Orbit Jet Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Orbit Jet Observatory clear sky chart from 2005-11-06 to 2026-06-16.

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	17% 13% 5% 10% 5% 5% 4 3 5% 6% 27%	137936
	Night	16% 16% 6% 12% 6% 5% 4 3 4 5% 24%	134080
Transparency	Day	56% 6% 11% 17% 9% 1	141530
	Night	60% 6% 10% 15% 8% 1	138573
Seeing	Day	27% 18% 28% 17% 7% 2	16562
	Night	27% 17% 27% 20% 8% 1	26016

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	14% 25% 10% 23% 7% 4 3 2 2 2 7%	4661
	11th to 20th	Day	9% 25% 12% 23% 9% 7% 3 2 3 2 5%	5124
	21st to end	Day	14% 16% 7% 19% 10% 11% 8% 3 3 3 7%	5780
February	1st to 10th	Day	15% 22% 7% 19% 8% 5% 4 2 2 3 13%	1890
	11th to 20th	Day	13% 20% 9% 18% 9% 5% 4 2 3 3 14%	1843
	21st to end	Day	17% 20% 6% 13% 8% 4 4 3 4 4 17%	1641
March	1st to 10th	Day	15% 15% 9% 13% 5% 4 3 2 3 5% 25%	5042
	11th to 20th	Day	11% 19% 8% 9% 3 4 4 3 4 5% 29%	5090
	21st to end	Day	18% 19% 6% 11% 5% 3 3 3 4 4 24%	5586
April	1st to 10th	Day	19% 18% 4 8% 5% 3 4 3 4 4 28%	2507
	11th to 20th	Day	19% 15% 3 7% 3 4 4 3 4 6% 32%	2494
	21st to end	Day	21% 13% 3 6% 4 4 4 3 4 5% 33%	2726
May	1st to 10th	Day	24% 10% 3 7% 5% 4 4 4 5% 6% 29%	7642
	11th to 20th	Day	19% 11% 3 7% 5% 5% 4 4 5% 7% 31%	8180
	21st to end	Day	20% 8% 2 6% 4 4 4 4 6% 7% 35%	9060
June	1st to 10th	Day	18% 7% 3 6% 4 5% 4 4 6% 7% 37%	2940
	11th to 20th	Day	16% 7% 2 6% 5% 5% 5% 4 7% 9% 34%	2870
	21st to end	Day	18% 6% 3 5% 4 4 5% 4 6% 8% 38%	2800
July	1st to 10th	Day	12% 5% 2 6% 4 5% 5% 4 6% 10% 40%	6360
	11th to 20th	Day	13% 7% 3 7% 5% 4 5% 4 6% 9% 37%	6360
	21st to end	Day	11% 6% 2 7% 5% 4 5% 4 6% 7% 43%	6471
August	1st to 10th	Day	17% 7% 3 6% 4 4 4 4 6% 8% 37%	4234
	11th to 20th	Day	16% 7% 3 8% 6% 5% 6% 6% 7% 8% 28%	4174
	21st to end	Day	15% 6% 2 5% 4 4 5% 4 6% 9% 40%	4395
September	1st to 10th	Day	17% 7% 3 6% 4 4 4 3 6% 8% 38%	2400
	11th to 20th	Day	16% 5% 2 6% 3 4 4 4 6% 8% 42%	2330
	21st to end	Day	19% 7% 3 8% 5% 5% 5% 3 6% 7% 31%	2129
October	1st to 10th	Day	24% 8% 3 7% 3 4 3 3 6% 6% 33%	2000
	11th to 20th	Day	24% 12% 3 9% 4 4 4 3 4 5% 28%	2000
	21st to end	Day	28% 17% 3 8% 4 4 4 3 4 5% 21%	2200
November	1st to 10th	Day	18% 17% 4 8% 4 4 4 3 4 5% 27%	1853
	11th to 20th	Day	16% 26% 6% 8% 3 4 3 4 4 5% 21%	1680
	21st to end	Day	20% 27% 6% 9% 5% 4 4 3 3 4 15%	1680
December	1st to 10th	Day	18% 31% 12% 14% 4 3 3 2 2 3 8%	2680
	11th to 20th	Day	19% 24% 6% 19% 5% 3 2 2 3 4 11%	3066
	21st to end	Day	19% 26% 7% 13% 7% 4 3 3 3 4 11%	4048
January	1st to 10th	Night	14% 26% 10% 25% 8% 4 3 2 2 2 6%	8234
	11th to 20th	Night	8% 23% 13% 26% 12% 5% 3 2 2 2 4	7759
	21st to end	Night	13% 17% 9% 18% 9% 11% 6% 2 3 3 9%	8401
February	1st to 10th	Night	16% 22% 6% 17% 9% 5% 3 3 3 4 13%	2730
	11th to 20th	Night	15% 17% 7% 18% 8% 5% 4 3 3 5% 14%	2663
	21st to end	Night	16% 18% 7% 16% 8% 5% 4 3 4 4 16%	2159
March	1st to 10th	Night	17% 16% 6% 11% 7% 5% 3 2 4 4 24%	5018
	11th to 20th	Night	15% 18% 6% 8% 4 3 4 3 4 6% 30%	5089
	21st to end	Night	15% 15% 6% 11% 5% 4 4 2 4 5% 29%	5588
April	1st to 10th	Night	20% 16% 5% 8% 5% 4 3 3 4 6% 27%	2112
	11th to 20th	Night	20% 12% 2 7% 5% 4 4 3 5% 5% 32%	2075
	21st to end	Night	18% 12% 4 6% 4 5% 5% 3 5% 7% 32%	1911
May	1st to 10th	Night	25% 11% 4 9% 4 4 4 3 5% 5% 25%	5257
	11th to 20th	Night	18% 11% 2 6% 4 4 5% 4 5% 7% 33%	4680
	21st to end	Night	21% 10% 3 6% 4 3 3 3 5% 7% 35%	5114
June	1st to 10th	Night	15% 6% 2 7% 6% 5% 5% 4 6% 7% 36%	1680
	11th to 20th	Night	14% 6% 3 6% 5% 5% 4 3 6% 8% 39%	1640
	21st to end	Night	16% 7% 2 6% 5% 4 4 4 6% 7% 39%	1600
July	1st to 10th	Night	13% 8% 3 6% 4 4 4 3 6% 9% 40%	3600
	11th to 20th	Night	13% 7% 2 6% 4 4 5% 4 6% 8% 42%	3600
	21st to end	Night	11% 6% 2 6% 4 3 4 4 6% 7% 47%	4377
August	1st to 10th	Night	13% 9% 3 8% 4 4 4 4 6% 8% 38%	2915
	11th to 20th	Night	17% 8% 4 9% 5% 4 5% 4 5% 6% 33%	2875
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 6% 9% 42%	3468
September	1st to 10th	Night	17% 6% 2 5% 4 4 3 4 5% 7% 43%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 4 4 4 6% 49%	2067
	21st to end	Night	19% 8% 3 6% 4 4 4 4 6% 7% 34%	2270
October	1st to 10th	Night	20% 7% 3 7% 4 5% 4 3 6% 6% 37%	2400
	11th to 20th	Night	24% 13% 3 6% 5% 4 4 3 5% 6% 28%	2400
	21st to end	Night	29% 13% 3 6% 5% 3 4 3 5% 5% 24%	2640
November	1st to 10th	Night	19% 16% 4 8% 4 3 3 3 4 5% 32%	2660
	11th to 20th	Night	18% 21% 5% 9% 5% 4 4 3 4 5% 22%	2940
	21st to end	Night	18% 24% 9% 10% 4 4 4 3 4 5% 16%	2940
December	1st to 10th	Night	17% 29% 11% 16% 5% 4 3 2 3 3 8%	4720
	11th to 20th	Night	18% 28% 8% 16% 5% 4 3 2 3 3 10%	5348
	21st to end	Night	19% 26% 8% 13% 6% 5% 3 3 3 4 11%	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	85% 3 4 5% 2	4662
	11th to 20th	Day	86% 4 5% 3 2	5158
	21st to end	Day	82% 5% 7% 4 1	5780
February	1st to 10th	Day	78% 4 7% 8% 2	1890
	11th to 20th	Day	75% 5% 7% 10% 3	1852
	21st to end	Day	70% 5% 10% 10% 4 1	1641
March	1st to 10th	Day	62% 5% 12% 16% 5%	5045
	11th to 20th	Day	55% 6% 17% 14% 6% 1	5090
	21st to end	Day	61% 6% 6% 18% 8% 1	5586
April	1st to 10th	Day	59% 6% 11% 14% 9%	2507
	11th to 20th	Day	53% 6% 10% 20% 10% 2	2494
	21st to end	Day	54% 6% 9% 17% 12% 1	2726
May	1st to 10th	Day	53% 6% 10% 19% 9% 2	7651
	11th to 20th	Day	51% 7% 11% 20% 10% 1	8184
	21st to end	Day	46% 6% 12% 22% 12% 2	9061
June	1st to 10th	Day	45% 7% 12% 20% 15% 1	2940
	11th to 20th	Day	44% 9% 13% 21% 12%	2870
	21st to end	Day	43% 8% 13% 23% 13% 1	2800
July	1st to 10th	Day	38% 8% 13% 26% 15% 1	6290
	11th to 20th	Day	41% 8% 14% 21% 16%	6285
	21st to end	Day	38% 8% 12% 26% 16%	6285
August	1st to 10th	Day	44% 8% 14% 22% 12%	4221
	11th to 20th	Day	47% 11% 15% 20% 6%	4213
	21st to end	Day	38% 9% 12% 30% 10% 1	4395
September	1st to 10th	Day	44% 7% 12% 25% 12% 1	2400
	11th to 20th	Day	38% 7% 12% 28% 14% 1	2330
	21st to end	Day	51% 7% 12% 19% 10% 1	2129
October	1st to 10th	Day	43% 7% 13% 23% 12% 1	3260
	11th to 20th	Day	50% 5% 15% 16% 12% 3	3240
	21st to end	Day	51% 6% 15% 20% 8% 1	3538
November	1st to 10th	Day	58% 6% 9% 17% 8% 2	1853
	11th to 20th	Day	64% 5% 11% 13% 5% 2	1680
	21st to end	Day	74% 5% 9% 9% 4	1680
December	1st to 10th	Day	84% 4 5% 5% 1	2680
	11th to 20th	Day	78% 5% 9% 7% 2	3066
	21st to end	Day	77% 5% 9% 6% 3	4048
January	1st to 10th	Night	84% 5% 5% 4 2	8234
	11th to 20th	Night	87% 4 5% 2 1	7800
	21st to end	Night	80% 5% 8% 6% 2	8401
February	1st to 10th	Night	77% 5% 7% 8% 3	2730
	11th to 20th	Night	73% 5% 8% 10% 3	2665
	21st to end	Night	71% 5% 9% 9% 5%	2159
March	1st to 10th	Night	62% 6% 10% 15% 6% 1	5028
	11th to 20th	Night	54% 6% 13% 18% 6% 3	5090
	21st to end	Night	55% 8% 8% 16% 11% 2	5588
April	1st to 10th	Night	59% 5% 9% 17% 9% 1	2112
	11th to 20th	Night	53% 5% 11% 18% 12% 1	2075
	21st to end	Night	51% 6% 10% 19% 13% 2	1911
May	1st to 10th	Night	59% 6% 8% 15% 9% 4	5264
	11th to 20th	Night	49% 8% 13% 19% 11% 1	4681
	21st to end	Night	47% 5% 11% 21% 14% 2	5115
June	1st to 10th	Night	42% 9% 12% 22% 14% 2	1680
	11th to 20th	Night	42% 8% 13% 21% 15% 1	1640
	21st to end	Night	42% 8% 14% 22% 13% 2	1600
July	1st to 10th	Night	40% 6% 13% 24% 15% 1	3560
	11th to 20th	Night	38% 8% 15% 23% 15% 1	3552
	21st to end	Night	35% 7% 14% 23% 19% 2	4248
August	1st to 10th	Night	40% 8% 15% 26% 10% 1	2904
	11th to 20th	Night	48% 8% 13% 22% 8%	2902
	21st to end	Night	35% 8% 15% 30% 11% 1	3468
September	1st to 10th	Night	39% 7% 13% 26% 13% 2	2000
	11th to 20th	Night	35% 6% 13% 28% 17% 1	2067
	21st to end	Night	48% 7% 12% 20% 11% 1	2270
October	1st to 10th	Night	42% 7% 11% 22% 16% 1	3920
	11th to 20th	Night	51% 5% 12% 16% 13% 2	3899
	21st to end	Night	48% 5% 16% 21% 9% 1	4252
November	1st to 10th	Night	55% 5% 10% 19% 9% 2	2660
	11th to 20th	Night	64% 6% 10% 12% 6% 2	2940
	21st to end	Night	71% 7% 10% 9% 3	2940
December	1st to 10th	Night	82% 5% 7% 4 1	4720
	11th to 20th	Night	80% 5% 7% 6% 2	5348
	21st to end	Night	77% 6% 7% 7% 3	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	33% 31% 26% 7% 2	220
	11th to 20th	Day	39% 34% 18% 6% 2	308
	21st to end	Day	33% 30% 26% 8% 2	363
February	1st to 10th	Day	38% 28% 25% 8% 1	330
	11th to 20th	Day	36% 32% 28% 3 1	330
	21st to end	Day	42% 24% 29% 5%	347
March	1st to 10th	Day	33% 25% 29% 10% 3	540
	11th to 20th	Day	35% 25% 30% 8% 2	540
	21st to end	Day	36% 22% 26% 12% 3	594
April	1st to 10th	Day	36% 22% 28% 10% 4	540
	11th to 20th	Day	36% 23% 23% 11% 5% 2	532
	21st to end	Day	30% 20% 32% 16% 1 1	540
May	1st to 10th	Day	34% 18% 29% 13% 4 2	543
	11th to 20th	Day	25% 16% 31% 19% 7% 1	567
	21st to end	Day	22% 15% 30% 21% 9% 3	617
June	1st to 10th	Day	22% 16% 35% 19% 6% 1	570
	11th to 20th	Day	20% 15% 30% 23% 10% 1	550
	21st to end	Day	20% 14% 35% 21% 8% 1	530
July	1st to 10th	Day	13% 11% 30% 27% 14% 3	525
	11th to 20th	Day	15% 10% 32% 26% 13% 4	524
	21st to end	Day	15% 9% 35% 26% 13% 3	576
August	1st to 10th	Day	15% 10% 25% 31% 14% 6%	526
	11th to 20th	Day	17% 9% 29% 26% 16% 4	519
	21st to end	Day	17% 9% 31% 25% 14% 4	583
September	1st to 10th	Day	18% 13% 25% 23% 15% 5%	530
	11th to 20th	Day	14% 7% 23% 28% 20% 8%	530
	21st to end	Day	19% 18% 28% 20% 11% 4	530
October	1st to 10th	Day	24% 12% 26% 20% 14% 3	530
	11th to 20th	Day	32% 21% 28% 14% 6% 1	530
	21st to end	Day	40% 18% 25% 15% 2	583
November	1st to 10th	Day	33% 22% 25% 13% 5% 1	393
	11th to 20th	Day	44% 19% 28% 8% 2	220
	21st to end	Day	42% 24% 28% 5% 1	220
December	1st to 10th	Day	43% 24% 25% 5% 3	220
	11th to 20th	Day	44% 25% 24% 8%	220
	21st to end	Day	40% 27% 26% 5% 2	242
January	1st to 10th	Night	33% 29% 27% 9% 3	840
	11th to 20th	Night	35% 28% 26% 10% 2	840
	21st to end	Night	28% 28% 30% 13% 2	924
February	1st to 10th	Night	32% 26% 28% 14% 1	840
	11th to 20th	Night	31% 27% 29% 11% 1	823
	21st to end	Night	34% 24% 28% 12% 1	692
March	1st to 10th	Night	30% 21% 31% 14% 3	840
	11th to 20th	Night	33% 21% 29% 14% 3 1	840
	21st to end	Night	27% 21% 30% 16% 5% 1	924
April	1st to 10th	Night	30% 20% 30% 18% 2	840
	11th to 20th	Night	29% 17% 29% 19% 5% 1	831
	21st to end	Night	25% 13% 31% 25% 6%	651
May	1st to 10th	Night	27% 11% 26% 28% 7% 1	630
	11th to 20th	Night	17% 9% 35% 32% 7%	430
	21st to end	Night	18% 9% 27% 33% 11% 1	455
June	1st to 10th	Night	16% 7% 32% 33% 11% 1	420
	11th to 20th	Night	16% 10% 29% 36% 8%	410
	21st to end	Night	18% 8% 34% 31% 9%	400
July	1st to 10th	Night	13% 5% 23% 43% 16% 1	390
	11th to 20th	Night	12% 5% 28% 36% 19% 1	388
	21st to end	Night	15% 6% 24% 36% 18% 1	632
August	1st to 10th	Night	12% 5% 22% 39% 20% 2	597
	11th to 20th	Night	13% 7% 22% 33% 23% 2	594
	21st to end	Night	15% 6% 26% 31% 20% 1	801
September	1st to 10th	Night	21% 8% 23% 30% 16% 3	800
	11th to 20th	Night	15% 7% 21% 29% 26% 2	800
	21st to end	Night	23% 11% 23% 27% 13% 3	800
October	1st to 10th	Night	23% 11% 27% 25% 15% 1	800
	11th to 20th	Night	32% 16% 26% 20% 6% 1	800
	21st to end	Night	37% 15% 28% 18% 2	880
November	1st to 10th	Night	31% 16% 28% 19% 6% 1	820
	11th to 20th	Night	33% 22% 27% 13% 5% 1	840
	21st to end	Night	35% 24% 26% 11% 3	840
December	1st to 10th	Night	39% 26% 21% 11% 3	840
	11th to 20th	Night	37% 27% 24% 10% 1	840
	21st to end	Night	37% 25% 27% 10% 1	924

Page generated at 2026-06-13 02:31:41. Version ac07

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