Davis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Davis clear sky chart from 2005-11-05 to 2017-12-20.

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%
15649
30%
48082
25%
15610
72%
15610
45%
24547

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
57%
719
20%
2434
18%
716
62%
716
30%
1390
January16th to endNight
57%
768
25%
2496
23%
768
63%
768
29%
1500
February1st to 15thNight
57%
696
24%
2288
22%
696
63%
696
26%
1384
February16th to endNight
54%
632
27%
1896
21%
632
62%
632
33%
1127
March1st to 15thNight
56%
720
18%
2031
15%
720
60%
720
31%
1288
March16th to endNight
52%
768
23%
2075
15%
768
58%
768
35%
1257
April1st to 15thNight
55%
719
25%
1799
12%
719
61%
719
38%
1127
April16th to endNight
61%
720
27%
1800
12%
720
66%
720
53%
975
May1st to 15thNight
67%
580
31%
1660
21%
580
72%
580
63%
752
May16th to endNight
70%
374
31%
1496
32%
374
78%
374
56%
548
June1st to 15thNight
69%
360
29%
1440
29%
360
80%
360
53%
554
June16th to endNight
78%
360
37%
1440
44%
360
86%
360
72%
453
July1st to 15thNight
87%
340
36%
1360
43%
340
93%
340
76%
412
July16th to endNight
87%
544
40%
1573
35%
511
90%
511
80%
586
August1st to 15thNight
83%
554
39%
1627
28%
551
87%
551
76%
647
August16th to endNight
87%
764
45%
1910
27%
764
89%
764
83%
853
September1st to 15thNight
86%
720
42%
1800
28%
720
89%
720
80%
810
September16th to endNight
80%
716
46%
1955
38%
716
86%
716
75%
845
October1st to 15thNight
72%
720
33%
2160
30%
720
80%
720
58%
986
October16th to endNight
72%
768
39%
2304
38%
768
79%
768
53%
1108
November1st to 15thNight
67%
760
28%
2412
26%
760
74%
760
42%
1250
November16th to endNight
60%
780
25%
2642
26%
780
65%
780
34%
1435
December1st to 15thNight
57%
780
22%
2730
20%
780
63%
780
28%
1585
December16th to endNight
49%
787
23%
2754
18%
787
58%
787
24%
1675

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
7%312212335%64%
48754
Night
8%212212336%63%
48266
TransparencyDay
23%38%19%25%19%
48437
Night
23%39%20%24%19%
48083
SeeingDay
8%416%26%28%15%
6226
Night
9%316%39%28%3
15660

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
17%6%23324346%44%
1501
16th to endDay
17%5%34324435%44%
1728
February1st to 15thDay
17%5%35%413236%45%
1576
16th to endDay
17%5%23334438%44%
1576
March1st to 15thDay
14%5%25%43446%7%42%
1927
16th to endDay
12%5%245%245%6%7%43%
2148
April1st to 15thDay
12%5%244245%5%7%45%
2149
16th to endDay
5%312224336%64%
2160
May1st to 15thDay
3212211237%72%
2285
16th to endDay
322313347%65%
2615
June1st to 15thDay
3212213236%70%
2520
16th to endDay
11113483%
2520
July1st to 15thDay
1111287%
2520
16th to endDay
12387%
2486
August1st to 15thDay
1111112384%
2322
16th to endDay
1112386%
2292
September1st to 15thDay
11111122383%
2160
16th to endDay
211111125%78%
2001
October1st to 15thDay
312212346%70%
1800
16th to endDay
7%32331333464%
1920
November1st to 15thDay
9%31322445%8%54%
1776
16th to endDay
12%5%24423446%48%
1644
December1st to 15thDay
16%8%24423336%44%
1560
16th to endDay
17%7%24323347%43%
1568
January1st to 15thNight
14%424313248%50%
2434
16th to endNight
15%423324336%49%
2496
February1st to 15thNight
15%413424446%46%
2276
16th to endNight
15%323213447%49%
1896
March1st to 15thNight
15%414424447%46%
2031
16th to endNight
13%323323446%51%
2075
April1st to 15thNight
9%413425%447%52%
1799
16th to endNight
6%212212436%67%
1800
May1st to 15thNight
3111111346%73%
1660
16th to endNight
311113347%72%
1496
June1st to 15thNight
32122225%75%
1440
16th to endNight
111111385%
1440
July1st to 15thNight
11111189%
1440
16th to endNight
11111486%
1680
August1st to 15thNight
1111112384%
1636
16th to endNight
11135%83%
1910
September1st to 15thNight
111111484%
1800
16th to endNight
11111225%81%
1955
October1st to 15thNight
3111212345%71%
2160
16th to endNight
413322346%67%
2304
November1st to 15thNight
8%31221335%7%58%
2412
16th to endNight
11%413313345%55%
2642
December1st to 15thNight
16%5%12323346%49%
2730
16th to endNight
20%413213346%46%
2754

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
41%5%13%14%20%3
1501
16th to endDay
43%49%15%18%9%
1728
February1st to 15thDay
42%49%22%16%4
1576
16th to endDay
39%411%26%13%4
1576
March1st to 15thDay
40%5%13%20%13%6%
1927
16th to endDay
38%7%14%17%17%4
2148
April1st to 15thDay
37%5%12%21%18%4
2149
16th to endDay
21%5%12%24%26%9%
2160
May1st to 15thDay
14%28%26%34%12%
2285
16th to endDay
18%412%29%24%10%
2619
June1st to 15thDay
17%310%24%24%19%
2520
16th to endDay
7%1415%37%34%
2520
July1st to 15thDay
5%129%27%53%
2371
16th to endDay
5%1212%24%53%
2330
August1st to 15thDay
7%2212%32%43%
2306
16th to endDay
5%1215%38%36%
2292
September1st to 15thDay
7%2314%35%37%
2160
16th to endDay
12%2421%37%21%
2001
October1st to 15thDay
15%39%20%27%23%
1800
16th to endDay
23%39%23%26%14%
1920
November1st to 15thDay
27%5%13%30%17%5%
1776
16th to endDay
37%6%10%22%18%4
1644
December1st to 15thDay
42%410%18%19%5%
1560
16th to endDay
42%5%11%19%16%4
1568
January1st to 15thNight
34%413%23%17%7%
2434
16th to endNight
37%49%16%17%13%
2496
February1st to 15thNight
39%49%21%17%8%
2288
16th to endNight
33%5%11%26%19%4
1896
March1st to 15thNight
37%5%14%18%16%7%
2031
16th to endNight
33%412%21%21%7%
2075
April1st to 15thNight
32%412%23%18%7%
1799
16th to endNight
19%414%23%27%11%
1800
May1st to 15thNight
11%49%23%34%16%
1661
16th to endNight
12%313%32%25%13%
1496
June1st to 15thNight
14%39%24%28%20%
1440
16th to endNight
7%1414%32%39%
1440
July1st to 15thNight
6%127%27%55%
1360
16th to endNight
6%1210%22%56%
1573
August1st to 15thNight
7%1211%28%47%
1627
16th to endNight
6%1211%35%43%
1910
September1st to 15thNight
7%1411%34%40%
1800
16th to endNight
8%15%21%36%26%
1955
October1st to 15thNight
15%38%20%26%26%
2160
16th to endNight
18%27%22%28%19%
2304
November1st to 15thNight
24%5%12%28%20%8%
2412
16th to endNight
30%49%22%24%8%
2642
December1st to 15thNight
36%410%19%20%8%
2730
16th to endNight
39%5%10%17%20%6%
2754

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
29%219%21%19%7%
129
16th to endDay
17%6%19%18%21%16%
256
February1st to 15thDay
22%5%16%19%25%12%
236
16th to endDay
21%8%18%21%18%11%
237
March1st to 15thDay
17%8%24%17%18%13%
270
16th to endDay
16%12%20%21%21%7%
288
April1st to 15thDay
15%11%23%24%13%12%
269
16th to endDay
7%11%24%24%20%11%
270
May1st to 15thDay
6%322%32%25%9%
288
16th to endDay
5%317%26%29%16%
330
June1st to 15thDay
6%5%22%28%28%9%
315
16th to endDay
113%32%37%14%
315
July1st to 15thDay
8%38%37%14%
305
16th to endDay
11%32%39%16%
327
August1st to 15thDay
2110%32%40%13%
315
16th to endDay
8%27%42%21%
332
September1st to 15thDay
18%30%36%22%
315
16th to endDay
3315%25%26%25%
315
October1st to 15thDay
5%7%18%24%21%22%
315
16th to endDay
9%212%25%28%21%
336
November1st to 15thDay
13%215%19%33%16%
192
16th to endDay
18%211%34%29%2
109
December1st to 15thDay
20%6%15%21%20%16%
90
16th to endDay
19%5%13%30%26%4
72
January1st to 15thNight
15%315%32%28%4
720
16th to endNight
17%413%32%26%6%
768
February1st to 15thNight
17%314%37%24%2
704
16th to endNight
15%320%35%20%3
632
March1st to 15thNight
16%415%34%26%2
720
16th to endNight
15%5%21%35%21%
768
April1st to 15thNight
10%5%21%39%20%2
719
16th to endNight
7%5%22%37%23%2
720
May1st to 15thNight
4222%45%23%1
581
16th to endNight
3122%46%24%
375
June1st to 15thNight
3123%48%22%
360
16th to endNight
118%53%26%
360
July1st to 15thNight
110%59%28%
340
16th to endNight
17%54%32%2
544
August1st to 15thNight
112%53%30%1
554
16th to endNight
9%49%38%1
764
September1st to 15thNight
19%43%41%3
720
16th to endNight
1114%37%37%7%
716
October1st to 15thNight
4316%38%31%5%
720
16th to endNight
5%215%32%34%9%
768
November1st to 15thNight
9%314%35%33%3
760
16th to endNight
12%416%37%24%5%
780
December1st to 15thNight
18%414%32%23%6%
780
16th to endNight
21%7%16%29%22%1
787
Page generated at 2017-12-21 04:04:55. Version ac04

Copyright 2017 A. Danko


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