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 2024-02-10.

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	14% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	78161
	Night	13% 10% 4 7% 6% 3 5% 5% 5% 7% 36%	80860
Transparency	Day	48% 5% 13% 23% 10% 1	77861
	Night	48% 5% 12% 23% 11% 1	80680
Seeing	Day	16% 10% 29% 26% 14% 5%	14914
	Night	17% 9% 32% 30% 11% 1	24980

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	11% 16% 8% 14% 7% 3 4 4 4 7% 23%	2527
	11th to 20th	Day	8% 13% 6% 13% 10% 6% 7% 9% 5% 5% 17%	2530
	21st to end	Day	12% 18% 9% 14% 7% 3 5% 4 4 6% 18%	2851
February	1st to 10th	Day	9% 11% 6% 9% 6% 4 6% 5% 5% 7% 32%	1701
	11th to 20th	Day	10% 12% 4 8% 7% 3 4 5% 6% 7% 33%	1622
	21st to end	Day	13% 11% 5% 10% 8% 4 7% 5% 5% 6% 27%	1480
March	1st to 10th	Day	13% 11% 5% 7% 6% 3 6% 3 5% 7% 34%	1800
	11th to 20th	Day	12% 10% 4 7% 7% 4 5% 4 5% 7% 34%	1935
	21st to end	Day	17% 10% 4 6% 7% 3 4 5% 5% 8% 30%	2325
April	1st to 10th	Day	15% 11% 5% 7% 6% 3 4 4 5% 7% 32%	2160
	11th to 20th	Day	21% 10% 4 6% 6% 4 4 4 5% 6% 30%	2134
	21st to end	Day	20% 10% 4 7% 6% 4 4 5% 5% 6% 30%	2238
May	1st to 10th	Day	17% 6% 3 7% 7% 4 6% 5% 6% 8% 33%	2520
	11th to 20th	Day	18% 7% 3 6% 5% 3 4 4 5% 6% 37%	2479
	21st to end	Day	15% 6% 3 6% 6% 3 5% 6% 6% 8% 37%	2725
June	1st to 10th	Day	13% 5% 3 6% 5% 3 4 4 6% 8% 43%	2520
	11th to 20th	Day	15% 6% 3 5% 5% 4 5% 5% 5% 8% 38%	2520
	21st to end	Day	11% 5% 2 5% 6% 4 5% 5% 7% 10% 40%	2520
July	1st to 10th	Day	7% 3 1 4 5% 3 5% 7% 8% 10% 46%	2520
	11th to 20th	Day	9% 5% 2 5% 5% 3 6% 6% 7% 9% 42%	2520
	21st to end	Day	7% 4 2 5% 5% 3 5% 5% 7% 9% 48%	2743
August	1st to 10th	Day	10% 5% 2 5% 6% 4 6% 6% 7% 9% 42%	2506
	11th to 20th	Day	15% 5% 2 5% 5% 2 5% 5% 6% 8% 41%	2250
	21st to end	Day	13% 6% 3 5% 4 3 4 4 6% 8% 44%	2376
September	1st to 10th	Day	13% 7% 3 5% 5% 2 4 5% 6% 7% 43%	2160
	11th to 20th	Day	13% 5% 2 5% 5% 3 5% 5% 6% 8% 44%	2130
	21st to end	Day	15% 7% 3 6% 5% 3 5% 5% 7% 7% 37%	1968
October	1st to 10th	Day	16% 7% 3 5% 5% 2 5% 5% 6% 7% 39%	1800
	11th to 20th	Day	20% 10% 4 7% 5% 3 4 4 5% 7% 31%	1800
	21st to end	Day	18% 11% 4 8% 5% 2 3 3 4 7% 33%	1805
November	1st to 10th	Day	14% 8% 4 6% 6% 3 4 5% 5% 7% 39%	1672
	11th to 20th	Day	15% 12% 5% 10% 7% 4 4 4 5% 7% 28%	1583
	21st to end	Day	14% 11% 4 6% 6% 3 6% 4 6% 7% 33%	1520
December	1st to 10th	Day	11% 12% 6% 10% 8% 5% 6% 5% 5% 5% 27%	1520
	11th to 20th	Day	13% 15% 7% 8% 9% 4 5% 5% 5% 7% 22%	1918
	21st to end	Day	21% 21% 6% 10% 6% 3 4 5% 3 4 17%	2783
January	1st to 10th	Night	12% 13% 7% 11% 7% 3 4 4 4 5% 30%	4428
	11th to 20th	Night	8% 12% 6% 12% 10% 6% 7% 8% 7% 5% 19%	4440
	21st to end	Night	12% 16% 9% 12% 7% 4 4 4 4 6% 22%	4811
February	1st to 10th	Night	8% 10% 5% 10% 6% 5% 5% 4 6% 7% 34%	2464
	11th to 20th	Night	9% 10% 4 8% 6% 3 6% 5% 5% 7% 38%	2224
	21st to end	Night	15% 12% 4 8% 7% 3 4 4 3 7% 32%	1776
March	1st to 10th	Night	13% 8% 4 6% 6% 4 4 5% 5% 6% 39%	2160
	11th to 20th	Night	12% 9% 3 7% 7% 4 4 5% 4 5% 40%	2039
	21st to end	Night	17% 9% 4 6% 6% 3 4 4 4 6% 36%	2030
April	1st to 10th	Night	18% 10% 4 6% 6% 3 5% 4 4 7% 33%	1800
	11th to 20th	Night	23% 8% 2 4 4 3 3 5% 5% 6% 37%	1775
	21st to end	Night	19% 8% 3 5% 6% 3 3 4 5% 7% 37%	1719
May	1st to 10th	Night	18% 10% 4 7% 6% 3 4 5% 5% 7% 32%	1440
	11th to 20th	Night	19% 7% 3 6% 4 2 4 4 6% 7% 39%	1416
	21st to end	Night	14% 6% 2 5% 5% 3 5% 5% 7% 8% 40%	1551
June	1st to 10th	Night	13% 5% 2 5% 5% 3 4 4 5% 7% 46%	1440
	11th to 20th	Night	11% 5% 3 6% 6% 4 6% 6% 6% 8% 40%	1440
	21st to end	Night	10% 5% 2 3 6% 3 4 6% 6% 9% 48%	1440
July	1st to 10th	Night	7% 3 2 5% 4 3 4 5% 5% 10% 54%	1440
	11th to 20th	Night	8% 5% 2 4 4 3 6% 5% 5% 11% 49%	1440
	21st to end	Night	6% 4 1 3 4 2 4 4 6% 9% 57%	1575
August	1st to 10th	Night	8% 5% 2 4 4 3 5% 4 6% 7% 51%	1432
	11th to 20th	Night	12% 5% 2 5% 4 3 3 4 5% 7% 48%	1649
	21st to end	Night	13% 5% 2 4 3 3 4 4 6% 6% 50%	1980
September	1st to 10th	Night	11% 4 2 5% 4 3 4 5% 5% 7% 51%	1800
	11th to 20th	Night	11% 5% 2 5% 4 3 4 4 5% 6% 51%	1811
	21st to end	Night	13% 6% 3 5% 5% 2 4 4 5% 8% 45%	1988
October	1st to 10th	Night	15% 5% 2 5% 4 3 4 5% 5% 7% 46%	2160
	11th to 20th	Night	16% 10% 3 6% 5% 3 4 5% 4 7% 36%	2160
	21st to end	Night	18% 10% 3 7% 5% 3 4 5% 5% 6% 33%	2550
November	1st to 10th	Night	15% 8% 4 6% 4 2 4 4 5% 7% 42%	2406
	11th to 20th	Night	14% 11% 4 9% 6% 3 5% 4 4 6% 33%	2593
	21st to end	Night	13% 11% 4 8% 6% 4 4 4 5% 7% 33%	2660
December	1st to 10th	Night	12% 12% 5% 9% 7% 4 5% 4 6% 7% 29%	2660
	11th to 20th	Night	11% 14% 6% 10% 8% 4 6% 5% 5% 6% 25%	3279
	21st to end	Night	24% 17% 6% 9% 5% 3 3 3 4 5% 21%	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	62% 4 10% 18% 6% 1	2528
	11th to 20th	Day	66% 5% 9% 13% 6% 1	2530
	21st to end	Day	67% 3 12% 13% 4	2851
February	1st to 10th	Day	51% 5% 11% 21% 11% 1	1701
	11th to 20th	Day	49% 6% 11% 23% 9% 1	1631
	21st to end	Day	58% 4 10% 17% 9% 1	1480
March	1st to 10th	Day	51% 4 14% 20% 11% 2	1800
	11th to 20th	Day	49% 4 13% 20% 12% 2	1935
	21st to end	Day	53% 5% 11% 21% 9% 1	2325
April	1st to 10th	Day	53% 4 11% 19% 12%	2160
	11th to 20th	Day	54% 4 8% 20% 11% 2	2134
	21st to end	Day	55% 5% 11% 18% 11% 1	2238
May	1st to 10th	Day	49% 5% 14% 22% 9%	2520
	11th to 20th	Day	48% 4 12% 24% 11% 1	2483
	21st to end	Day	44% 6% 12% 24% 13% 1	2725
June	1st to 10th	Day	38% 6% 14% 29% 12% 1	2520
	11th to 20th	Day	43% 7% 13% 24% 13% 1	2520
	21st to end	Day	39% 6% 18% 26% 10% 1	2520
July	1st to 10th	Day	30% 7% 17% 32% 12% 1	2451
	11th to 20th	Day	35% 7% 14% 27% 14% 3	2445
	21st to end	Day	31% 6% 18% 28% 16% 1	2591
August	1st to 10th	Day	37% 6% 16% 30% 10% 2	2491
	11th to 20th	Day	39% 6% 16% 28% 11%	2250
	21st to end	Day	37% 6% 11% 29% 15% 1	2376
September	1st to 10th	Day	38% 5% 14% 28% 14% 1	2160
	11th to 20th	Day	37% 5% 19% 30% 8% 1	2130
	21st to end	Day	45% 5% 13% 28% 9%	1968
October	1st to 10th	Day	43% 5% 13% 31% 9% 1	1800
	11th to 20th	Day	53% 5% 12% 20% 9% 1	1800
	21st to end	Day	53% 4 14% 21% 8%	1805
November	1st to 10th	Day	44% 5% 12% 24% 13% 2	1672
	11th to 20th	Day	56% 4 11% 20% 7% 1	1583
	21st to end	Day	51% 4 14% 23% 6% 2	1520
December	1st to 10th	Day	59% 4 12% 20% 5%	1520
	11th to 20th	Day	60% 5% 13% 14% 7% 1	1915
	21st to end	Day	71% 4 7% 13% 5%	2783
January	1st to 10th	Night	57% 4 10% 21% 7% 1	4428
	11th to 20th	Night	63% 5% 10% 16% 6%	4440
	21st to end	Night	65% 4 9% 17% 5%	4811
February	1st to 10th	Night	50% 4 10% 23% 11% 2	2464
	11th to 20th	Night	46% 5% 12% 23% 11% 2	2225
	21st to end	Night	54% 5% 11% 18% 10% 2	1776
March	1st to 10th	Night	45% 5% 13% 23% 11% 2	2160
	11th to 20th	Night	47% 4 11% 23% 14% 2	2039
	21st to end	Night	51% 4 9% 21% 13% 2	2030
April	1st to 10th	Night	51% 4 8% 19% 17% 2	1800
	11th to 20th	Night	47% 5% 9% 22% 14% 3	1775
	21st to end	Night	47% 5% 11% 22% 14% 2	1719
May	1st to 10th	Night	51% 6% 13% 18% 12% 1	1440
	11th to 20th	Night	45% 5% 11% 26% 12% 2	1417
	21st to end	Night	39% 6% 17% 22% 14% 1	1552
June	1st to 10th	Night	35% 5% 14% 30% 14% 1	1440
	11th to 20th	Night	40% 6% 13% 25% 14% 2	1440
	21st to end	Night	33% 6% 15% 32% 11% 3	1440
July	1st to 10th	Night	27% 5% 14% 33% 19% 2	1400
	11th to 20th	Night	30% 7% 16% 26% 18% 3	1392
	21st to end	Night	24% 5% 18% 32% 17% 3	1487
August	1st to 10th	Night	32% 6% 14% 31% 14% 3	1423
	11th to 20th	Night	35% 6% 15% 26% 17% 1	1649
	21st to end	Night	33% 6% 13% 27% 18% 3	1980
September	1st to 10th	Night	33% 5% 12% 31% 18% 1	1800
	11th to 20th	Night	33% 4 14% 35% 13%	1811
	21st to end	Night	37% 6% 13% 32% 12% 1	1988
October	1st to 10th	Night	39% 4 12% 31% 13% 1	2160
	11th to 20th	Night	47% 6% 12% 23% 11% 1	2160
	21st to end	Night	52% 5% 11% 21% 10%	2550
November	1st to 10th	Night	44% 3 12% 24% 15% 1	2406
	11th to 20th	Night	52% 4 14% 17% 11% 1	2593
	21st to end	Night	51% 4 14% 23% 6% 1	2660
December	1st to 10th	Night	55% 4 14% 21% 6%	2660
	11th to 20th	Night	59% 4 11% 18% 6% 1	3281
	21st to end	Night	67% 4 7% 17% 5%	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	16% 13% 31% 27% 10% 3	270
	11th to 20th	Day	22% 11% 36% 22% 7% 1	270
	21st to end	Day	19% 9% 33% 29% 8% 2	297
February	1st to 10th	Day	13% 14% 43% 18% 8% 3	267
	11th to 20th	Day	20% 17% 37% 17% 10%	240
	21st to end	Day	18% 15% 41% 24% 3	198
March	1st to 10th	Day	17% 15% 39% 20% 9%	240
	11th to 20th	Day	18% 10% 39% 20% 10% 3	240
	21st to end	Day	23% 12% 32% 22% 9% 2	411
April	1st to 10th	Day	23% 15% 30% 25% 7% 1	420
	11th to 20th	Day	30% 10% 26% 22% 10% 2	412
	21st to end	Day	24% 12% 31% 20% 10% 3	422
May	1st to 10th	Day	19% 14% 30% 25% 9% 2	603
	11th to 20th	Day	20% 12% 28% 21% 13% 4	625
	21st to end	Day	18% 10% 25% 27% 14% 7%	679
June	1st to 10th	Day	11% 8% 27% 32% 15% 6%	630
	11th to 20th	Day	15% 9% 30% 28% 13% 4	630
	21st to end	Day	11% 9% 28% 30% 15% 7%	630
July	1st to 10th	Day	8% 3 20% 30% 27% 11%	621
	11th to 20th	Day	9% 6% 26% 31% 19% 9%	618
	21st to end	Day	6% 5% 27% 30% 23% 9%	684
August	1st to 10th	Day	9% 3 26% 29% 24% 9%	626
	11th to 20th	Day	15% 5% 19% 26% 26% 10%	564
	21st to end	Day	14% 8% 21% 28% 22% 7%	495
September	1st to 10th	Day	18% 6% 24% 23% 22% 7%	450
	11th to 20th	Day	12% 8% 23% 33% 19% 5%	450
	21st to end	Day	20% 9% 26% 28% 13% 3	438
October	1st to 10th	Day	17% 13% 25% 24% 14% 6%	270
	11th to 20th	Day	22% 20% 27% 24% 6% 1	270
	21st to end	Day	24% 15% 39% 16% 4 1	297
November	1st to 10th	Day	19% 13% 31% 27% 8% 2	270
	11th to 20th	Day	18% 19% 35% 23% 4 1	270
	21st to end	Day	20% 13% 41% 19% 7%	270
December	1st to 10th	Day	15% 11% 44% 21% 9%	270
	11th to 20th	Day	19% 16% 40% 17% 6% 1	270
	21st to end	Day	29% 16% 34% 16% 4	297
January	1st to 10th	Night	15% 11% 37% 28% 8% 1	950
	11th to 20th	Night	17% 11% 37% 26% 6% 2	950
	21st to end	Night	17% 9% 37% 30% 7% 1	1045
February	1st to 10th	Night	13% 13% 37% 30% 7% 1	948
	11th to 20th	Night	14% 12% 41% 26% 7%	830
	21st to end	Night	20% 11% 37% 26% 6%	592
March	1st to 10th	Night	17% 12% 32% 31% 8% 1	720
	11th to 20th	Night	16% 13% 35% 27% 8% 1	599
	21st to end	Night	21% 8% 31% 28% 10% 2	594
April	1st to 10th	Night	23% 10% 34% 26% 7% 1	540
	11th to 20th	Night	27% 7% 31% 27% 8%	533
	21st to end	Night	22% 8% 31% 29% 8% 1	540
May	1st to 10th	Night	22% 10% 32% 29% 6% 1	540
	11th to 20th	Night	21% 5% 31% 33% 9% 1	531
	21st to end	Night	16% 6% 25% 36% 16% 1	584
June	1st to 10th	Night	16% 6% 26% 36% 15% 1	540
	11th to 20th	Night	13% 6% 29% 41% 11% 1	540
	21st to end	Night	12% 5% 22% 42% 17% 1	540
July	1st to 10th	Night	7% 3 22% 38% 27% 3	525
	11th to 20th	Night	9% 5% 24% 37% 24% 2	522
	21st to end	Night	7% 2 20% 46% 23% 3	591
August	1st to 10th	Night	9% 2 19% 43% 25% 2	537
	11th to 20th	Night	15% 2 20% 31% 30% 3	534
	21st to end	Night	15% 4 21% 35% 22% 3	594
September	1st to 10th	Night	12% 3 23% 37% 19% 5%	540
	11th to 20th	Night	13% 4 25% 36% 19% 3	551
	21st to end	Night	15% 8% 30% 30% 15% 1	720
October	1st to 10th	Night	16% 7% 29% 29% 18% 2	720
	11th to 20th	Night	22% 11% 31% 28% 8%	720
	21st to end	Night	22% 10% 32% 26% 9% 1	792
November	1st to 10th	Night	20% 9% 34% 28% 8% 1	740
	11th to 20th	Night	19% 11% 40% 22% 7%	883
	21st to end	Night	20% 13% 35% 26% 5% 1	950
December	1st to 10th	Night	18% 10% 39% 24% 7% 1	950
	11th to 20th	Night	21% 11% 34% 26% 7% 1	950
	21st to end	Night	26% 12% 33% 24% 5%	1045

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