Dreyfuss Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dreyfuss Planetarium clear sky chart from 2005-11-05 to 2018-10-08.

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
34%
16368
19%
51005
10%
16337
44%
16337
23%
32772

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
24%
780
20%
2716
9%
776
40%
776
19%
1702
January16th to endNight
20%
832
21%
2805
7%
832
39%
832
19%
1760
February1st to 15thNight
21%
764
18%
2418
5%
761
36%
761
19%
1605
February16th to endNight
21%
683
25%
2049
9%
683
41%
683
22%
1304
March1st to 15thNight
22%
780
19%
2327
7%
780
37%
780
21%
1535
March16th to endNight
25%
832
23%
2161
9%
832
37%
832
25%
1448
April1st to 15thNight
24%
778
17%
1946
4%
778
31%
778
25%
1351
April16th to endNight
30%
761
18%
1917
5%
761
37%
761
26%
1322
May1st to 15thNight
29%
542
17%
1712
8%
542
38%
542
18%
1167
May16th to endNight
41%
406
14%
1625
13%
406
48%
406
19%
1027
June1st to 15thNight
40%
390
15%
1560
12%
390
51%
390
18%
999
June16th to endNight
56%
390
15%
1560
15%
390
63%
390
26%
885
July1st to 15thNight
53%
370
14%
1480
15%
370
57%
370
20%
888
July16th to endNight
57%
408
15%
1546
16%
386
63%
386
25%
895
August1st to 15thNight
55%
595
17%
1736
12%
593
58%
593
30%
1098
August16th to endNight
57%
828
17%
2070
9%
828
59%
828
33%
1384
September1st to 15thNight
46%
780
22%
1950
12%
780
50%
780
31%
1307
September16th to endNight
50%
777
24%
2132
18%
777
54%
777
31%
1362
October1st to 15thNight
41%
752
20%
2200
14%
752
48%
752
26%
1411
October16th to endNight
30%
768
24%
2394
13%
768
46%
768
25%
1489
November1st to 15thNight
33%
760
22%
2472
11%
760
48%
760
24%
1523
November16th to endNight
28%
780
22%
2587
11%
780
43%
780
22%
1609
December1st to 15thNight
26%
780
16%
2730
6%
780
38%
780
16%
1808
December16th to endNight
19%
832
19%
2912
5%
832
37%
832
17%
1893

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
16%5%2442445%7%40%
52137
Night
16%6%24424446%42%
51175
Cloud CoverDay
16%5%2442445%7%41%
52146
Night
16%5%24424446%43%
51181
TransparencyDay
41%6%12%21%15%2
51825
Night
41%5%11%22%16%2
51005
SeeingDay
20%11%28%23%12%3
7137
Night
19%9%30%28%10%1
16369

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%6%235%3446%5%42%
1552
16th to endDay
15%7%34424436%43%
1769
February1st to 15thDay
16%7%35%434346%40%
1773
16th to endDay
17%5%25%42445%6%40%
1710
March1st to 15thDay
17%6%25%5%25%35%7%38%
1950
16th to endDay
17%6%35%423446%42%
2415
April1st to 15thDay
19%6%25%324447%39%
2332
16th to endDay
17%425%433347%43%
2318
May1st to 15thDay
22%5%25%42345%7%35%
2581
16th to endDay
20%5%24434449%36%
2842
June1st to 15thDay
18%6%3442445%8%36%
2730
16th to endDay
11%5%245%35%5%6%8%40%
2730
July1st to 15thDay
10%4246%36%6%6%9%37%
2730
16th to endDay
11%435%5%36%6%6%9%36%
2878
August1st to 15thDay
11%5%25%5%36%5%6%8%39%
2449
16th to endDay
13%425%5%3445%7%43%
2484
September1st to 15thDay
15%5%14424447%43%
2340
16th to endDay
16%5%25%5%24446%43%
2157
October1st to 15thDay
18%5%15%433447%40%
1927
16th to endDay
19%413423346%46%
1830
November1st to 15thDay
19%5%24413435%45%
1716
16th to endDay
15%5%23324346%47%
1700
December1st to 15thDay
18%7%24414346%41%
1560
16th to endDay
20%7%23423447%38%
1664
January1st to 15thNight
17%6%23424445%43%
2716
16th to endNight
16%8%34424345%43%
2805
February1st to 15thNight
15%8%35%43345%5%40%
2417
16th to endNight
18%5%24333345%44%
2049
March1st to 15thNight
18%7%24324336%42%
2314
16th to endNight
17%7%24322445%44%
2161
April1st to 15thNight
18%6%2442445%7%39%
1946
16th to endNight
18%5%24334336%43%
1917
May1st to 15thNight
19%6%26%5%24436%39%
1712
16th to endNight
20%4345%3335%7%39%
1623
June1st to 15thNight
19%5%3332436%7%38%
1560
16th to endNight
9%424425%5%6%10%44%
1560
July1st to 15thNight
11%424435%6%7%9%41%
1560
16th to endNight
10%4245%36%6%7%10%39%
1642
August1st to 15thNight
10%4244245%6%8%45%
1746
16th to endNight
12%425%5%35%45%8%43%
2070
September1st to 15thNight
17%414424446%44%
1950
16th to endNight
14%6%14433346%47%
2132
October1st to 15thNight
17%5%35%423347%43%
2200
16th to endNight
16%5%24412345%48%
2394
November1st to 15thNight
16%6%2431333447%
2472
16th to endNight
17%5%2442345%6%43%
2587
December1st to 15thNight
20%6%25%5%24446%37%
2730
16th to endNight
18%6%24424446%40%
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%6%2343436%6%42%
1552
16th to endDay
15%7%24433436%43%
1769
February1st to 15thDay
16%6%35%424336%40%
1773
16th to endDay
17%5%2442435%7%40%
1710
March1st to 15thDay
18%6%246%2445%7%38%
1960
16th to endDay
18%5%34324346%42%
2414
April1st to 15thDay
19%6%24423346%40%
2332
16th to endDay
16%425%433346%44%
2318
May1st to 15thDay
22%6%15%42345%7%35%
2581
16th to endDay
19%5%2442445%9%37%
2842
June1st to 15thDay
19%6%24425%45%7%36%
2730
16th to endDay
11%5%25%5%35%5%6%8%40%
2730
July1st to 15thDay
10%425%6%35%6%7%9%39%
2730
16th to endDay
11%425%5%37%7%6%8%37%
2878
August1st to 15thDay
12%425%5%35%5%6%7%40%
2449
16th to endDay
13%4145%35%45%7%44%
2484
September1st to 15thDay
15%42442435%7%44%
2340
16th to endDay
17%424434446%43%
2157
October1st to 15thDay
17%5%24433447%41%
1927
16th to endDay
19%413423346%46%
1830
November1st to 15thDay
18%5%24424335%45%
1716
16th to endDay
16%423423446%47%
1700
December1st to 15thDay
17%7%24423446%41%
1560
16th to endDay
20%7%24423446%38%
1664
January1st to 15thNight
18%6%23433446%43%
2716
16th to endNight
16%8%24423345%43%
2805
February1st to 15thNight
14%8%36%433446%40%
2410
16th to endNight
18%5%23423345%45%
2049
March1st to 15thNight
19%7%24324335%42%
2327
16th to endNight
17%6%24423445%44%
2161
April1st to 15thNight
18%5%2432445%7%39%
1946
16th to endNight
19%424324347%42%
1917
May1st to 15thNight
19%7%26%5%23436%39%
1712
16th to endNight
20%5%145%33347%39%
1623
June1st to 15thNight
19%6%24325%45%7%39%
1560
16th to endNight
9%424425%46%10%44%
1560
July1st to 15thNight
11%4245%245%7%9%42%
1560
16th to endNight
10%415%5%26%5%7%9%41%
1642
August1st to 15thNight
10%3244245%5%9%45%
1746
16th to endNight
13%4245%3445%8%43%
2070
September1st to 15thNight
17%424414447%44%
1950
16th to endNight
15%5%23423446%47%
2132
October1st to 15thNight
17%5%25%423347%44%
2200
16th to endNight
17%5%24412345%48%
2394
November1st to 15thNight
16%6%2442333448%
2472
16th to endNight
17%5%2442445%6%43%
2587
December1st to 15thNight
20%6%25%424446%37%
2730
16th to endNight
18%6%24424446%40%
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%414%23%12%3
1553
16th to endDay
42%313%23%14%2
1769
February1st to 15thDay
45%313%22%12%2
1776
16th to endDay
42%5%10%25%13%1
1710
March1st to 15thDay
44%5%14%21%11%2
1960
16th to endDay
44%410%20%17%3
2415
April1st to 15thDay
44%410%21%14%3
2332
16th to endDay
41%48%20%21%3
2318
May1st to 15thDay
46%5%10%19%15%2
2581
16th to endDay
45%6%13%20%13%1
2846
June1st to 15thDay
45%8%12%20%12%
2730
16th to endDay
39%8%13%22%14%1
2730
July1st to 15thDay
39%9%11%20%17%1
2581
16th to endDay
38%9%15%20%13%3
2711
August1st to 15thDay
38%9%15%19%16%
2435
16th to endDay
38%6%11%22%18%2
2484
September1st to 15thDay
38%6%11%20%20%1
2340
16th to endDay
41%5%9%19%21%2
2157
October1st to 15thDay
41%5%13%20%16%1
1927
16th to endDay
38%5%10%26%17%2
1830
November1st to 15thDay
42%410%20%19%2
1716
16th to endDay
38%411%27%15%2
1700
December1st to 15thDay
43%5%15%20%13%1
1560
16th to endDay
46%5%14%19%12%
1664
January1st to 15thNight
42%5%11%22%14%3
2716
16th to endNight
42%410%24%15%2
2805
February1st to 15thNight
45%5%12%20%13%2
2418
16th to endNight
41%38%24%18%3
2049
March1st to 15thNight
44%412%21%14%3
2327
16th to endNight
41%5%10%20%18%4
2161
April1st to 15thNight
43%5%11%20%16%2
1946
16th to endNight
42%5%7%19%21%2
1917
May1st to 15thNight
46%6%10%17%17%2
1712
16th to endNight
44%6%15%17%14%2
1625
June1st to 15thNight
44%6%11%18%16%1
1560
16th to endNight
34%7%15%25%15%1
1560
July1st to 15thNight
36%10%13%20%17%1
1480
16th to endNight
34%8%18%22%12%3
1546
August1st to 15thNight
34%9%14%24%15%2
1736
16th to endNight
37%6%13%21%18%1
2070
September1st to 15thNight
39%6%11%24%17%1
1950
16th to endNight
37%5%7%22%25%1
2132
October1st to 15thNight
40%5%12%22%15%2
2200
16th to endNight
38%5%10%26%17%1
2394
November1st to 15thNight
40%410%21%19%4
2472
16th to endNight
41%411%26%14%2
2587
December1st to 15thNight
47%5%13%20%11%1
2730
16th to endNight
44%6%12%22%13%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
17%30%31%16%31
90
16th to endDay
19%18%39%18%4
121
February1st to 15thDay
23%23%34%17%2
199
16th to endDay
21%15%39%18%4
291
March1st to 15thDay
20%20%33%20%4
330
16th to endDay
21%15%37%17%6%1
352
April1st to 15thDay
23%14%35%15%9%1
330
16th to endDay
21%13%35%16%10%2
319
May1st to 15thDay
31%13%28%17%7%2
348
16th to endDay
26%5%25%25%14%2
395
June1st to 15thDay
19%12%26%25%12%3
375
16th to endDay
16%9%31%28%13%1
375
July1st to 15thDay
11%426%32%18%5%
365
16th to endDay
15%5%21%31%21%4
390
August1st to 15thDay
15%321%32%18%8%
358
16th to endDay
13%221%30%22%9%
396
September1st to 15thDay
21%6%23%22%16%10%
375
16th to endDay
20%424%22%14%12%
374
October1st to 15thDay
23%423%26%18%3
345
16th to endDay
18%13%31%26%8%1
313
November1st to 15thDay
21%11%26%25%12%2
280
16th to endDay
16%20%32%21%8%1
230
December1st to 15thDay
22%27%30%11%8%
90
16th to endDay
33%21%37%6%1
96
January1st to 15thNight
19%14%36%23%4
780
16th to endNight
22%15%36%23%2
832
February1st to 15thNight
20%14%38%24%2
764
16th to endNight
20%15%38%22%2
683
March1st to 15thNight
23%13%37%19%5%
780
16th to endNight
20%13%36%23%5%
832
April1st to 15thNight
21%12%37%22%5%
778
16th to endNight
21%11%33%25%7%
761
May1st to 15thNight
21%10%33%26%8%
542
16th to endNight
21%425%35%11%1
407
June1st to 15thNight
21%6%25%33%12%
390
16th to endNight
11%223%48%14%
390
July1st to 15thNight
10%425%41%17%1
370
16th to endNight
12%120%43%19%1
408
August1st to 15thNight
14%219%41%21%1
595
16th to endNight
15%215%39%25%2
828
September1st to 15thNight
17%324%32%18%2
780
16th to endNight
18%220%31%21%4
777
October1st to 15thNight
19%7%24%30%15%2
752
16th to endNight
20%10%34%25%9%
768
November1st to 15thNight
19%10%30%26%12%1
760
16th to endNight
19%13%33%24%8%1
780
December1st to 15thNight
24%11%31%24%6%1
780
16th to endNight
22%13%40%21%2
832
Page generated at 2018-10-09 10:39:14. Version ac04

Copyright 2018 A. Danko


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