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 2025-01-07.

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% 8% 3 8% 5% 4 4 4 6% 7% 39%	105154
	Night	13% 9% 3 8% 4 4 4 3 5% 6% 41%	104023
Transparency	Day	43% 5% 12% 24% 14% 2	108763
	Night	43% 4 12% 24% 15% 2	108554
Seeing	Day	16% 8% 28% 28% 16% 4	16020
	Night	17% 8% 30% 32% 12% 1	25958

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% 16% 8% 6% 5% 4 5% 7% 22%	2575
	11th to 20th	Day	11% 13% 4 12% 9% 6% 6% 4 7% 5% 24%	2635
	21st to end	Day	16% 18% 7% 15% 7% 5% 3 3 4 4 18%	3135
February	1st to 10th	Day	13% 13% 4 10% 6% 5% 5% 4 6% 6% 28%	1710
	11th to 20th	Day	14% 11% 3 7% 5% 6% 5% 2 5% 7% 34%	1702
	21st to end	Day	14% 10% 4 11% 5% 4 4 3 5% 6% 35%	1570
March	1st to 10th	Day	17% 11% 3 7% 3 3 3 3 4 5% 41%	3266
	11th to 20th	Day	9% 7% 3 6% 5% 4 5% 3 6% 6% 47%	3480
	21st to end	Day	23% 13% 3 10% 5% 5% 4 4 5% 6% 23%	3955
April	1st to 10th	Day	16% 12% 3 7% 5% 5% 4 4 5% 5% 34%	2280
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 5% 37%	2254
	21st to end	Day	22% 9% 2 7% 3 3 4 3 5% 6% 35%	2280
May	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 34%	4213
	11th to 20th	Day	15% 7% 2 7% 4 4 4 3 5% 7% 41%	4399
	21st to end	Day	12% 6% 2 7% 4 4 5% 4 6% 7% 44%	4824
June	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 5% 7% 9% 44%	2660
	11th to 20th	Day	9% 5% 3 5% 4 4 5% 5% 6% 8% 47%	2660
	21st to end	Day	11% 6% 2 6% 6% 5% 5% 5% 7% 8% 40%	2660
July	1st to 10th	Day	9% 8% 3 8% 5% 6% 6% 4 7% 9% 37%	4440
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 6% 9% 52%	4440
	21st to end	Day	6% 4 2 6% 5% 5% 6% 5% 9% 12% 40%	4669
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 10% 45%	4104
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 9% 41%	3945
	21st to end	Day	7% 5% 2 6% 4 4 4 3 6% 8% 51%	4180
September	1st to 10th	Day	13% 3 2 4 4 3 4 3 5% 8% 51%	2280
	11th to 20th	Day	10% 4 2 5% 4 3 3 4 6% 9% 51%	2280
	21st to end	Day	10% 5% 2 5% 4 5% 4 4 6% 7% 48%	2015
October	1st to 10th	Day	12% 7% 3 6% 4 4 4 3 4 5% 49%	1900
	11th to 20th	Day	15% 7% 2 6% 4 4 3 3 4 6% 45%	1900
	21st to end	Day	17% 9% 3 6% 4 3 4 3 5% 5% 42%	2066
November	1st to 10th	Day	12% 8% 3 5% 4 4 4 4 6% 7% 44%	1762
	11th to 20th	Day	16% 10% 3 7% 4 4 4 3 4 7% 37%	1715
	21st to end	Day	16% 10% 4 6% 4 4 3 4 5% 7% 39%	1600
December	1st to 10th	Day	8% 9% 3 8% 3 4 4 3 5% 6% 48%	2610
	11th to 20th	Day	14% 11% 5% 14% 6% 5% 5% 4 5% 6% 26%	3008
	21st to end	Day	24% 21% 7% 11% 4 3 4 2 3 4 16%	3982
January	1st to 10th	Night	12% 11% 7% 15% 6% 4 4 3 4 5% 29%	4513
	11th to 20th	Night	12% 16% 6% 12% 5% 4 5% 4 7% 6% 23%	4330
	21st to end	Night	17% 17% 7% 11% 5% 4 3 2 4 5% 24%	4532
February	1st to 10th	Night	15% 12% 4 8% 6% 4 4 3 5% 6% 34%	2470
	11th to 20th	Night	12% 9% 3 7% 4 4 4 3 6% 6% 41%	2363
	21st to end	Night	14% 11% 3 9% 4 3 3 3 5% 5% 41%	1884
March	1st to 10th	Night	17% 9% 2 6% 4 3 3 3 4 5% 43%	3618
	11th to 20th	Night	11% 6% 2 6% 4 4 3 3 4 6% 52%	3480
	21st to end	Night	21% 11% 5% 12% 6% 5% 4 4 4 5% 23%	3675
April	1st to 10th	Night	15% 8% 3 8% 4 3 3 4 4 6% 42%	1900
	11th to 20th	Night	15% 9% 2 6% 5% 4 4 3 5% 6% 41%	1875
	21st to end	Night	17% 7% 2 6% 4 5% 4 4 5% 7% 39%	1900
May	1st to 10th	Night	19% 7% 2 7% 4 5% 4 3 5% 7% 38%	2690
	11th to 20th	Night	13% 5% 2 6% 4 4 6% 3 6% 7% 43%	2506
	21st to end	Night	8% 5% 2 6% 5% 4 4 4 6% 9% 48%	2743
June	1st to 10th	Night	7% 6% 2 4 4 4 4 5% 7% 9% 48%	1520
	11th to 20th	Night	7% 5% 2 6% 4 3 4 4 7% 11% 46%	1520
	21st to end	Night	9% 5% 2 6% 4 4 3 4 6% 8% 48%	1520
July	1st to 10th	Night	12% 4 2 6% 4 5% 6% 5% 7% 9% 41%	2530
	11th to 20th	Night	4 3 1 3 3 3 4 3 7% 9% 61%	2530
	21st to end	Night	6% 4 2 6% 4 5% 6% 5% 6% 8% 49%	2891
August	1st to 10th	Night	4 3 2 5% 4 3 5% 4 6% 10% 54%	2836
	11th to 20th	Night	7% 5% 2 5% 4 3 4 3 5% 7% 55%	2891
	21st to end	Night	7% 4 2 5% 3 4 4 3 5% 9% 54%	3476
September	1st to 10th	Night	10% 5% 2 4 3 3 3 3 5% 7% 56%	1900
	11th to 20th	Night	10% 6% 2 4 3 4 4 3 4 8% 52%	1900
	21st to end	Night	8% 4 2 5% 4 5% 4 3 5% 7% 53%	2142
October	1st to 10th	Night	12% 6% 2 5% 4 2 4 2 5% 6% 52%	2280
	11th to 20th	Night	14% 6% 2 5% 4 3 3 2 5% 6% 49%	2280
	21st to end	Night	16% 8% 3 7% 4 4 4 2 4 6% 42%	2532
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 5% 6% 53%	2536
	11th to 20th	Night	14% 8% 3 7% 4 4 4 3 5% 6% 42%	2685
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 5% 40%	2800
December	1st to 10th	Night	8% 8% 3 7% 4 4 3 3 5% 6% 49%	4580
	11th to 20th	Night	14% 11% 4 11% 6% 4 4 3 4 6% 32%	5199
	21st to end	Night	24% 18% 7% 11% 5% 4 4 3 3 4 17%	6996

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	61% 6% 12% 15% 6%	2576
	11th to 20th	Day	61% 3 11% 18% 8%	2635
	21st to end	Day	70% 4 9% 11% 5%	3135
February	1st to 10th	Day	55% 5% 13% 19% 8% 1	1710
	11th to 20th	Day	50% 4 12% 23% 10% 1	1711
	21st to end	Day	50% 4 11% 23% 9% 3	1570
March	1st to 10th	Day	47% 4 11% 23% 14% 1	3266
	11th to 20th	Day	37% 5% 12% 27% 18% 1	3480
	21st to end	Day	60% 6% 14% 15% 4 1	3955
April	1st to 10th	Day	52% 4 11% 23% 10%	2280
	11th to 20th	Day	48% 4 10% 24% 12% 2	2254
	21st to end	Day	49% 5% 11% 19% 14% 1	2280
May	1st to 10th	Day	47% 6% 11% 20% 15% 1	4251
	11th to 20th	Day	44% 5% 11% 27% 13%	4403
	21st to end	Day	39% 6% 10% 25% 18% 1	4837
June	1st to 10th	Day	34% 7% 15% 25% 16% 3	2660
	11th to 20th	Day	34% 6% 11% 23% 22% 3	2660
	21st to end	Day	38% 7% 15% 22% 16% 2	2660
July	1st to 10th	Day	44% 4 12% 28% 10% 2	4371
	11th to 20th	Day	28% 6% 15% 32% 18% 2	4365
	21st to end	Day	34% 7% 20% 21% 17% 1	4522
August	1st to 10th	Day	31% 7% 18% 30% 13% 1	4090
	11th to 20th	Day	39% 5% 14% 27% 15% 1	3984
	21st to end	Day	32% 4 14% 32% 16% 2	4179
September	1st to 10th	Day	32% 5% 11% 25% 23% 4	2280
	11th to 20th	Day	30% 5% 12% 31% 19% 3	2280
	21st to end	Day	34% 5% 10% 30% 19% 2	2015
October	1st to 10th	Day	23% 2 6% 27% 39% 2	3160
	11th to 20th	Day	27% 3 10% 24% 29% 6%	3140
	21st to end	Day	40% 3 9% 30% 16% 3	3380
November	1st to 10th	Day	39% 4 15% 25% 14% 3	1762
	11th to 20th	Day	47% 4 13% 21% 14% 1	1715
	21st to end	Day	46% 4 15% 24% 10%	1600
December	1st to 10th	Day	38% 3 14% 36% 8% 1	2610
	11th to 20th	Day	59% 3 12% 14% 10% 1	3005
	21st to end	Day	73% 4 8% 11% 3	3982
January	1st to 10th	Night	58% 4 12% 17% 9%	4513
	11th to 20th	Night	59% 4 12% 14% 11% 1	4330
	21st to end	Night	64% 4 11% 16% 6% 1	4532
February	1st to 10th	Night	52% 3 11% 22% 11% 1	2470
	11th to 20th	Night	43% 4 12% 26% 13% 2	2364
	21st to end	Night	46% 3 10% 24% 15% 2	1884
March	1st to 10th	Night	44% 3 10% 26% 16% 1	3618
	11th to 20th	Night	34% 4 11% 32% 15% 4	3480
	21st to end	Night	62% 7% 14% 12% 5% 1	3675
April	1st to 10th	Night	44% 4 9% 27% 14% 2	1900
	11th to 20th	Night	43% 5% 9% 22% 17% 4	1875
	21st to end	Night	45% 4 11% 22% 14% 3	1900
May	1st to 10th	Night	46% 5% 10% 20% 17% 2	2717
	11th to 20th	Night	38% 6% 13% 26% 15% 1	2507
	21st to end	Night	31% 7% 11% 27% 21% 2	2751
June	1st to 10th	Night	31% 7% 14% 28% 17% 3	1520
	11th to 20th	Night	31% 5% 12% 26% 22% 4	1520
	21st to end	Night	32% 6% 16% 23% 18% 4	1520
July	1st to 10th	Night	40% 5% 13% 27% 12% 3	2490
	11th to 20th	Night	20% 4 17% 35% 23% 1	2482
	21st to end	Night	31% 6% 18% 24% 18% 2	2799
August	1st to 10th	Night	26% 5% 18% 32% 17% 2	2826
	11th to 20th	Night	28% 5% 16% 33% 17% 1	2918
	21st to end	Night	29% 5% 13% 30% 18% 5%	3476
September	1st to 10th	Night	27% 6% 10% 27% 27% 4	1900
	11th to 20th	Night	31% 4 11% 30% 19% 4	1900
	21st to end	Night	30% 5% 9% 30% 24% 3	2142
October	1st to 10th	Night	24% 3 6% 26% 39% 3	3800
	11th to 20th	Night	26% 2 10% 23% 32% 8%	3779
	21st to end	Night	45% 3 8% 23% 17% 4	4168
November	1st to 10th	Night	32% 5% 14% 27% 18% 4	2536
	11th to 20th	Night	43% 4 12% 26% 14% 2	2685
	21st to end	Night	47% 3 12% 26% 12% 1	2800
December	1st to 10th	Night	37% 3 12% 36% 11% 1	4580
	11th to 20th	Night	53% 4 12% 23% 7% 1	5201
	21st to end	Night	71% 4 8% 12% 4	6996

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	23% 11% 32% 24% 9% 1	288
	11th to 20th	Day	23% 13% 41% 19% 5%	270
	21st to end	Day	21% 10% 40% 23% 5% 1	297
February	1st to 10th	Day	19% 17% 37% 21% 5%	270
	11th to 20th	Day	21% 16% 34% 21% 8%	270
	21st to end	Day	22% 13% 43% 19% 3	225
March	1st to 10th	Day	18% 18% 42% 17% 5%	270
	11th to 20th	Day	21% 14% 34% 20% 10% 1	270
	21st to end	Day	31% 12% 33% 18% 5% 1	374
April	1st to 10th	Day	23% 11% 37% 20% 7%	460
	11th to 20th	Day	22% 13% 32% 22% 9% 1	452
	21st to end	Day	26% 9% 35% 18% 10% 1	460
May	1st to 10th	Day	21% 9% 35% 26% 8% 2	638
	11th to 20th	Day	21% 9% 27% 27% 13% 3	675
	21st to end	Day	14% 9% 27% 28% 16% 7%	734
June	1st to 10th	Day	7% 4 27% 35% 21% 6%	680
	11th to 20th	Day	10% 4 26% 36% 19% 4	680
	21st to end	Day	12% 6% 31% 31% 15% 4	680
July	1st to 10th	Day	10% 2 16% 32% 27% 14%	671
	11th to 20th	Day	11% 2 21% 35% 23% 8%	668
	21st to end	Day	7% 1 20% 36% 29% 7%	739
August	1st to 10th	Day	8% 2 21% 36% 25% 9%	676
	11th to 20th	Day	10% 3 17% 34% 28% 8%	608
	21st to end	Day	9% 3 15% 34% 29% 10%	539
September	1st to 10th	Day	15% 5% 16% 30% 27% 8%	490
	11th to 20th	Day	9% 2 18% 39% 22% 10%	490
	21st to end	Day	13% 9% 24% 24% 24% 6%	386
October	1st to 10th	Day	16% 7% 28% 28% 15% 6%	300
	11th to 20th	Day	15% 20% 35% 19% 10% 1	300
	21st to end	Day	28% 11% 29% 24% 6% 1	330
November	1st to 10th	Day	19% 6% 40% 22% 10% 3	300
	11th to 20th	Day	24% 13% 31% 23% 8% 2	300
	21st to end	Day	24% 10% 33% 28% 5%	300
December	1st to 10th	Day	15% 12% 42% 22% 7% 2	300
	11th to 20th	Day	17% 13% 36% 26% 8%	300
	21st to end	Day	31% 11% 37% 17% 4	330
January	1st to 10th	Night	16% 12% 38% 27% 8% 1	981
	11th to 20th	Night	18% 12% 35% 28% 5% 1	950
	21st to end	Night	20% 10% 35% 29% 6%	1045
February	1st to 10th	Night	21% 10% 36% 27% 5% 1	950
	11th to 20th	Night	17% 13% 36% 30% 5%	889
	21st to end	Night	22% 10% 40% 24% 3 1	628
March	1st to 10th	Night	18% 12% 39% 24% 6% 1	697
	11th to 20th	Night	18% 9% 33% 32% 8%	570
	21st to end	Night	25% 10% 34% 25% 6% 1	627
April	1st to 10th	Night	20% 13% 38% 25% 4	570
	11th to 20th	Night	20% 12% 31% 29% 8%	563
	21st to end	Night	21% 7% 34% 29% 9% 1	570
May	1st to 10th	Night	20% 6% 36% 30% 7% 1	570
	11th to 20th	Night	19% 6% 29% 33% 12%	561
	21st to end	Night	13% 4 30% 35% 18% 1	617
June	1st to 10th	Night	11% 4 23% 44% 16% 2	570
	11th to 20th	Night	9% 4 26% 44% 17% 1	570
	21st to end	Night	10% 3 28% 39% 19% 1	570
July	1st to 10th	Night	8% 2 12% 41% 33% 4	555
	11th to 20th	Night	6% 1 19% 43% 28% 3	552
	21st to end	Night	8% 1 16% 46% 27% 2	624
August	1st to 10th	Night	6% 2 14% 46% 31% 2	567
	11th to 20th	Night	8% 2 13% 44% 28% 4	564
	21st to end	Night	10% 1 12% 45% 28% 4	627
September	1st to 10th	Night	13% 2 16% 40% 26% 3	570
	11th to 20th	Night	11% 3 17% 38% 26% 5%	570
	21st to end	Night	8% 6% 27% 35% 22% 2	710
October	1st to 10th	Night	15% 5% 26% 32% 19% 2	760
	11th to 20th	Night	18% 9% 31% 31% 11%	760
	21st to end	Night	22% 9% 33% 28% 8%	836
November	1st to 10th	Night	15% 9% 36% 29% 9% 1	780
	11th to 20th	Night	18% 13% 39% 24% 6%	885
	21st to end	Night	21% 11% 32% 29% 7%	1000
December	1st to 10th	Night	19% 10% 37% 28% 6% 1	1000
	11th to 20th	Night	21% 10% 33% 30% 6%	1000
	21st to end	Night	27% 13% 31% 26% 4	1100

Page generated at 2025-01-04 02:24:03. Version ac07

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