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 2024-01-15.

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% 3 5% 5% 3 4 5% 5% 7% 40%	74827
	Night	17% 7% 3 5% 5% 3 4 4 5% 6% 41%	74938
Transparency	Day	43% 6% 12% 21% 15% 3	74532
	Night	44% 6% 12% 21% 15% 2	74767
Seeing	Day	23% 17% 33% 18% 7% 2	13956
	Night	22% 14% 34% 23% 6% 1	22975

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% 9% 3 5% 5% 3 4 4 3 5% 44%	1517
	11th to 20th	Day	19% 7% 3 5% 4 3 4 5% 7% 7% 38%	1472
	21st to end	Day	14% 7% 2 5% 5% 3 4 4 6% 8% 43%	1584
February	1st to 10th	Day	20% 7% 3 5% 5% 3 5% 5% 5% 6% 36%	1688
	11th to 20th	Day	14% 8% 3 6% 6% 3 5% 5% 5% 7% 40%	1748
	21st to end	Day	19% 9% 3 6% 4 3 5% 4 5% 6% 37%	1480
March	1st to 10th	Day	17% 7% 2 5% 5% 3 4 5% 5% 8% 39%	1797
	11th to 20th	Day	17% 6% 3 6% 5% 3 5% 5% 5% 7% 39%	1898
	21st to end	Day	19% 7% 3 7% 4 3 3 4 4 5% 40%	2288
April	1st to 10th	Day	19% 8% 3 6% 5% 3 4 3 5% 6% 38%	2160
	11th to 20th	Day	17% 7% 2 5% 5% 3 5% 6% 5% 7% 39%	2148
	21st to end	Day	22% 5% 3 6% 6% 3 4 4 6% 6% 35%	2340
May	1st to 10th	Day	24% 9% 4 6% 5% 2 4 4 5% 6% 32%	2340
	11th to 20th	Day	18% 7% 3 4 6% 3 4 5% 5% 7% 40%	2322
	21st to end	Day	15% 5% 2 5% 4 4 5% 4 4 8% 43%	2725
June	1st to 10th	Day	20% 6% 3 5% 6% 3 5% 4 6% 9% 33%	2520
	11th to 20th	Day	17% 6% 3 5% 5% 3 6% 5% 6% 7% 37%	2520
	21st to end	Day	16% 6% 3 6% 6% 3 5% 6% 6% 8% 35%	2520
July	1st to 10th	Day	13% 5% 3 4 6% 4 6% 5% 6% 7% 41%	2520
	11th to 20th	Day	12% 6% 3 5% 5% 4 5% 6% 6% 9% 39%	2520
	21st to end	Day	11% 5% 3 5% 6% 4 5% 6% 6% 9% 40%	2744
August	1st to 10th	Day	10% 6% 2 6% 6% 4 6% 7% 7% 9% 37%	2345
	11th to 20th	Day	13% 7% 2 5% 6% 3 6% 6% 6% 7% 39%	2279
	21st to end	Day	12% 5% 2 5% 5% 3 4 5% 6% 8% 44%	2376
September	1st to 10th	Day	14% 5% 2 5% 5% 3 4 5% 5% 7% 45%	2152
	11th to 20th	Day	15% 5% 3 4 3 2 2 3 4 7% 51%	1980
	21st to end	Day	18% 5% 2 5% 3 2 4 4 5% 6% 45%	1980
October	1st to 10th	Day	25% 5% 3 4 4 2 3 3 3 6% 41%	1980
	11th to 20th	Day	15% 6% 2 4 5% 2 4 5% 4 6% 47%	1765
	21st to end	Day	20% 7% 2 4 4 3 4 4 4 6% 40%	1782
November	1st to 10th	Day	17% 7% 2 4 4 3 3 3 3 5% 50%	1671
	11th to 20th	Day	19% 7% 2 3 4 2 3 3 5% 5% 46%	1710
	21st to end	Day	18% 5% 3 5% 4 3 4 4 5% 6% 43%	1710
December	1st to 10th	Day	17% 8% 3 6% 5% 3 5% 4 5% 5% 40%	1568
	11th to 20th	Day	22% 6% 3 3 3 3 4 3 3 5% 45%	1906
	21st to end	Day	22% 10% 3 6% 5% 3 4 4 4 6% 34%	2772
January	1st to 10th	Night	16% 8% 2 5% 4 2 5% 3 4 5% 44%	2649
	11th to 20th	Night	19% 10% 4 6% 6% 3 4 4 4 7% 35%	2577
	21st to end	Night	13% 9% 3 6% 5% 3 4 4 5% 5% 41%	2772
February	1st to 10th	Night	18% 9% 3 5% 5% 3 5% 4 5% 6% 38%	2266
	11th to 20th	Night	15% 9% 3 5% 5% 3 5% 5% 4 7% 39%	2098
	21st to end	Night	18% 8% 3 4 4 3 5% 3 4 5% 41%	1776
March	1st to 10th	Night	16% 8% 2 5% 5% 3 4 5% 4 6% 41%	2150
	11th to 20th	Night	15% 9% 3 6% 4 3 4 5% 5% 6% 38%	2060
	21st to end	Night	17% 9% 2 5% 5% 3 4 4 4 5% 42%	2066
April	1st to 10th	Night	18% 7% 2 6% 5% 3 4 4 5% 7% 37%	1800
	11th to 20th	Night	19% 7% 2 5% 6% 3 4 4 5% 6% 39%	1760
	21st to end	Night	21% 7% 2 6% 4 3 4 4 4 6% 38%	1620
May	1st to 10th	Night	23% 9% 4 6% 5% 3 3 4 5% 6% 32%	1620
	11th to 20th	Night	19% 5% 3 5% 5% 3 5% 4 6% 8% 36%	1587
	21st to end	Night	17% 7% 4 5% 5% 2 3 4 5% 8% 39%	1550
June	1st to 10th	Night	18% 7% 3 6% 5% 3 6% 4 6% 7% 36%	1440
	11th to 20th	Night	18% 6% 3 6% 4 3 4 5% 5% 8% 36%	1440
	21st to end	Night	16% 5% 2 4 4 3 5% 6% 5% 10% 41%	1440
July	1st to 10th	Night	12% 6% 3 5% 5% 3 5% 5% 7% 8% 40%	1440
	11th to 20th	Night	12% 7% 3 6% 6% 3 4 5% 7% 10% 36%	1440
	21st to end	Night	12% 6% 3 5% 5% 3 5% 6% 6% 8% 41%	1574
August	1st to 10th	Night	8% 5% 2 5% 6% 3 4 6% 7% 9% 45%	1576
	11th to 20th	Night	10% 6% 2 6% 6% 5% 6% 6% 6% 9% 38%	1618
	21st to end	Night	13% 5% 2 4 4 3 5% 4 5% 8% 47%	1980
September	1st to 10th	Night	13% 6% 2 5% 6% 3 4 4 5% 6% 45%	1808
	11th to 20th	Night	14% 6% 2 4 3 2 3 4 4 6% 52%	1980
	21st to end	Night	16% 5% 3 4 5% 2 3 5% 5% 5% 45%	1980
October	1st to 10th	Night	22% 6% 2 5% 4 3 3 4 4 5% 42%	1980
	11th to 20th	Night	16% 5% 2 5% 4 2 4 5% 5% 7% 46%	2191
	21st to end	Night	22% 7% 3 6% 4 3 3 4 4 6% 38%	2574
November	1st to 10th	Night	15% 5% 2 5% 5% 3 4 3 4 5% 48%	2407
	11th to 20th	Night	18% 7% 2 5% 4 2 3 4 4 4 46%	2470
	21st to end	Night	16% 6% 3 4 4 3 4 4 5% 6% 45%	2470
December	1st to 10th	Night	19% 8% 3 5% 5% 3 4 4 5% 6% 39%	2607
	11th to 20th	Night	19% 7% 2 5% 4 2 4 4 5% 6% 41%	3288
	21st to end	Night	20% 10% 3 6% 5% 2 4 4 4 6% 35%	4884

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	43% 5% 9% 26% 15% 3	1518
	11th to 20th	Day	45% 8% 11% 21% 12% 3	1472
	21st to end	Day	39% 5% 13% 24% 16% 2	1584
February	1st to 10th	Day	49% 5% 13% 17% 14% 3	1688
	11th to 20th	Day	43% 6% 13% 21% 14% 3	1757
	21st to end	Day	48% 6% 9% 19% 15% 3	1480
March	1st to 10th	Day	43% 6% 13% 21% 13% 4	1800
	11th to 20th	Day	43% 6% 10% 21% 15% 4	1898
	21st to end	Day	46% 5% 9% 17% 17% 6%	2288
April	1st to 10th	Day	47% 5% 10% 18% 16% 4	2160
	11th to 20th	Day	42% 7% 11% 21% 16% 3	2148
	21st to end	Day	47% 6% 10% 18% 16% 4	2340
May	1st to 10th	Day	52% 6% 9% 19% 13% 2	2340
	11th to 20th	Day	43% 7% 11% 18% 18% 3	2326
	21st to end	Day	39% 7% 13% 24% 14% 2	2725
June	1st to 10th	Day	47% 8% 13% 21% 10% 1	2520
	11th to 20th	Day	43% 8% 13% 18% 16% 2	2520
	21st to end	Day	44% 8% 14% 21% 12% 1	2520
July	1st to 10th	Day	39% 8% 12% 23% 15% 3	2450
	11th to 20th	Day	40% 9% 13% 24% 12% 2	2445
	21st to end	Day	39% 9% 14% 21% 13% 4	2591
August	1st to 10th	Day	39% 10% 14% 22% 13% 1	2331
	11th to 20th	Day	41% 9% 13% 23% 13% 1	2279
	21st to end	Day	36% 8% 11% 24% 19% 2	2376
September	1st to 10th	Day	38% 7% 12% 23% 19% 2	2152
	11th to 20th	Day	35% 4 10% 26% 22% 3	1980
	21st to end	Day	40% 6% 8% 21% 23% 2	1980
October	1st to 10th	Day	46% 5% 9% 22% 14% 4	1980
	11th to 20th	Day	37% 6% 11% 28% 16% 2	1765
	21st to end	Day	45% 6% 13% 18% 15% 3	1782
November	1st to 10th	Day	39% 4 13% 25% 17% 2	1671
	11th to 20th	Day	40% 4 10% 23% 20% 2	1710
	21st to end	Day	42% 6% 13% 24% 12% 2	1710
December	1st to 10th	Day	46% 5% 14% 16% 17% 1	1568
	11th to 20th	Day	44% 4 14% 17% 16% 6%	1906
	21st to end	Day	52% 5% 11% 20% 11% 1	2772
January	1st to 10th	Night	43% 4 12% 22% 16% 3	2649
	11th to 20th	Night	50% 6% 13% 20% 10% 2	2577
	21st to end	Night	44% 5% 11% 19% 19% 3	2772
February	1st to 10th	Night	48% 5% 12% 20% 13% 2	2266
	11th to 20th	Night	47% 5% 9% 21% 14% 4	2100
	21st to end	Night	45% 4 9% 23% 16% 4	1776
March	1st to 10th	Night	44% 6% 8% 22% 15% 5%	2160
	11th to 20th	Night	47% 6% 11% 16% 18% 3	2061
	21st to end	Night	47% 4 7% 17% 19% 6%	2066
April	1st to 10th	Night	46% 6% 11% 19% 16% 3	1800
	11th to 20th	Night	45% 5% 9% 21% 17% 3	1760
	21st to end	Night	46% 6% 11% 18% 15% 4	1620
May	1st to 10th	Night	53% 6% 10% 16% 12% 3	1620
	11th to 20th	Night	45% 8% 12% 18% 13% 4	1588
	21st to end	Night	45% 7% 14% 20% 12% 1	1551
June	1st to 10th	Night	47% 7% 13% 21% 11% 1	1440
	11th to 20th	Night	46% 7% 12% 21% 13% 1	1440
	21st to end	Night	39% 9% 15% 23% 13% 1	1440
July	1st to 10th	Night	39% 9% 14% 22% 16% 1	1400
	11th to 20th	Night	41% 8% 15% 26% 9% 1	1392
	21st to end	Night	39% 8% 13% 27% 11% 2	1486
August	1st to 10th	Night	34% 9% 18% 25% 13% 2	1566
	11th to 20th	Night	40% 11% 16% 21% 13%	1618
	21st to end	Night	35% 7% 12% 25% 20% 1	1980
September	1st to 10th	Night	39% 7% 12% 22% 18% 1	1808
	11th to 20th	Night	33% 7% 10% 22% 26% 2	1980
	21st to end	Night	39% 7% 9% 22% 20% 3	1980
October	1st to 10th	Night	45% 5% 11% 22% 13% 4	1980
	11th to 20th	Night	38% 6% 13% 27% 14% 1	2191
	21st to end	Night	47% 6% 12% 19% 14% 2	2574
November	1st to 10th	Night	38% 6% 11% 22% 19% 4	2407
	11th to 20th	Night	41% 4 10% 22% 19% 3	2470
	21st to end	Night	40% 5% 13% 26% 14% 2	2470
December	1st to 10th	Night	46% 6% 12% 21% 14% 1	2607
	11th to 20th	Night	44% 4 16% 17% 18% 2	3288
	21st to end	Night	50% 5% 9% 25% 10% 1	4884

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% 23% 26% 16% 4	180
	11th to 20th	Day	31% 24% 32% 11% 1 1	168
	21st to end	Day	26% 27% 33% 11% 2 1	176
February	1st to 10th	Day	33% 21% 32% 12% 2	348
	11th to 20th	Day	28% 27% 35% 9% 1	416
	21st to end	Day	30% 22% 34% 12% 2	346
March	1st to 10th	Day	28% 21% 34% 13% 3	420
	11th to 20th	Day	29% 24% 31% 11% 4 1	420
	21st to end	Day	27% 23% 32% 8% 7% 1	462
April	1st to 10th	Day	33% 22% 25% 13% 6% 1	420
	11th to 20th	Day	26% 27% 30% 14% 4	412
	21st to end	Day	30% 19% 33% 15% 2 1	420
May	1st to 10th	Day	35% 24% 26% 11% 3 1	423
	11th to 20th	Day	23% 20% 38% 13% 5%	447
	21st to end	Day	18% 16% 36% 22% 6% 1	485
June	1st to 10th	Day	23% 12% 39% 19% 6% 1	450
	11th to 20th	Day	17% 15% 42% 19% 5% 2	450
	21st to end	Day	16% 12% 40% 22% 8% 1	450
July	1st to 10th	Day	18% 9% 33% 27% 11% 2	445
	11th to 20th	Day	15% 8% 32% 32% 10% 3	444
	21st to end	Day	11% 9% 39% 32% 8% 1	488
August	1st to 10th	Day	11% 11% 34% 33% 10% 2	446
	11th to 20th	Day	16% 10% 32% 27% 14% 2	439
	21st to end	Day	15% 9% 33% 27% 12% 4	495
September	1st to 10th	Day	20% 11% 28% 25% 12% 4	450
	11th to 20th	Day	21% 14% 29% 18% 12% 7%	450
	21st to end	Day	23% 12% 31% 22% 8% 4	450
October	1st to 10th	Day	29% 12% 26% 20% 8% 5%	450
	11th to 20th	Day	19% 16% 35% 20% 9% 2	399
	21st to end	Day	27% 16% 31% 17% 8% 1	396
November	1st to 10th	Day	21% 17% 34% 16% 10% 2	365
	11th to 20th	Day	27% 20% 33% 15% 5% 1	370
	21st to end	Day	28% 19% 31% 15% 6% 1	370
December	1st to 10th	Day	27% 27% 30% 13% 4	228
	11th to 20th	Day	33% 23% 34% 7% 2	180
	21st to end	Day	26% 24% 33% 12% 4 2	198
January	1st to 10th	Night	22% 19% 39% 17% 3	760
	11th to 20th	Night	28% 18% 36% 16% 2	737
	21st to end	Night	21% 20% 36% 20% 3	792
February	1st to 10th	Night	26% 17% 37% 18% 1	720
	11th to 20th	Night	25% 19% 39% 15% 1	703
	21st to end	Night	26% 21% 34% 17% 2	592
March	1st to 10th	Night	24% 18% 37% 17% 4	720
	11th to 20th	Night	22% 21% 37% 16% 3	720
	21st to end	Night	24% 19% 34% 19% 4	792
April	1st to 10th	Night	25% 20% 32% 19% 4	720
	11th to 20th	Night	23% 19% 34% 19% 5%	696
	21st to end	Night	25% 17% 36% 20% 2	540
May	1st to 10th	Night	29% 17% 31% 19% 4	540
	11th to 20th	Night	21% 18% 39% 19% 3	526
	21st to end	Night	20% 8% 39% 28% 5% 1	389
June	1st to 10th	Night	20% 8% 37% 28% 7% 1	360
	11th to 20th	Night	19% 8% 40% 28% 6%	360
	21st to end	Night	16% 6% 41% 32% 5%	360
July	1st to 10th	Night	14% 4 37% 37% 8%	350
	11th to 20th	Night	14% 4 31% 41% 9% 1	348
	21st to end	Night	13% 4 35% 39% 9%	394
August	1st to 10th	Night	12% 5% 36% 37% 10%	502
	11th to 20th	Night	13% 4 32% 40% 10% 1	554
	21st to end	Night	15% 5% 24% 39% 14% 2	792
September	1st to 10th	Night	15% 5% 34% 34% 11%	720
	11th to 20th	Night	17% 8% 30% 26% 17% 2	720
	21st to end	Night	21% 8% 28% 30% 11% 2	720
October	1st to 10th	Night	25% 10% 27% 24% 12% 2	720
	11th to 20th	Night	18% 13% 35% 23% 11% 1	720
	21st to end	Night	27% 14% 33% 20% 6% 1	792
November	1st to 10th	Night	18% 14% 34% 24% 8% 1	740
	11th to 20th	Night	22% 20% 32% 18% 7%	760
	21st to end	Night	23% 20% 34% 18% 5% 1	760
December	1st to 10th	Night	24% 18% 35% 17% 5%	760
	11th to 20th	Night	25% 18% 33% 21% 2 1	760
	21st to end	Night	26% 18% 35% 19% 2	836

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