Wayside Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wayside 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
30%
15737
21%
48817
9%
15700
42%
15700
21%
30662

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
19%
780
21%
2712
8%
776
37%
776
15%
1680
January16th to endNight
16%
832
24%
2704
6%
832
38%
832
17%
1681
February1st to 15thNight
14%
760
18%
2456
4%
757
31%
757
15%
1560
February16th to endNight
14%
631
25%
1893
5%
631
37%
631
16%
1186
March1st to 15thNight
18%
720
21%
2069
7%
720
34%
720
19%
1308
March16th to endNight
18%
768
22%
2046
7%
768
30%
768
22%
1355
April1st to 15thNight
20%
718
19%
1796
4%
718
29%
718
23%
1197
April16th to endNight
27%
720
18%
1800
4%
720
35%
720
24%
1206
May1st to 15thNight
25%
522
17%
1602
6%
522
34%
522
16%
1077
May16th to endNight
39%
374
16%
1497
12%
374
48%
374
16%
909
June1st to 15thNight
40%
360
17%
1440
15%
360
51%
360
20%
847
June16th to endNight
46%
360
16%
1440
15%
360
54%
360
22%
825
July1st to 15thNight
45%
340
13%
1360
13%
340
50%
340
17%
857
July16th to endNight
53%
445
15%
1482
13%
418
61%
418
26%
863
August1st to 15thNight
53%
566
18%
1636
11%
563
57%
563
27%
1034
August16th to endNight
55%
764
19%
1910
10%
764
57%
764
33%
1228
September1st to 15thNight
48%
720
25%
1800
13%
720
53%
720
33%
1176
September16th to endNight
48%
717
27%
1948
17%
717
56%
717
30%
1243
October1st to 15thNight
39%
720
21%
2160
16%
720
48%
720
25%
1355
October16th to endNight
31%
768
28%
2316
14%
768
50%
768
27%
1369
November1st to 15thNight
30%
760
23%
2472
13%
760
45%
760
22%
1511
November16th to endNight
24%
780
23%
2636
10%
780
42%
780
18%
1598
December1st to 15thNight
19%
780
17%
2730
4%
780
35%
780
13%
1767
December16th to endNight
16%
832
21%
2912
5%
832
36%
832
14%
1830

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
14%5%245%3445%7%40%
49254
Night
15%5%2442445%7%43%
48993
Cloud CoverDay
14%5%25%5%3445%7%40%
49264
Night
14%5%2442445%7%43%
48998
TransparencyDay
40%5%11%23%16%2
48949
Night
40%411%23%17%2
48817
SeeingDay
16%19%24%21%12%4
6161
Night
15%24%24%23%10%1
15738

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%25%5%24447%40%
1555
16th to endDay
15%7%24435%435%42%
1872
February1st to 15thDay
15%7%25%5%2445%6%39%
1705
16th to endDay
14%7%45%5%33445%40%
1580
March1st to 15thDay
15%6%25%5%34446%41%
1879
16th to endDay
18%6%245%33345%41%
2178
April1st to 15thDay
15%5%34423447%43%
2152
16th to endDay
15%424434447%43%
2160
May1st to 15thDay
17%6%25%5%3445%7%36%
2356
16th to endDay
15%5%25%5%25%5%6%7%38%
2618
June1st to 15thDay
12%5%345%35%5%7%10%36%
2520
16th to endDay
11%5%245%35%6%5%9%40%
2520
July1st to 15thDay
9%425%6%46%5%7%9%38%
2520
16th to endDay
6%425%6%46%6%8%11%36%
2582
August1st to 15thDay
11%425%6%36%6%6%8%37%
2300
16th to endDay
10%6%25%435%5%6%8%42%
2292
September1st to 15thDay
14%4245%2446%6%45%
2160
16th to endDay
13%5%25%5%245%47%42%
2008
October1st to 15thDay
16%6%245%2345%6%44%
1800
16th to endDay
17%5%14323445%47%
1906
November1st to 15thDay
16%6%25%324446%44%
1716
16th to endDay
15%5%24424345%47%
1651
December1st to 15thDay
16%5%236%3446%6%39%
1560
16th to endDay
17%5%35%5%34447%38%
1664
January1st to 15thNight
16%6%24434346%42%
2712
16th to endNight
16%7%24424345%44%
2704
February1st to 15thNight
14%7%26%43445%6%40%
2454
16th to endNight
16%5%24424445%44%
1893
March1st to 15thNight
16%5%24424447%43%
2057
16th to endNight
16%6%24414336%44%
2046
April1st to 15thNight
15%5%25%42445%7%42%
1796
16th to endNight
17%5%2442435%6%44%
1800
May1st to 15thNight
18%7%34434446%38%
1602
16th to endNight
14%5%25%43345%7%40%
1495
June1st to 15thNight
13%5%245%2435%8%44%
1440
16th to endNight
9%426%5%25%5%6%11%42%
1440
July1st to 15thNight
9%5%35%6%36%7%6%9%35%
1440
16th to endNight
7%3245%35%6%7%10%42%
1583
August1st to 15thNight
9%425%4345%6%8%44%
1647
16th to endNight
11%4145%2445%8%46%
1910
September1st to 15thNight
13%424423347%47%
1800
16th to endNight
13%5%245%2345%7%46%
1948
October1st to 15thNight
17%5%2432325%6%45%
2160
16th to endNight
16%413314346%51%
2316
November1st to 15thNight
13%5%25%42335%5%47%
2472
16th to endNight
16%4144245%5%6%43%
2636
December1st to 15thNight
18%6%25%6%2445%6%37%
2730
16th to endNight
17%6%2442445%7%39%
2912

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
15%5%25%5%2435%7%40%
1555
16th to endDay
15%7%24435%5%35%42%
1872
February1st to 15thDay
16%6%25%5%2445%6%40%
1705
16th to endDay
14%8%35%5%3345%5%40%
1580
March1st to 15thDay
15%6%245%34446%41%
1890
16th to endDay
18%6%245%34345%41%
2177
April1st to 15thDay
15%5%24423446%44%
2152
16th to endDay
16%4245%24446%43%
2160
May1st to 15thDay
16%6%25%5%35%46%7%37%
2356
16th to endDay
15%5%25%5%25%5%6%8%38%
2618
June1st to 15thDay
12%5%35%5%35%5%7%9%36%
2520
16th to endDay
11%5%245%45%5%6%9%39%
2520
July1st to 15thDay
8%426%6%46%6%7%9%38%
2520
16th to endDay
6%425%6%46%6%8%11%36%
2582
August1st to 15thDay
11%426%6%36%6%6%9%36%
2300
16th to endDay
9%6%24435%5%7%8%42%
2292
September1st to 15thDay
13%415%42445%6%44%
2160
16th to endDay
13%6%26%5%245%5%7%41%
2008
October1st to 15thDay
16%6%15%42345%5%44%
1800
16th to endDay
17%5%14312446%47%
1906
November1st to 15thDay
16%5%25%314446%44%
1716
16th to endDay
15%5%24424435%47%
1651
December1st to 15thDay
17%4245%3446%6%39%
1560
16th to endDay
17%5%345%24447%37%
1664
January1st to 15thNight
16%6%24434346%42%
2712
16th to endNight
16%6%24324445%44%
2704
February1st to 15thNight
14%6%26%43445%6%40%
2447
16th to endNight
15%5%2442445%5%45%
1893
March1st to 15thNight
15%5%23414347%43%
2069
16th to endNight
16%5%34424336%44%
2046
April1st to 15thNight
15%5%25%42445%6%42%
1796
16th to endNight
17%5%24424347%44%
1800
May1st to 15thNight
18%7%34434446%38%
1602
16th to endNight
14%5%35%43345%8%40%
1495
June1st to 15thNight
13%6%145%2435%8%44%
1440
16th to endNight
9%425%4346%5%11%41%
1440
July1st to 15thNight
9%5%35%6%36%7%6%9%35%
1440
16th to endNight
7%2246%25%6%7%10%42%
1583
August1st to 15thNight
9%425%4345%6%8%44%
1647
16th to endNight
11%4245%2445%9%46%
1910
September1st to 15thNight
13%5%24423447%47%
1800
16th to endNight
12%5%2442345%8%45%
1948
October1st to 15thNight
17%5%2442325%6%45%
2160
16th to endNight
16%413314345%52%
2316
November1st to 15thNight
13%5%25%413345%47%
2472
16th to endNight
16%4244345%5%6%43%
2636
December1st to 15thNight
18%5%25%6%25%45%5%37%
2730
16th to endNight
17%6%25%42445%7%39%
2912

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%413%21%13%4
1556
16th to endDay
43%311%23%14%3
1872
February1st to 15thDay
44%311%24%12%3
1707
16th to endDay
43%410%26%12%2
1580
March1st to 15thDay
42%311%24%15%1
1890
16th to endDay
45%49%20%18%2
2178
April1st to 15thDay
41%411%22%16%4
2152
16th to endDay
39%49%18%21%5%
2160
May1st to 15thDay
44%5%11%20%15%2
2356
16th to endDay
41%6%13%23%13%2
2622
June1st to 15thDay
40%7%12%26%12%1
2520
16th to endDay
36%8%14%21%17%1
2520
July1st to 15thDay
38%7%12%23%14%3
2371
16th to endDay
35%8%13%27%13%2
2421
August1st to 15thDay
39%7%12%21%17%1
2287
16th to endDay
35%6%12%23%18%3
2292
September1st to 15thDay
37%5%11%22%20%3
2160
16th to endDay
40%46%21%23%2
2008
October1st to 15thDay
40%5%11%22%18%2
1800
16th to endDay
37%38%28%20%1
1906
November1st to 15thDay
40%412%20%18%3
1716
16th to endDay
38%48%29%16%2
1651
December1st to 15thDay
42%414%23%12%1
1560
16th to endDay
45%414%21%12%1
1664
January1st to 15thNight
42%411%21%16%4
2712
16th to endNight
42%29%27%15%1
2704
February1st to 15thNight
44%312%23%14%2
2456
16th to endNight
40%39%23%19%3
1893
March1st to 15thNight
40%312%24%16%2
2069
16th to endNight
41%411%21%17%3
2046
April1st to 15thNight
40%310%21%19%4
1796
16th to endNight
39%5%10%18%19%6%
1800
May1st to 15thNight
45%5%10%18%17%2
1602
16th to endNight
41%6%15%17%15%3
1497
June1st to 15thNight
38%6%13%23%17%
1440
16th to endNight
34%7%13%26%16%2
1440
July1st to 15thNight
44%6%13%18%13%3
1360
16th to endNight
32%8%18%22%15%1
1482
August1st to 15thNight
34%8%12%22%19%2
1636
16th to endNight
34%6%12%23%19%3
1910
September1st to 15thNight
36%5%10%22%22%3
1800
16th to endNight
36%5%6%23%24%3
1948
October1st to 15thNight
40%311%23%18%2
2160
16th to endNight
34%49%30%19%2
2316
November1st to 15thNight
38%49%22%16%6%
2472
16th to endNight
39%49%25%18%2
2636
December1st to 15thNight
47%312%23%12%1
2730
16th to endNight
42%414%23%12%1
2912

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
18%32%31%10%41
91
16th to endDay
18%34%29%15%1
144
February1st to 15thDay
25%36%30%7%
141
16th to endDay
16%33%34%15%
239
March1st to 15thDay
16%32%27%18%5%
270
16th to endDay
20%28%32%11%43
288
April1st to 15thDay
20%26%31%12%6%2
270
16th to endDay
19%21%27%18%10%2
270
May1st to 15thDay
27%26%21%13%9%1
288
16th to endDay
19%17%20%22%17%3
331
June1st to 15thDay
13%19%24%23%15%4
315
16th to endDay
11%18%26%25%14%3
315
July1st to 15thDay
13%9%23%29%17%6%
305
16th to endDay
6%10%18%31%27%4
326
August1st to 15thDay
14%7%16%34%17%8%
313
16th to endDay
9%7%17%29%20%15%
332
September1st to 15thDay
12%12%20%23%18%11%
315
16th to endDay
18%8%16%29%17%9%
314
October1st to 15thDay
19%8%22%25%17%6%
315
16th to endDay
13%19%30%20%12%2
332
November1st to 15thDay
15%22%25%22%12%1
280
16th to endDay
14%34%27%14%7%
181
December1st to 15thDay
26%28%25%7%11%
90
16th to endDay
23%26%36%11%2
96
January1st to 15thNight
16%32%27%18%4
780
16th to endNight
18%30%31%17%1
832
February1st to 15thNight
16%32%32%17%1
760
16th to endNight
15%38%28%15%1
631
March1st to 15thNight
17%32%28%17%3
720
16th to endNight
17%26%34%14%6%1
768
April1st to 15thNight
15%31%29%18%4
718
16th to endNight
17%24%27%20%9%
720
May1st to 15thNight
20%24%24%23%5%
522
16th to endNight
15%22%16%32%13%
375
June1st to 15thNight
14%20%19%31%14%
360
16th to endNight
7%18%21%41%11%
360
July1st to 15thNight
10%15%20%36%18%
340
16th to endNight
8%17%12%34%23%3
445
August1st to 15thNight
12%10%13%38%23%2
566
16th to endNight
11%9%14%33%26%3
764
September1st to 15thNight
11%12%20%32%21%2
720
16th to endNight
14%11%17%27%24%4
717
October1st to 15thNight
19%14%21%25%15%3
720
16th to endNight
17%20%27%21%11%
768
November1st to 15thNight
14%24%26%22%10%1
760
16th to endNight
15%30%25%20%7%
780
December1st to 15thNight
19%29%26%16%7%
780
16th to endNight
16%34%28%17%2
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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