Beman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beman Observatory 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	13% 10% 4 8% 5% 5% 5% 4 6% 7% 34%	101436
	Night	14% 11% 4 9% 5% 4 4 3 5% 7% 33%	98233
Transparency	Day	47% 7% 12% 21% 12% 1	105023
	Night	49% 6% 11% 20% 12% 1	102760
Seeing	Day	17% 11% 29% 24% 13% 5%	15835
	Night	19% 9% 30% 30% 12% 1	25702

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% 20% 5% 11% 7% 5% 5% 3 4 5% 18%	2527
	11th to 20th	Day	15% 19% 6% 14% 9% 11% 7% 3 4 4 9%	2530
	21st to end	Day	25% 24% 7% 12% 5% 4 2 2 3 4 13%	2854
February	1st to 10th	Day	13% 15% 5% 13% 9% 7% 5% 4 5% 4 20%	1744
	11th to 20th	Day	13% 13% 6% 15% 8% 5% 4 4 4 4 25%	1848
	21st to end	Day	14% 16% 5% 12% 6% 5% 5% 4 5% 5% 23%	1570
March	1st to 10th	Day	15% 16% 5% 8% 5% 5% 4 4 4 6% 28%	3120
	11th to 20th	Day	11% 10% 4 10% 7% 5% 5% 4 6% 6% 31%	3440
	21st to end	Day	18% 14% 5% 9% 5% 5% 4 3 5% 5% 26%	3868
April	1st to 10th	Day	17% 13% 4 8% 5% 4 4 4 5% 5% 30%	2280
	11th to 20th	Day	16% 11% 3 6% 5% 4 4 4 4 7% 35%	2336
	21st to end	Day	17% 9% 3 7% 5% 5% 5% 3 5% 7% 34%	2470
May	1st to 10th	Day	17% 8% 3 8% 5% 5% 4 4 6% 7% 34%	4082
	11th to 20th	Day	15% 7% 2 7% 4 5% 4 4 7% 9% 36%	4081
	21st to end	Day	10% 7% 2 6% 5% 4 4 4 6% 9% 43%	4684
June	1st to 10th	Day	9% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	2660
	11th to 20th	Day	10% 5% 2 6% 4 5% 5% 4 7% 8% 43%	2660
	21st to end	Day	9% 6% 2 7% 6% 5% 6% 6% 8% 9% 37%	2660
July	1st to 10th	Day	11% 6% 2 7% 5% 5% 6% 5% 7% 9% 37%	4440
	11th to 20th	Day	7% 4 1 5% 4 4 5% 5% 7% 10% 48%	4440
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 43%	4730
August	1st to 10th	Day	11% 6% 2 5% 4 4 5% 5% 7% 9% 41%	4104
	11th to 20th	Day	10% 6% 2 6% 5% 5% 5% 4 5% 8% 44%	4044
	21st to end	Day	7% 6% 2 7% 4 5% 5% 5% 6% 10% 43%	4291
September	1st to 10th	Day	11% 7% 2 7% 5% 5% 5% 4 5% 8% 42%	2214
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 5% 9% 47%	2090
	21st to end	Day	12% 8% 3 6% 5% 5% 5% 4 6% 8% 38%	2090
October	1st to 10th	Day	13% 7% 3 8% 5% 4 4 4 5% 7% 42%	2090
	11th to 20th	Day	17% 9% 4 8% 4 5% 5% 4 6% 6% 32%	1878
	21st to end	Day	19% 12% 3 9% 5% 4 5% 4 5% 6% 28%	1881
November	1st to 10th	Day	11% 12% 3 7% 5% 5% 4 3 5% 6% 39%	1762
	11th to 20th	Day	14% 16% 5% 11% 6% 4 5% 4 5% 6% 24%	1800
	21st to end	Day	18% 16% 6% 9% 5% 4 4 3 4 6% 25%	1800
December	1st to 10th	Day	13% 19% 9% 11% 6% 5% 5% 3 5% 5% 19%	1667
	11th to 20th	Day	13% 19% 8% 12% 6% 5% 4 4 6% 6% 17%	1918
	21st to end	Day	20% 23% 8% 14% 7% 5% 3 3 4 4 10%	2783
January	1st to 10th	Night	17% 17% 9% 13% 6% 5% 5% 3 4 5% 17%	4428
	11th to 20th	Night	14% 17% 10% 16% 7% 6% 6% 3 5% 4 11%	4440
	21st to end	Night	24% 18% 9% 12% 6% 5% 3 3 3 4 12%	4809
February	1st to 10th	Night	14% 18% 5% 11% 9% 6% 4 3 4 4 21%	2432
	11th to 20th	Night	12% 15% 6% 10% 7% 6% 4 5% 5% 5% 26%	2218
	21st to end	Night	17% 13% 5% 10% 6% 4 4 4 5% 7% 26%	1884
March	1st to 10th	Night	15% 13% 4 8% 5% 4 3 3 4 6% 35%	3733
	11th to 20th	Night	10% 8% 2 6% 5% 4 4 3 6% 8% 45%	3518
	21st to end	Night	16% 11% 4 10% 5% 4 3 3 5% 5% 32%	3791
April	1st to 10th	Night	14% 12% 3 7% 5% 4 4 4 5% 7% 36%	1900
	11th to 20th	Night	18% 9% 2 6% 4 5% 4 3 6% 6% 37%	1792
	21st to end	Night	16% 9% 2 7% 4 4 4 4 5% 8% 37%	1710
May	1st to 10th	Night	14% 9% 3 7% 6% 4 5% 3 6% 9% 33%	2813
	11th to 20th	Night	17% 7% 2 6% 4 3 4 3 5% 7% 42%	2812
	21st to end	Night	10% 6% 3 6% 5% 4 5% 4 6% 8% 43%	2874
June	1st to 10th	Night	10% 7% 2 5% 4 3 4 2 7% 10% 46%	1520
	11th to 20th	Night	10% 6% 2 6% 5% 4 4 3 7% 10% 44%	1520
	21st to end	Night	8% 5% 2 6% 5% 3 5% 5% 7% 9% 45%	1520
July	1st to 10th	Night	8% 4 2 6% 4 5% 5% 4 8% 11% 44%	2530
	11th to 20th	Night	8% 4 2 4 3 3 4 3 5% 8% 57%	2530
	21st to end	Night	6% 5% 2 6% 4 4 5% 4 7% 9% 47%	2828
August	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 5% 9% 47%	2825
	11th to 20th	Night	11% 6% 2 6% 5% 4 3 5% 6% 8% 44%	2785
	21st to end	Night	9% 7% 2 7% 4 5% 4 4 5% 8% 46%	3348
September	1st to 10th	Night	9% 6% 2 6% 4 4 4 3 5% 8% 48%	1947
	11th to 20th	Night	10% 5% 2 4 4 3 3 3 4 8% 55%	2090
	21st to end	Night	14% 7% 3 6% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	14% 7% 2 6% 3 4 4 3 4 7% 46%	2090
	11th to 20th	Night	17% 11% 3 8% 5% 4 4 3 4 6% 34%	2298
	21st to end	Night	21% 9% 3 7% 5% 4 4 3 5% 6% 31%	2717
November	1st to 10th	Night	13% 11% 3 8% 5% 4 3 3 4 6% 40%	2536
	11th to 20th	Night	14% 15% 4 9% 5% 4 5% 5% 6% 6% 26%	2600
	21st to end	Night	17% 15% 5% 10% 4 5% 3 3 5% 6% 26%	2600
December	1st to 10th	Night	16% 18% 7% 13% 7% 5% 5% 4 4 6% 17%	2542
	11th to 20th	Night	15% 16% 7% 14% 7% 5% 5% 3 5% 5% 19%	3279
	21st to end	Night	26% 21% 6% 11% 5% 4 4 3 4 5% 12%	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	68% 6% 11% 13% 2	2528
	11th to 20th	Day	78% 6% 7% 6% 2	2530
	21st to end	Day	78% 4 9% 7% 2	2854
February	1st to 10th	Day	66% 6% 8% 13% 7%	1744
	11th to 20th	Day	63% 5% 8% 14% 9% 1	1858
	21st to end	Day	62% 5% 11% 14% 6% 1	1570
March	1st to 10th	Day	57% 6% 11% 19% 7% 1	3120
	11th to 20th	Day	50% 7% 13% 20% 9% 1	3440
	21st to end	Day	59% 6% 10% 15% 8% 1	3868
April	1st to 10th	Day	55% 5% 10% 20% 11%	2280
	11th to 20th	Day	48% 6% 10% 20% 13% 2	2336
	21st to end	Day	49% 6% 12% 17% 15% 2	2470
May	1st to 10th	Day	47% 7% 12% 21% 13% 1	4120
	11th to 20th	Day	43% 8% 14% 25% 9% 1	4085
	21st to end	Day	36% 7% 11% 20% 24% 2	4697
June	1st to 10th	Day	36% 8% 11% 28% 15% 2	2660
	11th to 20th	Day	36% 6% 14% 23% 18% 2	2660
	21st to end	Day	39% 9% 13% 21% 15% 2	2660
July	1st to 10th	Day	41% 7% 14% 20% 15% 3	4371
	11th to 20th	Day	28% 7% 15% 31% 18% 1	4365
	21st to end	Day	33% 9% 15% 19% 22% 2	4580
August	1st to 10th	Day	36% 8% 14% 25% 16% 1	4091
	11th to 20th	Day	37% 7% 11% 30% 14% 1	4083
	21st to end	Day	35% 7% 13% 30% 13% 2	4290
September	1st to 10th	Day	39% 6% 14% 23% 16% 2	2214
	11th to 20th	Day	32% 7% 12% 30% 18% 1	2090
	21st to end	Day	42% 6% 13% 23% 16%	2090
October	1st to 10th	Day	30% 5% 9% 36% 19% 1	3480
	11th to 20th	Day	40% 5% 10% 26% 18%	3081
	21st to end	Day	48% 5% 12% 23% 11% 2	3081
November	1st to 10th	Day	45% 6% 12% 22% 14% 1	1762
	11th to 20th	Day	60% 6% 10% 16% 7% 1	1800
	21st to end	Day	62% 4 14% 15% 5% 1	1800
December	1st to 10th	Day	66% 6% 10% 12% 4 1	1667
	11th to 20th	Day	66% 6% 13% 13% 3	1915
	21st to end	Day	78% 5% 8% 6% 3	2783
January	1st to 10th	Night	67% 7% 9% 12% 5% 1	4428
	11th to 20th	Night	74% 6% 9% 7% 4	4440
	21st to end	Night	75% 5% 8% 8% 3	4809
February	1st to 10th	Night	66% 5% 9% 13% 5% 1	2432
	11th to 20th	Night	59% 6% 9% 19% 8% 1	2219
	21st to end	Night	57% 5% 13% 16% 7% 2	1884
March	1st to 10th	Night	49% 5% 13% 25% 7% 1	3733
	11th to 20th	Night	35% 6% 16% 22% 19% 1	3518
	21st to end	Night	53% 6% 12% 20% 9% 1	3791
April	1st to 10th	Night	47% 6% 11% 22% 13% 1	1900
	11th to 20th	Night	47% 5% 10% 18% 17% 2	1792
	21st to end	Night	45% 6% 12% 20% 14% 3	1710
May	1st to 10th	Night	46% 7% 12% 20% 13% 1	2840
	11th to 20th	Night	41% 6% 11% 24% 17% 1	2813
	21st to end	Night	36% 8% 12% 21% 20% 2	2882
June	1st to 10th	Night	33% 7% 11% 30% 17% 3	1520
	11th to 20th	Night	35% 6% 15% 25% 17% 2	1520
	21st to end	Night	33% 8% 15% 26% 17% 2	1520
July	1st to 10th	Night	32% 8% 14% 26% 14% 7%	2490
	11th to 20th	Night	25% 6% 14% 31% 23% 1	2482
	21st to end	Night	32% 9% 16% 16% 24% 3	2738
August	1st to 10th	Night	33% 6% 15% 30% 15% 1	2814
	11th to 20th	Night	34% 7% 13% 30% 14% 1	2812
	21st to end	Night	35% 7% 10% 29% 17% 2	3348
September	1st to 10th	Night	34% 7% 11% 26% 20% 2	1947
	11th to 20th	Night	29% 4 10% 33% 23% 2	2090
	21st to end	Night	40% 6% 11% 26% 15% 1	2090
October	1st to 10th	Night	26% 4 10% 35% 24% 1	3480
	11th to 20th	Night	43% 6% 10% 20% 21%	3808
	21st to end	Night	40% 5% 10% 30% 15% 1	4467
November	1st to 10th	Night	46% 5% 10% 24% 14% 1	2536
	11th to 20th	Night	54% 8% 13% 16% 8% 1	2600
	21st to end	Night	59% 6% 12% 18% 5%	2600
December	1st to 10th	Night	67% 7% 9% 11% 6%	2542
	11th to 20th	Night	66% 6% 12% 12% 4	3281
	21st to end	Night	75% 6% 10% 7% 2	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	22% 14% 37% 20% 5% 1	270
	11th to 20th	Day	21% 18% 44% 11% 5% 1	270
	21st to end	Day	28% 15% 36% 17% 4	297
February	1st to 10th	Day	23% 22% 34% 17% 3 1	270
	11th to 20th	Day	26% 18% 37% 17% 2	270
	21st to end	Day	24% 28% 35% 12% 2	225
March	1st to 10th	Day	22% 21% 41% 11% 4	270
	11th to 20th	Day	21% 13% 35% 22% 8%	433
	21st to end	Day	27% 14% 33% 20% 5% 1	506
April	1st to 10th	Day	22% 15% 33% 22% 8%	460
	11th to 20th	Day	26% 17% 29% 17% 8% 3	452
	21st to end	Day	22% 11% 35% 21% 10% 1	460
May	1st to 10th	Day	23% 13% 28% 24% 9% 3	463
	11th to 20th	Day	21% 10% 26% 23% 13% 8%	487
	21st to end	Day	14% 7% 26% 28% 19% 6%	646
June	1st to 10th	Day	12% 8% 29% 32% 14% 5%	680
	11th to 20th	Day	12% 7% 29% 30% 18% 5%	680
	21st to end	Day	13% 8% 30% 30% 14% 5%	680
July	1st to 10th	Day	9% 5% 22% 29% 23% 13%	671
	11th to 20th	Day	10% 6% 26% 28% 21% 9%	668
	21st to end	Day	9% 3 24% 33% 22% 8%	692
August	1st to 10th	Day	10% 5% 18% 27% 23% 18%	486
	11th to 20th	Day	13% 4 17% 28% 28% 10%	479
	21st to end	Day	9% 5% 21% 29% 24% 12%	539
September	1st to 10th	Day	14% 7% 20% 25% 22% 11%	490
	11th to 20th	Day	9% 4 17% 27% 30% 13%	490
	21st to end	Day	17% 12% 21% 24% 17% 9%	490
October	1st to 10th	Day	16% 8% 28% 28% 13% 7%	490
	11th to 20th	Day	19% 18% 26% 30% 7% 1	451
	21st to end	Day	27% 15% 38% 14% 5% 1	330
November	1st to 10th	Day	16% 19% 36% 22% 6% 2	300
	11th to 20th	Day	23% 21% 34% 16% 6%	300
	21st to end	Day	27% 17% 41% 12% 2	300
December	1st to 10th	Day	25% 22% 34% 11% 6%	273
	11th to 20th	Day	22% 21% 39% 15% 3	270
	21st to end	Day	23% 25% 35% 15% 2	297
January	1st to 10th	Night	22% 14% 37% 22% 5% 1	950
	11th to 20th	Night	23% 14% 35% 22% 5% 1	950
	21st to end	Night	20% 12% 34% 29% 5%	996
February	1st to 10th	Night	24% 11% 38% 23% 3	760
	11th to 20th	Night	20% 15% 36% 26% 3	743
	21st to end	Night	25% 13% 40% 20% 3	628
March	1st to 10th	Night	21% 11% 36% 25% 6% 1	760
	11th to 20th	Night	16% 14% 38% 26% 6% 1	760
	21st to end	Night	23% 10% 33% 27% 7%	822
April	1st to 10th	Night	17% 11% 37% 28% 5% 1	570
	11th to 20th	Night	22% 10% 36% 24% 7% 1	563
	21st to end	Night	20% 7% 34% 30% 8% 1	570
May	1st to 10th	Night	21% 6% 30% 32% 9% 1	570
	11th to 20th	Night	21% 5% 29% 30% 13% 1	561
	21st to end	Night	13% 3 26% 38% 19% 2	617
June	1st to 10th	Night	11% 4 25% 42% 18%	570
	11th to 20th	Night	13% 3 25% 39% 18% 1	570
	21st to end	Night	10% 2 24% 41% 21% 2	570
July	1st to 10th	Night	8% 3 18% 40% 27% 5%	555
	11th to 20th	Night	9% 3 18% 43% 23% 3	552
	21st to end	Night	8% 1 16% 46% 28% 1	624
August	1st to 10th	Night	9% 2 12% 45% 29% 3	567
	11th to 20th	Night	10% 2 15% 40% 28% 5%	564
	21st to end	Night	12% 2 17% 37% 29% 4	627
September	1st to 10th	Night	11% 4 19% 38% 24% 6%	617
	11th to 20th	Night	11% 4 16% 36% 30% 4	760
	21st to end	Night	17% 6% 22% 29% 21% 5%	760
October	1st to 10th	Night	17% 6% 24% 33% 19% 2	760
	11th to 20th	Night	22% 12% 28% 28% 9% 1	760
	21st to end	Night	25% 12% 31% 25% 6%	836
November	1st to 10th	Night	21% 10% 29% 30% 9% 1	780
	11th to 20th	Night	22% 13% 36% 23% 5% 1	800
	21st to end	Night	25% 13% 33% 26% 4	800
December	1st to 10th	Night	22% 14% 37% 22% 6%	815
	11th to 20th	Night	23% 14% 38% 22% 4	950
	21st to end	Night	30% 13% 35% 21% 1	1045

Page generated at 2024-11-29 10:43:09. Version ac07

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