Lillooet
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lillooet clear sky chart from 2005-11-06 to 2024-01-13.

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 Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(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

By Month

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 Forecast	Data Points
Cloud Cover	Day	6% 9% 4 9% 8% 5% 7% 7% 7% 8% 31%	74555
	Night	5% 9% 5% 9% 8% 5% 7% 7% 8% 9% 28%	75142
Transparency	Day	48% 9% 14% 18% 9% 1	74241
	Night	47% 10% 15% 18% 8% 1	74974
Seeing	Day	14% 17% 32% 25% 9% 2	14348
	Night	10% 14% 42% 27% 7%	22788

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	3 14% 6% 12% 11% 6% 8% 9% 8% 9% 15%	1329
	11th to 20th	Day	3 9% 4 9% 9% 6% 8% 9% 8% 11% 23%	1274
	21st to end	Day	3 8% 5% 9% 8% 5% 9% 9% 9% 10% 24%	1548
February	1st to 10th	Day	3 10% 5% 11% 11% 7% 7% 9% 9% 9% 19%	1548
	11th to 20th	Day	3 7% 5% 11% 10% 5% 9% 8% 9% 9% 27%	1575
	21st to end	Day	2 9% 7% 11% 11% 7% 8% 8% 8% 8% 20%	1366
March	1st to 10th	Day	1 10% 6% 12% 10% 6% 8% 8% 8% 9% 23%	1800
	11th to 20th	Day	1 9% 6% 12% 9% 4 8% 8% 9% 8% 25%	1980
	21st to end	Day	3 12% 6% 11% 11% 6% 9% 8% 8% 8% 18%	2274
April	1st to 10th	Day	5% 12% 6% 10% 9% 5% 9% 9% 7% 8% 20%	2160
	11th to 20th	Day	4 11% 7% 12% 8% 5% 7% 8% 6% 8% 22%	2201
	21st to end	Day	5% 11% 5% 10% 9% 6% 7% 6% 8% 9% 24%	2467
May	1st to 10th	Day	7% 12% 5% 9% 8% 5% 7% 6% 6% 8% 28%	2520
	11th to 20th	Day	6% 9% 5% 9% 8% 5% 7% 7% 8% 9% 27%	2477
	21st to end	Day	14% 10% 4 10% 9% 5% 7% 6% 6% 6% 24%	2807
June	1st to 10th	Day	11% 9% 5% 9% 7% 4 6% 6% 7% 8% 28%	2704
	11th to 20th	Day	12% 10% 4 10% 9% 5% 8% 7% 7% 7% 21%	2880
	21st to end	Day	7% 7% 4 7% 8% 5% 6% 7% 7% 7% 35%	2734
July	1st to 10th	Day	6% 7% 3 7% 6% 3 6% 5% 6% 9% 43%	2700
	11th to 20th	Day	6% 4 2 4 6% 4 6% 6% 8% 10% 44%	2700
	21st to end	Day	4 4 2 5% 5% 3 5% 5% 6% 8% 53%	2813
August	1st to 10th	Day	6% 5% 2 5% 6% 4 5% 5% 7% 8% 48%	2507
	11th to 20th	Day	4 5% 2 4 5% 4 4 5% 5% 8% 54%	2378
	21st to end	Day	6% 7% 3 7% 6% 4 6% 7% 6% 8% 39%	2502
September	1st to 10th	Day	7% 6% 3 6% 5% 3 5% 5% 5% 8% 48%	2160
	11th to 20th	Day	10% 8% 3 7% 6% 4 4 5% 5% 7% 40%	2160
	21st to end	Day	7% 9% 3 7% 7% 4 6% 6% 6% 8% 38%	1909
October	1st to 10th	Day	8% 10% 3 7% 6% 4 5% 4 7% 8% 38%	1800
	11th to 20th	Day	8% 8% 3 7% 7% 5% 7% 7% 7% 8% 33%	1800
	21st to end	Day	5% 11% 4 9% 7% 4 7% 6% 7% 10% 29%	1774
November	1st to 10th	Day	6% 11% 6% 11% 9% 5% 8% 7% 7% 9% 22%	1488
	11th to 20th	Day	3 9% 5% 9% 8% 5% 6% 6% 7% 9% 31%	1520
	21st to end	Day	3 9% 6% 10% 8% 5% 7% 8% 8% 11% 25%	1520
December	1st to 10th	Day	4 11% 5% 10% 9% 5% 8% 8% 9% 9% 22%	1314
	11th to 20th	Day	3 10% 6% 12% 9% 6% 7% 7% 8% 10% 22%	1442
	21st to end	Day	4 8% 5% 12% 11% 6% 9% 7% 8% 10% 21%	2424
January	1st to 10th	Night	4 14% 7% 11% 10% 6% 10% 10% 8% 8% 11%	2836
	11th to 20th	Night	4 10% 6% 12% 11% 6% 10% 9% 9% 11% 12%	2730
	21st to end	Night	3 10% 5% 10% 10% 6% 11% 11% 9% 11% 14%	2808
February	1st to 10th	Night	4 11% 5% 13% 12% 6% 7% 9% 9% 10% 14%	2408
	11th to 20th	Night	4 9% 5% 10% 10% 6% 8% 7% 8% 13% 21%	2272
	21st to end	Night	2 10% 7% 12% 12% 7% 7% 9% 8% 9% 17%	1889
March	1st to 10th	Night	1 9% 6% 12% 10% 6% 8% 8% 7% 9% 24%	2157
	11th to 20th	Night	1 7% 5% 7% 9% 5% 7% 9% 10% 13% 28%	1979
	21st to end	Night	2 8% 5% 9% 8% 6% 9% 9% 8% 11% 26%	2081
April	1st to 10th	Night	3 9% 5% 8% 9% 6% 10% 7% 9% 9% 25%	1800
	11th to 20th	Night	4 8% 5% 8% 8% 5% 7% 7% 9% 10% 30%	1706
	21st to end	Night	4 8% 5% 10% 8% 5% 7% 7% 7% 10% 30%	1492
May	1st to 10th	Night	5% 10% 4 8% 6% 3 6% 5% 6% 9% 37%	1440
	11th to 20th	Night	6% 7% 3 6% 7% 4 5% 7% 8% 11% 36%	1416
	21st to end	Night	12% 8% 4 8% 6% 3 6% 7% 7% 9% 31%	1465
June	1st to 10th	Night	8% 10% 3 7% 6% 4 6% 5% 6% 10% 33%	1248
	11th to 20th	Night	9% 7% 4 7% 8% 5% 8% 6% 8% 10% 30%	1080
	21st to end	Night	7% 5% 3 7% 6% 3 5% 6% 8% 9% 43%	1216
July	1st to 10th	Night	6% 6% 4 5% 6% 3 5% 5% 6% 6% 49%	1260
	11th to 20th	Night	5% 3 1 4 4 3 6% 7% 8% 10% 48%	1260
	21st to end	Night	3 3 2 4 4 3 5% 6% 7% 9% 56%	1501
August	1st to 10th	Night	3 5% 1 5% 4 3 4 5% 6% 9% 55%	1432
	11th to 20th	Night	3 4 2 5% 3 3 4 5% 5% 10% 57%	1518
	21st to end	Night	5% 6% 3 6% 7% 4 6% 5% 6% 7% 44%	1854
September	1st to 10th	Night	6% 5% 2 4 4 3 4 4 7% 8% 53%	1800
	11th to 20th	Night	7% 6% 3 6% 5% 3 6% 6% 6% 9% 44%	1800
	21st to end	Night	8% 8% 2 5% 7% 3 5% 6% 5% 9% 42%	2047
October	1st to 10th	Night	6% 9% 3 7% 6% 5% 5% 5% 6% 8% 39%	2160
	11th to 20th	Night	6% 9% 4 7% 8% 4 6% 6% 6% 9% 36%	2160
	21st to end	Night	5% 11% 5% 10% 8% 4 6% 6% 7% 9% 29%	2582
November	1st to 10th	Night	5% 12% 6% 12% 8% 5% 6% 7% 9% 9% 22%	2590
	11th to 20th	Night	4 9% 6% 9% 8% 6% 7% 7% 7% 8% 28%	2660
	21st to end	Night	5% 10% 6% 12% 8% 5% 9% 8% 9% 11% 18%	2660
December	1st to 10th	Night	4 10% 6% 10% 9% 5% 9% 10% 9% 11% 18%	2839
	11th to 20th	Night	4 12% 7% 14% 11% 6% 8% 8% 8% 9% 12%	3750
	21st to end	Night	5% 13% 6% 12% 10% 6% 9% 8% 9% 9% 14%	5246

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	61% 14% 11% 9% 4 1	1329
	11th to 20th	Day	52% 12% 16% 13% 4 2	1274
	21st to end	Day	53% 11% 14% 16% 6%	1548
February	1st to 10th	Day	56% 12% 13% 11% 8% 1	1548
	11th to 20th	Day	50% 12% 14% 17% 7%	1584
	21st to end	Day	58% 9% 13% 13% 6% 1	1366
March	1st to 10th	Day	51% 13% 13% 14% 8% 1	1800
	11th to 20th	Day	50% 11% 17% 16% 5%	1980
	21st to end	Day	59% 11% 14% 14% 2	2274
April	1st to 10th	Day	57% 11% 13% 14% 4	2160
	11th to 20th	Day	57% 10% 11% 14% 8%	2201
	21st to end	Day	53% 10% 14% 17% 6%	2467
May	1st to 10th	Day	53% 7% 16% 15% 9%	2520
	11th to 20th	Day	50% 10% 15% 17% 8%	2480
	21st to end	Day	59% 7% 11% 16% 5% 1	2808
June	1st to 10th	Day	54% 8% 12% 15% 9% 3	2704
	11th to 20th	Day	60% 9% 13% 12% 6%	2880
	21st to end	Day	46% 9% 16% 17% 10% 2	2734
July	1st to 10th	Day	40% 7% 13% 24% 14% 3	2626
	11th to 20th	Day	34% 8% 15% 26% 14% 3	2619
	21st to end	Day	29% 6% 13% 29% 20% 4	2656
August	1st to 10th	Day	33% 7% 15% 26% 17% 3	2490
	11th to 20th	Day	28% 6% 16% 30% 17% 3	2378
	21st to end	Day	41% 6% 15% 26% 9% 2	2502
September	1st to 10th	Day	34% 8% 15% 28% 12% 3	2160
	11th to 20th	Day	43% 7% 12% 21% 14% 3	2160
	21st to end	Day	45% 9% 16% 19% 10% 2	1909
October	1st to 10th	Day	44% 8% 14% 26% 8%	1800
	11th to 20th	Day	45% 12% 16% 19% 8%	1800
	21st to end	Day	48% 10% 15% 20% 6%	1774
November	1st to 10th	Day	56% 10% 11% 16% 6%	1488
	11th to 20th	Day	47% 12% 15% 16% 9% 1	1520
	21st to end	Day	50% 10% 17% 16% 7% 1	1520
December	1st to 10th	Day	54% 12% 14% 16% 5%	1314
	11th to 20th	Day	53% 16% 14% 13% 3	1444
	21st to end	Day	50% 16% 14% 15% 5%	2424
January	1st to 10th	Night	64% 10% 13% 9% 4 1	2836
	11th to 20th	Night	61% 10% 12% 11% 4 1	2730
	21st to end	Night	58% 10% 12% 12% 7%	2808
February	1st to 10th	Night	56% 12% 12% 13% 6% 1	2408
	11th to 20th	Night	50% 11% 15% 15% 8%	2274
	21st to end	Night	57% 10% 12% 13% 8%	1889
March	1st to 10th	Night	53% 10% 13% 16% 8%	2157
	11th to 20th	Night	41% 13% 20% 21% 5% 1	1980
	21st to end	Night	46% 15% 19% 17% 3	2081
April	1st to 10th	Night	48% 10% 19% 18% 5%	1800
	11th to 20th	Night	44% 10% 16% 20% 9%	1706
	21st to end	Night	44% 11% 16% 21% 8%	1492
May	1st to 10th	Night	43% 9% 19% 18% 10% 1	1440
	11th to 20th	Night	39% 11% 23% 20% 6%	1416
	21st to end	Night	46% 10% 18% 20% 5% 1	1465
June	1st to 10th	Night	46% 10% 13% 20% 9% 2	1248
	11th to 20th	Night	46% 10% 19% 16% 8% 1	1080
	21st to end	Night	36% 9% 20% 23% 8% 4	1216
July	1st to 10th	Night	34% 7% 18% 23% 15% 3	1225
	11th to 20th	Night	28% 8% 20% 28% 14% 2	1218
	21st to end	Night	21% 7% 16% 30% 21% 5%	1418
August	1st to 10th	Night	26% 7% 17% 28% 18% 3	1424
	11th to 20th	Night	25% 5% 19% 32% 16% 3	1518
	21st to end	Night	38% 7% 17% 26% 10% 1	1854
September	1st to 10th	Night	30% 7% 16% 32% 12% 3	1800
	11th to 20th	Night	37% 7% 15% 23% 15% 3	1800
	21st to end	Night	38% 8% 22% 21% 10% 2	2047
October	1st to 10th	Night	41% 8% 15% 26% 9%	2160
	11th to 20th	Night	44% 10% 17% 21% 8%	2160
	21st to end	Night	49% 9% 14% 20% 8%	2582
November	1st to 10th	Night	55% 11% 15% 12% 6% 1	2590
	11th to 20th	Night	49% 12% 18% 13% 8% 1	2660
	21st to end	Night	53% 11% 15% 14% 6% 1	2660
December	1st to 10th	Night	53% 12% 13% 16% 5%	2839
	11th to 20th	Night	64% 13% 12% 9% 3	3747
	21st to end	Night	54% 17% 12% 11% 6% 1	5246

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
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	11% 11% 36% 25% 14% 2	180
	11th to 20th	Day	8% 12% 37% 29% 12% 2	164
	21st to end	Day	9% 10% 38% 31% 10% 3	176
February	1st to 10th	Day	10% 20% 46% 21% 3	268
	11th to 20th	Day	6% 19% 44% 25% 6% 1	335
	21st to end	Day	11% 20% 36% 23% 9% 1	296
March	1st to 10th	Day	15% 22% 33% 21% 8% 1	420
	11th to 20th	Day	15% 23% 33% 19% 8% 1	420
	21st to end	Day	14% 22% 36% 16% 10% 2	462
April	1st to 10th	Day	19% 20% 34% 20% 6%	420
	11th to 20th	Day	16% 21% 30% 20% 9% 4	412
	21st to end	Day	16% 24% 27% 20% 8% 3	420
May	1st to 10th	Day	16% 17% 32% 25% 7% 2	423
	11th to 20th	Day	15% 14% 31% 25% 11% 4	448
	21st to end	Day	19% 16% 30% 22% 11% 2	569
June	1st to 10th	Day	19% 26% 31% 20% 5% 1	634
	11th to 20th	Day	20% 18% 31% 24% 7%	810
	21st to end	Day	15% 16% 33% 25% 9% 1	664
July	1st to 10th	Day	12% 18% 32% 25% 12% 2	621
	11th to 20th	Day	11% 15% 33% 29% 10% 1	618
	21st to end	Day	6% 11% 32% 35% 11% 4	559
August	1st to 10th	Day	10% 10% 30% 31% 14% 6%	447
	11th to 20th	Day	8% 10% 31% 34% 11% 6%	437
	21st to end	Day	13% 14% 32% 29% 9% 4	495
September	1st to 10th	Day	14% 16% 33% 26% 7% 3	450
	11th to 20th	Day	18% 16% 27% 25% 11% 2	450
	21st to end	Day	19% 20% 29% 24% 8%	450
October	1st to 10th	Day	18% 18% 27% 25% 10% 3	450
	11th to 20th	Day	18% 22% 28% 20% 9% 2	450
	21st to end	Day	19% 14% 38% 20% 7% 1	302
November	1st to 10th	Day	17% 17% 38% 19% 9% 1	180
	11th to 20th	Day	12% 21% 27% 27% 9% 4	180
	21st to end	Day	10% 16% 33% 24% 11% 7%	180
December	1st to 10th	Day	5% 12% 29% 32% 17% 5%	180
	11th to 20th	Day	10% 10% 34% 28% 12% 6%	180
	21st to end	Day	11% 5% 35% 34% 12% 3	198
January	1st to 10th	Night	12% 19% 41% 21% 6%	850
	11th to 20th	Night	11% 14% 47% 22% 5%	810
	21st to end	Night	7% 16% 48% 23% 6%	808
February	1st to 10th	Night	9% 16% 51% 22% 3	720
	11th to 20th	Night	8% 14% 51% 22% 5%	704
	21st to end	Night	8% 15% 45% 27% 5%	592
March	1st to 10th	Night	7% 14% 52% 21% 5% 1	720
	11th to 20th	Night	6% 20% 49% 22% 3	720
	21st to end	Night	8% 16% 46% 25% 6%	792
April	1st to 10th	Night	9% 13% 44% 30% 4	720
	11th to 20th	Night	9% 16% 46% 22% 7%	638
	21st to end	Night	11% 14% 46% 24% 4	412
May	1st to 10th	Night	12% 12% 41% 30% 5%	360
	11th to 20th	Night	9% 8% 39% 39% 4	354
	21st to end	Night	15% 6% 39% 36% 4	389
June	1st to 10th	Night	15% 10% 44% 26% 4	360
	11th to 20th	Night	14% 9% 45% 29% 3	360
	21st to end	Night	9% 11% 38% 36% 7%	360
July	1st to 10th	Night	9% 7% 37% 36% 9% 1	350
	11th to 20th	Night	6% 9% 34% 45% 6% 1	348
	21st to end	Night	4 6% 26% 51% 12%	394
August	1st to 10th	Night	5% 3 23% 53% 16%	358
	11th to 20th	Night	4 4 31% 47% 13%	450
	21st to end	Night	9% 11% 34% 36% 10%	666
September	1st to 10th	Night	9% 9% 41% 32% 9%	720
	11th to 20th	Night	11% 10% 26% 35% 17%	720
	21st to end	Night	14% 16% 34% 27% 8%	720
October	1st to 10th	Night	11% 17% 37% 26% 8% 1	720
	11th to 20th	Night	12% 16% 40% 24% 8% 1	720
	21st to end	Night	14% 20% 41% 18% 6% 1	792
November	1st to 10th	Night	13% 19% 45% 19% 4 1	740
	11th to 20th	Night	12% 22% 40% 18% 7% 1	760
	21st to end	Night	12% 17% 44% 21% 6% 1	760
December	1st to 10th	Night	10% 16% 39% 24% 10% 1	907
	11th to 20th	Night	11% 16% 43% 24% 4 1	1040
	21st to end	Night	11% 15% 43% 25% 6%	954

Page generated at 2024-01-09 22:25:03. Version ac07

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