North Lake Sinclair
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Lake Sinclair clear sky chart from 2005-11-06 to 2024-12-02.

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	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	101241
	Night	13% 6% 2 6% 4 4 4 4 6% 8% 44%	98321
Transparency	Day	37% 7% 11% 19% 18% 6%	105048
	Night	36% 7% 11% 18% 20% 8%	102653
Seeing	Day	15% 10% 22% 24% 20% 9%	15133
	Night	15% 9% 22% 30% 21% 3	25175

By Month

Percentage Cloud Cover SE (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	16% 6% 2 5% 3 4 4 4 6% 6% 44%	2836
	11th to 20th	Day	12% 6% 2 4 3 3 3 3 5% 7% 54%	2840
	21st to end	Day	22% 8% 2 6% 3 3 3 2 3 5% 42%	3170
February	1st to 10th	Day	16% 7% 2 7% 5% 4 4 3 5% 7% 39%	1900
	11th to 20th	Day	19% 7% 2 5% 3 3 3 3 5% 6% 44%	1848
	21st to end	Day	18% 7% 2 6% 4 4 4 4 5% 6% 40%	1570
March	1st to 10th	Day	23% 9% 2 7% 3 3 3 3 5% 5% 37%	3328
	11th to 20th	Day	10% 5% 1 5% 4 3 4 4 5% 8% 50%	3480
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 6% 42%	3815
April	1st to 10th	Day	11% 5% 2 6% 5% 4 4 3 5% 5% 49%	2090
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 4 6% 7% 48%	2199
	21st to end	Day	8% 4 2 5% 4 4 5% 3 5% 8% 53%	2470
May	1st to 10th	Day	9% 6% 2 6% 5% 4 5% 4 6% 8% 46%	4082
	11th to 20th	Day	17% 7% 2 6% 4 5% 5% 4 6% 6% 37%	4081
	21st to end	Day	7% 4 2 5% 4 4 5% 4 7% 10% 47%	4476
June	1st to 10th	Day	10% 6% 2 7% 6% 6% 7% 5% 8% 9% 33%	2470
	11th to 20th	Day	5% 4 2 6% 5% 5% 5% 5% 7% 11% 45%	2470
	21st to end	Day	5% 5% 2 6% 6% 7% 6% 6% 9% 10% 37%	2470
July	1st to 10th	Day	12% 7% 3 8% 6% 7% 8% 6% 9% 11% 24%	4120
	11th to 20th	Day	5% 4 3 7% 7% 7% 7% 6% 9% 12% 34%	4120
	21st to end	Day	7% 8% 3 10% 7% 8% 8% 7% 9% 12% 20%	4466
August	1st to 10th	Day	12% 5% 2 7% 5% 6% 6% 6% 8% 14% 30%	4104
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 5% 7% 10% 45%	3897
	21st to end	Day	7% 5% 2 5% 4 4 5% 4 6% 9% 49%	4070
September	1st to 10th	Day	10% 6% 2 7% 6% 5% 5% 5% 7% 10% 38%	2090
	11th to 20th	Day	14% 6% 3 6% 4 5% 4 4 7% 8% 40%	2090
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 6% 45%	2090
October	1st to 10th	Day	13% 5% 2 5% 3 4 3 3 4 6% 52%	2090
	11th to 20th	Day	13% 4 1 2 3 3 3 2 4 7% 57%	1938
	21st to end	Day	11% 5% 1 4 3 4 4 3 4 5% 56%	2090
November	1st to 10th	Day	13% 6% 2 4 4 3 3 3 4 5% 52%	1885
	11th to 20th	Day	14% 6% 2 4 3 3 3 2 5% 6% 54%	1800
	21st to end	Day	14% 5% 2 5% 4 3 4 4 5% 7% 48%	1800
December	1st to 10th	Day	16% 6% 3 6% 4 5% 4 3 5% 7% 39%	1719
	11th to 20th	Day	19% 6% 1 5% 4 3 3 3 4 6% 46%	2153
	21st to end	Day	20% 8% 3 5% 3 4 3 3 5% 6% 41%	3124
January	1st to 10th	Night	17% 6% 2 6% 4 3 4 3 5% 7% 42%	4109
	11th to 20th	Night	11% 6% 2 5% 4 4 4 4 6% 6% 49%	4120
	21st to end	Night	19% 10% 3 7% 4 3 3 3 4 4 41%	4469
February	1st to 10th	Night	16% 6% 2 6% 4 4 4 4 5% 6% 44%	2280
	11th to 20th	Night	18% 6% 2 5% 3 3 4 3 4 5% 44%	2218
	21st to end	Night	14% 7% 2 6% 4 4 4 3 5% 7% 43%	1884
March	1st to 10th	Night	22% 9% 2 6% 4 4 3 2 5% 5% 38%	3523
	11th to 20th	Night	12% 4 2 4 3 3 4 3 6% 9% 49%	3480
	21st to end	Night	19% 6% 2 5% 4 4 4 4 5% 6% 42%	3817
April	1st to 10th	Night	11% 5% 2 6% 4 3 3 4 6% 7% 49%	2090
	11th to 20th	Night	13% 4 2 4 3 3 4 4 6% 8% 50%	1941
	21st to end	Night	7% 3 1 5% 4 4 4 3 6% 6% 55%	1710
May	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 7% 11% 44%	2813
	11th to 20th	Night	14% 6% 2 7% 4 4 4 5% 6% 7% 41%	2812
	21st to end	Night	7% 4 1 5% 4 3 3 4 6% 10% 52%	3079
June	1st to 10th	Night	9% 6% 2 6% 5% 6% 6% 5% 7% 10% 37%	1710
	11th to 20th	Night	4 4 2 6% 6% 6% 4 5% 7% 11% 44%	1710
	21st to end	Night	6% 5% 2 5% 5% 5% 6% 7% 10% 14% 36%	1710
July	1st to 10th	Night	12% 8% 3 9% 6% 6% 6% 5% 7% 11% 28%	2840
	11th to 20th	Night	5% 4 2 9% 6% 6% 7% 6% 11% 15% 29%	2840
	21st to end	Night	9% 8% 3 8% 6% 8% 7% 6% 10% 12% 23%	3087
August	1st to 10th	Night	11% 6% 3 7% 6% 7% 7% 5% 8% 13% 28%	2825
	11th to 20th	Night	7% 5% 2 7% 5% 6% 6% 5% 6% 10% 43%	2927
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 10% 49%	3540
September	1st to 10th	Night	9% 7% 2 7% 5% 5% 6% 5% 7% 10% 38%	2090
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 4 5% 7% 42%	2090
	21st to end	Night	12% 5% 2 6% 4 5% 4 3 6% 6% 46%	2090
October	1st to 10th	Night	13% 5% 1 5% 4 3 4 3 4 5% 53%	2090
	11th to 20th	Night	12% 4 1 4 3 2 3 3 4 6% 59%	2240
	21st to end	Night	10% 4 1 4 3 3 4 3 4 6% 57%	2508
November	1st to 10th	Night	12% 5% 2 5% 3 3 3 3 4 6% 53%	2410
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 3 5% 53%	2600
	21st to end	Night	13% 5% 2 6% 4 4 3 3 4 6% 50%	2600
December	1st to 10th	Night	15% 5% 2 5% 4 3 4 3 6% 7% 46%	2495
	11th to 20th	Night	17% 6% 2 4 4 3 3 2 4 5% 49%	3042
	21st to end	Night	18% 8% 3 7% 5% 4 4 4 5% 6% 36%	4532

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	37% 5% 7% 19% 25% 7%	2837
	11th to 20th	Day	31% 4 5% 20% 29% 11%	2840
	21st to end	Day	46% 3 4 15% 22% 9%	3170
February	1st to 10th	Day	45% 4 8% 17% 19% 7%	1900
	11th to 20th	Day	41% 5% 5% 19% 23% 7%	1858
	21st to end	Day	43% 5% 8% 13% 22% 8%	1570
March	1st to 10th	Day	49% 5% 8% 14% 16% 8%	3328
	11th to 20th	Day	31% 7% 9% 16% 25% 12%	3480
	21st to end	Day	44% 5% 7% 21% 17% 8%	3815
April	1st to 10th	Day	36% 5% 10% 19% 20% 9%	2090
	11th to 20th	Day	34% 6% 9% 19% 21% 11%	2199
	21st to end	Day	29% 6% 11% 25% 25% 4	2470
May	1st to 10th	Day	35% 9% 12% 24% 19% 3	4120
	11th to 20th	Day	44% 8% 12% 21% 14% 1	4085
	21st to end	Day	29% 9% 15% 24% 21% 2	4489
June	1st to 10th	Day	42% 10% 16% 18% 12% 2	2470
	11th to 20th	Day	31% 11% 17% 26% 15% 1	2470
	21st to end	Day	36% 12% 18% 18% 13% 3	2470
July	1st to 10th	Day	47% 15% 18% 15% 4 2	4055
	11th to 20th	Day	38% 14% 22% 21% 4 1	4051
	21st to end	Day	50% 17% 17% 13% 4	4324
August	1st to 10th	Day	41% 10% 19% 26% 3	4091
	11th to 20th	Day	31% 9% 17% 28% 14% 1	3936
	21st to end	Day	31% 7% 15% 28% 15% 3	4070
September	1st to 10th	Day	40% 10% 14% 16% 16% 4	2090
	11th to 20th	Day	40% 8% 11% 18% 20% 3	2090
	21st to end	Day	39% 6% 9% 21% 19% 6%	2090
October	1st to 10th	Day	29% 3 7% 14% 34% 13%	3480
	11th to 20th	Day	17% 2 5% 17% 27% 31%	3204
	21st to end	Day	23% 3 5% 20% 35% 15%	3428
November	1st to 10th	Day	35% 4 8% 14% 26% 13%	1885
	11th to 20th	Day	32% 3 7% 20% 25% 13%	1800
	21st to end	Day	35% 5% 8% 18% 25% 8%	1800
December	1st to 10th	Day	44% 6% 8% 15% 19% 7%	1719
	11th to 20th	Day	40% 4 7% 14% 26% 9%	2150
	21st to end	Day	43% 6% 8% 17% 23% 4	3124
January	1st to 10th	Night	40% 5% 7% 15% 24% 9%	4109
	11th to 20th	Night	33% 5% 7% 23% 23% 9%	4120
	21st to end	Night	47% 4 5% 11% 24% 8%	4469
February	1st to 10th	Night	41% 5% 7% 17% 21% 10%	2280
	11th to 20th	Night	42% 4 6% 16% 21% 10%	2219
	21st to end	Night	41% 5% 8% 15% 18% 13%	1884
March	1st to 10th	Night	48% 5% 10% 15% 14% 8%	3523
	11th to 20th	Night	31% 5% 11% 13% 27% 13%	3480
	21st to end	Night	41% 6% 8% 17% 17% 11%	3817
April	1st to 10th	Night	34% 5% 10% 20% 21% 11%	2090
	11th to 20th	Night	31% 5% 7% 24% 22% 11%	1941
	21st to end	Night	28% 7% 11% 22% 24% 8%	1710
May	1st to 10th	Night	29% 12% 14% 23% 17% 4	2840
	11th to 20th	Night	39% 9% 12% 24% 15% 2	2813
	21st to end	Night	26% 8% 15% 26% 22% 4	3087
June	1st to 10th	Night	38% 11% 17% 19% 14% 1	1710
	11th to 20th	Night	30% 10% 19% 26% 12% 2	1710
	21st to end	Night	31% 14% 23% 17% 11% 4	1710
July	1st to 10th	Night	47% 13% 21% 13% 4 2	2795
	11th to 20th	Night	37% 15% 27% 16% 5% 1	2786
	21st to end	Night	49% 17% 18% 12% 3 1	2988
August	1st to 10th	Night	44% 10% 21% 21% 3	2814
	11th to 20th	Night	34% 10% 18% 24% 12% 2	2954
	21st to end	Night	29% 9% 17% 27% 16% 2	3540
September	1st to 10th	Night	39% 10% 16% 16% 14% 4	2090
	11th to 20th	Night	40% 8% 12% 17% 18% 5%	2090
	21st to end	Night	37% 7% 11% 17% 22% 6%	2090
October	1st to 10th	Night	33% 4 9% 11% 32% 11%	3480
	11th to 20th	Night	17% 3 5% 13% 29% 33%	3713
	21st to end	Night	21% 3 5% 19% 32% 20%	4120
November	1st to 10th	Night	33% 5% 8% 14% 26% 14%	2410
	11th to 20th	Night	34% 4 6% 16% 26% 14%	2600
	21st to end	Night	36% 5% 7% 18% 25% 10%	2600
December	1st to 10th	Night	37% 7% 9% 19% 22% 7%	2495
	11th to 20th	Night	38% 4 7% 15% 28% 8%	3044
	21st to end	Night	48% 5% 7% 18% 19% 4	4532

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	20% 22% 44% 12% 2	270
	11th to 20th	Day	24% 22% 34% 13% 7% 1	270
	21st to end	Day	26% 26% 34% 10% 4	297
February	1st to 10th	Day	26% 17% 37% 18% 2	270
	11th to 20th	Day	34% 17% 33% 16% 1	270
	21st to end	Day	26% 20% 41% 10% 3	225
March	1st to 10th	Day	22% 19% 28% 23% 7% 1	387
	11th to 20th	Day	20% 16% 36% 18% 9%	460
	21st to end	Day	19% 17% 36% 20% 8%	506
April	1st to 10th	Day	22% 15% 28% 22% 12%	460
	11th to 20th	Day	13% 15% 29% 27% 13% 3	452
	21st to end	Day	12% 11% 28% 26% 20% 3	460
May	1st to 10th	Day	10% 13% 26% 29% 15% 7%	463
	11th to 20th	Day	15% 6% 22% 27% 21% 10%	487
	21st to end	Day	12% 6% 16% 30% 25% 12%	529
June	1st to 10th	Day	10% 5% 18% 28% 28% 12%	490
	11th to 20th	Day	5% 3 18% 27% 27% 20%	490
	21st to end	Day	6% 3 13% 33% 28% 17%	490
July	1st to 10th	Day	8% 2 10% 22% 33% 25%	485
	11th to 20th	Day	7% 2 6% 22% 37% 26%	484
	21st to end	Day	5% 2 9% 25% 37% 22%	532
August	1st to 10th	Day	14% 3 13% 24% 29% 18%	486
	11th to 20th	Day	9% 2 9% 21% 39% 19%	479
	21st to end	Day	13% 2 9% 28% 30% 17%	539
September	1st to 10th	Day	10% 5% 13% 28% 30% 14%	490
	11th to 20th	Day	16% 4 14% 25% 31% 11%	490
	21st to end	Day	16% 4 17% 26% 28% 9%	490
October	1st to 10th	Day	16% 7% 21% 29% 20% 8%	490
	11th to 20th	Day	12% 8% 22% 30% 21% 7%	490
	21st to end	Day	14% 9% 23% 27% 22% 5%	539
November	1st to 10th	Day	21% 7% 26% 28% 15% 4	423
	11th to 20th	Day	18% 15% 37% 22% 5% 2	300
	21st to end	Day	16% 13% 31% 29% 9% 2	300
December	1st to 10th	Day	26% 18% 32% 16% 7% 1	273
	11th to 20th	Day	26% 17% 34% 16% 7% 1	270
	21st to end	Day	28% 18% 33% 15% 6% 1	297
January	1st to 10th	Night	22% 18% 32% 22% 6% 1	760
	11th to 20th	Night	19% 16% 30% 27% 8%	760
	21st to end	Night	19% 18% 34% 25% 3	836
February	1st to 10th	Night	21% 12% 31% 30% 6%	760
	11th to 20th	Night	22% 16% 31% 28% 3	743
	21st to end	Night	18% 16% 35% 27% 3	628
March	1st to 10th	Night	17% 14% 31% 32% 6%	760
	11th to 20th	Night	17% 14% 32% 27% 10%	760
	21st to end	Night	18% 14% 29% 29% 10%	836
April	1st to 10th	Night	15% 14% 31% 28% 12%	760
	11th to 20th	Night	15% 12% 27% 31% 15% 1	637
	21st to end	Night	9% 9% 24% 38% 19% 1	570
May	1st to 10th	Night	7% 7% 26% 39% 19% 2	570
	11th to 20th	Night	11% 3 22% 35% 25% 4	561
	21st to end	Night	12% 3 15% 34% 31% 6%	617
June	1st to 10th	Night	11% 2 13% 39% 31% 3	570
	11th to 20th	Night	4 4 13% 33% 36% 11%	570
	21st to end	Night	8% 2 8% 36% 40% 7%	570
July	1st to 10th	Night	9% 1 9% 27% 41% 13%	555
	11th to 20th	Night	7% 2 6% 24% 48% 14%	552
	21st to end	Night	6% 1 7% 30% 47% 9%	624
August	1st to 10th	Night	8% 2 8% 31% 40% 12%	567
	11th to 20th	Night	11% 1 7% 29% 45% 7%	564
	21st to end	Night	13% 3 8% 29% 38% 9%	665
September	1st to 10th	Night	10% 3 11% 29% 39% 8%	760
	11th to 20th	Night	15% 2 11% 28% 39% 4	760
	21st to end	Night	14% 3 16% 30% 33% 4	760
October	1st to 10th	Night	14% 3 21% 31% 26% 5%	760
	11th to 20th	Night	14% 6% 19% 33% 24% 4	760
	21st to end	Night	12% 8% 23% 32% 23% 2	836
November	1st to 10th	Night	15% 7% 21% 34% 21% 2	780
	11th to 20th	Night	16% 12% 26% 30% 15% 1	800
	21st to end	Night	13% 12% 27% 32% 15% 1	800
December	1st to 10th	Night	18% 13% 29% 29% 10% 1	768
	11th to 20th	Night	22% 11% 27% 30% 10% 1	760
	21st to end	Night	26% 13% 25% 30% 7%	836

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