Prineville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prineville clear sky chart from 2005-11-06 to 2026-09-29.

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	7% 7% 2 5% 4 4 4 3 5% 6% 53%	158590
	Night	8% 8% 3 6% 4 4 4 3 5% 6% 48%	150204
Transparency	Day	34% 3 8% 23% 22% 11%	153387
	Night	38% 3 11% 24% 18% 7%	146405
Seeing	Day	13% 10% 24% 27% 18% 7%	17034
	Night	14% 6% 17% 40% 21% 2	26026

By Month

Percentage Cloud Cover SW (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	14% 17% 4 10% 6% 6% 6% 4 6% 7% 20%	4722
	11th to 20th	Day	11% 10% 3 5% 3 3 3 3 3 4 51%	4740
	21st to end	Day	9% 9% 3 8% 5% 5% 5% 4 7% 8% 38%	5501
February	1st to 10th	Day	11% 14% 3 9% 6% 5% 4 4 6% 8% 30%	1890
	11th to 20th	Day	11% 14% 3 11% 5% 4 4 4 6% 7% 31%	1873
	21st to end	Day	10% 15% 4 9% 5% 5% 5% 5% 6% 7% 27%	1730
March	1st to 10th	Day	9% 13% 5% 9% 5% 5% 6% 4 5% 9% 31%	4618
	11th to 20th	Day	9% 16% 4 8% 5% 5% 4 3 4 6% 36%	5099
	21st to end	Day	10% 13% 4 10% 6% 6% 6% 4 6% 7% 27%	5908
April	1st to 10th	Day	10% 15% 4 9% 7% 4 5% 4 5% 7% 29%	2520
	11th to 20th	Day	9% 13% 4 7% 6% 4 4 3 5% 7% 38%	2489
	21st to end	Day	8% 10% 3 7% 5% 4 4 4 6% 7% 43%	2583
May	1st to 10th	Day	9% 6% 2 4 3 3 4 3 5% 7% 55%	8195
	11th to 20th	Day	6% 5% 2 5% 4 4 4 3 5% 7% 54%	8160
	21st to end	Day	7% 6% 2 4 4 4 4 4 6% 7% 52%	8992
June	1st to 10th	Day	11% 8% 2 6% 5% 4 4 4 5% 6% 45%	2940
	11th to 20th	Day	8% 5% 2 5% 4 3 4 3 5% 7% 53%	2940
	21st to end	Day	4 4 1 3 4 3 3 3 5% 5% 66%	2940
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 80%	8219
	11th to 20th	Day	2 2 1 2 2 2 2 2 3 4 78%	8220
	21st to end	Day	2 1 1 2 1 2 2 2 3 4 79%	8922
August	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 76%	7839
	11th to 20th	Day	3 1 1 2 2 2 2 2 4 6% 75%	7454
	21st to end	Day	4 3 1 3 2 3 3 3 4 6% 67%	7750
September	1st to 10th	Day	3 2 1 2 2 2 3 2 4 6% 73%	2520
	11th to 20th	Day	5% 4 1 5% 3 4 3 3 5% 7% 60%	2520
	21st to end	Day	7% 5% 2 4 3 4 3 3 5% 5% 59%	2241
October	1st to 10th	Day	6% 4 1 4 3 2 3 3 3 6% 63%	3280
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 4 7% 8% 48%	3261
	21st to end	Day	12% 9% 3 8% 5% 5% 5% 5% 5% 6% 37%	3363
November	1st to 10th	Day	14% 11% 4 9% 6% 4 5% 4 5% 7% 32%	1854
	11th to 20th	Day	15% 10% 3 8% 7% 6% 6% 5% 7% 7% 27%	1727
	21st to end	Day	12% 12% 2 9% 4 4 4 4 6% 8% 34%	1680
December	1st to 10th	Day	10% 8% 3 5% 3 3 4 3 5% 7% 50%	2700
	11th to 20th	Day	15% 12% 4 9% 7% 6% 5% 5% 6% 7% 23%	3108
	21st to end	Day	13% 14% 4 11% 7% 6% 6% 4 5% 7% 23%	4092
January	1st to 10th	Night	15% 15% 5% 11% 6% 5% 5% 4 6% 7% 20%	8172
	11th to 20th	Night	11% 10% 2 5% 3 3 3 3 4 5% 50%	8220
	21st to end	Night	9% 10% 3 8% 6% 6% 5% 4 5% 7% 37%	8694
February	1st to 10th	Night	12% 13% 4 10% 6% 5% 5% 4 6% 7% 29%	2730
	11th to 20th	Night	10% 14% 4 8% 4 4 5% 4 5% 7% 34%	2633
	21st to end	Night	10% 15% 4 9% 6% 5% 5% 4 5% 7% 28%	2076
March	1st to 10th	Night	7% 12% 4 7% 5% 5% 5% 5% 7% 8% 35%	5496
	11th to 20th	Night	9% 11% 3 8% 5% 4 5% 3 6% 7% 40%	5118
	21st to end	Night	9% 14% 4 9% 7% 6% 6% 5% 6% 7% 26%	5308
April	1st to 10th	Night	10% 13% 3 8% 5% 4 4 4 6% 7% 34%	2100
	11th to 20th	Night	11% 12% 3 7% 5% 5% 4 4 5% 7% 38%	2079
	21st to end	Night	9% 10% 2 7% 4 4 4 4 7% 8% 41%	2035
May	1st to 10th	Night	6% 6% 2 5% 3 3 3 3 5% 8% 56%	4723
	11th to 20th	Night	7% 8% 2 5% 3 3 4 3 4 7% 53%	4700
	21st to end	Night	9% 6% 2 4 3 3 3 3 5% 7% 57%	5181
June	1st to 10th	Night	12% 6% 2 4 4 4 5% 3 5% 6% 50%	1680
	11th to 20th	Night	7% 5% 2 6% 4 3 3 3 4 8% 56%	1680
	21st to end	Night	5% 4 1 3 3 2 3 3 4 5% 68%	1680
July	1st to 10th	Night	1 1 2 2 2 3 2 3 4 80%	4740
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 3 78%	4740
	21st to end	Night	2 2 1 2 2 2 2 2 3 4 77%	5153
August	1st to 10th	Night	3 2 1 4 2 2 3 2 4 5% 72%	4952
	11th to 20th	Night	1 1 1 3 2 2 3 2 4 6% 76%	5406
	21st to end	Night	3 3 2 4 2 2 3 2 4 5% 71%	6499
September	1st to 10th	Night	3 2 1 3 2 2 3 2 3 5% 74%	2100
	11th to 20th	Night	5% 4 2 4 3 3 4 3 4 7% 61%	2100
	21st to end	Night	6% 5% 2 4 3 4 4 3 5% 6% 60%	2333
October	1st to 10th	Night	6% 4 1 4 2 2 2 2 3 4 68%	3920
	11th to 20th	Night	10% 5% 2 5% 3 3 4 3 5% 7% 52%	3897
	21st to end	Night	9% 8% 2 7% 5% 5% 5% 4 6% 7% 40%	4441
November	1st to 10th	Night	15% 11% 3 8% 5% 4 5% 4 5% 6% 33%	2665
	11th to 20th	Night	17% 11% 4 8% 6% 5% 6% 4 5% 6% 29%	2891
	21st to end	Night	12% 11% 3 6% 4 4 5% 4 6% 7% 39%	2940
December	1st to 10th	Night	8% 7% 2 5% 4 3 3 3 5% 7% 53%	4700
	11th to 20th	Night	15% 15% 4 11% 7% 5% 6% 5% 6% 7% 21%	5316
	21st to end	Night	16% 13% 4 9% 6% 5% 5% 4 5% 6% 27%	7106

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	64% 4 12% 15% 4	4723
	11th to 20th	Day	39% 2 8% 22% 23% 6%	4740
	21st to end	Day	46% 2 9% 16% 23% 4	5501
February	1st to 10th	Day	51% 6% 14% 20% 8% 1	1890
	11th to 20th	Day	52% 6% 13% 19% 9% 2	1882
	21st to end	Day	54% 6% 14% 16% 8% 2	1730
March	1st to 10th	Day	49% 4 8% 25% 12% 3	4618
	11th to 20th	Day	51% 3 8% 25% 13%	5099
	21st to end	Day	56% 4 12% 20% 7%	5908
April	1st to 10th	Day	53% 5% 10% 20% 9% 1	2520
	11th to 20th	Day	48% 4 11% 19% 15% 3	2492
	21st to end	Day	40% 4 12% 28% 13% 3	2583
May	1st to 10th	Day	30% 3 6% 31% 27% 3	8195
	11th to 20th	Day	31% 2 10% 30% 24% 3	8163
	21st to end	Day	31% 3 13% 33% 19% 1	8994
June	1st to 10th	Day	39% 4 9% 29% 16% 2	2940
	11th to 20th	Day	31% 3 9% 29% 24% 4	2940
	21st to end	Day	21% 2 9% 27% 30% 11%	2940
July	1st to 10th	Day	12% 1 3 19% 32% 34%	8151
	11th to 20th	Day	14% 1 3 9% 24% 50%	8145
	21st to end	Day	12% 1 2 23% 40% 22%	8723
August	1st to 10th	Day	13% 1 2 12% 33% 39%	6210
	11th to 20th	Day	14% 1 5% 31% 36% 14%	5877
	21st to end	Day	16% 1 4 28% 35% 16%	6077
September	1st to 10th	Day	15% 2 4 25% 32% 22%	2520
	11th to 20th	Day	26% 3 7% 25% 26% 13%	2520
	21st to end	Day	28% 3 8% 26% 23% 11%	2241
October	1st to 10th	Day	25% 3 9% 21% 26% 17%	3280
	11th to 20th	Day	33% 2 17% 25% 19% 3	3261
	21st to end	Day	48% 3 7% 25% 16% 2	3363
November	1st to 10th	Day	51% 3 12% 23% 10% 1	1854
	11th to 20th	Day	53% 6% 15% 18% 8%	1727
	21st to end	Day	47% 5% 15% 19% 13% 1	1680
December	1st to 10th	Day	36% 4 11% 27% 20% 1	2700
	11th to 20th	Day	60% 3 17% 16% 4	3108
	21st to end	Day	61% 3 13% 18% 4	4092
January	1st to 10th	Night	65% 3 14% 14% 4	8172
	11th to 20th	Night	38% 2 7% 25% 21% 6%	8220
	21st to end	Night	49% 2 10% 15% 20% 5%	8694
February	1st to 10th	Night	54% 5% 15% 17% 9%	2730
	11th to 20th	Night	49% 6% 14% 20% 9% 2	2635
	21st to end	Night	54% 6% 10% 20% 9% 1	2076
March	1st to 10th	Night	44% 4 9% 28% 11% 3	5496
	11th to 20th	Night	44% 3 11% 31% 11% 1	5118
	21st to end	Night	56% 6% 13% 19% 5%	5308
April	1st to 10th	Night	48% 5% 16% 22% 8% 1	2100
	11th to 20th	Night	46% 5% 13% 21% 13% 1	2079
	21st to end	Night	41% 6% 13% 27% 12% 2	2035
May	1st to 10th	Night	29% 3 9% 31% 26% 1	4721
	11th to 20th	Night	34% 2 14% 35% 15% 1	4700
	21st to end	Night	30% 2 21% 33% 13% 1	5182
June	1st to 10th	Night	37% 4 12% 30% 15% 2	1680
	11th to 20th	Night	29% 4 12% 34% 18% 4	1680
	21st to end	Night	21% 2 11% 32% 26% 7%	1680
July	1st to 10th	Night	12% 1 5% 27% 29% 26%	4700
	11th to 20th	Night	15% 1 3 12% 26% 43%	4692
	21st to end	Night	15% 1 2 27% 36% 19%	5040
August	1st to 10th	Night	13% 1 3 14% 36% 33%	3909
	11th to 20th	Night	13% 1 7% 36% 35% 8%	4257
	21st to end	Night	15% 1 6% 29% 36% 13%	5092
September	1st to 10th	Night	16% 2 5% 26% 34% 18%	2100
	11th to 20th	Night	24% 3 9% 27% 25% 12%	2100
	21st to end	Night	27% 3 8% 26% 24% 13%	2333
October	1st to 10th	Night	23% 2 8% 23% 33% 12%	3920
	11th to 20th	Night	32% 2 19% 24% 20% 3	3897
	21st to end	Night	43% 3 9% 29% 15% 2	4441
November	1st to 10th	Night	52% 5% 11% 18% 13% 2	2665
	11th to 20th	Night	54% 5% 13% 20% 7%	2891
	21st to end	Night	44% 4 14% 21% 16% 1	2940
December	1st to 10th	Night	33% 3 11% 28% 24% 1	4700
	11th to 20th	Night	63% 3 14% 16% 5%	5316
	21st to end	Night	59% 3 15% 18% 5%	7106

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	34% 8% 27% 20% 10% 1	220
	11th to 20th	Day	17% 10% 28% 29% 13% 4	220
	21st to end	Day	16% 10% 29% 27% 16% 1	350
February	1st to 10th	Day	22% 12% 26% 26% 13% 1	430
	11th to 20th	Day	20% 13% 31% 23% 12% 2	441
	21st to end	Day	21% 14% 28% 28% 9%	446
March	1st to 10th	Day	21% 15% 28% 29% 7%	540
	11th to 20th	Day	20% 15% 26% 25% 12% 2	540
	21st to end	Day	22% 15% 26% 25% 11% 1	594
April	1st to 10th	Day	21% 14% 23% 25% 12% 5%	540
	11th to 20th	Day	17% 13% 28% 25% 11% 5%	532
	21st to end	Day	13% 17% 25% 25% 15% 5%	540
May	1st to 10th	Day	15% 13% 25% 25% 17% 4	543
	11th to 20th	Day	19% 13% 24% 20% 17% 7%	568
	21st to end	Day	14% 9% 21% 25% 20% 11%	617
June	1st to 10th	Day	13% 11% 22% 22% 21% 10%	570
	11th to 20th	Day	10% 12% 28% 26% 19% 5%	570
	21st to end	Day	5% 7% 20% 32% 23% 12%	570
July	1st to 10th	Day	2 5% 26% 32% 23% 11%	566
	11th to 20th	Day	3 8% 26% 29% 25% 10%	564
	21st to end	Day	3 5% 27% 27% 25% 13%	619
August	1st to 10th	Day	4 4 22% 29% 26% 14%	567
	11th to 20th	Day	3 4 20% 29% 27% 17%	557
	21st to end	Day	5% 6% 21% 26% 28% 13%	627
September	1st to 10th	Day	4 5% 21% 31% 28% 11%	570
	11th to 20th	Day	8% 6% 20% 30% 28% 9%	570
	21st to end	Day	10% 8% 18% 29% 27% 9%	563
October	1st to 10th	Day	13% 8% 22% 27% 22% 8%	530
	11th to 20th	Day	13% 9% 21% 28% 22% 7%	530
	21st to end	Day	18% 8% 25% 25% 20% 5%	463
November	1st to 10th	Day	18% 10% 23% 35% 12% 1	330
	11th to 20th	Day	20% 10% 27% 27% 13% 2	245
	21st to end	Day	16% 11% 27% 33% 10% 2	220
December	1st to 10th	Day	21% 8% 30% 24% 11% 6%	220
	11th to 20th	Day	25% 9% 33% 27% 7%	220
	21st to end	Day	22% 12% 25% 27% 11% 2	242
January	1st to 10th	Night	22% 8% 24% 29% 15% 2	840
	11th to 20th	Night	18% 8% 21% 31% 20% 2	840
	21st to end	Night	18% 6% 19% 39% 16% 2	924
February	1st to 10th	Night	18% 8% 22% 37% 15% 1	840
	11th to 20th	Night	16% 6% 22% 40% 14% 2	824
	21st to end	Night	18% 10% 21% 39% 12% 1	692
March	1st to 10th	Night	17% 10% 23% 36% 12% 1	840
	11th to 20th	Night	16% 8% 21% 36% 18% 1	840
	21st to end	Night	17% 10% 22% 37% 13% 1	924
April	1st to 10th	Night	17% 8% 19% 36% 18% 2	840
	11th to 20th	Night	16% 8% 22% 35% 17% 3	831
	21st to end	Night	15% 8% 20% 38% 18% 2	775
May	1st to 10th	Night	11% 5% 16% 46% 20% 1	420
	11th to 20th	Night	14% 5% 13% 44% 23% 2	414
	21st to end	Night	14% 4 13% 42% 25% 2	455
June	1st to 10th	Night	14% 3 13% 46% 21% 2	420
	11th to 20th	Night	10% 4 18% 49% 19% 1	420
	21st to end	Night	7% 1 13% 52% 26% 1	420
July	1st to 10th	Night	3 1 10% 51% 34% 1	410
	11th to 20th	Night	2 11% 60% 25% 1	408
	21st to end	Night	2 10% 53% 33% 2	460
August	1st to 10th	Night	2 1 5% 53% 36% 4	509
	11th to 20th	Night	2 1 6% 43% 42% 7%	660
	21st to end	Night	2 2 14% 46% 31% 4	924
September	1st to 10th	Night	4 2 12% 45% 34% 4	840
	11th to 20th	Night	6% 3 10% 43% 31% 8%	840
	21st to end	Night	9% 3 12% 39% 32% 5%	832
October	1st to 10th	Night	12% 3 11% 43% 27% 4	800
	11th to 20th	Night	13% 4 15% 40% 24% 3	800
	21st to end	Night	15% 5% 17% 41% 19% 4	880
November	1st to 10th	Night	19% 6% 18% 41% 14% 1	820
	11th to 20th	Night	21% 7% 21% 36% 14% 2	840
	21st to end	Night	19% 8% 17% 36% 17% 3	840
December	1st to 10th	Night	18% 6% 19% 36% 20% 2	840
	11th to 20th	Night	22% 6% 22% 35% 14% 2	840
	21st to end	Night	25% 10% 23% 31% 10% 1	924

Page generated at 2026-09-26 01:18:44. Version ac07

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