Highwinds Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Highwinds Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	13% 10% 4 10% 6% 5% 5% 4 6% 7% 29%	131850
	Night	13% 11% 4 10% 6% 5% 5% 4 6% 7% 29%	130281
Transparency	Day	51% 8% 12% 19% 9% 1	135406
	Night	51% 8% 13% 18% 9% 1	134811
Seeing	Day	22% 19% 30% 18% 9% 3	16405
	Night	20% 18% 29% 23% 9% 1	25827

By Month

Percentage Cloud Cover NE (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% 19% 6% 18% 10% 4 4 3 4 4 15%	4661
	11th to 20th	Day	9% 16% 8% 18% 10% 8% 6% 5% 4 5% 13%	4808
	21st to end	Day	10% 12% 7% 12% 12% 9% 8% 4 5% 5% 15%	5780
February	1st to 10th	Day	14% 16% 7% 13% 9% 5% 6% 3 5% 4 19%	1890
	11th to 20th	Day	11% 16% 8% 16% 9% 5% 5% 3 4 5% 18%	1843
	21st to end	Day	17% 14% 4 13% 9% 4 4 3 5% 5% 23%	1719
March	1st to 10th	Day	16% 12% 6% 12% 6% 4 4 2 4 5% 29%	4843
	11th to 20th	Day	9% 15% 5% 10% 5% 5% 5% 3 5% 6% 33%	5090
	21st to end	Day	12% 12% 4 13% 7% 6% 5% 4 4 5% 27%	5726
April	1st to 10th	Day	15% 15% 4 8% 6% 5% 4 3 5% 6% 28%	2520
	11th to 20th	Day	16% 12% 4 9% 5% 5% 4 4 5% 5% 33%	2446
	21st to end	Day	17% 11% 4 8% 4 5% 4 3 5% 7% 32%	2483
May	1st to 10th	Day	26% 9% 3 7% 4 4 5% 4 5% 5% 28%	6108
	11th to 20th	Day	13% 10% 4 10% 5% 5% 5% 4 6% 7% 31%	6318
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	6949
June	1st to 10th	Day	16% 7% 3 7% 5% 5% 5% 4 7% 8% 34%	2800
	11th to 20th	Day	13% 6% 3 7% 5% 5% 6% 5% 7% 10% 34%	2800
	21st to end	Day	11% 6% 3 7% 5% 5% 6% 4 7% 9% 37%	2800
July	1st to 10th	Day	9% 6% 2 6% 5% 5% 6% 5% 7% 10% 39%	6360
	11th to 20th	Day	7% 5% 3 7% 5% 5% 7% 6% 9% 12% 35%	6360
	21st to end	Day	9% 5% 3 7% 5% 5% 5% 5% 6% 8% 42%	6757
August	1st to 10th	Day	16% 6% 3 7% 5% 5% 6% 4 7% 8% 35%	4234
	11th to 20th	Day	13% 7% 3 7% 6% 6% 7% 5% 8% 9% 29%	4123
	21st to end	Day	10% 6% 2 8% 6% 5% 5% 4 6% 9% 37%	4312
September	1st to 10th	Day	14% 6% 2 6% 5% 4 5% 4 5% 8% 40%	2400
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 3 6% 6% 46%	2400
	21st to end	Day	17% 7% 3 8% 6% 5% 5% 4 7% 7% 33%	2104
October	1st to 10th	Day	17% 7% 3 8% 5% 4 5% 4 6% 7% 37%	2000
	11th to 20th	Day	18% 10% 3 8% 5% 5% 5% 3 6% 6% 30%	2000
	21st to end	Day	21% 12% 4 8% 5% 4 4 4 5% 6% 26%	2175
November	1st to 10th	Day	12% 12% 4 9% 6% 5% 6% 3 5% 5% 33%	1851
	11th to 20th	Day	11% 14% 5% 10% 6% 5% 6% 4 6% 7% 25%	1716
	21st to end	Day	15% 16% 4 10% 7% 5% 5% 4 5% 6% 21%	1680
December	1st to 10th	Day	14% 19% 7% 15% 7% 5% 5% 4 6% 5% 13%	2680
	11th to 20th	Day	17% 14% 6% 13% 6% 6% 4 3 6% 5% 21%	3066
	21st to end	Day	17% 17% 6% 14% 7% 6% 5% 4 6% 6% 13%	4048
January	1st to 10th	Night	11% 15% 6% 19% 9% 6% 5% 3 4 5% 16%	8234
	11th to 20th	Night	8% 18% 7% 15% 9% 7% 5% 4 6% 7% 15%	8073
	21st to end	Night	11% 11% 5% 12% 8% 7% 7% 5% 6% 7% 21%	8401
February	1st to 10th	Night	12% 16% 5% 12% 8% 5% 6% 4 6% 5% 21%	2730
	11th to 20th	Night	10% 13% 6% 15% 9% 7% 6% 4 5% 5% 20%	2663
	21st to end	Night	13% 12% 5% 14% 6% 6% 5% 4 6% 6% 23%	2086
March	1st to 10th	Night	13% 9% 5% 11% 8% 6% 5% 4 6% 6% 28%	5213
	11th to 20th	Night	12% 13% 5% 8% 5% 4 4 3 4 7% 34%	5089
	21st to end	Night	14% 11% 4 12% 7% 5% 6% 4 5% 6% 27%	5434
April	1st to 10th	Night	16% 12% 4 8% 5% 5% 5% 4 6% 7% 29%	2100
	11th to 20th	Night	16% 11% 4 8% 5% 4 3 3 5% 6% 34%	2036
	21st to end	Night	15% 8% 3 8% 4 4 4 4 5% 7% 37%	1934
May	1st to 10th	Night	28% 9% 3 6% 5% 4 4 3 5% 6% 25%	3831
	11th to 20th	Night	14% 9% 3 8% 5% 5% 5% 4 6% 8% 35%	3575
	21st to end	Night	16% 8% 2 6% 5% 5% 5% 4 6% 8% 35%	3926
June	1st to 10th	Night	15% 6% 3 7% 5% 4 5% 3 5% 9% 38%	1600
	11th to 20th	Night	9% 6% 3 7% 5% 4 4 5% 7% 8% 43%	1600
	21st to end	Night	9% 5% 2 7% 5% 5% 4 6% 6% 9% 43%	1600
July	1st to 10th	Night	6% 7% 3 7% 6% 5% 4 4 7% 11% 40%	3600
	11th to 20th	Night	8% 5% 2 6% 4 4 5% 5% 7% 9% 45%	3600
	21st to end	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 48%	4078
August	1st to 10th	Night	14% 6% 2 6% 4 4 5% 4 7% 8% 39%	2915
	11th to 20th	Night	13% 7% 2 7% 4 5% 4 4 5% 7% 41%	2892
	21st to end	Night	8% 4 2 6% 5% 5% 4 4 6% 9% 45%	3586
September	1st to 10th	Night	13% 5% 2 5% 4 4 4 4 6% 7% 47%	2000
	11th to 20th	Night	13% 4 2 6% 4 4 3 4 6% 6% 47%	2000
	21st to end	Night	15% 8% 3 6% 4 4 6% 4 7% 7% 37%	2293
October	1st to 10th	Night	15% 7% 3 8% 5% 5% 4 3 6% 6% 39%	2400
	11th to 20th	Night	17% 8% 2 7% 5% 5% 4 3 6% 8% 35%	2400
	21st to end	Night	22% 10% 3 8% 4 4 4 3 5% 6% 30%	2664
November	1st to 10th	Night	13% 11% 3 7% 5% 4 5% 4 5% 6% 37%	2667
	11th to 20th	Night	14% 12% 3 9% 5% 5% 5% 4 6% 7% 29%	2903
	21st to end	Night	14% 14% 5% 10% 6% 6% 6% 4 6% 7% 23%	2940
December	1st to 10th	Night	10% 15% 6% 16% 8% 7% 6% 4 6% 7% 16%	4720
	11th to 20th	Night	16% 15% 5% 11% 6% 6% 5% 4 4 5% 23%	5348
	21st to end	Night	19% 18% 6% 11% 7% 5% 4 3 5% 5% 16%	7150

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	71% 6% 9% 11% 3	4662
	11th to 20th	Day	69% 8% 8% 9% 6% 1	4838
	21st to end	Day	66% 8% 11% 12% 4	5780
February	1st to 10th	Day	68% 7% 9% 12% 4	1890
	11th to 20th	Day	69% 5% 7% 14% 5%	1852
	21st to end	Day	62% 6% 10% 14% 5% 1	1719
March	1st to 10th	Day	57% 5% 11% 17% 9%	4846
	11th to 20th	Day	50% 7% 18% 16% 8% 2	5090
	21st to end	Day	55% 8% 7% 19% 9% 2	5726
April	1st to 10th	Day	56% 6% 10% 18% 9% 2	2520
	11th to 20th	Day	52% 7% 10% 17% 13% 1	2446
	21st to end	Day	51% 6% 9% 19% 13% 2	2483
May	1st to 10th	Day	56% 7% 9% 15% 10% 2	6117
	11th to 20th	Day	50% 10% 10% 19% 11% 1	6322
	21st to end	Day	48% 9% 11% 20% 10% 2	6949
June	1st to 10th	Day	46% 8% 12% 19% 15% 1	2800
	11th to 20th	Day	43% 10% 14% 21% 11% 1	2800
	21st to end	Day	41% 9% 15% 20% 13% 1	2800
July	1st to 10th	Day	38% 9% 14% 27% 12% 1	6290
	11th to 20th	Day	36% 11% 18% 22% 12% 1	6285
	21st to end	Day	37% 9% 13% 26% 14% 1	6562
August	1st to 10th	Day	45% 8% 15% 20% 12% 1	4221
	11th to 20th	Day	46% 10% 15% 23% 6%	4162
	21st to end	Day	41% 8% 12% 31% 7% 1	4312
September	1st to 10th	Day	41% 9% 11% 27% 12% 1	2400
	11th to 20th	Day	38% 6% 13% 27% 16% 1	2400
	21st to end	Day	48% 9% 11% 20% 11% 1	2104
October	1st to 10th	Day	38% 8% 13% 25% 15% 1	3260
	11th to 20th	Day	46% 7% 13% 17% 16%	3240
	21st to end	Day	43% 8% 14% 26% 9% 1	3489
November	1st to 10th	Day	51% 8% 11% 17% 10% 2	1851
	11th to 20th	Day	56% 8% 12% 15% 6% 2	1716
	21st to end	Day	62% 8% 14% 14% 3	1680
December	1st to 10th	Day	69% 9% 10% 9% 2	2680
	11th to 20th	Day	63% 8% 13% 11% 6%	3066
	21st to end	Day	68% 8% 13% 8% 3	4048
January	1st to 10th	Night	67% 8% 10% 10% 4	8234
	11th to 20th	Night	63% 8% 10% 11% 6% 1	8118
	21st to end	Night	59% 7% 11% 14% 9% 1	8401
February	1st to 10th	Night	62% 7% 12% 13% 6%	2730
	11th to 20th	Night	62% 8% 11% 13% 5% 1	2665
	21st to end	Night	60% 8% 11% 12% 8% 1	2086
March	1st to 10th	Night	53% 8% 15% 15% 8% 1	5223
	11th to 20th	Night	50% 8% 17% 17% 6% 3	5090
	21st to end	Night	53% 9% 10% 17% 10% 2	5434
April	1st to 10th	Night	53% 8% 11% 17% 9% 1	2100
	11th to 20th	Night	50% 7% 11% 17% 13% 1	2036
	21st to end	Night	45% 9% 11% 19% 13% 2	1934
May	1st to 10th	Night	59% 7% 9% 15% 8% 2	3838
	11th to 20th	Night	45% 10% 15% 19% 10% 1	3576
	21st to end	Night	44% 10% 14% 19% 12% 2	3927
June	1st to 10th	Night	41% 7% 13% 24% 14% 1	1600
	11th to 20th	Night	36% 9% 16% 24% 13% 2	1600
	21st to end	Night	36% 11% 13% 25% 14% 1	1600
July	1st to 10th	Night	37% 9% 16% 25% 13% 1	3560
	11th to 20th	Night	32% 10% 15% 28% 14% 1	3552
	21st to end	Night	32% 8% 13% 27% 18% 2	3958
August	1st to 10th	Night	40% 9% 15% 25% 10% 1	2904
	11th to 20th	Night	40% 8% 15% 28% 8%	2919
	21st to end	Night	32% 9% 16% 32% 10% 1	3586
September	1st to 10th	Night	35% 8% 17% 26% 12% 2	2000
	11th to 20th	Night	33% 7% 14% 29% 16% 1	2000
	21st to end	Night	44% 9% 14% 20% 12% 1	2293
October	1st to 10th	Night	41% 8% 12% 24% 14% 1	3920
	11th to 20th	Night	40% 7% 14% 22% 14% 3	3899
	21st to end	Night	41% 7% 16% 26% 9% 1	4300
November	1st to 10th	Night	46% 8% 11% 21% 11% 2	2667
	11th to 20th	Night	52% 9% 12% 18% 8% 2	2903
	21st to end	Night	57% 10% 15% 14% 4	2940
December	1st to 10th	Night	65% 9% 14% 10% 2	4720
	11th to 20th	Night	61% 8% 10% 13% 9%	5348
	21st to end	Night	69% 8% 8% 10% 5%	7150

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	27% 31% 29% 9% 4	220
	11th to 20th	Day	33% 32% 29% 5% 1 1	249
	21st to end	Day	27% 28% 35% 9% 1	363
February	1st to 10th	Day	35% 30% 25% 8% 2	330
	11th to 20th	Day	34% 29% 33% 4	330
	21st to end	Day	34% 25% 32% 8% 1	435
March	1st to 10th	Day	29% 27% 28% 13% 3 1	540
	11th to 20th	Day	31% 24% 30% 11% 3	540
	21st to end	Day	32% 23% 28% 12% 4 1	594
April	1st to 10th	Day	30% 26% 29% 11% 4 1	540
	11th to 20th	Day	29% 26% 26% 11% 6% 2	516
	21st to end	Day	27% 20% 31% 16% 5% 1	500
May	1st to 10th	Day	27% 21% 28% 14% 7% 3	503
	11th to 20th	Day	18% 18% 31% 21% 9% 2	527
	21st to end	Day	18% 13% 31% 23% 12% 3	573
June	1st to 10th	Day	18% 17% 31% 22% 10% 2	530
	11th to 20th	Day	13% 15% 32% 27% 11% 2	530
	21st to end	Day	13% 16% 35% 24% 8% 3	530
July	1st to 10th	Day	10% 8% 32% 31% 15% 4	525
	11th to 20th	Day	10% 10% 27% 32% 17% 4	524
	21st to end	Day	11% 9% 38% 27% 12% 3	576
August	1st to 10th	Day	9% 9% 28% 30% 17% 7%	526
	11th to 20th	Day	14% 8% 29% 28% 14% 7%	519
	21st to end	Day	13% 10% 29% 23% 16% 8%	583
September	1st to 10th	Day	18% 11% 25% 23% 15% 8%	530
	11th to 20th	Day	11% 8% 23% 26% 22% 10%	530
	21st to end	Day	18% 15% 28% 21% 13% 4	530
October	1st to 10th	Day	19% 14% 27% 22% 13% 5%	530
	11th to 20th	Day	24% 20% 31% 18% 6% 2	530
	21st to end	Day	26% 22% 32% 16% 4	569
November	1st to 10th	Day	22% 25% 28% 16% 8% 1	425
	11th to 20th	Day	27% 27% 29% 14% 2	256
	21st to end	Day	28% 32% 30% 9%	220
December	1st to 10th	Day	31% 25% 32% 8% 3 1	220
	11th to 20th	Day	35% 29% 27% 8%	220
	21st to end	Day	30% 27% 34% 7% 2	242
January	1st to 10th	Night	22% 29% 33% 14% 2	840
	11th to 20th	Night	25% 26% 30% 17% 3 1	840
	21st to end	Night	20% 26% 35% 17% 2	924
February	1st to 10th	Night	25% 25% 32% 18% 1	840
	11th to 20th	Night	23% 29% 31% 15% 2	823
	21st to end	Night	28% 24% 30% 15% 2	692
March	1st to 10th	Night	23% 25% 33% 18% 2	840
	11th to 20th	Night	27% 24% 28% 19% 2	840
	21st to end	Night	25% 22% 30% 18% 5%	924
April	1st to 10th	Night	25% 23% 29% 21% 2	840
	11th to 20th	Night	23% 19% 31% 20% 6% 1	816
	21st to end	Night	20% 13% 33% 26% 8%	734
May	1st to 10th	Night	21% 13% 24% 31% 10% 1	508
	11th to 20th	Night	15% 9% 34% 32% 10% 1	394
	21st to end	Night	12% 9% 30% 33% 16%	433
June	1st to 10th	Night	16% 8% 29% 33% 14% 1	400
	11th to 20th	Night	11% 11% 27% 35% 16%	400
	21st to end	Night	12% 8% 28% 42% 11% 1	400
July	1st to 10th	Night	8% 4 23% 45% 19% 2	390
	11th to 20th	Night	10% 3 23% 41% 21% 2	388
	21st to end	Night	11% 3 25% 42% 17% 2	502
August	1st to 10th	Night	10% 4 23% 37% 25% 2	597
	11th to 20th	Night	11% 6% 22% 32% 27% 3	598
	21st to end	Night	11% 6% 23% 35% 23% 2	880
September	1st to 10th	Night	15% 8% 24% 31% 19% 3	800
	11th to 20th	Night	13% 9% 18% 29% 28% 4	800
	21st to end	Night	17% 12% 25% 27% 16% 3	800
October	1st to 10th	Night	18% 12% 28% 22% 18% 2	800
	11th to 20th	Night	22% 17% 30% 24% 7% 1	800
	21st to end	Night	29% 15% 32% 20% 3	880
November	1st to 10th	Night	23% 17% 30% 21% 8%	820
	11th to 20th	Night	24% 22% 31% 16% 5% 2	840
	21st to end	Night	23% 25% 29% 19% 4	840
December	1st to 10th	Night	25% 25% 31% 16% 3	840
	11th to 20th	Night	26% 25% 31% 16% 3	840
	21st to end	Night	27% 25% 33% 14% 2	924

Page generated at 2026-04-14 02:44:26. Version ac07

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