Rusty's Backyard
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rusty's Backyard clear sky chart from 2005-11-06 to 2024-11-01.

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% 7% 3 6% 4 4 4 4 5% 7% 44%	101040
	Night	12% 8% 3 6% 4 4 4 3 5% 7% 46%	97961
Transparency	Day	40% 4 12% 26% 16% 3	100847
	Night	39% 4 11% 26% 17% 3	97824
Seeing	Day	17% 10% 28% 26% 15% 3	15568
	Night	17% 11% 31% 27% 12% 1	25362

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	13% 11% 4 7% 4 4 3 3 4 6% 41%	2793
	11th to 20th	Day	12% 12% 4 8% 4 3 4 3 4 6% 40%	2850
	21st to end	Day	21% 11% 4 7% 4 3 3 2 3 5% 37%	3135
February	1st to 10th	Day	13% 12% 4 9% 7% 4 4 2 4 5% 36%	1710
	11th to 20th	Day	13% 10% 3 7% 5% 5% 4 3 5% 6% 40%	1716
	21st to end	Day	15% 11% 3 5% 3 4 5% 3 5% 7% 38%	1585
March	1st to 10th	Day	16% 10% 3 6% 3 3 3 3 4 5% 44%	3436
	11th to 20th	Day	14% 8% 2 4 3 3 3 3 5% 7% 50%	3480
	21st to end	Day	16% 11% 3 7% 5% 4 4 4 5% 6% 34%	3831
April	1st to 10th	Day	13% 8% 2 5% 4 4 4 3 5% 7% 45%	2280
	11th to 20th	Day	16% 8% 3 6% 4 5% 4 3 5% 6% 40%	2254
	21st to end	Day	20% 9% 3 7% 5% 3 4 4 4 5% 36%	2280
May	1st to 10th	Day	16% 8% 2 8% 5% 5% 5% 4 6% 7% 34%	3957
	11th to 20th	Day	16% 7% 2 6% 4 5% 4 4 6% 7% 40%	4082
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 6% 8% 41%	4824
June	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 6% 9% 45%	2660
	11th to 20th	Day	8% 4 2 5% 5% 5% 5% 4 7% 8% 48%	2660
	21st to end	Day	5% 3 1 4 4 4 4 5% 7% 9% 52%	2660
July	1st to 10th	Day	12% 6% 2 6% 4 4 5% 5% 7% 9% 40%	4357
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 4 7% 9% 47%	4120
	21st to end	Day	8% 5% 2 7% 5% 6% 6% 5% 8% 11% 37%	4465
August	1st to 10th	Day	4 4 2 6% 4 5% 4 3 6% 10% 53%	4104
	11th to 20th	Day	10% 5% 3 6% 4 4 5% 4 6% 8% 45%	3892
	21st to end	Day	7% 4 2 5% 3 3 4 4 5% 9% 53%	4180
September	1st to 10th	Day	11% 5% 1 5% 5% 3 4 4 5% 8% 50%	2280
	11th to 20th	Day	10% 5% 2 6% 4 4 4 4 5% 6% 47%	2275
	21st to end	Day	8% 5% 2 6% 4 4 5% 4 6% 7% 51%	1982
October	1st to 10th	Day	11% 5% 2 5% 3 3 3 3 4 6% 56%	1900
	11th to 20th	Day	13% 6% 2 4 2 3 3 2 4 5% 54%	1900
	21st to end	Day	17% 8% 2 5% 3 3 3 3 4 5% 47%	2090
November	1st to 10th	Day	12% 5% 3 4 4 3 2 3 4 4 56%	1849
	11th to 20th	Day	14% 7% 2 6% 3 4 4 3 5% 6% 47%	1710
	21st to end	Day	15% 9% 3 5% 4 2 3 3 5% 6% 45%	1522
December	1st to 10th	Day	13% 11% 3 6% 4 3 4 3 5% 6% 42%	1520
	11th to 20th	Day	12% 11% 5% 8% 6% 3 3 3 3 6% 41%	1918
	21st to end	Day	14% 17% 5% 9% 5% 4 4 3 4 5% 30%	2783
January	1st to 10th	Night	11% 10% 5% 11% 6% 4 4 3 4 6% 37%	4158
	11th to 20th	Night	12% 8% 3 10% 7% 5% 7% 4 4 5% 35%	4120
	21st to end	Night	21% 13% 4 8% 3 3 3 2 3 5% 35%	4532
February	1st to 10th	Night	15% 10% 3 8% 4 3 3 3 5% 6% 39%	2470
	11th to 20th	Night	14% 9% 3 7% 4 3 3 3 5% 6% 43%	2350
	21st to end	Night	14% 10% 3 7% 4 5% 4 3 5% 5% 41%	1884
March	1st to 10th	Night	17% 11% 2 6% 3 3 2 2 4 5% 44%	3419
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 5% 6% 50%	3480
	21st to end	Night	14% 10% 4 8% 6% 5% 4 3 5% 5% 35%	3799
April	1st to 10th	Night	10% 6% 2 5% 3 3 4 3 5% 8% 50%	1900
	11th to 20th	Night	13% 8% 3 5% 3 3 3 3 4 8% 46%	1875
	21st to end	Night	18% 7% 3 7% 5% 4 3 3 5% 7% 39%	1900
May	1st to 10th	Night	15% 9% 2 5% 4 3 4 3 6% 8% 43%	2929
	11th to 20th	Night	13% 9% 3 6% 3 4 3 3 4 9% 43%	2806
	21st to end	Night	12% 6% 2 7% 4 4 4 4 5% 8% 41%	2743
June	1st to 10th	Night	8% 3 2 4 5% 3 5% 3 6% 9% 51%	1520
	11th to 20th	Night	5% 4 1 4 3 4 4 4 7% 10% 55%	1520
	21st to end	Night	3 2 1 3 2 3 3 4 6% 10% 62%	1520
July	1st to 10th	Night	11% 6% 3 5% 4 4 4 3 6% 7% 46%	2608
	11th to 20th	Night	5% 3 1 4 3 3 4 4 6% 10% 58%	2850
	21st to end	Night	6% 5% 1 5% 4 4 5% 4 7% 10% 50%	3098
August	1st to 10th	Night	4 3 1 4 3 3 3 3 5% 9% 62%	2836
	11th to 20th	Night	9% 4 2 5% 4 5% 4 4 5% 6% 50%	2942
	21st to end	Night	4 3 1 4 3 3 3 3 6% 9% 61%	3476
September	1st to 10th	Night	11% 5% 2 5% 3 3 3 3 4 6% 57%	1900
	11th to 20th	Night	10% 5% 2 5% 4 4 4 3 4 7% 53%	1900
	21st to end	Night	8% 5% 2 5% 3 3 3 3 4 7% 56%	2177
October	1st to 10th	Night	8% 3 1 3 3 3 3 3 4 8% 61%	2280
	11th to 20th	Night	14% 4 2 4 3 3 3 3 4 6% 54%	2280
	21st to end	Night	17% 7% 2 4 3 3 3 2 4 5% 50%	2508
November	1st to 10th	Night	11% 6% 1 4 3 2 3 2 4 6% 57%	2233
	11th to 20th	Night	13% 7% 2 5% 3 3 3 3 4 6% 50%	2470
	21st to end	Night	14% 10% 3 5% 3 4 3 3 4 5% 47%	2655
December	1st to 10th	Night	14% 10% 4 7% 4 4 4 3 5% 6% 40%	2660
	11th to 20th	Night	14% 11% 4 7% 4 3 3 3 4 5% 41%	3279
	21st to end	Night	17% 17% 6% 10% 5% 4 4 3 4 4 28%	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	45% 2 8% 28% 16% 1	2794
	11th to 20th	Day	47% 3 9% 26% 14% 2	2850
	21st to end	Day	51% 3 8% 17% 17% 4	3135
February	1st to 10th	Day	52% 2 10% 22% 12% 1	1710
	11th to 20th	Day	46% 3 11% 21% 16% 4	1725
	21st to end	Day	45% 3 8% 24% 14% 6%	1585
March	1st to 10th	Day	44% 3 7% 21% 17% 8%	3436
	11th to 20th	Day	35% 3 10% 30% 16% 7%	3480
	21st to end	Day	51% 4 15% 21% 9% 1	3831
April	1st to 10th	Day	39% 4 12% 24% 19% 2	2280
	11th to 20th	Day	46% 3 13% 21% 15% 3	2254
	21st to end	Day	50% 4 10% 23% 11% 2	2280
May	1st to 10th	Day	49% 6% 11% 20% 13% 1	3992
	11th to 20th	Day	43% 5% 14% 24% 14% 1	4086
	21st to end	Day	41% 6% 10% 26% 17% 1	4837
June	1st to 10th	Day	35% 6% 15% 27% 15% 2	2660
	11th to 20th	Day	31% 5% 14% 32% 16% 2	2660
	21st to end	Day	26% 6% 16% 31% 17% 5%	2660
July	1st to 10th	Day	40% 5% 14% 25% 13% 2	4290
	11th to 20th	Day	31% 5% 14% 32% 17% 2	4051
	21st to end	Day	38% 6% 20% 26% 9% 1	4325
August	1st to 10th	Day	27% 5% 18% 29% 21% 1	4090
	11th to 20th	Day	37% 4 14% 29% 15% 1	3931
	21st to end	Day	29% 4 13% 37% 13% 4	4179
September	1st to 10th	Day	33% 5% 12% 27% 16% 7%	2280
	11th to 20th	Day	36% 5% 8% 25% 25% 1	2275
	21st to end	Day	31% 5% 9% 27% 24% 4	1982
October	1st to 10th	Day	31% 3 9% 25% 27% 6%	1900
	11th to 20th	Day	34% 3 6% 28% 22% 7%	1900
	21st to end	Day	41% 2 7% 26% 18% 5%	2090
November	1st to 10th	Day	33% 3 10% 27% 23% 6%	1849
	11th to 20th	Day	38% 3 7% 24% 24% 5%	1710
	21st to end	Day	41% 3 8% 26% 20% 2	1522
December	1st to 10th	Day	43% 3 10% 29% 14% 2	1520
	11th to 20th	Day	46% 3 7% 21% 21% 2	1915
	21st to end	Day	58% 4 8% 18% 11% 2	2783
January	1st to 10th	Night	50% 3 10% 23% 14% 1	4158
	11th to 20th	Night	51% 4 9% 23% 11% 2	4120
	21st to end	Night	54% 2 9% 21% 13% 1	4532
February	1st to 10th	Night	47% 3 11% 23% 14% 2	2470
	11th to 20th	Night	43% 3 11% 23% 17% 3	2351
	21st to end	Night	46% 3 8% 21% 17% 5%	1884
March	1st to 10th	Night	45% 3 9% 20% 18% 5%	3419
	11th to 20th	Night	36% 3 11% 25% 21% 3	3480
	21st to end	Night	49% 4 13% 24% 9%	3799
April	1st to 10th	Night	32% 3 14% 26% 21% 4	1900
	11th to 20th	Night	37% 4 12% 25% 17% 5%	1875
	21st to end	Night	44% 5% 10% 26% 14% 1	1900
May	1st to 10th	Night	40% 5% 14% 24% 14% 3	2958
	11th to 20th	Night	41% 4 14% 27% 13% 2	2807
	21st to end	Night	40% 6% 12% 28% 13% 1	2751
June	1st to 10th	Night	30% 4 17% 27% 19% 3	1520
	11th to 20th	Night	22% 6% 14% 31% 22% 4	1520
	21st to end	Night	17% 5% 18% 35% 19% 7%	1520
July	1st to 10th	Night	37% 5% 12% 26% 17% 3	2566
	11th to 20th	Night	22% 5% 10% 41% 20% 2	2796
	21st to end	Night	29% 5% 19% 35% 11% 1	2999
August	1st to 10th	Night	21% 4 17% 33% 23% 1	2826
	11th to 20th	Night	34% 5% 15% 28% 16% 2	2969
	21st to end	Night	22% 4 15% 40% 16% 4	3476
September	1st to 10th	Night	30% 3 10% 28% 22% 7%	1900
	11th to 20th	Night	32% 3 9% 25% 27% 4	1900
	21st to end	Night	29% 4 9% 25% 30% 3	2177
October	1st to 10th	Night	24% 3 10% 28% 29% 6%	2280
	11th to 20th	Night	32% 3 7% 26% 25% 7%	2280
	21st to end	Night	38% 3 7% 24% 22% 5%	2508
November	1st to 10th	Night	31% 3 10% 27% 23% 7%	2233
	11th to 20th	Night	36% 3 6% 24% 25% 5%	2470
	21st to end	Night	41% 3 8% 25% 20% 3	2655
December	1st to 10th	Night	45% 3 10% 23% 17% 2	2660
	11th to 20th	Night	46% 2 9% 24% 18% 1	3281
	21st to end	Night	61% 3 9% 16% 8% 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	22% 21% 40% 16% 1	270
	11th to 20th	Day	32% 22% 37% 9% 1	270
	21st to end	Day	22% 25% 37% 14% 2	297
February	1st to 10th	Day	27% 21% 37% 12% 2	270
	11th to 20th	Day	30% 22% 33% 13% 3	270
	21st to end	Day	33% 21% 35% 9% 2	225
March	1st to 10th	Day	23% 19% 43% 13% 1	270
	11th to 20th	Day	33% 14% 34% 17% 1	270
	21st to end	Day	32% 21% 35% 11% 1	302
April	1st to 10th	Day	24% 15% 37% 19% 4 1	460
	11th to 20th	Day	28% 16% 33% 17% 5%	452
	21st to end	Day	27% 17% 32% 18% 5%	460
May	1st to 10th	Day	23% 14% 38% 19% 6%	577
	11th to 20th	Day	20% 10% 30% 24% 13% 2	675
	21st to end	Day	13% 9% 34% 24% 14% 4	734
June	1st to 10th	Day	10% 4 25% 32% 23% 6%	680
	11th to 20th	Day	8% 2 26% 41% 21% 3	680
	21st to end	Day	8% 6% 32% 36% 14% 4	680
July	1st to 10th	Day	15% 3 14% 32% 28% 8%	671
	11th to 20th	Day	6% 3 22% 39% 26% 5%	668
	21st to end	Day	10% 2 14% 36% 30% 8%	739
August	1st to 10th	Day	9% 3 18% 41% 25% 5%	676
	11th to 20th	Day	13% 4 17% 35% 25% 6%	581
	21st to end	Day	11% 2 10% 36% 31% 10%	539
September	1st to 10th	Day	12% 3 13% 36% 29% 6%	490
	11th to 20th	Day	9% 2 21% 34% 23% 10%	485
	21st to end	Day	10% 8% 25% 33% 19% 5%	300
October	1st to 10th	Day	15% 9% 28% 32% 14% 2	300
	11th to 20th	Day	18% 15% 38% 22% 7%	300
	21st to end	Day	30% 16% 32% 19% 3	330
November	1st to 10th	Day	16% 12% 40% 22% 9% 1	270
	11th to 20th	Day	23% 17% 34% 17% 7% 1	270
	21st to end	Day	29% 14% 32% 19% 5%	270
December	1st to 10th	Day	20% 20% 36% 16% 6% 2	270
	11th to 20th	Day	27% 16% 35% 18% 4 1	270
	21st to end	Day	25% 23% 37% 13% 3	297
January	1st to 10th	Night	19% 20% 37% 20% 4	950
	11th to 20th	Night	20% 24% 36% 16% 4	950
	21st to end	Night	21% 20% 37% 21% 1	1045
February	1st to 10th	Night	24% 19% 39% 16% 2	950
	11th to 20th	Night	22% 19% 40% 18% 2	876
	21st to end	Night	25% 22% 36% 14% 2	628
March	1st to 10th	Night	25% 12% 40% 21% 2	570
	11th to 20th	Night	24% 14% 35% 22% 4	570
	21st to end	Night	25% 14% 38% 19% 4	627
April	1st to 10th	Night	16% 17% 40% 24% 4	570
	11th to 20th	Night	20% 15% 36% 25% 6%	563
	21st to end	Night	22% 12% 38% 19% 8%	570
May	1st to 10th	Night	16% 7% 37% 33% 7% 1	570
	11th to 20th	Night	18% 6% 30% 32% 14% 1	561
	21st to end	Night	14% 8% 27% 29% 18% 3	617
June	1st to 10th	Night	11% 3 20% 38% 26% 2	570
	11th to 20th	Night	5% 1 27% 41% 24% 2	570
	21st to end	Night	3 2 29% 45% 20% 1	570
July	1st to 10th	Night	12% 1 14% 36% 31% 5%	555
	11th to 20th	Night	4 1 17% 45% 31% 3	552
	21st to end	Night	7% 1 13% 44% 32% 3	624
August	1st to 10th	Night	7% 1 15% 44% 31% 2	567
	11th to 20th	Night	9% 2 14% 44% 29% 2	564
	21st to end	Night	6% 1 13% 39% 37% 4	627
September	1st to 10th	Night	13% 2 13% 38% 31% 3	570
	11th to 20th	Night	14% 2 15% 36% 29% 4	570
	21st to end	Night	10% 5% 25% 36% 21% 3	657
October	1st to 10th	Night	10% 6% 26% 32% 22% 4	760
	11th to 20th	Night	16% 11% 36% 28% 9%	760
	21st to end	Night	24% 11% 33% 26% 6%	836
November	1st to 10th	Night	15% 13% 37% 25% 10%	743
	11th to 20th	Night	20% 13% 35% 24% 7% 1	760
	21st to end	Night	23% 15% 35% 21% 6%	945
December	1st to 10th	Night	21% 17% 36% 21% 4 1	950
	11th to 20th	Night	24% 14% 36% 22% 4	950
	21st to end	Night	24% 18% 36% 20% 2	1045

Page generated at 2024-10-29 10:20:46. Version ac07

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