Rattan Creek
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rattan Creek clear sky chart from 2005-11-06 to 2025-01-22.

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% 6% 2 5% 4 4 4 4 5% 7% 47%	105281
	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	104225
Transparency	Day	35% 5% 10% 21% 20% 9%	109076
	Night	33% 5% 10% 20% 20% 11%	108557
Seeing	Day	14% 7% 20% 29% 24% 7%	15111
	Night	16% 7% 24% 36% 16% 1	25143

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% 9% 2 5% 3 3 3 2 4 6% 50%	2937
	11th to 20th	Day	17% 5% 1 3 2 2 2 2 4 6% 56%	2940
	21st to end	Day	19% 8% 3 6% 4 2 3 2 3 6% 44%	3281
February	1st to 10th	Day	20% 7% 3 5% 3 4 3 2 4 5% 45%	1900
	11th to 20th	Day	17% 9% 2 4 3 3 3 3 4 5% 46%	1849
	21st to end	Day	18% 7% 2 5% 3 3 3 3 4 4 49%	1570
March	1st to 10th	Day	15% 8% 3 7% 4 4 4 3 5% 6% 42%	3430
	11th to 20th	Day	19% 11% 3 8% 5% 4 5% 4 5% 5% 32%	3480
	21st to end	Day	14% 9% 2 6% 4 3 4 3 5% 6% 44%	3814
April	1st to 10th	Day	15% 7% 2 7% 5% 3 4 4 5% 6% 41%	2090
	11th to 20th	Day	16% 8% 3 6% 4 4 3 4 4 6% 42%	2066
	21st to end	Day	15% 7% 2 5% 4 4 4 4 5% 6% 45%	2423
May	1st to 10th	Day	23% 9% 3 7% 5% 4 4 4 5% 7% 30%	4082
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 5% 6% 43%	4082
	21st to end	Day	11% 6% 3 7% 5% 6% 6% 5% 8% 10% 33%	4477
June	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 5% 6% 8% 50%	2470
	11th to 20th	Day	7% 4 1 5% 4 4 5% 6% 7% 9% 47%	2470
	21st to end	Day	7% 6% 2 5% 5% 5% 6% 5% 9% 10% 41%	2470
July	1st to 10th	Day	6% 4 2 5% 5% 5% 5% 4 6% 9% 50%	4120
	11th to 20th	Day	4 3 1 4 4 4 5% 4 7% 12% 51%	4120
	21st to end	Day	10% 6% 2 6% 4 5% 5% 5% 7% 10% 38%	4465
August	1st to 10th	Day	1 2 1 2 2 2 3 3 5% 7% 72%	4104
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 11% 60%	3824
	21st to end	Day	4 2 1 5% 4 4 6% 5% 8% 11% 49%	3967
September	1st to 10th	Day	9% 5% 2 6% 5% 4 5% 3 7% 8% 45%	2090
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 4 6% 7% 43%	2090
	21st to end	Day	7% 4 2 5% 3 5% 5% 4 5% 7% 53%	2090
October	1st to 10th	Day	6% 4 1 5% 3 3 3 3 5% 7% 59%	2090
	11th to 20th	Day	12% 5% 2 5% 3 3 4 2 4 6% 55%	1933
	21st to end	Day	12% 4 2 4 4 3 3 2 3 5% 59%	2090
November	1st to 10th	Day	14% 7% 3 5% 4 3 4 2 5% 7% 47%	1958
	11th to 20th	Day	10% 6% 2 6% 4 3 3 3 4 6% 52%	1890
	21st to end	Day	16% 7% 2 5% 4 3 3 3 4 5% 47%	1800
December	1st to 10th	Day	22% 8% 2 6% 4 3 3 2 4 4 41%	2940
	11th to 20th	Day	18% 8% 2 5% 3 3 4 3 5% 5% 44%	3391
	21st to end	Day	15% 5% 1 4 2 2 2 2 3 4 57%	4488
January	1st to 10th	Night	19% 7% 2 3 2 1 2 2 3 5% 53%	4238
	11th to 20th	Night	14% 4 1 3 1 2 2 2 2 4 65%	4250
	21st to end	Night	20% 7% 3 7% 3 3 2 3 4 5% 43%	4436
February	1st to 10th	Night	19% 7% 3 4 3 3 3 2 3 5% 48%	2280
	11th to 20th	Night	19% 7% 2 4 3 2 3 2 3 5% 49%	2218
	21st to end	Night	20% 6% 2 5% 3 2 3 3 4 5% 47%	1884
March	1st to 10th	Night	18% 8% 2 6% 4 4 4 4 4 5% 41%	3424
	11th to 20th	Night	22% 10% 3 6% 4 4 4 3 5% 5% 33%	3480
	21st to end	Night	16% 7% 3 7% 4 4 3 3 4 6% 42%	3817
April	1st to 10th	Night	14% 6% 2 5% 3 4 4 3 5% 7% 46%	2090
	11th to 20th	Night	18% 7% 2 5% 4 3 4 3 4 6% 44%	2063
	21st to end	Night	15% 8% 3 4 4 2 3 3 4 6% 48%	1748
May	1st to 10th	Night	26% 9% 2 5% 3 3 3 3 4 6% 35%	2823
	11th to 20th	Night	12% 5% 2 6% 4 3 3 3 5% 7% 49%	2823
	21st to end	Night	13% 7% 2 6% 3 4 4 4 6% 9% 42%	3090
June	1st to 10th	Night	5% 4 1 3 3 4 3 4 5% 11% 59%	1710
	11th to 20th	Night	5% 3 1 3 3 3 5% 3 6% 10% 56%	1710
	21st to end	Night	7% 4 1 4 4 4 4 3 6% 10% 53%	1710
July	1st to 10th	Night	5% 3 1 4 4 3 4 4 6% 10% 55%	2850
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 10% 57%	2850
	21st to end	Night	9% 7% 3 6% 4 4 5% 4 7% 9% 42%	3098
August	1st to 10th	Night	1 1 1 1 2 2 2 5% 8% 76%	2836
	11th to 20th	Night	4 2 1 3 2 3 3 4 6% 11% 61%	3010
	21st to end	Night	4 3 1 4 3 3 4 4 7% 10% 56%	3690
September	1st to 10th	Night	8% 5% 2 4 4 4 5% 4 5% 8% 51%	2090
	11th to 20th	Night	9% 7% 2 6% 5% 4 4 3 6% 7% 46%	2090
	21st to end	Night	8% 4 1 3 4 3 5% 3 5% 8% 55%	2090
October	1st to 10th	Night	6% 3 1 3 3 3 4 3 4 6% 64%	2090
	11th to 20th	Night	12% 5% 1 4 3 3 3 2 5% 5% 56%	2228
	21st to end	Night	14% 5% 2 3 3 3 3 2 3 4 60%	2508
November	1st to 10th	Night	14% 7% 2 5% 3 3 3 3 3 6% 52%	2340
	11th to 20th	Night	10% 5% 2 4 4 3 3 2 5% 6% 57%	2505
	21st to end	Night	18% 6% 2 5% 3 3 4 3 4 6% 48%	2600
December	1st to 10th	Night	20% 8% 2 6% 4 3 3 3 4 5% 42%	4250
	11th to 20th	Night	20% 10% 2 5% 2 2 3 2 3 4 47%	4816
	21st to end	Night	18% 6% 2 4 2 2 2 2 3 4 56%	6490

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	36% 3 5% 19% 24% 13%	2938
	11th to 20th	Day	32% 2 7% 16% 30% 14%	2940
	21st to end	Day	42% 4 4 11% 27% 12%	3281
February	1st to 10th	Day	43% 4 5% 13% 21% 14%	1900
	11th to 20th	Day	41% 3 7% 18% 19% 12%	1859
	21st to end	Day	41% 3 5% 19% 18% 15%	1570
March	1st to 10th	Day	43% 4 8% 14% 21% 10%	3430
	11th to 20th	Day	53% 5% 8% 10% 16% 8%	3480
	21st to end	Day	39% 5% 10% 15% 23% 8%	3814
April	1st to 10th	Day	43% 5% 7% 18% 15% 13%	2090
	11th to 20th	Day	43% 4 7% 16% 18% 11%	2066
	21st to end	Day	40% 4 6% 20% 21% 9%	2423
May	1st to 10th	Day	52% 6% 10% 15% 13% 5%	4120
	11th to 20th	Day	40% 6% 9% 17% 23% 5%	4086
	21st to end	Day	40% 8% 13% 26% 10% 2	4489
June	1st to 10th	Day	30% 6% 13% 28% 19% 4	2470
	11th to 20th	Day	30% 7% 13% 26% 18% 5%	2470
	21st to end	Day	35% 8% 12% 24% 18% 2	2470
July	1st to 10th	Day	29% 7% 17% 39% 7% 1	4056
	11th to 20th	Day	25% 7% 17% 33% 18% 2	4051
	21st to end	Day	37% 8% 18% 28% 9% 1	4325
August	1st to 10th	Day	12% 4 12% 39% 32% 1	4090
	11th to 20th	Day	19% 5% 22% 39% 13% 3	3863
	21st to end	Day	25% 10% 19% 26% 18% 2	3966
September	1st to 10th	Day	36% 7% 10% 22% 15% 10%	2090
	11th to 20th	Day	38% 8% 11% 19% 18% 6%	2090
	21st to end	Day	29% 6% 10% 22% 19% 14%	2090
October	1st to 10th	Day	16% 2 7% 13% 24% 38%	3480
	11th to 20th	Day	21% 3 8% 19% 30% 20%	3186
	21st to end	Day	26% 2 5% 20% 33% 14%	3428
November	1st to 10th	Day	37% 5% 8% 18% 20% 11%	1958
	11th to 20th	Day	35% 3 7% 18% 21% 16%	1890
	21st to end	Day	40% 3 6% 17% 20% 13%	1800
December	1st to 10th	Day	47% 2 6% 17% 18% 9%	2940
	11th to 20th	Day	42% 4 7% 12% 23% 13%	3389
	21st to end	Day	33% 2 4 17% 29% 15%	4488
January	1st to 10th	Night	35% 3 5% 17% 24% 17%	4238
	11th to 20th	Night	27% 2 4 16% 32% 19%	4250
	21st to end	Night	44% 3 5% 13% 25% 11%	4436
February	1st to 10th	Night	40% 3 6% 13% 20% 17%	2280
	11th to 20th	Night	39% 3 6% 17% 20% 15%	2218
	21st to end	Night	41% 4 5% 15% 18% 17%	1884
March	1st to 10th	Night	44% 6% 8% 15% 18% 10%	3424
	11th to 20th	Night	53% 5% 9% 11% 14% 8%	3480
	21st to end	Night	42% 5% 9% 15% 20% 8%	3817
April	1st to 10th	Night	37% 6% 8% 18% 17% 14%	2090
	11th to 20th	Night	41% 5% 9% 14% 16% 15%	2063
	21st to end	Night	39% 4 9% 20% 19% 9%	1748
May	1st to 10th	Night	49% 6% 8% 18% 14% 5%	2850
	11th to 20th	Night	34% 6% 11% 25% 17% 8%	2824
	21st to end	Night	38% 6% 14% 29% 10% 3	3099
June	1st to 10th	Night	21% 6% 17% 29% 24% 3	1710
	11th to 20th	Night	23% 6% 15% 30% 20% 6%	1710
	21st to end	Night	27% 7% 16% 29% 17% 3	1710
July	1st to 10th	Night	23% 8% 25% 36% 7% 1	2805
	11th to 20th	Night	21% 7% 19% 36% 16% 1	2796
	21st to end	Night	37% 7% 22% 27% 7%	2999
August	1st to 10th	Night	8% 4 14% 44% 29% 1	2826
	11th to 20th	Night	18% 5% 29% 33% 12% 2	3037
	21st to end	Night	22% 11% 21% 28% 17% 2	3690
September	1st to 10th	Night	30% 7% 14% 25% 16% 8%	2090
	11th to 20th	Night	36% 7% 14% 22% 15% 6%	2090
	21st to end	Night	27% 5% 14% 22% 18% 13%	2090
October	1st to 10th	Night	16% 3 6% 15% 19% 40%	3480
	11th to 20th	Night	20% 3 8% 17% 32% 21%	3701
	21st to end	Night	25% 3 5% 20% 31% 17%	4120
November	1st to 10th	Night	35% 4 8% 18% 22% 13%	2340
	11th to 20th	Night	30% 4 7% 21% 21% 17%	2505
	21st to end	Night	39% 4 7% 17% 18% 15%	2600
December	1st to 10th	Night	46% 3 6% 17% 18% 10%	4250
	11th to 20th	Night	43% 3 6% 9% 23% 16%	4817
	21st to end	Night	35% 3 3 15% 28% 16%	6490

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	19% 14% 37% 22% 7% 1	300
	11th to 20th	Day	23% 13% 32% 25% 6% 1	300
	21st to end	Day	22% 13% 33% 22% 9% 1	300
February	1st to 10th	Day	26% 15% 32% 19% 9%	270
	11th to 20th	Day	23% 14% 37% 21% 4 1	270
	21st to end	Day	30% 11% 40% 18% 2	225
March	1st to 10th	Day	20% 15% 39% 20% 6%	270
	11th to 20th	Day	21% 15% 37% 20% 6% 1	270
	21st to end	Day	21% 11% 39% 22% 6% 1	297
April	1st to 10th	Day	23% 15% 37% 19% 4 1	270
	11th to 20th	Day	19% 17% 30% 24% 9%	264
	21st to end	Day	20% 12% 35% 24% 9% 1	603
May	1st to 10th	Day	18% 9% 35% 29% 8%	653
	11th to 20th	Day	20% 5% 23% 35% 13% 3	675
	21st to end	Day	18% 5% 24% 34% 17% 3	734
June	1st to 10th	Day	7% 3 13% 41% 29% 7%	680
	11th to 20th	Day	9% 1 15% 46% 24% 5%	680
	21st to end	Day	8% 2 10% 34% 35% 11%	680
July	1st to 10th	Day	7% 3 7% 35% 37% 11%	671
	11th to 20th	Day	4 5% 33% 48% 9%	668
	21st to end	Day	5% 1 4 32% 47% 11%	739
August	1st to 10th	Day	2 2 2 29% 50% 15%	676
	11th to 20th	Day	5% 1 2 31% 47% 14%	539
	21st to end	Day	7% 1 5% 23% 37% 27%	417
September	1st to 10th	Day	8% 2 4 21% 41% 23%	300
	11th to 20th	Day	8% 2 4 28% 38% 20%	300
	21st to end	Day	9% 2 6% 28% 34% 21%	300
October	1st to 10th	Day	5% 3 11% 31% 38% 12%	300
	11th to 20th	Day	11% 3 23% 35% 22% 6%	300
	21st to end	Day	19% 10% 22% 26% 18% 4	330
November	1st to 10th	Day	20% 7% 21% 34% 14% 4	300
	11th to 20th	Day	18% 8% 29% 26% 16% 3	300
	21st to end	Day	20% 15% 31% 21% 11% 2	300
December	1st to 10th	Day	18% 7% 34% 27% 11% 4	300
	11th to 20th	Day	21% 12% 33% 24% 10%	300
	21st to end	Day	19% 12% 33% 26% 9% 2	330
January	1st to 10th	Night	21% 9% 30% 32% 8% 1	1000
	11th to 20th	Night	21% 11% 30% 32% 7%	1000
	21st to end	Night	21% 10% 30% 32% 7%	980
February	1st to 10th	Night	24% 13% 29% 28% 6%	760
	11th to 20th	Night	25% 11% 36% 26% 3	744
	21st to end	Night	26% 12% 39% 20% 2	628
March	1st to 10th	Night	23% 11% 36% 27% 4	575
	11th to 20th	Night	22% 10% 31% 32% 5%	570
	21st to end	Night	17% 11% 41% 27% 4	627
April	1st to 10th	Night	16% 10% 39% 32% 2	570
	11th to 20th	Night	22% 9% 38% 26% 4	563
	21st to end	Night	19% 8% 40% 25% 7%	570
May	1st to 10th	Night	18% 9% 36% 31% 6%	570
	11th to 20th	Night	15% 4 31% 37% 13% 1	561
	21st to end	Night	14% 6% 30% 36% 14%	617
June	1st to 10th	Night	6% 3 18% 48% 23% 2	570
	11th to 20th	Night	6% 2 28% 48% 15% 1	570
	21st to end	Night	8% 2 14% 46% 28% 3	570
July	1st to 10th	Night	8% 2 10% 47% 29% 5%	555
	11th to 20th	Night	4 1 8% 54% 32% 2	552
	21st to end	Night	6% 1 7% 49% 34% 3	624
August	1st to 10th	Night	1 6% 54% 35% 4	567
	11th to 20th	Night	6% 1 5% 50% 32% 5%	564
	21st to end	Night	6% 1 4 43% 41% 5%	627
September	1st to 10th	Night	10% 2 6% 41% 36% 6%	570
	11th to 20th	Night	12% 1 5% 39% 38% 4	570
	21st to end	Night	11% 1 10% 37% 37% 4	570
October	1st to 10th	Night	7% 1 11% 47% 29% 5%	570
	11th to 20th	Night	13% 4 21% 39% 21% 2	708
	21st to end	Night	17% 7% 24% 30% 21% 2	836
November	1st to 10th	Night	16% 5% 19% 40% 19% 1	780
	11th to 20th	Night	14% 7% 25% 37% 16% 1	905
	21st to end	Night	20% 9% 28% 30% 12% 1	1000
December	1st to 10th	Night	20% 8% 29% 33% 10% 1	1000
	11th to 20th	Night	24% 9% 27% 33% 7%	1000
	21st to end	Night	21% 9% 27% 35% 8%	1100

Page generated at 2025-01-19 02:06:43. Version ac07

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