Deerfield Academy Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerfield Academy Planetarium clear sky chart from 2005-11-05 to 2017-09-21.

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
32%
14894
18%
46879
9%
14862
42%
14862
21%
30685

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
23%
720
19%
2506
8%
716
38%
716
17%
1625
January16th to endNight
22%
768
17%
2688
7%
768
36%
768
16%
1761
February1st to 15thNight
19%
704
15%
2201
4%
701
32%
701
16%
1510
February16th to endNight
21%
631
20%
1893
8%
631
36%
631
18%
1270
March1st to 15thNight
20%
720
18%
2160
6%
720
34%
720
17%
1470
March16th to endNight
24%
768
22%
2007
7%
768
36%
768
23%
1350
April1st to 15thNight
24%
718
17%
1796
4%
718
31%
718
21%
1283
April16th to endNight
26%
630
18%
1710
5%
630
34%
630
22%
1166
May1st to 15thNight
25%
520
16%
1600
8%
520
33%
520
18%
1092
May16th to endNight
38%
375
13%
1497
12%
374
44%
374
17%
981
June1st to 15thNight
39%
360
13%
1440
11%
360
48%
360
16%
942
June16th to endNight
46%
360
11%
1440
14%
360
53%
360
22%
857
July1st to 15thNight
54%
340
13%
1360
16%
340
59%
340
23%
810
July16th to endNight
58%
376
16%
1418
18%
354
63%
354
26%
806
August1st to 15thNight
51%
467
17%
1538
12%
465
56%
465
28%
914
August16th to endNight
56%
764
20%
1910
11%
764
58%
764
34%
1257
September1st to 15thNight
48%
720
21%
1827
10%
720
52%
720
33%
1185
September16th to endNight
51%
681
26%
1880
18%
681
57%
681
34%
1149
October1st to 15thNight
39%
660
21%
1884
13%
660
48%
660
25%
1238
October16th to endNight
28%
704
14%
2260
7%
704
37%
704
20%
1494
November1st to 15thNight
33%
700
21%
2277
12%
700
46%
700
22%
1448
November16th to endNight
31%
720
18%
2379
10%
720
42%
720
18%
1577
December1st to 15thNight
24%
720
15%
2520
6%
720
36%
720
17%
1678
December16th to endNight
20%
768
17%
2688
5%
768
34%
768
14%
1822

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%38%
47994
Night
16%6%25%42445%6%41%
47049
Cloud CoverDay
16%6%25%5%3445%7%38%
48004
Night
16%6%25%42445%6%41%
47054
TransparencyDay
44%5%12%21%13%1
47682
Night
43%5%12%22%13%1
46879
SeeingDay
21%11%27%22%11%4
5811
Night
21%11%29%28%9%
14894

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%7%36%3345%7%6%36%
1432
16th to endDay
13%7%345%3346%7%39%
1536
February1st to 15thDay
13%8%46%6%36%6%5%7%30%
1657
16th to endDay
16%7%36%5%35%35%6%38%
1580
March1st to 15thDay
18%6%36%5%3435%6%34%
1790
16th to endDay
16%6%36%424345%43%
2212
April1st to 15thDay
17%6%36%6%2435%5%37%
2152
16th to endDay
15%5%25%4345%6%6%41%
2250
May1st to 15thDay
23%6%25%5%34445%32%
2361
16th to endDay
18%5%25%4345%5%7%37%
2618
June1st to 15thDay
22%5%2442446%7%33%
2520
16th to endDay
14%5%25%5%35%6%5%9%35%
2520
July1st to 15thDay
11%426%6%36%6%6%8%36%
2520
16th to endDay
12%5%35%5%346%6%7%38%
2654
August1st to 15thDay
11%6%25%6%35%5%6%8%38%
2398
16th to endDay
11%5%245%35%5%6%7%43%
2292
September1st to 15thDay
14%4245%2345%7%43%
2133
16th to endDay
15%423322346%50%
1873
October1st to 15thDay
20%6%145%34445%39%
1746
16th to endDay
17%6%25%5%43446%38%
1612
November1st to 15thDay
15%7%24424337%42%
1581
16th to endDay
18%6%24414346%42%
1581
December1st to 15thDay
18%6%35%5%35%45%5%36%
1440
16th to endDay
19%9%35%5%24447%33%
1536
January1st to 15thNight
16%7%35%42445%6%39%
2506
16th to endNight
13%8%35%5%35%5%5%6%37%
2688
February1st to 15thNight
11%8%36%6%35%5%5%6%36%
2200
16th to endNight
14%8%36%434445%40%
1893
March1st to 15thNight
17%7%15%435%446%38%
2147
16th to endNight
14%6%2442445%5%44%
2007
April1st to 15thNight
17%7%25%6%34445%39%
1796
16th to endNight
21%6%14323445%42%
1710
May1st to 15thNight
20%6%35%42445%6%35%
1600
16th to endNight
18%415%335%45%8%37%
1495
June1st to 15thNight
22%434414446%37%
1440
16th to endNight
15%42442446%6%43%
1440
July1st to 15thNight
11%5%24435%5%5%7%44%
1440
16th to endNight
11%314435%46%9%45%
1514
August1st to 15thNight
9%426%5%33448%47%
1548
16th to endNight
13%31343445%7%46%
1910
September1st to 15thNight
14%414323446%48%
1827
16th to endNight
14%414213447%51%
1880
October1st to 15thNight
20%5%24422246%44%
1884
16th to endNight
19%6%15%43445%5%39%
2260
November1st to 15thNight
15%6%24433345%45%
2277
16th to endNight
18%6%245%3435%440%
2379
December1st to 15thNight
19%7%245%2435%5%37%
2520
16th to endNight
20%7%25%5%2445%6%35%
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%35%3345%7%6%35%
1432
16th to endDay
13%8%345%2445%6%40%
1536
February1st to 15thDay
14%8%45%6%45%6%5%7%31%
1657
16th to endDay
16%7%37%5%3335%5%37%
1580
March1st to 15thDay
19%8%35%43435%6%34%
1800
16th to endDay
16%6%35%424345%42%
2212
April1st to 15thDay
18%6%37%6%23345%38%
2152
16th to endDay
15%5%25%42445%6%41%
2250
May1st to 15thDay
23%6%26%5%34446%32%
2361
16th to endDay
17%5%25%425%5%5%8%37%
2618
June1st to 15thDay
22%5%25%4245%6%8%32%
2520
16th to endDay
14%5%25%5%36%6%5%9%35%
2520
July1st to 15thDay
11%426%5%46%5%7%8%35%
2520
16th to endDay
11%5%25%6%346%6%7%38%
2654
August1st to 15thDay
11%5%247%35%5%5%8%37%
2398
16th to endDay
11%5%145%245%6%8%43%
2292
September1st to 15thDay
14%5%25%5%3345%7%43%
2133
16th to endDay
15%424323435%50%
1873
October1st to 15thDay
20%6%245%33445%39%
1746
16th to endDay
17%6%35%6%34446%38%
1612
November1st to 15thDay
16%7%24323446%42%
1581
16th to endDay
19%7%23423346%42%
1581
December1st to 15thDay
18%6%36%5%34445%37%
1440
16th to endDay
19%9%345%24447%33%
1536
January1st to 15thNight
16%7%35%424446%39%
2506
16th to endNight
13%8%35%5%3445%6%38%
2688
February1st to 15thNight
12%8%37%5%35%5%5%6%36%
2193
16th to endNight
14%7%36%5%24446%40%
1893
March1st to 15thNight
17%7%26%42445%6%37%
2160
16th to endNight
14%6%35%4245%45%43%
2006
April1st to 15thNight
17%7%26%6%34436%38%
1796
16th to endNight
20%6%15%324345%42%
1710
May1st to 15thNight
20%6%35%5%3435%6%35%
1600
16th to endNight
18%6%145%25%5%5%9%36%
1495
June1st to 15thNight
22%5%35%433446%37%
1440
16th to endNight
15%42443446%7%43%
1440
July1st to 15thNight
11%5%15%345%46%8%43%
1440
16th to endNight
10%4244245%5%9%44%
1514
August1st to 15thNight
9%5%26%5%2345%7%47%
1548
16th to endNight
13%41443445%8%45%
1910
September1st to 15thNight
15%423334346%47%
1827
16th to endNight
13%414423347%50%
1880
October1st to 15thNight
20%5%24422245%44%
1884
16th to endNight
19%6%245%3345%5%39%
2260
November1st to 15thNight
16%6%24423346%45%
2277
16th to endNight
18%6%34425%445%39%
2379
December1st to 15thNight
20%6%25%5%2345%5%38%
2520
16th to endNight
20%7%3442446%6%34%
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
45%5%13%23%10%1
1433
16th to endDay
43%415%23%12%1
1536
February1st to 15thDay
51%5%12%17%11%
1660
16th to endDay
48%311%20%14%1
1580
March1st to 15thDay
50%313%19%10%2
1800
16th to endDay
44%310%19%16%5%
2212
April1st to 15thDay
48%410%19%13%2
2152
16th to endDay
41%5%10%21%18%3
2250
May1st to 15thDay
53%48%19%12%1
2361
16th to endDay
44%7%13%19%13%1
2622
June1st to 15thDay
48%6%14%19%9%
2520
16th to endDay
43%8%14%20%12%
2520
July1st to 15thDay
43%6%12%22%13%1
2371
16th to endDay
40%6%16%21%13%1
2487
August1st to 15thDay
42%6%13%24%11%1
2384
16th to endDay
36%6%12%27%15%1
2292
September1st to 15thDay
39%5%13%22%17%1
2133
16th to endDay
36%37%26%23%1
1873
October1st to 15thDay
46%310%23%12%2
1746
16th to endDay
46%5%14%18%12%2
1612
November1st to 15thDay
42%5%15%22%13%1
1581
16th to endDay
43%412%22%14%1
1581
December1st to 15thDay
49%416%17%12%
1440
16th to endDay
51%6%14%18%9%
1536
January1st to 15thNight
46%413%20%13%2
2506
16th to endNight
46%412%20%13%2
2688
February1st to 15thNight
47%5%14%20%10%1
2201
16th to endNight
46%312%22%12%2
1893
March1st to 15thNight
47%311%22%12%2
2160
16th to endNight
41%411%19%17%5%
2007
April1st to 15thNight
48%310%19%16%1
1796
16th to endNight
45%48%20%16%4
1710
May1st to 15thNight
49%410%18%14%2
1600
16th to endNight
45%7%13%20%10%1
1497
June1st to 15thNight
48%5%13%22%9%
1440
16th to endNight
39%6%15%24%14%
1440
July1st to 15thNight
36%8%14%27%12%
1360
16th to endNight
35%6%16%27%12%1
1418
August1st to 15thNight
36%6%15%24%16%1
1538
16th to endNight
35%6%11%29%16%
1910
September1st to 15thNight
37%5%12%25%19%1
1827
16th to endNight
34%48%27%23%1
1880
October1st to 15thNight
42%412%22%15%3
1884
16th to endNight
46%415%21%11%
2260
November1st to 15thNight
41%6%11%21%16%2
2277
16th to endNight
46%412%20%12%1
2379
December1st to 15thNight
47%5%15%20%10%
2520
16th to endNight
49%5%13%20%10%
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
21%23%25%30%
60
16th to endDay
29%18%29%21%
64
February1st to 15thDay
25%20%32%18%3
175
16th to endDay
22%19%31%22%3
239
March1st to 15thDay
30%15%30%18%4
270
16th to endDay
25%19%30%14%6%3
288
April1st to 15thDay
27%15%30%16%9%1
270
16th to endDay
20%15%27%25%7%4
270
May1st to 15thDay
32%14%24%16%8%2
288
16th to endDay
20%10%33%20%12%2
331
June1st to 15thDay
22%13%27%21%11%2
315
16th to endDay
17%14%29%20%13%4
315
July1st to 15thDay
17%6%28%25%18%3
305
16th to endDay
13%6%27%29%18%4
326
August1st to 15thDay
11%5%27%29%19%6%
313
16th to endDay
13%6%22%26%19%10%
332
September1st to 15thDay
18%6%25%23%17%8%
315
16th to endDay
18%5%20%22%15%17%
275
October1st to 15thDay
21%8%21%24%17%7%
255
16th to endDay
22%13%26%26%10%
245
November1st to 15thDay
24%7%27%25%10%4
235
16th to endDay
28%8%28%23%9%1
201
December1st to 15thDay
23%20%31%16%8%
60
16th to endDay
35%18%34%10%
64
January1st to 15thNight
22%14%33%26%3
720
16th to endNight
22%14%34%26%2
768
February1st to 15thNight
19%15%39%23%1
704
16th to endNight
22%17%32%22%3
631
March1st to 15thNight
26%16%32%21%2
720
16th to endNight
21%15%32%23%6%
768
April1st to 15thNight
22%15%33%24%4
718
16th to endNight
25%14%30%20%8%
630
May1st to 15thNight
22%13%33%24%5%
520
16th to endNight
19%6%29%32%11%
375
June1st to 15thNight
23%6%23%35%10%
360
16th to endNight
15%428%41%9%
360
July1st to 15thNight
14%323%42%16%
340
16th to endNight
10%321%43%19%
376
August1st to 15thNight
13%222%45%15%1
467
16th to endNight
15%318%35%24%3
764
September1st to 15thNight
17%424%32%19%1
720
16th to endNight
16%422%30%22%3
681
October1st to 15thNight
21%10%22%31%12%1
660
16th to endNight
24%10%31%26%7%
704
November1st to 15thNight
20%12%29%27%9%1
700
16th to endNight
22%11%28%27%8%
720
December1st to 15thNight
25%11%33%23%5%
720
16th to endNight
27%15%32%22%2
768
Page generated at 2017-09-22 07:35:33. Version ac04

Copyright 2017 A. Danko


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