West Sweeney Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the West Sweeney Ridge Observatory clear sky chart from 2005-11-05 to 2017-03-24.

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
57%
14866
23%
45319
20%
14828
61%
14828
30%
27411

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
56%
718
18%
2360
17%
716
61%
716
26%
1452
January16th to endNight
54%
768
24%
2496
25%
768
57%
768
25%
1555
February1st to 15thNight
50%
700
22%
2288
20%
700
57%
700
23%
1449
February16th to endNight
45%
632
20%
1911
16%
632
52%
632
25%
1236
March1st to 15thNight
49%
720
17%
1987
14%
720
52%
720
25%
1342
March16th to endNight
46%
740
19%
2024
14%
740
51%
740
27%
1339
April1st to 15thNight
42%
659
22%
1649
11%
659
48%
659
30%
1083
April16th to endNight
51%
660
23%
1650
10%
660
56%
660
41%
969
May1st to 15thNight
58%
546
25%
1536
15%
546
63%
546
40%
880
May16th to endNight
51%
384
19%
1411
14%
384
58%
384
27%
795
June1st to 15thNight
56%
330
21%
1320
20%
330
64%
330
26%
734
June16th to endNight
74%
330
28%
1320
35%
330
77%
330
40%
586
July1st to 15thNight
70%
373
25%
1303
27%
373
73%
373
34%
684
July16th to endNight
59%
522
19%
1467
18%
489
59%
489
20%
992
August1st to 15thNight
59%
496
22%
1479
17%
493
61%
493
25%
956
August16th to endNight
65%
700
24%
1750
14%
700
66%
700
34%
1156
September1st to 15thNight
72%
660
33%
1650
22%
660
74%
660
44%
985
September16th to endNight
70%
656
33%
1810
29%
656
74%
656
47%
973
October1st to 15thNight
64%
660
27%
1980
26%
660
70%
660
39%
1106
October16th to endNight
65%
704
30%
2112
30%
704
69%
704
35%
1232
November1st to 15thNight
64%
700
26%
2163
26%
700
67%
700
35%
1230
November16th to endNight
60%
720
24%
2445
25%
720
63%
720
30%
1379
December1st to 15thNight
51%
720
20%
2520
18%
720
57%
720
21%
1609
December16th to endNight
45%
768
20%
2688
17%
768
52%
768
20%
1689

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
8%6%24423349%49%
45612
Night
9%6%25%5%24348%47%
45509
TransparencyDay
32%5%8%18%21%12%
45302
Night
35%6%8%18%19%12%
45320
SeeingDay
9%12%30%32%12%2
5358
Night
11%6%15%29%30%7%
14874

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
15%5%35%323347%45%
1575
16th to endDay
15%5%34424445%43%
1728
February1st to 15thDay
16%8%35%324445%41%
1576
16th to endDay
17%8%25%43335%8%37%
1562
March1st to 15thDay
14%8%36%43445%9%36%
1971
16th to endDay
13%6%35%5%35%45%7%39%
2043
April1st to 15thDay
13%6%3442445%7%43%
1969
16th to endDay
7%424323348%56%
1980
May1st to 15thDay
45%24423449%52%
2081
16th to endDay
8%9%34423249%47%
2349
June1st to 15thDay
7%6%23423447%51%
2310
16th to endDay
3312322249%63%
2310
July1st to 15thDay
26%245%2235%12%51%
2239
16th to endDay
25%244233413%51%
2286
August1st to 15thDay
27%25%42435%12%49%
2140
16th to endDay
16%35%31335%14%51%
2100
September1st to 15thDay
25%233232410%58%
1980
16th to endDay
4323223239%64%
1819
October1st to 15thDay
8%413323346%58%
1650
16th to endDay
9%5%14323347%54%
1760
November1st to 15thDay
9%5%24325%447%50%
1696
16th to endDay
12%8%35%422336%47%
1512
December1st to 15thDay
17%8%35%5%23345%39%
1440
16th to endDay
19%7%2342325%7%40%
1536
January1st to 15thNight
14%6%2442445%7%42%
2360
16th to endNight
16%6%35%323336%45%
2496
February1st to 15thNight
14%7%35%434346%42%
2276
16th to endNight
15%6%245%2445%9%38%
1911
March1st to 15thNight
15%6%26%425%45%7%39%
1987
16th to endNight
14%7%25%42335%7%43%
2024
April1st to 15thNight
9%5%35%4345%5%8%44%
1649
16th to endNight
5%314424348%56%
1650
May1st to 15thNight
35%26%423348%55%
1536
16th to endNight
6%7%25%5%33237%50%
1410
June1st to 15thNight
35%345%35%45%9%47%
1320
16th to endNight
1414412348%63%
1320
July1st to 15thNight
16%25%5%25%45%14%45%
1389
16th to endNight
29%39%9%46%5%6%11%32%
1575
August1st to 15thNight
38%48%8%3445%13%35%
1488
16th to endNight
17%27%7%5%5%46%11%41%
1750
September1st to 15thNight
2425%6%243411%51%
1650
16th to endNight
2424422239%60%
1810
October1st to 15thNight
5%5%25%423346%56%
1980
16th to endNight
7%5%15%434446%52%
2112
November1st to 15thNight
8%5%24323347%53%
2163
16th to endNight
9%5%245%33347%51%
2445
December1st to 15thNight
16%7%25%423437%41%
2520
16th to endNight
18%6%245%23345%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
39%5%11%19%15%8%
1575
16th to endDay
42%49%12%18%12%
1728
February1st to 15thDay
45%38%17%21%3
1576
16th to endDay
45%6%8%24%12%3
1562
March1st to 15thDay
44%411%19%14%4
1971
16th to endDay
42%6%13%19%14%2
2043
April1st to 15thDay
39%6%13%19%17%2
1969
16th to endDay
28%414%25%21%5%
1980
May1st to 15thDay
27%7%8%24%24%7%
2081
16th to endDay
34%6%12%23%18%4
2353
June1st to 15thDay
31%6%9%19%20%12%
2310
16th to endDay
20%4316%34%20%
2310
July1st to 15thDay
23%7%5%9%19%34%
2096
16th to endDay
21%8%5%8%26%29%
2131
August1st to 15thDay
24%9%37%28%25%
2124
16th to endDay
24%5%412%33%20%
2100
September1st to 15thDay
21%5%311%28%28%
1980
16th to endDay
20%4423%27%19%
1819
October1st to 15thDay
26%38%21%25%14%
1650
16th to endDay
30%5%9%23%20%11%
1760
November1st to 15thDay
32%5%12%27%14%7%
1696
16th to endDay
40%39%17%23%5%
1512
December1st to 15thDay
46%49%16%18%4
1440
16th to endDay
45%412%17%16%4
1536
January1st to 15thNight
39%411%19%15%8%
2360
16th to endNight
41%39%13%16%15%
2496
February1st to 15thNight
43%39%18%17%7%
2288
16th to endNight
41%5%13%24%12%2
1911
March1st to 15thNight
42%5%11%19%14%5%
1987
16th to endNight
41%5%11%19%17%4
2024
April1st to 15thNight
36%6%14%20%18%2
1649
16th to endNight
25%5%12%26%20%8%
1650
May1st to 15thNight
27%6%8%20%25%11%
1537
16th to endNight
33%6%12%22%19%6%
1411
June1st to 15thNight
30%9%10%17%17%13%
1320
16th to endNight
19%6%314%32%24%
1320
July1st to 15thNight
23%10%310%20%31%
1303
16th to endNight
40%12%45%12%23%
1467
August1st to 15thNight
37%10%27%20%20%
1479
16th to endNight
32%10%29%22%22%
1750
September1st to 15thNight
24%8%38%24%30%
1650
16th to endNight
23%4421%25%20%
1810
October1st to 15thNight
28%47%20%22%16%
1980
16th to endNight
30%6%6%21%21%14%
2112
November1st to 15thNight
30%5%13%26%16%7%
2163
16th to endNight
33%49%23%20%8%
2445
December1st to 15thNight
43%5%8%15%20%6%
2520
16th to endNight
43%412%16%16%6%
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%11%25%22%18%1
204
16th to endDay
15%12%25%28%16%1
256
February1st to 15thDay
16%15%26%29%11%1
236
16th to endDay
19%14%29%24%10%1
235
March1st to 15thDay
19%18%27%20%12%2
270
16th to endDay
13%17%38%21%7%1
260
April1st to 15thDay
15%23%35%18%5%
209
16th to endDay
430%33%25%41
210
May1st to 15thDay
8%20%37%28%4
228
16th to endDay
11%20%33%25%7%2
266
June1st to 15thDay
415%43%32%31
255
16th to endDay
7%34%42%14%
255
July1st to 15thDay
4332%51%8%
245
16th to endDay
2124%54%12%4
271
August1st to 15thDay
15%30%46%14%
255
16th to endDay
1232%45%15%2
268
September1st to 15thDay
35%25%42%16%7%
255
16th to endDay
210%26%31%22%6%
255
October1st to 15thDay
6%9%26%36%15%5%
255
16th to endDay
11%12%29%28%15%2
272
November1st to 15thDay
10%9%23%24%23%8%
202
16th to endDay
8%16%33%27%12%1
72
December1st to 15thDay
26%20%20%20%13%
60
16th to endDay
7%26%17%32%14%1
64
January1st to 15thNight
17%5%10%30%28%6%
720
16th to endNight
18%6%11%28%26%7%
768
February1st to 15thNight
15%8%14%28%28%5%
704
16th to endNight
16%9%20%27%20%5%
632
March1st to 15thNight
17%9%14%26%26%5%
720
16th to endNight
15%9%22%28%21%3
740
April1st to 15thNight
10%12%25%29%18%3
659
16th to endNight
7%11%24%25%24%6%
660
May1st to 15thNight
4322%34%28%6%
547
16th to endNight
9%7%20%32%23%5%
385
June1st to 15thNight
45%23%37%24%3
330
16th to endNight
2312%41%35%4
330
July1st to 15thNight
4110%33%38%11%
373
16th to endNight
5%28%25%43%13%
522
August1st to 15thNight
6%212%29%39%9%
496
16th to endNight
4213%31%39%8%
700
September1st to 15thNight
318%26%45%13%
660
16th to endNight
4212%27%39%13%
656
October1st to 15thNight
6%5%12%30%33%10%
660
16th to endNight
10%411%24%33%15%
704
November1st to 15thNight
10%213%29%36%8%
700
16th to endNight
10%6%12%31%30%7%
720
December1st to 15thNight
19%7%14%27%24%7%
720
16th to endNight
21%9%16%29%20%2
768
Page generated at 2017-03-25 09:39:47. Version ac04

Copyright 2017 A. Danko


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