Paslow Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Paslow Observatory clear sky chart from 2005-11-06 to 2026-05-02.

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	15% 10% 4 9% 5% 5% 5% 4 6% 7% 31%	131631
	Night	16% 11% 4 9% 5% 4 4 3 5% 6% 31%	130831
Transparency	Day	51% 5% 11% 21% 11% 1	135237
	Night	52% 5% 11% 20% 11% 2	135296
Seeing	Day	22% 15% 27% 20% 12% 4	16591
	Night	21% 12% 27% 28% 12% 1	26419

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	17% 17% 7% 20% 5% 4 4 2 4 5% 15%	5258
	11th to 20th	Day	13% 20% 8% 17% 9% 6% 3 2 3 3 16%	5280
	21st to end	Day	18% 15% 5% 13% 9% 6% 4 3 4 5% 18%	5780
February	1st to 10th	Day	19% 17% 5% 9% 6% 6% 4 3 4 5% 22%	1890
	11th to 20th	Day	16% 18% 5% 12% 5% 4 4 3 4 7% 22%	1843
	21st to end	Day	19% 15% 4 11% 6% 4 4 3 5% 5% 26%	1741
March	1st to 10th	Day	16% 14% 5% 9% 5% 5% 4 3 4 6% 30%	5045
	11th to 20th	Day	13% 8% 4 8% 6% 5% 5% 4 5% 6% 37%	5090
	21st to end	Day	16% 10% 3 9% 5% 5% 5% 3 5% 6% 31%	5586
April	1st to 10th	Day	16% 11% 3 9% 5% 5% 4 4 6% 7% 29%	2420
	11th to 20th	Day	15% 9% 3 8% 6% 4 5% 4 6% 7% 34%	2522
	21st to end	Day	19% 9% 3 7% 5% 4 4 3 5% 8% 33%	2730
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 6% 4 6% 7% 27%	5875
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	5861
	21st to end	Day	18% 7% 2 7% 5% 5% 5% 5% 7% 9% 32%	6770
June	1st to 10th	Day	12% 7% 3 6% 6% 6% 5% 4 8% 8% 35%	2800
	11th to 20th	Day	13% 7% 3 7% 6% 5% 5% 4 7% 8% 34%	2800
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 4 7% 10% 37%	2800
July	1st to 10th	Day	9% 6% 2 7% 6% 5% 5% 4 6% 8% 41%	6116
	11th to 20th	Day	10% 7% 3 8% 6% 6% 6% 5% 7% 10% 32%	5900
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 6% 8% 38%	6424
August	1st to 10th	Day	14% 7% 3 8% 5% 6% 6% 5% 7% 9% 30%	4234
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 8% 38%	4174
	21st to end	Day	8% 4 2 7% 5% 5% 6% 5% 8% 9% 41%	4446
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 5% 7% 45%	2400
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 6% 8% 46%	2205
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 5% 6% 34%	2198
October	1st to 10th	Day	15% 7% 2 6% 4 4 4 3 6% 7% 42%	2000
	11th to 20th	Day	17% 8% 3 8% 5% 4 4 4 5% 7% 36%	2000
	21st to end	Day	21% 9% 3 7% 4 3 4 3 6% 6% 35%	2200
November	1st to 10th	Day	12% 8% 3 7% 6% 4 4 4 4 6% 43%	1982
	11th to 20th	Day	16% 13% 4 8% 6% 4 5% 4 5% 5% 31%	1759
	21st to end	Day	17% 15% 5% 8% 6% 5% 4 4 4 6% 27%	1680
December	1st to 10th	Day	18% 12% 6% 15% 6% 5% 5% 3 4 4 22%	2680
	11th to 20th	Day	23% 16% 6% 11% 4 3 3 2 4 5% 22%	3070
	21st to end	Day	21% 18% 6% 13% 5% 5% 4 3 5% 5% 15%	4072
January	1st to 10th	Night	15% 16% 6% 20% 6% 5% 5% 3 4 4 16%	7635
	11th to 20th	Night	14% 17% 8% 14% 8% 6% 4 3 4 4 17%	7680
	21st to end	Night	18% 14% 5% 12% 8% 6% 4 3 4 5% 23%	8401
February	1st to 10th	Night	19% 13% 5% 10% 6% 4 4 4 4 5% 25%	2730
	11th to 20th	Night	19% 12% 5% 11% 6% 5% 4 4 4 5% 25%	2663
	21st to end	Night	18% 15% 4 11% 5% 4 5% 3 5% 4 25%	2061
March	1st to 10th	Night	21% 11% 4 8% 5% 3 3 3 4 5% 33%	5028
	11th to 20th	Night	11% 9% 3 8% 4 4 4 3 5% 7% 43%	5090
	21st to end	Night	16% 10% 3 8% 6% 5% 4 3 5% 6% 35%	5588
April	1st to 10th	Night	18% 12% 3 8% 5% 4 4 3 4 6% 34%	2200
	11th to 20th	Night	15% 9% 3 6% 5% 4 6% 3 6% 7% 36%	2064
	21st to end	Night	15% 9% 3 7% 4 4 5% 3 4 8% 37%	1890
May	1st to 10th	Night	24% 12% 3 8% 5% 4 5% 4 5% 6% 25%	4042
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 8% 36%	4032
	21st to end	Night	17% 8% 3 7% 4 4 5% 3 7% 8% 33%	4066
June	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 6% 8% 45%	1600
	11th to 20th	Night	11% 6% 2 7% 5% 5% 5% 5% 5% 10% 39%	1600
	21st to end	Night	9% 5% 2 6% 4 5% 6% 5% 8% 10% 41%	1600
July	1st to 10th	Night	10% 8% 3 8% 5% 4 4 4 6% 8% 42%	3822
	11th to 20th	Night	11% 7% 3 8% 5% 5% 6% 5% 7% 9% 35%	4057
	21st to end	Night	8% 7% 3 7% 5% 5% 5% 4 7% 8% 41%	4427
August	1st to 10th	Night	12% 8% 3 8% 5% 5% 5% 5% 7% 9% 34%	2915
	11th to 20th	Night	11% 7% 3 7% 5% 5% 4 3 5% 6% 43%	2875
	21st to end	Night	8% 5% 2 5% 5% 5% 6% 4 7% 8% 44%	3417
September	1st to 10th	Night	11% 5% 2 5% 4 4 4 3 5% 7% 49%	2000
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2190
	21st to end	Night	17% 8% 2 6% 5% 4 4 3 5% 6% 40%	2201
October	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 4 6% 46%	2400
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 5% 7% 40%	2400
	21st to end	Night	21% 7% 3 6% 4 3 3 3 4 7% 38%	2640
November	1st to 10th	Night	12% 8% 3 7% 4 4 3 4 5% 6% 46%	2534
	11th to 20th	Night	18% 12% 3 7% 5% 5% 4 4 5% 6% 32%	2857
	21st to end	Night	20% 13% 4 8% 4 4 4 3 4 6% 29%	2940
December	1st to 10th	Night	18% 14% 9% 14% 5% 4 4 3 5% 5% 19%	4720
	11th to 20th	Night	21% 15% 6% 11% 5% 4 4 3 3 4 24%	5345
	21st to end	Night	21% 17% 5% 12% 6% 5% 5% 3 4 5% 18%	7121

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	73% 3 10% 10% 3	5259
	11th to 20th	Day	74% 3 6% 9% 6% 2	5280
	21st to end	Day	70% 3 8% 15% 5%	5780
February	1st to 10th	Day	64% 5% 9% 15% 6% 1	1890
	11th to 20th	Day	63% 4 11% 16% 6%	1852
	21st to end	Day	60% 4 12% 16% 7% 1	1741
March	1st to 10th	Day	54% 6% 9% 22% 7% 1	5045
	11th to 20th	Day	47% 4 12% 26% 9% 2	5090
	21st to end	Day	52% 5% 9% 20% 12% 1	5586
April	1st to 10th	Day	53% 6% 11% 18% 10% 2	2420
	11th to 20th	Day	48% 7% 11% 18% 14% 2	2522
	21st to end	Day	49% 6% 10% 23% 10% 2	2730
May	1st to 10th	Day	54% 6% 11% 18% 8% 3	5910
	11th to 20th	Day	50% 7% 10% 23% 9% 1	5865
	21st to end	Day	46% 8% 14% 21% 10% 2	6785
June	1st to 10th	Day	43% 8% 14% 22% 11% 1	2800
	11th to 20th	Day	45% 8% 13% 21% 12% 1	2800
	21st to end	Day	42% 7% 13% 24% 13% 1	2800
July	1st to 10th	Day	41% 5% 10% 27% 16% 2	6051
	11th to 20th	Day	45% 5% 14% 24% 11%	5831
	21st to end	Day	42% 5% 11% 22% 18% 1	6240
August	1st to 10th	Day	48% 7% 14% 22% 9%	4221
	11th to 20th	Day	40% 7% 12% 28% 13%	4213
	21st to end	Day	36% 7% 14% 28% 14% 2	4446
September	1st to 10th	Day	37% 7% 10% 22% 21% 3	2400
	11th to 20th	Day	36% 5% 14% 27% 16% 1	2205
	21st to end	Day	50% 5% 11% 21% 14% 1	2198
October	1st to 10th	Day	34% 4 9% 31% 20% 1	3260
	11th to 20th	Day	43% 5% 12% 22% 14% 5%	3240
	21st to end	Day	37% 3 12% 28% 19% 1	3538
November	1st to 10th	Day	41% 5% 13% 21% 17% 3	1982
	11th to 20th	Day	54% 5% 10% 18% 11% 2	1759
	21st to end	Day	59% 5% 12% 17% 7% 1	1680
December	1st to 10th	Day	67% 4 13% 13% 4	2680
	11th to 20th	Day	66% 3 11% 15% 4	3066
	21st to end	Day	71% 4 9% 12% 4	4072
January	1st to 10th	Night	72% 4 10% 11% 3	7636
	11th to 20th	Night	71% 4 7% 11% 6% 1	7680
	21st to end	Night	66% 2 9% 16% 6% 1	8401
February	1st to 10th	Night	61% 5% 9% 18% 7%	2730
	11th to 20th	Night	62% 4 10% 17% 7%	2665
	21st to end	Night	61% 5% 8% 16% 9% 1	2061
March	1st to 10th	Night	54% 4 9% 22% 10% 1	5028
	11th to 20th	Night	42% 4 12% 29% 9% 3	5090
	21st to end	Night	50% 5% 10% 20% 14% 2	5588
April	1st to 10th	Night	52% 5% 9% 20% 12% 2	2200
	11th to 20th	Night	45% 7% 12% 19% 14% 3	2064
	21st to end	Night	46% 6% 11% 24% 12% 3	1890
May	1st to 10th	Night	59% 7% 9% 13% 9% 3	4069
	11th to 20th	Night	46% 7% 10% 25% 11% 1	4033
	21st to end	Night	46% 7% 13% 22% 8% 3	4073
June	1st to 10th	Night	37% 8% 13% 25% 16% 2	1600
	11th to 20th	Night	39% 8% 14% 24% 14% 2	1600
	21st to end	Night	35% 9% 13% 24% 17% 2	1600
July	1st to 10th	Night	41% 5% 10% 24% 18% 3	3780
	11th to 20th	Night	43% 6% 19% 22% 11% 1	4006
	21st to end	Night	39% 7% 11% 19% 22% 2	4297
August	1st to 10th	Night	46% 7% 14% 23% 10%	2904
	11th to 20th	Night	40% 6% 10% 26% 17% 1	2902
	21st to end	Night	36% 6% 13% 30% 12% 2	3417
September	1st to 10th	Night	34% 6% 11% 24% 21% 5%	2000
	11th to 20th	Night	31% 5% 13% 28% 22% 1	2190
	21st to end	Night	45% 5% 11% 21% 17% 1	2201
October	1st to 10th	Night	35% 4 9% 27% 23% 2	3920
	11th to 20th	Night	37% 4 11% 25% 16% 7%	3899
	21st to end	Night	35% 3 8% 29% 23% 2	4252
November	1st to 10th	Night	40% 4 11% 23% 18% 4	2534
	11th to 20th	Night	52% 5% 10% 20% 11% 2	2857
	21st to end	Night	56% 5% 11% 21% 7% 1	2940
December	1st to 10th	Night	67% 3 11% 15% 3	4720
	11th to 20th	Night	65% 3 14% 15% 3	5348
	21st to end	Night	68% 5% 11% 13% 3	7121

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	30% 28% 25% 13% 4 1	330
	11th to 20th	Day	36% 28% 27% 7% 2	330
	21st to end	Day	29% 33% 26% 9% 3 1	363
February	1st to 10th	Day	31% 22% 34% 11% 1 1	330
	11th to 20th	Day	37% 28% 27% 8% 1	330
	21st to end	Day	34% 22% 37% 6% 1	310
March	1st to 10th	Day	27% 23% 30% 16% 4	540
	11th to 20th	Day	32% 20% 30% 12% 5% 1	540
	21st to end	Day	30% 20% 30% 16% 4 1	594
April	1st to 10th	Day	29% 19% 26% 18% 6% 1	540
	11th to 20th	Day	22% 22% 30% 14% 8% 3	532
	21st to end	Day	25% 18% 32% 16% 7% 2	540
May	1st to 10th	Day	25% 18% 28% 17% 9% 2	507
	11th to 20th	Day	20% 15% 29% 20% 10% 5%	527
	21st to end	Day	16% 9% 26% 26% 17% 6%	573
June	1st to 10th	Day	15% 8% 31% 28% 15% 3	530
	11th to 20th	Day	15% 11% 26% 25% 18% 4	530
	21st to end	Day	13% 10% 28% 27% 18% 4	530
July	1st to 10th	Day	12% 7% 20% 29% 19% 12%	525
	11th to 20th	Day	11% 7% 26% 28% 19% 9%	524
	21st to end	Day	13% 6% 23% 30% 19% 8%	576
August	1st to 10th	Day	11% 4 26% 28% 22% 9%	526
	11th to 20th	Day	16% 4 20% 30% 20% 11%	519
	21st to end	Day	9% 5% 25% 26% 24% 12%	583
September	1st to 10th	Day	15% 8% 21% 27% 19% 10%	530
	11th to 20th	Day	12% 5% 15% 31% 25% 12%	530
	21st to end	Day	25% 9% 25% 20% 16% 5%	530
October	1st to 10th	Day	18% 8% 24% 25% 19% 5%	530
	11th to 20th	Day	20% 15% 30% 24% 9% 2	530
	21st to end	Day	26% 17% 30% 19% 6% 1	583
November	1st to 10th	Day	20% 18% 30% 20% 8% 3	460
	11th to 20th	Day	31% 17% 31% 15% 5% 1	261
	21st to end	Day	30% 20% 38% 9% 2	220
December	1st to 10th	Day	30% 25% 30% 10% 4 1	220
	11th to 20th	Day	32% 22% 30% 14% 2	220
	21st to end	Day	36% 20% 27% 13% 4	248
January	1st to 10th	Night	27% 21% 32% 17% 3	840
	11th to 20th	Night	33% 17% 30% 17% 3	840
	21st to end	Night	28% 19% 31% 19% 3	924
February	1st to 10th	Night	27% 17% 29% 25% 2	840
	11th to 20th	Night	29% 19% 34% 17% 1	823
	21st to end	Night	28% 16% 35% 18% 2	692
March	1st to 10th	Night	24% 17% 31% 25% 3	840
	11th to 20th	Night	25% 18% 28% 21% 6% 1	840
	21st to end	Night	23% 17% 33% 23% 4 1	924
April	1st to 10th	Night	26% 16% 30% 24% 5%	840
	11th to 20th	Night	21% 13% 32% 24% 9%	820
	21st to end	Night	19% 10% 33% 32% 6%	630
May	1st to 10th	Night	22% 10% 24% 33% 11% 1	603
	11th to 20th	Night	20% 7% 29% 32% 12% 1	591
	21st to end	Night	11% 4 24% 37% 21% 3	502
June	1st to 10th	Night	12% 4 25% 40% 20% 1	400
	11th to 20th	Night	13% 6% 23% 39% 19% 1	400
	21st to end	Night	10% 3 28% 37% 22% 1	400
July	1st to 10th	Night	8% 4 18% 43% 23% 5%	480
	11th to 20th	Night	9% 3 21% 34% 29% 4	582
	21st to end	Night	9% 3 16% 41% 29% 1	657
August	1st to 10th	Night	11% 1 17% 42% 28% 2	597
	11th to 20th	Night	11% 3 15% 38% 30% 3	594
	21st to end	Night	12% 4 18% 33% 29% 5%	776
September	1st to 10th	Night	14% 3 19% 36% 25% 4	800
	11th to 20th	Night	11% 4 15% 35% 29% 5%	800
	21st to end	Night	20% 7% 23% 28% 20% 3	800
October	1st to 10th	Night	16% 7% 21% 31% 23% 2	800
	11th to 20th	Night	20% 10% 30% 29% 11% 1	800
	21st to end	Night	24% 13% 26% 28% 8% 1	880
November	1st to 10th	Night	17% 11% 27% 31% 12%	820
	11th to 20th	Night	26% 14% 28% 25% 6% 1	840
	21st to end	Night	29% 14% 30% 23% 5% 1	840
December	1st to 10th	Night	31% 16% 29% 20% 4	840
	11th to 20th	Night	28% 17% 30% 21% 4	840
	21st to end	Night	27% 15% 33% 23% 2	924

Page generated at 2026-04-29 02:21:46. Version ac07

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