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 2026-01-02.

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	8% 8% 3 6% 4 4 4 3 5% 6% 49%	136298
	Night	9% 9% 3 6% 4 4 4 4 5% 6% 45%	132360
Transparency	Day	35% 6% 10% 23% 18% 8%	131039
	Night	39% 6% 12% 22% 15% 6%	128619
Seeing	Day	12% 12% 27% 28% 16% 4	15865
	Night	14% 9% 22% 33% 18% 3	25015

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	16% 18% 6% 10% 5% 5% 6% 5% 6% 6% 16%	3647
	11th to 20th	Day	12% 14% 4 8% 5% 5% 5% 3 5% 7% 33%	3640
	21st to end	Day	10% 13% 4 7% 5% 4 4 3 5% 5% 39%	4004
February	1st to 10th	Day	15% 18% 5% 8% 5% 4 5% 3 6% 5% 25%	1790
	11th to 20th	Day	13% 17% 4 7% 6% 4 5% 4 5% 7% 28%	1825
	21st to end	Day	12% 15% 5% 11% 6% 5% 4 4 5% 6% 26%	1650
March	1st to 10th	Day	8% 9% 3 8% 6% 7% 7% 6% 8% 10% 29%	4518
	11th to 20th	Day	7% 15% 4 9% 5% 4 5% 3 4 5% 38%	4797
	21st to end	Day	10% 14% 5% 11% 7% 7% 6% 5% 6% 7% 22%	5898
April	1st to 10th	Day	12% 14% 3 8% 6% 5% 6% 4 6% 7% 30%	2400
	11th to 20th	Day	9% 12% 3 7% 5% 4 4 4 6% 7% 39%	2369
	21st to end	Day	10% 9% 3 6% 5% 5% 4 4 6% 6% 41%	2520
May	1st to 10th	Day	8% 8% 2 5% 3 3 3 3 6% 7% 52%	6309
	11th to 20th	Day	9% 8% 2 6% 4 4 4 3 5% 7% 46%	6277
	21st to end	Day	7% 7% 2 5% 4 4 4 4 6% 8% 49%	6902
June	1st to 10th	Day	12% 7% 2 6% 4 4 4 4 7% 7% 43%	2800
	11th to 20th	Day	10% 7% 2 5% 4 3 3 3 5% 8% 50%	2800
	21st to end	Day	5% 4 1 4 3 3 3 3 5% 6% 64%	2800
July	1st to 10th	Day	2 2 1 2 2 2 2 2 3 4 79%	6319
	11th to 20th	Day	1 2 1 2 1 1 1 1 3 3 83%	6320
	21st to end	Day	2 1 1 2 2 2 2 2 4 5% 78%	6880
August	1st to 10th	Day	4 3 1 3 2 3 3 3 4 7% 67%	6210
	11th to 20th	Day	3 2 1 2 2 1 2 2 3 5% 78%	5712
	21st to end	Day	4 3 2 4 3 3 4 3 4 6% 64%	5984
September	1st to 10th	Day	3 2 1 2 2 3 3 3 5% 7% 69%	2400
	11th to 20th	Day	6% 5% 2 5% 3 4 4 3 4 5% 58%	2367
	21st to end	Day	8% 6% 1 5% 3 3 4 3 4 6% 56%	2200
October	1st to 10th	Day	9% 5% 2 4 3 3 3 2 5% 6% 59%	3290
	11th to 20th	Day	6% 6% 2 6% 4 4 5% 4 7% 9% 46%	3261
	21st to end	Day	12% 9% 3 8% 5% 6% 6% 4 6% 7% 34%	3215
November	1st to 10th	Day	16% 10% 4 9% 5% 5% 4 4 5% 7% 31%	1854
	11th to 20th	Day	14% 15% 4 8% 6% 6% 5% 5% 5% 7% 23%	1760
	21st to end	Day	11% 13% 5% 9% 5% 5% 5% 4 6% 7% 29%	1680
December	1st to 10th	Day	11% 9% 4 5% 5% 4 4 4 5% 7% 43%	2700
	11th to 20th	Day	13% 15% 4 11% 7% 5% 6% 4 7% 7% 20%	3108
	21st to end	Day	16% 17% 4 9% 6% 5% 6% 4 6% 5% 23%	4092
January	1st to 10th	Night	17% 20% 5% 11% 6% 5% 6% 5% 6% 5% 14%	6320
	11th to 20th	Night	13% 14% 4 8% 4 3 4 3 4 6% 36%	6320
	21st to end	Night	9% 11% 4 8% 5% 5% 5% 4 6% 6% 38%	6952
February	1st to 10th	Night	13% 16% 6% 9% 5% 4 4 4 5% 5% 27%	2607
	11th to 20th	Night	11% 18% 5% 9% 5% 4 4 3 5% 5% 30%	2462
	21st to end	Night	10% 15% 5% 10% 8% 5% 4 4 5% 6% 28%	1980
March	1st to 10th	Night	7% 9% 3 7% 6% 5% 6% 5% 9% 10% 34%	5376
	11th to 20th	Night	7% 12% 3 8% 5% 5% 5% 4 5% 6% 41%	5188
	21st to end	Night	9% 13% 4 10% 7% 6% 6% 5% 7% 8% 25%	5077
April	1st to 10th	Night	11% 12% 3 6% 6% 5% 4 4 6% 7% 36%	2000
	11th to 20th	Night	10% 10% 3 7% 4 4 4 3 6% 7% 42%	1979
	21st to end	Night	11% 8% 2 6% 5% 5% 4 4 5% 7% 43%	1880
May	1st to 10th	Night	8% 7% 2 5% 4 4 4 3 5% 5% 54%	3649
	11th to 20th	Night	9% 8% 2 6% 4 4 4 2 4 5% 52%	3616
	21st to end	Night	9% 6% 1 4 3 3 4 3 5% 6% 55%	3972
June	1st to 10th	Night	10% 5% 2 6% 4 3 4 3 6% 7% 49%	1600
	11th to 20th	Night	11% 7% 2 5% 3 4 4 4 5% 6% 49%	1600
	21st to end	Night	5% 4 1 4 3 3 3 3 5% 4 66%	1600
July	1st to 10th	Night	1 1 1 2 1 2 3 2 4 6% 76%	3640
	11th to 20th	Night	1 1 1 1 2 2 1 2 4 84%	3640
	21st to end	Night	2 2 1 2 1 2 2 2 4 6% 77%	3970
August	1st to 10th	Night	3 2 1 3 3 3 4 4 5% 7% 64%	3582
	11th to 20th	Night	2 2 1 3 2 3 3 2 3 5% 75%	4134
	21st to end	Night	3 3 1 4 3 3 3 3 4 6% 67%	5015
September	1st to 10th	Night	3 1 1 3 2 2 3 3 4 5% 73%	2000
	11th to 20th	Night	5% 3 2 4 3 3 3 4 6% 7% 60%	2032
	21st to end	Night	7% 5% 2 4 3 3 3 3 5% 6% 58%	2200
October	1st to 10th	Night	6% 4 2 4 3 3 3 2 4 5% 65%	3905
	11th to 20th	Night	9% 6% 2 5% 4 4 4 4 5% 8% 50%	3897
	21st to end	Night	10% 9% 3 7% 4 5% 5% 4 6% 8% 39%	4584
November	1st to 10th	Night	16% 13% 3 8% 5% 4 5% 4 5% 6% 32%	2665
	11th to 20th	Night	15% 12% 4 9% 5% 6% 5% 4 7% 6% 27%	2856
	21st to end	Night	12% 13% 4 7% 6% 5% 5% 5% 6% 6% 31%	2940
December	1st to 10th	Night	9% 9% 3 5% 4 4 5% 5% 7% 7% 44%	4700
	11th to 20th	Night	15% 16% 4 11% 7% 6% 6% 5% 6% 7% 17%	5316
	21st to end	Night	15% 15% 4 9% 6% 5% 5% 4 5% 6% 27%	7106

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	62% 12% 11% 12% 2	3647
	11th to 20th	Day	49% 6% 11% 23% 9% 1	3640
	21st to end	Day	45% 7% 10% 19% 15% 4	4004
February	1st to 10th	Day	60% 8% 11% 15% 6%	1790
	11th to 20th	Day	53% 8% 14% 15% 9% 1	1834
	21st to end	Day	57% 8% 11% 13% 9% 1	1650
March	1st to 10th	Day	46% 7% 11% 19% 15% 2	4518
	11th to 20th	Day	46% 5% 9% 29% 10%	4797
	21st to end	Day	58% 9% 12% 17% 5%	5898
April	1st to 10th	Day	52% 7% 14% 17% 9% 1	2400
	11th to 20th	Day	45% 6% 14% 20% 13% 2	2372
	21st to end	Day	42% 8% 10% 25% 13% 1	2520
May	1st to 10th	Day	30% 5% 9% 28% 25% 2	6309
	11th to 20th	Day	35% 5% 12% 26% 19% 3	6280
	21st to end	Day	31% 8% 16% 32% 13% 1	6904
June	1st to 10th	Day	40% 8% 10% 26% 15% 1	2800
	11th to 20th	Day	33% 5% 12% 28% 19% 4	2800
	21st to end	Day	21% 5% 10% 31% 24% 8%	2800
July	1st to 10th	Day	11% 2 5% 17% 32% 34%	6251
	11th to 20th	Day	9% 2 4 9% 33% 44%	6245
	21st to end	Day	10% 2 6% 26% 36% 19%	6681
August	1st to 10th	Day	16% 2 5% 16% 37% 24%	4524
	11th to 20th	Day	11% 3 5% 38% 33% 10%	4137
	21st to end	Day	19% 3 7% 29% 30% 12%	4311
September	1st to 10th	Day	15% 5% 9% 26% 30% 15%	2400
	11th to 20th	Day	27% 5% 8% 24% 25% 10%	2367
	21st to end	Day	30% 6% 9% 27% 21% 7%	2200
October	1st to 10th	Day	28% 3 9% 26% 26% 8%	3290
	11th to 20th	Day	34% 6% 17% 26% 17% 1	3261
	21st to end	Day	46% 6% 10% 25% 13%	3215
November	1st to 10th	Day	52% 7% 13% 21% 6% 1	1854
	11th to 20th	Day	59% 8% 14% 14% 5%	1760
	21st to end	Day	51% 8% 15% 17% 7% 1	1680
December	1st to 10th	Day	40% 8% 14% 30% 8% 1	2700
	11th to 20th	Day	60% 7% 18% 12% 3	3108
	21st to end	Day	60% 6% 13% 17% 3	4092
January	1st to 10th	Night	67% 11% 10% 10% 2	6320
	11th to 20th	Night	48% 5% 14% 23% 9% 1	6320
	21st to end	Night	44% 8% 12% 19% 14% 3	6952
February	1st to 10th	Night	58% 7% 13% 14% 8%	2607
	11th to 20th	Night	55% 7% 13% 17% 8% 2	2464
	21st to end	Night	56% 8% 10% 16% 9% 2	1980
March	1st to 10th	Night	40% 7% 9% 23% 18% 3	5376
	11th to 20th	Night	41% 7% 10% 32% 10%	5188
	21st to end	Night	52% 11% 14% 19% 4	5077
April	1st to 10th	Night	47% 9% 14% 23% 7%	2000
	11th to 20th	Night	41% 7% 13% 25% 12% 2	1979
	21st to end	Night	39% 7% 16% 21% 15% 2	1880
May	1st to 10th	Night	30% 6% 13% 22% 26% 2	3646
	11th to 20th	Night	33% 5% 13% 30% 18% 1	3616
	21st to end	Night	28% 8% 21% 30% 12%	3972
June	1st to 10th	Night	34% 8% 12% 28% 14% 3	1600
	11th to 20th	Night	34% 7% 11% 30% 14% 4	1600
	21st to end	Night	22% 5% 12% 30% 25% 7%	1600
July	1st to 10th	Night	10% 3 8% 18% 28% 33%	3600
	11th to 20th	Night	8% 2 5% 12% 29% 44%	3592
	21st to end	Night	11% 2 5% 28% 32% 22%	3857
August	1st to 10th	Night	16% 3 5% 15% 36% 26%	2601
	11th to 20th	Night	13% 3 6% 42% 26% 10%	2983
	21st to end	Night	16% 2 11% 27% 29% 15%	3608
September	1st to 10th	Night	15% 4 9% 28% 30% 15%	2000
	11th to 20th	Night	22% 6% 11% 26% 23% 12%	2032
	21st to end	Night	28% 5% 10% 26% 24% 8%	2200
October	1st to 10th	Night	24% 4 10% 25% 33% 4	3905
	11th to 20th	Night	33% 5% 17% 22% 21% 2	3897
	21st to end	Night	41% 6% 9% 27% 14% 2	4584
November	1st to 10th	Night	52% 8% 10% 19% 10% 1	2665
	11th to 20th	Night	55% 8% 12% 17% 8%	2856
	21st to end	Night	50% 7% 14% 17% 11% 1	2940
December	1st to 10th	Night	36% 9% 13% 31% 10%	4700
	11th to 20th	Night	64% 7% 13% 12% 4	5316
	21st to end	Night	56% 7% 14% 17% 5% 1	7106

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	27% 17% 25% 18% 9% 4	202
	11th to 20th	Day	22% 16% 29% 19% 11% 6%	200
	21st to end	Day	22% 13% 27% 21% 14% 3	220
February	1st to 10th	Day	23% 18% 29% 21% 7% 2	390
	11th to 20th	Day	23% 18% 25% 23% 10% 1	430
	21st to end	Day	20% 17% 26% 28% 8% 1	414
March	1st to 10th	Day	18% 16% 35% 21% 8% 1	500
	11th to 20th	Day	16% 18% 27% 23% 13% 3	500
	21st to end	Day	17% 16% 35% 22% 8% 1	550
April	1st to 10th	Day	18% 17% 28% 21% 12% 4	500
	11th to 20th	Day	14% 16% 34% 22% 11% 4	492
	21st to end	Day	9% 18% 32% 23% 15% 3	500
May	1st to 10th	Day	11% 13% 30% 28% 14% 4	503
	11th to 20th	Day	18% 10% 29% 26% 14% 3	528
	21st to end	Day	11% 10% 24% 30% 19% 7%	573
June	1st to 10th	Day	10% 12% 24% 28% 19% 6%	530
	11th to 20th	Day	12% 15% 30% 29% 12% 2	530
	21st to end	Day	3 10% 28% 34% 19% 7%	530
July	1st to 10th	Day	3 5% 26% 44% 19% 3	526
	11th to 20th	Day	2 6% 31% 35% 21% 5%	524
	21st to end	Day	1 5% 26% 39% 20% 8%	575
August	1st to 10th	Day	2 6% 26% 36% 22% 8%	527
	11th to 20th	Day	2 4 22% 34% 30% 9%	517
	21st to end	Day	6% 5% 26% 33% 23% 6%	583
September	1st to 10th	Day	4 5% 20% 31% 31% 7%	530
	11th to 20th	Day	7% 7% 21% 35% 25% 5%	530
	21st to end	Day	11% 8% 22% 34% 21% 5%	530
October	1st to 10th	Day	15% 7% 24% 33% 18% 4	530
	11th to 20th	Day	10% 15% 25% 26% 18% 5%	530
	21st to end	Day	17% 12% 28% 25% 15% 4	378
November	1st to 10th	Day	17% 16% 28% 26% 11% 1	330
	11th to 20th	Day	16% 20% 25% 25% 11% 3	261
	21st to end	Day	16% 14% 25% 26% 14% 4	220
December	1st to 10th	Day	17% 18% 20% 18% 20% 7%	220
	11th to 20th	Day	27% 16% 31% 18% 5% 2	220
	21st to end	Day	19% 17% 31% 21% 10% 2	242
January	1st to 10th	Night	24% 15% 23% 22% 15% 2	804
	11th to 20th	Night	21% 14% 22% 22% 18% 3	800
	21st to end	Night	20% 9% 22% 29% 18% 3	880
February	1st to 10th	Night	21% 15% 23% 27% 12% 2	800
	11th to 20th	Night	18% 12% 22% 29% 17% 2	784
	21st to end	Night	18% 15% 28% 28% 9% 2	660
March	1st to 10th	Night	15% 12% 28% 31% 13% 2	800
	11th to 20th	Night	15% 12% 24% 30% 18% 2	800
	21st to end	Night	14% 13% 31% 30% 11% 2	880
April	1st to 10th	Night	15% 10% 26% 32% 15% 2	800
	11th to 20th	Night	14% 11% 30% 27% 16% 3	791
	21st to end	Night	12% 10% 25% 36% 14% 2	680
May	1st to 10th	Night	9% 6% 29% 34% 19% 3	409
	11th to 20th	Night	12% 4 20% 38% 23% 3	394
	21st to end	Night	12% 5% 19% 40% 19% 4	433
June	1st to 10th	Night	10% 5% 26% 38% 20% 2	400
	11th to 20th	Night	15% 6% 29% 37% 12% 1	400
	21st to end	Night	6% 4 22% 46% 20% 3	400
July	1st to 10th	Night	3 1 16% 55% 22% 3	390
	11th to 20th	Night	1 1 21% 55% 19% 3	388
	21st to end	Night	1 17% 51% 27% 3	438
August	1st to 10th	Night	4 1 15% 50% 27% 3	398
	11th to 20th	Night	2 1 11% 42% 34% 9%	622
	21st to end	Night	4 3 17% 44% 28% 5%	880
September	1st to 10th	Night	4 2 15% 42% 32% 6%	800
	11th to 20th	Night	5% 3 15% 37% 31% 8%	800
	21st to end	Night	8% 5% 16% 37% 26% 8%	800
October	1st to 10th	Night	11% 4 17% 39% 24% 5%	800
	11th to 20th	Night	13% 8% 20% 30% 23% 7%	800
	21st to end	Night	15% 9% 23% 32% 16% 6%	880
November	1st to 10th	Night	22% 9% 23% 30% 14% 1	820
	11th to 20th	Night	22% 14% 23% 26% 12% 3	840
	21st to end	Night	18% 11% 22% 28% 15% 5%	840
December	1st to 10th	Night	17% 11% 22% 27% 18% 4	840
	11th to 20th	Night	24% 13% 25% 25% 12% 2	840
	21st to end	Night	25% 17% 26% 22% 10%	924

Page generated at 2025-12-29 22:14:08. Version ac07

Copyright © 2025 Attilla Danko.