Danbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danbury 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
28%
23314
19%
80724
8%
23221
40%
23221
18%
51682

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
15%
754
24%
4344
7%
737
36%
737
12%
2350
January11th to 20thNight
17%
760
22%
4337
5%
740
35%
740
9%
2544
January21st to endNight
15%
830
13%
4702
5%
814
35%
814
9%
3219
February1st to 10thNight
15%
760
19%
2437
5%
760
33%
760
15%
1611
February11th to 20thNight
12%
743
20%
2220
3%
740
31%
740
16%
1452
February21st to endNight
15%
628
23%
1884
8%
628
33%
628
17%
1238
March1st to 10thNight
18%
760
21%
2280
6%
760
37%
760
18%
1469
March11th to 20thNight
16%
760
20%
2209
6%
760
32%
760
17%
1454
March21st to endNight
17%
801
22%
2001
5%
801
30%
801
19%
1372
April1st to 10thNight
19%
720
18%
1800
3%
720
28%
720
18%
1276
April11th to 20thNight
22%
711
16%
1775
3%
711
29%
711
23%
1232
April21st to endNight
20%
653
19%
1733
4%
653
31%
653
21%
1214
May1st to 10thNight
21%
540
14%
1620
5%
540
30%
540
15%
1148
May11th to 20thNight
24%
408
19%
1470
10%
408
35%
408
15%
952
May21st to endNight
41%
388
14%
1551
12%
388
48%
388
18%
975
June1st to 10thNight
36%
360
16%
1440
13%
360
48%
360
17%
910
June11th to 20thNight
40%
360
14%
1440
13%
360
49%
360
20%
893
June21st to endNight
50%
360
14%
1440
14%
360
59%
360
23%
840
July1st to 10thNight
50%
350
13%
1400
16%
350
55%
350
21%
858
July11th to 20thNight
51%
348
13%
1392
15%
348
56%
348
21%
848
July21st to endNight
50%
394
18%
1486
19%
372
55%
372
23%
871
August1st to 10thNight
50%
423
16%
1487
12%
421
56%
421
25%
900
August11th to 20thNight
48%
710
13%
1774
7%
710
50%
710
26%
1272
August21st to endNight
51%
792
18%
1980
8%
792
54%
792
31%
1332
September1st to 10thNight
41%
720
21%
1800
9%
720
46%
720
29%
1212
September11th to 20thNight
47%
720
25%
1899
15%
720
53%
720
35%
1161
September21st to endNight
41%
720
24%
1980
14%
720
49%
720
27%
1308
October1st to 10thNight
33%
720
17%
2042
10%
720
40%
720
22%
1382
October11th to 20thNight
33%
720
23%
2160
12%
720
47%
720
25%
1355
October21st to endNight
24%
792
18%
2559
8%
792
37%
792
18%
1701
November1st to 10thNight
32%
740
23%
2407
11%
740
48%
740
25%
1435
November11th to 20thNight
24%
760
25%
2470
11%
760
42%
760
21%
1513
November21st to endNight
24%
760
22%
2531
8%
760
42%
760
20%
1537
December1st to 10thNight
20%
760
18%
2660
6%
760
35%
760
14%
1728
December11th to 20thNight
19%
760
18%
3194
4%
759
35%
759
12%
1994
December21st to endNight
16%
829
13%
4820
5%
817
35%
817
9%
3126

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%7%35%5%345%5%7%39%
78597
Night
17%7%35%5%3445%7%41%
81283
TransparencyDay
43%6%12%22%14%2
78302
Night
43%6%12%22%15%2
81112
SeeingDay
24%17%30%19%8%2
14095
Night
22%15%30%24%8%1
23334

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
15%7%35%5%34445%46%
2517
11th to 20thDay
16%9%46%7%45%5%45%35%
2520
21st to endDay
21%12%47%5%34345%31%
2909
February1st to 10thDay
18%7%35%6%35%5%5%6%37%
1740
11th to 20thDay
15%7%35%5%345%5%8%41%
1848
21st to endDay
20%8%45%5%35%346%37%
1570
March1st to 10thDay
16%7%36%6%3445%6%41%
1897
11th to 20thDay
15%7%35%6%45%5%6%7%37%
1965
21st to endDay
20%8%35%5%33435%40%
2400
April1st to 10thDay
18%9%36%43446%6%37%
2160
11th to 20thDay
17%6%25%434447%42%
2134
21st to endDay
21%6%24434446%40%
2227
May1st to 10thDay
23%8%35%4345%5%7%33%
2340
11th to 20thDay
20%6%245%345%5%7%40%
2440
21st to endDay
16%6%25%4346%6%7%41%
2725
June1st to 10thDay
19%5%25%445%6%6%9%36%
2520
11th to 20thDay
16%6%35%6%346%6%9%35%
2520
21st to endDay
13%6%35%6%45%5%7%9%38%
2520
July1st to 10thDay
13%5%26%5%46%5%6%8%40%
2520
11th to 20thDay
13%5%25%5%35%6%7%9%40%
2520
21st to endDay
12%6%35%6%35%6%6%9%38%
2744
August1st to 10thDay
12%6%25%6%5%5%7%6%9%37%
2420
11th to 20thDay
12%7%26%5%35%5%7%9%38%
2126
21st to endDay
12%6%35%5%345%6%9%42%
2376
September1st to 10thDay
13%7%25%7%35%5%6%6%41%
2160
11th to 20thDay
14%5%24434447%49%
2059
21st to endDay
16%7%35%5%34447%42%
1980
October1st to 10thDay
23%5%25%5%33445%41%
1916
11th to 20thDay
14%6%25%5%3446%8%45%
1800
21st to endDay
23%5%244345%5%6%38%
1796
November1st to 10thDay
13%6%25%42345%6%50%
1671
11th to 20thDay
19%5%2443335%7%45%
1710
21st to endDay
17%5%35%43346%7%44%
1649
December1st to 10thDay
18%7%46%7%34446%37%
1520
11th to 20thDay
22%5%35%323446%43%
1906
21st to endDay
19%10%47%6%44447%31%
2772
January1st to 10thNight
17%7%2442345%6%45%
4429
11th to 20thNight
16%8%36%5%3445%6%41%
4440
21st to endNight
23%11%46%5%23345%33%
4744
February1st to 10thNight
16%9%45%5%3445%6%40%
2437
11th to 20thNight
16%8%35%5%2445%7%40%
2218
21st to endNight
19%7%35%5%2445%5%41%
1884
March1st to 10thNight
18%7%25%42445%7%42%
2270
11th to 20thNight
16%6%36%5%34447%42%
2208
21st to endNight
17%7%35%43445%6%42%
2001
April1st to 10thNight
18%7%345%45%5%5%7%38%
1800
11th to 20thNight
18%7%25%5%345%48%39%
1775
21st to endNight
21%7%36%43335%6%40%
1733
May1st to 10thNight
21%7%36%6%3445%7%32%
1620
11th to 20thNight
20%7%26%435%448%37%
1469
21st to endNight
17%7%25%5%345%5%7%41%
1550
June1st to 10thNight
18%5%25%5%345%5%6%41%
1440
11th to 20thNight
15%5%35%5%345%6%9%39%
1440
21st to endNight
12%6%25%5%245%7%9%43%
1440
July1st to 10thNight
15%5%25%5%36%46%9%41%
1440
11th to 20thNight
13%5%36%5%45%5%6%9%39%
1440
21st to endNight
11%435%5%36%6%6%9%42%
1574
August1st to 10thNight
8%6%26%6%35%5%7%8%44%
1497
11th to 20thNight
12%6%36%7%45%6%6%8%36%
1774
21st to endNight
16%5%2443446%8%44%
1980
September1st to 10thNight
15%6%35%434447%45%
1800
11th to 20thNight
14%5%25%323246%54%
1899
21st to endNight
18%6%25%425%445%45%
1980
October1st to 10thNight
21%6%25%5%23446%42%
2042
11th to 20thNight
16%6%25%42345%7%46%
2160
21st to endNight
23%7%3433335%6%40%
2559
November1st to 10thNight
13%6%25%4245%5%6%48%
2407
11th to 20thNight
19%6%3433335%6%45%
2470
21st to endNight
15%6%25%5%3445%7%46%
2531
December1st to 10thNight
19%7%35%5%34446%39%
2660
11th to 20thNight
20%7%2443445%7%40%
3288
21st to endNight
21%10%36%5%3435%5%34%
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
39%5%10%32%10%3
2518
11th to 20thDay
49%6%11%23%9%1
2520
21st to endDay
56%5%8%20%10%2
2909
February1st to 10thDay
47%5%12%21%13%1
1740
11th to 20thDay
41%5%11%22%17%3
1857
21st to endDay
49%410%22%12%3
1570
March1st to 10thDay
43%5%13%21%14%3
1900
11th to 20thDay
43%5%13%23%14%2
1965
21st to endDay
47%48%18%18%5%
2400
April1st to 10thDay
45%6%10%20%15%4
2160
11th to 20thDay
42%6%11%21%17%3
2134
21st to endDay
44%6%10%21%15%4
2227
May1st to 10thDay
51%5%9%19%15%1
2340
11th to 20thDay
43%6%12%19%16%3
2444
21st to endDay
40%9%16%20%13%2
2725
June1st to 10thDay
44%8%15%21%12%1
2520
11th to 20thDay
44%9%13%22%11%1
2520
21st to endDay
41%8%14%23%13%1
2520
July1st to 10thDay
42%8%12%21%16%2
2450
11th to 20thDay
38%8%15%24%13%2
2445
21st to endDay
41%9%13%19%16%2
2591
August1st to 10thDay
40%10%14%23%12%1
2406
11th to 20thDay
40%8%18%22%12%1
2126
21st to endDay
39%8%11%23%18%2
2376
September1st to 10thDay
41%8%11%22%17%1
2160
11th to 20thDay
35%5%10%23%24%2
2059
21st to endDay
43%6%10%21%17%3
1980
October1st to 10thDay
46%5%9%22%15%3
1916
11th to 20thDay
37%6%12%27%16%2
1800
21st to endDay
46%5%10%22%15%3
1796
November1st to 10thDay
36%5%12%25%19%3
1671
11th to 20thDay
39%412%23%19%3
1710
21st to endDay
40%414%27%12%2
1649
December1st to 10thDay
48%5%14%17%14%1
1520
11th to 20thDay
43%415%21%15%2
1906
21st to endDay
52%7%11%21%9%1
2772
January1st to 10thNight
39%5%12%30%11%4
4429
11th to 20thNight
44%5%13%24%11%3
4440
21st to endNight
54%49%20%11%2
4744
February1st to 10thNight
46%5%12%22%13%2
2437
11th to 20thNight
44%5%10%19%18%4
2220
21st to endNight
45%410%23%15%4
1884
March1st to 10thNight
40%6%13%23%15%3
2280
11th to 20thNight
43%5%11%22%16%3
2209
21st to endNight
43%5%9%19%19%5%
2001
April1st to 10thNight
45%7%10%20%15%3
1800
11th to 20thNight
43%5%12%19%19%1
1775
21st to endNight
46%5%9%22%15%4
1733
May1st to 10thNight
52%5%10%17%14%2
1620
11th to 20thNight
46%6%10%18%18%2
1470
21st to endNight
43%7%16%21%12%1
1551
June1st to 10thNight
44%7%10%22%16%2
1440
11th to 20thNight
41%8%16%25%10%1
1440
21st to endNight
35%10%15%26%14%1
1440
July1st to 10thNight
39%9%15%20%14%2
1400
11th to 20thNight
41%7%16%25%10%1
1392
21st to endNight
35%10%17%21%15%2
1486
August1st to 10thNight
35%10%16%24%14%1
1487
11th to 20thNight
43%10%15%21%10%1
1774
21st to endNight
37%8%12%22%19%1
1980
September1st to 10thNight
41%5%10%26%16%1
1800
11th to 20thNight
33%5%11%23%25%2
1899
21st to endNight
41%6%7%22%22%2
1980
October1st to 10thNight
44%6%10%23%14%3
2042
11th to 20thNight
38%6%12%29%14%1
2160
21st to endNight
46%6%12%21%15%1
2559
November1st to 10thNight
36%6%12%22%20%4
2407
11th to 20thNight
41%410%23%18%4
2470
21st to endNight
39%5%13%30%12%1
2531
December1st to 10thNight
45%6%12%22%14%1
2660
11th to 20thNight
43%6%13%19%16%3
3288
21st to endNight
49%7%12%21%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
35%21%27%14%2
180
11th to 20thDay
32%26%31%10%1
180
21st to endDay
22%32%32%9%5%
238
February1st to 10thDay
35%26%28%10%1
300
11th to 20thDay
30%29%31%10%1
456
21st to endDay
32%24%30%12%2
382
March1st to 10thDay
30%20%33%14%3
460
11th to 20thDay
28%27%31%11%21
460
21st to endDay
31%22%31%10%41
470
April1st to 10thDay
31%26%25%11%7%1
420
11th to 20thDay
27%24%27%14%6%2
412
21st to endDay
32%19%31%13%41
420
May1st to 10thDay
35%18%28%12%5%2
423
11th to 20thDay
25%17%36%17%6%1
447
21st to endDay
21%11%29%26%11%3
485
June1st to 10thDay
21%14%30%22%11%2
450
11th to 20thDay
19%14%34%22%9%2
450
21st to endDay
16%12%31%28%13%1
450
July1st to 10thDay
16%9%30%26%16%4
445
11th to 20thDay
14%6%30%32%17%2
444
21st to endDay
14%10%33%30%12%1
488
August1st to 10thDay
13%9%27%33%13%5%
446
11th to 20thDay
16%6%27%31%14%6%
439
21st to endDay
12%12%29%25%14%8%
495
September1st to 10thDay
19%11%27%20%17%5%
450
11th to 20thDay
16%10%29%26%10%9%
450
21st to endDay
20%15%31%19%11%5%
450
October1st to 10thDay
30%10%26%16%14%3
450
11th to 20thDay
18%21%30%22%8%2
450
21st to endDay
31%14%29%18%8%
403
November1st to 10thDay
20%17%28%24%9%2
365
11th to 20thDay
27%23%27%17%5%1
370
21st to endDay
26%20%29%19%5%1
309
December1st to 10thDay
31%22%30%14%31
180
11th to 20thDay
36%25%26%11%2
180
21st to endDay
27%23%29%15%42
198
January1st to 10thNight
24%19%36%18%3
760
11th to 20thNight
27%21%31%19%2
760
21st to endNight
24%22%34%18%2
836
February1st to 10thNight
25%19%35%20%2
760
11th to 20thNight
25%24%36%14%1
743
21st to endNight
29%20%32%17%3
628
March1st to 10thNight
26%21%33%18%3
760
11th to 20thNight
24%25%32%16%3
760
21st to endNight
24%21%33%17%4
801
April1st to 10thNight
27%21%31%18%3
720
11th to 20thNight
22%19%34%21%4
711
21st to endNight
26%19%33%18%5%
653
May1st to 10thNight
27%15%33%20%5%
540
11th to 20thNight
22%18%34%22%4
408
21st to endNight
23%6%25%36%10%1
389
June1st to 10thNight
19%8%29%32%11%1
360
11th to 20thNight
18%7%28%34%13%
360
21st to endNight
14%426%47%9%
360
July1st to 10thNight
15%423%39%18%1
350
11th to 20thNight
12%5%24%41%16%2
348
21st to endNight
12%5%26%40%16%1
394
August1st to 10thNight
10%327%42%17%1
423
11th to 20thNight
16%5%20%36%20%2
710
21st to endNight
17%5%19%38%19%2
792
September1st to 10thNight
17%6%30%32%13%2
720
11th to 20thNight
17%8%23%31%17%4
720
21st to endNight
21%8%25%29%15%2
720
October1st to 10thNight
24%11%27%25%13%1
720
11th to 20thNight
18%14%30%28%9%1
720
21st to endNight
27%13%34%19%7%
792
November1st to 10thNight
17%14%33%27%9%1
740
11th to 20thNight
24%17%31%21%6%1
760
21st to endNight
23%17%31%23%6%1
760
December1st to 10thNight
27%19%31%18%41
760
11th to 20thNight
26%21%29%21%3
760
21st to endNight
27%17%35%19%2
836
Page generated at 2024-03-19 23:31:04. Version ac07

Copyright © 2024 Attilla Danko.


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