Randolph Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Randolph Center clear sky chart from 2005-11-06 to 2026-01-02.

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% 9% 3 9% 5% 5% 5% 4 6% 7% 31%	127243
	Night	14% 10% 4 10% 6% 5% 5% 4 6% 7% 31%	124117
Transparency	Day	52% 4 12% 21% 11% 1	130724
	Night	53% 4 12% 20% 10% 1	128723
Seeing	Day	25% 16% 29% 19% 9% 3	16195
	Night	21% 13% 27% 28% 10% 1	25195

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	10% 10% 5% 22% 9% 5% 5% 3 4 5% 22%	3605
	11th to 20th	Day	10% 13% 6% 14% 7% 5% 5% 4 5% 5% 26%	3570
	21st to end	Day	10% 12% 6% 11% 7% 5% 6% 4 6% 6% 27%	3960
February	1st to 10th	Day	11% 12% 4 11% 8% 6% 6% 4 5% 8% 26%	1754
	11th to 20th	Day	10% 10% 5% 13% 9% 6% 5% 4 5% 7% 26%	1948
	21st to end	Day	13% 12% 4 10% 6% 5% 5% 4 6% 5% 29%	1650
March	1st to 10th	Day	17% 15% 4 13% 5% 5% 4 4 4 4 25%	4476
	11th to 20th	Day	11% 11% 5% 10% 5% 4 5% 4 5% 6% 33%	4644
	21st to end	Day	18% 14% 4 9% 5% 5% 5% 3 4 5% 29%	5970
April	1st to 10th	Day	18% 13% 3 9% 5% 4 4 3 4 5% 32%	2400
	11th to 20th	Day	16% 10% 3 6% 5% 5% 5% 4 6% 6% 34%	2374
	21st to end	Day	20% 11% 3 8% 5% 5% 4 4 5% 5% 30%	2580
May	1st to 10th	Day	29% 12% 3 9% 5% 4 5% 3 4 4 21%	5928
	11th to 20th	Day	16% 9% 4 10% 6% 5% 5% 4 6% 7% 28%	6318
	21st to end	Day	18% 7% 3 7% 4 5% 6% 5% 7% 8% 31%	6949
June	1st to 10th	Day	19% 7% 2 8% 6% 5% 5% 5% 6% 7% 30%	2800
	11th to 20th	Day	16% 7% 2 6% 6% 5% 5% 4 7% 8% 34%	2800
	21st to end	Day	18% 8% 3 8% 6% 5% 5% 5% 7% 7% 29%	2800
July	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 5% 8% 11% 35%	6360
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 6% 8% 10% 34%	6360
	21st to end	Day	13% 5% 2 6% 4 5% 5% 5% 6% 9% 40%	6926
August	1st to 10th	Day	13% 6% 2 7% 6% 5% 6% 5% 7% 9% 33%	4506
	11th to 20th	Day	15% 7% 3 8% 5% 5% 5% 5% 7% 9% 32%	4050
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 10% 40%	4312
September	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 6% 8% 47%	2400
	11th to 20th	Day	12% 6% 3 5% 3 4 4 3 5% 7% 48%	2260
	21st to end	Day	15% 7% 2 6% 4 3 4 3 6% 8% 41%	2200
October	1st to 10th	Day	20% 7% 3 8% 5% 4 4 3 4 6% 36%	2155
	11th to 20th	Day	15% 10% 3 7% 5% 5% 4 3 5% 7% 36%	1930
	21st to end	Day	21% 13% 4 7% 5% 4 5% 3 4 5% 29%	1980
November	1st to 10th	Day	12% 9% 3 8% 6% 5% 5% 4 6% 6% 36%	1851
	11th to 20th	Day	15% 11% 3 9% 5% 5% 4 4 6% 6% 31%	1890
	21st to end	Day	15% 13% 4 9% 5% 5% 4 4 6% 7% 27%	1743
December	1st to 10th	Day	14% 15% 6% 17% 8% 6% 6% 4 5% 6% 16%	2680
	11th to 20th	Day	18% 10% 3 10% 6% 6% 5% 4 6% 6% 26%	3066
	21st to end	Day	17% 13% 5% 11% 6% 5% 5% 3 4 5% 27%	4048
January	1st to 10th	Night	11% 9% 5% 20% 9% 5% 5% 4 5% 6% 21%	6364
	11th to 20th	Night	8% 12% 5% 16% 10% 8% 6% 5% 5% 6% 19%	6315
	21st to end	Night	11% 11% 5% 12% 7% 7% 6% 5% 6% 6% 26%	6996
February	1st to 10th	Night	9% 12% 5% 11% 7% 6% 6% 6% 6% 8% 25%	2640
	11th to 20th	Night	8% 10% 5% 10% 8% 7% 6% 6% 7% 6% 27%	2338
	21st to end	Night	11% 10% 3 11% 7% 5% 5% 4 6% 7% 30%	1980
March	1st to 10th	Night	18% 12% 4 9% 6% 5% 5% 4 6% 6% 25%	5364
	11th to 20th	Night	11% 11% 4 9% 7% 6% 6% 4 5% 6% 33%	5297
	21st to end	Night	17% 14% 4 9% 5% 5% 4 3 4 5% 30%	4962
April	1st to 10th	Night	16% 11% 3 8% 5% 6% 5% 4 5% 6% 32%	2000
	11th to 20th	Night	16% 11% 3 7% 4 5% 3 4 6% 7% 33%	1975
	21st to end	Night	19% 8% 3 7% 5% 4 4 3 5% 6% 35%	1818
May	1st to 10th	Night	31% 11% 3 7% 4 4 4 3 4 6% 21%	4054
	11th to 20th	Night	15% 11% 3 9% 6% 5% 5% 4 5% 5% 31%	3575
	21st to end	Night	16% 8% 2 8% 5% 5% 6% 4 6% 7% 31%	3926
June	1st to 10th	Night	18% 7% 2 5% 5% 4 5% 4 6% 9% 34%	1600
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 5% 8% 39%	1600
	21st to end	Night	17% 5% 2 7% 6% 4 4 4 5% 8% 38%	1600
July	1st to 10th	Night	10% 5% 2 7% 5% 6% 6% 5% 8% 9% 38%	3600
	11th to 20th	Night	13% 8% 4 7% 5% 4 5% 4 6% 7% 37%	3600
	21st to end	Night	9% 6% 2 5% 5% 5% 4 5% 6% 7% 47%	3926
August	1st to 10th	Night	15% 8% 3 8% 5% 4 5% 4 5% 6% 36%	2610
	11th to 20th	Night	14% 7% 3 6% 5% 5% 4 3 6% 7% 40%	2994
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 9% 46%	3586
September	1st to 10th	Night	12% 5% 3 5% 3 4 3 3 6% 8% 48%	2000
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 6% 50%	2138
	21st to end	Night	13% 7% 2 4 4 4 5% 3 7% 7% 44%	2200
October	1st to 10th	Night	18% 7% 3 7% 4 5% 3 3 6% 7% 37%	2242
	11th to 20th	Night	15% 8% 3 7% 5% 5% 5% 4 5% 7% 35%	2470
	21st to end	Night	21% 9% 3 7% 5% 5% 5% 5% 6% 6% 29%	2860
November	1st to 10th	Night	13% 10% 4 8% 5% 5% 5% 3 5% 6% 35%	2667
	11th to 20th	Night	15% 8% 3 10% 5% 5% 5% 4 6% 7% 33%	2730
	21st to end	Night	13% 10% 4 10% 6% 5% 5% 4 6% 8% 29%	2872
December	1st to 10th	Night	13% 13% 5% 15% 7% 6% 6% 4 6% 7% 17%	4720
	11th to 20th	Night	21% 11% 5% 9% 5% 5% 4 4 4 6% 26%	5348
	21st to end	Night	16% 15% 5% 13% 6% 5% 4 3 5% 5% 23%	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	65% 2 7% 21% 4	3606
	11th to 20th	Day	61% 3 8% 17% 8% 3	3600
	21st to end	Day	55% 5% 9% 18% 12% 2	3960
February	1st to 10th	Day	55% 4 12% 19% 7% 2	1754
	11th to 20th	Day	57% 4 11% 19% 8% 2	1957
	21st to end	Day	56% 3 12% 16% 12% 2	1650
March	1st to 10th	Day	64% 3 7% 12% 9% 6%	4479
	11th to 20th	Day	52% 2 14% 20% 9% 3	4644
	21st to end	Day	59% 3 4 15% 17% 3	5970
April	1st to 10th	Day	55% 2 9% 19% 12% 3	2400
	11th to 20th	Day	50% 4 9% 19% 16% 1	2374
	21st to end	Day	56% 3 8% 18% 12% 2	2580
May	1st to 10th	Day	68% 2 7% 16% 6% 1	5939
	11th to 20th	Day	56% 4 14% 17% 9% 1	6322
	21st to end	Day	50% 4 12% 24% 9% 1	6949
June	1st to 10th	Day	53% 4 13% 19% 10%	2800
	11th to 20th	Day	47% 4 12% 22% 14% 2	2800
	21st to end	Day	52% 5% 12% 20% 10% 1	2800
July	1st to 10th	Day	42% 5% 17% 24% 11%	6290
	11th to 20th	Day	41% 7% 16% 25% 11% 1	6285
	21st to end	Day	40% 5% 13% 31% 11%	6728
August	1st to 10th	Day	47% 5% 15% 22% 10%	4492
	11th to 20th	Day	48% 5% 15% 25% 6%	4089
	21st to end	Day	38% 5% 17% 25% 13% 1	4312
September	1st to 10th	Day	35% 4 12% 33% 14% 1	2400
	11th to 20th	Day	37% 3 9% 32% 18% 1	2260
	21st to end	Day	41% 3 14% 28% 12% 2	2200
October	1st to 10th	Day	47% 4 10% 24% 14% 1	3506
	11th to 20th	Day	45% 2 13% 26% 13%	3120
	21st to end	Day	44% 4 11% 27% 13% 1	3180
November	1st to 10th	Day	47% 4 13% 23% 13%	1851
	11th to 20th	Day	52% 4 12% 17% 13% 2	1890
	21st to end	Day	57% 4 16% 19% 5%	1743
December	1st to 10th	Day	68% 5% 12% 12% 3	2680
	11th to 20th	Day	57% 6% 9% 18% 10% 1	3066
	21st to end	Day	61% 2 7% 14% 13% 2	4048
January	1st to 10th	Night	64% 2 13% 16% 5%	6364
	11th to 20th	Night	65% 4 10% 13% 7% 1	6360
	21st to end	Night	58% 5% 9% 14% 13% 2	6996
February	1st to 10th	Night	54% 4 13% 20% 9% 1	2640
	11th to 20th	Night	54% 4 10% 21% 11% 1	2340
	21st to end	Night	53% 2 13% 21% 9% 3	1980
March	1st to 10th	Night	59% 3 8% 15% 13% 2	5374
	11th to 20th	Night	52% 2 16% 17% 10% 2	5298
	21st to end	Night	57% 3 5% 16% 17% 3	4962
April	1st to 10th	Night	53% 2 9% 21% 13% 2	2000
	11th to 20th	Night	50% 3 10% 24% 13% 1	1975
	21st to end	Night	50% 3 9% 20% 13% 3	1818
May	1st to 10th	Night	66% 2 8% 15% 7% 1	4060
	11th to 20th	Night	56% 4 11% 20% 9% 1	3576
	21st to end	Night	52% 4 14% 19% 10% 1	3927
June	1st to 10th	Night	47% 4 14% 22% 12% 1	1600
	11th to 20th	Night	44% 5% 16% 23% 11% 2	1600
	21st to end	Night	46% 4 16% 23% 10% 1	1600
July	1st to 10th	Night	41% 5% 19% 24% 11%	3560
	11th to 20th	Night	45% 6% 14% 24% 11%	3552
	21st to end	Night	36% 6% 15% 33% 9%	3809
August	1st to 10th	Night	49% 5% 13% 24% 9%	2600
	11th to 20th	Night	43% 5% 18% 23% 10%	3021
	21st to end	Night	33% 5% 21% 28% 12% 1	3586
September	1st to 10th	Night	34% 5% 15% 31% 14%	2000
	11th to 20th	Night	35% 3 12% 33% 17% 1	2138
	21st to end	Night	39% 4 14% 26% 15% 2	2200
October	1st to 10th	Night	49% 4 12% 24% 10% 1	3671
	11th to 20th	Night	43% 5% 12% 24% 15% 1	4019
	21st to end	Night	44% 4 13% 29% 9% 1	4610
November	1st to 10th	Night	50% 4 11% 23% 10% 2	2667
	11th to 20th	Night	50% 3 11% 23% 11% 2	2730
	21st to end	Night	53% 4 15% 21% 7%	2872
December	1st to 10th	Night	65% 6% 11% 15% 3	4720
	11th to 20th	Night	58% 4 9% 15% 13% 1	5348
	21st to end	Night	65% 3 8% 15% 7% 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	22% 26% 31% 15% 6% 1	202
	11th to 20th	Day	31% 22% 28% 14% 5% 1	200
	21st to end	Day	23% 27% 26% 17% 5% 1	220
February	1st to 10th	Day	35% 26% 28% 9% 2	282
	11th to 20th	Day	31% 23% 30% 13% 3	496
	21st to end	Day	27% 21% 32% 16% 4	414
March	1st to 10th	Day	30% 17% 31% 17% 3	500
	11th to 20th	Day	32% 22% 27% 13% 5%	500
	21st to end	Day	33% 21% 26% 13% 5% 3	550
April	1st to 10th	Day	37% 17% 25% 15% 5% 1	500
	11th to 20th	Day	37% 20% 24% 13% 5% 2	492
	21st to end	Day	33% 18% 29% 11% 8% 1	500
May	1st to 10th	Day	35% 19% 24% 12% 7% 2	503
	11th to 20th	Day	22% 19% 31% 20% 6% 2	527
	21st to end	Day	19% 18% 32% 20% 9% 2	573
June	1st to 10th	Day	23% 14% 37% 17% 8% 1	530
	11th to 20th	Day	22% 15% 32% 21% 9% 2	530
	21st to end	Day	21% 14% 34% 21% 8% 2	530
July	1st to 10th	Day	17% 11% 32% 26% 11% 3	525
	11th to 20th	Day	15% 9% 35% 27% 10% 3	524
	21st to end	Day	15% 11% 38% 25% 10% 2	576
August	1st to 10th	Day	12% 11% 29% 25% 18% 5%	526
	11th to 20th	Day	18% 9% 26% 23% 15% 9%	519
	21st to end	Day	14% 12% 28% 26% 14% 7%	583
September	1st to 10th	Day	16% 13% 25% 25% 13% 9%	530
	11th to 20th	Day	15% 10% 25% 21% 15% 13%	530
	21st to end	Day	21% 10% 29% 22% 13% 7%	530
October	1st to 10th	Day	24% 13% 24% 19% 14% 6%	530
	11th to 20th	Day	23% 17% 25% 22% 11% 2	491
	21st to end	Day	34% 15% 24% 20% 6% 1	462
November	1st to 10th	Day	26% 17% 23% 21% 12% 1	425
	11th to 20th	Day	28% 20% 25% 18% 8% 1	430
	21st to end	Day	35% 16% 26% 16% 6% 1	283
December	1st to 10th	Day	30% 17% 31% 16% 5% 1	220
	11th to 20th	Day	34% 21% 28% 15% 2	220
	21st to end	Day	33% 16% 28% 19% 5%	242
January	1st to 10th	Night	20% 19% 35% 22% 4	805
	11th to 20th	Night	25% 17% 29% 25% 4	800
	21st to end	Night	16% 18% 33% 29% 4	880
February	1st to 10th	Night	19% 18% 35% 25% 3	800
	11th to 20th	Night	21% 19% 35% 22% 3	783
	21st to end	Night	22% 16% 31% 27% 3	660
March	1st to 10th	Night	24% 15% 33% 26% 3	800
	11th to 20th	Night	24% 19% 28% 24% 5% 1	800
	21st to end	Night	27% 16% 26% 24% 7%	880
April	1st to 10th	Night	26% 18% 29% 23% 5%	800
	11th to 20th	Night	25% 19% 27% 22% 7%	791
	21st to end	Night	29% 13% 28% 23% 7%	618
May	1st to 10th	Night	27% 13% 28% 24% 7%	600
	11th to 20th	Night	18% 12% 29% 34% 6% 1	394
	21st to end	Night	18% 9% 27% 34% 13%	433
June	1st to 10th	Night	20% 7% 28% 33% 12%	400
	11th to 20th	Night	21% 8% 23% 34% 14%	400
	21st to end	Night	19% 5% 24% 38% 14% 1	400
July	1st to 10th	Night	16% 4 20% 43% 15% 2	390
	11th to 20th	Night	15% 4 23% 39% 17% 2	388
	21st to end	Night	13% 5% 21% 44% 17% 1	438
August	1st to 10th	Night	15% 3 16% 41% 24%	409
	11th to 20th	Night	16% 6% 19% 35% 21% 3	662
	21st to end	Night	14% 7% 18% 36% 22% 3	880
September	1st to 10th	Night	14% 6% 25% 33% 20% 2	800
	11th to 20th	Night	15% 8% 19% 31% 24% 4	800
	21st to end	Night	16% 7% 25% 33% 18% 2	800
October	1st to 10th	Night	23% 12% 17% 29% 17% 2	800
	11th to 20th	Night	23% 11% 23% 30% 13% 1	800
	21st to end	Night	28% 12% 26% 27% 7%	880
November	1st to 10th	Night	22% 16% 25% 29% 8%	820
	11th to 20th	Night	21% 17% 28% 25% 8% 2	840
	21st to end	Night	22% 16% 28% 27% 6%	840
December	1st to 10th	Night	26% 18% 31% 20% 4	840
	11th to 20th	Night	26% 17% 27% 25% 4	840
	21st to end	Night	27% 17% 29% 23% 4	924

Page generated at 2025-12-30 01:14:11. Version ac07

Copyright © 2025 Attilla Danko.