Riverside
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Riverside clear sky chart from 2005-11-06 to 2026-05-02.

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% 8% 3 8% 5% 5% 5% 4 6% 7% 39%	132155
	Night	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	130628
Transparency	Day	43% 4 12% 24% 14% 2	135723
	Night	43% 4 12% 24% 15% 2	135138
Seeing	Day	16% 8% 29% 28% 15% 4	17785
	Night	17% 8% 30% 32% 12% 1	27758

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	9% 11% 5% 15% 7% 7% 6% 4 5% 6% 25%	4691
	11th to 20th	Day	6% 9% 4 10% 8% 6% 7% 4 7% 7% 32%	4927
	21st to end	Day	10% 13% 5% 12% 7% 6% 5% 4 4 5% 30%	5812
February	1st to 10th	Day	12% 13% 4 10% 6% 5% 5% 4 6% 6% 28%	1890
	11th to 20th	Day	14% 11% 3 8% 5% 6% 5% 2 5% 7% 34%	1887
	21st to end	Day	13% 10% 4 10% 5% 4 4 3 5% 6% 37%	1730
March	1st to 10th	Day	19% 10% 3 5% 3 2 3 2 3 5% 46%	4786
	11th to 20th	Day	8% 6% 3 6% 5% 4 5% 3 5% 8% 48%	5090
	21st to end	Day	20% 11% 3 10% 5% 5% 5% 4 5% 6% 26%	5784
April	1st to 10th	Day	16% 12% 4 7% 5% 5% 4 3 4 5% 34%	2520
	11th to 20th	Day	16% 9% 3 8% 5% 4 4 4 5% 6% 37%	2494
	21st to end	Day	20% 8% 3 7% 3 4 4 4 5% 6% 35%	2520
May	1st to 10th	Day	14% 7% 3 7% 6% 5% 5% 4 6% 7% 37%	6048
	11th to 20th	Day	14% 6% 2 5% 4 4 4 3 5% 7% 45%	6319
	21st to end	Day	13% 7% 3 8% 5% 5% 5% 4 6% 7% 38%	6935
June	1st to 10th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 44%	2800
	11th to 20th	Day	9% 5% 3 6% 5% 4 4 5% 6% 8% 46%	2800
	21st to end	Day	11% 6% 2 6% 6% 5% 4 5% 7% 8% 41%	2800
July	1st to 10th	Day	7% 7% 3 7% 5% 6% 5% 4 7% 9% 40%	6360
	11th to 20th	Day	9% 6% 2 7% 4 4 5% 4 6% 9% 44%	6360
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	6710
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 10% 45%	4234
	11th to 20th	Day	10% 5% 2 7% 5% 5% 5% 4 6% 9% 41%	4072
	21st to end	Day	7% 5% 2 6% 4 4 4 3 6% 8% 51%	4312
September	1st to 10th	Day	13% 3 2 4 4 3 4 4 5% 8% 51%	2400
	11th to 20th	Day	10% 4 2 5% 4 3 3 4 6% 9% 51%	2400
	21st to end	Day	10% 5% 2 6% 4 5% 4 4 6% 7% 48%	2120
October	1st to 10th	Day	11% 7% 3 6% 4 4 4 3 4 5% 50%	2000
	11th to 20th	Day	15% 7% 2 6% 4 5% 3 3 5% 6% 44%	2000
	21st to end	Day	16% 9% 3 6% 4 4 4 3 5% 6% 41%	2174
November	1st to 10th	Day	11% 8% 3 5% 4 4 4 4 6% 7% 44%	1852
	11th to 20th	Day	16% 10% 3 7% 4 4 5% 3 4 7% 37%	1800
	21st to end	Day	16% 10% 4 6% 4 4 3 3 5% 6% 39%	1680
December	1st to 10th	Day	8% 9% 3 9% 3 4 4 3 5% 6% 47%	2690
	11th to 20th	Day	14% 11% 4 14% 6% 5% 5% 4 5% 6% 27%	3088
	21st to end	Day	24% 21% 7% 11% 5% 3 4 2 3 4 16%	4070
January	1st to 10th	Night	10% 12% 6% 14% 5% 4 4 3 4 5% 33%	8232
	11th to 20th	Night	8% 11% 4 11% 7% 6% 6% 4 7% 6% 30%	8058
	21st to end	Night	11% 13% 5% 10% 5% 4 4 3 4 6% 35%	8402
February	1st to 10th	Night	14% 12% 4 8% 5% 4 4 3 5% 6% 35%	2730
	11th to 20th	Night	12% 10% 3 8% 4 4 4 3 6% 6% 40%	2618
	21st to end	Night	13% 10% 3 9% 4 3 3 3 5% 5% 42%	2076
March	1st to 10th	Night	18% 8% 3 6% 3 3 3 3 4 5% 45%	5319
	11th to 20th	Night	11% 7% 2 6% 4 4 3 3 4 6% 51%	5090
	21st to end	Night	17% 12% 5% 10% 6% 5% 4 4 4 5% 28%	5386
April	1st to 10th	Night	15% 9% 3 8% 4 3 3 4 4 6% 41%	2100
	11th to 20th	Night	14% 9% 2 6% 5% 4 4 3 5% 7% 41%	2075
	21st to end	Night	17% 7% 2 6% 4 5% 4 4 6% 7% 39%	2100
May	1st to 10th	Night	17% 7% 2 7% 4 4 4 3 5% 7% 42%	3874
	11th to 20th	Night	12% 4 2 5% 4 4 6% 4 6% 8% 45%	3596
	21st to end	Night	14% 7% 2 6% 5% 4 4 3 6% 7% 42%	3942
June	1st to 10th	Night	7% 6% 2 4 4 4 4 5% 7% 9% 48%	1600
	11th to 20th	Night	7% 5% 2 6% 4 4 4 4 7% 11% 45%	1600
	21st to end	Night	9% 5% 2 6% 4 4 3 4 6% 8% 49%	1600
July	1st to 10th	Night	10% 4 2 7% 4 4 5% 4 7% 10% 42%	3618
	11th to 20th	Night	7% 5% 2 5% 3 3 4 3 6% 9% 52%	3617
	21st to end	Night	10% 5% 2 7% 4 5% 5% 4 6% 8% 44%	4144
August	1st to 10th	Night	4 3 2 5% 4 3 5% 4 6% 10% 53%	2926
	11th to 20th	Night	7% 5% 2 5% 4 3 3 3 5% 7% 55%	2984
	21st to end	Night	7% 4 2 5% 3 4 4 3 5% 9% 54%	3586
September	1st to 10th	Night	9% 5% 2 4 3 3 4 3 5% 7% 56%	2000
	11th to 20th	Night	9% 5% 2 4 4 4 4 3 5% 8% 52%	2000
	21st to end	Night	8% 4 2 5% 4 5% 4 3 5% 7% 54%	2256
October	1st to 10th	Night	11% 6% 2 5% 4 3 3 2 5% 6% 53%	2400
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 6% 49%	2400
	21st to end	Night	15% 8% 3 7% 4 4 4 2 4 6% 43%	2665
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 5% 6% 53%	2666
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 5% 6% 42%	2819
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 5% 39%	2940
December	1st to 10th	Night	8% 8% 3 8% 5% 4 3 3 5% 6% 48%	4720
	11th to 20th	Night	14% 11% 4 11% 6% 4 4 3 4 6% 32%	5339
	21st to end	Night	23% 18% 7% 11% 5% 4 4 3 3 4 18%	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	59% 5% 13% 15% 8%	4692
	11th to 20th	Day	50% 4 8% 21% 15% 2	4927
	21st to end	Day	57% 3 12% 21% 7%	5812
February	1st to 10th	Day	55% 4 14% 19% 7% 1	1890
	11th to 20th	Day	51% 4 12% 23% 9% 2	1896
	21st to end	Day	49% 4 12% 24% 9% 2	1730
March	1st to 10th	Day	44% 3 9% 26% 16% 3	4786
	11th to 20th	Day	35% 4 10% 33% 17% 1	5090
	21st to end	Day	57% 5% 14% 17% 5% 1	5786
April	1st to 10th	Day	52% 4 11% 23% 10%	2520
	11th to 20th	Day	48% 4 10% 24% 12% 2	2494
	21st to end	Day	48% 5% 12% 21% 14% 1	2520
May	1st to 10th	Day	45% 5% 11% 20% 18% 1	6086
	11th to 20th	Day	39% 4 11% 27% 15% 3	6323
	21st to end	Day	44% 5% 11% 24% 15% 1	6949
June	1st to 10th	Day	35% 7% 15% 25% 16% 2	2800
	11th to 20th	Day	35% 6% 11% 24% 21% 3	2800
	21st to end	Day	38% 7% 14% 23% 16% 2	2800
July	1st to 10th	Day	40% 4 13% 29% 13% 1	6291
	11th to 20th	Day	37% 5% 13% 28% 15% 1	6285
	21st to end	Day	39% 6% 19% 22% 13% 1	6519
August	1st to 10th	Day	31% 7% 18% 30% 13% 1	4220
	11th to 20th	Day	38% 5% 14% 28% 14% 1	4111
	21st to end	Day	32% 4 14% 32% 16% 2	4311
September	1st to 10th	Day	31% 5% 11% 26% 22% 4	2400
	11th to 20th	Day	30% 5% 12% 31% 19% 3	2400
	21st to end	Day	34% 5% 10% 30% 19% 2	2120
October	1st to 10th	Day	23% 2 6% 27% 40% 2	3260
	11th to 20th	Day	28% 3 10% 24% 29% 6%	3240
	21st to end	Day	40% 3 9% 29% 16% 3	3488
November	1st to 10th	Day	38% 4 15% 25% 15% 3	1852
	11th to 20th	Day	47% 4 13% 21% 14% 1	1800
	21st to end	Day	47% 4 14% 24% 10%	1680
December	1st to 10th	Day	39% 3 14% 35% 8% 1	2690
	11th to 20th	Day	59% 3 12% 15% 10% 1	3085
	21st to end	Day	74% 4 8% 11% 3	4070
January	1st to 10th	Night	55% 3 15% 19% 7%	8233
	11th to 20th	Night	53% 4 11% 16% 16% 1	8058
	21st to end	Night	52% 3 13% 20% 11% 1	8402
February	1st to 10th	Night	51% 3 12% 23% 11% 1	2730
	11th to 20th	Night	44% 4 12% 26% 12% 2	2619
	21st to end	Night	44% 3 10% 25% 16% 2	2076
March	1st to 10th	Night	43% 2 7% 28% 18% 2	5319
	11th to 20th	Night	35% 3 9% 31% 18% 4	5090
	21st to end	Night	57% 6% 14% 15% 7% 1	5386
April	1st to 10th	Night	44% 4 9% 26% 14% 2	2100
	11th to 20th	Night	42% 5% 11% 22% 17% 4	2075
	21st to end	Night	44% 4 12% 23% 14% 3	2100
May	1st to 10th	Night	43% 4 10% 22% 19% 2	3901
	11th to 20th	Night	36% 6% 14% 24% 18% 3	3597
	21st to end	Night	39% 6% 10% 27% 16% 2	3950
June	1st to 10th	Night	31% 7% 14% 29% 17% 3	1600
	11th to 20th	Night	32% 5% 12% 25% 21% 4	1600
	21st to end	Night	32% 6% 16% 23% 19% 5%	1600
July	1st to 10th	Night	37% 4 13% 29% 14% 3	3580
	11th to 20th	Night	29% 4 15% 30% 20% 1	3572
	21st to end	Night	37% 5% 18% 25% 14% 2	4025
August	1st to 10th	Night	26% 5% 18% 32% 17% 2	2916
	11th to 20th	Night	28% 5% 16% 33% 17% 1	3011
	21st to end	Night	29% 5% 13% 30% 18% 5%	3586
September	1st to 10th	Night	27% 5% 10% 28% 26% 3	2000
	11th to 20th	Night	32% 4 11% 30% 19% 4	2000
	21st to end	Night	30% 5% 9% 29% 25% 3	2256
October	1st to 10th	Night	24% 3 6% 26% 39% 3	3920
	11th to 20th	Night	27% 2 10% 22% 31% 7%	3899
	21st to end	Night	45% 3 8% 22% 18% 4	4301
November	1st to 10th	Night	32% 5% 14% 28% 18% 4	2666
	11th to 20th	Night	43% 3 12% 26% 14% 2	2819
	21st to end	Night	47% 3 12% 26% 12% 1	2940
December	1st to 10th	Night	38% 3 12% 35% 11% 1	4720
	11th to 20th	Night	53% 4 12% 23% 7% 1	5341
	21st to end	Night	71% 4 9% 12% 4	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	21% 11% 32% 25% 9% 2	330
	11th to 20th	Day	19% 15% 43% 18% 4	330
	21st to end	Day	18% 13% 42% 22% 4 1	363
February	1st to 10th	Day	17% 18% 37% 22% 6%	330
	11th to 20th	Day	22% 17% 35% 18% 7%	330
	21st to end	Day	21% 14% 45% 18% 2	273
March	1st to 10th	Day	18% 16% 44% 17% 5%	330
	11th to 20th	Day	21% 16% 33% 21% 8% 1	330
	21st to end	Day	29% 14% 35% 17% 4 1	448
April	1st to 10th	Day	24% 13% 37% 20% 6%	540
	11th to 20th	Day	21% 16% 32% 21% 8% 1	532
	21st to end	Day	24% 10% 36% 20% 9% 1	540
May	1st to 10th	Day	20% 9% 36% 26% 8% 2	692
	11th to 20th	Day	21% 10% 26% 27% 14% 3	725
	21st to end	Day	14% 9% 28% 29% 15% 6%	789
June	1st to 10th	Day	7% 5% 27% 34% 21% 6%	730
	11th to 20th	Day	10% 4 26% 36% 20% 4	730
	21st to end	Day	11% 6% 31% 32% 15% 4	730
July	1st to 10th	Day	9% 2 16% 33% 26% 13%	721
	11th to 20th	Day	11% 3 20% 35% 23% 8%	718
	21st to end	Day	8% 1 21% 36% 28% 7%	794
August	1st to 10th	Day	8% 2 21% 36% 25% 9%	726
	11th to 20th	Day	10% 3 16% 34% 28% 8%	655
	21st to end	Day	9% 3 16% 34% 29% 10%	583
September	1st to 10th	Day	14% 6% 16% 31% 26% 8%	530
	11th to 20th	Day	9% 2 17% 39% 23% 10%	530
	21st to end	Day	12% 9% 23% 25% 25% 7%	420
October	1st to 10th	Day	16% 6% 28% 27% 16% 5%	330
	11th to 20th	Day	14% 20% 36% 20% 10% 1	330
	21st to end	Day	27% 12% 30% 24% 6% 1	363
November	1st to 10th	Day	19% 7% 41% 21% 9% 3	330
	11th to 20th	Day	23% 14% 32% 22% 7% 2	330
	21st to end	Day	25% 10% 33% 27% 5%	330
December	1st to 10th	Day	15% 12% 42% 22% 8% 2	330
	11th to 20th	Day	17% 13% 35% 26% 8%	330
	21st to end	Day	31% 11% 38% 16% 3	363
January	1st to 10th	Night	16% 12% 37% 28% 7%	1050
	11th to 20th	Night	17% 14% 36% 27% 5% 1	1050
	21st to end	Night	19% 12% 36% 28% 5%	1155
February	1st to 10th	Night	20% 11% 36% 28% 5%	1050
	11th to 20th	Night	18% 13% 35% 29% 4	984
	21st to end	Night	21% 10% 41% 23% 3 1	692
March	1st to 10th	Night	19% 13% 38% 24% 5% 1	770
	11th to 20th	Night	19% 9% 33% 31% 7%	630
	21st to end	Night	24% 11% 35% 25% 5% 1	693
April	1st to 10th	Night	21% 13% 38% 24% 3	630
	11th to 20th	Night	19% 13% 32% 29% 8%	623
	21st to end	Night	20% 8% 33% 30% 8% 1	630
May	1st to 10th	Night	19% 6% 36% 31% 7% 1	603
	11th to 20th	Night	19% 6% 29% 33% 13%	591
	21st to end	Night	14% 4 30% 36% 17% 1	650
June	1st to 10th	Night	11% 4 23% 44% 16% 2	600
	11th to 20th	Night	9% 4 25% 45% 17% 1	600
	21st to end	Night	11% 3 28% 39% 19% 1	600
July	1st to 10th	Night	8% 2 12% 42% 33% 3	585
	11th to 20th	Night	6% 2 18% 43% 28% 3	582
	21st to end	Night	8% 2 16% 45% 27% 2	657
August	1st to 10th	Night	6% 2 14% 45% 31% 2	597
	11th to 20th	Night	8% 3 13% 43% 29% 4	594
	21st to end	Night	10% 1 12% 46% 28% 3	660
September	1st to 10th	Night	13% 2 16% 40% 26% 4	600
	11th to 20th	Night	11% 3 16% 38% 27% 5%	600
	21st to end	Night	8% 5% 26% 35% 24% 2	748
October	1st to 10th	Night	15% 5% 26% 33% 20% 2	800
	11th to 20th	Night	19% 9% 31% 31% 11%	800
	21st to end	Night	21% 10% 33% 28% 8%	880
November	1st to 10th	Night	15% 9% 37% 29% 9% 1	820
	11th to 20th	Night	18% 13% 39% 23% 6%	929
	21st to end	Night	22% 12% 32% 28% 7%	1050
December	1st to 10th	Night	19% 10% 38% 27% 6% 1	1050
	11th to 20th	Night	21% 10% 33% 29% 6%	1050
	21st to end	Night	27% 12% 32% 26% 4	1155

Page generated at 2026-04-29 01:21:45. Version ac07

Copyright © 2026 Attilla Danko.