90W 45N Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 90W 45N Park clear sky chart from 2005-11-06 to 2026-07-16.

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 8% 5% 4 5% 4 6% 7% 37%	138560
	Night	12% 10% 4 9% 5% 4 4 4 5% 7% 37%	134450
Transparency	Day	45% 5% 12% 25% 13% 1	142020
	Night	47% 4 11% 23% 13% 1	139066
Seeing	Day	17% 11% 30% 25% 13% 4	18366
	Night	17% 9% 32% 30% 11% 1	28222

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	8% 14% 6% 16% 7% 5% 5% 3 4 6% 25%	4691
	11th to 20th	Day	7% 14% 6% 13% 6% 6% 6% 7% 7% 6% 22%	4710
	21st to end	Day	7% 12% 6% 13% 4 4 6% 4 5% 7% 32%	5294
February	1st to 10th	Day	9% 12% 5% 11% 5% 6% 6% 5% 5% 7% 30%	1890
	11th to 20th	Day	9% 12% 4 9% 6% 4 4 4 6% 8% 34%	1900
	21st to end	Day	11% 11% 4 10% 7% 6% 6% 4 5% 7% 28%	1730
March	1st to 10th	Day	13% 9% 3 5% 3 4 4 3 4 7% 46%	4580
	11th to 20th	Day	11% 8% 3 8% 5% 4 5% 4 6% 8% 37%	4987
	21st to end	Day	22% 11% 4 9% 6% 4 3 3 4 5% 29%	5975
April	1st to 10th	Day	16% 14% 4 8% 5% 4 4 3 5% 7% 31%	2520
	11th to 20th	Day	20% 11% 3 7% 5% 4 4 4 5% 6% 30%	2494
	21st to end	Day	19% 11% 3 8% 5% 5% 5% 4 4 6% 30%	2612
May	1st to 10th	Day	13% 5% 2 6% 5% 4 5% 4 5% 7% 44%	8212
	11th to 20th	Day	14% 6% 3 6% 4 4 5% 3 6% 7% 43%	8222
	21st to end	Day	15% 8% 2 6% 4 4 5% 4 6% 7% 39%	9047
June	1st to 10th	Day	13% 6% 3 7% 5% 4 5% 3 6% 8% 41%	2940
	11th to 20th	Day	16% 7% 3 6% 5% 5% 4 4 6% 8% 36%	2940
	21st to end	Day	13% 6% 3 6% 5% 5% 5% 4 7% 10% 37%	2940
July	1st to 10th	Day	11% 4 2 6% 4 5% 5% 5% 7% 9% 43%	6500
	11th to 20th	Day	8% 4 2 5% 3 4 5% 4 6% 9% 49%	6431
	21st to end	Day	9% 6% 2 7% 4 5% 4 4 6% 8% 44%	6924
August	1st to 10th	Day	13% 6% 2 6% 4 5% 5% 4 6% 7% 42%	4548
	11th to 20th	Day	14% 5% 2 5% 3 4 4 4 6% 8% 44%	4075
	21st to end	Day	13% 7% 3 7% 5% 4 5% 4 6% 8% 39%	4312
September	1st to 10th	Day	12% 7% 3 6% 4 3 4 4 6% 7% 44%	2400
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	2366
	21st to end	Day	14% 7% 3 7% 5% 4 5% 3 6% 7% 40%	2186
October	1st to 10th	Day	14% 7% 2 6% 4 3 5% 3 6% 7% 42%	2000
	11th to 20th	Day	19% 11% 3 8% 5% 4 4 3 5% 7% 31%	2000
	21st to end	Day	17% 11% 4 9% 5% 3 4 3 5% 7% 33%	2005
November	1st to 10th	Day	14% 9% 3 7% 5% 4 4 4 6% 7% 38%	1852
	11th to 20th	Day	14% 13% 3 11% 6% 5% 4 3 6% 7% 29%	1749
	21st to end	Day	14% 13% 4 9% 5% 4 5% 3 6% 6% 31%	1680
December	1st to 10th	Day	8% 12% 6% 17% 8% 7% 6% 4 5% 4 24%	2690
	11th to 20th	Day	11% 19% 6% 10% 6% 4 4 3 4 5% 27%	3088
	21st to end	Day	21% 21% 5% 13% 5% 4 4 4 3 4 16%	4070
January	1st to 10th	Night	10% 13% 5% 12% 8% 4 4 3 4 5% 31%	8232
	11th to 20th	Night	6% 14% 6% 14% 7% 6% 7% 6% 6% 6% 22%	8280
	21st to end	Night	7% 12% 6% 13% 6% 5% 5% 4 5% 6% 32%	8901
February	1st to 10th	Night	9% 12% 5% 10% 6% 6% 4 3 6% 7% 33%	2730
	11th to 20th	Night	9% 10% 3 9% 5% 4 5% 4 6% 6% 38%	2606
	21st to end	Night	13% 11% 3 10% 5% 4 5% 4 4 7% 33%	2076
March	1st to 10th	Night	11% 6% 2 7% 4 4 4 3 5% 7% 46%	5493
	11th to 20th	Night	10% 9% 3 9% 6% 5% 4 4 6% 8% 34%	5236
	21st to end	Night	21% 11% 4 10% 5% 4 4 3 4 5% 29%	5195
April	1st to 10th	Night	19% 11% 3 7% 5% 4 4 3 4 7% 33%	2100
	11th to 20th	Night	22% 9% 2 5% 4 4 3 4 5% 5% 38%	2075
	21st to end	Night	19% 9% 2 6% 4 3 3 3 5% 7% 38%	2003
May	1st to 10th	Night	11% 8% 3 6% 4 4 4 4 5% 8% 44%	4671
	11th to 20th	Night	13% 6% 2 6% 5% 5% 4 3 6% 6% 44%	4670
	21st to end	Night	15% 7% 2 7% 4 4 4 4 6% 7% 39%	5139
June	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 6% 7% 45%	1680
	11th to 20th	Night	13% 6% 3 7% 5% 5% 6% 4 6% 8% 38%	1680
	21st to end	Night	12% 5% 2 5% 5% 4 4 4 6% 9% 45%	1680
July	1st to 10th	Night	11% 4 2 6% 4 4 5% 4 6% 10% 44%	3698
	11th to 20th	Night	8% 5% 2 4 3 3 4 3 5% 9% 55%	3657
	21st to end	Night	8% 5% 2 6% 4 4 4 4 6% 8% 49%	3947
August	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 7% 46%	2597
	11th to 20th	Night	12% 6% 2 5% 3 4 3 3 6% 8% 48%	2979
	21st to end	Night	13% 6% 2 6% 4 4 4 4 6% 6% 45%	3586
September	1st to 10th	Night	11% 5% 2 6% 3 4 3 4 5% 6% 53%	2000
	11th to 20th	Night	11% 6% 2 6% 3 4 3 3 6% 6% 49%	2013
	21st to end	Night	12% 7% 2 5% 4 3 4 3 5% 8% 47%	2210
October	1st to 10th	Night	14% 5% 2 6% 4 4 4 4 5% 6% 47%	2400
	11th to 20th	Night	15% 10% 2 7% 4 4 5% 4 5% 7% 37%	2400
	21st to end	Night	17% 11% 3 8% 5% 4 4 4 5% 6% 33%	2834
November	1st to 10th	Night	15% 9% 3 6% 4 3 4 3 5% 7% 41%	2666
	11th to 20th	Night	13% 13% 4 9% 5% 4 5% 4 4 6% 34%	2867
	21st to end	Night	14% 12% 4 9% 6% 5% 4 4 5% 7% 32%	2940
December	1st to 10th	Night	10% 10% 4 10% 6% 5% 5% 4 7% 9% 30%	4720
	11th to 20th	Night	12% 16% 7% 14% 6% 4 4 3 4 5% 25%	5339
	21st to end	Night	23% 16% 5% 11% 5% 4 3 3 4 5% 22%	7150

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	60% 3 9% 17% 10%	4692
	11th to 20th	Day	59% 4 8% 16% 12% 1	4710
	21st to end	Day	52% 3 10% 24% 12%	5294
February	1st to 10th	Day	52% 5% 10% 21% 11% 1	1890
	11th to 20th	Day	47% 6% 10% 24% 11% 1	1909
	21st to end	Day	55% 4 11% 19% 10% 2	1730
March	1st to 10th	Day	40% 3 13% 23% 17% 5%	4580
	11th to 20th	Day	43% 5% 15% 21% 14% 2	4987
	21st to end	Day	58% 4 9% 16% 13% 1	5977
April	1st to 10th	Day	53% 4 10% 20% 12% 1	2520
	11th to 20th	Day	54% 5% 9% 20% 11% 2	2494
	21st to end	Day	54% 5% 10% 18% 12% 1	2612
May	1st to 10th	Day	38% 5% 10% 30% 17% 1	8250
	11th to 20th	Day	39% 5% 11% 27% 18% 1	8226
	21st to end	Day	43% 5% 9% 24% 18% 1	9061
June	1st to 10th	Day	39% 6% 13% 29% 13% 1	2940
	11th to 20th	Day	44% 6% 12% 25% 12% 1	2940
	21st to end	Day	41% 6% 18% 25% 10% 1	2940
July	1st to 10th	Day	35% 7% 16% 34% 7%	6431
	11th to 20th	Day	30% 6% 14% 37% 13% 1	6356
	21st to end	Day	38% 5% 13% 28% 16% 1	6728
August	1st to 10th	Day	40% 5% 15% 26% 13% 1	4533
	11th to 20th	Day	36% 5% 14% 34% 11%	4114
	21st to end	Day	42% 6% 12% 29% 11% 1	4311
September	1st to 10th	Day	38% 5% 15% 29% 14% 1	2400
	11th to 20th	Day	37% 5% 19% 31% 7% 1	2366
	21st to end	Day	42% 5% 12% 30% 11%	2186
October	1st to 10th	Day	28% 3 10% 36% 22% 1	3260
	11th to 20th	Day	46% 4 11% 24% 15% 1	3240
	21st to end	Day	45% 4 15% 27% 9%	3217
November	1st to 10th	Day	45% 5% 12% 24% 13% 2	1852
	11th to 20th	Day	55% 4 11% 21% 8% 1	1749
	21st to end	Day	53% 4 14% 23% 5% 1	1680
December	1st to 10th	Day	62% 4 11% 18% 5%	2690
	11th to 20th	Day	60% 4 8% 15% 12% 1	3085
	21st to end	Day	72% 3 6% 12% 7%	4070
January	1st to 10th	Night	57% 3 10% 20% 11%	8233
	11th to 20th	Night	61% 4 8% 14% 12%	8280
	21st to end	Night	53% 4 10% 19% 14%	8901
February	1st to 10th	Night	51% 3 10% 23% 11% 2	2730
	11th to 20th	Night	46% 5% 11% 24% 12% 2	2607
	21st to end	Night	51% 4 12% 19% 10% 3	2076
March	1st to 10th	Night	38% 4 14% 25% 15% 4	5493
	11th to 20th	Night	46% 5% 16% 20% 11% 2	5236
	21st to end	Night	59% 3 8% 17% 11% 1	5195
April	1st to 10th	Night	51% 4 7% 18% 17% 1	2100
	11th to 20th	Night	47% 5% 9% 21% 14% 3	2075
	21st to end	Night	46% 5% 11% 23% 14% 2	2003
May	1st to 10th	Night	37% 5% 10% 27% 18% 2	4695
	11th to 20th	Night	40% 6% 10% 24% 19% 2	4671
	21st to end	Night	43% 5% 11% 22% 16% 2	5149
June	1st to 10th	Night	36% 6% 13% 29% 15% 1	1680
	11th to 20th	Night	43% 6% 12% 24% 13% 2	1680
	21st to end	Night	36% 6% 15% 30% 11% 2	1680
July	1st to 10th	Night	35% 6% 19% 29% 9% 2	3660
	11th to 20th	Night	27% 5% 15% 38% 14% 2	3612
	21st to end	Night	33% 6% 15% 27% 18% 1	3832
August	1st to 10th	Night	37% 6% 15% 25% 15% 2	2588
	11th to 20th	Night	34% 6% 15% 31% 14% 1	3006
	21st to end	Night	39% 5% 13% 26% 15% 1	3586
September	1st to 10th	Night	32% 5% 13% 33% 17% 1	2000
	11th to 20th	Night	35% 5% 14% 34% 13%	2013
	21st to end	Night	36% 5% 12% 32% 14% 1	2210
October	1st to 10th	Night	28% 3 8% 36% 22% 3	3920
	11th to 20th	Night	37% 4 9% 31% 18%	3899
	21st to end	Night	51% 4 9% 23% 13%	4572
November	1st to 10th	Night	45% 3 12% 24% 15% 1	2666
	11th to 20th	Night	51% 4 13% 19% 11% 1	2867
	21st to end	Night	52% 4 14% 23% 7% 1	2940
December	1st to 10th	Night	50% 5% 19% 21% 5% 1	4720
	11th to 20th	Night	62% 3 9% 16% 10%	5341
	21st to end	Night	66% 3 6% 15% 9%	7150

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	15% 13% 33% 28% 9% 2	330
	11th to 20th	Day	21% 12% 37% 22% 7% 1	330
	21st to end	Day	17% 11% 36% 27% 7% 1	363
February	1st to 10th	Day	14% 15% 45% 17% 7% 2	330
	11th to 20th	Day	17% 17% 38% 19% 8%	330
	21st to end	Day	15% 16% 43% 24% 3	273
March	1st to 10th	Day	18% 15% 39% 21% 7%	330
	11th to 20th	Day	20% 12% 40% 17% 8% 2	330
	21st to end	Day	23% 14% 32% 22% 7% 2	535
April	1st to 10th	Day	24% 17% 31% 22% 5% 1	540
	11th to 20th	Day	28% 12% 28% 21% 9% 2	532
	21st to end	Day	25% 13% 30% 20% 9% 3	543
May	1st to 10th	Day	19% 14% 29% 26% 10% 2	753
	11th to 20th	Day	19% 13% 27% 23% 13% 4	775
	21st to end	Day	19% 9% 26% 27% 13% 6%	844
June	1st to 10th	Day	11% 8% 29% 30% 15% 5%	780
	11th to 20th	Day	17% 10% 31% 26% 12% 4	780
	21st to end	Day	14% 9% 29% 28% 14% 6%	780
July	1st to 10th	Day	8% 4 20% 30% 27% 10%	771
	11th to 20th	Day	9% 6% 26% 30% 19% 9%	744
	21st to end	Day	7% 4 27% 31% 23% 9%	794
August	1st to 10th	Day	10% 4 26% 28% 23% 9%	726
	11th to 20th	Day	14% 5% 19% 27% 26% 9%	658
	21st to end	Day	14% 7% 22% 29% 22% 7%	583
September	1st to 10th	Day	16% 7% 25% 23% 21% 8%	530
	11th to 20th	Day	12% 7% 22% 35% 20% 5%	530
	21st to end	Day	18% 8% 25% 28% 16% 5%	516
October	1st to 10th	Day	16% 13% 27% 24% 13% 6%	330
	11th to 20th	Day	20% 19% 31% 22% 6% 1	330
	21st to end	Day	21% 14% 40% 18% 6% 1	363
November	1st to 10th	Day	21% 13% 33% 24% 7% 2	330
	11th to 20th	Day	18% 20% 34% 22% 5% 1	330
	21st to end	Day	21% 13% 41% 19% 6%	330
December	1st to 10th	Day	14% 11% 45% 22% 8%	330
	11th to 20th	Day	18% 16% 42% 17% 5% 1	330
	21st to end	Day	29% 15% 34% 17% 4 1	363
January	1st to 10th	Night	15% 12% 37% 28% 7% 1	1050
	11th to 20th	Night	17% 12% 38% 26% 6% 1	1050
	21st to end	Night	16% 10% 38% 30% 6% 1	1155
February	1st to 10th	Night	14% 12% 37% 28% 7% 1	1050
	11th to 20th	Night	14% 12% 41% 26% 7%	972
	21st to end	Night	18% 11% 38% 27% 5%	692
March	1st to 10th	Night	17% 12% 33% 31% 7% 1	840
	11th to 20th	Night	16% 14% 35% 26% 7% 1	698
	21st to end	Night	21% 9% 33% 27% 9% 2	693
April	1st to 10th	Night	23% 11% 33% 25% 6% 1	630
	11th to 20th	Night	26% 8% 32% 27% 7%	623
	21st to end	Night	23% 9% 30% 30% 7% 1	630
May	1st to 10th	Night	20% 10% 32% 30% 7% 1	630
	11th to 20th	Night	19% 6% 32% 33% 9% 1	621
	21st to end	Night	16% 6% 26% 36% 15% 1	683
June	1st to 10th	Night	16% 7% 26% 36% 14% 1	630
	11th to 20th	Night	15% 7% 30% 39% 10% 1	630
	21st to end	Night	14% 6% 22% 41% 16% 1	630
July	1st to 10th	Night	8% 3 21% 39% 27% 2	615
	11th to 20th	Night	9% 5% 22% 38% 24% 3	597
	21st to end	Night	7% 2 19% 46% 23% 2	657
August	1st to 10th	Night	10% 2 20% 43% 24% 2	597
	11th to 20th	Night	14% 3 19% 33% 29% 3	594
	21st to end	Night	15% 4 20% 36% 23% 3	660
September	1st to 10th	Night	13% 4 24% 36% 19% 5%	600
	11th to 20th	Night	13% 4 23% 37% 21% 2	613
	21st to end	Night	14% 7% 28% 33% 17% 2	800
October	1st to 10th	Night	15% 7% 29% 30% 17% 2	800
	11th to 20th	Night	21% 11% 33% 28% 8%	800
	21st to end	Night	22% 10% 32% 27% 9% 1	880
November	1st to 10th	Night	20% 9% 35% 27% 8% 1	820
	11th to 20th	Night	20% 11% 39% 23% 7%	977
	21st to end	Night	20% 13% 36% 25% 5%	1050
December	1st to 10th	Night	18% 11% 39% 25% 7% 1	1050
	11th to 20th	Night	21% 12% 34% 26% 7% 1	1050
	21st to end	Night	27% 11% 32% 25% 5%	1155

Page generated at 2026-07-13 02:14:50. Version ac07

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