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 2024-07-31.

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% 11% 4 8% 5% 5% 5% 4 6% 7% 31%	89889
	Night	17% 11% 4 8% 5% 4 4 3 5% 6% 33%	89882
Transparency	Day	51% 7% 12% 20% 10% 1	89662
	Night	51% 6% 11% 20% 10% 2	89714
Seeing	Day	21% 14% 27% 21% 12% 4	14349
	Night	21% 11% 27% 28% 12% 1	24071

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% 4 3 2 4 5% 19%	2836
	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	10% 8% 3 6% 6% 5% 6% 5% 7% 8% 37%	2564
	11th to 20th	Day	10% 7% 2 7% 5% 6% 6% 5% 8% 10% 36%	2470
	21st to end	Day	12% 7% 2 8% 6% 6% 6% 5% 7% 9% 33%	2679
August	1st to 10th	Day	10% 6% 2 8% 6% 6% 6% 6% 8% 10% 32%	2327
	11th to 20th	Day	13% 6% 2 6% 5% 4 6% 5% 8% 9% 35%	2303
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 4 8% 9% 38%	2450
September	1st to 10th	Day	15% 6% 2 5% 4 4 4 4 5% 7% 42%	2160
	11th to 20th	Day	11% 7% 2 6% 4 4 4 4 6% 8% 45%	1985
	21st to end	Day	18% 8% 3 7% 5% 4 4 3 5% 7% 37%	1979
October	1st to 10th	Day	16% 7% 2 6% 5% 4 4 4 6% 7% 39%	1800
	11th to 20th	Day	18% 9% 3 8% 5% 4 4 3 5% 7% 34%	1800
	21st to end	Day	22% 10% 3 7% 4 4 3 2 5% 6% 33%	1980
November	1st to 10th	Day	12% 8% 3 7% 6% 4 4 4 5% 6% 42%	1790
	11th to 20th	Day	16% 12% 4 7% 6% 4 5% 4 5% 5% 32%	1592
	21st to end	Day	17% 15% 4 8% 5% 4 4 4 4 6% 28%	1520
December	1st to 10th	Day	22% 15% 6% 12% 6% 4 5% 3 4 4 19%	1520
	11th to 20th	Day	20% 17% 7% 10% 4 3 4 3 5% 6% 21%	1910
	21st to end	Day	23% 21% 6% 12% 5% 4 3 3 5% 5% 14%	2781
January	1st to 10th	Night	16% 18% 7% 13% 6% 4 4 3 4 4 20%	4109
	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	9% 6% 2 7% 5% 5% 5% 4 6% 9% 43%	1609
	11th to 20th	Night	8% 5% 2 5% 4 4 5% 5% 7% 9% 46%	1710
	21st to end	Night	8% 6% 3 6% 6% 5% 5% 5% 9% 9% 38%	1870
August	1st to 10th	Night	7% 5% 3 6% 5% 5% 5% 5% 8% 10% 41%	1611
	11th to 20th	Night	8% 7% 3 7% 5% 5% 4 4 6% 8% 44%	1598
	21st to end	Night	11% 6% 2 4 4 5% 5% 4 6% 8% 46%	1886
September	1st to 10th	Night	12% 5% 2 5% 4 4 4 4 6% 7% 48%	1800
	11th to 20th	Night	10% 5% 2 5% 3 4 4 3 5% 7% 52%	1970
	21st to end	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	1980
October	1st to 10th	Night	14% 6% 2 7% 4 4 4 4 4 7% 44%	2160
	11th to 20th	Night	17% 7% 2 6% 5% 4 4 4 5% 6% 37%	2160
	21st to end	Night	23% 8% 3 7% 4 3 3 3 4 6% 36%	2376
November	1st to 10th	Night	12% 8% 3 7% 4 3 4 4 5% 6% 45%	2286
	11th to 20th	Night	17% 12% 3 6% 4 5% 4 4 5% 6% 33%	2584
	21st to end	Night	19% 13% 4 8% 4 4 4 3 4 6% 30%	2660
December	1st to 10th	Night	22% 15% 6% 10% 5% 4 4 3 5% 5% 22%	2660
	11th to 20th	Night	18% 16% 5% 11% 5% 4 4 3 3 5% 25%	3285
	21st to end	Night	22% 18% 5% 11% 6% 4 5% 3 4 5% 15%	4870

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% 13% 4	2837
	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	42% 9% 12% 20% 13% 3	2499
	11th to 20th	Day	41% 7% 14% 23% 14% 1	2401
	21st to end	Day	44% 9% 13% 22% 12% 2	2537
August	1st to 10th	Day	43% 9% 15% 24% 8%	2314
	11th to 20th	Day	40% 10% 16% 24% 10% 1	2303
	21st to end	Day	40% 9% 14% 22% 12% 3	2450
September	1st to 10th	Day	39% 8% 11% 20% 18% 3	2160
	11th to 20th	Day	37% 6% 14% 28% 14% 1	1985
	21st to end	Day	47% 5% 10% 23% 14% 1	1979
October	1st to 10th	Day	43% 6% 13% 22% 15% 1	1800
	11th to 20th	Day	49% 5% 12% 23% 11%	1800
	21st to end	Day	52% 4 12% 20% 11% 1	1980
November	1st to 10th	Day	42% 5% 13% 22% 16% 3	1790
	11th to 20th	Day	53% 5% 10% 18% 11% 2	1592
	21st to end	Day	56% 5% 13% 18% 7% 1	1520
December	1st to 10th	Day	69% 5% 10% 13% 4	1520
	11th to 20th	Day	64% 4 10% 17% 4	1906
	21st to end	Day	72% 5% 10% 10% 3	2781
January	1st to 10th	Night	67% 5% 11% 14% 4	4109
	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	37% 8% 14% 22% 15% 4	1565
	11th to 20th	Night	30% 8% 16% 25% 18% 2	1656
	21st to end	Night	37% 11% 14% 20% 14% 3	1771
August	1st to 10th	Night	34% 9% 16% 26% 15%	1600
	11th to 20th	Night	37% 8% 15% 24% 15% 2	1598
	21st to end	Night	35% 8% 13% 26% 15% 4	1886
September	1st to 10th	Night	35% 6% 11% 24% 19% 5%	1800
	11th to 20th	Night	31% 6% 14% 27% 22% 1	1970
	21st to end	Night	41% 5% 11% 23% 19% 1	1980
October	1st to 10th	Night	40% 6% 12% 25% 14% 3	2160
	11th to 20th	Night	44% 6% 10% 25% 13% 1	2160
	21st to end	Night	50% 5% 10% 21% 12% 2	2376
November	1st to 10th	Night	40% 5% 12% 23% 17% 4	2286
	11th to 20th	Night	51% 5% 10% 20% 12% 2	2584
	21st to end	Night	55% 5% 11% 21% 7% 1	2660
December	1st to 10th	Night	64% 5% 12% 14% 5% 1	2660
	11th to 20th	Night	63% 5% 11% 18% 4	3288
	21st to end	Night	71% 5% 11% 10% 3	4870

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	29% 28% 25% 13% 5% 1	270
	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	14% 6% 23% 30% 18% 8%	529
August	1st to 10th	Day	12% 4 23% 28% 24% 10%	446
	11th to 20th	Day	16% 3 20% 29% 20% 12%	439
	21st to end	Day	10% 5% 24% 26% 23% 12%	495
September	1st to 10th	Day	16% 6% 21% 27% 19% 10%	450
	11th to 20th	Day	13% 5% 15% 32% 23% 11%	450
	21st to end	Day	22% 10% 25% 20% 16% 6%	450
October	1st to 10th	Day	19% 8% 25% 24% 19% 5%	450
	11th to 20th	Day	21% 16% 28% 25% 9% 1	450
	21st to end	Day	29% 16% 29% 19% 6% 1	495
November	1st to 10th	Day	20% 16% 30% 21% 10% 3	388
	11th to 20th	Day	28% 19% 28% 17% 7% 1	214
	21st to end	Day	26% 21% 42% 9% 3	180
December	1st to 10th	Day	29% 24% 29% 11% 5% 1	180
	11th to 20th	Day	31% 22% 31% 14% 2	180
	21st to end	Day	33% 22% 28% 13% 4	202
January	1st to 10th	Night	27% 21% 32% 16% 3	760
	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	10% 4 16% 40% 29% 1	624
August	1st to 10th	Night	11% 17% 42% 29% 2	537
	11th to 20th	Night	10% 3 15% 38% 30% 3	534
	21st to end	Night	13% 4 18% 33% 29% 5%	698
September	1st to 10th	Night	14% 3 18% 35% 27% 4	720
	11th to 20th	Night	11% 5% 16% 35% 29% 4	720
	21st to end	Night	18% 7% 23% 28% 21% 3	720
October	1st to 10th	Night	17% 8% 21% 31% 21% 2	720
	11th to 20th	Night	21% 11% 30% 27% 11% 1	720
	21st to end	Night	25% 13% 26% 28% 7% 1	792
November	1st to 10th	Night	17% 11% 27% 31% 13%	740
	11th to 20th	Night	24% 15% 28% 25% 7% 1	760
	21st to end	Night	28% 14% 29% 23% 5% 1	760
December	1st to 10th	Night	32% 15% 28% 20% 4	760
	11th to 20th	Night	26% 18% 30% 22% 4	760
	21st to end	Night	28% 15% 33% 22% 2	836

Page generated at 2024-07-28 09:52:08. Version ac07

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