Walter F. Barber, Jr. Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walter F. Barber, Jr. Memorial Observatory clear sky chart from 2005-11-06 to 2024-11-11.

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	12% 7% 3 7% 5% 5% 5% 4 6% 7% 40%	100979
	Night	12% 7% 2 6% 4 4 4 4 6% 7% 43%	98144
Transparency	Day	40% 6% 11% 20% 19% 5%	104810
	Night	37% 5% 10% 20% 21% 7%	102451
Seeing	Day	16% 11% 24% 24% 17% 9%	14815
	Night	15% 10% 23% 27% 20% 4	24814

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% 11% 4 7% 4 4 4 3 5% 5% 36%	2836
	11th to 20th	Day	12% 7% 2 5% 3 4 4 3 5% 5% 50%	2840
	21st to end	Day	23% 11% 3 5% 3 3 3 3 3 5% 39%	3348
February	1st to 10th	Day	16% 9% 3 6% 5% 5% 4 3 4 6% 38%	1900
	11th to 20th	Day	19% 8% 2 6% 5% 3 4 3 4 5% 41%	1848
	21st to end	Day	19% 8% 2 7% 4 4 4 4 4 5% 39%	1570
March	1st to 10th	Day	22% 12% 3 7% 4 3 3 3 5% 5% 33%	3151
	11th to 20th	Day	13% 7% 3 6% 4 4 4 3 5% 7% 44%	3480
	21st to end	Day	16% 7% 3 7% 4 4 4 4 6% 6% 38%	3815
April	1st to 10th	Day	12% 6% 2 7% 5% 4 4 4 5% 6% 45%	2207
	11th to 20th	Day	12% 6% 2 6% 5% 4 3 4 5% 6% 46%	2254
	21st to end	Day	10% 5% 2 5% 4 4 4 3 5% 8% 50%	2382
May	1st to 10th	Day	8% 6% 3 6% 5% 5% 5% 4 6% 9% 43%	4082
	11th to 20th	Day	15% 8% 3 6% 5% 5% 5% 4 6% 6% 35%	4081
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 7% 10% 43%	4476
June	1st to 10th	Day	10% 8% 2 9% 6% 6% 7% 5% 7% 9% 32%	2470
	11th to 20th	Day	5% 4 1 5% 6% 6% 6% 6% 9% 11% 40%	2470
	21st to end	Day	6% 5% 3 7% 7% 7% 7% 6% 8% 9% 36%	2470
July	1st to 10th	Day	7% 6% 3 9% 8% 9% 9% 6% 9% 11% 23%	4120
	11th to 20th	Day	7% 6% 3 9% 7% 7% 8% 6% 8% 10% 30%	4120
	21st to end	Day	9% 9% 4 11% 9% 9% 9% 7% 8% 9% 18%	4466
August	1st to 10th	Day	5% 4 2 6% 5% 6% 7% 6% 10% 11% 38%	4027
	11th to 20th	Day	7% 5% 2 5% 5% 5% 6% 4 7% 11% 43%	3729
	21st to end	Day	8% 4 1 5% 5% 5% 6% 4 6% 8% 47%	4180
September	1st to 10th	Day	10% 7% 3 6% 5% 6% 5% 5% 6% 8% 39%	2133
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 5% 7% 40%	2090
	21st to end	Day	14% 6% 2 6% 5% 3 4 4 4 6% 47%	2090
October	1st to 10th	Day	12% 5% 2 6% 3 3 4 3 4 6% 53%	2090
	11th to 20th	Day	11% 5% 1 4 4 3 3 3 4 6% 56%	2028
	21st to end	Day	13% 4 1 6% 3 3 3 3 4 5% 54%	2057
November	1st to 10th	Day	12% 7% 3 5% 4 3 2 2 5% 4 53%	1762
	11th to 20th	Day	13% 6% 2 4 4 2 3 4 5% 5% 51%	1710
	21st to end	Day	12% 7% 1 6% 4 4 4 4 5% 6% 46%	1710
December	1st to 10th	Day	18% 8% 2 7% 5% 4 4 3 5% 6% 38%	1710
	11th to 20th	Day	16% 8% 3 7% 4 4 4 2 4 5% 43%	2153
	21st to end	Day	20% 8% 3 6% 4 4 4 3 5% 7% 36%	3124
January	1st to 10th	Night	17% 10% 3 6% 4 3 4 3 5% 6% 40%	4109
	11th to 20th	Night	12% 9% 3 6% 5% 4 5% 3 4 5% 45%	4120
	21st to end	Night	23% 12% 3 5% 3 3 3 2 3 4 39%	4304
February	1st to 10th	Night	14% 7% 3 7% 5% 4 4 4 6% 6% 41%	2280
	11th to 20th	Night	20% 8% 3 6% 4 3 4 2 4 5% 42%	2218
	21st to end	Night	18% 8% 2 7% 4 4 4 3 5% 6% 39%	1884
March	1st to 10th	Night	22% 11% 3 6% 5% 4 4 3 4 5% 32%	3701
	11th to 20th	Night	11% 6% 1 4 3 3 4 3 6% 8% 49%	3480
	21st to end	Night	15% 6% 2 7% 5% 4 4 4 5% 6% 42%	3817
April	1st to 10th	Night	10% 6% 2 5% 5% 4 4 4 6% 7% 46%	1988
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 6% 7% 48%	1875
	21st to end	Night	8% 5% 3 5% 3 4 4 4 6% 7% 52%	1796
May	1st to 10th	Night	7% 6% 2 6% 4 6% 6% 4 7% 9% 43%	2813
	11th to 20th	Night	14% 8% 3 6% 5% 5% 4 4 6% 7% 39%	2812
	21st to end	Night	6% 4 2 5% 4 4 5% 4 8% 12% 46%	3079
June	1st to 10th	Night	5% 6% 2 6% 6% 6% 6% 4 9% 13% 37%	1710
	11th to 20th	Night	2 4 2 5% 5% 5% 5% 6% 8% 12% 47%	1710
	21st to end	Night	7% 3 2 6% 5% 4 6% 4 6% 14% 43%	1710
July	1st to 10th	Night	7% 7% 3 9% 6% 6% 7% 5% 8% 12% 30%	2840
	11th to 20th	Night	6% 5% 2 7% 6% 6% 6% 6% 9% 13% 34%	2840
	21st to end	Night	10% 10% 4 11% 7% 7% 6% 6% 8% 10% 23%	3087
August	1st to 10th	Night	6% 5% 2 6% 5% 5% 5% 5% 7% 12% 43%	2884
	11th to 20th	Night	6% 5% 2 6% 4 4 4 4 6% 9% 49%	3100
	21st to end	Night	8% 5% 2 4 3 4 4 3 6% 8% 52%	3476
September	1st to 10th	Night	9% 6% 2 7% 5% 4 6% 5% 6% 7% 44%	2028
	11th to 20th	Night	12% 7% 3 5% 4 4 4 3 5% 8% 44%	2090
	21st to end	Night	11% 5% 2 5% 4 4 3 3 5% 7% 50%	2090
October	1st to 10th	Night	10% 6% 2 4 2 3 3 3 4 7% 57%	2090
	11th to 20th	Night	10% 5% 2 5% 4 3 3 2 3 5% 58%	2150
	21st to end	Night	12% 5% 2 4 3 3 3 3 3 5% 57%	2536
November	1st to 10th	Night	12% 6% 2 5% 4 3 3 2 4 5% 55%	2536
	11th to 20th	Night	11% 6% 2 5% 4 3 3 3 4 6% 53%	2477
	21st to end	Night	13% 7% 2 5% 5% 4 4 4 5% 6% 46%	2470
December	1st to 10th	Night	16% 9% 2 7% 4 4 4 3 6% 6% 39%	2470
	11th to 20th	Night	16% 8% 3 6% 3 3 3 3 4 5% 47%	3042
	21st to end	Night	18% 9% 3 7% 5% 5% 4 3 6% 8% 33%	4532

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% 4 6% 16% 21% 6%	2837
	11th to 20th	Day	36% 2 8% 24% 24% 6%	2840
	21st to end	Day	50% 2 4 16% 21% 6%	3348
February	1st to 10th	Day	47% 4 6% 18% 21% 4	1900
	11th to 20th	Day	46% 4 5% 18% 21% 7%	1858
	21st to end	Day	48% 4 6% 13% 21% 8%	1570
March	1st to 10th	Day	53% 3 9% 11% 14% 9%	3151
	11th to 20th	Day	40% 5% 7% 17% 23% 9%	3480
	21st to end	Day	44% 4 10% 19% 19% 4	3815
April	1st to 10th	Day	40% 4 9% 21% 19% 7%	2207
	11th to 20th	Day	38% 5% 7% 18% 24% 8%	2254
	21st to end	Day	32% 5% 10% 27% 23% 3	2382
May	1st to 10th	Day	38% 4 13% 23% 19% 2	4120
	11th to 20th	Day	46% 6% 12% 23% 12% 1	4085
	21st to end	Day	35% 5% 13% 25% 19% 2	4489
June	1st to 10th	Day	46% 7% 14% 21% 11% 2	2470
	11th to 20th	Day	33% 8% 19% 24% 14% 2	2470
	21st to end	Day	39% 9% 16% 22% 12% 2	2470
July	1st to 10th	Day	48% 11% 20% 15% 5% 1	4055
	11th to 20th	Day	45% 11% 18% 19% 6% 1	4051
	21st to end	Day	58% 12% 14% 12% 5%	4324
August	1st to 10th	Day	32% 9% 15% 32% 11%	4014
	11th to 20th	Day	32% 7% 16% 28% 14% 3	3765
	21st to end	Day	32% 8% 14% 21% 21% 3	4179
September	1st to 10th	Day	41% 6% 16% 16% 17% 5%	2133
	11th to 20th	Day	42% 6% 10% 19% 19% 2	2090
	21st to end	Day	39% 4 9% 19% 23% 6%	2090
October	1st to 10th	Day	25% 3 6% 13% 37% 15%	3480
	11th to 20th	Day	20% 3 4 16% 29% 28%	3346
	21st to end	Day	25% 3 6% 21% 33% 12%	3371
November	1st to 10th	Day	35% 4 7% 16% 29% 10%	1762
	11th to 20th	Day	34% 3 7% 17% 28% 11%	1710
	21st to end	Day	38% 5% 7% 19% 25% 7%	1710
December	1st to 10th	Day	47% 3 7% 19% 18% 6%	1710
	11th to 20th	Day	45% 2 6% 15% 24% 7%	2150
	21st to end	Day	48% 3 8% 18% 21% 3	3124
January	1st to 10th	Night	44% 4 5% 16% 26% 5%	4109
	11th to 20th	Night	41% 4 5% 22% 21% 8%	4120
	21st to end	Night	51% 2 3 13% 25% 6%	4304
February	1st to 10th	Night	43% 4 6% 19% 19% 8%	2280
	11th to 20th	Night	46% 4 5% 17% 20% 8%	2219
	21st to end	Night	47% 3 7% 16% 18% 10%	1884
March	1st to 10th	Night	53% 4 9% 14% 14% 7%	3701
	11th to 20th	Night	32% 4 10% 17% 25% 11%	3480
	21st to end	Night	42% 4 7% 20% 20% 7%	3817
April	1st to 10th	Night	37% 4 10% 19% 22% 8%	1988
	11th to 20th	Night	35% 3 7% 22% 23% 10%	1875
	21st to end	Night	31% 5% 10% 28% 21% 5%	1796
May	1st to 10th	Night	35% 6% 16% 22% 18% 2	2840
	11th to 20th	Night	42% 6% 14% 26% 11% 1	2813
	21st to end	Night	27% 6% 17% 29% 19% 2	3087
June	1st to 10th	Night	36% 9% 18% 22% 14% 1	1710
	11th to 20th	Night	26% 9% 22% 26% 14% 2	1710
	21st to end	Night	31% 8% 20% 20% 16% 4	1710
July	1st to 10th	Night	44% 11% 20% 18% 6% 1	2795
	11th to 20th	Night	35% 13% 22% 21% 7% 1	2786
	21st to end	Night	53% 11% 16% 14% 5% 1	2988
August	1st to 10th	Night	31% 8% 16% 34% 10% 1	2873
	11th to 20th	Night	30% 7% 15% 31% 16% 2	3130
	21st to end	Night	29% 7% 15% 18% 28% 3	3476
September	1st to 10th	Night	36% 8% 15% 19% 16% 6%	2028
	11th to 20th	Night	39% 6% 11% 22% 19% 3	2090
	21st to end	Night	33% 6% 10% 21% 21% 8%	2090
October	1st to 10th	Night	25% 3 7% 15% 36% 15%	3480
	11th to 20th	Night	18% 2 4 17% 31% 28%	3571
	21st to end	Night	23% 2 4 23% 31% 17%	4172
November	1st to 10th	Night	33% 4 8% 17% 26% 12%	2536
	11th to 20th	Night	33% 3 6% 19% 27% 12%	2477
	21st to end	Night	38% 4 7% 18% 26% 8%	2470
December	1st to 10th	Night	44% 5% 8% 19% 19% 5%	2470
	11th to 20th	Night	40% 3 7% 15% 29% 6%	3044
	21st to end	Night	49% 4 7% 19% 19% 3	4532

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	24% 28% 34% 13% 1	270
	11th to 20th	Day	27% 22% 36% 11% 3 1	270
	21st to end	Day	26% 27% 37% 8% 2 1	297
February	1st to 10th	Day	25% 25% 36% 11% 3	270
	11th to 20th	Day	33% 21% 36% 9% 1	270
	21st to end	Day	28% 24% 37% 9% 1	225
March	1st to 10th	Day	26% 23% 32% 15% 3 1	288
	11th to 20th	Day	23% 22% 32% 17% 7% 1	460
	21st to end	Day	21% 19% 34% 19% 5% 1	506
April	1st to 10th	Day	19% 18% 34% 18% 10% 1	460
	11th to 20th	Day	14% 18% 33% 23% 9% 2	452
	21st to end	Day	14% 13% 30% 25% 15% 3	460
May	1st to 10th	Day	13% 12% 30% 27% 13% 4	463
	11th to 20th	Day	12% 8% 24% 30% 18% 8%	487
	21st to end	Day	12% 6% 23% 28% 21% 11%	529
June	1st to 10th	Day	13% 4 17% 30% 23% 11%	490
	11th to 20th	Day	6% 4 15% 28% 26% 21%	490
	21st to end	Day	8% 3 17% 31% 25% 15%	490
July	1st to 10th	Day	8% 1 11% 29% 29% 22%	485
	11th to 20th	Day	7% 2 9% 23% 30% 30%	484
	21st to end	Day	5% 2 9% 29% 35% 19%	532
August	1st to 10th	Day	10% 3 13% 27% 26% 22%	486
	11th to 20th	Day	10% 3 10% 30% 31% 16%	479
	21st to end	Day	15% 2 9% 27% 29% 17%	539
September	1st to 10th	Day	13% 4 14% 26% 29% 16%	490
	11th to 20th	Day	19% 3 14% 27% 27% 10%	490
	21st to end	Day	15% 4 22% 23% 27% 9%	490
October	1st to 10th	Day	15% 3 27% 29% 18% 8%	490
	11th to 20th	Day	13% 9% 24% 29% 21% 3	490
	21st to end	Day	17% 10% 25% 27% 18% 3	506
November	1st to 10th	Day	22% 14% 24% 26% 11% 2	300
	11th to 20th	Day	15% 20% 37% 22% 6%	270
	21st to end	Day	10% 20% 44% 20% 7% 1	270
December	1st to 10th	Day	26% 22% 30% 19% 3	270
	11th to 20th	Day	24% 19% 34% 19% 4 1	270
	21st to end	Day	29% 18% 35% 14% 4	297
January	1st to 10th	Night	22% 21% 31% 22% 4 1	760
	11th to 20th	Night	21% 18% 31% 24% 6%	760
	21st to end	Night	20% 21% 35% 22% 3	836
February	1st to 10th	Night	19% 16% 34% 26% 5%	760
	11th to 20th	Night	24% 19% 34% 21% 2	743
	21st to end	Night	22% 21% 35% 19% 3	628
March	1st to 10th	Night	18% 18% 34% 24% 6%	760
	11th to 20th	Night	19% 16% 32% 23% 10% 1	760
	21st to end	Night	16% 17% 30% 28% 8% 1	836
April	1st to 10th	Night	14% 16% 32% 26% 11% 1	658
	11th to 20th	Night	18% 14% 28% 27% 12% 1	563
	21st to end	Night	12% 9% 26% 35% 16% 2	570
May	1st to 10th	Night	10% 8% 28% 32% 21% 1	570
	11th to 20th	Night	11% 6% 22% 32% 25% 5%	561
	21st to end	Night	12% 2 14% 31% 34% 6%	617
June	1st to 10th	Night	8% 4 14% 34% 33% 8%	570
	11th to 20th	Night	2 2 17% 30% 34% 15%	570
	21st to end	Night	7% 2 9% 34% 41% 7%	570
July	1st to 10th	Night	8% 3 9% 25% 41% 14%	555
	11th to 20th	Night	8% 1 7% 22% 47% 15%	552
	21st to end	Night	8% 2 7% 29% 44% 10%	624
August	1st to 10th	Night	8% 2 7% 29% 40% 13%	567
	11th to 20th	Night	10% 3 9% 29% 40% 10%	564
	21st to end	Night	16% 3 7% 26% 36% 12%	627
September	1st to 10th	Night	11% 2 10% 26% 40% 12%	698
	11th to 20th	Night	15% 3 12% 28% 36% 6%	760
	21st to end	Night	14% 3 15% 33% 31% 3	760
October	1st to 10th	Night	12% 4 23% 33% 22% 6%	760
	11th to 20th	Night	12% 8% 25% 31% 20% 3	760
	21st to end	Night	15% 9% 21% 33% 18% 3	836
November	1st to 10th	Night	15% 8% 25% 30% 20% 2	780
	11th to 20th	Night	15% 15% 28% 28% 13% 1	763
	21st to end	Night	17% 14% 28% 29% 12% 1	760
December	1st to 10th	Night	21% 16% 29% 25% 9% 1	760
	11th to 20th	Night	23% 12% 32% 25% 8% 1	760
	21st to end	Night	27% 15% 28% 24% 6%	836

Page generated at 2024-11-08 06:44:48. Version ac07

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