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 2025-02-21.

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% 14% 5% 10% 5% 4 4 3 5% 6% 27%	108764
	Night	17% 16% 6% 12% 5% 4 4 3 4 5% 24%	109808
Transparency	Day	56% 7% 11% 17% 8% 1	112402
	Night	60% 6% 10% 15% 8% 1	114333
Seeing	Day	27% 18% 28% 17% 8% 2	14826
	Night	27% 17% 27% 20% 8% 1	24383

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	13% 26% 11% 23% 7% 4 3 2 2 2 8%	3597
	11th to 20th	Day	10% 26% 11% 24% 8% 5% 3 2 3 3 5%	3932
	21st to end	Day	17% 18% 8% 19% 7% 7% 7% 3 3 3 8%	4466
February	1st to 10th	Day	16% 22% 7% 19% 8% 5% 4 2 2 3 12%	1800
	11th to 20th	Day	13% 20% 9% 18% 8% 5% 4 2 3 3 14%	1753
	21st to end	Day	19% 18% 5% 13% 8% 4 4 3 4 4 17%	1488
March	1st to 10th	Day	18% 17% 6% 9% 4 4 3 2 4 5% 28%	3432
	11th to 20th	Day	10% 24% 8% 9% 3 4 4 3 4 5% 27%	3480
	21st to end	Day	18% 16% 5% 11% 5% 3 4 3 4 5% 25%	3815
April	1st to 10th	Day	18% 19% 3 7% 5% 3 4 3 4 4 29%	2268
	11th to 20th	Day	19% 15% 3 7% 3 4 4 3 4 6% 33%	2254
	21st to end	Day	22% 14% 3 6% 5% 4 4 2 4 5% 32%	2466
May	1st to 10th	Day	24% 9% 2 6% 5% 4 4 3 6% 6% 31%	4108
	11th to 20th	Day	19% 10% 3 7% 6% 5% 5% 4 5% 7% 28%	4384
	21st to end	Day	14% 7% 3 6% 4 4 4 4 5% 7% 42%	4837
June	1st to 10th	Day	19% 8% 3 6% 4 5% 4 4 6% 7% 36%	2660
	11th to 20th	Day	16% 6% 2 6% 5% 5% 5% 4 7% 9% 35%	2660
	21st to end	Day	18% 6% 3 5% 4 4 5% 4 6% 8% 38%	2660
July	1st to 10th	Day	12% 6% 2 6% 4 5% 5% 4 6% 10% 39%	4440
	11th to 20th	Day	14% 6% 3 6% 4 4 5% 4 7% 9% 38%	4440
	21st to end	Day	10% 6% 3 7% 6% 5% 6% 5% 7% 8% 37%	4499
August	1st to 10th	Day	18% 7% 3 6% 4 4 4 4 6% 8% 36%	4104
	11th to 20th	Day	15% 7% 3 8% 6% 5% 7% 6% 7% 9% 27%	4044
	21st to end	Day	15% 6% 2 5% 4 4 5% 4 6% 9% 40%	4260
September	1st to 10th	Day	18% 7% 3 6% 4 4 4 3 6% 8% 37%	2280
	11th to 20th	Day	17% 6% 2 6% 3 4 4 4 6% 8% 41%	2214
	21st to end	Day	20% 7% 3 8% 5% 5% 5% 3 6% 7% 31%	2023
October	1st to 10th	Day	24% 9% 3 7% 3 4 3 3 6% 6% 31%	1900
	11th to 20th	Day	25% 13% 3 8% 3 4 4 3 4 5% 28%	1900
	21st to end	Day	28% 17% 3 9% 4 4 4 3 4 5% 20%	2090
November	1st to 10th	Day	18% 18% 3 8% 4 4 4 3 5% 5% 28%	1764
	11th to 20th	Day	16% 26% 5% 8% 4 4 3 4 4 6% 21%	1600
	21st to end	Day	20% 27% 6% 9% 5% 4 4 3 3 4 15%	1600
December	1st to 10th	Day	18% 32% 13% 15% 4 3 3 2 2 3 7%	2600
	11th to 20th	Day	19% 24% 6% 19% 5% 3 2 2 3 4 11%	2986
	21st to end	Day	19% 26% 7% 12% 7% 4 3 3 3 4 11%	3960
January	1st to 10th	Night	14% 26% 9% 23% 8% 4 3 2 2 2 8%	6349
	11th to 20th	Night	8% 23% 12% 26% 10% 5% 3 2 2 2 5%	5951
	21st to end	Night	16% 19% 10% 19% 7% 7% 5% 2 3 3 9%	6490
February	1st to 10th	Night	17% 23% 6% 17% 9% 4 3 3 3 4 12%	2600
	11th to 20th	Night	15% 17% 7% 18% 9% 5% 4 2 3 5% 14%	2533
	21st to end	Night	18% 18% 6% 15% 7% 5% 4 3 4 4 17%	1962
March	1st to 10th	Night	20% 16% 4 9% 5% 4 3 2 4 4 28%	3408
	11th to 20th	Night	19% 22% 7% 9% 4 3 3 3 4 4 23%	3479
	21st to end	Night	16% 13% 6% 9% 5% 4 3 2 4 5% 34%	3817
April	1st to 10th	Night	20% 17% 4 7% 4 4 3 3 4 6% 28%	1911
	11th to 20th	Night	20% 12% 2 7% 5% 4 4 3 5% 5% 33%	1875
	21st to end	Night	19% 11% 4 6% 4 4 5% 3 5% 7% 32%	1729
May	1st to 10th	Night	26% 10% 3 7% 4 4 3 3 5% 5% 29%	2833
	11th to 20th	Night	15% 9% 2 7% 5% 5% 6% 4 6% 8% 33%	2509
	21st to end	Night	16% 6% 2 5% 4 3 3 3 6% 8% 43%	2738
June	1st to 10th	Night	15% 7% 2 7% 6% 5% 5% 4 6% 7% 35%	1520
	11th to 20th	Night	14% 7% 3 6% 5% 5% 4 3 6% 8% 40%	1520
	21st to end	Night	16% 7% 2 6% 5% 4 4 4 6% 7% 38%	1520
July	1st to 10th	Night	13% 8% 3 7% 4 4 4 3 6% 8% 40%	2520
	11th to 20th	Night	13% 7% 2 5% 4 4 4 4 6% 7% 43%	2520
	21st to end	Night	12% 6% 2 6% 4 4 4 5% 6% 8% 44%	3050
August	1st to 10th	Night	13% 9% 3 7% 4 4 4 4 6% 8% 38%	2825
	11th to 20th	Night	18% 8% 4 9% 5% 4 5% 4 5% 6% 33%	2785
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 7% 9% 42%	3362
September	1st to 10th	Night	17% 7% 2 5% 3 4 3 4 5% 7% 43%	1900
	11th to 20th	Night	15% 5% 2 5% 4 3 4 4 4 6% 48%	1963
	21st to end	Night	20% 8% 3 6% 4 4 4 4 6% 7% 33%	2156
October	1st to 10th	Night	21% 7% 3 7% 4 5% 4 3 6% 6% 35%	2280
	11th to 20th	Night	25% 13% 3 6% 5% 4 4 3 5% 5% 27%	2280
	21st to end	Night	30% 12% 3 6% 5% 3 4 3 5% 5% 23%	2508
November	1st to 10th	Night	19% 15% 4 8% 4 3 3 3 4 5% 32%	2531
	11th to 20th	Night	18% 21% 4 9% 5% 4 4 3 5% 5% 22%	2800
	21st to end	Night	18% 24% 9% 10% 4 4 4 3 4 5% 16%	2800
December	1st to 10th	Night	17% 29% 11% 16% 5% 4 3 2 3 3 7%	4580
	11th to 20th	Night	18% 28% 9% 16% 5% 4 3 2 3 2 10%	5208
	21st to end	Night	19% 26% 8% 13% 6% 5% 3 3 3 4 11%	6996

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 4 3	3598
	11th to 20th	Day	86% 4 6% 3 1	3966
	21st to end	Day	81% 5% 8% 5% 1	4466
February	1st to 10th	Day	79% 4 8% 7% 2	1800
	11th to 20th	Day	75% 5% 6% 10% 4	1762
	21st to end	Day	70% 5% 10% 11% 4 1	1488
March	1st to 10th	Day	58% 5% 10% 21% 5%	3435
	11th to 20th	Day	59% 7% 16% 13% 5% 1	3480
	21st to end	Day	59% 7% 7% 19% 7% 1	3815
April	1st to 10th	Day	58% 5% 11% 15% 10%	2268
	11th to 20th	Day	51% 6% 10% 20% 10% 2	2254
	21st to end	Day	56% 6% 9% 16% 13% 1	2466
May	1st to 10th	Day	52% 6% 12% 20% 9% 2	4120
	11th to 20th	Day	52% 9% 13% 18% 7% 1	4388
	21st to end	Day	39% 8% 14% 23% 14% 3	4837
June	1st to 10th	Day	46% 8% 12% 19% 14% 1	2660
	11th to 20th	Day	43% 8% 14% 22% 12%	2660
	21st to end	Day	43% 7% 13% 23% 12% 1	2660
July	1st to 10th	Day	39% 7% 13% 26% 14% 1	4370
	11th to 20th	Day	39% 8% 15% 22% 16%	4365
	21st to end	Day	40% 9% 14% 21% 15%	4355
August	1st to 10th	Day	45% 8% 14% 22% 12% 1	4091
	11th to 20th	Day	47% 12% 15% 20% 5%	4083
	21st to end	Day	38% 8% 12% 30% 11% 1	4260
September	1st to 10th	Day	45% 7% 12% 23% 11% 1	2280
	11th to 20th	Day	39% 7% 12% 26% 14% 1	2214
	21st to end	Day	52% 7% 12% 19% 10% 1	2023
October	1st to 10th	Day	44% 7% 14% 22% 11% 1	3160
	11th to 20th	Day	49% 5% 15% 16% 12% 3	3140
	21st to end	Day	52% 6% 15% 20% 7% 1	3428
November	1st to 10th	Day	58% 6% 9% 17% 9% 2	1764
	11th to 20th	Day	64% 5% 11% 13% 5% 2	1600
	21st to end	Day	73% 5% 9% 9% 4	1600
December	1st to 10th	Day	84% 4 5% 5% 1	2600
	11th to 20th	Day	78% 5% 9% 7% 2	2986
	21st to end	Day	77% 5% 9% 6% 3	3960
January	1st to 10th	Night	81% 6% 6% 4 2	6349
	11th to 20th	Night	86% 4 6% 3 1	5992
	21st to end	Night	80% 4 8% 5% 2	6490
February	1st to 10th	Night	78% 5% 7% 8% 3	2600
	11th to 20th	Night	74% 5% 8% 10% 3	2535
	21st to end	Night	70% 5% 9% 10% 5%	1962
March	1st to 10th	Night	60% 5% 9% 19% 6%	3418
	11th to 20th	Night	64% 6% 11% 13% 5% 1	3480
	21st to end	Night	50% 8% 9% 20% 12% 2	3817
April	1st to 10th	Night	57% 5% 10% 18% 9%	1911
	11th to 20th	Night	52% 5% 11% 18% 12% 2	1875
	21st to end	Night	51% 6% 10% 18% 13% 2	1729
May	1st to 10th	Night	56% 6% 9% 18% 9% 3	2840
	11th to 20th	Night	46% 9% 15% 21% 7% 1	2510
	21st to end	Night	37% 7% 13% 24% 17% 3	2739
June	1st to 10th	Night	44% 9% 12% 21% 13% 1	1520
	11th to 20th	Night	41% 8% 12% 23% 15% 1	1520
	21st to end	Night	43% 8% 14% 23% 12% 2	1520
July	1st to 10th	Night	41% 6% 12% 23% 16% 2	2480
	11th to 20th	Night	38% 7% 16% 24% 15% 1	2472
	21st to end	Night	37% 8% 16% 23% 14% 2	2953
August	1st to 10th	Night	41% 8% 15% 27% 9% 1	2814
	11th to 20th	Night	49% 8% 13% 22% 7%	2812
	21st to end	Night	35% 8% 15% 30% 11% 1	3362
September	1st to 10th	Night	40% 7% 12% 25% 13% 2	1900
	11th to 20th	Night	36% 6% 13% 26% 18% 1	1963
	21st to end	Night	49% 7% 12% 20% 11% 1	2156
October	1st to 10th	Night	43% 8% 11% 22% 15% 1	3800
	11th to 20th	Night	51% 5% 12% 16% 13% 2	3779
	21st to end	Night	48% 5% 16% 21% 8% 1	4120
November	1st to 10th	Night	54% 6% 9% 19% 9% 2	2531
	11th to 20th	Night	64% 6% 10% 13% 6% 2	2800
	21st to end	Night	71% 7% 10% 10% 3	2800
December	1st to 10th	Night	83% 5% 7% 4 1	4580
	11th to 20th	Night	80% 5% 7% 6% 2	5208
	21st to end	Night	77% 6% 7% 7% 3	6996

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	32% 30% 28% 8% 3 1	200
	11th to 20th	Day	38% 34% 19% 7% 2	280
	21st to end	Day	31% 31% 27% 8% 3	330
February	1st to 10th	Day	40% 29% 25% 6% 1	300
	11th to 20th	Day	36% 34% 27% 3 1	300
	21st to end	Day	44% 22% 29% 5%	291
March	1st to 10th	Day	32% 24% 29% 11% 3	460
	11th to 20th	Day	31% 25% 33% 8% 3	460
	21st to end	Day	35% 22% 26% 13% 4	506
April	1st to 10th	Day	35% 21% 29% 11% 5%	460
	11th to 20th	Day	35% 23% 23% 11% 6% 2	452
	21st to end	Day	31% 19% 32% 15% 2 2	460
May	1st to 10th	Day	32% 17% 29% 15% 5% 2	463
	11th to 20th	Day	25% 14% 30% 21% 8% 2	487
	21st to end	Day	18% 14% 31% 23% 10% 4	529
June	1st to 10th	Day	23% 16% 33% 19% 7% 1	490
	11th to 20th	Day	19% 13% 30% 25% 11% 1	490
	21st to end	Day	21% 15% 34% 21% 8% 1	490
July	1st to 10th	Day	14% 10% 30% 27% 15% 4	485
	11th to 20th	Day	15% 11% 31% 26% 13% 4	484
	21st to end	Day	15% 9% 35% 25% 13% 3	532
August	1st to 10th	Day	16% 10% 25% 30% 13% 6%	486
	11th to 20th	Day	16% 9% 30% 25% 16% 4	479
	21st to end	Day	18% 9% 30% 25% 14% 5%	539
September	1st to 10th	Day	18% 13% 26% 23% 14% 6%	490
	11th to 20th	Day	15% 7% 23% 27% 20% 8%	490
	21st to end	Day	20% 19% 26% 20% 10% 4	490
October	1st to 10th	Day	26% 12% 27% 19% 13% 3	490
	11th to 20th	Day	32% 20% 27% 15% 6% 1	490
	21st to end	Day	41% 18% 24% 15% 2	539
November	1st to 10th	Day	32% 21% 26% 13% 6% 1	364
	11th to 20th	Day	42% 21% 29% 7% 2 1	200
	21st to end	Day	41% 24% 28% 6% 2	200
December	1st to 10th	Day	41% 25% 25% 6% 3	200
	11th to 20th	Day	43% 25% 24% 9%	200
	21st to end	Day	38% 27% 27% 5% 3	220
January	1st to 10th	Night	33% 28% 27% 9% 3	800
	11th to 20th	Night	34% 27% 27% 10% 2	800
	21st to end	Night	27% 27% 31% 13% 2	880
February	1st to 10th	Night	33% 27% 27% 13% 1	800
	11th to 20th	Night	31% 28% 30% 10% 2	783
	21st to end	Night	34% 24% 28% 13% 1	629
March	1st to 10th	Night	29% 21% 31% 15% 4	760
	11th to 20th	Night	32% 21% 29% 14% 4 1	760
	21st to end	Night	26% 20% 31% 17% 6% 1	836
April	1st to 10th	Night	29% 19% 30% 19% 2	760
	11th to 20th	Night	29% 16% 30% 19% 5% 1	751
	21st to end	Night	25% 12% 32% 24% 6% 1	589
May	1st to 10th	Night	27% 10% 25% 29% 8% 1	570
	11th to 20th	Night	16% 9% 34% 33% 7%	388
	21st to end	Night	17% 8% 27% 35% 12% 1	411
June	1st to 10th	Night	16% 7% 32% 32% 12% 1	380
	11th to 20th	Night	17% 10% 27% 37% 9%	380
	21st to end	Night	18% 7% 34% 31% 9%	380
July	1st to 10th	Night	13% 5% 23% 42% 17% 1	370
	11th to 20th	Night	12% 5% 28% 36% 18% 1	368
	21st to end	Night	15% 6% 25% 35% 18% 1	600
August	1st to 10th	Night	13% 5% 22% 38% 20% 2	567
	11th to 20th	Night	14% 7% 22% 32% 23% 2	564
	21st to end	Night	14% 6% 26% 31% 21% 2	761
September	1st to 10th	Night	21% 8% 22% 30% 16% 3	760
	11th to 20th	Night	16% 7% 21% 28% 26% 3	760
	21st to end	Night	23% 11% 24% 26% 13% 3	760
October	1st to 10th	Night	23% 11% 28% 23% 14% 1	760
	11th to 20th	Night	33% 15% 25% 20% 6% 1	760
	21st to end	Night	38% 14% 28% 17% 2	836
November	1st to 10th	Night	29% 16% 28% 19% 6% 1	780
	11th to 20th	Night	33% 21% 27% 13% 5% 1	800
	21st to end	Night	34% 24% 27% 11% 4	800
December	1st to 10th	Night	39% 26% 21% 10% 4	800
	11th to 20th	Night	37% 26% 25% 11% 2	800
	21st to end	Night	36% 25% 27% 10% 1	880

Page generated at 2025-02-18 03:26:29. Version ac07

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