Tehachapi Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tehachapi Mountain Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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%
15677
32%
46842
24%
15638
65%
15638
45%
23838

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
49%
716
24%
2485
18%
716
58%
716
32%
1347
January16th to endNight
47%
768
29%
2431
23%
768
57%
768
31%
1400
February1st to 15thNight
47%
700
28%
2112
23%
700
55%
700
32%
1246
February16th to endNight
45%
632
25%
1895
22%
632
52%
632
30%
1159
March1st to 15thNight
47%
720
21%
2160
19%
720
53%
720
31%
1277
March16th to endNight
44%
768
25%
1995
14%
768
53%
768
36%
1206
April1st to 15thNight
37%
719
26%
1799
10%
719
45%
719
33%
1101
April16th to endNight
43%
720
31%
1800
11%
720
52%
720
47%
955
May1st to 15thNight
44%
613
30%
1693
15%
613
52%
613
51%
831
May16th to endNight
40%
561
30%
1685
15%
561
52%
561
43%
785
June1st to 15thNight
49%
378
34%
1458
23%
378
67%
378
56%
539
June16th to endNight
63%
360
41%
1440
38%
360
78%
360
75%
436
July1st to 15thNight
82%
340
35%
1360
36%
340
88%
340
65%
456
July16th to endNight
84%
545
38%
1572
33%
510
85%
510
68%
652
August1st to 15thNight
77%
717
38%
1790
23%
713
79%
713
80%
809
August16th to endNight
86%
764
45%
1910
29%
764
88%
764
81%
854
September1st to 15thNight
86%
720
42%
1812
30%
720
89%
720
77%
831
September16th to endNight
78%
664
46%
1837
37%
664
86%
664
74%
771
October1st to 15thNight
64%
660
36%
1859
28%
660
74%
660
53%
920
October16th to endNight
64%
704
38%
2136
35%
704
73%
704
51%
1009
November1st to 15thNight
63%
700
31%
2275
30%
700
70%
700
42%
1141
November16th to endNight
59%
720
29%
2340
28%
720
65%
720
39%
1209
December1st to 15thNight
48%
720
28%
2340
22%
720
58%
720
33%
1318
December16th to endNight
44%
768
25%
2658
23%
768
52%
768
25%
1586

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
2313323335%65%
47925
Night
2324423345%62%
47029
TransparencyDay
19%37%16%26%26%
47612
Night
22%37%17%26%22%
46843
SeeingDay
6%18%37%27%8%1
5889
Night
411%22%32%23%5%
15688

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
4425%5%35%447%52%
1450
16th to endDay
7%7%28%5%34326%48%
1791
February1st to 15thDay
35%36%6%24446%51%
1751
16th to endDay
6%6%36%5%4435%6%46%
1579
March1st to 15thDay
45%25%5%5%6%5%5%9%45%
1800
16th to endDay
35%26%435%35%7%51%
2224
April1st to 15thDay
5%4345%33446%54%
2149
16th to endDay
1313323348%62%
2160
May1st to 15thDay
1213313446%66%
2256
16th to endDay
1323223346%67%
2429
June1st to 15thDay
11112336%75%
2498
16th to endDay
111112286%
2520
July1st to 15thDay
111112225%78%
2520
16th to endDay
211221223475%
2482
August1st to 15thDay
111122283%
2160
16th to endDay
111123482%
2292
September1st to 15thDay
111222482%
2146
16th to endDay
112123481%
1828
October1st to 15thDay
2313312337%65%
1768
16th to endDay
2213323335%67%
1735
November1st to 15thDay
2424423346%60%
1584
16th to endDay
23246%34346%57%
1620
December1st to 15thDay
45%24425%5%6%6%51%
1620
16th to endDay
6%7%45%5%44345%47%
1563
January1st to 15thNight
4436%6%3445%6%49%
2485
16th to endNight
5%6%36%5%3435%6%49%
2431
February1st to 15thNight
36%47%7%24346%48%
2101
16th to endNight
6%447%6%4435%5%45%
1895
March1st to 15thNight
36%36%7%35%5%5%7%45%
2160
16th to endNight
25%37%6%44448%47%
1995
April1st to 15thNight
3435%6%34446%52%
1799
16th to endNight
1323333347%62%
1800
May1st to 15thNight
121331345%6%66%
1693
16th to endNight
1213312236%69%
1684
June1st to 15thNight
112212235%75%
1458
16th to endNight
1121387%
1440
July1st to 15thNight
11111223477%
1440
16th to endNight
2112112125%77%
1681
August1st to 15thNight
1111112384%
1800
16th to endNight
1112384%
1910
September1st to 15thNight
111222382%
1812
16th to endNight
111132382%
1837
October1st to 15thNight
3123323335%66%
1859
16th to endNight
1213423345%66%
2136
November1st to 15thNight
25%16%434345%59%
2275
16th to endNight
2336%5%3435%7%53%
2340
December1st to 15thNight
45%36%5%3445%7%49%
2340
16th to endNight
6%7%46%5%34446%44%
2658

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
29%5%8%19%22%14%
1450
16th to endDay
37%48%13%19%16%
1791
February1st to 15thDay
28%6%7%21%21%14%
1751
16th to endDay
35%5%9%20%25%4
1579
March1st to 15thDay
29%6%13%18%18%13%
1800
16th to endDay
29%411%24%19%10%
2224
April1st to 15thDay
26%411%25%22%9%
2149
16th to endDay
17%315%22%29%11%
2160
May1st to 15thDay
16%38%22%32%15%
2256
16th to endDay
17%37%24%35%10%
2432
June1st to 15thDay
10%35%16%30%33%
2498
16th to endDay
5%136%26%55%
2520
July1st to 15thDay
9%238%19%56%
2371
16th to endDay
13%2412%30%37%
2329
August1st to 15thDay
8%128%24%54%
2146
16th to endDay
7%127%37%43%
2292
September1st to 15thDay
7%1310%29%46%
2146
16th to endDay
8%1211%36%39%
1828
October1st to 15thDay
19%25%18%28%25%
1768
16th to endDay
17%26%14%28%29%
1735
November1st to 15thDay
22%38%15%30%18%
1584
16th to endDay
25%49%16%24%20%
1620
December1st to 15thDay
28%6%9%20%20%14%
1620
16th to endDay
35%6%9%20%17%10%
1563
January1st to 15thNight
31%47%18%22%15%
2485
16th to endNight
33%47%14%20%19%
2431
February1st to 15thNight
33%46%14%22%17%
2112
16th to endNight
35%5%8%20%22%7%
1895
March1st to 15thNight
32%6%9%18%18%14%
2160
16th to endNight
30%412%23%21%7%
1995
April1st to 15thNight
29%5%10%25%21%7%
1799
16th to endNight
19%212%30%26%8%
1800
May1st to 15thNight
15%48%25%36%9%
1694
16th to endNight
16%39%24%38%8%
1685
June1st to 15thNight
10%37%18%33%26%
1458
16th to endNight
5%138%31%50%
1440
July1st to 15thNight
9%2410%22%52%
1360
16th to endNight
11%15%16%27%37%
1572
August1st to 15thNight
7%128%29%49%
1790
16th to endNight
6%128%44%36%
1910
September1st to 15thNight
7%25%11%31%42%
1812
16th to endNight
7%1215%38%34%
1837
October1st to 15thNight
17%3419%29%25%
1859
16th to endNight
17%45%15%29%27%
2136
November1st to 15thNight
24%36%15%28%20%
2275
16th to endNight
26%47%16%22%22%
2340
December1st to 15thNight
30%6%7%16%25%14%
2340
16th to endNight
37%5%9%19%16%11%
2658

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
20%25%39%8%31
78
16th to endDay
13%26%31%22%5%
267
February1st to 15thDay
9%28%28%28%41
266
16th to endDay
13%30%32%19%3
238
March1st to 15thDay
11%28%28%21%9%
270
16th to endDay
10%27%34%20%5%1
288
April1st to 15thDay
14%29%34%14%5%1
269
16th to endDay
9%34%37%11%41
270
May1st to 15thDay
6%25%41%19%5%1
288
16th to endDay
6%24%34%27%6%
330
June1st to 15thDay
119%45%23%9%
315
16th to endDay
111%46%29%8%1
315
July1st to 15thDay
5%41%38%11%3
305
16th to endDay
1135%44%12%3
327
August1st to 15thDay
16%43%34%10%2
315
16th to endDay
339%40%11%5%
332
September1st to 15thDay
16%46%34%8%2
315
16th to endDay
29%40%34%11%1
260
October1st to 15thDay
322%36%32%4
255
16th to endDay
417%36%31%9%
247
November1st to 15thDay
6%10%20%37%24%1
90
16th to endDay
5%23%38%23%8%
90
December1st to 15thDay
12%14%38%28%5%
90
16th to endDay
20%21%30%18%7%1
69
January1st to 15thNight
6%9%28%33%15%6%
720
16th to endNight
8%14%23%32%15%4
768
February1st to 15thNight
414%27%28%19%5%
704
16th to endNight
10%14%25%28%15%4
632
March1st to 15thNight
5%17%25%32%15%4
720
16th to endNight
5%17%27%28%17%2
768
April1st to 15thNight
7%23%27%24%14%3
719
16th to endNight
421%29%25%16%3
720
May1st to 15thNight
314%34%30%14%1
614
16th to endNight
423%28%30%13%
563
June1st to 15thNight
110%37%35%14%1
378
16th to endNight
331%44%20%
360
July1st to 15thNight
210%45%40%1
340
16th to endNight
28%36%46%5%
545
August1st to 15thNight
117%35%38%6%
717
16th to endNight
9%33%43%11%
764
September1st to 15thNight
18%36%43%9%
720
16th to endNight
1414%32%36%10%
664
October1st to 15thNight
37%21%34%27%6%
660
16th to endNight
29%19%29%27%10%
704
November1st to 15thNight
49%19%33%25%8%
700
16th to endNight
49%21%34%22%6%
720
December1st to 15thNight
6%11%27%32%17%3
720
16th to endNight
11%13%26%31%13%2
768
Page generated at 2017-09-18 05:38:19. Version ac04

Copyright 2017 A. Danko


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