Smith Observing Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Smith Observing Site clear sky chart from 2005-11-06 to 2024-12-06.

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	13% 9% 3 7% 5% 4 4 4 6% 7% 37%	101596
	Night	14% 10% 4 7% 5% 4 4 3 5% 6% 38%	98200
Transparency	Day	44% 6% 12% 23% 14% 2	105152
	Night	45% 5% 11% 23% 14% 2	102785
Seeing	Day	16% 12% 30% 25% 12% 4	15936
	Night	18% 11% 30% 28% 12% 1	25816

By Month

Percentage Cloud Cover SE (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	13% 14% 9% 10% 5% 4 4 3 4 4 30%	2527
	11th to 20th	Day	12% 14% 5% 14% 5% 4 4 8% 8% 6% 20%	2530
	21st to end	Day	18% 23% 9% 9% 4 3 3 2 3 4 22%	2824
February	1st to 10th	Day	12% 16% 5% 8% 6% 4 5% 3 6% 7% 28%	1736
	11th to 20th	Day	14% 11% 4 8% 5% 4 4 3 5% 4 38%	1848
	21st to end	Day	13% 15% 4 11% 5% 5% 4 3 5% 7% 30%	1570
March	1st to 10th	Day	13% 12% 3 8% 4 4 4 3 5% 5% 37%	3120
	11th to 20th	Day	11% 6% 4 7% 6% 5% 4 4 6% 8% 40%	3268
	21st to end	Day	19% 13% 5% 12% 5% 5% 4 3 5% 5% 23%	4165
April	1st to 10th	Day	18% 13% 3 8% 6% 5% 4 3 4 6% 31%	2280
	11th to 20th	Day	17% 9% 3 6% 6% 5% 4 3 6% 7% 34%	2254
	21st to end	Day	19% 9% 3 7% 5% 5% 4 3 5% 6% 33%	2395
May	1st to 10th	Day	16% 7% 2 7% 5% 5% 5% 3 6% 8% 36%	4082
	11th to 20th	Day	15% 6% 2 6% 5% 3 5% 4 6% 7% 42%	4331
	21st to end	Day	11% 7% 3 6% 4 4 4 4 6% 9% 42%	4824
June	1st to 10th	Day	10% 6% 2 6% 5% 5% 4 4 6% 8% 45%	2660
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 6% 9% 45%	2660
	21st to end	Day	11% 7% 2 7% 5% 4 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	11% 8% 3 7% 5% 5% 6% 5% 7% 9% 33%	4440
	11th to 20th	Day	6% 4 2 5% 4 5% 4 4 6% 9% 51%	4440
	21st to end	Day	7% 6% 2 7% 5% 5% 5% 4 7% 9% 42%	4813
August	1st to 10th	Day	11% 6% 2 6% 4 4 5% 4 7% 9% 42%	4360
	11th to 20th	Day	10% 6% 2 5% 5% 4 4 4 6% 8% 45%	3772
	21st to end	Day	7% 6% 2 6% 5% 4 5% 4 6% 9% 47%	4180
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 5% 8% 47%	2280
	11th to 20th	Day	12% 4 1 4 3 3 5% 4 6% 7% 52%	2160
	21st to end	Day	11% 7% 2 7% 4 4 4 4 6% 8% 42%	2090
October	1st to 10th	Day	12% 8% 2 7% 4 3 4 3 4 6% 47%	2035
	11th to 20th	Day	18% 8% 3 8% 5% 5% 3 4 4 7% 35%	1878
	21st to end	Day	19% 10% 3 6% 4 5% 4 3 4 6% 36%	1881
November	1st to 10th	Day	12% 9% 3 7% 4 4 4 3 5% 7% 43%	1762
	11th to 20th	Day	15% 12% 3 10% 6% 4 4 4 5% 6% 32%	1800
	21st to end	Day	17% 13% 3 8% 5% 4 3 2 4 5% 36%	1710
December	1st to 10th	Day	14% 13% 4 10% 5% 5% 4 3 6% 6% 30%	1560
	11th to 20th	Day	11% 14% 4 9% 5% 5% 6% 4 6% 6% 29%	1918
	21st to end	Day	19% 22% 9% 11% 5% 4 3 3 4 4 16%	2783
January	1st to 10th	Night	14% 13% 9% 10% 5% 4 3 2 3 4 32%	4428
	11th to 20th	Night	15% 16% 6% 13% 5% 4 5% 6% 6% 4 19%	4440
	21st to end	Night	21% 19% 7% 10% 4 4 3 2 4 5% 22%	4838
February	1st to 10th	Night	13% 15% 5% 9% 6% 4 4 3 4 5% 33%	2442
	11th to 20th	Night	13% 11% 4 7% 5% 4 4 3 5% 6% 38%	2218
	21st to end	Night	18% 12% 4 7% 5% 4 4 2 4 5% 36%	1884
March	1st to 10th	Night	17% 11% 3 6% 5% 4 3 3 5% 5% 39%	3733
	11th to 20th	Night	9% 7% 3 6% 5% 5% 4 3 5% 7% 46%	3720
	21st to end	Night	22% 11% 5% 10% 4 4 4 3 4 4 29%	3466
April	1st to 10th	Night	16% 9% 3 7% 4 5% 4 3 5% 6% 38%	1900
	11th to 20th	Night	19% 8% 3 6% 4 5% 4 3 5% 5% 38%	1875
	21st to end	Night	18% 8% 3 7% 5% 3 3 4 5% 5% 40%	1783
May	1st to 10th	Night	15% 8% 3 7% 5% 5% 5% 4 6% 7% 36%	2813
	11th to 20th	Night	15% 7% 3 5% 4 4 4 4 7% 10% 37%	2568
	21st to end	Night	12% 9% 2 7% 5% 4 4 3 4 6% 44%	2743
June	1st to 10th	Night	9% 4 2 5% 4 5% 5% 4 6% 8% 46%	1520
	11th to 20th	Night	10% 6% 2 4 5% 4 4 4 6% 8% 46%	1520
	21st to end	Night	9% 6% 3 7% 5% 4 5% 4 7% 9% 42%	1520
July	1st to 10th	Night	12% 5% 3 7% 5% 5% 6% 4 6% 8% 39%	2530
	11th to 20th	Night	5% 4 1 5% 4 4 5% 5% 6% 8% 53%	2530
	21st to end	Night	5% 5% 2 6% 4 5% 6% 5% 8% 7% 47%	2750
August	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 7% 8% 50%	2575
	11th to 20th	Night	9% 5% 2 6% 4 4 3 3 6% 8% 51%	3055
	21st to end	Night	7% 4 2 5% 4 4 5% 3 6% 8% 51%	3476
September	1st to 10th	Night	10% 6% 2 5% 4 3 3 2 5% 6% 53%	1900
	11th to 20th	Night	10% 5% 2 5% 3 3 3 3 4 8% 55%	2000
	21st to end	Night	13% 6% 2 5% 4 5% 4 3 5% 7% 47%	2090
October	1st to 10th	Night	11% 5% 2 5% 4 3 3 3 5% 6% 51%	2142
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 4 5% 44%	2301
	21st to end	Night	20% 9% 3 7% 3 4 4 3 5% 6% 38%	2717
November	1st to 10th	Night	11% 9% 2 7% 4 4 3 3 5% 6% 47%	2536
	11th to 20th	Night	14% 11% 3 9% 5% 4 4 3 4 7% 36%	2600
	21st to end	Night	16% 10% 4 9% 4 4 3 4 5% 6% 36%	2687
December	1st to 10th	Night	15% 11% 4 9% 5% 5% 4 4 5% 6% 32%	2737
	11th to 20th	Night	14% 14% 4 8% 5% 4 4 3 5% 6% 32%	3279
	21st to end	Night	21% 19% 5% 10% 5% 4 4 3 4 5% 19%	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	59% 4 11% 18% 7%	2528
	11th to 20th	Day	59% 6% 13% 14% 8%	2530
	21st to end	Day	68% 2 7% 17% 6%	2824
February	1st to 10th	Day	55% 6% 12% 17% 10% 1	1736
	11th to 20th	Day	50% 4 10% 24% 11% 2	1858
	21st to end	Day	54% 6% 9% 19% 10% 2	1570
March	1st to 10th	Day	48% 7% 10% 22% 12% 3	3120
	11th to 20th	Day	41% 7% 10% 30% 11% 1	3268
	21st to end	Day	63% 7% 13% 13% 4	4165
April	1st to 10th	Day	54% 6% 10% 19% 11%	2280
	11th to 20th	Day	49% 6% 9% 22% 12% 3	2254
	21st to end	Day	50% 8% 11% 17% 13% 2	2395
May	1st to 10th	Day	44% 8% 10% 23% 13% 1	4120
	11th to 20th	Day	39% 8% 11% 27% 14% 1	4335
	21st to end	Day	37% 7% 13% 21% 18% 4	4837
June	1st to 10th	Day	36% 7% 12% 25% 17% 2	2660
	11th to 20th	Day	34% 7% 13% 23% 20% 3	2660
	21st to end	Day	40% 9% 13% 22% 14% 2	2660
July	1st to 10th	Day	44% 7% 12% 23% 11% 2	4371
	11th to 20th	Day	28% 7% 17% 31% 16% 1	4365
	21st to end	Day	37% 7% 16% 18% 20% 2	4662
August	1st to 10th	Day	36% 7% 15% 28% 12% 1	4345
	11th to 20th	Day	34% 7% 12% 33% 13% 1	3809
	21st to end	Day	33% 7% 12% 25% 21% 2	4179
September	1st to 10th	Day	35% 8% 12% 25% 18% 3	2280
	11th to 20th	Day	30% 6% 12% 30% 19% 2	2160
	21st to end	Day	38% 6% 11% 28% 17% 1	2090
October	1st to 10th	Day	25% 4 7% 39% 24% 1	3386
	11th to 20th	Day	35% 5% 10% 27% 22% 1	3094
	21st to end	Day	44% 4 7% 28% 13% 4	3081
November	1st to 10th	Day	42% 5% 13% 23% 16% 1	1762
	11th to 20th	Day	53% 5% 10% 21% 10% 1	1800
	21st to end	Day	52% 5% 11% 24% 8%	1710
December	1st to 10th	Day	53% 5% 14% 19% 7% 1	1560
	11th to 20th	Day	53% 6% 15% 17% 7% 2	1915
	21st to end	Day	74% 4 8% 10% 4	2783
January	1st to 10th	Night	57% 4 10% 18% 9% 1	4428
	11th to 20th	Night	66% 4 10% 12% 8%	4440
	21st to end	Night	66% 4 9% 14% 6% 1	4838
February	1st to 10th	Night	53% 5% 10% 18% 13% 2	2442
	11th to 20th	Night	47% 6% 11% 21% 14% 1	2219
	21st to end	Night	51% 5% 8% 22% 10% 4	1884
March	1st to 10th	Night	46% 5% 12% 24% 10% 3	3733
	11th to 20th	Night	36% 6% 11% 27% 18% 2	3720
	21st to end	Night	59% 5% 9% 18% 8% 1	3466
April	1st to 10th	Night	47% 6% 11% 22% 14% 1	1900
	11th to 20th	Night	48% 4 7% 18% 18% 4	1875
	21st to end	Night	46% 6% 10% 21% 15% 2	1783
May	1st to 10th	Night	45% 7% 12% 20% 14% 3	2840
	11th to 20th	Night	39% 9% 12% 28% 11% 1	2569
	21st to end	Night	41% 6% 9% 18% 19% 6%	2751
June	1st to 10th	Night	33% 8% 12% 26% 18% 3	1520
	11th to 20th	Night	35% 6% 10% 26% 21% 2	1520
	21st to end	Night	36% 8% 15% 22% 17% 2	1520
July	1st to 10th	Night	42% 7% 14% 21% 12% 4	2490
	11th to 20th	Night	26% 7% 15% 35% 16% 2	2482
	21st to end	Night	32% 8% 14% 19% 23% 4	2662
August	1st to 10th	Night	30% 7% 15% 28% 19% 1	2566
	11th to 20th	Night	31% 6% 13% 33% 17% 1	3084
	21st to end	Night	29% 6% 12% 31% 18% 4	3476
September	1st to 10th	Night	32% 7% 9% 27% 23% 2	1900
	11th to 20th	Night	29% 5% 8% 33% 23% 2	2000
	21st to end	Night	37% 6% 9% 31% 16% 1	2090
October	1st to 10th	Night	24% 4 7% 38% 26% 2	3571
	11th to 20th	Night	36% 4 8% 24% 26% 2	3824
	21st to end	Night	41% 5% 9% 25% 18% 3	4467
November	1st to 10th	Night	39% 4 9% 27% 18% 3	2536
	11th to 20th	Night	49% 5% 11% 22% 12% 2	2600
	21st to end	Night	50% 5% 12% 22% 11% 1	2687
December	1st to 10th	Night	52% 5% 12% 20% 10% 1	2737
	11th to 20th	Night	53% 5% 13% 19% 10% 1	3281
	21st to end	Night	68% 4 9% 13% 5%	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	21% 16% 35% 23% 5% 1	270
	11th to 20th	Day	21% 21% 34% 21% 3 1	270
	21st to end	Day	23% 16% 38% 18% 5% 1	297
February	1st to 10th	Day	16% 24% 38% 19% 3	270
	11th to 20th	Day	24% 21% 36% 16% 3	270
	21st to end	Day	23% 24% 40% 11% 2 1	225
March	1st to 10th	Day	19% 26% 40% 12% 2	270
	11th to 20th	Day	24% 16% 38% 15% 5% 1	294
	21st to end	Day	27% 14% 30% 21% 7% 2	506
April	1st to 10th	Day	24% 17% 33% 22% 4	460
	11th to 20th	Day	21% 23% 26% 19% 9% 2	452
	21st to end	Day	23% 16% 30% 18% 11% 2	460
May	1st to 10th	Day	21% 13% 34% 22% 9% 2	463
	11th to 20th	Day	20% 11% 32% 25% 9% 3	633
	21st to end	Day	16% 9% 31% 24% 15% 5%	734
June	1st to 10th	Day	10% 10% 32% 29% 15% 4	680
	11th to 20th	Day	13% 8% 29% 34% 12% 4	680
	21st to end	Day	12% 8% 30% 33% 13% 3	680
July	1st to 10th	Day	6% 4 26% 30% 23% 11%	671
	11th to 20th	Day	9% 5% 30% 32% 16% 8%	668
	21st to end	Day	7% 4 27% 39% 17% 6%	739
August	1st to 10th	Day	8% 5% 23% 33% 21% 9%	639
	11th to 20th	Day	11% 5% 21% 29% 23% 10%	479
	21st to end	Day	7% 4 23% 31% 27% 8%	539
September	1st to 10th	Day	14% 6% 25% 28% 22% 6%	490
	11th to 20th	Day	10% 4 20% 32% 22% 11%	490
	21st to end	Day	16% 12% 25% 25% 15% 8%	490
October	1st to 10th	Day	15% 13% 26% 27% 14% 4	435
	11th to 20th	Day	22% 20% 32% 20% 6%	300
	21st to end	Day	31% 15% 32% 15% 5% 1	330
November	1st to 10th	Day	17% 16% 33% 24% 8% 2	300
	11th to 20th	Day	22% 19% 38% 15% 6%	300
	21st to end	Day	24% 10% 44% 19% 2	300
December	1st to 10th	Day	15% 22% 41% 15% 5% 1	285
	11th to 20th	Day	19% 18% 39% 19% 6%	270
	21st to end	Day	26% 24% 34% 14% 1	297
January	1st to 10th	Night	18% 17% 38% 23% 4	950
	11th to 20th	Night	22% 16% 36% 19% 5% 1	950
	21st to end	Night	21% 13% 38% 24% 4	1045
February	1st to 10th	Night	21% 14% 37% 23% 5%	922
	11th to 20th	Night	21% 15% 36% 26% 3	743
	21st to end	Night	25% 15% 37% 20% 3	628
March	1st to 10th	Night	20% 13% 36% 22% 8%	760
	11th to 20th	Night	15% 13% 38% 26% 8%	745
	21st to end	Night	23% 11% 31% 27% 8% 1	627
April	1st to 10th	Night	20% 12% 36% 25% 6% 1	570
	11th to 20th	Night	23% 13% 32% 23% 8% 1	563
	21st to end	Night	23% 10% 27% 30% 9% 1	570
May	1st to 10th	Night	17% 8% 34% 31% 9% 1	570
	11th to 20th	Night	20% 5% 27% 30% 16% 1	561
	21st to end	Night	14% 6% 24% 34% 19% 2	617
June	1st to 10th	Night	10% 4 26% 41% 19% 1	570
	11th to 20th	Night	14% 5% 28% 38% 15% 1	570
	21st to end	Night	11% 4 26% 38% 19% 2	570
July	1st to 10th	Night	8% 3 15% 40% 31% 3	555
	11th to 20th	Night	9% 2 21% 37% 26% 5%	552
	21st to end	Night	6% 2 17% 47% 26% 2	624
August	1st to 10th	Night	6% 2 16% 44% 29% 4	567
	11th to 20th	Night	8% 3 15% 37% 31% 5%	564
	21st to end	Night	7% 3 18% 38% 31% 3	627
September	1st to 10th	Night	10% 4 20% 34% 27% 5%	570
	11th to 20th	Night	11% 4 20% 33% 27% 5%	670
	21st to end	Night	13% 9% 25% 28% 21% 3	760
October	1st to 10th	Night	14% 7% 25% 32% 20% 2	760
	11th to 20th	Night	21% 12% 31% 26% 9%	760
	21st to end	Night	24% 12% 32% 24% 8% 1	836
November	1st to 10th	Night	17% 14% 35% 24% 10% 1	780
	11th to 20th	Night	21% 19% 33% 22% 5% 1	800
	21st to end	Night	21% 14% 37% 23% 6%	887
December	1st to 10th	Night	21% 16% 38% 20% 5%	978
	11th to 20th	Night	22% 14% 37% 22% 4	950
	21st to end	Night	29% 16% 36% 18% 2	1045

Page generated at 2024-12-03 05:45:13. Version ac07

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