Powell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Powell Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
37%
16553
23%
48918
13%
16506
46%
16506
28%
29587

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
27%
975
21%
2522
7%
970
36%
970
28%
1602
January16th to endNight
26%
1040
26%
2704
8%
1040
38%
1040
28%
1708
February1st to 15thNight
20%
950
16%
2470
6%
946
27%
946
22%
1702
February16th to endNight
22%
660
24%
1922
7%
660
36%
660
24%
1187
March1st to 15thNight
27%
540
21%
1980
12%
540
40%
540
20%
1176
March16th to endNight
23%
576
15%
2112
10%
576
32%
576
17%
1385
April1st to 15thNight
28%
539
21%
1853
14%
539
42%
539
23%
1078
April16th to endNight
24%
540
20%
1719
10%
540
39%
540
18%
1119
May1st to 15thNight
33%
540
20%
1620
13%
540
44%
540
24%
1047
May16th to endNight
39%
563
19%
1670
12%
561
49%
561
25%
1029
June1st to 15thNight
52%
540
20%
1440
11%
540
57%
540
35%
840
June16th to endNight
53%
540
25%
1470
11%
540
62%
540
44%
790
July1st to 15thNight
63%
510
17%
1530
13%
510
66%
510
34%
873
July16th to endNight
63%
564
24%
1594
21%
531
72%
531
39%
843
August1st to 15thNight
72%
539
25%
1610
29%
536
75%
536
41%
857
August16th to endNight
68%
573
27%
1818
29%
573
72%
573
37%
998
September1st to 15thNight
57%
540
25%
1850
27%
540
61%
540
29%
1048
September16th to endNight
58%
537
29%
1980
24%
537
69%
537
31%
1032
October1st to 15thNight
43%
714
27%
2154
19%
714
48%
714
31%
1257
October16th to endNight
38%
768
30%
2304
15%
768
50%
768
34%
1288
November1st to 15thNight
33%
815
28%
2335
13%
815
45%
815
30%
1355
November16th to endNight
28%
975
26%
2697
9%
975
41%
975
29%
1636
December1st to 15thNight
26%
975
20%
2730
8%
975
36%
975
23%
1757
December16th to endNight
24%
1040
22%
2834
7%
1040
35%
1040
20%
1980

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
12%6%25%42445%7%44%
49141
Night
10%5%24424446%49%
49113
TransparencyDay
38%6%13%24%14%2
48841
Night
34%5%12%26%17%3
48918
SeeingDay
12%13%24%26%18%4
6342
Night
12%19%26%27%12%1
16553

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
11%5%36%5%2443447%
1746
16th to endDay
11%8%35%424347%44%
1872
February1st to 15thDay
11%10%5%6%433447%39%
1694
16th to endDay
13%9%35%42245%6%41%
1560
March1st to 15thDay
11%9%46%5%35%5%5%6%35%
1980
16th to endDay
21%9%46%42323435%
2110
April1st to 15thDay
15%8%25%5%23346%42%
2094
16th to endDay
21%7%26%5%34445%34%
2238
May1st to 15thDay
19%6%36%5%25%446%36%
2331
16th to endDay
14%6%36%5%3445%7%37%
2442
June1st to 15thDay
9%425%5%25%5%7%9%43%
2520
16th to endDay
5%2135%245%6%10%50%
2485
July1st to 15thDay
8%3244345%6%9%46%
2340
16th to endDay
6%314435%6%6%10%47%
2466
August1st to 15thDay
7%414425%5%7%10%45%
2340
16th to endDay
8%4245%245%6%8%48%
2382
September1st to 15thDay
12%424434446%49%
2107
16th to endDay
9%315%4245%5%7%51%
1974
October1st to 15thDay
14%6%24322346%49%
1800
16th to endDay
12%42432334454%
1920
November1st to 15thDay
11%6%24312347%52%
1849
16th to endDay
16%6%23213346%49%
1592
December1st to 15thDay
13%7%36%5%24246%43%
1560
16th to endDay
14%8%47%42445%6%39%
1739
January1st to 15thNight
9%6%345%14446%50%
2522
16th to endNight
8%6%35%424346%50%
2704
February1st to 15thNight
11%8%36%5%34445%41%
2460
16th to endNight
11%5%26%333346%47%
1922
March1st to 15thNight
11%8%2441335%6%46%
1980
16th to endNight
17%8%36%324446%38%
2112
April1st to 15thNight
11%6%245%13346%50%
1853
16th to endNight
16%7%35%42334444%
1719
May1st to 15thNight
14%5%25%42445%6%44%
1619
16th to endNight
12%41342435%9%47%
1668
June1st to 15thNight
5%313435%45%10%53%
1440
16th to endNight
41133135%5%10%60%
1470
July1st to 15thNight
7%21343449%9%50%
1620
16th to endNight
43133245%6%10%53%
1702
August1st to 15thNight
5%212425%5%5%9%55%
1620
16th to endNight
5%4245%24347%56%
1818
September1st to 15thNight
10%42442435%6%51%
1850
16th to endNight
6%3143345%47%54%
1980
October1st to 15thNight
13%413224335%54%
2154
16th to endNight
10%413313335%58%
2304
November1st to 15thNight
10%424322346%55%
2335
16th to endNight
14%6%24323245%52%
2697
December1st to 15thNight
14%7%24423446%45%
2730
16th to endNight
14%8%37%423445%39%
2834

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
39%5%11%25%17%1
1747
16th to endDay
40%415%24%13%1
1872
February1st to 15thDay
45%5%16%22%9%1
1695
16th to endDay
42%414%23%12%2
1560
March1st to 15thDay
46%7%10%21%11%2
1980
16th to endDay
53%5%12%19%8%1
2112
April1st to 15thDay
43%5%11%24%14%
2094
16th to endDay
51%5%11%19%11%
2238
May1st to 15thDay
49%6%10%20%12%
2331
16th to endDay
45%8%14%20%10%
2446
June1st to 15thDay
35%8%15%25%14%1
2520
16th to endDay
25%8%17%30%16%2
2485
July1st to 15thDay
33%8%16%27%12%2
2201
16th to endDay
28%8%15%32%13%1
2311
August1st to 15thDay
30%9%16%26%15%1
2326
16th to endDay
32%7%13%24%15%6%
2382
September1st to 15thDay
35%5%12%23%17%5%
2107
16th to endDay
30%6%12%29%19%2
1974
October1st to 15thDay
34%5%10%23%20%5%
1800
16th to endDay
33%410%25%20%5%
1920
November1st to 15thDay
32%5%11%25%19%5%
1849
16th to endDay
36%410%27%20%
1592
December1st to 15thDay
43%413%26%11%
1560
16th to endDay
45%5%14%20%11%2
1739
January1st to 15thNight
35%5%14%26%17%1
2522
16th to endNight
34%5%13%28%16%2
2704
February1st to 15thNight
43%6%13%23%12%1
2470
16th to endNight
36%412%24%18%2
1922
March1st to 15thNight
39%411%23%16%4
1980
16th to endNight
46%5%11%23%10%1
2112
April1st to 15thNight
35%48%26%20%2
1853
16th to endNight
42%5%10%23%15%1
1719
May1st to 15thNight
40%5%12%23%16%
1620
16th to endNight
35%6%16%25%12%2
1670
June1st to 15thNight
25%8%15%31%16%2
1440
16th to endNight
19%6%16%30%23%3
1470
July1st to 15thNight
27%6%15%31%15%3
1530
16th to endNight
22%7%14%32%21%2
1594
August1st to 15thNight
22%7%14%33%18%3
1610
16th to endNight
26%6%10%24%25%6%
1818
September1st to 15thNight
33%5%10%23%19%7%
1850
16th to endNight
27%6%11%29%22%3
1980
October1st to 15thNight
32%48%23%22%7%
2154
16th to endNight
29%48%28%23%5%
2304
November1st to 15thNight
31%411%23%21%7%
2335
16th to endNight
35%38%29%20%2
2697
December1st to 15thNight
39%414%26%13%
2730
16th to endNight
46%6%11%20%12%3
2834

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
25%11%36%20%5%
135
16th to endDay
15%12%44%22%4
144
February1st to 15thDay
10%21%43%21%3
130
16th to endDay
16%22%38%16%6%1
81
March1st to 15thDay
26%13%46%11%2
90
16th to endDay
28%17%30%19%4
96
April1st to 15thDay
17%22%30%19%10%
213
16th to endDay
23%20%29%17%6%1
348
May1st to 15thDay
18%19%28%22%9%1
468
16th to endDay
16%18%28%21%9%4
517
June1st to 15thDay
7%15%22%30%17%5%
495
16th to endDay
414%28%28%20%3
495
July1st to 15thDay
12%10%13%32%25%5%
475
16th to endDay
312%9%30%35%8%
515
August1st to 15thDay
7%7%7%35%36%5%
493
16th to endDay
9%6%12%26%36%8%
422
September1st to 15thDay
8%6%13%33%30%8%
262
16th to endDay
9%418%40%17%9%
135
October1st to 15thDay
14%434%31%6%8%
135
16th to endDay
12%9%38%29%9%
144
November1st to 15thDay
14%11%23%28%15%6%
135
16th to endDay
28%11%30%19%8%
135
December1st to 15thDay
12%17%42%18%43
135
16th to endDay
19%16%42%18%3
144
January1st to 15thNight
11%24%33%24%5%
975
16th to endNight
10%24%34%25%5%
1040
February1st to 15thNight
14%24%35%22%3
950
16th to endNight
14%26%33%21%3
660
March1st to 15thNight
15%22%30%24%6%
540
16th to endNight
18%23%31%20%5%
576
April1st to 15thNight
12%24%30%26%6%
539
16th to endNight
20%22%30%19%7%
540
May1st to 15thNight
15%20%27%25%10%1
540
16th to endNight
13%19%23%26%13%1
563
June1st to 15thNight
7%17%18%37%17%2
540
16th to endNight
217%22%39%15%
540
July1st to 15thNight
7%11%12%40%24%2
510
16th to endNight
5%16%8%33%34%2
564
August1st to 15thNight
6%10%5%41%34%1
539
16th to endNight
7%9%9%35%33%4
573
September1st to 15thNight
13%10%14%35%23%3
540
16th to endNight
8%9%18%34%24%5%
537
October1st to 15thNight
15%13%24%28%16%2
714
16th to endNight
10%15%32%28%12%
768
November1st to 15thNight
11%21%29%24%11%
815
16th to endNight
16%23%30%22%7%
975
December1st to 15thNight
18%24%27%25%4
975
16th to endNight
16%23%31%25%3
1040
Page generated at 2018-02-15 09:58:38. Version ac04

Copyright 2018 A. Danko


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