Ramsey Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ramsey Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	16% 10% 4 8% 5% 5% 5% 4 5% 7% 32%	101308
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 33%	98345
Transparency	Day	50% 6% 11% 21% 11% 1	104971
	Night	51% 5% 10% 21% 11% 2	102821
Seeing	Day	23% 14% 28% 20% 11% 4	14761
	Night	22% 12% 26% 26% 12% 1	24568

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	20% 20% 8% 10% 4 4 4 3 3 6% 18%	2836
	11th to 20th	Day	14% 23% 8% 14% 6% 4 3 2 3 4 18%	2840
	21st to end	Day	25% 22% 7% 12% 6% 3 4 2 3 4 12%	3124
February	1st to 10th	Day	18% 18% 5% 10% 7% 4 3 2 4 5% 23%	1710
	11th to 20th	Day	16% 15% 5% 14% 6% 4 5% 4 5% 5% 22%	1673
	21st to end	Day	19% 16% 4 11% 4 4 4 3 5% 4 27%	1570
March	1st to 10th	Day	21% 14% 5% 8% 5% 4 4 3 4 6% 26%	3432
	11th to 20th	Day	13% 11% 4 9% 6% 5% 4 3 5% 6% 34%	3480
	21st to end	Day	21% 9% 3 8% 5% 4 4 3 5% 6% 31%	3815
April	1st to 10th	Day	16% 13% 3 7% 5% 4 4 4 5% 8% 31%	2161
	11th to 20th	Day	17% 12% 3 7% 6% 4 4 3 5% 6% 34%	2333
	21st to end	Day	20% 10% 3 6% 5% 5% 5% 3 5% 6% 33%	2470
May	1st to 10th	Day	24% 9% 3 8% 4 5% 5% 4 5% 6% 28%	4082
	11th to 20th	Day	20% 9% 3 7% 5% 4 5% 4 5% 7% 32%	4081
	21st to end	Day	13% 7% 2 6% 4 5% 5% 5% 7% 10% 36%	4625
June	1st to 10th	Day	14% 7% 3 7% 5% 6% 5% 4 6% 8% 35%	2660
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 7% 9% 35%	2660
	21st to end	Day	13% 5% 3 6% 4 5% 5% 5% 6% 11% 37%	2660
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 5% 4 7% 9% 40%	4187
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 10% 40%	4120
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 5% 7% 8% 35%	4466
August	1st to 10th	Day	13% 7% 3 9% 6% 6% 6% 4 6% 8% 31%	4104
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 5% 7% 10% 33%	4044
	21st to end	Day	7% 5% 2 7% 5% 5% 6% 5% 7% 9% 41%	4372
September	1st to 10th	Day	15% 6% 2 5% 3 4 4 3 4 7% 45%	2237
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 44%	2090
	21st to end	Day	19% 8% 3 7% 5% 4 4 4 4 6% 36%	2090
October	1st to 10th	Day	15% 6% 3 6% 4 4 4 4 6% 6% 41%	1927
	11th to 20th	Day	19% 10% 2 8% 5% 3 4 3 6% 5% 34%	1900
	21st to end	Day	23% 10% 3 6% 4 4 4 3 4 7% 32%	2090
November	1st to 10th	Day	12% 8% 3 6% 5% 5% 5% 4 5% 7% 42%	1833
	11th to 20th	Day	17% 14% 4 7% 5% 4 4 4 4 5% 31%	1721
	21st to end	Day	17% 15% 6% 9% 6% 3 5% 3 5% 6% 25%	1600
December	1st to 10th	Day	21% 19% 7% 10% 5% 4 4 3 4 4 19%	1560
	11th to 20th	Day	19% 18% 7% 12% 5% 4 3 2 5% 6% 20%	1910
	21st to end	Day	25% 23% 6% 10% 5% 4 3 3 4 4 13%	2845
January	1st to 10th	Night	16% 21% 8% 13% 5% 4 4 3 4 5% 17%	4109
	11th to 20th	Night	17% 19% 7% 14% 6% 5% 5% 3 4 4 16%	4120
	21st to end	Night	28% 17% 7% 12% 6% 3 3 2 3 3 15%	4532
February	1st to 10th	Night	20% 15% 5% 10% 6% 4 4 3 5% 5% 24%	2470
	11th to 20th	Night	17% 15% 5% 12% 6% 5% 5% 3 4 5% 24%	2389
	21st to end	Night	21% 13% 5% 11% 6% 4 4 3 5% 4 23%	1884
March	1st to 10th	Night	24% 12% 4 7% 4 3 3 2 4 5% 33%	3419
	11th to 20th	Night	17% 13% 6% 8% 4 4 4 3 5% 6% 33%	3480
	21st to end	Night	19% 11% 3 7% 4 3 3 3 4 5% 38%	3817
April	1st to 10th	Night	17% 12% 3 6% 6% 4 4 3 5% 7% 33%	2018
	11th to 20th	Night	16% 10% 3 8% 4 4 4 4 5% 7% 35%	1811
	21st to end	Night	16% 10% 3 7% 4 4 4 3 5% 7% 37%	1710
May	1st to 10th	Night	26% 10% 3 7% 4 4 4 3 6% 6% 27%	2813
	11th to 20th	Night	17% 9% 3 6% 4 4 4 4 5% 7% 37%	2812
	21st to end	Night	10% 6% 2 6% 4 4 5% 5% 7% 10% 43%	2925
June	1st to 10th	Night	9% 6% 2 7% 5% 4 4 3 6% 8% 44%	1520
	11th to 20th	Night	10% 6% 2 7% 5% 4 3 3 6% 10% 44%	1520
	21st to end	Night	10% 4 2 5% 4 5% 6% 5% 6% 8% 44%	1520
July	1st to 10th	Night	9% 8% 3 7% 4 4 4 4 6% 8% 43%	2766
	11th to 20th	Night	10% 5% 2 5% 4 4 4 4 7% 9% 46%	2840
	21st to end	Night	9% 7% 3 8% 5% 5% 5% 4 6% 7% 43%	3087
August	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 4 6% 8% 35%	2825
	11th to 20th	Night	13% 8% 3 6% 4 3 4 4 5% 7% 43%	2785
	21st to end	Night	7% 5% 2 6% 5% 5% 6% 5% 6% 9% 45%	3250
September	1st to 10th	Night	13% 5% 2 5% 3 4 4 3 6% 6% 50%	1938
	11th to 20th	Night	9% 4 1 4 4 4 4 3 5% 9% 52%	2090
	21st to end	Night	17% 7% 2 6% 4 4 3 3 5% 6% 42%	2090
October	1st to 10th	Night	15% 5% 2 6% 4 3 4 3 4 8% 45%	2252
	11th to 20th	Night	17% 7% 3 7% 5% 4 5% 4 5% 7% 37%	2280
	21st to end	Night	23% 8% 2 6% 4 3 4 3 4 7% 36%	2508
November	1st to 10th	Night	13% 9% 2 5% 6% 4 5% 3 4 6% 44%	2462
	11th to 20th	Night	18% 13% 3 8% 4 4 4 3 5% 6% 32%	2675
	21st to end	Night	20% 14% 5% 8% 4 4 5% 3 4 6% 28%	2800
December	1st to 10th	Night	23% 17% 7% 9% 5% 4 4 3 4 5% 20%	2737
	11th to 20th	Night	19% 19% 6% 9% 4 4 3 3 4 5% 23%	3285
	21st to end	Night	26% 20% 6% 9% 5% 4 4 3 4 5% 14%	4806

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	69% 6% 9% 12% 5%	2837
	11th to 20th	Day	72% 3 8% 12% 5% 1	2840
	21st to end	Day	77% 5% 7% 8% 2	3124
February	1st to 10th	Day	65% 3 10% 14% 7% 1	1710
	11th to 20th	Day	64% 5% 9% 15% 8%	1682
	21st to end	Day	61% 4 9% 17% 7% 2	1570
March	1st to 10th	Day	60% 4 9% 21% 5%	3432
	11th to 20th	Day	50% 6% 12% 22% 8% 1	3480
	21st to end	Day	53% 6% 9% 18% 13% 1	3815
April	1st to 10th	Day	52% 5% 11% 18% 12% 1	2161
	11th to 20th	Day	51% 5% 10% 17% 14% 2	2333
	21st to end	Day	52% 6% 10% 21% 10% 2	2470
May	1st to 10th	Day	55% 6% 10% 19% 9% 1	4120
	11th to 20th	Day	51% 7% 11% 20% 9% 1	4085
	21st to end	Day	40% 8% 14% 23% 13% 4	4639
June	1st to 10th	Day	45% 7% 13% 22% 12% 1	2660
	11th to 20th	Day	44% 7% 13% 22% 12% 1	2660
	21st to end	Day	40% 8% 12% 25% 13% 1	2660
July	1st to 10th	Day	39% 7% 13% 24% 15% 3	4122
	11th to 20th	Day	37% 6% 12% 27% 17% 1	4051
	21st to end	Day	42% 6% 13% 19% 18% 1	4324
August	1st to 10th	Day	48% 8% 12% 22% 10%	4091
	11th to 20th	Day	43% 7% 11% 29% 9% 1	4083
	21st to end	Day	37% 8% 13% 29% 13% 2	4372
September	1st to 10th	Day	39% 5% 11% 22% 19% 4	2237
	11th to 20th	Day	36% 5% 15% 27% 16% 2	2090
	21st to end	Day	50% 5% 10% 22% 13% 1	2090
October	1st to 10th	Day	33% 5% 10% 31% 20% 1	3200
	11th to 20th	Day	47% 5% 9% 20% 15% 4	3140
	21st to end	Day	40% 4 12% 27% 16%	3428
November	1st to 10th	Day	42% 6% 11% 23% 17% 2	1833
	11th to 20th	Day	55% 4 9% 18% 10% 2	1721
	21st to end	Day	61% 4 11% 16% 7% 1	1600
December	1st to 10th	Day	69% 5% 9% 13% 4	1560
	11th to 20th	Day	67% 5% 9% 16% 3	1906
	21st to end	Day	76% 5% 9% 8% 3	2845
January	1st to 10th	Night	70% 6% 8% 13% 4	4109
	11th to 20th	Night	73% 5% 9% 11% 2	4120
	21st to end	Night	76% 3 6% 12% 3	4532
February	1st to 10th	Night	64% 4 10% 16% 6%	2470
	11th to 20th	Night	64% 4 8% 16% 7%	2391
	21st to end	Night	63% 5% 8% 13% 9% 1	1884
March	1st to 10th	Night	56% 4 9% 22% 9%	3419
	11th to 20th	Night	52% 5% 13% 22% 7% 1	3480
	21st to end	Night	48% 4 11% 22% 13% 1	3817
April	1st to 10th	Night	51% 6% 9% 18% 14% 2	2018
	11th to 20th	Night	47% 6% 11% 17% 15% 3	1811
	21st to end	Night	46% 5% 10% 21% 15% 2	1710
May	1st to 10th	Night	56% 6% 7% 19% 10% 2	2840
	11th to 20th	Night	46% 8% 11% 24% 10% 2	2813
	21st to end	Night	33% 8% 15% 27% 14% 4	2932
June	1st to 10th	Night	37% 8% 12% 24% 16% 2	1520
	11th to 20th	Night	36% 7% 15% 24% 16% 2	1520
	21st to end	Night	36% 9% 13% 24% 17% 2	1520
July	1st to 10th	Night	39% 7% 10% 23% 17% 3	2721
	11th to 20th	Night	33% 7% 14% 29% 16% 1	2786
	21st to end	Night	40% 7% 11% 18% 22% 2	2988
August	1st to 10th	Night	45% 7% 12% 23% 12% 1	2814
	11th to 20th	Night	40% 5% 11% 27% 16% 1	2812
	21st to end	Night	35% 6% 12% 31% 13% 2	3250
September	1st to 10th	Night	34% 7% 11% 23% 20% 5%	1938
	11th to 20th	Night	30% 6% 13% 27% 23% 2	2090
	21st to end	Night	43% 5% 11% 22% 18% 1	2090
October	1st to 10th	Night	34% 4 9% 28% 24% 2	3759
	11th to 20th	Night	39% 5% 11% 23% 14% 7%	3779
	21st to end	Night	37% 4 9% 30% 20% 2	4120
November	1st to 10th	Night	41% 5% 11% 23% 17% 3	2462
	11th to 20th	Night	54% 4 9% 20% 10% 3	2675
	21st to end	Night	58% 5% 11% 20% 6% 1	2800
December	1st to 10th	Night	67% 4 10% 13% 5%	2737
	11th to 20th	Night	65% 4 11% 16% 3	3288
	21st to end	Night	73% 5% 9% 10% 2	4806

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	35% 23% 27% 10% 5%	270
	11th to 20th	Day	37% 27% 29% 6% 1	270
	21st to end	Day	32% 29% 28% 7% 3	297
February	1st to 10th	Day	35% 20% 35% 9% 1	270
	11th to 20th	Day	38% 28% 29% 6%	270
	21st to end	Day	40% 24% 27% 8%	225
March	1st to 10th	Day	29% 24% 30% 14% 4	457
	11th to 20th	Day	32% 20% 30% 12% 5% 1	460
	21st to end	Day	31% 23% 28% 15% 3 1	506
April	1st to 10th	Day	30% 21% 27% 13% 7% 2	460
	11th to 20th	Day	28% 17% 29% 15% 8% 2	452
	21st to end	Day	29% 15% 33% 15% 7% 1	460
May	1st to 10th	Day	29% 18% 27% 16% 6% 3	463
	11th to 20th	Day	23% 12% 31% 22% 8% 4	487
	21st to end	Day	16% 9% 27% 26% 16% 6%	529
June	1st to 10th	Day	15% 12% 32% 25% 13% 4	490
	11th to 20th	Day	18% 10% 26% 27% 16% 3	490
	21st to end	Day	15% 9% 34% 26% 14% 3	490
July	1st to 10th	Day	14% 5% 24% 29% 20% 10%	485
	11th to 20th	Day	11% 7% 28% 29% 17% 8%	484
	21st to end	Day	12% 6% 26% 30% 18% 8%	532
August	1st to 10th	Day	15% 6% 22% 30% 18% 9%	486
	11th to 20th	Day	15% 6% 22% 28% 19% 10%	479
	21st to end	Day	12% 4 27% 26% 20% 10%	539
September	1st to 10th	Day	17% 8% 20% 27% 19% 9%	490
	11th to 20th	Day	12% 5% 20% 29% 22% 11%	490
	21st to end	Day	24% 11% 26% 20% 15% 4	490
October	1st to 10th	Day	15% 11% 28% 24% 17% 5%	490
	11th to 20th	Day	23% 13% 31% 21% 9% 2	490
	21st to end	Day	31% 15% 31% 17% 6%	539
November	1st to 10th	Day	19% 20% 35% 15% 9% 3	371
	11th to 20th	Day	30% 17% 32% 14% 6% 2	260
	21st to end	Day	28% 26% 37% 10% 1	200
December	1st to 10th	Day	31% 28% 28% 9% 3 2	190
	11th to 20th	Day	30% 23% 33% 11% 2	180
	21st to end	Day	37% 24% 27% 11% 1	220
January	1st to 10th	Night	30% 19% 34% 13% 3	760
	11th to 20th	Night	33% 18% 30% 16% 3	760
	21st to end	Night	31% 20% 28% 17% 3	836
February	1st to 10th	Night	30% 18% 30% 21% 2	760
	11th to 20th	Night	29% 21% 35% 13% 2	743
	21st to end	Night	30% 20% 31% 17% 2	628
March	1st to 10th	Night	26% 19% 31% 21% 4	760
	11th to 20th	Night	28% 18% 27% 22% 5% 1	760
	21st to end	Night	27% 16% 31% 21% 5% 1	836
April	1st to 10th	Night	25% 16% 30% 23% 6%	760
	11th to 20th	Night	23% 13% 35% 20% 8% 1	687
	21st to end	Night	22% 10% 35% 27% 6%	570
May	1st to 10th	Night	24% 9% 25% 31% 10% 1	570
	11th to 20th	Night	20% 9% 26% 30% 14% 1	561
	21st to end	Night	10% 5% 24% 37% 22% 3	527
June	1st to 10th	Night	12% 6% 26% 39% 17%	380
	11th to 20th	Night	13% 5% 24% 40% 18% 1	380
	21st to end	Night	9% 3 28% 35% 23% 1	380
July	1st to 10th	Night	7% 4 16% 40% 25% 7%	507
	11th to 20th	Night	9% 2 21% 36% 29% 4	552
	21st to end	Night	12% 3 15% 40% 28% 3	624
August	1st to 10th	Night	11% 3 14% 41% 30% 3	567
	11th to 20th	Night	14% 3 12% 38% 28% 4	564
	21st to end	Night	10% 4 21% 30% 29% 6%	701
September	1st to 10th	Night	15% 4 20% 31% 26% 5%	760
	11th to 20th	Night	10% 4 16% 36% 30% 4	760
	21st to end	Night	20% 8% 23% 26% 19% 4	760
October	1st to 10th	Night	17% 9% 22% 28% 21% 2	760
	11th to 20th	Night	21% 13% 29% 24% 12% 1	760
	21st to end	Night	29% 12% 28% 24% 8%	836
November	1st to 10th	Night	19% 13% 27% 30% 12%	780
	11th to 20th	Night	27% 16% 27% 21% 8% 1	800
	21st to end	Night	30% 15% 29% 20% 6%	800
December	1st to 10th	Night	33% 17% 28% 17% 5%	783
	11th to 20th	Night	30% 18% 28% 20% 4	760
	21st to end	Night	32% 17% 30% 19% 2	836

Page generated at 2024-12-03 06:45:14. Version ac07

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