Boundary Road
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Boundary Road clear sky chart from 2005-11-05 to 2017-10-31.

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
35%
14827
13%
47371
10%
14797
40%
14797
17%
33892

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
21%
720
7%
2506
6%
716
24%
716
8%
2028
January16th to endNight
26%
768
10%
2652
7%
768
31%
768
12%
2000
February1st to 15thNight
24%
702
10%
2287
6%
701
29%
701
11%
1787
February16th to endNight
28%
631
13%
1937
8%
631
37%
631
15%
1455
March1st to 15thNight
26%
720
13%
2114
9%
720
32%
720
15%
1595
March16th to endNight
36%
768
21%
2024
11%
768
42%
768
24%
1411
April1st to 15thNight
29%
718
16%
1796
7%
718
33%
718
22%
1332
April16th to endNight
33%
648
17%
1728
7%
648
39%
648
23%
1219
May1st to 15thNight
35%
360
16%
1440
15%
360
44%
360
16%
954
May16th to endNight
40%
375
13%
1497
11%
374
49%
374
19%
951
June1st to 15thNight
39%
360
9%
1440
8%
360
47%
360
14%
1008
June16th to endNight
48%
360
9%
1440
14%
360
52%
360
19%
908
July1st to 15thNight
57%
340
14%
1360
23%
340
61%
340
27%
755
July16th to endNight
60%
376
14%
1418
18%
354
63%
354
25%
824
August1st to 15thNight
52%
426
14%
1497
13%
424
56%
424
24%
933
August16th to endNight
57%
722
19%
1868
10%
722
61%
722
36%
1172
September1st to 15thNight
52%
720
15%
1800
8%
720
53%
720
29%
1252
September16th to endNight
53%
717
23%
1953
16%
717
57%
717
32%
1244
October1st to 15thNight
39%
720
17%
2160
12%
720
47%
720
22%
1488
October16th to endNight
29%
768
12%
2410
9%
768
35%
768
14%
1813
November1st to 15thNight
32%
700
17%
2316
14%
700
39%
700
17%
1638
November16th to endNight
23%
720
11%
2520
7%
720
28%
720
11%
1918
December1st to 15thNight
21%
720
7%
2520
5%
720
25%
720
9%
2043
December16th to endNight
19%
768
9%
2688
4%
768
24%
768
8%
2164

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
18%8%36%5%3445%6%32%
48386
Night
18%9%36%5%34445%32%
47540
Cloud CoverDay
18%8%36%5%3445%6%32%
48395
Night
18%9%36%5%34446%32%
47546
TransparencyDay
50%6%12%19%9%1
48073
Night
52%5%11%19%9%1
47371
SeeingDay
21%6%24%25%15%5%
5667
Night
22%6%27%30%12%
14829

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
22%15%6%8%6%33435%20%
1432
16th to endDay
14%15%5%8%6%45%5%35%23%
1569
February1st to 15thDay
14%14%5%10%7%44446%22%
1575
16th to endDay
18%13%5%6%6%45%45%5%25%
1536
March1st to 15thDay
18%10%5%8%7%35%44426%
1835
16th to endDay
17%7%34424446%39%
2199
April1st to 15thDay
23%9%35%423335%33%
2152
16th to endDay
21%7%25%5%2444437%
2240
May1st to 15thDay
20%7%36%5%34346%32%
2511
16th to endDay
17%6%25%6%345%5%7%34%
2618
June1st to 15thDay
22%7%35%6%34447%30%
2520
16th to endDay
18%5%25%5%45%6%6%7%32%
2520
July1st to 15thDay
12%5%25%5%35%5%6%8%38%
2520
16th to endDay
12%5%25%5%25%6%7%9%35%
2654
August1st to 15thDay
12%6%25%6%45%5%6%7%37%
2451
16th to endDay
10%424435%45%9%43%
2321
September1st to 15thDay
16%425%424447%42%
2160
16th to endDay
14%5%24433347%46%
2006
October1st to 15thDay
20%7%35%5%245%46%33%
1800
16th to endDay
25%8%36%7%44445%25%
1812
November1st to 15thDay
16%7%46%5%35%5%5%6%32%
1539
16th to endDay
22%13%37%5%24345%26%
1440
December1st to 15thDay
22%14%5%7%6%45%5%46%17%
1440
16th to endDay
24%16%5%7%6%3433420%
1536
January1st to 15thNight
19%16%6%9%7%35%43320%
2506
16th to endNight
15%15%5%8%6%35%345%25%
2652
February1st to 15thNight
13%13%6%11%7%46%5%4422%
2285
16th to endNight
17%12%47%7%35%44428%
1937
March1st to 15thNight
19%12%46%7%3434429%
2101
16th to endNight
16%8%36%6%3334341%
2024
April1st to 15thNight
24%8%345%2434435%
1796
16th to endNight
19%7%36%5%33445%37%
1728
May1st to 15thNight
23%7%25%423345%36%
1440
16th to endNight
17%6%244346%5%6%38%
1495
June1st to 15thNight
20%6%35%5%446%6%7%31%
1440
16th to endNight
17%5%25%5%245%6%8%36%
1440
July1st to 15thNight
10%4245%25%46%8%45%
1440
16th to endNight
9%4245%25%5%6%7%45%
1514
August1st to 15thNight
11%5%26%42446%10%39%
1507
16th to endNight
10%32442445%7%48%
1868
September1st to 15thNight
14%6%27%5%24346%42%
1800
16th to endNight
15%424323345%49%
1953
October1st to 15thNight
18%7%25%434346%37%
2160
16th to endNight
24%9%36%5%34446%27%
2410
November1st to 15thNight
20%9%36%5%24336%33%
2316
16th to endNight
21%11%48%6%34345%25%
2520
December1st to 15thNight
23%15%47%6%34445%20%
2520
16th to endNight
25%15%48%6%2434419%
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
22%15%6%8%6%33445%20%
1432
16th to endDay
14%14%5%9%7%35%446%23%
1569
February1st to 15thDay
15%13%5%10%7%35%5%5%6%22%
1575
16th to endDay
18%12%5%8%6%35%45%5%25%
1536
March1st to 15thDay
18%11%47%7%35%445%26%
1845
16th to endDay
17%7%35%425%346%39%
2198
April1st to 15thDay
23%9%45%5%23246%32%
2152
16th to endDay
20%8%25%5%24445%36%
2240
May1st to 15thDay
20%7%35%5%345%46%33%
2511
16th to endDay
18%6%346%35%5%5%7%35%
2618
June1st to 15thDay
22%6%25%6%3445%7%30%
2520
16th to endDay
18%6%25%5%35%5%6%8%32%
2520
July1st to 15thDay
13%5%345%35%5%5%8%39%
2520
16th to endDay
12%5%245%36%5%8%9%36%
2654
August1st to 15thDay
12%6%26%6%346%6%8%36%
2451
16th to endDay
9%5%244345%6%9%43%
2321
September1st to 15thDay
17%425%5%2345%7%42%
2160
16th to endDay
15%5%24433346%46%
2006
October1st to 15thDay
20%7%25%5%35%446%34%
1800
16th to endDay
24%9%35%6%45%45%5%25%
1812
November1st to 15thDay
16%7%45%5%35%5%5%7%32%
1539
16th to endDay
23%12%46%5%24335%27%
1440
December1st to 15thDay
23%14%48%6%36%5%45%17%
1440
16th to endDay
24%15%6%6%7%3432420%
1536
January1st to 15thNight
20%14%6%9%7%3444419%
2506
16th to endNight
15%15%5%9%6%35%336%26%
2652
February1st to 15thNight
14%12%6%11%8%45%5%45%22%
2278
16th to endNight
17%12%5%7%6%44435%29%
1937
March1st to 15thNight
20%11%46%7%3424429%
2114
16th to endNight
16%7%46%5%3333441%
2024
April1st to 15thNight
24%8%445%2333434%
1796
16th to endNight
18%7%36%43335%5%38%
1728
May1st to 15thNight
22%7%25%434346%35%
1440
16th to endNight
17%6%35%3345%5%7%38%
1495
June1st to 15thNight
20%7%25%5%346%5%7%30%
1440
16th to endNight
16%5%26%4345%6%8%36%
1440
July1st to 15thNight
10%3245%25%5%7%9%44%
1440
16th to endNight
10%3145%246%6%8%45%
1514
August1st to 15thNight
10%6%26%6%2345%11%39%
1507
16th to endNight
11%42442446%7%48%
1868
September1st to 15thNight
14%5%35%433446%42%
1800
16th to endNight
15%5%14323435%49%
1953
October1st to 15thNight
19%7%25%5%24347%37%
2160
16th to endNight
25%8%36%5%34446%26%
2410
November1st to 15thNight
20%9%35%6%34336%34%
2316
16th to endNight
22%11%5%8%6%3433426%
2520
December1st to 15thNight
23%15%47%6%245%45%20%
2520
16th to endNight
25%15%5%8%5%2444419%
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
66%5%8%13%5%
1433
16th to endDay
61%5%13%11%7%
1569
February1st to 15thDay
61%6%11%16%3
1577
16th to endDay
59%5%10%14%9%1
1536
March1st to 15thDay
60%411%14%7%
1845
16th to endDay
45%410%19%15%5%
2199
April1st to 15thDay
54%37%19%12%2
2152
16th to endDay
49%48%18%15%3
2240
May1st to 15thDay
50%5%8%19%12%2
2511
16th to endDay
47%7%13%19%11%1
2622
June1st to 15thDay
53%5%11%20%8%
2520
16th to endDay
47%8%13%20%9%
2520
July1st to 15thDay
39%7%14%26%11%
2371
16th to endDay
41%9%15%22%9%
2487
August1st to 15thDay
43%9%15%21%9%
2437
16th to endDay
35%7%17%28%11%
2321
September1st to 15thDay
40%6%13%27%11%
2160
16th to endDay
37%6%12%33%9%
2006
October1st to 15thDay
50%5%13%20%9%
1800
16th to endDay
59%7%12%13%6%
1812
November1st to 15thDay
49%7%13%18%9%
1539
16th to endDay
60%5%13%14%6%
1440
December1st to 15thDay
67%7%11%10%1
1440
16th to endDay
68%5%9%11%4
1536
January1st to 15thNight
67%5%9%10%5%
2506
16th to endNight
61%411%15%7%
2652
February1st to 15thNight
63%5%10%15%4
2287
16th to endNight
58%49%17%9%
1937
March1st to 15thNight
58%49%18%8%1
2114
16th to endNight
47%39%18%15%4
2024
April1st to 15thNight
53%37%19%15%1
1796
16th to endNight
47%5%8%18%17%3
1728
May1st to 15thNight
49%5%7%17%14%4
1440
16th to endNight
44%6%12%20%13%2
1497
June1st to 15thNight
50%8%10%19%9%1
1440
16th to endNight
43%7%14%18%15%
1440
July1st to 15thNight
33%7%14%30%14%
1360
16th to endNight
34%9%14%26%14%
1418
August1st to 15thNight
38%9%18%21%11%
1497
16th to endNight
32%7%16%32%11%
1868
September1st to 15thNight
42%6%11%26%12%
1800
16th to endNight
36%5%11%33%11%
1953
October1st to 15thNight
46%6%10%25%11%
2160
16th to endNight
57%5%13%17%5%
2410
November1st to 15thNight
52%5%13%17%10%1
2316
16th to endNight
61%5%12%15%4
2520
December1st to 15thNight
66%6%10%13%2
2520
16th to endNight
67%5%10%11%5%
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
25%8%28%26%8%3
60
16th to endDay
28%426%31%7%1
69
February1st to 15thDay
31%10%37%20%1
90
16th to endDay
31%8%28%24%7%
195
March1st to 15thDay
22%9%29%28%9%
270
16th to endDay
24%6%26%27%10%3
288
April1st to 15thDay
27%9%31%20%10%1
270
16th to endDay
22%9%25%22%16%3
270
May1st to 15thDay
26%8%25%22%11%5%
288
16th to endDay
17%10%30%22%15%3
331
June1st to 15thDay
25%6%22%30%9%4
315
16th to endDay
21%422%29%17%4
315
July1st to 15thDay
15%221%33%17%9%
305
16th to endDay
14%218%33%23%6%
326
August1st to 15thDay
13%319%30%24%8%
313
16th to endDay
11%419%26%22%15%
332
September1st to 15thDay
17%419%18%23%17%
315
16th to endDay
16%420%20%22%14%
314
October1st to 15thDay
20%6%26%23%18%4
315
16th to endDay
29%11%23%23%11%
309
November1st to 15thDay
19%8%25%26%17%2
193
16th to endDay
28%10%21%25%15%
60
December1st to 15thDay
23%8%33%23%11%
60
16th to endDay
37%14%32%15%
64
January1st to 15thNight
23%10%31%27%6%
720
16th to endNight
22%8%32%28%8%
768
February1st to 15thNight
20%8%36%28%6%
704
16th to endNight
24%6%32%29%6%
631
March1st to 15thNight
26%9%30%30%3
720
16th to endNight
19%9%27%30%10%
768
April1st to 15thNight
27%7%28%29%6%
718
16th to endNight
22%9%28%27%10%1
648
May1st to 15thNight
26%5%25%30%9%2
360
16th to endNight
17%5%30%32%13%
375
June1st to 15thNight
20%327%36%11%
360
16th to endNight
16%323%41%13%1
360
July1st to 15thNight
9%223%44%19%
340
16th to endNight
10%218%47%19%1
376
August1st to 15thNight
15%119%35%25%2
426
16th to endNight
12%319%36%26%1
722
September1st to 15thNight
18%219%36%20%1
720
16th to endNight
17%5%20%27%27%2
717
October1st to 15thNight
23%426%29%14%1
720
16th to endNight
28%9%25%27%9%
768
November1st to 15thNight
26%7%27%26%12%
700
16th to endNight
26%11%27%22%10%
720
December1st to 15thNight
31%9%30%23%5%
720
16th to endNight
32%8%30%22%5%1
768
Page generated at 2017-11-01 17:23:41. Version ac04

Copyright 2017 A. Danko


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