Ellicottville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ellicottville Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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% 13% 5% 9% 6% 3 4 4 5% 6% 27%	74789
	Night	16% 14% 6% 9% 7% 3 4 4 4 5% 26%	75251
Transparency	Day	57% 6% 11% 17% 9% 1	74506
	Night	59% 6% 10% 16% 8% 1	75069
Seeing	Day	26% 18% 28% 17% 9% 3	13502
	Night	25% 17% 26% 22% 9% 1	23072

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	13% 20% 11% 15% 11% 3 6% 4 3 4 11%	1517
	11th to 20th	Day	16% 21% 9% 17% 9% 3 3 3 3 4 12%	1686
	21st to end	Day	12% 17% 11% 17% 12% 4 5% 4 4 3 9%	1836
February	1st to 10th	Day	16% 20% 9% 16% 10% 4 5% 3 3 3 13%	1620
	11th to 20th	Day	14% 16% 9% 18% 10% 4 4 4 4 3 15%	1573
	21st to end	Day	19% 17% 6% 12% 9% 3 4 4 4 5% 19%	1414
March	1st to 10th	Day	16% 15% 7% 14% 7% 3 4 4 4 4 22%	1977
	11th to 20th	Day	15% 17% 8% 9% 5% 3 4 4 4 6% 26%	1980
	21st to end	Day	20% 15% 6% 8% 6% 3 3 4 4 4 26%	2178
April	1st to 10th	Day	16% 16% 7% 7% 5% 3 4 4 4 6% 27%	2147
	11th to 20th	Day	19% 14% 3 5% 5% 2 4 4 4 6% 32%	2134
	21st to end	Day	21% 13% 4 7% 6% 3 4 3 4 5% 31%	2324
May	1st to 10th	Day	21% 12% 3 7% 6% 4 4 4 5% 7% 28%	2340
	11th to 20th	Day	20% 9% 3 7% 6% 3 5% 4 5% 6% 32%	2450
	21st to end	Day	14% 6% 2 6% 5% 4 5% 6% 6% 8% 38%	2725
June	1st to 10th	Day	19% 8% 3 6% 5% 3 4 4 6% 8% 34%	2520
	11th to 20th	Day	17% 8% 3 6% 6% 3 4 6% 6% 9% 33%	2520
	21st to end	Day	17% 6% 3 5% 5% 4 6% 5% 6% 8% 36%	2520
July	1st to 10th	Day	12% 6% 2 6% 6% 3 6% 6% 7% 7% 39%	2520
	11th to 20th	Day	14% 6% 3 6% 6% 3 6% 6% 7% 10% 33%	2520
	21st to end	Day	12% 7% 3 7% 6% 4 6% 6% 6% 9% 33%	2547
August	1st to 10th	Day	13% 6% 3 6% 6% 4 6% 5% 7% 9% 36%	2327
	11th to 20th	Day	13% 7% 3 7% 7% 5% 6% 7% 7% 9% 29%	2303
	21st to end	Day	16% 7% 3 6% 5% 4 6% 5% 6% 9% 33%	2421
September	1st to 10th	Day	18% 7% 3 6% 5% 3 4 5% 6% 8% 34%	2160
	11th to 20th	Day	17% 6% 3 5% 6% 4 4 5% 5% 8% 38%	2098
	21st to end	Day	18% 8% 4 7% 6% 3 5% 6% 5% 7% 30%	1916
October	1st to 10th	Day	23% 9% 3 7% 6% 3 4 4 5% 6% 31%	1800
	11th to 20th	Day	23% 14% 4 7% 6% 3 4 4 3 5% 27%	1800
	21st to end	Day	26% 18% 4 8% 4 3 4 4 4 4 21%	1980
November	1st to 10th	Day	14% 19% 4 7% 5% 4 4 4 5% 6% 29%	1698
	11th to 20th	Day	15% 24% 7% 9% 5% 2 4 4 4 6% 20%	1520
	21st to end	Day	18% 25% 8% 10% 4 3 4 3 5% 5% 16%	1520
December	1st to 10th	Day	16% 26% 12% 16% 4 2 4 3 3 2 11%	1520
	11th to 20th	Day	16% 20% 9% 17% 6% 3 3 3 4 5% 13%	1906
	21st to end	Day	22% 27% 9% 11% 6% 2 3 2 2 3 11%	2772
January	1st to 10th	Night	15% 20% 10% 15% 11% 4 5% 3 3 3 11%	2649
	11th to 20th	Night	15% 21% 10% 14% 10% 3 3 3 3 4 13%	2490
	21st to end	Night	12% 19% 10% 15% 12% 5% 5% 4 4 3 11%	2664
February	1st to 10th	Night	16% 18% 8% 14% 13% 4 4 2 3 4 14%	2340
	11th to 20th	Night	12% 15% 10% 17% 10% 4 6% 3 4 4 14%	2273
	21st to end	Night	17% 16% 8% 14% 10% 3 4 3 4 4 19%	1839
March	1st to 10th	Night	12% 16% 9% 13% 9% 4 3 4 5% 4 22%	1970
	11th to 20th	Night	17% 15% 6% 9% 6% 3 4 3 3 5% 27%	1979
	21st to end	Night	15% 16% 7% 8% 7% 3 4 4 4 4 27%	2178
April	1st to 10th	Night	17% 15% 7% 8% 5% 3 4 4 4 5% 28%	1812
	11th to 20th	Night	19% 13% 3 5% 5% 3 4 4 4 6% 35%	1775
	21st to end	Night	16% 14% 4 6% 6% 3 6% 4 5% 8% 30%	1652
May	1st to 10th	Night	18% 11% 3 7% 6% 4 5% 5% 4 6% 32%	1620
	11th to 20th	Night	13% 10% 4 6% 6% 4 5% 6% 4 7% 36%	1443
	21st to end	Night	12% 7% 2 6% 4 2 5% 4 5% 9% 44%	1550
June	1st to 10th	Night	13% 7% 3 7% 6% 3 5% 6% 6% 8% 35%	1440
	11th to 20th	Night	13% 6% 3 6% 5% 3 5% 5% 6% 8% 39%	1440
	21st to end	Night	13% 6% 3 5% 6% 4 5% 3 6% 9% 41%	1440
July	1st to 10th	Night	9% 6% 2 6% 5% 3 4 4 6% 8% 46%	1440
	11th to 20th	Night	11% 5% 2 6% 5% 2 5% 5% 6% 8% 44%	1440
	21st to end	Night	13% 4 3 5% 5% 3 5% 6% 6% 9% 41%	1766
August	1st to 10th	Night	10% 6% 2 5% 4 3 5% 5% 6% 8% 45%	1611
	11th to 20th	Night	13% 7% 3 5% 5% 4 5% 6% 7% 8% 36%	1598
	21st to end	Night	12% 7% 2 5% 4 4 5% 5% 6% 9% 40%	1916
September	1st to 10th	Night	17% 7% 3 4 4 3 4 5% 5% 7% 41%	1800
	11th to 20th	Night	15% 7% 2 6% 4 3 3 4 5% 6% 45%	1858
	21st to end	Night	19% 7% 3 7% 6% 3 5% 5% 6% 7% 33%	2043
October	1st to 10th	Night	19% 8% 3 6% 5% 4 4 4 4 6% 36%	2160
	11th to 20th	Night	22% 11% 3 7% 6% 3 5% 5% 4 6% 28%	2160
	21st to end	Night	29% 14% 4 6% 4 3 4 4 4 5% 24%	2376
November	1st to 10th	Night	17% 16% 4 7% 5% 3 3 4 4 6% 32%	2377
	11th to 20th	Night	17% 20% 5% 7% 6% 3 5% 5% 4 6% 21%	2660
	21st to end	Night	17% 21% 8% 12% 6% 3 4 3 4 5% 18%	2660
December	1st to 10th	Night	18% 24% 13% 13% 6% 3 4 3 3 2 11%	2660
	11th to 20th	Night	17% 22% 11% 16% 7% 3 3 3 3 3 13%	3288
	21st to end	Night	21% 23% 10% 12% 8% 3 4 4 3 3 9%	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	76% 4 8% 8% 3	1518
	11th to 20th	Day	77% 4 8% 7% 4	1686
	21st to end	Day	79% 3 7% 7% 3 1	1836
February	1st to 10th	Day	78% 4 9% 6% 3	1620
	11th to 20th	Day	72% 4 6% 12% 5%	1582
	21st to end	Day	69% 4 9% 13% 4 1	1414
March	1st to 10th	Day	64% 4 11% 16% 6%	1980
	11th to 20th	Day	60% 5% 10% 15% 8% 2	1980
	21st to end	Day	61% 4 5% 17% 10% 2	2178
April	1st to 10th	Day	57% 5% 10% 16% 11%	2147
	11th to 20th	Day	51% 6% 10% 19% 12% 2	2134
	21st to end	Day	55% 5% 10% 17% 12% 1	2324
May	1st to 10th	Day	56% 6% 10% 18% 9% 2	2340
	11th to 20th	Day	53% 6% 9% 18% 12% 1	2454
	21st to end	Day	43% 8% 16% 21% 12% 1	2725
June	1st to 10th	Day	48% 5% 12% 20% 13% 1	2520
	11th to 20th	Day	47% 8% 13% 21% 11%	2520
	21st to end	Day	45% 8% 12% 23% 12%	2520
July	1st to 10th	Day	42% 9% 11% 24% 13% 1	2450
	11th to 20th	Day	44% 9% 16% 20% 11%	2445
	21st to end	Day	46% 9% 13% 18% 12% 1	2405
August	1st to 10th	Day	42% 9% 14% 25% 9%	2314
	11th to 20th	Day	49% 10% 13% 20% 8%	2303
	21st to end	Day	46% 8% 12% 23% 10% 1	2421
September	1st to 10th	Day	48% 7% 10% 22% 12% 1	2160
	11th to 20th	Day	43% 6% 12% 24% 14% 1	2098
	21st to end	Day	51% 7% 11% 21% 10% 1	1916
October	1st to 10th	Day	53% 6% 12% 16% 11% 2	1800
	11th to 20th	Day	60% 5% 12% 16% 7% 1	1800
	21st to end	Day	66% 4 10% 12% 7% 1	1980
November	1st to 10th	Day	55% 5% 11% 15% 11% 2	1698
	11th to 20th	Day	64% 5% 10% 13% 6% 2	1520
	21st to end	Day	71% 4 10% 11% 4 1	1520
December	1st to 10th	Day	79% 4 7% 8% 2	1520
	11th to 20th	Day	74% 5% 10% 8% 2 1	1906
	21st to end	Day	79% 4 9% 7% 1	2772
January	1st to 10th	Night	78% 4 7% 7% 4	2649
	11th to 20th	Night	76% 4 10% 7% 3 1	2490
	21st to end	Night	77% 4 8% 8% 3 1	2664
February	1st to 10th	Night	75% 3 10% 8% 3	2340
	11th to 20th	Night	74% 4 7% 11% 4	2275
	21st to end	Night	70% 4 7% 11% 7% 1	1839
March	1st to 10th	Night	65% 5% 8% 17% 5%	1980
	11th to 20th	Night	60% 5% 9% 17% 9% 1	1980
	21st to end	Night	61% 4 7% 14% 12% 2	2178
April	1st to 10th	Night	58% 5% 10% 16% 10%	1812
	11th to 20th	Night	52% 6% 11% 17% 14% 2	1775
	21st to end	Night	52% 6% 10% 19% 11% 2	1652
May	1st to 10th	Night	51% 8% 9% 19% 11% 2	1620
	11th to 20th	Night	48% 8% 9% 21% 12% 2	1444
	21st to end	Night	37% 8% 14% 25% 13% 2	1551
June	1st to 10th	Night	44% 7% 12% 23% 14%	1440
	11th to 20th	Night	41% 8% 13% 23% 14% 2	1440
	21st to end	Night	40% 7% 12% 28% 11% 1	1440
July	1st to 10th	Night	35% 8% 14% 23% 18% 1	1400
	11th to 20th	Night	36% 8% 13% 27% 15% 2	1392
	21st to end	Night	38% 9% 16% 21% 15% 1	1668
August	1st to 10th	Night	35% 9% 15% 31% 9% 1	1600
	11th to 20th	Night	41% 10% 16% 25% 9%	1598
	21st to end	Night	38% 9% 15% 25% 11% 2	1916
September	1st to 10th	Night	41% 7% 14% 24% 12% 2	1800
	11th to 20th	Night	38% 6% 14% 25% 16% 1	1858
	21st to end	Night	48% 8% 12% 19% 12% 1	2043
October	1st to 10th	Night	48% 6% 12% 19% 14% 1	2160
	11th to 20th	Night	55% 6% 12% 16% 9% 1	2160
	21st to end	Night	62% 5% 11% 14% 7% 1	2376
November	1st to 10th	Night	51% 6% 11% 19% 10% 3	2377
	11th to 20th	Night	63% 5% 11% 13% 6% 3	2660
	21st to end	Night	69% 5% 11% 12% 3	2660
December	1st to 10th	Night	81% 4 6% 7% 2	2660
	11th to 20th	Night	77% 3 9% 8% 2	3288
	21st to end	Night	80% 5% 8% 7% 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	30% 31% 26% 10% 3 1	180
	11th to 20th	Day	36% 33% 23% 6% 2	258
	21st to end	Day	30% 33% 27% 8% 2	282
February	1st to 10th	Day	40% 28% 29% 2	240
	11th to 20th	Day	36% 34% 28% 3	240
	21st to end	Day	44% 25% 25% 6% 1	269
March	1st to 10th	Day	34% 23% 28% 12% 3	420
	11th to 20th	Day	30% 26% 30% 11% 2 1	420
	21st to end	Day	36% 23% 23% 14% 4 1	462
April	1st to 10th	Day	31% 24% 24% 14% 5% 1	420
	11th to 20th	Day	33% 22% 23% 11% 8% 3	412
	21st to end	Day	30% 18% 32% 15% 4 1	420
May	1st to 10th	Day	33% 20% 24% 15% 6% 2	423
	11th to 20th	Day	27% 15% 28% 20% 8% 1	447
	21st to end	Day	16% 15% 30% 20% 14% 5%	485
June	1st to 10th	Day	21% 18% 31% 20% 9% 2	450
	11th to 20th	Day	21% 13% 27% 24% 14% 2	450
	21st to end	Day	18% 14% 36% 23% 8% 2	450
July	1st to 10th	Day	13% 9% 28% 26% 18% 7%	445
	11th to 20th	Day	14% 9% 28% 28% 16% 5%	444
	21st to end	Day	14% 9% 37% 23% 12% 5%	488
August	1st to 10th	Day	11% 9% 29% 27% 16% 9%	446
	11th to 20th	Day	15% 9% 29% 25% 15% 8%	439
	21st to end	Day	17% 11% 27% 23% 14% 8%	495
September	1st to 10th	Day	21% 11% 23% 23% 15% 7%	450
	11th to 20th	Day	16% 9% 25% 21% 22% 8%	450
	21st to end	Day	20% 17% 27% 17% 14% 5%	450
October	1st to 10th	Day	25% 13% 26% 17% 14% 4	450
	11th to 20th	Day	31% 20% 28% 14% 6% 1	450
	21st to end	Day	39% 16% 27% 16% 2	495
November	1st to 10th	Day	29% 19% 27% 17% 6% 3	354
	11th to 20th	Day	41% 20% 26% 9% 2 1	180
	21st to end	Day	36% 24% 32% 7% 1	180
December	1st to 10th	Day	43% 23% 23% 5% 4 1	180
	11th to 20th	Day	39% 25% 28% 6% 1	180
	21st to end	Day	40% 24% 32% 3 1	198
January	1st to 10th	Night	31% 29% 26% 11% 3	760
	11th to 20th	Night	31% 26% 28% 13% 2	760
	21st to end	Night	25% 29% 30% 14% 2	820
February	1st to 10th	Night	32% 26% 29% 13% 1	720
	11th to 20th	Night	29% 27% 32% 11% 1	703
	21st to end	Night	33% 25% 29% 12% 2	592
March	1st to 10th	Night	28% 22% 34% 14% 3	720
	11th to 20th	Night	34% 19% 25% 18% 4 1	720
	21st to end	Night	24% 20% 34% 16% 6% 1	792
April	1st to 10th	Night	28% 19% 29% 20% 3	720
	11th to 20th	Night	29% 17% 27% 19% 7% 1	711
	21st to end	Night	23% 12% 31% 28% 6%	572
May	1st to 10th	Night	22% 12% 24% 29% 13%	540
	11th to 20th	Night	16% 11% 30% 35% 8%	382
	21st to end	Night	16% 9% 24% 31% 17% 2	389
June	1st to 10th	Night	15% 6% 28% 37% 13% 1	360
	11th to 20th	Night	19% 9% 22% 38% 12%	360
	21st to end	Night	14% 6% 32% 34% 14%	360
July	1st to 10th	Night	11% 6% 17% 45% 17% 4	350
	11th to 20th	Night	12% 3 24% 37% 23% 1	348
	21st to end	Night	15% 4 21% 36% 23% 1	586
August	1st to 10th	Night	12% 3 20% 36% 27% 2	537
	11th to 20th	Night	14% 4 18% 31% 30% 2	534
	21st to end	Night	13% 7% 22% 34% 22% 3	728
September	1st to 10th	Night	19% 8% 20% 30% 21% 2	720
	11th to 20th	Night	16% 8% 18% 27% 26% 4	720
	21st to end	Night	21% 11% 21% 26% 17% 3	720
October	1st to 10th	Night	24% 11% 24% 23% 16% 2	720
	11th to 20th	Night	29% 15% 29% 21% 6%	720
	21st to end	Night	36% 16% 27% 18% 3	792
November	1st to 10th	Night	27% 15% 28% 24% 7%	740
	11th to 20th	Night	31% 20% 27% 16% 5% 1	760
	21st to end	Night	30% 23% 28% 14% 4	760
December	1st to 10th	Night	36% 25% 26% 11% 3	760
	11th to 20th	Night	33% 25% 27% 12% 2	760
	21st to end	Night	34% 24% 30% 12% 1	836

Page generated at 2024-01-24 09:37:29. Version ac07

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