This page made possible by the sponsorship of:

Michael A. Covington, writer
.

Deerlick Astronomy Village
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerlick Astronomy Village clear sky chart from 2005-11-05 to 2020-06-03.

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
47%
19283
22%
57835
14%
19240
56%
19240
27%
36200

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
27%
900
23%
2912
9%
896
43%
896
20%
1814
January16th to endNight
27%
960
26%
3120
13%
960
44%
960
22%
1921
February1st to 15thNight
32%
884
24%
2670
11%
881
45%
881
24%
1678
February16th to endNight
25%
791
24%
2373
9%
791
41%
791
24%
1501
March1st to 15thNight
29%
900
24%
2507
9%
900
42%
900
26%
1604
March16th to endNight
35%
960
22%
2640
10%
960
44%
960
28%
1670
April1st to 15thNight
38%
898
25%
2471
13%
898
48%
898
33%
1475
April16th to endNight
46%
692
28%
2062
16%
692
57%
692
33%
1186
May1st to 15thNight
52%
675
22%
2025
13%
675
58%
675
33%
1197
May16th to endNight
60%
705
19%
2114
14%
705
63%
705
26%
1361
June1st to 15thNight
63%
637
15%
1913
12%
637
65%
637
27%
1259
June16th to endNight
72%
630
15%
1890
12%
630
73%
630
30%
1191
July1st to 15thNight
66%
600
11%
1800
10%
600
67%
600
23%
1258
July16th to endNight
76%
660
12%
1883
11%
627
76%
627
27%
1243
August1st to 15thNight
68%
620
16%
1850
15%
617
68%
617
22%
1280
August16th to endNight
67%
718
14%
2209
14%
718
67%
718
23%
1500
September1st to 15thNight
65%
840
17%
2310
15%
840
66%
840
26%
1564
September16th to endNight
62%
837
22%
2310
18%
837
65%
837
30%
1488
October1st to 15thNight
56%
840
29%
2380
23%
840
63%
840
35%
1428
October16th to endNight
49%
896
33%
2688
25%
896
62%
896
35%
1509
November1st to 15thNight
50%
880
29%
2738
23%
880
60%
880
34%
1551
November16th to endNight
43%
900
28%
2925
18%
900
57%
900
29%
1663
December1st to 15thNight
38%
900
25%
2925
15%
900
51%
900
23%
1805
December16th to endNight
34%
960
21%
3120
14%
960
44%
960
19%
2054

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
12%5%25%5%35%5%5%7%42%
58568
Night
12%5%2443445%7%45%
58035
TransparencyDay
39%7%11%18%17%5%
58269
Night
36%7%11%18%18%7%
57838
SeeingDay
16%7%22%23%20%9%
9104
Night
14%8%22%30%20%3
19285

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%5%24424345%43%
2016
16th to endDay
15%5%2442335%5%46%
2160
February1st to 15thDay
16%6%245%2445%6%41%
2177
16th to endDay
20%6%15%314335%44%
1980
March1st to 15thDay
15%425%423446%45%
2441
16th to endDay
15%425%324446%44%
2639
April1st to 15thDay
10%42443445%6%48%
2467
16th to endDay
9%324435%45%6%50%
2845
May1st to 15thDay
8%424435%5%5%8%46%
2916
16th to endDay
11%5%25%5%36%46%7%39%
3055
June1st to 15thDay
10%425%6%46%6%6%9%35%
2756
16th to endDay
43245%47%6%8%11%40%
2730
July1st to 15thDay
8%5%26%8%47%7%8%9%31%
2730
16th to endDay
6%427%7%48%7%8%11%30%
2881
August1st to 15thDay
8%5%27%8%5%7%7%8%10%28%
2682
16th to endDay
13%6%26%7%46%6%8%8%29%
2677
September1st to 15thDay
10%6%25%6%35%6%6%8%37%
2310
16th to endDay
15%5%25%5%3345%5%44%
2310
October1st to 15thDay
15%413313346%50%
2240
16th to endDay
11%41432333457%
2240
November1st to 15thDay
14%413423235%52%
2106
16th to endDay
12%424423445%51%
2025
December1st to 15thDay
17%6%25%42445%5%41%
2025
16th to endDay
22%6%25%423346%37%
2160
January1st to 15thNight
14%7%25%423446%44%
2912
16th to endNight
16%6%3432334447%
3120
February1st to 15thNight
16%414434446%45%
2662
16th to endNight
15%6%24424345%45%
2373
March1st to 15thNight
13%5%24334436%47%
2507
16th to endNight
13%424424447%47%
2640
April1st to 15thNight
10%414424347%51%
2471
16th to endNight
9%413434347%53%
2062
May1st to 15thNight
7%424425%46%8%49%
2024
16th to endNight
9%416%5%35%5%6%8%42%
2114
June1st to 15thNight
8%5%345%446%7%12%36%
1913
16th to endNight
43245%26%8%8%11%41%
1890
July1st to 15thNight
6%5%35%6%36%8%8%12%31%
1890
16th to endNight
4425%5%47%7%9%14%35%
1991
August1st to 15thNight
7%426%6%5%6%8%8%11%32%
1861
16th to endNight
10%5%25%5%35%6%7%10%35%
2209
September1st to 15thNight
9%5%25%5%45%6%6%10%38%
2310
16th to endNight
13%5%245%23446%46%
2310
October1st to 15thNight
13%413323445%52%
2380
16th to endNight
10%313423345%56%
2688
November1st to 15thNight
12%414312336%55%
2738
16th to endNight
11%423423446%51%
2925
December1st to 15thNight
16%5%24324446%44%
2925
16th to endNight
19%7%24434446%39%
3120

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%47%15%24%5%
2017
16th to endDay
38%36%19%23%8%
2160
February1st to 15thDay
41%48%19%18%5%
2179
16th to endDay
43%45%18%20%7%
1980
March1st to 15thDay
39%5%8%18%18%9%
2441
16th to endDay
40%5%10%21%17%4
2640
April1st to 15thDay
35%5%10%21%20%6%
2467
16th to endDay
32%6%10%20%23%6%
2845
May1st to 15thDay
34%6%13%20%20%4
2916
16th to endDay
40%7%13%21%14%2
3059
June1st to 15thDay
41%9%16%20%11%1
2756
16th to endDay
32%10%19%21%12%2
2730
July1st to 15thDay
41%13%17%17%6%2
2591
16th to endDay
40%13%19%18%7%1
2726
August1st to 15thDay
46%12%15%16%7%1
2669
16th to endDay
47%12%15%14%9%1
2677
September1st to 15thDay
41%9%12%16%16%3
2310
16th to endDay
39%6%11%18%19%3
2310
October1st to 15thDay
34%410%21%23%6%
2240
16th to endDay
31%4417%29%12%
2240
November1st to 15thDay
35%37%18%24%10%
2106
16th to endDay
33%5%7%20%25%7%
2025
December1st to 15thDay
43%5%9%16%17%7%
2025
16th to endDay
47%5%8%16%14%7%
2160
January1st to 15thNight
41%47%15%24%7%
2912
16th to endNight
40%35%17%22%10%
3120
February1st to 15thNight
40%38%18%19%9%
2671
16th to endNight
40%47%17%21%8%
2373
March1st to 15thNight
37%6%9%15%21%9%
2507
16th to endNight
36%5%11%19%20%6%
2640
April1st to 15thNight
32%49%25%20%8%
2471
16th to endNight
29%6%9%22%21%11%
2062
May1st to 15thNight
31%7%14%21%20%5%
2025
16th to endNight
36%10%12%22%14%3
2116
June1st to 15thNight
36%11%18%20%11%1
1913
16th to endNight
30%13%19%22%11%2
1890
July1st to 15thNight
38%15%19%16%6%3
1800
16th to endNight
33%14%24%18%7%2
1883
August1st to 15thNight
41%12%16%20%7%1
1850
16th to endNight
39%12%20%16%9%1
2209
September1st to 15thNight
38%11%15%15%14%4
2310
16th to endNight
37%6%13%18%18%4
2310
October1st to 15thNight
32%5%11%20%22%7%
2380
16th to endNight
30%36%16%29%14%
2688
November1st to 15thNight
32%36%17%26%13%
2738
16th to endNight
33%48%16%25%11%
2925
December1st to 15thNight
39%5%9%18%19%7%
2925
16th to endNight
45%5%8%17%16%6%
3120

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
26%18%35%16%3
225
16th to endDay
17%25%37%13%5%
240
February1st to 15thDay
26%21%36%14%1
225
16th to endDay
35%17%29%12%5%
201
March1st to 15thDay
21%15%34%22%5%
416
16th to endDay
18%13%36%20%10%
480
April1st to 15thDay
17%15%31%20%13%2
450
16th to endDay
13%9%27%25%20%3
439
May1st to 15thDay
10%8%28%27%16%8%
468
16th to endDay
16%415%26%24%12%
523
June1st to 15thDay
13%213%24%27%18%
443
16th to endDay
5%14%28%27%21%
435
July1st to 15thDay
11%9%21%35%22%
425
16th to endDay
7%17%28%37%18%
454
August1st to 15thDay
15%12%26%27%18%
418
16th to endDay
12%10%26%32%18%
460
September1st to 15thDay
13%211%23%34%14%
435
16th to endDay
17%210%29%28%11%
434
October1st to 15thDay
20%218%27%19%11%
435
16th to endDay
15%9%24%26%19%5%
464
November1st to 15thDay
24%6%27%22%15%2
344
16th to endDay
11%14%30%28%14%1
225
December1st to 15thDay
29%16%32%18%4
225
16th to endDay
30%15%32%16%31
240
January1st to 15thNight
20%17%30%23%8%
900
16th to endNight
19%15%32%26%4
960
February1st to 15thNight
19%14%29%31%4
884
16th to endNight
20%15%34%25%3
791
March1st to 15thNight
15%15%35%29%4
900
16th to endNight
15%11%32%27%11%
960
April1st to 15thNight
14%14%30%27%13%
898
16th to endNight
12%8%27%34%14%1
692
May1st to 15thNight
8%5%27%34%20%3
675
16th to endNight
12%214%33%31%4
707
June1st to 15thNight
10%113%34%30%8%
637
16th to endNight
6%11%34%35%10%
630
July1st to 15thNight
9%8%31%39%11%
600
16th to endNight
6%17%29%47%7%
660
August1st to 15thNight
10%5%33%41%9%
620
16th to endNight
11%8%30%39%8%
718
September1st to 15thNight
11%110%29%38%8%
840
16th to endNight
17%111%29%35%3
837
October1st to 15thNight
15%319%28%25%6%
840
16th to endNight
12%8%23%30%22%2
896
November1st to 15thNight
15%6%23%31%19%3
880
16th to endNight
13%10%28%29%16%1
900
December1st to 15thNight
20%11%24%30%11%1
900
16th to endNight
22%13%26%30%7%
960
Page generated at 2020-06-04 03:18:55. Version ac04

Copyright 2020 A. Danko


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