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 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	7% 6% 3 6% 5% 3 5% 4 5% 7% 50%	74797
	Night	8% 7% 3 6% 6% 3 5% 5% 5% 7% 45%	74948
Transparency	Day	33% 7% 11% 19% 18% 11%	74501
	Night	36% 7% 13% 19% 16% 8%	74765
Seeing	Day	9% 8% 21% 26% 23% 13%	13494
	Night	10% 6% 20% 38% 23% 3	22818

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	11% 12% 4 10% 10% 7% 7% 6% 6% 7% 21%	1519
	11th to 20th	Day	9% 9% 5% 9% 8% 5% 8% 6% 6% 8% 27%	1451
	21st to end	Day	9% 12% 5% 9% 9% 4 5% 4 6% 8% 29%	1611
February	1st to 10th	Day	8% 9% 4 9% 6% 4 7% 5% 7% 8% 33%	1620
	11th to 20th	Day	7% 10% 5% 8% 5% 3 7% 6% 5% 7% 37%	1710
	21st to end	Day	6% 10% 6% 6% 7% 5% 6% 6% 7% 9% 32%	1480
March	1st to 10th	Day	9% 12% 5% 9% 6% 4 6% 5% 6% 8% 31%	1800
	11th to 20th	Day	8% 11% 4 9% 6% 3 6% 5% 6% 7% 36%	1862
	21st to end	Day	9% 10% 5% 8% 8% 5% 6% 6% 5% 7% 31%	2366
April	1st to 10th	Day	9% 10% 4 8% 6% 4 6% 4 5% 7% 38%	2160
	11th to 20th	Day	10% 9% 3 7% 5% 4 5% 4 5% 7% 42%	2129
	21st to end	Day	8% 7% 3 5% 5% 3 4 4 4 7% 49%	2250
May	1st to 10th	Day	5% 5% 2 5% 4 3 5% 5% 5% 7% 53%	2394
	11th to 20th	Day	10% 6% 3 5% 5% 4 5% 4 6% 8% 45%	2477
	21st to end	Day	8% 7% 3 7% 7% 3 5% 5% 6% 7% 40%	2723
June	1st to 10th	Day	8% 6% 3 5% 6% 3 5% 5% 5% 8% 45%	2520
	11th to 20th	Day	7% 4 2 4 4 3 3 4 5% 7% 58%	2520
	21st to end	Day	3 3 2 4 2 2 3 3 4 4 71%	2520
July	1st to 10th	Day	2 2 1 2 2 2 3 3 4 5% 75%	2520
	11th to 20th	Day	1 1 1 2 2 1 2 3 3 3 82%	2520
	21st to end	Day	1 2 1 2 3 2 3 3 3 4 77%	2741
August	1st to 10th	Day	4 2 2 3 3 2 3 4 5% 8% 66%	2507
	11th to 20th	Day	2 1 1 1 2 2 3 3 3 5% 77%	2158
	21st to end	Day	2 1 1 2 2 1 2 2 4 5% 79%	2376
September	1st to 10th	Day	2 2 1 2 2 1 3 3 3 5% 76%	2160
	11th to 20th	Day	4 2 1 4 4 2 3 3 5% 6% 67%	2099
	21st to end	Day	6% 5% 2 5% 4 2 3 3 4 5% 61%	1980
October	1st to 10th	Day	9% 5% 2 4 4 2 3 4 4 6% 57%	1867
	11th to 20th	Day	8% 5% 2 4 5% 3 4 4 5% 7% 55%	1800
	21st to end	Day	9% 6% 2 4 4 3 4 6% 5% 6% 50%	1801
November	1st to 10th	Day	12% 9% 4 5% 5% 3 4 5% 7% 9% 38%	1674
	11th to 20th	Day	10% 8% 3 6% 7% 5% 6% 6% 6% 8% 34%	1710
	21st to end	Day	9% 7% 3 6% 7% 5% 7% 7% 8% 8% 34%	1530
December	1st to 10th	Day	10% 9% 4 9% 7% 4 6% 6% 7% 8% 30%	1520
	11th to 20th	Day	12% 12% 5% 10% 9% 5% 7% 5% 6% 8% 21%	1928
	21st to end	Day	9% 12% 6% 12% 10% 4 7% 6% 6% 6% 21%	2794
January	1st to 10th	Night	10% 11% 5% 8% 7% 4 7% 7% 6% 9% 25%	2646
	11th to 20th	Night	10% 11% 4 9% 9% 4 6% 5% 6% 6% 30%	2548
	21st to end	Night	9% 12% 3 7% 7% 5% 5% 5% 5% 8% 33%	2743
February	1st to 10th	Night	9% 10% 4 8% 6% 3 5% 4 7% 8% 35%	2340
	11th to 20th	Night	9% 9% 3 6% 6% 3 7% 5% 6% 7% 39%	2138
	21st to end	Night	6% 10% 6% 7% 7% 4 8% 6% 7% 7% 32%	1776
March	1st to 10th	Night	9% 11% 5% 8% 6% 3 6% 5% 5% 8% 33%	2160
	11th to 20th	Night	7% 8% 4 6% 6% 4 6% 6% 7% 9% 37%	2095
	21st to end	Night	8% 10% 4 7% 6% 4 5% 6% 5% 8% 37%	1989
April	1st to 10th	Night	11% 7% 4 6% 6% 2 4 5% 6% 8% 41%	1800
	11th to 20th	Night	8% 9% 3 6% 6% 3 5% 4 5% 6% 45%	1779
	21st to end	Night	8% 6% 2 5% 5% 3 5% 5% 6% 8% 47%	1710
May	1st to 10th	Night	6% 5% 3 3 4 3 5% 6% 6% 7% 53%	1564
	11th to 20th	Night	10% 4 2 6% 5% 3 5% 5% 7% 7% 46%	1416
	21st to end	Night	9% 6% 4 7% 6% 4 5% 5% 6% 6% 42%	1552
June	1st to 10th	Night	9% 5% 3 5% 5% 3 5% 5% 5% 7% 47%	1440
	11th to 20th	Night	7% 5% 2 4 3 3 4 4 5% 5% 57%	1440
	21st to end	Night	3 3 1 3 3 3 3 4 5% 8% 67%	1440
July	1st to 10th	Night	2 2 1 3 3 2 4 4 4 6% 71%	1440
	11th to 20th	Night	1 1 1 2 1 2 2 4 5% 81%	1440
	21st to end	Night	2 1 1 2 3 2 3 3 4 5% 74%	1576
August	1st to 10th	Night	3 2 1 3 4 2 3 5% 5% 8% 62%	1432
	11th to 20th	Night	1 1 1 2 2 1 2 2 4 8% 76%	1740
	21st to end	Night	2 2 1 2 2 1 2 4 3 5% 75%	1980
September	1st to 10th	Night	2 2 1 1 1 1 2 3 4 5% 78%	1800
	11th to 20th	Night	3 2 1 3 3 1 2 3 5% 6% 69%	1860
	21st to end	Night	5% 3 2 3 3 2 4 3 5% 5% 66%	1980
October	1st to 10th	Night	8% 4 2 4 4 2 3 4 3 6% 60%	2091
	11th to 20th	Night	6% 4 2 4 4 2 4 4 4 6% 60%	2160
	21st to end	Night	7% 7% 2 4 5% 3 5% 5% 6% 7% 49%	2553
November	1st to 10th	Night	13% 9% 3 5% 5% 4 3 4 5% 7% 42%	2405
	11th to 20th	Night	13% 8% 3 5% 6% 3 5% 6% 7% 9% 35%	2470
	21st to end	Night	10% 8% 3 6% 5% 3 7% 7% 7% 7% 37%	2647
December	1st to 10th	Night	11% 10% 4 7% 7% 4 6% 6% 6% 7% 33%	2660
	11th to 20th	Night	11% 12% 4 8% 9% 5% 7% 6% 6% 7% 24%	3276
	21st to end	Night	10% 11% 4 11% 11% 5% 6% 7% 7% 7% 21%	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	59% 11% 13% 13% 4	1519
	11th to 20th	Day	50% 12% 16% 13% 7% 2	1451
	21st to end	Day	51% 9% 17% 16% 5% 1	1611
February	1st to 10th	Day	45% 11% 19% 19% 6%	1620
	11th to 20th	Day	44% 10% 18% 19% 9% 1	1720
	21st to end	Day	46% 9% 17% 17% 10% 1	1480
March	1st to 10th	Day	50% 8% 13% 19% 9% 2	1800
	11th to 20th	Day	45% 8% 14% 22% 12%	1862
	21st to end	Day	51% 10% 14% 17% 7% 1	2366
April	1st to 10th	Day	46% 6% 14% 19% 13% 2	2160
	11th to 20th	Day	41% 5% 14% 20% 17% 4	2132
	21st to end	Day	35% 8% 12% 26% 16% 4	2250
May	1st to 10th	Day	28% 6% 12% 29% 21% 4	2394
	11th to 20th	Day	37% 6% 11% 26% 16% 4	2480
	21st to end	Day	40% 9% 14% 21% 15% 2	2724
June	1st to 10th	Day	35% 7% 10% 26% 19% 2	2520
	11th to 20th	Day	26% 6% 9% 26% 25% 9%	2520
	21st to end	Day	17% 4 7% 21% 31% 20%	2520
July	1st to 10th	Day	13% 3 5% 17% 29% 33%	2451
	11th to 20th	Day	9% 2 4 12% 29% 45%	2445
	21st to end	Day	13% 2 3 9% 27% 46%	2589
August	1st to 10th	Day	17% 3 7% 19% 27% 27%	2490
	11th to 20th	Day	10% 3 5% 16% 32% 33%	2158
	21st to end	Day	10% 2 5% 15% 39% 29%	2376
September	1st to 10th	Day	13% 3 4 17% 32% 31%	2160
	11th to 20th	Day	19% 4 8% 19% 29% 22%	2099
	21st to end	Day	26% 4 7% 21% 25% 16%	1980
October	1st to 10th	Day	29% 5% 11% 19% 24% 11%	1867
	11th to 20th	Day	28% 6% 11% 25% 23% 8%	1800
	21st to end	Day	33% 7% 14% 23% 19% 4	1801
November	1st to 10th	Day	43% 6% 14% 22% 15% 1	1674
	11th to 20th	Day	44% 10% 16% 21% 9% 1	1710
	21st to end	Day	41% 9% 17% 19% 12% 1	1530
December	1st to 10th	Day	48% 11% 17% 17% 6% 1	1520
	11th to 20th	Day	54% 13% 12% 15% 5%	1928
	21st to end	Day	55% 15% 13% 15% 3	2794
January	1st to 10th	Night	52% 12% 17% 15% 4 1	2646
	11th to 20th	Night	50% 10% 14% 16% 9% 2	2548
	21st to end	Night	48% 7% 17% 20% 7% 1	2743
February	1st to 10th	Night	44% 9% 17% 20% 9%	2340
	11th to 20th	Night	42% 9% 18% 19% 10% 2	2139
	21st to end	Night	47% 8% 16% 17% 10% 2	1776
March	1st to 10th	Night	48% 8% 13% 19% 10% 3	2160
	11th to 20th	Night	41% 9% 15% 25% 10% 1	2095
	21st to end	Night	43% 9% 15% 23% 8% 1	1989
April	1st to 10th	Night	41% 6% 17% 20% 14% 2	1800
	11th to 20th	Night	40% 5% 13% 25% 13% 3	1779
	21st to end	Night	34% 7% 16% 25% 15% 2	1710
May	1st to 10th	Night	27% 7% 12% 28% 23% 3	1564
	11th to 20th	Night	35% 7% 12% 25% 18% 4	1416
	21st to end	Night	40% 9% 14% 24% 12% 2	1552
June	1st to 10th	Night	38% 6% 13% 26% 15% 1	1440
	11th to 20th	Night	29% 6% 7% 26% 24% 7%	1440
	21st to end	Night	16% 4 9% 23% 33% 15%	1440
July	1st to 10th	Night	14% 4 5% 21% 29% 28%	1400
	11th to 20th	Night	7% 2 6% 15% 30% 41%	1392
	21st to end	Night	13% 3 5% 8% 27% 44%	1488
August	1st to 10th	Night	19% 4 8% 18% 24% 26%	1424
	11th to 20th	Night	9% 2 6% 19% 30% 34%	1740
	21st to end	Night	13% 3 3 18% 34% 29%	1980
September	1st to 10th	Night	11% 3 5% 16% 30% 36%	1800
	11th to 20th	Night	16% 3 9% 20% 29% 24%	1860
	21st to end	Night	20% 4 6% 21% 28% 21%	1980
October	1st to 10th	Night	27% 4 11% 19% 25% 13%	2091
	11th to 20th	Night	25% 5% 10% 26% 26% 8%	2160
	21st to end	Night	32% 6% 15% 20% 21% 5%	2553
November	1st to 10th	Night	42% 6% 13% 20% 17% 3	2405
	11th to 20th	Night	42% 8% 17% 21% 12%	2470
	21st to end	Night	41% 8% 18% 17% 15% 2	2647
December	1st to 10th	Night	47% 9% 18% 18% 7% 1	2660
	11th to 20th	Night	51% 12% 17% 16% 4	3276
	21st to end	Night	55% 12% 14% 12% 6%	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	24% 8% 22% 22% 17% 7%	180
	11th to 20th	Day	17% 9% 20% 26% 19% 9%	163
	21st to end	Day	14% 5% 23% 30% 16% 12%	203
February	1st to 10th	Day	10% 14% 29% 24% 18% 5%	340
	11th to 20th	Day	14% 15% 28% 24% 15% 4	397
	21st to end	Day	11% 16% 31% 21% 16% 4	346
March	1st to 10th	Day	15% 17% 33% 23% 12% 1	420
	11th to 20th	Day	13% 14% 25% 25% 20% 3	420
	21st to end	Day	14% 15% 29% 26% 14% 2	462
April	1st to 10th	Day	15% 17% 23% 20% 17% 8%	420
	11th to 20th	Day	15% 15% 30% 19% 13% 9%	412
	21st to end	Day	11% 12% 26% 25% 19% 7%	420
May	1st to 10th	Day	6% 11% 25% 27% 20% 12%	423
	11th to 20th	Day	15% 11% 20% 23% 19% 13%	448
	21st to end	Day	9% 8% 16% 23% 25% 18%	485
June	1st to 10th	Day	10% 7% 19% 22% 23% 20%	450
	11th to 20th	Day	9% 10% 22% 28% 21% 10%	450
	21st to end	Day	3 4 17% 29% 28% 20%	450
July	1st to 10th	Day	3 1 15% 32% 35% 13%	446
	11th to 20th	Day	2 1 17% 31% 31% 19%	444
	21st to end	Day	1 2 11% 30% 34% 21%	487
August	1st to 10th	Day	5% 2 14% 30% 30% 20%	447
	11th to 20th	Day	2 4 11% 25% 30% 28%	437
	21st to end	Day	2 4 16% 27% 27% 24%	495
September	1st to 10th	Day	3 2 14% 30% 28% 23%	450
	11th to 20th	Day	7% 4 15% 24% 30% 21%	450
	21st to end	Day	7% 5% 16% 25% 32% 14%	450
October	1st to 10th	Day	10% 6% 20% 21% 22% 19%	450
	11th to 20th	Day	10% 6% 22% 21% 26% 16%	450
	21st to end	Day	13% 5% 21% 24% 26% 12%	316
November	1st to 10th	Day	14% 7% 19% 29% 21% 10%	270
	11th to 20th	Day	13% 3 21% 27% 25% 10%	270
	21st to end	Day	11% 5% 18% 31% 27% 8%	185
December	1st to 10th	Day	18% 6% 17% 28% 14% 16%	180
	11th to 20th	Day	21% 10% 23% 26% 17% 3	180
	21st to end	Day	11% 11% 23% 26% 24% 5%	198
January	1st to 10th	Night	13% 9% 24% 33% 17% 4	760
	11th to 20th	Night	12% 10% 19% 33% 22% 4	728
	21st to end	Night	13% 6% 17% 39% 22% 3	792
February	1st to 10th	Night	12% 7% 30% 32% 19% 1	720
	11th to 20th	Night	13% 7% 24% 35% 20% 2	704
	21st to end	Night	8% 13% 25% 38% 16% 1	592
March	1st to 10th	Night	14% 6% 29% 34% 17% 1	720
	11th to 20th	Night	10% 9% 24% 36% 20% 2	720
	21st to end	Night	11% 10% 29% 35% 14% 1	792
April	1st to 10th	Night	13% 9% 22% 36% 18% 2	720
	11th to 20th	Night	11% 9% 27% 30% 21% 3	711
	21st to end	Night	12% 5% 25% 38% 18% 1	630
May	1st to 10th	Night	8% 7% 26% 39% 18% 1	484
	11th to 20th	Night	10% 6% 22% 36% 23% 3	354
	21st to end	Night	11% 5% 21% 33% 28% 3	389
June	1st to 10th	Night	10% 3 20% 40% 24% 2	360
	11th to 20th	Night	8% 6% 22% 43% 18% 3	360
	21st to end	Night	3 3 17% 48% 28% 1	360
July	1st to 10th	Night	2 2 16% 53% 27% 1	350
	11th to 20th	Night	1 1 17% 59% 21% 1	348
	21st to end	Night	1 2 14% 58% 25% 1	394
August	1st to 10th	Night	3 2 11% 53% 30% 1	358
	11th to 20th	Night	2 9% 47% 40% 2	672
	21st to end	Night	3 2 12% 49% 32% 3	792
September	1st to 10th	Night	3 2 12% 44% 37% 2	720
	11th to 20th	Night	3 2 13% 35% 41% 5%	720
	21st to end	Night	6% 4 13% 38% 34% 6%	720
October	1st to 10th	Night	9% 2 18% 40% 28% 4	720
	11th to 20th	Night	7% 4 20% 36% 27% 6%	720
	21st to end	Night	11% 4 17% 37% 26% 5%	792
November	1st to 10th	Night	17% 5% 18% 37% 21% 2	740
	11th to 20th	Night	14% 8% 19% 37% 19% 3	760
	21st to end	Night	13% 7% 20% 33% 21% 5%	760
December	1st to 10th	Night	14% 6% 19% 38% 18% 4	760
	11th to 20th	Night	17% 7% 21% 34% 20% 2	760
	21st to end	Night	18% 9% 24% 35% 12% 1	836

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