Webster Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Webster Park clear sky chart from 2005-11-06 to 2026-04-17.

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	15% 11% 4 9% 5% 5% 4 4 5% 7% 31%	131885
	Night	17% 13% 5% 11% 6% 5% 4 3 5% 6% 25%	130259
Transparency	Day	53% 6% 12% 19% 10% 1	135440
	Night	57% 6% 11% 16% 9% 1	134790
Seeing	Day	22% 15% 29% 21% 10% 2	16324
	Night	23% 14% 28% 23% 10% 1	25740

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	16% 19% 9% 18% 7% 4 4 3 4 4 11%	4661
	11th to 20th	Day	11% 23% 9% 16% 8% 5% 4 4 4 5% 10%	4786
	21st to end	Day	14% 16% 6% 16% 12% 9% 5% 4 5% 4 9%	5780
February	1st to 10th	Day	14% 17% 6% 15% 8% 6% 5% 4 5% 4 15%	1890
	11th to 20th	Day	14% 17% 8% 17% 8% 6% 5% 4 4 4 14%	1843
	21st to end	Day	19% 15% 5% 15% 8% 4 4 3 5% 5% 17%	1689
March	1st to 10th	Day	17% 13% 5% 12% 8% 4 3 2 4 5% 27%	4858
	11th to 20th	Day	11% 13% 5% 9% 6% 5% 5% 3 4 7% 32%	5090
	21st to end	Day	17% 12% 4 10% 5% 4 4 3 5% 6% 30%	5715
April	1st to 10th	Day	18% 11% 4 8% 5% 4 3 3 5% 6% 33%	2520
	11th to 20th	Day	19% 9% 3 7% 4 4 4 4 5% 6% 36%	2446
	21st to end	Day	19% 10% 3 7% 5% 5% 4 3 5% 6% 34%	2526
May	1st to 10th	Day	24% 10% 3 7% 4 4 4 3 5% 6% 30%	6112
	11th to 20th	Day	13% 9% 4 9% 5% 4 4 4 6% 9% 32%	6318
	21st to end	Day	18% 7% 3 6% 4 4 5% 4 6% 8% 35%	6949
June	1st to 10th	Day	15% 6% 2 7% 5% 4 4 4 6% 8% 39%	2800
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 8% 11% 40%	2800
	21st to end	Day	12% 6% 3 6% 4 5% 4 4 7% 8% 43%	2800
July	1st to 10th	Day	9% 5% 2 6% 4 5% 5% 4 6% 10% 44%	6360
	11th to 20th	Day	9% 5% 3 6% 5% 5% 5% 4 7% 9% 43%	6360
	21st to end	Day	9% 4 2 6% 4 4 4 4 6% 9% 47%	6792
August	1st to 10th	Day	16% 6% 3 6% 4 4 5% 3 6% 8% 41%	4234
	11th to 20th	Day	13% 6% 3 7% 5% 4 5% 5% 6% 8% 38%	4174
	21st to end	Day	13% 6% 2 5% 4 4 4 4 5% 8% 45%	4317
September	1st to 10th	Day	12% 7% 2 6% 4 5% 4 4 6% 7% 45%	2400
	11th to 20th	Day	14% 5% 2 6% 4 4 4 4 5% 8% 45%	2400
	21st to end	Day	16% 6% 3 7% 5% 5% 4 4 6% 7% 35%	2095
October	1st to 10th	Day	18% 9% 2 7% 4 3 3 4 5% 7% 37%	2000
	11th to 20th	Day	20% 12% 4 7% 5% 5% 4 3 5% 8% 29%	2000
	21st to end	Day	27% 11% 3 8% 5% 5% 3 4 5% 6% 23%	2176
November	1st to 10th	Day	15% 13% 4 9% 5% 5% 5% 4 5% 6% 30%	1840
	11th to 20th	Day	15% 16% 4 11% 5% 6% 5% 5% 4 7% 23%	1680
	21st to end	Day	20% 18% 7% 10% 5% 4 5% 4 5% 7% 17%	1680
December	1st to 10th	Day	19% 23% 8% 14% 6% 6% 4 3 4 4 9%	2680
	11th to 20th	Day	19% 21% 7% 13% 5% 3 3 3 4 4 17%	3066
	21st to end	Day	22% 19% 7% 15% 8% 4 4 3 4 5% 10%	4048
January	1st to 10th	Night	16% 21% 9% 21% 7% 4 4 3 4 3 9%	8234
	11th to 20th	Night	11% 22% 9% 18% 7% 5% 4 3 5% 5% 10%	8097
	21st to end	Night	15% 17% 6% 15% 10% 8% 5% 3 4 4 12%	8401
February	1st to 10th	Night	17% 17% 5% 16% 8% 5% 4 3 5% 5% 16%	2730
	11th to 20th	Night	14% 16% 6% 16% 9% 6% 5% 4 4 5% 16%	2663
	21st to end	Night	17% 15% 6% 16% 6% 4 4 3 5% 6% 18%	2116
March	1st to 10th	Night	16% 12% 6% 13% 7% 5% 4 3 5% 5% 23%	5186
	11th to 20th	Night	14% 15% 4 9% 5% 4 4 3 5% 7% 31%	5089
	21st to end	Night	18% 11% 4 12% 5% 4 4 3 4 5% 29%	5459
April	1st to 10th	Night	20% 12% 4 8% 5% 4 4 4 5% 6% 28%	2100
	11th to 20th	Night	18% 9% 3 8% 5% 4 5% 3 5% 7% 33%	2036
	21st to end	Night	20% 9% 3 6% 5% 3 5% 3 5% 7% 35%	1890
May	1st to 10th	Night	29% 10% 3 8% 5% 4 4 3 4 5% 25%	3828
	11th to 20th	Night	16% 7% 3 7% 5% 4 5% 4 7% 8% 35%	3575
	21st to end	Night	19% 7% 3 6% 4 4 4 4 6% 7% 36%	3926
June	1st to 10th	Night	13% 8% 3 8% 5% 5% 5% 5% 6% 8% 36%	1600
	11th to 20th	Night	11% 7% 2 6% 4 6% 5% 4 7% 8% 40%	1600
	21st to end	Night	11% 6% 3 8% 5% 4 5% 5% 6% 7% 40%	1600
July	1st to 10th	Night	13% 5% 2 6% 5% 4 5% 4 6% 10% 40%	3600
	11th to 20th	Night	11% 6% 3 7% 4 5% 5% 3 6% 8% 43%	3600
	21st to end	Night	10% 5% 2 7% 4 4 5% 4 6% 7% 47%	4056
August	1st to 10th	Night	12% 6% 2 6% 4 4 5% 3 7% 9% 41%	2915
	11th to 20th	Night	14% 6% 3 7% 4 4 5% 4 6% 9% 38%	2875
	21st to end	Night	10% 5% 2 6% 4 5% 5% 5% 7% 10% 42%	3546
September	1st to 10th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 45%	2000
	11th to 20th	Night	15% 6% 2 5% 4 3 4 4 5% 8% 45%	2000
	21st to end	Night	17% 6% 3 7% 5% 4 5% 4 6% 8% 35%	2301
October	1st to 10th	Night	19% 8% 3 7% 6% 4 5% 3 5% 6% 35%	2400
	11th to 20th	Night	22% 10% 3 8% 5% 5% 5% 3 6% 7% 28%	2400
	21st to end	Night	28% 12% 4 7% 4 4 4 3 5% 5% 24%	2662
November	1st to 10th	Night	18% 12% 3 8% 5% 4 4 4 5% 6% 31%	2676
	11th to 20th	Night	16% 17% 5% 9% 6% 4 5% 3 6% 6% 23%	2940
	21st to end	Night	22% 18% 5% 10% 5% 4 4 4 6% 6% 18%	2940
December	1st to 10th	Night	18% 24% 7% 12% 7% 6% 5% 4 5% 4 8%	4720
	11th to 20th	Night	20% 20% 7% 12% 5% 4 4 3 4 4 18%	5348
	21st to end	Night	26% 19% 7% 11% 6% 4 4 3 4 5% 11%	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	76% 6% 9% 7% 2	4662
	11th to 20th	Day	75% 6% 7% 6% 6% 1	4816
	21st to end	Day	76% 6% 8% 7% 2	5780
February	1st to 10th	Day	72% 6% 9% 11% 2	1890
	11th to 20th	Day	74% 5% 7% 11% 3	1852
	21st to end	Day	70% 5% 10% 11% 4	1689
March	1st to 10th	Day	60% 5% 11% 16% 8%	4861
	11th to 20th	Day	53% 5% 19% 13% 9% 1	5090
	21st to end	Day	54% 6% 9% 20% 10% 1	5715
April	1st to 10th	Day	54% 5% 11% 17% 11% 1	2520
	11th to 20th	Day	50% 6% 10% 20% 13% 1	2446
	21st to end	Day	52% 6% 9% 19% 13% 2	2526
May	1st to 10th	Day	56% 6% 10% 15% 11% 2	6121
	11th to 20th	Day	49% 8% 11% 18% 12% 2	6322
	21st to end	Day	46% 7% 12% 21% 12% 2	6949
June	1st to 10th	Day	44% 7% 12% 20% 16% 1	2800
	11th to 20th	Day	38% 8% 14% 25% 13% 1	2800
	21st to end	Day	40% 8% 13% 22% 16% 1	2800
July	1st to 10th	Day	36% 5% 13% 30% 15% 1	6290
	11th to 20th	Day	38% 6% 15% 27% 13% 1	6285
	21st to end	Day	35% 6% 13% 31% 14%	6596
August	1st to 10th	Day	42% 7% 15% 22% 14% 1	4221
	11th to 20th	Day	44% 7% 15% 26% 8%	4213
	21st to end	Day	38% 6% 13% 35% 8% 1	4317
September	1st to 10th	Day	38% 7% 13% 30% 11% 1	2400
	11th to 20th	Day	38% 7% 12% 28% 15%	2400
	21st to end	Day	48% 7% 12% 22% 11%	2095
October	1st to 10th	Day	42% 6% 14% 25% 12%	3260
	11th to 20th	Day	48% 4 15% 20% 12%	3240
	21st to end	Day	51% 6% 13% 23% 7%	3490
November	1st to 10th	Day	55% 6% 10% 18% 9% 1	1840
	11th to 20th	Day	60% 7% 13% 13% 6% 1	1680
	21st to end	Day	66% 6% 12% 13% 2	1680
December	1st to 10th	Day	77% 4 11% 7% 1	2680
	11th to 20th	Day	70% 6% 10% 7% 8%	3066
	21st to end	Day	76% 5% 10% 7% 2	4048
January	1st to 10th	Night	79% 6% 7% 6% 2	8234
	11th to 20th	Night	74% 7% 7% 7% 5%	8142
	21st to end	Night	73% 5% 8% 8% 6%	8401
February	1st to 10th	Night	69% 5% 9% 12% 5%	2730
	11th to 20th	Night	69% 6% 10% 12% 3	2665
	21st to end	Night	65% 7% 10% 12% 6%	2116
March	1st to 10th	Night	61% 6% 12% 16% 6%	5196
	11th to 20th	Night	51% 5% 17% 17% 7% 2	5090
	21st to end	Night	56% 6% 8% 20% 9% 1	5459
April	1st to 10th	Night	57% 5% 10% 19% 8% 1	2100
	11th to 20th	Night	51% 6% 11% 17% 13% 1	2036
	21st to end	Night	48% 5% 11% 19% 14% 2	1890
May	1st to 10th	Night	61% 6% 7% 12% 11% 3	3835
	11th to 20th	Night	45% 8% 15% 19% 11% 2	3576
	21st to end	Night	45% 7% 13% 19% 15% 1	3927
June	1st to 10th	Night	44% 7% 12% 22% 15% 2	1600
	11th to 20th	Night	40% 6% 13% 22% 17% 2	1600
	21st to end	Night	40% 9% 12% 22% 16% 2	1600
July	1st to 10th	Night	40% 5% 14% 23% 17% 2	3560
	11th to 20th	Night	39% 4 12% 26% 16% 2	3552
	21st to end	Night	36% 5% 12% 26% 20% 1	3937
August	1st to 10th	Night	38% 6% 14% 27% 13% 1	2904
	11th to 20th	Night	41% 6% 16% 27% 9%	2902
	21st to end	Night	35% 6% 13% 33% 12% 1	3546
September	1st to 10th	Night	37% 8% 12% 28% 13% 2	2000
	11th to 20th	Night	37% 6% 12% 29% 16% 1	2000
	21st to end	Night	44% 8% 12% 24% 12% 1	2301
October	1st to 10th	Night	46% 6% 9% 26% 12% 1	3920
	11th to 20th	Night	50% 5% 12% 19% 13%	3899
	21st to end	Night	50% 5% 11% 26% 8% 1	4298
November	1st to 10th	Night	52% 6% 12% 18% 9% 2	2676
	11th to 20th	Night	58% 8% 13% 13% 8% 1	2940
	21st to end	Night	64% 7% 14% 13% 3	2940
December	1st to 10th	Night	76% 6% 10% 7% 1	4720
	11th to 20th	Night	68% 6% 8% 10% 8% 1	5348
	21st to end	Night	75% 6% 8% 8% 3	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	31% 28% 27% 9% 5%	220
	11th to 20th	Day	30% 27% 31% 11% 1	245
	21st to end	Day	30% 22% 30% 14% 4	363
February	1st to 10th	Day	29% 24% 34% 11% 2	330
	11th to 20th	Day	31% 28% 34% 6% 1	330
	21st to end	Day	36% 21% 32% 10% 1	405
March	1st to 10th	Day	23% 26% 34% 14% 3 1	540
	11th to 20th	Day	31% 20% 31% 14% 3 1	540
	21st to end	Day	32% 21% 29% 13% 5% 1	594
April	1st to 10th	Day	29% 20% 29% 17% 4 1	540
	11th to 20th	Day	29% 21% 28% 14% 6% 2	516
	21st to end	Day	27% 17% 31% 18% 6% 1	500
May	1st to 10th	Day	25% 12% 33% 17% 9% 3	503
	11th to 20th	Day	18% 12% 29% 29% 10% 2	527
	21st to end	Day	19% 10% 29% 24% 14% 3	573
June	1st to 10th	Day	16% 15% 30% 28% 9% 1	530
	11th to 20th	Day	15% 12% 30% 28% 13% 3	530
	21st to end	Day	14% 11% 33% 31% 10% 2	530
July	1st to 10th	Day	11% 6% 26% 35% 18% 3	525
	11th to 20th	Day	13% 6% 28% 30% 18% 4	524
	21st to end	Day	11% 7% 33% 33% 14% 2	576
August	1st to 10th	Day	12% 6% 25% 35% 18% 5%	526
	11th to 20th	Day	14% 7% 25% 30% 19% 5%	519
	21st to end	Day	13% 7% 29% 30% 16% 5%	583
September	1st to 10th	Day	14% 11% 23% 28% 17% 7%	530
	11th to 20th	Day	14% 9% 19% 27% 21% 11%	530
	21st to end	Day	17% 12% 26% 25% 15% 4	530
October	1st to 10th	Day	22% 11% 29% 19% 14% 5%	530
	11th to 20th	Day	27% 16% 31% 16% 8% 2	530
	21st to end	Day	34% 15% 29% 18% 3	569
November	1st to 10th	Day	26% 19% 28% 16% 10% 1	414
	11th to 20th	Day	29% 24% 30% 12% 5%	220
	21st to end	Day	38% 21% 27% 12% 2	220
December	1st to 10th	Day	33% 21% 32% 9% 4 1	220
	11th to 20th	Day	34% 25% 28% 12%	220
	21st to end	Day	37% 22% 26% 13% 2	242
January	1st to 10th	Night	28% 25% 30% 13% 3	840
	11th to 20th	Night	29% 23% 29% 16% 3	840
	21st to end	Night	24% 23% 33% 16% 4	924
February	1st to 10th	Night	28% 21% 33% 17% 1	840
	11th to 20th	Night	26% 24% 32% 15% 2	823
	21st to end	Night	26% 20% 35% 16% 2	692
March	1st to 10th	Night	28% 18% 33% 18% 4	840
	11th to 20th	Night	27% 20% 30% 19% 4	840
	21st to end	Night	26% 15% 32% 20% 6% 1	924
April	1st to 10th	Night	26% 15% 33% 22% 4	840
	11th to 20th	Night	24% 14% 29% 25% 7% 1	816
	21st to end	Night	24% 10% 29% 26% 11%	690
May	1st to 10th	Night	25% 8% 21% 30% 14% 1	505
	11th to 20th	Night	16% 6% 29% 38% 11% 1	394
	21st to end	Night	13% 6% 29% 31% 20% 1	433
June	1st to 10th	Night	17% 5% 30% 30% 17% 2	400
	11th to 20th	Night	16% 8% 24% 32% 19% 2	400
	21st to end	Night	13% 5% 28% 38% 16% 1	400
July	1st to 10th	Night	10% 3 23% 39% 23% 3	390
	11th to 20th	Night	11% 2 26% 36% 23% 3	388
	21st to end	Night	12% 4 22% 39% 22% 2	493
August	1st to 10th	Night	9% 4 22% 41% 21% 4	597
	11th to 20th	Night	12% 4 20% 36% 25% 4	594
	21st to end	Night	11% 5% 23% 34% 25% 2	853
September	1st to 10th	Night	16% 6% 21% 29% 25% 4	800
	11th to 20th	Night	16% 5% 15% 30% 27% 7%	800
	21st to end	Night	19% 9% 21% 30% 18% 5%	800
October	1st to 10th	Night	22% 12% 24% 23% 17% 3	800
	11th to 20th	Night	25% 14% 31% 22% 8% 1	800
	21st to end	Night	34% 12% 30% 21% 3	880
November	1st to 10th	Night	27% 13% 30% 22% 8% 1	820
	11th to 20th	Night	26% 21% 29% 16% 7% 1	840
	21st to end	Night	32% 18% 29% 16% 5%	840
December	1st to 10th	Night	32% 24% 28% 13% 3	840
	11th to 20th	Night	29% 25% 28% 15% 3	840
	21st to end	Night	36% 20% 29% 14% 2	924

Page generated at 2026-04-14 02:44:29. Version ac07

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