Smithsferry Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smithsferry Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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	10% 10% 4 6% 5% 3 4 4 5% 6% 44%	74831
	Night	10% 10% 3 6% 5% 3 4 4 5% 6% 44%	74904
Transparency	Day	40% 6% 11% 18% 16% 8%	74535
	Night	40% 6% 12% 20% 15% 7%	74721
Seeing	Day	15% 12% 29% 29% 13% 2	13292
	Night	16% 5% 19% 36% 21% 3	22707

By Month

Percentage Cloud Cover SW (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% 18% 8% 10% 7% 4 4 5% 4 6% 25%	1519
	11th to 20th	Day	15% 15% 6% 7% 4 2 4 4 4 6% 32%	1451
	21st to end	Day	11% 17% 4 9% 5% 3 4 4 5% 7% 31%	1584
February	1st to 10th	Day	12% 18% 6% 11% 6% 3 3 4 4 4 29%	1550
	11th to 20th	Day	11% 20% 6% 8% 5% 4 5% 4 5% 6% 27%	1750
	21st to end	Day	11% 20% 10% 11% 6% 3 3 4 6% 5% 21%	1480
March	1st to 10th	Day	14% 19% 7% 9% 6% 4 4 5% 5% 6% 22%	1800
	11th to 20th	Day	14% 15% 5% 7% 7% 3 5% 5% 5% 6% 30%	1903
	21st to end	Day	13% 20% 5% 9% 7% 3 5% 4 4 6% 23%	2272
April	1st to 10th	Day	13% 15% 5% 9% 7% 4 5% 4 5% 7% 28%	2160
	11th to 20th	Day	10% 13% 4 8% 6% 3 5% 4 4 7% 36%	2185
	21st to end	Day	11% 12% 3 7% 6% 3 5% 4 5% 6% 38%	2340
May	1st to 10th	Day	8% 9% 4 6% 6% 3 5% 5% 6% 6% 42%	2340
	11th to 20th	Day	12% 8% 4 5% 6% 4 5% 5% 6% 8% 36%	2393
	21st to end	Day	11% 10% 4 9% 7% 4 6% 5% 7% 7% 30%	2723
June	1st to 10th	Day	13% 7% 4 7% 7% 4 6% 6% 6% 8% 34%	2520
	11th to 20th	Day	11% 7% 3 5% 6% 3 5% 5% 5% 5% 45%	2520
	21st to end	Day	4 4 2 4 3 2 3 4 4 5% 63%	2520
July	1st to 10th	Day	2 2 1 3 3 2 3 5% 5% 6% 68%	2520
	11th to 20th	Day	2 2 1 2 2 1 3 3 3 5% 76%	2520
	21st to end	Day	3 2 1 3 3 2 4 3 4 5% 70%	2741
August	1st to 10th	Day	4 3 1 4 4 3 4 4 4 6% 63%	2426
	11th to 20th	Day	2 2 1 2 2 1 3 3 4 5% 73%	2299
	21st to end	Day	3 3 2 3 3 2 3 4 4 5% 69%	2416
September	1st to 10th	Day	4 3 1 3 2 2 3 3 4 4 71%	2160
	11th to 20th	Day	7% 4 2 4 3 2 4 4 4 6% 60%	1994
	21st to end	Day	8% 5% 1 3 4 2 4 5% 4 6% 59%	1980
October	1st to 10th	Day	11% 6% 2 5% 5% 3 4 5% 3 6% 49%	1980
	11th to 20th	Day	11% 8% 2 5% 5% 3 3 3 5% 6% 50%	1724
	21st to end	Day	10% 10% 4 7% 6% 3 4 5% 5% 6% 41%	1782
November	1st to 10th	Day	17% 12% 4 6% 6% 2 4 4 5% 6% 34%	1674
	11th to 20th	Day	16% 14% 5% 6% 5% 3 4 4 5% 6% 33%	1710
	21st to end	Day	12% 12% 5% 8% 5% 4 5% 4 5% 6% 35%	1653
December	1st to 10th	Day	16% 16% 6% 7% 4 2 3 3 5% 7% 32%	1520
	11th to 20th	Day	15% 18% 5% 9% 5% 3 4 4 5% 7% 25%	1928
	21st to end	Day	12% 14% 5% 9% 5% 3 4 4 5% 7% 34%	2794
January	1st to 10th	Night	14% 18% 6% 7% 6% 3 4 4 4 6% 26%	2646
	11th to 20th	Night	15% 15% 4 7% 5% 3 3 4 4 6% 33%	2548
	21st to end	Night	9% 19% 4 7% 5% 4 4 3 3 7% 34%	2772
February	1st to 10th	Night	13% 16% 4 8% 6% 3 5% 4 4 5% 31%	2404
	11th to 20th	Night	11% 16% 5% 7% 5% 3 4 4 4 6% 34%	2098
	21st to end	Night	13% 17% 6% 9% 7% 3 4 4 5% 6% 27%	1776
March	1st to 10th	Night	14% 16% 5% 7% 6% 3 4 3 4 6% 32%	2160
	11th to 20th	Night	12% 13% 4 6% 7% 2 6% 6% 5% 7% 33%	2057
	21st to end	Night	13% 13% 4 7% 6% 3 5% 4 6% 8% 31%	2080
April	1st to 10th	Night	12% 10% 3 6% 5% 3 5% 4 5% 6% 40%	1800
	11th to 20th	Night	12% 9% 4 7% 5% 3 4 4 4 6% 42%	1722
	21st to end	Night	8% 7% 3 5% 6% 3 5% 4 4 7% 49%	1620
May	1st to 10th	Night	7% 6% 2 3 4 3 5% 5% 5% 8% 51%	1620
	11th to 20th	Night	7% 6% 3 6% 6% 4 5% 5% 6% 9% 43%	1498
	21st to end	Night	10% 8% 3 6% 6% 3 4 5% 6% 10% 38%	1552
June	1st to 10th	Night	12% 6% 2 5% 5% 2 5% 5% 6% 10% 42%	1440
	11th to 20th	Night	10% 6% 2 3 4 3 3 4 5% 6% 55%	1440
	21st to end	Night	4 3 1 4 3 2 4 4 4 6% 64%	1440
July	1st to 10th	Night	1 2 1 2 3 3 3 5% 6% 7% 68%	1440
	11th to 20th	Night	1 1 2 2 1 3 3 4 6% 75%	1440
	21st to end	Night	2 3 1 2 2 3 2 4 4 5% 72%	1576
August	1st to 10th	Night	4 3 2 3 3 3 3 4 5% 7% 63%	1511
	11th to 20th	Night	1 1 1 2 3 2 3 4 4 6% 75%	1602
	21st to end	Night	3 3 1 3 3 2 3 3 4 5% 69%	1937
September	1st to 10th	Night	3 3 1 3 3 2 3 2 4 5% 72%	1800
	11th to 20th	Night	6% 4 2 4 4 2 3 3 5% 6% 62%	1966
	21st to end	Night	8% 4 1 3 3 2 3 3 4 5% 64%	1980
October	1st to 10th	Night	8% 5% 2 5% 4 2 4 4 6% 6% 55%	1980
	11th to 20th	Night	10% 6% 2 4 5% 2 3 3 4 7% 53%	2230
	21st to end	Night	11% 8% 3 5% 4 3 4 5% 6% 7% 44%	2574
November	1st to 10th	Night	15% 11% 3 5% 5% 3 3 3 6% 7% 38%	2405
	11th to 20th	Night	18% 10% 3 6% 5% 3 4 4 5% 6% 37%	2470
	21st to end	Night	12% 11% 4 7% 6% 2 4 4 4 6% 40%	2522
December	1st to 10th	Night	13% 15% 5% 6% 6% 3 5% 5% 5% 6% 33%	2660
	11th to 20th	Night	15% 17% 5% 8% 7% 3 5% 4 5% 5% 27%	3276
	21st to end	Night	12% 14% 5% 8% 6% 3 4 4 5% 6% 34%	4862

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	61% 10% 14% 12% 2 1	1519
	11th to 20th	Day	54% 7% 13% 19% 7% 1	1451
	21st to end	Day	53% 9% 16% 16% 5% 1	1584
February	1st to 10th	Day	58% 7% 13% 16% 4 1	1550
	11th to 20th	Day	58% 8% 12% 15% 6%	1760
	21st to end	Day	62% 8% 9% 14% 5% 1	1480
March	1st to 10th	Day	60% 9% 10% 14% 6% 1	1800
	11th to 20th	Day	53% 8% 12% 19% 7%	1903
	21st to end	Day	63% 7% 11% 14% 5%	2272
April	1st to 10th	Day	55% 8% 14% 15% 8% 1	2160
	11th to 20th	Day	48% 6% 12% 20% 13% 2	2188
	21st to end	Day	47% 8% 11% 23% 11%	2340
May	1st to 10th	Day	39% 6% 13% 26% 14% 1	2340
	11th to 20th	Day	42% 7% 14% 24% 11% 2	2396
	21st to end	Day	48% 10% 13% 17% 10% 1	2724
June	1st to 10th	Day	44% 9% 12% 22% 13% 1	2520
	11th to 20th	Day	38% 5% 9% 22% 20% 7%	2520
	21st to end	Day	21% 4 7% 20% 34% 13%	2520
July	1st to 10th	Day	16% 4 6% 17% 28% 29%	2451
	11th to 20th	Day	12% 3 5% 9% 32% 40%	2445
	21st to end	Day	16% 3 5% 10% 27% 39%	2589
August	1st to 10th	Day	22% 5% 8% 16% 26% 23%	2409
	11th to 20th	Day	13% 3 7% 19% 36% 22%	2299
	21st to end	Day	17% 3 6% 18% 36% 20%	2416
September	1st to 10th	Day	16% 4 5% 19% 30% 26%	2160
	11th to 20th	Day	25% 5% 8% 20% 29% 13%	1994
	21st to end	Day	26% 5% 7% 28% 26% 9%	1980
October	1st to 10th	Day	35% 7% 10% 23% 20% 5%	1980
	11th to 20th	Day	35% 5% 10% 27% 20% 3	1724
	21st to end	Day	43% 8% 12% 21% 15% 1	1782
November	1st to 10th	Day	50% 6% 13% 20% 11% 1	1674
	11th to 20th	Day	52% 6% 14% 19% 7%	1710
	21st to end	Day	48% 7% 14% 18% 11% 2	1653
December	1st to 10th	Day	52% 8% 18% 15% 7% 1	1520
	11th to 20th	Day	59% 9% 13% 13% 5%	1928
	21st to end	Day	50% 5% 14% 20% 10% 1	2794
January	1st to 10th	Night	59% 9% 16% 12% 3 1	2646
	11th to 20th	Night	53% 7% 12% 18% 9% 1	2548
	21st to end	Night	50% 8% 16% 18% 7% 1	2772
February	1st to 10th	Night	54% 9% 15% 16% 5% 1	2404
	11th to 20th	Night	51% 8% 14% 17% 10% 1	2099
	21st to end	Night	58% 6% 10% 16% 8% 2	1776
March	1st to 10th	Night	53% 7% 14% 18% 8% 2	2160
	11th to 20th	Night	48% 8% 12% 22% 9% 1	2057
	21st to end	Night	50% 8% 18% 17% 7%	2080
April	1st to 10th	Night	43% 7% 13% 23% 12% 1	1800
	11th to 20th	Night	43% 7% 11% 23% 14% 2	1722
	21st to end	Night	36% 5% 15% 27% 16% 1	1620
May	1st to 10th	Night	29% 6% 12% 31% 20% 1	1620
	11th to 20th	Night	35% 8% 14% 30% 13%	1498
	21st to end	Night	40% 7% 16% 26% 9% 1	1552
June	1st to 10th	Night	36% 9% 14% 29% 12%	1440
	11th to 20th	Night	29% 5% 11% 26% 22% 7%	1440
	21st to end	Night	19% 5% 8% 21% 33% 14%	1440
July	1st to 10th	Night	14% 4 7% 16% 34% 25%	1400
	11th to 20th	Night	11% 3 5% 13% 28% 40%	1392
	21st to end	Night	14% 3 6% 11% 28% 39%	1488
August	1st to 10th	Night	20% 4 8% 17% 28% 24%	1503
	11th to 20th	Night	11% 3 5% 19% 33% 29%	1602
	21st to end	Night	17% 3 6% 17% 33% 24%	1937
September	1st to 10th	Night	16% 3 6% 18% 31% 26%	1800
	11th to 20th	Night	23% 4 8% 19% 29% 17%	1966
	21st to end	Night	24% 3 7% 27% 28% 12%	1980
October	1st to 10th	Night	28% 5% 11% 26% 23% 6%	1980
	11th to 20th	Night	32% 4 13% 27% 21% 3	2230
	21st to end	Night	37% 7% 13% 22% 19% 2	2574
November	1st to 10th	Night	44% 7% 13% 21% 13% 2	2405
	11th to 20th	Night	47% 7% 13% 23% 10%	2470
	21st to end	Night	46% 5% 13% 21% 12% 3	2522
December	1st to 10th	Night	51% 8% 15% 15% 10% 1	2660
	11th to 20th	Night	59% 7% 12% 17% 5% 1	3276
	21st to end	Night	49% 7% 17% 17% 9% 2	4862

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	21% 16% 27% 22% 13% 2	180
	11th to 20th	Day	25% 13% 18% 24% 12% 9%	163
	21st to end	Day	24% 7% 29% 26% 11% 3	176
February	1st to 10th	Day	27% 15% 26% 20% 10% 2	225
	11th to 20th	Day	22% 17% 31% 21% 7%	415
	21st to end	Day	25% 18% 27% 21% 8% 1	346
March	1st to 10th	Day	25% 17% 32% 23% 3	420
	11th to 20th	Day	21% 14% 29% 26% 9%	420
	21st to end	Day	25% 18% 31% 20% 6%	462
April	1st to 10th	Day	24% 18% 27% 20% 9% 2	420
	11th to 20th	Day	22% 20% 29% 21% 7% 1	412
	21st to end	Day	18% 21% 28% 22% 10% 1	420
May	1st to 10th	Day	12% 18% 31% 26% 12% 1	423
	11th to 20th	Day	25% 12% 27% 23% 11% 1	448
	21st to end	Day	15% 12% 24% 31% 15% 4	485
June	1st to 10th	Day	14% 15% 26% 27% 14% 3	450
	11th to 20th	Day	16% 17% 32% 23% 10% 1	450
	21st to end	Day	5% 10% 34% 33% 16% 2	450
July	1st to 10th	Day	3 5% 41% 37% 11% 2	446
	11th to 20th	Day	1 11% 37% 37% 13% 2	444
	21st to end	Day	3 5% 32% 39% 18% 2	487
August	1st to 10th	Day	5% 7% 35% 34% 16% 2	447
	11th to 20th	Day	2 5% 26% 42% 22% 3	437
	21st to end	Day	5% 8% 28% 38% 18% 2	495
September	1st to 10th	Day	7% 6% 24% 42% 18% 2	450
	11th to 20th	Day	10% 8% 28% 33% 21% 1	450
	21st to end	Day	9% 11% 30% 33% 16% 2	450
October	1st to 10th	Day	14% 12% 24% 31% 18% 1	450
	11th to 20th	Day	17% 11% 23% 29% 16% 4	333
	21st to end	Day	18% 16% 22% 29% 12% 3	297
November	1st to 10th	Day	25% 9% 23% 29% 13% 1	270
	11th to 20th	Day	18% 11% 28% 27% 12% 3	270
	21st to end	Day	17% 8% 29% 27% 16% 3	243
December	1st to 10th	Day	32% 10% 18% 18% 14% 7%	180
	11th to 20th	Day	28% 13% 25% 23% 9% 2	180
	21st to end	Day	22% 16% 24% 24% 11% 3	198
January	1st to 10th	Night	24% 7% 22% 28% 17% 3	760
	11th to 20th	Night	26% 6% 19% 27% 19% 3	728
	21st to end	Night	22% 4 20% 30% 20% 4	792
February	1st to 10th	Night	22% 7% 25% 32% 12% 2	720
	11th to 20th	Night	22% 5% 23% 32% 15% 1	704
	21st to end	Night	21% 7% 23% 33% 14% 3	592
March	1st to 10th	Night	22% 10% 22% 30% 13% 2	720
	11th to 20th	Night	18% 7% 22% 35% 17% 1	720
	21st to end	Night	21% 8% 21% 37% 11% 1	792
April	1st to 10th	Night	18% 7% 22% 33% 18% 2	720
	11th to 20th	Night	17% 9% 27% 31% 14% 2	654
	21st to end	Night	12% 6% 25% 39% 17% 2	540
May	1st to 10th	Night	10% 7% 23% 38% 21% 1	540
	11th to 20th	Night	11% 6% 17% 36% 27% 3	436
	21st to end	Night	14% 5% 16% 34% 28% 3	389
June	1st to 10th	Night	13% 5% 14% 39% 25% 4	360
	11th to 20th	Night	12% 3 19% 41% 23% 2	360
	21st to end	Night	5% 1 13% 51% 29% 1	360
July	1st to 10th	Night	3 1 12% 50% 32% 3	350
	11th to 20th	Night	1 1 15% 58% 23% 1	348
	21st to end	Night	4 1 10% 50% 33% 2	394
August	1st to 10th	Night	8% 2 8% 46% 33% 3	437
	11th to 20th	Night	1 1 8% 46% 39% 3	534
	21st to end	Night	5% 2 12% 46% 31% 5%	749
September	1st to 10th	Night	5% 1 10% 49% 33% 3	720
	11th to 20th	Night	7% 3 13% 39% 32% 6%	720
	21st to end	Night	10% 2 18% 36% 28% 7%	720
October	1st to 10th	Night	11% 2 18% 42% 25% 3	720
	11th to 20th	Night	13% 5% 16% 38% 23% 5%	720
	21st to end	Night	18% 4 20% 36% 19% 3	792
November	1st to 10th	Night	24% 4 19% 35% 16% 2	740
	11th to 20th	Night	25% 4 21% 32% 16% 1	760
	21st to end	Night	18% 7% 23% 32% 16% 4	760
December	1st to 10th	Night	21% 6% 22% 33% 15% 2	760
	11th to 20th	Night	27% 6% 20% 31% 14% 2	760
	21st to end	Night	29% 8% 24% 27% 11% 2	836

Page generated at 2024-01-09 14:24:22. Version ac07

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