Tamarack California
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tamarack California clear sky chart from 2005-11-06 to 2025-09-04.

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	5% 6% 2 4 2 2 3 2 3 5% 66%	134428
	Night	5% 6% 2 4 2 2 2 2 4 5% 65%	131747
Transparency	Day	22% 3 6% 21% 27% 20%	129474
	Night	23% 3 7% 21% 27% 19%	127678
Seeing	Day	11% 13% 33% 28% 11% 3	16325
	Night	10% 5% 21% 34% 25% 6%	25803

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	7% 10% 3 5% 2 2 3 2 4 6% 55%	3639
	11th to 20th	Day	8% 7% 2 6% 3 3 3 2 3 4 58%	3845
	21st to end	Day	9% 8% 3 5% 3 4 4 3 5% 7% 48%	4510
February	1st to 10th	Day	12% 10% 4 4 3 2 3 4 5% 5% 47%	1927
	11th to 20th	Day	7% 14% 3 5% 3 3 3 3 4 5% 49%	1950
	21st to end	Day	11% 14% 4 7% 3 4 3 2 4 5% 42%	1650
March	1st to 10th	Day	7% 16% 7% 8% 4 4 4 4 5% 7% 36%	4518
	11th to 20th	Day	7% 12% 4 7% 3 2 3 3 5% 8% 44%	4819
	21st to end	Day	9% 19% 5% 6% 3 3 3 2 4 7% 40%	5915
April	1st to 10th	Day	8% 12% 3 6% 3 2 3 3 4 7% 49%	2400
	11th to 20th	Day	9% 11% 2 5% 4 3 3 3 5% 6% 50%	2369
	21st to end	Day	8% 10% 2 4 3 3 3 3 5% 7% 52%	2400
May	1st to 10th	Day	6% 7% 2 4 2 2 2 2 3 5% 67%	5655
	11th to 20th	Day	3 6% 2 3 3 2 2 2 3 5% 68%	5841
	21st to end	Day	3 4 1 3 2 2 2 2 3 5% 73%	6851
June	1st to 10th	Day	4 4 1 4 3 3 4 3 5% 6% 63%	2800
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 4 80%	2800
	21st to end	Day	2 2 1 2 1 2 1 2 2 3 82%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 2 90%	6319
	11th to 20th	Day	1 1 1 2 1 1 2 1 3 3 84%	6320
	21st to end	Day	1 1 1 2 1 1 2 2 3 4 83%	6625
August	1st to 10th	Day	1 1 1 1 1 1 1 1 2 89%	5436
	11th to 20th	Day	1 1 1 1 1 2 2 91%	5364
	21st to end	Day	1 1 1 2 2 2 2 2 3 4 80%	5981
September	1st to 10th	Day	2 1 1 2 2 1 2 2 2 3 83%	2317
	11th to 20th	Day	2 2 1 3 2 2 2 1 3 5% 77%	2209
	21st to end	Day	3 3 1 2 1 2 2 2 3 4 77%	2090
October	1st to 10th	Day	3 3 1 3 2 2 3 2 3 3 74%	3353
	11th to 20th	Day	4 3 1 2 2 2 2 2 3 3 76%	3161
	21st to end	Day	4 5% 2 4 3 3 3 3 4 6% 64%	3368
November	1st to 10th	Day	6% 8% 2 5% 3 3 3 3 5% 7% 56%	1764
	11th to 20th	Day	7% 5% 2 3 3 2 4 3 5% 6% 62%	1800
	21st to end	Day	8% 7% 3 5% 3 3 3 2 4 7% 56%	1800
December	1st to 10th	Day	6% 5% 1 4 3 3 3 3 4 6% 61%	2800
	11th to 20th	Day	13% 10% 4 5% 4 4 4 3 4 7% 43%	3028
	21st to end	Day	12% 9% 4 5% 4 4 4 4 5% 9% 41%	4004
January	1st to 10th	Night	6% 7% 3 4 2 2 3 3 5% 7% 57%	6306
	11th to 20th	Night	9% 7% 3 5% 3 3 3 3 4 5% 57%	6122
	21st to end	Night	6% 10% 3 5% 3 3 3 3 5% 7% 50%	6468
February	1st to 10th	Night	12% 9% 3 5% 3 3 2 3 5% 5% 50%	2470
	11th to 20th	Night	9% 10% 2 4 4 3 3 3 5% 7% 52%	2338
	21st to end	Night	10% 10% 3 6% 3 3 3 3 4 5% 50%	1980
March	1st to 10th	Night	7% 15% 4 7% 3 4 4 3 6% 6% 41%	5376
	11th to 20th	Night	4 12% 3 7% 4 4 3 3 4 6% 51%	5176
	21st to end	Night	11% 14% 3 6% 3 2 3 3 5% 7% 44%	5060
April	1st to 10th	Night	8% 10% 3 3 3 3 3 3 5% 6% 54%	2000
	11th to 20th	Night	5% 8% 2 5% 4 3 3 3 4 5% 57%	1979
	21st to end	Night	5% 7% 1 4 3 2 3 3 5% 7% 60%	2000
May	1st to 10th	Night	3 5% 1 3 2 2 2 2 3 4 72%	4333
	11th to 20th	Night	2 3 1 2 3 2 2 2 3 5% 75%	4074
	21st to end	Night	2 2 1 2 1 1 1 1 2 4 82%	4021
June	1st to 10th	Night	3 3 2 4 2 2 2 2 4 6% 69%	1600
	11th to 20th	Night	1 1 1 2 1 1 2 2 2 3 83%	1600
	21st to end	Night	1 1 2 1 1 1 2 2 3 86%	1600
July	1st to 10th	Night	1 1 1 1 2 93%	3640
	11th to 20th	Night	2 2 1 2 1 2 1 1 2 3 83%	3640
	21st to end	Night	1 1 1 1 1 2 2 3 4 83%	4233
August	1st to 10th	Night	1 1 1 1 1 2 1 2 3 86%	4390
	11th to 20th	Night	1 1 1 1 1 1 1 2 91%	4506
	21st to end	Night	2 1 1 2 2 2 1 2 2 3 82%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 89%	1930
	11th to 20th	Night	2 2 1 2 1 2 1 2 2 3 82%	1971
	21st to end	Night	2 2 1 1 1 1 2 3 2 3 82%	2090
October	1st to 10th	Night	2 2 1 2 1 2 2 2 3 4 81%	3611
	11th to 20th	Night	3 1 1 2 2 2 2 2 3 4 79%	3777
	21st to end	Night	3 3 1 3 2 2 1 2 3 5% 74%	4197
November	1st to 10th	Night	6% 7% 2 3 2 2 3 3 4 6% 62%	2535
	11th to 20th	Night	7% 4 2 4 2 2 3 2 5% 7% 62%	2600
	21st to end	Night	7% 8% 2 4 2 3 3 3 4 7% 55%	2600
December	1st to 10th	Night	7% 5% 2 4 2 3 2 3 4 5% 62%	4381
	11th to 20th	Night	13% 10% 3 6% 4 3 4 3 6% 9% 40%	5176
	21st to end	Night	9% 8% 3 8% 5% 5% 5% 4 7% 8% 38%	6952

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	30% 3 12% 26% 20% 9%	3639
	11th to 20th	Day	32% 4 5% 15% 22% 22%	3845
	21st to end	Day	35% 5% 8% 20% 18% 14%	4510
February	1st to 10th	Day	39% 3 6% 23% 17% 12%	1927
	11th to 20th	Day	38% 5% 7% 21% 22% 7%	1960
	21st to end	Day	44% 4 7% 23% 16% 5%	1650
March	1st to 10th	Day	48% 5% 6% 15% 19% 7%	4518
	11th to 20th	Day	36% 6% 15% 26% 10% 7%	4819
	21st to end	Day	45% 6% 11% 22% 12% 3	5915
April	1st to 10th	Day	37% 4 13% 24% 17% 4	2400
	11th to 20th	Day	35% 5% 12% 26% 20% 3	2372
	21st to end	Day	32% 5% 13% 32% 16% 2	2400
May	1st to 10th	Day	21% 5% 8% 34% 28% 5%	5655
	11th to 20th	Day	17% 4 9% 37% 29% 4	5844
	21st to end	Day	14% 3 6% 40% 34% 3	6852
June	1st to 10th	Day	19% 4 12% 28% 30% 7%	2800
	11th to 20th	Day	10% 2 8% 24% 39% 17%	2800
	21st to end	Day	10% 1 2 16% 41% 29%	2800
July	1st to 10th	Day	4 1 1 7% 21% 66%	6251
	11th to 20th	Day	7% 2 2 7% 28% 53%	6245
	21st to end	Day	7% 2 3 15% 37% 36%	6433
August	1st to 10th	Day	9% 1 2 12% 40% 35%	3954
	11th to 20th	Day	4 1 2 9% 32% 51%	3880
	21st to end	Day	7% 2 1 12% 38% 40%	4311
September	1st to 10th	Day	8% 2 3 13% 38% 36%	2317
	11th to 20th	Day	12% 3 4 24% 34% 23%	2209
	21st to end	Day	12% 3 3 21% 38% 22%	2090
October	1st to 10th	Day	16% 3 3 12% 37% 29%	3353
	11th to 20th	Day	15% 2 3 16% 40% 23%	3161
	21st to end	Day	22% 4 3 20% 36% 15%	3368
November	1st to 10th	Day	28% 4 7% 20% 26% 15%	1764
	11th to 20th	Day	23% 4 7% 23% 31% 12%	1800
	21st to end	Day	29% 5% 6% 17% 29% 15%	1800
December	1st to 10th	Day	25% 3 6% 24% 26% 18%	2800
	11th to 20th	Day	42% 4 9% 18% 19% 8%	3028
	21st to end	Day	41% 4 11% 21% 16% 7%	4004
January	1st to 10th	Night	27% 3 11% 25% 22% 12%	6306
	11th to 20th	Night	31% 3 5% 16% 25% 19%	6122
	21st to end	Night	34% 4 7% 16% 18% 20%	6468
February	1st to 10th	Night	36% 3 5% 24% 19% 12%	2470
	11th to 20th	Night	33% 4 8% 23% 23% 9%	2339
	21st to end	Night	36% 3 10% 23% 20% 8%	1980
March	1st to 10th	Night	41% 5% 6% 18% 19% 11%	5376
	11th to 20th	Night	33% 4 10% 31% 13% 9%	5176
	21st to end	Night	39% 5% 17% 23% 12% 4	5060
April	1st to 10th	Night	30% 5% 15% 28% 17% 6%	2000
	11th to 20th	Night	28% 5% 12% 28% 20% 6%	1979
	21st to end	Night	23% 5% 15% 38% 18% 2	2000
May	1st to 10th	Night	16% 4 11% 41% 23% 6%	4330
	11th to 20th	Night	11% 4 11% 41% 30% 4	4075
	21st to end	Night	9% 2 6% 42% 39% 3	4021
June	1st to 10th	Night	16% 3 13% 30% 33% 5%	1600
	11th to 20th	Night	8% 2 7% 28% 37% 17%	1600
	21st to end	Night	6% 1 4 15% 43% 30%	1600
July	1st to 10th	Night	3 1 6% 19% 71%	3600
	11th to 20th	Night	9% 1 3 8% 29% 50%	3592
	21st to end	Night	7% 2 2 19% 32% 39%	4113
August	1st to 10th	Night	9% 1 4 15% 34% 37%	3187
	11th to 20th	Night	4 1 1 11% 28% 54%	3256
	21st to end	Night	8% 1 1 10% 39% 41%	3608
September	1st to 10th	Night	5% 2 1 14% 39% 39%	1930
	11th to 20th	Night	9% 3 5% 22% 40% 21%	1971
	21st to end	Night	9% 2 3 24% 40% 22%	2090
October	1st to 10th	Night	10% 2 4 12% 39% 33%	3611
	11th to 20th	Night	11% 2 3 15% 39% 29%	3777
	21st to end	Night	14% 2 2 17% 45% 18%	4197
November	1st to 10th	Night	24% 4 7% 22% 26% 17%	2535
	11th to 20th	Night	21% 4 7% 21% 33% 15%	2600
	21st to end	Night	29% 4 5% 19% 29% 14%	2600
December	1st to 10th	Night	25% 2 7% 21% 25% 20%	4381
	11th to 20th	Night	41% 3 9% 19% 20% 7%	5176
	21st to end	Night	41% 5% 10% 17% 20% 7%	6952

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	28% 16% 25% 23% 9% 1	200
	11th to 20th	Day	19% 10% 33% 23% 10% 4	288
	21st to end	Day	17% 14% 30% 24% 13% 3	440
February	1st to 10th	Day	23% 18% 23% 22% 11% 3	465
	11th to 20th	Day	18% 22% 31% 21% 6% 2	495
	21st to end	Day	16% 22% 39% 16% 6%	414
March	1st to 10th	Day	20% 22% 35% 17% 5% 1	500
	11th to 20th	Day	21% 21% 29% 21% 7% 2	500
	21st to end	Day	23% 23% 31% 18% 4	550
April	1st to 10th	Day	16% 18% 33% 26% 5% 1	500
	11th to 20th	Day	19% 19% 33% 23% 6% 1	492
	21st to end	Day	15% 14% 34% 25% 10% 3	500
May	1st to 10th	Day	17% 18% 31% 24% 8% 3	503
	11th to 20th	Day	20% 14% 25% 26% 12% 3	528
	21st to end	Day	14% 12% 27% 30% 13% 4	573
June	1st to 10th	Day	5% 14% 30% 30% 15% 6%	530
	11th to 20th	Day	6% 13% 32% 32% 12% 5%	530
	21st to end	Day	4 10% 36% 31% 11% 7%	530
July	1st to 10th	Day	2 7% 35% 35% 16% 5%	526
	11th to 20th	Day	3 2 32% 40% 13% 10%	524
	21st to end	Day	2 5% 32% 40% 12% 9%	575
August	1st to 10th	Day	2 9% 42% 30% 11% 6%	527
	11th to 20th	Day	2 8% 39% 32% 12% 7%	517
	21st to end	Day	3 6% 36% 37% 15% 4	583
September	1st to 10th	Day	4 8% 42% 31% 12% 2	503
	11th to 20th	Day	6% 12% 40% 32% 9% 1	490
	21st to end	Day	8% 11% 36% 34% 10% 1	490
October	1st to 10th	Day	6% 16% 33% 34% 11% 1	490
	11th to 20th	Day	7% 12% 35% 35% 9% 1	490
	21st to end	Day	8% 12% 34% 32% 12% 2	495
November	1st to 10th	Day	9% 16% 32% 27% 13% 4	300
	11th to 20th	Day	9% 15% 30% 29% 13% 4	300
	21st to end	Day	13% 12% 32% 25% 16% 2	300
December	1st to 10th	Day	18% 5% 29% 30% 16% 3	257
	11th to 20th	Day	15% 13% 30% 27% 12% 4	200
	21st to end	Day	23% 14% 30% 20% 8% 5%	220
January	1st to 10th	Night	17% 9% 25% 25% 17% 7%	800
	11th to 20th	Night	12% 8% 31% 29% 15% 5%	800
	21st to end	Night	16% 11% 25% 28% 15% 4	880
February	1st to 10th	Night	18% 9% 24% 30% 16% 4	800
	11th to 20th	Night	14% 8% 27% 29% 16% 7%	784
	21st to end	Night	15% 8% 30% 32% 12% 3	660
March	1st to 10th	Night	18% 11% 23% 31% 15% 3	800
	11th to 20th	Night	14% 10% 22% 27% 21% 6%	800
	21st to end	Night	15% 9% 22% 35% 17% 2	880
April	1st to 10th	Night	14% 7% 24% 35% 17% 3	800
	11th to 20th	Night	10% 7% 28% 32% 19% 4	791
	21st to end	Night	9% 6% 27% 33% 20% 6%	800
May	1st to 10th	Night	8% 5% 24% 37% 21% 5%	703
	11th to 20th	Night	7% 5% 21% 37% 26% 4	591
	21st to end	Night	6% 4 21% 33% 31% 5%	457
June	1st to 10th	Night	5% 3 14% 42% 32% 6%	400
	11th to 20th	Night	2 2 19% 40% 33% 5%	400
	21st to end	Night	2 2 14% 41% 37% 6%	400
July	1st to 10th	Night	1 1 13% 33% 46% 6%	390
	11th to 20th	Night	4 1 11% 34% 43% 7%	388
	21st to end	Night	2 1 11% 28% 46% 12%	548
August	1st to 10th	Night	3 1 12% 36% 41% 7%	751
	11th to 20th	Night	2 9% 37% 45% 7%	792
	21st to end	Night	3 10% 34% 45% 8%	880
September	1st to 10th	Night	2 2 8% 38% 42% 8%	772
	11th to 20th	Night	2 2 11% 40% 34% 10%	760
	21st to end	Night	3 1 18% 35% 34% 8%	760
October	1st to 10th	Night	5% 2 15% 47% 24% 7%	760
	11th to 20th	Night	6% 3 19% 38% 26% 8%	760
	21st to end	Night	6% 4 20% 32% 26% 12%	836
November	1st to 10th	Night	10% 5% 16% 36% 23% 9%	780
	11th to 20th	Night	9% 6% 25% 36% 18% 7%	800
	21st to end	Night	11% 6% 26% 34% 17% 6%	800
December	1st to 10th	Night	16% 6% 22% 36% 15% 5%	800
	11th to 20th	Night	20% 8% 26% 30% 13% 4	800
	21st to end	Night	18% 10% 29% 27% 13% 3	880

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