AstroGeek's Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the AstroGeek's Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	18% 8% 2 6% 4 4 4 3 5% 7% 39%	130510
	Night	18% 8% 3 6% 4 4 4 3 5% 6% 40%	130647
Transparency	Day	44% 5% 11% 22% 15% 3	134044
	Night	45% 5% 11% 21% 16% 3	135187
Seeing	Day	22% 18% 33% 18% 7% 2	16744
	Night	22% 15% 33% 24% 7% 1	25742

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	11% 9% 3 7% 4 3 4 4 4 6% 45%	4661
	11th to 20th	Day	16% 10% 3 5% 3 3 3 2 4 4 46%	4650
	21st to end	Day	14% 10% 2 5% 3 3 3 3 4 5% 47%	5124
February	1st to 10th	Day	19% 8% 3 6% 5% 5% 4 4 5% 6% 35%	1998
	11th to 20th	Day	14% 9% 3 6% 4 4 4 4 5% 6% 41%	2048
	21st to end	Day	17% 10% 3 6% 4 4 3 3 4 5% 39%	1730
March	1st to 10th	Day	22% 13% 2 5% 4 3 3 3 4 5% 36%	4496
	11th to 20th	Day	16% 10% 2 6% 4 3 4 4 5% 7% 39%	4813
	21st to end	Day	26% 11% 2 6% 4 4 4 3 4 5% 31%	5711
April	1st to 10th	Day	21% 9% 2 6% 4 3 4 3 4 6% 37%	2400
	11th to 20th	Day	19% 6% 2 6% 4 4 4 3 6% 6% 39%	2398
	21st to end	Day	20% 6% 2 6% 5% 5% 4 3 5% 6% 39%	2600
May	1st to 10th	Day	27% 11% 3 7% 4 3 4 3 4 7% 26%	5886
	11th to 20th	Day	22% 10% 3 7% 5% 5% 4 3 4 6% 31%	5861
	21st to end	Day	21% 7% 3 6% 4 4 4 4 5% 7% 35%	6936
June	1st to 10th	Day	19% 7% 2 6% 4 4 5% 4 6% 9% 34%	2800
	11th to 20th	Day	16% 6% 2 6% 5% 4 5% 4 6% 9% 36%	2800
	21st to end	Day	16% 7% 2 5% 4 4 5% 4 6% 9% 38%	2800
July	1st to 10th	Day	18% 7% 3 6% 4 4 5% 4 7% 10% 32%	6360
	11th to 20th	Day	12% 7% 3 7% 4 5% 5% 5% 7% 11% 34%	6360
	21st to end	Day	16% 6% 2 6% 4 4 4 4 5% 7% 41%	6890
August	1st to 10th	Day	16% 7% 3 8% 5% 5% 5% 4 6% 9% 31%	4235
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 6% 8% 37%	4143
	21st to end	Day	8% 4 1 5% 4 6% 6% 4 7% 9% 45%	4312
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 5% 6% 46%	2375
	11th to 20th	Day	14% 6% 2 5% 4 4 3 2 4 6% 51%	2200
	21st to end	Day	19% 6% 2 5% 4 4 4 3 4 7% 42%	2200
October	1st to 10th	Day	22% 6% 1 6% 3 3 4 2 4 6% 44%	2200
	11th to 20th	Day	16% 6% 2 5% 4 3 3 3 4 7% 46%	1972
	21st to end	Day	18% 6% 3 6% 3 3 3 3 5% 6% 42%	1980
November	1st to 10th	Day	17% 7% 2 5% 3 4 3 3 4 5% 48%	1851
	11th to 20th	Day	17% 7% 1 4 4 3 3 3 4 5% 48%	1890
	21st to end	Day	18% 8% 2 4 4 3 4 3 4 6% 44%	1890
December	1st to 10th	Day	15% 9% 2 4 3 3 3 3 4 6% 49%	2826
	11th to 20th	Day	20% 6% 2 4 3 3 3 2 3 5% 49%	3066
	21st to end	Day	20% 11% 3 7% 4 3 3 3 5% 4 37%	4048
January	1st to 10th	Night	15% 6% 2 5% 4 3 3 3 4 6% 49%	8234
	11th to 20th	Night	16% 10% 3 8% 4 4 3 3 4 5% 40%	8235
	21st to end	Night	15% 10% 3 7% 5% 5% 4 3 4 5% 40%	9057
February	1st to 10th	Night	16% 9% 3 7% 4 4 4 4 5% 6% 40%	2615
	11th to 20th	Night	18% 8% 3 6% 5% 4 3 4 5% 6% 40%	2458
	21st to end	Night	18% 9% 2 6% 5% 4 3 3 5% 5% 41%	2076
March	1st to 10th	Night	24% 9% 2 4 3 4 4 3 4 5% 37%	5389
	11th to 20th	Night	17% 11% 3 6% 4 4 4 3 4 6% 38%	5145
	21st to end	Night	25% 10% 2 7% 4 4 4 3 4 4 33%	5205
April	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 5% 6% 36%	2000
	11th to 20th	Night	20% 8% 2 5% 5% 4 4 3 6% 6% 38%	1950
	21st to end	Night	20% 8% 3 5% 5% 4 4 3 5% 6% 39%	1800
May	1st to 10th	Night	28% 10% 3 8% 4 4 4 3 5% 7% 25%	4054
	11th to 20th	Night	19% 11% 3 8% 5% 5% 5% 4 6% 7% 27%	4033
	21st to end	Night	20% 8% 3 8% 5% 5% 5% 4 5% 7% 30%	3980
June	1st to 10th	Night	17% 7% 3 6% 5% 4 5% 4 5% 7% 36%	1600
	11th to 20th	Night	18% 7% 3 6% 5% 4 4 3 5% 8% 36%	1600
	21st to end	Night	16% 8% 2 6% 4 3 4 4 6% 9% 39%	1600
July	1st to 10th	Night	18% 8% 3 5% 4 3 4 4 7% 10% 34%	3600
	11th to 20th	Night	15% 8% 3 6% 5% 4 5% 3 7% 8% 35%	3600
	21st to end	Night	13% 7% 2 7% 4 4 5% 4 5% 7% 41%	3926
August	1st to 10th	Night	21% 8% 2 7% 4 5% 5% 4 7% 8% 29%	2905
	11th to 20th	Night	9% 8% 2 8% 5% 6% 5% 5% 7% 8% 37%	2900
	21st to end	Night	8% 3 2 5% 4 4 4 3 6% 8% 54%	3586
September	1st to 10th	Night	13% 6% 3 6% 4 4 5% 4 6% 6% 43%	2024
	11th to 20th	Night	14% 6% 2 5% 3 3 3 3 4 6% 51%	2200
	21st to end	Night	19% 7% 2 6% 4 4 4 4 4 5% 41%	2200
October	1st to 10th	Night	19% 7% 2 6% 4 4 3 3 3 6% 44%	2200
	11th to 20th	Night	15% 6% 2 4 4 3 3 4 5% 7% 46%	2421
	21st to end	Night	19% 8% 3 6% 4 4 4 3 4 6% 40%	2860
November	1st to 10th	Night	15% 5% 2 6% 3 3 4 3 5% 6% 47%	2667
	11th to 20th	Night	17% 7% 2 5% 3 4 3 3 4 5% 47%	2730
	21st to end	Night	16% 6% 2 5% 4 3 4 3 5% 7% 44%	2730
December	1st to 10th	Night	18% 8% 2 5% 4 3 3 2 4 5% 46%	4569
	11th to 20th	Night	22% 9% 3 5% 3 3 3 3 4 5% 41%	5348
	21st to end	Night	17% 11% 3 7% 3 3 3 2 4 5% 40%	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	41% 3 9% 24% 20% 3	4662
	11th to 20th	Day	42% 4 8% 21% 18% 8%	4680
	21st to end	Day	41% 3 9% 23% 21% 2	5124
February	1st to 10th	Day	47% 7% 12% 17% 15% 3	1998
	11th to 20th	Day	42% 6% 11% 23% 16% 3	2057
	21st to end	Day	47% 4 9% 21% 15% 3	1730
March	1st to 10th	Day	51% 3 10% 14% 12% 10%	4499
	11th to 20th	Day	43% 6% 13% 27% 11% 2	4813
	21st to end	Day	56% 5% 5% 14% 14% 7%	5711
April	1st to 10th	Day	48% 5% 9% 19% 16% 4	2400
	11th to 20th	Day	45% 5% 9% 21% 17% 3	2398
	21st to end	Day	47% 4 9% 20% 16% 4	2600
May	1st to 10th	Day	59% 6% 14% 14% 7% 1	5897
	11th to 20th	Day	53% 6% 14% 16% 10% 1	5865
	21st to end	Day	46% 7% 11% 21% 14% 1	6936
June	1st to 10th	Day	47% 7% 12% 22% 12%	2800
	11th to 20th	Day	43% 7% 14% 22% 13% 2	2800
	21st to end	Day	41% 8% 15% 21% 14% 1	2800
July	1st to 10th	Day	46% 8% 12% 19% 12% 2	6290
	11th to 20th	Day	42% 7% 16% 23% 10% 1	6285
	21st to end	Day	40% 6% 11% 26% 15% 1	6692
August	1st to 10th	Day	49% 7% 16% 19% 8% 1	4222
	11th to 20th	Day	43% 8% 13% 26% 10%	4182
	21st to end	Day	32% 7% 14% 26% 19% 1	4312
September	1st to 10th	Day	38% 6% 10% 24% 20% 1	2375
	11th to 20th	Day	35% 5% 9% 25% 23% 3	2200
	21st to end	Day	44% 5% 8% 20% 21% 2	2200
October	1st to 10th	Day	39% 4 9% 26% 18% 4	3590
	11th to 20th	Day	32% 3 7% 29% 26% 3	3175
	21st to end	Day	31% 4 14% 29% 20% 3	3180
November	1st to 10th	Day	40% 4 13% 22% 19% 2	1851
	11th to 20th	Day	38% 5% 10% 23% 21% 3	1890
	21st to end	Day	42% 5% 11% 26% 14% 2	1890
December	1st to 10th	Day	39% 3 13% 27% 16% 1	2826
	11th to 20th	Day	40% 3 14% 17% 20% 6%	3066
	21st to end	Day	50% 4 8% 21% 13% 4	4048
January	1st to 10th	Night	37% 3 9% 31% 17% 2	8234
	11th to 20th	Night	48% 3 9% 20% 15% 5%	8280
	21st to end	Night	48% 4 7% 18% 19% 4	9057
February	1st to 10th	Night	45% 5% 12% 21% 15% 2	2615
	11th to 20th	Night	46% 4 8% 21% 17% 4	2460
	21st to end	Night	46% 5% 8% 23% 15% 4	2076
March	1st to 10th	Night	50% 4 9% 16% 15% 7%	5399
	11th to 20th	Night	48% 5% 15% 18% 13% 2	5146
	21st to end	Night	56% 4 4 11% 19% 6%	5205
April	1st to 10th	Night	49% 4 9% 19% 16% 4	2000
	11th to 20th	Night	46% 6% 9% 19% 18% 2	1950
	21st to end	Night	47% 5% 9% 19% 16% 4	1800
May	1st to 10th	Night	59% 6% 14% 12% 7% 2	4060
	11th to 20th	Night	54% 7% 14% 14% 8% 2	4034
	21st to end	Night	52% 8% 11% 19% 10%	3981
June	1st to 10th	Night	46% 7% 13% 21% 13%	1600
	11th to 20th	Night	46% 6% 11% 23% 13% 1	1600
	21st to end	Night	41% 8% 14% 23% 13% 1	1600
July	1st to 10th	Night	47% 7% 10% 21% 15%	3560
	11th to 20th	Night	46% 7% 15% 22% 10% 1	3552
	21st to end	Night	43% 6% 11% 25% 14% 1	3809
August	1st to 10th	Night	51% 8% 12% 18% 10% 1	2894
	11th to 20th	Night	41% 8% 14% 28% 9%	2927
	21st to end	Night	28% 6% 15% 28% 23% 1	3586
September	1st to 10th	Night	40% 6% 11% 24% 18% 1	2024
	11th to 20th	Night	35% 5% 10% 24% 25% 2	2200
	21st to end	Night	44% 6% 8% 21% 18% 2	2200
October	1st to 10th	Night	40% 5% 10% 26% 16% 3	3590
	11th to 20th	Night	27% 3 9% 26% 32% 3	3944
	21st to end	Night	34% 4 11% 28% 21% 2	4610
November	1st to 10th	Night	38% 6% 11% 23% 18% 3	2667
	11th to 20th	Night	40% 4 9% 22% 21% 4	2730
	21st to end	Night	39% 4 14% 27% 13% 2	2730
December	1st to 10th	Night	43% 3 11% 27% 15% 1	4569
	11th to 20th	Night	47% 3 14% 15% 19% 2	5348
	21st to end	Night	47% 5% 8% 22% 17% 2	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% 28% 30% 15% 1	220
	11th to 20th	Day	27% 29% 34% 8% 2	220
	21st to end	Day	26% 27% 35% 9% 2 1	242
February	1st to 10th	Day	29% 23% 35% 13% 2	480
	11th to 20th	Day	29% 28% 32% 8% 2	536
	21st to end	Day	25% 28% 33% 12% 3	446
March	1st to 10th	Day	29% 25% 31% 12% 2	508
	11th to 20th	Day	26% 28% 32% 11% 3 1	500
	21st to end	Day	29% 23% 31% 11% 4 1	550
April	1st to 10th	Day	30% 25% 28% 11% 5% 1	500
	11th to 20th	Day	27% 27% 31% 12% 3	492
	21st to end	Day	27% 20% 34% 15% 3 2	500
May	1st to 10th	Day	31% 24% 31% 11% 3 1	503
	11th to 20th	Day	23% 17% 41% 13% 6% 1	527
	21st to end	Day	20% 15% 35% 22% 7% 1	573
June	1st to 10th	Day	20% 15% 33% 23% 7% 1	530
	11th to 20th	Day	16% 18% 38% 20% 7% 1	530
	21st to end	Day	16% 13% 38% 25% 6% 2	530
July	1st to 10th	Day	16% 10% 32% 30% 10% 2	525
	11th to 20th	Day	14% 8% 32% 31% 13% 2	524
	21st to end	Day	12% 11% 36% 28% 11% 1	576
August	1st to 10th	Day	13% 9% 36% 29% 10% 2	526
	11th to 20th	Day	14% 10% 30% 29% 14% 3	519
	21st to end	Day	13% 9% 35% 26% 12% 5%	583
September	1st to 10th	Day	19% 10% 32% 23% 12% 4	530
	11th to 20th	Day	17% 11% 28% 25% 11% 8%	530
	21st to end	Day	24% 12% 30% 23% 7% 4	530
October	1st to 10th	Day	25% 13% 27% 21% 9% 6%	530
	11th to 20th	Day	20% 17% 33% 18% 10% 2	461
	21st to end	Day	25% 18% 28% 19% 6% 3	462
November	1st to 10th	Day	20% 19% 34% 17% 9% 2	425
	11th to 20th	Day	25% 22% 33% 14% 5%	430
	21st to end	Day	24% 24% 29% 15% 8%	430
December	1st to 10th	Day	21% 25% 35% 15% 4	314
	11th to 20th	Day	31% 27% 32% 8% 2	220
	21st to end	Day	29% 23% 33% 10% 4 2	242
January	1st to 10th	Night	22% 21% 37% 17% 3	840
	11th to 20th	Night	28% 22% 33% 14% 3	840
	21st to end	Night	22% 21% 36% 18% 3	924
February	1st to 10th	Night	23% 18% 38% 19% 2	840
	11th to 20th	Night	26% 21% 38% 14% 1	823
	21st to end	Night	25% 21% 34% 18% 3	692
March	1st to 10th	Night	26% 19% 33% 18% 3	809
	11th to 20th	Night	21% 20% 38% 17% 4	800
	21st to end	Night	26% 19% 35% 17% 3	880
April	1st to 10th	Night	25% 18% 35% 18% 4	800
	11th to 20th	Night	24% 19% 35% 19% 3	766
	21st to end	Night	22% 18% 37% 20% 4	600
May	1st to 10th	Night	30% 13% 33% 20% 4	600
	11th to 20th	Night	21% 15% 40% 20% 4	592
	21st to end	Night	22% 7% 32% 32% 6%	461
June	1st to 10th	Night	18% 9% 32% 33% 9% 1	400
	11th to 20th	Night	20% 6% 33% 33% 8%	400
	21st to end	Night	19% 7% 29% 39% 6%	400
July	1st to 10th	Night	17% 4 29% 40% 9% 1	390
	11th to 20th	Night	16% 5% 27% 41% 11% 1	388
	21st to end	Night	14% 4 28% 44% 10%	438
August	1st to 10th	Night	13% 6% 31% 39% 9%	588
	11th to 20th	Night	14% 6% 27% 42% 12%	607
	21st to end	Night	14% 4 25% 39% 16% 2	880
September	1st to 10th	Night	15% 6% 30% 35% 13% 1	800
	11th to 20th	Night	16% 7% 25% 31% 18% 3	800
	21st to end	Night	23% 7% 27% 30% 13% 2	800
October	1st to 10th	Night	23% 9% 26% 27% 14% 2	800
	11th to 20th	Night	19% 12% 33% 24% 12% 1	800
	21st to end	Night	24% 13% 35% 20% 7%	880
November	1st to 10th	Night	19% 15% 33% 24% 9% 1	820
	11th to 20th	Night	20% 22% 33% 18% 7%	840
	21st to end	Night	21% 21% 32% 21% 4 1	840
December	1st to 10th	Night	25% 18% 34% 18% 4	840
	11th to 20th	Night	25% 20% 32% 20% 3	840
	21st to end	Night	26% 20% 33% 19% 2	924

Page generated at 2026-02-28 01:40:21. Version ac07

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