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 2024-11-10.

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 10% 7% 6% 6% 5% 7% 8% 34%	105402
	Night	4 10% 4 10% 7% 6% 6% 5% 8% 9% 30%	102281
Transparency	Day	45% 9% 14% 20% 10% 2	105151
	Night	46% 9% 15% 19% 9% 2	102178
Seeing	Day	14% 17% 32% 25% 9% 2	15528
	Night	10% 14% 41% 27% 7% 1	23760

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	4 14% 6% 14% 10% 8% 7% 6% 8% 9% 14%	2219
	11th to 20th	Day	2 14% 5% 12% 8% 5% 6% 5% 6% 9% 27%	2199
	21st to end	Day	7% 12% 6% 15% 8% 8% 7% 5% 7% 7% 17%	2730
February	1st to 10th	Day	2 12% 5% 13% 9% 9% 7% 8% 9% 9% 18%	1634
	11th to 20th	Day	2 7% 5% 12% 9% 6% 8% 7% 8% 9% 27%	1665
	21st to end	Day	2 12% 5% 13% 10% 9% 9% 6% 8% 8% 20%	1449
March	1st to 10th	Day	11% 7% 17% 8% 7% 7% 5% 6% 8% 23%	3138
	11th to 20th	Day	1 9% 4 10% 7% 5% 6% 6% 9% 8% 35%	3490
	21st to end	Day	2 13% 5% 13% 9% 8% 8% 6% 7% 7% 21%	3998
April	1st to 10th	Day	4 14% 4 11% 8% 7% 8% 7% 8% 8% 20%	2280
	11th to 20th	Day	4 12% 6% 13% 8% 7% 7% 6% 7% 8% 23%	2325
	21st to end	Day	5% 12% 5% 12% 8% 7% 6% 5% 8% 8% 24%	2605
May	1st to 10th	Day	5% 11% 4 10% 6% 6% 5% 5% 6% 8% 33%	4420
	11th to 20th	Day	5% 8% 4 10% 7% 7% 7% 5% 9% 10% 28%	4377
	21st to end	Day	13% 13% 4 13% 8% 6% 6% 5% 5% 6% 20%	4967
June	1st to 10th	Day	11% 11% 4 10% 6% 6% 6% 5% 6% 7% 28%	2855
	11th to 20th	Day	11% 11% 4 11% 8% 7% 7% 6% 7% 7% 21%	3040
	21st to end	Day	7% 7% 4 9% 7% 7% 6% 5% 7% 7% 34%	2885
July	1st to 10th	Day	3 5% 2 5% 4 4 4 3 5% 7% 59%	4740
	11th to 20th	Day	3 3 1 3 3 4 3 4 6% 7% 62%	4740
	21st to end	Day	3 4 2 5% 4 4 4 4 6% 9% 55%	4918
August	1st to 10th	Day	4 4 2 4 5% 4 5% 4 6% 8% 54%	4401
	11th to 20th	Day	5% 6% 2 7% 5% 6% 6% 5% 7% 11% 43%	4155
	21st to end	Day	7% 6% 2 7% 4 5% 6% 4 6% 8% 43%	4397
September	1st to 10th	Day	6% 6% 2 6% 4 4 4 5% 6% 8% 49%	2280
	11th to 20th	Day	9% 9% 3 8% 5% 5% 5% 4 5% 7% 40%	2280
	21st to end	Day	7% 9% 3 9% 5% 6% 6% 4 6% 8% 38%	2014
October	1st to 10th	Day	5% 7% 2 7% 5% 5% 6% 4 7% 8% 43%	3180
	11th to 20th	Day	8% 8% 3 9% 6% 7% 6% 5% 7% 7% 34%	3161
	21st to end	Day	4 8% 3 10% 5% 6% 6% 6% 8% 11% 33%	3080
November	1st to 10th	Day	5% 12% 5% 12% 8% 7% 9% 5% 7% 9% 23%	1560
	11th to 20th	Day	3 10% 5% 10% 8% 7% 5% 5% 7% 9% 31%	1520
	21st to end	Day	3 11% 5% 10% 8% 7% 7% 6% 8% 10% 25%	1520
December	1st to 10th	Day	3 13% 4 12% 8% 7% 7% 6% 9% 9% 22%	1314
	11th to 20th	Day	3 11% 5% 13% 9% 7% 6% 6% 8% 10% 22%	1442
	21st to end	Day	4 9% 5% 14% 9% 7% 8% 5% 8% 10% 21%	2424
January	1st to 10th	Night	3 17% 8% 14% 8% 8% 8% 7% 8% 8% 12%	4726
	11th to 20th	Night	3 13% 5% 14% 8% 6% 7% 5% 10% 10% 18%	4699
	21st to end	Night	7% 16% 6% 13% 8% 7% 9% 7% 8% 9% 11%	4926
February	1st to 10th	Night	3 12% 5% 14% 11% 9% 7% 7% 9% 9% 14%	2542
	11th to 20th	Night	3 10% 4 11% 8% 8% 7% 5% 8% 12% 22%	2402
	21st to end	Night	2 12% 6% 13% 10% 8% 8% 7% 7% 9% 17%	2004
March	1st to 10th	Night	1 8% 6% 14% 7% 6% 6% 6% 8% 10% 27%	3720
	11th to 20th	Night	1 6% 4 7% 6% 6% 5% 5% 8% 11% 41%	3489
	21st to end	Night	5% 13% 4 10% 6% 7% 6% 5% 7% 8% 29%	3654
April	1st to 10th	Night	2 11% 4 9% 9% 8% 8% 5% 9% 9% 25%	1900
	11th to 20th	Night	4 10% 4 9% 7% 6% 6% 6% 8% 10% 31%	1801
	21st to end	Night	4 10% 4 11% 7% 7% 7% 5% 8% 9% 30%	1574
May	1st to 10th	Night	3 10% 4 10% 5% 5% 5% 4 5% 8% 41%	2540
	11th to 20th	Night	4 8% 3 8% 5% 6% 5% 5% 8% 11% 36%	2516
	21st to end	Night	11% 9% 4 10% 6% 7% 6% 5% 7% 9% 26%	2605
June	1st to 10th	Night	8% 11% 3 7% 6% 5% 5% 5% 6% 9% 34%	1317
	11th to 20th	Night	9% 8% 3 8% 7% 7% 6% 6% 8% 9% 29%	1140
	21st to end	Night	7% 6% 2 8% 5% 4 6% 4 8% 8% 42%	1284
July	1st to 10th	Night	4 5% 2 4 4 3 4 4 5% 7% 59%	2220
	11th to 20th	Night	3 2 1 3 2 3 4 4 6% 7% 66%	2220
	21st to end	Night	3 3 1 4 4 5% 5% 4 6% 8% 56%	2631
August	1st to 10th	Night	3 5% 2 5% 3 4 5% 4 6% 8% 56%	2529
	11th to 20th	Night	5% 5% 2 5% 3 4 5% 5% 8% 11% 46%	2675
	21st to end	Night	7% 5% 2 6% 5% 5% 4 4 7% 8% 46%	3274
September	1st to 10th	Night	6% 5% 2 5% 3 4 4 3 7% 8% 53%	1900
	11th to 20th	Night	7% 6% 2 7% 5% 4 5% 5% 6% 9% 44%	1900
	21st to end	Night	8% 8% 2 7% 5% 5% 4 4 6% 9% 42%	2162
October	1st to 10th	Night	4 7% 3 8% 5% 6% 5% 4 7% 8% 43%	3800
	11th to 20th	Night	4 7% 3 7% 6% 6% 7% 4 7% 11% 37%	3777
	21st to end	Night	5% 11% 4 10% 5% 5% 5% 5% 7% 12% 32%	4477
November	1st to 10th	Night	5% 13% 5% 13% 7% 6% 6% 6% 8% 9% 22%	2722
	11th to 20th	Night	4 11% 4 10% 8% 8% 7% 6% 7% 8% 28%	2660
	21st to end	Night	5% 12% 4 13% 7% 7% 8% 7% 9% 10% 18%	2660
December	1st to 10th	Night	4 12% 4 11% 8% 8% 8% 8% 9% 11% 17%	2839
	11th to 20th	Night	3 13% 7% 16% 10% 8% 8% 7% 8% 8% 11%	3750
	21st to end	Night	5% 14% 6% 14% 9% 8% 9% 6% 9% 8% 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	58% 16% 12% 10% 3	2219
	11th to 20th	Day	52% 8% 16% 13% 3 7%	2220
	21st to end	Day	63% 12% 10% 11% 4	2730
February	1st to 10th	Day	56% 12% 12% 12% 7% 1	1634
	11th to 20th	Day	49% 12% 13% 17% 9%	1674
	21st to end	Day	58% 10% 13% 13% 6% 1	1449
March	1st to 10th	Day	51% 14% 10% 16% 9% 1	3138
	11th to 20th	Day	39% 12% 18% 24% 7%	3490
	21st to end	Day	55% 13% 13% 11% 7%	3998
April	1st to 10th	Day	57% 11% 14% 13% 5%	2280
	11th to 20th	Day	55% 10% 11% 14% 9% 1	2325
	21st to end	Day	54% 10% 13% 17% 6%	2605
May	1st to 10th	Day	45% 8% 13% 22% 10% 1	4420
	11th to 20th	Day	46% 10% 16% 20% 7%	4380
	21st to end	Day	62% 8% 12% 14% 4	4968
June	1st to 10th	Day	53% 8% 12% 15% 9% 3	2855
	11th to 20th	Day	59% 8% 13% 12% 6%	3040
	21st to end	Day	46% 9% 15% 17% 10% 2	2885
July	1st to 10th	Day	27% 4 8% 21% 26% 13%	4666
	11th to 20th	Day	22% 5% 11% 28% 27% 9%	4659
	21st to end	Day	28% 4 18% 27% 19% 5%	4762
August	1st to 10th	Day	29% 5% 11% 34% 19% 2	4384
	11th to 20th	Day	37% 5% 21% 25% 10% 2	4197
	21st to end	Day	40% 5% 22% 27% 6% 1	4396
September	1st to 10th	Day	33% 7% 15% 28% 13% 3	2280
	11th to 20th	Day	43% 7% 12% 22% 14% 3	2280
	21st to end	Day	45% 8% 16% 19% 10% 2	2014
October	1st to 10th	Day	42% 6% 17% 24% 11%	3180
	11th to 20th	Day	48% 7% 13% 24% 7%	3161
	21st to end	Day	48% 7% 20% 21% 5%	3080
November	1st to 10th	Day	56% 10% 11% 16% 6%	1560
	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	61% 11% 13% 11% 3	4726
	11th to 20th	Night	57% 7% 14% 12% 5% 5%	4740
	21st to end	Night	63% 12% 11% 8% 4	4926
February	1st to 10th	Night	57% 11% 12% 13% 5% 1	2542
	11th to 20th	Night	49% 11% 15% 15% 9% 1	2404
	21st to end	Night	57% 10% 12% 13% 7%	2004
March	1st to 10th	Night	46% 10% 12% 18% 14%	3720
	11th to 20th	Night	29% 13% 20% 26% 12%	3490
	21st to end	Night	47% 13% 14% 17% 9%	3654
April	1st to 10th	Night	48% 10% 19% 18% 5%	1900
	11th to 20th	Night	43% 11% 15% 21% 10%	1801
	21st to end	Night	45% 11% 16% 20% 8%	1574
May	1st to 10th	Night	40% 8% 14% 28% 11% 1	2540
	11th to 20th	Night	38% 10% 22% 25% 5% 1	2516
	21st to end	Night	48% 12% 15% 19% 5%	2605
June	1st to 10th	Night	45% 9% 13% 20% 10% 2	1317
	11th to 20th	Night	46% 10% 19% 16% 9% 1	1140
	21st to end	Night	37% 9% 19% 23% 8% 4	1284
July	1st to 10th	Night	26% 5% 11% 25% 23% 11%	2185
	11th to 20th	Night	18% 5% 13% 29% 30% 5%	2178
	21st to end	Night	27% 4 16% 26% 16% 11%	2548
August	1st to 10th	Night	27% 6% 13% 29% 24% 2	2521
	11th to 20th	Night	35% 5% 22% 26% 11% 2	2699
	21st to end	Night	38% 5% 23% 25% 7% 1	3274
September	1st to 10th	Night	30% 6% 16% 32% 13% 3	1900
	11th to 20th	Night	37% 6% 17% 22% 15% 3	1900
	21st to end	Night	38% 9% 22% 20% 10% 2	2162
October	1st to 10th	Night	42% 5% 18% 25% 10%	3800
	11th to 20th	Night	43% 6% 21% 23% 6%	3777
	21st to end	Night	51% 6% 17% 21% 5%	4477
November	1st to 10th	Night	55% 11% 15% 13% 6% 1	2722
	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	12% 11% 36% 24% 15% 2	180
	11th to 20th	Day	7% 11% 37% 31% 13% 2	180
	21st to end	Day	10% 9% 35% 30% 13% 3	198
February	1st to 10th	Day	10% 19% 45% 20% 5% 1	294
	11th to 20th	Day	5% 18% 43% 25% 8% 1	365
	21st to end	Day	13% 20% 35% 22% 9% 1	325
March	1st to 10th	Day	14% 22% 33% 22% 8% 1	460
	11th to 20th	Day	14% 22% 33% 20% 10% 1	460
	21st to end	Day	14% 22% 35% 17% 10% 2	506
April	1st to 10th	Day	20% 20% 33% 21% 6%	460
	11th to 20th	Day	15% 21% 32% 20% 9% 4	452
	21st to end	Day	17% 24% 26% 21% 8% 4	460
May	1st to 10th	Day	15% 17% 32% 25% 7% 3	463
	11th to 20th	Day	16% 13% 32% 24% 10% 4	488
	21st to end	Day	20% 17% 30% 22% 10% 2	618
June	1st to 10th	Day	20% 25% 30% 20% 4 1	685
	11th to 20th	Day	20% 18% 30% 23% 8%	870
	21st to end	Day	15% 17% 32% 25% 9% 1	715
July	1st to 10th	Day	11% 18% 32% 25% 11% 2	671
	11th to 20th	Day	10% 15% 33% 29% 10% 1	668
	21st to end	Day	6% 12% 32% 34% 11% 4	607
August	1st to 10th	Day	9% 10% 30% 31% 15% 6%	487
	11th to 20th	Day	8% 11% 29% 34% 12% 6%	477
	21st to end	Day	13% 14% 32% 28% 9% 4	539
September	1st to 10th	Day	13% 15% 32% 28% 7% 4	490
	11th to 20th	Day	17% 16% 27% 26% 11% 3	490
	21st to end	Day	20% 22% 29% 22% 7%	490
October	1st to 10th	Day	18% 18% 27% 24% 10% 3	490
	11th to 20th	Day	17% 23% 29% 20% 8% 2	490
	21st to end	Day	17% 16% 39% 20% 7% 1	334
November	1st to 10th	Day	15% 17% 40% 19% 8% 1	198
	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% 13% 45% 24% 6%	850
	21st to end	Night	8% 15% 46% 24% 7%	854
February	1st to 10th	Night	9% 15% 49% 22% 4 1	760
	11th to 20th	Night	8% 14% 48% 23% 6% 1	744
	21st to end	Night	8% 15% 43% 27% 6%	628
March	1st to 10th	Night	7% 14% 51% 22% 6% 1	760
	11th to 20th	Night	5% 19% 48% 23% 4	760
	21st to end	Night	9% 15% 44% 26% 6%	836
April	1st to 10th	Night	10% 13% 43% 30% 4	760
	11th to 20th	Night	9% 16% 47% 21% 7%	673
	21st to end	Night	11% 14% 46% 24% 4 1	434
May	1st to 10th	Night	12% 12% 40% 31% 6%	380
	11th to 20th	Night	9% 8% 40% 39% 4	374
	21st to end	Night	14% 6% 39% 37% 3	411
June	1st to 10th	Night	16% 10% 44% 25% 5%	380
	11th to 20th	Night	14% 10% 45% 28% 3	380
	21st to end	Night	9% 11% 38% 36% 6%	380
July	1st to 10th	Night	9% 7% 36% 37% 10% 1	370
	11th to 20th	Night	6% 8% 33% 45% 7% 1	368
	21st to end	Night	4 6% 26% 51% 13%	416
August	1st to 10th	Night	4 3 23% 52% 17% 1	378
	11th to 20th	Night	5% 4 29% 46% 15%	476
	21st to end	Night	9% 11% 33% 37% 10%	703
September	1st to 10th	Night	8% 9% 39% 33% 11% 1	760
	11th to 20th	Night	11% 10% 25% 35% 18% 1	760
	21st to end	Night	14% 16% 34% 28% 7%	760
October	1st to 10th	Night	10% 17% 37% 27% 8% 1	760
	11th to 20th	Night	12% 15% 39% 24% 9% 1	760
	21st to end	Night	14% 20% 40% 18% 6% 1	836
November	1st to 10th	Night	12% 19% 44% 20% 4 1	778
	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 2024-11-07 03:55:46. Version ac07

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