Prineville Reservoir State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Prineville Reservoir State Park clear sky chart from 2005-11-06 to 2024-01-14.

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% 8% 3 6% 5% 3 4 4 5% 6% 47%	74783
	Night	9% 10% 3 6% 5% 3 4 4 5% 6% 44%	74993
Transparency	Day	37% 6% 11% 20% 17% 8%	74486
	Night	40% 7% 12% 20% 16% 5%	74811
Seeing	Day	12% 11% 25% 27% 18% 7%	13516
	Night	13% 7% 19% 37% 22% 3	22723

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% 13% 4 9% 6% 5% 6% 5% 6% 8% 23%	1519
	11th to 20th	Day	13% 11% 4 8% 7% 4 5% 5% 6% 7% 30%	1464
	21st to end	Day	9% 13% 5% 8% 5% 3 6% 4 6% 8% 31%	1677
February	1st to 10th	Day	11% 12% 5% 7% 6% 4 5% 6% 6% 8% 30%	1620
	11th to 20th	Day	10% 12% 5% 7% 6% 4 6% 5% 5% 7% 32%	1607
	21st to end	Day	9% 14% 7% 7% 8% 4 6% 5% 6% 8% 26%	1480
March	1st to 10th	Day	10% 12% 6% 9% 7% 4 6% 7% 6% 7% 26%	1800
	11th to 20th	Day	10% 15% 5% 7% 6% 4 5% 5% 6% 7% 31%	1966
	21st to end	Day	11% 14% 6% 9% 7% 4 5% 5% 5% 6% 27%	2295
April	1st to 10th	Day	11% 15% 6% 9% 6% 4 6% 5% 5% 5% 29%	2160
	11th to 20th	Day	10% 12% 5% 8% 6% 3 5% 4 5% 6% 35%	2129
	21st to end	Day	10% 10% 3 6% 4 3 4 6% 6% 8% 41%	2200
May	1st to 10th	Day	10% 9% 3 5% 4 3 5% 4 5% 7% 46%	2520
	11th to 20th	Day	13% 9% 3 6% 5% 3 5% 4 5% 8% 40%	2477
	21st to end	Day	14% 10% 3 6% 5% 3 4 5% 5% 7% 40%	2723
June	1st to 10th	Day	13% 8% 3 5% 5% 3 5% 5% 5% 8% 41%	2520
	11th to 20th	Day	9% 5% 2 4 5% 2 3 4 5% 7% 52%	2520
	21st to end	Day	5% 3 2 3 3 2 3 4 4 6% 65%	2520
July	1st to 10th	Day	2 2 1 2 2 2 3 3 4 5% 73%	2520
	11th to 20th	Day	2 2 1 2 2 2 3 3 3 4 75%	2520
	21st to end	Day	2 1 1 1 2 1 2 2 3 4 79%	2741
August	1st to 10th	Day	2 1 1 3 4 2 3 4 5% 7% 69%	2428
	11th to 20th	Day	2 2 1 2 3 2 2 2 3 5% 75%	2259
	21st to end	Day	2 3 1 2 2 1 3 3 3 4 75%	2376
September	1st to 10th	Day	2 2 1 2 2 1 3 3 4 5% 76%	2160
	11th to 20th	Day	5% 3 2 4 4 2 4 4 5% 7% 60%	2160
	21st to end	Day	7% 6% 2 4 4 2 3 4 4 6% 57%	1940
October	1st to 10th	Day	12% 7% 3 5% 4 3 4 4 3 5% 50%	1800
	11th to 20th	Day	11% 8% 2 5% 4 3 4 4 6% 8% 46%	1800
	21st to end	Day	12% 7% 2 6% 5% 4 5% 4 5% 5% 45%	1872
November	1st to 10th	Day	14% 11% 3 6% 6% 3 5% 5% 6% 7% 35%	1674
	11th to 20th	Day	14% 10% 4 7% 6% 3 6% 7% 7% 7% 30%	1574
	21st to end	Day	10% 12% 4 7% 5% 4 5% 5% 6% 7% 35%	1520
December	1st to 10th	Day	10% 11% 4 7% 7% 4 5% 5% 5% 6% 36%	1520
	11th to 20th	Day	11% 13% 4 8% 7% 4 6% 5% 6% 8% 26%	1928
	21st to end	Day	12% 15% 5% 10% 7% 4 5% 5% 6% 7% 25%	2794
January	1st to 10th	Night	12% 15% 5% 8% 7% 4 7% 4 6% 6% 26%	2646
	11th to 20th	Night	12% 12% 5% 6% 6% 4 5% 6% 6% 8% 32%	2568
	21st to end	Night	11% 13% 4 8% 5% 4 6% 5% 5% 6% 34%	2678
February	1st to 10th	Night	11% 13% 5% 8% 7% 3 6% 4 5% 7% 31%	2340
	11th to 20th	Night	9% 12% 5% 7% 6% 3 6% 5% 5% 7% 35%	2240
	21st to end	Night	9% 14% 6% 8% 8% 4 5% 5% 5% 8% 28%	1776
March	1st to 10th	Night	11% 14% 6% 8% 5% 3 5% 6% 6% 8% 28%	2160
	11th to 20th	Night	9% 11% 4 9% 7% 4 6% 5% 7% 8% 30%	1992
	21st to end	Night	11% 13% 6% 7% 7% 5% 6% 5% 6% 7% 27%	2060
April	1st to 10th	Night	12% 15% 5% 7% 6% 3 4 5% 5% 7% 32%	1800
	11th to 20th	Night	11% 13% 5% 6% 4 3 5% 5% 5% 6% 37%	1779
	21st to end	Night	9% 13% 3 6% 5% 3 4 5% 5% 8% 39%	1756
May	1st to 10th	Night	7% 9% 3 5% 5% 3 4 4 5% 7% 48%	1440
	11th to 20th	Night	12% 5% 2 5% 5% 4 4 5% 6% 8% 44%	1416
	21st to end	Night	13% 10% 2 6% 5% 4 4 3 7% 7% 39%	1552
June	1st to 10th	Night	12% 6% 3 5% 5% 3 4 5% 5% 7% 45%	1440
	11th to 20th	Night	9% 7% 2 4 3 2 3 3 4 8% 55%	1440
	21st to end	Night	4 4 1 3 3 2 3 3 4 6% 67%	1440
July	1st to 10th	Night	1 1 1 2 3 2 4 4 4 6% 72%	1440
	11th to 20th	Night	1 1 1 2 2 1 2 3 3 4 80%	1440
	21st to end	Night	1 1 1 2 2 1 2 2 4 3 81%	1576
August	1st to 10th	Night	1 2 1 2 3 1 3 3 5% 7% 72%	1509
	11th to 20th	Night	1 2 3 2 2 3 2 3 5% 77%	1640
	21st to end	Night	2 2 1 2 1 1 2 2 3 5% 78%	1980
September	1st to 10th	Night	2 2 1 1 2 2 2 3 3 5% 78%	1800
	11th to 20th	Night	5% 3 1 4 3 3 3 4 5% 6% 63%	1800
	21st to end	Night	8% 6% 2 4 3 2 3 4 5% 6% 59%	2015
October	1st to 10th	Night	9% 7% 3 5% 3 2 3 4 4 5% 55%	2160
	11th to 20th	Night	11% 6% 2 4 4 3 3 3 4 7% 54%	2160
	21st to end	Night	12% 8% 3 5% 6% 3 4 4 5% 6% 43%	2484
November	1st to 10th	Night	14% 12% 4 6% 6% 4 5% 5% 4 6% 35%	2405
	11th to 20th	Night	15% 10% 4 7% 7% 4 6% 5% 6% 6% 31%	2603
	21st to end	Night	11% 12% 3 6% 4 3 4 5% 6% 7% 39%	2660
December	1st to 10th	Night	11% 12% 3 8% 6% 4 4 4 5% 8% 36%	2660
	11th to 20th	Night	10% 14% 5% 8% 9% 4 6% 5% 6% 7% 26%	3276
	21st to end	Night	11% 14% 6% 9% 6% 4 5% 6% 5% 6% 29%	4862

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	57% 10% 13% 15% 5% 1	1519
	11th to 20th	Day	49% 9% 14% 16% 7% 4	1464
	21st to end	Day	50% 9% 13% 17% 8% 3	1677
February	1st to 10th	Day	50% 8% 16% 19% 7%	1620
	11th to 20th	Day	48% 9% 15% 16% 9% 3	1616
	21st to end	Day	53% 11% 15% 12% 8% 2	1480
March	1st to 10th	Day	54% 9% 15% 14% 7% 1	1800
	11th to 20th	Day	51% 7% 12% 21% 8%	1966
	21st to end	Day	56% 9% 13% 16% 6%	2295
April	1st to 10th	Day	54% 7% 13% 15% 10% 1	2160
	11th to 20th	Day	48% 6% 12% 18% 12% 3	2132
	21st to end	Day	40% 7% 14% 24% 12% 3	2200
May	1st to 10th	Day	37% 6% 12% 27% 17% 1	2520
	11th to 20th	Day	42% 6% 12% 24% 13% 3	2480
	21st to end	Day	44% 6% 13% 23% 11% 2	2724
June	1st to 10th	Day	41% 7% 10% 28% 12% 1	2520
	11th to 20th	Day	31% 4 11% 30% 19% 3	2520
	21st to end	Day	20% 4 10% 26% 30% 11%	2520
July	1st to 10th	Day	15% 3 8% 21% 26% 27%	2451
	11th to 20th	Day	13% 4 7% 13% 30% 34%	2445
	21st to end	Day	11% 2 5% 12% 36% 34%	2589
August	1st to 10th	Day	15% 4 8% 23% 31% 19%	2411
	11th to 20th	Day	15% 2 5% 20% 34% 23%	2259
	21st to end	Day	14% 2 6% 22% 38% 18%	2376
September	1st to 10th	Day	12% 3 5% 24% 32% 24%	2160
	11th to 20th	Day	24% 6% 8% 21% 26% 15%	2160
	21st to end	Day	29% 5% 9% 24% 23% 11%	1940
October	1st to 10th	Day	38% 5% 10% 18% 21% 9%	1800
	11th to 20th	Day	36% 6% 12% 21% 18% 7%	1800
	21st to end	Day	41% 7% 11% 20% 18% 3	1872
November	1st to 10th	Day	47% 7% 13% 21% 12% 1	1674
	11th to 20th	Day	49% 12% 15% 15% 9%	1574
	21st to end	Day	47% 7% 15% 15% 15% 1	1520
December	1st to 10th	Day	46% 10% 13% 20% 9% 1	1520
	11th to 20th	Day	54% 9% 14% 15% 7%	1928
	21st to end	Day	56% 9% 12% 18% 4 1	2794
January	1st to 10th	Night	56% 10% 15% 12% 6% 1	2646
	11th to 20th	Night	48% 8% 13% 17% 8% 5%	2568
	21st to end	Night	50% 7% 12% 18% 12% 1	2678
February	1st to 10th	Night	52% 8% 17% 15% 9%	2340
	11th to 20th	Night	46% 10% 15% 18% 9% 3	2242
	21st to end	Night	54% 8% 11% 18% 7% 1	1776
March	1st to 10th	Night	51% 8% 13% 17% 8% 2	2160
	11th to 20th	Night	49% 9% 14% 20% 7% 1	1992
	21st to end	Night	53% 10% 14% 17% 5%	2060
April	1st to 10th	Night	51% 7% 16% 17% 9% 1	1800
	11th to 20th	Night	46% 7% 15% 19% 12% 2	1779
	21st to end	Night	43% 7% 15% 22% 10% 2	1756
May	1st to 10th	Night	35% 6% 14% 29% 15%	1440
	11th to 20th	Night	39% 6% 17% 26% 10% 3	1416
	21st to end	Night	42% 7% 17% 24% 9% 1	1552
June	1st to 10th	Night	38% 8% 12% 30% 12%	1440
	11th to 20th	Night	29% 6% 15% 34% 14% 3	1440
	21st to end	Night	19% 4 12% 30% 27% 8%	1440
July	1st to 10th	Night	13% 5% 11% 25% 26% 20%	1400
	11th to 20th	Night	10% 3 7% 19% 32% 29%	1392
	21st to end	Night	11% 2 3 16% 41% 28%	1488
August	1st to 10th	Night	13% 4 9% 28% 34% 14%	1501
	11th to 20th	Night	11% 2 8% 26% 33% 19%	1640
	21st to end	Night	11% 3 6% 26% 38% 16%	1980
September	1st to 10th	Night	11% 3 6% 25% 36% 19%	1800
	11th to 20th	Night	20% 5% 9% 24% 28% 14%	1800
	21st to end	Night	27% 4 9% 23% 22% 15%	2015
October	1st to 10th	Night	32% 5% 10% 21% 25% 8%	2160
	11th to 20th	Night	31% 6% 14% 22% 21% 6%	2160
	21st to end	Night	41% 7% 12% 16% 20% 3	2484
November	1st to 10th	Night	50% 7% 11% 17% 14% 2	2405
	11th to 20th	Night	50% 9% 13% 19% 9% 1	2603
	21st to end	Night	42% 8% 13% 17% 18% 2	2660
December	1st to 10th	Night	47% 10% 14% 19% 10% 1	2660
	11th to 20th	Night	55% 9% 13% 15% 8%	3276
	21st to end	Night	53% 10% 12% 18% 6% 1	4862

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% 16% 29% 17% 15% 1	180
	11th to 20th	Day	20% 13% 30% 20% 13% 3	166
	21st to end	Day	15% 12% 28% 27% 16% 3	269
February	1st to 10th	Day	19% 17% 22% 29% 13%	340
	11th to 20th	Day	15% 15% 35% 22% 12% 1	349
	21st to end	Day	16% 13% 28% 32% 10% 1	346
March	1st to 10th	Day	16% 15% 30% 29% 10% 1	420
	11th to 20th	Day	18% 15% 26% 27% 13% 2	420
	21st to end	Day	17% 18% 26% 28% 10% 1	462
April	1st to 10th	Day	20% 20% 24% 23% 10% 5%	420
	11th to 20th	Day	15% 18% 29% 23% 11% 4	412
	21st to end	Day	14% 17% 30% 21% 15% 4	420
May	1st to 10th	Day	14% 16% 26% 25% 16% 4	423
	11th to 20th	Day	22% 12% 23% 19% 17% 8%	448
	21st to end	Day	14% 8% 24% 25% 20% 9%	485
June	1st to 10th	Day	10% 12% 25% 23% 21% 10%	450
	11th to 20th	Day	11% 16% 27% 25% 17% 4	450
	21st to end	Day	4 9% 21% 28% 25% 12%	450
July	1st to 10th	Day	4 4 27% 33% 22% 11%	446
	11th to 20th	Day	2 7% 26% 28% 27% 10%	444
	21st to end	Day	3 5% 26% 28% 25% 13%	487
August	1st to 10th	Day	3 6% 23% 28% 27% 13%	447
	11th to 20th	Day	1 5% 19% 30% 28% 17%	437
	21st to end	Day	5% 6% 22% 27% 27% 12%	495
September	1st to 10th	Day	3 4 20% 33% 28% 12%	450
	11th to 20th	Day	6% 8% 19% 30% 28% 8%	450
	21st to end	Day	11% 9% 21% 26% 26% 6%	450
October	1st to 10th	Day	15% 9% 20% 28% 20% 9%	450
	11th to 20th	Day	14% 12% 19% 27% 22% 7%	450
	21st to end	Day	15% 11% 26% 25% 18% 5%	387
November	1st to 10th	Day	16% 12% 23% 34% 14% 1	270
	11th to 20th	Day	14% 14% 24% 31% 13% 3	205
	21st to end	Day	14% 14% 23% 36% 12% 1	180
December	1st to 10th	Day	17% 14% 29% 25% 9% 6%	180
	11th to 20th	Day	22% 14% 24% 33% 6% 1	180
	21st to end	Day	18% 14% 24% 31% 12% 2	198
January	1st to 10th	Night	18% 12% 26% 28% 15% 3	760
	11th to 20th	Night	16% 12% 24% 25% 20% 2	734
	21st to end	Night	18% 7% 18% 36% 18% 3	792
February	1st to 10th	Night	16% 9% 24% 34% 16% 1	720
	11th to 20th	Night	15% 7% 23% 37% 16% 2	704
	21st to end	Night	16% 11% 24% 36% 13% 1	592
March	1st to 10th	Night	15% 12% 25% 33% 14% 1	720
	11th to 20th	Night	15% 8% 21% 37% 17% 2	720
	21st to end	Night	16% 10% 23% 35% 15% 1	792
April	1st to 10th	Night	18% 10% 21% 31% 18% 2	720
	11th to 20th	Night	16% 9% 24% 30% 18% 3	711
	21st to end	Night	17% 9% 20% 36% 17% 1	676
May	1st to 10th	Night	11% 6% 19% 41% 21% 1	360
	11th to 20th	Night	14% 3 15% 40% 26% 2	354
	21st to end	Night	18% 4 14% 37% 25% 2	389
June	1st to 10th	Night	13% 5% 16% 41% 23% 1	360
	11th to 20th	Night	12% 3 22% 43% 19% 1	360
	21st to end	Night	6% 2 16% 48% 28% 1	360
July	1st to 10th	Night	2 1 11% 51% 34% 1	350
	11th to 20th	Night	1 1 14% 57% 24% 2	348
	21st to end	Night	1 1 14% 53% 30% 1	394
August	1st to 10th	Night	2 1 8% 49% 36% 5%	435
	11th to 20th	Night	2 8% 38% 45% 8%	572
	21st to end	Night	3 2 14% 45% 32% 4	792
September	1st to 10th	Night	3 2 12% 44% 35% 4	720
	11th to 20th	Night	6% 3 12% 38% 35% 7%	720
	21st to end	Night	10% 4 12% 37% 32% 5%	720
October	1st to 10th	Night	13% 3 14% 39% 28% 5%	720
	11th to 20th	Night	13% 4 16% 37% 26% 4	720
	21st to end	Night	16% 6% 17% 37% 20% 5%	792
November	1st to 10th	Night	18% 7% 19% 40% 15% 1	740
	11th to 20th	Night	18% 9% 21% 35% 15% 2	760
	21st to end	Night	16% 9% 19% 35% 18% 3	760
December	1st to 10th	Night	17% 8% 21% 32% 20% 2	760
	11th to 20th	Night	17% 10% 24% 34% 13% 1	760
	21st to end	Night	22% 14% 25% 28% 11%	836

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