Mattatuck Astronomical Society Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mattatuck Astronomical Society Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
26%
15544
18%
48793
7%
15512
38%
15512
20%
31698

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
14%
780
20%
2716
6%
776
32%
776
17%
1691
January16th to endNight
14%
832
19%
2871
4%
832
33%
832
16%
1816
February1st to 15thNight
13%
760
16%
2382
3%
757
28%
757
14%
1606
February16th to endNight
15%
631
23%
1893
6%
631
35%
631
17%
1240
March1st to 15thNight
15%
720
17%
2160
6%
720
29%
720
16%
1463
March16th to endNight
19%
768
23%
2001
7%
768
32%
768
22%
1319
April1st to 15thNight
17%
718
16%
1796
3%
718
24%
718
20%
1299
April16th to endNight
22%
660
16%
1740
2%
660
31%
660
22%
1196
May1st to 15thNight
22%
517
17%
1597
6%
517
32%
517
17%
1102
May16th to endNight
31%
375
12%
1497
9%
374
38%
374
16%
957
June1st to 15thNight
29%
360
13%
1440
8%
360
42%
360
16%
954
June16th to endNight
40%
360
14%
1440
13%
360
50%
360
23%
849
July1st to 15thNight
44%
340
12%
1360
13%
340
50%
340
21%
827
July16th to endNight
49%
376
15%
1418
16%
354
54%
354
23%
852
August1st to 15thNight
47%
506
16%
1577
9%
504
53%
504
29%
941
August16th to endNight
52%
764
19%
1910
9%
764
55%
764
31%
1272
September1st to 15thNight
38%
720
21%
1814
9%
720
44%
720
31%
1186
September16th to endNight
46%
717
27%
1980
18%
717
52%
717
31%
1222
October1st to 15thNight
34%
720
21%
2073
11%
720
44%
720
24%
1350
October16th to endNight
24%
768
18%
2439
8%
768
37%
768
20%
1588
November1st to 15thNight
27%
760
20%
2472
8%
760
43%
760
20%
1587
November16th to endNight
22%
780
21%
2575
9%
780
37%
780
18%
1640
December1st to 15thNight
20%
780
15%
2730
4%
780
33%
780
14%
1824
December16th to endNight
13%
832
18%
2912
4%
832
32%
832
14%
1917

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%
49293
Night
16%6%25%42445%6%41%
48963
Cloud CoverDay
16%6%25%5%3445%7%38%
49303
Night
16%6%25%424446%41%
48968
TransparencyDay
44%6%12%21%14%1
48981
Night
42%5%12%22%14%1
48793
SeeingDay
21%15%30%19%9%3
6228
Night
21%15%32%22%7%
15544

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
14%7%24435%5%45%41%
1552
16th to endDay
15%6%35%4245%5%7%38%
1703
February1st to 15thDay
15%6%27%6%46%45%6%34%
1780
16th to endDay
16%7%26%435%35%6%38%
1580
March1st to 15thDay
17%7%26%6%3436%7%34%
1790
16th to endDay
18%7%34424346%39%
2220
April1st to 15thDay
19%7%25%434445%38%
2152
16th to endDay
16%5%25%423446%42%
2220
May1st to 15thDay
24%6%3442436%6%33%
2364
16th to endDay
16%6%25%5%245%5%7%37%
2618
June1st to 15thDay
23%5%245%345%6%7%32%
2520
16th to endDay
14%5%26%5%35%6%6%8%34%
2520
July1st to 15thDay
13%5%25%6%35%5%5%8%37%
2520
16th to endDay
12%5%25%5%36%5%6%8%37%
2654
August1st to 15thDay
13%5%346%45%46%8%35%
2359
16th to endDay
12%5%25%435%46%8%41%
2292
September1st to 15thDay
13%6%35%5%35%447%41%
2145
16th to endDay
13%5%2442335%6%47%
1980
October1st to 15thDay
19%7%24423345%41%
1886
16th to endDay
17%6%145%3445%6%39%
1785
November1st to 15thDay
18%6%15%32325%7%41%
1716
16th to endDay
18%6%24323247%44%
1713
December1st to 15thDay
18%6%35%5%2445%6%37%
1560
16th to endDay
19%8%35%5%245%5%6%32%
1664
January1st to 15thNight
16%6%25%5%2445%6%41%
2716
16th to endNight
15%9%34324446%40%
2871
February1st to 15thNight
15%8%35%5%35%45%6%37%
2381
16th to endNight
16%8%2442345%5%42%
1893
March1st to 15thNight
17%7%35%425%446%38%
2147
16th to endNight
16%5%25%413446%43%
2001
April1st to 15thNight
18%7%25%5%345%46%36%
1796
16th to endNight
18%5%25%43434442%
1740
May1st to 15thNight
20%7%26%434446%35%
1597
16th to endNight
18%7%344135%48%37%
1495
June1st to 15thNight
21%6%35%324447%37%
1440
16th to endNight
14%425%42446%9%42%
1440
July1st to 15thNight
13%415%425%5%6%8%41%
1440
16th to endNight
10%5%26%5%35%46%8%39%
1514
August1st to 15thNight
12%42342445%8%45%
1587
16th to endNight
13%4234345%5%7%45%
1910
September1st to 15thNight
15%5%24323336%47%
1814
16th to endNight
13%42431334452%
1980
October1st to 15thNight
16%6%25%432336%44%
2073
16th to endNight
20%5%15%424446%40%
2439
November1st to 15thNight
16%7%35%323445%43%
2472
16th to endNight
18%6%25%424345%41%
2575
December1st to 15thNight
20%6%25%5%245%5%6%34%
2730
16th to endNight
19%8%2442445%6%37%
2912

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%6%25%426%5%46%40%
1552
16th to endDay
15%6%35%4245%47%39%
1703
February1st to 15thDay
15%7%27%5%45%5%47%34%
1780
16th to endDay
15%7%35%5%35%35%6%39%
1580
March1st to 15thDay
16%7%36%5%3445%7%34%
1800
16th to endDay
17%7%35%424436%40%
2220
April1st to 15thDay
19%7%24435%45%5%38%
2152
16th to endDay
17%5%25%324347%43%
2220
May1st to 15thDay
23%6%35%42445%6%33%
2364
16th to endDay
17%5%245%245%5%7%37%
2618
June1st to 15thDay
22%5%24435%5%47%32%
2520
16th to endDay
14%5%26%5%35%6%5%9%35%
2520
July1st to 15thDay
12%5%26%6%35%5%5%8%36%
2520
16th to endDay
12%6%35%5%36%5%6%8%37%
2654
August1st to 15thDay
13%5%25%5%36%6%6%8%35%
2359
16th to endDay
12%5%345%25%45%9%41%
2292
September1st to 15thDay
13%6%35%435%446%43%
2145
16th to endDay
13%5%2442345%7%46%
1980
October1st to 15thDay
17%8%24423346%41%
1886
16th to endDay
17%5%245%25%446%40%
1785
November1st to 15thDay
18%5%24413347%42%
1716
16th to endDay
17%6%23323346%44%
1713
December1st to 15thDay
17%6%36%5%24346%38%
1560
16th to endDay
18%9%345%25%46%6%33%
1664
January1st to 15thNight
16%6%25%43345%6%42%
2716
16th to endNight
14%9%34423446%41%
2871
February1st to 15thNight
14%8%36%435%5%5%6%37%
2374
16th to endNight
16%7%25%5%14446%42%
1893
March1st to 15thNight
17%7%36%324446%38%
2160
16th to endNight
16%6%25%42335%7%43%
2000
April1st to 15thNight
17%7%245%345%46%37%
1796
16th to endNight
18%5%35%433435%42%
1740
May1st to 15thNight
20%7%26%434446%36%
1597
16th to endNight
19%6%2442345%7%38%
1495
June1st to 15thNight
21%7%343235%46%38%
1440
16th to endNight
13%5%25%4245%5%8%43%
1440
July1st to 15thNight
14%424425%47%9%39%
1440
16th to endNight
9%5%36%5%35%5%7%9%39%
1514
August1st to 15thNight
12%41433445%9%46%
1587
16th to endNight
12%424435%45%7%44%
1910
September1st to 15thNight
15%414333446%47%
1814
16th to endNight
13%5%24324335%51%
1980
October1st to 15thNight
16%6%25%423346%44%
2073
16th to endNight
20%5%24424346%42%
2439
November1st to 15thNight
15%7%35%42335%5%43%
2472
16th to endNight
17%6%25%424345%41%
2575
December1st to 15thNight
19%6%25%42445%6%36%
2730
16th to endNight
19%7%2442445%6%37%
2912

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
42%5%12%24%11%3
1553
16th to endDay
41%5%13%25%12%1
1703
February1st to 15thDay
48%5%13%19%12%1
1783
16th to endDay
45%411%23%12%2
1580
March1st to 15thDay
47%5%13%22%9%2
1800
16th to endDay
44%410%19%16%3
2220
April1st to 15thDay
45%6%10%19%14%3
2152
16th to endDay
41%5%9%22%18%3
2220
May1st to 15thDay
50%5%9%18%13%2
2364
16th to endDay
44%8%12%20%12%1
2622
June1st to 15thDay
49%7%12%19%9%1
2520
16th to endDay
42%8%14%21%11%
2520
July1st to 15thDay
45%7%10%20%14%1
2371
16th to endDay
42%7%14%20%13%1
2487
August1st to 15thDay
43%6%15%20%13%
2345
16th to endDay
38%6%11%25%17%1
2292
September1st to 15thDay
40%6%11%20%18%1
2145
16th to endDay
35%5%9%22%24%2
1980
October1st to 15thDay
44%5%9%23%14%2
1886
16th to endDay
43%413%22%13%2
1785
November1st to 15thDay
42%5%12%21%16%2
1716
16th to endDay
40%312%26%14%2
1713
December1st to 15thDay
45%5%15%19%12%
1560
16th to endDay
48%7%14%18%10%
1664
January1st to 15thNight
42%413%23%13%2
2716
16th to endNight
42%5%13%21%15%2
2871
February1st to 15thNight
46%6%13%19%11%2
2382
16th to endNight
43%311%21%16%2
1893
March1st to 15thNight
45%5%13%21%11%2
2160
16th to endNight
40%310%22%18%4
2001
April1st to 15thNight
46%6%10%21%14%1
1796
16th to endNight
44%49%21%17%2
1740
May1st to 15thNight
48%5%10%18%14%2
1597
16th to endNight
43%7%17%17%11%1
1497
June1st to 15thNight
47%5%13%19%11%1
1440
16th to endNight
38%6%14%25%13%
1440
July1st to 15thNight
38%8%13%25%13%1
1360
16th to endNight
39%6%17%22%11%2
1418
August1st to 15thNight
34%6%16%25%14%1
1577
16th to endNight
36%8%11%25%17%
1910
September1st to 15thNight
37%6%11%24%19%
1814
16th to endNight
35%5%6%24%26%1
1980
October1st to 15thNight
42%5%10%21%17%2
2073
16th to endNight
43%414%23%13%
2439
November1st to 15thNight
42%5%11%20%17%3
2472
16th to endNight
44%412%24%12%1
2575
December1st to 15thNight
46%6%14%20%11%
2730
16th to endNight
46%5%13%21%12%
2912

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
22%34%27%12%3
90
16th to endDay
22%23%44%8%
105
February1st to 15thDay
27%26%33%11%
216
16th to endDay
24%23%34%15%2
239
March1st to 15thDay
25%23%31%15%3
270
16th to endDay
21%22%36%11%5%1
288
April1st to 15thDay
25%19%32%14%5%1
270
16th to endDay
21%17%33%18%6%2
270
May1st to 15thDay
36%15%22%14%9%2
288
16th to endDay
22%13%31%21%9%1
331
June1st to 15thDay
24%15%26%20%12%1
315
16th to endDay
18%12%33%26%8%
315
July1st to 15thDay
16%11%30%27%13%1
305
16th to endDay
13%7%31%28%15%3
326
August1st to 15thDay
14%7%29%27%13%7%
313
16th to endDay
12%6%29%25%16%9%
332
September1st to 15thDay
14%12%27%22%15%7%
315
16th to endDay
17%8%26%20%13%13%
314
October1st to 15thDay
21%9%26%23%12%5%
315
16th to endDay
22%19%29%20%7%
302
November1st to 15thDay
25%15%27%21%9%
280
16th to endDay
23%22%27%16%8%
243
December1st to 15thDay
20%30%32%12%5%
90
16th to endDay
30%31%29%9%
96
January1st to 15thNight
22%21%38%15%2
780
16th to endNight
23%21%37%16%1
832
February1st to 15thNight
22%21%37%17%1
760
16th to endNight
24%23%33%16%2
631
March1st to 15thNight
24%23%32%17%2
720
16th to endNight
21%23%31%18%4
768
April1st to 15thNight
23%20%36%16%2
718
16th to endNight
21%18%33%19%5%
660
May1st to 15thNight
26%14%33%20%4
517
16th to endNight
22%9%32%28%6%
375
June1st to 15thNight
24%8%31%26%9%
360
16th to endNight
17%332%37%8%
360
July1st to 15thNight
15%5%29%33%16%
340
16th to endNight
12%327%38%17%
376
August1st to 15thNight
12%330%38%13%
506
16th to endNight
15%223%36%20%2
764
September1st to 15thNight
18%6%31%29%12%1
720
16th to endNight
16%7%25%26%21%3
717
October1st to 15thNight
20%9%30%25%10%1
720
16th to endNight
24%16%33%20%6%
768
November1st to 15thNight
21%16%31%20%8%1
760
16th to endNight
23%15%32%20%6%
780
December1st to 15thNight
25%17%33%17%5%
780
16th to endNight
25%21%35%15%1
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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