Reid Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Reid Lake Observatory clear sky chart from 2005-11-05 to 2017-03-21.

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
41%
14339
9%
45321
6%
14311
44%
14311
17%
32785

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
28%
805
6%
2742
4%
802
31%
802
8%
2265
January16th to endNight
33%
800
10%
2880
8%
800
37%
800
11%
2229
February1st to 15thNight
35%
704
7%
2401
6%
704
38%
704
12%
1821
February16th to endNight
44%
632
12%
2053
10%
632
48%
632
18%
1427
March1st to 15thNight
32%
720
11%
2112
7%
720
36%
720
15%
1605
March16th to endNight
45%
728
12%
1950
7%
727
47%
727
20%
1439
April1st to 15thNight
44%
601
11%
1591
7%
601
46%
601
20%
1169
April16th to endNight
38%
397
9%
1387
8%
397
43%
397
15%
986
May1st to 15thNight
44%
329
6%
1295
5%
329
46%
329
16%
868
May16th to endNight
44%
342
0%
1123
0%
342
44%
342
17%
782
June1st to 15thNight
45%
330
0%
990
0%
330
45%
330
21%
688
June16th to endNight
51%
330
0%
990
0%
330
51%
330
22%
690
July1st to 15thNight
50%
310
0%
975
0%
310
50%
310
22%
651
July16th to endNight
62%
348
3%
1141
1%
326
65%
326
33%
626
August1st to 15thNight
71%
330
11%
1266
15%
328
72%
328
30%
657
August16th to endNight
54%
499
12%
1549
12%
499
57%
499
24%
1011
September1st to 15thNight
62%
652
17%
1642
11%
652
63%
652
38%
1030
September16th to endNight
47%
656
15%
1812
8%
656
50%
656
23%
1264
October1st to 15thNight
44%
660
12%
1980
8%
660
49%
660
21%
1362
October16th to endNight
33%
704
9%
2326
4%
704
39%
704
13%
1732
November1st to 15thNight
33%
700
9%
2450
7%
700
37%
700
13%
1787
November16th to endNight
33%
840
10%
2714
6%
840
37%
840
13%
2055
December1st to 15thNight
37%
930
9%
2880
6%
930
40%
930
13%
2212
December16th to endNight
31%
992
9%
3072
5%
992
35%
992
11%
2429

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
11%10%48%7%46%6%6%7%26%
45583
Night
11%11%5%8%7%46%5%5%6%27%
45463
TransparencyDay
53%317%20%5%
45225
Night
55%315%19%5%
45325
SeeingDay
15%7%24%28%19%4
6014
Night
18%5%18%33%20%3
14348

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
11%16%6%10%10%5%7%6%5%415%
1206
16th to endDay
10%13%6%10%8%5%7%45%6%22%
1344
February1st to 15thDay
15%13%48%6%45%5%6%6%23%
1462
16th to endDay
7%12%5%8%8%46%5%48%29%
1421
March1st to 15thDay
9%14%7%9%7%47%45%6%22%
1848
16th to endDay
7%11%6%8%7%5%7%6%7%8%23%
2039
April1st to 15thDay
8%12%7%10%9%5%7%6%5%5%19%
2026
16th to endDay
13%13%6%9%9%46%5%5%5%20%
2242
May1st to 15thDay
10%9%6%8%7%5%6%5%5%6%27%
2323
16th to endDay
13%9%49%9%47%6%6%6%22%
2638
June1st to 15thDay
13%8%38%7%5%6%5%5%7%26%
2640
16th to endDay
12%8%5%7%8%46%7%7%7%23%
2640
July1st to 15thDay
14%6%47%6%46%5%6%7%29%
2588
16th to endDay
8%5%26%6%5%6%5%7%8%36%
2636
August1st to 15thDay
5%5%27%6%5%6%6%5%9%38%
2357
16th to endDay
11%8%47%7%37%5%6%7%31%
2299
September1st to 15thDay
7%6%35%6%45%6%6%6%41%
1988
16th to endDay
15%7%27%6%45%6%6%7%29%
1817
October1st to 15thDay
14%10%27%7%35%7%6%7%25%
1650
16th to endDay
16%11%5%7%6%5%5%5%5%7%22%
1546
November1st to 15thDay
15%13%5%8%6%35%5%5%5%24%
1408
16th to endDay
10%15%411%9%5%8%6%45%18%
1233
December1st to 15thDay
13%11%5%11%7%46%5%5%6%24%
1080
16th to endDay
7%16%411%9%47%6%7%6%19%
1152
January1st to 15thNight
11%15%7%10%10%46%5%46%16%
2742
16th to endNight
12%13%5%8%8%45%5%47%22%
2880
February1st to 15thNight
13%15%5%8%7%45%45%5%23%
2389
16th to endNight
7%10%5%10%7%36%5%5%7%29%
2053
March1st to 15thNight
10%13%6%11%8%36%5%45%24%
2112
16th to endNight
7%10%49%8%5%8%7%6%6%26%
1950
April1st to 15thNight
9%13%5%7%7%47%5%5%6%27%
1591
16th to endNight
10%10%5%8%8%5%6%5%46%26%
1387
May1st to 15thNight
12%8%5%8%7%36%5%5%8%28%
1294
16th to endNight
13%7%47%8%47%7%6%8%22%
1123
June1st to 15thNight
15%5%37%6%5%5%6%7%9%26%
990
16th to endNight
10%7%47%8%47%5%7%9%27%
990
July1st to 15thNight
12%6%26%6%47%6%7%8%32%
1039
16th to endNight
9%6%234245%7%8%44%
1225
August1st to 15thNight
7%5%134445%6%9%47%
1273
16th to endNight
11%7%27%6%45%6%6%7%35%
1549
September1st to 15thNight
7%6%26%5%345%5%8%44%
1642
16th to endNight
14%8%36%6%45%6%5%7%31%
1812
October1st to 15thNight
13%9%36%6%45%5%6%6%33%
1980
16th to endNight
17%12%5%7%6%36%6%5%5%23%
2326
November1st to 15thNight
14%11%47%7%46%6%5%6%23%
2450
16th to endNight
11%14%6%8%7%45%45%7%24%
2714
December1st to 15thNight
14%12%5%8%7%4445%5%26%
2880
16th to endNight
7%14%7%11%9%5%6%45%6%20%
3072

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
69%5%14%8%1
1206
16th to endDay
63%413%12%41
1344
February1st to 15thDay
60%316%13%5%
1462
16th to endDay
52%215%19%8%
1421
March1st to 15thDay
59%211%19%6%
1848
16th to endDay
54%218%19%5%
2039
April1st to 15thDay
61%311%18%5%
2026
16th to endDay
63%310%17%4
2242
May1st to 15thDay
52%312%22%8%
2323
16th to endDay
55%317%18%4
2642
June1st to 15thDay
51%314%23%7%
2640
16th to endDay
52%317%21%4
2640
July1st to 15thDay
48%316%22%8%1
2423
16th to endDay
37%424%27%5%
2457
August1st to 15thDay
37%426%27%4
2339
16th to endDay
46%420%24%4
2299
September1st to 15thDay
36%327%25%5%
1988
16th to endDay
49%5%17%23%3
1817
October1st to 15thDay
53%420%18%2
1650
16th to endDay
58%420%14%2
1546
November1st to 15thDay
59%214%16%6%
1408
16th to endDay
67%48%16%2
1233
December1st to 15thDay
61%5%15%15%2
1080
16th to endDay
63%5%13%15%2
1152
January1st to 15thNight
69%5%13%10%1
2742
16th to endNight
62%5%13%11%5%1
2880
February1st to 15thNight
62%315%12%6%
2401
16th to endNight
53%216%19%7%
2053
March1st to 15thNight
58%410%18%6%1
2112
16th to endNight
52%5%14%19%7%
1954
April1st to 15thNight
54%39%23%8%
1591
16th to endNight
56%211%20%7%
1387
May1st to 15thNight
53%211%20%11%
1295
16th to endNight
52%315%22%5%
1123
June1st to 15thNight
51%212%23%8%
990
16th to endNight
50%316%25%3
990
July1st to 15thNight
48%314%20%12%1
975
16th to endNight
33%226%30%6%
1141
August1st to 15thNight
32%321%35%6%
1266
16th to endNight
45%320%25%5%
1549
September1st to 15thNight
35%220%31%8%
1642
16th to endNight
48%414%24%7%
1812
October1st to 15thNight
49%320%22%4
1980
16th to endNight
59%318%16%1
2326
November1st to 15thNight
57%417%15%4
2450
16th to endNight
59%5%13%17%4
2714
December1st to 15thNight
61%414%17%2
2880
16th to endNight
64%412%15%3
3072

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%313%20%41%15%
60
16th to endDay
20%410%31%18%14%
64
February1st to 15thDay
18%8%25%26%16%4
152
16th to endDay
13%6%22%33%15%8%
211
March1st to 15thDay
17%10%39%23%7%1
266
16th to endDay
15%14%27%26%14%1
245
April1st to 15thDay
19%13%26%26%11%3
209
16th to endDay
16%15%32%21%11%2
210
May1st to 15thDay
14%10%27%25%17%4
250
16th to endDay
14%8%22%27%22%4
512
June1st to 15thDay
16%7%21%27%22%4
585
16th to endDay
14%422%28%23%6%
585
July1st to 15thDay
16%6%18%29%22%6%
507
16th to endDay
12%5%19%35%23%3
445
August1st to 15thDay
4320%33%31%6%
302
16th to endDay
13%7%27%33%15%2
268
September1st to 15thDay
11%227%35%18%3
255
16th to endDay
16%6%37%23%14%1
255
October1st to 15thDay
18%7%25%26%18%3
255
16th to endDay
20%5%23%25%20%5%
134
November1st to 15thDay
25%133%25%5%10%
60
16th to endDay
11%5%10%41%18%13%
60
December1st to 15thDay
13%113%23%35%13%
60
16th to endDay
14%17%34%29%12%
64
January1st to 15thNight
21%8%19%30%17%3
807
16th to endNight
21%7%21%33%13%2
800
February1st to 15thNight
22%7%16%31%18%3
709
16th to endNight
14%416%37%23%3
632
March1st to 15thNight
17%9%23%34%13%2
720
16th to endNight
12%7%17%32%26%3
728
April1st to 15thNight
18%5%14%33%22%4
601
16th to endNight
18%5%22%32%17%3
397
May1st to 15thNight
16%5%16%36%21%3
330
16th to endNight
18%5%14%31%27%2
343
June1st to 15thNight
18%323%26%26%2
330
16th to endNight
12%216%34%30%3
330
July1st to 15thNight
15%17%32%29%3
310
16th to endNight
10%215%37%29%4
348
August1st to 15thNight
7%27%33%40%8%
330
16th to endNight
15%212%34%30%4
499
September1st to 15thNight
10%213%34%34%4
652
16th to endNight
18%415%36%19%5%
656
October1st to 15thNight
19%419%32%20%3
660
16th to endNight
23%6%21%31%15%2
704
November1st to 15thNight
23%7%22%33%11%1
700
16th to endNight
21%7%21%32%12%3
840
December1st to 15thNight
21%5%17%35%18%1
930
16th to endNight
16%6%20%34%17%3
992
Page generated at 2017-03-21 23:42:26. Version ac04

Copyright 2017 A. Danko


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