Rosemere
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rosemere clear sky chart from 2005-11-06 to 2026-03-18.

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% 3 8% 5% 5% 5% 4 5% 7% 32%	131255
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	130270
Transparency	Day	51% 3 12% 22% 10% 1	134700
	Night	55% 3 11% 20% 11% 1	134912
Seeing	Day	22% 9% 28% 25% 13% 4	16174
	Night	23% 7% 28% 31% 11% 1	25280

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	14% 16% 6% 13% 5% 4 4 3 4 5% 25%	4661
	11th to 20th	Day	11% 16% 6% 13% 7% 4 4 3 4 6% 24%	4650
	21st to end	Day	9% 13% 5% 11% 9% 7% 6% 4 5% 5% 25%	5124
February	1st to 10th	Day	13% 15% 4 10% 6% 4 5% 4 4 6% 28%	1843
	11th to 20th	Day	13% 12% 5% 10% 6% 5% 5% 4 5% 6% 28%	1947
	21st to end	Day	17% 16% 5% 9% 4 4 4 3 5% 5% 27%	1730
March	1st to 10th	Day	19% 13% 4 11% 6% 6% 4 3 5% 5% 26%	4576
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 3 5% 7% 32%	4770
	21st to end	Day	19% 9% 4 9% 5% 4 4 3 4 5% 34%	5965
April	1st to 10th	Day	21% 11% 3 7% 6% 4 4 3 4 5% 32%	2400
	11th to 20th	Day	20% 9% 3 7% 6% 4 4 3 3 5% 37%	2374
	21st to end	Day	21% 10% 4 7% 5% 3 4 4 4 5% 33%	2560
May	1st to 10th	Day	25% 10% 4 9% 5% 4 5% 4 5% 6% 23%	6288
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 3 5% 7% 30%	6318
	21st to end	Day	21% 9% 2 6% 5% 4 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	20% 8% 3 7% 5% 5% 5% 4 5% 7% 31%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 4 5% 5% 6% 8% 37%	2800
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 4 6% 7% 30%	2800
July	1st to 10th	Day	13% 6% 2 8% 6% 6% 6% 5% 6% 8% 33%	6360
	11th to 20th	Day	11% 6% 2 6% 5% 5% 5% 5% 7% 9% 41%	6360
	21st to end	Day	10% 6% 2 5% 4 4 4 4 6% 9% 47%	6926
August	1st to 10th	Day	13% 6% 2 8% 5% 5% 7% 5% 7% 9% 34%	4563
	11th to 20th	Day	13% 6% 3 8% 5% 5% 4 3 6% 8% 39%	4142
	21st to end	Day	15% 5% 2 6% 5% 4 4 4 6% 8% 40%	4312
September	1st to 10th	Day	11% 5% 2 6% 4 5% 5% 4 6% 9% 43%	2400
	11th to 20th	Day	13% 5% 2 5% 3 4 4 3 5% 6% 51%	2318
	21st to end	Day	16% 6% 3 6% 5% 4 4 3 5% 7% 42%	2200
October	1st to 10th	Day	19% 6% 2 7% 4 4 4 3 5% 7% 38%	2060
	11th to 20th	Day	18% 7% 3 8% 7% 5% 5% 4 6% 7% 31%	1957
	21st to end	Day	23% 9% 3 7% 4 4 3 3 5% 6% 31%	1980
November	1st to 10th	Day	16% 11% 3 8% 4 5% 4 4 5% 8% 33%	1851
	11th to 20th	Day	17% 12% 3 7% 4 5% 5% 3 5% 7% 31%	1797
	21st to end	Day	22% 12% 3 8% 5% 5% 5% 4 5% 6% 25%	1680
December	1st to 10th	Day	20% 18% 6% 13% 5% 4 4 3 4 4 19%	2680
	11th to 20th	Day	18% 14% 4 9% 5% 4 4 4 5% 4 28%	3066
	21st to end	Day	23% 14% 3 10% 5% 4 5% 4 4 5% 24%	4048
January	1st to 10th	Night	13% 16% 7% 16% 6% 5% 4 3 4 4 23%	8234
	11th to 20th	Night	11% 16% 7% 16% 8% 6% 5% 3 5% 5% 19%	8235
	21st to end	Night	10% 13% 5% 13% 8% 6% 5% 3 5% 6% 27%	9057
February	1st to 10th	Night	13% 14% 5% 12% 6% 5% 5% 3 5% 6% 25%	2773
	11th to 20th	Night	14% 12% 4 10% 6% 5% 5% 4 5% 5% 31%	2559
	21st to end	Night	15% 14% 4 9% 5% 4 5% 3 5% 5% 31%	2076
March	1st to 10th	Night	21% 14% 3 8% 5% 4 4 3 4 5% 30%	5484
	11th to 20th	Night	14% 14% 4 8% 4 4 5% 3 6% 7% 30%	5342
	21st to end	Night	15% 11% 4 9% 5% 5% 5% 3 5% 5% 33%	4967
April	1st to 10th	Night	23% 11% 2 7% 4 4 4 4 4 6% 32%	2000
	11th to 20th	Night	21% 9% 3 7% 6% 4 4 3 4 5% 35%	1975
	21st to end	Night	21% 9% 3 6% 4 3 4 3 5% 5% 36%	1839
May	1st to 10th	Night	25% 10% 3 9% 5% 4 4 3 5% 6% 25%	3696
	11th to 20th	Night	22% 8% 3 8% 4 4 4 3 5% 7% 31%	3575
	21st to end	Night	19% 9% 3 8% 5% 5% 4 4 5% 7% 31%	3926
June	1st to 10th	Night	19% 8% 4 7% 4 4 5% 3 7% 7% 32%	1600
	11th to 20th	Night	16% 7% 3 7% 4 4 4 4 6% 7% 39%	1600
	21st to end	Night	18% 7% 3 7% 4 4 6% 3 6% 7% 35%	1600
July	1st to 10th	Night	14% 6% 2 7% 5% 6% 6% 5% 7% 10% 34%	3600
	11th to 20th	Night	14% 6% 2 6% 4 4 5% 4 6% 8% 42%	3600
	21st to end	Night	10% 5% 2 6% 5% 4 4 4 7% 8% 45%	3926
August	1st to 10th	Night	14% 7% 3 7% 5% 4 5% 3 5% 7% 39%	2586
	11th to 20th	Night	14% 7% 3 7% 5% 4 4 3 5% 7% 40%	2871
	21st to end	Night	16% 5% 2 8% 5% 5% 4 4 5% 7% 39%	3586
September	1st to 10th	Night	11% 5% 2 7% 5% 4 4 4 6% 7% 46%	2000
	11th to 20th	Night	13% 5% 3 5% 3 3 3 3 4 7% 51%	2080
	21st to end	Night	16% 5% 2 7% 4 4 4 4 4 7% 44%	2200
October	1st to 10th	Night	18% 6% 2 7% 4 4 4 3 4 6% 41%	2337
	11th to 20th	Night	18% 8% 3 7% 4 4 4 3 5% 6% 38%	2442
	21st to end	Night	21% 9% 3 8% 4 4 4 3 5% 6% 32%	2860
November	1st to 10th	Night	19% 9% 3 7% 5% 4 5% 4 5% 6% 33%	2667
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 6% 33%	2819
	21st to end	Night	21% 13% 3 9% 6% 4 4 3 5% 5% 28%	2940
December	1st to 10th	Night	17% 16% 5% 11% 6% 6% 5% 4 4 5% 20%	4720
	11th to 20th	Night	23% 13% 4 9% 4 4 4 3 5% 5% 26%	5348
	21st to end	Night	25% 15% 4 9% 4 3 3 3 5% 5% 24%	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	64% 2 11% 19% 4	4662
	11th to 20th	Day	63% 3 8% 15% 10% 1	4680
	21st to end	Day	60% 3 10% 14% 11% 1	5124
February	1st to 10th	Day	58% 2 9% 22% 7% 2	1843
	11th to 20th	Day	58% 4 11% 18% 9% 1	1956
	21st to end	Day	60% 2 9% 16% 11% 2	1730
March	1st to 10th	Day	62% 2 7% 14% 11% 4	4579
	11th to 20th	Day	53% 3 16% 14% 11% 2	4770
	21st to end	Day	54% 2 6% 17% 19% 2	5965
April	1st to 10th	Day	56% 3 7% 19% 14% 2	2400
	11th to 20th	Day	51% 2 6% 22% 16% 2	2374
	21st to end	Day	55% 3 8% 18% 13% 3	2560
May	1st to 10th	Day	62% 2 6% 21% 8% 1	6299
	11th to 20th	Day	54% 3 13% 19% 9% 2	6322
	21st to end	Day	52% 3 10% 21% 12% 1	6949
June	1st to 10th	Day	52% 4 9% 21% 13% 2	2800
	11th to 20th	Day	43% 4 10% 25% 14% 3	2800
	21st to end	Day	52% 4 12% 21% 11% 1	2800
July	1st to 10th	Day	46% 5% 13% 27% 9%	6290
	11th to 20th	Day	38% 5% 14% 31% 12%	6285
	21st to end	Day	34% 4 14% 38% 9%	6728
August	1st to 10th	Day	45% 5% 17% 24% 8%	4549
	11th to 20th	Day	43% 5% 17% 28% 7%	4184
	21st to end	Day	41% 5% 16% 23% 15% 1	4312
September	1st to 10th	Day	38% 4 14% 32% 12% 1	2400
	11th to 20th	Day	34% 3 12% 34% 15% 1	2318
	21st to end	Day	43% 4 13% 27% 12% 1	2200
October	1st to 10th	Day	44% 4 14% 28% 10%	3359
	11th to 20th	Day	45% 4 16% 28% 7%	3160
	21st to end	Day	44% 4 19% 24% 9% 1	3180
November	1st to 10th	Day	50% 3 12% 25% 9% 1	1851
	11th to 20th	Day	54% 3 11% 20% 12% 1	1797
	21st to end	Day	61% 3 13% 16% 6%	1680
December	1st to 10th	Day	70% 3 9% 15% 3	2680
	11th to 20th	Day	59% 4 9% 18% 10%	3066
	21st to end	Day	65% 3 11% 14% 7%	4048
January	1st to 10th	Night	67% 2 11% 15% 5% 1	8234
	11th to 20th	Night	68% 3 8% 14% 6%	8280
	21st to end	Night	61% 3 8% 15% 13%	9057
February	1st to 10th	Night	61% 3 9% 19% 8% 1	2773
	11th to 20th	Night	56% 2 10% 22% 10%	2561
	21st to end	Night	56% 2 9% 19% 13% 1	2076
March	1st to 10th	Night	59% 1 7% 15% 12% 5%	5494
	11th to 20th	Night	54% 3 13% 15% 13% 2	5343
	21st to end	Night	55% 2 5% 22% 14% 2	4967
April	1st to 10th	Night	55% 3 6% 20% 15% 2	2000
	11th to 20th	Night	53% 2 5% 22% 15% 2	1975
	21st to end	Night	51% 2 7% 20% 15% 4	1839
May	1st to 10th	Night	63% 2 8% 19% 7% 2	3702
	11th to 20th	Night	55% 3 10% 21% 10% 2	3576
	21st to end	Night	54% 3 9% 18% 15% 1	3927
June	1st to 10th	Night	51% 4 9% 22% 14% 1	1600
	11th to 20th	Night	43% 4 11% 24% 15% 3	1600
	21st to end	Night	48% 5% 11% 20% 14% 1	1600
July	1st to 10th	Night	44% 5% 18% 23% 10%	3560
	11th to 20th	Night	40% 5% 16% 28% 10%	3552
	21st to end	Night	37% 4 16% 29% 13%	3809
August	1st to 10th	Night	46% 4 13% 27% 10%	2576
	11th to 20th	Night	44% 5% 18% 24% 9%	2895
	21st to end	Night	45% 5% 13% 23% 14% 1	3586
September	1st to 10th	Night	38% 4 13% 29% 16% 1	2000
	11th to 20th	Night	35% 3 14% 34% 13% 1	2080
	21st to end	Night	42% 4 11% 28% 16%	2200
October	1st to 10th	Night	44% 4 13% 27% 11% 1	3818
	11th to 20th	Night	43% 3 12% 32% 10%	3978
	21st to end	Night	47% 4 16% 20% 12% 2	4610
November	1st to 10th	Night	52% 3 11% 24% 8% 1	2667
	11th to 20th	Night	53% 3 12% 21% 10% 1	2819
	21st to end	Night	61% 3 11% 19% 7%	2940
December	1st to 10th	Night	68% 4 11% 14% 4	4720
	11th to 20th	Night	61% 3 8% 16% 12%	5348
	21st to end	Night	64% 2 8% 15% 11%	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	27% 7% 29% 27% 10%	220
	11th to 20th	Day	29% 15% 29% 21% 4 2	220
	21st to end	Day	19% 15% 30% 27% 7% 2	242
February	1st to 10th	Day	27% 16% 33% 20% 4	305
	11th to 20th	Day	21% 14% 36% 25% 4	434
	21st to end	Day	26% 12% 33% 25% 4	446
March	1st to 10th	Day	26% 13% 32% 22% 8%	540
	11th to 20th	Day	24% 11% 35% 23% 6% 1	528
	21st to end	Day	28% 11% 32% 19% 8% 3	550
April	1st to 10th	Day	29% 14% 25% 21% 9% 2	500
	11th to 20th	Day	29% 13% 25% 21% 10% 2	492
	21st to end	Day	28% 11% 30% 20% 9% 3	500
May	1st to 10th	Day	23% 9% 31% 25% 9% 3	503
	11th to 20th	Day	20% 7% 29% 26% 13% 4	527
	21st to end	Day	20% 9% 29% 25% 13% 3	573
June	1st to 10th	Day	23% 8% 27% 26% 12% 3	530
	11th to 20th	Day	17% 10% 24% 31% 14% 4	530
	21st to end	Day	21% 8% 26% 26% 15% 4	530
July	1st to 10th	Day	14% 5% 24% 32% 18% 6%	525
	11th to 20th	Day	14% 5% 27% 32% 18% 4	524
	21st to end	Day	13% 4 25% 34% 19% 5%	576
August	1st to 10th	Day	14% 4 22% 32% 21% 7%	526
	11th to 20th	Day	13% 4 18% 32% 22% 11%	519
	21st to end	Day	15% 6% 24% 25% 21% 8%	583
September	1st to 10th	Day	13% 6% 25% 28% 19% 9%	530
	11th to 20th	Day	13% 5% 20% 26% 23% 13%	530
	21st to end	Day	19% 6% 26% 24% 18% 6%	530
October	1st to 10th	Day	19% 9% 27% 24% 15% 6%	530
	11th to 20th	Day	21% 10% 33% 23% 12% 3	505
	21st to end	Day	32% 10% 24% 25% 8% 1	462
November	1st to 10th	Day	29% 12% 25% 23% 10% 1	425
	11th to 20th	Day	25% 11% 34% 21% 8% 1	337
	21st to end	Day	35% 10% 27% 20% 6% 1	220
December	1st to 10th	Day	29% 10% 24% 26% 9% 2	220
	11th to 20th	Day	26% 12% 38% 19% 4 1	220
	21st to end	Day	29% 13% 31% 19% 7% 1	242
January	1st to 10th	Night	26% 9% 32% 26% 6%	840
	11th to 20th	Night	25% 10% 31% 27% 7%	840
	21st to end	Night	20% 7% 34% 30% 8% 1	924
February	1st to 10th	Night	21% 6% 36% 29% 7% 1	840
	11th to 20th	Night	22% 9% 36% 28% 5%	823
	21st to end	Night	24% 7% 32% 33% 4	692
March	1st to 10th	Night	25% 10% 30% 29% 6%	840
	11th to 20th	Night	27% 9% 31% 25% 7%	829
	21st to end	Night	23% 9% 29% 31% 8%	880
April	1st to 10th	Night	27% 10% 28% 30% 6%	800
	11th to 20th	Night	28% 8% 29% 28% 7% 1	791
	21st to end	Night	28% 7% 30% 26% 8%	639
May	1st to 10th	Night	26% 5% 31% 30% 8% 1	450
	11th to 20th	Night	23% 5% 28% 35% 9% 1	394
	21st to end	Night	19% 5% 33% 33% 9%	433
June	1st to 10th	Night	26% 4 23% 34% 13%	400
	11th to 20th	Night	18% 6% 25% 37% 13% 1	400
	21st to end	Night	22% 4 22% 37% 15% 1	400
July	1st to 10th	Night	12% 3 26% 42% 16% 1	390
	11th to 20th	Night	12% 3 22% 45% 17% 1	388
	21st to end	Night	12% 3 18% 47% 19% 1	438
August	1st to 10th	Night	15% 3 13% 44% 24% 1	398
	11th to 20th	Night	14% 2 18% 37% 26% 3	587
	21st to end	Night	17% 2 21% 38% 22% 2	880
September	1st to 10th	Night	15% 3 22% 42% 18% 1	800
	11th to 20th	Night	17% 3 15% 38% 24% 2	800
	21st to end	Night	18% 3 25% 34% 18% 2	800
October	1st to 10th	Night	20% 5% 27% 33% 14% 1	800
	11th to 20th	Night	24% 5% 26% 33% 11% 1	800
	21st to end	Night	27% 8% 28% 30% 7%	880
November	1st to 10th	Night	25% 10% 27% 29% 9%	820
	11th to 20th	Night	24% 8% 31% 26% 10%	840
	21st to end	Night	30% 10% 28% 23% 8%	840
December	1st to 10th	Night	30% 8% 29% 26% 7%	840
	11th to 20th	Night	28% 11% 32% 22% 6% 1	840
	21st to end	Night	34% 10% 27% 22% 6% 1	924

Page generated at 2026-03-15 02:23:51. Version ac07

Copyright © 2026 Attilla Danko.