York Factory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the York Factory clear sky chart from 2005-11-06 to 2025-02-25.

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% 11% 4 11% 6% 6% 6% 5% 7% 7% 24%	108401
	Night	10% 12% 5% 13% 8% 7% 7% 6% 7% 7% 18%	110480
Transparency	Day	58% 5% 12% 19% 5%	111653
	Night	63% 5% 11% 16% 5%	115399
Seeing	Day	17% 5% 20% 31% 21% 7%	16193
	Night	17% 4 21% 34% 20% 4	25403

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	5% 10% 6% 19% 11% 8% 9% 5% 8% 6% 14%	2719
	11th to 20th	Day	3 9% 5% 16% 11% 13% 10% 7% 8% 6% 11%	2853
	21st to end	Day	6% 11% 6% 13% 7% 6% 10% 10% 11% 8% 12%	3498
February	1st to 10th	Day	2 9% 3 15% 10% 9% 8% 8% 9% 8% 17%	1465
	11th to 20th	Day	3 10% 4 9% 8% 9% 10% 7% 12% 11% 17%	1709
	21st to end	Day	3 10% 5% 9% 7% 10% 8% 8% 13% 9% 19%	1449
March	1st to 10th	Day	7% 11% 4 9% 6% 6% 8% 8% 10% 12% 19%	3045
	11th to 20th	Day	8% 14% 5% 15% 12% 9% 7% 7% 8% 5% 11%	3468
	21st to end	Day	5% 11% 4 11% 10% 8% 11% 7% 7% 6% 18%	4005
April	1st to 10th	Day	8% 11% 4 10% 8% 10% 8% 6% 6% 6% 22%	2304
	11th to 20th	Day	9% 10% 4 9% 8% 8% 8% 5% 6% 7% 27%	2506
	21st to end	Day	6% 9% 3 11% 10% 8% 6% 4 6% 7% 29%	2660
May	1st to 10th	Day	21% 18% 6% 18% 5% 4 3 3 3 4 15%	4516
	11th to 20th	Day	19% 12% 5% 11% 5% 4 4 4 5% 6% 25%	4950
	21st to end	Day	15% 12% 5% 12% 5% 5% 5% 4 6% 8% 24%	5521
June	1st to 10th	Day	16% 12% 5% 10% 5% 4 4 4 5% 8% 29%	3040
	11th to 20th	Day	15% 7% 2 6% 5% 5% 5% 4 6% 8% 37%	3088
	21st to end	Day	13% 7% 3 8% 5% 5% 6% 4 7% 7% 35%	3230
July	1st to 10th	Day	12% 8% 3 8% 6% 5% 5% 4 7% 9% 32%	5078
	11th to 20th	Day	14% 8% 2 7% 5% 4 4 4 6% 8% 38%	5070
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 5% 6% 10% 36%	5284
August	1st to 10th	Day	15% 5% 2 6% 4 4 5% 5% 7% 9% 40%	4686
	11th to 20th	Day	15% 7% 2 7% 4 4 4 3 5% 7% 41%	4356
	21st to end	Day	22% 8% 2 8% 4 4 4 4 6% 8% 30%	4638
September	1st to 10th	Day	23% 11% 4 9% 4 5% 5% 3 5% 7% 23%	2313
	11th to 20th	Day	22% 13% 4 9% 5% 5% 4 3 5% 7% 23%	2280
	21st to end	Day	18% 16% 3 8% 5% 3 4 3 5% 6% 26%	1990
October	1st to 10th	Day	21% 20% 4 10% 5% 4 4 3 4 5% 20%	1900
	11th to 20th	Day	26% 18% 6% 10% 4 5% 4 3 4 5% 14%	1808
	21st to end	Day	20% 22% 8% 13% 5% 4 3 2 4 4 16%	1679
November	1st to 10th	Day	14% 19% 8% 14% 8% 6% 6% 4 4 4 13%	1561
	11th to 20th	Day	11% 20% 7% 13% 9% 6% 6% 4 5% 6% 13%	1324
	21st to end	Day	8% 22% 9% 14% 8% 7% 8% 5% 7% 5% 8%	1200
December	1st to 10th	Day	4 16% 6% 22% 10% 6% 6% 5% 9% 8% 8%	1960
	11th to 20th	Day	8% 14% 7% 17% 8% 7% 6% 5% 9% 7% 11%	2256
	21st to end	Day	9% 20% 8% 16% 7% 7% 7% 5% 5% 5% 12%	2992
January	1st to 10th	Night	5% 12% 5% 16% 10% 9% 9% 7% 8% 8% 11%	7247
	11th to 20th	Night	3 8% 5% 20% 13% 16% 11% 6% 8% 5% 7%	7049
	21st to end	Night	7% 13% 5% 12% 8% 7% 10% 9% 11% 7% 11%	7480
February	1st to 10th	Night	4 9% 4 12% 10% 10% 11% 9% 11% 7% 13%	2935
	11th to 20th	Night	3 9% 4 9% 8% 10% 10% 8% 12% 8% 17%	2574
	21st to end	Night	4 10% 5% 10% 6% 7% 8% 10% 13% 10% 17%	2100
March	1st to 10th	Night	4 9% 3 9% 6% 7% 8% 9% 10% 11% 22%	3796
	11th to 20th	Night	6% 14% 6% 17% 11% 9% 6% 5% 7% 5% 14%	3521
	21st to end	Night	5% 10% 5% 11% 10% 9% 9% 8% 8% 7% 19%	3626
April	1st to 10th	Night	8% 12% 3 10% 8% 6% 9% 5% 7% 6% 26%	1874
	11th to 20th	Night	9% 10% 4 10% 7% 7% 7% 3 6% 7% 31%	1625
	21st to end	Night	7% 10% 4 10% 8% 7% 5% 4 6% 6% 35%	1520
May	1st to 10th	Night	20% 14% 6% 21% 6% 3 3 2 3 4 17%	2433
	11th to 20th	Night	18% 11% 5% 12% 5% 4 4 3 4 4 29%	1954
	21st to end	Night	18% 10% 5% 11% 6% 5% 5% 3 6% 8% 24%	2066
June	1st to 10th	Night	17% 9% 4 8% 5% 4 5% 4 5% 7% 32%	1140
	11th to 20th	Night	13% 7% 2 8% 7% 5% 6% 4 7% 7% 34%	1084
	21st to end	Night	10% 11% 3 8% 6% 6% 5% 4 6% 8% 33%	950
July	1st to 10th	Night	13% 9% 4 9% 6% 5% 6% 4 7% 9% 28%	1887
	11th to 20th	Night	13% 8% 3 8% 4 5% 6% 5% 5% 9% 34%	1900
	21st to end	Night	10% 6% 3 8% 6% 6% 6% 5% 7% 9% 34%	2278
August	1st to 10th	Night	14% 6% 2 6% 4 5% 5% 4 6% 8% 38%	2253
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 6% 8% 43%	2483
	21st to end	Night	20% 7% 2 5% 4 4 5% 4 5% 8% 37%	3026
September	1st to 10th	Night	21% 10% 3 8% 7% 5% 4 3 6% 7% 26%	1867
	11th to 20th	Night	21% 11% 2 7% 5% 5% 6% 4 6% 7% 26%	1900
	21st to end	Night	19% 17% 5% 7% 4 4 4 3 4 6% 28%	2166
October	1st to 10th	Night	25% 18% 5% 9% 4 4 4 4 4 5% 20%	2280
	11th to 20th	Night	24% 21% 5% 9% 5% 4 3 2 4 5% 18%	2372
	21st to end	Night	21% 21% 7% 10% 6% 5% 4 2 3 5% 16%	2916
November	1st to 10th	Night	14% 20% 8% 15% 7% 6% 5% 4 5% 5% 12%	2736
	11th to 20th	Night	11% 17% 6% 13% 8% 8% 7% 5% 5% 5% 15%	3075
	21st to end	Night	9% 20% 7% 16% 8% 6% 6% 5% 6% 6% 11%	3200
December	1st to 10th	Night	4 14% 7% 21% 9% 8% 7% 6% 10% 7% 7%	5230
	11th to 20th	Night	6% 14% 7% 15% 10% 10% 9% 8% 8% 6% 8%	5951
	21st to end	Night	9% 16% 8% 16% 7% 7% 8% 4 6% 5% 14%	7986

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	68% 4 10% 14% 5%	2720
	11th to 20th	Day	69% 5% 9% 15% 2	2878
	21st to end	Day	63% 4 7% 19% 8%	3498
February	1st to 10th	Day	58% 6% 11% 20% 5%	1465
	11th to 20th	Day	53% 6% 15% 20% 6%	1718
	21st to end	Day	53% 6% 9% 19% 14%	1449
March	1st to 10th	Day	52% 6% 11% 26% 5%	3047
	11th to 20th	Day	71% 4 8% 12% 5%	3468
	21st to end	Day	60% 7% 9% 15% 7% 1	4005
April	1st to 10th	Day	60% 7% 7% 19% 7%	2304
	11th to 20th	Day	55% 7% 10% 20% 7% 1	2506
	21st to end	Day	53% 7% 13% 19% 8% 1	2660
May	1st to 10th	Day	74% 5% 6% 12% 2	4528
	11th to 20th	Day	59% 5% 8% 15% 13%	4954
	21st to end	Day	57% 6% 11% 22% 5%	5521
June	1st to 10th	Day	54% 5% 11% 22% 7%	3040
	11th to 20th	Day	43% 6% 12% 28% 10% 1	3088
	21st to end	Day	45% 8% 12% 27% 8%	3230
July	1st to 10th	Day	49% 6% 16% 22% 7%	4999
	11th to 20th	Day	44% 5% 22% 28% 2	4983
	21st to end	Day	43% 6% 21% 26% 4	5116
August	1st to 10th	Day	42% 5% 22% 28% 3	4669
	11th to 20th	Day	44% 5% 15% 25% 11%	4398
	21st to end	Day	53% 5% 17% 22% 3	4637
September	1st to 10th	Day	60% 8% 17% 14% 2	2313
	11th to 20th	Day	63% 6% 14% 16% 2	2280
	21st to end	Day	58% 7% 14% 17% 4	1990
October	1st to 10th	Day	67% 4 6% 20% 2	3160
	11th to 20th	Day	66% 5% 8% 18% 3	2985
	21st to end	Day	72% 4 10% 11% 4	2751
November	1st to 10th	Day	76% 8% 7% 7% 2	1561
	11th to 20th	Day	73% 7% 9% 10% 1	1324
	21st to end	Day	73% 8% 9% 9% 1	1200
December	1st to 10th	Day	74% 4 12% 9% 2	1960
	11th to 20th	Day	71% 4 7% 16% 2	2256
	21st to end	Day	74% 5% 8% 11% 3	2992
January	1st to 10th	Night	69% 5% 9% 11% 6%	7247
	11th to 20th	Night	77% 4 11% 8% 1	7099
	21st to end	Night	65% 3 7% 18% 7%	7480
February	1st to 10th	Night	60% 6% 11% 17% 5%	2935
	11th to 20th	Night	55% 7% 13% 19% 6%	2575
	21st to end	Night	51% 7% 11% 21% 10%	2100
March	1st to 10th	Night	48% 7% 15% 23% 7%	3807
	11th to 20th	Night	68% 5% 8% 14% 4	3522
	21st to end	Night	59% 4 8% 17% 11% 1	3626
April	1st to 10th	Night	55% 6% 9% 20% 10%	1874
	11th to 20th	Night	53% 4 9% 21% 11% 1	1625
	21st to end	Night	49% 7% 12% 23% 9% 1	1520
May	1st to 10th	Night	73% 4 7% 14% 3	2440
	11th to 20th	Night	58% 4 8% 15% 16%	1955
	21st to end	Night	56% 6% 10% 22% 5%	2066
June	1st to 10th	Night	51% 6% 8% 25% 10%	1140
	11th to 20th	Night	47% 6% 10% 23% 14% 1	1084
	21st to end	Night	47% 8% 10% 24% 10% 1	950
July	1st to 10th	Night	52% 6% 12% 24% 6%	1857
	11th to 20th	Night	47% 4 19% 26% 3	1864
	21st to end	Night	46% 6% 20% 22% 6%	2206
August	1st to 10th	Night	43% 6% 23% 26% 3	2246
	11th to 20th	Night	40% 6% 14% 28% 13%	2507
	21st to end	Night	47% 4 19% 24% 6%	3026
September	1st to 10th	Night	58% 8% 15% 17% 2	1867
	11th to 20th	Night	57% 9% 16% 16% 3	1900
	21st to end	Night	59% 7% 12% 16% 5%	2166
October	1st to 10th	Night	66% 4 8% 18% 4	3800
	11th to 20th	Night	63% 3 11% 17% 5%	3934
	21st to end	Night	67% 4 7% 17% 5%	4804
November	1st to 10th	Night	76% 6% 9% 8% 1	2736
	11th to 20th	Night	72% 8% 9% 10% 1	3075
	21st to end	Night	71% 7% 11% 9% 1	3200
December	1st to 10th	Night	74% 5% 9% 11% 1	5230
	11th to 20th	Night	72% 5% 10% 11% 2	5950
	21st to end	Night	71% 6% 7% 14% 2	7986

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	7% 1 30% 38% 21% 5%	200
	11th to 20th	Day	6% 3 25% 40% 21% 4	235
	21st to end	Day	12% 4 18% 34% 27% 6%	330
February	1st to 10th	Day	6% 5% 19% 39% 27% 4	300
	11th to 20th	Day	8% 2 20% 40% 24% 7%	300
	21st to end	Day	6% 3 20% 33% 27% 11%	237
March	1st to 10th	Day	9% 2 17% 33% 23% 16%	270
	11th to 20th	Day	7% 4 23% 31% 21% 12%	270
	21st to end	Day	7% 5% 21% 30% 26% 10%	411
April	1st to 10th	Day	11% 3 18% 25% 31% 12%	484
	11th to 20th	Day	10% 4 22% 33% 23% 8%	640
	21st to end	Day	9% 5% 19% 33% 25% 9%	650
May	1st to 10th	Day	19% 6% 19% 30% 20% 7%	653
	11th to 20th	Day	18% 6% 27% 30% 16% 4	675
	21st to end	Day	18% 4 25% 32% 18% 2	734
June	1st to 10th	Day	20% 5% 21% 29% 20% 5%	680
	11th to 20th	Day	16% 3 19% 32% 23% 8%	680
	21st to end	Day	16% 3 17% 34% 23% 8%	680
July	1st to 10th	Day	21% 3 14% 32% 25% 6%	671
	11th to 20th	Day	16% 4 13% 33% 25% 8%	668
	21st to end	Day	18% 4 14% 30% 23% 10%	739
August	1st to 10th	Day	21% 3 15% 30% 23% 8%	676
	11th to 20th	Day	19% 4 14% 28% 23% 12%	665
	21st to end	Day	26% 4 15% 28% 20% 7%	748
September	1st to 10th	Day	28% 6% 20% 26% 15% 4	523
	11th to 20th	Day	24% 6% 22% 27% 17% 3	490
	21st to end	Day	28% 4 24% 28% 13% 3	338
October	1st to 10th	Day	19% 7% 28% 28% 15% 3	300
	11th to 20th	Day	32% 5% 23% 21% 14% 5%	300
	21st to end	Day	23% 8% 29% 22% 16% 2	330
November	1st to 10th	Day	18% 7% 27% 30% 14% 5%	296
	11th to 20th	Day	19% 7% 30% 32% 11% 2	200
	21st to end	Day	22% 13% 20% 24% 14% 9%	200
December	1st to 10th	Day	14% 5% 25% 35% 21% 2	200
	11th to 20th	Day	10% 7% 28% 35% 19% 3	200
	21st to end	Day	8% 6% 20% 33% 27% 7%	220
January	1st to 10th	Night	12% 4 23% 36% 19% 6%	1000
	11th to 20th	Night	9% 4 22% 38% 22% 4	1000
	21st to end	Night	11% 5% 21% 36% 23% 4	1100
February	1st to 10th	Night	7% 4 23% 37% 26% 3	1000
	11th to 20th	Night	7% 2 17% 42% 25% 6%	979
	21st to end	Night	8% 3 18% 41% 22% 9%	808
March	1st to 10th	Night	11% 2 20% 33% 28% 5%	812
	11th to 20th	Night	10% 5% 22% 37% 22% 4	599
	21st to end	Night	9% 4 23% 31% 26% 7%	627
April	1st to 10th	Night	13% 3 19% 35% 26% 5%	570
	11th to 20th	Night	13% 3 19% 36% 23% 5%	563
	21st to end	Night	9% 5% 22% 38% 23% 4	570
May	1st to 10th	Night	25% 4 19% 32% 18% 3	570
	11th to 20th	Night	20% 5% 22% 36% 15% 1	419
	21st to end	Night	22% 3 26% 34% 15%	411
June	1st to 10th	Night	19% 4 19% 38% 18% 2	380
	11th to 20th	Night	15% 4 19% 37% 24% 2	324
	21st to end	Night	14% 2 17% 44% 23% 2	190
July	1st to 10th	Night	20% 1 15% 38% 24% 2	357
	11th to 20th	Night	18% 4 13% 36% 25% 4	368
	21st to end	Night	19% 3 11% 31% 29% 6%	540
August	1st to 10th	Night	20% 3 13% 33% 28% 5%	567
	11th to 20th	Night	19% 2 14% 34% 27% 4	564
	21st to end	Night	26% 4 14% 35% 18% 3	627
September	1st to 10th	Night	27% 2 23% 33% 13% 2	570
	11th to 20th	Night	28% 5% 23% 26% 16% 2	570
	21st to end	Night	28% 6% 24% 28% 13% 1	688
October	1st to 10th	Night	35% 7% 22% 25% 9% 1	760
	11th to 20th	Night	35% 6% 18% 26% 12% 3	760
	21st to end	Night	31% 6% 26% 25% 10% 3	1035
November	1st to 10th	Night	23% 7% 28% 27% 12% 2	975
	11th to 20th	Night	18% 5% 30% 31% 14% 2	1000
	21st to end	Night	17% 9% 25% 33% 12% 5%	1000
December	1st to 10th	Night	12% 4 29% 36% 17% 3	1000
	11th to 20th	Night	11% 4 23% 35% 24% 4	1000
	21st to end	Night	12% 3 22% 35% 20% 7%	1100

Page generated at 2025-02-22 05:51:37. Version ac07

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