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 2024-11-08.

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	8% 10% 3 7% 4 4 4 3 4 5% 48%	105205
	Night	9% 11% 3 6% 4 3 4 3 5% 6% 47%	102574
Transparency	Day	37% 6% 9% 18% 18% 12%	104949
	Night	38% 6% 11% 20% 17% 9%	102419
Seeing	Day	15% 13% 29% 28% 13% 2	14415
	Night	16% 5% 20% 36% 20% 3	23698

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	7% 22% 9% 12% 6% 4 4 3 4 6% 24%	2539
	11th to 20th	Day	13% 19% 9% 11% 4 4 4 2 4 5% 27%	2540
	21st to end	Day	16% 21% 4 8% 4 4 4 3 4 7% 25%	2794
February	1st to 10th	Day	12% 20% 6% 11% 6% 4 3 3 4 4 28%	1635
	11th to 20th	Day	10% 21% 6% 9% 4 5% 4 4 5% 6% 26%	1850
	21st to end	Day	10% 22% 8% 13% 5% 4 3 3 5% 5% 21%	1570
March	1st to 10th	Day	9% 19% 8% 11% 5% 4 4 3 4 5% 25%	3138
	11th to 20th	Day	8% 13% 4 5% 4 3 3 3 3 4 49%	3361
	21st to end	Day	11% 19% 4 12% 8% 7% 6% 5% 5% 6% 18%	3996
April	1st to 10th	Day	12% 17% 5% 10% 6% 5% 4 3 4 7% 28%	2280
	11th to 20th	Day	9% 14% 3 9% 6% 4 4 3 4 7% 36%	2309
	21st to end	Day	10% 12% 3 8% 5% 4 4 4 5% 6% 37%	2470
May	1st to 10th	Day	8% 13% 4 9% 5% 4 5% 3 5% 5% 39%	4110
	11th to 20th	Day	7% 5% 2 4 3 4 4 4 6% 6% 54%	4241
	21st to end	Day	8% 10% 3 7% 5% 5% 4 4 6% 6% 43%	4813
June	1st to 10th	Day	12% 8% 3 8% 6% 5% 6% 4 7% 7% 34%	2660
	11th to 20th	Day	10% 7% 2 6% 5% 4 4 4 5% 5% 46%	2660
	21st to end	Day	4 4 2 5% 3 3 4 3 4 6% 63%	2660
July	1st to 10th	Day	1 1 1 2 2 2 3 2 3 4 79%	4420
	11th to 20th	Day	2 2 1 2 2 2 3 2 3 4 76%	4420
	21st to end	Day	2 2 1 3 2 2 3 2 4 5% 73%	4790
August	1st to 10th	Day	3 4 2 7% 4 4 4 3 5% 6% 59%	4254
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 5% 76%	4028
	21st to end	Day	3 3 1 3 3 2 2 2 3 4 72%	4246
September	1st to 10th	Day	4 3 1 3 2 3 2 3 4 5% 71%	2280
	11th to 20th	Day	7% 5% 1 5% 3 3 4 3 5% 6% 58%	2104
	21st to end	Day	7% 5% 1 4 3 3 4 3 4 5% 61%	2090
October	1st to 10th	Day	6% 4 2 5% 3 3 3 2 3 5% 64%	3490
	11th to 20th	Day	9% 6% 2 7% 4 4 4 2 5% 6% 51%	3014
	21st to end	Day	8% 12% 4 8% 5% 4 4 3 4 6% 41%	3101
November	1st to 10th	Day	16% 13% 4 8% 5% 3 3 3 5% 6% 34%	1737
	11th to 20th	Day	16% 15% 4 7% 4 5% 3 3 5% 6% 33%	1710
	21st to end	Day	11% 13% 4 8% 5% 5% 4 3 5% 6% 35%	1653
December	1st to 10th	Day	16% 18% 5% 7% 4 3 3 2 5% 6% 31%	1520
	11th to 20th	Day	15% 19% 5% 10% 4 4 3 3 5% 6% 25%	1928
	21st to end	Day	12% 14% 5% 10% 4 3 4 3 5% 7% 34%	2794
January	1st to 10th	Night	10% 19% 7% 9% 5% 4 4 3 5% 5% 27%	4406
	11th to 20th	Night	15% 20% 7% 10% 4 3 3 3 4 5% 27%	4420
	21st to end	Night	15% 23% 4 7% 4 4 3 2 4 6% 27%	4862
February	1st to 10th	Night	12% 18% 4 9% 5% 4 4 3 4 5% 30%	2539
	11th to 20th	Night	11% 17% 5% 8% 5% 4 4 3 4 6% 33%	2218
	21st to end	Night	11% 19% 6% 10% 6% 4 4 3 5% 5% 27%	1884
March	1st to 10th	Night	9% 20% 5% 7% 5% 3 3 2 4 6% 35%	3736
	11th to 20th	Night	9% 14% 3 5% 4 3 3 3 4 4 49%	3619
	21st to end	Night	10% 12% 4 8% 6% 5% 5% 4 7% 9% 29%	3653
April	1st to 10th	Night	11% 12% 3 7% 4 4 4 3 5% 6% 40%	1900
	11th to 20th	Night	11% 10% 3 7% 4 4 4 4 4 5% 44%	1818
	21st to end	Night	8% 7% 3 6% 5% 4 5% 3 4 6% 48%	1710
May	1st to 10th	Night	9% 10% 2 4 3 4 5% 3 6% 7% 47%	2860
	11th to 20th	Night	4 4 2 4 3 3 3 3 6% 7% 59%	2654
	21st to end	Night	7% 8% 2 6% 5% 4 3 3 5% 7% 49%	2762
June	1st to 10th	Night	11% 6% 1 6% 4 4 5% 4 7% 10% 42%	1520
	11th to 20th	Night	9% 6% 2 4 3 3 3 3 6% 6% 56%	1520
	21st to end	Night	3 3 1 4 3 4 4 3 4 6% 65%	1520
July	1st to 10th	Night	1 1 1 2 2 2 3 4 4 79%	2540
	11th to 20th	Night	1 1 2 1 2 3 3 4 5% 78%	2540
	21st to end	Night	2 3 1 3 2 3 3 3 5% 6% 70%	2761
August	1st to 10th	Night	4 4 2 4 3 4 4 4 6% 6% 59%	2678
	11th to 20th	Night	1 1 1 2 2 2 2 3 4 5% 77%	2811
	21st to end	Night	4 3 1 3 2 2 2 2 3 4 73%	3427
September	1st to 10th	Night	3 3 1 3 2 2 3 2 4 5% 72%	1900
	11th to 20th	Night	6% 5% 2 5% 3 3 4 3 5% 6% 60%	2076
	21st to end	Night	8% 4 2 4 3 2 2 2 4 5% 65%	2090
October	1st to 10th	Night	4 3 1 4 3 3 3 2 4 5% 67%	3490
	11th to 20th	Night	7% 6% 2 5% 3 3 4 3 4 6% 57%	3911
	21st to end	Night	9% 8% 2 6% 4 4 5% 4 7% 7% 44%	4457
November	1st to 10th	Night	15% 11% 3 6% 4 4 3 3 6% 6% 38%	2502
	11th to 20th	Night	17% 11% 3 6% 4 4 4 3 5% 6% 36%	2470
	21st to end	Night	11% 12% 3 8% 5% 3 4 3 4 5% 40%	2522
December	1st to 10th	Night	12% 15% 4 7% 5% 4 4 4 5% 6% 33%	2660
	11th to 20th	Night	15% 18% 5% 9% 5% 5% 5% 3 5% 5% 26%	3276
	21st to end	Night	11% 15% 5% 9% 5% 4 4 3 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% 13% 2 1	2539
	11th to 20th	Day	60% 7% 9% 17% 7% 1	2540
	21st to end	Day	59% 8% 16% 13% 3 1	2794
February	1st to 10th	Day	59% 7% 13% 16% 4 1	1635
	11th to 20th	Day	58% 9% 12% 15% 7%	1860
	21st to end	Day	62% 8% 9% 15% 5% 1	1570
March	1st to 10th	Day	57% 8% 8% 15% 12%	3138
	11th to 20th	Day	38% 6% 8% 34% 13%	3361
	21st to end	Day	61% 11% 11% 12% 4	3996
April	1st to 10th	Day	55% 7% 14% 16% 7% 1	2280
	11th to 20th	Day	46% 6% 12% 20% 13% 2	2312
	21st to end	Day	46% 8% 12% 22% 12%	2470
May	1st to 10th	Day	44% 7% 9% 23% 15% 2	4110
	11th to 20th	Day	25% 6% 10% 31% 22% 7%	4244
	21st to end	Day	37% 9% 12% 30% 11% 2	4814
June	1st to 10th	Day	44% 9% 12% 22% 13% 1	2660
	11th to 20th	Day	36% 5% 9% 22% 20% 7%	2660
	21st to end	Day	21% 4 7% 19% 35% 14%	2660
July	1st to 10th	Day	10% 2 4 10% 20% 54%	4351
	11th to 20th	Day	13% 2 3 6% 23% 54%	4345
	21st to end	Day	14% 3 3 9% 31% 41%	4639
August	1st to 10th	Day	26% 4 5% 11% 27% 28%	4238
	11th to 20th	Day	12% 2 4 15% 43% 24%	4067
	21st to end	Day	17% 2 4 20% 34% 23%	4245
September	1st to 10th	Day	16% 4 5% 19% 32% 24%	2280
	11th to 20th	Day	26% 5% 9% 21% 27% 12%	2104
	21st to end	Day	25% 4 7% 28% 27% 9%	2090
October	1st to 10th	Day	25% 4 6% 18% 38% 9%	3490
	11th to 20th	Day	34% 3 12% 23% 24% 3	3014
	21st to end	Day	44% 5% 8% 24% 18% 1	3101
November	1st to 10th	Day	50% 6% 12% 20% 12% 1	1737
	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	57% 9% 15% 16% 2 1	4406
	11th to 20th	Night	61% 6% 11% 14% 8% 1	4420
	21st to end	Night	57% 9% 13% 15% 4 1	4862
February	1st to 10th	Night	56% 9% 14% 16% 5% 1	2539
	11th to 20th	Night	51% 8% 15% 16% 10% 1	2219
	21st to end	Night	58% 6% 10% 16% 8% 2	1884
March	1st to 10th	Night	49% 7% 10% 19% 13% 1	3736
	11th to 20th	Night	38% 6% 9% 31% 15% 1	3619
	21st to end	Night	45% 13% 17% 19% 6%	3653
April	1st to 10th	Night	43% 7% 13% 24% 12% 1	1900
	11th to 20th	Night	41% 6% 11% 24% 15% 3	1818
	21st to end	Night	35% 6% 15% 28% 15% 1	1710
May	1st to 10th	Night	33% 7% 9% 29% 19% 2	2860
	11th to 20th	Night	21% 6% 10% 34% 26% 3	2654
	21st to end	Night	33% 7% 12% 36% 12% 1	2762
June	1st to 10th	Night	35% 9% 14% 29% 12%	1520
	11th to 20th	Night	29% 5% 10% 26% 23% 7%	1520
	21st to end	Night	19% 4 8% 21% 33% 14%	1520
July	1st to 10th	Night	8% 2 4 10% 24% 51%	2500
	11th to 20th	Night	9% 2 3 9% 21% 56%	2492
	21st to end	Night	15% 2 3 11% 30% 38%	2674
August	1st to 10th	Night	24% 3 4 11% 33% 25%	2670
	11th to 20th	Night	11% 2 3 15% 39% 30%	2838
	21st to end	Night	16% 2 4 19% 33% 26%	3427
September	1st to 10th	Night	15% 3 6% 18% 33% 25%	1900
	11th to 20th	Night	24% 4 9% 19% 28% 16%	2076
	21st to end	Night	23% 3 6% 28% 28% 13%	2090
October	1st to 10th	Night	21% 3 7% 19% 35% 15%	3490
	11th to 20th	Night	29% 3 13% 23% 28% 4	3911
	21st to end	Night	37% 5% 13% 23% 21% 1	4457
November	1st to 10th	Night	44% 7% 13% 22% 13% 2	2502
	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% 12% 20% 23% 12% 8%	180
	21st to end	Day	22% 10% 28% 26% 10% 5%	198
February	1st to 10th	Day	27% 17% 26% 19% 9% 2	250
	11th to 20th	Day	22% 18% 33% 20% 7%	455
	21st to end	Day	24% 20% 27% 21% 8% 1	382
March	1st to 10th	Day	25% 17% 31% 22% 3	460
	11th to 20th	Day	20% 14% 28% 26% 10% 2	460
	21st to end	Day	25% 18% 30% 21% 6% 1	506
April	1st to 10th	Day	23% 19% 27% 20% 9% 2	460
	11th to 20th	Day	21% 20% 29% 22% 7% 1	452
	21st to end	Day	17% 21% 30% 22% 10% 1	460
May	1st to 10th	Day	12% 19% 31% 25% 11% 1	463
	11th to 20th	Day	23% 13% 28% 24% 11% 1	488
	21st to end	Day	14% 12% 25% 30% 16% 3	529
June	1st to 10th	Day	14% 15% 28% 27% 14% 3	490
	11th to 20th	Day	16% 18% 32% 24% 9% 1	490
	21st to end	Day	6% 11% 35% 32% 15% 2	490
July	1st to 10th	Day	3 6% 41% 35% 12% 2	486
	11th to 20th	Day	1 11% 37% 37% 13% 2	484
	21st to end	Day	3 6% 33% 39% 18% 2	531
August	1st to 10th	Day	6% 8% 34% 33% 16% 2	487
	11th to 20th	Day	2 7% 28% 40% 20% 3	477
	21st to end	Day	6% 9% 29% 36% 19% 2	539
September	1st to 10th	Day	7% 6% 24% 41% 19% 3	490
	11th to 20th	Day	11% 8% 28% 32% 20% 1	490
	21st to end	Day	9% 10% 30% 33% 16% 2	490
October	1st to 10th	Day	13% 11% 25% 31% 19% 1	490
	11th to 20th	Day	16% 11% 23% 31% 16% 4	366
	21st to end	Day	18% 17% 22% 28% 12% 3	330
November	1st to 10th	Day	25% 10% 24% 28% 12% 1	291
	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	25% 7% 19% 27% 19% 3	760
	21st to end	Night	22% 5% 20% 30% 19% 4	836
February	1st to 10th	Night	22% 8% 25% 31% 12% 2	760
	11th to 20th	Night	22% 6% 24% 32% 15% 1	744
	21st to end	Night	21% 7% 24% 33% 13% 2	628
March	1st to 10th	Night	21% 11% 23% 30% 13% 2	760
	11th to 20th	Night	18% 8% 22% 35% 17% 1	760
	21st to end	Night	20% 9% 22% 37% 11% 1	836
April	1st to 10th	Night	18% 8% 22% 33% 17% 2	760
	11th to 20th	Night	16% 9% 28% 32% 13% 2	690
	21st to end	Night	12% 6% 26% 39% 16% 2	570
May	1st to 10th	Night	10% 6% 24% 38% 20% 1	570
	11th to 20th	Night	10% 6% 18% 36% 27% 3	460
	21st to end	Night	13% 5% 17% 36% 27% 2	411
June	1st to 10th	Night	12% 5% 15% 40% 24% 4	380
	11th to 20th	Night	12% 3 20% 41% 22% 2	380
	21st to end	Night	5% 1 16% 50% 28% 1	380
July	1st to 10th	Night	2 2 14% 49% 31% 2	370
	11th to 20th	Night	1 2 17% 56% 22% 1	368
	21st to end	Night	4 1 11% 51% 32% 2	416
August	1st to 10th	Night	8% 2 10% 45% 32% 2	462
	11th to 20th	Night	1 2 11% 46% 37% 3	564
	21st to end	Night	5% 2 13% 45% 31% 4	791
September	1st to 10th	Night	5% 1 10% 48% 33% 3	760
	11th to 20th	Night	8% 3 13% 40% 31% 5%	760
	21st to end	Night	10% 2 18% 37% 26% 7%	760
October	1st to 10th	Night	11% 2 18% 43% 24% 2	760
	11th to 20th	Night	13% 5% 16% 40% 23% 5%	760
	21st to end	Night	18% 4 22% 36% 18% 3	836
November	1st to 10th	Night	24% 5% 19% 34% 16% 2	770
	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 2024-11-05 06:15:51. Version ac07

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