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Tracy Airport
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tracy Airport clear sky chart from 2005-11-06 to 2024-01-13.

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
68%
23645
33%
74711
27%
23600
75%
23600
49%
36070

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 10thNight
54%
757
20%
2604
19%
756
59%
756
31%
1451
January11th to 20thNight
61%
728
24%
2366
22%
728
69%
728
34%
1330
January21st to endNight
57%
792
27%
2574
25%
792
63%
792
33%
1442
February1st to 10thNight
58%
720
29%
2340
25%
720
67%
720
36%
1263
February11th to 20thNight
56%
700
31%
2152
25%
700
67%
700
41%
1114
February21st to endNight
52%
592
30%
1776
22%
592
63%
592
40%
958
March1st to 10thNight
53%
720
22%
2066
17%
720
59%
720
33%
1244
March11th to 20thNight
55%
720
29%
1980
22%
720
62%
720
39%
1140
March21st to endNight
49%
792
25%
2112
13%
792
59%
792
41%
1206
April1st to 10thNight
53%
720
27%
1800
13%
720
60%
720
42%
1065
April11th to 20thNight
53%
711
35%
1779
13%
711
62%
711
50%
970
April21st to endNight
56%
720
33%
1800
13%
720
65%
720
61%
905
May1st to 10thNight
62%
706
32%
1786
16%
706
68%
706
64%
876
May11th to 20thNight
73%
417
41%
1479
35%
417
81%
417
67%
540
May21st to endNight
71%
388
35%
1552
32%
388
82%
388
64%
511
June1st to 10thNight
69%
360
33%
1440
32%
360
80%
360
58%
512
June11th to 20thNight
76%
360
41%
1440
43%
360
88%
360
77%
417
June21st to endNight
88%
360
41%
1440
50%
360
94%
360
79%
429
July1st to 10thNight
93%
350
41%
1400
51%
350
96%
350
86%
392
July11th to 20thNight
94%
430
40%
1474
42%
430
96%
430
83%
486
July21st to endNight
92%
591
42%
1674
36%
558
93%
558
77%
653
August1st to 10thNight
90%
537
42%
1602
34%
534
92%
534
76%
627
August11th to 20thNight
88%
686
43%
1754
26%
686
91%
686
84%
758
August21st to endNight
93%
792
46%
1980
30%
792
94%
792
88%
846
September1st to 10thNight
89%
720
48%
1800
33%
720
92%
720
89%
766
September11th to 20thNight
83%
720
49%
1800
35%
720
88%
720
80%
809
September21st to endNight
82%
720
46%
2019
41%
720
88%
720
78%
825
October1st to 10thNight
75%
720
37%
2160
33%
720
85%
720
67%
903
October11th to 20thNight
76%
720
42%
2160
41%
720
84%
720
64%
926
October21st to endNight
74%
792
43%
2376
41%
792
82%
792
65%
1014
November1st to 10thNight
71%
740
35%
2310
32%
740
80%
740
54%
1072
November11th to 20thNight
68%
760
32%
2470
30%
760
75%
760
45%
1198
November21st to endNight
67%
760
31%
2565
30%
760
75%
760
44%
1242
December1st to 10thNight
56%
760
24%
2660
20%
760
65%
760
33%
1448
December11th to 20thNight
55%
759
20%
3216
21%
759
62%
759
20%
2032
December21st to endNight
48%
825
15%
4805
19%
817
59%
817
17%
2700

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
5%313323346%68%
74714
Night
6%313323346%66%
75023
TransparencyDay
20%28%20%27%23%
74430
Night
21%29%20%25%23%
74828
SeeingDay
6%7%20%31%26%10%
14190
Night
7%417%35%31%6%
23665

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 10thDay
14%7%35%8%45%45%9%36%
1557
11th to 20thDay
8%5%347%345%6%7%49%
1639
21st to endDay
10%6%36%6%35%6%6%8%43%
1782
February1st to 10thDay
12%5%25%43446%5%50%
1620
11th to 20thDay
8%5%24445%45%7%52%
1696
21st to endDay
11%415%3245%5%7%53%
1480
March1st to 10thDay
9%6%37%5%35%5%6%9%42%
1890
11th to 20thDay
9%6%26%5%35%5%6%8%44%
1980
21st to endDay
9%424435%6%5%8%52%
2242
April1st to 10thDay
9%5%2442446%7%53%
2160
11th to 20thDay
7%32332335%6%64%
2129
21st to endDay
4212223346%71%
2160
May1st to 10thDay
3212213347%71%
2169
11th to 20thDay
2212213345%75%
2413
21st to endDay
2212223346%74%
2723
June1st to 10thDay
2211222347%73%
2520
11th to 20thDay
1111225%86%
2520
21st to endDay
11111112288%
2520
July1st to 10thDay
1111392%
2520
11th to 20thDay
111122388%
2432
21st to endDay
111222388%
2546
August1st to 10thDay
111121122287%
2328
11th to 20thDay
1111112489%
2146
21st to endDay
11111390%
2376
September1st to 10thDay
1111112291%
2160
11th to 20thDay
1111112335%82%
2160
21st to endDay
21111122482%
1937
October1st to 10thDay
2112222246%77%
1800
11th to 20thDay
312213345%75%
1800
21st to endDay
4312322347%69%
1980
November1st to 10thDay
5%3234335%5%7%59%
1766
11th to 20thDay
6%3245%35%46%8%55%
1710
21st to endDay
8%5%235%2345%8%55%
1611
December1st to 10thDay
8%6%25%5%345%5%8%49%
1520
11th to 20thDay
16%8%48%7%45%46%6%32%
1928
21st to endDay
9%7%36%7%46%6%6%9%37%
2794
January1st to 10thNight
10%6%245%345%6%8%47%
2604
11th to 20thNight
8%6%24435%45%7%51%
2366
21st to endNight
11%4244345%5%8%51%
2574
February1st to 10thNight
12%42433445%6%55%
2340
11th to 20thNight
8%32342446%7%57%
2151
21st to endNight
9%32433345%5%58%
1776
March1st to 10thNight
10%5%25%435%5%6%7%49%
2066
11th to 20thNight
9%5%2443445%7%53%
1980
21st to endNight
8%5%24324446%58%
2112
April1st to 10thNight
7%4144345%5%7%56%
1800
11th to 20thNight
5%323324446%65%
1779
21st to endNight
3112323347%71%
1800
May1st to 10thNight
3212312337%73%
1786
11th to 20thNight
1212112237%78%
1479
21st to endNight
2111111345%80%
1552
June1st to 10thNight
2112222237%76%
1440
11th to 20thNight
111123488%
1440
21st to endNight
1122290%
1440
July1st to 10thNight
111111292%
1440
11th to 20thNight
1111112390%
1522
21st to endNight
11111213484%
1773
August1st to 10thNight
11121122286%
1611
11th to 20thNight
1111122488%
1754
21st to endNight
111112391%
1980
September1st to 10thNight
11112291%
1800
11th to 20thNight
11111122387%
1800
21st to endNight
11111112486%
2019
October1st to 10thNight
322212235%79%
2160
11th to 20thNight
2212212335%77%
2160
21st to endNight
4111212246%76%
2376
November1st to 10thNight
6%31232235%8%67%
2310
11th to 20thNight
6%32333335%8%60%
2470
21st to endNight
7%32332445%6%62%
2565
December1st to 10thNight
10%5%25%5%335%46%54%
2660
11th to 20thNight
15%6%35%6%45%5%6%8%37%
3276
21st to endNight
13%6%36%6%35%5%6%8%39%
4862

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 10thDay
43%415%23%12%3
1557
11th to 20thDay
33%413%23%20%8%
1639
21st to endDay
38%413%18%23%4
1782
February1st to 10thDay
35%39%26%20%7%
1620
11th to 20thDay
33%311%23%24%7%
1706
21st to endDay
32%410%26%23%6%
1480
March1st to 10thDay
38%5%10%25%18%4
1890
11th to 20thDay
37%410%25%19%5%
1980
21st to endDay
31%5%15%23%20%5%
2242
April1st to 10thDay
32%313%25%20%7%
2160
11th to 20thDay
24%311%28%27%7%
2132
21st to endDay
17%210%32%32%7%
2160
May1st to 10thDay
16%28%25%37%12%
2169
11th to 20thDay
14%25%26%36%17%
2416
21st to endDay
14%310%34%30%10%
2724
June1st to 10thDay
14%28%23%34%17%
2520
11th to 20thDay
5%15%20%35%33%
2520
21st to endDay
7%1110%29%52%
2520
July1st to 10thDay
3117%22%65%
2451
11th to 20thDay
6%129%24%57%
2357
21st to endDay
5%116%30%57%
2405
August1st to 10thDay
8%1110%29%51%
2312
11th to 20thDay
419%35%50%
2146
21st to endDay
4119%37%49%
2376
September1st to 10thDay
5%118%29%56%
2160
11th to 20thDay
8%2321%40%27%
2160
21st to endDay
9%1320%39%28%
1937
October1st to 10thDay
12%26%20%31%30%
1800
11th to 20thDay
13%28%24%27%27%
1800
21st to endDay
18%18%21%30%21%
1980
November1st to 10thDay
24%47%27%26%11%
1766
11th to 20thDay
25%312%31%24%5%
1710
21st to endDay
26%212%25%27%8%
1611
December1st to 10thDay
32%413%23%19%8%
1520
11th to 20thDay
50%312%16%15%3
1928
21st to endDay
43%220%22%12%2
2794
January1st to 10thNight
35%316%28%14%5%
2604
11th to 20thNight
33%413%23%16%12%
2366
21st to endNight
33%414%18%23%9%
2574
February1st to 10thNight
30%38%24%24%10%
2340
11th to 20thNight
26%311%24%26%10%
2152
21st to endNight
29%210%28%23%7%
1776
March1st to 10thNight
35%312%22%21%6%
2066
11th to 20thNight
31%310%26%21%10%
1980
21st to endNight
28%412%24%22%9%
2112
April1st to 10thNight
29%413%23%22%11%
1800
11th to 20thNight
22%310%30%22%13%
1779
21st to endNight
15%211%28%34%10%
1800
May1st to 10thNight
13%28%22%35%19%
1786
11th to 20thNight
10%16%25%35%22%
1479
21st to endNight
9%210%32%33%14%
1552
June1st to 10thNight
12%210%19%31%26%
1440
11th to 20thNight
415%16%32%41%
1440
21st to endNight
5%1110%27%57%
1440
July1st to 10thNight
3115%18%73%
1400
11th to 20thNight
4137%22%63%
1474
21st to endNight
8%116%22%62%
1674
August1st to 10thNight
8%119%26%55%
1602
11th to 20thNight
6%119%30%54%
1754
21st to endNight
4117%33%53%
1980
September1st to 10thNight
4127%25%62%
1800
11th to 20thNight
7%1217%37%36%
1800
21st to endNight
7%1217%36%37%
2019
October1st to 10thNight
12%16%20%26%35%
2160
11th to 20thNight
12%26%19%28%33%
2160
21st to endNight
13%16%21%32%27%
2376
November1st to 10thNight
19%210%28%25%17%
2310
11th to 20thNight
23%310%27%30%7%
2470
21st to endNight
23%311%24%28%11%
2565
December1st to 10thNight
31%412%22%18%12%
2660
11th to 20thNight
45%412%18%18%4
3276
21st to endNight
43%217%22%12%4
4862

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 10thDay
24%6%21%31%16%3
218
11th to 20thDay
12%7%23%29%21%8%
347
21st to endDay
11%7%21%29%24%8%
374
February1st to 10thDay
15%9%22%23%21%11%
340
11th to 20thDay
12%13%28%24%18%6%
391
21st to endDay
13%14%25%29%17%3
346
March1st to 10thDay
13%10%25%34%14%3
420
11th to 20thDay
14%12%25%25%19%5%
420
21st to endDay
15%14%25%28%16%2
462
April1st to 10thDay
14%13%27%25%18%4
420
11th to 20thDay
8%14%27%28%16%6%
412
21st to endDay
415%27%28%20%6%
420
May1st to 10thDay
6%13%26%30%18%6%
423
11th to 20thDay
410%27%28%23%7%
448
21st to endDay
39%21%29%26%12%
485
June1st to 10thDay
48%21%32%24%11%
450
11th to 20thDay
27%22%39%23%7%
450
21st to endDay
15%18%37%29%10%
450
July1st to 10thDay
113%38%37%11%
446
11th to 20thDay
11%36%39%13%
444
21st to endDay
9%40%35%16%
487
August1st to 10thDay
3212%36%34%13%
447
11th to 20thDay
1116%35%30%18%
437
21st to endDay
117%39%35%18%
495
September1st to 10thDay
1111%40%36%12%
450
11th to 20thDay
1218%35%30%12%
450
21st to endDay
26%15%34%36%8%
450
October1st to 10thDay
16%22%26%33%11%
450
11th to 20thDay
47%15%26%34%13%
450
21st to endDay
5%6%17%30%29%13%
495
November1st to 10thDay
8%6%19%22%33%12%
362
11th to 20thDay
5%6%19%27%33%11%
270
21st to endDay
8%6%17%33%30%7%
223
December1st to 10thDay
10%10%21%27%21%12%
180
11th to 20thDay
9%14%20%24%22%11%
180
21st to endDay
12%13%23%28%18%6%
198
January1st to 10thNight
14%418%33%23%9%
760
11th to 20thNight
12%415%34%27%7%
728
21st to endNight
12%419%34%25%6%
792
February1st to 10thNight
14%5%16%34%26%5%
720
11th to 20thNight
9%9%21%31%24%7%
704
21st to endNight
10%7%26%36%18%3
592
March1st to 10thNight
13%7%20%34%23%4
720
11th to 20thNight
12%5%22%32%24%5%
720
21st to endNight
11%7%27%33%21%2
792
April1st to 10thNight
10%7%23%37%20%3
720
11th to 20thNight
6%9%27%33%20%5%
711
21st to endNight
38%30%30%24%6%
720
May1st to 10thNight
36%26%38%22%6%
706
11th to 20thNight
3319%41%31%4
417
21st to endNight
3420%38%33%2
389
June1st to 10thNight
3421%39%29%4
360
11th to 20thNight
1418%41%33%4
360
21st to endNight
110%49%35%5%
360
July1st to 10thNight
15%43%48%3
350
11th to 20thNight
336%52%8%
430
21st to endNight
11329%57%9%
591
August1st to 10thNight
2438%48%8%
537
11th to 20thNight
19%41%42%7%
686
21st to endNight
1438%49%8%
792
September1st to 10thNight
18%36%48%7%
720
11th to 20thNight
1212%37%42%7%
720
21st to endNight
2311%32%42%10%
720
October1st to 10thNight
4413%36%36%8%
720
11th to 20thNight
3413%34%37%8%
720
21st to endNight
4314%33%32%14%
792
November1st to 10thNight
6%315%33%34%9%
740
11th to 20thNight
8%315%36%32%7%
760
21st to endNight
8%316%37%29%6%
760
December1st to 10thNight
11%420%34%24%7%
760
11th to 20thNight
15%417%34%25%5%
760
21st to endNight
13%7%22%33%22%3
836
Page generated at 2024-01-09 22:25:06. Version ac07

Copyright 2024 Attilla Danko


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