Draper Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Draper Park clear sky chart from 2005-11-06 to 2024-03-23.

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
33%
23363
19%
80673
10%
23273
44%
23273
21%
51294

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 10thNight
19%
753
24%
4335
8%
737
38%
737
14%
2318
January11th to 20thNight
22%
758
23%
4335
6%
740
38%
740
11%
2512
January21st to endNight
20%
830
14%
4633
8%
814
37%
814
11%
3122
February1st to 10thNight
21%
760
19%
2452
8%
760
36%
760
20%
1590
February11th to 20thNight
18%
743
20%
2220
5%
740
37%
740
19%
1475
February21st to endNight
21%
628
24%
1884
8%
628
40%
628
20%
1244
March1st to 10thNight
23%
760
21%
2280
8%
760
40%
760
23%
1450
March11th to 20thNight
23%
760
21%
2190
8%
760
37%
760
23%
1442
March21st to endNight
23%
801
22%
2012
6%
801
34%
801
24%
1392
April1st to 10thNight
24%
720
18%
1800
5%
720
32%
720
23%
1267
April11th to 20thNight
30%
711
18%
1775
5%
711
37%
711
26%
1239
April21st to endNight
30%
684
19%
1764
6%
684
37%
684
24%
1220
May1st to 10thNight
27%
540
15%
1620
7%
540
34%
540
17%
1142
May11th to 20thNight
30%
395
19%
1457
11%
395
41%
395
17%
957
May21st to endNight
50%
388
14%
1551
15%
388
55%
388
19%
957
June1st to 10thNight
42%
360
17%
1440
17%
360
51%
360
19%
886
June11th to 20thNight
48%
360
15%
1440
16%
360
56%
360
21%
875
June21st to endNight
56%
360
15%
1440
18%
360
63%
360
25%
842
July1st to 10thNight
54%
350
13%
1400
16%
350
58%
350
20%
874
July11th to 20thNight
56%
348
14%
1392
18%
348
60%
348
20%
854
July21st to endNight
56%
394
18%
1486
20%
372
61%
372
26%
850
August1st to 10thNight
56%
457
16%
1521
13%
455
60%
455
26%
953
August11th to 20thNight
53%
710
14%
1774
8%
710
55%
710
26%
1278
August21st to endNight
53%
792
17%
1980
8%
792
56%
792
31%
1340
September1st to 10thNight
48%
720
20%
1800
11%
720
52%
720
29%
1228
September11th to 20thNight
49%
720
25%
1884
16%
720
54%
720
36%
1164
September21st to endNight
45%
720
25%
1980
16%
720
53%
720
29%
1292
October1st to 10thNight
35%
720
16%
2065
11%
720
40%
720
23%
1393
October11th to 20thNight
37%
720
23%
2160
13%
720
50%
720
28%
1325
October21st to endNight
27%
792
20%
2529
10%
792
40%
792
21%
1660
November1st to 10thNight
34%
740
24%
2407
11%
740
50%
740
27%
1424
November11th to 20thNight
28%
760
26%
2470
13%
760
45%
760
23%
1501
November21st to endNight
28%
760
22%
2540
10%
760
45%
760
24%
1512
December1st to 10thNight
22%
760
18%
2660
7%
760
37%
760
17%
1721
December11th to 20thNight
23%
760
18%
3185
6%
759
38%
759
15%
1951
December21st to endNight
22%
829
13%
4812
7%
817
39%
817
11%
3044

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
17%6%35%5%345%5%7%40%
78614
Night
18%7%35%43445%6%42%
81263
TransparencyDay
42%7%12%22%15%2
78319
Night
42%6%12%23%15%2
81092
SeeingDay
20%12%29%24%11%3
14105
Night
20%11%31%28%10%1
23386

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 10thDay
16%7%25%42345%6%47%
2517
11th to 20thDay
16%9%36%6%45%446%36%
2520
21st to endDay
22%10%47%5%24446%32%
2977
February1st to 10thDay
18%7%36%5%3446%6%38%
1726
11th to 20thDay
15%6%35%5%35%346%44%
1848
21st to endDay
19%8%3443446%5%39%
1570
March1st to 10thDay
16%6%345%35%45%7%42%
1897
11th to 20thDay
15%5%25%6%46%5%5%7%40%
1987
21st to endDay
20%8%25%43445%5%40%
2388
April1st to 10thDay
18%8%35%42445%6%41%
2160
11th to 20thDay
18%6%25%5%2445%7%42%
2134
21st to endDay
20%5%34435%46%7%40%
2196
May1st to 10thDay
24%7%35%42445%7%35%
2340
11th to 20thDay
19%6%35%5%345%5%8%36%
2451
21st to endDay
15%6%25%5%25%45%8%42%
2725
June1st to 10thDay
18%5%345%345%7%8%37%
2520
11th to 20thDay
16%6%35%5%35%5%6%8%36%
2520
21st to endDay
13%6%36%5%346%7%9%39%
2520
July1st to 10thDay
12%5%27%6%35%6%6%9%38%
2520
11th to 20thDay
11%5%25%6%35%6%6%11%39%
2520
21st to endDay
13%6%36%6%36%6%7%8%36%
2744
August1st to 10thDay
10%6%25%6%47%6%7%9%37%
2384
11th to 20thDay
13%6%26%5%35%6%7%9%38%
2126
21st to endDay
12%6%36%5%45%5%7%8%41%
2376
September1st to 10thDay
14%6%26%5%35%46%7%43%
2160
11th to 20thDay
14%42442345%7%50%
2075
21st to endDay
16%6%26%6%345%5%6%41%
1980
October1st to 10thDay
23%6%2432345%6%42%
1890
11th to 20thDay
16%5%25%42445%6%47%
1800
21st to endDay
23%5%244245%47%41%
1825
November1st to 10thDay
15%6%24323445%51%
1671
11th to 20thDay
20%6%2342345%6%47%
1710
21st to endDay
15%6%35%4345%6%7%44%
1639
December1st to 10thDay
20%7%26%5%3446%7%37%
1520
11th to 20thDay
23%5%34323346%44%
1906
21st to endDay
19%8%37%6%445%46%32%
2772
January1st to 10thNight
17%6%2442335%6%47%
4429
11th to 20thNight
17%8%36%434446%42%
4440
21st to endNight
25%11%35%424445%34%
4678
February1st to 10thNight
17%8%35%424446%42%
2452
11th to 20thNight
17%7%36%5%2445%5%41%
2218
21st to endNight
19%7%35%433445%41%
1884
March1st to 10thNight
18%6%34324448%44%
2270
11th to 20thNight
17%7%26%5%2445%6%42%
2189
21st to endNight
18%7%35%43445%6%41%
2012
April1st to 10thNight
18%8%26%5%245%5%7%38%
1800
11th to 20thNight
20%6%25%4245%5%7%41%
1775
21st to endNight
20%6%26%433436%42%
1764
May1st to 10thNight
23%5%36%6%35%445%35%
1620
11th to 20thNight
20%7%35%5%25%447%38%
1456
21st to endNight
17%7%25%43445%7%42%
1550
June1st to 10thNight
18%5%24425%45%7%41%
1440
11th to 20thNight
13%7%25%425%47%8%41%
1440
21st to endNight
11%5%246%25%6%6%9%44%
1440
July1st to 10thNight
12%5%36%7%45%5%6%10%38%
1440
11th to 20thNight
12%5%346%46%47%9%40%
1440
21st to endNight
12%5%245%25%5%6%11%41%
1574
August1st to 10thNight
9%5%25%6%35%6%6%9%43%
1531
11th to 20thNight
12%5%37%8%45%6%6%9%36%
1774
21st to endNight
14%6%25%5%3446%8%43%
1980
September1st to 10thNight
16%5%25%5%3445%7%44%
1800
11th to 20thNight
16%5%13413345%53%
1884
21st to endNight
17%5%35%5%2335%6%46%
1980
October1st to 10thNight
20%8%36%5%23346%42%
2065
11th to 20thNight
16%5%2443335%6%48%
2160
21st to endNight
23%7%25%323446%42%
2529
November1st to 10thNight
14%5%245%2445%6%49%
2407
11th to 20thNight
20%6%24313345%48%
2470
21st to endNight
16%5%24424447%47%
2540
December1st to 10thNight
20%7%25%5%3445%7%40%
2660
11th to 20thNight
20%6%2443445%5%41%
3288
21st to endNight
21%8%35%5%345%5%5%36%
4884

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 10thDay
37%411%32%13%3
2518
11th to 20thDay
47%6%12%23%11%2
2520
21st to endDay
53%6%9%21%9%2
2977
February1st to 10thDay
45%5%13%22%13%2
1726
11th to 20thDay
42%5%10%25%17%2
1857
21st to endDay
45%5%12%21%14%3
1570
March1st to 10thDay
40%5%14%24%14%3
1900
11th to 20thDay
40%7%13%24%14%2
1987
21st to endDay
45%5%8%19%17%5%
2388
April1st to 10thDay
44%5%11%19%16%5%
2160
11th to 20thDay
41%5%12%21%18%3
2134
21st to endDay
43%7%10%20%16%4
2196
May1st to 10thDay
47%6%10%19%16%2
2340
11th to 20thDay
44%7%11%20%14%3
2455
21st to endDay
40%8%15%22%14%2
2725
June1st to 10thDay
41%9%14%21%14%1
2520
11th to 20thDay
44%8%12%22%12%2
2520
21st to endDay
39%8%15%22%15%1
2520
July1st to 10thDay
41%9%12%22%15%1
2450
11th to 20thDay
35%8%18%23%13%2
2445
21st to endDay
42%9%13%18%15%3
2591
August1st to 10thDay
38%11%15%22%13%1
2370
11th to 20thDay
40%7%16%23%13%1
2126
21st to endDay
38%8%11%23%18%3
2376
September1st to 10thDay
39%7%13%22%17%2
2160
11th to 20thDay
33%6%12%23%24%2
2075
21st to endDay
42%6%10%19%19%3
1980
October1st to 10thDay
43%6%10%23%16%3
1890
11th to 20thDay
37%6%12%25%18%2
1800
21st to endDay
44%6%9%22%16%3
1825
November1st to 10thDay
35%5%11%24%22%3
1671
11th to 20thDay
39%410%23%20%3
1710
21st to endDay
39%5%14%28%12%2
1639
December1st to 10thDay
45%6%15%20%13%1
1520
11th to 20thDay
41%415%24%14%2
1906
21st to endDay
50%9%10%23%8%
2772
January1st to 10thNight
39%412%30%12%4
4429
11th to 20thNight
43%5%13%25%12%2
4440
21st to endNight
51%6%9%21%11%2
4678
February1st to 10thNight
44%5%12%24%13%2
2452
11th to 20thNight
44%6%9%19%17%5%
2220
21st to endNight
43%5%8%23%16%4
1884
March1st to 10thNight
40%5%12%24%15%4
2280
11th to 20thNight
41%6%11%22%16%3
2190
21st to endNight
42%6%10%18%18%5%
2012
April1st to 10thNight
45%6%10%20%16%3
1800
11th to 20thNight
42%7%9%20%20%2
1775
21st to endNight
44%6%8%21%17%4
1764
May1st to 10thNight
50%6%10%18%14%2
1620
11th to 20thNight
46%7%10%17%18%2
1457
21st to endNight
42%7%17%20%12%2
1551
June1st to 10thNight
42%7%10%21%18%2
1440
11th to 20thNight
40%7%16%25%11%1
1440
21st to endNight
34%9%16%24%15%1
1440
July1st to 10thNight
40%9%13%20%15%3
1400
11th to 20thNight
38%10%13%25%12%1
1392
21st to endNight
33%8%18%22%16%3
1486
August1st to 10thNight
35%11%15%21%16%2
1521
11th to 20thNight
42%10%14%23%10%1
1774
21st to endNight
38%8%13%20%19%2
1980
September1st to 10thNight
41%7%11%24%16%1
1800
11th to 20thNight
33%6%11%23%24%3
1884
21st to endNight
40%5%8%22%22%2
1980
October1st to 10thNight
45%6%12%22%14%3
2065
11th to 20thNight
36%6%14%27%16%2
2160
21st to endNight
45%5%11%22%16%1
2529
November1st to 10thNight
35%6%11%22%21%4
2407
11th to 20thNight
40%49%24%19%5%
2470
21st to endNight
37%5%13%29%14%2
2540
December1st to 10thNight
45%6%12%22%14%1
2660
11th to 20thNight
43%5%13%19%17%3
3288
21st to endNight
46%8%13%22%11%1
4884

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 10thDay
21%25%32%17%41
180
11th to 20thDay
24%24%37%12%21
180
21st to endDay
19%19%41%14%5%2
258
February1st to 10thDay
27%16%37%18%2
286
11th to 20thDay
23%19%38%18%2
456
21st to endDay
25%18%34%19%4
382
March1st to 10thDay
20%21%33%21%4
460
11th to 20thDay
17%21%37%19%5%1
460
21st to endDay
26%19%30%19%6%1
470
April1st to 10thDay
24%18%33%17%7%1
420
11th to 20thDay
20%16%33%19%10%2
412
21st to endDay
27%15%34%17%5%1
420
May1st to 10thDay
31%13%30%17%7%2
423
11th to 20thDay
20%11%35%23%10%2
447
21st to endDay
19%8%24%28%16%4
485
June1st to 10thDay
18%8%28%28%15%4
450
11th to 20thDay
17%11%28%32%11%2
450
21st to endDay
15%8%28%27%18%4
450
July1st to 10thDay
13%322%35%20%7%
445
11th to 20thDay
12%321%34%25%5%
444
21st to endDay
14%6%23%35%20%2
488
August1st to 10thDay
11%5%20%37%19%8%
446
11th to 20thDay
15%420%34%22%5%
439
21st to endDay
13%5%25%32%18%8%
495
September1st to 10thDay
18%5%28%22%20%8%
450
11th to 20thDay
16%5%28%24%16%11%
450
21st to endDay
19%9%27%26%13%5%
450
October1st to 10thDay
28%8%24%21%16%4
450
11th to 20thDay
18%12%28%25%14%2
450
21st to endDay
25%13%30%22%9%1
417
November1st to 10thDay
17%13%29%27%11%3
365
11th to 20thDay
21%16%34%22%6%1
370
21st to endDay
16%19%32%25%6%1
299
December1st to 10thDay
22%22%33%17%42
180
11th to 20thDay
28%21%36%12%3
180
21st to endDay
28%14%36%14%8%1
198
January1st to 10thNight
20%14%43%20%4
760
11th to 20thNight
23%16%34%23%4
760
21st to endNight
20%15%40%22%2
836
February1st to 10thNight
23%12%37%26%2
760
11th to 20thNight
22%17%40%20%1
743
21st to endNight
25%15%35%21%4
628
March1st to 10thNight
23%15%36%22%5%
760
11th to 20thNight
22%14%38%21%41
760
21st to endNight
22%14%36%22%5%
801
April1st to 10thNight
21%16%35%23%5%
720
11th to 20thNight
21%12%33%27%6%
711
21st to endNight
23%11%32%27%6%1
684
May1st to 10thNight
24%11%33%24%7%1
540
11th to 20thNight
21%11%33%28%7%
395
21st to endNight
20%5%17%41%15%2
389
June1st to 10thNight
20%5%26%34%14%1
360
11th to 20thNight
14%426%39%17%
360
21st to endNight
10%223%51%14%1
360
July1st to 10thNight
11%322%43%20%
350
11th to 20thNight
11%419%43%21%2
348
21st to endNight
14%418%46%17%2
394
August1st to 10thNight
12%220%45%21%1
457
11th to 20thNight
15%416%37%25%3
710
21st to endNight
15%417%37%24%2
792
September1st to 10thNight
17%423%35%19%2
720
11th to 20thNight
18%5%23%32%19%4
720
21st to endNight
20%5%24%32%17%2
720
October1st to 10thNight
23%9%27%23%14%2
720
11th to 20thNight
18%11%28%32%10%1
720
21st to endNight
26%12%32%23%7%
792
November1st to 10thNight
16%10%34%26%12%1
740
11th to 20thNight
23%13%32%24%8%1
760
21st to endNight
19%13%35%25%7%1
760
December1st to 10thNight
24%14%36%20%5%1
760
11th to 20thNight
23%14%35%24%4
760
21st to endNight
25%13%36%24%3
836
Page generated at 2024-03-19 23:31:07. Version ac07

Copyright © 2024 Attilla Danko.


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