Far Reach Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Far Reach Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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	17% 7% 2 6% 4 4 4 4 5% 7% 39%	127061
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 40%	124605
Transparency	Day	43% 6% 11% 22% 15% 3	130594
	Night	44% 6% 11% 21% 16% 3	129159
Seeing	Day	24% 17% 33% 18% 7% 2	16535
	Night	22% 15% 34% 23% 6%	25514

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% 8% 3 8% 5% 4 4 3 4 7% 44%	3677
	11th to 20th	Day	14% 7% 3 6% 3 3 4 3 5% 5% 47%	3618
	21st to end	Day	17% 9% 2 5% 4 3 4 3 5% 6% 43%	3960
February	1st to 10th	Day	19% 7% 2 6% 5% 5% 4 4 6% 6% 37%	1877
	11th to 20th	Day	13% 8% 3 7% 5% 4 5% 4 5% 6% 40%	1948
	21st to end	Day	18% 9% 3 7% 4 4 4 3 5% 6% 38%	1650
March	1st to 10th	Day	20% 12% 2 6% 3 4 4 3 4 6% 35%	4476
	11th to 20th	Day	15% 8% 2 6% 4 4 4 4 6% 7% 39%	4786
	21st to end	Day	26% 9% 2 6% 4 4 4 4 6% 5% 30%	5756
April	1st to 10th	Day	19% 9% 2 7% 5% 4 3 3 5% 6% 37%	2400
	11th to 20th	Day	18% 7% 2 6% 4 4 4 5% 4 7% 38%	2390
	21st to end	Day	20% 6% 2 7% 4 4 4 3 6% 6% 37%	2600
May	1st to 10th	Day	28% 11% 3 7% 4 4 4 3 5% 6% 25%	5886
	11th to 20th	Day	20% 9% 3 8% 5% 4 4 4 5% 7% 31%	5924
	21st to end	Day	19% 7% 3 6% 4 4 4 4 5% 8% 35%	6949
June	1st to 10th	Day	19% 6% 3 6% 5% 4 5% 4 7% 9% 34%	2800
	11th to 20th	Day	16% 7% 2 6% 5% 4 5% 4 6% 7% 38%	2800
	21st to end	Day	16% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	2800
July	1st to 10th	Day	17% 7% 2 6% 4 6% 6% 4 7% 9% 33%	6360
	11th to 20th	Day	9% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	6360
	21st to end	Day	14% 6% 2 6% 4 4 4 4 5% 8% 43%	6926
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 8% 32%	4254
	11th to 20th	Day	12% 8% 3 7% 5% 5% 5% 5% 6% 7% 39%	4120
	21st to end	Day	7% 4 2 6% 4 5% 6% 4 7% 8% 47%	4312
September	1st to 10th	Day	13% 5% 2 6% 4 4 3 4 5% 7% 46%	2390
	11th to 20th	Day	14% 6% 3 5% 3 3 2 3 4 7% 51%	2200
	21st to end	Day	18% 6% 2 5% 3 4 4 3 5% 7% 43%	2200
October	1st to 10th	Day	23% 5% 2 5% 3 3 3 2 4 6% 43%	2200
	11th to 20th	Day	16% 6% 1 5% 5% 3 4 3 4 6% 47%	1959
	21st to end	Day	19% 7% 2 5% 4 4 4 4 4 6% 41%	1980
November	1st to 10th	Day	15% 6% 2 4 4 4 3 2 4 5% 50%	1851
	11th to 20th	Day	17% 7% 2 4 3 4 3 3 5% 5% 48%	1890
	21st to end	Day	18% 7% 3 5% 4 3 4 3 5% 6% 43%	1890
December	1st to 10th	Day	15% 8% 2 5% 3 3 4 2 4 5% 49%	2758
	11th to 20th	Day	19% 6% 2 4 3 3 3 3 4 5% 48%	3066
	21st to end	Day	20% 10% 3 7% 4 4 3 3 4 5% 38%	4048
January	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 5% 6% 50%	6489
	11th to 20th	Night	14% 9% 3 8% 5% 4 4 3 4 6% 40%	6400
	21st to end	Night	15% 11% 3 7% 5% 4 4 3 4 5% 38%	6996
February	1st to 10th	Night	17% 9% 3 6% 4 4 4 4 5% 6% 38%	2517
	11th to 20th	Night	15% 10% 3 6% 5% 4 4 4 4 7% 38%	2338
	21st to end	Night	17% 9% 3 5% 4 4 4 3 4 5% 41%	1980
March	1st to 10th	Night	24% 9% 2 5% 4 4 3 3 4 5% 37%	5364
	11th to 20th	Night	16% 11% 3 7% 4 4 4 3 5% 6% 38%	5172
	21st to end	Night	25% 10% 2 6% 4 3 4 3 5% 4 33%	5160
April	1st to 10th	Night	19% 8% 2 7% 4 4 4 3 5% 6% 36%	2000
	11th to 20th	Night	19% 8% 2 6% 5% 4 4 3 5% 6% 38%	1958
	21st to end	Night	20% 8% 2 6% 4 4 4 3 4 5% 39%	1800
May	1st to 10th	Night	29% 10% 4 7% 4 4 3 3 5% 6% 26%	4054
	11th to 20th	Night	18% 8% 3 8% 5% 6% 6% 4 7% 7% 28%	3999
	21st to end	Night	20% 8% 3 8% 5% 4 4 3 5% 7% 32%	3926
June	1st to 10th	Night	17% 8% 3 7% 4 4 5% 3 6% 7% 37%	1600
	11th to 20th	Night	17% 7% 2 7% 4 4 5% 4 6% 8% 36%	1600
	21st to end	Night	16% 6% 2 5% 4 4 4 5% 5% 10% 40%	1600
July	1st to 10th	Night	12% 7% 3 7% 5% 4 5% 4 7% 10% 36%	3600
	11th to 20th	Night	12% 7% 3 7% 5% 4 4 4 7% 9% 38%	3600
	21st to end	Night	11% 7% 2 7% 5% 4 5% 4 5% 7% 43%	3926
August	1st to 10th	Night	19% 7% 3 7% 5% 5% 5% 4 6% 7% 32%	2850
	11th to 20th	Night	9% 7% 3 7% 6% 6% 6% 5% 6% 8% 37%	2923
	21st to end	Night	9% 4 1 5% 3 3 4 3 5% 8% 55%	3586
September	1st to 10th	Night	12% 6% 2 7% 4 4 4 4 5% 6% 47%	2010
	11th to 20th	Night	14% 6% 2 4 3 3 3 4 4 6% 53%	2200
	21st to end	Night	18% 6% 3 6% 4 3 4 4 5% 5% 43%	2200
October	1st to 10th	Night	20% 6% 2 5% 4 3 3 3 4 6% 44%	2200
	11th to 20th	Night	16% 5% 2 5% 3 3 3 3 5% 7% 47%	2436
	21st to end	Night	21% 7% 3 6% 4 4 3 3 4 6% 40%	2860
November	1st to 10th	Night	14% 5% 2 6% 4 4 4 3 5% 5% 49%	2667
	11th to 20th	Night	17% 7% 2 5% 3 3 3 3 4 4 47%	2730
	21st to end	Night	16% 7% 2 5% 4 4 4 3 5% 5% 45%	2730
December	1st to 10th	Night	18% 8% 2 5% 4 4 3 3 4 5% 44%	4636
	11th to 20th	Night	21% 8% 3 5% 3 3 3 3 4 4 41%	5348
	21st to end	Night	17% 10% 3 6% 4 3 3 3 4 6% 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	40% 4 7% 27% 19% 2	3678
	11th to 20th	Day	39% 5% 10% 22% 18% 6%	3648
	21st to end	Day	42% 6% 10% 21% 19% 2	3960
February	1st to 10th	Day	47% 6% 13% 17% 14% 2	1877
	11th to 20th	Day	43% 5% 12% 21% 15% 3	1957
	21st to end	Day	47% 6% 9% 20% 15% 3	1650
March	1st to 10th	Day	50% 4 10% 15% 11% 10%	4479
	11th to 20th	Day	42% 7% 13% 26% 10% 2	4786
	21st to end	Day	54% 5% 6% 15% 13% 7%	5756
April	1st to 10th	Day	48% 4 10% 18% 16% 4	2400
	11th to 20th	Day	43% 7% 11% 20% 16% 3	2390
	21st to end	Day	45% 6% 9% 19% 17% 4	2600
May	1st to 10th	Day	58% 8% 12% 13% 8% 1	5897
	11th to 20th	Day	51% 8% 13% 16% 10% 2	5928
	21st to end	Day	46% 7% 11% 22% 13% 1	6949
June	1st to 10th	Day	46% 7% 13% 22% 12% 1	2800
	11th to 20th	Day	42% 8% 14% 19% 15% 2	2800
	21st to end	Day	44% 7% 14% 20% 14% 1	2800
July	1st to 10th	Day	47% 8% 11% 20% 13% 1	6290
	11th to 20th	Day	40% 8% 16% 24% 11% 1	6285
	21st to end	Day	40% 6% 12% 26% 16% 1	6728
August	1st to 10th	Day	46% 9% 15% 21% 8% 1	4240
	11th to 20th	Day	42% 7% 13% 27% 10%	4159
	21st to end	Day	31% 8% 12% 30% 19% 2	4312
September	1st to 10th	Day	37% 6% 12% 23% 20% 2	2390
	11th to 20th	Day	35% 4 10% 27% 22% 3	2200
	21st to end	Day	42% 6% 8% 21% 22% 2	2200
October	1st to 10th	Day	39% 5% 8% 25% 19% 4	3590
	11th to 20th	Day	32% 4 7% 28% 25% 4	3162
	21st to end	Day	33% 5% 11% 28% 21% 3	3180
November	1st to 10th	Day	39% 4 13% 24% 18% 2	1851
	11th to 20th	Day	38% 4 9% 23% 22% 3	1890
	21st to end	Day	42% 6% 12% 25% 13% 2	1890
December	1st to 10th	Day	39% 4 14% 27% 15% 1	2758
	11th to 20th	Day	39% 3 14% 17% 20% 6%	3066
	21st to end	Day	49% 4 8% 20% 14% 4	4048
January	1st to 10th	Night	35% 4 9% 34% 16% 2	6489
	11th to 20th	Night	46% 4 12% 21% 14% 4	6445
	21st to end	Night	49% 5% 9% 16% 18% 4	6996
February	1st to 10th	Night	46% 5% 12% 21% 14% 2	2517
	11th to 20th	Night	46% 5% 9% 20% 15% 4	2340
	21st to end	Night	45% 4 8% 23% 16% 4	1980
March	1st to 10th	Night	49% 4 8% 15% 16% 7%	5374
	11th to 20th	Night	45% 7% 15% 18% 13% 2	5173
	21st to end	Night	54% 3 5% 12% 19% 6%	5160
April	1st to 10th	Night	48% 5% 10% 19% 15% 3	2000
	11th to 20th	Night	46% 5% 9% 20% 17% 3	1958
	21st to end	Night	45% 6% 10% 18% 17% 4	1800
May	1st to 10th	Night	58% 7% 13% 12% 7% 2	4060
	11th to 20th	Night	51% 10% 13% 15% 8% 2	4000
	21st to end	Night	50% 8% 13% 19% 10% 1	3927
June	1st to 10th	Night	46% 7% 13% 21% 12% 1	1600
	11th to 20th	Night	45% 7% 13% 22% 13% 1	1600
	21st to end	Night	40% 9% 14% 23% 14% 1	1600
July	1st to 10th	Night	43% 6% 12% 22% 16%	3560
	11th to 20th	Night	41% 7% 18% 22% 11% 1	3552
	21st to end	Night	40% 7% 10% 28% 15% 1	3809
August	1st to 10th	Night	50% 8% 13% 19% 9% 1	2840
	11th to 20th	Night	42% 10% 14% 24% 10%	2950
	21st to end	Night	27% 6% 16% 28% 23% 1	3586
September	1st to 10th	Night	38% 7% 11% 23% 19% 1	2010
	11th to 20th	Night	33% 6% 10% 23% 26% 2	2200
	21st to end	Night	42% 6% 9% 22% 19% 2	2200
October	1st to 10th	Night	39% 4 13% 24% 16% 3	3590
	11th to 20th	Night	27% 4 10% 27% 29% 3	3972
	21st to end	Night	34% 4 11% 29% 19% 2	4610
November	1st to 10th	Night	37% 6% 11% 24% 19% 3	2667
	11th to 20th	Night	40% 4 10% 23% 21% 3	2730
	21st to end	Night	40% 5% 13% 26% 13% 2	2730
December	1st to 10th	Night	42% 5% 11% 28% 13% 1	4636
	11th to 20th	Night	46% 3 15% 14% 20% 2	5348
	21st to end	Night	46% 5% 8% 22% 16% 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	31% 25% 26% 14% 4	220
	11th to 20th	Day	31% 24% 35% 9% 1	212
	21st to end	Day	27% 25% 34% 11% 2	220
February	1st to 10th	Day	31% 20% 35% 12% 2	417
	11th to 20th	Day	29% 28% 33% 8% 1	496
	21st to end	Day	28% 22% 34% 12% 3	414
March	1st to 10th	Day	32% 22% 31% 12% 3	500
	11th to 20th	Day	30% 24% 30% 12% 4 1	500
	21st to end	Day	31% 23% 32% 8% 6% 1	550
April	1st to 10th	Day	35% 23% 24% 12% 5% 1	500
	11th to 20th	Day	29% 26% 29% 12% 3	492
	21st to end	Day	28% 19% 35% 15% 2 1	500
May	1st to 10th	Day	33% 24% 28% 11% 3 1	503
	11th to 20th	Day	24% 20% 37% 13% 6% 1	527
	21st to end	Day	19% 15% 36% 23% 5% 1	573
June	1st to 10th	Day	23% 13% 38% 19% 6% 1	530
	11th to 20th	Day	17% 16% 40% 20% 5% 1	530
	21st to end	Day	16% 14% 39% 22% 8% 1	530
July	1st to 10th	Day	19% 10% 34% 26% 10% 1	525
	11th to 20th	Day	15% 8% 33% 31% 11% 2	524
	21st to end	Day	12% 9% 40% 30% 8% 1	576
August	1st to 10th	Day	11% 11% 34% 31% 11% 2	526
	11th to 20th	Day	14% 10% 32% 27% 14% 2	519
	21st to end	Day	13% 10% 35% 26% 12% 4	583
September	1st to 10th	Day	18% 12% 30% 24% 11% 4	530
	11th to 20th	Day	19% 12% 28% 21% 13% 8%	530
	21st to end	Day	23% 11% 33% 22% 8% 4	530
October	1st to 10th	Day	27% 12% 26% 21% 9% 5%	530
	11th to 20th	Day	21% 16% 33% 19% 9% 2	467
	21st to end	Day	26% 16% 32% 16% 8% 1	462
November	1st to 10th	Day	23% 18% 35% 14% 10% 1	425
	11th to 20th	Day	26% 21% 33% 15% 4 1	430
	21st to end	Day	28% 22% 30% 14% 5%	430
December	1st to 10th	Day	28% 25% 29% 14% 3	272
	11th to 20th	Day	36% 23% 32% 7% 2	220
	21st to end	Day	28% 23% 32% 12% 3 2	242
January	1st to 10th	Night	23% 20% 39% 17% 2	840
	11th to 20th	Night	29% 19% 35% 16% 2	825
	21st to end	Night	21% 20% 37% 19% 3	880
February	1st to 10th	Night	25% 18% 36% 19% 1	800
	11th to 20th	Night	26% 20% 39% 14% 1	783
	21st to end	Night	25% 21% 34% 17% 3	660
March	1st to 10th	Night	26% 18% 35% 16% 4	800
	11th to 20th	Night	22% 21% 36% 17% 3	800
	21st to end	Night	26% 19% 34% 18% 4	880
April	1st to 10th	Night	26% 20% 32% 19% 3	800
	11th to 20th	Night	24% 20% 34% 18% 4	774
	21st to end	Night	24% 18% 37% 19% 2	600
May	1st to 10th	Night	29% 17% 32% 19% 4	600
	11th to 20th	Night	20% 18% 39% 20% 3	584
	21st to end	Night	19% 9% 39% 27% 4 1	433
June	1st to 10th	Night	20% 9% 38% 28% 6% 1	400
	11th to 20th	Night	18% 8% 41% 28% 6%	400
	21st to end	Night	17% 5% 40% 32% 6%	400
July	1st to 10th	Night	13% 5% 37% 37% 8%	390
	11th to 20th	Night	14% 5% 32% 40% 9% 1	388
	21st to end	Night	13% 4 36% 39% 8%	438
August	1st to 10th	Night	13% 5% 35% 37% 9%	558
	11th to 20th	Night	12% 5% 32% 40% 10% 1	617
	21st to end	Night	14% 5% 26% 39% 14% 2	880
September	1st to 10th	Night	15% 6% 34% 34% 11% 1	800
	11th to 20th	Night	16% 8% 29% 28% 17% 2	800
	21st to end	Night	22% 8% 27% 31% 11% 2	800
October	1st to 10th	Night	23% 10% 27% 26% 12% 1	800
	11th to 20th	Night	18% 13% 34% 23% 11% 1	800
	21st to end	Night	25% 14% 32% 21% 7%	880
November	1st to 10th	Night	18% 15% 34% 24% 7% 1	820
	11th to 20th	Night	22% 20% 33% 18% 7%	840
	21st to end	Night	23% 20% 33% 19% 5% 1	840
December	1st to 10th	Night	25% 18% 35% 17% 5%	840
	11th to 20th	Night	26% 18% 33% 20% 2	840
	21st to end	Night	26% 18% 34% 19% 2	924

Page generated at 2026-01-14 01:14:30. Version ac07

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