Mammoth Hot Springs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mammoth Hot Springs clear sky chart from 2005-11-06 to 2025-03-27.

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	4 10% 4 9% 6% 5% 5% 4 6% 7% 39%	112884
	Night	3 10% 4 10% 6% 5% 5% 4 6% 8% 39%	115235
Transparency	Day	43% 6% 13% 20% 14% 4	112626
	Night	43% 6% 16% 21% 12% 3	115082
Seeing	Day	15% 22% 31% 21% 9% 2	15954
	Night	12% 16% 31% 29% 11% 1	25693

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	2 12% 7% 19% 10% 7% 7% 5% 6% 7% 18%	3179
	11th to 20th	Day	1 10% 4 13% 7% 6% 5% 6% 5% 9% 33%	3729
	21st to end	Day	1 18% 7% 10% 5% 4 4 3 4 5% 36%	4510
February	1st to 10th	Day	2 14% 9% 17% 8% 7% 5% 4 7% 5% 22%	1800
	11th to 20th	Day	2 14% 7% 19% 8% 6% 6% 4 5% 7% 22%	1755
	21st to end	Day	2 16% 7% 16% 10% 6% 7% 4 5% 5% 21%	1557
March	1st to 10th	Day	1 11% 5% 17% 10% 6% 6% 4 5% 6% 29%	3483
	11th to 20th	Day	2 13% 5% 10% 6% 6% 6% 4 4 7% 37%	3600
	21st to end	Day	3 18% 8% 16% 9% 8% 7% 4 6% 6% 15%	3892
April	1st to 10th	Day	5% 18% 6% 13% 7% 6% 5% 3 6% 6% 24%	2204
	11th to 20th	Day	5% 14% 6% 12% 7% 7% 5% 5% 6% 7% 27%	2407
	21st to end	Day	8% 17% 5% 11% 7% 6% 5% 4 5% 7% 26%	2470
May	1st to 10th	Day	9% 17% 5% 10% 6% 6% 5% 4 5% 6% 24%	4110
	11th to 20th	Day	6% 9% 3 9% 6% 7% 6% 5% 8% 9% 32%	4319
	21st to end	Day	10% 15% 4 8% 6% 6% 6% 4 6% 8% 28%	4825
June	1st to 10th	Day	11% 9% 3 8% 6% 6% 6% 5% 7% 8% 31%	2781
	11th to 20th	Day	11% 9% 3 7% 6% 5% 5% 4 5% 7% 36%	2850
	21st to end	Day	4 3 2 5% 4 5% 5% 4 7% 8% 53%	2850
July	1st to 10th	Day	3 2 1 4 4 4 5% 4 7% 9% 57%	4740
	11th to 20th	Day	2 2 1 4 4 5% 6% 5% 6% 8% 57%	4688
	21st to end	Day	2 2 1 3 3 4 5% 4 8% 9% 59%	4458
August	1st to 10th	Day	4 4 1 5% 5% 6% 6% 5% 7% 10% 47%	4092
	11th to 20th	Day	3 3 1 4 3 4 5% 4 6% 8% 59%	4028
	21st to end	Day	4 3 1 4 3 4 4 4 6% 6% 60%	4496
September	1st to 10th	Day	6% 5% 2 5% 4 3 3 2 5% 7% 58%	2280
	11th to 20th	Day	7% 5% 2 5% 4 4 4 3 6% 8% 49%	2096
	21st to end	Day	6% 6% 2 5% 4 3 5% 3 5% 7% 53%	2090
October	1st to 10th	Day	6% 6% 2 5% 4 4 3 2 3 4 59%	3207
	11th to 20th	Day	5% 8% 3 6% 3 3 3 3 4 6% 57%	3150
	21st to end	Day	4 9% 4 8% 5% 5% 6% 4 6% 7% 41%	3335
November	1st to 10th	Day	6% 14% 5% 9% 5% 5% 5% 4 5% 6% 35%	1679
	11th to 20th	Day	4 13% 5% 12% 7% 6% 5% 4 6% 6% 32%	1600
	21st to end	Day	2 11% 5% 11% 7% 6% 7% 4 5% 6% 36%	1600
December	1st to 10th	Day	1 7% 4 11% 6% 5% 6% 5% 8% 7% 42%	2620
	11th to 20th	Day	2 14% 7% 16% 7% 7% 6% 5% 7% 8% 20%	2906
	21st to end	Day	2 15% 5% 15% 8% 7% 6% 6% 6% 8% 22%	3498
January	1st to 10th	Night	1 9% 7% 15% 10% 8% 7% 6% 7% 7% 23%	6766
	11th to 20th	Night	2 10% 4 13% 8% 8% 6% 5% 7% 8% 30%	6263
	21st to end	Night	2 17% 7% 11% 5% 5% 6% 4 5% 7% 33%	6468
February	1st to 10th	Night	2 15% 7% 15% 9% 8% 5% 5% 6% 7% 21%	2600
	11th to 20th	Night	2 12% 5% 15% 9% 6% 7% 5% 7% 6% 25%	2532
	21st to end	Night	1 11% 6% 17% 9% 8% 7% 5% 6% 6% 25%	2070
March	1st to 10th	Night	1 10% 6% 18% 9% 6% 5% 4 6% 6% 31%	3611
	11th to 20th	Night	2 9% 5% 7% 5% 6% 6% 5% 6% 10% 40%	3600
	21st to end	Night	3 16% 5% 12% 6% 6% 6% 5% 7% 9% 24%	3899
April	1st to 10th	Night	4 15% 4 10% 7% 6% 6% 4 7% 6% 33%	1976
	11th to 20th	Night	4 12% 3 8% 7% 6% 4 5% 7% 8% 36%	1720
	21st to end	Night	7% 13% 3 7% 5% 5% 5% 4 5% 7% 38%	1710
May	1st to 10th	Night	6% 13% 5% 9% 7% 6% 6% 5% 6% 6% 31%	2860
	11th to 20th	Night	6% 8% 3 8% 5% 4 5% 4 5% 8% 41%	2583
	21st to end	Night	10% 12% 3 8% 6% 4 5% 4 6% 9% 32%	2762
June	1st to 10th	Night	10% 7% 2 7% 5% 4 6% 4 6% 10% 40%	1395
	11th to 20th	Night	9% 7% 2 5% 5% 5% 4 5% 7% 8% 43%	1330
	21st to end	Night	3 2 1 4 3 4 5% 5% 6% 9% 59%	1330
July	1st to 10th	Night	4 3 1 3 4 3 4 3 6% 8% 61%	2220
	11th to 20th	Night	2 2 1 3 4 4 5% 4 6% 8% 62%	2270
	21st to end	Night	2 2 1 3 3 3 4 4 7% 11% 61%	3101
August	1st to 10th	Night	3 3 1 5% 3 5% 6% 5% 8% 10% 51%	2847
	11th to 20th	Night	2 2 1 4 3 4 4 5% 8% 10% 57%	2811
	21st to end	Night	4 3 2 4 3 2 3 2 4 6% 68%	3170
September	1st to 10th	Night	5% 4 2 4 3 3 4 5% 5% 7% 59%	1900
	11th to 20th	Night	6% 4 1 4 4 4 4 4 7% 7% 55%	2080
	21st to end	Night	7% 5% 2 5% 4 3 3 2 4 6% 59%	2090
October	1st to 10th	Night	5% 5% 1 3 2 2 3 3 4 6% 64%	3764
	11th to 20th	Night	5% 8% 2 6% 3 3 4 3 5% 6% 55%	3778
	21st to end	Night	4 9% 3 8% 4 4 4 3 5% 8% 47%	4210
November	1st to 10th	Night	6% 12% 4 11% 6% 6% 5% 3 5% 7% 35%	2600
	11th to 20th	Night	3 13% 5% 12% 7% 5% 6% 5% 6% 7% 31%	2800
	21st to end	Night	2 11% 6% 10% 7% 6% 5% 4 7% 8% 36%	2800
December	1st to 10th	Night	2 8% 4 11% 6% 6% 6% 4 6% 6% 43%	4570
	11th to 20th	Night	2 12% 6% 16% 7% 6% 7% 5% 8% 9% 24%	5291
	21st to end	Night	2 14% 6% 16% 6% 7% 7% 6% 7% 8% 21%	7458

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	60% 9% 12% 15% 4	3179
	11th to 20th	Day	47% 5% 20% 14% 10% 6%	3729
	21st to end	Day	52% 3 10% 21% 14% 1	4510
February	1st to 10th	Day	64% 6% 12% 12% 4	1800
	11th to 20th	Day	63% 6% 13% 13% 3 1	1764
	21st to end	Day	67% 6% 7% 11% 6% 3	1557
March	1st to 10th	Day	55% 9% 12% 16% 7% 1	3483
	11th to 20th	Day	45% 5% 22% 21% 6%	3600
	21st to end	Day	69% 9% 12% 8% 1	3892
April	1st to 10th	Day	62% 7% 12% 14% 5%	2204
	11th to 20th	Day	56% 7% 14% 17% 5%	2410
	21st to end	Day	58% 6% 15% 17% 4 1	2470
May	1st to 10th	Day	57% 6% 10% 19% 6% 1	4110
	11th to 20th	Day	42% 8% 17% 23% 10% 1	4323
	21st to end	Day	51% 7% 17% 19% 5%	4825
June	1st to 10th	Day	48% 9% 18% 21% 5%	2781
	11th to 20th	Day	46% 7% 11% 18% 15% 3	2850
	21st to end	Day	26% 7% 11% 28% 22% 6%	2850
July	1st to 10th	Day	20% 5% 7% 23% 35% 9%	4666
	11th to 20th	Day	23% 5% 7% 20% 28% 18%	4607
	21st to end	Day	18% 5% 7% 22% 33% 16%	4317
August	1st to 10th	Day	30% 7% 9% 22% 22% 10%	4078
	11th to 20th	Day	22% 4 8% 29% 29% 8%	4067
	21st to end	Day	23% 4 7% 25% 29% 13%	4495
September	1st to 10th	Day	27% 4 7% 23% 32% 8%	2280
	11th to 20th	Day	33% 5% 13% 23% 22% 5%	2096
	21st to end	Day	31% 5% 12% 30% 17% 5%	2090
October	1st to 10th	Day	30% 3 8% 23% 33% 3	3207
	11th to 20th	Day	31% 3 16% 32% 15% 3	3150
	21st to end	Day	43% 5% 18% 26% 8% 1	3335
November	1st to 10th	Day	51% 7% 14% 19% 9% 1	1679
	11th to 20th	Day	52% 8% 17% 15% 5% 2	1600
	21st to end	Day	50% 6% 17% 16% 9% 2	1600
December	1st to 10th	Day	40% 6% 27% 21% 5% 1	2620
	11th to 20th	Day	61% 6% 20% 11% 2	2904
	21st to end	Day	58% 4 14% 13% 4 8%	3498
January	1st to 10th	Night	56% 5% 12% 20% 6%	6766
	11th to 20th	Night	50% 5% 17% 16% 8% 4	6263
	21st to end	Night	50% 4 12% 22% 11% 1	6468
February	1st to 10th	Night	63% 6% 11% 14% 6%	2600
	11th to 20th	Night	61% 7% 13% 12% 6% 1	2533
	21st to end	Night	61% 8% 9% 13% 6% 3	2070
March	1st to 10th	Night	53% 7% 10% 18% 9% 2	3611
	11th to 20th	Night	37% 6% 25% 25% 6% 1	3600
	21st to end	Night	55% 8% 21% 13% 3	3899
April	1st to 10th	Night	52% 9% 15% 17% 6% 1	1976
	11th to 20th	Night	44% 8% 19% 22% 6% 1	1720
	21st to end	Night	44% 8% 19% 23% 5%	1710
May	1st to 10th	Night	50% 7% 14% 22% 7%	2860
	11th to 20th	Night	39% 7% 15% 30% 7% 2	2584
	21st to end	Night	49% 8% 14% 23% 5%	2762
June	1st to 10th	Night	39% 11% 20% 24% 5%	1395
	11th to 20th	Night	38% 6% 16% 20% 16% 3	1330
	21st to end	Night	20% 7% 15% 29% 23% 6%	1330
July	1st to 10th	Night	20% 5% 10% 27% 31% 6%	2185
	11th to 20th	Night	19% 4 10% 20% 33% 13%	2228
	21st to end	Night	16% 4 11% 29% 30% 11%	3004
August	1st to 10th	Night	25% 6% 13% 25% 22% 9%	2838
	11th to 20th	Night	20% 4 12% 31% 26% 6%	2838
	21st to end	Night	20% 3 9% 27% 32% 10%	3170
September	1st to 10th	Night	24% 5% 9% 25% 28% 9%	1900
	11th to 20th	Night	28% 6% 15% 25% 21% 5%	2080
	21st to end	Night	28% 5% 12% 31% 21% 3	2090
October	1st to 10th	Night	23% 3 11% 30% 31% 2	3764
	11th to 20th	Night	31% 4 19% 29% 17% 1	3778
	21st to end	Night	37% 5% 18% 27% 12% 1	4210
November	1st to 10th	Night	50% 6% 16% 20% 7% 1	2600
	11th to 20th	Night	53% 7% 17% 16% 6% 1	2800
	21st to end	Night	47% 7% 20% 14% 10% 2	2800
December	1st to 10th	Night	42% 6% 27% 20% 4 1	4570
	11th to 20th	Night	56% 6% 24% 12% 2	5292
	21st to end	Night	57% 5% 15% 13% 5% 6%	7458

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	18% 27% 32% 17% 5% 2	200
	11th to 20th	Day	16% 28% 30% 16% 7% 2	237
	21st to end	Day	11% 25% 36% 22% 5% 1	330
February	1st to 10th	Day	22% 38% 28% 10% 1	300
	11th to 20th	Day	21% 30% 30% 15% 3 2	300
	21st to end	Day	24% 31% 26% 16% 3	321
March	1st to 10th	Day	20% 34% 30% 13% 3 1	500
	11th to 20th	Day	17% 31% 28% 19% 4 1	500
	21st to end	Day	22% 29% 32% 12% 5% 1	531
April	1st to 10th	Day	26% 30% 31% 10% 2	460
	11th to 20th	Day	22% 29% 33% 13% 3	452
	21st to end	Day	22% 25% 28% 16% 6% 3	460
May	1st to 10th	Day	18% 20% 31% 21% 8% 1	463
	11th to 20th	Day	16% 19% 29% 23% 12% 2	632
	21st to end	Day	20% 17% 25% 21% 15% 2	734
June	1st to 10th	Day	15% 19% 26% 23% 14% 3	680
	11th to 20th	Day	22% 24% 27% 19% 7% 1	680
	21st to end	Day	7% 17% 31% 30% 13% 1	680
July	1st to 10th	Day	5% 15% 30% 30% 18% 2	671
	11th to 20th	Day	4 13% 36% 31% 15% 1	668
	21st to end	Day	4 15% 36% 29% 12% 3	535
August	1st to 10th	Day	9% 11% 40% 26% 12% 2	487
	11th to 20th	Day	6% 13% 32% 30% 15% 3	477
	21st to end	Day	9% 18% 35% 22% 13% 4	539
September	1st to 10th	Day	8% 20% 33% 24% 12% 2	490
	11th to 20th	Day	15% 20% 31% 23% 9% 2	490
	21st to end	Day	14% 19% 34% 20% 10% 2	490
October	1st to 10th	Day	14% 18% 30% 21% 13% 4	324
	11th to 20th	Day	19% 17% 29% 19% 9% 7%	300
	21st to end	Day	18% 27% 33% 16% 5% 1	330
November	1st to 10th	Day	22% 27% 26% 16% 7% 2	300
	11th to 20th	Day	16% 33% 31% 15% 5%	300
	21st to end	Day	11% 25% 39% 22% 4	300
December	1st to 10th	Day	18% 26% 28% 21% 7%	300
	11th to 20th	Day	17% 33% 29% 18% 2	273
	21st to end	Day	21% 26% 27% 17% 7% 1	220
January	1st to 10th	Night	15% 20% 34% 26% 6%	1000
	11th to 20th	Night	14% 20% 37% 20% 8% 2	850
	21st to end	Night	7% 22% 41% 23% 6% 1	880
February	1st to 10th	Night	13% 27% 36% 21% 3	800
	11th to 20th	Night	12% 22% 38% 22% 5%	784
	21st to end	Night	13% 24% 35% 21% 7%	660
March	1st to 10th	Night	10% 24% 34% 25% 6% 1	800
	11th to 20th	Night	10% 20% 30% 29% 10% 1	800
	21st to end	Night	13% 16% 31% 32% 8% 1	862
April	1st to 10th	Night	13% 19% 36% 23% 8%	646
	11th to 20th	Night	11% 18% 37% 26% 7%	563
	21st to end	Night	15% 12% 26% 31% 15% 1	570
May	1st to 10th	Night	11% 14% 27% 30% 16% 1	570
	11th to 20th	Night	10% 10% 27% 33% 19% 1	561
	21st to end	Night	16% 11% 28% 30% 13% 1	617
June	1st to 10th	Night	13% 11% 24% 33% 19%	445
	11th to 20th	Night	12% 11% 33% 31% 14%	380
	21st to end	Night	4 5% 24% 46% 21% 1	380
July	1st to 10th	Night	5% 4 16% 43% 32% 1	370
	11th to 20th	Night	2 5% 20% 54% 19%	392
	21st to end	Night	2 5% 24% 46% 22% 1	624
August	1st to 10th	Night	6% 3 21% 45% 25% 1	567
	11th to 20th	Night	4 4 20% 45% 26% 1	564
	21st to end	Night	6% 7% 24% 38% 24% 1	627
September	1st to 10th	Night	7% 5% 26% 39% 21% 2	570
	11th to 20th	Night	8% 6% 23% 41% 20% 2	750
	21st to end	Night	11% 9% 26% 33% 20% 1	760
October	1st to 10th	Night	14% 7% 27% 35% 16% 1	760
	11th to 20th	Night	13% 13% 26% 33% 13% 2	760
	21st to end	Night	13% 18% 35% 24% 8% 3	836
November	1st to 10th	Night	16% 19% 32% 26% 7%	845
	11th to 20th	Night	14% 28% 32% 23% 3	1000
	21st to end	Night	13% 20% 36% 25% 6%	1000
December	1st to 10th	Night	15% 24% 31% 24% 5% 1	1000
	11th to 20th	Night	15% 26% 33% 21% 5% 1	1000
	21st to end	Night	17% 23% 34% 19% 6%	1100

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