Malheur Field Station
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Malheur Field Station clear sky chart from 2005-11-06 to 2025-11-18.

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	6% 7% 2 6% 4 4 4 3 5% 6% 52%	135714
	Night	7% 8% 3 7% 5% 4 4 4 5% 7% 46%	131988
Transparency	Day	31% 6% 9% 20% 20% 14%	130523
	Night	36% 6% 11% 20% 17% 10%	128173
Seeing	Day	9% 8% 20% 25% 23% 14%	15934
	Night	10% 6% 20% 38% 23% 3	25109

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	13% 14% 5% 13% 10% 9% 6% 4 6% 5% 16%	3639
	11th to 20th	Day	9% 12% 3 9% 6% 6% 8% 6% 7% 7% 26%	3640
	21st to end	Day	10% 11% 4 8% 5% 4 4 3 5% 9% 37%	4073
February	1st to 10th	Day	8% 11% 4 10% 6% 6% 6% 4 7% 8% 31%	1800
	11th to 20th	Day	8% 12% 4 9% 6% 5% 5% 4 5% 7% 35%	1905
	21st to end	Day	5% 12% 4 8% 6% 5% 6% 5% 7% 8% 33%	1650
March	1st to 10th	Day	6% 14% 5% 11% 5% 5% 5% 4 6% 8% 30%	4518
	11th to 20th	Day	4 10% 3 8% 5% 4 5% 3 6% 7% 43%	4726
	21st to end	Day	6% 10% 4 10% 7% 6% 6% 4 6% 7% 33%	5959
April	1st to 10th	Day	8% 10% 3 9% 5% 5% 5% 3 6% 7% 38%	2400
	11th to 20th	Day	9% 9% 2 7% 5% 4 4 3 5% 7% 44%	2369
	21st to end	Day	8% 8% 3 6% 5% 4 4 4 5% 7% 48%	2500
May	1st to 10th	Day	8% 6% 1 4 3 4 4 3 5% 6% 55%	6012
	11th to 20th	Day	6% 5% 2 5% 4 4 4 3 5% 7% 56%	6277
	21st to end	Day	4 5% 1 5% 4 3 4 3 5% 6% 59%	6902
June	1st to 10th	Day	8% 6% 3 6% 5% 4 5% 4 5% 8% 47%	2800
	11th to 20th	Day	6% 4 2 4 4 4 3 3 5% 7% 58%	2800
	21st to end	Day	3 3 1 4 2 3 3 3 4 4 71%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 3 4 81%	6319
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 3 81%	6320
	21st to end	Day	2 2 1 3 3 3 4 3 5% 7% 68%	6880
August	1st to 10th	Day	3 2 1 3 3 3 3 3 5% 9% 66%	6210
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 4 81%	5438
	21st to end	Day	4 3 1 4 3 2 2 2 3 5% 70%	5984
September	1st to 10th	Day	2 2 1 3 2 2 3 3 3 5% 74%	2400
	11th to 20th	Day	4 3 1 5% 3 3 3 3 5% 6% 65%	2331
	21st to end	Day	6% 5% 2 5% 3 3 3 2 4 5% 63%	2200
October	1st to 10th	Day	5% 3 1 4 3 2 2 2 4 5% 69%	3389
	11th to 20th	Day	6% 6% 2 5% 4 4 4 3 5% 7% 53%	3261
	21st to end	Day	8% 8% 3 7% 4 5% 5% 5% 7% 8% 41%	3233
November	1st to 10th	Day	11% 10% 3 6% 5% 4 4 3 7% 9% 37%	1854
	11th to 20th	Day	12% 9% 2 7% 6% 7% 5% 5% 6% 8% 33%	1863
	21st to end	Day	8% 8% 2 7% 6% 6% 7% 5% 7% 8% 34%	1610
December	1st to 10th	Day	6% 7% 3 8% 5% 5% 5% 6% 7% 9% 40%	2620
	11th to 20th	Day	13% 15% 4 11% 6% 7% 6% 3 5% 8% 21%	3028
	21st to end	Day	12% 12% 5% 13% 8% 6% 7% 5% 6% 6% 20%	4004
January	1st to 10th	Night	11% 16% 5% 13% 9% 7% 7% 5% 5% 6% 17%	6306
	11th to 20th	Night	11% 13% 3 7% 6% 5% 5% 5% 7% 8% 29%	6320
	21st to end	Night	9% 11% 3 8% 6% 5% 4 4 5% 9% 36%	6884
February	1st to 10th	Night	9% 11% 4 9% 5% 5% 5% 4 7% 8% 33%	2600
	11th to 20th	Night	9% 10% 3 7% 6% 5% 5% 4 6% 6% 37%	2382
	21st to end	Night	6% 11% 5% 8% 6% 6% 7% 5% 7% 6% 33%	1980
March	1st to 10th	Night	7% 13% 4 9% 6% 7% 6% 5% 7% 8% 29%	5376
	11th to 20th	Night	6% 11% 3 7% 5% 5% 5% 4 6% 7% 42%	5271
	21st to end	Night	6% 12% 4 9% 6% 6% 6% 5% 6% 8% 33%	5015
April	1st to 10th	Night	11% 8% 3 7% 5% 3 5% 4 6% 8% 41%	2000
	11th to 20th	Night	7% 8% 3 7% 5% 4 4 3 5% 6% 47%	1979
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 6% 8% 47%	1899
May	1st to 10th	Night	6% 7% 2 4 3 3 4 3 5% 6% 57%	3946
	11th to 20th	Night	6% 6% 2 4 3 3 4 3 5% 5% 58%	3616
	21st to end	Night	6% 4 2 5% 3 3 3 3 4 4 61%	3972
June	1st to 10th	Night	8% 6% 2 6% 5% 4 5% 4 5% 7% 48%	1600
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 4 5% 58%	1600
	21st to end	Night	3 3 1 3 2 3 2 3 5% 7% 67%	1600
July	1st to 10th	Night	1 2 1 3 2 2 3 2 3 4 77%	3640
	11th to 20th	Night	1 1 2 1 2 2 2 3 5% 81%	3640
	21st to end	Night	3 3 1 6% 4 5% 4 4 5% 6% 59%	3970
August	1st to 10th	Night	3 2 2 5% 4 4 4 4 6% 8% 57%	3582
	11th to 20th	Night	3 2 1 3 2 2 2 2 3 6% 75%	4425
	21st to end	Night	3 4 2 5% 3 3 3 3 4 5% 65%	5015
September	1st to 10th	Night	2 3 1 2 2 2 2 3 4 5% 75%	2000
	11th to 20th	Night	4 3 1 3 3 2 2 3 6% 6% 67%	2068
	21st to end	Night	5% 3 1 3 2 3 3 2 4 5% 68%	2200
October	1st to 10th	Night	5% 3 1 4 2 2 2 2 3 4 71%	3808
	11th to 20th	Night	4 4 2 4 3 3 3 3 4 6% 63%	3897
	21st to end	Night	6% 7% 2 6% 3 4 5% 4 6% 7% 49%	4566
November	1st to 10th	Night	12% 10% 3 6% 5% 4 4 3 5% 7% 42%	2665
	11th to 20th	Night	13% 9% 2 7% 5% 4 5% 4 7% 9% 34%	2691
	21st to end	Night	10% 9% 3 6% 4 5% 6% 5% 7% 7% 36%	2787
December	1st to 10th	Night	7% 6% 2 5% 4 4 6% 6% 10% 10% 41%	4560
	11th to 20th	Night	13% 15% 4 10% 7% 7% 7% 5% 7% 6% 19%	5176
	21st to end	Night	13% 13% 4 12% 9% 6% 5% 5% 6% 6% 21%	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	65% 10% 10% 11% 3	3639
	11th to 20th	Day	52% 11% 13% 15% 8% 1	3640
	21st to end	Day	43% 8% 11% 18% 17% 4	4073
February	1st to 10th	Day	47% 10% 18% 17% 7%	1800
	11th to 20th	Day	46% 9% 16% 19% 9% 1	1915
	21st to end	Day	44% 10% 17% 18% 10% 1	1650
March	1st to 10th	Day	47% 7% 9% 24% 9% 3	4518
	11th to 20th	Day	36% 6% 13% 33% 12%	4726
	21st to end	Day	46% 11% 15% 20% 9% 1	5959
April	1st to 10th	Day	44% 6% 15% 20% 13% 2	2400
	11th to 20th	Day	39% 5% 13% 20% 19% 4	2372
	21st to end	Day	35% 8% 13% 26% 15% 4	2500
May	1st to 10th	Day	28% 5% 9% 23% 31% 4	6012
	11th to 20th	Day	27% 4 8% 26% 26% 8%	6280
	21st to end	Day	24% 6% 11% 28% 29% 3	6904
June	1st to 10th	Day	34% 7% 10% 27% 20% 2	2800
	11th to 20th	Day	25% 5% 9% 25% 26% 10%	2800
	21st to end	Day	16% 4 7% 21% 32% 20%	2800
July	1st to 10th	Day	10% 2 2 12% 22% 52%	6251
	11th to 20th	Day	10% 2 2 8% 19% 59%	6245
	21st to end	Day	14% 4 3 18% 29% 33%	6681
August	1st to 10th	Day	18% 2 4 12% 26% 36%	4524
	11th to 20th	Day	8% 2 3 15% 35% 36%	3930
	21st to end	Day	13% 2 4 19% 32% 30%	4311
September	1st to 10th	Day	14% 3 4 17% 32% 30%	2400
	11th to 20th	Day	21% 4 8% 20% 28% 20%	2331
	21st to end	Day	25% 3 7% 21% 26% 18%	2200
October	1st to 10th	Day	20% 3 7% 20% 31% 18%	3389
	11th to 20th	Day	30% 4 9% 27% 25% 5%	3261
	21st to end	Day	37% 6% 11% 26% 17% 3	3233
November	1st to 10th	Day	43% 6% 14% 22% 14% 1	1854
	11th to 20th	Day	45% 9% 16% 21% 8% 1	1863
	21st to end	Day	41% 9% 17% 20% 12% 1	1610
December	1st to 10th	Day	36% 8% 12% 30% 13% 1	2620
	11th to 20th	Day	57% 9% 14% 16% 4	3028
	21st to end	Day	57% 12% 12% 16% 3	4004
January	1st to 10th	Night	62% 12% 13% 10% 3	6306
	11th to 20th	Night	48% 9% 13% 19% 11% 1	6320
	21st to end	Night	42% 9% 11% 17% 13% 7%	6884
February	1st to 10th	Night	46% 9% 16% 19% 9%	2600
	11th to 20th	Night	44% 8% 17% 19% 10% 1	2383
	21st to end	Night	46% 8% 16% 18% 11% 2	1980
March	1st to 10th	Night	46% 7% 11% 23% 11% 2	5376
	11th to 20th	Night	38% 5% 12% 31% 13%	5271
	21st to end	Night	44% 12% 14% 23% 7%	5015
April	1st to 10th	Night	40% 6% 17% 21% 14% 2	2000
	11th to 20th	Night	38% 5% 13% 26% 14% 4	1979
	21st to end	Night	33% 7% 16% 26% 16% 2	1899
May	1st to 10th	Night	26% 5% 10% 21% 32% 6%	3943
	11th to 20th	Night	26% 5% 7% 29% 29% 3	3616
	21st to end	Night	26% 5% 9% 30% 27% 3	3972
June	1st to 10th	Night	36% 6% 13% 26% 18% 2	1600
	11th to 20th	Night	28% 6% 7% 25% 26% 9%	1600
	21st to end	Night	16% 4 8% 23% 33% 16%	1600
July	1st to 10th	Night	12% 3 3 12% 23% 48%	3600
	11th to 20th	Night	8% 2 2 9% 21% 58%	3592
	21st to end	Night	25% 4 3 11% 28% 29%	3857
August	1st to 10th	Night	24% 4 5% 12% 23% 32%	2601
	11th to 20th	Night	13% 2 4 14% 33% 34%	3201
	21st to end	Night	16% 3 3 19% 30% 30%	3608
September	1st to 10th	Night	14% 3 5% 15% 30% 34%	2000
	11th to 20th	Night	18% 3 8% 20% 28% 22%	2068
	21st to end	Night	19% 4 6% 22% 28% 22%	2200
October	1st to 10th	Night	20% 3 6% 16% 29% 26%	3808
	11th to 20th	Night	23% 3 9% 29% 29% 5%	3897
	21st to end	Night	32% 5% 10% 26% 23% 4	4566
November	1st to 10th	Night	42% 5% 14% 20% 16% 3	2665
	11th to 20th	Night	43% 8% 16% 21% 11%	2691
	21st to end	Night	41% 8% 17% 18% 14% 2	2787
December	1st to 10th	Night	33% 6% 14% 33% 13%	4560
	11th to 20th	Night	58% 9% 14% 16% 3	5176
	21st to end	Night	58% 10% 13% 13% 6%	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	25% 9% 21% 24% 16% 7%	200
	11th to 20th	Day	16% 8% 19% 27% 20% 11%	200
	21st to end	Day	13% 5% 22% 31% 17% 12%	250
February	1st to 10th	Day	12% 13% 30% 22% 19% 5%	400
	11th to 20th	Day	15% 14% 27% 24% 16% 3	472
	21st to end	Day	11% 15% 28% 22% 18% 6%	414
March	1st to 10th	Day	14% 15% 32% 23% 13% 2	500
	11th to 20th	Day	13% 15% 25% 24% 18% 5%	500
	21st to end	Day	13% 16% 29% 26% 13% 2	550
April	1st to 10th	Day	14% 16% 23% 22% 16% 9%	500
	11th to 20th	Day	13% 13% 30% 21% 14% 9%	492
	21st to end	Day	9% 11% 27% 25% 20% 7%	500
May	1st to 10th	Day	7% 11% 23% 27% 20% 12%	503
	11th to 20th	Day	14% 11% 22% 23% 18% 12%	528
	21st to end	Day	8% 8% 16% 23% 26% 19%	573
June	1st to 10th	Day	9% 7% 18% 22% 25% 20%	530
	11th to 20th	Day	8% 10% 21% 28% 22% 11%	530
	21st to end	Day	2 4 17% 28% 28% 20%	530
July	1st to 10th	Day	3 1 15% 31% 34% 15%	526
	11th to 20th	Day	2 1 16% 30% 32% 19%	524
	21st to end	Day	2 2 11% 29% 35% 21%	575
August	1st to 10th	Day	5% 2 14% 28% 31% 20%	527
	11th to 20th	Day	2 4 12% 27% 30% 25%	517
	21st to end	Day	3 4 16% 26% 26% 25%	583
September	1st to 10th	Day	3 2 13% 28% 29% 24%	530
	11th to 20th	Day	7% 3 15% 23% 29% 22%	530
	21st to end	Day	7% 5% 15% 24% 32% 18%	530
October	1st to 10th	Day	9% 6% 19% 23% 24% 19%	530
	11th to 20th	Day	10% 7% 21% 20% 26% 16%	530
	21st to end	Day	12% 5% 19% 25% 26% 12%	384
November	1st to 10th	Day	15% 8% 19% 28% 21% 10%	330
	11th to 20th	Day	17% 3 22% 26% 23% 8%	321
	21st to end	Day	11% 6% 19% 29% 27% 9%	205
December	1st to 10th	Day	17% 6% 17% 27% 16% 20%	200
	11th to 20th	Day	20% 10% 23% 27% 17% 4	200
	21st to end	Day	13% 12% 21% 26% 23% 5%	220
January	1st to 10th	Night	13% 10% 23% 33% 17% 4	800
	11th to 20th	Night	12% 10% 19% 34% 21% 4	800
	21st to end	Night	13% 5% 18% 39% 22% 3	880
February	1st to 10th	Night	13% 8% 29% 32% 18% 1	800
	11th to 20th	Night	13% 7% 24% 36% 19% 2	784
	21st to end	Night	8% 12% 24% 38% 17% 1	660
March	1st to 10th	Night	14% 6% 29% 33% 17% 1	800
	11th to 20th	Night	9% 10% 24% 35% 20% 2	800
	21st to end	Night	11% 11% 29% 34% 15% 1	880
April	1st to 10th	Night	13% 9% 22% 36% 18% 2	800
	11th to 20th	Night	10% 8% 28% 30% 21% 3	791
	21st to end	Night	11% 5% 25% 38% 19% 1	699
May	1st to 10th	Night	8% 8% 27% 38% 18% 1	537
	11th to 20th	Night	9% 6% 24% 35% 23% 3	394
	21st to end	Night	10% 5% 22% 33% 27% 3	433
June	1st to 10th	Night	10% 3 21% 40% 25% 2	400
	11th to 20th	Night	7% 7% 23% 44% 17% 3	400
	21st to end	Night	3 3 17% 48% 28% 1	400
July	1st to 10th	Night	2 2 15% 54% 26% 1	390
	11th to 20th	Night	1 1 16% 60% 21% 1	388
	21st to end	Night	2 2 14% 57% 24%	438
August	1st to 10th	Night	3 2 12% 53% 29% 1	398
	11th to 20th	Night	1 2 10% 48% 37% 2	749
	21st to end	Night	3 2 12% 48% 33% 3	880
September	1st to 10th	Night	3 2 12% 44% 37% 2	800
	11th to 20th	Night	4 2 13% 36% 40% 5%	800
	21st to end	Night	6% 4 13% 38% 33% 7%	800
October	1st to 10th	Night	8% 2 18% 40% 28% 4	800
	11th to 20th	Night	7% 4 21% 37% 26% 6%	800
	21st to end	Night	11% 4 18% 38% 25% 4	880
November	1st to 10th	Night	16% 5% 19% 35% 22% 2	820
	11th to 20th	Night	16% 8% 20% 36% 18% 3	828
	21st to end	Night	14% 7% 19% 33% 21% 5%	800
December	1st to 10th	Night	13% 6% 19% 37% 20% 5%	800
	11th to 20th	Night	18% 7% 21% 34% 19% 2	800
	21st to end	Night	19% 9% 24% 34% 12% 1	880

Page generated at 2025-11-14 21:55:57. Version ac07

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