Starlifter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Starlifter Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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	15% 11% 4 10% 6% 6% 5% 4 6% 6% 26%	131794
	Night	14% 12% 5% 12% 7% 6% 5% 4 5% 6% 24%	131017
Transparency	Day	55% 8% 11% 17% 8% 1	135262
	Night	58% 8% 11% 15% 8% 1	135636
Seeing	Day	24% 19% 29% 18% 8% 2	16592
	Night	22% 17% 26% 25% 9% 1	25611

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	10% 13% 9% 21% 13% 8% 4 3 4 3 11%	4661
	11th to 20th	Day	8% 15% 6% 19% 13% 8% 6% 4 5% 4 12%	4650
	21st to end	Day	8% 14% 6% 12% 9% 12% 8% 4 5% 5% 17%	5124
February	1st to 10th	Day	11% 13% 5% 14% 11% 7% 5% 3 5% 5% 20%	1809
	11th to 20th	Day	9% 14% 7% 16% 10% 7% 5% 4 4 5% 18%	2038
	21st to end	Day	11% 14% 6% 14% 10% 6% 4 5% 5% 5% 20%	1730
March	1st to 10th	Day	17% 15% 6% 15% 6% 5% 5% 3 4 4 20%	4576
	11th to 20th	Day	12% 14% 6% 12% 6% 4 5% 3 5% 6% 27%	4747
	21st to end	Day	19% 13% 5% 12% 5% 4 4 3 4 5% 26%	6102
April	1st to 10th	Day	17% 16% 5% 9% 5% 5% 3 4 4 6% 26%	2520
	11th to 20th	Day	17% 13% 4 8% 5% 4 4 3 4 5% 31%	2494
	21st to end	Day	22% 11% 3 8% 5% 5% 4 3 5% 6% 28%	2727
May	1st to 10th	Day	29% 13% 4 8% 5% 4 4 3 5% 4 20%	6128
	11th to 20th	Day	16% 10% 3 10% 7% 6% 5% 4 6% 7% 26%	6402
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 5% 7% 7% 29%	6949
June	1st to 10th	Day	23% 7% 3 7% 5% 5% 5% 4 6% 7% 27%	2800
	11th to 20th	Day	15% 8% 3 6% 5% 4 6% 5% 6% 9% 33%	2800
	21st to end	Day	20% 8% 3 8% 6% 6% 5% 4 6% 7% 28%	2800
July	1st to 10th	Day	10% 8% 3 7% 6% 6% 6% 6% 8% 10% 29%	6360
	11th to 20th	Day	10% 6% 3 8% 6% 5% 7% 5% 8% 10% 33%	6360
	21st to end	Day	13% 7% 2 6% 4 4 5% 5% 6% 9% 38%	6926
August	1st to 10th	Day	15% 8% 3 8% 6% 6% 6% 5% 7% 8% 28%	4538
	11th to 20th	Day	14% 9% 3 8% 6% 5% 6% 5% 7% 9% 29%	4087
	21st to end	Day	13% 7% 3 7% 4 5% 5% 4 7% 9% 36%	4312
September	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 7% 7% 42%	2400
	11th to 20th	Day	14% 7% 2 5% 4 3 4 4 4 8% 45%	2263
	21st to end	Day	16% 8% 2 7% 5% 5% 4 4 5% 8% 36%	2200
October	1st to 10th	Day	20% 10% 3 7% 4 5% 4 3 5% 6% 32%	2149
	11th to 20th	Day	15% 11% 3 9% 5% 5% 5% 4 6% 6% 31%	1916
	21st to end	Day	20% 20% 5% 8% 4 5% 5% 3 4 3 24%	1980
November	1st to 10th	Day	14% 16% 4 8% 7% 4 5% 4 5% 6% 27%	1851
	11th to 20th	Day	14% 17% 7% 12% 5% 5% 5% 3 4 5% 23%	1890
	21st to end	Day	16% 16% 7% 14% 5% 4 4 4 5% 5% 20%	1711
December	1st to 10th	Day	11% 18% 7% 23% 9% 6% 5% 2 4 4 10%	2680
	11th to 20th	Day	15% 13% 7% 14% 9% 6% 5% 2 5% 5% 20%	3066
	21st to end	Day	16% 15% 7% 14% 6% 5% 6% 3 4 4 18%	4048
January	1st to 10th	Night	9% 14% 7% 24% 11% 8% 5% 3 4 3 12%	8234
	11th to 20th	Night	8% 14% 7% 20% 13% 9% 6% 4 4 4 11%	8235
	21st to end	Night	8% 13% 5% 12% 9% 11% 9% 6% 6% 5% 15%	9057
February	1st to 10th	Night	10% 13% 5% 16% 11% 7% 6% 4 5% 5% 17%	2809
	11th to 20th	Night	9% 13% 6% 14% 11% 8% 6% 4 5% 5% 19%	2466
	21st to end	Night	10% 13% 5% 14% 8% 6% 5% 3 5% 6% 24%	2076
March	1st to 10th	Night	17% 15% 5% 13% 7% 7% 4 3 4 5% 20%	5484
	11th to 20th	Night	13% 15% 5% 11% 6% 5% 4 4 5% 6% 27%	5414
	21st to end	Night	16% 15% 5% 13% 7% 5% 5% 2 3 3 25%	5072
April	1st to 10th	Night	18% 13% 4 9% 5% 5% 4 3 5% 5% 27%	2100
	11th to 20th	Night	18% 12% 3 7% 7% 6% 4 3 5% 4 31%	2075
	21st to end	Night	18% 11% 3 7% 5% 4 5% 3 5% 6% 32%	1891
May	1st to 10th	Night	27% 14% 3 8% 4 4 3 3 4 6% 23%	4062
	11th to 20th	Night	18% 11% 3 8% 5% 5% 5% 4 5% 6% 30%	3623
	21st to end	Night	16% 10% 3 10% 5% 4 5% 4 6% 7% 31%	3926
June	1st to 10th	Night	24% 8% 3 7% 5% 4 5% 3 5% 7% 30%	1600
	11th to 20th	Night	16% 6% 2 7% 5% 6% 4 4 6% 8% 36%	1600
	21st to end	Night	20% 7% 3 6% 5% 5% 5% 4 6% 8% 32%	1600
July	1st to 10th	Night	11% 7% 3 8% 5% 6% 7% 5% 7% 8% 33%	3600
	11th to 20th	Night	14% 8% 3 9% 6% 5% 5% 5% 5% 7% 34%	3600
	21st to end	Night	10% 6% 3 7% 5% 5% 6% 4 6% 8% 41%	3926
August	1st to 10th	Night	16% 10% 3 8% 5% 5% 5% 4 5% 7% 33%	2586
	11th to 20th	Night	15% 8% 3 7% 6% 5% 4 3 6% 7% 37%	2948
	21st to end	Night	13% 7% 3 7% 5% 5% 5% 5% 6% 7% 37%	3586
September	1st to 10th	Night	13% 6% 2 6% 4 4 5% 4 5% 6% 44%	2000
	11th to 20th	Night	14% 7% 2 5% 4 3 3 3 4 7% 47%	2136
	21st to end	Night	16% 7% 3 5% 5% 5% 4 4 4 6% 41%	2200
October	1st to 10th	Night	20% 9% 3 7% 4 5% 5% 3 5% 7% 34%	2250
	11th to 20th	Night	16% 12% 3 9% 5% 5% 5% 4 5% 5% 32%	2483
	21st to end	Night	21% 15% 3 8% 6% 4 6% 3 5% 6% 23%	2860
November	1st to 10th	Night	15% 14% 4 9% 5% 5% 4 4 5% 5% 29%	2667
	11th to 20th	Night	14% 14% 7% 12% 6% 4 4 3 5% 5% 26%	2730
	21st to end	Night	14% 14% 7% 14% 7% 6% 4 3 5% 5% 21%	2903
December	1st to 10th	Night	13% 15% 7% 22% 9% 6% 6% 4 5% 4 10%	4720
	11th to 20th	Night	18% 17% 6% 14% 7% 6% 4 3 5% 5% 15%	5348
	21st to end	Night	16% 16% 6% 16% 7% 5% 5% 3 4 7% 15%	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	75% 7% 8% 8% 2	4662
	11th to 20th	Day	69% 10% 8% 8% 5% 1	4680
	21st to end	Day	64% 8% 10% 10% 7%	5124
February	1st to 10th	Day	65% 7% 7% 13% 6% 1	1809
	11th to 20th	Day	68% 6% 8% 13% 5% 1	2047
	21st to end	Day	64% 7% 8% 11% 8% 2	1730
March	1st to 10th	Day	66% 7% 8% 8% 8% 4	4579
	11th to 20th	Day	56% 6% 14% 13% 9% 2	4747
	21st to end	Day	59% 5% 7% 13% 15% 1	6102
April	1st to 10th	Day	59% 5% 8% 17% 9% 1	2520
	11th to 20th	Day	55% 6% 8% 17% 13% 1	2494
	21st to end	Day	56% 8% 9% 16% 10% 2	2727
May	1st to 10th	Day	67% 6% 7% 14% 5% 1	6139
	11th to 20th	Day	54% 9% 13% 16% 7% 1	6406
	21st to end	Day	50% 10% 11% 21% 8%	6949
June	1st to 10th	Day	55% 8% 11% 17% 9%	2800
	11th to 20th	Day	46% 8% 12% 21% 11% 1	2800
	21st to end	Day	54% 8% 11% 19% 8% 1	2800
July	1st to 10th	Day	43% 10% 17% 21% 9%	6290
	11th to 20th	Day	40% 11% 15% 25% 9%	6285
	21st to end	Day	39% 9% 12% 31% 8%	6728
August	1st to 10th	Day	48% 11% 15% 20% 6%	4524
	11th to 20th	Day	48% 9% 16% 21% 5%	4126
	21st to end	Day	40% 10% 16% 19% 13% 1	4312
September	1st to 10th	Day	38% 8% 12% 30% 12% 1	2400
	11th to 20th	Day	38% 6% 11% 29% 16% 1	2263
	21st to end	Day	45% 9% 13% 22% 11% 1	2200
October	1st to 10th	Day	43% 9% 14% 23% 11%	3500
	11th to 20th	Day	46% 8% 15% 21% 10%	3093
	21st to end	Day	50% 6% 12% 23% 8% 1	3180
November	1st to 10th	Day	55% 9% 12% 16% 8%	1851
	11th to 20th	Day	62% 7% 10% 11% 8% 2	1890
	21st to end	Day	64% 9% 13% 11% 3	1711
December	1st to 10th	Day	76% 7% 8% 6% 2	2680
	11th to 20th	Day	62% 9% 8% 16% 5%	3066
	21st to end	Day	68% 5% 6% 10% 9% 1	4048
January	1st to 10th	Night	73% 8% 9% 7% 2	8234
	11th to 20th	Night	72% 9% 8% 6% 4	8280
	21st to end	Night	63% 9% 9% 10% 8% 1	9057
February	1st to 10th	Night	67% 8% 8% 12% 5%	2809
	11th to 20th	Night	65% 7% 8% 13% 6%	2468
	21st to end	Night	60% 7% 9% 14% 8% 1	2076
March	1st to 10th	Night	65% 6% 8% 11% 9% 1	5494
	11th to 20th	Night	56% 7% 14% 13% 8% 1	5415
	21st to end	Night	61% 6% 6% 14% 12% 1	5072
April	1st to 10th	Night	57% 6% 10% 15% 10% 2	2100
	11th to 20th	Night	55% 7% 8% 18% 12%	2075
	21st to end	Night	51% 8% 9% 16% 13% 3	1891
May	1st to 10th	Night	63% 6% 9% 15% 6% 1	4068
	11th to 20th	Night	52% 10% 11% 19% 7% 1	3624
	21st to end	Night	51% 9% 11% 18% 11% 1	3927
June	1st to 10th	Night	53% 8% 9% 21% 9% 1	1600
	11th to 20th	Night	44% 8% 14% 20% 10% 2	1600
	21st to end	Night	48% 11% 12% 20% 9% 1	1600
July	1st to 10th	Night	43% 10% 19% 20% 8%	3560
	11th to 20th	Night	43% 12% 12% 25% 9%	3552
	21st to end	Night	37% 10% 16% 28% 9%	3809
August	1st to 10th	Night	48% 9% 15% 22% 6%	2576
	11th to 20th	Night	46% 8% 17% 19% 9% 1	2975
	21st to end	Night	39% 12% 14% 20% 13%	3586
September	1st to 10th	Night	38% 9% 14% 28% 11% 1	2000
	11th to 20th	Night	37% 7% 13% 31% 12% 1	2136
	21st to end	Night	43% 8% 12% 23% 12% 2	2200
October	1st to 10th	Night	50% 8% 13% 20% 9%	3679
	11th to 20th	Night	48% 8% 13% 20% 10%	4045
	21st to end	Night	50% 7% 14% 20% 8% 1	4610
November	1st to 10th	Night	54% 8% 13% 16% 7% 1	2667
	11th to 20th	Night	59% 7% 9% 15% 8% 2	2730
	21st to end	Night	64% 9% 10% 13% 4	2903
December	1st to 10th	Night	74% 9% 9% 7% 1	4720
	11th to 20th	Night	69% 8% 6% 11% 7%	5348
	21st to end	Night	69% 6% 6% 11% 7% 1	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	19% 28% 34% 15% 4	220
	11th to 20th	Day	28% 26% 31% 10% 3 1	220
	21st to end	Day	22% 26% 35% 13% 4	242
February	1st to 10th	Day	30% 32% 26% 9% 2	289
	11th to 20th	Day	28% 24% 34% 12% 2	526
	21st to end	Day	28% 23% 33% 13% 3	446
March	1st to 10th	Day	31% 21% 30% 15% 3	540
	11th to 20th	Day	30% 25% 28% 14% 3	540
	21st to end	Day	33% 24% 24% 11% 7% 1	594
April	1st to 10th	Day	36% 19% 24% 14% 5% 1	540
	11th to 20th	Day	33% 25% 23% 13% 5% 2	532
	21st to end	Day	33% 20% 26% 12% 6% 2	540
May	1st to 10th	Day	35% 20% 26% 12% 5% 2	543
	11th to 20th	Day	20% 19% 34% 20% 6% 2	551
	21st to end	Day	22% 20% 31% 20% 7% 1	573
June	1st to 10th	Day	25% 18% 32% 16% 8% 1	530
	11th to 20th	Day	21% 16% 30% 22% 9% 2	530
	21st to end	Day	22% 20% 33% 17% 7% 1	530
July	1st to 10th	Day	17% 14% 33% 23% 11% 2	525
	11th to 20th	Day	13% 12% 35% 25% 11% 2	524
	21st to end	Day	16% 12% 34% 25% 11% 2	576
August	1st to 10th	Day	15% 12% 27% 29% 13% 4	526
	11th to 20th	Day	16% 13% 29% 22% 13% 7%	519
	21st to end	Day	15% 17% 28% 23% 12% 5%	583
September	1st to 10th	Day	15% 16% 29% 19% 15% 6%	530
	11th to 20th	Day	17% 11% 23% 21% 17% 11%	530
	21st to end	Day	16% 15% 28% 22% 13% 6%	530
October	1st to 10th	Day	25% 14% 24% 19% 13% 4	530
	11th to 20th	Day	23% 23% 23% 21% 8% 2	483
	21st to end	Day	33% 21% 22% 18% 5%	462
November	1st to 10th	Day	29% 20% 24% 20% 7%	425
	11th to 20th	Day	25% 26% 26% 14% 7% 1	430
	21st to end	Day	35% 18% 30% 15% 1 1	251
December	1st to 10th	Day	26% 21% 33% 15% 4	220
	11th to 20th	Day	30% 27% 30% 11% 1	220
	21st to end	Day	31% 21% 31% 13% 2 1	242
January	1st to 10th	Night	21% 25% 32% 18% 4	840
	11th to 20th	Night	25% 23% 29% 19% 4	840
	21st to end	Night	17% 22% 33% 23% 4 1	924
February	1st to 10th	Night	19% 21% 36% 22% 3	840
	11th to 20th	Night	21% 24% 31% 20% 3	823
	21st to end	Night	20% 21% 31% 25% 3	692
March	1st to 10th	Night	24% 19% 30% 23% 3	840
	11th to 20th	Night	25% 22% 26% 21% 6%	840
	21st to end	Night	25% 21% 26% 21% 6% 1	924
April	1st to 10th	Night	28% 19% 27% 21% 5%	840
	11th to 20th	Night	26% 18% 27% 21% 7% 1	831
	21st to end	Night	27% 16% 28% 23% 6%	631
May	1st to 10th	Night	28% 14% 27% 24% 7% 1	600
	11th to 20th	Night	18% 13% 30% 28% 9% 1	406
	21st to end	Night	18% 11% 23% 36% 11%	433
June	1st to 10th	Night	26% 10% 24% 30% 11% 1	400
	11th to 20th	Night	20% 8% 23% 34% 15% 1	400
	21st to end	Night	19% 11% 19% 39% 13% 1	400
July	1st to 10th	Night	14% 5% 23% 41% 16% 1	390
	11th to 20th	Night	12% 5% 21% 42% 19% 1	388
	21st to end	Night	14% 5% 21% 44% 16%	438
August	1st to 10th	Night	14% 6% 16% 42% 23%	398
	11th to 20th	Night	14% 8% 21% 31% 23% 2	629
	21st to end	Night	17% 6% 21% 34% 21% 2	880
September	1st to 10th	Night	15% 9% 24% 32% 18% 2	800
	11th to 20th	Night	17% 8% 18% 29% 24% 4	800
	21st to end	Night	19% 10% 24% 27% 18% 2	800
October	1st to 10th	Night	25% 12% 20% 27% 15% 2	800
	11th to 20th	Night	23% 17% 21% 27% 12% 1	800
	21st to end	Night	28% 18% 25% 24% 5%	880
November	1st to 10th	Night	24% 20% 25% 23% 8% 1	820
	11th to 20th	Night	23% 21% 27% 20% 8% 2	840
	21st to end	Night	26% 19% 28% 20% 6% 1	840
December	1st to 10th	Night	26% 23% 27% 20% 4	840
	11th to 20th	Night	27% 21% 26% 20% 5%	840
	21st to end	Night	28% 23% 26% 20% 3	924

Page generated at 2026-05-14 01:58:55. Version ac07

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