This page made possible by the sponsorship of:

Michael A. Covington, writer
, SkyShack Observatory.

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 2019-09-17.

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
48%
18290
22%
54837
15%
18247
57%
18247
27%
34237

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
29%
840
24%
2717
10%
836
45%
836
21%
1671
January16th to endNight
28%
896
25%
2912
13%
896
44%
896
23%
1780
February1st to 15thNight
33%
824
25%
2488
12%
821
47%
821
25%
1547
February16th to endNight
25%
735
24%
2205
8%
735
41%
735
25%
1379
March1st to 15thNight
30%
840
25%
2340
10%
840
43%
840
27%
1476
March16th to endNight
36%
896
21%
2464
10%
896
45%
896
29%
1542
April1st to 15thNight
40%
838
25%
2306
13%
838
49%
838
33%
1378
April16th to endNight
48%
646
27%
1924
16%
646
57%
646
34%
1106
May1st to 15thNight
53%
630
21%
1890
13%
630
59%
630
32%
1132
May16th to endNight
61%
657
20%
1970
14%
657
64%
657
28%
1252
June1st to 15thNight
63%
630
15%
1890
13%
630
65%
630
27%
1248
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
60%
782
21%
2159
17%
782
63%
782
29%
1413
October1st to 15thNight
56%
780
29%
2210
23%
780
63%
780
35%
1324
October16th to endNight
51%
832
34%
2496
26%
832
64%
832
37%
1368
November1st to 15thNight
50%
820
29%
2552
23%
820
60%
820
34%
1441
November16th to endNight
44%
840
27%
2730
18%
840
57%
840
30%
1545
December1st to 15thNight
40%
840
25%
2730
16%
840
53%
840
23%
1687
December16th to endNight
34%
896
21%
2912
13%
896
44%
896
19%
1912

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%
55843
Night
11%5%2443445%7%45%
55037
TransparencyDay
39%7%11%19%17%5%
55544
Night
36%7%11%18%18%7%
54840
SeeingDay
15%7%20%24%21%10%
8178
Night
14%8%22%30%21%3
18292

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
16%5%24423345%44%
1881
16th to endDay
15%5%2442335%5%47%
2016
February1st to 15thDay
17%6%2442345%6%42%
2029
16th to endDay
18%6%14314335%45%
1840
March1st to 15thDay
14%425%423436%47%
2278
16th to endDay
14%425%324446%45%
2463
April1st to 15thDay
11%42443445%6%47%
2302
16th to endDay
9%324435%45%6%49%
2652
May1st to 15thDay
9%5%25%435%5%5%8%45%
2721
16th to endDay
11%5%25%5%36%46%7%40%
2847
June1st to 15thDay
10%425%6%46%6%6%9%34%
2730
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%42%
2156
October1st to 15thDay
15%413222346%51%
2080
16th to endDay
10%31432323458%
2080
November1st to 15thDay
14%413423235%52%
1962
16th to endDay
12%424323445%51%
1890
December1st to 15thDay
17%6%25%42445%5%41%
1890
16th to endDay
22%6%25%423346%37%
2016
January1st to 15thNight
13%6%25%424446%45%
2717
16th to endNight
16%6%3432234447%
2912
February1st to 15thNight
16%424424346%46%
2480
16th to endNight
14%6%24424446%46%
2205
March1st to 15thNight
12%5%24334436%48%
2340
16th to endNight
12%424424447%48%
2464
April1st to 15thNight
11%414413347%51%
2306
16th to endNight
8%414435%347%53%
1924
May1st to 15thNight
7%4245%25%46%8%47%
1889
16th to endNight
8%415%5%35%5%6%8%43%
1970
June1st to 15thNight
8%5%345%446%7%12%35%
1890
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
14%5%245%2445%6%45%
2159
October1st to 15thNight
13%413323445%53%
2210
16th to endNight
8%313423345%58%
2496
November1st to 15thNight
12%414313336%55%
2552
16th to endNight
11%423323446%52%
2730
December1st to 15thNight
16%5%24324346%45%
2730
16th to endNight
19%7%24434446%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
41%48%16%24%4
1882
16th to endDay
37%36%19%23%8%
2016
February1st to 15thDay
41%48%20%18%6%
2031
16th to endDay
41%46%19%21%6%
1840
March1st to 15thDay
38%5%8%18%19%10%
2278
16th to endDay
38%5%9%21%18%5%
2464
April1st to 15thDay
36%5%10%21%19%6%
2302
16th to endDay
32%6%10%20%23%6%
2652
May1st to 15thDay
35%7%13%20%19%3
2721
16th to endDay
40%7%13%21%14%2
2851
June1st to 15thDay
41%9%16%19%11%1
2730
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
41%6%10%18%18%4
2156
October1st to 15thDay
33%410%21%22%6%
2080
16th to endDay
29%35%18%29%13%
2080
November1st to 15thDay
34%37%18%24%11%
1962
16th to endDay
33%47%19%25%8%
1890
December1st to 15thDay
43%5%9%16%17%7%
1890
16th to endDay
47%5%8%17%14%6%
2016
January1st to 15thNight
39%47%16%24%6%
2717
16th to endNight
40%35%18%22%10%
2912
February1st to 15thNight
39%38%18%20%9%
2489
16th to endNight
38%48%17%22%8%
2205
March1st to 15thNight
36%6%9%16%21%9%
2340
16th to endNight
35%5%11%18%21%7%
2464
April1st to 15thNight
32%48%24%21%8%
2306
16th to endNight
29%6%9%22%20%10%
1924
May1st to 15thNight
32%7%14%21%18%5%
1890
16th to endNight
34%10%13%23%15%3
1972
June1st to 15thNight
36%11%18%20%11%1
1890
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
39%6%12%18%17%4
2159
October1st to 15thNight
32%5%11%19%23%8%
2210
16th to endNight
28%36%17%30%13%
2496
November1st to 15thNight
31%37%17%25%13%
2552
16th to endNight
33%48%16%26%11%
2730
December1st to 15thNight
39%5%9%18%19%7%
2730
16th to endNight
45%5%8%18%16%6%
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
24%17%35%18%4
180
16th to endDay
16%26%35%15%6%
192
February1st to 15thDay
27%21%34%15%1
180
16th to endDay
29%16%33%13%5%
159
March1st to 15thDay
20%15%34%23%5%
358
16th to endDay
16%13%35%22%11%
416
April1st to 15thDay
17%14%28%21%15%2
390
16th to endDay
12%6%26%27%23%4
379
May1st to 15thDay
11%6%27%27%17%9%
408
16th to endDay
16%5%14%25%24%13%
459
June1st to 15thDay
13%213%23%27%18%
435
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
20%211%30%23%12%
378
October1st to 15thDay
20%218%28%18%12%
375
16th to endDay
13%8%22%27%22%5%
400
November1st to 15thDay
25%6%24%22%17%2
290
16th to endDay
11%13%29%27%16%1
180
December1st to 15thDay
29%13%33%18%4
180
16th to endDay
30%16%32%16%31
192
January1st to 15thNight
19%17%29%24%8%
840
16th to endNight
19%15%31%27%5%
896
February1st to 15thNight
18%13%29%32%5%
824
16th to endNight
18%16%36%25%3
735
March1st to 15thNight
15%15%35%28%5%
840
16th to endNight
15%11%31%28%12%
896
April1st to 15thNight
14%13%29%27%14%
838
16th to endNight
11%8%26%35%15%1
646
May1st to 15thNight
9%426%34%22%3
630
16th to endNight
11%215%33%32%4
659
June1st to 15thNight
10%113%34%31%8%
630
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
18%112%29%34%3
782
October1st to 15thNight
15%320%27%25%7%
780
16th to endNight
10%8%24%31%23%2
832
November1st to 15thNight
15%5%23%31%20%3
820
16th to endNight
13%11%27%28%17%1
840
December1st to 15thNight
19%11%24%31%11%1
840
16th to endNight
21%13%26%30%7%
896
Page generated at 2019-09-17 21:12:19. Version ac04

Copyright 2019 A. Danko


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