Union City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Union City clear sky chart from 2005-11-05 to 2017-10-06.

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
37%
15995
15%
47012
10%
15953
41%
15953
21%
32948

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
16%
900
9%
2506
3%
895
20%
895
12%
2016
January16th to endNight
18%
928
6%
2656
2%
928
21%
928
10%
2215
February1st to 15thNight
18%
701
9%
2193
4%
701
23%
701
12%
1696
February16th to endNight
24%
631
12%
1893
5%
631
30%
631
13%
1443
March1st to 15thNight
27%
720
13%
2121
9%
720
31%
720
18%
1539
March16th to endNight
30%
751
17%
2095
9%
751
37%
751
20%
1477
April1st to 15thNight
30%
539
13%
1797
9%
539
36%
539
19%
1221
April16th to endNight
36%
540
20%
1638
10%
540
44%
540
24%
1090
May1st to 15thNight
35%
540
14%
1620
8%
540
41%
540
21%
1128
May16th to endNight
48%
562
16%
1609
10%
561
53%
561
30%
1013
June1st to 15thNight
53%
540
16%
1440
10%
540
57%
540
35%
901
June16th to endNight
59%
540
16%
1440
12%
540
62%
540
33%
908
July1st to 15thNight
65%
510
16%
1360
14%
510
66%
510
39%
811
July16th to endNight
68%
564
21%
1445
17%
531
70%
531
40%
842
August1st to 15thNight
70%
539
21%
1609
18%
536
73%
536
37%
928
August16th to endNight
64%
573
21%
1819
19%
573
68%
573
33%
1052
September1st to 15thNight
62%
626
26%
1886
23%
626
66%
626
36%
1088
September16th to endNight
57%
717
26%
1980
21%
717
61%
717
36%
1206
October1st to 15thNight
47%
684
23%
1917
17%
684
52%
684
30%
1228
October16th to endNight
27%
704
16%
2258
10%
704
35%
704
18%
1578
November1st to 15thNight
35%
700
20%
2276
16%
700
41%
700
21%
1500
November16th to endNight
26%
720
13%
2340
10%
720
30%
720
14%
1763
December1st to 15thNight
16%
806
7%
2426
3%
806
21%
806
9%
2004
December16th to endNight
13%
960
7%
2688
2%
960
18%
960
8%
2301

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
14%8%47%6%35%5%5%7%33%
48189
Night
15%9%46%5%34446%34%
47184
Cloud CoverDay
14%8%47%5%35%5%5%7%33%
48198
Night
15%9%46%5%34446%34%
47189
TransparencyDay
49%5%12%20%11%1
47879
Night
49%411%20%11%1
47012
SeeingDay
16%8%25%25%16%7%
5997
Night
19%8%27%29%13%1
15999

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
18%15%6%11%9%46%44414%
1432
16th to endDay
13%17%9%12%9%5%6%43412%
1566
February1st to 15thDay
14%14%5%11%9%46%5%45%17%
1666
16th to endDay
15%12%7%12%7%45%5%5%5%18%
1580
March1st to 15thDay
15%11%5%8%7%45%5%5%7%24%
1829
16th to endDay
18%8%37%5%35%446%30%
2139
April1st to 15thDay
20%11%45%5%24345%31%
2151
16th to endDay
16%7%25%425%45%7%37%
2322
May1st to 15thDay
19%8%36%6%35%35%6%31%
2331
16th to endDay
12%6%25%4245%5%8%40%
2503
June1st to 15thDay
9%5%35%6%36%45%8%41%
2520
16th to endDay
10%5%346%45%6%7%9%36%
2520
July1st to 15thDay
6%4245%35%6%6%8%45%
2520
16th to endDay
7%325%5%45%6%7%10%41%
2625
August1st to 15thDay
7%325%5%46%6%6%10%40%
2340
16th to endDay
11%5%26%5%35%5%5%8%40%
2381
September1st to 15thDay
12%425%425%45%7%44%
2061
16th to endDay
11%5%25%4235%6%9%43%
1980
October1st to 15thDay
15%6%37%5%3445%6%38%
1840
16th to endDay
21%8%36%5%3445%7%29%
1612
November1st to 15thDay
14%8%26%5%2435%5%39%
1582
16th to endDay
18%16%5%9%6%34445%21%
1620
December1st to 15thDay
16%15%10%9%6%24446%18%
1533
16th to endDay
21%17%7%12%7%3444412%
1536
January1st to 15thNight
21%15%6%8%7%34345%18%
2506
16th to endNight
13%13%9%12%9%45%45%5%15%
2656
February1st to 15thNight
14%15%6%9%6%35%435%24%
2191
16th to endNight
16%10%5%9%7%45%446%25%
1893
March1st to 15thNight
16%11%47%5%23346%33%
2108
16th to endNight
15%7%47%5%3445%6%33%
2095
April1st to 15thNight
18%8%36%43445%7%32%
1797
16th to endNight
17%7%245%3345%6%38%
1638
May1st to 15thNight
20%6%35%5%34348%33%
1620
16th to endNight
11%6%245%245%5%8%43%
1607
June1st to 15thNight
10%5%25%5%3335%9%46%
1440
16th to endNight
7%4245%25%5%7%10%43%
1440
July1st to 15thNight
6%3144245%5%8%52%
1440
16th to endNight
6%4135%245%5%9%51%
1543
August1st to 15thNight
5%3144346%5%9%50%
1620
16th to endNight
9%5%24424446%50%
1819
September1st to 15thNight
11%413424446%51%
1886
16th to endNight
12%5%24423445%50%
1980
October1st to 15thNight
14%6%25%42345%6%44%
1917
16th to endNight
21%9%36%433346%33%
2258
November1st to 15thNight
14%10%35%5%23446%37%
2276
16th to endNight
20%11%6%8%5%3345%6%25%
2340
December1st to 15thNight
20%15%7%10%7%3433418%
2426
16th to endNight
22%17%6%10%6%4444414%
2688

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
18%15%6%11%8%46%445%14%
1432
16th to endDay
13%17%9%11%9%6%6%33413%
1566
February1st to 15thDay
14%14%6%11%8%46%5%45%18%
1666
16th to endDay
15%12%7%12%7%445%5%5%18%
1580
March1st to 15thDay
16%10%5%8%6%45%5%5%7%24%
1839
16th to endDay
18%8%46%435%446%30%
2138
April1st to 15thDay
20%12%45%5%34445%31%
2151
16th to endDay
16%7%35%42445%7%37%
2322
May1st to 15thDay
19%8%36%6%35%45%7%30%
2331
16th to endDay
13%6%25%4245%5%8%40%
2503
June1st to 15thDay
9%5%25%5%46%45%8%41%
2520
16th to endDay
10%5%245%45%6%7%9%36%
2520
July1st to 15thDay
6%425%435%6%6%8%45%
2520
16th to endDay
7%325%5%46%6%6%10%41%
2625
August1st to 15thDay
7%425%5%46%7%6%9%41%
2340
16th to endDay
11%5%25%6%35%5%5%8%40%
2381
September1st to 15thDay
12%325%425%45%7%43%
2061
16th to endDay
11%5%25%42445%9%43%
1980
October1st to 15thDay
14%5%37%5%3446%6%38%
1840
16th to endDay
21%8%26%6%34447%29%
1612
November1st to 15thDay
14%8%36%5%3446%5%39%
1582
16th to endDay
18%15%6%9%5%34345%21%
1620
December1st to 15thDay
16%15%9%9%6%2445%6%18%
1533
16th to endDay
21%17%7%11%7%345%3412%
1536
January1st to 15thNight
21%15%6%8%6%24445%19%
2506
16th to endNight
13%13%9%12%9%45%45%5%15%
2656
February1st to 15thNight
14%15%6%10%5%35%345%24%
2184
16th to endNight
16%10%6%9%7%45%446%25%
1893
March1st to 15thNight
17%10%47%5%24336%32%
2121
16th to endNight
15%7%47%6%3445%6%34%
2095
April1st to 15thNight
18%8%36%43445%7%32%
1797
16th to endNight
17%7%25%5%2345%7%38%
1638
May1st to 15thNight
20%7%35%5%34347%33%
1619
16th to endNight
11%6%25%425%45%8%43%
1607
June1st to 15thNight
10%5%245%3246%9%45%
1440
16th to endNight
7%325%5%35%5%7%10%43%
1440
July1st to 15thNight
6%3235%2445%8%53%
1440
16th to endNight
5%4145%235%6%9%51%
1543
August1st to 15thNight
5%324435%6%5%9%49%
1620
16th to endNight
10%5%24424447%49%
1819
September1st to 15thNight
11%31342436%6%52%
1886
16th to endNight
12%5%24423446%50%
1980
October1st to 15thNight
14%5%25%424446%44%
1917
16th to endNight
21%8%35%433336%34%
2258
November1st to 15thNight
15%10%35%5%2345%6%37%
2276
16th to endNight
21%11%6%7%5%33446%25%
2340
December1st to 15thNight
20%16%7%10%6%33335%18%
2426
16th to endNight
22%16%6%10%6%4444414%
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
70%5%11%9%3
1433
16th to endDay
74%410%7%3
1566
February1st to 15thDay
65%5%8%13%5%
1668
16th to endDay
66%5%10%12%5%
1580
March1st to 15thDay
58%5%13%16%6%
1839
16th to endDay
53%414%20%6%
2139
April1st to 15thDay
54%410%21%10%
2151
16th to endDay
45%414%18%13%3
2322
May1st to 15thDay
52%6%11%20%8%
2331
16th to endDay
40%5%14%26%11%1
2507
June1st to 15thDay
39%5%12%26%15%1
2520
16th to endDay
40%7%13%20%16%1
2520
July1st to 15thDay
34%5%11%24%21%2
2371
16th to endDay
33%7%15%24%15%2
2460
August1st to 15thDay
35%7%14%25%14%2
2327
16th to endDay
39%6%10%25%14%2
2381
September1st to 15thDay
38%5%12%24%17%1
2061
16th to endDay
36%411%28%18%
1980
October1st to 15thDay
44%411%25%12%1
1840
16th to endDay
53%414%19%7%
1612
November1st to 15thDay
45%411%23%13%1
1582
16th to endDay
64%410%16%4
1620
December1st to 15thDay
65%412%13%3
1533
16th to endDay
73%411%7%2
1536
January1st to 15thNight
65%411%13%4
2506
16th to endNight
69%5%12%10%2
2656
February1st to 15thNight
62%411%16%41
2193
16th to endNight
60%411%18%4
1893
March1st to 15thNight
53%412%18%9%1
2121
16th to endNight
49%5%12%22%9%1
2095
April1st to 15thNight
49%411%19%14%
1797
16th to endNight
44%410%19%16%3
1638
May1st to 15thNight
49%411%21%10%2
1620
16th to endNight
37%6%14%25%14%2
1609
June1st to 15thNight
33%6%12%27%17%1
1440
16th to endNight
33%7%17%21%17%1
1440
July1st to 15thNight
29%6%14%25%21%2
1360
16th to endNight
27%7%15%24%21%3
1445
August1st to 15thNight
29%6%12%29%19%2
1609
16th to endNight
32%5%10%25%20%4
1819
September1st to 15thNight
32%49%30%20%2
1886
16th to endNight
34%39%30%20%1
1980
October1st to 15thNight
39%410%25%19%
1917
16th to endNight
52%310%23%8%1
2258
November1st to 15thNight
46%311%21%14%2
2276
16th to endNight
59%412%19%4
2340
December1st to 15thNight
69%48%12%4
2426
16th to endNight
72%49%9%3
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
23%15%38%13%8%
90
16th to endDay
30%9%41%15%3
96
February1st to 15thDay
21%18%43%14%2
90
16th to endDay
18%16%35%22%7%
81
March1st to 15thDay
29%13%32%19%4
129
16th to endDay
28%9%32%18%9%2
288
April1st to 15thDay
27%10%30%24%6%1
270
16th to endDay
20%8%31%20%11%7%
270
May1st to 15thDay
24%7%25%26%10%5%
288
16th to endDay
18%9%26%22%15%7%
403
June1st to 15thDay
12%6%27%32%15%6%
495
16th to endDay
12%8%28%28%16%5%
495
July1st to 15thDay
10%326%25%22%10%
475
16th to endDay
8%220%31%25%11%
485
August1st to 15thDay
9%214%28%25%19%
313
16th to endDay
13%317%24%26%14%
332
September1st to 15thDay
13%318%22%28%14%
315
16th to endDay
13%6%12%26%30%11%
314
October1st to 15thDay
16%7%21%34%13%6%
278
16th to endDay
24%12%31%26%5%
124
November1st to 15thDay
414%26%35%14%4
90
16th to endDay
32%20%33%10%4
90
December1st to 15thDay
27%28%25%15%2
90
16th to endDay
27%32%35%5%
96
January1st to 15thNight
27%13%33%20%4
900
16th to endNight
17%12%36%27%5%
928
February1st to 15thNight
22%12%38%23%3
704
16th to endNight
21%12%33%27%4
631
March1st to 15thNight
22%10%33%24%8%
720
16th to endNight
18%10%33%28%8%
751
April1st to 15thNight
21%10%33%28%6%
539
16th to endNight
21%5%32%29%8%1
540
May1st to 15thNight
24%5%27%31%10%
540
16th to endNight
15%426%36%16%1
563
June1st to 15thNight
12%322%44%17%
540
16th to endNight
9%121%45%20%1
540
July1st to 15thNight
9%116%44%25%3
510
16th to endNight
6%216%42%30%2
564
August1st to 15thNight
8%12%46%26%5%
539
16th to endNight
11%112%34%32%6%
573
September1st to 15thNight
13%216%32%28%6%
626
16th to endNight
14%417%28%29%5%
717
October1st to 15thNight
18%6%23%32%18%1
684
16th to endNight
24%11%32%24%7%
704
November1st to 15thNight
20%11%28%28%10%1
700
16th to endNight
27%12%27%25%6%
720
December1st to 15thNight
28%12%33%20%4
806
16th to endNight
30%12%35%18%3
960
Page generated at 2017-10-07 14:07:55. Version ac04

Copyright 2017 A. Danko


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