Horse Heaven Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Horse Heaven Observatory clear sky chart from 2005-11-06 to 2024-11-06.

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% 51%	105328
	Night	7% 8% 3 7% 4 4 4 4 5% 7% 46%	102397
Transparency	Day	33% 6% 10% 22% 19% 10%	105074
	Night	37% 7% 11% 22% 16% 8%	102240
Seeing	Day	9% 8% 21% 27% 24% 11%	14419
	Night	10% 7% 23% 35% 22% 3	23454

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	12% 20% 6% 13% 6% 5% 4 4 6% 6% 18%	2539
	11th to 20th	Day	18% 17% 6% 10% 6% 4 4 3 4 5% 23%	2540
	21st to end	Day	19% 18% 6% 16% 8% 5% 4 4 4 4 12%	2794
February	1st to 10th	Day	12% 14% 4 9% 6% 5% 6% 4 5% 7% 27%	1677
	11th to 20th	Day	10% 12% 4 9% 6% 5% 5% 3 6% 6% 34%	1707
	21st to end	Day	9% 9% 3 8% 6% 5% 7% 4 7% 9% 34%	1570
March	1st to 10th	Day	6% 8% 2 7% 5% 5% 7% 5% 8% 11% 36%	3138
	11th to 20th	Day	4 6% 2 6% 4 4 4 3 5% 7% 55%	3356
	21st to end	Day	8% 9% 4 9% 7% 6% 7% 5% 8% 7% 31%	4103
April	1st to 10th	Day	7% 8% 3 7% 7% 5% 6% 5% 6% 9% 38%	2280
	11th to 20th	Day	6% 7% 3 7% 5% 4 5% 5% 6% 8% 45%	2249
	21st to end	Day	4 6% 2 6% 5% 5% 5% 4 7% 8% 46%	2432
May	1st to 10th	Day	8% 6% 1 4 4 3 4 3 6% 7% 54%	4420
	11th to 20th	Day	4 3 2 4 3 3 4 3 6% 6% 62%	4377
	21st to end	Day	6% 7% 2 7% 5% 5% 6% 4 6% 7% 45%	4813
June	1st to 10th	Day	8% 6% 2 6% 4 3 5% 4 6% 7% 48%	2660
	11th to 20th	Day	5% 5% 2 4 4 4 4 3 7% 8% 54%	2660
	21st to end	Day	3 3 1 4 3 3 3 3 5% 6% 66%	2660
July	1st to 10th	Day	1 1 2 2 1 1 2 3 3 83%	4420
	11th to 20th	Day	1 1 1 2 1 1 1 2 3 4 82%	4420
	21st to end	Day	1 1 1 2 1 2 2 2 3 5% 80%	4790
August	1st to 10th	Day	3 2 1 3 2 2 3 2 4 5% 74%	4400
	11th to 20th	Day	1 1 1 2 2 2 3 3 4 7% 74%	4038
	21st to end	Day	2 4 1 4 3 3 3 2 4 5% 68%	4180
September	1st to 10th	Day	2 2 1 3 2 2 2 3 4 7% 71%	2280
	11th to 20th	Day	3 4 2 5% 4 4 4 4 5% 8% 58%	2256
	21st to end	Day	5% 5% 2 5% 3 3 4 3 5% 7% 58%	2086
October	1st to 10th	Day	5% 3 1 3 2 2 3 3 6% 9% 62%	3180
	11th to 20th	Day	4 4 2 5% 5% 5% 6% 5% 8% 9% 48%	3161
	21st to end	Day	9% 6% 3 7% 5% 5% 5% 5% 6% 8% 42%	3107
November	1st to 10th	Day	9% 9% 3 8% 6% 6% 6% 4 7% 7% 35%	1719
	11th to 20th	Day	11% 14% 4 9% 7% 5% 5% 3 6% 6% 30%	1554
	21st to end	Day	10% 12% 4 12% 7% 6% 6% 5% 6% 7% 25%	1520
December	1st to 10th	Day	9% 13% 6% 13% 9% 5% 6% 4 5% 6% 25%	1520
	11th to 20th	Day	13% 16% 7% 16% 9% 6% 5% 4 5% 5% 14%	1928
	21st to end	Day	13% 13% 7% 15% 9% 7% 6% 4 5% 4 17%	2794
January	1st to 10th	Night	13% 16% 6% 13% 7% 6% 5% 4 6% 6% 18%	4406
	11th to 20th	Night	17% 15% 5% 10% 5% 5% 4 3 5% 8% 25%	4420
	21st to end	Night	16% 16% 7% 17% 8% 5% 4 3 4 4 16%	4862
February	1st to 10th	Night	11% 12% 3 8% 6% 5% 5% 4 6% 7% 33%	2499
	11th to 20th	Night	8% 10% 4 8% 6% 5% 6% 4 6% 7% 35%	2360
	21st to end	Night	7% 10% 4 9% 5% 5% 5% 5% 8% 7% 35%	1884
March	1st to 10th	Night	6% 7% 3 7% 5% 5% 6% 5% 8% 10% 40%	3736
	11th to 20th	Night	5% 6% 2 5% 3 4 4 3 5% 6% 57%	3623
	21st to end	Night	5% 8% 3 8% 7% 6% 7% 7% 8% 9% 34%	3537
April	1st to 10th	Night	8% 9% 3 8% 6% 5% 4 5% 7% 8% 37%	1900
	11th to 20th	Night	5% 8% 3 7% 5% 4 5% 3 6% 6% 48%	1879
	21st to end	Night	5% 6% 3 6% 5% 5% 6% 4 7% 7% 49%	1744
May	1st to 10th	Night	6% 6% 2 6% 3 4 4 3 5% 6% 54%	2540
	11th to 20th	Night	4 3 1 4 3 3 3 4 5% 7% 63%	2516
	21st to end	Night	4 4 2 4 3 4 4 4 6% 10% 55%	2762
June	1st to 10th	Night	7% 5% 1 4 5% 5% 4 4 5% 9% 50%	1520
	11th to 20th	Night	7% 6% 2 4 4 3 4 3 5% 6% 57%	1520
	21st to end	Night	3 3 1 4 3 3 3 4 5% 5% 65%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 2 3 84%	2540
	11th to 20th	Night	1 1 1 1 2 1 2 3 4 83%	2540
	21st to end	Night	1 1 1 2 1 1 2 2 3 4 83%	2761
August	1st to 10th	Night	3 3 1 3 2 2 2 3 4 6% 72%	2529
	11th to 20th	Night	2 2 3 2 2 3 3 4 6% 73%	2797
	21st to end	Night	1 2 1 3 3 3 3 3 5% 6% 70%	3498
September	1st to 10th	Night	2 2 1 2 2 2 3 2 3 5% 74%	1900
	11th to 20th	Night	3 3 2 4 3 4 4 4 5% 7% 62%	1924
	21st to end	Night	4 4 1 4 2 3 4 3 6% 8% 61%	2090
October	1st to 10th	Night	4 3 1 4 3 2 3 3 5% 7% 65%	3800
	11th to 20th	Night	6% 4 2 5% 3 5% 5% 5% 7% 9% 50%	3777
	21st to end	Night	7% 5% 2 7% 5% 4 5% 4 6% 9% 46%	4449
November	1st to 10th	Night	12% 9% 3 9% 5% 5% 4 4 5% 6% 38%	2482
	11th to 20th	Night	10% 10% 4 9% 6% 6% 5% 5% 6% 6% 34%	2624
	21st to end	Night	10% 11% 3 8% 5% 5% 6% 5% 6% 6% 35%	2660
December	1st to 10th	Night	11% 13% 5% 12% 7% 5% 5% 4 5% 6% 27%	2660
	11th to 20th	Night	14% 15% 7% 13% 8% 7% 5% 4 6% 6% 16%	3276
	21st to end	Night	12% 15% 6% 10% 6% 6% 6% 4 5% 6% 23%	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	65% 10% 8% 12% 5%	2539
	11th to 20th	Day	64% 7% 15% 12% 2	2540
	21st to end	Day	76% 7% 8% 6% 2	2794
February	1st to 10th	Day	56% 9% 16% 14% 4 1	1677
	11th to 20th	Day	50% 7% 14% 20% 8% 1	1716
	21st to end	Day	44% 10% 17% 19% 9% 1	1570
March	1st to 10th	Day	37% 8% 12% 26% 17%	3138
	11th to 20th	Day	28% 5% 13% 41% 13%	3356
	21st to end	Day	46% 10% 15% 19% 9% 1	4103
April	1st to 10th	Day	40% 8% 15% 22% 15% 1	2280
	11th to 20th	Day	36% 5% 13% 23% 17% 4	2252
	21st to end	Day	32% 7% 13% 28% 17% 4	2432
May	1st to 10th	Day	28% 4 9% 28% 26% 5%	4420
	11th to 20th	Day	21% 4 8% 30% 28% 9%	4380
	21st to end	Day	34% 8% 16% 28% 11% 3	4814
June	1st to 10th	Day	34% 6% 10% 28% 19% 4	2660
	11th to 20th	Day	26% 6% 11% 29% 24% 5%	2660
	21st to end	Day	20% 3 8% 29% 29% 11%	2660
July	1st to 10th	Day	9% 2 3 13% 26% 47%	4351
	11th to 20th	Day	9% 2 3 8% 24% 54%	4345
	21st to end	Day	9% 2 4 16% 34% 34%	4639
August	1st to 10th	Day	15% 2 4 12% 37% 29%	4384
	11th to 20th	Day	12% 2 5% 34% 35% 11%	4080
	21st to end	Day	20% 3 7% 26% 34% 11%	4179
September	1st to 10th	Day	13% 4 8% 27% 31% 17%	2280
	11th to 20th	Day	23% 6% 10% 26% 25% 9%	2256
	21st to end	Day	26% 6% 13% 31% 18% 6%	2086
October	1st to 10th	Day	20% 4 11% 36% 27% 3	3180
	11th to 20th	Day	30% 7% 19% 27% 16% 1	3161
	21st to end	Day	39% 6% 13% 28% 12% 1	3107
November	1st to 10th	Day	47% 8% 15% 21% 7% 1	1719
	11th to 20th	Day	55% 8% 14% 17% 5% 1	1554
	21st to end	Day	57% 10% 15% 11% 7% 1	1520
December	1st to 10th	Day	61% 9% 10% 14% 5%	1520
	11th to 20th	Day	72% 7% 10% 8% 2	1928
	21st to end	Day	69% 9% 9% 10% 3	2794
January	1st to 10th	Night	64% 10% 13% 10% 4	4406
	11th to 20th	Night	58% 7% 16% 16% 3	4420
	21st to end	Night	72% 7% 10% 9% 2	4862
February	1st to 10th	Night	49% 9% 19% 18% 5% 1	2499
	11th to 20th	Night	46% 8% 15% 21% 9% 1	2362
	21st to end	Night	45% 10% 13% 21% 8% 2	1884
March	1st to 10th	Night	35% 8% 12% 30% 14% 1	3736
	11th to 20th	Night	27% 5% 11% 37% 19%	3623
	21st to end	Night	40% 13% 15% 25% 6%	3537
April	1st to 10th	Night	43% 7% 15% 22% 12% 2	1900
	11th to 20th	Night	35% 6% 11% 26% 17% 5%	1879
	21st to end	Night	32% 8% 14% 24% 17% 5%	1744
May	1st to 10th	Night	29% 5% 7% 25% 29% 5%	2540
	11th to 20th	Night	20% 4 10% 29% 32% 6%	2516
	21st to end	Night	22% 10% 19% 36% 11% 2	2762
June	1st to 10th	Night	30% 7% 9% 28% 20% 6%	1520
	11th to 20th	Night	29% 5% 7% 32% 22% 6%	1520
	21st to end	Night	21% 5% 7% 24% 29% 15%	1520
July	1st to 10th	Night	8% 2 3 14% 24% 49%	2500
	11th to 20th	Night	8% 2 3 9% 23% 55%	2492
	21st to end	Night	8% 2 3 14% 30% 42%	2674
August	1st to 10th	Night	16% 2 3 9% 34% 35%	2521
	11th to 20th	Night	14% 3 5% 31% 31% 16%	2821
	21st to end	Night	14% 4 7% 26% 31% 18%	3498
September	1st to 10th	Night	13% 3 7% 25% 30% 22%	1900
	11th to 20th	Night	21% 6% 9% 25% 25% 15%	1924
	21st to end	Night	22% 5% 11% 30% 23% 9%	2090
October	1st to 10th	Night	20% 3 8% 32% 34% 2	3800
	11th to 20th	Night	28% 6% 14% 28% 22% 2	3777
	21st to end	Night	34% 5% 11% 32% 16% 1	4449
November	1st to 10th	Night	45% 7% 13% 23% 10% 1	2482
	11th to 20th	Night	48% 10% 16% 19% 7% 1	2624
	21st to end	Night	47% 9% 17% 19% 8% 1	2660
December	1st to 10th	Night	58% 8% 14% 15% 4	2660
	11th to 20th	Night	67% 10% 13% 8% 2	3276
	21st to end	Night	60% 9% 12% 11% 7%	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% 12% 24% 23% 13% 3	180
	11th to 20th	Day	21% 8% 19% 33% 13% 4	180
	21st to end	Day	17% 7% 21% 32% 21% 3	198
February	1st to 10th	Day	20% 9% 24% 28% 16% 3	337
	11th to 20th	Day	15% 12% 26% 27% 16% 3	385
	21st to end	Day	11% 16% 26% 29% 15% 4	382
March	1st to 10th	Day	13% 12% 32% 23% 15% 3	460
	11th to 20th	Day	11% 12% 23% 29% 18% 7%	460
	21st to end	Day	12% 15% 27% 29% 15% 3	506
April	1st to 10th	Day	13% 17% 24% 25% 16% 5%	460
	11th to 20th	Day	10% 15% 29% 25% 13% 8%	452
	21st to end	Day	7% 13% 27% 25% 20% 7%	460
May	1st to 10th	Day	9% 9% 27% 26% 22% 7%	463
	11th to 20th	Day	11% 8% 22% 26% 20% 13%	488
	21st to end	Day	11% 5% 18% 28% 24% 13%	529
June	1st to 10th	Day	9% 9% 20% 24% 24% 13%	490
	11th to 20th	Day	7% 10% 28% 31% 16% 8%	490
	21st to end	Day	3 6% 18% 27% 31% 16%	490
July	1st to 10th	Day	1 2 15% 28% 43% 11%	486
	11th to 20th	Day	2 3 14% 29% 37% 15%	484
	21st to end	Day	1 3 12% 25% 36% 24%	531
August	1st to 10th	Day	2 4 13% 23% 33% 25%	487
	11th to 20th	Day	2 2 10% 23% 34% 29%	477
	21st to end	Day	4 5% 17% 26% 27% 21%	539
September	1st to 10th	Day	3 2 12% 29% 36% 18%	490
	11th to 20th	Day	5% 4 16% 27% 32% 15%	490
	21st to end	Day	7% 9% 15% 30% 30% 9%	490
October	1st to 10th	Day	8% 8% 23% 24% 26% 11%	490
	11th to 20th	Day	8% 10% 18% 28% 24% 11%	490
	21st to end	Day	14% 10% 25% 30% 14% 8%	336
November	1st to 10th	Day	11% 14% 24% 33% 15% 2	285
	11th to 20th	Day	17% 12% 28% 21% 16% 7%	196
	21st to end	Day	10% 7% 23% 29% 22% 8%	180
December	1st to 10th	Day	9% 10% 23% 31% 14% 13%	180
	11th to 20th	Day	21% 6% 25% 33% 13% 3	180
	21st to end	Day	19% 6% 26% 32% 14% 4	198
January	1st to 10th	Night	22% 9% 23% 31% 13% 2	760
	11th to 20th	Night	17% 7% 23% 31% 19% 3	760
	21st to end	Night	17% 5% 19% 38% 19% 3	836
February	1st to 10th	Night	16% 8% 25% 33% 15% 2	760
	11th to 20th	Night	12% 10% 24% 33% 20% 2	744
	21st to end	Night	12% 12% 25% 34% 15% 1	628
March	1st to 10th	Night	12% 9% 25% 34% 18% 2	760
	11th to 20th	Night	8% 11% 23% 36% 20% 2	760
	21st to end	Night	10% 10% 33% 33% 13% 1	836
April	1st to 10th	Night	12% 11% 27% 32% 17% 2	760
	11th to 20th	Night	8% 13% 30% 28% 17% 3	751
	21st to end	Night	6% 12% 31% 31% 18% 1	604
May	1st to 10th	Night	4 9% 28% 34% 20% 3	380
	11th to 20th	Night	8% 7% 21% 33% 25% 5%	374
	21st to end	Night	4 5% 22% 41% 23% 4	411
June	1st to 10th	Night	8% 6% 26% 35% 24% 2	380
	11th to 20th	Night	9% 8% 32% 35% 14% 1	380
	21st to end	Night	5% 5% 23% 37% 28% 2	380
July	1st to 10th	Night	4 2 15% 48% 28% 3	370
	11th to 20th	Night	4 2 21% 45% 26% 2	368
	21st to end	Night	1 2 13% 47% 32% 4	416
August	1st to 10th	Night	3 2 14% 40% 36% 4	378
	11th to 20th	Night	3 1 12% 35% 38% 11%	546
	21st to end	Night	2 3 18% 37% 34% 7%	836
September	1st to 10th	Night	3 2 16% 38% 35% 5%	760
	11th to 20th	Night	5% 1 17% 31% 37% 9%	760
	21st to end	Night	6% 5% 19% 33% 31% 6%	760
October	1st to 10th	Night	10% 5% 19% 33% 29% 4	760
	11th to 20th	Night	9% 6% 22% 33% 25% 6%	760
	21st to end	Night	11% 7% 26% 33% 19% 5%	836
November	1st to 10th	Night	16% 7% 23% 37% 16% 1	764
	11th to 20th	Night	15% 9% 25% 32% 17% 3	760
	21st to end	Night	13% 6% 22% 36% 20% 3	760
December	1st to 10th	Night	15% 5% 21% 36% 20% 2	760
	11th to 20th	Night	19% 7% 21% 36% 17% 1	760
	21st to end	Night	19% 8% 26% 34% 12% 1	836

Page generated at 2024-11-03 10:19:06. Version ac07

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