WhistleStop Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WhistleStop Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
31%
15153
14%
48086
8%
15121
38%
15121
17%
33386

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%
719
7%
2506
3%
716
19%
716
7%
1963
January16th to endNight
18%
768
11%
2528
5%
768
26%
768
9%
1970
February1st to 15thNight
14%
702
9%
2287
3%
701
21%
701
10%
1770
February16th to endNight
19%
631
13%
1999
5%
631
31%
631
13%
1463
March1st to 15thNight
22%
720
14%
2010
6%
720
29%
720
15%
1485
March16th to endNight
29%
768
20%
2094
7%
768
40%
768
22%
1409
April1st to 15thNight
27%
718
16%
1796
4%
718
33%
718
21%
1302
April16th to endNight
31%
618
20%
1698
6%
618
41%
618
23%
1112
May1st to 15thNight
36%
428
16%
1508
11%
428
45%
428
16%
987
May16th to endNight
40%
374
17%
1497
14%
374
53%
374
19%
857
June1st to 15thNight
39%
360
12%
1440
10%
360
50%
360
18%
888
June16th to endNight
48%
360
11%
1440
14%
360
54%
360
19%
860
July1st to 15thNight
58%
340
17%
1360
23%
340
63%
340
29%
695
July16th to endNight
53%
412
16%
1451
17%
387
62%
387
27%
808
August1st to 15thNight
57%
539
16%
1609
12%
536
61%
536
29%
977
August16th to endNight
59%
663
22%
1809
12%
663
64%
663
36%
1080
September1st to 15thNight
52%
720
19%
1800
10%
720
55%
720
32%
1177
September16th to endNight
53%
717
24%
1989
18%
717
57%
717
31%
1252
October1st to 15thNight
36%
720
16%
2160
13%
720
42%
720
20%
1503
October16th to endNight
23%
768
13%
2310
7%
768
32%
768
15%
1695
November1st to 15thNight
32%
760
17%
2580
15%
760
39%
760
17%
1728
November16th to endNight
19%
780
11%
2730
5%
780
27%
780
10%
2025
December1st to 15thNight
14%
780
6%
2730
2%
780
19%
780
8%
2163
December16th to endNight
11%
788
8%
2755
2%
788
18%
788
6%
2217

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%7%36%5%345%5%7%36%
48753
Night
16%8%36%5%34446%34%
48260
Cloud CoverDay
14%7%36%5%35%5%5%7%36%
48763
Night
16%8%36%5%3445%6%34%
48265
TransparencyDay
46%7%12%21%10%1
48445
Night
48%6%12%19%11%1
48086
SeeingDay
16%13%23%25%14%5%
5695
Night
17%20%23%24%12%1
15157

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
18%14%48%6%45%5%46%21%
1432
16th to endDay
12%14%6%10%9%47%5%5%5%19%
1695
February1st to 15thDay
12%12%5%13%9%35%5%6%5%19%
1575
16th to endDay
19%9%5%8%6%34446%25%
1473
March1st to 15thDay
15%10%37%6%35%5%5%6%29%
1936
16th to endDay
16%8%26%433446%40%
2130
April1st to 15thDay
19%6%36%5%24447%33%
2152
16th to endDay
16%5%25%434446%40%
2271
May1st to 15thDay
13%5%36%5%25%5%6%6%38%
2442
16th to endDay
11%5%245%25%5%5%8%43%
2618
June1st to 15thDay
15%5%25%5%345%5%9%36%
2520
16th to endDay
12%425%5%2446%8%43%
2520
July1st to 15thDay
7%214435%5%6%10%48%
2520
16th to endDay
8%324435%6%8%10%41%
2615
August1st to 15thDay
7%4245%25%6%6%8%46%
2340
16th to endDay
10%41342446%9%47%
2379
September1st to 15thDay
13%5%1442345%7%46%
2160
16th to endDay
12%5%2343345%7%47%
1968
October1st to 15thDay
18%7%35%5%34447%35%
1800
16th to endDay
22%9%35%5%3446%5%29%
1914
November1st to 15thDay
14%8%37%5%445%5%7%34%
1605
16th to endDay
18%11%36%7%45%447%26%
1560
December1st to 15thDay
17%15%5%8%6%36%5%47%19%
1560
16th to endDay
21%14%49%6%35%5%45%19%
1568
January1st to 15thNight
21%14%5%8%6%34446%19%
2506
16th to endNight
15%15%5%9%7%35%5%45%22%
2528
February1st to 15thNight
15%14%6%9%6%35%446%22%
2285
16th to endNight
16%8%46%8%45%5%46%28%
1999
March1st to 15thNight
19%9%36%6%34345%32%
1998
16th to endNight
15%5%35%423445%44%
2094
April1st to 15thNight
20%7%3443445%6%35%
1796
16th to endNight
15%5%2442345%6%44%
1698
May1st to 15thNight
15%5%245%45%5%5%6%37%
1508
16th to endNight
12%5%26%424347%46%
1495
June1st to 15thNight
13%5%35%5%2446%8%39%
1440
16th to endNight
12%425%43446%8%42%
1440
July1st to 15thNight
5%31443445%8%53%
1440
16th to endNight
8%5%2442445%9%48%
1550
August1st to 15thNight
7%4244345%5%9%47%
1620
16th to endNight
7%415%325%446%53%
1809
September1st to 15thNight
14%423423447%47%
1800
16th to endNight
14%424424345%49%
1989
October1st to 15thNight
19%7%25%5%23446%36%
2160
16th to endNight
21%8%36%5%25%45%6%30%
2310
November1st to 15thNight
18%6%35%5%3445%7%35%
2580
16th to endNight
23%9%36%5%345%47%26%
2730
December1st to 15thNight
21%13%47%6%45%45%6%20%
2730
16th to endNight
21%14%5%8%6%35%45%5%18%
2755

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
18%13%5%8%7%45%6%36%19%
1432
16th to endDay
12%14%6%10%8%47%6%46%17%
1695
February1st to 15thDay
12%12%6%12%8%35%5%6%6%19%
1575
16th to endDay
18%9%49%6%45%5%5%6%24%
1473
March1st to 15thDay
16%10%37%6%35%5%5%5%29%
1947
16th to endDay
15%7%26%434446%40%
2129
April1st to 15thDay
19%6%35%5%335%48%34%
2152
16th to endDay
16%5%35%5%3445%6%40%
2271
May1st to 15thDay
13%6%36%5%25%6%6%7%37%
2442
16th to endDay
11%5%245%25%5%5%7%43%
2618
June1st to 15thDay
15%5%35%5%345%5%9%36%
2520
16th to endDay
11%4245%245%5%9%43%
2520
July1st to 15thDay
6%324435%5%6%9%48%
2520
16th to endDay
8%323436%6%7%10%42%
2615
August1st to 15thDay
7%424425%7%6%8%46%
2340
16th to endDay
9%42342446%8%48%
2379
September1st to 15thDay
13%42442345%6%46%
2160
16th to endDay
11%5%2332446%7%47%
1968
October1st to 15thDay
17%8%25%5%34446%36%
1800
16th to endDay
21%8%35%6%335%6%5%29%
1914
November1st to 15thDay
13%8%46%5%245%6%7%34%
1605
16th to endDay
18%11%46%6%35%45%7%25%
1560
December1st to 15thDay
17%14%6%8%7%36%46%7%17%
1560
16th to endDay
21%14%5%7%7%36%45%5%18%
1568
January1st to 15thNight
21%14%5%8%7%3445%5%18%
2506
16th to endNight
15%15%6%9%7%35%5%5%6%20%
2528
February1st to 15thNight
14%16%5%9%6%45%447%21%
2278
16th to endNight
16%9%47%8%45%46%6%27%
1999
March1st to 15thNight
19%10%36%6%34445%31%
2010
16th to endNight
15%6%36%423435%43%
2094
April1st to 15thNight
19%8%345%2445%6%35%
1796
16th to endNight
15%6%2442446%5%44%
1698
May1st to 15thNight
15%5%25%5%446%5%6%37%
1508
16th to endNight
11%5%25%4335%37%46%
1495
June1st to 15thNight
13%6%27%425%5%5%8%38%
1440
16th to endNight
11%5%25%5%345%6%7%42%
1440
July1st to 15thNight
5%313425%5%5%8%53%
1440
16th to endNight
8%4244245%5%8%49%
1550
August1st to 15thNight
8%415%435%47%8%46%
1620
16th to endNight
7%314425%45%7%52%
1809
September1st to 15thNight
14%42443345%7%46%
1800
16th to endNight
14%424423346%48%
1989
October1st to 15thNight
19%7%35%6%34446%36%
2160
16th to endNight
21%7%36%5%35%5%5%6%29%
2310
November1st to 15thNight
17%6%25%5%3445%7%34%
2580
16th to endNight
22%9%46%6%35%45%7%25%
2730
December1st to 15thNight
21%13%47%6%45%46%6%19%
2730
16th to endNight
21%14%6%9%7%35%446%17%
2755

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
60%6%11%14%5%
1433
16th to endDay
65%6%9%11%5%
1695
February1st to 15thDay
61%8%10%15%3
1577
16th to endDay
57%6%10%14%9%
1473
March1st to 15thDay
54%6%14%17%7%1
1947
16th to endDay
45%5%8%21%15%2
2130
April1st to 15thDay
50%49%19%13%1
2152
16th to endDay
44%5%9%22%16%2
2271
May1st to 15thDay
44%8%10%20%14%1
2442
16th to endDay
39%7%13%23%13%1
2622
June1st to 15thDay
45%6%13%23%10%
2520
16th to endDay
37%8%16%22%14%
2520
July1st to 15thDay
30%8%12%32%15%
2371
16th to endDay
35%11%15%26%10%
2451
August1st to 15thDay
34%10%16%23%13%1
2327
16th to endDay
32%8%14%30%12%1
2379
September1st to 15thDay
36%7%14%28%12%
2160
16th to endDay
35%8%12%31%11%
1968
October1st to 15thDay
48%7%10%22%10%
1800
16th to endDay
54%7%15%15%6%
1914
November1st to 15thDay
47%6%16%17%10%
1605
16th to endDay
56%7%14%14%6%
1560
December1st to 15thDay
61%9%13%12%2
1560
16th to endDay
64%8%11%12%3
1568
January1st to 15thNight
63%6%11%13%4
2506
16th to endNight
61%6%10%14%6%
2528
February1st to 15thNight
60%6%12%14%4
2287
16th to endNight
53%6%12%19%7%
1999
March1st to 15thNight
53%5%11%20%8%
2010
16th to endNight
43%5%9%22%17%2
2094
April1st to 15thNight
47%6%9%18%15%1
1796
16th to endNight
39%6%11%19%20%2
1698
May1st to 15thNight
44%7%10%19%15%3
1508
16th to endNight
36%6%12%24%17%2
1497
June1st to 15thNight
42%6%12%22%15%1
1440
16th to endNight
38%7%14%21%16%2
1440
July1st to 15thNight
27%7%11%28%24%
1360
16th to endNight
32%6%12%28%17%2
1451
August1st to 15thNight
32%8%17%27%13%
1609
16th to endNight
29%6%13%33%16%
1809
September1st to 15thNight
35%7%15%25%14%1
1800
16th to endNight
37%49%30%17%
1989
October1st to 15thNight
48%5%10%21%13%
2160
16th to endNight
52%7%14%16%8%
2310
November1st to 15thNight
45%7%14%18%12%1
2580
16th to endNight
55%8%14%15%5%
2730
December1st to 15thNight
60%9%13%12%3
2730
16th to endNight
64%8%11%10%4
2755

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%16%41%15%33
60
16th to endDay
27%14%30%23%4
91
February1st to 15thDay
20%26%44%7%1
90
16th to endDay
30%18%28%18%3
132
March1st to 15thDay
20%21%27%23%5%
270
16th to endDay
22%17%28%23%5%1
288
April1st to 15thDay
19%18%30%22%7%1
270
16th to endDay
17%15%31%19%10%4
270
May1st to 15thDay
22%14%20%25%10%6%
288
16th to endDay
14%12%24%29%14%4
331
June1st to 15thDay
17%14%20%29%15%2
315
16th to endDay
15%12%22%29%13%6%
315
July1st to 15thDay
9%9%13%32%27%8%
305
16th to endDay
10%11%19%33%17%7%
326
August1st to 15thDay
8%7%14%30%27%11%
313
16th to endDay
10%8%14%29%25%11%
332
September1st to 15thDay
12%6%18%24%26%12%
315
16th to endDay
12%7%19%25%20%15%
314
October1st to 15thDay
19%11%25%23%15%5%
315
16th to endDay
20%18%29%22%9%
334
November1st to 15thDay
20%13%27%27%9%1
169
16th to endDay
24%13%30%22%10%
90
December1st to 15thDay
17%28%23%16%13%
90
16th to endDay
27%33%33%5%
72
January1st to 15thNight
21%29%26%15%5%
720
16th to endNight
17%26%28%21%4
768
February1st to 15thNight
20%25%33%18%2
704
16th to endNight
19%23%29%22%4
631
March1st to 15thNight
20%25%25%24%3
720
16th to endNight
17%21%26%24%8%1
768
April1st to 15thNight
18%21%27%24%7%
718
16th to endNight
13%22%26%22%12%1
618
May1st to 15thNight
18%19%17%27%14%1
428
16th to endNight
11%18%21%28%18%
375
June1st to 15thNight
12%18%23%30%13%2
360
16th to endNight
10%17%15%36%19%
360
July1st to 15thNight
5%12%17%38%22%3
340
16th to endNight
6%17%15%36%21%1
412
August1st to 15thNight
9%10%12%33%29%4
539
16th to endNight
7%10%14%32%31%3
663
September1st to 15thNight
12%10%16%26%28%5%
720
16th to endNight
12%11%16%23%27%8%
717
October1st to 15thNight
21%13%23%22%16%2
720
16th to endNight
22%17%29%24%5%
768
November1st to 15thNight
17%20%23%26%11%1
760
16th to endNight
22%25%26%17%7%
780
December1st to 15thNight
24%27%28%15%4
780
16th to endNight
24%25%30%15%4
788
Page generated at 2017-12-21 07:04:44. Version ac04

Copyright 2017 A. Danko


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