Danbury
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Danbury clear sky chart from 2005-11-05 to 2017-08-12.

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%
14828
18%
46475
8%
14797
40%
14797
20%
30060

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
17%
720
20%
2506
8%
716
35%
716
17%
1559
January16th to endNight
15%
768
21%
2633
5%
768
36%
768
16%
1646
February1st to 15thNight
15%
704
17%
2210
3%
701
31%
701
15%
1467
February16th to endNight
16%
631
24%
1893
7%
631
36%
631
18%
1215
March1st to 15thNight
17%
720
17%
2160
5%
720
31%
720
16%
1444
March16th to endNight
20%
768
24%
1995
7%
768
33%
768
20%
1317
April1st to 15thNight
19%
718
17%
1796
3%
718
26%
718
21%
1262
April16th to endNight
22%
675
17%
1755
3%
675
32%
675
22%
1208
May1st to 15thNight
23%
516
17%
1596
5%
516
34%
516
16%
1096
May16th to endNight
36%
374
14%
1497
12%
374
44%
374
17%
950
June1st to 15thNight
37%
360
14%
1440
10%
360
48%
360
17%
938
June16th to endNight
48%
360
14%
1440
13%
360
58%
360
25%
816
July1st to 15thNight
45%
340
12%
1360
13%
340
50%
340
21%
837
July16th to endNight
53%
376
15%
1418
16%
354
59%
354
21%
856
August1st to 15thNight
47%
509
17%
1558
10%
507
53%
507
29%
952
August16th to endNight
56%
700
16%
1750
9%
700
59%
700
30%
1191
September1st to 15thNight
43%
660
23%
1656
11%
660
49%
660
31%
1089
September16th to endNight
48%
657
25%
1815
17%
657
54%
657
31%
1140
October1st to 15thNight
33%
660
21%
1908
13%
660
43%
660
24%
1231
October16th to endNight
25%
704
18%
2225
6%
704
40%
704
20%
1444
November1st to 15thNight
29%
700
21%
2277
9%
700
44%
700
22%
1428
November16th to endNight
25%
720
20%
2379
9%
720
38%
720
18%
1526
December1st to 15thNight
22%
720
16%
2520
6%
720
35%
720
14%
1672
December16th to endNight
14%
768
18%
2688
4%
768
33%
768
14%
1776

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%6%25%5%3445%7%39%
47507
Night
16%6%2442445%6%41%
46645
Cloud CoverDay
16%6%25%42445%7%39%
47517
Night
17%6%2442445%6%42%
46650
TransparencyDay
43%6%12%21%14%1
47195
Night
42%5%12%22%15%2
46475
SeeingDay
21%14%29%21%10%3
5654
Night
21%14%30%24%8%
14829

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%246%35%446%40%
1432
16th to endDay
14%7%25%42445%7%40%
1590
February1st to 15thDay
16%7%25%5%25%45%7%37%
1648
16th to endDay
16%6%345%35%45%7%39%
1580
March1st to 15thDay
17%7%35%5%3445%6%36%
1790
16th to endDay
18%7%34434336%40%
2226
April1st to 15thDay
19%7%25%32435%5%39%
2152
16th to endDay
17%6%23433347%44%
2205
May1st to 15thDay
22%7%24434446%34%
2366
16th to endDay
17%6%25%5%245%5%6%37%
2618
June1st to 15thDay
22%5%344345%5%8%32%
2520
16th to endDay
13%5%246%35%5%6%9%36%
2520
July1st to 15thDay
13%425%5%45%5%6%8%38%
2520
16th to endDay
12%5%25%6%35%6%6%8%38%
2654
August1st to 15thDay
13%5%24445%6%6%8%38%
2292
16th to endDay
11%5%26%5%3445%8%40%
2100
September1st to 15thDay
13%5%146%35%46%6%42%
1973
16th to endDay
13%5%24424436%46%
1815
October1st to 15thDay
19%5%25%433335%43%
1721
16th to endDay
18%4145%3445%6%41%
1647
November1st to 15thDay
18%5%24323346%45%
1581
16th to endDay
18%5%2442335%7%43%
1581
December1st to 15thDay
16%6%35%5%24446%39%
1440
16th to endDay
19%8%3442445%6%35%
1536
January1st to 15thNight
17%6%2442335%6%43%
2506
16th to endNight
15%7%34423347%42%
2633
February1st to 15thNight
14%8%345%3445%6%38%
2209
16th to endNight
16%6%24414345%43%
1893
March1st to 15thNight
19%6%15%42445%6%40%
2147
16th to endNight
16%6%25%323346%44%
1995
April1st to 15thNight
17%7%345%34446%38%
1796
16th to endNight
18%6%25%423346%42%
1755
May1st to 15thNight
19%7%25%5%2435%7%35%
1596
16th to endNight
19%6%243245%5%7%38%
1495
June1st to 15thNight
20%5%2442445%7%38%
1440
16th to endNight
11%5%15%42346%9%45%
1440
July1st to 15thNight
13%425%435%46%8%40%
1440
16th to endNight
10%425%5%36%6%6%8%39%
1514
August1st to 15thNight
10%5%144245%6%7%46%
1568
16th to endNight
13%3245%35%46%7%43%
1750
September1st to 15thNight
14%424334346%48%
1656
16th to endNight
14%5%2432333451%
1815
October1st to 15thNight
17%6%24422346%45%
1908
16th to endNight
19%5%24333345%42%
2225
November1st to 15thNight
16%6%24423445%44%
2277
16th to endNight
18%6%25%43345%5%40%
2379
December1st to 15thNight
20%7%24434446%37%
2520
16th to endNight
20%7%2442445%6%37%
2688

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%7%25%5%35%446%40%
1432
16th to endDay
14%6%35%4245%48%40%
1590
February1st to 15thDay
16%6%26%5%26%446%39%
1648
16th to endDay
17%6%24435%447%39%
1580
March1st to 15thDay
18%7%25%5%35%35%6%36%
1800
16th to endDay
18%7%24434345%41%
2226
April1st to 15thDay
19%7%25%324446%39%
2152
16th to endDay
17%5%14334346%44%
2205
May1st to 15thDay
22%7%24425%446%34%
2366
16th to endDay
18%6%25%4245%6%6%37%
2618
June1st to 15thDay
23%5%25%4245%5%7%33%
2520
16th to endDay
13%5%25%5%445%6%9%36%
2520
July1st to 15thDay
14%425%5%35%5%5%8%37%
2520
16th to endDay
12%5%25%6%35%5%7%8%37%
2654
August1st to 15thDay
13%5%25%435%6%6%8%38%
2292
16th to endDay
12%5%36%6%34448%40%
2100
September1st to 15thDay
13%415%5%3445%6%42%
1973
16th to endDay
14%425%5%24346%45%
1815
October1st to 15thDay
19%5%25%423335%43%
1721
16th to endDay
18%4245%2445%5%41%
1647
November1st to 15thDay
18%6%33323346%44%
1581
16th to endDay
18%5%2441335%7%43%
1581
December1st to 15thDay
16%6%35%4235%46%38%
1440
16th to endDay
19%9%34325%45%6%35%
1536
January1st to 15thNight
17%6%2432335%6%43%
2506
16th to endNight
15%8%34423346%42%
2633
February1st to 15thNight
14%8%35%5%3435%6%39%
2202
16th to endNight
16%6%34423346%43%
1893
March1st to 15thNight
19%6%25%42445%6%39%
2160
16th to endNight
16%6%34313336%45%
1994
April1st to 15thNight
18%6%25%335%45%6%38%
1796
16th to endNight
19%6%25%423345%42%
1755
May1st to 15thNight
19%7%35%5%2445%7%34%
1596
16th to endNight
19%7%24324348%38%
1495
June1st to 15thNight
20%5%2442435%6%39%
1440
16th to endNight
11%5%344235%5%9%45%
1440
July1st to 15thNight
13%5%25%5%25%5%5%9%39%
1440
16th to endNight
10%425%5%35%6%7%8%39%
1514
August1st to 15thNight
11%416%4245%5%7%47%
1568
16th to endNight
14%324435%5%5%8%43%
1750
September1st to 15thNight
15%414424347%46%
1656
16th to endNight
15%424323435%50%
1815
October1st to 15thNight
17%6%245%23345%45%
1908
16th to endNight
18%6%14334446%42%
2225
November1st to 15thNight
16%6%25%313445%45%
2277
16th to endNight
18%6%24424445%41%
2379
December1st to 15thNight
20%7%2342445%6%37%
2520
16th to endNight
20%7%2442345%6%37%
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
43%5%12%22%12%3
1433
16th to endDay
42%413%24%13%2
1590
February1st to 15thDay
46%5%11%20%13%1
1651
16th to endDay
44%411%24%13%1
1580
March1st to 15thDay
47%414%21%10%2
1800
16th to endDay
45%310%18%18%3
2226
April1st to 15thDay
45%5%10%20%15%3
2152
16th to endDay
40%5%9%22%19%3
2205
May1st to 15thDay
49%5%10%18%14%1
2366
16th to endDay
44%8%13%19%12%1
2622
June1st to 15thDay
48%7%13%19%9%1
2520
16th to endDay
41%8%13%22%11%
2520
July1st to 15thDay
44%7%11%21%15%1
2371
16th to endDay
40%8%14%21%12%2
2487
August1st to 15thDay
39%8%15%20%14%
2278
16th to endDay
41%7%9%23%17%1
2100
September1st to 15thDay
40%7%11%19%19%
1973
16th to endDay
39%5%8%22%22%2
1815
October1st to 15thDay
44%410%22%15%2
1721
16th to endDay
42%5%11%24%14%1
1647
November1st to 15thDay
40%5%13%20%17%3
1581
16th to endDay
41%312%26%14%2
1581
December1st to 15thDay
45%5%15%19%12%1
1440
16th to endDay
49%414%19%10%
1536
January1st to 15thNight
42%413%23%12%3
2506
16th to endNight
42%311%23%15%2
2633
February1st to 15thNight
45%5%12%20%13%2
2210
16th to endNight
41%410%23%17%2
1893
March1st to 15thNight
44%5%13%20%12%3
2160
16th to endNight
41%410%21%18%4
1995
April1st to 15thNight
44%5%11%20%15%1
1796
16th to endNight
44%48%20%18%2
1755
May1st to 15thNight
48%5%10%18%14%2
1596
16th to endNight
44%7%16%18%12%1
1497
June1st to 15thNight
46%6%12%20%12%1
1440
16th to endNight
35%6%16%26%14%1
1440
July1st to 15thNight
40%7%13%22%13%1
1360
16th to endNight
38%8%16%22%12%2
1418
August1st to 15thNight
34%8%14%25%15%1
1558
16th to endNight
37%8%11%23%17%
1750
September1st to 15thNight
37%5%11%26%17%
1656
16th to endNight
37%46%22%26%1
1815
October1st to 15thNight
41%411%22%16%2
1908
16th to endNight
43%5%14%22%14%
2225
November1st to 15thNight
40%5%11%20%17%3
2277
16th to endNight
44%412%24%11%2
2379
December1st to 15thNight
46%6%13%19%13%
2520
16th to endNight
46%5%12%20%12%
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
23%31%30%10%5%
60
16th to endDay
23%23%41%12%
73
February1st to 15thDay
26%30%27%14%1
164
16th to endDay
20%25%35%15%3
239
March1st to 15thDay
25%19%33%15%5%
270
16th to endDay
24%22%33%12%41
288
April1st to 15thDay
27%20%27%15%8%1
270
16th to endDay
24%13%34%16%8%2
270
May1st to 15thDay
36%13%25%15%6%2
288
16th to endDay
21%9%30%25%11%2
331
June1st to 15thDay
24%12%27%21%13%1
315
16th to endDay
15%9%34%26%12%2
315
July1st to 15thDay
16%7%31%29%12%2
305
16th to endDay
13%5%27%30%20%2
326
August1st to 15thDay
14%427%30%15%6%
297
16th to endDay
11%5%21%28%20%13%
268
September1st to 15thDay
14%8%27%23%17%9%
255
16th to endDay
16%9%26%20%13%13%
254
October1st to 15thDay
25%8%25%21%14%4
255
16th to endDay
20%19%29%21%8%
251
November1st to 15thDay
22%14%27%22%10%2
235
16th to endDay
21%23%25%19%6%1
201
December1st to 15thDay
23%28%31%11%5%
60
16th to endDay
35%21%31%9%1
64
January1st to 15thNight
23%20%33%19%3
720
16th to endNight
23%20%34%18%1
768
February1st to 15thNight
22%18%37%19%1
704
16th to endNight
23%22%33%17%2
631
March1st to 15thNight
25%22%32%17%2
720
16th to endNight
22%22%30%18%5%
768
April1st to 15thNight
23%19%35%17%3
718
16th to endNight
22%16%34%19%5%
675
May1st to 15thNight
23%16%33%20%6%
516
16th to endNight
23%6%27%33%7%
375
June1st to 15thNight
21%7%27%30%12%
360
16th to endNight
13%328%44%10%
360
July1st to 15thNight
14%328%37%15%
340
16th to endNight
10%425%38%19%2
376
August1st to 15thNight
14%227%37%16%1
509
16th to endNight
16%217%36%23%3
700
September1st to 15thNight
16%6%28%31%15%1
660
16th to endNight
17%6%23%28%20%3
657
October1st to 15thNight
20%10%29%26%11%1
660
16th to endNight
23%15%33%21%5%
704
November1st to 15thNight
21%15%29%24%8%1
700
16th to endNight
24%15%29%21%8%
720
December1st to 15thNight
26%18%29%20%4
720
16th to endNight
27%19%34%15%2
768
Page generated at 2017-08-13 14:16:30. Version ac04

Copyright 2017 A. Danko


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