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.

Starfield Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starfield Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
29%
15512
18%
49068
8%
15480
40%
15480
21%
31914

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
18%
780
20%
2716
6%
776
36%
776
17%
1724
January16th to endNight
16%
832
18%
2912
5%
832
34%
832
15%
1867
February1st to 15thNight
14%
764
17%
2418
4%
761
30%
761
15%
1640
February16th to endNight
21%
683
21%
2049
7%
683
37%
683
18%
1374
March1st to 15thNight
17%
764
17%
2269
6%
764
30%
764
17%
1581
March16th to endNight
23%
768
22%
2058
7%
768
36%
768
24%
1360
April1st to 15thNight
23%
718
18%
1796
5%
718
31%
718
23%
1258
April16th to endNight
26%
557
18%
1637
6%
557
34%
557
21%
1105
May1st to 15thNight
28%
540
15%
1620
7%
540
36%
540
20%
1102
May16th to endNight
30%
415
10%
1537
9%
414
36%
414
13%
1084
June1st to 15thNight
32%
360
11%
1440
9%
360
41%
360
14%
999
June16th to endNight
44%
360
10%
1440
12%
360
49%
360
21%
883
July1st to 15thNight
51%
340
12%
1360
17%
340
55%
340
22%
825
July16th to endNight
55%
376
15%
1418
17%
354
60%
354
24%
836
August1st to 15thNight
50%
509
16%
1580
12%
507
53%
507
27%
992
August16th to endNight
50%
669
22%
1815
13%
669
54%
669
32%
1145
September1st to 15thNight
45%
720
20%
1878
10%
720
50%
720
34%
1184
September16th to endNight
45%
717
28%
1980
17%
717
54%
717
36%
1166
October1st to 15thNight
35%
720
21%
2019
10%
720
45%
720
26%
1314
October16th to endNight
24%
768
19%
2496
8%
768
38%
768
19%
1603
November1st to 15thNight
28%
760
21%
2472
10%
760
43%
760
22%
1563
November16th to endNight
27%
780
22%
2535
10%
780
42%
780
20%
1596
December1st to 15thNight
17%
780
18%
2711
5%
780
33%
780
16%
1781
December16th to endNight
16%
832
19%
2912
5%
832
33%
832
15%
1932

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
17%6%25%42445%6%39%
49562
Night
17%6%25%424446%40%
49238
Cloud CoverDay
17%6%2442445%6%39%
49572
Night
17%6%25%424446%40%
49243
TransparencyDay
44%412%22%14%2
49250
Night
44%411%23%14%2
49068
SeeingDay
22%14%30%20%8%3
6403
Night
21%12%31%25%8%
15512

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
16%7%2442436%6%41%
1552
16th to endDay
15%7%35%335%446%41%
1664
February1st to 15thDay
17%7%36%43446%6%36%
1767
16th to endDay
13%10%35%6%24445%37%
1710
March1st to 15thDay
20%9%35%5%33346%34%
1917
16th to endDay
15%8%36%323245%42%
2164
April1st to 15thDay
17%7%24424346%39%
2152
16th to endDay
19%5%25%424346%40%
2322
May1st to 15thDay
25%7%35%5%24446%30%
2332
16th to endDay
20%5%25%42445%7%35%
2587
June1st to 15thDay
25%7%25%434446%31%
2520
16th to endDay
18%5%25%5%25%5%5%7%35%
2520
July1st to 15thDay
13%5%25%5%35%6%6%9%36%
2520
16th to endDay
13%5%25%5%35%6%7%7%36%
2654
August1st to 15thDay
13%5%246%345%6%9%37%
2355
16th to endDay
11%414425%5%6%8%44%
2384
September1st to 15thDay
14%414424447%46%
2082
16th to endDay
13%413323345%54%
1980
October1st to 15thDay
19%6%25%42434442%
1941
16th to endDay
18%6%2433435%5%42%
1728
November1st to 15thDay
20%6%23223447%43%
1716
16th to endDay
20%6%14323335%44%
1755
December1st to 15thDay
19%6%35%5%23345%39%
1576
16th to endDay
22%9%3442224436%
1664
January1st to 15thNight
14%7%25%43445%6%40%
2716
16th to endNight
14%9%36%5%2445%5%38%
2912
February1st to 15thNight
14%9%45%5%35%446%35%
2417
16th to endNight
15%9%35%5%34335%39%
2049
March1st to 15thNight
19%8%25%5%24445%36%
2256
16th to endNight
16%6%24423345%45%
2058
April1st to 15thNight
18%7%344245%46%38%
1796
16th to endNight
21%7%24423345%39%
1637
May1st to 15thNight
20%6%35%43445%7%34%
1620
16th to endNight
21%7%26%6%36%447%30%
1535
June1st to 15thNight
25%7%25%425%35%6%31%
1440
16th to endNight
18%6%245%2345%7%40%
1440
July1st to 15thNight
14%425%6%26%45%8%38%
1440
16th to endNight
12%414435%5%9%9%39%
1514
August1st to 15thNight
13%4245%345%5%9%41%
1590
16th to endNight
13%42433345%7%45%
1815
September1st to 15thNight
14%414423346%49%
1878
16th to endNight
15%312323247%54%
1980
October1st to 15thNight
17%5%25%424445%43%
2019
16th to endNight
20%6%14424446%40%
2496
November1st to 15thNight
18%5%24424445%43%
2472
16th to endNight
18%6%24424346%43%
2535
December1st to 15thNight
21%8%35%423345%38%
2711
16th to endNight
20%8%25%423445%38%
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
16%7%2342445%6%42%
1552
16th to endDay
15%7%25%315%45%6%41%
1664
February1st to 15thDay
17%6%36%42445%7%36%
1767
16th to endDay
14%10%35%5%2445%5%38%
1710
March1st to 15thDay
22%8%35%5%2435%5%33%
1927
16th to endDay
16%8%25%324346%42%
2164
April1st to 15thDay
18%7%24433446%40%
2152
16th to endDay
19%6%24434446%41%
2322
May1st to 15thDay
24%7%25%5%34445%31%
2332
16th to endDay
20%5%25%42445%7%35%
2587
June1st to 15thDay
26%5%245%2445%6%31%
2520
16th to endDay
18%6%25%5%345%5%8%35%
2520
July1st to 15thDay
13%424435%6%7%8%37%
2520
16th to endDay
12%425%5%35%6%7%8%37%
2654
August1st to 15thDay
13%5%245%35%5%6%9%39%
2355
16th to endDay
11%4143345%5%9%45%
2384
September1st to 15thDay
14%424423446%47%
2082
16th to endDay
14%5%13313245%53%
1980
October1st to 15thDay
19%5%2443334443%
1941
16th to endDay
18%5%2333435%5%42%
1728
November1st to 15thDay
20%5%23323346%43%
1716
16th to endDay
19%6%14323336%44%
1755
December1st to 15thDay
20%6%25%424345%40%
1576
16th to endDay
23%9%34324246%36%
1664
January1st to 15thNight
15%7%3442445%6%40%
2716
16th to endNight
15%9%35%5%2445%5%39%
2912
February1st to 15thNight
14%9%35%5%35%445%36%
2410
16th to endNight
16%8%25%5%24435%39%
2049
March1st to 15thNight
20%8%25%424445%36%
2269
16th to endNight
17%6%24423345%44%
2057
April1st to 15thNight
18%7%34424447%38%
1796
16th to endNight
21%6%25%423345%39%
1637
May1st to 15thNight
20%5%25%43445%7%34%
1620
16th to endNight
21%7%27%5%35%5%46%30%
1535
June1st to 15thNight
25%6%25%5%245%46%31%
1440
16th to endNight
18%6%3442345%7%40%
1440
July1st to 15thNight
14%425%5%35%46%8%38%
1440
16th to endNight
13%414435%5%8%9%38%
1514
August1st to 15thNight
13%5%245%345%6%8%41%
1590
16th to endNight
14%41442445%8%45%
1815
September1st to 15thNight
14%324323446%49%
1878
16th to endNight
14%413312336%53%
1980
October1st to 15thNight
16%5%25%424446%43%
2019
16th to endNight
21%425%423445%41%
2496
November1st to 15thNight
18%5%25%423435%43%
2472
16th to endNight
18%5%24423346%43%
2535
December1st to 15thNight
21%7%35%423346%38%
2711
16th to endNight
20%7%25%42344438%
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%9%24%15%2
1553
16th to endDay
43%312%24%13%1
1664
February1st to 15thDay
46%412%22%12%1
1770
16th to endDay
48%311%20%13%2
1710
March1st to 15thDay
52%312%16%13%3
1927
16th to endDay
44%27%21%17%6%
2164
April1st to 15thDay
45%39%20%16%3
2152
16th to endDay
44%49%21%16%3
2322
May1st to 15thDay
53%38%16%15%2
2332
16th to endDay
46%6%13%19%11%2
2591
June1st to 15thDay
52%412%20%9%1
2520
16th to endDay
45%5%12%21%12%
2520
July1st to 15thDay
39%7%16%23%13%
2371
16th to endDay
41%5%15%22%12%1
2487
August1st to 15thDay
41%5%18%23%10%
2341
16th to endDay
35%415%27%15%1
2384
September1st to 15thDay
36%5%10%26%19%1
2082
16th to endDay
32%39%27%24%2
1980
October1st to 15thDay
44%48%25%15%2
1941
16th to endDay
42%311%26%13%1
1728
November1st to 15thDay
40%413%25%14%1
1716
16th to endDay
43%313%20%18%1
1755
December1st to 15thDay
47%313%20%14%
1576
16th to endDay
51%310%19%13%1
1664
January1st to 15thNight
43%5%11%23%14%2
2716
16th to endNight
46%310%21%15%2
2912
February1st to 15thNight
48%311%19%14%1
2418
16th to endNight
47%310%22%13%3
2049
March1st to 15thNight
50%38%21%13%2
2269
16th to endNight
42%310%18%20%6%
2058
April1st to 15thNight
45%48%20%18%3
1796
16th to endNight
47%39%20%14%4
1637
May1st to 15thNight
47%5%10%19%14%3
1620
16th to endNight
54%5%11%16%9%1
1537
June1st to 15thNight
53%5%10%20%9%1
1440
16th to endNight
42%5%13%22%13%1
1440
July1st to 15thNight
40%6%15%25%11%
1360
16th to endNight
37%6%16%27%10%
1418
August1st to 15thNight
38%6%14%24%14%1
1580
16th to endNight
36%5%11%28%17%
1815
September1st to 15thNight
35%410%29%18%1
1878
16th to endNight
32%47%32%21%2
1980
October1st to 15thNight
41%410%25%14%3
2019
16th to endNight
44%310%27%12%1
2496
November1st to 15thNight
42%411%23%16%2
2472
16th to endNight
43%312%23%15%1
2535
December1st to 15thNight
48%312%22%12%
2711
16th to endNight
49%310%21%13%1
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%25%34%16%1
90
16th to endDay
23%23%41%10%
96
February1st to 15thDay
27%15%37%15%2
271
16th to endDay
21%23%31%18%5%
291
March1st to 15thDay
28%19%34%12%4
312
16th to endDay
22%22%31%14%5%3
288
April1st to 15thDay
28%15%30%15%8%1
270
16th to endDay
23%17%32%15%8%2
270
May1st to 15thDay
35%13%25%16%5%3
288
16th to endDay
24%14%32%19%6%1
331
June1st to 15thDay
24%15%33%18%6%
315
16th to endDay
21%12%38%16%7%2
315
July1st to 15thDay
16%7%33%29%9%3
305
16th to endDay
15%6%32%30%11%3
326
August1st to 15thDay
17%9%27%23%17%3
313
16th to endDay
16%6%26%27%14%8%
332
September1st to 15thDay
17%10%24%28%12%7%
315
16th to endDay
16%8%30%21%9%12%
314
October1st to 15thDay
22%11%21%27%14%2
306
16th to endDay
23%15%32%19%7%
288
November1st to 15thDay
25%12%30%23%7%1
280
16th to endDay
25%17%24%22%7%1
285
December1st to 15thDay
17%26%34%16%3
106
16th to endDay
36%28%27%8%
96
January1st to 15thNight
20%19%38%19%2
780
16th to endNight
23%18%36%19%2
832
February1st to 15thNight
19%18%40%18%1
764
16th to endNight
22%16%33%21%5%
683
March1st to 15thNight
25%16%36%18%2
764
16th to endNight
22%15%33%21%6%
768
April1st to 15thNight
23%15%32%23%4
718
16th to endNight
24%13%30%23%8%
557
May1st to 15thNight
22%9%32%25%7%1
540
16th to endNight
25%7%28%28%7%1
415
June1st to 15thNight
28%8%23%30%10%
360
16th to endNight
21%126%35%14%
360
July1st to 15thNight
16%120%40%18%1
340
16th to endNight
13%319%43%18%2
376
August1st to 15thNight
14%323%40%17%
509
16th to endNight
15%422%35%20%2
669
September1st to 15thNight
15%426%33%18%1
720
16th to endNight
17%426%26%19%5%
717
October1st to 15thNight
19%8%28%25%15%1
720
16th to endNight
25%13%31%22%7%
768
November1st to 15thNight
21%12%31%23%8%1
760
16th to endNight
20%17%29%25%7%
780
December1st to 15thNight
26%14%36%19%3
780
16th to endNight
26%17%35%18%2
832
Page generated at 2018-03-12 13:28:15. Version ac04

Copyright 2018 A. Danko


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