Tantalus Lookout
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tantalus Lookout clear sky chart from 2005-11-06 to 2024-11-08.

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
28%
23436
8%
99672
6%
23172
31%
23172
9%
74823

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 10thNight
15%
845
8%
4696
6%
816
20%
816
4%
3966
January11th to 20thNight
17%
849
13%
4640
4%
820
20%
820
5%
3259
January21st to endNight
16%
867
5%
4972
4%
842
22%
842
4%
4390
February1st to 10thNight
15%
760
8%
2470
4%
760
21%
760
9%
2013
February11th to 20thNight
17%
741
9%
2404
4%
740
24%
740
9%
1917
February21st to endNight
20%
628
9%
2038
4%
628
27%
628
9%
1642
March1st to 10thNight
20%
753
9%
3544
5%
744
24%
744
6%
2885
March11th to 20thNight
21%
750
7%
3366
4%
740
24%
740
6%
2430
March21st to endNight
18%
830
4%
3638
2%
814
21%
814
5%
2961
April1st to 10thNight
25%
760
5%
1900
2%
760
26%
760
10%
1628
April11th to 20thNight
26%
634
8%
1762
4%
634
29%
634
12%
1415
April21st to endNight
25%
504
7%
1644
4%
504
28%
504
11%
1321
May1st to 10thNight
38%
378
12%
2387
9%
373
43%
373
9%
1532
May11th to 20thNight
40%
370
6%
2479
12%
364
44%
364
8%
1539
May21st to endNight
34%
408
3%
2573
6%
399
38%
399
7%
2036
June1st to 10thNight
27%
380
1%
1330
0%
380
28%
380
11%
1025
June11th to 20thNight
29%
380
1%
1330
0%
380
30%
380
9%
1062
June21st to endNight
41%
380
4%
1330
0%
380
41%
380
15%
951
July1st to 10thNight
55%
364
3%
1868
3%
360
56%
360
23%
854
July11th to 20thNight
61%
360
10%
1760
11%
359
63%
359
29%
722
July21st to endNight
67%
411
9%
2344
20%
383
72%
383
20%
1255
August1st to 10thNight
68%
371
26%
2168
22%
369
72%
369
30%
794
August11th to 20thNight
68%
559
11%
2805
17%
554
71%
554
19%
1765
August21st to endNight
52%
661
13%
3072
12%
656
54%
656
16%
1980
September1st to 10thNight
48%
760
17%
1900
8%
760
51%
760
33%
1248
September11th to 20thNight
44%
760
16%
1905
8%
760
46%
760
25%
1364
September21st to endNight
36%
760
14%
2175
9%
760
40%
760
18%
1595
October1st to 10thNight
34%
755
7%
3766
8%
740
37%
740
10%
2815
October11th to 20thNight
28%
756
10%
3632
9%
740
32%
740
8%
2807
October21st to endNight
19%
832
7%
4336
5%
813
26%
813
6%
3432
November1st to 10thNight
14%
770
6%
2694
3%
770
18%
770
6%
2268
November11th to 20thNight
13%
760
7%
2660
3%
760
18%
760
7%
2208
November21st to endNight
19%
760
7%
2660
2%
760
24%
760
8%
2146
December1st to 10thNight
18%
796
11%
2736
5%
796
25%
796
10%
2114
December11th to 20thNight
9%
850
3%
3515
1%
849
12%
849
4%
3074
December21st to endNight
10%
934
5%
5173
3%
905
16%
905
3%
4410

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
21%15%37%444345%30%
105532
Night
23%19%47%433345%27%
102171
TransparencyDay
58%5%11%16%9%2
105278
Night
61%5%11%15%7%2
102071
SeeingDay
30%13%26%21%8%1
15449
Night
33%8%24%24%11%1
23535

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 10thDay
26%31%45%32223319%
2219
11th to 20thDay
21%20%39%6%3322427%
2199
21st to endDay
45%23%45%32212212%
2680
February1st to 10thDay
22%24%5%8%433335%19%
1710
11th to 20thDay
17%26%5%7%34333425%
1665
21st to endDay
12%30%6%10%7%4334319%
1415
March1st to 10thDay
16%28%6%9%5%4434418%
3249
11th to 20thDay
16%24%48%42323430%
3490
21st to endDay
19%24%5%10%6%5%434417%
3917
April1st to 10thDay
21%26%49%6%44345%14%
2280
11th to 20thDay
20%25%49%5%5%324419%
2368
21st to endDay
23%21%5%10%5%5%5%23317%
2536
May1st to 10thDay
15%16%49%5%5%434430%
4420
11th to 20thDay
15%11%38%5%5%5%5%7%9%26%
4377
21st to endDay
28%18%49%5%44345%15%
4999
June1st to 10thDay
31%12%49%5%44345%20%
2850
11th to 20thDay
28%15%49%6%5%435%5%15%
2850
21st to endDay
22%11%48%5%44345%30%
2850
July1st to 10thDay
9%5%25%32334460%
4740
11th to 20thDay
8%413232245%66%
4740
21st to endDay
12%5%25%34447%9%46%
4955
August1st to 10thDay
8%41322335%7%63%
4384
11th to 20thDay
12%7%27%5%45%46%7%40%
4026
21st to endDay
17%7%26%44446%7%38%
4441
September1st to 10thDay
16%5%26%443346%46%
2280
11th to 20thDay
23%8%36%5%33235%39%
2271
21st to endDay
27%9%36%333246%33%
2005
October1st to 10thDay
22%12%39%5%5%5%35%5%25%
3180
11th to 20thDay
35%11%37%44434421%
3161
21st to endDay
29%16%410%6%5%433415%
3124
November1st to 10thDay
35%18%36%43333418%
1544
11th to 20thDay
33%24%36%32323320%
1520
21st to endDay
30%22%36%34333320%
1520
December1st to 10thDay
24%23%45%42213329%
1440
11th to 20thDay
32%24%5%7%43222217%
1685
21st to endDay
31%24%5%9%43323313%
2442
January1st to 10thNight
26%30%5%8%43223315%
4726
11th to 20thNight
25%17%35%33445%6%25%
4699
21st to endNight
41%25%35%32213311%
4972
February1st to 10thNight
23%23%5%8%444345%17%
2470
11th to 20thNight
18%27%5%8%43323424%
2402
21st to endNight
14%30%5%8%5%3424421%
2038
March1st to 10thNight
20%26%5%9%5%4434317%
3622
11th to 20thNight
15%26%46%33423430%
3489
21st to endNight
19%26%5%9%5%4323321%
3736
April1st to 10thNight
20%24%38%6%6%444318%
1900
11th to 20thNight
19%23%46%445%346%23%
1762
21st to endNight
23%19%48%5%43247%21%
1644
May1st to 10thNight
14%16%36%33433440%
2540
11th to 20thNight
15%11%36%5%45%36%8%33%
2516
21st to endNight
28%18%37%44434421%
2573
June1st to 10thNight
25%11%38%5%5%445%5%25%
1330
11th to 20thNight
25%13%39%5%45%36%5%21%
1330
21st to endNight
21%9%36%5%4435%6%33%
1330
July1st to 10thNight
10%413333245%63%
2220
11th to 20thNight
6%413222235%70%
2220
21st to endNight
12%7%25%34435%6%49%
2595
August1st to 10thNight
7%412122246%69%
2545
11th to 20thNight
17%8%26%44445%6%39%
2812
21st to endNight
15%9%37%44436%6%39%
3228
September1st to 10thNight
13%7%26%23345%8%47%
1900
11th to 20thNight
23%10%25%334245%39%
1905
21st to endNight
25%11%37%433246%33%
2175
October1st to 10thNight
20%16%410%5%4433424%
3800
11th to 20thNight
30%15%47%33334424%
3777
21st to endNight
28%21%5%8%43333418%
4431
November1st to 10thNight
36%19%47%33323415%
2694
11th to 20thNight
32%23%35%42323418%
2660
21st to endNight
29%23%46%33324320%
2660
December1st to 10thNight
24%20%46%5%3334425%
2736
11th to 20thNight
33%25%5%7%43322313%
3520
21st to endNight
34%26%5%7%33212314%
5214

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 10thDay
73%49%9%41
2219
11th to 20thDay
63%411%10%7%5%
2220
21st to endDay
82%248%31
2680
February1st to 10thDay
69%49%9%7%2
1710
11th to 20thDay
66%48%13%7%2
1674
21st to endDay
71%39%10%42
1415
March1st to 10thDay
70%5%9%10%6%
3249
11th to 20thDay
61%38%23%5%
3490
21st to endDay
72%5%10%8%41
3917
April1st to 10thDay
75%6%10%8%1
2280
11th to 20thDay
71%48%9%7%1
2368
21st to endDay
75%47%9%5%
2536
May1st to 10thDay
57%5%15%17%6%
4420
11th to 20thDay
50%11%20%15%4
4380
21st to endDay
70%9%10%9%3
5000
June1st to 10thDay
68%6%11%9%43
2850
11th to 20thDay
73%5%10%9%3
2850
21st to endDay
58%412%17%7%1
2850
July1st to 10thDay
29%39%25%21%12%
4666
11th to 20thDay
23%311%38%22%3
4659
21st to endDay
35%419%23%16%3
4798
August1st to 10thDay
23%410%39%23%1
4367
11th to 20thDay
44%423%17%10%2
4065
21st to endDay
45%6%18%20%9%1
4440
September1st to 10thDay
41%6%13%24%12%5%
2280
11th to 20thDay
50%5%9%17%16%3
2271
21st to endDay
54%6%12%16%9%2
2005
October1st to 10thDay
60%312%17%7%
3180
11th to 20thDay
68%49%15%5%
3161
21st to endDay
74%28%11%5%1
3124
November1st to 10thDay
72%5%8%8%6%1
1544
11th to 20thDay
73%38%7%7%2
1520
21st to endDay
70%46%10%8%2
1520
December1st to 10thDay
64%39%12%10%1
1440
11th to 20thDay
76%49%6%32
1688
21st to endDay
78%45%9%31
2442
January1st to 10thNight
77%35%9%5%1
4726
11th to 20thNight
58%6%12%13%7%4
4740
21st to endNight
80%35%7%41
4972
February1st to 10thNight
70%49%9%7%1
2470
11th to 20thNight
66%5%8%11%7%3
2404
21st to endNight
68%48%12%6%2
2038
March1st to 10thNight
68%6%7%11%7%
3622
11th to 20thNight
59%5%10%21%5%
3490
21st to endNight
68%6%12%9%41
3736
April1st to 10thNight
70%7%11%11%1
1900
11th to 20thNight
63%6%9%14%7%1
1762
21st to endNight
66%5%12%12%6%
1644
May1st to 10thNight
48%7%14%26%5%
2540
11th to 20thNight
46%10%23%18%2
2516
21st to endNight
66%7%14%10%3
2573
June1st to 10thNight
63%5%16%8%5%3
1330
11th to 20thNight
64%7%13%11%4
1330
21st to endNight
52%9%14%17%6%2
1330
July1st to 10thNight
26%412%28%24%7%
2185
11th to 20thNight
19%413%38%24%1
2178
21st to endNight
35%416%27%14%4
2513
August1st to 10thNight
18%412%39%26%1
2537
11th to 20thNight
45%5%23%16%9%3
2839
21st to endNight
46%5%19%22%7%1
3228
September1st to 10thNight
36%7%16%24%13%4
1900
11th to 20thNight
48%5%12%17%14%4
1905
21st to endNight
54%5%13%17%9%2
2175
October1st to 10thNight
63%414%14%6%
3800
11th to 20thNight
65%47%18%7%
3777
21st to endNight
69%37%15%5%1
4431
November1st to 10thNight
73%48%8%5%1
2694
11th to 20thNight
72%48%8%6%2
2660
21st to endNight
69%38%9%9%2
2660
December1st to 10thNight
63%5%10%12%8%2
2736
11th to 20thNight
77%5%7%6%42
3516
21st to endNight
78%25%8%5%1
5214

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 10thDay
40%13%23%16%8%1
180
11th to 20thDay
41%9%22%23%4
180
21st to endDay
38%9%28%19%5%
204
February1st to 10thDay
37%17%26%15%4
370
11th to 20thDay
35%15%28%19%31
365
21st to endDay
29%22%27%17%41
309
March1st to 10thDay
32%16%27%19%6%
460
11th to 20thDay
35%14%23%19%8%1
460
21st to endDay
37%15%25%14%7%1
506
April1st to 10thDay
39%18%22%16%5%1
460
11th to 20thDay
36%17%23%16%7%1
452
21st to endDay
36%20%18%18%7%
460
May1st to 10thDay
27%15%25%25%6%1
463
11th to 20thDay
28%9%25%25%12%1
488
21st to endDay
31%13%26%20%8%2
637
June1st to 10thDay
36%16%25%17%6%1
680
11th to 20thDay
36%16%24%17%6%1
680
21st to endDay
26%12%29%26%5%1
680
July1st to 10thDay
21%12%29%29%7%2
671
11th to 20thDay
14%13%35%28%7%2
668
21st to endDay
14%11%31%31%11%3
631
August1st to 10thDay
15%9%27%31%14%5%
487
11th to 20thDay
12%9%31%32%13%3
477
21st to endDay
20%14%32%22%11%2
539
September1st to 10thDay
22%17%29%23%8%2
490
11th to 20thDay
30%11%28%21%8%1
490
21st to endDay
30%14%26%22%7%1
490
October1st to 10thDay
34%12%24%21%8%1
490
11th to 20thDay
43%7%22%17%8%2
490
21st to endDay
40%13%24%16%6%1
380
November1st to 10thDay
39%10%30%15%5%
194
11th to 20thDay
44%10%17%18%9%2
180
21st to endDay
44%11%18%14%9%3
180
December1st to 10thDay
41%9%19%18%12%1
180
11th to 20thDay
43%12%22%20%31
180
21st to endDay
32%10%41%15%21
198
January1st to 10thNight
45%10%23%17%41
850
11th to 20thNight
40%8%27%20%4
850
21st to endNight
37%9%30%19%4
868
February1st to 10thNight
35%9%33%20%3
760
11th to 20thNight
31%10%32%24%4
744
21st to endNight
29%13%28%21%9%
628
March1st to 10thNight
33%11%25%21%10%1
760
11th to 20thNight
39%10%22%22%6%
760
21st to endNight
37%10%23%20%10%1
836
April1st to 10thNight
35%8%21%26%10%
760
11th to 20thNight
31%8%25%29%7%1
634
21st to endNight
34%7%25%24%10%
504
May1st to 10thNight
21%8%23%33%14%1
380
11th to 20thNight
27%5%19%32%16%1
374
21st to endNight
29%6%23%27%14%
411
June1st to 10thNight
31%5%27%23%13%1
380
11th to 20thNight
30%7%24%26%11%2
380
21st to endNight
28%419%33%15%1
380
July1st to 10thNight
16%5%17%36%25%1
370
11th to 20thNight
14%314%38%29%2
368
21st to endNight
12%314%34%34%4
416
August1st to 10thNight
15%211%31%37%4
381
11th to 20thNight
13%39%38%33%3
564
21st to endNight
21%5%15%34%23%2
670
September1st to 10thNight
17%5%24%34%19%1
760
11th to 20thNight
28%5%16%25%23%3
760
21st to endNight
33%5%18%30%13%1
760
October1st to 10thNight
30%6%23%28%13%1
760
11th to 20thNight
39%5%22%23%11%1
760
21st to endNight
42%8%25%19%41
836
November1st to 10thNight
49%7%24%18%2
770
11th to 20thNight
45%9%26%16%41
760
21st to endNight
40%12%24%19%5%1
760
December1st to 10thNight
34%10%32%18%7%
796
11th to 20thNight
45%10%30%14%2
850
21st to endNight
40%10%33%15%1
935
Page generated at 2024-11-05 05:15:52. Version ac07

Copyright © 2024 Attilla Danko.


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