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Astronomical Society of Northern New England
.

Starfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starfield Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
29%
14784
18%
46738
8%
14752
40%
14752
21%
30391

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
19%
720
20%
2506
6%
716
36%
716
16%
1591
January16th to endNight
16%
768
19%
2688
5%
768
34%
768
16%
1708
February1st to 15thNight
14%
704
16%
2229
4%
701
29%
701
15%
1510
February16th to endNight
21%
631
21%
1893
7%
631
39%
631
18%
1259
March1st to 15thNight
18%
720
17%
2138
7%
720
31%
720
18%
1475
March16th to endNight
23%
768
22%
2058
7%
768
36%
768
24%
1360
April1st to 15thNight
23%
718
18%
1796
5%
718
31%
718
23%
1258
April16th to endNight
26%
557
18%
1637
6%
557
34%
557
21%
1105
May1st to 15thNight
28%
540
15%
1620
7%
540
36%
540
20%
1102
May16th to endNight
30%
415
10%
1537
9%
414
36%
414
13%
1084
June1st to 15thNight
32%
360
11%
1440
9%
360
41%
360
14%
999
June16th to endNight
44%
360
10%
1440
12%
360
49%
360
21%
883
July1st to 15thNight
51%
340
12%
1360
17%
340
55%
340
22%
825
July16th to endNight
55%
376
15%
1418
17%
354
60%
354
24%
836
August1st to 15thNight
50%
509
16%
1580
12%
507
53%
507
27%
992
August16th to endNight
50%
669
22%
1815
13%
669
54%
669
32%
1145
September1st to 15thNight
45%
700
20%
1822
10%
700
50%
700
34%
1153
September16th to endNight
46%
657
28%
1815
16%
657
56%
657
37%
1048
October1st to 15thNight
33%
660
22%
1851
10%
660
44%
660
25%
1221
October16th to endNight
24%
704
18%
2288
7%
704
38%
704
20%
1476
November1st to 15thNight
29%
700
22%
2277
10%
700
45%
700
22%
1424
November16th to endNight
27%
720
20%
2340
10%
720
41%
720
19%
1496
December1st to 15thNight
17%
720
18%
2502
5%
720
33%
720
17%
1634
December16th to endNight
16%
768
18%
2688
5%
768
32%
768
15%
1807

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%25%42445%6%39%
47892
Night
17%6%24424446%40%
46908
Cloud CoverDay
17%6%2442445%6%39%
47902
Night
17%6%25%424446%40%
46913
TransparencyDay
44%412%22%14%2
47580
Night
44%411%23%14%2
46738
SeeingDay
22%13%30%20%8%3
5858
Night
21%12%31%25%8%
14784

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
16%7%2442435%6%41%
1432
16th to endDay
15%7%25%325%446%41%
1536
February1st to 15thDay
16%7%36%43346%6%36%
1627
16th to endDay
13%10%35%6%2445%5%38%
1580
March1st to 15thDay
19%9%35%433346%35%
1811
16th to endDay
15%8%36%323245%42%
2164
April1st to 15thDay
17%7%24424346%39%
2152
16th to endDay
19%5%25%424346%40%
2322
May1st to 15thDay
25%7%35%5%24446%30%
2332
16th to endDay
20%5%25%42445%7%35%
2587
June1st to 15thDay
25%7%25%434446%31%
2520
16th to endDay
18%5%25%5%25%5%5%7%35%
2520
July1st to 15thDay
13%5%25%5%35%6%6%9%36%
2520
16th to endDay
13%5%25%5%35%6%7%7%36%
2654
August1st to 15thDay
13%5%246%345%6%9%37%
2355
16th to endDay
11%414425%5%6%8%44%
2384
September1st to 15thDay
14%414424447%46%
2026
16th to endDay
14%413322245%54%
1815
October1st to 15thDay
19%7%25%42434441%
1779
16th to endDay
18%6%2433435%5%41%
1584
November1st to 15thDay
20%6%23323347%43%
1581
16th to endDay
21%6%14313335%43%
1620
December1st to 15thDay
20%6%345%2344439%
1455
16th to endDay
23%10%3442224436%
1536
January1st to 15thNight
15%8%25%43445%6%40%
2506
16th to endNight
15%8%36%5%24445%40%
2688
February1st to 15thNight
13%9%46%5%35%5%46%35%
2228
16th to endNight
15%9%345%34335%40%
1893
March1st to 15thNight
19%8%245%24445%37%
2125
16th to endNight
16%6%24423345%45%
2058
April1st to 15thNight
18%7%344245%46%38%
1796
16th to endNight
21%7%24423345%39%
1637
May1st to 15thNight
20%6%35%43445%7%34%
1620
16th to endNight
21%7%26%6%36%447%30%
1535
June1st to 15thNight
25%7%25%425%35%6%31%
1440
16th to endNight
18%6%245%2345%7%40%
1440
July1st to 15thNight
14%425%6%26%45%8%38%
1440
16th to endNight
12%414435%5%9%9%39%
1514
August1st to 15thNight
13%4245%345%5%9%41%
1590
16th to endNight
13%42433345%7%45%
1815
September1st to 15thNight
14%414423346%49%
1822
16th to endNight
15%312222237%55%
1815
October1st to 15thNight
18%5%25%424345%42%
1851
16th to endNight
20%6%14423445%40%
2288
November1st to 15thNight
17%5%24424445%44%
2277
16th to endNight
18%6%24424346%41%
2340
December1st to 15thNight
21%8%35%323345%38%
2502
16th to endNight
21%8%25%423445%36%
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
16%7%2342445%6%42%
1432
16th to endDay
15%7%25%315%45%6%41%
1536
February1st to 15thDay
17%6%36%42445%7%36%
1627
16th to endDay
14%10%35%5%2445%5%38%
1580
March1st to 15thDay
21%8%25%424445%34%
1821
16th to endDay
16%8%25%324346%42%
2164
April1st to 15thDay
18%7%24433446%40%
2152
16th to endDay
19%6%24434446%41%
2322
May1st to 15thDay
24%7%25%5%34445%31%
2332
16th to endDay
20%5%25%42445%7%35%
2587
June1st to 15thDay
26%5%245%2445%6%31%
2520
16th to endDay
18%6%25%5%345%5%8%35%
2520
July1st to 15thDay
13%424435%6%7%8%37%
2520
16th to endDay
12%425%5%35%6%7%8%37%
2654
August1st to 15thDay
13%5%245%35%5%6%9%39%
2355
16th to endDay
11%4143345%5%9%45%
2384
September1st to 15thDay
14%424423446%47%
2026
16th to endDay
14%412313236%54%
1815
October1st to 15thDay
20%5%25%43334441%
1779
16th to endDay
18%5%2433445%6%41%
1584
November1st to 15thDay
21%5%23323346%44%
1581
16th to endDay
20%6%14323345%43%
1620
December1st to 15thDay
21%6%25%42433440%
1455
16th to endDay
24%9%34324246%35%
1536
January1st to 15thNight
15%8%3442445%6%40%
2506
16th to endNight
15%9%35%5%23445%40%
2688
February1st to 15thNight
13%9%46%5%35%45%5%36%
2221
16th to endNight
16%9%25%5%25%436%40%
1893
March1st to 15thNight
20%8%25%424445%36%
2138
16th to endNight
17%6%24423345%44%
2057
April1st to 15thNight
18%7%34424447%38%
1796
16th to endNight
21%6%25%423345%39%
1637
May1st to 15thNight
20%5%25%43445%7%34%
1620
16th to endNight
21%7%27%5%35%5%46%30%
1535
June1st to 15thNight
25%6%25%5%245%46%31%
1440
16th to endNight
18%6%3442345%7%40%
1440
July1st to 15thNight
14%425%5%35%46%8%38%
1440
16th to endNight
13%414435%5%8%9%38%
1514
August1st to 15thNight
13%5%245%345%6%8%41%
1590
16th to endNight
14%41442445%8%45%
1815
September1st to 15thNight
14%324423447%49%
1822
16th to endNight
14%413212336%55%
1815
October1st to 15thNight
17%5%25%424346%42%
1851
16th to endNight
20%5%25%423445%41%
2288
November1st to 15thNight
17%5%24423445%44%
2277
16th to endNight
19%5%24423346%42%
2340
December1st to 15thNight
21%7%35%423336%38%
2502
16th to endNight
21%7%35%43344437%
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
41%49%25%14%2
1433
16th to endDay
42%312%25%13%1
1536
February1st to 15thDay
46%313%22%12%1
1630
16th to endDay
47%211%21%13%3
1580
March1st to 15thDay
51%312%16%13%3
1821
16th to endDay
44%27%21%17%6%
2164
April1st to 15thDay
45%39%20%16%3
2152
16th to endDay
44%49%21%16%3
2322
May1st to 15thDay
53%38%16%15%2
2332
16th to endDay
46%6%13%19%11%2
2591
June1st to 15thDay
52%412%20%9%1
2520
16th to endDay
45%5%12%21%12%
2520
July1st to 15thDay
39%7%16%23%13%
2371
16th to endDay
41%5%15%22%12%1
2487
August1st to 15thDay
41%5%18%23%10%
2341
16th to endDay
35%415%27%15%1
2384
September1st to 15thDay
36%5%11%27%18%
2026
16th to endDay
32%39%27%24%2
1815
October1st to 15thDay
44%48%25%14%2
1779
16th to endDay
43%311%26%13%1
1584
November1st to 15thDay
40%413%25%14%1
1581
16th to endDay
44%313%19%17%1
1620
December1st to 15thDay
47%313%20%14%
1455
16th to endDay
52%310%20%11%1
1536
January1st to 15thNight
43%5%11%23%13%2
2506
16th to endNight
46%310%21%15%2
2688
February1st to 15thNight
48%411%19%13%1
2229
16th to endNight
46%310%22%13%3
1893
March1st to 15thNight
49%39%20%13%2
2138
16th to endNight
42%310%18%20%6%
2058
April1st to 15thNight
45%48%20%18%3
1796
16th to endNight
47%39%20%14%4
1637
May1st to 15thNight
47%5%10%19%14%3
1620
16th to endNight
54%5%11%16%9%1
1537
June1st to 15thNight
53%5%10%20%9%1
1440
16th to endNight
42%5%13%22%13%1
1440
July1st to 15thNight
40%6%15%25%11%
1360
16th to endNight
37%6%16%27%10%
1418
August1st to 15thNight
38%6%14%24%14%1
1580
16th to endNight
36%5%11%28%17%
1815
September1st to 15thNight
35%411%29%17%
1822
16th to endNight
30%37%32%23%2
1815
October1st to 15thNight
43%310%24%14%3
1851
16th to endNight
44%310%27%12%1
2288
November1st to 15thNight
41%411%23%16%2
2277
16th to endNight
44%312%23%14%2
2340
December1st to 15thNight
48%312%23%12%
2502
16th to endNight
50%311%21%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
21%28%28%20%1
60
16th to endDay
23%20%43%12%
64
February1st to 15thDay
24%15%38%17%3
221
16th to endDay
19%22%30%21%6%
239
March1st to 15thDay
28%20%32%13%4
270
16th to endDay
22%22%31%14%5%3
288
April1st to 15thDay
28%15%30%15%8%1
270
16th to endDay
23%17%32%15%8%2
270
May1st to 15thDay
35%13%25%16%5%3
288
16th to endDay
24%14%32%19%6%1
331
June1st to 15thDay
24%15%33%18%6%
315
16th to endDay
21%12%38%16%7%2
315
July1st to 15thDay
16%7%33%29%9%3
305
16th to endDay
15%6%32%30%11%3
326
August1st to 15thDay
17%9%27%23%17%3
313
16th to endDay
16%6%26%27%14%8%
332
September1st to 15thDay
17%11%22%27%12%7%
294
16th to endDay
16%7%31%21%9%13%
254
October1st to 15thDay
23%12%19%25%16%3
249
16th to endDay
23%13%34%20%7%
240
November1st to 15thDay
25%12%28%22%8%1
235
16th to endDay
27%17%23%23%7%1
240
December1st to 15thDay
21%22%37%14%4
75
16th to endDay
39%23%26%10%
64
January1st to 15thNight
20%18%37%20%2
720
16th to endNight
22%18%36%19%2
768
February1st to 15thNight
18%19%41%18%1
704
16th to endNight
22%17%32%22%5%
631
March1st to 15thNight
25%16%36%18%2
720
16th to endNight
22%15%33%21%6%
768
April1st to 15thNight
23%15%32%23%4
718
16th to endNight
24%13%30%23%8%
557
May1st to 15thNight
22%9%32%25%7%1
540
16th to endNight
25%7%28%28%7%1
415
June1st to 15thNight
28%8%23%30%10%
360
16th to endNight
21%126%35%14%
360
July1st to 15thNight
16%120%40%18%1
340
16th to endNight
13%319%43%18%2
376
August1st to 15thNight
14%323%40%17%
509
16th to endNight
15%422%35%20%2
669
September1st to 15thNight
16%425%32%19%1
700
16th to endNight
17%426%28%18%4
657
October1st to 15thNight
21%9%28%23%15%1
660
16th to endNight
24%13%32%23%5%
704
November1st to 15thNight
21%11%32%24%8%1
700
16th to endNight
21%17%27%25%7%
720
December1st to 15thNight
26%14%36%18%3
720
16th to endNight
27%16%36%17%2
768
Page generated at 2017-09-11 19:35:24. Version ac04

Copyright 2017 A. Danko


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