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 2024-11-12.

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	8% 9% 3 6% 4 4 4 3 5% 6% 48%	105377
	Night	9% 10% 3 6% 4 4 4 4 5% 6% 44%	102481
Transparency	Day	36% 6% 10% 21% 17% 9%	105122
	Night	39% 7% 12% 21% 15% 6%	102325
Seeing	Day	12% 12% 27% 28% 16% 4	14497
	Night	14% 9% 22% 32% 18% 4	23569

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	14% 20% 6% 10% 6% 5% 6% 5% 7% 6% 16%	2539
	11th to 20th	Day	17% 18% 4 9% 6% 5% 4 4 5% 7% 20%	2540
	21st to end	Day	14% 17% 5% 9% 6% 5% 5% 4 5% 6% 24%	2794
February	1st to 10th	Day	15% 17% 5% 8% 5% 4 5% 3 6% 5% 26%	1700
	11th to 20th	Day	13% 16% 4 7% 6% 4 5% 4 5% 7% 28%	1731
	21st to end	Day	12% 15% 5% 11% 6% 5% 4 4 5% 5% 25%	1570
March	1st to 10th	Day	7% 10% 4 9% 6% 6% 7% 5% 7% 10% 29%	3138
	11th to 20th	Day	6% 11% 3 7% 4 4 4 3 5% 5% 48%	3352
	21st to end	Day	11% 16% 5% 10% 7% 7% 6% 5% 7% 7% 22%	4120
April	1st to 10th	Day	12% 15% 3 8% 6% 5% 6% 4 6% 6% 30%	2280
	11th to 20th	Day	10% 13% 3 8% 5% 4 4 4 6% 7% 37%	2249
	21st to end	Day	10% 10% 3 7% 5% 5% 5% 4 6% 6% 40%	2394
May	1st to 10th	Day	9% 10% 2 7% 4 4 4 3 6% 7% 43%	4409
	11th to 20th	Day	6% 5% 2 4 3 4 3 3 4 7% 59%	4377
	21st to end	Day	9% 9% 2 6% 5% 5% 5% 4 7% 8% 40%	4813
June	1st to 10th	Day	13% 7% 2 6% 5% 4 4 4 7% 7% 41%	2660
	11th to 20th	Day	10% 7% 2 5% 4 3 3 3 5% 8% 49%	2660
	21st to end	Day	5% 4 1 3 3 3 3 3 5% 6% 64%	2660
July	1st to 10th	Day	1 1 2 2 1 2 2 3 3 83%	4420
	11th to 20th	Day	1 1 1 2 2 1 2 2 3 4 81%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 4 5% 80%	4790
August	1st to 10th	Day	3 2 1 3 2 3 3 3 4 6% 71%	4400
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 6% 77%	3968
	21st to end	Day	3 3 1 4 3 3 3 2 3 5% 70%	4180
September	1st to 10th	Day	3 2 1 2 2 2 3 2 4 7% 71%	2280
	11th to 20th	Day	6% 5% 2 5% 4 4 4 4 5% 5% 57%	2249
	21st to end	Day	8% 6% 1 5% 3 3 4 3 5% 7% 54%	2090
October	1st to 10th	Day	9% 5% 2 4 3 3 3 2 5% 6% 59%	3190
	11th to 20th	Day	6% 6% 2 6% 4 4 5% 4 7% 9% 46%	3161
	21st to end	Day	12% 9% 3 8% 5% 6% 6% 4 6% 7% 34%	3115
November	1st to 10th	Day	16% 10% 4 9% 5% 5% 4 4 5% 7% 30%	1764
	11th to 20th	Day	14% 15% 4 9% 6% 6% 5% 5% 5% 7% 23%	1602
	21st to end	Day	12% 13% 5% 8% 5% 5% 5% 5% 6% 7% 29%	1520
December	1st to 10th	Day	12% 12% 5% 8% 6% 5% 5% 3 6% 7% 30%	1520
	11th to 20th	Day	11% 17% 4 10% 7% 5% 7% 4 7% 7% 22%	1928
	21st to end	Day	13% 18% 5% 9% 6% 5% 5% 4 5% 5% 25%	2794
January	1st to 10th	Night	14% 21% 6% 11% 6% 5% 6% 4 6% 6% 16%	4406
	11th to 20th	Night	19% 19% 5% 9% 5% 3 4 3 5% 7% 21%	4420
	21st to end	Night	12% 13% 5% 10% 7% 5% 6% 5% 7% 7% 23%	4862
February	1st to 10th	Night	14% 16% 6% 9% 5% 4 4 4 5% 5% 27%	2477
	11th to 20th	Night	12% 18% 5% 9% 5% 4 4 3 5% 5% 30%	2336
	21st to end	Night	10% 15% 5% 10% 8% 5% 4 4 5% 6% 27%	1884
March	1st to 10th	Night	6% 11% 4 7% 6% 4 5% 5% 9% 10% 34%	3736
	11th to 20th	Night	6% 10% 2 5% 4 4 4 4 5% 6% 50%	3626
	21st to end	Night	9% 14% 4 10% 7% 7% 7% 5% 7% 8% 23%	3533
April	1st to 10th	Night	11% 13% 3 6% 6% 5% 4 4 6% 7% 35%	1900
	11th to 20th	Night	11% 10% 4 7% 4 4 4 3 6% 7% 40%	1879
	21st to end	Night	11% 8% 2 7% 5% 5% 4 4 6% 7% 42%	1786
May	1st to 10th	Night	11% 9% 2 5% 4 4 5% 4 5% 6% 45%	2549
	11th to 20th	Night	7% 4 2 3 2 3 3 2 4 5% 63%	2516
	21st to end	Night	12% 7% 2 4 3 4 3 3 5% 6% 50%	2762
June	1st to 10th	Night	11% 6% 2 7% 4 3 4 4 6% 7% 46%	1520
	11th to 20th	Night	12% 7% 2 4 3 3 4 4 5% 6% 49%	1520
	21st to end	Night	5% 4 1 4 3 3 3 3 5% 4 66%	1520
July	1st to 10th	Night	2 1 1 1 1 2 2 3 4 83%	2540
	11th to 20th	Night	1 1 2 2 2 3 2 3 4 81%	2540
	21st to end	Night	1 1 1 2 2 2 2 2 3 4 80%	2761
August	1st to 10th	Night	4 2 1 2 2 2 3 3 4 6% 70%	2529
	11th to 20th	Night	2 2 1 3 2 2 3 2 3 5% 75%	2866
	21st to end	Night	2 2 1 3 2 3 3 2 3 5% 73%	3498
September	1st to 10th	Night	3 1 1 3 2 2 3 3 3 4 75%	1900
	11th to 20th	Night	5% 3 2 4 3 3 3 4 6% 7% 60%	1930
	21st to end	Night	8% 5% 2 4 3 3 3 3 5% 6% 57%	2090
October	1st to 10th	Night	6% 4 2 4 3 3 3 2 4 5% 65%	3786
	11th to 20th	Night	8% 6% 2 5% 4 4 4 4 5% 8% 50%	3777
	21st to end	Night	10% 9% 3 7% 4 5% 5% 4 6% 8% 39%	4442
November	1st to 10th	Night	16% 13% 3 8% 5% 4 5% 4 5% 6% 33%	2535
	11th to 20th	Night	16% 12% 4 9% 5% 6% 5% 4 6% 6% 28%	2597
	21st to end	Night	11% 14% 4 7% 6% 5% 5% 5% 6% 6% 31%	2660
December	1st to 10th	Night	13% 13% 3 8% 5% 5% 6% 5% 7% 6% 29%	2660
	11th to 20th	Night	12% 14% 4 10% 7% 6% 6% 5% 7% 7% 22%	3276
	21st to end	Night	13% 14% 4 9% 6% 5% 5% 4 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	62% 13% 10% 12% 2	2539
	11th to 20th	Day	62% 8% 11% 15% 4 1	2540
	21st to end	Day	59% 10% 13% 12% 5% 1	2794
February	1st to 10th	Day	59% 8% 12% 16% 6%	1700
	11th to 20th	Day	53% 9% 14% 15% 8% 1	1740
	21st to end	Day	58% 8% 12% 13% 9% 1	1570
March	1st to 10th	Day	45% 8% 13% 18% 16%	3138
	11th to 20th	Day	37% 6% 11% 36% 10%	3352
	21st to end	Day	58% 11% 11% 16% 4	4120
April	1st to 10th	Day	53% 7% 14% 16% 9% 1	2280
	11th to 20th	Day	46% 6% 14% 18% 13% 2	2252
	21st to end	Day	43% 8% 10% 25% 12% 1	2394
May	1st to 10th	Day	37% 7% 12% 28% 15% 1	4409
	11th to 20th	Day	26% 5% 9% 32% 24% 4	4380
	21st to end	Day	38% 10% 18% 24% 9% 1	4814
June	1st to 10th	Day	41% 8% 10% 25% 14% 1	2660
	11th to 20th	Day	33% 5% 12% 28% 18% 3	2660
	21st to end	Day	21% 5% 10% 31% 24% 8%	2660
July	1st to 10th	Day	9% 3 5% 13% 24% 46%	4351
	11th to 20th	Day	9% 3 4 8% 24% 51%	4345
	21st to end	Day	10% 2 6% 17% 38% 27%	4639
August	1st to 10th	Day	16% 2 5% 15% 37% 25%	4384
	11th to 20th	Day	11% 3 5% 38% 34% 9%	4009
	21st to end	Day	19% 3 7% 29% 31% 12%	4179
September	1st to 10th	Day	15% 4 8% 27% 30% 16%	2280
	11th to 20th	Day	28% 6% 8% 23% 25% 10%	2249
	21st to end	Day	30% 6% 10% 27% 21% 6%	2090
October	1st to 10th	Day	28% 3 9% 25% 26% 9%	3190
	11th to 20th	Day	33% 6% 17% 26% 17% 1	3161
	21st to end	Day	46% 6% 10% 25% 13% 1	3115
November	1st to 10th	Day	52% 7% 13% 20% 6% 1	1764
	11th to 20th	Day	59% 8% 13% 15% 5%	1602
	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	66% 10% 12% 10% 2	4406
	11th to 20th	Night	63% 6% 13% 12% 5% 1	4420
	21st to end	Night	55% 11% 16% 12% 5% 1	4862
February	1st to 10th	Night	57% 7% 14% 14% 8%	2477
	11th to 20th	Night	55% 7% 13% 17% 7% 1	2338
	21st to end	Night	57% 8% 11% 15% 8% 2	1884
March	1st to 10th	Night	41% 8% 11% 22% 17% 2	3736
	11th to 20th	Night	33% 7% 10% 38% 11% 1	3626
	21st to end	Night	51% 13% 16% 16% 3	3533
April	1st to 10th	Night	47% 9% 14% 22% 7%	1900
	11th to 20th	Night	43% 7% 14% 23% 11% 2	1879
	21st to end	Night	40% 8% 16% 20% 14% 2	1786
May	1st to 10th	Night	36% 8% 15% 24% 16% 1	2549
	11th to 20th	Night	23% 5% 12% 35% 24% 1	2516
	21st to end	Night	33% 9% 25% 25% 7%	2762
June	1st to 10th	Night	36% 8% 12% 28% 13% 3	1520
	11th to 20th	Night	34% 7% 11% 30% 14% 4	1520
	21st to end	Night	22% 5% 12% 30% 25% 7%	1520
July	1st to 10th	Night	7% 3 7% 14% 29% 40%	2500
	11th to 20th	Night	9% 2 5% 12% 21% 50%	2492
	21st to end	Night	10% 2 4 18% 34% 31%	2674
August	1st to 10th	Night	15% 3 5% 14% 36% 26%	2521
	11th to 20th	Night	13% 3 6% 42% 26% 10%	2891
	21st to end	Night	16% 2 11% 27% 29% 15%	3498
September	1st to 10th	Night	14% 4 8% 28% 31% 15%	1900
	11th to 20th	Night	22% 6% 11% 25% 22% 13%	1930
	21st to end	Night	28% 5% 10% 26% 23% 7%	2090
October	1st to 10th	Night	24% 3 10% 25% 33% 5%	3786
	11th to 20th	Night	33% 5% 17% 22% 21% 3	3777
	21st to end	Night	42% 6% 10% 27% 14% 2	4442
November	1st to 10th	Night	52% 8% 9% 19% 10% 1	2535
	11th to 20th	Night	54% 9% 13% 17% 8%	2597
	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% 16% 28% 17% 9% 6%	180
	21st to end	Day	23% 14% 29% 18% 14% 2	198
February	1st to 10th	Day	24% 17% 29% 21% 8% 2	360
	11th to 20th	Day	22% 20% 26% 21% 10% 1	396
	21st to end	Day	19% 18% 26% 27% 8% 2	382
March	1st to 10th	Day	18% 17% 36% 20% 8% 1	460
	11th to 20th	Day	15% 17% 27% 24% 13% 4	460
	21st to end	Day	17% 16% 35% 22% 8% 1	506
April	1st to 10th	Day	19% 18% 28% 21% 11% 3	460
	11th to 20th	Day	15% 17% 33% 21% 11% 4	452
	21st to end	Day	10% 19% 32% 22% 15% 2	460
May	1st to 10th	Day	11% 14% 31% 27% 14% 3	463
	11th to 20th	Day	16% 9% 29% 27% 15% 4	488
	21st to end	Day	12% 10% 24% 30% 19% 6%	529
June	1st to 10th	Day	10% 13% 24% 28% 18% 6%	490
	11th to 20th	Day	12% 16% 29% 29% 12% 2	490
	21st to end	Day	3 10% 28% 33% 20% 6%	490
July	1st to 10th	Day	2 5% 26% 45% 18% 3	486
	11th to 20th	Day	2 6% 31% 35% 20% 5%	484
	21st to end	Day	1 5% 26% 41% 20% 8%	531
August	1st to 10th	Day	2 6% 26% 36% 23% 8%	487
	11th to 20th	Day	2 4 21% 34% 31% 9%	477
	21st to end	Day	6% 6% 27% 32% 24% 6%	539
September	1st to 10th	Day	5% 6% 21% 31% 31% 7%	490
	11th to 20th	Day	7% 7% 22% 35% 25% 4	490
	21st to end	Day	11% 8% 23% 33% 21% 4	490
October	1st to 10th	Day	15% 7% 23% 32% 18% 4	490
	11th to 20th	Day	9% 15% 25% 26% 19% 6%	490
	21st to end	Day	17% 13% 28% 24% 14% 4	344
November	1st to 10th	Day	17% 17% 28% 26% 11% 1	300
	11th to 20th	Day	16% 20% 23% 26% 12% 4	217
	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% 3	760
	21st to end	Night	21% 10% 22% 28% 17% 3	836
February	1st to 10th	Night	20% 16% 23% 27% 13% 2	760
	11th to 20th	Night	18% 12% 22% 29% 17% 1	744
	21st to end	Night	18% 16% 27% 28% 9% 2	628
March	1st to 10th	Night	15% 12% 28% 30% 13% 3	760
	11th to 20th	Night	14% 12% 24% 29% 19% 2	760
	21st to end	Night	14% 13% 31% 30% 11% 2	836
April	1st to 10th	Night	15% 11% 25% 32% 14% 3	760
	11th to 20th	Night	14% 11% 29% 26% 16% 3	751
	21st to end	Night	13% 11% 26% 34% 14% 2	646
May	1st to 10th	Night	10% 6% 29% 33% 19% 3	389
	11th to 20th	Night	12% 5% 18% 38% 24% 3	374
	21st to end	Night	13% 6% 19% 40% 18% 4	411
June	1st to 10th	Night	11% 5% 26% 37% 19% 2	380
	11th to 20th	Night	15% 6% 30% 35% 13% 1	380
	21st to end	Night	6% 3 22% 46% 20% 3	380
July	1st to 10th	Night	3 1 16% 55% 22% 3	370
	11th to 20th	Night	1 1 22% 56% 17% 3	368
	21st to end	Night	1 18% 51% 27% 3	416
August	1st to 10th	Night	4 16% 50% 27% 3	378
	11th to 20th	Night	2 1 12% 41% 34% 10%	590
	21st to end	Night	3 3 18% 43% 28% 6%	836
September	1st to 10th	Night	4 2 15% 41% 32% 6%	760
	11th to 20th	Night	5% 4 16% 36% 31% 9%	760
	21st to end	Night	8% 5% 16% 36% 25% 8%	760
October	1st to 10th	Night	11% 4 18% 39% 24% 5%	760
	11th to 20th	Night	12% 8% 19% 30% 23% 7%	760
	21st to end	Night	15% 8% 23% 31% 16% 6%	836
November	1st to 10th	Night	22% 10% 23% 30% 14% 1	780
	11th to 20th	Night	22% 14% 23% 24% 13% 4	764
	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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