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 2024-02-05.

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	15% 12% 5% 8% 6% 3 4 4 5% 6% 31%	78140
	Night	15% 13% 6% 9% 7% 4 4 4 4 6% 28%	80767
Transparency	Day	54% 6% 11% 18% 10% 1	77841
	Night	57% 7% 10% 17% 8% 1	80587
Seeing	Day	22% 16% 31% 20% 9% 3	14796
	Night	22% 12% 29% 27% 9% 1	24841

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	12% 27% 15% 17% 8% 4 4 3 2 2 7%	2527
	11th to 20th	Day	14% 18% 11% 19% 15% 8% 5% 2 2 2 5%	2530
	21st to end	Day	19% 22% 13% 13% 9% 3 5% 3 3 3 8%	2783
February	1st to 10th	Day	11% 15% 9% 12% 17% 5% 6% 3 3 4 14%	1610
	11th to 20th	Day	13% 15% 9% 15% 13% 4 4 4 4 3 16%	1748
	21st to end	Day	14% 17% 10% 14% 9% 3 4 3 3 5% 18%	1480
March	1st to 10th	Day	15% 13% 6% 8% 8% 3 5% 4 5% 5% 27%	1800
	11th to 20th	Day	12% 11% 6% 9% 7% 3 4 4 6% 6% 32%	1906
	21st to end	Day	18% 13% 4 7% 6% 3 5% 5% 4 6% 29%	2282
April	1st to 10th	Day	19% 16% 5% 6% 5% 3 3 4 5% 7% 28%	2160
	11th to 20th	Day	21% 14% 3 5% 5% 3 4 3 4 5% 33%	2190
	21st to end	Day	16% 12% 4 7% 5% 3 4 5% 5% 7% 33%	2340
May	1st to 10th	Day	17% 8% 3 6% 5% 3 4 4 5% 8% 37%	2340
	11th to 20th	Day	17% 7% 3 6% 5% 2 4 4 5% 7% 40%	2377
	21st to end	Day	12% 6% 2 5% 5% 3 5% 5% 6% 8% 42%	2725
June	1st to 10th	Day	13% 5% 3 5% 5% 3 5% 4 4 7% 45%	2520
	11th to 20th	Day	13% 6% 3 5% 5% 3 4 5% 7% 8% 42%	2520
	21st to end	Day	14% 5% 2 5% 5% 3 4 6% 6% 9% 42%	2520
July	1st to 10th	Day	8% 4 1 4 4 3 4 5% 6% 9% 51%	2520
	11th to 20th	Day	11% 5% 3 4 5% 3 4 5% 5% 8% 47%	2520
	21st to end	Day	10% 5% 2 4 4 3 5% 5% 6% 9% 47%	2743
August	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 5% 7% 9% 43%	2413
	11th to 20th	Day	12% 4 2 5% 5% 3 5% 5% 6% 8% 45%	2303
	21st to end	Day	14% 6% 2 5% 4 3 5% 5% 6% 7% 44%	2417
September	1st to 10th	Day	16% 6% 2 6% 5% 4 4 4 5% 6% 41%	2152
	11th to 20th	Day	13% 6% 3 5% 4 3 5% 5% 5% 7% 45%	1980
	21st to end	Day	16% 7% 3 6% 6% 3 5% 5% 5% 8% 36%	1980
October	1st to 10th	Day	17% 9% 3 6% 6% 3 4 3 4 6% 39%	1980
	11th to 20th	Day	24% 13% 4 9% 6% 4 5% 4 4 6% 21%	1717
	21st to end	Day	26% 14% 5% 8% 6% 3 3 4 4 7% 21%	1782
November	1st to 10th	Day	17% 15% 4 5% 6% 3 4 4 5% 6% 30%	1672
	11th to 20th	Day	15% 20% 7% 11% 6% 4 4 5% 4 6% 17%	1710
	21st to end	Day	21% 21% 8% 10% 5% 3 3 4 3 4 17%	1672
December	1st to 10th	Day	16% 21% 12% 16% 6% 3 4 3 3 3 12%	1520
	11th to 20th	Day	16% 21% 10% 13% 10% 3 4 4 4 5% 10%	1918
	21st to end	Day	21% 23% 10% 12% 8% 4 4 3 3 3 9%	2783
January	1st to 10th	Night	14% 23% 11% 15% 8% 4 4 3 3 3 13%	4428
	11th to 20th	Night	12% 16% 9% 19% 13% 10% 5% 3 3 3 8%	4440
	21st to end	Night	16% 23% 11% 14% 9% 5% 4 4 3 3 8%	4884
February	1st to 10th	Night	11% 15% 8% 14% 14% 6% 6% 3 3 4 16%	2440
	11th to 20th	Night	13% 14% 7% 12% 11% 4 5% 4 5% 6% 17%	2098
	21st to end	Night	15% 16% 7% 11% 9% 4 4 4 4 4 21%	1776
March	1st to 10th	Night	14% 10% 5% 8% 7% 4 4 4 4 6% 33%	2160
	11th to 20th	Night	13% 10% 4 8% 6% 4 4 4 4 7% 35%	2053
	21st to end	Night	18% 10% 3 7% 6% 3 4 5% 4 7% 34%	2088
April	1st to 10th	Night	17% 11% 5% 8% 5% 3 4 5% 6% 7% 32%	1800
	11th to 20th	Night	21% 8% 4 5% 5% 3 4 4 4 6% 36%	1719
	21st to end	Night	18% 8% 4 6% 5% 3 4 4 5% 6% 38%	1620
May	1st to 10th	Night	15% 6% 3 7% 7% 4 6% 6% 6% 7% 34%	1620
	11th to 20th	Night	16% 6% 3 6% 5% 3 5% 5% 6% 7% 37%	1514
	21st to end	Night	13% 5% 2 5% 5% 3 3 4 5% 10% 45%	1551
June	1st to 10th	Night	14% 5% 3 5% 4 2 3 4 7% 8% 44%	1440
	11th to 20th	Night	11% 6% 3 5% 5% 2 4 4 6% 9% 45%	1440
	21st to end	Night	12% 5% 3 5% 5% 2 4 5% 5% 8% 46%	1440
July	1st to 10th	Night	8% 2 1 3 3 3 4 5% 7% 9% 54%	1440
	11th to 20th	Night	6% 3 3 5% 4 3 4 5% 5% 9% 52%	1440
	21st to end	Night	8% 4 3 6% 5% 3 5% 4 5% 7% 50%	1575
August	1st to 10th	Night	8% 5% 2 5% 3 3 4 5% 7% 9% 47%	1523
	11th to 20th	Night	9% 3 1 4 4 3 5% 5% 5% 8% 52%	1598
	21st to end	Night	11% 7% 3 5% 4 3 4 4 4 7% 48%	1935
September	1st to 10th	Night	12% 5% 2 5% 4 2 4 5% 5% 6% 50%	1800
	11th to 20th	Night	13% 4 1 3 4 2 4 4 5% 8% 51%	1969
	21st to end	Night	14% 7% 3 6% 4 3 5% 4 6% 7% 40%	1980
October	1st to 10th	Night	18% 8% 2 4 5% 3 3 4 4 6% 42%	1980
	11th to 20th	Night	25% 10% 4 6% 6% 3 4 3 5% 5% 29%	2240
	21st to end	Night	26% 13% 3 6% 6% 2 4 4 4 6% 26%	2574
November	1st to 10th	Night	14% 14% 5% 6% 7% 3 5% 4 5% 6% 31%	2406
	11th to 20th	Night	16% 18% 6% 10% 7% 4 5% 5% 5% 5% 20%	2470
	21st to end	Night	18% 20% 8% 10% 5% 3 5% 4 4 4 18%	2503
December	1st to 10th	Night	16% 20% 11% 14% 8% 3 4 4 3 3 14%	2660
	11th to 20th	Night	16% 22% 8% 15% 8% 3 4 4 4 4 12%	3279
	21st to end	Night	24% 23% 8% 10% 6% 3 4 3 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	75% 6% 6% 12% 2	1610
	11th to 20th	Day	72% 6% 7% 10% 5%	1758
	21st to end	Day	70% 4 9% 12% 4	1480
March	1st to 10th	Day	58% 6% 13% 16% 7% 1	1800
	11th to 20th	Day	52% 6% 12% 18% 10% 2	1906
	21st to end	Day	56% 6% 10% 19% 8% 1	2282
April	1st to 10th	Day	57% 5% 10% 18% 10%	2160
	11th to 20th	Day	53% 5% 8% 18% 13% 2	2190
	21st to end	Day	51% 6% 11% 16% 14% 2	2340
May	1st to 10th	Day	46% 6% 10% 24% 13% 2	2340
	11th to 20th	Day	44% 6% 11% 21% 16% 2	2381
	21st to end	Day	38% 8% 13% 25% 14% 2	2725
June	1st to 10th	Day	39% 6% 10% 26% 17% 2	2520
	11th to 20th	Day	39% 6% 12% 23% 19% 1	2520
	21st to end	Day	39% 6% 15% 23% 16% 1	2520
July	1st to 10th	Day	29% 7% 13% 30% 19% 3	2451
	11th to 20th	Day	34% 7% 12% 28% 18% 2	2445
	21st to end	Day	32% 8% 13% 26% 18% 3	2591
August	1st to 10th	Day	35% 8% 15% 29% 12% 2	2398
	11th to 20th	Day	36% 7% 15% 27% 14% 2	2303
	21st to end	Day	37% 7% 14% 24% 16% 2	2417
September	1st to 10th	Day	43% 5% 13% 24% 13% 2	2152
	11th to 20th	Day	37% 7% 13% 29% 12% 1	1980
	21st to end	Day	45% 7% 13% 26% 10%	1980
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	72% 6% 6% 11% 4	2440
	11th to 20th	Night	67% 7% 8% 13% 5%	2099
	21st to end	Night	66% 5% 10% 14% 5%	1776
March	1st to 10th	Night	52% 6% 12% 20% 9%	2160
	11th to 20th	Night	49% 6% 12% 20% 12% 2	2053
	21st to end	Night	51% 6% 9% 24% 8% 1	2088
April	1st to 10th	Night	52% 6% 10% 19% 13% 1	1800
	11th to 20th	Night	50% 6% 8% 19% 15% 2	1719
	21st to end	Night	47% 6% 11% 20% 13% 4	1620
May	1st to 10th	Night	47% 7% 12% 21% 12% 2	1620
	11th to 20th	Night	44% 6% 10% 21% 14% 3	1515
	21st to end	Night	37% 5% 11% 28% 16% 2	1552
June	1st to 10th	Night	36% 6% 13% 26% 16% 2	1440
	11th to 20th	Night	35% 7% 13% 23% 19% 2	1440
	21st to end	Night	35% 8% 13% 28% 14% 2	1440
July	1st to 10th	Night	25% 9% 14% 29% 20% 3	1400
	11th to 20th	Night	28% 7% 16% 30% 18% 3	1392
	21st to end	Night	32% 8% 14% 25% 18% 2	1487
August	1st to 10th	Night	31% 9% 16% 31% 12% 2	1514
	11th to 20th	Night	30% 7% 15% 33% 15% 1	1598
	21st to end	Night	35% 7% 12% 25% 19% 2	1935
September	1st to 10th	Night	33% 7% 11% 29% 18% 2	1800
	11th to 20th	Night	30% 7% 14% 34% 13% 2	1969
	21st to end	Night	42% 7% 14% 27% 10% 1	1980
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	23% 34% 26% 13% 3 2	252
	11th to 20th	Day	28% 31% 31% 9% 1	240
	21st to end	Day	35% 34% 26% 5% 1	198
March	1st to 10th	Day	28% 33% 29% 10% 1	240
	11th to 20th	Day	25% 17% 32% 16% 9% 1	346
	21st to end	Day	34% 16% 28% 16% 6% 1	462
April	1st to 10th	Day	30% 16% 35% 15% 4 1	420
	11th to 20th	Day	35% 17% 25% 13% 8% 1	412
	21st to end	Day	26% 18% 29% 18% 8% 2	420
May	1st to 10th	Day	26% 22% 31% 13% 7% 1	423
	11th to 20th	Day	21% 15% 35% 19% 6% 4	523
	21st to end	Day	16% 13% 35% 22% 11% 3	679
June	1st to 10th	Day	15% 14% 39% 22% 8% 3	630
	11th to 20th	Day	19% 14% 35% 23% 7% 2	630
	21st to end	Day	19% 12% 35% 24% 8% 2	630
July	1st to 10th	Day	10% 9% 33% 29% 14% 5%	621
	11th to 20th	Day	13% 11% 33% 28% 10% 6%	618
	21st to end	Day	10% 10% 36% 26% 13% 5%	684
August	1st to 10th	Day	13% 6% 28% 27% 19% 6%	532
	11th to 20th	Day	13% 6% 23% 29% 19% 10%	439
	21st to end	Day	20% 8% 24% 27% 16% 5%	495
September	1st to 10th	Day	18% 8% 26% 24% 17% 6%	450
	11th to 20th	Day	13% 6% 29% 30% 18% 5%	450
	21st to end	Day	20% 16% 22% 25% 12% 5%	450
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% 16% 32% 26% 3 1	829
	11th to 20th	Night	26% 16% 32% 21% 5%	703
	21st to end	Night	27% 19% 33% 18% 3	592
March	1st to 10th	Night	20% 16% 32% 23% 8% 1	720
	11th to 20th	Night	19% 18% 36% 21% 6%	720
	21st to end	Night	23% 15% 28% 27% 6% 1	702
April	1st to 10th	Night	23% 15% 33% 23% 6% 1	540
	11th to 20th	Night	29% 10% 32% 23% 6% 1	533
	21st to end	Night	23% 11% 32% 26% 7%	540
May	1st to 10th	Night	18% 10% 38% 27% 7% 1	540
	11th to 20th	Night	18% 12% 31% 30% 8% 1	531
	21st to end	Night	15% 7% 28% 34% 15% 1	584
June	1st to 10th	Night	15% 6% 28% 38% 11% 1	540
	11th to 20th	Night	14% 6% 29% 34% 15% 1	540
	21st to end	Night	14% 5% 25% 41% 14% 1	540
July	1st to 10th	Night	9% 2 22% 40% 24% 2	525
	11th to 20th	Night	8% 3 25% 41% 21% 2	522
	21st to end	Night	11% 3 20% 43% 22% 1	591
August	1st to 10th	Night	11% 3 20% 44% 20% 2	537
	11th to 20th	Night	12% 3 18% 37% 25% 5%	534
	21st to end	Night	14% 5% 22% 40% 18% 2	594
September	1st to 10th	Night	14% 4 22% 36% 19% 5%	540
	11th to 20th	Night	15% 6% 22% 34% 20% 3	709
	21st to end	Night	18% 11% 24% 28% 17% 3	720
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 2024-02-02 05:20:33. Version ac07

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