Mountain High observatory
Clear Sky Chart
History

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

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	15% 6% 2 6% 5% 5% 5% 4 6% 7% 38%	101020
	Night	16% 7% 2 5% 4 4 4 4 6% 7% 41%	97889
Transparency	Day	22% 50% 7% 10% 8% 3	100833
	Night	21% 50% 7% 10% 8% 3	97746
Seeing	Day	21% 12% 24% 22% 14% 7%	14977
	Night	20% 10% 20% 27% 19% 4	25006

By Month

Percentage Cloud Cover SE (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	18% 5% 1 4 3 2 3 3 5% 8% 46%	2836
	11th to 20th	Day	16% 7% 2 5% 3 3 3 2 4 4 51%	2840
	21st to end	Day	26% 4 1 4 3 2 3 3 4 5% 45%	3124
February	1st to 10th	Day	18% 8% 3 6% 4 4 3 3 5% 5% 42%	1856
	11th to 20th	Day	20% 6% 2 6% 4 3 3 3 4 6% 41%	1848
	21st to end	Day	22% 8% 3 6% 4 3 4 3 3 6% 39%	1570
March	1st to 10th	Day	26% 6% 2 5% 3 3 3 3 5% 6% 40%	3307
	11th to 20th	Day	15% 6% 2 4 3 3 3 3 4 5% 52%	3480
	21st to end	Day	20% 7% 2 6% 4 4 4 4 4 5% 40%	3815
April	1st to 10th	Day	14% 5% 2 7% 4 4 5% 4 6% 8% 41%	2090
	11th to 20th	Day	16% 6% 2 6% 4 5% 5% 4 5% 6% 41%	2274
	21st to end	Day	15% 5% 1 5% 4 4 4 4 5% 6% 46%	2470
May	1st to 10th	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	4082
	11th to 20th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 7% 31%	4081
	21st to end	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 38%	4476
June	1st to 10th	Day	13% 7% 3 8% 6% 6% 7% 5% 7% 9% 28%	2470
	11th to 20th	Day	8% 6% 2 6% 6% 6% 7% 6% 9% 11% 33%	2470
	21st to end	Day	9% 6% 2 7% 7% 6% 7% 6% 7% 9% 34%	2470
July	1st to 10th	Day	8% 6% 3 9% 7% 7% 7% 6% 10% 9% 28%	4120
	11th to 20th	Day	11% 6% 3 9% 7% 7% 8% 5% 7% 10% 26%	4120
	21st to end	Day	15% 10% 4 12% 8% 8% 8% 6% 6% 7% 16%	4466
August	1st to 10th	Day	11% 7% 3 8% 6% 7% 7% 6% 8% 10% 27%	4104
	11th to 20th	Day	11% 6% 3 7% 5% 7% 7% 5% 8% 11% 32%	4044
	21st to end	Day	8% 5% 2 7% 5% 5% 6% 5% 7% 9% 41%	4101
September	1st to 10th	Day	14% 8% 3 6% 6% 6% 7% 4 7% 7% 34%	2090
	11th to 20th	Day	17% 8% 2 7% 5% 6% 5% 5% 6% 7% 32%	2090
	21st to end	Day	17% 7% 3 6% 6% 5% 4 4 5% 7% 37%	2090
October	1st to 10th	Day	16% 6% 2 4 3 3 3 3 4 6% 50%	2090
	11th to 20th	Day	13% 4 1 4 3 3 3 3 5% 6% 55%	1909
	21st to end	Day	15% 4 1 4 3 2 4 3 4 4 55%	2090
November	1st to 10th	Day	13% 6% 1 4 3 3 3 2 4 5% 57%	1740
	11th to 20th	Day	16% 5% 1 3 3 3 3 3 5% 6% 52%	1710
	21st to end	Day	18% 4 1 5% 3 3 3 3 5% 7% 47%	1710
December	1st to 10th	Day	23% 6% 2 6% 4 4 4 3 5% 6% 36%	1710
	11th to 20th	Day	18% 6% 2 4 2 3 3 3 5% 6% 48%	2153
	21st to end	Day	23% 5% 1 4 3 3 4 3 6% 6% 43%	3124
January	1st to 10th	Night	18% 6% 2 5% 3 3 3 3 5% 6% 47%	4109
	11th to 20th	Night	13% 7% 2 6% 5% 3 3 3 5% 6% 47%	4120
	21st to end	Night	26% 6% 2 4 3 3 3 2 4 6% 41%	4532
February	1st to 10th	Night	16% 6% 3 5% 4 3 3 3 6% 7% 45%	2322
	11th to 20th	Night	20% 7% 2 4 5% 4 4 3 4 4 42%	2218
	21st to end	Night	22% 6% 2 6% 4 4 4 3 5% 6% 38%	1884
March	1st to 10th	Night	25% 10% 2 5% 3 3 3 3 5% 8% 32%	3546
	11th to 20th	Night	11% 5% 2 4 3 3 4 4 5% 9% 49%	3480
	21st to end	Night	21% 6% 2 5% 5% 3 4 3 4 6% 41%	3817
April	1st to 10th	Night	14% 6% 2 5% 4 3 3 4 4 6% 48%	2090
	11th to 20th	Night	16% 6% 2 4 3 3 4 3 5% 6% 48%	1871
	21st to end	Night	13% 5% 2 4 3 3 4 3 5% 6% 49%	1710
May	1st to 10th	Night	15% 8% 2 7% 4 4 5% 4 7% 9% 36%	2813
	11th to 20th	Night	21% 8% 2 5% 4 3 4 4 6% 8% 35%	2812
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 8% 11% 41%	3079
June	1st to 10th	Night	13% 7% 2 6% 6% 5% 5% 5% 8% 10% 32%	1710
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 7% 11% 41%	1710
	21st to end	Night	9% 5% 2 6% 5% 5% 5% 5% 8% 11% 41%	1710
July	1st to 10th	Night	12% 8% 3 8% 7% 6% 6% 5% 7% 10% 29%	2840
	11th to 20th	Night	10% 6% 3 6% 6% 6% 6% 5% 9% 11% 32%	2840
	21st to end	Night	16% 10% 4 10% 6% 6% 5% 5% 7% 8% 22%	3087
August	1st to 10th	Night	12% 7% 3 8% 5% 5% 6% 5% 8% 12% 30%	2825
	11th to 20th	Night	16% 9% 3 7% 5% 5% 5% 4 7% 8% 32%	2785
	21st to end	Night	9% 5% 2 5% 5% 5% 5% 4 7% 10% 45%	3515
September	1st to 10th	Night	14% 6% 2 7% 5% 5% 5% 4 8% 7% 37%	2090
	11th to 20th	Night	19% 9% 2 6% 5% 4 5% 4 6% 6% 34%	2090
	21st to end	Night	19% 6% 2 5% 4 4 4 3 5% 6% 43%	2090
October	1st to 10th	Night	16% 5% 2 5% 3 3 3 3 4 6% 51%	2090
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 5% 52%	2270
	21st to end	Night	15% 5% 1 3 3 3 4 2 4 5% 55%	2508
November	1st to 10th	Night	15% 6% 1 4 3 3 3 2 4 7% 53%	2342
	11th to 20th	Night	16% 6% 2 4 3 2 4 3 4 5% 50%	2470
	21st to end	Night	17% 5% 2 5% 4 3 3 4 6% 7% 44%	2470
December	1st to 10th	Night	22% 8% 3 6% 3 3 4 4 4 6% 38%	2470
	11th to 20th	Night	16% 6% 2 4 3 3 3 2 4 6% 49%	3042
	21st to end	Night	23% 8% 2 5% 4 3 4 4 5% 7% 35%	4532

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	22% 36% 5% 14% 15% 8%	2837
	11th to 20th	Day	23% 37% 4 9% 18% 9%	2840
	21st to end	Day	26% 39% 3 13% 13% 7%	3124
February	1st to 10th	Day	16% 65% 2 7% 8% 2	1856
	11th to 20th	Day	17% 65% 3 6% 7% 3	1858
	21st to end	Day	19% 65% 2 4 6% 3	1570
March	1st to 10th	Day	32% 41% 5% 9% 7% 7%	3307
	11th to 20th	Day	17% 41% 3 9% 21% 10%	3480
	21st to end	Day	26% 40% 4 13% 12% 4	3815
April	1st to 10th	Day	15% 65% 5% 5% 7% 2	2090
	11th to 20th	Day	18% 66% 3 6% 5% 2	2274
	21st to end	Day	13% 65% 5% 9% 7% 1	2470
May	1st to 10th	Day	27% 44% 8% 13% 7% 1	4120
	11th to 20th	Day	31% 43% 7% 13% 6%	4085
	21st to end	Day	21% 44% 10% 11% 13% 1	4489
June	1st to 10th	Day	19% 67% 4 7% 2 1	2470
	11th to 20th	Day	15% 68% 8% 6% 3	2470
	21st to end	Day	16% 65% 8% 7% 4	2470
July	1st to 10th	Day	26% 45% 13% 14% 2	4055
	11th to 20th	Day	29% 44% 17% 9% 1	4051
	21st to end	Day	47% 40% 6% 5% 2	4324
August	1st to 10th	Day	29% 43% 12% 13% 2	4091
	11th to 20th	Day	19% 46% 17% 7% 8% 3	4083
	21st to end	Day	16% 42% 11% 23% 7% 1	4101
September	1st to 10th	Day	18% 62% 5% 8% 7% 1	2090
	11th to 20th	Day	20% 62% 5% 7% 5% 1	2090
	21st to end	Day	19% 62% 6% 8% 5%	2090
October	1st to 10th	Day	16% 60% 5% 7% 9% 2	2090
	11th to 20th	Day	11% 60% 5% 8% 9% 7%	1909
	21st to end	Day	13% 58% 3 10% 10% 5%	2090
November	1st to 10th	Day	17% 59% 2 8% 10% 4	1740
	11th to 20th	Day	15% 59% 2 9% 11% 4	1710
	21st to end	Day	14% 60% 3 9% 11% 3	1710
December	1st to 10th	Day	22% 60% 3 8% 5% 3	1710
	11th to 20th	Day	18% 47% 2 8% 15% 10%	2150
	21st to end	Day	25% 37% 5% 15% 15% 2	3124
January	1st to 10th	Night	25% 36% 5% 9% 17% 8%	4109
	11th to 20th	Night	22% 37% 5% 6% 20% 10%	4120
	21st to end	Night	29% 39% 5% 7% 13% 7%	4532
February	1st to 10th	Night	14% 64% 4 9% 7% 2	2322
	11th to 20th	Night	19% 64% 3 6% 7% 2	2219
	21st to end	Night	18% 64% 2 7% 6% 3	1884
March	1st to 10th	Night	35% 42% 7% 10% 4 2	3546
	11th to 20th	Night	15% 41% 4 12% 16% 11%	3480
	21st to end	Night	28% 41% 4 11% 9% 7%	3817
April	1st to 10th	Night	14% 65% 5% 7% 8% 2	2090
	11th to 20th	Night	16% 66% 3 8% 4 2	1871
	21st to end	Night	12% 65% 4 11% 7% 1	1710
May	1st to 10th	Night	26% 45% 8% 14% 6% 1	2840
	11th to 20th	Night	27% 44% 9% 12% 8%	2813
	21st to end	Night	15% 46% 13% 18% 8%	3087
June	1st to 10th	Night	17% 66% 6% 6% 3 1	1710
	11th to 20th	Night	12% 67% 9% 7% 4	1710
	21st to end	Night	12% 66% 9% 9% 5%	1710
July	1st to 10th	Night	28% 45% 15% 11% 1	2795
	11th to 20th	Night	22% 46% 19% 11% 1	2786
	21st to end	Night	39% 43% 10% 5% 2	2988
August	1st to 10th	Night	27% 45% 16% 10% 1	2814
	11th to 20th	Night	26% 45% 13% 9% 6% 1	2812
	21st to end	Night	13% 42% 13% 24% 7% 1	3515
September	1st to 10th	Night	16% 62% 7% 7% 7% 1	2090
	11th to 20th	Night	19% 63% 6% 7% 6%	2090
	21st to end	Night	18% 61% 6% 9% 5% 1	2090
October	1st to 10th	Night	15% 62% 5% 7% 9% 2	2090
	11th to 20th	Night	13% 60% 5% 8% 9% 6%	2270
	21st to end	Night	12% 59% 2 9% 13% 5%	2508
November	1st to 10th	Night	18% 58% 4 9% 7% 4	2342
	11th to 20th	Night	15% 60% 3 6% 10% 5%	2470
	21st to end	Night	15% 60% 3 10% 10% 2	2470
December	1st to 10th	Night	22% 60% 3 7% 6% 2	2470
	11th to 20th	Night	16% 48% 4 11% 16% 6%	3044
	21st to end	Night	31% 37% 6% 12% 11% 3	4532

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	32% 21% 33% 10% 3	270
	11th to 20th	Day	36% 21% 28% 13% 2	270
	21st to end	Day	32% 27% 29% 9% 2	297
February	1st to 10th	Day	28% 24% 38% 9% 1	270
	11th to 20th	Day	44% 23% 27% 5%	270
	21st to end	Day	42% 26% 26% 4 2	225
March	1st to 10th	Day	32% 15% 30% 16% 6%	379
	11th to 20th	Day	30% 21% 29% 15% 4 1	460
	21st to end	Day	28% 22% 28% 16% 5% 1	506
April	1st to 10th	Day	27% 15% 29% 20% 8% 1	460
	11th to 20th	Day	20% 21% 27% 21% 10% 2	452
	21st to end	Day	22% 15% 26% 21% 12% 4	460
May	1st to 10th	Day	18% 21% 26% 20% 9% 5%	463
	11th to 20th	Day	22% 10% 23% 25% 13% 7%	487
	21st to end	Day	19% 9% 19% 27% 14% 12%	529
June	1st to 10th	Day	16% 7% 20% 28% 17% 11%	490
	11th to 20th	Day	11% 6% 21% 23% 23% 15%	490
	21st to end	Day	11% 7% 26% 29% 15% 13%	490
July	1st to 10th	Day	9% 4 13% 30% 26% 17%	485
	11th to 20th	Day	10% 3 15% 27% 25% 20%	484
	21st to end	Day	10% 3 14% 29% 25% 19%	532
August	1st to 10th	Day	17% 5% 21% 23% 19% 16%	486
	11th to 20th	Day	11% 5% 15% 29% 25% 15%	479
	21st to end	Day	16% 3 13% 25% 29% 14%	539
September	1st to 10th	Day	12% 5% 18% 26% 29% 10%	490
	11th to 20th	Day	18% 6% 16% 24% 26% 10%	490
	21st to end	Day	21% 6% 17% 28% 22% 5%	490
October	1st to 10th	Day	19% 7% 21% 27% 18% 8%	490
	11th to 20th	Day	15% 12% 26% 28% 14% 4	490
	21st to end	Day	20% 11% 25% 30% 11% 3	539
November	1st to 10th	Day	19% 11% 30% 25% 12% 2	338
	11th to 20th	Day	22% 20% 33% 21% 4	270
	21st to end	Day	18% 17% 37% 20% 6% 1	270
December	1st to 10th	Day	34% 20% 30% 13% 3 1	270
	11th to 20th	Day	27% 16% 33% 20% 4	270
	21st to end	Day	33% 18% 33% 11% 4 1	297
January	1st to 10th	Night	28% 15% 29% 23% 6%	760
	11th to 20th	Night	23% 19% 27% 25% 6%	760
	21st to end	Night	24% 16% 35% 22% 3	836
February	1st to 10th	Night	21% 14% 27% 33% 4	760
	11th to 20th	Night	27% 17% 32% 21% 2	743
	21st to end	Night	29% 19% 28% 20% 4	628
March	1st to 10th	Night	24% 15% 29% 28% 5%	760
	11th to 20th	Night	24% 14% 30% 23% 8% 1	760
	21st to end	Night	23% 14% 30% 24% 8%	836
April	1st to 10th	Night	21% 17% 27% 25% 9% 1	760
	11th to 20th	Night	23% 10% 25% 26% 13% 2	609
	21st to end	Night	15% 11% 21% 33% 18% 2	570
May	1st to 10th	Night	16% 12% 21% 29% 21% 1	570
	11th to 20th	Night	20% 7% 18% 29% 23% 4	561
	21st to end	Night	16% 3 13% 28% 30% 9%	617
June	1st to 10th	Night	14% 3 14% 31% 31% 7%	570
	11th to 20th	Night	9% 3 15% 28% 32% 13%	570
	21st to end	Night	8% 2 14% 28% 40% 7%	570
July	1st to 10th	Night	11% 3 8% 23% 45% 9%	555
	11th to 20th	Night	12% 1 10% 22% 41% 13%	552
	21st to end	Night	9% 3 9% 26% 42% 12%	624
August	1st to 10th	Night	17% 3 10% 24% 35% 11%	567
	11th to 20th	Night	16% 5% 11% 25% 34% 10%	564
	21st to end	Night	13% 3 9% 26% 38% 11%	649
September	1st to 10th	Night	13% 3 12% 28% 34% 10%	760
	11th to 20th	Night	22% 3 12% 25% 32% 5%	760
	21st to end	Night	21% 5% 10% 34% 26% 4	760
October	1st to 10th	Night	17% 7% 17% 25% 26% 8%	760
	11th to 20th	Night	19% 11% 17% 31% 19% 3	760
	21st to end	Night	19% 9% 18% 35% 16% 3	836
November	1st to 10th	Night	17% 8% 20% 32% 20% 3	743
	11th to 20th	Night	20% 13% 21% 32% 12% 3	760
	21st to end	Night	19% 13% 21% 33% 14% 1	760
December	1st to 10th	Night	27% 14% 22% 29% 7% 1	760
	11th to 20th	Night	21% 13% 25% 32% 9% 1	760
	21st to end	Night	30% 13% 24% 29% 5%	836

Page generated at 2024-10-29 11:20:45. Version ac07

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