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 2025-01-22.

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%	105104
	Night	17% 8% 3 7% 4 4 4 4 5% 6% 37%	104275
Transparency	Day	46% 8% 13% 20% 12% 2	108629
	Night	46% 7% 13% 20% 12% 2	108839
Seeing	Day	23% 19% 28% 19% 9% 2	15060
	Night	21% 16% 27% 26% 9% 1	24004

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% 8% 3 8% 5% 6% 5% 4 6% 6% 35%	2597
	11th to 20th	Day	14% 8% 3 8% 6% 4 5% 4 6% 7% 34%	2600
	21st to end	Day	13% 12% 3 8% 5% 5% 4 4 5% 7% 34%	2780
February	1st to 10th	Day	13% 10% 3 7% 6% 5% 6% 5% 5% 6% 35%	1654
	11th to 20th	Day	10% 10% 3 9% 4 5% 5% 3 6% 7% 38%	1848
	21st to end	Day	15% 10% 3 7% 7% 5% 5% 4 6% 5% 34%	1570
March	1st to 10th	Day	21% 15% 3 8% 4 4 4 3 4 5% 28%	3116
	11th to 20th	Day	14% 10% 3 8% 5% 4 4 4 6% 6% 36%	3367
	21st to end	Day	21% 8% 3 7% 4 4 3 3 5% 7% 35%	3996
April	1st to 10th	Day	17% 11% 3 7% 5% 4 4 4 4 6% 35%	2280
	11th to 20th	Day	17% 6% 2 6% 4 5% 5% 4 6% 7% 38%	2321
	21st to end	Day	22% 8% 3 7% 4 5% 5% 3 4 6% 33%	2470
May	1st to 10th	Day	23% 11% 4 8% 5% 4 5% 4 6% 6% 26%	4106
	11th to 20th	Day	18% 7% 3 9% 6% 6% 5% 4 5% 6% 30%	4257
	21st to end	Day	14% 5% 2 6% 5% 5% 5% 4 7% 10% 37%	4837
June	1st to 10th	Day	22% 7% 2 6% 5% 5% 5% 5% 6% 7% 29%	2660
	11th to 20th	Day	17% 6% 2 6% 5% 4 4 5% 6% 7% 38%	2660
	21st to end	Day	22% 7% 3 8% 5% 5% 4 4 6% 7% 29%	2660
July	1st to 10th	Day	14% 5% 2 6% 5% 6% 6% 5% 8% 10% 33%	4440
	11th to 20th	Day	12% 5% 1 6% 5% 5% 6% 5% 8% 10% 36%	4440
	21st to end	Day	19% 6% 2 6% 4 5% 5% 4 6% 7% 36%	4814
August	1st to 10th	Day	15% 6% 2 7% 5% 5% 6% 5% 7% 7% 34%	4215
	11th to 20th	Day	19% 8% 3 6% 5% 5% 5% 5% 5% 7% 31%	4045
	21st to end	Day	11% 5% 1 5% 4 4 5% 4 7% 10% 44%	4276
September	1st to 10th	Day	11% 5% 1 4 4 4 5% 5% 6% 9% 47%	2268
	11th to 20th	Day	13% 4 1 5% 3 4 3 2 4 6% 53%	2090
	21st to end	Day	16% 5% 2 5% 3 4 4 4 5% 9% 43%	2090
October	1st to 10th	Day	19% 7% 3 6% 5% 4 5% 3 4 6% 38%	2090
	11th to 20th	Day	17% 7% 2 6% 4 4 5% 4 5% 6% 41%	1809
	21st to end	Day	23% 10% 3 6% 4 4 4 4 4 5% 34%	1881
November	1st to 10th	Day	15% 7% 2 5% 4 4 4 4 5% 6% 44%	1761
	11th to 20th	Day	18% 6% 2 4 5% 4 4 5% 6% 8% 40%	1800
	21st to end	Day	19% 9% 2 5% 3 3 4 4 6% 7% 38%	1760
December	1st to 10th	Day	15% 9% 3 10% 5% 4 5% 4 6% 7% 32%	2600
	11th to 20th	Day	18% 8% 3 4 4 4 5% 4 5% 6% 40%	2986
	21st to end	Day	18% 9% 3 7% 4 4 4 4 4 6% 35%	3960
January	1st to 10th	Night	14% 10% 3 8% 4 3 4 4 5% 6% 38%	4569
	11th to 20th	Night	11% 11% 4 13% 8% 6% 5% 4 5% 7% 27%	4580
	21st to end	Night	15% 11% 5% 12% 5% 5% 5% 4 4 6% 28%	4899
February	1st to 10th	Night	12% 9% 4 7% 6% 5% 5% 5% 6% 6% 34%	2523
	11th to 20th	Night	9% 10% 4 6% 5% 5% 5% 4 5% 7% 41%	2218
	21st to end	Night	12% 10% 4 7% 5% 4 4 4 5% 6% 39%	1884
March	1st to 10th	Night	23% 12% 3 5% 4 4 4 4 5% 5% 31%	3724
	11th to 20th	Night	12% 8% 4 9% 7% 6% 6% 5% 5% 6% 32%	3591
	21st to end	Night	22% 9% 3 7% 4 4 4 3 5% 7% 32%	3635
April	1st to 10th	Night	18% 10% 3 6% 4 4 4 3 5% 5% 37%	1900
	11th to 20th	Night	17% 8% 2 7% 4 4 4 3 6% 6% 37%	1806
	21st to end	Night	22% 8% 2 6% 4 4 3 4 5% 6% 36%	1710
May	1st to 10th	Night	23% 11% 3 8% 4 4 4 4 5% 6% 28%	2834
	11th to 20th	Night	18% 9% 3 7% 6% 5% 5% 5% 6% 7% 29%	2665
	21st to end	Night	15% 6% 2 6% 4 3 4 4 6% 9% 41%	2738
June	1st to 10th	Night	20% 8% 3 6% 4 4 4 4 6% 6% 36%	1520
	11th to 20th	Night	18% 6% 2 4 3 4 4 4 6% 8% 40%	1520
	21st to end	Night	20% 6% 2 7% 4 5% 4 3 6% 8% 35%	1520
July	1st to 10th	Night	12% 5% 2 5% 5% 5% 5% 5% 8% 9% 40%	2520
	11th to 20th	Night	16% 5% 2 6% 4 4 3 4 5% 7% 45%	2520
	21st to end	Night	17% 5% 2 5% 4 4 5% 3 7% 7% 42%	2739
August	1st to 10th	Night	21% 8% 3 6% 4 4 4 3 6% 5% 35%	2683
	11th to 20th	Night	18% 8% 3 6% 4 4 5% 4 6% 6% 37%	2782
	21st to end	Night	11% 5% 1 5% 4 4 4 4 6% 7% 48%	3376
September	1st to 10th	Night	13% 4 1 4 3 4 4 3 5% 7% 52%	1910
	11th to 20th	Night	15% 5% 2 4 3 3 2 3 5% 6% 53%	2090
	21st to end	Night	16% 6% 2 5% 4 4 3 3 4 7% 46%	2090
October	1st to 10th	Night	20% 6% 3 5% 4 4 4 4 6% 6% 38%	2090
	11th to 20th	Night	17% 6% 2 5% 4 5% 4 3 6% 7% 41%	2366
	21st to end	Night	23% 7% 2 6% 4 3 4 4 5% 7% 35%	2717
November	1st to 10th	Night	15% 6% 2 5% 5% 4 5% 3 5% 7% 43%	2537
	11th to 20th	Night	16% 7% 2 6% 5% 5% 5% 4 4 6% 41%	2600
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 6% 41%	2635
December	1st to 10th	Night	17% 11% 3 9% 4 5% 4 4 6% 6% 32%	4580
	11th to 20th	Night	23% 9% 2 5% 4 4 4 3 4 4 37%	5208
	21st to end	Night	18% 10% 3 7% 4 4 4 4 5% 6% 36%	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	44% 8% 14% 22% 10% 1	2598
	11th to 20th	Day	46% 8% 16% 19% 9% 2	2600
	21st to end	Day	48% 8% 12% 19% 11% 1	2780
February	1st to 10th	Day	48% 8% 11% 19% 11% 2	1654
	11th to 20th	Day	46% 7% 13% 17% 14% 3	1857
	21st to end	Day	50% 6% 12% 16% 11% 4	1570
March	1st to 10th	Day	60% 6% 8% 10% 13% 2	3119
	11th to 20th	Day	46% 9% 13% 15% 13% 4	3367
	21st to end	Day	49% 5% 8% 15% 19% 4	3996
April	1st to 10th	Day	51% 5% 10% 17% 13% 4	2280
	11th to 20th	Day	45% 8% 11% 21% 13% 2	2321
	21st to end	Day	52% 7% 9% 17% 12% 4	2470
May	1st to 10th	Day	57% 9% 9% 16% 7% 1	4120
	11th to 20th	Day	52% 9% 14% 15% 9% 1	4261
	21st to end	Day	39% 10% 14% 21% 15% 1	4837
June	1st to 10th	Day	51% 8% 13% 19% 8% 1	2660
	11th to 20th	Day	44% 8% 13% 19% 14% 2	2660
	21st to end	Day	53% 10% 11% 16% 10% 1	2660
July	1st to 10th	Day	43% 8% 16% 22% 11%	4370
	11th to 20th	Day	39% 9% 16% 28% 8%	4365
	21st to end	Day	45% 8% 11% 22% 14% 1	4661
August	1st to 10th	Day	46% 8% 15% 22% 8%	4201
	11th to 20th	Day	49% 8% 15% 21% 6%	4084
	21st to end	Day	34% 7% 16% 25% 16% 2	4276
September	1st to 10th	Day	33% 9% 15% 26% 16%	2268
	11th to 20th	Day	33% 6% 10% 32% 17% 2	2090
	21st to end	Day	38% 7% 14% 24% 16% 1	2090
October	1st to 10th	Day	47% 7% 11% 22% 13% 1	3480
	11th to 20th	Day	37% 6% 14% 25% 16% 2	2986
	21st to end	Day	37% 6% 13% 22% 18% 4	3081
November	1st to 10th	Day	40% 7% 15% 21% 15% 2	1761
	11th to 20th	Day	42% 8% 14% 15% 17% 3	1800
	21st to end	Day	46% 7% 16% 20% 10% 1	1760
December	1st to 10th	Day	50% 6% 16% 21% 6% 1	2600
	11th to 20th	Day	44% 5% 12% 17% 18% 5%	2986
	21st to end	Day	50% 7% 9% 16% 12% 6%	3960
January	1st to 10th	Night	45% 8% 14% 22% 9% 2	4569
	11th to 20th	Night	53% 8% 16% 13% 7% 2	4580
	21st to end	Night	55% 7% 10% 16% 10% 2	4899
February	1st to 10th	Night	46% 9% 14% 16% 13% 3	2523
	11th to 20th	Night	43% 6% 14% 20% 14% 2	2220
	21st to end	Night	45% 5% 13% 20% 12% 4	1884
March	1st to 10th	Night	54% 6% 12% 16% 9% 3	3734
	11th to 20th	Night	50% 10% 12% 16% 10% 2	3592
	21st to end	Night	52% 6% 8% 14% 17% 3	3635
April	1st to 10th	Night	49% 5% 11% 18% 16% 2	1900
	11th to 20th	Night	46% 8% 10% 21% 14% 1	1806
	21st to end	Night	48% 7% 12% 16% 14% 3	1710
May	1st to 10th	Night	55% 9% 10% 16% 8% 1	2840
	11th to 20th	Night	50% 11% 13% 17% 7% 2	2666
	21st to end	Night	39% 10% 17% 20% 13% 1	2739
June	1st to 10th	Night	48% 9% 14% 18% 10%	1520
	11th to 20th	Night	42% 7% 14% 23% 12% 2	1520
	21st to end	Night	47% 10% 13% 19% 10% 1	1520
July	1st to 10th	Night	40% 7% 20% 21% 11% 1	2480
	11th to 20th	Night	39% 6% 15% 28% 11%	2472
	21st to end	Night	40% 8% 13% 26% 12%	2651
August	1st to 10th	Night	51% 7% 14% 21% 7%	2673
	11th to 20th	Night	46% 7% 17% 19% 11%	2809
	21st to end	Night	34% 7% 17% 27% 15% 1	3376
September	1st to 10th	Night	32% 9% 14% 31% 15%	1910
	11th to 20th	Night	33% 7% 12% 31% 16% 1	2090
	21st to end	Night	38% 7% 13% 27% 14% 1	2090
October	1st to 10th	Night	46% 7% 13% 22% 12% 1	3480
	11th to 20th	Night	35% 7% 11% 28% 17% 3	3928
	21st to end	Night	42% 6% 12% 24% 15% 2	4467
November	1st to 10th	Night	41% 7% 13% 24% 13% 1	2537
	11th to 20th	Night	44% 6% 13% 21% 15% 2	2600
	21st to end	Night	43% 7% 17% 21% 11% 1	2635
December	1st to 10th	Night	51% 6% 12% 24% 6%	4580
	11th to 20th	Night	50% 5% 10% 14% 19% 2	5208
	21st to end	Night	49% 6% 11% 17% 14% 2	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	28% 24% 28% 19% 3	200
	11th to 20th	Day	25% 25% 32% 14% 5% 1	200
	21st to end	Day	19% 25% 35% 16% 7%	200
February	1st to 10th	Day	26% 27% 29% 16% 3	296
	11th to 20th	Day	24% 32% 30% 12% 2	456
	21st to end	Day	27% 24% 28% 17% 3	382
March	1st to 10th	Day	25% 23% 33% 14% 5%	460
	11th to 20th	Day	25% 26% 30% 13% 5% 1	460
	21st to end	Day	27% 25% 25% 14% 6% 2	506
April	1st to 10th	Day	30% 24% 25% 14% 6% 2	460
	11th to 20th	Day	28% 26% 24% 13% 7% 1	452
	21st to end	Day	32% 24% 26% 11% 5% 2	460
May	1st to 10th	Day	32% 21% 27% 14% 3 2	463
	11th to 20th	Day	22% 20% 34% 14% 7% 2	487
	21st to end	Day	21% 18% 32% 21% 7% 2	529
June	1st to 10th	Day	22% 18% 34% 17% 9% 1	490
	11th to 20th	Day	18% 16% 30% 23% 9% 2	490
	21st to end	Day	25% 14% 32% 20% 8% 2	490
July	1st to 10th	Day	18% 13% 32% 23% 12% 2	485
	11th to 20th	Day	14% 10% 33% 28% 11% 3	484
	21st to end	Day	16% 10% 35% 24% 12% 2	532
August	1st to 10th	Day	17% 8% 29% 26% 15% 4	486
	11th to 20th	Day	17% 14% 25% 24% 14% 6%	479
	21st to end	Day	13% 11% 31% 24% 15% 5%	539
September	1st to 10th	Day	16% 13% 27% 24% 16% 4	490
	11th to 20th	Day	19% 13% 23% 20% 16% 10%	490
	21st to end	Day	16% 17% 25% 25% 11% 6%	490
October	1st to 10th	Day	22% 17% 24% 20% 13% 4	490
	11th to 20th	Day	24% 18% 26% 19% 13% 1	410
	21st to end	Day	35% 16% 23% 19% 6%	429
November	1st to 10th	Day	25% 19% 22% 24% 9% 1	395
	11th to 20th	Day	29% 20% 25% 19% 7% 1	400
	21st to end	Day	28% 24% 23% 18% 7%	360
December	1st to 10th	Day	23% 21% 30% 19% 7%	200
	11th to 20th	Day	33% 23% 31% 9% 5%	200
	21st to end	Day	27% 23% 26% 17% 5%	220
January	1st to 10th	Night	18% 24% 30% 24% 4	800
	11th to 20th	Night	23% 21% 30% 24% 3	800
	21st to end	Night	16% 23% 35% 22% 3	841
February	1st to 10th	Night	18% 22% 34% 23% 3	760
	11th to 20th	Night	16% 27% 36% 18% 3	743
	21st to end	Night	21% 21% 30% 25% 4	628
March	1st to 10th	Night	23% 21% 32% 21% 2	760
	11th to 20th	Night	23% 22% 28% 21% 6% 1	760
	21st to end	Night	23% 20% 30% 21% 6% 1	836
April	1st to 10th	Night	27% 18% 28% 22% 4	760
	11th to 20th	Night	22% 17% 30% 25% 6%	682
	21st to end	Night	26% 19% 29% 21% 5%	570
May	1st to 10th	Night	26% 12% 28% 27% 6% 1	570
	11th to 20th	Night	22% 11% 31% 27% 9%	479
	21st to end	Night	19% 8% 25% 37% 10% 1	411
June	1st to 10th	Night	24% 11% 24% 31% 10% 1	380
	11th to 20th	Night	18% 8% 24% 33% 17%	380
	21st to end	Night	21% 6% 22% 39% 12%	380
July	1st to 10th	Night	16% 4 24% 40% 16% 1	370
	11th to 20th	Night	15% 3 23% 40% 17% 2	368
	21st to end	Night	18% 4 17% 42% 19% 1	416
August	1st to 10th	Night	18% 4 20% 38% 18% 1	477
	11th to 20th	Night	18% 5% 25% 34% 17% 2	562
	21st to end	Night	15% 6% 22% 33% 21% 2	775
September	1st to 10th	Night	16% 5% 24% 34% 18% 2	760
	11th to 20th	Night	16% 10% 23% 25% 21% 4	760
	21st to end	Night	19% 9% 24% 31% 16% 2	760
October	1st to 10th	Night	25% 10% 19% 30% 14% 1	760
	11th to 20th	Night	21% 13% 28% 22% 13% 2	760
	21st to end	Night	29% 15% 25% 26% 5%	836
November	1st to 10th	Night	20% 18% 27% 25% 8% 1	780
	11th to 20th	Night	22% 18% 28% 23% 8% 1	800
	21st to end	Night	23% 21% 24% 27% 5% 1	800
December	1st to 10th	Night	26% 19% 31% 20% 5%	800
	11th to 20th	Night	23% 22% 30% 20% 5%	800
	21st to end	Night	23% 22% 29% 23% 4	880

Page generated at 2025-01-19 03:06:45. Version ac07

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