Evergreen
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Evergreen clear sky chart from 2005-11-05 to 2018-02-14.

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
52%
16600
29%
48815
17%
16556
63%
16556
40%
25782

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
39%
974
32%
2716
15%
970
56%
970
40%
1381
January16th to endNight
37%
861
36%
2733
18%
861
58%
861
37%
1352
February1st to 15thNight
35%
755
27%
2433
12%
753
54%
753
36%
1217
February16th to endNight
38%
632
35%
1894
15%
632
59%
632
40%
974
March1st to 15thNight
42%
720
30%
2103
12%
720
57%
720
40%
1108
March16th to endNight
39%
685
29%
2029
14%
685
54%
685
37%
1113
April1st to 15thNight
41%
539
26%
1798
15%
539
57%
539
35%
909
April16th to endNight
39%
540
24%
1800
16%
540
53%
540
28%
1033
May1st to 15thNight
50%
539
20%
1611
15%
539
57%
539
29%
1001
May16th to endNight
59%
563
19%
1498
12%
561
65%
561
37%
883
June1st to 15thNight
70%
540
24%
1440
19%
540
73%
540
54%
737
June16th to endNight
77%
540
28%
1440
23%
540
81%
540
59%
711
July1st to 15thNight
74%
510
19%
1360
16%
510
76%
510
40%
799
July16th to endNight
79%
564
23%
1458
22%
531
80%
531
44%
798
August1st to 15thNight
78%
539
19%
1662
21%
536
78%
536
38%
903
August16th to endNight
75%
573
28%
1910
31%
573
77%
573
38%
1004
September1st to 15thNight
72%
540
29%
1800
28%
540
77%
540
41%
930
September16th to endNight
66%
537
36%
1926
31%
537
76%
537
45%
884
October1st to 15thNight
57%
720
30%
2160
20%
720
65%
720
43%
1140
October16th to endNight
55%
789
36%
2325
20%
789
66%
789
44%
1198
November1st to 15thNight
51%
950
33%
2470
16%
950
61%
950
49%
1297
November16th to endNight
48%
975
37%
2607
18%
975
61%
975
51%
1325
December1st to 15thNight
41%
975
28%
2730
11%
975
55%
975
40%
1443
December16th to endNight
39%
1040
29%
2912
12%
1040
53%
1040
35%
1642

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%5%24425%5%6%8%49%
49271
Night
342332345%7%58%
48991
TransparencyDay
31%410%25%20%7%
48950
Night
24%311%27%24%8%
48815
SeeingDay
10%11%29%29%14%4
6300
Night
5%10%24%38%17%3
16607

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
15%34423348%58%
1552
16th to endDay
1445%32335%8%58%
1853
February1st to 15thDay
6%25%414449%54%
1727
16th to endDay
6%45%313347%58%
1580
March1st to 15thDay
35%2442445%7%53%
1854
16th to endDay
49%25%41445%10%46%
2193
April1st to 15thDay
5%8%25%325%46%7%48%
2150
16th to endDay
10%11%35%5%25%45%6%40%
2160
May1st to 15thDay
10%8%36%6%25%5%5%7%36%
2337
16th to endDay
10%6%25%5%36%5%7%8%37%
2616
June1st to 15thDay
5%3145%35%6%7%10%47%
2520
16th to endDay
2213436%6%8%9%49%
2520
July1st to 15thDay
8%5%246%36%7%7%9%38%
2520
16th to endDay
6%5%26%5%47%6%7%9%38%
2608
August1st to 15thDay
7%5%36%7%36%6%8%9%35%
2288
16th to endDay
6%425%5%36%6%6%8%43%
2292
September1st to 15thDay
8%415%425%45%7%50%
2160
16th to endDay
5%323323346%60%
2032
October1st to 15thDay
6%4133245%46%57%
1800
16th to endDay
45%13322247%60%
1887
November1st to 15thDay
132331335%8%62%
1718
16th to endDay
1325%21435%7%61%
1680
December1st to 15thDay
143443235%8%57%
1560
16th to endDay
25%25%32435%9%55%
1664
January1st to 15thNight
324323347%64%
2716
16th to endNight
15%24413336%62%
2733
February1st to 15thNight
16%23324448%58%
2423
16th to endNight
5%3432346%6%59%
1894
March1st to 15thNight
143422446%8%57%
2103
16th to endNight
5%6%32323347%57%
2029
April1st to 15thNight
46%2321246%7%57%
1798
16th to endNight
10%9%34313336%51%
1800
May1st to 15thNight
11%8%2423345%8%44%
1610
16th to endNight
6%5%233245%6%10%49%
1497
June1st to 15thNight
421313449%64%
1440
16th to endNight
21221336%10%65%
1440
July1st to 15thNight
5%223425%5%7%10%49%
1440
16th to endNight
4123326%5%8%10%50%
1557
August1st to 15thNight
3313425%5%7%8%52%
1671
16th to endNight
5%4144245%5%8%54%
1910
September1st to 15thNight
8%22332345%8%55%
1800
16th to endNight
5%313222446%64%
1926
October1st to 15thNight
6%422213446%61%
2160
16th to endNight
46%23212237%61%
2325
November1st to 15thNight
231322335%7%65%
2470
16th to endNight
1424312348%64%
2607
December1st to 15thNight
1424423348%59%
2730
16th to endNight
15%3442445%8%54%
2912

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
24%311%32%22%5%
1553
16th to endDay
23%39%32%21%7%
1853
February1st to 15thDay
27%314%33%16%5%
1728
16th to endDay
26%26%30%27%6%
1580
March1st to 15thDay
28%210%28%23%5%
1854
16th to endDay
33%411%24%20%5%
2193
April1st to 15thDay
32%5%10%25%18%7%
2150
16th to endDay
43%48%23%16%3
2160
May1st to 15thDay
44%5%12%20%14%2
2337
16th to endDay
41%6%13%21%11%5%
2620
June1st to 15thDay
28%6%14%20%18%11%
2520
16th to endDay
26%6%10%23%24%10%
2520
July1st to 15thDay
37%8%11%18%15%8%
2371
16th to endDay
37%7%13%23%12%5%
2445
August1st to 15thDay
41%7%12%17%13%7%
2273
16th to endDay
34%6%9%22%20%5%
2292
September1st to 15thDay
31%47%24%19%11%
2160
16th to endDay
25%36%26%31%7%
2032
October1st to 15thDay
27%48%24%27%8%
1800
16th to endDay
23%38%26%29%9%
1887
November1st to 15thDay
21%38%27%27%11%
1718
16th to endDay
20%36%26%33%9%
1680
December1st to 15thDay
24%210%33%22%5%
1560
16th to endDay
26%313%26%23%6%
1664
January1st to 15thNight
20%211%31%26%6%
2716
16th to endNight
23%29%28%26%9%
2733
February1st to 15thNight
24%212%35%19%5%
2433
16th to endNight
23%25%32%26%8%
1894
March1st to 15thNight
24%38%28%29%6%
2103
16th to endNight
28%29%30%23%5%
2029
April1st to 15thNight
26%311%28%22%8%
1798
16th to endNight
36%310%27%18%4
1800
May1st to 15thNight
37%5%12%23%16%4
1611
16th to endNight
29%5%19%24%14%6%
1498
June1st to 15thNight
17%417%28%17%13%
1440
16th to endNight
15%411%25%29%13%
1440
July1st to 15thNight
28%6%15%22%17%9%
1360
16th to endNight
23%6%18%30%15%5%
1458
August1st to 15thNight
27%6%17%24%17%7%
1662
16th to endNight
27%411%25%24%6%
1910
September1st to 15thNight
26%312%24%20%12%
1800
16th to endNight
21%38%28%30%7%
1926
October1st to 15thNight
23%49%22%27%11%
2160
16th to endNight
23%37%24%32%9%
2325
November1st to 15thNight
19%38%26%28%13%
2470
16th to endNight
20%18%26%32%10%
2607
December1st to 15thNight
23%313%30%21%8%
2730
16th to endNight
27%413%25%23%4
2912

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
5%11%39%27%13%2
135
16th to endDay
412%38%34%8%1
144
February1st to 15thDay
329%45%20%
130
16th to endDay
325%29%27%12%1
81
March1st to 15thDay
226%42%21%6%
144
16th to endDay
17%29%30%18%3
288
April1st to 15thDay
13%27%30%21%5%2
269
16th to endDay
25%23%29%15%4
270
May1st to 15thDay
17%11%29%29%8%3
411
16th to endDay
15%9%25%28%18%3
517
June1st to 15thDay
7%6%27%32%20%5%
495
16th to endDay
4331%31%20%8%
495
July1st to 15thDay
9%5%17%30%24%11%
475
16th to endDay
8%416%30%27%12%
467
August1st to 15thDay
13%6%24%35%14%4
315
16th to endDay
12%5%25%36%17%3
332
September1st to 15thDay
13%7%29%33%13%2
315
16th to endDay
9%8%33%30%12%6%
189
October1st to 15thDay
6%8%37%27%14%5%
135
16th to endDay
9%7%40%29%10%2
144
November1st to 15thDay
211%31%30%20%4
135
16th to endDay
8%17%38%31%4
135
December1st to 15thDay
6%24%33%30%5%
135
16th to endDay
220%43%28%4
144
January1st to 15thNight
220%31%33%8%3
975
16th to endNight
319%32%34%8%1
861
February1st to 15thNight
316%37%34%7%
760
16th to endNight
217%35%37%6%
632
March1st to 15thNight
315%33%35%10%1
720
16th to endNight
7%12%33%37%6%1
685
April1st to 15thNight
9%13%31%35%8%1
539
16th to endNight
15%9%28%32%12%
540
May1st to 15thNight
16%5%20%40%15%2
540
16th to endNight
7%6%19%43%19%4
563
June1st to 15thNight
6%216%48%22%3
540
16th to endNight
3212%42%34%3
540
July1st to 15thNight
6%15%33%44%7%
510
16th to endNight
43431%48%7%
564
August1st to 15thNight
5%1441%41%6%
539
16th to endNight
6%25%38%36%8%
573
September1st to 15thNight
8%28%40%30%9%
540
16th to endNight
5%317%38%25%8%
537
October1st to 15thNight
7%5%24%40%16%4
720
16th to endNight
6%9%22%39%17%3
789
November1st to 15thNight
412%26%39%14%2
950
16th to endNight
310%31%42%10%1
975
December1st to 15thNight
417%30%39%6%1
975
16th to endNight
416%32%35%9%1
1040
Page generated at 2018-02-15 08:58:42. Version ac04

Copyright 2018 A. Danko


Evergreen Clear Sky Chart |Charts Home