Benson Lake Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Benson Lake Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	13% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	101828
	Night	14% 10% 4 8% 5% 4 4 3 5% 6% 37%	98042
Transparency	Day	45% 7% 13% 22% 12% 1	105336
	Night	45% 6% 13% 23% 11% 1	102675
Seeing	Day	18% 16% 33% 21% 9% 3	16136
	Night	18% 11% 34% 27% 9% 1	26051

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	13% 14% 5% 10% 6% 6% 5% 3 6% 6% 26%	2527
	11th to 20th	Day	12% 13% 4 11% 6% 6% 6% 4 7% 7% 24%	2530
	21st to end	Day	13% 18% 6% 13% 6% 5% 4 3 5% 5% 23%	2783
February	1st to 10th	Day	9% 12% 3 9% 6% 5% 5% 3 6% 7% 34%	1638
	11th to 20th	Day	10% 13% 4 8% 6% 4 5% 3 5% 6% 36%	1791
	21st to end	Day	12% 14% 3 9% 5% 4 4 4 5% 8% 33%	1570
March	1st to 10th	Day	11% 11% 2 6% 5% 4 4 3 5% 5% 44%	3120
	11th to 20th	Day	8% 11% 4 10% 8% 6% 6% 3 5% 6% 34%	3269
	21st to end	Day	19% 12% 4 13% 6% 5% 5% 3 4 5% 25%	4165
April	1st to 10th	Day	16% 13% 4 9% 5% 5% 5% 4 5% 6% 29%	2280
	11th to 20th	Day	20% 11% 3 7% 5% 4 4 4 4 5% 32%	2254
	21st to end	Day	18% 9% 3 7% 5% 4 5% 4 5% 6% 33%	2460
May	1st to 10th	Day	14% 7% 3 8% 5% 6% 4 4 5% 6% 39%	4242
	11th to 20th	Day	13% 6% 3 6% 5% 5% 4 3 6% 8% 41%	4399
	21st to end	Day	13% 8% 2 7% 6% 5% 5% 4 6% 7% 37%	4824
June	1st to 10th	Day	11% 5% 2 7% 6% 5% 5% 4 5% 7% 42%	2660
	11th to 20th	Day	14% 6% 3 7% 6% 5% 5% 4 6% 7% 38%	2660
	21st to end	Day	12% 7% 2 7% 6% 5% 4 4 7% 9% 38%	2660
July	1st to 10th	Day	14% 4 2 6% 5% 5% 5% 4 6% 8% 39%	4440
	11th to 20th	Day	5% 4 1 5% 4 6% 5% 5% 7% 9% 48%	4440
	21st to end	Day	8% 5% 2 6% 5% 5% 4 5% 6% 8% 47%	4813
August	1st to 10th	Day	9% 7% 2 7% 6% 5% 6% 5% 7% 8% 39%	4423
	11th to 20th	Day	12% 5% 3 6% 4 4 5% 3 5% 7% 47%	4042
	21st to end	Day	14% 7% 3 6% 5% 5% 5% 4 4 7% 41%	4180
September	1st to 10th	Day	12% 6% 2 8% 4 4 4 3 6% 8% 43%	2280
	11th to 20th	Day	11% 5% 2 6% 4 5% 5% 5% 6% 8% 41%	2176
	21st to end	Day	12% 6% 3 8% 6% 5% 5% 3 7% 8% 37%	2090
October	1st to 10th	Day	15% 7% 3 7% 4 4 5% 4 5% 7% 39%	1998
	11th to 20th	Day	20% 11% 3 8% 5% 6% 4 3 6% 7% 28%	1831
	21st to end	Day	21% 10% 3 8% 5% 5% 4 4 4 7% 29%	1881
November	1st to 10th	Day	14% 10% 3 7% 5% 3 5% 4 5% 7% 38%	1762
	11th to 20th	Day	15% 12% 5% 10% 6% 5% 5% 4 5% 6% 27%	1755
	21st to end	Day	15% 12% 5% 8% 5% 5% 5% 5% 6% 7% 28%	1600
December	1st to 10th	Day	11% 12% 4 10% 7% 5% 5% 4 5% 5% 31%	1584
	11th to 20th	Day	16% 13% 4 8% 7% 6% 6% 4 6% 5% 26%	1918
	21st to end	Day	22% 22% 6% 10% 5% 3 3 3 3 4 19%	2783
January	1st to 10th	Night	13% 14% 6% 11% 5% 4 4 3 4 5% 31%	4428
	11th to 20th	Night	10% 15% 5% 12% 8% 5% 5% 4 5% 6% 23%	4440
	21st to end	Night	12% 17% 7% 12% 5% 5% 4 3 5% 6% 24%	4884
February	1st to 10th	Night	9% 13% 5% 9% 6% 5% 4 4 5% 6% 34%	2541
	11th to 20th	Night	10% 11% 3 9% 6% 5% 4 4 5% 7% 36%	2274
	21st to end	Night	14% 13% 5% 8% 5% 4 3 3 5% 6% 34%	1884
March	1st to 10th	Night	11% 9% 3 7% 4 4 4 3 4 7% 43%	3733
	11th to 20th	Night	9% 10% 3 10% 5% 5% 5% 4 6% 8% 37%	3720
	21st to end	Night	16% 11% 4 10% 6% 5% 5% 4 5% 6% 28%	3466
April	1st to 10th	Night	19% 10% 3 8% 6% 4 5% 4 5% 6% 31%	1900
	11th to 20th	Night	21% 8% 3 6% 4 3 4 3 5% 7% 37%	1875
	21st to end	Night	16% 8% 3 8% 5% 5% 5% 3 5% 7% 35%	1719
May	1st to 10th	Night	16% 7% 3 7% 5% 4 4 4 5% 6% 39%	2643
	11th to 20th	Night	12% 8% 2 7% 5% 4 5% 3 5% 6% 43%	2506
	21st to end	Night	17% 6% 2 6% 5% 4 5% 4 5% 7% 39%	2743
June	1st to 10th	Night	11% 5% 2 6% 5% 4 4 4 5% 7% 47%	1520
	11th to 20th	Night	13% 7% 2 7% 4 4 6% 4 7% 6% 39%	1520
	21st to end	Night	13% 6% 2 5% 4 4 3 4 6% 8% 44%	1520
July	1st to 10th	Night	14% 5% 2 5% 4 4 5% 4 5% 8% 44%	2530
	11th to 20th	Night	6% 3 1 4 3 3 4 4 6% 9% 56%	2530
	21st to end	Night	9% 5% 2 6% 4 4 3 3 4 7% 52%	2750
August	1st to 10th	Night	10% 6% 3 7% 4 4 4 4 5% 7% 45%	2517
	11th to 20th	Night	11% 5% 2 4 4 4 4 4 5% 7% 50%	2786
	21st to end	Night	12% 7% 2 6% 5% 4 3 3 5% 6% 48%	3476
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 6% 53%	1900
	11th to 20th	Night	11% 4 2 5% 4 4 4 3 5% 7% 50%	1985
	21st to end	Night	15% 6% 3 6% 4 3 4 3 5% 7% 44%	2090
October	1st to 10th	Night	15% 6% 3 5% 3 3 5% 3 6% 6% 45%	2180
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 4 5% 6% 35%	2347
	21st to end	Night	20% 10% 4 7% 5% 4 4 3 4 7% 32%	2717
November	1st to 10th	Night	15% 9% 3 6% 4 5% 4 3 5% 7% 39%	2536
	11th to 20th	Night	15% 11% 4 8% 6% 4 4 4 5% 7% 33%	2640
	21st to end	Night	14% 12% 3 8% 5% 5% 5% 5% 5% 7% 31%	2800
December	1st to 10th	Night	13% 13% 5% 8% 5% 4 5% 3 5% 6% 32%	2779
	11th to 20th	Night	13% 14% 5% 9% 5% 6% 5% 3 4 5% 30%	3279
	21st to end	Night	24% 19% 6% 8% 5% 3 2 2 3 4 22%	4884

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	56% 8% 13% 16% 6%	2528
	11th to 20th	Day	57% 8% 13% 16% 6% 1	2530
	21st to end	Day	62% 5% 14% 13% 4 1	2783
February	1st to 10th	Day	48% 5% 14% 20% 12% 1	1638
	11th to 20th	Day	47% 6% 13% 23% 9% 1	1801
	21st to end	Day	51% 5% 12% 19% 11% 2	1570
March	1st to 10th	Day	41% 5% 13% 21% 19% 2	3120
	11th to 20th	Day	47% 7% 14% 21% 9% 1	3269
	21st to end	Day	61% 5% 10% 15% 8%	4165
April	1st to 10th	Day	54% 7% 11% 17% 10% 1	2280
	11th to 20th	Day	52% 6% 9% 21% 11% 1	2254
	21st to end	Day	50% 7% 9% 18% 13% 2	2460
May	1st to 10th	Day	43% 8% 11% 22% 16% 1	4280
	11th to 20th	Day	38% 8% 12% 26% 14% 1	4403
	21st to end	Day	43% 8% 11% 19% 17% 2	4837
June	1st to 10th	Day	37% 8% 14% 25% 15% 2	2660
	11th to 20th	Day	44% 7% 14% 19% 15% 1	2660
	21st to end	Day	41% 8% 15% 23% 12% 1	2660
July	1st to 10th	Day	41% 6% 16% 24% 12% 1	4371
	11th to 20th	Day	28% 7% 14% 34% 15% 2	4365
	21st to end	Day	33% 7% 12% 29% 18% 1	4662
August	1st to 10th	Day	40% 8% 15% 24% 13% 1	4408
	11th to 20th	Day	36% 6% 16% 30% 12%	4083
	21st to end	Day	42% 6% 15% 22% 14% 1	4179
September	1st to 10th	Day	39% 7% 13% 28% 13%	2280
	11th to 20th	Day	37% 9% 19% 27% 8%	2176
	21st to end	Day	43% 7% 15% 27% 9%	2090
October	1st to 10th	Day	31% 6% 13% 29% 22%	3323
	11th to 20th	Day	50% 5% 10% 22% 13%	3021
	21st to end	Day	51% 6% 15% 22% 6%	3081
November	1st to 10th	Day	45% 7% 12% 24% 11%	1762
	11th to 20th	Day	56% 7% 14% 14% 8% 1	1755
	21st to end	Day	53% 9% 15% 18% 4 1	1600
December	1st to 10th	Day	53% 7% 13% 20% 7%	1584
	11th to 20th	Day	56% 8% 12% 15% 7% 1	1915
	21st to end	Day	69% 5% 8% 13% 6%	2783
January	1st to 10th	Night	54% 7% 12% 19% 8% 1	4428
	11th to 20th	Night	58% 7% 13% 16% 4	4440
	21st to end	Night	61% 6% 12% 16% 5%	4884
February	1st to 10th	Night	51% 5% 10% 20% 12% 2	2541
	11th to 20th	Night	47% 7% 13% 22% 10% 3	2275
	21st to end	Night	51% 5% 13% 20% 9% 1	1884
March	1st to 10th	Night	40% 6% 19% 23% 11% 1	3733
	11th to 20th	Night	43% 6% 13% 26% 11% 1	3720
	21st to end	Night	54% 8% 11% 16% 10% 1	3466
April	1st to 10th	Night	53% 6% 9% 16% 15% 1	1900
	11th to 20th	Night	47% 5% 10% 23% 12% 3	1875
	21st to end	Night	47% 7% 11% 20% 13% 2	1719
May	1st to 10th	Night	42% 7% 13% 23% 13% 1	2670
	11th to 20th	Night	38% 8% 14% 25% 13% 2	2507
	21st to end	Night	44% 8% 14% 17% 13% 4	2751
June	1st to 10th	Night	35% 8% 14% 26% 16% 2	1520
	11th to 20th	Night	42% 7% 13% 22% 16% 1	1520
	21st to end	Night	36% 7% 16% 28% 12% 2	1520
July	1st to 10th	Night	39% 6% 16% 23% 13% 3	2490
	11th to 20th	Night	23% 7% 17% 36% 15% 2	2482
	21st to end	Night	31% 6% 13% 27% 21% 1	2662
August	1st to 10th	Night	37% 7% 14% 22% 18% 2	2508
	11th to 20th	Night	33% 8% 14% 29% 14% 2	2811
	21st to end	Night	37% 6% 13% 25% 17% 1	3476
September	1st to 10th	Night	31% 7% 14% 32% 16%	1900
	11th to 20th	Night	32% 7% 17% 34% 11%	1985
	21st to end	Night	39% 6% 16% 28% 10% 1	2090
October	1st to 10th	Night	31% 6% 11% 35% 16% 2	3635
	11th to 20th	Night	39% 5% 13% 27% 15%	3896
	21st to end	Night	50% 5% 11% 24% 9%	4467
November	1st to 10th	Night	44% 6% 14% 23% 12% 1	2536
	11th to 20th	Night	51% 7% 14% 18% 10%	2640
	21st to end	Night	52% 7% 14% 21% 5% 1	2800
December	1st to 10th	Night	51% 7% 16% 19% 7%	2779
	11th to 20th	Night	55% 6% 13% 19% 7% 1	3281
	21st to end	Night	66% 5% 8% 15% 5%	4884

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	19% 15% 36% 21% 7% 1	270
	11th to 20th	Day	24% 19% 34% 17% 4 1	270
	21st to end	Day	21% 14% 44% 18% 3	297
February	1st to 10th	Day	17% 24% 40% 13% 5% 1	270
	11th to 20th	Day	19% 31% 34% 13% 4	270
	21st to end	Day	23% 20% 47% 8% 1	225
March	1st to 10th	Day	17% 26% 42% 13% 2	270
	11th to 20th	Day	21% 21% 38% 15% 5%	294
	21st to end	Day	26% 20% 29% 16% 8% 1	506
April	1st to 10th	Day	27% 20% 30% 18% 5% 1	460
	11th to 20th	Day	28% 21% 27% 16% 7% 1	452
	21st to end	Day	27% 17% 28% 19% 8% 2	460
May	1st to 10th	Day	21% 22% 33% 15% 7% 2	558
	11th to 20th	Day	20% 17% 34% 19% 7% 2	675
	21st to end	Day	18% 15% 33% 22% 8% 5%	734
June	1st to 10th	Day	12% 19% 35% 22% 9% 3	680
	11th to 20th	Day	18% 14% 36% 21% 10% 2	680
	21st to end	Day	16% 13% 32% 27% 9% 3	680
July	1st to 10th	Day	8% 10% 31% 32% 13% 5%	671
	11th to 20th	Day	9% 12% 34% 26% 14% 5%	668
	21st to end	Day	8% 9% 34% 29% 15% 6%	739
August	1st to 10th	Day	10% 8% 32% 29% 16% 5%	676
	11th to 20th	Day	15% 8% 24% 26% 20% 8%	533
	21st to end	Day	18% 12% 24% 24% 18% 5%	539
September	1st to 10th	Day	16% 11% 27% 27% 13% 6%	490
	11th to 20th	Day	11% 8% 29% 32% 16% 3	490
	21st to end	Day	17% 15% 28% 24% 13% 3	490
October	1st to 10th	Day	22% 18% 29% 19% 11% 2	398
	11th to 20th	Day	25% 26% 31% 15% 3	300
	21st to end	Day	29% 22% 35% 12% 2	330
November	1st to 10th	Day	20% 18% 39% 15% 7% 1	300
	11th to 20th	Day	21% 26% 34% 14% 4 1	300
	21st to end	Day	23% 21% 38% 14% 5%	300
December	1st to 10th	Day	18% 19% 41% 15% 6% 1	294
	11th to 20th	Day	23% 23% 35% 14% 4	270
	21st to end	Day	31% 20% 35% 11% 3	297
January	1st to 10th	Night	17% 15% 40% 24% 4	950
	11th to 20th	Night	20% 15% 38% 20% 7% 1	950
	21st to end	Night	18% 11% 39% 24% 7% 1	1045
February	1st to 10th	Night	16% 15% 40% 23% 6%	950
	11th to 20th	Night	19% 17% 36% 22% 6%	799
	21st to end	Night	20% 15% 39% 22% 2	628
March	1st to 10th	Night	17% 14% 37% 25% 8%	760
	11th to 20th	Night	16% 17% 41% 20% 6% 1	743
	21st to end	Night	19% 11% 33% 29% 7% 1	627
April	1st to 10th	Night	22% 15% 33% 25% 5%	570
	11th to 20th	Night	26% 11% 30% 27% 6%	563
	21st to end	Night	21% 12% 33% 27% 8% 1	570
May	1st to 10th	Night	20% 12% 33% 27% 6% 1	570
	11th to 20th	Night	19% 12% 34% 29% 6% 1	561
	21st to end	Night	14% 7% 31% 36% 12%	617
June	1st to 10th	Night	12% 9% 32% 37% 10%	570
	11th to 20th	Night	17% 8% 28% 37% 9% 1	570
	21st to end	Night	15% 6% 28% 38% 13% 1	570
July	1st to 10th	Night	8% 4 26% 44% 17%	555
	11th to 20th	Night	9% 4 30% 39% 18%	552
	21st to end	Night	9% 6% 29% 38% 17% 1	624
August	1st to 10th	Night	11% 2 28% 41% 17% 2	567
	11th to 20th	Night	10% 4 24% 36% 24% 2	564
	21st to end	Night	13% 6% 24% 38% 17% 1	627
September	1st to 10th	Night	12% 6% 26% 31% 20% 4	570
	11th to 20th	Night	13% 6% 31% 30% 18% 2	655
	21st to end	Night	19% 9% 30% 27% 15% 1	760
October	1st to 10th	Night	18% 12% 32% 25% 13% 1	760
	11th to 20th	Night	20% 15% 33% 24% 7%	760
	21st to end	Night	26% 11% 32% 24% 7%	836
November	1st to 10th	Night	21% 11% 38% 23% 7% 1	780
	11th to 20th	Night	21% 17% 36% 21% 5%	840
	21st to end	Night	21% 15% 34% 24% 5%	1000
December	1st to 10th	Night	22% 14% 38% 20% 5%	993
	11th to 20th	Night	20% 15% 34% 24% 6% 1	950
	21st to end	Night	27% 13% 36% 20% 4	1045

Page generated at 2024-12-06 02:54:48. Version ac07

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