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 2024-01-14.

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	3 6% 3 4 4 2 3 4 5% 6% 60%	74783
	Night	3 6% 3 5% 4 2 4 4 5% 7% 57%	74994
Transparency	Day	14% 38% 7% 13% 16% 11%	74492
	Night	16% 39% 8% 13% 15% 9%	74806
Seeing	Day	14% 18% 29% 22% 13% 3	13925
	Night	11% 12% 20% 30% 22% 5%	23378

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	3 8% 4 6% 7% 4 5% 5% 7% 7% 43%	1519
	11th to 20th	Day	2 9% 3 4 5% 3 6% 4 5% 7% 51%	1518
	21st to end	Day	4 12% 6% 6% 4 2 4 6% 6% 8% 42%	1782
February	1st to 10th	Day	4 9% 4 6% 5% 2 4 5% 5% 7% 49%	1620
	11th to 20th	Day	2 8% 6% 7% 5% 3 4 4 5% 6% 49%	1736
	21st to end	Day	2 10% 6% 8% 5% 2 3 4 6% 7% 46%	1480
March	1st to 10th	Day	3 13% 8% 10% 6% 4 5% 5% 4 6% 37%	1800
	11th to 20th	Day	3 13% 5% 7% 7% 3 5% 4 5% 7% 41%	1962
	21st to end	Day	2 12% 5% 6% 6% 3 4 5% 6% 8% 43%	2308
April	1st to 10th	Day	4 11% 4 6% 4 2 4 4 5% 8% 46%	2160
	11th to 20th	Day	4 10% 4 5% 4 2 5% 4 4 6% 51%	2129
	21st to end	Day	4 9% 3 4 3 2 4 3 5% 7% 57%	2160
May	1st to 10th	Day	5% 7% 1 4 3 2 4 3 5% 8% 58%	2252
	11th to 20th	Day	4 7% 2 5% 4 2 3 4 4 6% 58%	2452
	21st to end	Day	7% 8% 2 6% 5% 3 4 4 5% 6% 49%	2723
June	1st to 10th	Day	4 4 2 4 4 3 4 4 5% 8% 58%	2520
	11th to 20th	Day	2 3 1 2 2 1 3 3 3 5% 75%	2520
	21st to end	Day	2 2 1 2 2 1 2 2 3 5% 77%	2520
July	1st to 10th	Day	1 1 1 2 1 2 3 3 3 83%	2520
	11th to 20th	Day	1 1 1 1 2 1 2 2 4 4 80%	2520
	21st to end	Day	2 2 1 2 2 1 3 3 4 5% 74%	2665
August	1st to 10th	Day	3 2 1 3 2 1 2 3 4 4 75%	2320
	11th to 20th	Day	2 1 2 2 2 2 3 3 5% 80%	2122
	21st to end	Day	1 1 1 1 1 2 2 2 3 86%	2376
September	1st to 10th	Day	2 1 1 2 1 1 2 3 4 82%	2160
	11th to 20th	Day	2 3 1 3 3 2 2 2 4 5% 73%	2142
	21st to end	Day	3 3 1 2 3 1 2 2 3 5% 75%	1980
October	1st to 10th	Day	5% 5% 2 3 2 2 2 4 3 5% 66%	1814
	11th to 20th	Day	3 4 1 4 3 1 3 3 4 6% 68%	1800
	21st to end	Day	3 4 1 3 4 1 2 3 5% 6% 66%	1945
November	1st to 10th	Day	4 7% 3 5% 3 3 4 4 4 7% 55%	1674
	11th to 20th	Day	2 7% 1 4 4 2 5% 5% 6% 10% 54%	1710
	21st to end	Day	2 6% 3 6% 4 3 4 4 6% 9% 52%	1632
December	1st to 10th	Day	4 10% 3 5% 5% 3 4 4 6% 8% 47%	1520
	11th to 20th	Day	8% 16% 5% 7% 6% 3 6% 5% 6% 7% 33%	1928
	21st to end	Day	3 9% 4 6% 6% 3 5% 5% 7% 11% 40%	2794
January	1st to 10th	Night	4 9% 4 7% 6% 3 4 6% 7% 10% 42%	2646
	11th to 20th	Night	2 7% 4 7% 6% 3 5% 6% 6% 8% 46%	2514
	21st to end	Night	3 10% 5% 6% 5% 3 5% 5% 5% 6% 45%	2574
February	1st to 10th	Night	2 7% 3 7% 7% 3 4 4 5% 7% 49%	2340
	11th to 20th	Night	1 8% 4 6% 6% 2 5% 5% 6% 9% 47%	2110
	21st to end	Night	2 8% 5% 8% 6% 3 4 5% 5% 9% 47%	1776
March	1st to 10th	Night	2 9% 5% 9% 6% 4 6% 5% 5% 8% 42%	2160
	11th to 20th	Night	2 11% 5% 7% 5% 3 5% 5% 6% 8% 44%	1995
	21st to end	Night	2 8% 4 7% 6% 3 4 5% 6% 7% 47%	2048
April	1st to 10th	Night	3 7% 4 6% 5% 3 5% 5% 7% 8% 47%	1800
	11th to 20th	Night	3 9% 3 5% 4 2 4 5% 5% 8% 53%	1779
	21st to end	Night	3 8% 3 3 3 2 4 4 4 7% 59%	1800
May	1st to 10th	Night	4 6% 3 4 4 2 3 4 5% 5% 61%	1706
	11th to 20th	Night	3 6% 2 5% 3 3 4 4 5% 7% 59%	1438
	21st to end	Night	5% 7% 3 4 3 3 3 4 4 8% 55%	1552
June	1st to 10th	Night	4 5% 2 3 3 3 4 4 4 6% 62%	1440
	11th to 20th	Night	1 2 2 2 2 3 3 4 5% 78%	1440
	21st to end	Night	3 2 1 2 2 1 2 3 3 5% 76%	1440
July	1st to 10th	Night	1 1 1 1 2 1 3 3 2 4 82%	1440
	11th to 20th	Night	2 2 1 1 2 1 2 3 3 3 80%	1440
	21st to end	Night	4 2 1 2 2 2 3 3 4 4 74%	1649
August	1st to 10th	Night	3 3 1 2 3 2 3 3 3 5% 72%	1619
	11th to 20th	Night	2 2 1 2 2 1 2 3 3 4 77%	1780
	21st to end	Night	2 1 1 2 2 1 2 2 3 3 83%	1980
September	1st to 10th	Night	2 1 1 1 1 1 1 1 3 5% 84%	1800
	11th to 20th	Night	2 2 2 2 1 2 2 4 5% 78%	1818
	21st to end	Night	2 2 2 3 2 1 2 3 4 5% 75%	1980
October	1st to 10th	Night	4 4 2 4 3 2 2 2 3 5% 70%	2142
	11th to 20th	Night	4 3 1 3 2 1 2 3 3 6% 72%	2160
	21st to end	Night	3 4 1 2 2 2 2 4 4 7% 69%	2409
November	1st to 10th	Night	4 6% 2 5% 4 2 3 5% 5% 8% 56%	2405
	11th to 20th	Night	2 6% 2 5% 3 2 3 3 6% 10% 58%	2470
	21st to end	Night	2 5% 3 6% 5% 3 4 5% 5% 8% 54%	2546
December	1st to 10th	Night	4 8% 4 6% 5% 2 4 5% 6% 7% 49%	2660
	11th to 20th	Night	5% 17% 5% 8% 5% 3 4 5% 6% 9% 34%	3276
	21st to end	Night	2 11% 5% 9% 7% 4 6% 6% 6% 8% 36%	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	16% 48% 10% 16% 9% 1	1519
	11th to 20th	Day	15% 43% 8% 16% 12% 6%	1518
	21st to end	Day	24% 41% 8% 12% 11% 4	1782
February	1st to 10th	Day	17% 38% 9% 15% 15% 6%	1620
	11th to 20th	Day	19% 40% 10% 15% 13% 3	1746
	21st to end	Day	23% 40% 9% 15% 11% 2	1480
March	1st to 10th	Day	24% 43% 8% 16% 9%	1800
	11th to 20th	Day	22% 45% 8% 12% 10% 2	1962
	21st to end	Day	20% 44% 14% 14% 7% 1	2308
April	1st to 10th	Day	21% 40% 12% 12% 12% 3	2160
	11th to 20th	Day	20% 39% 9% 16% 12% 3	2132
	21st to end	Day	15% 38% 11% 19% 15% 2	2160
May	1st to 10th	Day	13% 38% 8% 20% 17% 3	2252
	11th to 20th	Day	12% 38% 9% 19% 17% 5%	2455
	21st to end	Day	19% 39% 11% 17% 13% 2	2724
June	1st to 10th	Day	17% 39% 8% 15% 18% 3	2520
	11th to 20th	Day	7% 37% 6% 13% 26% 11%	2520
	21st to end	Day	7% 36% 4 12% 26% 16%	2520
July	1st to 10th	Day	3 36% 2 6% 16% 39%	2451
	11th to 20th	Day	4 36% 2 6% 17% 34%	2445
	21st to end	Day	7% 37% 2 7% 14% 33%	2517
August	1st to 10th	Day	6% 36% 3 8% 18% 30%	2304
	11th to 20th	Day	7% 34% 2 6% 20% 32%	2122
	21st to end	Day	4 34% 1 6% 23% 31%	2376
September	1st to 10th	Day	4 35% 3 6% 25% 27%	2160
	11th to 20th	Day	7% 37% 4 11% 25% 15%	2142
	21st to end	Day	7% 35% 3 15% 23% 17%	1980
October	1st to 10th	Day	16% 37% 6% 11% 20% 9%	1814
	11th to 20th	Day	10% 36% 5% 20% 19% 11%	1800
	21st to end	Day	11% 38% 7% 17% 19% 9%	1945
November	1st to 10th	Day	20% 44% 8% 11% 11% 6%	1674
	11th to 20th	Day	12% 44% 11% 13% 16% 3	1710
	21st to end	Day	13% 41% 6% 17% 16% 7%	1632
December	1st to 10th	Day	16% 43% 8% 14% 14% 4	1520
	11th to 20th	Day	37% 36% 6% 10% 7% 3	1928
	21st to end	Day	26% 31% 14% 16% 12% 1	2794
January	1st to 10th	Night	18% 45% 10% 16% 10% 1	2646
	11th to 20th	Night	15% 45% 9% 14% 11% 6%	2514
	21st to end	Night	24% 42% 8% 12% 11% 4	2574
February	1st to 10th	Night	18% 39% 7% 16% 15% 6%	2340
	11th to 20th	Night	18% 42% 9% 17% 11% 3	2111
	21st to end	Night	22% 42% 9% 14% 11% 3	1776
March	1st to 10th	Night	21% 42% 10% 17% 8% 2	2160
	11th to 20th	Night	20% 44% 9% 15% 9% 2	1995
	21st to end	Night	19% 44% 14% 14% 7% 2	2048
April	1st to 10th	Night	21% 41% 11% 15% 9% 4	1800
	11th to 20th	Night	18% 39% 13% 17% 10% 4	1779
	21st to end	Night	16% 38% 12% 20% 12% 3	1800
May	1st to 10th	Night	14% 39% 8% 15% 21% 3	1706
	11th to 20th	Night	12% 38% 10% 20% 16% 5%	1438
	21st to end	Night	18% 39% 10% 19% 12% 1	1552
June	1st to 10th	Night	16% 39% 8% 17% 15% 4	1440
	11th to 20th	Night	7% 36% 5% 15% 25% 10%	1440
	21st to end	Night	9% 35% 4 12% 23% 16%	1440
July	1st to 10th	Night	3 35% 2 5% 19% 35%	1400
	11th to 20th	Night	7% 36% 3 5% 18% 31%	1392
	21st to end	Night	9% 37% 2 5% 15% 32%	1557
August	1st to 10th	Night	9% 36% 3 9% 16% 27%	1610
	11th to 20th	Night	8% 35% 3 6% 20% 28%	1780
	21st to end	Night	6% 34% 1 6% 23% 30%	1980
September	1st to 10th	Night	5% 35% 3 6% 23% 29%	1800
	11th to 20th	Night	6% 36% 5% 13% 24% 16%	1818
	21st to end	Night	7% 36% 4 14% 23% 16%	1980
October	1st to 10th	Night	14% 36% 6% 14% 21% 8%	2142
	11th to 20th	Night	9% 37% 4 18% 22% 9%	2160
	21st to end	Night	10% 38% 7% 17% 21% 8%	2409
November	1st to 10th	Night	18% 44% 8% 11% 12% 7%	2405
	11th to 20th	Night	13% 43% 9% 16% 16% 4	2470
	21st to end	Night	13% 42% 6% 16% 16% 7%	2546
December	1st to 10th	Night	16% 44% 8% 13% 14% 5%	2660
	11th to 20th	Night	32% 38% 7% 11% 11% 2	3276
	21st to end	Night	29% 35% 12% 11% 11% 2	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	33% 21% 22% 13% 9% 1	180
	11th to 20th	Day	27% 19% 23% 18% 12% 2	220
	21st to end	Day	17% 23% 26% 20% 10% 3	374
February	1st to 10th	Day	24% 20% 26% 20% 9% 1	340
	11th to 20th	Day	23% 21% 27% 22% 7%	409
	21st to end	Day	23% 21% 32% 18% 5%	346
March	1st to 10th	Day	29% 28% 23% 12% 6% 1	420
	11th to 20th	Day	24% 24% 24% 16% 10% 2	420
	21st to end	Day	24% 27% 25% 18% 6%	462
April	1st to 10th	Day	20% 27% 28% 17% 7% 1	420
	11th to 20th	Day	24% 27% 26% 14% 7% 2	412
	21st to end	Day	17% 24% 27% 19% 11% 2	420
May	1st to 10th	Day	19% 23% 27% 21% 7% 2	423
	11th to 20th	Day	19% 23% 26% 19% 8% 4	448
	21st to end	Day	17% 17% 25% 23% 14% 4	485
June	1st to 10th	Day	12% 20% 29% 24% 12% 4	450
	11th to 20th	Day	13% 19% 35% 20% 11% 3	450
	21st to end	Day	4 16% 31% 30% 14% 4	450
July	1st to 10th	Day	2 12% 42% 28% 13% 2	446
	11th to 20th	Day	2 10% 42% 26% 17% 4	444
	21st to end	Day	2 7% 39% 29% 18% 5%	487
August	1st to 10th	Day	6% 13% 32% 29% 16% 4	447
	11th to 20th	Day	2 11% 34% 27% 20% 6%	437
	21st to end	Day	3 9% 41% 27% 17% 2	495
September	1st to 10th	Day	4 10% 36% 28% 20% 3	450
	11th to 20th	Day	9% 16% 29% 26% 18% 2	450
	21st to end	Day	7% 15% 36% 27% 14% 1	450
October	1st to 10th	Day	9% 19% 27% 25% 17% 4	450
	11th to 20th	Day	12% 15% 23% 27% 19% 4	450
	21st to end	Day	12% 18% 26% 21% 20% 3	460
November	1st to 10th	Day	19% 17% 18% 20% 23% 3	270
	11th to 20th	Day	12% 18% 24% 21% 17% 7%	270
	21st to end	Day	13% 22% 22% 23% 16% 2	232
December	1st to 10th	Day	25% 16% 21% 18% 15% 6%	180
	11th to 20th	Day	21% 25% 24% 12% 12% 6%	180
	21st to end	Day	27% 18% 25% 18% 11% 2	198
January	1st to 10th	Night	15% 16% 23% 24% 16% 7%	760
	11th to 20th	Night	15% 13% 22% 32% 13% 4	734
	21st to end	Night	13% 14% 26% 24% 18% 4	792
February	1st to 10th	Night	14% 14% 24% 29% 16% 3	720
	11th to 20th	Night	13% 16% 22% 27% 16% 6%	704
	21st to end	Night	19% 15% 21% 30% 11% 3	592
March	1st to 10th	Night	19% 19% 23% 22% 13% 3	720
	11th to 20th	Night	15% 19% 20% 21% 22% 4	720
	21st to end	Night	15% 24% 22% 25% 13% 1	792
April	1st to 10th	Night	11% 21% 26% 26% 15% 1	720
	11th to 20th	Night	16% 17% 23% 26% 14% 4	711
	21st to end	Night	11% 16% 22% 27% 19% 5%	720
May	1st to 10th	Night	11% 18% 24% 26% 19% 3	626
	11th to 20th	Night	9% 11% 21% 34% 22% 3	376
	21st to end	Night	9% 9% 17% 34% 25% 5%	389
June	1st to 10th	Night	7% 9% 18% 36% 26% 4	360
	11th to 20th	Night	3 10% 21% 36% 29% 1	360
	21st to end	Night	4 5% 17% 39% 32% 3	360
July	1st to 10th	Night	1 3 16% 46% 31% 3	350
	11th to 20th	Night	1 3 19% 39% 36% 1	348
	21st to end	Night	3 3 9% 42% 38% 6%	467
August	1st to 10th	Night	3 3 13% 37% 39% 5%	545
	11th to 20th	Night	3 4 18% 38% 33% 5%	712
	21st to end	Night	2 3 21% 42% 28% 3	792
September	1st to 10th	Night	2 5% 18% 38% 33% 5%	720
	11th to 20th	Night	4 9% 17% 29% 33% 7%	720
	21st to end	Night	5% 9% 20% 32% 25% 9%	720
October	1st to 10th	Night	8% 11% 18% 32% 24% 7%	720
	11th to 20th	Night	10% 6% 15% 37% 26% 6%	720
	21st to end	Night	10% 11% 17% 25% 27% 10%	792
November	1st to 10th	Night	14% 12% 17% 23% 26% 7%	740
	11th to 20th	Night	12% 14% 21% 29% 18% 5%	760
	21st to end	Night	12% 15% 20% 27% 21% 5%	760
December	1st to 10th	Night	19% 13% 20% 28% 16% 4	760
	11th to 20th	Night	19% 15% 22% 25% 14% 4	760
	21st to end	Night	18% 18% 26% 26% 11% 2	836

Page generated at 2024-01-11 01:22:39. Version ac07

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