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 2017-04-25.

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%
14559
18%
45566
7%
14527
36%
14527
17%
30003

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
18%
585
18%
1635
2%
585
28%
585
18%
1128
May1st to 15thNight
19%
495
16%
1485
5%
495
28%
495
14%
1039
May16th to endNight
21%
395
10%
1421
6%
394
29%
394
13%
960
June1st to 15thNight
27%
330
12%
1320
9%
330
36%
330
12%
904
June16th to endNight
35%
330
11%
1320
10%
330
43%
330
19%
799
July1st to 15thNight
35%
310
13%
1240
11%
310
44%
310
19%
756
July16th to endNight
38%
348
14%
1306
13%
326
48%
326
18%
814
August1st to 15thNight
38%
475
17%
1456
10%
473
43%
473
23%
922
August16th to endNight
47%
673
19%
1723
9%
673
51%
673
30%
1128
September1st to 15thNight
39%
660
20%
1708
10%
660
45%
660
28%
1147
September16th to endNight
41%
657
23%
1815
13%
657
49%
657
28%
1145
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%
46078
Night
17%6%25%424446%41%
45736
Cloud CoverDay
17%6%2442445%7%39%
46088
Night
17%6%25%424446%40%
45741
TransparencyDay
43%6%11%21%15%2
45766
Night
44%5%11%21%15%2
45566
SeeingDay
19%21%29%18%8%2
5361
Night
19%25%27%20%6%
14559

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%42%
2214
May1st to 15thDay
25%7%24423345%36%
2137
16th to endDay
15%5%244345%5%7%41%
2351
June1st to 15thDay
24%6%2442445%8%31%
2310
16th to endDay
13%5%25%5%35%46%9%37%
2310
July1st to 15thDay
12%5%15%5%35%5%7%9%35%
2310
16th to endDay
13%5%26%6%36%5%6%9%35%
2458
August1st to 15thDay
13%5%26%5%35%5%6%7%37%
2151
16th to endDay
11%5%26%4345%5%7%41%
2124
September1st to 15thDay
14%6%1442445%5%45%
1922
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%40%
1635
May1st to 15thNight
21%6%445%24345%37%
1485
16th to endNight
19%426%6%245%5%7%34%
1419
June1st to 15thNight
21%5%36%5%2345%7%34%
1320
16th to endNight
15%424425%5%6%9%40%
1320
July1st to 15thNight
12%6%344245%7%9%39%
1320
16th to endNight
11%435%5%36%6%6%9%36%
1402
August1st to 15thNight
8%6%35%435%46%8%42%
1466
16th to endNight
11%5%244336%5%7%45%
1723
September1st to 15thNight
14%4245%245%5%6%43%
1708
16th to endNight
14%6%24423335%48%
1815
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%14424447%41%
2214
May1st to 15thDay
25%7%34323346%35%
2137
16th to endDay
16%424425%45%7%40%
2351
June1st to 15thDay
25%6%244245%5%7%31%
2310
16th to endDay
13%5%26%435%5%7%9%37%
2310
July1st to 15thDay
12%5%35%6%35%5%7%10%35%
2310
16th to endDay
12%5%25%6%36%6%7%8%34%
2458
August1st to 15thDay
13%6%25%5%45%5%6%7%37%
2151
16th to endDay
11%5%25%5%345%5%7%41%
2124
September1st to 15thDay
14%5%24424446%44%
1922
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%25%5%2333441%
1635
May1st to 15thNight
22%6%35%424336%36%
1485
16th to endNight
18%5%26%5%345%5%7%34%
1419
June1st to 15thNight
21%6%35%4345%46%33%
1320
16th to endNight
15%425%325%46%8%40%
1320
July1st to 15thNight
12%6%34416%6%6%9%38%
1320
16th to endNight
12%435%446%6%5%11%35%
1402
August1st to 15thNight
9%6%26%445%46%8%41%
1466
16th to endNight
12%4244335%6%7%44%
1723
September1st to 15thNight
14%4235%245%5%6%44%
1708
16th to endNight
14%6%25%323335%48%
1815
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
41%6%8%20%19%4
2214
May1st to 15thDay
50%5%9%17%14%3
2137
16th to endDay
40%7%15%20%13%2
2355
June1st to 15thDay
51%7%11%18%9%
2310
16th to endDay
40%8%13%22%13%1
2310
July1st to 15thDay
42%8%11%22%13%1
2161
16th to endDay
41%9%13%20%11%3
2291
August1st to 15thDay
42%7%14%19%14%1
2137
16th to endDay
39%6%10%23%17%2
2124
September1st to 15thDay
38%6%11%20%21%1
1922
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
46%5%8%19%16%4
1635
May1st to 15thNight
49%5%11%15%14%3
1485
16th to endNight
47%8%16%16%8%2
1421
June1st to 15thNight
51%6%12%17%11%
1320
16th to endNight
39%7%13%24%14%1
1320
July1st to 15thNight
39%8%13%24%13%
1240
16th to endNight
40%9%14%24%9%2
1306
August1st to 15thNight
39%6%13%23%14%2
1456
16th to endNight
35%8%11%27%16%
1723
September1st to 15thNight
38%7%12%22%18%
1708
16th to endNight
38%46%22%26%1
1815
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
19%28%26%19%43
250
May1st to 15thDay
29%26%19%16%5%1
228
16th to endDay
16%21%32%23%5%
267
June1st to 15thDay
25%24%26%15%6%1
255
16th to endDay
16%20%32%21%7%1
255
July1st to 15thDay
15%14%30%25%12%1
245
16th to endDay
11%18%30%27%10%1
270
August1st to 15thDay
14%10%29%29%13%2
253
16th to endDay
11%11%25%26%17%7%
268
September1st to 15thDay
15%12%21%26%18%4
255
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
18%29%29%15%5%
585
May1st to 15thNight
21%28%27%17%4
495
16th to endNight
20%25%28%20%5%
395
June1st to 15thNight
19%23%25%26%5%
330
16th to endNight
14%19%27%30%7%
330
July1st to 15thNight
13%15%30%30%10%
310
16th to endNight
12%18%24%36%6%1
348
August1st to 15thNight
13%13%28%35%9%
475
16th to endNight
12%11%21%35%16%2
673
September1st to 15thNight
15%12%26%31%11%
660
16th to endNight
17%15%20%25%16%3
657
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 2017-04-26 17:21:43. Version ac04

Copyright 2017 A. Danko


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