Heppner
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heppner clear sky chart from 2005-11-06 to 2024-01-14.

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	10% 8% 3 5% 5% 3 4 4 5% 7% 45%	74798
	Night	10% 9% 3 6% 5% 3 4 5% 5% 6% 42%	74975
Transparency	Day	39% 7% 11% 21% 17% 6%	74501
	Night	42% 7% 12% 20% 14% 5%	74793
Seeing	Day	12% 12% 27% 28% 17% 4	13361
	Night	14% 9% 22% 32% 19% 4	22577

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	15% 14% 5% 10% 7% 4 6% 6% 7% 6% 20%	1519
	11th to 20th	Day	15% 12% 4 5% 8% 4 6% 6% 5% 9% 27%	1464
	21st to end	Day	13% 15% 4 7% 6% 3 5% 5% 6% 6% 30%	1584
February	1st to 10th	Day	16% 15% 6% 7% 6% 3 5% 5% 6% 5% 27%	1611
	11th to 20th	Day	13% 16% 5% 6% 6% 3 4 6% 4 7% 29%	1638
	21st to end	Day	13% 14% 6% 9% 8% 5% 4 6% 5% 6% 26%	1480
March	1st to 10th	Day	12% 12% 5% 9% 7% 5% 5% 5% 5% 8% 26%	1800
	11th to 20th	Day	11% 14% 5% 9% 8% 4 5% 5% 5% 6% 27%	1894
	21st to end	Day	13% 15% 5% 8% 7% 4 6% 6% 7% 7% 22%	2344
April	1st to 10th	Day	13% 13% 4 7% 7% 4 6% 6% 6% 6% 29%	2160
	11th to 20th	Day	11% 12% 3 7% 6% 3 5% 5% 6% 8% 36%	2129
	21st to end	Day	11% 9% 3 6% 5% 4 5% 5% 6% 7% 41%	2268
May	1st to 10th	Day	8% 7% 2 6% 5% 3 4 4 6% 7% 47%	2509
	11th to 20th	Day	11% 7% 3 7% 6% 4 5% 5% 6% 9% 37%	2477
	21st to end	Day	14% 7% 3 5% 6% 4 6% 4 5% 7% 39%	2723
June	1st to 10th	Day	13% 7% 2 6% 5% 2 5% 5% 6% 8% 41%	2520
	11th to 20th	Day	11% 6% 2 4 4 2 4 4 5% 8% 49%	2520
	21st to end	Day	5% 3 1 3 3 2 3 4 5% 6% 64%	2520
July	1st to 10th	Day	2 2 1 2 3 2 3 4 4 4 74%	2520
	11th to 20th	Day	2 2 1 2 3 1 2 3 4 5% 74%	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 2 4 3 3 6% 72%	2507
	11th to 20th	Day	3 1 1 2 3 1 2 3 4 6% 75%	2268
	21st to end	Day	3 3 1 2 3 2 3 3 3 5% 71%	2376
September	1st to 10th	Day	3 2 1 2 3 2 2 3 4 7% 71%	2160
	11th to 20th	Day	6% 5% 2 4 4 3 4 4 5% 5% 59%	2131
	21st to end	Day	9% 7% 1 4 5% 3 3 4 5% 7% 53%	1980
October	1st to 10th	Day	14% 8% 2 5% 5% 3 3 3 5% 6% 47%	1810
	11th to 20th	Day	10% 7% 2 5% 4 3 5% 5% 6% 8% 46%	1800
	21st to end	Day	14% 8% 4 6% 5% 4 5% 4 5% 6% 40%	1796
November	1st to 10th	Day	17% 10% 4 8% 6% 3 5% 5% 5% 7% 31%	1674
	11th to 20th	Day	14% 14% 5% 7% 7% 4 6% 6% 5% 7% 23%	1593
	21st to end	Day	13% 12% 5% 7% 6% 4 5% 5% 7% 7% 29%	1520
December	1st to 10th	Day	13% 11% 6% 7% 7% 4 5% 5% 5% 8% 30%	1520
	11th to 20th	Day	11% 16% 4 9% 7% 4 6% 6% 7% 8% 22%	1928
	21st to end	Day	14% 17% 5% 8% 7% 3 5% 5% 5% 5% 25%	2794
January	1st to 10th	Night	16% 16% 4 9% 7% 4 6% 5% 5% 7% 20%	2646
	11th to 20th	Night	16% 13% 5% 7% 7% 3 5% 5% 5% 7% 27%	2568
	21st to end	Night	14% 13% 5% 7% 6% 3 5% 5% 6% 6% 29%	2772
February	1st to 10th	Night	14% 14% 6% 8% 7% 3 4 5% 6% 5% 28%	2346
	11th to 20th	Night	12% 17% 5% 8% 5% 4 4 4 5% 5% 31%	2209
	21st to end	Night	11% 14% 5% 9% 9% 4 5% 4 5% 6% 27%	1776
March	1st to 10th	Night	11% 12% 4 6% 7% 3 5% 6% 7% 8% 30%	2160
	11th to 20th	Night	10% 12% 3 6% 7% 4 6% 6% 6% 7% 32%	2064
	21st to end	Night	11% 12% 4 8% 8% 4 6% 6% 6% 8% 28%	2012
April	1st to 10th	Night	12% 12% 4 5% 7% 4 4 5% 5% 7% 35%	1800
	11th to 20th	Night	11% 10% 4 7% 5% 3 3 4 6% 7% 40%	1779
	21st to end	Night	11% 8% 3 5% 6% 4 4 5% 5% 7% 41%	1692
May	1st to 10th	Night	8% 5% 1 4 4 3 5% 5% 5% 8% 53%	1449
	11th to 20th	Night	11% 6% 3 5% 4 3 5% 4 5% 8% 45%	1416
	21st to end	Night	11% 6% 2 4 5% 3 5% 5% 5% 8% 45%	1552
June	1st to 10th	Night	11% 5% 2 6% 5% 2 4 4 6% 8% 46%	1440
	11th to 20th	Night	12% 6% 3 4 4 3 4 5% 4 7% 49%	1440
	21st to end	Night	5% 4 1 3 3 2 3 4 5% 4 66%	1440
July	1st to 10th	Night	3 1 1 2 2 1 3 4 5% 7% 70%	1440
	11th to 20th	Night	1 1 1 2 2 2 3 3 3 5% 77%	1440
	21st to end	Night	1 1 1 2 2 1 3 2 3 5% 79%	1576
August	1st to 10th	Night	3 2 1 2 2 2 3 4 5% 7% 70%	1432
	11th to 20th	Night	2 1 1 2 2 2 2 3 3 5% 77%	1626
	21st to end	Night	3 2 1 2 2 2 2 3 3 5% 74%	1980
September	1st to 10th	Night	3 2 1 2 2 1 3 3 3 4 76%	1800
	11th to 20th	Night	5% 3 1 4 3 2 3 5% 6% 7% 61%	1828
	21st to end	Night	8% 5% 2 4 4 2 4 3 4 6% 57%	1980
October	1st to 10th	Night	10% 5% 2 4 4 3 4 4 5% 5% 53%	2146
	11th to 20th	Night	10% 6% 2 5% 5% 4 4 4 5% 7% 47%	2160
	21st to end	Night	12% 9% 3 6% 5% 4 3 4 5% 6% 41%	2559
November	1st to 10th	Night	17% 12% 3 6% 6% 3 5% 5% 5% 6% 32%	2405
	11th to 20th	Night	16% 11% 4 8% 6% 4 6% 6% 6% 6% 28%	2584
	21st to end	Night	11% 13% 4 8% 7% 4 5% 6% 6% 6% 32%	2660
December	1st to 10th	Night	13% 12% 3 7% 6% 4 6% 6% 7% 7% 29%	2660
	11th to 20th	Night	12% 13% 4 9% 8% 5% 6% 7% 7% 8% 22%	3276
	21st to end	Night	13% 14% 5% 8% 7% 4 6% 5% 5% 5% 29%	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	63% 10% 11% 13% 3	1519
	11th to 20th	Day	55% 8% 13% 16% 6% 2	1464
	21st to end	Day	53% 8% 16% 13% 8% 1	1584
February	1st to 10th	Day	58% 8% 12% 16% 6%	1611
	11th to 20th	Day	53% 8% 14% 15% 9% 1	1647
	21st to end	Day	58% 8% 11% 13% 9% 1	1480
March	1st to 10th	Day	56% 8% 13% 14% 8% 1	1800
	11th to 20th	Day	56% 6% 13% 18% 6%	1894
	21st to end	Day	60% 10% 12% 15% 3	2344
April	1st to 10th	Day	54% 7% 13% 15% 9% 1	2160
	11th to 20th	Day	47% 6% 14% 18% 12% 2	2132
	21st to end	Day	43% 8% 10% 24% 13% 1	2268
May	1st to 10th	Day	36% 8% 11% 29% 16% 1	2509
	11th to 20th	Day	43% 8% 12% 24% 12% 1	2480
	21st to end	Day	44% 8% 12% 23% 12% 1	2724
June	1st to 10th	Day	41% 8% 11% 25% 13% 1	2520
	11th to 20th	Day	34% 5% 13% 28% 16% 3	2520
	21st to end	Day	22% 6% 10% 30% 24% 8%	2520
July	1st to 10th	Day	14% 4 9% 22% 31% 20%	2451
	11th to 20th	Day	13% 4 8% 13% 35% 27%	2445
	21st to end	Day	9% 3 4 15% 44% 26%	2589
August	1st to 10th	Day	14% 3 8% 22% 36% 16%	2490
	11th to 20th	Day	12% 4 6% 26% 36% 16%	2268
	21st to end	Day	17% 4 6% 28% 34% 11%	2376
September	1st to 10th	Day	14% 5% 8% 27% 30% 16%	2160
	11th to 20th	Day	27% 6% 8% 22% 26% 11%	2131
	21st to end	Day	31% 7% 9% 26% 21% 6%	1980
October	1st to 10th	Day	39% 5% 11% 21% 20% 4	1810
	11th to 20th	Day	36% 7% 13% 24% 17% 2	1800
	21st to end	Day	44% 7% 12% 23% 13% 1	1796
November	1st to 10th	Day	51% 7% 12% 21% 6% 2	1674
	11th to 20th	Day	59% 8% 14% 15% 5%	1593
	21st to end	Day	51% 8% 15% 16% 8% 1	1520
December	1st to 10th	Day	53% 10% 14% 17% 5% 1	1520
	11th to 20th	Day	57% 9% 19% 11% 3	1928
	21st to end	Day	59% 7% 13% 18% 3	2794
January	1st to 10th	Night	63% 9% 13% 12% 3	2646
	11th to 20th	Night	57% 8% 13% 13% 8% 1	2568
	21st to end	Night	54% 7% 14% 15% 9% 1	2772
February	1st to 10th	Night	57% 7% 14% 15% 8%	2346
	11th to 20th	Night	55% 7% 13% 17% 7% 1	2211
	21st to end	Night	58% 7% 11% 15% 8% 2	1776
March	1st to 10th	Night	51% 8% 12% 18% 9% 2	2160
	11th to 20th	Night	48% 9% 13% 23% 5% 1	2064
	21st to end	Night	52% 10% 16% 18% 3	2012
April	1st to 10th	Night	47% 9% 13% 22% 8%	1800
	11th to 20th	Night	44% 7% 13% 23% 11% 2	1779
	21st to end	Night	42% 7% 15% 19% 14% 2	1692
May	1st to 10th	Night	30% 8% 16% 29% 17% 1	1449
	11th to 20th	Night	37% 8% 15% 26% 12% 2	1416
	21st to end	Night	37% 9% 17% 24% 12% 1	1552
June	1st to 10th	Night	36% 8% 13% 28% 12% 2	1440
	11th to 20th	Night	34% 7% 12% 30% 13% 4	1440
	21st to end	Night	22% 5% 12% 30% 24% 7%	1440
July	1st to 10th	Night	13% 6% 12% 22% 27% 21%	1400
	11th to 20th	Night	12% 4 9% 18% 29% 29%	1392
	21st to end	Night	9% 2 5% 15% 40% 28%	1488
August	1st to 10th	Night	14% 4 8% 22% 34% 18%	1424
	11th to 20th	Night	12% 3 8% 26% 33% 18%	1626
	21st to end	Night	14% 3 8% 26% 36% 12%	1980
September	1st to 10th	Night	14% 4 8% 29% 30% 15%	1800
	11th to 20th	Night	21% 6% 11% 25% 23% 14%	1828
	21st to end	Night	29% 5% 10% 24% 23% 8%	1980
October	1st to 10th	Night	34% 5% 10% 26% 21% 4	2146
	11th to 20th	Night	37% 6% 11% 22% 20% 4	2160
	21st to end	Night	43% 7% 12% 20% 15% 3	2559
November	1st to 10th	Night	52% 7% 9% 20% 10% 1	2405
	11th to 20th	Night	54% 9% 13% 17% 8%	2584
	21st to end	Night	50% 7% 13% 17% 12% 1	2660
December	1st to 10th	Night	52% 9% 16% 16% 6% 1	2660
	11th to 20th	Night	57% 9% 16% 12% 6%	3276
	21st to end	Night	54% 8% 13% 18% 6% 1	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	26% 17% 26% 17% 10% 4	180
	11th to 20th	Day	24% 14% 31% 16% 9% 6%	166
	21st to end	Day	24% 15% 26% 18% 16% 2	176
February	1st to 10th	Day	25% 17% 28% 21% 8% 2	331
	11th to 20th	Day	23% 20% 25% 21% 10% 1	363
	21st to end	Day	19% 18% 25% 28% 9% 1	346
March	1st to 10th	Day	19% 16% 37% 20% 8% 1	420
	11th to 20th	Day	16% 17% 27% 24% 13% 3	420
	21st to end	Day	18% 15% 34% 22% 9% 2	462
April	1st to 10th	Day	20% 19% 26% 21% 11% 3	420
	11th to 20th	Day	16% 16% 33% 21% 10% 4	412
	21st to end	Day	10% 18% 31% 23% 15% 2	420
May	1st to 10th	Day	11% 13% 30% 29% 15% 3	423
	11th to 20th	Day	17% 9% 27% 28% 15% 4	448
	21st to end	Day	11% 9% 24% 31% 19% 6%	485
June	1st to 10th	Day	10% 13% 25% 27% 19% 6%	450
	11th to 20th	Day	12% 16% 28% 30% 12% 2	450
	21st to end	Day	3 10% 28% 34% 20% 5%	450
July	1st to 10th	Day	2 6% 26% 46% 18% 2	446
	11th to 20th	Day	2 7% 32% 35% 20% 5%	444
	21st to end	Day	1 6% 25% 41% 20% 7%	487
August	1st to 10th	Day	2 6% 25% 36% 23% 9%	447
	11th to 20th	Day	2 3 20% 34% 31% 10%	437
	21st to end	Day	5% 5% 28% 33% 23% 5%	495
September	1st to 10th	Day	4 6% 21% 32% 30% 6%	450
	11th to 20th	Day	6% 7% 22% 36% 25% 4	450
	21st to end	Day	12% 7% 23% 33% 21% 3	450
October	1st to 10th	Day	16% 7% 22% 32% 18% 4	450
	11th to 20th	Day	10% 15% 24% 26% 20% 6%	450
	21st to end	Day	18% 13% 27% 24% 15% 5%	311
November	1st to 10th	Day	17% 17% 28% 27% 10% 1	270
	11th to 20th	Day	15% 20% 23% 27% 12% 4	214
	21st to end	Day	16% 14% 26% 26% 14% 4	180
December	1st to 10th	Day	14% 18% 23% 19% 18% 7%	180
	11th to 20th	Day	27% 14% 32% 20% 5% 2	180
	21st to end	Day	18% 18% 30% 22% 12% 2	198
January	1st to 10th	Night	23% 16% 24% 21% 15% 2	760
	11th to 20th	Night	21% 14% 22% 21% 18% 4	734
	21st to end	Night	22% 9% 21% 28% 18% 3	792
February	1st to 10th	Night	20% 15% 23% 27% 13% 2	720
	11th to 20th	Night	19% 12% 22% 28% 18% 2	704
	21st to end	Night	18% 16% 28% 28% 9% 2	592
March	1st to 10th	Night	15% 12% 28% 29% 13% 3	720
	11th to 20th	Night	15% 12% 24% 30% 18% 2	720
	21st to end	Night	14% 13% 30% 29% 12% 2	792
April	1st to 10th	Night	15% 11% 24% 32% 15% 3	720
	11th to 20th	Night	15% 11% 28% 26% 16% 4	711
	21st to end	Night	13% 11% 26% 34% 14% 3	612
May	1st to 10th	Night	9% 5% 30% 33% 20% 3	369
	11th to 20th	Night	13% 4 18% 37% 25% 3	354
	21st to end	Night	13% 6% 19% 39% 19% 4	389
June	1st to 10th	Night	11% 5% 26% 37% 20% 2	360
	11th to 20th	Night	15% 7% 30% 35% 13% 1	360
	21st to end	Night	5% 4 22% 46% 21% 3	360
July	1st to 10th	Night	3 1 17% 54% 21% 3	350
	11th to 20th	Night	1 1 23% 54% 18% 3	348
	21st to end	Night	1 18% 50% 27% 3	394
August	1st to 10th	Night	4 16% 49% 28% 4	358
	11th to 20th	Night	3 1 11% 39% 35% 10%	558
	21st to end	Night	4 3 17% 42% 28% 6%	792
September	1st to 10th	Night	4 2 15% 41% 31% 6%	720
	11th to 20th	Night	5% 3 15% 35% 32% 9%	720
	21st to end	Night	9% 5% 16% 37% 25% 8%	720
October	1st to 10th	Night	12% 4 18% 38% 24% 5%	720
	11th to 20th	Night	12% 9% 19% 30% 23% 7%	720
	21st to end	Night	16% 9% 22% 31% 16% 7%	792
November	1st to 10th	Night	22% 9% 23% 30% 14% 1	740
	11th to 20th	Night	22% 14% 23% 25% 13% 4	760
	21st to end	Night	17% 12% 24% 27% 16% 5%	760
December	1st to 10th	Night	18% 11% 22% 28% 18% 4	760
	11th to 20th	Night	23% 14% 25% 24% 13% 2	760
	21st to end	Night	25% 18% 25% 22% 9%	836

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