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 2025-10-04.

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% 7% 2 6% 4 4 4 3 5% 6% 50%	135490
	Night	12% 9% 3 7% 4 4 4 3 5% 6% 44%	131189
Transparency	Day	35% 5% 11% 22% 18% 9%	130208
	Night	40% 6% 12% 21% 14% 6%	127473
Seeing	Day	13% 10% 23% 29% 20% 6%	15567
	Night	16% 7% 20% 33% 19% 4	24615

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	20% 18% 6% 13% 7% 5% 5% 4 5% 5% 13%	3639
	11th to 20th	Day	17% 13% 3 8% 5% 4 4 4 5% 6% 30%	3640
	21st to end	Day	17% 11% 4 8% 5% 4 3 3 4 6% 35%	4004
February	1st to 10th	Day	19% 16% 5% 9% 4 4 4 3 4 7% 25%	1737
	11th to 20th	Day	16% 13% 5% 8% 5% 5% 4 3 4 6% 30%	1855
	21st to end	Day	14% 12% 5% 9% 6% 5% 5% 4 7% 5% 27%	1650
March	1st to 10th	Day	13% 10% 3 8% 5% 5% 6% 4 7% 9% 31%	4518
	11th to 20th	Day	10% 10% 3 7% 5% 4 5% 4 5% 6% 40%	4689
	21st to end	Day	14% 10% 4 10% 6% 7% 6% 4 6% 8% 25%	5966
April	1st to 10th	Day	11% 9% 3 8% 5% 5% 5% 5% 7% 7% 35%	2400
	11th to 20th	Day	9% 7% 2 7% 5% 5% 4 4 6% 8% 43%	2369
	21st to end	Day	9% 8% 3 6% 4 4 4 4 6% 6% 45%	2565
May	1st to 10th	Day	9% 5% 2 4 3 3 3 3 5% 8% 55%	6223
	11th to 20th	Day	8% 5% 2 6% 4 4 4 3 5% 6% 52%	6277
	21st to end	Day	6% 5% 2 4 4 4 4 4 6% 8% 53%	6902
June	1st to 10th	Day	11% 6% 2 5% 4 4 4 4 6% 8% 46%	2800
	11th to 20th	Day	9% 5% 2 4 4 4 4 4 5% 7% 53%	2800
	21st to end	Day	4 4 1 3 2 2 3 3 5% 6% 67%	2800
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 3 79%	6319
	11th to 20th	Day	1 2 1 2 1 2 2 2 2 3 83%	6320
	21st to end	Day	2 1 1 2 1 1 2 2 3 7% 78%	6880
August	1st to 10th	Day	3 4 1 4 3 3 3 2 5% 6% 66%	6210
	11th to 20th	Day	3 2 1 2 2 2 2 3 3 5% 76%	5780
	21st to end	Day	3 3 2 4 3 3 3 3 4 6% 66%	5984
September	1st to 10th	Day	3 2 1 3 2 2 2 3 5% 7% 71%	2400
	11th to 20th	Day	6% 4 2 4 3 3 4 3 5% 7% 59%	2335
	21st to end	Day	7% 5% 3 5% 5% 3 4 3 3 5% 58%	2200
October	1st to 10th	Day	7% 4 2 4 3 3 4 2 4 5% 62%	3291
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 5% 7% 10% 46%	3112
	21st to end	Day	13% 8% 3 7% 5% 5% 5% 4 5% 7% 37%	3101
November	1st to 10th	Day	20% 9% 3 6% 5% 5% 5% 4 7% 6% 31%	1764
	11th to 20th	Day	20% 12% 5% 8% 6% 6% 5% 4 5% 7% 22%	1708
	21st to end	Day	16% 13% 4 8% 6% 6% 5% 4 6% 7% 24%	1600
December	1st to 10th	Day	13% 9% 3 11% 6% 5% 3 3 7% 7% 32%	2620
	11th to 20th	Day	22% 12% 6% 16% 8% 6% 4 4 4 4 14%	3028
	21st to end	Day	20% 12% 4 15% 7% 5% 5% 4 5% 6% 17%	4004
January	1st to 10th	Night	25% 18% 7% 16% 6% 5% 4 3 3 3 10%	6306
	11th to 20th	Night	17% 13% 4 8% 4 3 4 3 4 6% 33%	6320
	21st to end	Night	14% 10% 4 9% 5% 5% 4 3 5% 5% 35%	6952
February	1st to 10th	Night	19% 16% 4 9% 5% 4 4 3 4 5% 27%	2660
	11th to 20th	Night	17% 13% 4 9% 5% 4 4 3 4 5% 31%	2430
	21st to end	Night	15% 15% 4 7% 6% 5% 4 4 5% 7% 29%	1980
March	1st to 10th	Night	10% 9% 3 7% 6% 5% 5% 4 7% 8% 36%	5376
	11th to 20th	Night	13% 12% 3 7% 4 4 3 3 5% 5% 41%	5308
	21st to end	Night	13% 13% 4 9% 7% 6% 5% 4 7% 7% 25%	5008
April	1st to 10th	Night	14% 10% 3 6% 6% 4 5% 4 7% 7% 35%	2000
	11th to 20th	Night	12% 9% 3 7% 4 4 3 3 5% 6% 44%	1979
	21st to end	Night	9% 7% 3 7% 4 5% 5% 4 6% 6% 43%	1835
May	1st to 10th	Night	9% 4 2 5% 3 4 4 3 5% 6% 53%	3737
	11th to 20th	Night	10% 7% 3 7% 4 3 3 4 4 6% 48%	3616
	21st to end	Night	8% 6% 2 5% 3 3 4 3 5% 7% 55%	3972
June	1st to 10th	Night	10% 6% 2 6% 4 3 4 5% 7% 8% 46%	1600
	11th to 20th	Night	9% 6% 2 7% 5% 4 4 4 5% 6% 49%	1600
	21st to end	Night	4 3 2 4 3 4 3 4 5% 6% 63%	1600
July	1st to 10th	Night	1 2 1 2 2 2 2 2 4 5% 76%	3640
	11th to 20th	Night	1 1 1 1 2 2 3 4 85%	3640
	21st to end	Night	3 2 2 1 1 2 2 4 6% 78%	3970
August	1st to 10th	Night	3 3 1 4 3 3 4 2 5% 8% 64%	3582
	11th to 20th	Night	2 2 2 3 2 2 2 3 4 6% 71%	4065
	21st to end	Night	3 3 1 5% 3 3 3 3 4 6% 66%	5015
September	1st to 10th	Night	3 2 1 4 2 2 2 2 3 6% 72%	2000
	11th to 20th	Night	6% 4 1 4 3 4 3 3 5% 6% 61%	2064
	21st to end	Night	7% 4 2 4 3 4 4 3 4 7% 58%	2200
October	1st to 10th	Night	7% 5% 2 4 2 3 2 2 3 5% 65%	3740
	11th to 20th	Night	8% 4 2 5% 4 5% 4 4 6% 8% 50%	3824
	21st to end	Night	12% 8% 3 7% 4 5% 5% 3 5% 8% 41%	4457
November	1st to 10th	Night	18% 10% 3 8% 5% 4 4 4 4 6% 35%	2535
	11th to 20th	Night	21% 12% 4 8% 5% 5% 5% 3 6% 6% 26%	2690
	21st to end	Night	17% 12% 3 8% 6% 4 5% 4 5% 6% 30%	2800
December	1st to 10th	Night	11% 9% 3 9% 5% 4 4 4 6% 7% 38%	4560
	11th to 20th	Night	20% 17% 6% 14% 7% 6% 5% 3 5% 5% 12%	5176
	21st to end	Night	20% 13% 4 15% 7% 5% 5% 4 4 5% 19%	6952

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	70% 11% 12% 6% 1	3639
	11th to 20th	Day	51% 8% 17% 20% 4	3640
	21st to end	Day	49% 8% 9% 22% 11%	4004
February	1st to 10th	Day	60% 7% 15% 13% 4	1737
	11th to 20th	Day	55% 7% 15% 15% 7%	1864
	21st to end	Day	56% 8% 13% 15% 8% 1	1650
March	1st to 10th	Day	47% 5% 10% 24% 12% 1	4518
	11th to 20th	Day	43% 5% 14% 27% 11%	4689
	21st to end	Day	54% 8% 14% 19% 5%	5966
April	1st to 10th	Day	47% 6% 17% 21% 10%	2400
	11th to 20th	Day	38% 6% 16% 23% 15% 3	2372
	21st to end	Day	38% 7% 14% 24% 16% 2	2565
May	1st to 10th	Day	28% 4 9% 28% 28% 3	6223
	11th to 20th	Day	32% 4 10% 27% 21% 6%	6280
	21st to end	Day	27% 6% 17% 31% 17% 2	6904
June	1st to 10th	Day	36% 5% 14% 25% 16% 3	2800
	11th to 20th	Day	29% 5% 12% 28% 21% 5%	2800
	21st to end	Day	18% 4 11% 30% 27% 10%	2800
July	1st to 10th	Day	12% 1 5% 15% 30% 37%	6251
	11th to 20th	Day	9% 1 4 10% 31% 45%	6245
	21st to end	Day	10% 2 5% 26% 35% 23%	6681
August	1st to 10th	Day	17% 2 5% 15% 35% 27%	4524
	11th to 20th	Day	12% 2 6% 36% 32% 11%	4182
	21st to end	Day	18% 3 8% 27% 32% 12%	4311
September	1st to 10th	Day	15% 3 11% 26% 30% 16%	2400
	11th to 20th	Day	25% 4 12% 24% 25% 10%	2335
	21st to end	Day	30% 4 13% 28% 20% 5%	2200
October	1st to 10th	Day	25% 3 9% 31% 25% 5%	3291
	11th to 20th	Day	31% 6% 19% 28% 15% 1	3112
	21st to end	Day	45% 4 13% 28% 10% 1	3101
November	1st to 10th	Day	51% 7% 15% 21% 6% 1	1764
	11th to 20th	Day	60% 8% 15% 15% 2	1708
	21st to end	Day	55% 10% 16% 15% 4	1600
December	1st to 10th	Day	49% 9% 18% 21% 3	2620
	11th to 20th	Day	65% 14% 13% 8%	3028
	21st to end	Day	60% 13% 15% 10% 2	4004
January	1st to 10th	Night	76% 9% 9% 6% 1	6306
	11th to 20th	Night	50% 6% 20% 18% 6%	6320
	21st to end	Night	47% 9% 12% 21% 10%	6952
February	1st to 10th	Night	59% 6% 15% 15% 4	2660
	11th to 20th	Night	55% 6% 15% 18% 6% 1	2432
	21st to end	Night	55% 7% 13% 18% 6% 1	1980
March	1st to 10th	Night	43% 5% 8% 25% 18% 1	5376
	11th to 20th	Night	44% 4 11% 32% 9%	5308
	21st to end	Night	54% 8% 15% 19% 4	5008
April	1st to 10th	Night	47% 7% 14% 23% 9%	2000
	11th to 20th	Night	41% 5% 14% 23% 12% 3	1979
	21st to end	Night	38% 7% 15% 21% 17% 2	1835
May	1st to 10th	Night	29% 4 14% 21% 30% 2	3734
	11th to 20th	Night	35% 5% 10% 32% 17% 2	3616
	21st to end	Night	28% 7% 18% 31% 15% 1	3972
June	1st to 10th	Night	34% 7% 12% 26% 17% 5%	1600
	11th to 20th	Night	35% 5% 11% 29% 16% 5%	1600
	21st to end	Night	22% 4 10% 30% 23% 10%	1600
July	1st to 10th	Night	12% 2 6% 18% 25% 37%	3600
	11th to 20th	Night	5% 2 5% 11% 30% 47%	3592
	21st to end	Night	10% 2 3 25% 34% 26%	3857
August	1st to 10th	Night	15% 2 5% 15% 35% 29%	2601
	11th to 20th	Night	14% 3 6% 35% 29% 12%	2939
	21st to end	Night	16% 3 8% 28% 30% 14%	3608
September	1st to 10th	Night	16% 3 10% 23% 31% 18%	2000
	11th to 20th	Night	24% 5% 11% 25% 22% 13%	2064
	21st to end	Night	26% 5% 12% 27% 23% 8%	2200
October	1st to 10th	Night	24% 3 10% 28% 32% 3	3740
	11th to 20th	Night	32% 5% 17% 24% 20% 2	3824
	21st to end	Night	42% 5% 11% 29% 13% 1	4457
November	1st to 10th	Night	51% 6% 11% 23% 7% 1	2535
	11th to 20th	Night	57% 7% 14% 18% 4	2690
	21st to end	Night	51% 10% 15% 18% 6%	2800
December	1st to 10th	Night	43% 7% 20% 26% 4	4560
	11th to 20th	Night	69% 10% 11% 9% 1	5176
	21st to end	Night	58% 14% 13% 11% 4	6952

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% 11% 23% 18% 12% 5%	200
	11th to 20th	Day	25% 10% 20% 29% 10% 7%	200
	21st to end	Day	23% 9% 18% 28% 18% 4	220
February	1st to 10th	Day	29% 11% 23% 25% 10% 1	337
	11th to 20th	Day	26% 13% 22% 25% 12% 2	446
	21st to end	Day	19% 15% 25% 27% 13% 1	414
March	1st to 10th	Day	20% 14% 27% 26% 12% 1	500
	11th to 20th	Day	16% 14% 25% 24% 16% 4	500
	21st to end	Day	17% 13% 31% 24% 13% 2	550
April	1st to 10th	Day	18% 15% 27% 22% 14% 4	500
	11th to 20th	Day	12% 16% 30% 23% 15% 4	492
	21st to end	Day	11% 16% 23% 28% 18% 4	500
May	1st to 10th	Day	11% 11% 26% 31% 18% 4	503
	11th to 20th	Day	17% 9% 23% 29% 15% 7%	528
	21st to end	Day	11% 8% 22% 27% 25% 8%	573
June	1st to 10th	Day	12% 9% 20% 29% 22% 9%	530
	11th to 20th	Day	10% 14% 32% 27% 16% 2	530
	21st to end	Day	5% 7% 23% 31% 25% 8%	530
July	1st to 10th	Day	2 5% 21% 42% 26% 5%	526
	11th to 20th	Day	2 6% 23% 38% 26% 5%	524
	21st to end	Day	2 5% 19% 39% 27% 8%	575
August	1st to 10th	Day	3 5% 19% 38% 27% 9%	527
	11th to 20th	Day	2 3 19% 31% 34% 10%	517
	21st to end	Day	6% 5% 20% 36% 25% 8%	583
September	1st to 10th	Day	3 5% 18% 32% 29% 11%	530
	11th to 20th	Day	7% 6% 21% 30% 28% 7%	530
	21st to end	Day	9% 8% 19% 29% 27% 7%	530
October	1st to 10th	Day	13% 7% 21% 29% 25% 5%	503
	11th to 20th	Day	11% 11% 21% 29% 20% 8%	466
	21st to end	Day	22% 9% 24% 26% 15% 5%	330
November	1st to 10th	Day	23% 9% 26% 23% 18% 2	300
	11th to 20th	Day	23% 12% 22% 26% 14% 4	253
	21st to end	Day	16% 9% 21% 32% 17% 6%	200
December	1st to 10th	Day	19% 9% 23% 20% 19% 12%	200
	11th to 20th	Day	28% 12% 27% 22% 11% 2	200
	21st to end	Day	23% 8% 27% 29% 10% 3	220
January	1st to 10th	Night	31% 11% 18% 24% 15% 3	800
	11th to 20th	Night	26% 10% 18% 25% 17% 3	800
	21st to end	Night	22% 7% 19% 31% 18% 4	880
February	1st to 10th	Night	28% 10% 21% 26% 14% 2	800
	11th to 20th	Night	22% 9% 20% 32% 15% 2	784
	21st to end	Night	22% 13% 24% 30% 10% 2	660
March	1st to 10th	Night	18% 11% 23% 31% 14% 3	800
	11th to 20th	Night	18% 9% 22% 32% 17% 3	800
	21st to end	Night	20% 11% 26% 29% 14% 1	880
April	1st to 10th	Night	18% 10% 20% 35% 14% 3	800
	11th to 20th	Night	16% 10% 26% 28% 16% 4	791
	21st to end	Night	12% 10% 27% 32% 17% 2	635
May	1st to 10th	Night	9% 8% 27% 36% 16% 4	445
	11th to 20th	Night	13% 7% 18% 35% 22% 6%	394
	21st to end	Night	9% 8% 20% 39% 19% 5%	433
June	1st to 10th	Night	12% 5% 26% 33% 21% 3	400
	11th to 20th	Night	12% 10% 31% 34% 13% 1	400
	21st to end	Night	6% 5% 27% 41% 19% 3	400
July	1st to 10th	Night	2 4 23% 45% 23% 4	390
	11th to 20th	Night	2 2 27% 48% 18% 3	388
	21st to end	Night	2 2 18% 50% 25% 3	438
August	1st to 10th	Night	3 2 17% 47% 28% 3	398
	11th to 20th	Night	3 1 14% 39% 33% 10%	591
	21st to end	Night	5% 3 17% 38% 30% 7%	880
September	1st to 10th	Night	4 3 14% 42% 32% 7%	800
	11th to 20th	Night	6% 3 15% 35% 30% 10%	800
	21st to end	Night	9% 4 17% 33% 28% 9%	800
October	1st to 10th	Night	13% 3 15% 40% 25% 4	772
	11th to 20th	Night	12% 6% 19% 32% 25% 6%	760
	21st to end	Night	16% 8% 22% 31% 18% 6%	836
November	1st to 10th	Night	22% 7% 21% 34% 15% 1	780
	11th to 20th	Night	25% 9% 21% 28% 13% 4	800
	21st to end	Night	20% 9% 18% 31% 18% 5%	800
December	1st to 10th	Night	25% 7% 17% 30% 17% 5%	800
	11th to 20th	Night	28% 8% 19% 31% 12% 2	800
	21st to end	Night	31% 10% 21% 25% 11% 1	880

Page generated at 2025-09-30 22:39:04. Version ac07

Copyright © 2025 Attilla Danko.