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 2025-01-07.

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	16% 10% 4 8% 5% 5% 5% 4 6% 7% 31%	104730
	Night	16% 11% 4 9% 5% 4 4 3 5% 6% 32%	104232
Transparency	Day	50% 6% 12% 21% 11% 1	108380
	Night	51% 5% 11% 20% 11% 2	108722
Seeing	Day	21% 14% 27% 21% 12% 4	14880
	Night	21% 11% 27% 28% 12% 1	24683

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	20% 19% 8% 11% 5% 3 3 2 4 5% 19%	2890
	11th to 20th	Day	13% 22% 9% 15% 7% 5% 3 2 3 4 17%	2840
	21st to end	Day	24% 20% 6% 13% 6% 4 3 3 3 5% 13%	3124
February	1st to 10th	Day	20% 18% 4 9% 6% 6% 4 2 4 5% 22%	1710
	11th to 20th	Day	15% 17% 5% 12% 5% 4 4 3 5% 7% 22%	1663
	21st to end	Day	20% 15% 4 11% 5% 4 4 3 5% 4 25%	1579
March	1st to 10th	Day	20% 13% 4 8% 5% 4 4 3 5% 6% 28%	3435
	11th to 20th	Day	14% 10% 4 9% 6% 6% 5% 4 5% 5% 33%	3480
	21st to end	Day	18% 10% 3 8% 5% 4 5% 4 5% 6% 32%	3815
April	1st to 10th	Day	15% 12% 4 9% 5% 5% 4 4 6% 7% 29%	2190
	11th to 20th	Day	16% 10% 3 8% 5% 4 5% 4 5% 6% 34%	2279
	21st to end	Day	20% 9% 3 7% 5% 4 4 3 5% 7% 32%	2470
May	1st to 10th	Day	23% 10% 3 7% 5% 5% 5% 3 5% 6% 27%	4082
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 4 6% 7% 31%	4081
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 4 7% 10% 37%	4715
June	1st to 10th	Day	12% 7% 3 6% 6% 6% 5% 4 8% 8% 35%	2660
	11th to 20th	Day	12% 7% 3 7% 6% 5% 6% 4 8% 8% 35%	2660
	21st to end	Day	12% 6% 3 6% 5% 5% 5% 5% 7% 10% 37%	2660
July	1st to 10th	Day	9% 7% 3 6% 6% 5% 6% 4 7% 7% 41%	4266
	11th to 20th	Day	9% 6% 3 6% 5% 5% 5% 5% 7% 10% 39%	4120
	21st to end	Day	12% 7% 3 8% 5% 5% 6% 5% 6% 8% 35%	4466
August	1st to 10th	Day	14% 7% 3 8% 5% 6% 6% 5% 7% 9% 30%	4104
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 5% 8% 9% 37%	4044
	21st to end	Day	8% 4 2 7% 5% 5% 6% 5% 8% 9% 41%	4310
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 5% 7% 44%	2280
	11th to 20th	Day	11% 6% 2 6% 4 4 4 3 6% 8% 45%	2095
	21st to end	Day	20% 8% 3 7% 5% 4 4 3 5% 7% 35%	2088
October	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 6% 7% 40%	1900
	11th to 20th	Day	17% 9% 3 8% 5% 4 4 3 5% 7% 35%	1900
	21st to end	Day	21% 9% 3 7% 4 3 4 2 6% 6% 34%	2090
November	1st to 10th	Day	12% 8% 2 7% 6% 4 4 4 4 6% 43%	1886
	11th to 20th	Day	16% 12% 3 7% 6% 4 5% 4 5% 5% 32%	1675
	21st to end	Day	17% 15% 5% 8% 6% 4 4 4 4 6% 27%	1600
December	1st to 10th	Day	18% 12% 6% 15% 6% 5% 5% 3 4 4 22%	2600
	11th to 20th	Day	24% 16% 6% 11% 4 3 3 2 4 5% 22%	2990
	21st to end	Day	21% 18% 6% 13% 5% 5% 4 3 5% 5% 15%	3983
January	1st to 10th	Night	16% 18% 7% 13% 6% 4 4 3 4 4 20%	4188
	11th to 20th	Night	17% 18% 7% 13% 6% 6% 5% 3 4 4 17%	4120
	21st to end	Night	27% 16% 6% 12% 6% 4 3 2 3 3 17%	4532
February	1st to 10th	Night	20% 14% 4 10% 7% 4 4 4 4 5% 25%	2470
	11th to 20th	Night	20% 12% 4 11% 6% 5% 4 3 4 5% 26%	2403
	21st to end	Night	19% 15% 5% 10% 6% 4 5% 3 4 4 26%	1871
March	1st to 10th	Night	23% 11% 3 7% 5% 3 3 3 4 5% 33%	3418
	11th to 20th	Night	15% 12% 4 9% 5% 3 3 3 4 6% 36%	3480
	21st to end	Night	17% 9% 3 7% 5% 4 4 3 4 6% 39%	3817
April	1st to 10th	Night	17% 12% 3 8% 4 4 4 3 4 6% 35%	1990
	11th to 20th	Night	16% 8% 3 6% 5% 4 5% 3 6% 7% 37%	1866
	21st to end	Night	15% 9% 4 7% 4 4 5% 3 4 7% 37%	1710
May	1st to 10th	Night	24% 12% 3 7% 5% 4 5% 4 4 7% 26%	2813
	11th to 20th	Night	16% 9% 3 7% 5% 4 4 3 5% 7% 37%	2812
	21st to end	Night	10% 6% 3 7% 4 4 5% 4 8% 10% 39%	2836
June	1st to 10th	Night	10% 5% 2 7% 4 4 4 4 6% 8% 44%	1520
	11th to 20th	Night	11% 5% 2 6% 5% 5% 5% 5% 6% 10% 39%	1520
	21st to end	Night	10% 4 2 6% 4 5% 6% 5% 8% 10% 41%	1520
July	1st to 10th	Night	10% 7% 2 8% 5% 4 5% 3 6% 8% 42%	2674
	11th to 20th	Night	10% 6% 2 7% 4 4 5% 4 6% 9% 42%	2840
	21st to end	Night	9% 8% 4 7% 5% 5% 5% 4 7% 7% 38%	3087
August	1st to 10th	Night	12% 9% 3 8% 5% 5% 5% 5% 7% 9% 33%	2825
	11th to 20th	Night	11% 7% 3 7% 5% 5% 4 3 5% 6% 43%	2785
	21st to end	Night	8% 5% 2 5% 5% 5% 6% 4 7% 8% 44%	3312
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 3 5% 7% 49%	1900
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	2080
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 7% 41%	2091
October	1st to 10th	Night	14% 6% 2 7% 5% 4 4 3 4 7% 45%	2280
	11th to 20th	Night	16% 7% 2 6% 5% 4 4 4 5% 6% 39%	2280
	21st to end	Night	22% 8% 3 6% 4 3 3 3 4 7% 37%	2508
November	1st to 10th	Night	12% 8% 3 7% 4 3 3 4 4 6% 46%	2410
	11th to 20th	Night	18% 12% 3 7% 5% 5% 4 4 5% 6% 32%	2721
	21st to end	Night	20% 13% 4 8% 4 4 4 3 4 6% 30%	2800
December	1st to 10th	Night	18% 14% 9% 14% 5% 4 4 3 5% 5% 19%	4580
	11th to 20th	Night	21% 16% 6% 11% 5% 4 4 3 3 4 24%	5205
	21st to end	Night	21% 17% 5% 11% 6% 5% 5% 3 4 5% 18%	6968

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	68% 5% 10% 12% 4	2891
	11th to 20th	Day	72% 4 8% 12% 4 1	2840
	21st to end	Day	76% 4 8% 10% 2	3124
February	1st to 10th	Day	65% 5% 9% 14% 6% 1	1710
	11th to 20th	Day	62% 4 11% 16% 7%	1672
	21st to end	Day	61% 4 11% 15% 7% 2	1579
March	1st to 10th	Day	55% 8% 9% 21% 6%	3435
	11th to 20th	Day	51% 5% 12% 23% 7% 1	3480
	21st to end	Day	51% 6% 11% 20% 10% 1	3815
April	1st to 10th	Day	52% 6% 11% 18% 10% 2	2190
	11th to 20th	Day	48% 7% 11% 17% 15% 2	2279
	21st to end	Day	50% 7% 10% 22% 10% 2	2470
May	1st to 10th	Day	55% 7% 10% 20% 8% 1	4120
	11th to 20th	Day	50% 8% 11% 22% 9% 1	4085
	21st to end	Day	38% 9% 16% 22% 11% 3	4729
June	1st to 10th	Day	44% 8% 14% 22% 11% 1	2660
	11th to 20th	Day	44% 8% 13% 22% 12% 1	2660
	21st to end	Day	42% 7% 13% 24% 12% 1	2660
July	1st to 10th	Day	41% 6% 12% 24% 15% 3	4201
	11th to 20th	Day	38% 6% 13% 27% 15% 1	4051
	21st to end	Day	45% 6% 11% 20% 16% 2	4324
August	1st to 10th	Day	49% 7% 14% 22% 8%	4091
	11th to 20th	Day	40% 7% 12% 27% 13%	4083
	21st to end	Day	37% 7% 14% 27% 14% 2	4310
September	1st to 10th	Day	38% 8% 10% 21% 20% 3	2280
	11th to 20th	Day	37% 6% 13% 27% 15% 2	2095
	21st to end	Day	49% 5% 10% 22% 14% 1	2088
October	1st to 10th	Day	35% 4 10% 31% 19% 1	3160
	11th to 20th	Day	43% 5% 12% 22% 14% 5%	3140
	21st to end	Day	36% 3 12% 29% 19% 1	3428
November	1st to 10th	Day	41% 5% 13% 22% 17% 3	1886
	11th to 20th	Day	53% 5% 10% 18% 11% 2	1675
	21st to end	Day	58% 5% 13% 17% 7% 1	1600
December	1st to 10th	Day	66% 4 13% 13% 4	2600
	11th to 20th	Day	66% 3 11% 15% 4	2986
	21st to end	Day	71% 4 9% 12% 4	3983
January	1st to 10th	Night	67% 5% 10% 14% 4	4188
	11th to 20th	Night	71% 5% 11% 11% 3	4120
	21st to end	Night	73% 3 8% 13% 3 1	4532
February	1st to 10th	Night	61% 5% 10% 17% 7%	2470
	11th to 20th	Night	60% 4 10% 17% 8%	2405
	21st to end	Night	61% 5% 9% 15% 9% 1	1871
March	1st to 10th	Night	53% 5% 10% 24% 8%	3418
	11th to 20th	Night	49% 5% 12% 26% 7% 1	3480
	21st to end	Night	45% 6% 10% 25% 13% 2	3817
April	1st to 10th	Night	50% 5% 9% 20% 12% 3	1990
	11th to 20th	Night	44% 7% 11% 18% 15% 4	1866
	21st to end	Night	45% 6% 11% 23% 12% 3	1710
May	1st to 10th	Night	57% 8% 7% 17% 10% 2	2840
	11th to 20th	Night	46% 8% 12% 23% 9% 2	2813
	21st to end	Night	36% 9% 16% 23% 11% 4	2843
June	1st to 10th	Night	37% 8% 13% 25% 15% 2	1520
	11th to 20th	Night	38% 8% 14% 25% 14% 2	1520
	21st to end	Night	35% 9% 13% 24% 16% 2	1520
July	1st to 10th	Night	41% 6% 11% 24% 16% 4	2630
	11th to 20th	Night	36% 6% 15% 27% 15% 1	2786
	21st to end	Night	42% 8% 11% 17% 19% 3	2988
August	1st to 10th	Night	47% 7% 14% 22% 10%	2814
	11th to 20th	Night	40% 6% 10% 26% 17% 1	2812
	21st to end	Night	36% 6% 13% 30% 13% 2	3312
September	1st to 10th	Night	35% 6% 11% 23% 20% 5%	1900
	11th to 20th	Night	31% 6% 13% 27% 22% 1	2080
	21st to end	Night	43% 5% 11% 22% 18% 1	2091
October	1st to 10th	Night	35% 5% 9% 27% 22% 2	3800
	11th to 20th	Night	38% 4 11% 25% 15% 8%	3779
	21st to end	Night	35% 3 8% 29% 22% 2	4120
November	1st to 10th	Night	40% 4 12% 23% 18% 4	2410
	11th to 20th	Night	52% 5% 10% 19% 11% 3	2721
	21st to end	Night	56% 5% 11% 21% 7% 1	2800
December	1st to 10th	Night	67% 4 11% 15% 3	4580
	11th to 20th	Night	65% 3 14% 14% 3	5208
	21st to end	Night	68% 5% 11% 13% 3	6968

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	31% 26% 25% 12% 5% 1	288
	11th to 20th	Day	33% 27% 29% 8% 3	270
	21st to end	Day	28% 33% 26% 9% 3 1	297
February	1st to 10th	Day	33% 21% 34% 11% 1	270
	11th to 20th	Day	35% 30% 28% 7% 1	270
	21st to end	Day	37% 22% 33% 7% 1	258
March	1st to 10th	Day	27% 22% 30% 17% 4	460
	11th to 20th	Day	31% 19% 32% 13% 4 1	460
	21st to end	Day	31% 18% 31% 16% 4 1	506
April	1st to 10th	Day	27% 20% 27% 18% 7% 1	460
	11th to 20th	Day	22% 21% 29% 15% 9% 4	452
	21st to end	Day	26% 18% 31% 16% 7% 2	460
May	1st to 10th	Day	26% 19% 26% 17% 9% 3	463
	11th to 20th	Day	20% 14% 30% 21% 10% 5%	487
	21st to end	Day	14% 8% 26% 27% 18% 7%	529
June	1st to 10th	Day	16% 8% 31% 27% 16% 3	490
	11th to 20th	Day	15% 11% 27% 25% 19% 4	490
	21st to end	Day	14% 10% 29% 28% 16% 3	490
July	1st to 10th	Day	12% 8% 21% 28% 19% 13%	485
	11th to 20th	Day	11% 7% 26% 29% 20% 8%	484
	21st to end	Day	13% 7% 24% 31% 18% 8%	532
August	1st to 10th	Day	12% 5% 25% 27% 22% 9%	486
	11th to 20th	Day	16% 4 22% 29% 19% 11%	479
	21st to end	Day	10% 5% 24% 25% 25% 12%	539
September	1st to 10th	Day	15% 7% 21% 28% 19% 9%	490
	11th to 20th	Day	13% 5% 16% 31% 24% 11%	490
	21st to end	Day	24% 10% 25% 20% 16% 5%	490
October	1st to 10th	Day	18% 9% 26% 23% 19% 5%	490
	11th to 20th	Day	21% 15% 28% 25% 9% 3	490
	21st to end	Day	26% 17% 30% 19% 7% 1	539
November	1st to 10th	Day	20% 16% 30% 21% 9% 3	424
	11th to 20th	Day	27% 18% 32% 16% 6% 1	237
	21st to end	Day	30% 20% 41% 8% 3	200
December	1st to 10th	Day	29% 25% 30% 11% 5% 1	200
	11th to 20th	Day	33% 21% 29% 15% 3	200
	21st to end	Day	33% 21% 28% 14% 4	225
January	1st to 10th	Night	27% 22% 32% 16% 3	785
	11th to 20th	Night	33% 16% 30% 18% 3	760
	21st to end	Night	28% 18% 31% 19% 4	836
February	1st to 10th	Night	28% 17% 29% 24% 3	760
	11th to 20th	Night	28% 19% 35% 16% 1	743
	21st to end	Night	29% 17% 34% 18% 3	628
March	1st to 10th	Night	23% 18% 31% 25% 3	760
	11th to 20th	Night	25% 19% 28% 21% 7% 1	760
	21st to end	Night	23% 16% 32% 24% 4 1	836
April	1st to 10th	Night	24% 16% 31% 24% 5%	760
	11th to 20th	Night	21% 12% 33% 24% 10%	742
	21st to end	Night	18% 10% 34% 32% 6%	570
May	1st to 10th	Night	21% 10% 24% 33% 11% 1	570
	11th to 20th	Night	20% 7% 29% 31% 12%	561
	21st to end	Night	9% 4 23% 38% 22% 3	477
June	1st to 10th	Night	11% 4 25% 39% 20% 1	380
	11th to 20th	Night	12% 6% 23% 39% 19% 1	380
	21st to end	Night	10% 3 28% 37% 21% 1	380
July	1st to 10th	Night	8% 4 18% 42% 22% 6%	455
	11th to 20th	Night	9% 3 21% 36% 28% 4	552
	21st to end	Night	9% 3 17% 41% 28% 1	624
August	1st to 10th	Night	11% 1 17% 41% 28% 2	567
	11th to 20th	Night	10% 3 16% 38% 29% 3	564
	21st to end	Night	12% 4 17% 33% 29% 5%	737
September	1st to 10th	Night	14% 3 18% 36% 26% 4	760
	11th to 20th	Night	11% 5% 16% 35% 29% 4	760
	21st to end	Night	19% 7% 23% 28% 20% 3	760
October	1st to 10th	Night	17% 7% 21% 31% 22% 2	760
	11th to 20th	Night	20% 10% 30% 27% 11% 1	760
	21st to end	Night	24% 13% 26% 28% 8% 1	836
November	1st to 10th	Night	17% 11% 28% 31% 13%	780
	11th to 20th	Night	25% 14% 28% 25% 7% 1	800
	21st to end	Night	28% 14% 30% 23% 5% 1	800
December	1st to 10th	Night	32% 15% 29% 20% 4	800
	11th to 20th	Night	27% 17% 30% 22% 4	800
	21st to end	Night	27% 15% 33% 24% 2	880

Page generated at 2025-01-04 03:24:04. Version ac07

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