Telescope Row
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Telescope Row clear sky chart from 2005-11-05 to 2017-09-16.

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
66%
15415
29%
46905
25%
15379
70%
15379
40%
25437

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
60%
716
20%
2392
21%
716
63%
716
30%
1410
January16th to endNight
56%
768
25%
2496
25%
768
60%
768
27%
1525
February1st to 15thNight
56%
700
25%
2273
24%
700
62%
700
26%
1408
February16th to endNight
50%
632
25%
1895
21%
632
57%
632
27%
1205
March1st to 15thNight
51%
720
19%
2022
17%
720
55%
720
27%
1344
March16th to endNight
50%
768
21%
2078
15%
768
55%
768
30%
1334
April1st to 15thNight
48%
719
22%
1799
11%
719
53%
719
30%
1199
April16th to endNight
54%
720
25%
1800
11%
720
58%
720
41%
1072
May1st to 15thNight
66%
644
28%
1724
18%
644
69%
644
54%
880
May16th to endNight
68%
382
28%
1504
27%
382
75%
382
41%
661
June1st to 15thNight
71%
360
29%
1440
30%
360
79%
360
44%
607
June16th to endNight
87%
360
38%
1440
48%
360
90%
360
67%
479
July1st to 15thNight
92%
369
34%
1389
42%
369
93%
369
71%
469
July16th to endNight
92%
564
37%
1593
34%
531
93%
531
67%
670
August1st to 15thNight
89%
577
37%
1650
29%
574
89%
574
65%
727
August16th to endNight
92%
764
43%
1910
29%
764
92%
764
77%
884
September1st to 15thNight
89%
720
42%
1800
31%
720
90%
720
74%
857
September16th to endNight
83%
660
42%
1801
38%
660
85%
660
62%
854
October1st to 15thNight
72%
660
30%
1980
31%
660
76%
660
46%
1013
October16th to endNight
72%
704
35%
2112
36%
704
76%
704
46%
1093
November1st to 15thNight
66%
700
29%
2196
28%
700
71%
700
40%
1172
November16th to endNight
62%
720
26%
2403
27%
720
67%
720
33%
1338
December1st to 15thNight
54%
720
23%
2520
20%
720
60%
720
25%
1533
December16th to endNight
48%
768
21%
2688
19%
768
54%
768
21%
1703

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
9%413313335%61%
47855
Night
9%423323346%57%
47092
TransparencyDay
26%26%18%25%20%
47541
Night
28%37%17%23%20%
46906
SeeingDay
11%10%24%32%17%4
6000
Night
11%410%29%33%11%
15425

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
16%425%423336%46%
1543
16th to endDay
18%6%35%423335%44%
1728
February1st to 15thDay
18%7%23423345%41%
1591
16th to endDay
21%7%24433345%38%
1579
March1st to 15thDay
17%6%25%5%35%45%8%34%
1936
16th to endDay
16%6%345%35%5%46%39%
2145
April1st to 15thDay
18%5%34423346%42%
2149
16th to endDay
10%413222336%58%
2160
May1st to 15thDay
5%312213336%66%
2223
16th to endDay
6%5%23322346%60%
2606
June1st to 15thDay
5%412212326%65%
2520
16th to endDay
1111112383%
2520
July1st to 15thDay
11221285%
2485
16th to endDay
1222383%
2468
August1st to 15thDay
211121482%
2301
16th to endDay
11112485%
2292
September1st to 15thDay
1111122382%
2160
16th to endDay
321121223474%
1846
October1st to 15thDay
6%213313346%63%
1650
16th to endDay
7%413313335%60%
1760
November1st to 15thDay
10%5%33324345%52%
1663
16th to endDay
14%6%23323345%50%
1554
December1st to 15thDay
17%7%45%42343441%
1440
16th to endDay
19%7%35%423346%38%
1536
January1st to 15thNight
14%423425%45%7%45%
2392
16th to endNight
17%6%24313446%45%
2496
February1st to 15thNight
16%6%2432445%7%42%
2261
16th to endNight
18%6%25%323447%41%
1895
March1st to 15thNight
17%7%34424337%41%
2022
16th to endNight
15%5%3443335%8%42%
2078
April1st to 15thNight
14%6%245%25%45%7%42%
1799
16th to endNight
7%5%23313347%57%
1800
May1st to 15thNight
3323212339%63%
1724
16th to endNight
5%41332335%8%59%
1504
June1st to 15thNight
3223313337%65%
1440
16th to endNight
11111222382%
1440
July1st to 15thNight
112225%81%
1471
16th to endNight
1212236%76%
1701
August1st to 15thNight
1111212335%75%
1659
16th to endNight
112335%79%
1910
September1st to 15thNight
11121223479%
1800
16th to endNight
22211232473%
1801
October1st to 15thNight
6%323213336%61%
1980
16th to endNight
6%313323345%61%
2112
November1st to 15thNight
9%423213347%55%
2196
16th to endNight
9%5%24423447%51%
2403
December1st to 15thNight
16%6%335%24345%44%
2520
16th to endNight
19%7%23433335%42%
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%39%20%16%10%
1543
16th to endDay
43%36%14%19%13%
1728
February1st to 15thDay
43%26%19%20%6%
1591
16th to endDay
48%36%22%15%4
1579
March1st to 15thDay
47%48%18%15%6%
1936
16th to endDay
44%5%11%18%16%3
2145
April1st to 15thDay
42%311%19%19%3
2149
16th to endDay
27%412%24%23%8%
2160
May1st to 15thDay
19%37%28%32%8%
2223
16th to endDay
26%29%28%26%7%
2610
June1st to 15thDay
21%38%23%25%18%
2520
16th to endDay
8%1316%33%35%
2520
July1st to 15thDay
7%117%25%56%
2338
16th to endDay
7%129%27%51%
2313
August1st to 15thDay
9%1112%29%46%
2285
16th to endDay
6%113%38%40%
2292
September1st to 15thDay
8%1114%36%37%
2160
16th to endDay
14%2325%32%22%
1846
October1st to 15thDay
21%38%21%25%20%
1650
16th to endDay
25%37%20%26%16%
1760
November1st to 15thDay
32%38%21%23%9%
1663
16th to endDay
36%28%18%28%5%
1554
December1st to 15thDay
45%37%16%19%6%
1440
16th to endDay
45%310%15%17%7%
1536
January1st to 15thNight
36%49%20%18%10%
2392
16th to endNight
39%48%12%16%18%
2496
February1st to 15thNight
41%26%19%19%9%
2273
16th to endNight
41%39%24%15%5%
1895
March1st to 15thNight
43%38%19%15%8%
2022
16th to endNight
39%311%18%17%8%
2078
April1st to 15thNight
39%5%11%21%18%3
1799
16th to endNight
27%410%23%23%10%
1800
May1st to 15thNight
20%28%22%33%13%
1725
16th to endNight
23%29%24%31%8%
1504
June1st to 15thNight
18%38%20%22%25%
1440
16th to endNight
9%1213%30%42%
1440
July1st to 15thNight
7%11424%60%
1389
16th to endNight
11%228%25%50%
1593
August1st to 15thNight
13%110%28%45%
1650
16th to endNight
8%119%36%42%
1910
September1st to 15thNight
9%2110%29%46%
1800
16th to endNight
15%2120%32%28%
1801
October1st to 15thNight
23%36%21%23%22%
1980
16th to endNight
24%25%21%27%18%
2112
November1st to 15thNight
28%39%21%25%11%
2196
16th to endNight
32%37%21%23%11%
2403
December1st to 15thNight
41%38%16%21%9%
2520
16th to endNight
44%410%14%17%9%
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
27%11%27%21%9%1
171
16th to endDay
21%10%27%22%14%3
256
February1st to 15thDay
22%15%22%23%15%1
239
16th to endDay
23%15%27%22%9%1
238
March1st to 15thDay
22%16%22%21%12%4
270
16th to endDay
21%17%30%20%8%1
288
April1st to 15thDay
23%20%29%18%7%
269
16th to endDay
14%22%32%21%8%1
270
May1st to 15thDay
11%14%36%27%7%2
288
16th to endDay
11%13%23%29%16%5%
330
June1st to 15thDay
8%13%31%29%12%4
315
16th to endDay
1424%43%17%7%
315
July1st to 15thDay
1115%45%29%6%
305
16th to endDay
13%49%25%9%
327
August1st to 15thDay
1120%37%30%7%
315
16th to endDay
1117%39%28%11%
332
September1st to 15thDay
317%46%23%7%
315
16th to endDay
6%8%16%42%20%5%
258
October1st to 15thDay
9%10%25%36%12%4
255
16th to endDay
12%6%31%34%13%
272
November1st to 15thDay
10%9%16%23%31%8%
169
16th to endDay
12%10%29%36%7%3
79
December1st to 15thDay
23%21%20%25%10%
60
16th to endDay
17%14%10%29%21%6%
64
January1st to 15thNight
15%410%30%27%11%
720
16th to endNight
19%49%29%23%12%
768
February1st to 15thNight
19%6%10%29%25%8%
704
16th to endNight
20%6%13%31%20%6%
632
March1st to 15thNight
19%7%12%27%26%7%
720
16th to endNight
17%8%15%28%24%4
768
April1st to 15thNight
17%9%15%31%21%4
719
16th to endNight
10%9%20%27%22%9%
720
May1st to 15thNight
4418%33%30%8%
645
16th to endNight
6%412%31%36%8%
383
June1st to 15thNight
3413%36%35%6%
360
16th to endNight
26%36%47%6%
360
July1st to 15thNight
1126%55%14%
369
16th to endNight
117%55%23%
564
August1st to 15thNight
1226%54%15%
577
16th to endNight
1224%54%16%
764
September1st to 15thNight
2326%49%16%
720
16th to endNight
325%31%39%17%
660
October1st to 15thNight
8%38%31%33%15%
660
16th to endNight
8%28%29%30%19%
704
November1st to 15thNight
10%312%30%30%12%
700
16th to endNight
11%311%32%28%12%
720
December1st to 15thNight
18%5%10%31%25%8%
720
16th to endNight
21%9%11%30%22%5%
768
Page generated at 2017-09-17 09:05:41. Version ac04

Copyright 2017 A. Danko


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