38%
768
16%
1867

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%6%23323346%51%
47463
Night
12%7%23323346%50%
46702
TransparencyDay
31%411%19%19%12%
47143
Night
33%5%13%20%18%9%
46523
SeeingDay
17%18%30%23%8%1
5665
Night
16%7%23%31%18%2
14869

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
16%8%245%2335%9%37%
1438
16th to endDay
18%13%24312325%40%
1728
February1st to 15thDay
19%9%3432346%7%35%
1576
16th to endDay
13%14%445%24447%33%
1523
March1st to 15thDay
19%16%35%323446%29%
1930
16th to endDay
19%14%3441335%8%30%
2141
April1st to 15thDay
17%12%26%6%23448%31%
2149
16th to endDay
8%7%35%42435%8%45%
2181
May1st to 15thDay
7%5%2332446%8%52%
2409
16th to endDay
13%8%23424448%44%
2615
June1st to 15thDay
9%424424346%51%
2520
16th to endDay
6%21121233470%
2520
July1st to 15thDay
112213335%73%
2520
16th to endDay
21111233477%
2561
August1st to 15thDay
212213346%71%
2291
16th to endDay
11111222480%
2140
September1st to 15thDay
11121233478%
1980
16th to endDay
4212212336%67%
1824
October1st to 15thDay
11%312312346%58%
1650
16th to endDay
15%6%1332435%6%47%
1760
November1st to 15thDay
14%6%145%336%48%40%
1591
16th to endDay
15%9%26%424347%38%
1440
December1st to 15thDay
20%12%2442336%5%34%
1440
16th to endDay
26%11%23313445%32%
1536
January1st to 15thNight
14%9%35%4245%5%5%39%
2497
16th to endNight
16%10%34323347%40%
2496
February1st to 15thNight
19%10%25%334448%34%
2276
16th to endNight
15%14%23433347%36%
1951
March1st to 15thNight
21%13%35%423347%30%
2028
16th to endNight
18%12%3332345%8%34%
2082
April1st to 15thNight
14%12%25%5%3445%8%34%
1799
16th to endNight
10%5%13323347%53%
1778
May1st to 15thNight
6%31242445%7%58%
1541
16th to endNight
10%41442235%8%51%
1496
June1st to 15thNight
8%425%41335%6%55%
1440
16th to endNight
4211112235%74%
1440
July1st to 15thNight
112212336%74%
1440
16th to endNight
2111112281%
1605
August1st to 15thNight
11111233478%
1584
16th to endNight
1111212383%
1710
September1st to 15thNight
13485%
1650
16th to endNight
412223236%69%
1804
October1st to 15thNight
8%312322245%62%
1980
16th to endNight
12%5%14313347%51%
2112
November1st to 15thNight
14%5%244245%6%8%41%
2265
16th to endNight
15%8%2442445%6%39%
2520
December1st to 15thNight
21%10%33213346%37%
2520
16th to endNight
22%14%23313446%33%
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
41%8%14%20%10%4
1438
16th to endDay
46%39%17%11%9%
1728
February1st to 15thDay
45%6%14%19%11%2
1576
16th to endDay
48%5%15%20%7%1
1523
March1st to 15thDay
54%5%12%14%11%1
1930
16th to endDay
51%8%16%13%8%2
2141
April1st to 15thDay
50%5%15%18%10%
2149
16th to endDay
34%5%17%27%12%2
2181
May1st to 15thDay
28%6%13%27%18%5%
2409
16th to endDay
35%6%15%23%15%2
2619
June1st to 15thDay
31%412%19%24%6%
2520
16th to endDay
16%39%24%32%15%
2520
July1st to 15thDay
12%26%16%31%30%
2371
16th to endDay
10%26%12%28%39%
2402
August1st to 15thDay
12%37%18%29%28%
2275
16th to endDay
9%2416%38%28%
2140
September1st to 15thDay
9%16%13%33%35%
1980
16th to endDay
17%49%23%28%17%
1824
October1st to 15thDay
25%312%25%23%9%
1650
16th to endDay
35%5%12%21%16%9%
1760
November1st to 15thDay
39%7%16%19%11%4
1591
16th to endDay
45%5%11%17%12%5%
1440
December1st to 15thDay
48%5%12%18%13%
1440
16th to endDay
52%6%11%16%9%3
1536
January1st to 15thNight
43%8%12%17%12%5%
2497
16th to endNight
43%5%9%17%13%10%
2496
February1st to 15thNight
47%6%15%15%11%3
2288
16th to endNight
46%5%14%19%11%2
1951
March1st to 15thNight
54%412%14%13%1
2028
16th to endNight
46%9%17%15%8%1
2082
April1st to 15thNight
46%6%19%17%8%1
1799
16th to endNight
28%8%21%28%10%2
1778
May1st to 15thNight
23%7%18%30%16%4
1542
16th to endNight
30%7%17%30%11%1
1496
June1st to 15thNight
28%6%15%23%22%3
1440
16th to endNight
14%29%31%33%7%
1440
July1st to 15thNight
9%36%23%31%26%
1360
16th to endNight
10%1413%34%34%
1502
August1st to 15thNight
9%36%24%33%23%
1575
16th to endNight
7%17%19%39%24%
1710
September1st to 15thNight
415%16%38%34%
1650
16th to endNight
16%311%24%23%21%
1804
October1st to 15thNight
23%312%26%25%9%
1980
16th to endNight
31%6%13%21%18%8%
2112
November1st to 15thNight
38%9%19%17%11%4
2265
16th to endNight
42%7%13%16%14%6%
2520
December1st to 15thNight
47%411%18%16%1
2520
16th to endNight
50%6%11%14%13%3
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
39%15%25%12%6%1
66
16th to endDay
31%16%23%15%11%1
256
February1st to 15thDay
30%14%27%20%5%
236
16th to endDay
25%21%30%19%2
229
March1st to 15thDay
35%21%24%10%7%
270
16th to endDay
32%27%22%12%4
288
April1st to 15thDay
33%20%28%14%21
269
16th to endDay
22%29%25%17%3
270
May1st to 15thDay
14%29%32%16%5%1
288
16th to endDay
20%20%22%23%9%3
330
June1st to 15thDay
16%20%32%21%7%
315
16th to endDay
7%16%36%26%10%1
315
July1st to 15thDay
39%39%33%10%3
305
16th to endDay
111%36%35%11%3
327
August1st to 15thDay
110%39%32%11%5%
300
16th to endDay
413%42%24%11%4
268
September1st to 15thDay
315%29%40%9%2
255
16th to endDay
8%18%28%32%10%1
255
October1st to 15thDay
15%20%29%21%10%1
255
16th to endDay
24%18%26%23%8%
272
November1st to 15thDay
19%10%25%27%14%1
112
16th to endDay
16%23%38%15%6%
60
December1st to 15thDay
36%21%28%13%
60
16th to endDay
21%10%25%28%12%1
64
January1st to 15thNight
19%6%26%29%14%3
720
16th to endNight
22%7%21%25%16%5%
768
February1st to 15thNight
24%8%23%28%13%1
704
16th to endNight
24%8%25%28%11%1
632
March1st to 15thNight
29%10%20%21%14%2
720
16th to endNight
26%14%23%22%11%
768
April1st to 15thNight
23%15%26%22%11%
719
16th to endNight
14%12%30%27%12%2
698
May1st to 15thNight
9%11%33%29%16%
462
16th to endNight
15%7%27%32%15%1
375
June1st to 15thNight
8%8%31%35%14%
360
16th to endNight
6%5%27%48%11%
360
July1st to 15thNight
2217%44%33%
340
16th to endNight
2111%49%33%1
469
August1st to 15thNight
211%45%36%3
526
16th to endNight
3218%45%27%3
660
September1st to 15thNight
1417%34%37%5%
660
16th to endNight
6%5%17%35%30%4
656
October1st to 15thNight
10%7%23%33%21%3
660
16th to endNight
17%6%17%32%20%5%
704
November1st to 15thNight
16%5%29%31%12%4
700
16th to endNight
20%8%24%29%15%2
720
December1st to 15thNight
27%7%21%25%14%2
720
16th to endNight
30%9%24%23%9%1
768
Page generated at 2017-08-13 11:16:40. Version ac04

Copyright 2017 A. Danko


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