Park Place Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Park Place Observatory clear sky chart from 2005-11-06 to 2026-01-17.

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% 7% 2 6% 4 4 5% 4 6% 7% 38%	127534
	Night	17% 7% 2 6% 4 4 4 3 5% 6% 41%	124134
Transparency	Day	42% 7% 13% 22% 14% 2	131065
	Night	41% 6% 12% 23% 16% 3	128690
Seeing	Day	21% 16% 28% 21% 11% 3	16365
	Night	20% 13% 30% 27% 10% 1	25725

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% 6% 2 5% 4 4 5% 4 6% 6% 45%	3677
	11th to 20th	Day	14% 10% 5% 9% 5% 5% 5% 4 6% 6% 32%	3707
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 4 4 5% 37%	4466
February	1st to 10th	Day	15% 7% 3 7% 6% 5% 5% 4 5% 8% 34%	1800
	11th to 20th	Day	15% 9% 2 6% 5% 4 5% 4 6% 6% 38%	1866
	21st to end	Day	20% 7% 3 6% 5% 5% 4 3 6% 6% 36%	1650
March	1st to 10th	Day	22% 5% 1 5% 4 4 5% 3 5% 6% 40%	4522
	11th to 20th	Day	12% 6% 3 7% 5% 4 5% 4 6% 7% 42%	4980
	21st to end	Day	18% 7% 2 5% 3 3 4 4 5% 7% 42%	5758
April	1st to 10th	Day	18% 8% 3 6% 5% 5% 5% 3 7% 7% 35%	2400
	11th to 20th	Day	17% 7% 2 6% 4 5% 4 3 6% 6% 39%	2374
	21st to end	Day	16% 6% 2 6% 4 4 4 5% 7% 7% 39%	2400
May	1st to 10th	Day	27% 6% 2 6% 4 4 5% 4 6% 8% 29%	5944
	11th to 20th	Day	25% 8% 3 6% 4 4 4 3 5% 6% 32%	6318
	21st to end	Day	20% 6% 2 5% 4 4 5% 4 7% 9% 35%	6949
June	1st to 10th	Day	14% 6% 2 6% 5% 5% 5% 5% 7% 9% 37%	2800
	11th to 20th	Day	16% 5% 2 6% 4 5% 5% 5% 7% 9% 35%	2800
	21st to end	Day	13% 6% 2 5% 5% 4 5% 4 6% 9% 41%	2800
July	1st to 10th	Day	8% 6% 2 7% 5% 5% 6% 5% 8% 10% 37%	6360
	11th to 20th	Day	12% 7% 3 7% 5% 5% 6% 5% 8% 10% 32%	6360
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 6% 9% 40%	6823
August	1st to 10th	Day	21% 6% 2 7% 4 4 6% 4 6% 8% 32%	4234
	11th to 20th	Day	14% 5% 3 6% 5% 4 5% 4 7% 9% 40%	3915
	21st to end	Day	15% 5% 2 4 3 3 4 3 6% 9% 46%	4312
September	1st to 10th	Day	17% 5% 2 5% 5% 4 5% 3 5% 7% 43%	2400
	11th to 20th	Day	14% 4 2 5% 3 3 4 3 6% 6% 51%	2385
	21st to end	Day	21% 8% 2 6% 4 4 5% 3 5% 5% 38%	2170
October	1st to 10th	Day	18% 6% 2 5% 3 4 4 3 6% 6% 43%	2000
	11th to 20th	Day	17% 5% 2 5% 4 4 5% 3 5% 7% 44%	2000
	21st to end	Day	19% 5% 3 5% 3 3 5% 4 5% 7% 40%	2133
November	1st to 10th	Day	14% 6% 2 4 3 3 3 2 3 7% 52%	1851
	11th to 20th	Day	16% 6% 2 5% 4 4 5% 4 6% 6% 43%	1890
	21st to end	Day	18% 7% 2 5% 4 4 3 4 6% 7% 40%	1696
December	1st to 10th	Day	17% 7% 2 6% 4 4 5% 4 5% 5% 39%	2680
	11th to 20th	Day	23% 8% 2 4 3 3 3 4 5% 5% 39%	3066
	21st to end	Day	19% 7% 3 6% 5% 4 5% 4 6% 7% 34%	4048
January	1st to 10th	Night	13% 6% 2 6% 4 4 4 3 5% 7% 46%	6489
	11th to 20th	Night	14% 8% 3 7% 4 4 5% 4 6% 7% 40%	6308
	21st to end	Night	18% 8% 2 6% 4 4 4 3 5% 6% 40%	6490
February	1st to 10th	Night	17% 8% 3 5% 4 4 4 4 5% 7% 40%	2600
	11th to 20th	Night	17% 7% 3 5% 4 4 4 4 5% 6% 39%	2418
	21st to end	Night	19% 8% 2 5% 4 3 4 3 5% 5% 41%	1980
March	1st to 10th	Night	19% 9% 3 6% 3 3 4 3 5% 5% 42%	5304
	11th to 20th	Night	12% 6% 3 5% 4 4 4 3 4 6% 50%	4979
	21st to end	Night	18% 8% 3 7% 4 4 4 3 4 6% 42%	5160
April	1st to 10th	Night	18% 7% 3 7% 5% 4 5% 4 5% 6% 36%	2000
	11th to 20th	Night	16% 7% 2 6% 4 4 5% 4 6% 7% 40%	1975
	21st to end	Night	20% 5% 2 5% 3 3 4 3 5% 6% 45%	2000
May	1st to 10th	Night	30% 7% 2 5% 4 4 4 3 5% 7% 28%	4038
	11th to 20th	Night	24% 9% 3 7% 4 4 4 3 5% 6% 32%	3575
	21st to end	Night	23% 6% 2 6% 3 4 4 4 5% 7% 37%	3926
June	1st to 10th	Night	17% 6% 2 5% 5% 4 4 4 5% 8% 42%	1600
	11th to 20th	Night	15% 5% 2 4 4 5% 5% 4 6% 8% 42%	1600
	21st to end	Night	12% 4 1 5% 3 4 5% 5% 6% 9% 45%	1600
July	1st to 10th	Night	11% 6% 2 8% 5% 5% 6% 4 6% 9% 38%	3600
	11th to 20th	Night	16% 8% 3 7% 5% 4 6% 4 7% 9% 31%	3600
	21st to end	Night	14% 5% 1 5% 3 4 4 4 5% 8% 46%	4013
August	1st to 10th	Night	21% 7% 3 6% 4 4 4 3 6% 7% 34%	2915
	11th to 20th	Night	16% 7% 3 6% 5% 4 4 3 4 7% 41%	3099
	21st to end	Night	13% 5% 2 4 3 3 4 4 6% 8% 48%	3586
September	1st to 10th	Night	15% 7% 2 6% 4 4 3 3 4 6% 47%	2000
	11th to 20th	Night	13% 6% 2 4 4 4 3 3 4 6% 52%	2015
	21st to end	Night	19% 7% 2 6% 3 3 3 3 5% 5% 43%	2225
October	1st to 10th	Night	22% 5% 2 5% 3 3 3 2 4 6% 45%	2400
	11th to 20th	Night	18% 5% 2 4 3 3 4 3 4 6% 49%	2400
	21st to end	Night	20% 5% 2 4 3 3 3 3 5% 6% 46%	2705
November	1st to 10th	Night	13% 5% 2 5% 3 4 4 4 5% 6% 51%	2667
	11th to 20th	Night	17% 7% 2 5% 4 3 4 3 4 6% 45%	2730
	21st to end	Night	15% 6% 2 6% 5% 4 4 3 5% 7% 42%	2919
December	1st to 10th	Night	15% 8% 3 6% 4 4 4 3 4 6% 42%	4720
	11th to 20th	Night	24% 7% 2 4 3 3 4 3 5% 6% 39%	5348
	21st to end	Night	21% 9% 3 6% 4 4 4 3 5% 5% 38%	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	36% 6% 12% 26% 18% 2	3678
	11th to 20th	Day	49% 6% 10% 19% 12% 4	3737
	21st to end	Day	47% 7% 12% 21% 12% 1	4466
February	1st to 10th	Day	46% 8% 14% 20% 12% 1	1800
	11th to 20th	Day	45% 7% 11% 22% 14% 2	1875
	21st to end	Day	48% 6% 11% 22% 11% 3	1650
March	1st to 10th	Day	42% 5% 11% 24% 11% 7%	4525
	11th to 20th	Day	39% 6% 15% 27% 10% 4	4980
	21st to end	Day	40% 6% 13% 15% 22% 4	5758
April	1st to 10th	Day	46% 6% 10% 19% 14% 4	2400
	11th to 20th	Day	43% 6% 11% 21% 15% 3	2374
	21st to end	Day	41% 7% 11% 22% 15% 4	2400
May	1st to 10th	Day	52% 7% 14% 17% 9% 1	5954
	11th to 20th	Day	52% 6% 10% 21% 11% 1	6322
	21st to end	Day	43% 7% 12% 23% 13% 2	6949
June	1st to 10th	Day	41% 9% 15% 22% 13% 1	2800
	11th to 20th	Day	42% 9% 14% 22% 11% 2	2800
	21st to end	Day	37% 10% 14% 24% 14% 1	2800
July	1st to 10th	Day	39% 11% 13% 22% 14% 1	6290
	11th to 20th	Day	41% 10% 18% 20% 9% 1	6285
	21st to end	Day	39% 7% 12% 20% 21% 1	6627
August	1st to 10th	Day	47% 9% 13% 20% 10%	4221
	11th to 20th	Day	38% 8% 13% 28% 12% 1	3953
	21st to end	Day	33% 7% 13% 31% 15% 2	4312
September	1st to 10th	Day	40% 6% 12% 21% 19% 2	2400
	11th to 20th	Day	32% 6% 11% 24% 24% 3	2385
	21st to end	Day	47% 7% 9% 17% 18% 2	2170
October	1st to 10th	Day	37% 6% 10% 20% 23% 5%	3260
	11th to 20th	Day	29% 6% 12% 28% 22% 4	3240
	21st to end	Day	28% 4 16% 24% 25% 3	3423
November	1st to 10th	Day	33% 5% 15% 24% 20% 3	1851
	11th to 20th	Day	39% 7% 10% 25% 17% 3	1890
	21st to end	Day	42% 5% 14% 28% 9% 2	1696
December	1st to 10th	Day	44% 5% 16% 24% 10% 1	2680
	11th to 20th	Day	46% 5% 16% 23% 10% 1	3066
	21st to end	Day	46% 7% 14% 20% 12% 1	4048
January	1st to 10th	Night	36% 5% 11% 26% 18% 3	6489
	11th to 20th	Night	40% 7% 14% 20% 14% 6%	6353
	21st to end	Night	43% 5% 12% 21% 16% 3	6490
February	1st to 10th	Night	45% 5% 14% 24% 10% 2	2600
	11th to 20th	Night	45% 5% 11% 20% 16% 3	2420
	21st to end	Night	44% 4 9% 23% 17% 3	1980
March	1st to 10th	Night	44% 4 11% 22% 12% 8%	5314
	11th to 20th	Night	35% 6% 16% 26% 13% 5%	4980
	21st to end	Night	44% 5% 7% 17% 23% 5%	5160
April	1st to 10th	Night	46% 6% 10% 21% 14% 3	2000
	11th to 20th	Night	42% 7% 10% 19% 20% 1	1975
	21st to end	Night	39% 6% 11% 21% 18% 5%	2000
May	1st to 10th	Night	55% 6% 11% 17% 10% 2	4044
	11th to 20th	Night	52% 8% 11% 15% 12% 1	3576
	21st to end	Night	45% 7% 11% 23% 11% 2	3927
June	1st to 10th	Night	41% 6% 11% 23% 18% 1	1600
	11th to 20th	Night	38% 9% 14% 24% 13% 1	1600
	21st to end	Night	34% 9% 15% 28% 14% 1	1600
July	1st to 10th	Night	42% 9% 14% 18% 16% 2	3560
	11th to 20th	Night	47% 8% 14% 19% 11% 1	3552
	21st to end	Night	34% 7% 14% 23% 20% 1	3895
August	1st to 10th	Night	47% 8% 16% 18% 10% 1	2904
	11th to 20th	Night	42% 7% 12% 23% 15% 1	3127
	21st to end	Night	33% 7% 11% 31% 17% 1	3586
September	1st to 10th	Night	38% 6% 10% 23% 20% 2	2000
	11th to 20th	Night	34% 5% 9% 23% 26% 3	2015
	21st to end	Night	43% 5% 10% 20% 21% 1	2225
October	1st to 10th	Night	41% 6% 10% 21% 21% 2	3920
	11th to 20th	Night	28% 5% 9% 30% 25% 4	3899
	21st to end	Night	28% 4 14% 29% 23% 2	4365
November	1st to 10th	Night	33% 6% 14% 23% 20% 4	2667
	11th to 20th	Night	40% 5% 11% 23% 18% 3	2730
	21st to end	Night	41% 5% 12% 27% 13% 2	2919
December	1st to 10th	Night	42% 5% 14% 30% 9% 1	4720
	11th to 20th	Night	46% 4 12% 22% 13% 2	5348
	21st to end	Night	48% 5% 11% 20% 15% 2	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	27% 29% 28% 14% 2	220
	11th to 20th	Day	31% 30% 28% 9% 2	231
	21st to end	Day	21% 28% 33% 13% 5% 1	330
February	1st to 10th	Day	21% 34% 33% 10% 2	300
	11th to 20th	Day	27% 27% 36% 9% 1	414
	21st to end	Day	29% 21% 31% 17% 1	414
March	1st to 10th	Day	27% 24% 29% 18% 3	500
	11th to 20th	Day	25% 24% 31% 15% 4 1	500
	21st to end	Day	27% 23% 31% 12% 5% 1	550
April	1st to 10th	Day	25% 26% 27% 15% 5% 1	500
	11th to 20th	Day	23% 25% 26% 16% 7% 2	492
	21st to end	Day	25% 19% 32% 15% 5% 3	500
May	1st to 10th	Day	29% 21% 26% 14% 7% 3	503
	11th to 20th	Day	24% 17% 31% 20% 8% 2	527
	21st to end	Day	20% 9% 30% 20% 17% 3	573
June	1st to 10th	Day	17% 16% 26% 24% 15% 2	530
	11th to 20th	Day	21% 13% 27% 25% 12% 3	530
	21st to end	Day	14% 12% 32% 26% 14% 3	530
July	1st to 10th	Day	12% 6% 24% 29% 22% 6%	525
	11th to 20th	Day	10% 5% 26% 31% 23% 5%	524
	21st to end	Day	14% 7% 29% 31% 15% 5%	576
August	1st to 10th	Day	14% 5% 22% 31% 21% 7%	526
	11th to 20th	Day	14% 6% 21% 32% 20% 7%	519
	21st to end	Day	13% 8% 29% 25% 16% 9%	583
September	1st to 10th	Day	18% 10% 21% 25% 19% 8%	530
	11th to 20th	Day	14% 4 26% 27% 18% 11%	530
	21st to end	Day	25% 13% 21% 22% 13% 5%	530
October	1st to 10th	Day	23% 10% 23% 22% 16% 6%	530
	11th to 20th	Day	19% 17% 29% 22% 11% 3	530
	21st to end	Day	23% 14% 32% 20% 9% 1	545
November	1st to 10th	Day	18% 16% 30% 24% 9% 3	425
	11th to 20th	Day	22% 22% 30% 21% 4	430
	21st to end	Day	25% 23% 36% 12% 4	236
December	1st to 10th	Day	24% 30% 30% 11% 5%	220
	11th to 20th	Day	30% 27% 26% 13% 4	220
	21st to end	Day	26% 22% 34% 12% 5% 1	242
January	1st to 10th	Night	18% 21% 39% 19% 3	840
	11th to 20th	Night	25% 19% 31% 23% 3	825
	21st to end	Night	17% 19% 40% 23% 1	880
February	1st to 10th	Night	21% 17% 37% 24% 2	800
	11th to 20th	Night	23% 22% 37% 16% 1	783
	21st to end	Night	23% 20% 35% 20% 2	660
March	1st to 10th	Night	22% 19% 33% 23% 3	800
	11th to 20th	Night	22% 18% 34% 21% 5% 1	800
	21st to end	Night	22% 16% 37% 20% 4	880
April	1st to 10th	Night	22% 19% 36% 19% 4	800
	11th to 20th	Night	20% 14% 36% 23% 6%	791
	21st to end	Night	23% 12% 33% 25% 7%	800
May	1st to 10th	Night	26% 10% 29% 27% 7% 1	597
	11th to 20th	Night	19% 9% 32% 31% 8%	394
	21st to end	Night	18% 5% 23% 39% 13% 1	433
June	1st to 10th	Night	18% 7% 24% 34% 18%	400
	11th to 20th	Night	14% 8% 25% 41% 11% 1	400
	21st to end	Night	13% 5% 26% 41% 16%	400
July	1st to 10th	Night	12% 4 19% 42% 22% 2	390
	11th to 20th	Night	11% 4 20% 41% 23% 1	388
	21st to end	Night	12% 3 20% 40% 23% 1	475
August	1st to 10th	Night	14% 3 14% 43% 24% 2	597
	11th to 20th	Night	16% 5% 16% 36% 26% 2	728
	21st to end	Night	16% 4 19% 35% 25% 2	880
September	1st to 10th	Night	17% 4 24% 33% 21% 1	800
	11th to 20th	Night	15% 5% 18% 34% 23% 5%	800
	21st to end	Night	22% 7% 21% 32% 18% 1	800
October	1st to 10th	Night	23% 8% 23% 26% 18% 3	800
	11th to 20th	Night	20% 10% 26% 33% 10% 1	800
	21st to end	Night	23% 10% 31% 27% 8%	880
November	1st to 10th	Night	16% 12% 33% 28% 10%	820
	11th to 20th	Night	19% 18% 30% 26% 7% 1	840
	21st to end	Night	18% 17% 33% 26% 6%	840
December	1st to 10th	Night	23% 16% 33% 22% 4	840
	11th to 20th	Night	23% 15% 34% 24% 4	840
	21st to end	Night	23% 16% 33% 24% 3	924

Page generated at 2026-01-14 01:14:26. Version ac07

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