Pleasant Grove Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pleasant Grove Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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%
15634
23%
47006
15%
15591
56%
15591
27%
29332

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
29%
720
24%
2327
11%
716
44%
716
20%
1438
January16th to endNight
26%
768
25%
2496
11%
768
44%
768
21%
1529
February1st to 15thNight
30%
704
27%
2126
10%
701
48%
701
25%
1277
February16th to endNight
26%
631
26%
1893
10%
631
42%
631
26%
1150
March1st to 15thNight
33%
720
24%
2022
12%
720
42%
720
28%
1267
March16th to endNight
38%
768
21%
2112
11%
768
46%
768
29%
1328
April1st to 15thNight
41%
706
25%
1964
14%
706
50%
706
33%
1167
April16th to endNight
47%
540
24%
1651
15%
540
55%
540
30%
988
May1st to 15thNight
47%
540
19%
1620
10%
540
54%
540
29%
1020
May16th to endNight
61%
561
19%
1683
14%
561
64%
561
28%
1064
June1st to 15thNight
65%
540
16%
1620
13%
540
67%
540
30%
1027
June16th to endNight
72%
540
15%
1620
14%
540
72%
540
31%
1014
July1st to 15thNight
66%
510
10%
1530
9%
510
67%
510
22%
1068
July16th to endNight
73%
564
15%
1595
12%
531
75%
531
26%
1063
August1st to 15thNight
68%
539
15%
1609
14%
536
68%
536
22%
1121
August16th to endNight
64%
598
15%
1882
15%
598
65%
598
21%
1304
September1st to 15thNight
63%
720
17%
1980
15%
720
65%
720
27%
1340
September16th to endNight
55%
693
22%
1914
17%
693
60%
693
29%
1254
October1st to 15thNight
51%
660
31%
1864
24%
660
59%
660
33%
1131
October16th to endNight
54%
704
34%
2112
26%
704
67%
704
39%
1150
November1st to 15thNight
53%
700
31%
2210
26%
700
63%
700
38%
1188
November16th to endNight
40%
720
27%
2340
19%
720
53%
720
29%
1346
December1st to 15thNight
39%
720
24%
2340
16%
720
50%
720
23%
1444
December16th to endNight
32%
768
22%
2496
15%
768
43%
768
19%
1654

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
13%4245%3445%7%42%
47918
Night
13%42442445%7%45%
47204
TransparencyDay
38%7%11%19%17%5%
47619
Night
36%6%11%19%19%6%
47007
SeeingDay
17%6%18%23%21%12%
5497
Night
15%7%22%29%21%3
15636

By Month

Percentage Cloud Cover SE (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
17%5%2442334445%
1611
16th to endDay
18%5%1431335%5%47%
1728
February1st to 15thDay
15%424433445%47%
1735
16th to endDay
17%5%35%323336%45%
1580
March1st to 15thDay
16%413423347%47%
1938
16th to endDay
17%423424346%44%
2111
April1st to 15thDay
12%325%32445%7%46%
1993
16th to endDay
10%414424447%48%
2307
May1st to 15thDay
11%4245%35%46%7%43%
2331
16th to endDay
11%4245%35%5%6%9%41%
2431
June1st to 15thDay
9%425%5%5%6%6%7%11%35%
2340
16th to endDay
5%2146%37%7%8%11%40%
2340
July1st to 15thDay
10%5%36%6%36%7%7%11%32%
2340
16th to endDay
7%425%6%46%7%8%12%32%
2465
August1st to 15thDay
11%5%17%6%47%7%7%9%31%
2340
16th to endDay
14%6%37%7%36%5%7%9%28%
2303
September1st to 15thDay
13%5%246%35%5%6%8%38%
1980
16th to endDay
19%42342345%7%42%
1905
October1st to 15thDay
15%413212235%55%
1766
16th to endDay
11%31331223460%
1760
November1st to 15thDay
12%32332334456%
1646
16th to endDay
15%414313346%49%
1620
December1st to 15thDay
18%7%24333345%42%
1620
16th to endDay
25%7%2442233439%
1728
January1st to 15thNight
18%5%25%32433447%
2327
16th to endNight
17%6%23423345%46%
2496
February1st to 15thNight
15%413424335%50%
2117
16th to endNight
16%413423345%49%
1893
March1st to 15thNight
14%424424445%49%
2022
16th to endNight
14%42432436%7%47%
2112
April1st to 15thNight
13%313323346%52%
1964
16th to endNight
11%4144245%46%49%
1651
May1st to 15thNight
10%5%2443445%7%44%
1619
16th to endNight
8%415%445%5%6%9%43%
1682
June1st to 15thNight
8%5%245%35%6%7%13%38%
1620
16th to endNight
6%3245%25%7%9%11%41%
1620
July1st to 15thNight
9%5%37%5%45%6%7%11%33%
1620
16th to endNight
6%425%6%37%7%9%14%32%
1703
August1st to 15thNight
11%5%15%6%5%6%8%10%9%31%
1620
16th to endNight
10%5%25%6%46%7%7%10%33%
1882
September1st to 15thNight
11%4145%36%7%6%9%37%
1980
16th to endNight
15%5%244235%5%7%43%
1914
October1st to 15thNight
15%323313245%53%
1864
16th to endNight
10%313323335%59%
2112
November1st to 15thNight
11%313313235%59%
2210
16th to endNight
16%323412345%51%
2340
December1st to 15thNight
15%5%25%423345%45%
2340
16th to endNight
22%5%25%423336%39%
2496

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%49%15%24%4
1612
16th to endDay
38%36%19%22%8%
1728
February1st to 15thDay
39%39%19%23%5%
1737
16th to endDay
40%36%21%20%7%
1580
March1st to 15thDay
37%5%8%20%19%8%
1938
16th to endDay
40%5%11%21%17%4
2112
April1st to 15thDay
36%410%19%22%5%
1993
16th to endDay
34%6%9%21%22%6%
2307
May1st to 15thDay
36%8%12%19%18%3
2331
16th to endDay
37%9%14%22%14%1
2435
June1st to 15thDay
39%9%19%20%8%1
2340
16th to endDay
32%11%17%20%13%3
2340
July1st to 15thDay
40%12%17%18%7%2
2201
16th to endDay
38%13%20%18%8%2
2310
August1st to 15thDay
44%11%14%19%9%1
2327
16th to endDay
49%10%15%13%9%1
2303
September1st to 15thDay
42%8%12%18%16%2
1980
16th to endDay
40%6%11%20%17%4
1905
October1st to 15thDay
32%310%20%25%7%
1766
16th to endDay
29%35%20%30%11%
1760
November1st to 15thDay
31%37%17%28%11%
1646
16th to endDay
35%37%18%26%7%
1620
December1st to 15thDay
43%5%7%19%16%8%
1620
16th to endDay
49%37%17%14%7%
1728
January1st to 15thNight
41%37%15%25%6%
2327
16th to endNight
40%35%18%22%9%
2496
February1st to 15thNight
37%36%19%24%8%
2126
16th to endNight
37%37%21%22%7%
1893
March1st to 15thNight
36%5%10%16%22%8%
2022
16th to endNight
36%5%11%19%20%6%
2112
April1st to 15thNight
32%39%23%23%7%
1964
16th to endNight
34%6%10%21%18%9%
1651
May1st to 15thNight
37%6%13%19%19%2
1620
16th to endNight
34%10%14%25%12%2
1684
June1st to 15thNight
35%8%20%23%10%1
1620
16th to endNight
29%13%18%22%13%3
1620
July1st to 15thNight
40%12%19%18%6%1
1530
16th to endNight
35%14%22%18%8%2
1595
August1st to 15thNight
41%11%16%19%8%
1609
16th to endNight
40%13%18%14%11%1
1882
September1st to 15thNight
37%11%15%17%13%3
1980
16th to endNight
38%7%12%19%15%5%
1914
October1st to 15thNight
34%48%18%25%8%
1864
16th to endNight
28%36%19%29%13%
2112
November1st to 15thNight
29%36%17%31%13%
2210
16th to endNight
34%36%17%27%10%
2340
December1st to 15thNight
40%37%19%18%8%
2340
16th to endNight
46%48%15%18%6%
2496

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
27%6%34%26%4
90
16th to endDay
26%27%33%11%2
96
February1st to 15thDay
17%20%47%14%
90
16th to endDay
27%11%40%19%1
81
March1st to 15thDay
18%17%25%28%8%
228
16th to endDay
19%11%30%22%14%1
288
April1st to 15thDay
20%10%23%21%20%2
270
16th to endDay
12%427%27%20%6%
270
May1st to 15thDay
12%10%30%17%18%11%
288
16th to endDay
17%5%14%22%23%16%
331
June1st to 15thDay
12%310%26%25%21%
315
16th to endDay
9%16%23%22%26%
315
July1st to 15thDay
12%110%24%27%22%
305
16th to endDay
7%16%26%33%24%
326
August1st to 15thDay
18%18%23%28%19%
313
16th to endDay
16%110%23%28%18%
332
September1st to 15thDay
16%210%20%32%18%
315
16th to endDay
24%111%24%27%10%
287
October1st to 15thDay
22%418%27%20%7%
255
16th to endDay
14%5%18%27%28%6%
272
November1st to 15thDay
26%9%18%25%17%2
154
16th to endDay
15%5%25%36%12%4
90
December1st to 15thDay
32%11%32%16%7%
90
16th to endDay
40%14%23%15%41
96
January1st to 15thNight
23%15%26%25%8%
720
16th to endNight
21%16%31%27%2
768
February1st to 15thNight
17%15%31%31%3
704
16th to endNight
17%16%34%26%3
631
March1st to 15thNight
18%12%32%29%6%
720
16th to endNight
16%11%28%28%14%
768
April1st to 15thNight
15%11%29%29%13%
706
16th to endNight
13%7%25%31%21%
540
May1st to 15thNight
12%5%26%33%19%2
540
16th to endNight
12%215%32%31%5%
563
June1st to 15thNight
10%113%31%33%9%
540
16th to endNight
7%11%29%38%12%
540
July1st to 15thNight
11%16%29%40%10%
510
16th to endNight
6%8%30%44%9%
564
August1st to 15thNight
12%6%28%41%8%
539
16th to endNight
14%9%26%38%10%
598
September1st to 15thNight
12%112%24%39%9%
720
16th to endNight
18%116%29%29%4
693
October1st to 15thNight
16%5%21%25%25%4
660
16th to endNight
11%6%22%32%23%2
704
November1st to 15thNight
13%5%22%33%21%2
700
16th to endNight
17%10%26%29%15%
720
December1st to 15thNight
19%11%24%31%12%
720
16th to endNight
25%10%25%30%7%
768
Page generated at 2017-09-25 09:02:30. Version ac04

Copyright 2017 A. Danko


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