Pendleton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pendleton clear sky chart from 2005-11-06 to 2024-01-12.

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	11% 7% 3 6% 5% 3 4 4 5% 6% 46%	74788
	Night	13% 8% 3 7% 6% 3 4 4 5% 6% 40%	74940
Transparency	Day	38% 6% 13% 20% 16% 6%	74491
	Night	43% 7% 12% 20% 13% 5%	74758
Seeing	Day	13% 10% 24% 29% 20% 5%	13299
	Night	17% 7% 20% 32% 19% 4	22533

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	22% 13% 6% 9% 7% 4 4 5% 6% 6% 18%	1519
	11th to 20th	Day	20% 12% 4 8% 7% 4 5% 5% 6% 7% 22%	1448
	21st to end	Day	17% 11% 5% 9% 6% 4 5% 4 5% 7% 26%	1584
February	1st to 10th	Day	19% 13% 5% 8% 5% 3 5% 5% 4 7% 26%	1563
	11th to 20th	Day	16% 12% 5% 7% 6% 4 5% 5% 4 6% 31%	1664
	21st to end	Day	14% 12% 6% 9% 6% 4 5% 5% 7% 6% 26%	1480
March	1st to 10th	Day	16% 10% 5% 8% 7% 3 6% 5% 6% 8% 26%	1800
	11th to 20th	Day	13% 9% 5% 7% 7% 4 6% 6% 6% 8% 28%	1851
	21st to end	Day	15% 10% 4 8% 8% 5% 7% 5% 6% 7% 25%	2373
April	1st to 10th	Day	11% 9% 3 7% 6% 4 5% 6% 7% 7% 34%	2160
	11th to 20th	Day	10% 8% 2 6% 5% 4 4 5% 6% 8% 41%	2129
	21st to end	Day	10% 7% 3 6% 5% 3 5% 5% 5% 6% 45%	2308
May	1st to 10th	Day	7% 5% 2 5% 5% 3 4 5% 7% 9% 48%	2475
	11th to 20th	Day	10% 5% 3 5% 7% 4 5% 5% 7% 7% 42%	2477
	21st to end	Day	11% 7% 3 5% 6% 4 5% 5% 5% 7% 43%	2723
June	1st to 10th	Day	12% 5% 2 4 5% 3 4 6% 6% 8% 45%	2520
	11th to 20th	Day	10% 5% 2 4 4 3 4 5% 5% 8% 52%	2520
	21st to end	Day	4 3 1 3 2 1 3 4 5% 6% 67%	2520
July	1st to 10th	Day	2 2 1 2 3 1 3 3 4 5% 75%	2520
	11th to 20th	Day	1 2 1 2 3 2 3 3 4 5% 76%	2520
	21st to end	Day	1 1 1 2 1 1 2 2 3 5% 82%	2741
August	1st to 10th	Day	2 2 1 2 2 1 3 3 4 6% 74%	2507
	11th to 20th	Day	2 2 1 2 2 1 2 3 4 5% 76%	2298
	21st to end	Day	4 2 2 2 3 2 3 3 4 5% 72%	2376
September	1st to 10th	Day	3 2 1 2 3 1 2 3 4 6% 73%	2160
	11th to 20th	Day	6% 3 2 3 4 3 4 5% 5% 8% 59%	2102
	21st to end	Day	8% 5% 3 4 6% 3 3 4 3 5% 56%	1980
October	1st to 10th	Day	10% 6% 3 5% 5% 2 4 4 5% 6% 50%	1851
	11th to 20th	Day	10% 6% 2 4 5% 2 4 5% 7% 8% 47%	1778
	21st to end	Day	16% 6% 3 5% 6% 3 5% 4 4 7% 41%	1782
November	1st to 10th	Day	19% 7% 4 5% 6% 4 5% 6% 6% 6% 31%	1674
	11th to 20th	Day	19% 11% 5% 7% 6% 4 7% 5% 5% 7% 23%	1623
	21st to end	Day	17% 11% 6% 7% 7% 4 6% 5% 6% 7% 25%	1520
December	1st to 10th	Day	18% 11% 5% 8% 6% 4 5% 6% 7% 6% 25%	1520
	11th to 20th	Day	19% 12% 6% 17% 10% 4 5% 5% 3 4 13%	1928
	21st to end	Day	18% 12% 4 14% 10% 4 6% 5% 5% 6% 16%	2794
January	1st to 10th	Night	23% 15% 6% 9% 8% 4 5% 5% 4 5% 16%	2646
	11th to 20th	Night	22% 13% 6% 9% 6% 3 4 4 5% 6% 22%	2540
	21st to end	Night	18% 11% 5% 9% 6% 4 5% 6% 5% 7% 24%	2772
February	1st to 10th	Night	19% 13% 4 7% 6% 3 5% 4 4 5% 30%	2394
	11th to 20th	Night	17% 12% 5% 8% 5% 3 4 4 4 5% 31%	2181
	21st to end	Night	14% 15% 5% 7% 6% 4 5% 5% 4 7% 28%	1776
March	1st to 10th	Night	16% 10% 4 6% 6% 4 5% 5% 6% 7% 30%	2160
	11th to 20th	Night	13% 10% 4 5% 6% 3 5% 6% 7% 8% 33%	2106
	21st to end	Night	14% 11% 4 6% 7% 4 6% 5% 6% 8% 29%	1982
April	1st to 10th	Night	14% 9% 3 5% 7% 3 5% 5% 6% 8% 35%	1800
	11th to 20th	Night	14% 8% 3 6% 5% 3 3 4 5% 6% 42%	1779
	21st to end	Night	10% 7% 4 6% 5% 4 5% 4 6% 7% 41%	1652
May	1st to 10th	Night	8% 5% 3 5% 4 3 6% 5% 5% 7% 49%	1481
	11th to 20th	Night	11% 4 2 4 5% 3 5% 6% 6% 10% 44%	1416
	21st to end	Night	10% 6% 3 6% 5% 3 5% 6% 7% 8% 42%	1552
June	1st to 10th	Night	10% 5% 3 5% 5% 2 4 6% 7% 8% 45%	1440
	11th to 20th	Night	10% 5% 2 6% 5% 3 4 5% 4 6% 49%	1440
	21st to end	Night	4 3 1 3 3 3 3 5% 5% 6% 64%	1440
July	1st to 10th	Night	2 2 1 3 2 2 3 3 5% 7% 72%	1440
	11th to 20th	Night	1 1 1 1 2 1 3 3 4 6% 77%	1440
	21st to end	Night	1 1 1 2 1 1 2 3 4 5% 79%	1576
August	1st to 10th	Night	3 2 2 2 1 3 3 5% 8% 71%	1432
	11th to 20th	Night	3 1 1 1 2 2 2 3 4 6% 75%	1598
	21st to end	Night	3 2 1 2 2 1 3 3 3 6% 73%	1980
September	1st to 10th	Night	4 2 1 3 3 2 2 2 3 5% 74%	1800
	11th to 20th	Night	6% 3 1 3 3 3 4 4 5% 6% 62%	1857
	21st to end	Night	8% 4 2 4 4 3 4 4 5% 7% 56%	1980
October	1st to 10th	Night	10% 6% 3 4 4 3 3 5% 5% 6% 52%	2106
	11th to 20th	Night	9% 6% 3 6% 6% 4 4 4 5% 6% 48%	2182
	21st to end	Night	14% 7% 3 6% 5% 3 5% 4 5% 7% 41%	2574
November	1st to 10th	Night	19% 9% 3 7% 6% 3 4 5% 4 6% 34%	2405
	11th to 20th	Night	21% 10% 5% 7% 6% 4 5% 4 6% 6% 27%	2555
	21st to end	Night	17% 9% 5% 7% 6% 3 5% 5% 6% 6% 30%	2660
December	1st to 10th	Night	18% 12% 5% 9% 8% 3 5% 5% 5% 6% 24%	2660
	11th to 20th	Night	20% 15% 7% 13% 9% 4 5% 4 5% 6% 14%	3276
	21st to end	Night	18% 12% 4 15% 10% 4 5% 5% 4 5% 19%	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	65% 11% 12% 9% 2	1519
	11th to 20th	Day	59% 10% 13% 14% 4	1448
	21st to end	Day	58% 8% 16% 14% 4	1584
February	1st to 10th	Day	59% 8% 15% 13% 4	1563
	11th to 20th	Day	54% 7% 16% 15% 7%	1673
	21st to end	Day	57% 8% 13% 15% 7% 1	1480
March	1st to 10th	Day	54% 6% 15% 17% 8%	1800
	11th to 20th	Day	53% 8% 17% 18% 5%	1851
	21st to end	Day	56% 8% 16% 16% 4	2373
April	1st to 10th	Day	48% 6% 16% 19% 10% 1	2160
	11th to 20th	Day	40% 6% 16% 21% 14% 3	2132
	21st to end	Day	39% 7% 15% 22% 16% 2	2308
May	1st to 10th	Day	30% 6% 14% 30% 17% 2	2475
	11th to 20th	Day	40% 6% 13% 25% 14% 2	2480
	21st to end	Day	41% 6% 13% 24% 13% 2	2724
June	1st to 10th	Day	37% 6% 15% 26% 15% 2	2520
	11th to 20th	Day	30% 5% 13% 30% 18% 4	2520
	21st to end	Day	18% 4 11% 30% 27% 10%	2520
July	1st to 10th	Day	14% 3 9% 22% 31% 23%	2451
	11th to 20th	Day	13% 3 8% 14% 33% 30%	2445
	21st to end	Day	8% 2 4 14% 41% 31%	2589
August	1st to 10th	Day	14% 3 7% 21% 37% 18%	2490
	11th to 20th	Day	11% 3 8% 25% 35% 18%	2298
	21st to end	Day	16% 3 8% 26% 37% 10%	2376
September	1st to 10th	Day	14% 3 10% 26% 30% 17%	2160
	11th to 20th	Day	24% 4 12% 22% 26% 11%	2102
	21st to end	Day	32% 4 13% 27% 20% 5%	1980
October	1st to 10th	Day	35% 5% 13% 26% 18% 3	1851
	11th to 20th	Day	33% 7% 15% 30% 14% 2	1778
	21st to end	Day	43% 5% 16% 23% 11% 1	1782
November	1st to 10th	Day	50% 7% 15% 21% 6% 1	1674
	11th to 20th	Day	60% 8% 15% 15% 2	1623
	21st to end	Day	55% 10% 16% 15% 4	1520
December	1st to 10th	Day	57% 10% 14% 15% 4 1	1520
	11th to 20th	Day	63% 18% 10% 8% 1	1928
	21st to end	Day	59% 16% 13% 10% 2	2794
January	1st to 10th	Night	69% 8% 12% 10% 1	2646
	11th to 20th	Night	63% 7% 12% 13% 5%	2540
	21st to end	Night	57% 9% 15% 16% 3	2772
February	1st to 10th	Night	57% 6% 15% 17% 4	2394
	11th to 20th	Night	55% 6% 16% 17% 6%	2183
	21st to end	Night	56% 7% 13% 17% 6% 2	1776
March	1st to 10th	Night	53% 6% 11% 20% 8% 1	2160
	11th to 20th	Night	47% 8% 16% 24% 5%	2106
	21st to end	Night	52% 8% 17% 19% 4	1982
April	1st to 10th	Night	47% 7% 14% 22% 10%	1800
	11th to 20th	Night	44% 5% 14% 23% 11% 3	1779
	21st to end	Night	41% 7% 15% 19% 16% 3	1652
May	1st to 10th	Night	33% 6% 14% 27% 18% 2	1481
	11th to 20th	Night	35% 6% 15% 26% 15% 2	1416
	21st to end	Night	38% 7% 16% 24% 13% 2	1552
June	1st to 10th	Night	36% 7% 13% 26% 15% 4	1440
	11th to 20th	Night	35% 5% 12% 30% 14% 4	1440
	21st to end	Night	21% 5% 10% 31% 23% 10%	1440
July	1st to 10th	Night	13% 3 10% 21% 28% 25%	1400
	11th to 20th	Night	10% 3 9% 19% 28% 31%	1392
	21st to end	Night	8% 3 5% 14% 34% 36%	1488
August	1st to 10th	Night	14% 3 7% 22% 33% 22%	1424
	11th to 20th	Night	12% 3 9% 20% 35% 21%	1598
	21st to end	Night	15% 3 7% 25% 36% 15%	1980
September	1st to 10th	Night	16% 2 10% 24% 31% 18%	1800
	11th to 20th	Night	22% 5% 11% 25% 23% 14%	1857
	21st to end	Night	28% 5% 12% 25% 23% 7%	1980
October	1st to 10th	Night	34% 4 11% 29% 20% 3	2106
	11th to 20th	Night	37% 6% 12% 25% 17% 4	2182
	21st to end	Night	43% 6% 13% 22% 13% 2	2574
November	1st to 10th	Night	52% 6% 10% 24% 7% 1	2405
	11th to 20th	Night	57% 7% 14% 18% 4	2555
	21st to end	Night	50% 10% 15% 19% 6%	2660
December	1st to 10th	Night	60% 9% 14% 14% 3	2660
	11th to 20th	Night	64% 13% 11% 10% 2	3276
	21st to end	Night	55% 17% 11% 12% 4	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	32% 12% 24% 16% 12% 5%	180
	11th to 20th	Day	27% 9% 22% 26% 9% 7%	162
	21st to end	Day	26% 9% 18% 28% 16% 3	176
February	1st to 10th	Day	30% 11% 24% 25% 9% 1	283
	11th to 20th	Day	26% 13% 23% 24% 12% 2	375
	21st to end	Day	19% 15% 25% 27% 13% 1	346
March	1st to 10th	Day	22% 14% 27% 25% 11% 1	420
	11th to 20th	Day	16% 14% 26% 24% 17% 3	420
	21st to end	Day	18% 14% 31% 23% 14% 2	462
April	1st to 10th	Day	20% 15% 27% 22% 13% 3	420
	11th to 20th	Day	14% 17% 29% 21% 15% 4	412
	21st to end	Day	12% 17% 23% 25% 19% 3	420
May	1st to 10th	Day	11% 11% 26% 31% 18% 4	423
	11th to 20th	Day	17% 9% 22% 29% 16% 7%	448
	21st to end	Day	12% 7% 22% 27% 26% 7%	485
June	1st to 10th	Day	13% 9% 20% 29% 21% 8%	450
	11th to 20th	Day	10% 15% 31% 26% 17% 2	450
	21st to end	Day	5% 8% 24% 31% 25% 8%	450
July	1st to 10th	Day	2 5% 22% 42% 25% 3	446
	11th to 20th	Day	2 7% 25% 39% 24% 4	444
	21st to end	Day	2 5% 20% 39% 26% 8%	487
August	1st to 10th	Day	3 4 21% 38% 25% 9%	447
	11th to 20th	Day	2 3 19% 30% 34% 11%	437
	21st to end	Day	5% 6% 22% 37% 23% 7%	495
September	1st to 10th	Day	3 6% 21% 33% 29% 8%	450
	11th to 20th	Day	7% 7% 22% 30% 28% 7%	450
	21st to end	Day	10% 9% 20% 29% 27% 5%	450
October	1st to 10th	Day	13% 8% 21% 29% 25% 4	450
	11th to 20th	Day	11% 12% 20% 29% 21% 7%	428
	21st to end	Day	22% 9% 24% 25% 14% 5%	297
November	1st to 10th	Day	22% 8% 27% 24% 17% 1	270
	11th to 20th	Day	21% 12% 21% 26% 15% 5%	228
	21st to end	Day	18% 9% 21% 31% 17% 6%	180
December	1st to 10th	Day	20% 9% 24% 21% 17% 9%	180
	11th to 20th	Day	28% 11% 28% 22% 11% 2	180
	21st to end	Day	23% 7% 27% 29% 10% 4	198
January	1st to 10th	Night	30% 11% 18% 23% 15% 3	760
	11th to 20th	Night	27% 10% 18% 24% 18% 4	726
	21st to end	Night	24% 7% 19% 28% 18% 4	792
February	1st to 10th	Night	27% 9% 20% 26% 14% 2	720
	11th to 20th	Night	22% 10% 19% 31% 15% 2	704
	21st to end	Night	21% 14% 24% 29% 10% 3	592
March	1st to 10th	Night	20% 12% 23% 30% 14% 3	720
	11th to 20th	Night	18% 8% 22% 32% 17% 3	720
	21st to end	Night	21% 11% 25% 29% 14% 1	792
April	1st to 10th	Night	19% 9% 20% 34% 15% 3	720
	11th to 20th	Night	18% 10% 25% 26% 17% 5%	711
	21st to end	Night	13% 10% 27% 30% 17% 3	572
May	1st to 10th	Night	9% 8% 27% 36% 16% 4	401
	11th to 20th	Night	13% 6% 16% 36% 23% 6%	354
	21st to end	Night	10% 8% 19% 38% 20% 5%	389
June	1st to 10th	Night	12% 6% 26% 33% 20% 3	360
	11th to 20th	Night	13% 11% 30% 32% 13% 1	360
	21st to end	Night	6% 4 27% 41% 19% 3	360
July	1st to 10th	Night	2 4 23% 44% 23% 4	350
	11th to 20th	Night	2 3 28% 46% 18% 3	348
	21st to end	Night	1 2 19% 48% 26% 4	394
August	1st to 10th	Night	3 2 18% 45% 28% 3	358
	11th to 20th	Night	4 1 13% 36% 35% 12%	530
	21st to end	Night	4 3 17% 38% 30% 7%	792
September	1st to 10th	Night	4 3 15% 42% 30% 6%	720
	11th to 20th	Night	6% 3 15% 34% 31% 11%	720
	21st to end	Night	10% 4 17% 33% 27% 9%	720
October	1st to 10th	Night	14% 3 15% 39% 25% 4	720
	11th to 20th	Night	12% 6% 19% 32% 24% 7%	720
	21st to end	Night	16% 8% 22% 29% 18% 6%	792
November	1st to 10th	Night	22% 7% 21% 34% 15% 1	740
	11th to 20th	Night	24% 9% 21% 28% 14% 4	760
	21st to end	Night	19% 9% 17% 31% 18% 5%	760
December	1st to 10th	Night	26% 7% 17% 30% 16% 4	760
	11th to 20th	Night	28% 8% 19% 31% 12% 2	760
	21st to end	Night	31% 10% 21% 26% 12% 1	836

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