Slater Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Slater Creek Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
44%
15965
26%
47088
13%
15919
56%
15919
36%
25863

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
34%
900
30%
2506
12%
895
51%
895
40%
1279
January16th to endNight
32%
774
34%
2502
16%
774
54%
774
42%
1170
February1st to 15thNight
26%
703
25%
2241
8%
699
46%
699
34%
1161
February16th to endNight
26%
632
34%
1894
9%
632
51%
632
38%
960
March1st to 15thNight
35%
720
26%
2102
10%
720
49%
720
38%
1123
March16th to endNight
34%
686
28%
2030
11%
686
50%
686
34%
1131
April1st to 15thNight
34%
539
23%
1798
11%
539
51%
539
30%
940
April16th to endNight
30%
540
20%
1800
9%
540
47%
540
26%
1056
May1st to 15thNight
42%
540
18%
1650
13%
540
50%
540
25%
1051
May16th to endNight
44%
562
16%
1498
8%
561
52%
561
31%
951
June1st to 15thNight
62%
540
21%
1440
13%
540
68%
540
45%
786
June16th to endNight
68%
540
23%
1440
18%
540
71%
540
47%
782
July1st to 15thNight
65%
510
15%
1360
13%
510
67%
510
27%
917
July16th to endNight
71%
564
15%
1479
15%
531
72%
531
28%
971
August1st to 15thNight
69%
539
15%
1677
15%
536
70%
536
26%
1047
August16th to endNight
72%
573
21%
1910
23%
573
74%
573
29%
1122
September1st to 15thNight
64%
540
23%
1800
21%
540
70%
540
31%
1043
September16th to endNight
57%
537
32%
1929
25%
537
68%
537
38%
950
October1st to 15thNight
51%
678
29%
2046
15%
678
62%
678
43%
1079
October16th to endNight
52%
713
34%
2121
18%
713
63%
713
46%
1081
November1st to 15thNight
44%
875
33%
2275
15%
875
55%
875
48%
1196
November16th to endNight
40%
900
36%
2382
14%
900
54%
900
50%
1221
December1st to 15thNight
30%
900
25%
2520
7%
900
45%
900
37%
1336
December16th to endNight
27%
960
26%
2688
8%
960
43%
960
33%
1510

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
45%25%5%35%5%6%8%48%
48121
Night
242442446%8%55%
47266
Cloud CoverDay
45%25%5%35%5%6%8%48%
48119
Night
242442446%8%56%
47266
TransparencyDay
31%7%13%22%19%6%
47802
Night
25%6%15%26%20%6%
47088
SeeingDay
11%15%32%22%13%3
5870
Night
5%11%33%32%15%1
15967

By Month

Percentage Cloud Cover SW (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
324323448%61%
1435
16th to endDay
42441335%7%61%
1728
February1st to 15thDay
5%26%43346%8%54%
1621
16th to endDay
5%35%42345%7%56%
1580
March1st to 15thDay
16%36%5%2436%7%50%
1857
16th to endDay
17%36%43446%9%47%
2193
April1st to 15thDay
37%26%5%445%5%8%45%
2150
16th to endDay
6%10%47%5%45%45%6%39%
2160
May1st to 15thDay
7%8%38%6%45%5%6%8%35%
2300
16th to endDay
6%6%25%6%35%6%6%8%41%
2616
June1st to 15thDay
4435%435%5%8%10%45%
2520
16th to endDay
3215%435%6%7%8%50%
2520
July1st to 15thDay
7%426%6%37%7%8%7%37%
2520
16th to endDay
7%6%37%6%37%7%7%8%33%
2585
August1st to 15thDay
9%6%36%7%47%5%6%8%35%
2273
16th to endDay
6%5%35%7%35%5%6%9%42%
2292
September1st to 15thDay
7%435%6%35%46%7%44%
2160
16th to endDay
4414334445%59%
2031
October1st to 15thDay
3314424448%56%
1708
16th to endDay
35%23312335%63%
1738
November1st to 15thDay
42332345%7%62%
1583
16th to endDay
22441335%8%63%
1575
December1st to 15thDay
335%324447%58%
1440
16th to endDay
1425%32447%9%53%
1536
January1st to 15thNight
21332346%7%63%
2506
16th to endNight
323323346%67%
2502
February1st to 15thNight
435%42345%8%58%
2231
16th to endNight
43332345%7%61%
1894
March1st to 15thNight
141432446%7%56%
2102
16th to endNight
25%24423448%56%
2030
April1st to 15thNight
27%25%324347%56%
1798
16th to endNight
5%8%36%5%2335%5%49%
1800
May1st to 15thNight
5%8%36%435%45%8%42%
1649
16th to endNight
4426%5%2447%8%47%
1497
June1st to 15thNight
22133245%6%9%58%
1440
16th to endNight
2113325%6%8%8%57%
1440
July1st to 15thNight
5%437%6%26%6%8%8%40%
1440
16th to endNight
5%4245%47%6%9%11%37%
1580
August1st to 15thNight
5%415%6%36%7%7%8%43%
1686
16th to endNight
5%5%14436%7%7%10%45%
1910
September1st to 15thNight
5%4244346%7%10%45%
1800
16th to endNight
331343335%7%59%
1929
October1st to 15thNight
331232445%6%61%
2046
16th to endNight
331331346%6%62%
2121
November1st to 15thNight
22332345%7%64%
2275
16th to endNight
1312323237%66%
2382
December1st to 15thNight
131442345%10%58%
2520
16th to endNight
5%35%43445%7%54%
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
324423349%61%
1435
16th to endDay
425%31235%8%61%
1728
February1st to 15thDay
426%43446%8%54%
1621
16th to endDay
5%35%424348%56%
1580
March1st to 15thDay
16%36%6%2436%7%51%
1857
16th to endDay
27%36%4345%6%9%47%
2191
April1st to 15thDay
36%35%6%345%6%8%46%
2150
16th to endDay
5%11%46%5%35%5%5%7%39%
2160
May1st to 15thDay
7%8%47%6%36%5%7%8%36%
2300
16th to endDay
6%6%25%6%45%6%6%9%41%
2616
June1st to 15thDay
3434435%6%7%10%46%
2520
16th to endDay
3215%425%6%7%8%51%
2520
July1st to 15thDay
7%427%6%37%6%8%8%37%
2520
16th to endDay
7%6%36%6%47%6%8%9%33%
2585
August1st to 15thDay
9%5%36%6%46%6%7%7%35%
2273
16th to endDay
6%425%7%35%5%6%9%42%
2292
September1st to 15thDay
7%435%6%35%5%6%7%45%
2160
16th to endDay
441442335%5%59%
2031
October1st to 15thDay
431332445%7%57%
1708
16th to endDay
3423323345%62%
1738
November1st to 15thDay
41331435%8%62%
1583
16th to endDay
224313348%63%
1575
December1st to 15thDay
325%42435%8%57%
1440
16th to endDay
33443447%9%53%
1536
January1st to 15thNight
21332335%8%64%
2506
16th to endNight
323323346%66%
2502
February1st to 15thNight
435%42335%8%58%
2231
16th to endNight
42331345%8%60%
1894
March1st to 15thNight
142432446%8%57%
2102
16th to endNight
25%24424348%56%
2030
April1st to 15thNight
17%14424348%56%
1798
16th to endNight
410%36%5%23346%49%
1800
May1st to 15thNight
5%8%36%5%245%6%8%43%
1649
16th to endNight
4425%5%35%47%9%47%
1497
June1st to 15thNight
22132145%6%9%59%
1440
16th to endNight
1112336%5%7%8%58%
1440
July1st to 15thNight
5%337%5%35%6%7%9%41%
1440
16th to endNight
5%325%5%37%6%9%11%38%
1580
August1st to 15thNight
5%425%5%35%7%7%7%44%
1686
16th to endNight
4424435%6%7%10%45%
1910
September1st to 15thNight
6%323435%6%7%9%46%
1800
16th to endNight
332332336%6%60%
1929
October1st to 15thNight
321331446%7%61%
2046
16th to endNight
331331445%6%62%
2121
November1st to 15thNight
22331345%8%64%
2275
16th to endNight
322323347%66%
2382
December1st to 15thNight
121342345%11%58%
2520
16th to endNight
435%425%46%7%54%
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
20%5%18%31%19%4
1436
16th to endDay
20%415%32%19%7%
1728
February1st to 15thDay
24%5%17%30%16%4
1622
16th to endDay
25%311%29%24%5%
1580
March1st to 15thDay
29%413%25%21%5%
1857
16th to endDay
31%6%13%25%19%3
2193
April1st to 15thDay
33%6%13%24%16%6%
2150
16th to endDay
42%6%12%19%15%3
2160
May1st to 15thDay
43%9%13%18%14%1
2300
16th to endDay
36%9%15%19%13%5%
2620
June1st to 15thDay
30%8%13%16%20%10%
2520
16th to endDay
26%8%11%20%23%10%
2520
July1st to 15thDay
38%9%12%17%15%6%
2371
16th to endDay
42%11%15%18%9%2
2424
August1st to 15thDay
43%9%13%14%13%5%
2258
16th to endDay
35%8%13%22%16%3
2292
September1st to 15thDay
35%6%12%19%17%7%
2160
16th to endDay
25%49%23%29%5%
2031
October1st to 15thDay
24%6%12%24%26%5%
1708
16th to endDay
22%310%26%29%7%
1738
November1st to 15thDay
19%413%24%26%12%
1583
16th to endDay
17%310%29%29%9%
1575
December1st to 15thDay
23%5%18%28%20%3
1440
16th to endDay
23%7%19%25%17%6%
1536
January1st to 15thNight
18%5%17%31%23%3
2506
16th to endNight
18%413%31%24%7%
2502
February1st to 15thNight
24%5%15%35%15%3
2241
16th to endNight
21%311%30%26%6%
1894
March1st to 15thNight
22%5%13%27%25%4
2102
16th to endNight
27%5%11%29%22%3
2030
April1st to 15thNight
26%414%28%19%5%
1798
16th to endNight
34%5%15%25%14%4
1800
May1st to 15thNight
38%8%13%22%14%2
1650
16th to endNight
32%9%17%21%13%5%
1498
June1st to 15thNight
21%7%19%21%15%14%
1440
16th to endNight
19%8%15%21%21%13%
1440
July1st to 15thNight
37%11%14%18%11%6%
1360
16th to endNight
33%13%20%21%9%1
1479
August1st to 15thNight
35%10%16%19%12%5%
1677
16th to endNight
30%10%16%24%14%3
1910
September1st to 15thNight
31%8%16%21%15%7%
1800
16th to endNight
24%5%11%28%25%5%
1929
October1st to 15thNight
21%7%13%23%26%7%
2046
16th to endNight
20%5%10%28%29%6%
2121
November1st to 15thNight
17%5%13%26%24%13%
2275
16th to endNight
17%311%28%29%8%
2382
December1st to 15thNight
20%6%20%29%18%4
2520
16th to endNight
25%6%19%24%19%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
15%15%34%14%20%
90
16th to endDay
317%41%29%8%
96
February1st to 15thDay
11%32%43%11%2
90
16th to endDay
9%28%32%20%7%1
81
March1st to 15thDay
12%22%44%14%6%
147
16th to endDay
15%34%36%11%1
288
April1st to 15thDay
15%36%30%12%41
269
16th to endDay
27%36%24%8%2
270
May1st to 15thDay
11%18%37%24%6%1
396
16th to endDay
11%18%29%23%13%2
517
June1st to 15thDay
6%13%30%25%19%4
495
16th to endDay
47%34%26%22%5%
495
July1st to 15thDay
11%424%26%26%7%
475
16th to endDay
11%220%30%26%8%
444
August1st to 15thDay
18%6%27%29%12%5%
315
16th to endDay
12%5%34%27%16%3
332
September1st to 15thDay
11%13%35%25%9%3
315
16th to endDay
10%13%38%20%12%3
186
October1st to 15thDay
215%30%28%15%6%
107
16th to endDay
9%19%27%28%11%4
96
November1st to 15thDay
6%8%30%20%28%5%
90
16th to endDay
12%20%45%15%6%
90
December1st to 15thDay
10%28%45%13%2
90
16th to endDay
7%25%43%19%31
96
January1st to 15thNight
418%38%26%10%1
900
16th to endNight
213%46%27%7%1
774
February1st to 15thNight
415%49%26%3
704
16th to endNight
320%45%26%3
632
March1st to 15thNight
315%42%30%7%
720
16th to endNight
6%15%39%31%6%
686
April1st to 15thNight
7%20%34%31%5%
539
16th to endNight
11%15%37%27%7%
540
May1st to 15thNight
11%9%30%37%10%1
540
16th to endNight
7%8%32%34%15%1
563
June1st to 15thNight
5%425%44%18%3
540
16th to endNight
3120%44%28%1
540
July1st to 15thNight
7%11%40%36%3
510
16th to endNight
7%8%34%43%5%
564
August1st to 15thNight
8%212%35%37%3
539
16th to endNight
8%110%36%37%5%
573
September1st to 15thNight
8%118%36%28%6%
540
16th to endNight
45%26%37%22%3
537
October1st to 15thNight
47%33%35%15%3
678
16th to endNight
5%6%32%34%17%3
713
November1st to 15thNight
312%34%35%12%1
875
16th to endNight
414%38%31%10%1
900
December1st to 15thNight
319%42%27%6%
900
16th to endNight
5%17%43%26%6%
960
Page generated at 2017-10-07 12:07:47. Version ac04

Copyright 2017 A. Danko


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