Gateway
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gateway clear sky chart from 2005-11-06 to 2024-01-15.

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	3 5% 2 4 4 3 5% 5% 6% 8% 55%	74654
	Night	3 5% 2 4 4 3 4 4 5% 7% 58%	75129
Transparency	Day	26% 3 9% 24% 24% 14%	74379
	Night	24% 3 10% 26% 25% 12%	74925
Seeing	Day	7% 12% 28% 30% 18% 4	14083
	Night	6% 4 17% 41% 27% 5%	24400

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	3 5% 2 5% 5% 3 4 5% 7% 8% 53%	1708
	11th to 20th	Day	2 5% 2 5% 5% 3 4 5% 6% 7% 56%	1656
	21st to end	Day	4 9% 2 4 4 3 3 4 6% 7% 53%	1782
February	1st to 10th	Day	1 7% 2 5% 5% 2 5% 4 6% 10% 51%	1620
	11th to 20th	Day	4 8% 4 6% 4 3 5% 5% 5% 8% 48%	1575
	21st to end	Day	3 9% 3 6% 6% 3 4 5% 6% 8% 48%	1512
March	1st to 10th	Day	3 8% 3 6% 6% 4 5% 5% 5% 7% 49%	1980
	11th to 20th	Day	3 6% 3 5% 5% 2 5% 5% 6% 7% 52%	1980
	21st to end	Day	4 8% 3 6% 6% 3 5% 5% 5% 7% 48%	2178
April	1st to 10th	Day	4 5% 2 5% 5% 3 5% 4 6% 7% 54%	2110
	11th to 20th	Day	4 4 2 5% 5% 3 6% 5% 6% 8% 51%	2131
	21st to end	Day	3 5% 2 4 5% 4 6% 5% 5% 8% 54%	2224
May	1st to 10th	Day	4 4 2 4 6% 3 6% 7% 7% 8% 49%	2340
	11th to 20th	Day	4 5% 2 3 5% 3 5% 6% 7% 9% 50%	2301
	21st to end	Day	4 4 2 4 4 3 5% 5% 7% 9% 53%	2649
June	1st to 10th	Day	3 3 1 2 3 2 4 3 6% 8% 65%	2520
	11th to 20th	Day	3 3 1 3 3 2 3 4 4 5% 70%	2520
	21st to end	Day	1 2 1 3 3 3 3 4 4 7% 69%	2520
July	1st to 10th	Day	3 3 2 3 5% 3 5% 5% 7% 8% 55%	2404
	11th to 20th	Day	3 2 2 4 5% 4 6% 6% 8% 11% 50%	2340
	21st to end	Day	4 3 2 5% 6% 4 7% 8% 9% 12% 41%	2545
August	1st to 10th	Day	5% 4 2 5% 6% 4 7% 7% 9% 9% 43%	2328
	11th to 20th	Day	3 3 2 4 5% 4 5% 5% 7% 8% 55%	2299
	21st to end	Day	3 3 1 4 5% 4 6% 5% 6% 8% 54%	2386
September	1st to 10th	Day	5% 3 1 3 4 3 4 5% 5% 7% 61%	2160
	11th to 20th	Day	4 3 1 4 5% 3 4 5% 6% 7% 58%	2051
	21st to end	Day	5% 3 1 4 3 2 2 3 4 7% 67%	1954
October	1st to 10th	Day	7% 4 2 5% 4 2 5% 4 5% 6% 57%	1800
	11th to 20th	Day	3 3 1 2 3 2 3 3 4 6% 70%	1800
	21st to end	Day	3 3 1 3 4 2 3 4 5% 6% 65%	1980
November	1st to 10th	Day	3 3 2 3 3 2 4 4 4 6% 68%	1859
	11th to 20th	Day	3 3 2 3 3 2 3 3 4 6% 67%	1639
	21st to end	Day	4 5% 1 4 4 2 4 3 5% 7% 62%	1520
December	1st to 10th	Day	3 5% 2 6% 5% 3 4 4 4 7% 56%	1520
	11th to 20th	Day	4 8% 3 5% 6% 3 5% 6% 6% 8% 48%	1926
	21st to end	Day	4 8% 3 5% 4 2 5% 5% 5% 8% 51%	2837
January	1st to 10th	Night	3 5% 2 4 4 3 4 5% 5% 6% 57%	2457
	11th to 20th	Night	2 6% 3 4 5% 3 4 5% 4 7% 58%	2392
	21st to end	Night	4 7% 3 5% 4 3 3 5% 6% 7% 53%	2574
February	1st to 10th	Night	2 4 2 4 4 3 5% 4 6% 8% 58%	2340
	11th to 20th	Night	4 7% 3 5% 4 2 5% 4 5% 8% 53%	2272
	21st to end	Night	3 7% 3 6% 5% 3 4 4 5% 7% 52%	1739
March	1st to 10th	Night	4 6% 2 4 5% 3 5% 5% 4 7% 55%	1980
	11th to 20th	Night	3 5% 2 5% 4 2 4 4 6% 6% 58%	1980
	21st to end	Night	3 6% 3 5% 5% 3 6% 5% 6% 8% 50%	2178
April	1st to 10th	Night	4 6% 2 4 5% 3 6% 5% 5% 7% 53%	1850
	11th to 20th	Night	4 6% 2 4 4 3 5% 5% 5% 8% 54%	1777
	21st to end	Night	4 4 3 4 4 3 5% 5% 6% 10% 52%	1732
May	1st to 10th	Night	5% 4 2 6% 5% 3 6% 5% 5% 8% 52%	1620
	11th to 20th	Night	4 5% 2 4 4 3 4 5% 5% 8% 58%	1594
	21st to end	Night	6% 3 2 4 5% 3 4 5% 5% 7% 57%	1622
June	1st to 10th	Night	2 2 1 2 3 3 5% 4 5% 9% 65%	1440
	11th to 20th	Night	4 2 2 3 3 1 4 4 5% 7% 65%	1440
	21st to end	Night	3 2 1 2 3 1 3 4 4 8% 70%	1440
July	1st to 10th	Night	3 2 2 3 4 3 5% 5% 6% 9% 59%	1551
	11th to 20th	Night	2 2 2 4 5% 3 6% 6% 8% 11% 51%	1620
	21st to end	Night	3 4 2 5% 5% 3 6% 7% 8% 12% 44%	1773
August	1st to 10th	Night	2 3 2 4 6% 3 6% 6% 7% 10% 51%	1611
	11th to 20th	Night	3 3 2 4 4 3 3 5% 5% 9% 58%	1602
	21st to end	Night	2 3 2 4 4 2 5% 5% 7% 8% 57%	1968
September	1st to 10th	Night	4 3 1 3 4 2 5% 4 6% 7% 61%	1800
	11th to 20th	Night	3 2 1 3 3 2 3 3 5% 8% 65%	1906
	21st to end	Night	5% 3 1 3 3 2 3 3 3 6% 70%	2006
October	1st to 10th	Night	6% 3 1 4 4 2 4 4 4 6% 62%	2160
	11th to 20th	Night	3 3 1 2 2 2 3 3 4 5% 73%	2160
	21st to end	Night	4 4 2 3 3 2 3 3 4 4 69%	2376
November	1st to 10th	Night	3 4 1 3 3 2 3 4 5% 6% 67%	2220
	11th to 20th	Night	3 3 2 2 4 2 3 3 4 6% 69%	2514
	21st to end	Night	4 5% 3 4 4 2 3 4 4 7% 59%	2660
December	1st to 10th	Night	4 7% 2 3 4 2 4 4 4 7% 58%	2660
	11th to 20th	Night	4 8% 3 4 5% 3 4 6% 7% 10% 48%	3271
	21st to end	Night	4 8% 3 5% 4 3 4 5% 4 7% 53%	4844

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	27% 4 22% 34% 12% 1	1709
	11th to 20th	Day	25% 3 17% 36% 18% 2	1656
	21st to end	Day	29% 4 14% 36% 13% 4	1782
February	1st to 10th	Day	27% 3 21% 26% 20% 3	1620
	11th to 20th	Day	33% 3 11% 28% 22% 3	1584
	21st to end	Day	33% 3 9% 28% 22% 6%	1512
March	1st to 10th	Day	33% 3 8% 29% 23% 4	1980
	11th to 20th	Day	29% 2 8% 36% 18% 6%	1980
	21st to end	Day	34% 2 8% 30% 20% 5%	2178
April	1st to 10th	Day	28% 3 8% 25% 25% 12%	2110
	11th to 20th	Day	28% 4 7% 26% 26% 10%	2134
	21st to end	Day	26% 3 6% 27% 31% 8%	2224
May	1st to 10th	Day	27% 4 7% 23% 29% 10%	2340
	11th to 20th	Day	28% 3 6% 24% 28% 10%	2304
	21st to end	Day	25% 4 6% 20% 32% 13%	2649
June	1st to 10th	Day	17% 2 4 20% 34% 23%	2520
	11th to 20th	Day	17% 3 3 11% 26% 40%	2520
	21st to end	Day	15% 3 2 14% 24% 43%	2520
July	1st to 10th	Day	24% 5% 6% 13% 19% 32%	2340
	11th to 20th	Day	24% 4 11% 20% 19% 21%	2271
	21st to end	Day	30% 5% 16% 21% 15% 12%	2404
August	1st to 10th	Day	32% 6% 11% 17% 16% 18%	2313
	11th to 20th	Day	27% 3 7% 18% 23% 23%	2299
	21st to end	Day	25% 4 6% 20% 24% 19%	2386
September	1st to 10th	Day	23% 3 6% 13% 25% 30%	2160
	11th to 20th	Day	24% 4 7% 18% 24% 24%	2051
	21st to end	Day	19% 2 5% 15% 41% 18%	1954
October	1st to 10th	Day	28% 2 7% 22% 27% 13%	1800
	11th to 20th	Day	16% 3 3 24% 40% 14%	1800
	21st to end	Day	20% 3 8% 31% 30% 7%	1980
November	1st to 10th	Day	19% 3 7% 31% 32% 8%	1859
	11th to 20th	Day	19% 2 8% 37% 30% 3	1639
	21st to end	Day	23% 2 12% 32% 27% 5%	1520
December	1st to 10th	Day	28% 3 19% 28% 17% 4	1520
	11th to 20th	Day	32% 4 14% 37% 12% 1	1924
	21st to end	Day	31% 2 16% 19% 26% 4	2837
January	1st to 10th	Night	25% 2 19% 37% 14% 2	2457
	11th to 20th	Night	25% 3 17% 37% 16% 2	2392
	21st to end	Night	30% 3 14% 35% 15% 4	2574
February	1st to 10th	Night	22% 3 18% 36% 17% 3	2340
	11th to 20th	Night	29% 3 11% 30% 23% 4	2273
	21st to end	Night	30% 2 8% 30% 25% 4	1739
March	1st to 10th	Night	28% 2 10% 29% 29% 3	1980
	11th to 20th	Night	25% 2 6% 34% 28% 5%	1980
	21st to end	Night	31% 4 9% 32% 20% 4	2178
April	1st to 10th	Night	29% 2 6% 25% 27% 11%	1850
	11th to 20th	Night	27% 3 7% 23% 29% 11%	1777
	21st to end	Night	26% 3 7% 27% 31% 8%	1732
May	1st to 10th	Night	29% 4 9% 18% 30% 10%	1620
	11th to 20th	Night	24% 3 7% 26% 31% 8%	1595
	21st to end	Night	26% 3 6% 18% 33% 14%	1622
June	1st to 10th	Night	16% 3 3 18% 35% 26%	1440
	11th to 20th	Night	18% 2 5% 13% 20% 41%	1440
	21st to end	Night	14% 2 2 12% 25% 45%	1440
July	1st to 10th	Night	20% 4 8% 14% 18% 36%	1506
	11th to 20th	Night	23% 4 9% 23% 18% 23%	1566
	21st to end	Night	30% 3 19% 20% 16% 12%	1674
August	1st to 10th	Night	25% 4 14% 20% 20% 17%	1602
	11th to 20th	Night	22% 3 9% 20% 18% 28%	1602
	21st to end	Night	22% 3 8% 19% 24% 24%	1968
September	1st to 10th	Night	21% 3 7% 15% 21% 34%	1800
	11th to 20th	Night	18% 2 10% 20% 22% 27%	1906
	21st to end	Night	17% 2 5% 14% 39% 22%	2006
October	1st to 10th	Night	24% 2 6% 21% 29% 18%	2160
	11th to 20th	Night	14% 2 4 23% 38% 18%	2160
	21st to end	Night	19% 2 6% 32% 32% 9%	2376
November	1st to 10th	Night	18% 2 8% 28% 32% 11%	2220
	11th to 20th	Night	17% 3 8% 35% 33% 5%	2514
	21st to end	Night	25% 2 8% 29% 28% 8%	2660
December	1st to 10th	Night	26% 3 17% 29% 21% 5%	2660
	11th to 20th	Night	30% 4 14% 35% 16% 1	3272
	21st to end	Night	31% 3 15% 23% 24% 5%	4844

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	9% 9% 34% 29% 16% 4	270
	11th to 20th	Day	10% 6% 38% 29% 14% 2	252
	21st to end	Day	5% 9% 33% 37% 16% 1	264
February	1st to 10th	Day	5% 17% 37% 30% 10% 1	240
	11th to 20th	Day	9% 14% 39% 26% 11% 1	240
	21st to end	Day	11% 20% 33% 24% 10% 1	270
March	1st to 10th	Day	13% 23% 33% 23% 7% 2	420
	11th to 20th	Day	12% 18% 34% 25% 10% 2	420
	21st to end	Day	11% 34% 31% 19% 5%	462
April	1st to 10th	Day	12% 20% 35% 21% 10% 2	420
	11th to 20th	Day	15% 26% 34% 17% 6% 1	412
	21st to end	Day	12% 24% 32% 24% 7% 1	420
May	1st to 10th	Day	10% 24% 36% 20% 8% 1	423
	11th to 20th	Day	6% 16% 34% 28% 14% 2	448
	21st to end	Day	8% 14% 28% 27% 18% 4	604
June	1st to 10th	Day	4 9% 25% 35% 23% 4	630
	11th to 20th	Day	7% 9% 28% 31% 21% 4	630
	21st to end	Day	3 9% 26% 36% 22% 4	630
July	1st to 10th	Day	2 5% 20% 38% 29% 7%	510
	11th to 20th	Day	2 2 16% 42% 31% 7%	444
	21st to end	Day	5% 1 12% 38% 37% 6%	487
August	1st to 10th	Day	6% 2 21% 38% 28% 6%	447
	11th to 20th	Day	4 3 20% 38% 29% 6%	437
	21st to end	Day	5% 2 21% 38% 30% 4	495
September	1st to 10th	Day	5% 4 25% 33% 24% 9%	450
	11th to 20th	Day	5% 8% 27% 36% 18% 5%	450
	21st to end	Day	8% 12% 19% 33% 21% 7%	424
October	1st to 10th	Day	13% 12% 24% 19% 20% 13%	270
	11th to 20th	Day	6% 9% 27% 29% 23% 6%	270
	21st to end	Day	5% 15% 27% 32% 19% 1	297
November	1st to 10th	Day	7% 16% 26% 28% 18% 4	270
	11th to 20th	Day	5% 10% 31% 36% 13% 6%	270
	21st to end	Day	7% 13% 29% 29% 17% 5%	270
December	1st to 10th	Day	8% 9% 33% 29% 16% 6%	270
	11th to 20th	Day	6% 12% 31% 31% 17% 3	270
	21st to end	Day	12% 12% 35% 29% 8% 3	297
January	1st to 10th	Night	5% 3 18% 46% 24% 4	760
	11th to 20th	Night	5% 4 20% 42% 25% 3	736
	21st to end	Night	7% 4 21% 45% 20% 4	792
February	1st to 10th	Night	3 3 26% 48% 17% 3	720
	11th to 20th	Night	7% 5% 25% 45% 16% 3	704
	21st to end	Night	6% 5% 27% 49% 11% 2	592
March	1st to 10th	Night	7% 5% 26% 45% 16% 2	720
	11th to 20th	Night	6% 5% 18% 45% 24% 3	720
	21st to end	Night	7% 7% 25% 44% 16% 2	792
April	1st to 10th	Night	6% 9% 26% 43% 15% 1	590
	11th to 20th	Night	10% 9% 25% 39% 15% 2	533
	21st to end	Night	6% 9% 27% 36% 18% 5%	540
May	1st to 10th	Night	7% 8% 18% 44% 21% 2	540
	11th to 20th	Night	5% 5% 15% 41% 29% 5%	531
	21st to end	Night	8% 6% 20% 34% 27% 4	584
June	1st to 10th	Night	3 3 16% 40% 34% 5%	540
	11th to 20th	Night	5% 4 16% 44% 26% 4	540
	21st to end	Night	4 1 9% 41% 39% 6%	540
July	1st to 10th	Night	3 2 6% 32% 48% 9%	525
	11th to 20th	Night	2 2 3 33% 50% 11%	522
	21st to end	Night	4 2 3 25% 55% 12%	591
August	1st to 10th	Night	3 2 4 31% 51% 9%	537
	11th to 20th	Night	5% 5% 40% 42% 8%	534
	21st to end	Night	4 1 5% 36% 44% 11%	594
September	1st to 10th	Night	5% 2 7% 38% 40% 8%	540
	11th to 20th	Night	4 2 10% 40% 36% 8%	646
	21st to end	Night	7% 2 13% 32% 36% 11%	720
October	1st to 10th	Night	8% 3 15% 38% 28% 7%	720
	11th to 20th	Night	4 3 14% 42% 29% 7%	720
	21st to end	Night	7% 4 16% 40% 28% 6%	792
November	1st to 10th	Night	5% 3 16% 42% 28% 5%	740
	11th to 20th	Night	4 2 19% 48% 22% 5%	866
	21st to end	Night	7% 6% 20% 39% 23% 4	950
December	1st to 10th	Night	7% 3 20% 48% 19% 3	950
	11th to 20th	Night	10% 4 22% 41% 21% 2	950
	21st to end	Night	10% 6% 22% 45% 14% 2	1029

Page generated at 2024-01-11 20:33:46. Version ac07

Copyright 2024 Attilla Danko