Thomas E. Resor Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Thomas E. Resor Memorial 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
55%
15291
24%
47054
19%
15248
61%
15248
31%
28412

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
36%
720
26%
2306
14%
716
50%
716
27%
1398
January16th to endNight
33%
768
26%
2304
15%
768
44%
768
26%
1489
February1st to 15thNight
38%
704
26%
2112
15%
701
48%
701
29%
1292
February16th to endNight
35%
631
26%
1893
13%
631
45%
631
30%
1167
March1st to 15thNight
39%
720
22%
2151
13%
720
46%
720
30%
1322
March16th to endNight
49%
714
26%
2058
16%
714
57%
714
35%
1224
April1st to 15thNight
51%
539
25%
1797
21%
539
59%
539
33%
1004
April16th to endNight
55%
540
28%
1800
24%
540
64%
540
36%
971
May1st to 15thNight
59%
539
23%
1664
19%
539
64%
539
34%
981
May16th to endNight
70%
561
23%
1682
21%
561
72%
561
32%
1019
June1st to 15thNight
72%
540
13%
1620
12%
540
73%
540
28%
1040
June16th to endNight
75%
540
18%
1620
16%
540
75%
540
32%
994
July1st to 15thNight
81%
510
13%
1530
13%
510
81%
510
30%
965
July16th to endNight
75%
564
16%
1659
16%
531
76%
531
30%
1037
August1st to 15thNight
76%
539
15%
1788
18%
536
76%
536
27%
1117
August16th to endNight
69%
573
18%
1910
22%
573
69%
573
22%
1274
September1st to 15thNight
65%
624
21%
1884
21%
624
66%
624
27%
1203
September16th to endNight
68%
693
27%
1914
23%
693
70%
693
34%
1176
October1st to 15thNight
68%
660
33%
1815
28%
660
72%
660
44%
1027
October16th to endNight
58%
704
34%
2095
30%
704
65%
704
42%
1141
November1st to 15thNight
56%
700
30%
2276
27%
700
64%
700
38%
1220
November16th to endNight
48%
720
29%
2340
22%
720
60%
720
33%
1316
December1st to 15thNight
47%
720
25%
2340
21%
720
54%
720
29%
1384
December16th to endNight
36%
768
20%
2496
15%
768
43%
768
21%
1651

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%5%25%5%35%5%5%8%41%
47862
Night
11%42443445%7%46%
47259
TransparencyDay
38%6%11%19%18%5%
47570
Night
35%5%10%18%20%8%
47056
SeeingDay
12%314%23%27%19%
5213
Night
13%319%31%25%5%
15294

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%6%25%423335%44%
1629
16th to endDay
17%5%23424435%45%
1920
February1st to 15thDay
16%434423347%45%
1750
16th to endDay
18%6%25%413436%42%
1580
March1st to 15thDay
14%7%345%24347%42%
1809
16th to endDay
12%5%35%5%3445%6%44%
2174
April1st to 15thDay
12%42443445%8%45%
2151
16th to endDay
8%4245%3445%7%50%
2160
May1st to 15thDay
9%425%5%26%45%7%44%
2286
16th to endDay
7%5%25%5%345%6%9%43%
2431
June1st to 15thDay
8%5%25%6%5%7%6%8%10%33%
2340
16th to endDay
5%3245%37%8%7%12%39%
2340
July1st to 15thDay
9%425%7%5%8%7%9%12%28%
2340
16th to endDay
7%426%7%48%9%9%11%28%
2392
August1st to 15thDay
8%4246%48%7%10%11%31%
2160
16th to endDay
10%6%27%8%46%7%6%9%30%
2292
September1st to 15thDay
10%6%36%6%45%5%7%8%35%
2064
16th to endDay
10%5%25%5%345%5%7%45%
1905
October1st to 15thDay
10%434423346%52%
1815
16th to endDay
9%42342334358%
1774
November1st to 15thDay
11%424313346%53%
1582
16th to endDay
13%434413346%51%
1620
December1st to 15thDay
16%5%35%423436%44%
1620
16th to endDay
21%8%35%5%24335%35%
1728
January1st to 15thNight
16%6%24323335%47%
2306
16th to endNight
18%6%34423335%43%
2304
February1st to 15thNight
13%425%42434448%
2103
16th to endNight
15%5%25%423245%48%
1893
March1st to 15thNight
14%5%2442335%6%46%
2151
16th to endNight
12%42332445%7%50%
2058
April1st to 15thNight
9%3235%245%6%9%47%
1797
16th to endNight
9%413324448%54%
1800
May1st to 15thNight
9%32442446%8%48%
1663
16th to endNight
4326%5%36%5%6%10%45%
1682
June1st to 15thNight
5%326%6%36%6%9%12%36%
1620
16th to endNight
5%425%5%35%6%7%12%42%
1620
July1st to 15thNight
4325%5%47%8%8%11%38%
1620
16th to endNight
5%434446%6%8%12%39%
1772
August1st to 15thNight
6%425%436%7%8%12%37%
1800
16th to endNight
8%5%26%6%46%5%7%9%37%
1910
September1st to 15thNight
9%5%25%6%35%5%6%7%42%
1884
16th to endNight
8%5%2442446%7%47%
1914
October1st to 15thNight
7%414323348%55%
1815
16th to endNight
11%314223245%58%
2095
November1st to 15thNight
10%314323346%56%
2276
16th to endNight
10%424334345%53%
2340
December1st to 15thNight
13%6%24423446%47%
2340
16th to endNight
21%6%35%433345%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
42%26%14%25%7%
1630
16th to endDay
41%36%16%24%8%
1920
February1st to 15thDay
38%26%22%22%6%
1752
16th to endDay
43%35%16%23%7%
1580
March1st to 15thDay
41%39%18%20%6%
1809
16th to endDay
40%410%19%21%4
2175
April1st to 15thDay
36%48%22%20%7%
2151
16th to endDay
32%410%22%25%4
2160
May1st to 15thDay
36%5%11%17%23%5%
2286
16th to endDay
35%6%12%24%17%3
2435
June1st to 15thDay
42%7%14%23%10%1
2340
16th to endDay
32%10%17%21%14%3
2340
July1st to 15thDay
41%12%20%17%6%1
2201
16th to endDay
40%11%19%21%5%
2243
August1st to 15thDay
39%10%19%17%11%2
2148
16th to endDay
47%8%14%16%9%2
2292
September1st to 15thDay
42%8%12%17%14%5%
2064
16th to endDay
37%6%9%21%19%6%
1905
October1st to 15thDay
33%39%17%24%12%
1815
16th to endDay
29%3417%29%15%
1774
November1st to 15thDay
32%26%18%27%12%
1582
16th to endDay
34%48%15%25%11%
1620
December1st to 15thDay
42%48%21%16%7%
1620
16th to endDay
50%38%17%14%5%
1728
January1st to 15thNight
39%35%16%26%7%
2306
16th to endNight
43%3414%23%10%
2304
February1st to 15thNight
39%25%18%21%12%
2112
16th to endNight
39%26%16%23%11%
1893
March1st to 15thNight
38%310%18%20%8%
2151
16th to endNight
32%49%20%25%7%
2058
April1st to 15thNight
31%5%11%17%24%9%
1797
16th to endNight
29%49%24%23%9%
1800
May1st to 15thNight
32%5%12%17%23%8%
1664
16th to endNight
32%8%13%23%15%6%
1684
June1st to 15thNight
34%11%19%19%13%1
1620
16th to endNight
31%9%17%21%15%3
1620
July1st to 15thNight
32%11%24%22%7%2
1530
16th to endNight
32%11%24%24%7%
1659
August1st to 15thNight
32%12%20%21%9%3
1788
16th to endNight
41%9%15%15%14%3
1910
September1st to 15thNight
38%8%13%20%13%6%
1884
16th to endNight
33%6%10%21%19%8%
1914
October1st to 15thNight
27%39%19%24%15%
1815
16th to endNight
28%26%11%30%19%
2095
November1st to 15thNight
29%26%16%27%16%
2276
16th to endNight
33%36%17%23%15%
2340
December1st to 15thNight
38%29%20%22%6%
2340
16th to endNight
47%37%16%18%5%
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
20%6%35%22%10%5%
90
16th to endDay
14%18%33%28%41
96
February1st to 15thDay
17%15%33%25%7%
90
16th to endDay
19%8%33%34%3
81
March1st to 15thDay
16%14%39%24%5%1
99
16th to endDay
15%225%35%18%2
288
April1st to 15thDay
16%8%21%26%22%3
270
16th to endDay
8%420%31%25%10%
270
May1st to 15thDay
11%316%28%28%10%
288
16th to endDay
12%212%23%27%22%
331
June1st to 15thDay
13%320%29%33%
315
16th to endDay
7%5%15%30%40%
315
July1st to 15thDay
7%113%33%42%
305
16th to endDay
7%211%34%43%
326
August1st to 15thDay
14%314%31%34%
313
16th to endDay
12%416%37%28%
332
September1st to 15thDay
11%19%17%37%22%
315
16th to endDay
10%18%29%35%15%
287
October1st to 15thDay
12%114%30%34%7%
255
16th to endDay
12%416%28%24%13%
181
November1st to 15thDay
20%136%22%17%2
90
16th to endDay
5%12%27%31%21%2
90
December1st to 15thDay
18%10%41%22%5%2
90
16th to endDay
23%15%20%31%8%
96
January1st to 15thNight
21%7%29%31%9%
720
16th to endNight
21%6%32%33%6%
768
February1st to 15thNight
16%7%31%39%5%
704
16th to endNight
17%7%35%34%5%
631
March1st to 15thNight
16%7%34%31%10%
720
16th to endNight
14%5%26%34%17%
714
April1st to 15thNight
10%5%29%33%21%
539
16th to endNight
10%325%37%22%
540
May1st to 15thNight
9%219%37%26%4
540
16th to endNight
6%18%36%38%7%
563
June1st to 15thNight
7%5%29%45%10%
540
16th to endNight
7%1419%50%15%
540
July1st to 15thNight
5%219%54%17%
510
16th to endNight
7%1319%49%19%
564
August1st to 15thNight
8%5%15%50%19%
539
16th to endNight
12%15%20%42%18%
573
September1st to 15thNight
12%19%21%40%14%
624
16th to endNight
13%19%34%36%5%
693
October1st to 15thNight
9%213%38%32%2
660
16th to endNight
12%320%31%28%4
704
November1st to 15thNight
11%322%35%23%3
700
16th to endNight
13%5%27%37%14%1
720
December1st to 15thNight
18%5%24%37%13%
720
16th to endNight
25%6%25%33%8%
768
Page generated at 2017-09-25 08:02:25. Version ac04

Copyright 2017 A. Danko


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