North Wind Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Wind Observatory clear sky chart from 2005-11-06 to 2024-09-29.

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	14% 11% 4 9% 5% 4 4 3 5% 6% 33%	100986
	Night	15% 13% 5% 10% 6% 5% 4 3 5% 6% 30%	97312
Transparency	Day	51% 6% 11% 20% 11% 1	100777
	Night	54% 7% 10% 18% 9% 1	97193
Seeing	Day	22% 16% 31% 20% 9% 3	15787
	Night	22% 11% 29% 27% 9% 1	25623

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	11% 29% 14% 18% 7% 5% 3 2 2 2 7%	2527
	11th to 20th	Day	13% 19% 9% 21% 12% 9% 5% 2 2 2 5%	2530
	21st to end	Day	18% 24% 12% 14% 7% 5% 4 3 3 3 8%	2783
February	1st to 10th	Day	10% 17% 8% 14% 15% 7% 5% 3 3 5% 14%	1665
	11th to 20th	Day	12% 16% 8% 16% 11% 5% 4 3 4 4 16%	1848
	21st to end	Day	13% 18% 8% 15% 7% 4 4 2 4 5% 20%	1570
March	1st to 10th	Day	13% 16% 6% 8% 6% 4 4 4 5% 5% 31%	3120
	11th to 20th	Day	11% 10% 9% 14% 5% 4 3 3 5% 6% 31%	3350
	21st to end	Day	20% 12% 7% 13% 5% 4 4 3 4 4 25%	4001
April	1st to 10th	Day	18% 17% 4 7% 4 4 3 4 5% 6% 28%	2280
	11th to 20th	Day	21% 14% 3 6% 4 4 4 3 4 5% 33%	2314
	21st to end	Day	16% 12% 3 8% 4 4 4 4 5% 7% 33%	2470
May	1st to 10th	Day	16% 8% 3 7% 3 4 4 3 5% 7% 40%	4082
	11th to 20th	Day	12% 7% 2 6% 4 4 4 3 5% 7% 45%	4227
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 6% 8% 42%	4824
June	1st to 10th	Day	13% 5% 2 7% 5% 4 5% 3 4 7% 44%	2660
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 7% 7% 42%	2660
	21st to end	Day	14% 5% 2 6% 5% 4 4 4 7% 8% 42%	2660
July	1st to 10th	Day	16% 7% 2 6% 4 4 4 4 6% 8% 38%	4440
	11th to 20th	Day	8% 4 2 4 4 3 4 4 6% 10% 52%	4440
	21st to end	Day	9% 5% 2 5% 4 4 5% 4 6% 8% 46%	4813
August	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 8% 40%	4245
	11th to 20th	Day	13% 5% 2 5% 4 3 4 4 5% 6% 48%	4044
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 6% 7% 42%	4249
September	1st to 10th	Day	15% 6% 2 7% 4 5% 4 3 5% 7% 42%	2271
	11th to 20th	Day	12% 6% 2 6% 3 3 5% 4 5% 7% 46%	2090
	21st to end	Day	16% 7% 2 7% 4 5% 5% 3 6% 8% 37%	2069
October	1st to 10th	Day	17% 9% 3 7% 5% 4 3 3 5% 7% 38%	1980
	11th to 20th	Day	24% 14% 4 10% 5% 5% 5% 3 4 6% 21%	1717
	21st to end	Day	25% 15% 4 8% 5% 4 3 4 4 7% 21%	1782
November	1st to 10th	Day	17% 16% 4 5% 5% 4 4 3 6% 6% 30%	1672
	11th to 20th	Day	15% 22% 7% 12% 5% 5% 4 4 5% 5% 17%	1710
	21st to end	Day	20% 23% 7% 11% 4 3 3 3 3 4 17%	1672
December	1st to 10th	Day	15% 24% 10% 18% 5% 5% 4 2 3 3 12%	1520
	11th to 20th	Day	16% 23% 9% 15% 8% 4 4 3 4 4 10%	1918
	21st to end	Day	20% 24% 9% 13% 7% 5% 4 2 3 3 9%	2783
January	1st to 10th	Night	14% 23% 11% 16% 7% 5% 3 2 3 3 13%	4428
	11th to 20th	Night	12% 17% 8% 21% 11% 12% 4 2 3 3 8%	4440
	21st to end	Night	16% 24% 10% 16% 8% 6% 4 2 3 3 7%	4884
February	1st to 10th	Night	11% 17% 6% 15% 13% 7% 4 3 4 4 16%	2510
	11th to 20th	Night	12% 16% 6% 14% 10% 6% 5% 3 5% 6% 18%	2218
	21st to end	Night	14% 17% 6% 13% 7% 5% 4 3 5% 4 22%	1884
March	1st to 10th	Night	16% 10% 5% 8% 4 4 3 3 4 6% 37%	3733
	11th to 20th	Night	9% 11% 4 10% 5% 4 4 3 4 7% 37%	3609
	21st to end	Night	16% 13% 5% 13% 5% 4 4 3 4 6% 27%	3658
April	1st to 10th	Night	17% 12% 4 8% 4 3 4 4 6% 6% 32%	1900
	11th to 20th	Night	21% 9% 4 6% 5% 4 4 3 4 6% 35%	1815
	21st to end	Night	18% 9% 3 7% 4 5% 4 3 5% 5% 37%	1710
May	1st to 10th	Night	14% 7% 3 7% 5% 5% 4 4 6% 6% 38%	2813
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 6% 8% 40%	2669
	21st to end	Night	19% 6% 2 5% 4 3 4 3 5% 7% 43%	2743
June	1st to 10th	Night	14% 6% 3 5% 4 4 3 3 7% 8% 43%	1520
	11th to 20th	Night	11% 6% 3 5% 4 3 5% 3 7% 8% 44%	1520
	21st to end	Night	12% 6% 2 6% 5% 4 4 4 6% 7% 45%	1520
July	1st to 10th	Night	13% 8% 2 5% 4 5% 4 5% 7% 7% 41%	2530
	11th to 20th	Night	6% 4 2 4 3 3 4 3 5% 8% 58%	2530
	21st to end	Night	8% 6% 2 6% 4 4 4 3 5% 7% 51%	2750
August	1st to 10th	Night	13% 6% 2 6% 3 4 4 3 7% 8% 42%	2686
	11th to 20th	Night	14% 5% 1 4 3 3 3 3 4 7% 51%	2785
	21st to end	Night	8% 6% 2 7% 4 4 5% 4 5% 7% 48%	3403
September	1st to 10th	Night	12% 5% 1 5% 3 3 4 4 4 6% 51%	1900
	11th to 20th	Night	12% 4 1 4 3 3 4 3 6% 8% 52%	2079
	21st to end	Night	14% 7% 3 6% 4 4 4 4 5% 7% 41%	2079
October	1st to 10th	Night	18% 8% 2 6% 4 3 3 3 4 6% 42%	1980
	11th to 20th	Night	24% 11% 3 7% 5% 4 3 3 5% 5% 29%	2240
	21st to end	Night	25% 14% 3 8% 4 3 4 3 4 6% 25%	2574
November	1st to 10th	Night	14% 14% 5% 7% 6% 4 4 3 5% 6% 31%	2406
	11th to 20th	Night	15% 20% 6% 11% 6% 5% 5% 3 5% 5% 19%	2470
	21st to end	Night	17% 22% 7% 11% 4 5% 5% 3 4 4 18%	2503
December	1st to 10th	Night	15% 23% 8% 15% 8% 4 4 3 3 3 14%	2660
	11th to 20th	Night	15% 24% 7% 16% 7% 4 4 3 4 4 12%	3279
	21st to end	Night	24% 24% 7% 12% 5% 4 3 2 4 4 11%	4884

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	84% 6% 4 5% 1	2528
	11th to 20th	Day	88% 4 3 3 1	2530
	21st to end	Day	82% 7% 6% 4 1	2783
February	1st to 10th	Day	73% 6% 6% 12% 2	1665
	11th to 20th	Day	71% 7% 7% 10% 5%	1858
	21st to end	Day	68% 4 10% 13% 4	1570
March	1st to 10th	Day	54% 6% 12% 19% 8%	3120
	11th to 20th	Day	54% 6% 15% 18% 7% 1	3350
	21st to end	Day	60% 6% 8% 18% 6% 1	4001
April	1st to 10th	Day	56% 5% 10% 19% 10%	2280
	11th to 20th	Day	53% 5% 8% 19% 13% 2	2314
	21st to end	Day	50% 6% 11% 17% 14% 2	2470
May	1st to 10th	Day	42% 6% 10% 23% 17% 2	4120
	11th to 20th	Day	37% 8% 11% 25% 18% 2	4231
	21st to end	Day	37% 9% 11% 22% 19% 3	4837
June	1st to 10th	Day	39% 6% 10% 26% 17% 2	2660
	11th to 20th	Day	39% 6% 12% 23% 19% 1	2660
	21st to end	Day	39% 6% 14% 24% 16% 1	2660
July	1st to 10th	Day	43% 6% 12% 22% 14% 2	4371
	11th to 20th	Day	26% 6% 14% 32% 19% 2	4365
	21st to end	Day	34% 8% 12% 26% 20% 2	4662
August	1st to 10th	Day	39% 7% 12% 27% 14% 1	4230
	11th to 20th	Day	36% 5% 13% 27% 17% 1	4083
	21st to end	Day	38% 6% 13% 27% 14% 1	4248
September	1st to 10th	Day	41% 5% 12% 26% 13% 2	2271
	11th to 20th	Day	36% 7% 12% 28% 15% 1	2090
	21st to end	Day	44% 7% 12% 27% 10%	2069
October	1st to 10th	Day	47% 5% 11% 24% 12%	1980
	11th to 20th	Day	64% 5% 11% 16% 4	1717
	21st to end	Day	64% 6% 12% 12% 6%	1782
November	1st to 10th	Day	53% 8% 10% 20% 9%	1672
	11th to 20th	Day	67% 6% 11% 11% 4	1710
	21st to end	Day	72% 4 12% 9% 3	1672
December	1st to 10th	Day	80% 5% 6% 8% 2	1520
	11th to 20th	Day	77% 7% 10% 6% 1	1915
	21st to end	Day	80% 6% 6% 6% 1	2783
January	1st to 10th	Night	77% 6% 7% 9% 1	4428
	11th to 20th	Night	83% 5% 6% 5% 2	4440
	21st to end	Night	81% 8% 6% 4 1	4884
February	1st to 10th	Night	71% 6% 6% 11% 4 1	2510
	11th to 20th	Night	66% 7% 8% 13% 5%	2219
	21st to end	Night	64% 5% 11% 14% 5%	1884
March	1st to 10th	Night	48% 7% 14% 22% 8%	3733
	11th to 20th	Night	46% 7% 13% 23% 10% 1	3609
	21st to end	Night	57% 7% 8% 21% 6% 1	3658
April	1st to 10th	Night	51% 6% 10% 19% 13% 1	1900
	11th to 20th	Night	50% 6% 8% 20% 14% 2	1815
	21st to end	Night	48% 6% 11% 19% 13% 3	1710
May	1st to 10th	Night	43% 8% 12% 19% 16% 3	2840
	11th to 20th	Night	40% 7% 10% 28% 13% 2	2670
	21st to end	Night	41% 6% 10% 21% 16% 5%	2751
June	1st to 10th	Night	37% 7% 13% 26% 16% 2	1520
	11th to 20th	Night	36% 7% 13% 23% 19% 2	1520
	21st to end	Night	36% 7% 12% 28% 14% 2	1520
July	1st to 10th	Night	41% 7% 12% 23% 12% 6%	2490
	11th to 20th	Night	24% 6% 14% 36% 17% 2	2482
	21st to end	Night	32% 7% 14% 23% 22% 2	2662
August	1st to 10th	Night	37% 7% 14% 27% 14% 1	2677
	11th to 20th	Night	33% 5% 11% 34% 16%	2812
	21st to end	Night	34% 6% 13% 24% 21% 2	3403
September	1st to 10th	Night	32% 7% 11% 30% 18% 2	1900
	11th to 20th	Night	29% 7% 14% 34% 15% 2	2079
	21st to end	Night	42% 7% 13% 26% 11% 1	2079
October	1st to 10th	Night	43% 6% 10% 26% 14% 1	1980
	11th to 20th	Night	55% 7% 13% 20% 5% 1	2240
	21st to end	Night	60% 6% 11% 16% 6%	2574
November	1st to 10th	Night	53% 7% 10% 21% 8% 1	2406
	11th to 20th	Night	65% 7% 12% 10% 5% 1	2470
	21st to end	Night	68% 7% 13% 10% 2 1	2503
December	1st to 10th	Night	75% 6% 8% 8% 2	2660
	11th to 20th	Night	75% 7% 9% 7% 2	3281
	21st to end	Night	77% 7% 9% 6% 2	4884

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	21% 20% 37% 13% 8%	270
	11th to 20th	Day	27% 20% 38% 13% 2	270
	21st to end	Day	29% 16% 36% 15% 3	297
February	1st to 10th	Day	22% 33% 26% 14% 3 1	270
	11th to 20th	Day	27% 31% 30% 11% 1	270
	21st to end	Day	32% 34% 28% 5%	225
March	1st to 10th	Day	27% 31% 33% 9% 1	270
	11th to 20th	Day	27% 18% 31% 15% 8% 1	382
	21st to end	Day	34% 16% 29% 15% 5% 1	506
April	1st to 10th	Day	30% 17% 35% 14% 3 1	460
	11th to 20th	Day	36% 17% 26% 12% 7% 1	452
	21st to end	Day	26% 18% 29% 17% 8% 2	460
May	1st to 10th	Day	26% 20% 33% 13% 6% 1	463
	11th to 20th	Day	20% 15% 35% 20% 6% 4	568
	21st to end	Day	17% 13% 35% 22% 11% 2	734
June	1st to 10th	Day	16% 14% 39% 21% 8% 2	680
	11th to 20th	Day	19% 15% 36% 21% 7% 2	680
	21st to end	Day	20% 12% 34% 23% 8% 2	680
July	1st to 10th	Day	11% 10% 33% 28% 13% 5%	671
	11th to 20th	Day	13% 11% 32% 29% 11% 5%	668
	21st to end	Day	10% 9% 35% 27% 14% 5%	739
August	1st to 10th	Day	13% 7% 28% 27% 18% 6%	576
	11th to 20th	Day	13% 6% 23% 29% 18% 10%	479
	21st to end	Day	19% 8% 24% 28% 16% 5%	539
September	1st to 10th	Day	18% 9% 26% 24% 17% 6%	490
	11th to 20th	Day	12% 6% 28% 30% 19% 5%	490
	21st to end	Day	20% 16% 22% 27% 11% 5%	483
October	1st to 10th	Day	23% 13% 27% 22% 13% 2	450
	11th to 20th	Day	32% 17% 33% 14% 3	321
	21st to end	Day	38% 21% 28% 9% 3	297
November	1st to 10th	Day	30% 19% 32% 13% 5%	270
	11th to 20th	Day	27% 28% 33% 9% 2	270
	21st to end	Day	30% 23% 36% 9% 2	270
December	1st to 10th	Day	31% 24% 29% 13% 4	270
	11th to 20th	Day	31% 27% 29% 10% 2	270
	21st to end	Day	34% 26% 30% 8% 2 1	297
January	1st to 10th	Night	26% 17% 31% 22% 5%	950
	11th to 20th	Night	27% 17% 31% 19% 5%	950
	21st to end	Night	25% 12% 33% 24% 6%	1045
February	1st to 10th	Night	21% 17% 32% 25% 4 1	851
	11th to 20th	Night	25% 16% 33% 22% 4	743
	21st to end	Night	26% 19% 35% 18% 3	628
March	1st to 10th	Night	21% 16% 33% 22% 8% 1	760
	11th to 20th	Night	19% 17% 37% 21% 6%	760
	21st to end	Night	23% 15% 29% 26% 6% 1	741
April	1st to 10th	Night	23% 14% 34% 22% 5% 1	570
	11th to 20th	Night	29% 11% 32% 22% 6% 1	563
	21st to end	Night	23% 12% 32% 26% 7%	570
May	1st to 10th	Night	18% 10% 37% 28% 6% 1	570
	11th to 20th	Night	17% 11% 32% 30% 8% 1	561
	21st to end	Night	16% 7% 28% 34% 14% 1	617
June	1st to 10th	Night	15% 6% 29% 38% 11% 1	570
	11th to 20th	Night	14% 6% 31% 33% 15% 1	570
	21st to end	Night	15% 5% 26% 40% 14% 1	570
July	1st to 10th	Night	10% 3 22% 40% 23% 2	555
	11th to 20th	Night	8% 3 24% 42% 21% 2	552
	21st to end	Night	11% 3 20% 43% 23% 1	624
August	1st to 10th	Night	11% 4 20% 43% 20% 2	567
	11th to 20th	Night	13% 3 18% 37% 24% 5%	564
	21st to end	Night	14% 4 21% 41% 18% 1	627
September	1st to 10th	Night	14% 5% 22% 36% 19% 5%	570
	11th to 20th	Night	14% 6% 22% 35% 21% 3	749
	21st to end	Night	18% 10% 25% 29% 16% 3	756
October	1st to 10th	Night	23% 7% 24% 33% 12% 1	720
	11th to 20th	Night	32% 9% 27% 26% 7% 1	720
	21st to end	Night	34% 11% 26% 21% 7% 1	792
November	1st to 10th	Night	24% 12% 31% 24% 8% 1	740
	11th to 20th	Night	28% 16% 33% 19% 4	760
	21st to end	Night	31% 12% 32% 21% 4	793
December	1st to 10th	Night	28% 18% 32% 18% 4	950
	11th to 20th	Night	30% 16% 32% 17% 4 1	950
	21st to end	Night	32% 15% 31% 19% 2	1045

Page generated at 2024-09-26 09:52:20. Version ac07

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