Attic Bluffs Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Attic Bluffs 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
36%
15400
21%
46839
11%
15364
47%
15364
22%
29716

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
21%
716
23%
2381
9%
716
39%
716
18%
1449
January16th to endNight
20%
768
22%
2496
7%
768
39%
768
20%
1570
February1st to 15thNight
19%
701
20%
2270
8%
701
36%
701
20%
1379
February16th to endNight
21%
631
26%
1893
9%
631
41%
631
23%
1163
March1st to 15thNight
25%
720
22%
2013
10%
720
38%
720
23%
1290
March16th to endNight
24%
768
20%
2077
8%
768
34%
768
21%
1414
April1st to 15thNight
25%
718
21%
1796
5%
718
35%
718
25%
1193
April16th to endNight
34%
720
19%
1800
7%
720
40%
720
28%
1185
May1st to 15thNight
31%
652
14%
1732
5%
652
37%
652
20%
1221
May16th to endNight
48%
382
19%
1505
15%
382
56%
382
20%
874
June1st to 15thNight
53%
360
16%
1440
16%
360
59%
360
21%
857
June16th to endNight
50%
360
16%
1440
11%
360
58%
360
19%
878
July1st to 15thNight
57%
368
13%
1388
13%
368
59%
368
19%
871
July16th to endNight
59%
564
17%
1595
12%
531
67%
531
30%
995
August1st to 15thNight
57%
579
13%
1649
9%
576
59%
576
23%
1129
August16th to endNight
59%
764
17%
1910
10%
764
61%
764
29%
1295
September1st to 15thNight
59%
700
22%
1750
15%
700
61%
700
31%
1169
September16th to endNight
44%
657
17%
1799
11%
657
50%
657
20%
1273
October1st to 15thNight
42%
660
24%
1980
19%
660
51%
660
24%
1268
October16th to endNight
37%
704
29%
2112
18%
704
53%
704
29%
1239
November1st to 15thNight
35%
700
23%
2208
14%
700
48%
700
24%
1333
November16th to endNight
33%
720
24%
2397
13%
720
48%
720
22%
1449
December1st to 15thNight
27%
720
20%
2520
10%
720
41%
720
16%
1562
December16th to endNight
22%
768
23%
2688
10%
768
40%
768
16%
1660

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
13%5%2442445%7%43%
47772
Night
13%5%2442445%7%43%
47024
Cloud CoverDay
12%5%244245%5%7%43%
47782
Night
13%5%2442445%7%43%
47028
TransparencyDay
38%7%12%22%16%3
47475
Night
38%6%11%21%17%3
46839
SeeingDay
15%14%22%24%17%6%
5772
Night
14%20%23%26%12%1
15408

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%24324446%45%
1555
16th to endDay
15%6%24423445%46%
1728
February1st to 15thDay
14%7%34324446%44%
1590
16th to endDay
12%6%13435%45%7%43%
1580
March1st to 15thDay
15%5%13423346%48%
1933
16th to endDay
17%5%25%433345%43%
2145
April1st to 15thDay
12%424423335%51%
2152
16th to endDay
13%5%25%424447%45%
2160
May1st to 15thDay
15%6%25%5%34446%41%
2229
16th to endDay
11%4143245%6%8%45%
2607
June1st to 15thDay
10%324436%6%6%9%42%
2520
16th to endDay
7%4245%45%6%7%11%40%
2520
July1st to 15thDay
7%435%5%37%6%8%12%36%
2487
16th to endDay
5%325%6%47%7%8%12%36%
2465
August1st to 15thDay
11%6%35%5%36%6%7%8%35%
2286
16th to endDay
12%415%5%35%5%7%10%37%
2292
September1st to 15thDay
13%4245%25%5%5%8%41%
2098
16th to endDay
18%7%37%5%3445%7%32%
1829
October1st to 15thDay
17%6%24414345%44%
1650
16th to endDay
11%424423345%53%
1760
November1st to 15thDay
15%5%24414336%48%
1649
16th to endDay
13%314313246%53%
1561
December1st to 15thDay
15%424423447%45%
1440
16th to endDay
19%7%1432443443%
1536
January1st to 15thNight
14%6%15%42435%7%44%
2381
16th to endNight
16%6%35%42335%5%43%
2496
February1st to 15thNight
16%5%2442345%6%44%
2268
16th to endNight
13%6%24413436%48%
1893
March1st to 15thNight
14%424434446%46%
2001
16th to endNight
18%435%5%34436%40%
2077
April1st to 15thNight
11%6%25%4335%5%7%44%
1796
16th to endNight
15%5%2432345%7%45%
1800
May1st to 15thNight
14%6%26%6%35%5%48%36%
1732
16th to endNight
11%414434349%47%
1503
June1st to 15thNight
10%324435%6%7%9%42%
1440
16th to endNight
8%425%6%5%5%5%6%8%40%
1440
July1st to 15thNight
8%4246%47%6%6%9%39%
1470
16th to endNight
6%324435%6%8%12%40%
1703
August1st to 15thNight
7%5%35%7%45%6%7%10%37%
1660
16th to endNight
9%5%25%5%35%5%7%10%39%
1910
September1st to 15thNight
12%4145%345%6%8%44%
1750
16th to endNight
19%5%26%5%34446%37%
1799
October1st to 15thNight
16%5%25%424346%45%
1980
16th to endNight
14%413323445%52%
2112
November1st to 15thNight
15%415%313345%49%
2208
16th to endNight
14%414425%45%5%48%
2397
December1st to 15thNight
15%5%345%3444443%
2520
16th to endNight
17%7%2442335%5%43%
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%5%24415%446%44%
1555
16th to endDay
15%6%24423346%45%
1728
February1st to 15thDay
14%7%25%334435%44%
1590
16th to endDay
12%6%23425%46%7%43%
1580
March1st to 15thDay
14%5%23412446%48%
1944
16th to endDay
17%5%35%423345%43%
2144
April1st to 15thDay
11%5%24424336%51%
2152
16th to endDay
13%5%245%2445%7%44%
2160
May1st to 15thDay
14%6%345%25%447%40%
2229
16th to endDay
11%4244245%6%8%45%
2607
June1st to 15thDay
10%424436%6%6%9%42%
2520
16th to endDay
7%4246%36%6%7%10%39%
2520
July1st to 15thDay
7%325%5%45%7%8%12%36%
2487
16th to endDay
5%3246%47%6%8%13%36%
2465
August1st to 15thDay
10%6%25%5%36%6%7%9%34%
2286
16th to endDay
11%425%5%35%7%6%10%37%
2292
September1st to 15thDay
13%425%5%25%5%6%8%41%
2098
16th to endDay
18%7%37%5%445%5%6%31%
1829
October1st to 15thDay
18%6%25%323346%43%
1650
16th to endDay
11%425%413345%53%
1760
November1st to 15thDay
15%5%24414336%47%
1649
16th to endDay
13%414323336%53%
1561
December1st to 15thDay
14%5%2442345%7%45%
1440
16th to endDay
19%7%1442443443%
1536
January1st to 15thNight
14%5%2442445%6%44%
2381
16th to endNight
17%6%25%423346%43%
2496
February1st to 15thNight
16%5%24423446%45%
2261
16th to endNight
13%6%34423346%48%
1893
March1st to 15thNight
14%5%245%34446%46%
2013
16th to endNight
18%435%5%24447%40%
2077
April1st to 15thNight
11%6%3443446%7%44%
1796
16th to endNight
15%5%2432335%8%45%
1800
May1st to 15thNight
14%6%26%5%345%6%7%37%
1731
16th to endNight
11%415%424448%47%
1503
June1st to 15thNight
10%324435%7%6%10%41%
1440
16th to endNight
6%5%26%6%45%5%7%8%40%
1440
July1st to 15thNight
7%425%6%36%6%7%11%38%
1470
16th to endNight
6%335%435%6%8%10%40%
1703
August1st to 15thNight
6%6%36%6%45%6%6%11%37%
1660
16th to endNight
10%425%5%35%48%10%38%
1910
September1st to 15thNight
11%5%2443446%8%44%
1750
16th to endNight
19%5%26%435%446%37%
1799
October1st to 15thNight
17%425%433435%45%
1980
16th to endNight
14%413323445%51%
2112
November1st to 15thNight
16%424324345%49%
2208
16th to endNight
14%424425%45%448%
2397
December1st to 15thNight
15%5%25%5%24445%43%
2520
16th to endNight
18%6%24423346%43%
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
40%5%9%22%18%3
1556
16th to endDay
39%49%23%18%5%
1728
February1st to 15thDay
41%48%24%17%4
1592
16th to endDay
38%5%11%24%17%3
1580
March1st to 15thDay
37%412%22%19%4
1944
16th to endDay
42%6%8%19%18%3
2145
April1st to 15thDay
34%5%8%26%18%5%
2152
16th to endDay
38%5%11%18%18%7%
2160
May1st to 15thDay
42%7%13%21%13%1
2229
16th to endDay
34%8%14%25%15%1
2611
June1st to 15thDay
35%9%15%25%13%1
2520
16th to endDay
35%9%16%21%14%2
2520
July1st to 15thDay
35%12%16%20%12%2
2340
16th to endDay
34%10%16%22%14%1
2310
August1st to 15thDay
41%9%14%20%11%1
2273
16th to endDay
37%10%15%20%13%2
2292
September1st to 15thDay
39%9%12%18%18%3
2098
16th to endDay
50%7%9%15%16%
1829
October1st to 15thDay
41%38%23%19%2
1650
16th to endDay
33%38%25%22%6%
1760
November1st to 15thDay
39%39%21%21%5%
1649
16th to endDay
32%5%9%25%21%4
1561
December1st to 15thDay
37%5%11%23%17%4
1440
16th to endDay
45%310%22%15%2
1536
January1st to 15thNight
38%5%10%19%20%5%
2381
16th to endNight
42%49%22%17%4
2496
February1st to 15thNight
39%47%24%19%4
2270
16th to endNight
36%5%8%24%20%5%
1893
March1st to 15thNight
39%49%26%15%3
2013
16th to endNight
43%5%7%21%17%4
2077
April1st to 15thNight
37%6%10%20%20%4
1796
16th to endNight
37%5%11%20%19%5%
1800
May1st to 15thNight
43%9%12%21%12%1
1732
16th to endNight
35%7%16%25%13%1
1505
June1st to 15thNight
35%10%16%22%14%1
1440
16th to endNight
38%9%14%18%16%2
1440
July1st to 15thNight
38%11%14%22%11%2
1388
16th to endNight
31%10%18%26%11%1
1595
August1st to 15thNight
38%11%17%18%13%
1649
16th to endNight
37%9%17%21%13%1
1910
September1st to 15thNight
36%8%15%18%18%3
1750
16th to endNight
47%6%9%15%18%2
1799
October1st to 15thNight
40%5%9%21%19%3
1980
16th to endNight
33%48%24%23%5%
2112
November1st to 15thNight
37%49%19%22%6%
2208
16th to endNight
37%5%7%23%19%6%
2397
December1st to 15thNight
41%5%10%21%17%3
2520
16th to endNight
41%5%10%23%15%4
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
25%12%43%17%1
81
16th to endDay
20%25%33%16%4
96
February1st to 15thDay
18%22%37%16%4
106
16th to endDay
9%25%38%21%4
239
March1st to 15thDay
14%25%33%20%6%
270
16th to endDay
19%20%31%22%41
288
April1st to 15thDay
12%24%27%21%10%2
270
16th to endDay
15%15%25%28%11%3
270
May1st to 15thDay
19%18%29%19%10%2
288
16th to endDay
19%12%16%20%22%8%
331
June1st to 15thDay
14%11%15%26%21%9%
315
16th to endDay
8%10%20%33%22%5%
315
July1st to 15thDay
11%7%12%33%28%7%
305
16th to endDay
8%10%9%25%34%12%
326
August1st to 15thDay
14%6%15%26%27%10%
313
16th to endDay
11%5%10%26%32%12%
332
September1st to 15thDay
17%7%15%23%18%16%
294
16th to endDay
27%8%16%19%16%11%
254
October1st to 15thDay
23%11%17%27%13%6%
255
16th to endDay
9%15%26%25%19%3
272
November1st to 15thDay
19%17%26%18%15%3
247
16th to endDay
16%23%23%20%14%1
181
December1st to 15thDay
18%10%38%20%8%5%
60
16th to endDay
37%12%26%15%7%
64
January1st to 15thNight
14%30%28%21%4
720
16th to endNight
17%23%34%22%2
768
February1st to 15thNight
17%26%32%21%1
704
16th to endNight
14%27%33%21%2
631
March1st to 15thNight
16%24%30%22%5%
720
16th to endNight
18%23%30%20%6%
768
April1st to 15thNight
12%25%34%21%6%
718
16th to endNight
17%20%24%28%8%
720
May1st to 15thNight
15%22%25%27%7%1
652
16th to endNight
10%18%15%39%13%2
383
June1st to 15thNight
8%17%13%35%21%3
360
16th to endNight
7%18%16%36%19%1
360
July1st to 15thNight
8%12%14%36%25%1
368
16th to endNight
5%17%11%35%26%4
564
August1st to 15thNight
9%10%12%37%26%3
579
16th to endNight
11%9%10%32%31%4
764
September1st to 15thNight
12%9%13%35%26%3
700
16th to endNight
22%10%14%28%21%2
657
October1st to 15thNight
19%13%18%26%17%3
660
16th to endNight
15%16%26%23%16%1
704
November1st to 15thNight
16%19%24%25%11%2
700
16th to endNight
12%25%25%23%11%
720
December1st to 15thNight
17%25%25%22%8%
720
16th to endNight
20%26%28%22%2
768
Page generated at 2017-09-11 19:35:21. Version ac04

Copyright 2017 A. Danko


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