Mountville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mountville Observatory clear sky chart from 2005-11-05 to 2017-09-21.

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
49%
15463
23%
46996
16%
15419
57%
15419
28%
28857

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
26%
720
23%
2327
9%
716
43%
716
21%
1448
January16th to endNight
25%
768
23%
2394
11%
768
39%
768
21%
1544
February1st to 15thNight
30%
704
25%
2111
10%
700
44%
700
26%
1309
February16th to endNight
27%
631
25%
1893
10%
631
41%
631
25%
1181
March1st to 15thNight
31%
720
24%
2083
12%
720
42%
720
28%
1285
March16th to endNight
39%
768
23%
2112
12%
768
48%
768
30%
1297
April1st to 15thNight
44%
605
25%
1863
17%
605
54%
605
32%
1065
April16th to endNight
48%
540
27%
1743
19%
540
58%
540
33%
971
May1st to 15thNight
51%
539
22%
1620
14%
539
58%
539
32%
972
May16th to endNight
62%
561
21%
1682
15%
561
66%
561
33%
1008
June1st to 15thNight
68%
540
17%
1620
15%
540
69%
540
30%
1036
June16th to endNight
77%
540
17%
1620
16%
540
77%
540
33%
1000
July1st to 15thNight
76%
510
13%
1530
13%
510
77%
510
28%
997
July16th to endNight
75%
564
16%
1595
15%
531
76%
531
29%
1039
August1st to 15thNight
74%
539
17%
1710
19%
536
74%
536
27%
1111
August16th to endNight
68%
573
18%
1910
20%
573
69%
573
23%
1266
September1st to 15thNight
66%
688
21%
1948
19%
688
67%
688
29%
1272
September16th to endNight
62%
681
25%
1881
19%
681
66%
681
29%
1225
October1st to 15thNight
56%
660
32%
1815
24%
660
64%
660
40%
1046
October16th to endNight
51%
704
34%
2087
27%
704
60%
704
38%
1137
November1st to 15thNight
51%
700
30%
2276
25%
700
61%
700
35%
1219
November16th to endNight
40%
720
27%
2340
18%
720
53%
720
29%
1326
December1st to 15thNight
35%
720
23%
2340
15%
720
47%
720
25%
1446
December16th to endNight
33%
768
20%
2496
14%
768
42%
768
19%
1657

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%5%25%5%35%5%5%7%40%
47855
Night
10%5%2442445%7%46%
47196
TransparencyDay
40%7%11%17%17%5%
47556
Night
35%6%11%19%19%7%
46999
SeeingDay
14%6%20%23%22%12%
5355
Night
13%8%22%28%21%4
15466

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
14%8%23424445%44%
1611
16th to endDay
17%7%24423435%44%
1828
February1st to 15thDay
14%6%245%23345%44%
1750
16th to endDay
15%6%25%434345%43%
1580
March1st to 15thDay
14%8%36%424345%43%
1875
16th to endDay
15%4235%245%5%7%43%
2111
April1st to 15thDay
12%5%25%434346%46%
2094
16th to endDay
10%42442345%7%49%
2214
May1st to 15thDay
10%6%25%435%46%7%45%
2331
16th to endDay
7%316%6%36%5%7%7%43%
2431
June1st to 15thDay
8%5%36%7%5%7%7%6%10%31%
2340
16th to endDay
5%415%7%37%7%7%12%37%
2340
July1st to 15thDay
11%435%7%5%8%7%8%11%25%
2340
16th to endDay
8%5%27%7%5%8%8%8%11%25%
2465
August1st to 15thDay
7%5%37%7%5%8%8%9%10%27%
2236
16th to endDay
13%6%26%7%46%7%7%7%28%
2292
September1st to 15thDay
12%5%35%6%45%6%5%7%36%
1998
16th to endDay
14%6%145%4445%6%40%
1872
October1st to 15thDay
12%5%24323346%52%
1815
16th to endDay
11%42321323458%
1782
November1st to 15thDay
10%5%24313345%55%
1582
16th to endDay
14%414423345%51%
1620
December1st to 15thDay
15%6%3442345%6%43%
1620
16th to endDay
22%7%35%433335%35%
1728
January1st to 15thNight
15%7%245%23345%45%
2327
16th to endNight
17%6%35%42334443%
2394
February1st to 15thNight
14%5%245%23345%47%
2103
16th to endNight
14%6%343235%45%46%
1893
March1st to 15thNight
11%5%3442435%6%48%
2083
16th to endNight
9%6%25%42435%8%47%
2112
April1st to 15thNight
12%41332445%7%50%
1863
16th to endNight
8%5%14325%45%7%52%
1743
May1st to 15thNight
9%323425%5%5%8%49%
1619
16th to endNight
5%5%25%4346%5%8%47%
1682
June1st to 15thNight
5%425%6%346%8%10%41%
1620
16th to endNight
43245%36%6%9%12%41%
1620
July1st to 15thNight
5%4146%35%7%9%13%37%
1620
16th to endNight
6%2246%36%7%8%12%38%
1703
August1st to 15thNight
4425%5%36%7%9%11%38%
1721
16th to endNight
10%425%5%38%5%7%10%34%
1910
September1st to 15thNight
8%425%5%35%5%7%9%41%
1948
16th to endNight
10%4245%35%5%6%7%44%
1881
October1st to 15thNight
10%414323346%55%
1815
16th to endNight
9%32342223461%
2087
November1st to 15thNight
11%423322335%58%
2276
16th to endNight
12%423323335%53%
2340
December1st to 15thNight
13%6%25%424335%46%
2340
16th to endNight
19%7%35%433445%38%
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
40%48%14%25%6%
1612
16th to endDay
42%36%15%23%8%
1828
February1st to 15thDay
41%36%18%23%5%
1752
16th to endDay
42%46%16%22%7%
1580
March1st to 15thDay
43%48%15%20%7%
1875
16th to endDay
39%6%10%19%19%3
2112
April1st to 15thDay
38%49%20%19%8%
2094
16th to endDay
32%5%11%19%25%5%
2214
May1st to 15thDay
37%7%11%16%20%5%
2331
16th to endDay
35%9%13%23%13%3
2435
June1st to 15thDay
45%10%15%19%8%1
2340
16th to endDay
35%10%17%20%13%2
2340
July1st to 15thDay
44%15%19%13%5%1
2201
16th to endDay
45%12%17%16%7%
2310
August1st to 15thDay
45%13%16%16%8%
2223
16th to endDay
50%10%15%14%8%
2292
September1st to 15thDay
45%10%12%15%13%4
1998
16th to endDay
42%7%10%19%16%4
1872
October1st to 15thDay
33%410%19%23%8%
1815
16th to endDay
30%26%15%31%13%
1782
November1st to 15thDay
32%36%16%26%14%
1582
16th to endDay
35%47%16%24%11%
1620
December1st to 15thDay
41%48%20%17%7%
1620
16th to endDay
52%27%16%13%7%
1728
January1st to 15thNight
40%46%17%24%6%
2327
16th to endNight
43%35%15%21%9%
2394
February1st to 15thNight
38%35%19%20%11%
2112
16th to endNight
38%5%6%17%24%8%
1893
March1st to 15thNight
36%49%20%20%8%
2083
16th to endNight
34%5%10%21%22%6%
2112
April1st to 15thNight
32%49%22%20%10%
1863
16th to endNight
29%6%9%24%21%8%
1743
May1st to 15thNight
31%8%13%19%24%3
1620
16th to endNight
31%8%14%23%15%5%
1684
June1st to 15thNight
34%9%18%24%12%
1620
16th to endNight
30%10%20%22%13%2
1620
July1st to 15thNight
32%14%23%19%7%2
1530
16th to endNight
33%12%22%20%9%1
1595
August1st to 15thNight
34%13%19%21%10%1
1710
16th to endNight
40%10%17%16%12%2
1910
September1st to 15thNight
36%9%13%21%14%4
1948
16th to endNight
37%8%9%21%17%6%
1881
October1st to 15thNight
29%410%22%21%11%
1815
16th to endNight
28%35%14%31%16%
2087
November1st to 15thNight
29%37%15%28%15%
2276
16th to endNight
34%37%16%25%13%
2340
December1st to 15thNight
40%48%19%20%7%
2340
16th to endNight
47%48%16%17%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
21%21%34%14%5%3
90
16th to endDay
22%21%44%5%5%
96
February1st to 15thDay
20%23%41%13%2
90
16th to endDay
25%16%41%16%
81
March1st to 15thDay
19%20%33%18%7%1
165
16th to endDay
17%11%32%24%12%1
288
April1st to 15thDay
20%14%26%19%16%2
270
16th to endDay
10%8%32%24%20%3
270
May1st to 15thDay
13%9%28%21%14%12%
288
16th to endDay
9%416%32%22%14%
331
June1st to 15thDay
12%114%21%27%21%
315
16th to endDay
7%113%23%27%25%
315
July1st to 15thDay
8%11%21%31%26%
305
16th to endDay
10%7%20%34%26%
326
August1st to 15thDay
12%8%23%34%19%
313
16th to endDay
13%26%28%31%18%
332
September1st to 15thDay
12%312%24%29%18%
315
16th to endDay
19%111%30%28%9%
275
October1st to 15thDay
17%321%27%21%7%
255
16th to endDay
17%5%21%26%23%6%
269
November1st to 15thDay
22%16%25%24%10%1
90
16th to endDay
13%7%43%21%11%3
90
December1st to 15thDay
21%20%35%15%7%
90
16th to endDay
34%12%31%15%42
96
January1st to 15thNight
19%16%32%24%7%
720
16th to endNight
20%16%32%25%5%
768
February1st to 15thNight
17%14%32%28%6%
704
16th to endNight
18%18%33%25%3
631
March1st to 15thNight
15%14%35%26%8%
720
16th to endNight
13%14%28%27%15%
768
April1st to 15thNight
13%11%30%28%15%
605
16th to endNight
10%7%29%33%17%1
540
May1st to 15thNight
9%6%26%26%26%4
540
16th to endNight
9%117%35%31%5%
563
June1st to 15thNight
7%12%34%34%10%
540
16th to endNight
6%7%31%39%14%
540
July1st to 15thNight
7%6%25%45%14%
510
16th to endNight
7%15%22%47%15%
564
August1st to 15thNight
6%428%43%15%
539
16th to endNight
13%16%26%38%13%
573
September1st to 15thNight
11%210%24%40%10%
688
16th to endNight
12%113%36%31%3
681
October1st to 15thNight
13%321%34%23%4
660
16th to endNight
11%7%23%30%23%3
704
November1st to 15thNight
13%8%23%33%19%1
700
16th to endNight
15%11%29%29%13%
720
December1st to 15thNight
16%12%30%27%10%1
720
16th to endNight
22%12%27%29%7%
768
Page generated at 2017-09-22 07:35:38. Version ac04

Copyright 2017 A. Danko


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