River House Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the River House Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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	13% 6% 2 5% 5% 3 4 5% 5% 8% 44%	78340
	Night	14% 6% 2 5% 5% 3 4 4 5% 7% 44%	80634
Transparency	Day	37% 5% 13% 25% 16% 3	78050
	Night	40% 5% 11% 24% 17% 3	80443
Seeing	Day	16% 4 15% 31% 26% 9%	14098
	Night	17% 6% 22% 33% 19% 3	23744

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% 4 2 4 3 2 3 3 4 7% 51%	2582
	11th to 20th	Day	13% 8% 3 5% 6% 2 4 4 5% 6% 43%	2840
	21st to end	Day	14% 11% 3 7% 5% 3 4 4 4 5% 39%	3124
February	1st to 10th	Day	12% 9% 2 5% 5% 3 5% 5% 5% 8% 40%	1701
	11th to 20th	Day	20% 6% 2 5% 4 2 3 3 3 5% 47%	1693
	21st to end	Day	17% 8% 3 5% 5% 4 5% 4 5% 6% 38%	1480
March	1st to 10th	Day	14% 6% 2 5% 4 2 4 3 5% 7% 50%	1898
	11th to 20th	Day	17% 6% 2 4 4 3 4 4 5% 8% 43%	1980
	21st to end	Day	17% 6% 3 5% 5% 3 5% 4 5% 7% 41%	2245
April	1st to 10th	Day	12% 5% 2 5% 4 2 3 4 5% 8% 49%	2160
	11th to 20th	Day	11% 5% 2 5% 5% 4 5% 4 5% 6% 49%	2134
	21st to end	Day	15% 6% 3 4 4 3 4 4 5% 7% 44%	2160
May	1st to 10th	Day	13% 6% 3 5% 5% 3 4 4 6% 9% 40%	2186
	11th to 20th	Day	16% 5% 3 5% 5% 3 5% 5% 5% 8% 39%	2427
	21st to end	Day	13% 5% 2 5% 5% 3 4 5% 6% 8% 44%	2725
June	1st to 10th	Day	11% 5% 2 4 4 3 5% 5% 7% 10% 44%	2520
	11th to 20th	Day	10% 4 2 5% 6% 3 4 6% 8% 11% 42%	2520
	21st to end	Day	7% 4 2 4 4 4 6% 6% 7% 11% 43%	2520
July	1st to 10th	Day	7% 5% 2 5% 6% 3 5% 6% 7% 10% 42%	2520
	11th to 20th	Day	6% 3 2 4 5% 4 5% 7% 9% 13% 41%	2455
	21st to end	Day	7% 4 2 5% 6% 4 6% 9% 9% 10% 37%	2547
August	1st to 10th	Day	9% 6% 2 6% 5% 4 6% 6% 8% 11% 38%	2327
	11th to 20th	Day	10% 6% 3 6% 8% 4 6% 6% 7% 9% 37%	2135
	21st to end	Day	12% 5% 2 5% 5% 4 5% 5% 6% 10% 42%	2376
September	1st to 10th	Day	13% 5% 2 5% 4 3 5% 6% 6% 8% 44%	2160
	11th to 20th	Day	12% 6% 3 5% 5% 2 4 4 6% 7% 45%	2160
	21st to end	Day	20% 7% 3 5% 5% 2 4 4 4 7% 39%	1925
October	1st to 10th	Day	14% 6% 2 6% 5% 3 5% 4 5% 7% 45%	1800
	11th to 20th	Day	17% 6% 2 4 3 3 3 4 4 5% 51%	1800
	21st to end	Day	13% 5% 2 5% 5% 2 4 4 4 6% 48%	1980
November	1st to 10th	Day	15% 6% 2 4 3 1 4 3 3 6% 53%	1737
	11th to 20th	Day	13% 6% 2 5% 5% 2 4 3 5% 7% 48%	1710
	21st to end	Day	15% 4 2 4 5% 2 4 4 5% 5% 51%	1611
December	1st to 10th	Day	15% 7% 3 5% 4 3 3 4 5% 7% 44%	1520
	11th to 20th	Day	16% 7% 2 5% 5% 2 3 4 3 5% 50%	1910
	21st to end	Day	16% 7% 1 5% 5% 2 4 4 5% 7% 43%	2772
January	1st to 10th	Night	13% 6% 3 5% 5% 3 4 4 5% 6% 46%	4361
	11th to 20th	Night	16% 7% 3 5% 5% 3 3 4 4 5% 46%	4120
	21st to end	Night	18% 10% 3 5% 4 2 3 4 4 5% 42%	4532
February	1st to 10th	Night	15% 9% 2 5% 4 3 4 5% 5% 7% 43%	2464
	11th to 20th	Night	19% 7% 3 4 4 2 3 4 4 6% 43%	2151
	21st to end	Night	18% 7% 2 4 4 2 3 4 5% 5% 46%	1776
March	1st to 10th	Night	14% 5% 2 4 4 2 4 4 4 6% 49%	2060
	11th to 20th	Night	19% 6% 2 4 4 2 4 4 6% 7% 41%	1980
	21st to end	Night	16% 7% 3 6% 4 2 3 3 5% 7% 42%	2111
April	1st to 10th	Night	14% 8% 2 6% 5% 3 5% 4 6% 8% 42%	1800
	11th to 20th	Night	12% 5% 2 5% 4 2 3 4 5% 8% 49%	1775
	21st to end	Night	17% 6% 1 4 4 2 4 4 6% 6% 45%	1800
May	1st to 10th	Night	14% 6% 3 6% 5% 4 5% 5% 5% 9% 39%	1787
	11th to 20th	Night	15% 7% 3 6% 5% 3 4 4 5% 7% 41%	1465
	21st to end	Night	12% 8% 2 5% 4 4 4 4 6% 9% 42%	1550
June	1st to 10th	Night	13% 5% 2 4 5% 3 5% 5% 5% 9% 43%	1440
	11th to 20th	Night	11% 4 2 5% 6% 3 5% 6% 8% 11% 40%	1440
	21st to end	Night	8% 4 2 5% 6% 4 6% 6% 7% 9% 43%	1440
July	1st to 10th	Night	8% 6% 2 7% 5% 4 5% 6% 8% 10% 40%	1440
	11th to 20th	Night	4 4 2 5% 5% 4 6% 6% 8% 11% 45%	1501
	21st to end	Night	7% 5% 3 6% 6% 3 7% 6% 7% 10% 41%	1771
August	1st to 10th	Night	7% 5% 2 5% 7% 4 7% 7% 7% 11% 37%	1611
	11th to 20th	Night	10% 6% 2 7% 5% 3 6% 6% 8% 9% 39%	1748
	21st to end	Night	9% 6% 2 6% 6% 4 6% 5% 6% 10% 41%	1980
September	1st to 10th	Night	13% 5% 2 4 5% 3 4 5% 4 7% 48%	1800
	11th to 20th	Night	10% 5% 3 5% 4 3 4 5% 5% 8% 48%	1800
	21st to end	Night	19% 6% 3 5% 5% 3 5% 4 5% 6% 38%	2032
October	1st to 10th	Night	16% 5% 2 5% 5% 3 4 4 5% 7% 46%	2160
	11th to 20th	Night	17% 5% 2 5% 4 2 3 3 4 5% 51%	2160
	21st to end	Night	16% 5% 1 4 4 2 3 4 4 7% 49%	2376
November	1st to 10th	Night	13% 6% 2 5% 5% 2 3 3 4 6% 50%	2339
	11th to 20th	Night	16% 7% 2 4 4 2 4 4 4 5% 48%	2470
	21st to end	Night	12% 4 3 4 4 3 4 4 5% 7% 51%	2565
December	1st to 10th	Night	17% 7% 3 6% 4 3 4 4 5% 6% 41%	2660
	11th to 20th	Night	18% 6% 2 5% 4 3 4 4 4 7% 44%	3285
	21st to end	Night	14% 7% 3 5% 5% 3 4 5% 5% 8% 43%	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	35% 4 7% 34% 16% 3	2583
	11th to 20th	Day	42% 4 8% 21% 20% 5%	2840
	21st to end	Day	47% 4 10% 24% 13% 2	3124
February	1st to 10th	Day	42% 4 11% 27% 13% 2	1701
	11th to 20th	Day	41% 3 8% 23% 20% 5%	1702
	21st to end	Day	46% 5% 11% 19% 16% 4	1480
March	1st to 10th	Day	36% 4 11% 25% 21% 3	1898
	11th to 20th	Day	39% 5% 11% 22% 18% 5%	1980
	21st to end	Day	42% 5% 11% 20% 18% 4	2245
April	1st to 10th	Day	33% 5% 13% 24% 19% 6%	2160
	11th to 20th	Day	35% 4 11% 24% 21% 5%	2134
	21st to end	Day	37% 4 13% 24% 17% 5%	2160
May	1st to 10th	Day	39% 5% 13% 25% 15% 3	2186
	11th to 20th	Day	40% 6% 15% 24% 13% 2	2431
	21st to end	Day	35% 6% 17% 28% 12% 1	2725
June	1st to 10th	Day	32% 6% 18% 29% 13% 2	2520
	11th to 20th	Day	32% 8% 18% 24% 15% 2	2520
	21st to end	Day	31% 7% 17% 26% 18% 1	2520
July	1st to 10th	Day	34% 8% 17% 24% 15% 3	2450
	11th to 20th	Day	28% 9% 20% 29% 12% 2	2380
	21st to end	Day	34% 8% 17% 23% 16% 2	2405
August	1st to 10th	Day	34% 7% 18% 27% 11% 2	2314
	11th to 20th	Day	38% 7% 17% 23% 14% 1	2135
	21st to end	Day	34% 6% 16% 25% 14% 4	2376
September	1st to 10th	Day	35% 6% 17% 22% 16% 4	2160
	11th to 20th	Day	35% 5% 10% 28% 20% 3	2160
	21st to end	Day	44% 5% 8% 23% 17% 3	1925
October	1st to 10th	Day	38% 4 11% 25% 19% 3	1800
	11th to 20th	Day	36% 4 8% 27% 21% 4	1800
	21st to end	Day	37% 4 7% 26% 21% 5%	1980
November	1st to 10th	Day	36% 3 9% 27% 20% 5%	1737
	11th to 20th	Day	38% 4 11% 19% 22% 5%	1710
	21st to end	Day	37% 3 9% 28% 19% 4	1611
December	1st to 10th	Day	41% 4 13% 25% 14% 3	1520
	11th to 20th	Day	39% 3 8% 28% 16% 5%	1906
	21st to end	Day	42% 5% 12% 28% 13% 1	2772
January	1st to 10th	Night	40% 4 8% 25% 18% 5%	4361
	11th to 20th	Night	42% 4 7% 24% 19% 3	4120
	21st to end	Night	47% 4 6% 24% 16% 3	4532
February	1st to 10th	Night	41% 3 11% 26% 17% 2	2464
	11th to 20th	Night	43% 4 7% 22% 18% 6%	2153
	21st to end	Night	41% 3 9% 22% 19% 5%	1776
March	1st to 10th	Night	37% 4 9% 27% 19% 3	2060
	11th to 20th	Night	42% 4 11% 22% 18% 4	1980
	21st to end	Night	43% 4 9% 22% 17% 5%	2111
April	1st to 10th	Night	42% 4 10% 19% 20% 5%	1800
	11th to 20th	Night	35% 4 11% 22% 22% 5%	1775
	21st to end	Night	39% 4 13% 24% 15% 5%	1800
May	1st to 10th	Night	42% 6% 12% 23% 14% 3	1787
	11th to 20th	Night	43% 6% 14% 20% 16% 1	1466
	21st to end	Night	38% 7% 14% 27% 12% 1	1551
June	1st to 10th	Night	38% 6% 13% 26% 16% 1	1440
	11th to 20th	Night	38% 7% 15% 24% 14% 2	1440
	21st to end	Night	36% 7% 16% 22% 17% 2	1440
July	1st to 10th	Night	38% 7% 19% 20% 14% 3	1400
	11th to 20th	Night	30% 10% 19% 29% 11% 1	1453
	21st to end	Night	35% 8% 16% 28% 13%	1672
August	1st to 10th	Night	39% 9% 18% 23% 11%	1600
	11th to 20th	Night	39% 8% 17% 22% 13% 1	1748
	21st to end	Night	38% 6% 16% 22% 15% 2	1980
September	1st to 10th	Night	36% 5% 17% 21% 17% 4	1800
	11th to 20th	Night	34% 6% 11% 27% 21% 2	1800
	21st to end	Night	46% 7% 8% 18% 17% 3	2032
October	1st to 10th	Night	39% 6% 10% 24% 18% 3	2160
	11th to 20th	Night	38% 4 7% 25% 23% 4	2160
	21st to end	Night	37% 4 8% 26% 21% 4	2376
November	1st to 10th	Night	37% 4 10% 26% 19% 4	2339
	11th to 20th	Night	41% 3 9% 20% 20% 6%	2470
	21st to end	Night	35% 3 9% 28% 21% 4	2565
December	1st to 10th	Night	44% 5% 11% 24% 14% 3	2660
	11th to 20th	Night	42% 4 10% 22% 18% 4	3288
	21st to end	Night	39% 5% 14% 28% 12% 2	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	18% 4 24% 44% 10% 1	199
	11th to 20th	Day	17% 9% 32% 32% 9% 1	270
	21st to end	Day	18% 4 23% 43% 12% 1	297
February	1st to 10th	Day	17% 6% 20% 41% 16%	267
	11th to 20th	Day	25% 5% 30% 33% 7%	361
	21st to end	Day	23% 4 28% 36% 8% 1	346
March	1st to 10th	Day	17% 6% 28% 35% 13% 1	420
	11th to 20th	Day	20% 6% 24% 38% 10% 2	420
	21st to end	Day	19% 4 22% 38% 15% 2	462
April	1st to 10th	Day	15% 4 27% 35% 16% 3	420
	11th to 20th	Day	9% 3 22% 38% 23% 5%	412
	21st to end	Day	17% 5% 18% 33% 25% 2	420
May	1st to 10th	Day	17% 4 17% 34% 23% 5%	423
	11th to 20th	Day	19% 2 13% 32% 29% 6%	447
	21st to end	Day	19% 3 6% 25% 34% 13%	485
June	1st to 10th	Day	12% 2 6% 30% 37% 13%	450
	11th to 20th	Day	11% 1 9% 29% 34% 15%	450
	21st to end	Day	11% 2 6% 30% 39% 12%	450
July	1st to 10th	Day	10% 2 3 26% 37% 22%	445
	11th to 20th	Day	5% 2 2 19% 50% 23%	444
	21st to end	Day	10% 2 3 26% 43% 15%	488
August	1st to 10th	Day	10% 2 5% 27% 41% 15%	446
	11th to 20th	Day	11% 3 5% 23% 38% 20%	439
	21st to end	Day	11% 1 4 26% 36% 21%	495
September	1st to 10th	Day	16% 1 6% 23% 32% 22%	450
	11th to 20th	Day	14% 1 8% 24% 34% 19%	450
	21st to end	Day	24% 5% 11% 27% 25% 8%	450
October	1st to 10th	Day	20% 3 8% 28% 26% 14%	450
	11th to 20th	Day	17% 4 18% 27% 25% 9%	450
	21st to end	Day	14% 5% 21% 32% 23% 5%	495
November	1st to 10th	Day	17% 5% 21% 28% 21% 7%	398
	11th to 20th	Day	15% 8% 29% 29% 16% 2	370
	21st to end	Day	16% 8% 24% 30% 20% 3	271
December	1st to 10th	Day	18% 4 26% 39% 12% 1	180
	11th to 20th	Day	21% 5% 24% 35% 14% 1	180
	21st to end	Day	19% 5% 22% 40% 13% 1	198
January	1st to 10th	Night	18% 12% 36% 28% 6%	760
	11th to 20th	Night	20% 9% 31% 31% 9%	760
	21st to end	Night	21% 10% 33% 32% 4	836
February	1st to 10th	Night	18% 7% 31% 38% 5% 1	759
	11th to 20th	Night	22% 11% 36% 28% 4	703
	21st to end	Night	21% 10% 30% 34% 5%	592
March	1st to 10th	Night	17% 8% 32% 34% 8% 1	720
	11th to 20th	Night	20% 6% 30% 33% 9% 3	720
	21st to end	Night	19% 5% 29% 38% 8% 1	792
April	1st to 10th	Night	17% 6% 34% 32% 11% 1	720
	11th to 20th	Night	14% 4 25% 39% 17% 1	711
	21st to end	Night	19% 4 22% 39% 14% 2	720
May	1st to 10th	Night	18% 5% 22% 39% 14% 2	707
	11th to 20th	Night	18% 4 19% 38% 20% 2	404
	21st to end	Night	15% 2 10% 31% 36% 6%	389
June	1st to 10th	Night	14% 2 15% 32% 34% 4	360
	11th to 20th	Night	11% 3 10% 38% 32% 6%	360
	21st to end	Night	8% 4 10% 39% 35% 5%	360
July	1st to 10th	Night	9% 3 4 38% 37% 9%	350
	11th to 20th	Night	5% 2 3 33% 48% 9%	409
	21st to end	Night	8% 2 6% 37% 42% 5%	591
August	1st to 10th	Night	9% 1 5% 37% 41% 7%	537
	11th to 20th	Night	13% 3 6% 32% 39% 8%	684
	21st to end	Night	12% 2 6% 31% 40% 10%	792
September	1st to 10th	Night	16% 2 7% 28% 36% 11%	720
	11th to 20th	Night	13% 2 9% 28% 40% 9%	720
	21st to end	Night	24% 3 12% 31% 27% 4	720
October	1st to 10th	Night	20% 3 17% 26% 26% 8%	720
	11th to 20th	Night	19% 6% 20% 30% 22% 2	720
	21st to end	Night	19% 7% 24% 29% 18% 4	792
November	1st to 10th	Night	18% 6% 22% 30% 19% 5%	740
	11th to 20th	Night	19% 8% 26% 31% 14% 1	760
	21st to end	Night	14% 11% 27% 32% 15% 2	760
December	1st to 10th	Night	21% 8% 32% 27% 10% 2	760
	11th to 20th	Night	18% 8% 36% 29% 9%	760
	21st to end	Night	18% 8% 29% 34% 11%	836

Page generated at 2024-02-07 06:11:56. Version ac07

Copyright 2024 Attilla Danko