South Lake Tahoe
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the South Lake Tahoe clear sky chart from 2005-11-05 to 2017-09-17.

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
59%
15205
29%
46868
23%
15175
66%
15175
44%
23193

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
52%
717
24%
2506
19%
716
63%
716
32%
1311
January16th to endNight
51%
768
25%
2517
21%
768
58%
768
33%
1369
February1st to 15thNight
48%
698
24%
2229
21%
698
55%
698
33%
1187
February16th to endNight
48%
632
27%
1895
21%
632
59%
632
34%
1038
March1st to 15thNight
47%
720
21%
2115
15%
720
56%
720
35%
1134
March16th to endNight
43%
768
20%
2019
12%
768
51%
768
37%
1140
April1st to 15thNight
46%
719
22%
1799
10%
719
52%
719
38%
1064
April16th to endNight
53%
720
23%
1800
10%
720
58%
720
44%
998
May1st to 15thNight
57%
566
26%
1646
18%
566
62%
566
48%
797
May16th to endNight
61%
374
24%
1496
26%
374
65%
374
37%
689
June1st to 15thNight
66%
360
27%
1440
31%
360
74%
360
44%
603
June16th to endNight
71%
360
35%
1440
40%
360
81%
360
64%
480
July1st to 15thNight
83%
340
33%
1360
43%
340
87%
340
64%
466
July16th to endNight
79%
427
39%
1463
40%
401
84%
401
61%
559
August1st to 15thNight
76%
616
35%
1689
23%
613
80%
613
63%
800
August16th to endNight
77%
764
43%
1910
25%
764
80%
764
75%
884
September1st to 15thNight
82%
720
42%
1800
27%
720
86%
720
78%
817
September16th to endNight
70%
664
42%
1796
32%
664
78%
664
63%
824
October1st to 15thNight
62%
660
33%
1961
27%
660
73%
660
49%
947
October16th to endNight
67%
704
37%
2134
33%
704
76%
704
55%
948
November1st to 15thNight
62%
700
31%
2275
30%
700
70%
700
42%
1136
November16th to endNight
52%
720
32%
2370
24%
720
65%
720
41%
1110
December1st to 15thNight
49%
720
21%
2520
18%
720
57%
720
29%
1369
December16th to endNight
42%
768
23%
2688
18%
768
52%
768
24%
1523

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
231332445%7%61%
47918
Night
131332346%8%60%
47046
TransparencyDay
22%310%22%24%16%
47594
Night
20%412%25%24%12%
46869
SeeingDay
14%17%33%22%9%2
5780
Night
8%8%19%31%25%7%
15216

By Month

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
313336%6%8%10%51%
1432
16th to endDay
26%245%46%7%5%10%45%
1704
February1st to 15thDay
1425%4346%5%10%51%
1634
16th to endDay
1435%6%25%5%7%9%46%
1579
March1st to 15thDay
4346%46%7%7%11%44%
1842
16th to endDay
14145%35%5%6%11%49%
2204
April1st to 15thDay
3425%5%36%5%7%9%46%
2149
16th to endDay
241331445%8%57%
2160
May1st to 15thDay
3413423347%61%
2301
16th to endDay
5%6%234345%5%7%52%
2615
June1st to 15thDay
231331335%7%63%
2520
16th to endDay
11121223478%
2520
July1st to 15thDay
11111333476%
2520
16th to endDay
21111232377%
2604
August1st to 15thDay
11221223475%
2261
16th to endDay
11111222381%
2292
September1st to 15thDay
111312235%77%
2160
16th to endDay
2112212235%75%
1869
October1st to 15thDay
3314313346%63%
1667
16th to endDay
2114424346%65%
1738
November1st to 15thDay
2222335%5%6%8%56%
1584
16th to endDay
3133245%7%10%56%
1587
December1st to 15thDay
14335%346%8%10%48%
1440
16th to endDay
436%6%36%7%8%11%42%
1536
January1st to 15thNight
225%5%45%5%7%12%48%
2506
16th to endNight
15%25%425%5%8%9%47%
2517
February1st to 15thNight
1325%335%6%8%11%49%
2218
16th to endNight
424425%6%9%12%47%
1895
March1st to 15thNight
423335%7%9%10%50%
2115
16th to endNight
3234345%7%10%54%
2019
April1st to 15thNight
2314435%7%8%10%47%
1799
16th to endNight
331322337%8%60%
1800
May1st to 15thNight
321232236%7%64%
1646
16th to endNight
35%23423348%58%
1496
June1st to 15thNight
3211233445%67%
1440
16th to endNight
1111222381%
1440
July1st to 15thNight
1121223379%
1440
16th to endNight
111221223377%
1563
August1st to 15thNight
21221233375%
1698
16th to endNight
11111113481%
1910
September1st to 15thNight
111112483%
1800
16th to endNight
211211223376%
1796
October1st to 15thNight
322312345%67%
1961
16th to endNight
121231235%8%68%
2134
November1st to 15thNight
22122135%8%10%58%
2275
16th to endNight
122321336%9%61%
2370
December1st to 15thNight
1223435%6%8%11%49%
2520
16th to endNight
325%6%35%7%9%11%43%
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
26%5%17%29%17%3
1432
16th to endDay
33%412%22%18%8%
1704
February1st to 15thDay
28%416%26%18%4
1634
16th to endDay
33%314%29%16%2
1579
March1st to 15thDay
32%5%19%21%17%3
1842
16th to endDay
28%5%24%24%14%3
2204
April1st to 15thDay
32%416%25%18%3
2149
16th to endDay
25%218%28%20%4
2160
May1st to 15thDay
24%210%33%24%4
2301
16th to endDay
31%210%28%22%5%
2619
June1st to 15thDay
21%210%21%28%14%
2520
16th to endDay
11%1316%37%29%
2520
July1st to 15thDay
12%128%25%49%
2371
16th to endDay
13%1211%22%47%
2441
August1st to 15thDay
14%1110%26%44%
2245
16th to endDay
10%110%39%37%
2292
September1st to 15thDay
13%1212%37%32%
2160
16th to endDay
14%424%37%18%
1869
October1st to 15thDay
22%26%26%29%12%
1667
16th to endDay
21%19%29%28%9%
1738
November1st to 15thDay
24%5%13%28%20%7%
1584
16th to endDay
21%416%26%27%4
1587
December1st to 15thDay
29%7%15%27%17%1
1440
16th to endDay
34%6%14%20%20%3
1536
January1st to 15thNight
27%415%29%19%3
2506
16th to endNight
30%415%22%19%8%
2517
February1st to 15thNight
26%416%30%15%6%
2229
16th to endNight
26%5%16%31%16%4
1895
March1st to 15thNight
23%5%21%25%18%5%
2115
16th to endNight
22%6%25%26%15%3
2019
April1st to 15thNight
27%421%28%16%2
1799
16th to endNight
21%5%20%31%17%3
1800
May1st to 15thNight
18%312%33%26%5%
1647
16th to endNight
24%314%29%22%5%
1496
June1st to 15thNight
18%39%25%28%14%
1440
16th to endNight
9%1320%35%28%
1440
July1st to 15thNight
10%119%30%46%
1360
16th to endNight
12%1212%22%47%
1463
August1st to 15thNight
14%1213%27%40%
1689
16th to endNight
9%113%39%35%
1910
September1st to 15thNight
8%414%41%31%
1800
16th to endNight
13%328%33%19%
1796
October1st to 15thNight
20%17%32%29%8%
1961
16th to endNight
15%111%29%35%6%
2134
November1st to 15thNight
18%8%11%30%21%8%
2275
16th to endNight
18%413%31%26%5%
2370
December1st to 15thNight
26%8%17%26%16%3
2520
16th to endNight
31%7%16%22%17%3
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
38%6%38%10%6%
60
16th to endDay
25%13%28%17%13%2
232
February1st to 15thDay
19%18%29%21%10%
247
16th to endDay
23%19%32%17%6%
238
March1st to 15thDay
26%27%20%13%11%1
270
16th to endDay
22%30%24%17%5%
288
April1st to 15thDay
26%22%27%16%7%
269
16th to endDay
22%24%30%15%5%1
270
May1st to 15thDay
17%21%32%20%5%2
288
16th to endDay
17%16%28%23%10%4
330
June1st to 15thDay
14%23%31%22%6%1
315
16th to endDay
6%13%46%22%6%4
315
July1st to 15thDay
211%44%28%11%1
305
16th to endDay
413%39%31%7%3
327
August1st to 15thDay
5%15%40%25%9%3
315
16th to endDay
410%39%28%13%4
332
September1st to 15thDay
29%41%31%13%2
315
16th to endDay
9%12%35%29%10%2
260
October1st to 15thDay
14%19%29%23%12%1
255
16th to endDay
15%16%29%27%10%
250
November1st to 15thDay
13%11%18%14%33%8%
90
16th to endDay
22%16%30%16%11%2
85
December1st to 15thDay
33%25%31%35%1
60
16th to endDay
20%10%23%25%14%6%
64
January1st to 15thNight
9%7%22%27%21%10%
720
16th to endNight
9%8%24%31%17%10%
768
February1st to 15thNight
10%10%23%27%21%6%
704
16th to endNight
14%11%20%30%17%5%
632
March1st to 15thNight
11%13%23%25%18%6%
720
16th to endNight
11%16%25%24%19%2
768
April1st to 15thNight
11%12%24%28%21%2
719
16th to endNight
11%11%20%28%20%7%
720
May1st to 15thNight
5%11%20%31%24%5%
567
16th to endNight
7%419%30%34%3
375
June1st to 15thNight
5%420%35%30%3
360
16th to endNight
1221%39%32%3
360
July1st to 15thNight
218%47%36%3
340
16th to endNight
319%37%40%7%
427
August1st to 15thNight
3113%40%35%6%
616
16th to endNight
2213%37%37%6%
764
September1st to 15thNight
1110%33%42%9%
720
16th to endNight
5%416%28%33%11%
664
October1st to 15thNight
10%5%16%31%25%10%
660
16th to endNight
8%6%14%31%26%13%
704
November1st to 15thNight
7%7%20%31%25%8%
700
16th to endNight
12%10%20%26%20%8%
720
December1st to 15thNight
11%10%22%31%16%7%
720
16th to endNight
12%13%26%27%14%5%
768
Page generated at 2017-09-18 05:38:18. Version ac04

Copyright 2017 A. Danko


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