Longway Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Longway Planetarium clear sky chart from 2005-11-05 to 2017-09-19.

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
36%
15716
15%
46915
10%
15674
42%
15674
21%
32506

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
17%
900
9%
2506
3%
895
22%
895
12%
2009
January16th to endNight
21%
884
10%
2612
4%
884
27%
884
12%
2066
February1st to 15thNight
18%
701
10%
2262
3%
701
25%
701
11%
1744
February16th to endNight
26%
631
14%
1893
7%
631
34%
631
14%
1411
March1st to 15thNight
28%
720
16%
2083
10%
720
33%
720
18%
1491
March16th to endNight
33%
768
19%
2112
10%
768
40%
768
23%
1480
April1st to 15thNight
28%
578
14%
1800
8%
578
35%
578
19%
1238
April16th to endNight
33%
540
21%
1620
9%
540
44%
540
27%
1047
May1st to 15thNight
36%
540
15%
1620
8%
540
43%
540
23%
1086
May16th to endNight
45%
562
16%
1648
11%
561
52%
561
30%
1029
June1st to 15thNight
55%
420
16%
1320
15%
420
60%
420
30%
786
June16th to endNight
55%
438
17%
1338
14%
438
61%
438
33%
793
July1st to 15thNight
62%
510
16%
1360
14%
510
65%
510
41%
814
July16th to endNight
64%
564
18%
1480
15%
531
68%
531
41%
865
August1st to 15thNight
67%
539
20%
1609
16%
536
70%
536
36%
944
August16th to endNight
60%
573
23%
1738
18%
573
64%
573
35%
1001
September1st to 15thNight
58%
660
24%
1920
18%
660
63%
660
34%
1147
September16th to endNight
58%
673
23%
1858
17%
673
61%
673
33%
1153
October1st to 15thNight
45%
660
21%
1895
16%
660
50%
660
26%
1258
October16th to endNight
26%
704
14%
2216
8%
704
34%
704
16%
1589
November1st to 15thNight
34%
700
20%
2276
17%
700
41%
700
21%
1481
November16th to endNight
25%
720
13%
2406
8%
720
32%
720
15%
1755
December1st to 15thNight
15%
771
7%
2571
2%
771
20%
771
10%
2012
December16th to endNight
15%
960
8%
2772
2%
960
21%
960
10%
2307

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
14%9%47%6%35%45%7%32%
47882
Night
15%9%46%5%3445%6%34%
47091
Cloud CoverDay
14%9%37%6%35%45%7%32%
47892
Night
15%9%46%5%34446%35%
47095
TransparencyDay
49%411%21%11%1
47576
Night
49%411%21%11%1
46915
SeeingDay
17%7%25%24%16%7%
5870
Night
20%8%27%30%12%1
15720

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
17%15%6%11%7%45%5%3417%
1432
16th to endDay
15%17%8%12%9%4434414%
1611
February1st to 15thDay
13%17%6%11%7%45%45%6%18%
1599
16th to endDay
13%14%6%11%8%35%5%45%21%
1580
March1st to 15thDay
15%10%410%7%2445%6%27%
1865
16th to endDay
17%11%48%6%44345%29%
2112
April1st to 15thDay
20%10%45%5%23446%30%
2158
16th to endDay
15%8%26%5%3435%6%37%
2340
May1st to 15thDay
20%7%35%425%45%7%33%
2331
16th to endDay
13%6%26%5%345%6%8%38%
2464
June1st to 15thDay
10%6%36%5%35%5%6%7%39%
2634
16th to endDay
9%6%36%5%36%6%7%9%35%
2615
July1st to 15thDay
7%5%24435%5%6%9%43%
2520
16th to endDay
9%4245%46%5%8%9%39%
2586
August1st to 15thDay
9%5%26%5%36%6%7%9%37%
2340
16th to endDay
11%5%25%5%45%5%6%7%41%
2462
September1st to 15thDay
11%425%6%35%5%6%8%40%
2028
16th to endDay
12%6%25%435%5%5%9%39%
1848
October1st to 15thDay
15%7%35%5%3445%6%37%
1735
16th to endDay
22%10%35%5%34446%28%
1653
November1st to 15thDay
15%9%36%6%33447%35%
1582
16th to endDay
16%13%5%7%6%35%45%5%25%
1551
December1st to 15thDay
15%15%7%12%7%33435%21%
1388
16th to endDay
20%17%8%9%5%23346%17%
1448
January1st to 15thNight
22%13%6%8%6%3444422%
2506
16th to endNight
14%13%7%11%7%35%45%5%20%
2612
February1st to 15thNight
15%15%5%9%7%35%44425%
2260
16th to endNight
16%12%49%7%345%45%25%
1893
March1st to 15thNight
16%11%46%5%33435%33%
2071
16th to endNight
16%8%36%6%2445%6%35%
2112
April1st to 15thNight
20%9%35%5%2345%7%33%
1800
16th to endNight
15%7%25%3335%6%6%40%
1620
May1st to 15thNight
15%6%36%6%335%47%36%
1620
16th to endNight
12%4245%345%5%6%44%
1646
June1st to 15thNight
10%424435%6%5%8%44%
1320
16th to endNight
9%425%425%46%9%45%
1338
July1st to 15thNight
7%315%425%36%7%51%
1440
16th to endNight
6%3235%246%6%9%49%
1581
August1st to 15thNight
6%3145%35%6%6%7%48%
1620
16th to endNight
9%5%24324447%51%
1738
September1st to 15thNight
11%5%134245%5%5%50%
1920
16th to endNight
10%5%25%5%2445%6%47%
1858
October1st to 15thNight
16%6%16%434346%40%
1895
16th to endNight
22%8%36%6%24445%30%
2216
November1st to 15thNight
15%9%245%345%46%37%
2276
16th to endNight
21%11%47%5%2445%5%26%
2406
December1st to 15thNight
19%14%7%9%5%2443422%
2571
16th to endNight
20%16%8%10%6%34445%17%
2772

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
17%15%6%11%6%45%445%17%
1432
16th to endDay
15%17%9%12%8%5%434414%
1611
February1st to 15thDay
13%16%6%10%8%35%447%17%
1599
16th to endDay
12%15%6%10%8%35%45%5%21%
1580
March1st to 15thDay
16%10%49%7%3445%7%26%
1876
16th to endDay
17%10%47%7%34445%29%
2111
April1st to 15thDay
20%11%35%5%24446%30%
2158
16th to endDay
16%8%25%5%34346%37%
2340
May1st to 15thDay
20%7%26%435%45%6%34%
2331
16th to endDay
13%6%25%5%3445%8%38%
2464
June1st to 15thDay
10%6%26%5%35%5%6%8%38%
2634
16th to endDay
10%6%26%445%6%7%9%35%
2615
July1st to 15thDay
8%4245%35%5%6%9%44%
2520
16th to endDay
9%4245%46%5%7%9%39%
2586
August1st to 15thDay
9%5%26%5%45%6%8%8%37%
2340
16th to endDay
12%425%5%345%6%7%41%
2462
September1st to 15thDay
12%325%6%445%6%7%40%
2028
16th to endDay
12%5%34436%5%5%9%39%
1848
October1st to 15thDay
15%7%26%5%34446%37%
1735
16th to endDay
22%10%26%5%24446%29%
1653
November1st to 15thDay
14%9%36%6%34347%35%
1582
16th to endDay
16%13%5%8%6%35%446%24%
1551
December1st to 15thDay
15%15%7%11%7%2434421%
1388
16th to endDay
21%17%8%9%42435%5%17%
1448
January1st to 15thNight
22%12%6%9%5%4434422%
2506
16th to endNight
14%14%7%11%7%4445%5%21%
2612
February1st to 15thNight
15%13%5%9%6%45%44425%
2253
16th to endNight
16%12%48%7%345%45%26%
1893
March1st to 15thNight
16%12%5%6%5%24335%33%
2083
16th to endNight
16%8%46%5%34446%35%
2112
April1st to 15thNight
20%8%45%5%23447%33%
1800
16th to endNight
15%7%25%4235%5%7%40%
1620
May1st to 15thNight
16%6%37%5%34448%37%
1619
16th to endNight
13%3245%345%47%44%
1646
June1st to 15thNight
10%414435%5%5%9%44%
1320
16th to endNight
9%43442446%8%46%
1338
July1st to 15thNight
7%32442435%8%51%
1440
16th to endNight
6%3145%335%6%9%50%
1581
August1st to 15thNight
7%3145%35%5%6%8%48%
1620
16th to endNight
10%5%24324347%52%
1738
September1st to 15thNight
12%5%224245%5%5%50%
1920
16th to endNight
11%5%25%5%2345%6%47%
1858
October1st to 15thNight
16%6%15%5%25%346%40%
1895
16th to endNight
23%7%36%6%24445%30%
2216
November1st to 15thNight
16%8%24435%45%6%37%
2276
16th to endNight
21%12%46%5%25%45%6%26%
2406
December1st to 15thNight
20%14%7%9%5%34435%22%
2571
16th to endNight
20%16%8%9%6%3444417%
2772

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%410%12%3
1433
16th to endDay
73%38%9%4
1611
February1st to 15thDay
65%411%13%4
1601
16th to endDay
62%49%15%6%
1580
March1st to 15thDay
56%412%17%7%
1876
16th to endDay
57%210%21%7%
2112
April1st to 15thDay
53%39%22%10%
2158
16th to endDay
47%314%16%15%2
2340
May1st to 15thDay
48%411%21%11%2
2331
16th to endDay
43%413%23%13%1
2468
June1st to 15thDay
41%5%12%24%14%1
2634
16th to endDay
41%6%12%23%16%
2615
July1st to 15thDay
35%5%10%28%17%2
2371
16th to endDay
38%6%13%23%15%2
2424
August1st to 15thDay
39%5%13%25%13%2
2327
16th to endDay
40%5%10%26%15%1
2462
September1st to 15thDay
40%5%12%28%12%1
2028
16th to endDay
40%412%29%12%
1848
October1st to 15thDay
46%311%23%12%1
1735
16th to endDay
55%315%19%5%
1653
November1st to 15thDay
49%411%24%10%
1582
16th to endDay
59%313%17%5%1
1551
December1st to 15thDay
65%313%13%3
1388
16th to endDay
68%312%11%3
1448
January1st to 15thNight
65%39%13%6%
2506
16th to endNight
64%312%15%3
2612
February1st to 15thNight
62%5%8%16%7%
2262
16th to endNight
58%311%18%7%
1893
March1st to 15thNight
53%39%21%10%1
2083
16th to endNight
49%310%23%11%1
2112
April1st to 15thNight
50%310%20%14%
1800
16th to endNight
42%411%21%17%3
1620
May1st to 15thNight
46%410%22%12%3
1620
16th to endNight
38%411%25%14%4
1648
June1st to 15thNight
36%413%26%17%1
1320
16th to endNight
34%414%27%17%1
1338
July1st to 15thNight
30%5%8%30%21%2
1360
16th to endNight
28%5%17%24%21%2
1480
August1st to 15thNight
32%5%12%32%15%2
1609
16th to endNight
31%412%31%17%1
1738
September1st to 15thNight
33%5%10%30%18%1
1920
16th to endNight
36%411%31%15%
1858
October1st to 15thNight
44%39%25%16%1
1895
16th to endNight
55%312%21%6%
2216
November1st to 15thNight
46%312%23%12%1
2276
16th to endNight
57%314%18%5%
2406
December1st to 15thNight
65%312%12%5%
2571
16th to endNight
69%310%11%4
2772

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
18%10%48%15%6%
90
16th to endDay
35%9%34%16%31
96
February1st to 15thDay
27%22%35%13%1
90
16th to endDay
19%14%39%17%8%
81
March1st to 15thDay
29%10%28%24%7%
166
16th to endDay
26%6%30%21%12%2
288
April1st to 15thDay
27%10%27%23%8%2
270
16th to endDay
22%8%27%21%13%5%
270
May1st to 15thDay
26%6%27%21%12%4
288
16th to endDay
18%7%26%25%13%9%
364
June1st to 15thDay
13%8%29%28%13%6%
495
16th to endDay
13%8%28%25%18%6%
495
July1st to 15thDay
10%7%22%28%20%10%
475
16th to endDay
9%325%30%20%10%
446
August1st to 15thDay
10%215%27%25%19%
313
16th to endDay
16%317%19%25%18%
332
September1st to 15thDay
10%319%22%27%17%
315
16th to endDay
16%412%25%28%12%
266
October1st to 15thDay
17%8%22%26%20%4
255
16th to endDay
29%9%30%22%7%
165
November1st to 15thDay
12%14%28%26%13%4
90
16th to endDay
30%13%32%15%7%
79
December1st to 15thDay
21%18%40%20%
60
16th to endDay
30%22%34%12%
81
January1st to 15thNight
27%13%33%20%5%
900
16th to endNight
20%11%33%28%5%
884
February1st to 15thNight
23%12%35%23%4
704
16th to endNight
22%12%28%30%4
631
March1st to 15thNight
22%10%30%28%7%
720
16th to endNight
19%10%29%31%8%1
768
April1st to 15thNight
24%10%32%26%6%
578
16th to endNight
20%6%35%27%9%1
540
May1st to 15thNight
20%431%33%9%1
540
16th to endNight
15%328%34%15%2
563
June1st to 15thNight
14%221%46%13%
420
16th to endNight
10%124%44%17%1
438
July1st to 15thNight
10%117%43%25%2
510
16th to endNight
8%217%46%23%1
564
August1st to 15thNight
8%114%43%28%3
539
16th to endNight
11%216%35%30%4
573
September1st to 15thNight
14%417%33%25%5%
660
16th to endNight
13%415%32%27%5%
673
October1st to 15thNight
21%5%21%33%17%1
660
16th to endNight
27%10%30%26%5%
704
November1st to 15thNight
22%9%29%26%11%1
700
16th to endNight
27%12%29%23%7%
720
December1st to 15thNight
28%12%33%20%3
771
16th to endNight
28%11%35%21%3
960
Page generated at 2017-09-20 04:49:51. Version ac04

Copyright 2017 A. Danko


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