Wellsville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Wellsville clear sky chart from 2005-11-06 to 2026-07-31.

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	16% 10% 4 9% 5% 5% 4 4 5% 7% 31%	137884
	Night	17% 12% 4 9% 5% 4 4 3 5% 6% 31%	135100
Transparency	Day	52% 5% 10% 20% 11% 1	141503
	Night	53% 5% 10% 20% 11% 1	139551
Seeing	Day	23% 15% 28% 19% 11% 4	16907
	Night	23% 12% 26% 25% 12% 1	26671

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	17% 19% 7% 18% 5% 4 4 3 3 5% 14%	5258
	11th to 20th	Day	12% 19% 9% 18% 8% 6% 4 2 3 4 16%	5280
	21st to end	Day	18% 17% 6% 12% 10% 7% 4 3 4 5% 16%	5780
February	1st to 10th	Day	18% 17% 6% 9% 7% 4 3 2 4 5% 25%	1890
	11th to 20th	Day	17% 15% 6% 13% 5% 4 4 4 5% 5% 22%	1855
	21st to end	Day	18% 15% 5% 11% 4 4 3 3 5% 5% 27%	1730
March	1st to 10th	Day	17% 14% 5% 10% 5% 4 4 3 4 6% 28%	5044
	11th to 20th	Day	13% 9% 4 9% 5% 5% 4 3 5% 6% 37%	5090
	21st to end	Day	19% 10% 4 8% 5% 4 4 3 5% 6% 30%	5586
April	1st to 10th	Day	16% 13% 3 7% 5% 5% 4 3 5% 8% 31%	2389
	11th to 20th	Day	16% 11% 3 8% 5% 4 4 3 5% 6% 34%	2580
	21st to end	Day	21% 9% 3 6% 4 4 5% 3 5% 6% 34%	2730
May	1st to 10th	Day	21% 9% 3 8% 5% 5% 5% 4 6% 6% 28%	7616
	11th to 20th	Day	18% 8% 3 7% 5% 4 5% 4 6% 8% 33%	7626
	21st to end	Day	21% 8% 2 6% 4 4 4 4 5% 7% 34%	8666
June	1st to 10th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	2940
	11th to 20th	Day	14% 7% 2 7% 5% 5% 5% 4 7% 9% 35%	2940
	21st to end	Day	13% 6% 2 6% 4 5% 5% 5% 6% 11% 37%	2940
July	1st to 10th	Day	10% 6% 2 7% 4 5% 5% 4 7% 9% 42%	6125
	11th to 20th	Day	11% 6% 2 8% 6% 5% 5% 5% 7% 10% 35%	6030
	21st to end	Day	12% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	6554
August	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 4 6% 9% 32%	4234
	11th to 20th	Day	13% 6% 2 7% 5% 5% 6% 5% 7% 9% 35%	4174
	21st to end	Day	8% 5% 2 6% 5% 5% 6% 5% 7% 9% 41%	4510
September	1st to 10th	Day	16% 6% 2 5% 3 4 4 3 4 7% 47%	2356
	11th to 20th	Day	11% 6% 2 6% 4 4 5% 4 6% 8% 46%	2200
	21st to end	Day	20% 7% 3 7% 5% 4 4 3 5% 6% 36%	2200
October	1st to 10th	Day	15% 6% 3 6% 3 5% 4 4 6% 6% 43%	2027
	11th to 20th	Day	19% 9% 2 8% 4 4 4 3 5% 5% 36%	2000
	21st to end	Day	23% 10% 3 6% 4 5% 4 3 4 7% 32%	2200
November	1st to 10th	Day	12% 8% 3 7% 5% 5% 4 4 4 6% 42%	1927
	11th to 20th	Day	17% 14% 4 8% 4 5% 4 4 5% 5% 31%	1808
	21st to end	Day	18% 15% 5% 9% 5% 3 4 4 5% 5% 25%	1680
December	1st to 10th	Day	19% 14% 6% 14% 5% 4 4 3 4 4 22%	2680
	11th to 20th	Day	23% 17% 6% 11% 4 3 2 2 4 4 22%	3070
	21st to end	Day	24% 21% 6% 12% 6% 5% 3 3 4 4 14%	4169
January	1st to 10th	Night	15% 19% 7% 21% 6% 4 5% 3 4 4 13%	7635
	11th to 20th	Night	13% 18% 8% 16% 9% 5% 5% 3 4 4 15%	7680
	21st to end	Night	19% 16% 6% 11% 7% 6% 4 2 3 4 21%	8401
February	1st to 10th	Night	19% 15% 5% 11% 6% 4 4 3 5% 4 24%	2730
	11th to 20th	Night	18% 15% 5% 13% 5% 5% 4 4 4 5% 23%	2647
	21st to end	Night	20% 14% 5% 12% 6% 4 4 3 4 5% 23%	2076
March	1st to 10th	Night	23% 12% 5% 9% 4 3 3 2 3 5% 32%	5028
	11th to 20th	Night	14% 11% 4 7% 4 3 4 3 5% 7% 38%	5090
	21st to end	Night	19% 11% 3 8% 5% 4 4 3 4 5% 35%	5588
April	1st to 10th	Night	18% 12% 3 6% 6% 4 4 3 5% 7% 33%	2229
	11th to 20th	Night	17% 10% 2 7% 5% 4 5% 4 5% 7% 34%	2006
	21st to end	Night	16% 10% 3 7% 5% 3 4 3 5% 7% 37%	1890
May	1st to 10th	Night	23% 10% 3 7% 4 4 4 3 6% 6% 29%	5237
	11th to 20th	Night	16% 9% 3 6% 4 4 4 4 5% 7% 38%	5234
	21st to end	Night	22% 7% 2 5% 4 4 4 3 5% 7% 36%	5472
June	1st to 10th	Night	9% 6% 3 7% 5% 4 4 3 6% 8% 45%	1680
	11th to 20th	Night	12% 6% 2 6% 5% 4 4 4 5% 11% 42%	1680
	21st to end	Night	10% 5% 2 6% 4 6% 6% 5% 6% 8% 43%	1680
July	1st to 10th	Night	10% 8% 3 7% 4 4 4 3 5% 8% 43%	4046
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 7% 10% 39%	4147
	21st to end	Night	9% 6% 3 7% 5% 4 4 4 6% 8% 44%	4517
August	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 4 6% 8% 37%	2915
	11th to 20th	Night	14% 7% 3 6% 3 4 3 4 5% 6% 44%	2875
	21st to end	Night	8% 5% 2 6% 5% 5% 6% 5% 6% 9% 45%	3355
September	1st to 10th	Night	13% 4 2 5% 3 4 3 3 6% 6% 51%	2040
	11th to 20th	Night	9% 4 1 4 4 4 4 2 5% 9% 53%	2200
	21st to end	Night	18% 7% 2 6% 4 4 4 4 5% 6% 41%	2200
October	1st to 10th	Night	15% 4 2 6% 4 3 4 3 5% 7% 47%	2371
	11th to 20th	Night	17% 6% 3 6% 5% 4 5% 4 5% 7% 39%	2400
	21st to end	Night	24% 8% 2 5% 4 2 4 3 4 6% 37%	2640
November	1st to 10th	Night	12% 9% 2 5% 6% 4 4 3 5% 7% 44%	2586
	11th to 20th	Night	18% 13% 4 7% 4 4 4 3 5% 6% 31%	2809
	21st to end	Night	21% 14% 5% 8% 4 4 4 3 5% 5% 28%	2940
December	1st to 10th	Night	18% 16% 9% 13% 5% 4 4 3 5% 5% 18%	4720
	11th to 20th	Night	21% 19% 8% 9% 4 3 3 3 4 5% 21%	5345
	21st to end	Night	24% 19% 6% 10% 5% 4 4 3 4 6% 16%	7011

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	74% 4 9% 10% 3	5259
	11th to 20th	Day	75% 2 6% 9% 6% 1	5280
	21st to end	Day	73% 3 7% 13% 4	5780
February	1st to 10th	Day	64% 3 9% 15% 8% 1	1890
	11th to 20th	Day	65% 4 9% 15% 7%	1864
	21st to end	Day	60% 4 10% 18% 7% 2	1730
March	1st to 10th	Day	58% 4 9% 22% 7% 1	5044
	11th to 20th	Day	47% 5% 11% 25% 9% 2	5090
	21st to end	Day	55% 4 8% 19% 13% 1	5586
April	1st to 10th	Day	53% 5% 11% 18% 12% 1	2389
	11th to 20th	Day	51% 5% 10% 18% 14% 2	2580
	21st to end	Day	51% 5% 10% 22% 10% 2	2730
May	1st to 10th	Day	55% 6% 10% 19% 8% 3	7651
	11th to 20th	Day	49% 6% 11% 23% 11% 1	7630
	21st to end	Day	49% 6% 9% 18% 15% 4	8681
June	1st to 10th	Day	44% 7% 12% 23% 13% 1	2940
	11th to 20th	Day	44% 7% 13% 22% 12% 1	2940
	21st to end	Day	41% 8% 12% 25% 13% 1	2940
July	1st to 10th	Day	38% 7% 11% 27% 15% 2	6060
	11th to 20th	Day	42% 7% 13% 25% 13% 1	5961
	21st to end	Day	41% 6% 11% 22% 19% 1	6370
August	1st to 10th	Day	47% 7% 13% 22% 10%	4221
	11th to 20th	Day	42% 7% 10% 30% 10% 1	4213
	21st to end	Day	36% 8% 13% 29% 12% 2	4510
September	1st to 10th	Day	38% 5% 10% 23% 20% 3	2356
	11th to 20th	Day	35% 5% 15% 27% 17% 2	2200
	21st to end	Day	50% 5% 10% 22% 13% 1	2200
October	1st to 10th	Day	32% 5% 9% 31% 21% 1	3300
	11th to 20th	Day	47% 5% 9% 20% 15% 4	3240
	21st to end	Day	41% 4 12% 27% 17% 1	3538
November	1st to 10th	Day	42% 6% 11% 23% 16% 2	1927
	11th to 20th	Day	56% 4 9% 19% 10% 2	1808
	21st to end	Day	61% 4 11% 16% 6% 1	1680
December	1st to 10th	Day	67% 4 12% 13% 4	2680
	11th to 20th	Day	67% 3 10% 14% 5%	3066
	21st to end	Day	75% 4 8% 10% 3	4169
January	1st to 10th	Night	76% 4 8% 10% 3	7636
	11th to 20th	Night	74% 4 8% 10% 5% 1	7680
	21st to end	Night	70% 3 7% 14% 6% 1	8401
February	1st to 10th	Night	64% 4 9% 17% 6%	2730
	11th to 20th	Night	65% 4 8% 16% 7%	2649
	21st to end	Night	64% 5% 8% 14% 9% 1	2076
March	1st to 10th	Night	58% 3 9% 20% 9% 1	5028
	11th to 20th	Night	46% 4 13% 26% 8% 3	5090
	21st to end	Night	52% 4 10% 18% 15% 1	5588
April	1st to 10th	Night	52% 5% 9% 18% 13% 2	2229
	11th to 20th	Night	48% 6% 12% 17% 14% 3	2006
	21st to end	Night	46% 5% 10% 21% 15% 2	1890
May	1st to 10th	Night	55% 5% 9% 17% 11% 3	5264
	11th to 20th	Night	45% 6% 9% 26% 13% 1	5235
	21st to end	Night	47% 5% 11% 22% 13% 2	5479
June	1st to 10th	Night	37% 7% 12% 23% 18% 3	1680
	11th to 20th	Night	37% 6% 15% 24% 16% 2	1680
	21st to end	Night	37% 9% 13% 23% 17% 1	1680
July	1st to 10th	Night	40% 6% 9% 25% 18% 2	4003
	11th to 20th	Night	39% 7% 16% 25% 12% 1	4096
	21st to end	Night	37% 6% 11% 19% 24% 2	4387
August	1st to 10th	Night	44% 7% 12% 24% 12% 1	2904
	11th to 20th	Night	40% 5% 11% 27% 16% 1	2902
	21st to end	Night	35% 6% 12% 31% 13% 2	3355
September	1st to 10th	Night	33% 7% 10% 24% 21% 5%	2040
	11th to 20th	Night	29% 6% 13% 28% 22% 2	2200
	21st to end	Night	43% 5% 12% 21% 18% 1	2200
October	1st to 10th	Night	33% 4 9% 28% 25% 2	3878
	11th to 20th	Night	39% 5% 11% 23% 15% 7%	3899
	21st to end	Night	37% 4 8% 29% 20% 2	4252
November	1st to 10th	Night	41% 5% 11% 24% 17% 3	2586
	11th to 20th	Night	54% 4 10% 20% 9% 3	2809
	21st to end	Night	59% 4 11% 20% 5% 1	2940
December	1st to 10th	Night	69% 3 10% 14% 3	4720
	11th to 20th	Night	67% 4 12% 14% 3	5348
	21st to end	Night	71% 5% 9% 13% 2	7011

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	35% 24% 27% 9% 4	330
	11th to 20th	Day	38% 29% 27% 5% 1	330
	21st to end	Day	33% 31% 26% 7% 2	363
February	1st to 10th	Day	34% 22% 34% 8% 2	330
	11th to 20th	Day	39% 27% 28% 6%	330
	21st to end	Day	37% 25% 30% 8%	273
March	1st to 10th	Day	29% 25% 30% 13% 3	539
	11th to 20th	Day	33% 21% 29% 11% 5% 1	540
	21st to end	Day	31% 24% 28% 14% 3 1	594
April	1st to 10th	Day	32% 21% 27% 13% 6% 1	540
	11th to 20th	Day	28% 20% 28% 15% 8% 2	532
	21st to end	Day	29% 15% 32% 16% 7% 1	540
May	1st to 10th	Day	29% 19% 28% 16% 6% 3	543
	11th to 20th	Day	23% 13% 32% 22% 7% 4	567
	21st to end	Day	20% 11% 26% 24% 14% 5%	617
June	1st to 10th	Day	15% 12% 33% 25% 12% 4	570
	11th to 20th	Day	18% 12% 28% 26% 14% 3	570
	21st to end	Day	14% 9% 32% 27% 15% 3	570
July	1st to 10th	Day	13% 5% 23% 30% 21% 9%	565
	11th to 20th	Day	11% 7% 27% 29% 18% 8%	564
	21st to end	Day	13% 6% 25% 30% 17% 8%	616
August	1st to 10th	Day	13% 6% 23% 30% 19% 9%	526
	11th to 20th	Day	15% 6% 21% 28% 20% 9%	519
	21st to end	Day	12% 5% 28% 26% 20% 10%	583
September	1st to 10th	Day	16% 9% 20% 26% 19% 10%	530
	11th to 20th	Day	12% 4 19% 28% 24% 13%	530
	21st to end	Day	23% 11% 25% 21% 15% 4	530
October	1st to 10th	Day	15% 11% 27% 24% 19% 5%	530
	11th to 20th	Day	22% 14% 32% 21% 9% 2	530
	21st to end	Day	31% 16% 31% 16% 5%	583
November	1st to 10th	Day	20% 20% 35% 14% 9% 2	405
	11th to 20th	Day	33% 16% 30% 13% 6% 1	286
	21st to end	Day	29% 25% 35% 9% 1	220
December	1st to 10th	Day	31% 28% 29% 8% 2 1	220
	11th to 20th	Day	34% 23% 31% 10% 2	220
	21st to end	Day	40% 22% 26% 11% 1	272
January	1st to 10th	Night	30% 20% 34% 13% 3	840
	11th to 20th	Night	32% 21% 29% 15% 3	840
	21st to end	Night	31% 21% 28% 17% 3	924
February	1st to 10th	Night	30% 18% 30% 21% 2	840
	11th to 20th	Night	30% 21% 34% 14% 2	823
	21st to end	Night	30% 20% 32% 16% 2	692
March	1st to 10th	Night	27% 19% 31% 20% 3	840
	11th to 20th	Night	29% 17% 27% 22% 5% 1	840
	21st to end	Night	27% 17% 32% 20% 4 1	924
April	1st to 10th	Night	26% 16% 29% 22% 5%	840
	11th to 20th	Night	23% 13% 35% 20% 8% 1	762
	21st to end	Night	21% 10% 35% 28% 6%	630
May	1st to 10th	Night	25% 9% 25% 31% 9% 1	630
	11th to 20th	Night	20% 10% 27% 30% 13% 1	621
	21st to end	Night	13% 5% 23% 36% 20% 2	586
June	1st to 10th	Night	12% 6% 25% 40% 17%	420
	11th to 20th	Night	13% 6% 26% 38% 17%	420
	21st to end	Night	9% 3 28% 35% 24% 1	420
July	1st to 10th	Night	7% 4 16% 40% 26% 7%	565
	11th to 20th	Night	8% 2 20% 36% 30% 4	612
	21st to end	Night	12% 3 16% 39% 27% 3	687
August	1st to 10th	Night	10% 3 14% 41% 29% 3	597
	11th to 20th	Night	14% 3 12% 38% 29% 4	594
	21st to end	Night	10% 4 21% 31% 28% 6%	740
September	1st to 10th	Night	14% 4 20% 31% 26% 5%	800
	11th to 20th	Night	9% 4 15% 37% 31% 4	800
	21st to end	Night	20% 8% 22% 26% 19% 4	800
October	1st to 10th	Night	17% 9% 22% 28% 23% 3	800
	11th to 20th	Night	20% 13% 30% 24% 12% 1	800
	21st to end	Night	29% 12% 28% 24% 7%	880
November	1st to 10th	Night	19% 13% 27% 30% 11%	820
	11th to 20th	Night	28% 16% 27% 21% 7% 1	840
	21st to end	Night	31% 15% 29% 20% 6%	840
December	1st to 10th	Night	32% 18% 28% 17% 5%	840
	11th to 20th	Night	31% 18% 28% 19% 3	840
	21st to end	Night	32% 17% 29% 19% 2	924

Page generated at 2026-07-28 03:25:26. Version ac07

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