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 2024-11-08.

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%	105231
	Night	7% 8% 3 7% 5% 4 4 4 5% 6% 46%	102550
Transparency	Day	31% 6% 10% 19% 19% 15%	104972
	Night	35% 7% 12% 19% 17% 11%	102398
Seeing	Day	9% 8% 20% 26% 23% 13%	14628
	Night	10% 6% 20% 38% 23% 3	23815

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	10% 13% 4 14% 8% 8% 6% 4 7% 6% 21%	2539
	11th to 20th	Day	13% 17% 4 11% 7% 7% 8% 5% 5% 6% 17%	2540
	21st to end	Day	14% 15% 5% 11% 7% 6% 5% 3 5% 7% 21%	2835
February	1st to 10th	Day	7% 10% 4 10% 5% 5% 6% 4 7% 8% 32%	1710
	11th to 20th	Day	7% 12% 4 9% 5% 5% 6% 5% 5% 7% 36%	1807
	21st to end	Day	5% 12% 5% 8% 6% 5% 6% 5% 7% 8% 32%	1570
March	1st to 10th	Day	6% 15% 4 11% 6% 6% 6% 4 7% 8% 27%	3138
	11th to 20th	Day	5% 8% 2 7% 4 3 5% 3 5% 6% 51%	3294
	21st to end	Day	6% 11% 4 11% 8% 7% 7% 4 6% 7% 29%	4155
April	1st to 10th	Day	8% 11% 3 9% 5% 5% 5% 3 5% 6% 39%	2280
	11th to 20th	Day	9% 9% 2 7% 5% 5% 5% 3 5% 7% 43%	2249
	21st to end	Day	8% 8% 2 6% 4 4 4 4 5% 7% 48%	2375
May	1st to 10th	Day	8% 8% 2 5% 4 5% 5% 4 6% 6% 48%	4203
	11th to 20th	Day	5% 4 2 4 2 3 3 2 4 6% 64%	4377
	21st to end	Day	6% 6% 2 6% 5% 4 4 4 6% 7% 50%	4813
June	1st to 10th	Day	8% 6% 3 6% 5% 4 5% 4 5% 8% 45%	2660
	11th to 20th	Day	6% 4 2 4 4 4 3 3 5% 7% 58%	2660
	21st to end	Day	3 3 1 4 2 2 3 3 4 4 71%	2660
July	1st to 10th	Day	1 1 1 2 1 2 2 2 3 3 84%	4420
	11th to 20th	Day	2 2 1 3 2 2 2 2 3 3 77%	4420
	21st to end	Day	1 1 1 2 2 3 3 2 3 4 77%	4790
August	1st to 10th	Day	4 3 1 4 3 3 3 3 5% 8% 65%	4400
	11th to 20th	Day	1 1 1 1 2 2 2 3 5% 80%	3772
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 78%	4180
September	1st to 10th	Day	2 2 1 3 2 2 3 2 3 5% 76%	2280
	11th to 20th	Day	4 3 1 5% 3 3 3 3 5% 6% 65%	2215
	21st to end	Day	6% 5% 2 5% 3 3 3 2 4 5% 63%	2090
October	1st to 10th	Day	5% 3 1 4 3 2 2 2 3 5% 70%	3286
	11th to 20th	Day	6% 6% 2 5% 4 4 4 3 5% 7% 53%	3161
	21st to end	Day	8% 8% 3 7% 5% 5% 5% 5% 6% 8% 41%	3133
November	1st to 10th	Day	12% 10% 3 7% 5% 4 4 4 7% 9% 37%	1737
	11th to 20th	Day	10% 9% 2 8% 6% 7% 5% 5% 6% 8% 34%	1710
	21st to end	Day	8% 8% 2 7% 7% 6% 7% 5% 7% 8% 34%	1530
December	1st to 10th	Day	10% 10% 3 10% 6% 6% 5% 5% 7% 8% 29%	1520
	11th to 20th	Day	12% 12% 4 12% 7% 8% 6% 4 6% 8% 21%	1928
	21st to end	Day	8% 13% 6% 15% 8% 6% 6% 5% 6% 6% 21%	2794
January	1st to 10th	Night	9% 14% 5% 12% 9% 6% 7% 5% 6% 8% 20%	4406
	11th to 20th	Night	16% 18% 4 10% 7% 6% 5% 4 5% 5% 20%	4420
	21st to end	Night	13% 15% 4 11% 7% 6% 5% 4 5% 7% 24%	4820
February	1st to 10th	Night	9% 10% 4 9% 5% 5% 5% 4 7% 8% 34%	2470
	11th to 20th	Night	10% 10% 3 7% 5% 5% 6% 4 6% 6% 38%	2260
	21st to end	Night	6% 11% 5% 8% 6% 6% 7% 5% 7% 7% 33%	1884
March	1st to 10th	Night	7% 14% 4 10% 7% 7% 7% 6% 8% 8% 23%	3736
	11th to 20th	Night	5% 9% 2 5% 4 5% 5% 5% 6% 7% 47%	3683
	21st to end	Night	7% 12% 3 10% 6% 6% 6% 5% 6% 8% 32%	3497
April	1st to 10th	Night	11% 8% 3 7% 5% 3 4 4 6% 8% 42%	1900
	11th to 20th	Night	7% 9% 3 7% 5% 4 4 3 5% 6% 46%	1879
	21st to end	Night	8% 6% 2 5% 4 4 5% 4 6% 8% 46%	1804
May	1st to 10th	Night	7% 9% 3 5% 3 4 4 4 6% 6% 49%	2748
	11th to 20th	Night	6% 3 1 4 3 3 3 3 5% 5% 65%	2516
	21st to end	Night	8% 5% 3 6% 4 4 4 3 5% 5% 53%	2762
June	1st to 10th	Night	9% 6% 3 6% 5% 3 5% 4 5% 7% 47%	1520
	11th to 20th	Night	7% 5% 2 5% 3 4 4 3 4 5% 58%	1520
	21st to end	Night	3 3 1 3 2 3 2 3 5% 7% 67%	1520
July	1st to 10th	Night	1 1 2 2 2 2 2 2 4 82%	2540
	11th to 20th	Night	1 1 2 2 2 3 3 4 4 77%	2540
	21st to end	Night	1 2 1 4 3 4 3 3 4 5% 71%	2761
August	1st to 10th	Night	3 3 2 6% 4 4 4 4 5% 7% 58%	2529
	11th to 20th	Night	2 2 1 3 2 2 2 2 4 7% 73%	3073
	21st to end	Night	1 3 1 3 2 2 2 2 4 4 74%	3498
September	1st to 10th	Night	2 2 1 1 1 2 2 2 3 5% 78%	1900
	11th to 20th	Night	4 3 1 4 3 2 2 3 6% 5% 68%	1964
	21st to end	Night	5% 3 1 3 2 3 3 2 4 5% 67%	2090
October	1st to 10th	Night	5% 3 1 4 3 2 2 2 2 4 72%	3692
	11th to 20th	Night	4 4 2 4 3 3 3 3 4 6% 63%	3777
	21st to end	Night	6% 7% 2 6% 3 4 5% 4 6% 7% 49%	4424
November	1st to 10th	Night	12% 9% 3 6% 5% 5% 3 3 6% 7% 42%	2502
	11th to 20th	Night	13% 9% 2 6% 5% 5% 5% 4 8% 9% 35%	2470
	21st to end	Night	10% 9% 3 6% 5% 5% 6% 5% 7% 7% 37%	2647
December	1st to 10th	Night	11% 10% 4 8% 7% 5% 6% 5% 6% 7% 32%	2660
	11th to 20th	Night	11% 13% 4 10% 7% 7% 7% 5% 6% 7% 23%	3276
	21st to end	Night	10% 12% 4 12% 10% 7% 6% 6% 7% 7% 20%	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% 13% 13% 14% 3	2539
	11th to 20th	Day	62% 12% 13% 8% 4 1	2540
	21st to end	Day	57% 11% 15% 12% 3 1	2835
February	1st to 10th	Day	46% 11% 19% 18% 6%	1710
	11th to 20th	Day	45% 10% 17% 19% 8% 1	1817
	21st to end	Day	45% 10% 17% 18% 9% 1	1570
March	1st to 10th	Day	47% 10% 12% 19% 11% 1	3138
	11th to 20th	Day	29% 7% 14% 36% 13%	3294
	21st to end	Day	47% 12% 14% 20% 6% 1	4155
April	1st to 10th	Day	44% 6% 15% 19% 13% 2	2280
	11th to 20th	Day	40% 5% 14% 20% 17% 4	2252
	21st to end	Day	34% 8% 13% 26% 15% 4	2375
May	1st to 10th	Day	32% 7% 13% 27% 18% 4	4203
	11th to 20th	Day	21% 4 7% 25% 31% 11%	4380
	21st to end	Day	30% 7% 14% 26% 21% 2	4814
June	1st to 10th	Day	35% 7% 11% 26% 19% 2	2660
	11th to 20th	Day	25% 5% 9% 25% 26% 10%	2660
	21st to end	Day	16% 4 7% 20% 32% 20%	2660
July	1st to 10th	Day	8% 2 3 9% 19% 59%	4351
	11th to 20th	Day	13% 2 3 8% 18% 56%	4345
	21st to end	Day	12% 3 2 9% 28% 46%	4639
August	1st to 10th	Day	19% 2 4 11% 26% 37%	4384
	11th to 20th	Day	8% 2 3 15% 35% 37%	3808
	21st to end	Day	12% 2 4 20% 32% 31%	4179
September	1st to 10th	Day	13% 3 4 17% 32% 31%	2280
	11th to 20th	Day	20% 4 8% 20% 28% 21%	2215
	21st to end	Day	25% 3 7% 21% 26% 16%	2090
October	1st to 10th	Day	20% 3 7% 20% 31% 19%	3286
	11th to 20th	Day	30% 4 9% 27% 24% 5%	3161
	21st to end	Day	38% 6% 11% 26% 17% 3	3133
November	1st to 10th	Day	43% 6% 13% 21% 15% 1	1737
	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	55% 15% 15% 11% 3	4406
	11th to 20th	Night	62% 10% 12% 10% 5% 1	4420
	21st to end	Night	54% 12% 15% 14% 4 1	4820
February	1st to 10th	Night	44% 10% 17% 20% 9%	2470
	11th to 20th	Night	43% 9% 18% 19% 10% 2	2261
	21st to end	Night	46% 8% 16% 18% 10% 1	1884
March	1st to 10th	Night	49% 9% 14% 18% 9% 2	3736
	11th to 20th	Night	31% 6% 14% 34% 14%	3683
	21st to end	Night	42% 13% 18% 19% 7% 1	3497
April	1st to 10th	Night	41% 6% 17% 20% 14% 2	1900
	11th to 20th	Night	39% 5% 13% 26% 13% 3	1879
	21st to end	Night	33% 7% 16% 25% 15% 2	1804
May	1st to 10th	Night	31% 6% 13% 26% 22% 3	2748
	11th to 20th	Night	21% 5% 8% 26% 36% 5%	2516
	21st to end	Night	32% 7% 12% 28% 19% 2	2762
June	1st to 10th	Night	37% 6% 13% 27% 16% 1	1520
	11th to 20th	Night	28% 6% 7% 25% 26% 8%	1520
	21st to end	Night	16% 4 9% 22% 33% 16%	1520
July	1st to 10th	Night	9% 2 3 12% 19% 55%	2500
	11th to 20th	Night	11% 2 3 9% 19% 55%	2492
	21st to end	Night	16% 2 3 6% 30% 42%	2674
August	1st to 10th	Night	24% 4 5% 11% 22% 33%	2521
	11th to 20th	Night	13% 2 4 14% 33% 34%	3103
	21st to end	Night	15% 3 3 19% 31% 30%	3498
September	1st to 10th	Night	11% 3 5% 15% 31% 35%	1900
	11th to 20th	Night	18% 3 8% 21% 28% 22%	1964
	21st to end	Night	19% 4 6% 22% 29% 21%	2090
October	1st to 10th	Night	20% 3 6% 16% 29% 27%	3692
	11th to 20th	Night	23% 3 9% 29% 29% 6%	3777
	21st to end	Night	32% 5% 11% 26% 22% 4	4424
November	1st to 10th	Night	42% 6% 13% 20% 17% 3	2502
	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	18% 8% 19% 27% 19% 9%	180
	21st to end	Day	14% 6% 24% 30% 16% 11%	226
February	1st to 10th	Day	10% 14% 30% 23% 19% 5%	370
	11th to 20th	Day	14% 15% 28% 24% 16% 3	434
	21st to end	Day	11% 16% 29% 23% 17% 5%	382
March	1st to 10th	Day	15% 16% 33% 23% 12% 2	460
	11th to 20th	Day	12% 14% 25% 25% 20% 5%	460
	21st to end	Day	13% 16% 29% 27% 14% 2	506
April	1st to 10th	Day	15% 17% 24% 21% 16% 8%	460
	11th to 20th	Day	14% 14% 30% 21% 13% 9%	452
	21st to end	Day	10% 12% 27% 25% 19% 7%	460
May	1st to 10th	Day	7% 12% 24% 26% 19% 11%	463
	11th to 20th	Day	14% 11% 20% 24% 19% 13%	488
	21st to end	Day	9% 8% 16% 23% 26% 18%	529
June	1st to 10th	Day	9% 7% 18% 23% 23% 19%	490
	11th to 20th	Day	9% 11% 21% 28% 21% 11%	490
	21st to end	Day	2 4 17% 29% 27% 20%	490
July	1st to 10th	Day	3 1 16% 31% 34% 15%	486
	11th to 20th	Day	2 1 16% 30% 32% 19%	484
	21st to end	Day	1 2 12% 30% 34% 21%	531
August	1st to 10th	Day	5% 2 14% 29% 31% 20%	487
	11th to 20th	Day	2 4 12% 27% 30% 26%	477
	21st to end	Day	2 4 16% 27% 26% 25%	539
September	1st to 10th	Day	3 2 13% 29% 28% 24%	490
	11th to 20th	Day	8% 4 15% 24% 29% 21%	490
	21st to end	Day	7% 5% 15% 24% 32% 16%	490
October	1st to 10th	Day	10% 6% 19% 21% 24% 20%	490
	11th to 20th	Day	10% 6% 21% 21% 27% 16%	490
	21st to end	Day	13% 5% 21% 25% 25% 11%	350
November	1st to 10th	Day	15% 8% 20% 27% 20% 10%	291
	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	13% 10% 19% 33% 21% 4	760
	21st to end	Night	14% 6% 18% 39% 21% 3	836
February	1st to 10th	Night	12% 7% 30% 33% 18% 1	760
	11th to 20th	Night	13% 7% 24% 35% 19% 2	744
	21st to end	Night	8% 13% 25% 37% 17% 1	628
March	1st to 10th	Night	14% 7% 30% 33% 17% 1	760
	11th to 20th	Night	9% 9% 24% 35% 21% 2	760
	21st to end	Night	11% 10% 30% 34% 14% 1	836
April	1st to 10th	Night	13% 9% 22% 36% 18% 2	760
	11th to 20th	Night	10% 8% 28% 30% 21% 3	751
	21st to end	Night	11% 5% 26% 38% 19% 1	664
May	1st to 10th	Night	8% 8% 27% 39% 18% 1	510
	11th to 20th	Night	9% 6% 23% 35% 24% 3	374
	21st to end	Night	10% 5% 22% 32% 27% 3	411
June	1st to 10th	Night	10% 3 21% 40% 24% 2	380
	11th to 20th	Night	8% 6% 22% 44% 17% 3	380
	21st to end	Night	3 3 17% 48% 27% 1	380
July	1st to 10th	Night	2 2 16% 53% 26% 1	370
	11th to 20th	Night	1 1 16% 60% 21% 1	368
	21st to end	Night	1 2 14% 57% 25%	416
August	1st to 10th	Night	3 2 12% 53% 29% 1	378
	11th to 20th	Night	1 2 10% 48% 38% 2	711
	21st to end	Night	3 2 12% 48% 33% 3	836
September	1st to 10th	Night	3 2 12% 44% 37% 2	760
	11th to 20th	Night	4 3 13% 35% 40% 5%	760
	21st to end	Night	6% 4 13% 38% 33% 6%	760
October	1st to 10th	Night	8% 2 17% 40% 28% 4	760
	11th to 20th	Night	7% 4 19% 36% 27% 6%	760
	21st to end	Night	11% 4 18% 38% 25% 4	836
November	1st to 10th	Night	17% 5% 19% 36% 21% 2	770
	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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