Northstar Ski Resort
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northstar Ski Resort clear sky chart from 2005-11-06 to 2026-01-02.

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	2 6% 2 4 3 3 3 3 4 5% 65%	135861
	Night	2 7% 3 5% 3 3 3 3 5% 6% 61%	132877
Transparency	Day	12% 39% 5% 12% 18% 14%	130825
	Night	14% 39% 6% 14% 17% 10%	128895
Seeing	Day	14% 18% 29% 22% 13% 3	16511
	Night	11% 12% 21% 31% 21% 4	25906

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 9% 4 6% 4 4 4 4 6% 7% 51%	3647
	11th to 20th	Day	1 9% 2 5% 4 3 4 3 4 5% 59%	3778
	21st to end	Day	4 13% 4 7% 3 3 4 4 4 6% 49%	4510
February	1st to 10th	Day	4 11% 4 7% 5% 3 4 4 5% 6% 47%	1800
	11th to 20th	Day	2 11% 4 8% 4 4 4 4 6% 7% 47%	1935
	21st to end	Day	2 11% 5% 8% 4 3 4 3 6% 6% 47%	1650
March	1st to 10th	Day	2 17% 8% 12% 4 3 4 3 4 7% 35%	4518
	11th to 20th	Day	1 11% 3 6% 4 3 3 3 5% 7% 54%	4956
	21st to end	Day	2 16% 5% 8% 5% 4 4 3 5% 6% 42%	5810
April	1st to 10th	Day	3 12% 3 7% 4 3 4 4 5% 8% 47%	2400
	11th to 20th	Day	3 11% 2 5% 4 4 4 4 4 6% 52%	2369
	21st to end	Day	4 10% 2 4 3 3 3 3 6% 7% 56%	2400
May	1st to 10th	Day	3 6% 1 4 2 1 2 2 3 5% 70%	5675
	11th to 20th	Day	2 5% 2 4 3 3 3 3 4 5% 68%	6226
	21st to end	Day	3 4 1 4 3 2 2 3 4 5% 70%	6902
June	1st to 10th	Day	4 4 2 4 4 3 3 4 5% 7% 60%	2800
	11th to 20th	Day	2 2 1 2 2 2 2 2 4 5% 75%	2800
	21st to end	Day	2 2 1 2 2 2 2 2 3 4 78%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 2 89%	6319
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 3 82%	6320
	21st to end	Day	2 1 1 1 1 2 3 3 4 5% 76%	6677
August	1st to 10th	Day	2 1 1 2 1 1 2 2 3 3 83%	5744
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	5364
	21st to end	Day	2 2 1 3 2 3 3 2 3 3 77%	5984
September	1st to 10th	Day	2 1 2 2 2 2 2 4 4 81%	2400
	11th to 20th	Day	2 3 1 3 3 2 2 2 4 5% 72%	2379
	21st to end	Day	3 3 1 3 2 2 2 2 3 4 76%	2200
October	1st to 10th	Day	3 3 1 3 2 2 2 3 4 6% 71%	3295
	11th to 20th	Day	3 4 1 4 2 1 2 2 3 4 73%	3261
	21st to end	Day	2 4 1 4 3 2 3 3 5% 7% 65%	3495
November	1st to 10th	Day	4 7% 2 6% 3 3 4 3 4 8% 57%	1854
	11th to 20th	Day	3 8% 1 4 3 3 4 4 6% 10% 52%	1890
	21st to end	Day	2 8% 2 6% 3 3 3 4 6% 9% 54%	1803
December	1st to 10th	Day	2 6% 2 4 3 3 3 3 5% 9% 59%	2700
	11th to 20th	Day	5% 15% 5% 7% 5% 4 6% 4 6% 8% 35%	3108
	21st to end	Day	4 13% 4 8% 4 4 4 3 7% 11% 37%	4092
January	1st to 10th	Night	2 6% 3 6% 4 4 4 5% 8% 10% 49%	6320
	11th to 20th	Night	1 10% 3 7% 4 4 4 3 4 6% 55%	6175
	21st to end	Night	3 13% 4 6% 4 4 4 3 5% 5% 48%	6468
February	1st to 10th	Night	3 9% 4 9% 6% 4 4 3 6% 6% 46%	2600
	11th to 20th	Night	1 9% 3 7% 6% 4 5% 4 6% 8% 46%	2351
	21st to end	Night	2 9% 4 8% 5% 4 3 4 5% 8% 48%	1980
March	1st to 10th	Night	2 13% 8% 10% 5% 4 4 3 5% 8% 39%	5376
	11th to 20th	Night	2 12% 5% 8% 4 3 3 3 5% 6% 51%	5028
	21st to end	Night	1 15% 6% 9% 6% 4 4 4 6% 6% 37%	5152
April	1st to 10th	Night	3 8% 3 6% 5% 4 4 4 7% 8% 48%	2000
	11th to 20th	Night	2 10% 2 5% 4 3 4 4 5% 8% 54%	1979
	21st to end	Night	3 9% 2 4 2 3 3 3 4 7% 59%	2000
May	1st to 10th	Night	2 4 2 3 2 2 2 2 3 5% 72%	4312
	11th to 20th	Night	1 5% 2 3 2 2 2 2 3 4 72%	3666
	21st to end	Night	2 4 1 3 2 2 3 2 3 5% 73%	3972
June	1st to 10th	Night	3 5% 2 4 3 4 4 3 5% 6% 62%	1600
	11th to 20th	Night	1 2 2 2 2 2 2 4 5% 79%	1600
	21st to end	Night	2 2 1 2 2 2 2 2 2 4 78%	1600
July	1st to 10th	Night	1 1 1 1 1 1 2 91%	3640
	11th to 20th	Night	2 2 1 3 2 2 2 1 2 2 82%	3640
	21st to end	Night	3 2 1 2 2 3 2 3 5% 5% 72%	4166
August	1st to 10th	Night	2 2 1 2 2 2 2 2 2 4 81%	4070
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 87%	4506
	21st to end	Night	2 2 1 3 2 2 3 2 4 3 78%	5015
September	1st to 10th	Night	2 1 1 1 1 1 1 1 3 5% 83%	2000
	11th to 20th	Night	2 3 1 2 2 2 2 1 4 5% 76%	2020
	21st to end	Night	2 2 1 3 2 2 2 3 4 5% 76%	2200
October	1st to 10th	Night	2 3 1 2 2 2 2 2 4 4 77%	3901
	11th to 20th	Night	2 2 1 3 2 1 2 2 3 5% 77%	3897
	21st to end	Night	2 6% 1 4 3 3 3 3 5% 7% 64%	4312
November	1st to 10th	Night	3 6% 2 6% 3 3 3 4 5% 8% 57%	2665
	11th to 20th	Night	3 6% 3 5% 3 3 3 3 6% 9% 56%	2730
	21st to end	Night	2 6% 2 6% 4 3 4 3 5% 8% 56%	2814
December	1st to 10th	Night	2 5% 2 4 3 3 3 3 5% 6% 62%	4700
	11th to 20th	Night	3 13% 4 7% 5% 5% 5% 4 7% 11% 36%	5316
	21st to end	Night	2 14% 4 9% 6% 5% 5% 5% 6% 8% 35%	7106

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	18% 33% 15% 17% 15% 2	3647
	11th to 20th	Day	19% 32% 7% 11% 24% 7%	3778
	21st to end	Day	22% 32% 6% 11% 20% 8%	4510
February	1st to 10th	Day	19% 63% 4 7% 4 3	1800
	11th to 20th	Day	15% 63% 4 10% 7% 2	1945
	21st to end	Day	11% 64% 6% 10% 6% 4	1650
March	1st to 10th	Day	30% 37% 6% 9% 13% 5%	4518
	11th to 20th	Day	16% 31% 9% 29% 14% 1	4956
	21st to end	Day	25% 35% 10% 17% 11% 1	5810
April	1st to 10th	Day	14% 63% 5% 11% 6% 1	2400
	11th to 20th	Day	10% 63% 4 12% 9% 2	2372
	21st to end	Day	11% 63% 6% 11% 9% 1	2400
May	1st to 10th	Day	11% 29% 5% 20% 29% 5%	5675
	11th to 20th	Day	12% 29% 5% 16% 33% 6%	6229
	21st to end	Day	7% 29% 4 15% 37% 8%	6904
June	1st to 10th	Day	5% 62% 3 10% 15% 5%	2800
	11th to 20th	Day	4 61% 2 10% 13% 10%	2800
	21st to end	Day	3 60% 1 4 13% 18%	2800
July	1st to 10th	Day	4 24% 1 3 14% 55%	6251
	11th to 20th	Day	7% 25% 1 4 7% 55%	6245
	21st to end	Day	8% 26% 2 12% 24% 29%	6483
August	1st to 10th	Day	9% 35% 1 5% 15% 35%	4184
	11th to 20th	Day	3 35% 1 3 20% 37%	3880
	21st to end	Day	5% 34% 1 8% 28% 23%	4311
September	1st to 10th	Day	5% 56% 2 5% 17% 15%	2400
	11th to 20th	Day	8% 57% 3 10% 15% 7%	2379
	21st to end	Day	8% 56% 3 9% 16% 8%	2200
October	1st to 10th	Day	7% 35% 2 8% 27% 22%	3295
	11th to 20th	Day	10% 35% 2 9% 36% 7%	3261
	21st to end	Day	12% 36% 4 18% 22% 8%	3495
November	1st to 10th	Day	8% 54% 5% 14% 14% 4	1854
	11th to 20th	Day	13% 56% 6% 11% 11% 3	1890
	21st to end	Day	15% 56% 5% 9% 9% 5%	1803
December	1st to 10th	Day	13% 35% 6% 19% 22% 5%	2700
	11th to 20th	Day	31% 34% 8% 12% 10% 5%	3108
	21st to end	Day	27% 30% 14% 16% 12% 1	4092
January	1st to 10th	Night	17% 32% 16% 19% 14% 1	6320
	11th to 20th	Night	21% 31% 7% 13% 22% 6%	6175
	21st to end	Night	23% 33% 5% 10% 23% 6%	6468
February	1st to 10th	Night	18% 65% 4 6% 4 3	2600
	11th to 20th	Night	12% 64% 5% 9% 9% 2	2352
	21st to end	Night	10% 64% 5% 10% 7% 5%	1980
March	1st to 10th	Night	27% 36% 6% 17% 10% 4	5376
	11th to 20th	Night	21% 31% 8% 30% 9% 1	5028
	21st to end	Night	29% 37% 13% 16% 5% 1	5152
April	1st to 10th	Night	12% 65% 5% 11% 7%	2000
	11th to 20th	Night	11% 63% 4 12% 8% 2	1979
	21st to end	Night	10% 63% 6% 13% 7% 1	2000
May	1st to 10th	Night	7% 31% 6% 26% 26% 3	4309
	11th to 20th	Night	10% 28% 6% 22% 28% 5%	3666
	21st to end	Night	5% 29% 5% 20% 35% 5%	3972
June	1st to 10th	Night	4 62% 3 13% 13% 4	1600
	11th to 20th	Night	2 62% 3 10% 13% 11%	1600
	21st to end	Night	4 59% 2 5% 13% 18%	1600
July	1st to 10th	Night	3 24% 1 3 17% 53%	3600
	11th to 20th	Night	8% 24% 1 4 10% 53%	3592
	21st to end	Night	9% 25% 3 14% 22% 27%	4049
August	1st to 10th	Night	9% 35% 1 5% 20% 30%	2952
	11th to 20th	Night	3 35% 1 4 24% 33%	3256
	21st to end	Night	5% 34% 2 11% 27% 21%	3608
September	1st to 10th	Night	3 56% 2 5% 20% 14%	2000
	11th to 20th	Night	6% 57% 3 11% 19% 5%	2020
	21st to end	Night	7% 56% 2 10% 18% 8%	2200
October	1st to 10th	Night	5% 35% 2 7% 27% 25%	3901
	11th to 20th	Night	6% 36% 3 13% 34% 8%	3897
	21st to end	Night	13% 35% 4 20% 21% 8%	4312
November	1st to 10th	Night	9% 54% 6% 15% 13% 5%	2665
	11th to 20th	Night	12% 55% 5% 14% 11% 3	2730
	21st to end	Night	14% 56% 4 11% 10% 6%	2814
December	1st to 10th	Night	12% 36% 7% 17% 19% 9%	4700
	11th to 20th	Night	26% 36% 8% 14% 14% 3	5316
	21st to end	Night	29% 32% 12% 15% 9% 3	7106

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	31% 22% 23% 14% 9% 1	202
	11th to 20th	Day	25% 20% 24% 18% 12% 2	260
	21st to end	Day	16% 23% 27% 21% 10% 3	440
February	1st to 10th	Day	26% 21% 25% 19% 8% 1	400
	11th to 20th	Day	24% 22% 26% 21% 7%	488
	21st to end	Day	22% 20% 32% 21% 5%	414
March	1st to 10th	Day	29% 29% 23% 13% 5% 1	500
	11th to 20th	Day	26% 23% 24% 16% 10% 1	500
	21st to end	Day	25% 28% 25% 17% 6%	550
April	1st to 10th	Day	19% 26% 28% 18% 8% 1	500
	11th to 20th	Day	22% 27% 26% 15% 8% 2	492
	21st to end	Day	16% 23% 29% 19% 12% 2	500
May	1st to 10th	Day	18% 24% 28% 19% 8% 3	503
	11th to 20th	Day	18% 22% 25% 21% 9% 5%	528
	21st to end	Day	14% 16% 27% 24% 14% 3	573
June	1st to 10th	Day	11% 18% 28% 24% 15% 4	530
	11th to 20th	Day	12% 20% 35% 19% 12% 3	530
	21st to end	Day	4 15% 31% 31% 15% 4	530
July	1st to 10th	Day	2 12% 40% 28% 15% 3	526
	11th to 20th	Day	2 9% 40% 28% 18% 4	524
	21st to end	Day	2 7% 37% 29% 18% 7%	575
August	1st to 10th	Day	5% 12% 32% 29% 16% 6%	527
	11th to 20th	Day	2 13% 33% 26% 20% 6%	517
	21st to end	Day	4 9% 38% 26% 18% 4	583
September	1st to 10th	Day	4 11% 35% 27% 20% 3	530
	11th to 20th	Day	9% 16% 28% 26% 17% 3	530
	21st to end	Day	7% 14% 33% 28% 16% 2	530
October	1st to 10th	Day	9% 18% 25% 25% 18% 5%	530
	11th to 20th	Day	12% 15% 23% 26% 18% 5%	530
	21st to end	Day	13% 18% 26% 21% 19% 3	544
November	1st to 10th	Day	16% 18% 19% 20% 22% 3	330
	11th to 20th	Day	16% 17% 24% 22% 15% 5%	330
	21st to end	Day	14% 21% 22% 24% 16% 3	283
December	1st to 10th	Day	20% 14% 21% 20% 18% 8%	220
	11th to 20th	Day	23% 22% 21% 15% 13% 7%	220
	21st to end	Day	30% 17% 25% 17% 10% 1	242
January	1st to 10th	Night	15% 16% 25% 24% 15% 7%	804
	11th to 20th	Night	15% 13% 23% 33% 13% 4	800
	21st to end	Night	12% 14% 26% 26% 17% 4	880
February	1st to 10th	Night	17% 14% 24% 28% 15% 3	800
	11th to 20th	Night	14% 15% 23% 28% 15% 5%	784
	21st to end	Night	18% 15% 21% 32% 11% 3	660
March	1st to 10th	Night	20% 18% 24% 22% 13% 3	800
	11th to 20th	Night	16% 19% 20% 21% 20% 3	800
	21st to end	Night	16% 23% 23% 24% 12% 1	880
April	1st to 10th	Night	10% 21% 26% 27% 15% 1	800
	11th to 20th	Night	15% 16% 23% 28% 15% 4	791
	21st to end	Night	11% 15% 22% 30% 18% 4	800
May	1st to 10th	Night	11% 18% 25% 26% 18% 3	695
	11th to 20th	Night	8% 11% 22% 34% 22% 3	418
	21st to end	Night	8% 8% 18% 35% 26% 4	433
June	1st to 10th	Night	7% 8% 18% 37% 27% 4	400
	11th to 20th	Night	3 10% 21% 38% 28% 1	400
	21st to end	Night	4 4 19% 41% 31% 3	400
July	1st to 10th	Night	1 3 16% 48% 30% 2	390
	11th to 20th	Night	1 3 18% 40% 36% 1	388
	21st to end	Night	3 3 9% 42% 39% 6%	520
August	1st to 10th	Night	3 3 14% 39% 37% 4	607
	11th to 20th	Night	2 4 19% 39% 31% 5%	792
	21st to end	Night	2 4 20% 42% 29% 3	880
September	1st to 10th	Night	2 4 20% 39% 31% 4	800
	11th to 20th	Night	5% 8% 17% 30% 33% 7%	800
	21st to end	Night	4 9% 20% 33% 25% 8%	800
October	1st to 10th	Night	7% 11% 19% 32% 25% 7%	800
	11th to 20th	Night	10% 6% 16% 37% 25% 6%	800
	21st to end	Night	10% 11% 18% 27% 25% 9%	880
November	1st to 10th	Night	13% 12% 18% 24% 26% 6%	820
	11th to 20th	Night	13% 15% 22% 29% 17% 5%	840
	21st to end	Night	13% 15% 20% 28% 20% 5%	840
December	1st to 10th	Night	17% 12% 21% 29% 16% 5%	840
	11th to 20th	Night	19% 15% 22% 26% 14% 4	840
	21st to end	Night	19% 18% 26% 25% 10% 2	924

Page generated at 2025-12-29 22:14:06. Version ac07

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