Ladd Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ladd Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
23%
14940
18%
46800
7%
14908
36%
14908
17%
30795

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
13%
720
19%
2506
6%
716
30%
716
14%
1607
January16th to endNight
12%
768
18%
2688
3%
768
32%
768
12%
1766
February1st to 15thNight
14%
704
17%
2165
4%
701
30%
701
14%
1462
February16th to endNight
14%
631
24%
1893
6%
631
35%
631
16%
1241
March1st to 15thNight
16%
720
17%
2157
6%
720
30%
720
13%
1469
March16th to endNight
17%
768
23%
2031
6%
768
31%
768
18%
1377
April1st to 15thNight
16%
718
17%
1796
3%
718
25%
718
16%
1289
April16th to endNight
17%
600
18%
1680
2%
600
28%
600
17%
1164
May1st to 15thNight
19%
540
15%
1620
5%
540
28%
540
13%
1142
May16th to endNight
20%
432
10%
1554
6%
431
28%
431
13%
1057
June1st to 15thNight
29%
360
12%
1440
9%
360
38%
360
13%
971
June16th to endNight
33%
360
12%
1440
10%
360
43%
360
19%
876
July1st to 15thNight
37%
340
12%
1360
11%
340
45%
340
18%
835
July16th to endNight
39%
376
15%
1418
14%
354
48%
354
18%
886
August1st to 15thNight
38%
518
16%
1589
10%
516
43%
516
24%
999
August16th to endNight
47%
735
21%
1881
11%
735
52%
735
32%
1218
September1st to 15thNight
38%
720
19%
1863
9%
720
43%
720
29%
1240
September16th to endNight
41%
658
23%
1818
13%
658
49%
658
28%
1146
October1st to 15thNight
30%
660
23%
1829
10%
660
43%
660
23%
1203
October16th to endNight
22%
704
17%
2288
6%
704
37%
704
19%
1485
November1st to 15thNight
23%
700
19%
2277
9%
700
37%
700
18%
1471
November16th to endNight
20%
720
21%
2340
7%
720
37%
720
17%
1482
December1st to 15thNight
17%
720
18%
2479
5%
720
32%
720
13%
1616
December16th to endNight
12%
768
19%
2688
3%
768
31%
768
11%
1793

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
17%6%2442445%7%40%
47949
Night
16%6%25%424446%41%
46970
Cloud CoverDay
17%6%2442445%7%39%
47959
Night
17%6%25%424446%40%
46975
TransparencyDay
43%6%11%21%15%2
47637
Night
44%5%11%21%15%2
46800
SeeingDay
20%21%29%18%7%2
5925
Night
19%25%27%20%6%
14940

By Month

Percentage Cloud Cover NE (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
15%5%26%324446%42%
1432
16th to endDay
15%6%245%22445%44%
1536
February1st to 15thDay
18%7%23326%45%7%37%
1693
16th to endDay
16%6%235%25%446%42%
1580
March1st to 15thDay
20%7%2442345%6%39%
1793
16th to endDay
17%6%35%423336%43%
2191
April1st to 15thDay
19%6%35%424446%38%
2152
16th to endDay
18%424423447%41%
2280
May1st to 15thDay
26%7%24423345%34%
2332
16th to endDay
16%5%2443445%7%40%
2571
June1st to 15thDay
23%6%2442445%8%32%
2520
16th to endDay
13%5%25%5%45%5%6%9%37%
2520
July1st to 15thDay
13%5%15%5%35%5%7%9%35%
2520
16th to endDay
13%5%26%5%36%5%6%9%35%
2654
August1st to 15thDay
13%5%26%5%35%5%6%7%37%
2346
16th to endDay
11%5%26%4345%5%7%42%
2318
September1st to 15thDay
14%5%1442445%5%46%
2097
16th to endDay
14%5%14223345%50%
1815
October1st to 15thDay
20%5%14323435%44%
1799
16th to endDay
15%3245%24446%44%
1584
November1st to 15thDay
22%6%22323335%42%
1581
16th to endDay
16%6%24324446%44%
1620
December1st to 15thDay
18%7%15%323446%42%
1479
16th to endDay
21%8%24425%345%37%
1536
January1st to 15thNight
18%8%25%423335%41%
2506
16th to endNight
17%9%35%42334440%
2688
February1st to 15thNight
15%7%35%5%2445%5%39%
2164
16th to endNight
16%7%35%41433443%
1893
March1st to 15thNight
18%7%245%3435%6%38%
2144
16th to endNight
16%7%34423345%42%
2031
April1st to 15thNight
16%8%35%5%35%445%37%
1796
16th to endNight
20%5%25%5%23336%39%
1680
May1st to 15thNight
21%6%445%24345%36%
1620
16th to endNight
18%5%25%6%25%45%8%34%
1552
June1st to 15thNight
21%5%36%42335%6%36%
1440
16th to endNight
15%424425%5%6%9%40%
1440
July1st to 15thNight
12%6%344245%7%9%39%
1440
16th to endNight
11%5%35%5%36%6%5%10%36%
1514
August1st to 15thNight
8%6%35%435%46%8%42%
1599
16th to endNight
11%4244235%5%7%46%
1881
September1st to 15thNight
14%4245%2445%6%44%
1863
16th to endNight
14%6%24423335%48%
1818
October1st to 15thNight
18%6%23423336%45%
1829
16th to endNight
18%5%15%424446%42%
2288
November1st to 15thNight
18%6%2442344444%
2277
16th to endNight
18%6%24323446%42%
2340
December1st to 15thNight
19%7%24333435%40%
2479
16th to endNight
18%8%35%42345%6%37%
2688

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
16%6%26%324346%42%
1432
16th to endDay
16%6%35%423446%44%
1536
February1st to 15thDay
18%7%23435%5%47%37%
1693
16th to endDay
16%7%34434445%41%
1580
March1st to 15thDay
21%8%2441435%7%37%
1803
16th to endDay
17%7%34424335%42%
2191
April1st to 15thDay
19%7%25%424446%38%
2152
16th to endDay
18%5%14423447%41%
2280
May1st to 15thDay
26%7%34323346%33%
2332
16th to endDay
16%5%2442445%7%39%
2571
June1st to 15thDay
24%6%2442445%7%32%
2520
16th to endDay
13%5%26%5%35%5%7%8%36%
2520
July1st to 15thDay
13%5%35%6%35%5%7%9%35%
2520
16th to endDay
13%5%25%6%36%6%7%8%35%
2654
August1st to 15thDay
13%6%25%6%45%5%6%7%37%
2346
16th to endDay
11%5%25%5%345%5%8%41%
2318
September1st to 15thDay
14%5%25%5%24446%45%
2097
16th to endDay
14%5%13223345%50%
1815
October1st to 15thDay
20%5%24323345%44%
1799
16th to endDay
15%5%245%24446%44%
1584
November1st to 15thDay
22%7%13323235%42%
1581
16th to endDay
17%6%24423446%43%
1620
December1st to 15thDay
19%7%25%323347%41%
1479
16th to endDay
22%7%335%24445%36%
1536
January1st to 15thNight
18%8%24423235%41%
2506
16th to endNight
17%10%35%42333440%
2688
February1st to 15thNight
15%8%36%43345%6%39%
2157
16th to endNight
17%7%35%424335%42%
1893
March1st to 15thNight
18%7%24434446%38%
2157
16th to endNight
16%8%35%42334442%
2030
April1st to 15thNight
17%8%25%425%45%5%36%
1796
16th to endNight
21%5%35%42333440%
1680
May1st to 15thNight
22%6%35%424436%35%
1620
16th to endNight
18%6%26%5%35%5%5%7%34%
1552
June1st to 15thNight
21%6%35%4345%46%35%
1440
16th to endNight
15%425%325%5%6%8%40%
1440
July1st to 15thNight
12%6%34425%6%6%9%38%
1440
16th to endNight
11%5%35%5%36%6%5%10%35%
1514
August1st to 15thNight
9%6%26%445%46%8%41%
1599
16th to endNight
12%4144335%6%7%46%
1881
September1st to 15thNight
14%4235%245%46%45%
1863
16th to endNight
14%6%25%323335%48%
1818
October1st to 15thNight
19%5%24333336%44%
1829
16th to endNight
17%6%24424347%41%
2288
November1st to 15thNight
18%6%25%32344444%
2277
16th to endNight
18%6%34324346%42%
2340
December1st to 15thNight
21%6%24423345%39%
2479
16th to endNight
19%9%35%42335%7%36%
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
42%6%10%24%12%3
1433
16th to endDay
41%410%26%14%1
1536
February1st to 15thDay
45%5%13%19%13%2
1696
16th to endDay
43%410%22%14%3
1580
March1st to 15thDay
45%5%12%22%10%3
1803
16th to endDay
43%48%21%15%5%
2191
April1st to 15thDay
46%49%19%16%2
2152
16th to endDay
42%6%8%20%18%3
2280
May1st to 15thDay
51%5%9%16%14%2
2332
16th to endDay
41%7%14%20%13%2
2575
June1st to 15thDay
50%7%10%20%10%1
2520
16th to endDay
40%8%13%22%13%1
2520
July1st to 15thDay
42%8%11%21%14%1
2371
16th to endDay
41%9%14%20%11%3
2487
August1st to 15thDay
42%7%14%19%14%1
2332
16th to endDay
38%6%10%24%18%2
2318
September1st to 15thDay
38%6%11%20%21%2
2097
16th to endDay
35%5%6%23%26%2
1815
October1st to 15thDay
42%410%23%17%3
1799
16th to endDay
40%412%22%16%2
1584
November1st to 15thDay
45%411%20%16%2
1581
16th to endDay
42%412%23%15%2
1620
December1st to 15thDay
44%5%14%18%17%
1479
16th to endDay
50%5%12%18%10%1
1536
January1st to 15thNight
46%312%21%13%1
2506
16th to endNight
47%49%20%15%3
2688
February1st to 15thNight
46%5%11%21%12%2
2165
16th to endNight
44%49%21%18%2
1893
March1st to 15thNight
45%6%10%19%14%3
2157
16th to endNight
44%38%19%18%5%
2031
April1st to 15thNight
47%5%9%18%15%2
1796
16th to endNight
47%5%8%19%16%4
1680
May1st to 15thNight
50%5%10%15%14%3
1620
16th to endNight
47%8%16%16%8%2
1554
June1st to 15thNight
50%6%12%17%12%
1440
16th to endNight
40%7%13%23%14%1
1440
July1st to 15thNight
39%8%12%24%14%
1360
16th to endNight
40%9%13%24%9%2
1418
August1st to 15thNight
38%6%14%23%14%2
1589
16th to endNight
34%7%11%27%17%
1881
September1st to 15thNight
38%6%11%23%18%
1863
16th to endNight
38%46%22%26%1
1818
October1st to 15thNight
42%410%22%16%3
1829
16th to endNight
42%6%12%22%15%1
2288
November1st to 15thNight
43%5%11%20%16%3
2277
16th to endNight
42%411%24%14%2
2340
December1st to 15thNight
46%413%20%13%
2479
16th to endNight
48%412%21%12%
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
25%28%31%13%1
60
16th to endDay
20%26%39%14%
64
February1st to 15thDay
26%26%35%8%2
237
16th to endDay
17%30%35%12%4
239
March1st to 15thDay
29%29%25%12%2
270
16th to endDay
19%31%30%10%5%1
288
April1st to 15thDay
22%24%34%11%6%
270
16th to endDay
20%27%26%18%43
270
May1st to 15thDay
34%25%20%13%41
288
16th to endDay
19%19%35%21%5%
331
June1st to 15thDay
25%21%27%17%6%
315
16th to endDay
16%20%34%20%6%1
315
July1st to 15thDay
17%13%32%24%10%
305
16th to endDay
12%16%29%27%11%2
326
August1st to 15thDay
14%11%29%29%12%2
313
16th to endDay
11%10%30%25%15%6%
332
September1st to 15thDay
15%14%24%25%16%3
315
16th to endDay
18%10%32%18%9%11%
254
October1st to 15thDay
21%16%24%21%10%5%
255
16th to endDay
14%24%30%20%7%1
240
November1st to 15thDay
25%21%26%13%8%3
235
16th to endDay
20%27%30%13%7%1
240
December1st to 15thDay
25%30%23%15%6%
99
16th to endDay
35%26%28%6%3
64
January1st to 15thNight
20%32%30%13%3
720
16th to endNight
22%33%28%14%1
768
February1st to 15thNight
19%30%30%17%
704
16th to endNight
20%33%28%15%2
631
March1st to 15thNight
21%32%27%15%2
720
16th to endNight
19%32%26%16%4
768
April1st to 15thNight
19%32%29%15%3
718
16th to endNight
19%29%30%15%5%
600
May1st to 15thNight
22%27%28%17%4
540
16th to endNight
20%24%29%20%4
432
June1st to 15thNight
20%21%25%27%5%
360
16th to endNight
15%18%29%30%6%
360
July1st to 15thNight
13%14%30%31%10%
340
16th to endNight
11%17%24%37%7%1
376
August1st to 15thNight
12%12%29%35%10%
518
16th to endNight
12%11%21%36%15%1
735
September1st to 15thNight
16%12%28%30%11%
720
16th to endNight
17%15%20%25%16%3
658
October1st to 15thNight
21%16%28%22%8%1
660
16th to endNight
20%21%31%19%6%
704
November1st to 15thNight
19%27%26%17%9%1
700
16th to endNight
18%31%27%17%5%
720
December1st to 15thNight
24%27%27%15%4
720
16th to endNight
22%33%27%13%1
768
Page generated at 2017-09-16 17:07:03. Version ac04

Copyright 2017 A. Danko


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