Mt. Stony Brook Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mt. Stony Brook Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
38%
23124
19%
74605
11%
23083
48%
23083
23%
48018

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 10thNight
23%
760
23%
2649
9%
757
40%
757
23%
1582
January11th to 20thNight
25%
739
19%
2583
7%
739
42%
739
17%
1693
January21st to endNight
23%
792
22%
2691
10%
792
39%
792
23%
1628
February1st to 10thNight
24%
720
17%
2275
6%
720
37%
720
20%
1516
February11th to 20thNight
21%
703
20%
2100
7%
700
36%
700
22%
1395
February21st to endNight
23%
592
25%
1776
10%
592
42%
592
22%
1159
March1st to 10thNight
30%
720
22%
2160
11%
720
45%
720
26%
1364
March11th to 20thNight
30%
720
21%
2102
10%
720
42%
720
25%
1366
March21st to endNight
30%
792
22%
1980
7%
792
41%
792
27%
1371
April1st to 10thNight
32%
720
19%
1800
6%
720
39%
720
26%
1276
April11th to 20thNight
39%
711
18%
1775
6%
711
44%
711
28%
1230
April21st to endNight
39%
646
19%
1726
8%
646
45%
646
27%
1198
May1st to 10thNight
37%
540
14%
1620
7%
540
43%
540
19%
1168
May11th to 20thNight
37%
454
17%
1516
12%
454
44%
454
19%
1022
May21st to endNight
54%
388
13%
1551
15%
388
57%
388
18%
991
June1st to 10thNight
48%
360
16%
1440
19%
360
55%
360
19%
908
June11th to 20thNight
60%
360
15%
1440
19%
360
63%
360
20%
891
June21st to endNight
62%
360
14%
1440
18%
360
66%
360
23%
862
July1st to 10thNight
62%
350
12%
1400
17%
350
64%
350
20%
870
July11th to 20thNight
64%
348
15%
1392
21%
348
65%
348
21%
842
July21st to endNight
63%
394
17%
1486
20%
372
67%
372
22%
890
August1st to 10thNight
66%
454
17%
1518
16%
452
68%
452
28%
895
August11th to 20thNight
60%
710
16%
1774
10%
710
61%
710
28%
1236
August21st to endNight
63%
792
18%
1980
10%
792
65%
792
33%
1320
September1st to 10thNight
54%
720
20%
1800
13%
720
56%
720
30%
1230
September11th to 20thNight
57%
720
26%
1916
18%
720
61%
720
35%
1201
September21st to endNight
46%
720
23%
1980
15%
720
53%
720
28%
1326
October1st to 10thNight
37%
720
16%
2014
12%
720
42%
720
23%
1397
October11th to 20thNight
43%
720
23%
2160
15%
720
53%
720
29%
1326
October21st to endNight
30%
792
18%
2566
10%
792
40%
792
21%
1710
November1st to 10thNight
39%
740
23%
2407
14%
740
51%
740
27%
1458
November11th to 20thNight
31%
760
24%
2470
13%
760
46%
760
24%
1529
November21st to endNight
33%
760
23%
2482
11%
760
48%
760
25%
1488
December1st to 10thNight
26%
760
18%
2660
8%
760
40%
760
18%
1728
December11th to 20thNight
25%
760
18%
3179
7%
759
38%
759
15%
1973
December21st to endNight
24%
827
13%
4797
8%
817
39%
817
11%
2979

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
15%6%25%43445%8%42%
74798
Night
17%7%35%5%3445%7%42%
74972
TransparencyDay
40%7%13%22%16%2
74503
Night
42%6%12%22%16%2
74801
SeeingDay
18%5%22%31%19%5%
13939
Night
20%6%29%31%13%2
23134

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 10thDay
14%6%26%5%35%45%7%44%
1517
11th to 20thDay
16%8%46%6%235%5%7%37%
1472
21st to endDay
15%7%36%5%35%45%6%42%
1662
February1st to 10thDay
19%6%36%5%3445%6%39%
1683
11th to 20thDay
15%5%35%5%34447%45%
1748
21st to endDay
19%8%36%5%3435%6%39%
1480
March1st to 10thDay
13%7%26%43345%8%44%
1797
11th to 20thDay
15%6%25%4345%6%8%41%
1853
21st to endDay
18%8%35%5%23346%41%
2376
April1st to 10thDay
16%8%36%42445%7%41%
2160
11th to 20thDay
16%6%25%5%34446%45%
2134
21st to endDay
21%5%2332445%7%43%
2232
May1st to 10thDay
22%7%24424447%39%
2340
11th to 20thDay
19%5%1443446%7%42%
2392
21st to endDay
13%6%25%4345%6%10%43%
2725
June1st to 10thDay
17%5%25%43446%9%41%
2520
11th to 20thDay
14%6%35%5%35%5%6%10%39%
2520
21st to endDay
11%6%35%5%3446%10%44%
2520
July1st to 10thDay
9%5%35%4346%6%10%43%
2520
11th to 20thDay
10%5%35%4346%7%10%43%
2520
21st to endDay
12%5%25%5%35%6%7%9%41%
2744
August1st to 10thDay
10%5%25%5%35%5%7%10%43%
2390
11th to 20thDay
12%6%35%5%345%6%10%43%
2126
21st to endDay
12%5%35%5%345%6%9%44%
2376
September1st to 10thDay
14%6%24425%46%7%46%
2160
11th to 20thDay
13%5%24323448%51%
2044
21st to endDay
18%6%25%435%447%42%
1980
October1st to 10thDay
22%6%14324347%44%
1944
11th to 20thDay
15%5%25%4235%6%7%45%
1800
21st to endDay
19%6%35%4345%47%40%
1788
November1st to 10thDay
15%5%26%424346%49%
1671
11th to 20thDay
18%6%24423338%47%
1710
21st to endDay
15%6%25%43445%7%45%
1696
December1st to 10thDay
18%6%26%5%3447%8%36%
1520
11th to 20thDay
22%7%24322346%45%
1906
21st to endDay
18%10%37%5%4445%7%33%
2772
January1st to 10thNight
16%6%245%2345%7%45%
2649
11th to 20thNight
20%7%35%5%34447%39%
2583
21st to endNight
14%8%36%43335%7%43%
2691
February1st to 10thNight
16%9%36%434447%39%
2275
11th to 20thNight
19%7%35%5%2446%6%39%
2098
21st to endNight
21%6%25%434446%42%
1776
March1st to 10thNight
17%6%24435%35%6%45%
2150
11th to 20thNight
17%6%35%5%3446%6%42%
2101
21st to endNight
17%9%35%43445%6%40%
1980
April1st to 10thNight
19%7%35%5%4445%6%39%
1800
11th to 20thNight
17%7%35%5%33447%41%
1775
21st to endNight
18%9%35%5%23436%41%
1726
May1st to 10thNight
21%8%35%6%35%45%6%34%
1620
11th to 20thNight
19%7%36%5%345%5%7%35%
1515
21st to endNight
18%6%346%3446%8%38%
1550
June1st to 10thNight
19%6%34435%349%40%
1440
11th to 20thNight
15%7%25%335%46%9%40%
1440
21st to endNight
10%6%25%6%35%6%6%10%41%
1440
July1st to 10thNight
10%7%35%5%45%6%7%9%39%
1440
11th to 20thNight
12%6%35%5%45%5%8%8%40%
1440
21st to endNight
11%5%35%435%5%7%9%41%
1574
August1st to 10thNight
7%4246%35%7%8%10%43%
1528
11th to 20thNight
11%6%36%6%45%6%7%9%38%
1774
21st to endNight
13%5%244346%5%9%44%
1980
September1st to 10thNight
15%425%6%346%5%7%44%
1800
11th to 20thNight
14%42442345%6%52%
1916
21st to endNight
18%5%26%5%34346%43%
1980
October1st to 10thNight
21%8%36%43425%6%39%
2014
11th to 20thNight
15%6%245%2345%6%48%
2160
21st to endNight
21%7%35%433446%39%
2566
November1st to 10thNight
13%6%345%3435%6%48%
2407
11th to 20thNight
19%6%34423345%47%
2470
21st to endNight
14%6%25%5%2446%8%45%
2482
December1st to 10thNight
20%7%345%33446%39%
2660
11th to 20thNight
20%7%2443445%6%42%
3288
21st to endNight
20%9%35%5%34446%38%
4884

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 10thDay
40%5%13%28%12%3
1518
11th to 20thDay
45%6%14%21%12%2
1472
21st to endDay
42%412%25%15%2
1662
February1st to 10thDay
45%5%14%23%13%1
1683
11th to 20thDay
41%411%26%16%3
1757
21st to endDay
47%5%10%21%15%3
1480
March1st to 10thDay
39%6%13%22%16%3
1800
11th to 20thDay
39%6%13%24%16%2
1853
21st to endDay
45%5%8%19%19%5%
2376
April1st to 10thDay
42%5%12%21%16%4
2160
11th to 20thDay
40%5%12%21%19%3
2134
21st to endDay
40%6%12%21%17%4
2232
May1st to 10thDay
45%7%10%21%15%2
2340
11th to 20thDay
41%7%12%21%17%3
2396
21st to endDay
37%9%18%21%14%2
2725
June1st to 10thDay
40%9%13%23%14%1
2520
11th to 20thDay
40%8%13%24%13%1
2520
21st to endDay
36%8%16%24%15%1
2520
July1st to 10thDay
35%10%14%22%17%1
2450
11th to 20thDay
34%8%15%26%14%2
2445
21st to endDay
36%9%13%22%17%3
2591
August1st to 10thDay
35%9%16%24%15%1
2376
11th to 20thDay
37%7%16%25%15%1
2126
21st to endDay
36%8%13%21%20%2
2376
September1st to 10thDay
38%7%14%21%19%2
2160
11th to 20thDay
32%5%12%24%25%2
2044
21st to endDay
42%6%10%20%20%3
1980
October1st to 10thDay
42%6%10%22%18%2
1944
11th to 20thDay
36%6%13%25%18%2
1800
21st to endDay
43%6%10%21%17%2
1788
November1st to 10thDay
38%5%13%22%20%2
1671
11th to 20thDay
39%411%23%21%3
1710
21st to endDay
39%5%15%27%12%2
1696
December1st to 10thDay
44%5%16%18%14%1
1520
11th to 20thDay
42%416%20%17%2
1906
21st to endDay
50%7%12%21%9%1
2772
January1st to 10thNight
40%412%24%17%3
2649
11th to 20thNight
46%6%13%23%11%2
2583
21st to endNight
41%412%23%19%2
2691
February1st to 10thNight
45%6%13%22%12%2
2275
11th to 20thNight
45%5%11%20%15%4
2100
21st to endNight
45%48%24%16%4
1776
March1st to 10thNight
40%5%13%23%16%4
2160
11th to 20thNight
42%5%10%23%16%4
2102
21st to endNight
44%5%8%18%18%6%
1980
April1st to 10thNight
46%5%10%18%17%3
1800
11th to 20thNight
44%5%11%19%20%2
1775
21st to endNight
45%6%9%20%15%5%
1726
May1st to 10thNight
50%7%9%17%15%2
1620
11th to 20thNight
47%7%11%17%16%2
1516
21st to endNight
44%8%15%20%12%1
1551
June1st to 10thNight
44%6%10%20%18%2
1440
11th to 20thNight
40%9%13%25%12%1
1440
21st to endNight
37%9%14%25%13%1
1440
July1st to 10thNight
39%10%15%20%14%2
1400
11th to 20thNight
39%8%13%27%12%1
1392
21st to endNight
36%10%14%24%14%2
1486
August1st to 10thNight
32%11%18%24%14%1
1518
11th to 20thNight
40%9%14%24%11%1
1774
21st to endNight
36%9%14%22%18%2
1980
September1st to 10thNight
40%7%11%24%16%2
1800
11th to 20thNight
33%7%10%23%24%3
1916
21st to endNight
42%6%8%20%20%3
1980
October1st to 10thNight
46%6%9%22%13%3
2014
11th to 20thNight
37%6%13%28%15%1
2160
21st to endNight
46%6%11%20%16%1
2566
November1st to 10thNight
38%5%12%22%20%3
2407
11th to 20thNight
41%49%24%18%4
2470
21st to endNight
37%5%14%29%13%2
2482
December1st to 10thNight
46%5%13%21%14%1
2660
11th to 20thNight
44%5%12%19%18%2
3288
21st to endNight
47%6%12%23%12%1
4884

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 10thDay
21%10%33%27%9%1
180
11th to 20thDay
14%16%38%25%6%1
168
21st to endDay
20%5%40%26%8%2
212
February1st to 10thDay
26%8%38%26%3
303
11th to 20thDay
19%9%40%29%3
416
21st to endDay
24%11%33%26%6%
346
March1st to 10thDay
15%9%38%33%6%
420
11th to 20thDay
18%5%38%32%6%1
420
21st to endDay
22%7%32%28%8%2
462
April1st to 10thDay
20%7%32%27%12%1
420
11th to 20thDay
18%6%24%35%16%1
412
21st to endDay
26%5%23%34%10%1
420
May1st to 10thDay
28%424%33%10%2
423
11th to 20thDay
20%421%36%18%2
447
21st to endDay
19%113%29%32%6%
485
June1st to 10thDay
18%213%37%25%5%
450
11th to 20thDay
16%315%39%24%4
450
21st to endDay
12%214%37%28%6%
450
July1st to 10thDay
13%210%32%34%10%
445
11th to 20thDay
9%39%30%38%12%
444
21st to endDay
13%311%34%35%4
488
August1st to 10thDay
11%19%38%32%9%
446
11th to 20thDay
14%37%33%34%8%
439
21st to endDay
11%412%35%26%13%
495
September1st to 10thDay
18%313%27%25%14%
450
11th to 20thDay
15%214%31%25%13%
450
21st to endDay
20%319%33%20%5%
450
October1st to 10thDay
26%417%24%20%8%
450
11th to 20thDay
14%6%27%32%17%4
450
21st to endDay
23%7%30%25%13%2
399
November1st to 10thDay
15%7%22%36%16%3
365
11th to 20thDay
19%12%31%28%9%1
370
21st to endDay
18%8%33%28%12%1
356
December1st to 10thDay
21%9%36%24%11%1
180
11th to 20thDay
27%15%26%27%6%
180
21st to endDay
22%11%33%25%9%1
198
January1st to 10thNight
19%11%41%23%6%
760
11th to 20thNight
25%9%34%27%4
739
21st to endNight
19%10%43%25%3
792
February1st to 10thNight
21%10%37%29%3
720
11th to 20thNight
23%9%43%23%3
703
21st to endNight
25%8%37%26%4
592
March1st to 10thNight
20%8%37%28%6%
720
11th to 20thNight
19%8%38%28%7%1
720
21st to endNight
20%5%37%29%7%1
792
April1st to 10thNight
23%5%34%31%7%1
720
11th to 20thNight
20%5%29%35%11%
711
21st to endNight
22%427%37%9%1
646
May1st to 10thNight
24%5%25%31%12%2
540
11th to 20thNight
21%427%35%12%1
454
21st to endNight
20%312%38%26%2
389
June1st to 10thNight
21%221%34%21%2
360
11th to 20thNight
19%212%44%23%1
360
21st to endNight
11%215%49%23%1
360
July1st to 10thNight
11%315%39%28%3
350
11th to 20thNight
13%111%42%31%3
348
21st to endNight
13%313%46%24%1
394
August1st to 10thNight
7%213%45%30%3
454
11th to 20thNight
14%212%36%32%4
710
21st to endNight
14%212%36%30%6%
792
September1st to 10thNight
17%218%36%22%5%
720
11th to 20thNight
17%216%36%22%7%
720
21st to endNight
21%221%33%19%4
720
October1st to 10thNight
24%6%26%23%17%4
720
11th to 20thNight
20%5%27%33%15%1
720
21st to endNight
24%7%33%26%9%1
792
November1st to 10thNight
16%7%32%30%14%2
740
11th to 20thNight
21%10%33%26%10%1
760
21st to endNight
17%11%33%29%9%1
760
December1st to 10thNight
24%12%33%24%7%1
760
11th to 20thNight
22%10%37%26%5%
760
21st to endNight
23%10%38%24%4
836
Page generated at 2024-01-12 07:31:52. Version ac07

Copyright 2024 Attilla Danko


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