Summer Village of Yellowstone
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Summer Village of Yellowstone clear sky chart from 2005-11-06 to 2025-07-21.

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	9% 9% 3 9% 6% 5% 5% 4 6% 8% 35%	124712
	Night	8% 10% 4 10% 6% 6% 5% 4 6% 8% 33%	123045
Transparency	Day	45% 8% 16% 22% 9% 1	124450
	Night	48% 7% 15% 20% 9% 1	122951
Seeing	Day	13% 7% 25% 30% 19% 6%	16945
	Night	13% 6% 29% 35% 16% 2	25301

By Month

Percentage Cloud Cover NW (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	5% 14% 5% 13% 7% 5% 5% 4 8% 9% 27%	3148
	11th to 20th	Day	4 10% 3 9% 8% 6% 5% 6% 7% 10% 31%	3159
	21st to end	Day	8% 13% 3 8% 6% 5% 5% 5% 6% 7% 35%	3820
February	1st to 10th	Day	9% 12% 5% 11% 8% 6% 6% 5% 9% 8% 21%	1600
	11th to 20th	Day	5% 13% 5% 11% 7% 6% 7% 4 6% 8% 28%	1662
	21st to end	Day	4 13% 5% 10% 9% 8% 6% 6% 8% 7% 25%	1570
March	1st to 10th	Day	5% 11% 4 10% 7% 7% 5% 4 6% 9% 31%	4518
	11th to 20th	Day	5% 13% 5% 9% 6% 4 5% 4 6% 8% 35%	4898
	21st to end	Day	9% 14% 6% 15% 6% 5% 5% 4 6% 7% 22%	5653
April	1st to 10th	Day	7% 13% 4 9% 6% 7% 6% 5% 7% 7% 30%	2473
	11th to 20th	Day	10% 10% 4 8% 7% 5% 6% 5% 7% 7% 31%	2570
	21st to end	Day	9% 11% 3 9% 7% 6% 5% 5% 6% 8% 31%	2616
May	1st to 10th	Day	11% 9% 3 8% 6% 5% 5% 4 5% 7% 37%	6632
	11th to 20th	Day	13% 10% 4 9% 6% 7% 6% 5% 7% 8% 27%	6734
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 4 6% 10% 38%	7405
June	1st to 10th	Day	16% 8% 3 7% 6% 5% 5% 5% 6% 7% 33%	3021
	11th to 20th	Day	18% 9% 3 8% 7% 6% 5% 5% 6% 7% 25%	3200
	21st to end	Day	9% 7% 2 7% 5% 5% 5% 5% 7% 8% 38%	3200
July	1st to 10th	Day	9% 5% 2 5% 4 5% 4 4 6% 8% 48%	5220
	11th to 20th	Day	8% 4 1 6% 5% 5% 4 4 7% 9% 47%	4890
	21st to end	Day	11% 5% 2 6% 4 4 4 4 6% 9% 44%	5139
August	1st to 10th	Day	12% 5% 2 5% 5% 4 4 4 7% 9% 42%	4470
	11th to 20th	Day	9% 6% 2 6% 4 4 4 5% 7% 10% 42%	4211
	21st to end	Day	11% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	4521
September	1st to 10th	Day	12% 7% 3 7% 4 4 4 3 6% 8% 42%	2390
	11th to 20th	Day	14% 7% 2 6% 5% 4 4 3 5% 9% 42%	2109
	21st to end	Day	9% 6% 3 9% 5% 5% 5% 4 7% 8% 41%	2090
October	1st to 10th	Day	9% 8% 3 9% 5% 4 4 4 6% 7% 40%	3317
	11th to 20th	Day	12% 11% 5% 8% 5% 4 4 4 6% 8% 33%	2842
	21st to end	Day	6% 12% 6% 9% 5% 5% 5% 4 5% 8% 34%	3101
November	1st to 10th	Day	11% 15% 5% 10% 6% 5% 4 4 6% 8% 25%	1563
	11th to 20th	Day	7% 13% 4 11% 6% 6% 5% 3 6% 7% 32%	1400
	21st to end	Day	6% 11% 6% 14% 8% 7% 6% 4 5% 7% 28%	1400
December	1st to 10th	Day	9% 15% 6% 13% 7% 7% 6% 4 5% 6% 22%	2290
	11th to 20th	Day	8% 13% 5% 12% 8% 7% 7% 4 5% 7% 24%	2642
	21st to end	Day	4 7% 3 9% 5% 5% 5% 4 6% 8% 42%	3238
January	1st to 10th	Night	4 11% 5% 16% 9% 7% 5% 4 5% 7% 26%	6770
	11th to 20th	Night	3 9% 4 11% 8% 6% 6% 5% 6% 7% 35%	6739
	21st to end	Night	7% 14% 5% 9% 5% 5% 5% 3 5% 7% 34%	7165
February	1st to 10th	Night	6% 12% 5% 14% 7% 7% 6% 4 6% 6% 26%	2800
	11th to 20th	Night	5% 12% 5% 13% 8% 7% 5% 5% 6% 7% 28%	2623
	21st to end	Night	6% 12% 4 10% 8% 6% 6% 6% 6% 8% 28%	2057
March	1st to 10th	Night	4 9% 4 12% 7% 6% 5% 5% 7% 9% 32%	5376
	11th to 20th	Night	5% 10% 4 10% 7% 6% 6% 5% 7% 10% 29%	5101
	21st to end	Night	11% 14% 6% 14% 6% 5% 5% 4 5% 7% 24%	5319
April	1st to 10th	Night	8% 11% 3 10% 8% 7% 7% 5% 6% 8% 29%	1926
	11th to 20th	Night	9% 11% 4 10% 7% 6% 6% 4 6% 8% 29%	1781
	21st to end	Night	12% 9% 4 8% 5% 5% 6% 4 7% 7% 33%	1781
May	1st to 10th	Night	15% 9% 3 8% 5% 4 4 4 5% 7% 36%	3328
	11th to 20th	Night	14% 10% 4 11% 7% 6% 6% 5% 6% 6% 26%	3159
	21st to end	Night	12% 8% 3 7% 5% 6% 5% 4 6% 7% 37%	3470
June	1st to 10th	Night	15% 10% 3 8% 6% 5% 5% 4 6% 7% 30%	1375
	11th to 20th	Night	15% 9% 3 10% 7% 6% 8% 6% 9% 8% 19%	1200
	21st to end	Night	11% 6% 3 8% 4 5% 6% 6% 7% 9% 34%	1200
July	1st to 10th	Night	10% 5% 2 7% 3 5% 4 3 6% 8% 46%	1960
	11th to 20th	Night	9% 6% 2 7% 5% 5% 5% 5% 7% 11% 37%	2287
	21st to end	Night	14% 5% 2 6% 5% 5% 4 3 7% 8% 41%	2414
August	1st to 10th	Night	12% 6% 3 7% 5% 5% 5% 5% 6% 7% 40%	2458
	11th to 20th	Night	14% 8% 3 7% 4 4 4 4 6% 10% 35%	2620
	21st to end	Night	13% 5% 2 6% 4 3 4 4 7% 9% 43%	3146
September	1st to 10th	Night	12% 6% 2 5% 4 4 4 4 6% 8% 43%	1787
	11th to 20th	Night	11% 9% 2 6% 4 4 4 3 6% 8% 43%	2071
	21st to end	Night	10% 8% 2 7% 4 4 5% 3 7% 7% 42%	2090
October	1st to 10th	Night	9% 7% 3 9% 5% 6% 5% 4 6% 8% 37%	3657
	11th to 20th	Night	10% 8% 3 8% 5% 5% 5% 4 7% 8% 38%	4086
	21st to end	Night	7% 10% 4 8% 5% 5% 5% 4 7% 9% 35%	4457
November	1st to 10th	Night	13% 16% 5% 10% 6% 5% 5% 4 5% 6% 26%	2714
	11th to 20th	Night	8% 14% 6% 12% 6% 6% 5% 4 5% 7% 28%	3000
	21st to end	Night	7% 13% 4 12% 8% 6% 6% 4 6% 7% 27%	3000
December	1st to 10th	Night	9% 16% 5% 12% 7% 6% 5% 4 5% 6% 25%	4890
	11th to 20th	Night	9% 15% 6% 13% 7% 6% 6% 4 6% 7% 21%	5550
	21st to end	Night	3 7% 4 10% 6% 6% 5% 4 6% 8% 42%	7688

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	51% 6% 14% 17% 10% 1	3148
	11th to 20th	Day	46% 5% 13% 13% 22% 1	3180
	21st to end	Day	46% 7% 22% 20% 5%	3820
February	1st to 10th	Day	56% 6% 15% 13% 9% 1	1600
	11th to 20th	Day	52% 8% 14% 17% 8%	1670
	21st to end	Day	54% 8% 12% 18% 8%	1570
March	1st to 10th	Day	48% 5% 16% 19% 11%	4518
	11th to 20th	Day	45% 7% 13% 25% 9%	4899
	21st to end	Day	58% 7% 9% 18% 8%	5653
April	1st to 10th	Day	48% 9% 15% 19% 8% 1	2473
	11th to 20th	Day	47% 8% 13% 21% 10%	2570
	21st to end	Day	49% 7% 13% 23% 7% 1	2616
May	1st to 10th	Day	45% 5% 8% 24% 16% 1	6632
	11th to 20th	Day	50% 8% 13% 23% 6%	6738
	21st to end	Day	39% 9% 19% 24% 8% 1	7406
June	1st to 10th	Day	48% 7% 15% 20% 8% 1	3021
	11th to 20th	Day	54% 10% 14% 16% 5%	3200
	21st to end	Day	40% 11% 19% 24% 5% 1	3200
July	1st to 10th	Day	32% 8% 15% 31% 13% 1	5141
	11th to 20th	Day	33% 8% 17% 29% 13%	4809
	21st to end	Day	36% 8% 22% 22% 12%	4977
August	1st to 10th	Day	37% 9% 19% 33% 2	4452
	11th to 20th	Day	34% 10% 21% 28% 7%	4253
	21st to end	Day	39% 9% 25% 23% 4	4520
September	1st to 10th	Day	39% 8% 18% 25% 7% 2	2390
	11th to 20th	Day	40% 8% 20% 26% 7%	2109
	21st to end	Day	39% 9% 16% 25% 8% 2	2090
October	1st to 10th	Day	41% 7% 24% 23% 5%	3317
	11th to 20th	Day	47% 6% 13% 26% 8%	2842
	21st to end	Day	47% 6% 17% 25% 4	3101
November	1st to 10th	Day	57% 7% 14% 15% 5% 1	1563
	11th to 20th	Day	51% 7% 16% 19% 7%	1400
	21st to end	Day	55% 8% 15% 17% 6% 1	1400
December	1st to 10th	Day	61% 6% 16% 10% 5% 1	2290
	11th to 20th	Day	58% 7% 16% 14% 5%	2644
	21st to end	Day	37% 6% 15% 28% 14% 1	3238
January	1st to 10th	Night	56% 5% 12% 16% 9% 1	6770
	11th to 20th	Night	47% 5% 14% 14% 19% 1	6780
	21st to end	Night	48% 7% 19% 18% 7%	7165
February	1st to 10th	Night	56% 6% 12% 16% 9% 1	2800
	11th to 20th	Night	53% 8% 13% 15% 11% 1	2625
	21st to end	Night	51% 7% 11% 20% 10% 1	2057
March	1st to 10th	Night	46% 6% 18% 20% 10%	5376
	11th to 20th	Night	47% 7% 15% 19% 10%	5101
	21st to end	Night	58% 8% 9% 18% 8%	5319
April	1st to 10th	Night	50% 7% 13% 18% 10% 1	1926
	11th to 20th	Night	52% 6% 11% 19% 11% 2	1781
	21st to end	Night	46% 8% 11% 23% 11% 1	1781
May	1st to 10th	Night	47% 5% 8% 19% 18% 3	3325
	11th to 20th	Night	54% 9% 11% 19% 6% 1	3159
	21st to end	Night	42% 10% 17% 21% 10% 1	3470
June	1st to 10th	Night	51% 7% 13% 19% 10% 1	1375
	11th to 20th	Night	56% 13% 14% 14% 4	1200
	21st to end	Night	42% 12% 19% 22% 5%	1200
July	1st to 10th	Night	35% 8% 17% 25% 15%	1930
	11th to 20th	Night	39% 10% 16% 27% 9%	2246
	21st to end	Night	39% 8% 18% 26% 9%	2337
August	1st to 10th	Night	41% 10% 18% 30% 1	2451
	11th to 20th	Night	43% 8% 18% 21% 9%	2644
	21st to end	Night	35% 8% 24% 27% 5%	3146
September	1st to 10th	Night	36% 9% 16% 28% 9% 2	1787
	11th to 20th	Night	38% 6% 16% 29% 9% 1	2071
	21st to end	Night	38% 9% 14% 25% 13% 2	2090
October	1st to 10th	Night	43% 7% 20% 24% 6%	3657
	11th to 20th	Night	41% 7% 14% 31% 7%	4086
	21st to end	Night	43% 7% 21% 22% 5%	4457
November	1st to 10th	Night	58% 6% 10% 19% 6%	2714
	11th to 20th	Night	56% 7% 12% 17% 7% 1	3000
	21st to end	Night	54% 8% 15% 17% 5% 1	3000
December	1st to 10th	Night	60% 6% 14% 14% 6% 1	4890
	11th to 20th	Night	61% 7% 15% 13% 5%	5547
	21st to end	Night	40% 6% 13% 26% 14% 2	7688

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	13% 4 31% 29% 18% 7%	200
	11th to 20th	Day	11% 10% 29% 31% 16% 5%	200
	21st to end	Day	13% 12% 28% 28% 15% 5%	220
February	1st to 10th	Day	15% 9% 30% 32% 14% 3	200
	11th to 20th	Day	14% 5% 31% 32% 14% 4	253
	21st to end	Day	6% 10% 35% 28% 17% 5%	334
March	1st to 10th	Day	12% 7% 30% 32% 16% 3	500
	11th to 20th	Day	10% 6% 28% 34% 17% 5%	500
	21st to end	Day	14% 7% 31% 25% 20% 3	550
April	1st to 10th	Day	9% 12% 32% 32% 11% 4	500
	11th to 20th	Day	12% 9% 25% 31% 16% 6%	492
	21st to end	Day	13% 9% 28% 30% 15% 5%	500
May	1st to 10th	Day	15% 10% 25% 30% 17% 3	633
	11th to 20th	Day	12% 6% 23% 34% 19% 5%	725
	21st to end	Day	16% 5% 22% 30% 20% 7%	789
June	1st to 10th	Day	18% 10% 25% 30% 14% 4	751
	11th to 20th	Day	20% 5% 21% 27% 20% 7%	930
	21st to end	Day	12% 5% 19% 31% 25% 9%	930
July	1st to 10th	Day	12% 3 20% 34% 24% 8%	916
	11th to 20th	Day	12% 4 20% 32% 25% 7%	718
	21st to end	Day	12% 4 14% 32% 26% 11%	740
August	1st to 10th	Day	10% 5% 16% 31% 22% 15%	530
	11th to 20th	Day	8% 4 25% 32% 23% 8%	477
	21st to end	Day	16% 5% 18% 30% 23% 7%	539
September	1st to 10th	Day	15% 9% 26% 23% 21% 6%	490
	11th to 20th	Day	17% 6% 24% 30% 19% 6%	490
	21st to end	Day	12% 11% 31% 29% 13% 4	490
October	1st to 10th	Day	15% 8% 25% 30% 18% 4	403
	11th to 20th	Day	15% 9% 29% 27% 15% 4	300
	21st to end	Day	15% 10% 36% 26% 10% 2	330
November	1st to 10th	Day	19% 6% 33% 28% 12% 3	295
	11th to 20th	Day	11% 6% 39% 30% 12% 3	200
	21st to end	Day	9% 7% 35% 32% 14% 5%	200
December	1st to 10th	Day	9% 10% 31% 34% 12% 6%	200
	11th to 20th	Day	9% 11% 30% 35% 14% 2	200
	21st to end	Day	6% 4 23% 35% 27% 4	220
January	1st to 10th	Night	11% 6% 35% 33% 13% 2	1001
	11th to 20th	Night	11% 8% 34% 33% 13% 2	1000
	21st to end	Night	13% 10% 36% 28% 11% 2	976
February	1st to 10th	Night	11% 7% 28% 35% 18% 3	800
	11th to 20th	Night	10% 4 34% 35% 16% 2	784
	21st to end	Night	10% 5% 30% 34% 17% 4	660
March	1st to 10th	Night	10% 5% 32% 35% 17% 2	800
	11th to 20th	Night	11% 4 30% 38% 14% 2	800
	21st to end	Night	15% 5% 26% 38% 15% 3	880
April	1st to 10th	Night	11% 7% 28% 37% 16% 2	726
	11th to 20th	Night	13% 6% 29% 34% 16% 1	593
	21st to end	Night	15% 6% 27% 37% 14% 1	581
May	1st to 10th	Night	15% 6% 26% 38% 14% 2	400
	11th to 20th	Night	14% 3 29% 34% 20% 2	394
	21st to end	Night	19% 6% 23% 34% 17% 1	433
June	1st to 10th	Night	19% 6% 25% 36% 13% 2	400
	11th to 20th	Night	19% 4 21% 33% 20% 3	400
	21st to end	Night	14% 3 18% 36% 25% 4	400
July	1st to 10th	Night	15% 3 15% 43% 24% 1	390
	11th to 20th	Night	13% 5% 19% 37% 24% 2	388
	21st to end	Night	12% 3 17% 40% 25% 3	416
August	1st to 10th	Night	10% 4 18% 32% 31% 5%	378
	11th to 20th	Night	13% 4 17% 38% 25% 3	447
	21st to end	Night	13% 3 23% 37% 22% 1	627
September	1st to 10th	Night	15% 3 17% 40% 22% 2	647
	11th to 20th	Night	16% 4 19% 39% 21% 2	760
	21st to end	Night	14% 5% 30% 34% 15% 2	760
October	1st to 10th	Night	16% 4 27% 35% 16% 1	760
	11th to 20th	Night	14% 4 31% 36% 13% 1	760
	21st to end	Night	12% 9% 33% 33% 12% 1	836
November	1st to 10th	Night	21% 5% 31% 31% 10% 2	954
	11th to 20th	Night	13% 8% 37% 30% 10% 3	1000
	21st to end	Night	12% 6% 36% 33% 11% 2	1000
December	1st to 10th	Night	14% 7% 34% 30% 13% 2	1000
	11th to 20th	Night	13% 7% 31% 34% 14% 1	1000
	21st to end	Night	11% 4 30% 37% 15% 3	1150

Page generated at 2025-07-17 23:10:01. Version ac07

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