Lac Sacacomie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Sacacomie clear sky chart from 2005-11-06 to 2025-01-07.

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	17% 10% 4 9% 5% 5% 5% 4 5% 6% 31%	105183
	Night	16% 11% 4 8% 5% 4 4 4 5% 6% 33%	103848
Transparency	Day	51% 7% 12% 20% 10% 1	108633
	Night	51% 6% 12% 20% 10% 1	108487
Seeing	Day	22% 18% 32% 19% 7% 2	14651
	Night	22% 13% 31% 25% 8% 1	23658

By Month

Percentage Cloud Cover NE (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	13% 15% 6% 13% 7% 4 4 3 4 5% 26%	2565
	11th to 20th	Day	11% 16% 6% 15% 8% 5% 3 2 3 4 27%	2520
	21st to end	Day	11% 12% 6% 15% 7% 5% 5% 4 5% 6% 26%	2772
February	1st to 10th	Day	10% 18% 6% 12% 7% 6% 4 3 4 5% 25%	1610
	11th to 20th	Day	11% 17% 6% 10% 6% 5% 4 3 4 5% 28%	1762
	21st to end	Day	15% 17% 6% 10% 6% 5% 4 3 5% 4 27%	1570
March	1st to 10th	Day	17% 17% 4 10% 6% 5% 4 3 4 4 26%	3116
	11th to 20th	Day	11% 16% 6% 12% 6% 5% 5% 3 4 5% 27%	3255
	21st to end	Day	12% 14% 3 7% 5% 4 5% 3 5% 6% 36%	4166
April	1st to 10th	Day	20% 15% 4 8% 5% 3 4 4 4 5% 29%	2280
	11th to 20th	Day	22% 9% 3 7% 5% 4 3 3 4 6% 34%	2259
	21st to end	Day	21% 11% 4 7% 4 4 4 3 5% 5% 30%	2470
May	1st to 10th	Day	21% 9% 3 7% 5% 4 4 4 5% 6% 32%	4381
	11th to 20th	Day	17% 7% 3 7% 5% 5% 4 4 6% 8% 34%	4398
	21st to end	Day	17% 7% 3 8% 6% 5% 6% 4 6% 6% 32%	4837
June	1st to 10th	Day	21% 8% 3 8% 5% 5% 5% 4 5% 7% 27%	2660
	11th to 20th	Day	17% 7% 2 7% 5% 5% 6% 4 6% 8% 32%	2660
	21st to end	Day	23% 9% 3 8% 6% 5% 5% 5% 6% 6% 25%	2660
July	1st to 10th	Day	15% 7% 3 8% 6% 6% 6% 4 7% 7% 32%	4440
	11th to 20th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 8% 32%	4440
	21st to end	Day	12% 6% 2 7% 6% 5% 5% 4 6% 8% 40%	4814
August	1st to 10th	Day	15% 6% 3 7% 5% 6% 7% 5% 7% 9% 31%	4423
	11th to 20th	Day	18% 6% 2 7% 5% 5% 6% 4 7% 8% 31%	4096
	21st to end	Day	17% 6% 3 7% 5% 4 5% 5% 5% 8% 36%	4180
September	1st to 10th	Day	15% 5% 2 7% 4 4 4 4 6% 8% 40%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 6% 44%	2184
	21st to end	Day	20% 8% 2 6% 3 4 4 3 4 6% 39%	2090
October	1st to 10th	Day	23% 8% 3 7% 3 4 4 3 5% 7% 33%	1981
	11th to 20th	Day	22% 10% 3 9% 5% 5% 5% 4 5% 5% 26%	1821
	21st to end	Day	25% 13% 3 7% 4 4 4 3 4 6% 27%	1881
November	1st to 10th	Day	16% 14% 3 9% 5% 5% 3 3 5% 5% 32%	1761
	11th to 20th	Day	18% 14% 3 10% 5% 4 4 4 4 6% 27%	1705
	21st to end	Day	19% 18% 4 7% 5% 4 5% 4 4 6% 23%	1600
December	1st to 10th	Day	19% 17% 7% 13% 6% 5% 3 3 5% 4 20%	2600
	11th to 20th	Day	18% 13% 5% 10% 5% 4 4 3 4 5% 29%	2986
	21st to end	Day	17% 15% 6% 11% 6% 4 4 3 3 5% 27%	3960
January	1st to 10th	Night	13% 17% 6% 11% 5% 5% 5% 4 4 5% 25%	4514
	11th to 20th	Night	9% 14% 5% 13% 7% 6% 4 3 4 6% 29%	4440
	21st to end	Night	10% 13% 5% 14% 8% 6% 6% 4 4 6% 24%	4884
February	1st to 10th	Night	10% 14% 6% 9% 6% 7% 6% 4 5% 5% 28%	2565
	11th to 20th	Night	10% 14% 5% 11% 6% 5% 5% 4 5% 6% 30%	2302
	21st to end	Night	14% 12% 4 9% 5% 5% 5% 3 5% 6% 31%	1884
March	1st to 10th	Night	19% 14% 4 8% 5% 4 5% 3 4 5% 27%	3724
	11th to 20th	Night	14% 18% 5% 10% 5% 4 4 3 4 4 27%	3687
	21st to end	Night	13% 9% 4 10% 6% 6% 4 4 4 5% 35%	3466
April	1st to 10th	Night	21% 11% 4 7% 5% 4 4 4 5% 6% 30%	1900
	11th to 20th	Night	19% 7% 3 6% 4 3 5% 3 6% 5% 38%	1868
	21st to end	Night	22% 9% 3 7% 4 3 3 3 6% 6% 34%	1710
May	1st to 10th	Night	20% 10% 3 7% 5% 5% 4 4 5% 7% 32%	2588
	11th to 20th	Night	22% 6% 2 6% 3 3 4 4 4 7% 39%	2495
	21st to end	Night	18% 6% 3 7% 6% 6% 4 4 6% 7% 32%	2738
June	1st to 10th	Night	20% 7% 3 7% 4 4 4 3 6% 6% 36%	1520
	11th to 20th	Night	18% 7% 2 7% 4 5% 4 4 5% 7% 37%	1520
	21st to end	Night	20% 6% 3 7% 6% 4 4 4 6% 7% 34%	1520
July	1st to 10th	Night	13% 6% 2 7% 5% 6% 6% 6% 6% 9% 34%	2520
	11th to 20th	Night	16% 4 2 6% 5% 4 4 4 6% 7% 43%	2520
	21st to end	Night	12% 4 1 5% 3 3 4 5% 6% 8% 48%	2739
August	1st to 10th	Night	12% 6% 3 7% 6% 5% 5% 4 5% 7% 39%	2506
	11th to 20th	Night	17% 6% 2 6% 4 4 4 4 5% 7% 42%	2697
	21st to end	Night	16% 6% 2 7% 5% 4 4 3 4 6% 42%	3476
September	1st to 10th	Night	13% 6% 3 5% 3 4 5% 4 5% 6% 47%	1900
	11th to 20th	Night	15% 5% 1 4 3 3 3 3 6% 6% 50%	1995
	21st to end	Night	18% 6% 2 5% 4 4 3 3 4 7% 45%	2090
October	1st to 10th	Night	17% 10% 3 6% 3 4 5% 3 4 5% 41%	2194
	11th to 20th	Night	22% 8% 2 7% 4 3 4 3 4 7% 35%	2358
	21st to end	Night	23% 9% 3 8% 4 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	16% 10% 4 8% 5% 4 4 4 5% 6% 33%	2537
	11th to 20th	Night	18% 11% 3 8% 5% 4 5% 4 6% 6% 30%	2690
	21st to end	Night	19% 16% 5% 8% 5% 4 3 3 5% 6% 27%	2800
December	1st to 10th	Night	14% 15% 5% 11% 6% 6% 5% 5% 6% 7% 22%	4580
	11th to 20th	Night	21% 14% 4 9% 5% 5% 5% 3 4 4 26%	5208
	21st to end	Night	19% 15% 6% 11% 5% 3 3 3 3 4 28%	6996

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	57% 8% 12% 18% 5% 1	2566
	11th to 20th	Day	58% 8% 8% 18% 8% 1	2520
	21st to end	Day	58% 5% 10% 17% 7% 1	2772
February	1st to 10th	Day	61% 4 8% 17% 9% 2	1610
	11th to 20th	Day	58% 5% 9% 15% 11% 1	1771
	21st to end	Day	60% 5% 8% 16% 9% 3	1570
March	1st to 10th	Day	60% 7% 7% 15% 10% 2	3119
	11th to 20th	Day	57% 7% 9% 13% 11% 3	3255
	21st to end	Day	48% 5% 8% 20% 15% 4	4166
April	1st to 10th	Day	57% 5% 9% 15% 12% 3	2280
	11th to 20th	Day	50% 5% 9% 21% 12% 3	2259
	21st to end	Day	54% 6% 9% 16% 12% 3	2470
May	1st to 10th	Day	50% 7% 11% 19% 12% 1	4395
	11th to 20th	Day	45% 8% 18% 19% 8% 1	4402
	21st to end	Day	47% 9% 10% 18% 15% 2	4837
June	1st to 10th	Day	55% 8% 9% 18% 9% 2	2660
	11th to 20th	Day	46% 7% 13% 21% 11% 2	2660
	21st to end	Day	57% 7% 11% 15% 9%	2660
July	1st to 10th	Day	46% 8% 14% 23% 8%	4370
	11th to 20th	Day	44% 8% 19% 22% 7%	4365
	21st to end	Day	41% 8% 16% 27% 9%	4661
August	1st to 10th	Day	46% 9% 17% 21% 7%	4409
	11th to 20th	Day	46% 9% 17% 22% 5%	4138
	21st to end	Day	44% 6% 14% 20% 14% 1	4180
September	1st to 10th	Day	38% 7% 18% 25% 11% 1	2280
	11th to 20th	Day	39% 7% 14% 29% 11% 1	2184
	21st to end	Day	46% 5% 13% 27% 10%	2090
October	1st to 10th	Day	48% 5% 13% 28% 6% 1	3293
	11th to 20th	Day	49% 6% 14% 24% 5%	2998
	21st to end	Day	46% 6% 21% 18% 8% 1	3081
November	1st to 10th	Day	52% 6% 13% 19% 9% 1	1761
	11th to 20th	Day	55% 5% 11% 17% 11%	1705
	21st to end	Day	62% 6% 10% 15% 6%	1600
December	1st to 10th	Day	66% 4 9% 16% 5%	2600
	11th to 20th	Day	57% 4 7% 19% 13%	2986
	21st to end	Day	61% 3 8% 16% 11%	3960
January	1st to 10th	Night	59% 6% 13% 15% 6%	4514
	11th to 20th	Night	56% 6% 12% 20% 5% 1	4440
	21st to end	Night	59% 7% 10% 15% 8% 1	4884
February	1st to 10th	Night	56% 5% 10% 18% 9% 1	2565
	11th to 20th	Night	55% 6% 10% 18% 11% 1	2304
	21st to end	Night	53% 5% 9% 18% 13% 2	1884
March	1st to 10th	Night	57% 6% 10% 14% 9% 3	3734
	11th to 20th	Night	59% 5% 7% 15% 11% 2	3688
	21st to end	Night	49% 5% 8% 22% 12% 4	3466
April	1st to 10th	Night	54% 5% 9% 17% 14% 2	1900
	11th to 20th	Night	47% 5% 10% 23% 13% 2	1868
	21st to end	Night	50% 4 8% 21% 15% 2	1710
May	1st to 10th	Night	52% 6% 15% 17% 8% 2	2594
	11th to 20th	Night	45% 7% 15% 20% 11% 2	2496
	21st to end	Night	47% 9% 11% 18% 14% 1	2739
June	1st to 10th	Night	45% 7% 13% 22% 11% 1	1520
	11th to 20th	Night	45% 7% 11% 21% 13% 3	1520
	21st to end	Night	49% 7% 14% 17% 13%	1520
July	1st to 10th	Night	45% 6% 20% 20% 9% 1	2480
	11th to 20th	Night	41% 6% 20% 27% 6%	2472
	21st to end	Night	33% 6% 21% 28% 11%	2651
August	1st to 10th	Night	43% 7% 17% 24% 8%	2496
	11th to 20th	Night	43% 6% 21% 23% 7%	2721
	21st to end	Night	44% 5% 15% 24% 12%	3476
September	1st to 10th	Night	37% 6% 17% 26% 14% 1	1900
	11th to 20th	Night	35% 5% 16% 32% 10% 1	1995
	21st to end	Night	41% 4 12% 30% 12%	2090
October	1st to 10th	Night	47% 5% 13% 25% 10%	3662
	11th to 20th	Night	43% 5% 14% 30% 8%	3920
	21st to end	Night	45% 4 18% 19% 11% 2	4467
November	1st to 10th	Night	51% 5% 13% 22% 8% 1	2537
	11th to 20th	Night	52% 6% 11% 18% 10% 1	2690
	21st to end	Night	59% 5% 11% 17% 8% 1	2800
December	1st to 10th	Night	60% 6% 14% 15% 5%	4580
	11th to 20th	Night	60% 5% 7% 17% 10% 1	5208
	21st to end	Night	61% 3 6% 15% 13% 1	6996

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	24% 18% 38% 16% 5%	192
	11th to 20th	Day	24% 19% 36% 17% 4 1	180
	21st to end	Day	17% 18% 44% 16% 5% 1	198
February	1st to 10th	Day	28% 27% 37% 7% 1	222
	11th to 20th	Day	23% 25% 39% 12% 1	369
	21st to end	Day	25% 26% 31% 14% 3	382
March	1st to 10th	Day	26% 18% 35% 18% 4	460
	11th to 20th	Day	23% 22% 36% 14% 4	460
	21st to end	Day	28% 25% 25% 14% 6% 2	506
April	1st to 10th	Day	28% 18% 32% 16% 6%	460
	11th to 20th	Day	29% 21% 28% 13% 6% 2	452
	21st to end	Day	30% 21% 33% 10% 5% 1	460
May	1st to 10th	Day	25% 21% 32% 16% 5% 1	463
	11th to 20th	Day	20% 20% 32% 22% 5% 1	487
	21st to end	Day	22% 22% 34% 16% 5% 1	529
June	1st to 10th	Day	21% 15% 40% 17% 6%	490
	11th to 20th	Day	18% 21% 31% 21% 9% 1	490
	21st to end	Day	27% 12% 31% 22% 7% 1	490
July	1st to 10th	Day	14% 12% 37% 27% 8% 2	485
	11th to 20th	Day	14% 14% 35% 28% 7% 2	484
	21st to end	Day	13% 10% 32% 31% 12% 2	532
August	1st to 10th	Day	15% 10% 33% 27% 12% 2	486
	11th to 20th	Day	17% 7% 28% 28% 14% 5%	479
	21st to end	Day	16% 14% 28% 23% 13% 6%	539
September	1st to 10th	Day	17% 14% 33% 20% 11% 5%	490
	11th to 20th	Day	15% 12% 29% 25% 14% 6%	490
	21st to end	Day	22% 14% 30% 19% 11% 4	490
October	1st to 10th	Day	25% 15% 28% 20% 10% 2	490
	11th to 20th	Day	27% 19% 30% 16% 9% 1	447
	21st to end	Day	32% 17% 29% 18% 4	429
November	1st to 10th	Day	27% 20% 28% 18% 6% 1	395
	11th to 20th	Day	25% 21% 32% 18% 5%	305
	21st to end	Day	24% 30% 31% 14% 2 1	200
December	1st to 10th	Day	30% 18% 30% 16% 6% 1	200
	11th to 20th	Day	31% 23% 32% 12% 2 1	200
	21st to end	Day	29% 21% 30% 15% 4 2	220
January	1st to 10th	Night	26% 15% 35% 20% 4	785
	11th to 20th	Night	24% 16% 33% 21% 6%	760
	21st to end	Night	15% 13% 39% 26% 7%	836
February	1st to 10th	Night	19% 14% 37% 24% 6%	760
	11th to 20th	Night	19% 18% 37% 21% 5%	743
	21st to end	Night	21% 17% 35% 23% 4	628
March	1st to 10th	Night	25% 13% 34% 23% 4	760
	11th to 20th	Night	23% 20% 32% 18% 6% 1	760
	21st to end	Night	22% 17% 31% 23% 7% 1	836
April	1st to 10th	Night	28% 14% 30% 23% 5%	760
	11th to 20th	Night	24% 16% 31% 22% 6%	744
	21st to end	Night	27% 17% 30% 20% 5%	570
May	1st to 10th	Night	26% 13% 31% 22% 7% 1	428
	11th to 20th	Night	23% 11% 31% 27% 8%	374
	21st to end	Night	20% 9% 41% 21% 8%	411
June	1st to 10th	Night	22% 9% 29% 34% 7%	380
	11th to 20th	Night	20% 8% 28% 31% 13%	380
	21st to end	Night	21% 6% 32% 30% 11%	380
July	1st to 10th	Night	13% 6% 32% 35% 13% 1	370
	11th to 20th	Night	13% 4 29% 40% 13% 1	368
	21st to end	Night	16% 4 28% 37% 14% 1	416
August	1st to 10th	Night	11% 5% 24% 43% 16% 1	378
	11th to 20th	Night	15% 4 25% 36% 18% 2	499
	21st to end	Night	18% 6% 27% 30% 17% 2	836
September	1st to 10th	Night	15% 6% 32% 34% 11% 1	760
	11th to 20th	Night	17% 7% 29% 26% 19% 1	760
	21st to end	Night	21% 10% 28% 25% 15% 2	760
October	1st to 10th	Night	21% 13% 29% 25% 11%	760
	11th to 20th	Night	24% 12% 31% 24% 8% 1	760
	21st to end	Night	28% 15% 30% 22% 6%	836
November	1st to 10th	Night	24% 14% 29% 24% 7% 1	780
	11th to 20th	Night	23% 15% 31% 21% 8% 1	800
	21st to end	Night	27% 20% 25% 23% 5% 1	800
December	1st to 10th	Night	28% 14% 30% 23% 6%	800
	11th to 20th	Night	27% 16% 32% 19% 6% 1	800
	21st to end	Night	29% 16% 29% 21% 5%	880

Page generated at 2025-01-04 03:24:00. Version ac07

Copyright © 2025 Attilla Danko.