Red Barn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Red Barn Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	10% 6% 2 6% 5% 5% 5% 4 6% 9% 42%	131554
	Night	10% 6% 2 6% 4 4 5% 4 6% 8% 44%	130263
Transparency	Day	37% 6% 13% 20% 17% 8%	135340
	Night	36% 6% 12% 18% 19% 9%	134547
Seeing	Day	12% 5% 18% 25% 24% 17%	16906
	Night	12% 5% 21% 33% 24% 5%	27001

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	10% 6% 2 7% 4 4 4 3 4 7% 49%	5258
	11th to 20th	Day	14% 5% 2 4 3 3 4 3 6% 9% 47%	5280
	21st to end	Day	10% 8% 3 7% 5% 4 4 4 5% 8% 42%	6174
February	1st to 10th	Day	14% 7% 2 7% 5% 3 4 4 5% 7% 42%	2100
	11th to 20th	Day	16% 7% 2 5% 4 4 3 3 5% 6% 45%	2048
	21st to end	Day	15% 7% 2 5% 3 4 3 3 5% 6% 46%	1730
March	1st to 10th	Day	18% 8% 3 6% 4 4 4 4 5% 7% 38%	4862
	11th to 20th	Day	7% 4 2 5% 4 4 4 3 5% 8% 55%	5090
	21st to end	Day	13% 6% 2 6% 4 3 4 3 5% 6% 47%	5586
April	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 4 6% 6% 46%	2211
	11th to 20th	Day	10% 4 2 5% 5% 3 4 4 5% 8% 50%	2296
	21st to end	Day	7% 4 2 5% 4 4 5% 4 5% 7% 54%	2545
May	1st to 10th	Day	10% 6% 2 7% 5% 5% 5% 4 6% 9% 42%	5862
	11th to 20th	Day	13% 6% 3 6% 4 4 5% 4 7% 10% 40%	5861
	21st to end	Day	4 3 2 5% 4 5% 6% 5% 8% 11% 47%	6433
June	1st to 10th	Day	9% 7% 3 8% 6% 6% 7% 6% 8% 10% 32%	2600
	11th to 20th	Day	5% 4 2 6% 6% 6% 7% 6% 8% 12% 39%	2600
	21st to end	Day	6% 6% 3 8% 6% 6% 7% 7% 10% 11% 31%	2600
July	1st to 10th	Day	7% 7% 3 9% 7% 8% 9% 8% 10% 12% 19%	5900
	11th to 20th	Day	4 3 1 5% 5% 5% 6% 6% 8% 14% 43%	5900
	21st to end	Day	5% 5% 3 8% 7% 7% 7% 7% 10% 14% 27%	6424
August	1st to 10th	Day	12% 5% 2 8% 6% 6% 7% 6% 9% 12% 27%	4218
	11th to 20th	Day	6% 4 2 6% 5% 5% 6% 5% 8% 12% 42%	3849
	21st to end	Day	7% 6% 3 8% 6% 6% 7% 5% 8% 11% 33%	4190
September	1st to 10th	Day	10% 7% 3 7% 5% 7% 7% 5% 7% 10% 32%	2200
	11th to 20th	Day	11% 7% 3 7% 6% 5% 5% 3 7% 9% 38%	2200
	21st to end	Day	11% 5% 2 5% 4 5% 5% 5% 6% 8% 45%	2200
October	1st to 10th	Day	11% 6% 2 6% 4 5% 4 3 5% 6% 49%	2200
	11th to 20th	Day	8% 4 2 4 3 3 3 3 5% 7% 58%	2085
	21st to end	Day	9% 4 2 5% 3 4 3 4 4 6% 56%	2200
November	1st to 10th	Day	9% 5% 2 5% 4 3 4 3 5% 7% 53%	2024
	11th to 20th	Day	10% 6% 2 4 4 2 3 3 5% 4 57%	1890
	21st to end	Day	11% 6% 2 5% 4 3 4 3 6% 8% 47%	1890
December	1st to 10th	Day	13% 5% 2 6% 4 3 3 3 4 6% 51%	3020
	11th to 20th	Day	13% 6% 2 6% 4 3 4 3 5% 6% 47%	3463
	21st to end	Day	16% 10% 3 6% 4 3 3 3 5% 6% 42%	4565
January	1st to 10th	Night	9% 5% 2 5% 4 4 4 4 5% 7% 50%	7635
	11th to 20th	Night	12% 6% 2 7% 5% 4 4 3 4 7% 45%	7680
	21st to end	Night	15% 8% 3 6% 4 4 4 3 5% 8% 40%	8002
February	1st to 10th	Night	12% 7% 3 6% 4 4 4 4 6% 6% 46%	2520
	11th to 20th	Night	15% 7% 2 6% 4 4 3 3 4 6% 45%	2458
	21st to end	Night	11% 7% 2 5% 3 4 4 3 5% 7% 47%	2076
March	1st to 10th	Night	19% 9% 2 6% 4 3 3 3 4 7% 41%	5197
	11th to 20th	Night	9% 5% 1 4 3 4 4 4 7% 8% 51%	5090
	21st to end	Night	12% 6% 2 5% 3 4 4 3 5% 7% 49%	5588
April	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 7% 48%	2212
	11th to 20th	Night	7% 5% 2 6% 4 4 5% 4 5% 7% 51%	2067
	21st to end	Night	5% 4 1 5% 4 4 4 3 5% 7% 57%	1854
May	1st to 10th	Night	8% 6% 3 7% 5% 4 5% 5% 6% 10% 42%	4033
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 6% 8% 42%	4032
	21st to end	Night	4 4 2 6% 4 5% 5% 5% 8% 11% 46%	4421
June	1st to 10th	Night	7% 5% 3 7% 6% 6% 6% 6% 10% 12% 32%	1800
	11th to 20th	Night	5% 5% 2 5% 5% 5% 6% 6% 9% 12% 39%	1800
	21st to end	Night	6% 5% 2 8% 7% 6% 7% 5% 8% 11% 35%	1800
July	1st to 10th	Night	9% 9% 4 12% 7% 7% 7% 6% 8% 12% 19%	4058
	11th to 20th	Night	3 4 2 5% 6% 5% 6% 6% 12% 16% 34%	4057
	21st to end	Night	5% 6% 3 9% 7% 7% 8% 6% 9% 12% 28%	4427
August	1st to 10th	Night	11% 5% 2 8% 6% 6% 6% 5% 8% 12% 29%	2915
	11th to 20th	Night	5% 5% 2 6% 5% 5% 7% 5% 7% 12% 41%	3198
	21st to end	Night	6% 6% 3 7% 6% 5% 5% 5% 8% 11% 39%	3673
September	1st to 10th	Night	9% 7% 3 9% 5% 5% 5% 4 8% 12% 33%	2200
	11th to 20th	Night	10% 7% 3 8% 5% 5% 5% 5% 6% 8% 39%	2200
	21st to end	Night	9% 5% 2 7% 5% 4 5% 4 6% 9% 44%	2200
October	1st to 10th	Night	9% 6% 2 5% 3 4 3 3 6% 8% 50%	2200
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 6% 60%	2314
	21st to end	Night	8% 6% 1 5% 4 3 4 4 4 5% 56%	2640
November	1st to 10th	Night	9% 5% 2 5% 3 3 4 3 4 6% 55%	2491
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 6% 54%	2730
	21st to end	Night	10% 7% 2 5% 3 4 4 3 7% 7% 49%	2730
December	1st to 10th	Night	10% 6% 2 5% 4 4 3 2 4 6% 55%	4380
	11th to 20th	Night	12% 7% 3 6% 3 3 3 2 4 5% 51%	4952
	21st to end	Night	15% 9% 2 7% 4 3 3 3 4 6% 44%	6633

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	37% 3 7% 18% 28% 8%	5259
	11th to 20th	Day	35% 2 5% 15% 25% 18%	5280
	21st to end	Day	42% 3 7% 19% 17% 13%	6174
February	1st to 10th	Day	42% 3 8% 16% 22% 9%	2100
	11th to 20th	Day	40% 3 5% 17% 25% 10%	2058
	21st to end	Day	39% 3 9% 18% 19% 12%	1730
March	1st to 10th	Day	46% 4 8% 16% 16% 10%	4862
	11th to 20th	Day	28% 3 10% 14% 22% 22%	5090
	21st to end	Day	38% 4 9% 22% 17% 11%	5586
April	1st to 10th	Day	36% 5% 9% 22% 16% 12%	2211
	11th to 20th	Day	34% 4 7% 20% 24% 11%	2296
	21st to end	Day	29% 4 10% 25% 24% 7%	2545
May	1st to 10th	Day	38% 6% 15% 23% 15% 3	5897
	11th to 20th	Day	38% 5% 15% 28% 12% 1	5865
	21st to end	Day	28% 6% 21% 24% 19% 1	6447
June	1st to 10th	Day	43% 8% 15% 22% 11% 1	2600
	11th to 20th	Day	34% 9% 20% 23% 14% 1	2600
	21st to end	Day	40% 9% 22% 18% 9% 2	2600
July	1st to 10th	Day	49% 16% 24% 9% 2	5835
	11th to 20th	Day	28% 12% 36% 22% 2	5831
	21st to end	Day	41% 15% 24% 19% 2	6240
August	1st to 10th	Day	45% 10% 21% 20% 4	4205
	11th to 20th	Day	31% 8% 20% 29% 11% 1	3885
	21st to end	Day	42% 8% 20% 25% 4 1	4190
September	1st to 10th	Day	44% 8% 15% 19% 11% 3	2200
	11th to 20th	Day	44% 6% 12% 19% 16% 3	2200
	21st to end	Day	36% 5% 12% 23% 18% 6%	2200
October	1st to 10th	Day	41% 3 6% 12% 19% 19%	3590
	11th to 20th	Day	17% 3 4 18% 26% 33%	3377
	21st to end	Day	20% 2 4 20% 38% 17%	3538
November	1st to 10th	Day	31% 4 8% 17% 25% 15%	2024
	11th to 20th	Day	31% 3 6% 18% 27% 15%	1890
	21st to end	Day	35% 3 8% 19% 23% 11%	1890
December	1st to 10th	Day	36% 3 7% 15% 28% 11%	3020
	11th to 20th	Day	38% 3 5% 24% 23% 8%	3460
	21st to end	Day	45% 2 4 19% 25% 4	4565
January	1st to 10th	Night	33% 4 9% 15% 28% 10%	7636
	11th to 20th	Night	40% 2 4 13% 28% 13%	7680
	21st to end	Night	43% 3 6% 18% 21% 9%	8002
February	1st to 10th	Night	38% 4 7% 16% 23% 12%	2520
	11th to 20th	Night	41% 4 7% 13% 21% 14%	2459
	21st to end	Night	37% 4 6% 19% 19% 15%	2076
March	1st to 10th	Night	45% 3 8% 15% 17% 11%	5197
	11th to 20th	Night	29% 4 8% 16% 23% 19%	5090
	21st to end	Night	36% 3 8% 17% 23% 13%	5588
April	1st to 10th	Night	33% 6% 11% 18% 19% 13%	2212
	11th to 20th	Night	32% 4 9% 19% 25% 12%	2067
	21st to end	Night	27% 5% 9% 27% 23% 9%	1854
May	1st to 10th	Night	36% 7% 16% 25% 12% 4	4060
	11th to 20th	Night	39% 6% 19% 24% 11% 2	4033
	21st to end	Night	30% 6% 17% 28% 17% 2	4429
June	1st to 10th	Night	39% 9% 20% 19% 12% 1	1800
	11th to 20th	Night	33% 9% 25% 21% 11% 1	1800
	21st to end	Night	39% 11% 20% 19% 9% 2	1800
July	1st to 10th	Night	55% 13% 21% 9% 2 1	4015
	11th to 20th	Night	31% 16% 33% 18% 2	4006
	21st to end	Night	44% 14% 24% 17% 1	4297
August	1st to 10th	Night	44% 10% 27% 16% 3	2904
	11th to 20th	Night	32% 11% 22% 25% 8% 1	3228
	21st to end	Night	36% 9% 26% 23% 4 1	3673
September	1st to 10th	Night	43% 9% 18% 17% 12% 2	2200
	11th to 20th	Night	42% 8% 14% 16% 18% 3	2200
	21st to end	Night	36% 6% 14% 20% 17% 7%	2200
October	1st to 10th	Night	38% 4 9% 14% 19% 16%	3590
	11th to 20th	Night	17% 2 3 15% 29% 34%	3761
	21st to end	Night	20% 3 4 17% 38% 19%	4252
November	1st to 10th	Night	30% 3 8% 18% 24% 17%	2491
	11th to 20th	Night	32% 3 6% 16% 27% 16%	2730
	21st to end	Night	34% 3 9% 20% 20% 13%	2730
December	1st to 10th	Night	32% 2 9% 17% 28% 12%	4380
	11th to 20th	Night	36% 3 7% 21% 23% 10%	4954
	21st to end	Night	43% 3 5% 18% 27% 3	6633

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	12% 15% 42% 24% 7% 1	330
	11th to 20th	Day	12% 15% 32% 27% 11% 3	330
	21st to end	Day	20% 13% 42% 19% 5% 1	363
February	1st to 10th	Day	18% 12% 34% 26% 10% 1	330
	11th to 20th	Day	22% 11% 36% 24% 6%	330
	21st to end	Day	16% 15% 36% 27% 5% 1	273
March	1st to 10th	Day	15% 8% 29% 30% 17% 1	456
	11th to 20th	Day	13% 8% 31% 32% 13% 2	540
	21st to end	Day	13% 7% 31% 33% 14% 2	594
April	1st to 10th	Day	14% 11% 26% 27% 19% 3	504
	11th to 20th	Day	12% 7% 26% 31% 20% 5%	492
	21st to end	Day	9% 3 19% 33% 26% 9%	500
May	1st to 10th	Day	6% 6% 22% 30% 24% 11%	503
	11th to 20th	Day	10% 3 16% 28% 26% 17%	527
	21st to end	Day	9% 2 10% 25% 32% 23%	573
June	1st to 10th	Day	11% 1 9% 24% 32% 24%	530
	11th to 20th	Day	7% 2 9% 21% 31% 31%	530
	21st to end	Day	8% 1 4 18% 37% 33%	530
July	1st to 10th	Day	8% 1 4 13% 31% 44%	525
	11th to 20th	Day	8% 2 1 8% 31% 51%	524
	21st to end	Day	7% 2 3 10% 36% 42%	576
August	1st to 10th	Day	12% 2 4 14% 32% 37%	526
	11th to 20th	Day	7% 2 2 12% 32% 46%	519
	21st to end	Day	12% 2 5% 19% 34% 29%	583
September	1st to 10th	Day	14% 3 4 22% 29% 27%	530
	11th to 20th	Day	14% 1 5% 30% 35% 15%	530
	21st to end	Day	12% 1 9% 24% 32% 22%	530
October	1st to 10th	Day	15% 2 17% 35% 23% 7%	530
	11th to 20th	Day	8% 3 20% 31% 27% 12%	530
	21st to end	Day	10% 5% 21% 34% 25% 5%	583
November	1st to 10th	Day	14% 3 21% 32% 22% 7%	502
	11th to 20th	Day	13% 5% 32% 31% 13% 5%	330
	21st to end	Day	10% 11% 33% 28% 15% 3	330
December	1st to 10th	Day	19% 8% 32% 26% 12% 4	330
	11th to 20th	Day	21% 7% 32% 26% 10% 4	330
	21st to end	Day	19% 8% 28% 27% 17% 1	363
January	1st to 10th	Night	14% 10% 36% 33% 5% 1	840
	11th to 20th	Night	14% 10% 32% 32% 11% 1	840
	21st to end	Night	19% 8% 37% 31% 4	924
February	1st to 10th	Night	15% 9% 30% 38% 8%	840
	11th to 20th	Night	18% 9% 35% 31% 7%	823
	21st to end	Night	15% 9% 36% 36% 4	692
March	1st to 10th	Night	15% 7% 30% 39% 10%	840
	11th to 20th	Night	13% 7% 32% 35% 13% 1	840
	21st to end	Night	11% 8% 32% 36% 13%	924
April	1st to 10th	Night	13% 6% 29% 37% 14% 1	805
	11th to 20th	Night	9% 6% 28% 41% 14% 1	685
	21st to end	Night	8% 3 25% 40% 23% 2	600
May	1st to 10th	Night	8% 4 23% 39% 24% 3	600
	11th to 20th	Night	9% 2 20% 39% 25% 5%	591
	21st to end	Night	9% 1 10% 38% 35% 7%	650
June	1st to 10th	Night	10% 2 6% 38% 37% 8%	600
	11th to 20th	Night	7% 2 6% 31% 42% 13%	600
	21st to end	Night	7% 1 3 31% 48% 11%	600
July	1st to 10th	Night	9% 2 3 24% 44% 18%	585
	11th to 20th	Night	8% 1 1 15% 53% 23%	582
	21st to end	Night	6% 1 2 19% 57% 15%	657
August	1st to 10th	Night	10% 1 2 24% 51% 14%	597
	11th to 20th	Night	8% 2 2 18% 51% 19%	594
	21st to end	Night	9% 2 5% 28% 40% 16%	708
September	1st to 10th	Night	12% 2 6% 26% 43% 12%	800
	11th to 20th	Night	14% 2 5% 37% 38% 5%	800
	21st to end	Night	11% 2 11% 30% 41% 5%	800
October	1st to 10th	Night	12% 2 17% 38% 28% 3	800
	11th to 20th	Night	11% 3 19% 37% 28% 3	800
	21st to end	Night	11% 4 22% 38% 25% 1	880
November	1st to 10th	Night	12% 4 21% 39% 21% 2	820
	11th to 20th	Night	13% 6% 26% 37% 16% 2	840
	21st to end	Night	12% 5% 30% 35% 17% 1	840
December	1st to 10th	Night	15% 6% 32% 32% 14% 1	840
	11th to 20th	Night	16% 6% 30% 32% 15% 1	840
	21st to end	Night	21% 8% 25% 33% 13%	924

Page generated at 2026-03-30 02:18:45. Version ac07

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