Observation Tower at The Beech
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observation Tower at The Beech clear sky chart from 2005-11-06 to 2026-05-17.

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% 8% 2 7% 5% 5% 5% 4 6% 7% 36%	131610
	Night	16% 8% 3 7% 5% 4 4 4 5% 6% 37%	131228
Transparency	Day	46% 7% 12% 20% 12% 2	135117
	Night	46% 7% 12% 20% 13% 2	135808
Seeing	Day	24% 19% 29% 19% 8% 2	16760
	Night	21% 15% 28% 26% 9% 1	25682

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	10% 8% 3 10% 6% 6% 5% 4 7% 6% 34%	4661
	11th to 20th	Day	11% 10% 4 9% 5% 4 4 4 6% 6% 37%	4650
	21st to end	Day	8% 10% 2 7% 5% 5% 5% 4 5% 6% 42%	5124
February	1st to 10th	Day	12% 9% 3 8% 6% 5% 6% 5% 5% 6% 36%	1829
	11th to 20th	Day	10% 10% 2 9% 5% 5% 5% 4 6% 7% 38%	2048
	21st to end	Day	14% 10% 3 7% 7% 5% 5% 4 5% 5% 35%	1730
March	1st to 10th	Day	20% 13% 3 9% 4 3 4 3 4 5% 31%	4576
	11th to 20th	Day	17% 11% 2 7% 5% 4 4 3 5% 6% 37%	4917
	21st to end	Day	22% 10% 3 7% 4 4 3 3 5% 7% 32%	5856
April	1st to 10th	Day	17% 11% 3 7% 5% 4 4 4 4 6% 34%	2520
	11th to 20th	Day	17% 7% 2 6% 4 5% 5% 4 6% 7% 37%	2569
	21st to end	Day	22% 8% 3 7% 4 5% 4 3 4 6% 35%	2730
May	1st to 10th	Day	32% 10% 3 7% 5% 4 4 3 5% 6% 22%	6016
	11th to 20th	Day	19% 7% 3 10% 6% 5% 5% 4 5% 7% 29%	6200
	21st to end	Day	20% 6% 2 6% 5% 5% 5% 4 6% 9% 31%	6949
June	1st to 10th	Day	22% 7% 3 6% 5% 5% 5% 5% 6% 7% 29%	2800
	11th to 20th	Day	17% 6% 2 6% 5% 4 5% 5% 6% 7% 38%	2800
	21st to end	Day	21% 6% 3 7% 5% 5% 4 4 6% 7% 31%	2800
July	1st to 10th	Day	17% 6% 2 7% 5% 5% 6% 5% 8% 10% 30%	6360
	11th to 20th	Day	14% 6% 2 6% 4 5% 5% 5% 7% 10% 36%	6360
	21st to end	Day	16% 5% 2 5% 4 4 4 4 6% 8% 43%	6926
August	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 5% 7% 7% 35%	4349
	11th to 20th	Day	19% 8% 3 6% 5% 5% 5% 4 5% 8% 32%	4175
	21st to end	Day	11% 5% 1 5% 4 4 5% 4 7% 10% 44%	4411
September	1st to 10th	Day	11% 5% 1 4 4 4 5% 4 6% 9% 47%	2387
	11th to 20th	Day	13% 4 1 5% 3 4 3 3 4 6% 54%	2200
	21st to end	Day	16% 5% 2 5% 3 3 4 4 5% 8% 44%	2200
October	1st to 10th	Day	18% 7% 3 6% 4 4 4 3 4 6% 40%	2200
	11th to 20th	Day	18% 6% 2 6% 4 4 5% 4 5% 7% 41%	1904
	21st to end	Day	23% 10% 3 6% 4 4 4 4 5% 5% 34%	1980
November	1st to 10th	Day	15% 8% 2 5% 4 4 4 4 5% 6% 43%	1851
	11th to 20th	Day	17% 6% 2 4 5% 4 4 5% 6% 8% 40%	1890
	21st to end	Day	19% 9% 2 5% 3 4 4 4 6% 7% 38%	1848
December	1st to 10th	Day	14% 9% 3 10% 5% 4 5% 4 6% 6% 33%	2680
	11th to 20th	Day	18% 7% 3 4 4 4 5% 4 5% 6% 40%	3066
	21st to end	Day	18% 9% 3 7% 4 4 4 4 4 6% 35%	4048
January	1st to 10th	Night	11% 10% 4 10% 5% 4 4 3 4 5% 38%	8234
	11th to 20th	Night	11% 13% 5% 12% 7% 6% 5% 4 5% 7% 25%	8235
	21st to end	Night	9% 8% 3 9% 5% 6% 6% 4 5% 6% 37%	9057
February	1st to 10th	Night	11% 9% 4 8% 6% 5% 5% 5% 6% 6% 35%	2787
	11th to 20th	Night	9% 10% 4 7% 5% 5% 5% 4 5% 7% 41%	2458
	21st to end	Night	11% 10% 4 7% 4 4 4 4 5% 6% 40%	2076
March	1st to 10th	Night	20% 11% 3 8% 4 5% 5% 4 5% 5% 30%	5484
	11th to 20th	Night	15% 8% 4 8% 5% 5% 6% 4 5% 6% 33%	5261
	21st to end	Night	22% 9% 3 7% 4 4 4 3 5% 7% 32%	5316
April	1st to 10th	Night	18% 11% 3 6% 4 4 4 3 5% 5% 36%	2100
	11th to 20th	Night	18% 9% 2 7% 5% 5% 4 3 6% 6% 36%	1998
	21st to end	Night	21% 8% 2 6% 5% 4 3 4 5% 6% 37%	1890
May	1st to 10th	Night	33% 10% 3 7% 4 4 4 3 4 6% 23%	4144
	11th to 20th	Night	17% 9% 3 7% 6% 5% 5% 5% 6% 7% 30%	3869
	21st to end	Night	19% 7% 2 6% 4 4 4 4 5% 8% 36%	3926
June	1st to 10th	Night	20% 7% 3 6% 4 4 4 4 6% 6% 36%	1600
	11th to 20th	Night	18% 6% 2 4 3 4 4 4 6% 8% 40%	1600
	21st to end	Night	19% 6% 2 7% 4 4 4 3 6% 8% 37%	1600
July	1st to 10th	Night	14% 5% 2 5% 4 4 5% 5% 7% 8% 40%	3600
	11th to 20th	Night	16% 7% 3 6% 4 4 4 4 5% 7% 42%	3600
	21st to end	Night	12% 4 1 4 4 4 5% 4 7% 7% 49%	3926
August	1st to 10th	Night	20% 8% 3 6% 4 4 4 3 6% 5% 36%	2768
	11th to 20th	Night	17% 8% 3 6% 4 4 4 4 6% 6% 38%	2872
	21st to end	Night	11% 5% 1 5% 4 4 4 4 6% 7% 48%	3483
September	1st to 10th	Night	13% 5% 1 4 2 4 4 3 5% 7% 52%	2011
	11th to 20th	Night	14% 5% 2 4 3 3 2 3 5% 6% 54%	2200
	21st to end	Night	16% 6% 2 5% 4 4 3 3 4 7% 46%	2200
October	1st to 10th	Night	19% 6% 3 5% 4 3 4 4 6% 6% 40%	2200
	11th to 20th	Night	16% 7% 2 5% 4 5% 4 3 5% 7% 41%	2491
	21st to end	Night	23% 7% 2 6% 5% 3 4 4 5% 7% 35%	2860
November	1st to 10th	Night	15% 7% 2 6% 5% 4 5% 3 5% 6% 42%	2667
	11th to 20th	Night	16% 6% 3 6% 5% 5% 5% 4 4 6% 41%	2730
	21st to end	Night	15% 8% 2 6% 5% 4 4 4 5% 6% 40%	2767
December	1st to 10th	Night	16% 11% 3 9% 4 5% 4 4 6% 6% 32%	4720
	11th to 20th	Night	23% 9% 2 5% 4 4 4 3 5% 4 37%	5348
	21st to end	Night	18% 10% 3 7% 4 4 4 4 5% 6% 36%	7150

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	47% 7% 14% 21% 12% 1	4662
	11th to 20th	Day	44% 6% 12% 22% 13% 3	4680
	21st to end	Day	40% 6% 10% 23% 17% 4	5124
February	1st to 10th	Day	47% 8% 10% 20% 12% 3	1829
	11th to 20th	Day	45% 7% 13% 18% 14% 3	2057
	21st to end	Day	49% 6% 12% 17% 12% 4	1730
March	1st to 10th	Day	56% 5% 8% 11% 13% 6%	4579
	11th to 20th	Day	48% 6% 15% 16% 11% 3	4917
	21st to end	Day	51% 5% 6% 17% 17% 3	5856
April	1st to 10th	Day	51% 5% 10% 17% 14% 4	2520
	11th to 20th	Day	46% 8% 10% 20% 13% 3	2569
	21st to end	Day	51% 6% 8% 18% 13% 4	2730
May	1st to 10th	Day	63% 7% 9% 15% 6% 1	6027
	11th to 20th	Day	54% 8% 12% 16% 8% 2	6204
	21st to end	Day	46% 8% 13% 20% 12% 1	6949
June	1st to 10th	Day	51% 8% 13% 19% 8% 1	2800
	11th to 20th	Day	44% 8% 13% 19% 14% 2	2800
	21st to end	Day	52% 9% 11% 17% 10% 1	2800
July	1st to 10th	Day	47% 7% 17% 19% 10%	6290
	11th to 20th	Day	41% 8% 15% 24% 12% 1	6285
	21st to end	Day	38% 6% 13% 27% 16%	6728
August	1st to 10th	Day	45% 8% 15% 23% 8%	4335
	11th to 20th	Day	48% 8% 15% 22% 6%	4214
	21st to end	Day	34% 7% 16% 25% 16% 2	4411
September	1st to 10th	Day	33% 9% 14% 26% 17%	2387
	11th to 20th	Day	33% 6% 10% 31% 18% 2	2200
	21st to end	Day	38% 7% 13% 24% 17% 1	2200
October	1st to 10th	Day	45% 7% 11% 23% 13% 1	3590
	11th to 20th	Day	37% 6% 14% 26% 16% 2	3081
	21st to end	Day	37% 6% 13% 22% 18% 4	3180
November	1st to 10th	Day	40% 8% 14% 21% 15% 2	1851
	11th to 20th	Day	41% 8% 15% 16% 17% 3	1890
	21st to end	Day	46% 7% 16% 20% 10% 1	1848
December	1st to 10th	Day	50% 6% 15% 21% 7% 1	2680
	11th to 20th	Day	44% 5% 12% 17% 18% 5%	3066
	21st to end	Day	50% 6% 9% 16% 12% 6%	4048
January	1st to 10th	Night	47% 6% 12% 23% 11% 1	8234
	11th to 20th	Night	56% 7% 12% 13% 9% 3	8280
	21st to end	Night	42% 6% 10% 21% 17% 4	9057
February	1st to 10th	Night	46% 9% 12% 17% 13% 2	2787
	11th to 20th	Night	43% 6% 14% 20% 14% 2	2460
	21st to end	Night	44% 5% 12% 21% 14% 4	2076
March	1st to 10th	Night	55% 6% 10% 13% 13% 4	5494
	11th to 20th	Night	50% 7% 17% 16% 9% 2	5262
	21st to end	Night	51% 5% 7% 15% 19% 3	5316
April	1st to 10th	Night	50% 5% 10% 17% 16% 2	2100
	11th to 20th	Night	47% 7% 10% 21% 14% 1	1998
	21st to end	Night	48% 7% 11% 17% 14% 3	1890
May	1st to 10th	Night	63% 7% 9% 14% 7% 1	4150
	11th to 20th	Night	52% 9% 11% 19% 7% 2	3870
	21st to end	Night	46% 8% 15% 21% 10% 1	3927
June	1st to 10th	Night	48% 9% 13% 18% 11% 1	1600
	11th to 20th	Night	42% 7% 14% 23% 12% 2	1600
	21st to end	Night	46% 9% 13% 20% 10% 1	1600
July	1st to 10th	Night	41% 6% 19% 23% 10%	3560
	11th to 20th	Night	43% 6% 14% 25% 12%	3552
	21st to end	Night	33% 7% 15% 34% 11%	3809
August	1st to 10th	Night	50% 7% 14% 22% 7%	2758
	11th to 20th	Night	45% 7% 17% 20% 11%	2899
	21st to end	Night	34% 6% 16% 27% 15% 1	3483
September	1st to 10th	Night	32% 8% 13% 31% 15%	2011
	11th to 20th	Night	32% 7% 12% 32% 17% 1	2200
	21st to end	Night	38% 7% 13% 27% 15% 1	2200
October	1st to 10th	Night	44% 7% 13% 22% 13% 1	3590
	11th to 20th	Night	35% 7% 11% 28% 16% 3	4053
	21st to end	Night	41% 6% 11% 25% 15% 2	4610
November	1st to 10th	Night	42% 7% 13% 24% 14% 1	2667
	11th to 20th	Night	44% 6% 13% 21% 14% 2	2730
	21st to end	Night	43% 7% 17% 21% 11% 1	2767
December	1st to 10th	Night	51% 6% 12% 24% 7% 1	4720
	11th to 20th	Night	50% 5% 10% 14% 18% 2	5348
	21st to end	Night	49% 6% 11% 17% 14% 2	7150

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	28% 23% 29% 18% 3	220
	11th to 20th	Day	27% 23% 31% 14% 4	220
	21st to end	Day	20% 25% 35% 15% 5%	242
February	1st to 10th	Day	26% 27% 28% 16% 3	351
	11th to 20th	Day	24% 30% 31% 12% 2	536
	21st to end	Day	26% 23% 32% 16% 3	446
March	1st to 10th	Day	25% 24% 33% 14% 4	540
	11th to 20th	Day	27% 26% 29% 13% 5% 1	540
	21st to end	Day	29% 25% 25% 13% 5% 2	594
April	1st to 10th	Day	31% 24% 24% 13% 5% 1	540
	11th to 20th	Day	31% 25% 23% 13% 6% 1	532
	21st to end	Day	32% 23% 27% 11% 6% 2	540
May	1st to 10th	Day	35% 20% 27% 13% 3 2	543
	11th to 20th	Day	24% 20% 33% 15% 7% 2	551
	21st to end	Day	22% 17% 31% 22% 7% 1	573
June	1st to 10th	Day	22% 17% 35% 16% 8% 1	530
	11th to 20th	Day	19% 18% 30% 22% 9% 2	530
	21st to end	Day	25% 14% 33% 19% 8% 2	530
July	1st to 10th	Day	18% 13% 33% 23% 12% 2	525
	11th to 20th	Day	16% 11% 31% 29% 10% 3	524
	21st to end	Day	16% 11% 35% 24% 12% 2	576
August	1st to 10th	Day	15% 8% 29% 28% 15% 5%	526
	11th to 20th	Day	16% 14% 25% 24% 15% 6%	519
	21st to end	Day	12% 11% 32% 25% 14% 5%	583
September	1st to 10th	Day	16% 13% 27% 24% 16% 4	530
	11th to 20th	Day	18% 12% 23% 20% 17% 10%	530
	21st to end	Day	16% 17% 26% 25% 11% 6%	530
October	1st to 10th	Day	22% 17% 24% 20% 13% 5%	530
	11th to 20th	Day	24% 18% 25% 19% 12% 1	442
	21st to end	Day	34% 16% 23% 20% 6%	462
November	1st to 10th	Day	26% 20% 22% 23% 8% 1	425
	11th to 20th	Day	28% 20% 25% 19% 7% 1	430
	21st to end	Day	27% 24% 23% 19% 6%	388
December	1st to 10th	Day	23% 21% 30% 19% 6%	220
	11th to 20th	Day	34% 22% 30% 9% 5%	220
	21st to end	Day	27% 23% 27% 17% 5%	242
January	1st to 10th	Night	18% 24% 31% 24% 3	840
	11th to 20th	Night	23% 20% 30% 24% 3	840
	21st to end	Night	16% 23% 36% 22% 3	924
February	1st to 10th	Night	18% 22% 34% 23% 3	840
	11th to 20th	Night	16% 26% 37% 18% 3	823
	21st to end	Night	20% 21% 32% 24% 3	692
March	1st to 10th	Night	23% 21% 33% 21% 2	840
	11th to 20th	Night	24% 21% 28% 21% 6% 1	840
	21st to end	Night	23% 20% 30% 22% 5% 1	924
April	1st to 10th	Night	28% 19% 29% 21% 4	840
	11th to 20th	Night	23% 17% 30% 24% 5%	754
	21st to end	Night	26% 18% 30% 21% 5%	630
May	1st to 10th	Night	27% 12% 29% 26% 6% 1	630
	11th to 20th	Night	22% 11% 31% 26% 9%	522
	21st to end	Night	20% 8% 24% 38% 9% 1	433
June	1st to 10th	Night	24% 11% 24% 31% 10% 1	400
	11th to 20th	Night	19% 8% 25% 33% 16%	400
	21st to end	Night	20% 6% 23% 39% 11%	400
July	1st to 10th	Night	16% 4 24% 40% 15% 1	390
	11th to 20th	Night	16% 3 22% 40% 17% 2	388
	21st to end	Night	17% 3 18% 43% 18% 1	438
August	1st to 10th	Night	17% 4 20% 38% 19% 1	502
	11th to 20th	Night	17% 5% 25% 34% 17% 2	592
	21st to end	Night	15% 6% 23% 34% 21% 2	816
September	1st to 10th	Night	17% 6% 24% 35% 18% 2	800
	11th to 20th	Night	16% 10% 22% 27% 22% 4	800
	21st to end	Night	19% 9% 25% 31% 16% 2	800
October	1st to 10th	Night	24% 10% 19% 31% 15% 1	800
	11th to 20th	Night	21% 13% 29% 23% 13% 2	800
	21st to end	Night	28% 14% 25% 27% 5%	880
November	1st to 10th	Night	21% 18% 27% 24% 8% 1	820
	11th to 20th	Night	22% 18% 28% 23% 8% 1	840
	21st to end	Night	23% 20% 24% 27% 5% 1	840
December	1st to 10th	Night	26% 19% 31% 20% 5%	840
	11th to 20th	Night	24% 21% 30% 20% 5%	840
	21st to end	Night	24% 22% 29% 22% 3	924

Page generated at 2026-05-14 01:59:00. Version ac07

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