Lillooet
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lillooet 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
27%
14601
9%
46778
5%
14572
32%
14572
16%
33863

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
16%
750
5%
2686
2%
746
21%
746
7%
2210
January16th to endNight
22%
782
6%
2772
3%
782
27%
782
9%
2249
February1st to 15thNight
16%
696
7%
2333
2%
696
22%
696
10%
1827
February16th to endNight
24%
632
9%
2030
5%
632
30%
632
15%
1509
March1st to 15thNight
15%
720
9%
2098
2%
720
22%
720
14%
1593
March16th to endNight
20%
768
9%
2042
2%
767
26%
767
16%
1553
April1st to 15thNight
31%
719
6%
1799
2%
719
33%
719
18%
1361
April16th to endNight
24%
462
10%
1542
5%
462
31%
462
15%
1145
May1st to 15thNight
34%
359
9%
1439
11%
359
40%
359
19%
927
May16th to endNight
36%
374
4%
1438
4%
374
38%
374
14%
1030
June1st to 15thNight
31%
360
2%
1191
0%
360
31%
360
17%
817
June16th to endNight
33%
360
1%
1171
0%
360
33%
360
21%
775
July1st to 15thNight
49%
340
4%
1190
1%
340
50%
340
32%
652
July16th to endNight
59%
376
11%
1313
14%
354
64%
354
35%
666
August1st to 15thNight
64%
363
16%
1435
19%
361
70%
361
33%
738
August16th to endNight
48%
621
18%
1767
13%
621
52%
621
32%
1079
September1st to 15thNight
48%
720
19%
1800
9%
720
52%
720
38%
1126
September16th to endNight
37%
671
17%
1838
8%
671
43%
671
28%
1202
October1st to 15thNight
30%
660
14%
1980
8%
660
37%
660
23%
1337
October16th to endNight
20%
704
9%
2238
3%
704
28%
704
14%
1672
November1st to 15thNight
13%
700
7%
2450
3%
700
19%
700
11%
1844
November16th to endNight
15%
720
7%
2520
2%
720
22%
720
10%
1961
December1st to 15thNight
16%
872
8%
2754
2%
872
22%
872
11%
2172
December16th to endNight
12%
872
6%
2952
1%
872
18%
872
8%
2418

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
6%8%49%8%47%6%7%8%28%
48042
Night
48%5%9%8%5%7%7%7%9%26%
46934
TransparencyDay
51%8%14%17%6%
47698
Night
49%10%16%17%6%
46783
SeeingDay
12%22%33%23%7%1
6229
Night
9%13%43%25%8%
14611

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
312%5%12%9%6%8%9%7%8%16%
1253
16th to endDay
49%49%9%5%7%9%8%9%21%
1452
February1st to 15thDay
49%412%11%5%7%8%8%8%18%
1528
16th to endDay
27%6%10%11%5%8%7%8%8%22%
1443
March1st to 15thDay
8%6%12%9%5%8%8%8%9%21%
1860
16th to endDay
210%6%12%11%5%9%8%8%8%15%
2177
April1st to 15thDay
412%6%11%9%5%8%8%6%8%16%
2149
16th to endDay
5%11%7%12%9%6%8%6%7%7%17%
2413
May1st to 15thDay
5%10%5%9%8%5%7%6%6%8%26%
2511
16th to endDay
12%10%5%11%9%5%7%6%6%6%17%
2672
June1st to 15thDay
12%10%5%9%7%46%5%6%7%24%
2763
16th to endDay
9%7%49%9%47%7%6%7%26%
2782
July1st to 15thDay
6%5%25%5%35%46%9%44%
2700
16th to endDay
5%426%6%35%5%6%8%44%
2763
August1st to 15thDay
5%5%26%6%45%5%5%9%44%
2514
16th to endDay
5%7%27%6%45%6%6%8%39%
2435
September1st to 15thDay
7%6%25%5%34447%48%
2160
16th to endDay
7%6%37%7%45%5%6%8%36%
1864
October1st to 15thDay
7%10%27%7%45%46%8%35%
1650
16th to endDay
5%10%48%7%5%7%7%7%9%25%
1634
November1st to 15thDay
6%10%6%7%10%5%8%6%7%8%23%
1408
16th to endDay
210%7%11%8%6%7%8%7%9%21%
1440
December1st to 15thDay
411%5%9%7%47%7%8%8%23%
1190
16th to endDay
48%5%12%10%5%7%7%8%10%18%
1281
January1st to 15thNight
5%12%7%11%10%6%9%9%7%7%11%
2686
16th to endNight
310%6%11%10%6%12%11%8%10%8%
2772
February1st to 15thNight
6%11%5%11%10%6%7%8%8%10%13%
2321
16th to endNight
28%5%10%11%6%8%9%9%11%16%
2030
March1st to 15thNight
19%6%10%10%5%8%7%8%8%23%
2098
16th to endNight
16%48%8%5%9%10%9%11%22%
2042
April1st to 15thNight
39%47%8%5%10%7%8%9%24%
1799
16th to endNight
37%5%10%10%5%8%6%8%9%24%
1542
May1st to 15thNight
48%37%7%26%5%7%9%37%
1439
16th to endNight
11%8%47%6%46%7%7%10%25%
1438
June1st to 15thNight
9%9%46%6%46%5%6%9%32%
1191
16th to endNight
6%6%37%7%37%5%8%8%35%
1171
July1st to 15thNight
3424425%5%6%7%52%
1260
16th to endNight
4213335%7%7%9%49%
1403
August1st to 15thNight
3415%3245%6%10%52%
1443
16th to endNight
3425%6%45%5%5%7%48%
1767
September1st to 15thNight
7%5%2442446%7%52%
1800
16th to endNight
7%6%25%6%25%5%5%9%42%
1838
October1st to 15thNight
48%37%6%5%5%5%6%8%38%
1980
16th to endNight
5%9%410%9%5%7%7%7%9%24%
2238
November1st to 15thNight
411%6%8%8%5%6%6%9%8%22%
2450
16th to endNight
5%10%7%11%9%5%9%8%8%8%16%
2520
December1st to 15thNight
411%6%10%9%5%8%8%9%10%14%
2754
16th to endNight
211%7%14%10%5%8%8%8%8%11%
2952

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
61%13%11%10%3
1253
16th to endDay
55%11%15%12%31
1452
February1st to 15thDay
57%12%14%11%3
1528
16th to endDay
55%10%12%14%6%
1443
March1st to 15thDay
55%11%16%13%3
1860
16th to endDay
59%11%14%11%2
2177
April1st to 15thDay
62%9%13%12%2
2149
16th to endDay
60%10%13%11%3
2413
May1st to 15thDay
53%6%16%14%9%
2511
16th to endDay
64%7%12%11%2
2676
June1st to 15thDay
59%6%14%12%6%1
2763
16th to endDay
55%8%15%14%5%
2782
July1st to 15thDay
37%5%14%25%14%2
2541
16th to endDay
36%6%16%26%12%1
2591
August1st to 15thDay
36%7%15%26%12%2
2497
16th to endDay
41%5%16%25%9%1
2435
September1st to 15thDay
35%5%13%27%15%1
2160
16th to endDay
45%9%14%19%9%2
1864
October1st to 15thDay
46%8%16%21%7%
1650
16th to endDay
51%11%17%17%2
1634
November1st to 15thDay
56%11%11%16%4
1408
16th to endDay
54%10%14%15%5%
1440
December1st to 15thDay
54%11%16%14%3
1190
16th to endDay
57%12%14%12%3
1281
January1st to 15thNight
65%9%11%9%3
2686
16th to endNight
62%10%12%9%4
2772
February1st to 15thNight
58%10%12%13%4
2333
16th to endNight
51%10%16%15%5%
2030
March1st to 15thNight
52%10%16%16%3
2098
16th to endNight
45%16%20%15%2
2046
April1st to 15thNight
49%10%19%16%4
1799
16th to endNight
49%12%16%16%4
1542
May1st to 15thNight
40%10%20%19%8%
1440
16th to endNight
51%10%20%14%3
1438
June1st to 15thNight
46%8%16%19%6%1
1191
16th to endNight
42%8%21%19%5%1
1171
July1st to 15thNight
28%7%18%24%16%3
1190
16th to endNight
24%7%20%30%15%1
1313
August1st to 15thNight
26%7%19%30%12%2
1435
16th to endNight
34%6%19%27%10%2
1767
September1st to 15thNight
31%6%14%31%15%1
1800
16th to endNight
37%7%19%22%9%3
1838
October1st to 15thNight
42%8%16%22%9%
1980
16th to endNight
52%10%15%17%3
2238
November1st to 15thNight
54%11%16%12%4
2450
16th to endNight
57%10%13%12%5%
2520
December1st to 15thNight
58%10%13%14%3
2754
16th to endNight
62%11%11%10%4
2952

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
15%28%35%23%6%
60
16th to endDay
420%35%25%10%3
64
February1st to 15thDay
11%22%42%21%2
188
16th to endDay
7%22%39%23%6%
215
March1st to 15thDay
17%37%32%11%1
270
16th to endDay
13%34%36%11%3
288
April1st to 15thDay
19%21%33%18%6%
269
16th to endDay
16%30%31%17%4
270
May1st to 15thDay
10%28%33%20%5%1
288
16th to endDay
18%18%29%20%11%2
387
June1st to 15thDay
21%20%27%22%6%
558
16th to endDay
14%21%35%22%6%
577
July1st to 15thDay
9%21%32%29%6%
475
16th to endDay
7%15%32%33%9%1
432
August1st to 15thDay
8%9%29%32%16%2
315
16th to endDay
8%18%35%30%5%2
332
September1st to 15thDay
13%20%29%26%8%
315
16th to endDay
11%24%36%20%6%
268
October1st to 15thDay
18%29%28%18%5%
255
16th to endDay
8%19%38%25%6%
159
November1st to 15thDay
41%45%13%
60
16th to endDay
11%10%35%26%6%10%
60
December1st to 15thDay
321%36%20%13%5%
60
16th to endDay
6%450%21%14%3
64
January1st to 15thNight
12%18%43%19%5%
750
16th to endNight
10%13%46%21%6%
782
February1st to 15thNight
12%12%47%21%5%
704
16th to endNight
6%10%50%25%7%
632
March1st to 15thNight
8%18%51%18%3
720
16th to endNight
417%50%21%6%
768
April1st to 15thNight
7%14%40%31%6%
719
16th to endNight
9%10%49%26%4
462
May1st to 15thNight
10%9%38%31%10%
360
16th to endNight
14%437%35%8%
375
June1st to 15thNight
14%9%38%29%7%
360
16th to endNight
8%7%44%33%5%
360
July1st to 15thNight
48%35%41%10%
340
16th to endNight
45%25%48%16%
376
August1st to 15thNight
6%221%45%24%
363
16th to endNight
6%9%30%41%12%
621
September1st to 15thNight
8%8%31%31%20%
720
16th to endNight
10%14%34%29%11%
671
October1st to 15thNight
7%15%43%25%8%
660
16th to endNight
11%17%46%17%7%
704
November1st to 15thNight
11%18%52%15%2
700
16th to endNight
10%18%46%17%6%
720
December1st to 15thNight
9%14%49%20%6%
872
16th to endNight
7%16%53%17%5%
872
Page generated at 2017-09-20 01:49:48. Version ac04

Copyright 2017 A. Danko


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