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 2025-12-03.

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	5% 9% 4 9% 6% 6% 6% 5% 7% 9% 35%	130695
	Night	4 9% 4 10% 6% 6% 6% 5% 8% 10% 32%	128645
Transparency	Day	46% 7% 14% 21% 10% 2	130402
	Night	47% 8% 16% 19% 8% 1	128515
Seeing	Day	14% 17% 32% 25% 9% 2	16879
	Night	10% 14% 40% 28% 8% 1	25128

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 16% 6% 13% 9% 7% 7% 6% 8% 12% 14%	3179
	11th to 20th	Day	2 11% 5% 11% 7% 5% 6% 6% 8% 10% 29%	3159
	21st to end	Day	5% 10% 6% 12% 7% 6% 7% 5% 6% 7% 29%	3912
February	1st to 10th	Day	2 11% 5% 12% 10% 10% 7% 7% 9% 8% 19%	1721
	11th to 20th	Day	2 7% 4 12% 9% 6% 8% 6% 8% 9% 28%	1755
	21st to end	Day	2 12% 5% 13% 10% 9% 8% 6% 8% 8% 20%	1523
March	1st to 10th	Day	1 11% 6% 15% 7% 6% 7% 5% 7% 8% 26%	4518
	11th to 20th	Day	1 10% 4 10% 7% 6% 6% 6% 9% 10% 32%	5000
	21st to end	Day	3 12% 5% 12% 9% 8% 8% 6% 8% 9% 21%	5737
April	1st to 10th	Day	4 14% 4 11% 8% 7% 8% 7% 8% 8% 21%	2400
	11th to 20th	Day	3 12% 6% 13% 8% 7% 7% 6% 7% 8% 24%	2449
	21st to end	Day	5% 12% 5% 11% 8% 7% 6% 5% 8% 9% 26%	2742
May	1st to 10th	Day	4 9% 3 8% 6% 6% 6% 5% 7% 8% 39%	6320
	11th to 20th	Day	5% 8% 4 10% 7% 7% 7% 6% 10% 11% 26%	6277
	21st to end	Day	10% 10% 4 11% 6% 6% 7% 5% 7% 8% 26%	7127
June	1st to 10th	Day	11% 10% 4 9% 6% 6% 5% 5% 6% 8% 30%	3005
	11th to 20th	Day	11% 11% 4 11% 8% 7% 7% 6% 7% 7% 21%	3200
	21st to end	Day	7% 7% 4 9% 6% 7% 6% 5% 7% 7% 34%	3036
July	1st to 10th	Day	3 4 2 5% 4 4 5% 4 6% 9% 55%	6780
	11th to 20th	Day	5% 4 1 4 4 4 4 4 6% 7% 58%	6780
	21st to end	Day	4 4 2 5% 3 4 4 4 6% 9% 55%	7058
August	1st to 10th	Day	4 4 2 4 5% 4 5% 4 6% 8% 54%	4541
	11th to 20th	Day	5% 6% 2 6% 5% 6% 6% 4 7% 11% 43%	4289
	21st to end	Day	7% 6% 2 7% 4 5% 6% 4 6% 8% 44%	4536
September	1st to 10th	Day	6% 6% 2 6% 4 4 4 5% 6% 8% 50%	2400
	11th to 20th	Day	9% 8% 3 7% 5% 5% 5% 4 5% 7% 42%	2400
	21st to end	Day	7% 9% 3 9% 5% 6% 6% 4 6% 8% 38%	2120
October	1st to 10th	Day	5% 7% 3 7% 5% 5% 6% 4 7% 8% 42%	3280
	11th to 20th	Day	8% 8% 3 8% 6% 7% 6% 5% 7% 7% 34%	3261
	21st to end	Day	4 8% 3 10% 5% 6% 6% 6% 8% 11% 32%	3178
November	1st to 10th	Day	5% 11% 5% 11% 8% 6% 8% 5% 7% 9% 23%	1648
	11th to 20th	Day	3 11% 5% 10% 8% 7% 5% 5% 7% 9% 30%	1680
	21st to end	Day	3 11% 5% 11% 8% 7% 8% 6% 8% 11% 23%	1680
December	1st to 10th	Day	3 10% 3 10% 8% 7% 8% 6% 9% 10% 26%	2262
	11th to 20th	Day	3 12% 5% 11% 8% 8% 8% 6% 9% 10% 20%	2262
	21st to end	Day	3 8% 5% 14% 9% 7% 9% 6% 9% 11% 19%	3480
January	1st to 10th	Night	2 15% 7% 13% 9% 7% 8% 6% 8% 10% 15%	6766
	11th to 20th	Night	2 12% 5% 12% 7% 6% 6% 5% 10% 12% 23%	6739
	21st to end	Night	5% 12% 5% 11% 7% 7% 7% 6% 7% 8% 26%	7030
February	1st to 10th	Night	3 11% 5% 14% 11% 9% 7% 7% 9% 9% 14%	2675
	11th to 20th	Night	3 10% 4 11% 8% 8% 7% 5% 8% 12% 22%	2532
	21st to end	Night	2 12% 6% 13% 10% 8% 7% 7% 8% 9% 18%	2106
March	1st to 10th	Night	1 8% 5% 13% 7% 6% 7% 6% 9% 11% 28%	5360
	11th to 20th	Night	1 5% 3 6% 6% 6% 6% 6% 10% 12% 39%	4999
	21st to end	Night	4 12% 4 10% 7% 7% 7% 6% 7% 9% 28%	5237
April	1st to 10th	Night	2 12% 3 9% 9% 8% 8% 5% 9% 10% 24%	2000
	11th to 20th	Night	3 9% 4 9% 7% 6% 6% 6% 8% 10% 31%	1897
	21st to end	Night	3 9% 4 11% 7% 7% 7% 5% 8% 9% 31%	1657
May	1st to 10th	Night	2 8% 3 7% 5% 5% 6% 5% 7% 9% 44%	3640
	11th to 20th	Night	4 8% 4 8% 5% 6% 6% 6% 8% 11% 34%	3616
	21st to end	Night	8% 7% 3 8% 6% 6% 6% 5% 8% 10% 35%	3745
June	1st to 10th	Night	8% 11% 2 7% 6% 5% 5% 5% 6% 9% 35%	1386
	11th to 20th	Night	8% 8% 3 9% 7% 7% 6% 6% 7% 9% 31%	1200
	21st to end	Night	7% 5% 2 8% 5% 4 6% 4 8% 8% 42%	1352
July	1st to 10th	Night	4 6% 3 6% 4 4 5% 4 5% 7% 51%	3180
	11th to 20th	Night	3 3 1 3 2 3 4 3 5% 7% 66%	3180
	21st to end	Night	5% 4 1 4 4 4 4 4 5% 7% 57%	3782
August	1st to 10th	Night	3 5% 2 5% 3 4 5% 4 7% 8% 55%	2609
	11th to 20th	Night	5% 5% 2 5% 3 5% 5% 4 8% 11% 46%	2761
	21st to end	Night	7% 5% 2 6% 5% 5% 5% 4 6% 8% 47%	3377
September	1st to 10th	Night	6% 5% 2 5% 3 4 4 3 7% 8% 54%	2000
	11th to 20th	Night	7% 6% 2 7% 5% 4 5% 5% 6% 9% 45%	2000
	21st to end	Night	8% 8% 2 7% 5% 5% 5% 4 6% 9% 42%	2276
October	1st to 10th	Night	4 8% 3 8% 5% 6% 5% 4 7% 8% 43%	3920
	11th to 20th	Night	4 7% 3 7% 6% 6% 7% 4 7% 11% 38%	3897
	21st to end	Night	5% 10% 4 10% 5% 5% 5% 5% 7% 12% 32%	4621
November	1st to 10th	Night	5% 13% 5% 13% 7% 6% 6% 6% 8% 9% 22%	2870
	11th to 20th	Night	4 11% 4 10% 7% 7% 7% 6% 8% 8% 28%	2940
	21st to end	Night	5% 13% 4 12% 7% 7% 8% 7% 9% 10% 18%	2940
December	1st to 10th	Night	3 9% 3 9% 6% 7% 7% 7% 10% 13% 27%	4921
	11th to 20th	Night	3 11% 6% 15% 9% 9% 8% 7% 9% 9% 14%	5930
	21st to end	Night	4 12% 5% 13% 8% 8% 9% 7% 10% 10% 15%	7504

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	63% 12% 12% 11% 3	3179
	11th to 20th	Day	49% 7% 16% 19% 3 5%	3180
	21st to end	Day	55% 8% 12% 18% 7%	3912
February	1st to 10th	Day	55% 12% 12% 12% 9% 1	1721
	11th to 20th	Day	49% 11% 13% 17% 9%	1764
	21st to end	Day	59% 10% 12% 13% 6% 1	1523
March	1st to 10th	Day	52% 10% 12% 17% 9%	4518
	11th to 20th	Day	43% 10% 13% 24% 10%	5000
	21st to end	Day	57% 10% 11% 15% 6%	5737
April	1st to 10th	Day	56% 11% 14% 14% 4	2400
	11th to 20th	Day	54% 9% 11% 15% 10% 1	2449
	21st to end	Day	52% 9% 14% 19% 7%	2742
May	1st to 10th	Day	42% 6% 12% 25% 14% 1	6320
	11th to 20th	Day	51% 8% 15% 20% 6%	6280
	21st to end	Day	56% 6% 14% 19% 4 1	7128
June	1st to 10th	Day	52% 7% 12% 17% 10% 3	3005
	11th to 20th	Day	59% 8% 13% 13% 6%	3200
	21st to end	Day	46% 8% 16% 17% 10% 2	3036
July	1st to 10th	Day	30% 3 13% 23% 21% 9%	6706
	11th to 20th	Day	27% 4 14% 28% 20% 6%	6699
	21st to end	Day	28% 3 19% 28% 18% 4	6860
August	1st to 10th	Day	29% 5% 11% 34% 19% 2	4524
	11th to 20th	Day	37% 4 21% 25% 10% 2	4331
	21st to end	Day	39% 4 22% 27% 7% 1	4535
September	1st to 10th	Day	32% 7% 16% 29% 13% 3	2400
	11th to 20th	Day	41% 6% 13% 23% 14% 3	2400
	21st to end	Day	46% 8% 16% 18% 10% 2	2120
October	1st to 10th	Day	42% 6% 17% 24% 11%	3280
	11th to 20th	Day	48% 7% 13% 24% 8%	3261
	21st to end	Day	48% 6% 20% 21% 5%	3178
November	1st to 10th	Day	56% 10% 12% 16% 6%	1648
	11th to 20th	Day	49% 11% 15% 17% 8%	1680
	21st to end	Day	53% 9% 16% 15% 6% 1	1680
December	1st to 10th	Day	54% 9% 19% 14% 3	2262
	11th to 20th	Day	57% 12% 13% 13% 5%	2264
	21st to end	Day	54% 13% 13% 15% 4	3480
January	1st to 10th	Night	62% 9% 13% 12% 4	6766
	11th to 20th	Night	52% 7% 16% 16% 5% 4	6780
	21st to end	Night	54% 9% 17% 15% 4	7030
February	1st to 10th	Night	57% 11% 11% 14% 6% 1	2675
	11th to 20th	Night	49% 10% 15% 15% 9% 1	2534
	21st to end	Night	56% 9% 13% 14% 7%	2106
March	1st to 10th	Night	49% 7% 14% 19% 11%	5360
	11th to 20th	Night	36% 10% 16% 23% 15%	5000
	21st to end	Night	51% 11% 12% 18% 9%	5237
April	1st to 10th	Night	49% 10% 19% 17% 5%	2000
	11th to 20th	Night	43% 10% 16% 21% 10%	1897
	21st to end	Night	44% 10% 17% 20% 8%	1657
May	1st to 10th	Night	37% 6% 16% 26% 13% 1	3637
	11th to 20th	Night	43% 8% 19% 27% 4	3616
	21st to end	Night	42% 8% 17% 26% 5%	3745
June	1st to 10th	Night	44% 9% 13% 21% 11% 2	1386
	11th to 20th	Night	46% 9% 18% 17% 10% 1	1200
	21st to end	Night	37% 9% 20% 23% 7% 4	1352
July	1st to 10th	Night	35% 4 14% 23% 17% 8%	3145
	11th to 20th	Night	20% 3 22% 29% 22% 4	3138
	21st to end	Night	28% 3 20% 26% 16% 8%	3675
August	1st to 10th	Night	28% 6% 13% 29% 23% 2	2601
	11th to 20th	Night	35% 5% 21% 26% 11% 2	2785
	21st to end	Night	37% 5% 23% 26% 8% 1	3377
September	1st to 10th	Night	30% 6% 16% 31% 14% 3	2000
	11th to 20th	Night	37% 6% 17% 23% 15% 3	2000
	21st to end	Night	38% 8% 23% 20% 10% 2	2276
October	1st to 10th	Night	42% 5% 18% 25% 10%	3920
	11th to 20th	Night	43% 6% 21% 23% 7%	3897
	21st to end	Night	51% 6% 17% 21% 5%	4621
November	1st to 10th	Night	55% 10% 15% 13% 7% 1	2870
	11th to 20th	Night	51% 11% 17% 14% 7% 1	2940
	21st to end	Night	55% 10% 15% 14% 6% 1	2940
December	1st to 10th	Night	50% 10% 20% 15% 5%	4921
	11th to 20th	Night	64% 9% 14% 9% 3	5927
	21st to end	Night	56% 15% 11% 13% 4	7504

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% 10% 39% 24% 15% 2	200
	11th to 20th	Day	7% 10% 38% 31% 14% 2	200
	21st to end	Day	10% 8% 35% 30% 13% 4	220
February	1st to 10th	Day	9% 18% 44% 22% 6% 1	321
	11th to 20th	Day	6% 17% 44% 26% 7% 1	395
	21st to end	Day	13% 20% 36% 21% 9% 1	351
March	1st to 10th	Day	14% 21% 32% 23% 8% 1	500
	11th to 20th	Day	14% 22% 33% 20% 10% 1	500
	21st to end	Day	14% 22% 35% 16% 10% 2	550
April	1st to 10th	Day	19% 20% 33% 22% 6%	500
	11th to 20th	Day	15% 20% 33% 20% 9% 3	492
	21st to end	Day	17% 23% 26% 21% 9% 4	500
May	1st to 10th	Day	15% 17% 32% 25% 7% 3	503
	11th to 20th	Day	17% 13% 31% 25% 10% 4	528
	21st to end	Day	21% 17% 30% 21% 9% 2	667
June	1st to 10th	Day	19% 25% 31% 19% 4 1	735
	11th to 20th	Day	20% 18% 30% 24% 8%	930
	21st to end	Day	15% 16% 32% 25% 10% 1	766
July	1st to 10th	Day	12% 19% 32% 25% 11% 2	721
	11th to 20th	Day	11% 16% 33% 29% 10% 1	718
	21st to end	Day	6% 13% 32% 33% 12% 4	655
August	1st to 10th	Day	9% 9% 30% 32% 14% 6%	527
	11th to 20th	Day	9% 13% 29% 33% 11% 6%	517
	21st to end	Day	12% 13% 31% 30% 9% 5%	583
September	1st to 10th	Day	13% 14% 31% 28% 9% 5%	530
	11th to 20th	Day	16% 16% 27% 26% 12% 4	530
	21st to end	Day	20% 23% 28% 21% 7%	530
October	1st to 10th	Day	18% 18% 28% 23% 10% 3	530
	11th to 20th	Day	17% 23% 29% 20% 8% 2	530
	21st to end	Day	18% 17% 37% 20% 7% 1	366
November	1st to 10th	Day	16% 19% 41% 16% 7%	220
	11th to 20th	Day	13% 21% 28% 26% 8% 4	220
	21st to end	Day	10% 15% 34% 25% 10% 6%	220
December	1st to 10th	Day	6% 10% 30% 31% 17% 6%	204
	11th to 20th	Day	10% 12% 33% 29% 12% 5%	200
	21st to end	Day	10% 7% 35% 33% 12% 3	220
January	1st to 10th	Night	12% 18% 40% 23% 7%	900
	11th to 20th	Night	11% 13% 44% 26% 6%	900
	21st to end	Night	8% 15% 44% 26% 8%	899
February	1st to 10th	Night	8% 16% 48% 23% 5% 1	800
	11th to 20th	Night	7% 13% 47% 25% 7% 1	784
	21st to end	Night	8% 15% 45% 26% 6%	660
March	1st to 10th	Night	7% 14% 50% 23% 6% 1	800
	11th to 20th	Night	5% 19% 48% 24% 5%	800
	21st to end	Night	9% 15% 44% 27% 6%	880
April	1st to 10th	Night	10% 13% 43% 30% 5%	800
	11th to 20th	Night	9% 16% 47% 22% 7%	709
	21st to end	Night	11% 14% 45% 24% 5% 1	457
May	1st to 10th	Night	11% 13% 41% 30% 6%	400
	11th to 20th	Night	9% 9% 39% 39% 5%	394
	21st to end	Night	14% 7% 38% 38% 3	433
June	1st to 10th	Night	16% 10% 43% 27% 5%	400
	11th to 20th	Night	13% 10% 44% 30% 4	400
	21st to end	Night	9% 11% 37% 36% 8%	400
July	1st to 10th	Night	8% 8% 36% 37% 10% 1	390
	11th to 20th	Night	5% 8% 33% 44% 8% 1	388
	21st to end	Night	5% 6% 25% 50% 14%	438
August	1st to 10th	Night	5% 3 23% 51% 18% 1	398
	11th to 20th	Night	5% 4 29% 47% 15%	502
	21st to end	Night	8% 10% 32% 37% 12% 1	740
September	1st to 10th	Night	8% 8% 37% 33% 12% 2	800
	11th to 20th	Night	10% 10% 25% 35% 19% 1	800
	21st to end	Night	14% 16% 34% 28% 7%	800
October	1st to 10th	Night	11% 17% 37% 27% 8% 1	800
	11th to 20th	Night	12% 15% 39% 25% 9% 1	800
	21st to end	Night	14% 20% 40% 19% 6% 1	880
November	1st to 10th	Night	12% 18% 44% 21% 4 1	820
	11th to 20th	Night	12% 22% 38% 21% 7% 1	840
	21st to end	Night	12% 16% 41% 23% 7% 1	840
December	1st to 10th	Night	9% 16% 38% 26% 10% 1	966
	11th to 20th	Night	11% 16% 42% 25% 5% 1	1100
	21st to end	Night	11% 15% 42% 25% 7%	1010

Page generated at 2025-11-29 22:00:55. Version ac07

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