Dick Clark Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dick Clark Memorial Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
58%
15956
28%
46851
19%
15915
66%
15915
42%
25022

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
42%
897
32%
2506
17%
895
57%
895
43%
1293
January16th to endNight
44%
819
34%
2547
20%
819
61%
819
41%
1280
February1st to 15thNight
39%
698
25%
2262
13%
697
55%
697
33%
1228
February16th to endNight
42%
632
32%
1894
16%
632
57%
632
38%
1033
March1st to 15thNight
51%
720
29%
2112
16%
720
63%
720
43%
1126
March16th to endNight
49%
681
27%
2025
17%
681
59%
681
40%
1110
April1st to 15thNight
51%
539
24%
1798
19%
539
61%
539
35%
962
April16th to endNight
46%
540
24%
1800
20%
540
56%
540
31%
1022
May1st to 15thNight
53%
540
20%
1576
17%
540
57%
540
30%
987
May16th to endNight
63%
563
19%
1498
14%
561
67%
561
39%
892
June1st to 15thNight
73%
540
21%
1440
17%
540
76%
540
49%
788
June16th to endNight
80%
540
29%
1440
24%
540
82%
540
59%
718
July1st to 15thNight
76%
510
19%
1360
16%
510
77%
510
42%
777
July16th to endNight
82%
564
28%
1432
26%
531
82%
531
47%
786
August1st to 15thNight
81%
539
23%
1653
24%
536
81%
536
44%
844
August16th to endNight
81%
573
30%
1910
35%
573
82%
573
42%
969
September1st to 15thNight
75%
540
29%
1800
30%
540
79%
540
42%
906
September16th to endNight
77%
492
37%
1769
37%
492
84%
492
53%
754
October1st to 15thNight
63%
657
29%
1977
22%
657
68%
657
42%
1063
October16th to endNight
61%
737
34%
2145
20%
737
69%
737
46%
1122
November1st to 15thNight
59%
875
33%
2275
19%
875
65%
875
51%
1225
November16th to endNight
55%
900
36%
2424
20%
900
65%
900
53%
1241
December1st to 15thNight
44%
900
26%
2520
11%
900
57%
900
40%
1384
December16th to endNight
45%
960
28%
2688
14%
960
57%
960
39%
1512

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
5%42342446%8%52%
47909
Night
442332335%7%58%
47025
TransparencyDay
27%6%11%25%21%7%
47585
Night
24%5%11%27%23%8%
46851
SeeingDay
9%6%24%32%19%7%
5879
Night
6%5%22%40%20%3
15965

By Month

Percentage Cloud Cover SW (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%2342335%7%59%
1432
16th to endDay
15%24413346%62%
1686
February1st to 15thDay
16%25%32435%8%55%
1600
16th to endDay
16%2332345%8%58%
1580
March1st to 15thDay
23245%235%5%8%54%
1845
16th to endDay
5%6%34325%45%9%49%
2199
April1st to 15thDay
6%6%2332345%9%53%
2150
16th to endDay
11%8%144345%6%6%42%
2160
May1st to 15thDay
11%7%245%35%46%8%40%
2370
16th to endDay
10%5%245%35%6%7%8%41%
2616
June1st to 15thDay
5%213335%6%7%10%48%
2520
16th to endDay
311326%6%7%8%56%
2520
July1st to 15thDay
6%313436%6%7%9%46%
2520
16th to endDay
32135%36%6%8%9%47%
2638
August1st to 15thDay
43145%35%6%9%10%43%
2297
16th to endDay
4313336%5%7%9%51%
2292
September1st to 15thDay
8%31232445%6%55%
2160
16th to endDay
4312312346%65%
1863
October1st to 15thDay
6%5%1332325%7%57%
1650
16th to endDay
5%41121235%7%64%
1716
November1st to 15thDay
242232336%8%60%
1583
16th to endDay
233231336%8%60%
1536
December1st to 15thDay
26%2442345%8%54%
1440
16th to endDay
35%2441336%7%55%
1536
January1st to 15thNight
1333313338%63%
2506
16th to endNight
243432335%5%62%
2547
February1st to 15thNight
16%26%424347%56%
2252
16th to endNight
16%445%23346%57%
1894
March1st to 15thNight
2423323448%58%
2112
16th to endNight
5%6%23314248%56%
2025
April1st to 15thNight
5%5%24334348%54%
1798
16th to endNight
13%7%13313247%50%
1800
May1st to 15thNight
14%5%24332448%46%
1575
16th to endNight
9%413324447%54%
1497
June1st to 15thNight
5%21221445%8%59%
1440
16th to endNight
21222345%8%66%
1440
July1st to 15thNight
7%2122245%8%10%52%
1440
16th to endNight
32133345%7%8%56%
1529
August1st to 15thNight
321432448%9%55%
1662
16th to endNight
421333445%6%59%
1910
September1st to 15thNight
8%21232345%6%59%
1800
16th to endNight
41221235%6%68%
1769
October1st to 15thNight
8%413312347%58%
1977
16th to endNight
6%5%13213235%63%
2145
November1st to 15thNight
2313313446%63%
2275
16th to endNight
142221335%6%65%
2424
December1st to 15thNight
25%25%423349%56%
2520
16th to endNight
36%2442335%7%55%
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
22%412%34%21%4
1433
16th to endDay
21%39%35%22%6%
1686
February1st to 15thDay
26%416%34%14%3
1601
16th to endDay
22%5%8%32%25%5%
1580
March1st to 15thDay
26%5%10%28%24%5%
1845
16th to endDay
29%5%13%27%19%5%
2199
April1st to 15thDay
27%6%11%27%19%7%
2150
16th to endDay
37%7%10%22%17%3
2160
May1st to 15thDay
39%8%12%23%14%2
2370
16th to endDay
35%9%15%21%12%4
2620
June1st to 15thDay
26%9%14%21%18%9%
2520
16th to endDay
20%7%11%20%27%11%
2520
July1st to 15thDay
31%9%11%19%15%13%
2371
16th to endDay
27%10%12%24%16%8%
2472
August1st to 15thDay
30%10%14%18%16%10%
2282
16th to endDay
24%7%11%23%23%8%
2292
September1st to 15thDay
26%5%8%23%22%13%
2160
16th to endDay
19%46%25%36%7%
1863
October1st to 15thDay
26%412%21%26%8%
1650
16th to endDay
19%310%27%29%9%
1716
November1st to 15thDay
20%411%26%26%10%
1583
16th to endDay
20%38%28%30%8%
1536
December1st to 15thDay
25%5%12%35%17%2
1440
16th to endDay
26%415%27%20%5%
1536
January1st to 15thNight
20%312%31%26%4
2506
16th to endNight
22%310%29%26%8%
2547
February1st to 15thNight
28%411%33%18%4
2262
16th to endNight
27%37%28%24%7%
1894
March1st to 15thNight
23%5%7%29%28%6%
2112
16th to endNight
27%411%27%24%4
2025
April1st to 15thNight
28%5%10%27%20%8%
1798
16th to endNight
33%49%26%20%4
1800
May1st to 15thNight
36%6%14%21%17%3
1576
16th to endNight
28%7%19%26%12%6%
1498
June1st to 15thNight
21%6%17%27%15%12%
1440
16th to endNight
14%5%9%24%30%15%
1440
July1st to 15thNight
24%8%15%22%19%10%
1360
16th to endNight
20%8%11%30%18%10%
1432
August1st to 15thNight
20%7%16%26%18%10%
1653
16th to endNight
22%6%9%26%24%10%
1910
September1st to 15thNight
23%5%13%24%17%16%
1800
16th to endNight
15%47%29%33%9%
1769
October1st to 15thNight
24%5%13%18%28%8%
1977
16th to endNight
23%48%25%30%8%
2145
November1st to 15thNight
19%410%25%27%12%
2275
16th to endNight
18%38%29%30%9%
2424
December1st to 15thNight
24%413%31%19%5%
2520
16th to endNight
27%414%30%19%3
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
10%8%15%41%11%13%
90
16th to endDay
45%27%42%18%2
96
February1st to 15thDay
218%34%38%5%
90
16th to endDay
6%16%29%38%8%1
81
March1st to 15thDay
420%25%42%24
135
16th to endDay
12%15%41%22%6%1
288
April1st to 15thDay
13%18%35%22%8%1
269
16th to endDay
22%17%27%23%6%2
270
May1st to 15thDay
15%8%24%34%11%5%
429
16th to endDay
17%5%23%25%19%7%
517
June1st to 15thDay
6%221%33%26%8%
495
16th to endDay
2225%32%27%9%
495
July1st to 15thDay
12%114%31%26%12%
475
16th to endDay
6%114%29%35%11%
497
August1st to 15thDay
6%5%27%35%17%6%
315
16th to endDay
8%317%39%24%6%
332
September1st to 15thDay
7%330%33%17%7%
315
16th to endDay
2223%33%26%10%
138
October1st to 15thDay
7%420%37%17%12%
90
16th to endDay
8%8%22%36%16%7%
96
November1st to 15thDay
6%223%28%22%16%
90
16th to endDay
12%8%32%40%6%
90
December1st to 15thDay
11%12%33%37%5%
90
16th to endDay
2330%56%7%1
96
January1st to 15thNight
313%33%33%12%3
900
16th to endNight
5%12%32%39%9%1
819
February1st to 15thNight
5%9%35%40%8%
704
16th to endNight
48%35%42%8%
632
March1st to 15thNight
46%31%45%10%2
720
16th to endNight
7%8%28%44%10%
681
April1st to 15thNight
8%7%28%46%8%
539
16th to endNight
16%425%37%14%1
540
May1st to 15thNight
16%418%38%18%3
540
16th to endNight
11%215%37%28%4
563
June1st to 15thNight
7%112%50%24%3
540
16th to endNight
2110%47%34%3
540
July1st to 15thNight
7%18%30%42%8%
510
16th to endNight
45%29%51%8%
564
August1st to 15thNight
415%34%48%5%
539
16th to endNight
5%1434%43%10%
573
September1st to 15thNight
10%17%39%32%9%
540
16th to endNight
5%112%41%29%10%
492
October1st to 15thNight
11%217%43%20%5%
657
16th to endNight
9%5%18%44%17%4
737
November1st to 15thNight
47%23%44%15%3
875
16th to endNight
35%29%45%13%1
900
December1st to 15thNight
5%10%32%41%10%
900
16th to endNight
6%7%32%42%9%1
960
Page generated at 2017-09-16 15:07:00. Version ac04

Copyright 2017 A. Danko


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