Lake Runnemede Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Runnemede 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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	101629
	Night	16% 9% 3 8% 5% 5% 5% 4 5% 6% 35%	98095
Transparency	Day	47% 8% 13% 20% 11% 1	105141
	Night	48% 8% 13% 19% 11% 1	102672
Seeing	Day	24% 17% 29% 19% 8% 2	14933
	Night	22% 14% 28% 27% 9% 1	23897

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	11% 10% 4 9% 7% 6% 5% 4 6% 6% 32%	2517
	11th to 20th	Day	15% 11% 5% 12% 8% 6% 4 3 5% 5% 26%	2520
	21st to end	Day	14% 15% 6% 11% 6% 5% 5% 4 5% 5% 25%	2772
February	1st to 10th	Day	12% 13% 3 9% 7% 6% 5% 5% 5% 7% 28%	1695
	11th to 20th	Day	9% 11% 4 10% 7% 6% 5% 4 5% 6% 32%	1848
	21st to end	Day	16% 12% 4 8% 5% 4 4 4 5% 6% 31%	1570
March	1st to 10th	Day	19% 15% 5% 10% 5% 4 4 4 5% 4 25%	3116
	11th to 20th	Day	13% 11% 4 10% 6% 5% 5% 5% 6% 6% 30%	3251
	21st to end	Day	18% 11% 3 8% 6% 5% 4 3 4 6% 33%	4152
April	1st to 10th	Day	17% 12% 3 8% 5% 4 4 3 5% 6% 35%	2280
	11th to 20th	Day	17% 8% 3 7% 5% 5% 4 4 6% 6% 36%	2254
	21st to end	Day	21% 10% 3 8% 5% 4 4 4 4 6% 32%	2454
May	1st to 10th	Day	22% 11% 3 8% 5% 4 4 4 5% 6% 27%	4106
	11th to 20th	Day	17% 8% 3 9% 5% 5% 5% 4 6% 7% 30%	4366
	21st to end	Day	12% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	4837
June	1st to 10th	Day	17% 6% 2 8% 7% 5% 6% 5% 6% 8% 30%	2660
	11th to 20th	Day	16% 7% 2 6% 4 5% 5% 5% 6% 9% 36%	2660
	21st to end	Day	17% 7% 3 9% 6% 5% 5% 5% 6% 7% 30%	2660
July	1st to 10th	Day	12% 5% 2 7% 5% 5% 5% 4 7% 10% 36%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 6% 5% 5% 8% 11% 36%	4440
	21st to end	Day	16% 6% 2 6% 5% 4 6% 4 7% 8% 36%	4814
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 6% 4 8% 9% 33%	4329
	11th to 20th	Day	14% 7% 3 8% 5% 5% 6% 5% 7% 8% 33%	3925
	21st to end	Day	9% 5% 2 6% 4 5% 5% 4 8% 10% 42%	4180
September	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 3 6% 9% 44%	2280
	11th to 20th	Day	12% 5% 2 5% 4 5% 4 3 4 6% 49%	2138
	21st to end	Day	15% 7% 2 5% 4 4 4 4 5% 7% 43%	2090
October	1st to 10th	Day	20% 8% 3 7% 5% 4 5% 4 4 5% 35%	2066
	11th to 20th	Day	14% 8% 2 7% 4 4 4 3 6% 7% 39%	1829
	21st to end	Day	22% 10% 3 8% 4 4 4 4 4 5% 32%	1881
November	1st to 10th	Day	12% 8% 3 6% 4 4 5% 3 6% 8% 41%	1761
	11th to 20th	Day	15% 9% 3 7% 5% 4 4 4 5% 6% 39%	1800
	21st to end	Day	18% 11% 3 7% 4 4 5% 4 6% 6% 33%	1700
December	1st to 10th	Day	17% 13% 4 10% 6% 5% 4 4 6% 6% 25%	1560
	11th to 20th	Day	21% 11% 3 8% 4 3 3 3 4 5% 33%	1906
	21st to end	Day	22% 14% 4 11% 6% 5% 5% 3 4 4 25%	2772
January	1st to 10th	Night	16% 8% 3 8% 5% 4 5% 4 6% 6% 35%	4429
	11th to 20th	Night	11% 12% 5% 13% 7% 5% 5% 4 6% 6% 26%	4440
	21st to end	Night	17% 13% 4 11% 6% 6% 5% 4 4 5% 25%	4884
February	1st to 10th	Night	11% 11% 4 10% 6% 5% 5% 5% 6% 7% 29%	2481
	11th to 20th	Night	9% 9% 4 7% 6% 6% 7% 5% 8% 7% 32%	2218
	21st to end	Night	14% 9% 3 8% 6% 5% 5% 4 6% 5% 35%	1884
March	1st to 10th	Night	22% 13% 2 7% 6% 4 5% 3 5% 5% 28%	3724
	11th to 20th	Night	12% 10% 3 9% 6% 6% 5% 4 5% 6% 34%	3706
	21st to end	Night	17% 12% 3 9% 4 4 4 3 5% 5% 33%	3476
April	1st to 10th	Night	17% 8% 3 6% 6% 4 4 4 6% 7% 35%	1900
	11th to 20th	Night	17% 9% 3 7% 4 4 5% 3 5% 6% 37%	1875
	21st to end	Night	20% 8% 3 7% 5% 3 4 3 5% 6% 36%	1724
May	1st to 10th	Night	24% 11% 2 6% 4 5% 5% 4 6% 7% 27%	2834
	11th to 20th	Night	16% 10% 3 10% 6% 5% 6% 4 6% 6% 29%	2543
	21st to end	Night	14% 5% 2 6% 5% 5% 4 4 6% 9% 41%	2738
June	1st to 10th	Night	18% 6% 2 6% 5% 5% 4 4 6% 7% 36%	1520
	11th to 20th	Night	17% 6% 2 6% 5% 3 4 3 5% 8% 40%	1520
	21st to end	Night	15% 6% 2 7% 5% 5% 5% 6% 7% 7% 36%	1520
July	1st to 10th	Night	11% 5% 2 6% 5% 6% 6% 5% 7% 7% 41%	2520
	11th to 20th	Night	15% 6% 2 4 4 4 4 3 6% 9% 42%	2520
	21st to end	Night	17% 6% 2 5% 3 4 4 4 6% 7% 41%	2739
August	1st to 10th	Night	19% 8% 3 7% 5% 4 5% 3 5% 7% 35%	2570
	11th to 20th	Night	16% 6% 3 6% 4 4 4 3 6% 8% 40%	2900
	21st to end	Night	8% 4 1 5% 3 4 3 4 6% 11% 50%	3476
September	1st to 10th	Night	12% 6% 2 4 4 3 4 3 5% 6% 51%	1900
	11th to 20th	Night	13% 5% 2 5% 3 4 3 2 5% 6% 52%	2042
	21st to end	Night	15% 7% 1 5% 4 3 4 3 5% 7% 46%	2090
October	1st to 10th	Night	19% 7% 3 7% 5% 4 4 4 5% 6% 37%	2110
	11th to 20th	Night	15% 6% 2 6% 5% 5% 5% 5% 6% 7% 38%	2351
	21st to end	Night	22% 8% 2 7% 5% 4 4 4 5% 5% 33%	2717
November	1st to 10th	Night	12% 8% 2 7% 5% 5% 4 3 5% 7% 41%	2537
	11th to 20th	Night	15% 8% 3 7% 4 5% 4 4 6% 6% 38%	2600
	21st to end	Night	13% 9% 3 8% 5% 5% 5% 4 6% 6% 35%	2698
December	1st to 10th	Night	17% 11% 4 9% 6% 5% 5% 4 5% 7% 27%	2737
	11th to 20th	Night	19% 10% 4 8% 4 4 5% 4 5% 5% 31%	3288
	21st to end	Night	21% 13% 6% 11% 5% 4 4 3 4 5% 24%	4884

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	48% 8% 14% 24% 6%	2518
	11th to 20th	Day	58% 10% 11% 16% 5% 1	2520
	21st to end	Day	58% 9% 11% 15% 6% 1	2772
February	1st to 10th	Day	53% 8% 13% 17% 8% 1	1695
	11th to 20th	Day	52% 7% 11% 17% 10% 2	1857
	21st to end	Day	54% 5% 11% 17% 12% 1	1570
March	1st to 10th	Day	62% 6% 9% 11% 10% 2	3119
	11th to 20th	Day	48% 12% 15% 14% 10% 2	3251
	21st to end	Day	52% 7% 7% 14% 17% 3	4152
April	1st to 10th	Day	52% 5% 10% 19% 12% 3	2280
	11th to 20th	Day	48% 8% 11% 18% 14% 1	2254
	21st to end	Day	53% 7% 9% 16% 12% 2	2454
May	1st to 10th	Day	56% 8% 10% 17% 6% 1	4120
	11th to 20th	Day	49% 12% 14% 15% 9% 2	4370
	21st to end	Day	36% 11% 14% 25% 13% 1	4837
June	1st to 10th	Day	51% 10% 12% 17% 10%	2660
	11th to 20th	Day	45% 8% 13% 18% 14% 2	2660
	21st to end	Day	51% 9% 12% 16% 10% 1	2660
July	1st to 10th	Day	40% 9% 15% 21% 14%	4370
	11th to 20th	Day	39% 10% 17% 24% 9%	4365
	21st to end	Day	44% 8% 14% 21% 12% 1	4661
August	1st to 10th	Day	46% 10% 16% 19% 10%	4315
	11th to 20th	Day	46% 10% 15% 23% 6%	3964
	21st to end	Day	34% 9% 17% 25% 13% 1	4180
September	1st to 10th	Day	36% 8% 14% 28% 14% 1	2280
	11th to 20th	Day	37% 6% 11% 27% 19% 1	2138
	21st to end	Day	39% 7% 15% 25% 13% 2	2090
October	1st to 10th	Day	46% 7% 10% 21% 15% 1	3430
	11th to 20th	Day	43% 5% 13% 24% 14% 1	3019
	21st to end	Day	41% 5% 9% 31% 12% 2	3081
November	1st to 10th	Day	40% 8% 16% 21% 14% 1	1761
	11th to 20th	Day	46% 7% 12% 17% 16% 2	1800
	21st to end	Day	52% 7% 17% 17% 6% 1	1700
December	1st to 10th	Day	59% 6% 15% 13% 6% 1	1560
	11th to 20th	Day	54% 7% 11% 16% 11% 1	1906
	21st to end	Day	63% 6% 9% 13% 8%	2772
January	1st to 10th	Night	47% 10% 14% 19% 9% 1	4429
	11th to 20th	Night	55% 11% 13% 14% 7% 1	4440
	21st to end	Night	60% 10% 9% 13% 7% 1	4884
February	1st to 10th	Night	53% 9% 12% 17% 9% 1	2481
	11th to 20th	Night	50% 8% 12% 19% 11% 1	2220
	21st to end	Night	48% 7% 14% 20% 8% 3	1884
March	1st to 10th	Night	56% 7% 12% 15% 9% 1	3734
	11th to 20th	Night	50% 9% 12% 18% 10% 1	3707
	21st to end	Night	51% 7% 8% 13% 18% 3	3476
April	1st to 10th	Night	51% 6% 10% 18% 13% 2	1900
	11th to 20th	Night	48% 7% 10% 21% 14% 1	1875
	21st to end	Night	49% 7% 10% 17% 14% 3	1724
May	1st to 10th	Night	56% 9% 12% 14% 9% 1	2840
	11th to 20th	Night	52% 11% 13% 14% 8% 1	2544
	21st to end	Night	38% 11% 16% 20% 13% 2	2739
June	1st to 10th	Night	47% 10% 14% 18% 11% 1	1520
	11th to 20th	Night	44% 9% 14% 19% 12% 2	1520
	21st to end	Night	46% 10% 13% 21% 11% 1	1520
July	1st to 10th	Night	40% 10% 16% 21% 12% 1	2480
	11th to 20th	Night	40% 8% 14% 25% 12%	2472
	21st to end	Night	42% 7% 12% 27% 11% 1	2651
August	1st to 10th	Night	50% 8% 13% 20% 9%	2560
	11th to 20th	Night	43% 9% 19% 20% 10%	2927
	21st to end	Night	30% 8% 20% 28% 13% 1	3476
September	1st to 10th	Night	33% 7% 16% 28% 15% 1	1900
	11th to 20th	Night	35% 6% 12% 29% 18% 1	2042
	21st to end	Night	36% 7% 13% 27% 15% 2	2090
October	1st to 10th	Night	46% 8% 14% 21% 9% 1	3526
	11th to 20th	Night	39% 6% 13% 24% 15% 2	3900
	21st to end	Night	43% 6% 10% 29% 10% 1	4467
November	1st to 10th	Night	45% 7% 13% 21% 12% 2	2537
	11th to 20th	Night	45% 6% 12% 21% 14% 2	2600
	21st to end	Night	50% 7% 15% 19% 8%	2698
December	1st to 10th	Night	58% 8% 12% 17% 5%	2737
	11th to 20th	Night	53% 8% 13% 14% 11% 1	3288
	21st to end	Night	62% 7% 10% 16% 5%	4884

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% 24% 24% 17% 7%	180
	11th to 20th	Day	31% 27% 26% 13% 2 1	180
	21st to end	Day	20% 28% 33% 13% 6%	198
February	1st to 10th	Day	29% 31% 31% 7% 3	280
	11th to 20th	Day	28% 27% 31% 12% 2	456
	21st to end	Day	29% 22% 30% 17% 3	382
March	1st to 10th	Day	30% 19% 33% 16% 3	460
	11th to 20th	Day	32% 23% 28% 11% 4	460
	21st to end	Day	33% 21% 25% 13% 5% 3	506
April	1st to 10th	Day	35% 19% 26% 12% 6% 2	460
	11th to 20th	Day	33% 23% 24% 12% 8% 1	452
	21st to end	Day	31% 21% 28% 12% 6% 1	460
May	1st to 10th	Day	32% 21% 27% 13% 5% 2	463
	11th to 20th	Day	22% 17% 34% 21% 5% 2	487
	21st to end	Day	20% 15% 32% 25% 8% 1	529
June	1st to 10th	Day	23% 15% 37% 15% 10% 1	490
	11th to 20th	Day	19% 16% 33% 19% 10% 2	490
	21st to end	Day	23% 17% 31% 18% 9% 2	490
July	1st to 10th	Day	15% 12% 35% 24% 11% 3	485
	11th to 20th	Day	13% 10% 35% 28% 11% 3	484
	21st to end	Day	14% 10% 39% 25% 11% 2	532
August	1st to 10th	Day	13% 11% 31% 25% 16% 3	486
	11th to 20th	Day	16% 10% 30% 24% 13% 7%	479
	21st to end	Day	12% 15% 26% 26% 15% 6%	539
September	1st to 10th	Day	17% 12% 25% 24% 15% 7%	490
	11th to 20th	Day	16% 13% 24% 20% 17% 10%	490
	21st to end	Day	17% 13% 29% 23% 12% 6%	490
October	1st to 10th	Day	26% 12% 26% 20% 12% 4	490
	11th to 20th	Day	22% 19% 21% 27% 9% 2	453
	21st to end	Day	34% 15% 23% 21% 7%	429
November	1st to 10th	Day	24% 17% 25% 21% 12% 1	395
	11th to 20th	Day	31% 20% 24% 19% 6% 1	400
	21st to end	Day	35% 19% 26% 15% 5% 1	300
December	1st to 10th	Day	28% 24% 26% 15% 6%	190
	11th to 20th	Day	35% 22% 31% 8% 4	180
	21st to end	Day	34% 20% 28% 14% 4 1	198
January	1st to 10th	Night	22% 18% 35% 22% 3	760
	11th to 20th	Night	25% 18% 32% 22% 3	760
	21st to end	Night	20% 19% 36% 22% 4	836
February	1st to 10th	Night	22% 19% 36% 19% 3	760
	11th to 20th	Night	22% 19% 36% 21% 2	743
	21st to end	Night	24% 20% 32% 21% 3	628
March	1st to 10th	Night	25% 18% 30% 24% 3	760
	11th to 20th	Night	25% 19% 28% 22% 5%	760
	21st to end	Night	28% 16% 27% 22% 6% 1	836
April	1st to 10th	Night	26% 19% 27% 24% 4	760
	11th to 20th	Night	22% 23% 27% 21% 7%	751
	21st to end	Night	27% 16% 29% 22% 5%	584
May	1st to 10th	Night	27% 14% 30% 22% 7%	570
	11th to 20th	Night	19% 13% 30% 32% 6%	409
	21st to end	Night	18% 9% 26% 36% 11%	411
June	1st to 10th	Night	21% 8% 29% 32% 10%	380
	11th to 20th	Night	19% 11% 26% 33% 11%	380
	21st to end	Night	16% 8% 26% 40% 9% 1	380
July	1st to 10th	Night	15% 5% 21% 45% 13% 1	370
	11th to 20th	Night	14% 4 25% 38% 17% 2	368
	21st to end	Night	13% 6% 21% 43% 16% 1	416
August	1st to 10th	Night	14% 4 19% 44% 19%	416
	11th to 20th	Night	13% 7% 26% 34% 17% 3	628
	21st to end	Night	15% 6% 21% 36% 21% 2	836
September	1st to 10th	Night	14% 8% 26% 31% 19% 1	760
	11th to 20th	Night	16% 8% 21% 30% 20% 5%	760
	21st to end	Night	18% 8% 24% 30% 18% 2	760
October	1st to 10th	Night	26% 10% 20% 28% 15% 1	760
	11th to 20th	Night	21% 12% 24% 30% 11% 1	760
	21st to end	Night	28% 15% 26% 25% 6%	836
November	1st to 10th	Night	20% 17% 26% 28% 8%	780
	11th to 20th	Night	24% 15% 30% 23% 8% 1	800
	21st to end	Night	25% 17% 29% 22% 6%	800
December	1st to 10th	Night	23% 19% 34% 19% 4	783
	11th to 20th	Night	27% 18% 31% 20% 3	760
	21st to end	Night	29% 17% 33% 18% 3	836

Page generated at 2024-12-03 06:45:08. Version ac07

Copyright © 2024 Attilla Danko.