Leader
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Leader 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
43%
15515
12%
46963
8%
15490
47%
15490
22%
31711

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
36%
895
7%
2685
5%
895
39%
895
16%
1994
January16th to endNight
31%
939
14%
2853
7%
939
39%
939
18%
2026
February1st to 15thNight
43%
697
9%
2282
9%
697
46%
697
18%
1601
February16th to endNight
45%
632
13%
2052
12%
632
49%
632
19%
1461
March1st to 15thNight
38%
720
12%
2064
6%
720
44%
720
21%
1472
March16th to endNight
37%
759
10%
2103
5%
759
42%
759
17%
1571
April1st to 15thNight
36%
539
12%
1729
6%
539
41%
539
18%
1205
April16th to endNight
42%
540
14%
1596
11%
540
45%
540
22%
1102
May1st to 15thNight
51%
539
12%
1440
8%
539
53%
539
29%
944
May16th to endNight
48%
403
7%
1338
7%
402
49%
402
21%
895
June1st to 15thNight
45%
360
1%
1260
1%
360
45%
360
19%
828
June16th to endNight
54%
360
1%
1260
0%
360
54%
360
27%
731
July1st to 15thNight
62%
340
3%
1190
2%
340
63%
340
32%
652
July16th to endNight
64%
376
14%
1239
13%
354
68%
354
41%
593
August1st to 15thNight
67%
527
13%
1502
12%
525
69%
525
39%
858
August16th to endNight
60%
573
22%
1719
17%
573
64%
573
41%
943
September1st to 15thNight
56%
540
18%
1786
17%
540
60%
540
31%
1027
September16th to endNight
52%
701
23%
1990
16%
701
58%
701
38%
1165
October1st to 15thNight
42%
684
18%
2052
11%
684
48%
684
25%
1354
October16th to endNight
41%
756
16%
2249
9%
756
47%
756
24%
1479
November1st to 15thNight
34%
875
16%
2450
7%
875
41%
875
24%
1667
November16th to endNight
33%
900
13%
2544
7%
900
38%
900
19%
1864
December1st to 15thNight
33%
900
7%
2700
4%
900
35%
900
12%
2144
December16th to endNight
36%
960
11%
2880
5%
960
41%
960
16%
2135

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
10%8%36%5%35%5%5%7%37%
48265
Night
8%8%37%6%35%5%5%8%37%
47115
Cloud CoverDay
10%8%36%5%35%5%5%7%37%
48266
Night
8%8%37%6%35%5%5%8%37%
47117
TransparencyDay
44%7%16%21%7%
47916
Night
43%7%16%21%9%1
46969
SeeingDay
14%7%26%29%18%4
6181
Night
12%6%28%34%16%2
15528

By Month

Percentage Cloud Cover NW (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
9%12%6%9%6%46%6%6%8%24%
1253
16th to endDay
313%5%10%7%47%5%5%8%27%
1380
February1st to 15thDay
7%12%7%12%8%5%6%35%7%23%
1575
16th to endDay
7%13%7%11%7%4446%6%25%
1422
March1st to 15thDay
5%9%5%9%8%5%6%6%7%7%29%
1893
16th to endDay
10%13%5%10%6%45%5%6%8%23%
2120
April1st to 15thDay
8%9%38%7%36%6%6%7%31%
2218
16th to endDay
14%9%47%5%44446%33%
2362
May1st to 15thDay
13%8%25%5%34446%40%
2511
16th to endDay
18%7%36%5%3445%8%30%
2773
June1st to 15thDay
17%7%36%5%35%45%8%32%
2700
16th to endDay
13%424435%5%6%9%39%
2700
July1st to 15thDay
7%314436%6%7%9%45%
2700
16th to endDay
5%3233245%5%9%55%
2846
August1st to 15thDay
8%414425%45%8%48%
2448
16th to endDay
7%31333435%8%53%
2483
September1st to 15thDay
13%5%24422335%50%
2173
16th to endDay
11%5%1322346%7%51%
1967
October1st to 15thDay
12%8%25%5%33447%41%
1705
16th to endDay
8%8%36%6%35%46%8%37%
1608
November1st to 15thDay
8%10%5%6%5%246%6%6%36%
1408
16th to endDay
8%11%6%9%7%35%446%30%
1416
December1st to 15thDay
9%12%6%10%11%47%5%5%6%19%
1260
16th to endDay
6%14%49%8%5%6%6%6%8%24%
1344
January1st to 15thNight
6%9%49%8%5%7%7%5%8%28%
2685
16th to endNight
5%9%48%8%5%5%5%6%9%30%
2853
February1st to 15thNight
7%9%49%8%45%46%9%30%
2277
16th to endNight
5%10%7%9%7%45%46%8%31%
2052
March1st to 15thNight
6%9%36%7%46%6%7%7%33%
2064
16th to endNight
9%10%48%8%35%5%6%9%28%
2100
April1st to 15thNight
11%9%35%7%36%6%5%7%32%
1729
16th to endNight
13%9%36%5%45%35%6%37%
1596
May1st to 15thNight
13%6%23425%5%48%42%
1439
16th to endNight
14%7%45%425%47%7%35%
1338
June1st to 15thNight
16%4246%346%5%10%34%
1260
16th to endNight
10%3235%3436%8%46%
1260
July1st to 15thNight
6%31343445%10%52%
1260
16th to endNight
321332246%9%58%
1323
August1st to 15thNight
6%2133245%7%10%51%
1509
16th to endNight
7%31432445%8%55%
1719
September1st to 15thNight
10%5%14423435%53%
1786
16th to endNight
7%4244245%5%7%51%
1990
October1st to 15thNight
10%7%36%5%2445%8%39%
2052
16th to endNight
10%8%36%5%3445%7%40%
2249
November1st to 15thNight
9%8%45%5%25%45%8%39%
2450
16th to endNight
7%11%5%8%7%45%36%5%33%
2544
December1st to 15thNight
7%13%5%11%9%5%5%46%7%22%
2700
16th to endNight
5%11%5%9%8%46%7%6%7%26%
2880

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
9%12%5%9%7%46%6%6%7%25%
1253
16th to endDay
311%6%11%7%6%5%5%5%8%27%
1380
February1st to 15thDay
7%12%6%11%9%46%45%6%24%
1575
16th to endDay
7%14%7%10%7%45%5%5%6%25%
1422
March1st to 15thDay
5%8%5%9%8%5%6%6%6%8%28%
1893
16th to endDay
10%12%6%9%7%35%5%5%8%23%
2121
April1st to 15thDay
8%9%47%8%36%6%6%7%30%
2218
16th to endDay
15%9%36%6%35%446%32%
2362
May1st to 15thDay
13%7%26%435%45%6%39%
2511
16th to endDay
18%7%36%6%3445%7%31%
2773
June1st to 15thDay
17%7%35%5%35%5%5%7%32%
2700
16th to endDay
12%5%25%435%6%6%9%39%
2700
July1st to 15thDay
7%314435%6%7%9%46%
2700
16th to endDay
6%31332446%8%55%
2846
August1st to 15thDay
8%5%14325%45%8%48%
2448
16th to endDay
7%21342445%8%53%
2483
September1st to 15thDay
14%5%25%423235%50%
2173
16th to endDay
10%5%2232246%8%50%
1967
October1st to 15thDay
12%8%25%433446%42%
1705
16th to endDay
8%9%35%6%45%5%5%8%37%
1608
November1st to 15thDay
8%11%46%4345%7%7%35%
1408
16th to endDay
9%10%6%9%7%35%447%30%
1416
December1st to 15thDay
9%13%5%12%9%5%6%6%5%6%19%
1260
16th to endDay
6%13%5%10%8%5%7%5%6%7%23%
1344
January1st to 15thNight
6%9%5%8%7%48%7%6%7%28%
2685
16th to endNight
5%9%48%9%46%5%6%9%30%
2853
February1st to 15thNight
7%9%49%8%45%5%5%9%30%
2277
16th to endNight
5%10%6%9%7%45%46%8%31%
2052
March1st to 15thNight
6%9%37%6%5%5%6%6%9%33%
2064
16th to endNight
9%9%49%7%45%5%7%9%27%
2103
April1st to 15thNight
12%8%35%6%36%6%6%7%32%
1729
16th to endNight
13%9%36%5%4435%6%37%
1596
May1st to 15thNight
14%6%2343445%7%42%
1439
16th to endNight
15%6%36%4245%6%7%35%
1337
June1st to 15thNight
16%435%5%446%6%8%34%
1260
16th to endNight
10%5%145%3445%9%46%
1260
July1st to 15thNight
7%2234235%6%9%52%
1260
16th to endNight
322332345%10%58%
1323
August1st to 15thNight
6%2123235%7%10%52%
1509
16th to endNight
7%314323348%56%
1719
September1st to 15thNight
10%5%145%23435%53%
1786
16th to endNight
7%5%2441446%7%51%
1990
October1st to 15thNight
11%8%36%5%3345%8%40%
2052
16th to endNight
10%8%45%5%3445%7%40%
2249
November1st to 15thNight
10%8%36%425%45%8%39%
2450
16th to endNight
7%11%6%8%6%45%45%6%33%
2544
December1st to 15thNight
7%13%5%11%9%5%5%46%8%21%
2700
16th to endNight
5%11%5%9%8%5%6%7%6%7%27%
2880

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
55%9%16%12%4
1253
16th to endDay
53%8%16%13%5%1
1380
February1st to 15thDay
60%6%13%16%4
1575
16th to endDay
57%6%15%12%6%
1422
March1st to 15thDay
50%9%21%15%2
1893
16th to endDay
57%8%15%14%2
2121
April1st to 15thDay
49%8%14%19%7%
2218
16th to endDay
51%6%14%19%6%1
2362
May1st to 15thDay
43%6%14%24%9%
2511
16th to endDay
51%7%13%18%8%
2778
June1st to 15thDay
49%7%14%20%7%
2700
16th to endDay
39%9%19%23%7%
2700
July1st to 15thDay
29%10%20%29%9%
2541
16th to endDay
25%8%20%32%12%1
2667
August1st to 15thDay
32%9%21%26%8%1
2431
16th to endDay
27%6%16%31%16%1
2483
September1st to 15thDay
36%5%12%24%16%4
2173
16th to endDay
30%6%16%30%13%2
1967
October1st to 15thDay
41%5%19%25%7%
1705
16th to endDay
42%8%18%23%6%
1608
November1st to 15thDay
44%8%19%21%5%
1408
16th to endDay
53%9%15%16%4
1416
December1st to 15thDay
62%8%16%11%1
1260
16th to endDay
56%8%15%15%3
1344
January1st to 15thNight
51%9%18%15%3
2685
16th to endNight
48%8%17%18%5%1
2853
February1st to 15thNight
49%6%18%16%8%
2288
16th to endNight
50%6%14%19%8%
2052
March1st to 15thNight
44%11%21%17%5%
2064
16th to endNight
51%8%14%18%5%
2103
April1st to 15thNight
48%8%13%20%8%
1729
16th to endNight
47%6%11%18%13%2
1596
May1st to 15thNight
39%6%11%25%16%1
1440
16th to endNight
44%7%16%19%11%1
1338
June1st to 15thNight
43%8%16%20%9%
1260
16th to endNight
34%7%20%25%11%
1260
July1st to 15thNight
27%9%19%29%12%2
1190
16th to endNight
21%6%18%35%15%2
1239
August1st to 15thNight
24%9%22%31%9%2
1502
16th to endNight
27%413%31%19%2
1719
September1st to 15thNight
33%5%11%23%17%8%
1786
16th to endNight
30%5%15%27%19%2
1990
October1st to 15thNight
41%7%14%24%12%
2052
16th to endNight
41%6%18%24%7%
2249
November1st to 15thNight
42%8%18%21%8%
2450
16th to endNight
50%7%17%17%6%
2544
December1st to 15thNight
59%9%15%12%2
2700
16th to endNight
52%8%17%16%5%
2880

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
6%318%36%26%8%
60
16th to endDay
7%341%30%15%1
65
February1st to 15thDay
17%7%25%36%11%1
90
16th to endDay
20%27%33%14%3
81
March1st to 15thDay
10%12%41%25%7%1
222
16th to endDay
14%13%35%27%9%1
288
April1st to 15thDay
14%15%34%25%8%
269
16th to endDay
21%9%27%27%12%1
292
May1st to 15thDay
14%7%27%30%16%3
468
16th to endDay
18%8%20%26%18%7%
517
June1st to 15thDay
17%6%28%26%16%3
495
16th to endDay
14%7%25%28%19%4
495
July1st to 15thDay
8%417%36%27%6%
475
16th to endDay
7%326%33%23%5%
515
August1st to 15thDay
11%418%29%26%10%
410
16th to endDay
7%5%21%31%28%4
332
September1st to 15thDay
20%7%20%28%18%5%
315
16th to endDay
12%7%26%31%15%6%
289
October1st to 15thDay
28%5%27%22%14%1
107
16th to endDay
13%6%22%29%23%4
96
November1st to 15thDay
13%6%34%30%15%
90
16th to endDay
10%8%33%20%17%9%
86
December1st to 15thDay
16%338%23%10%8%
60
16th to endDay
17%6%28%32%12%3
64
January1st to 15thNight
10%9%31%32%12%2
900
16th to endNight
9%9%36%30%12%1
939
February1st to 15thNight
9%7%25%39%15%2
704
16th to endNight
9%6%24%37%19%2
632
March1st to 15thNight
10%436%33%13%1
720
16th to endNight
13%7%29%36%11%2
759
April1st to 15thNight
15%5%35%31%11%
539
16th to endNight
19%6%25%32%15%
540
May1st to 15thNight
17%5%21%35%19%1
540
16th to endNight
18%420%33%20%2
403
June1st to 15thNight
19%323%32%17%2
360
16th to endNight
12%5%20%38%20%1
360
July1st to 15thNight
10%318%47%19%1
340
16th to endNight
5%422%40%25%2
376
August1st to 15thNight
8%315%39%29%3
527
16th to endNight
9%222%38%25%1
573
September1st to 15thNight
13%421%37%21%2
540
16th to endNight
9%428%35%18%2
701
October1st to 15thNight
15%428%34%12%3
684
16th to endNight
14%7%28%36%11%1
756
November1st to 15thNight
14%7%36%30%9%1
875
16th to endNight
13%8%33%34%10%
900
December1st to 15thNight
13%6%30%32%15%2
900
16th to endNight
9%6%31%32%16%3
960
Page generated at 2017-10-07 12:07:53. Version ac04

Copyright 2017 A. Danko


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