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 2024-11-12.

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 8% 5% 5% 5% 4 6% 7% 32%	101464
	Night	15% 9% 4 9% 5% 5% 5% 4 6% 7% 32%	97731
Transparency	Day	51% 3 12% 22% 11% 1	104963
	Night	51% 3 13% 22% 10% 1	102321
Seeing	Day	24% 16% 29% 19% 9% 3	14808
	Night	21% 13% 27% 28% 10% 1	23739

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	11% 11% 5% 14% 7% 6% 5% 4 5% 6% 27%	2517
	11th to 20th	Day	13% 12% 6% 13% 9% 6% 5% 4 4 4 23%	2520
	21st to end	Day	13% 16% 8% 12% 7% 5% 5% 3 5% 5% 21%	2772
February	1st to 10th	Day	12% 11% 4 10% 7% 6% 6% 4 5% 8% 26%	1665
	11th to 20th	Day	10% 10% 5% 13% 8% 6% 5% 4 5% 6% 26%	1848
	21st to end	Day	14% 12% 4 10% 6% 5% 5% 4 6% 5% 29%	1570
March	1st to 10th	Day	19% 17% 4 10% 5% 5% 5% 4 4 4 24%	3116
	11th to 20th	Day	12% 13% 6% 11% 6% 4 5% 4 6% 5% 27%	3256
	21st to end	Day	17% 12% 5% 10% 5% 5% 4 4 3 5% 31%	4166
April	1st to 10th	Day	18% 13% 3 9% 5% 4 3 3 4 5% 32%	2280
	11th to 20th	Day	16% 10% 3 6% 5% 5% 5% 4 6% 6% 34%	2254
	21st to end	Day	21% 11% 3 8% 5% 5% 5% 4 5% 6% 29%	2451
May	1st to 10th	Day	22% 12% 3 9% 5% 5% 5% 3 5% 5% 27%	4134
	11th to 20th	Day	16% 8% 3 9% 6% 5% 5% 5% 6% 6% 30%	4398
	21st to end	Day	12% 5% 2 6% 4 5% 6% 5% 7% 9% 39%	4837
June	1st to 10th	Day	19% 7% 2 8% 6% 5% 5% 5% 6% 7% 29%	2660
	11th to 20th	Day	16% 7% 2 6% 6% 4 5% 4 7% 8% 35%	2660
	21st to end	Day	18% 8% 3 8% 6% 5% 5% 5% 7% 7% 28%	2660
July	1st to 10th	Day	12% 5% 2 6% 4 5% 6% 5% 8% 10% 36%	4440
	11th to 20th	Day	10% 5% 2 6% 5% 5% 6% 6% 8% 11% 34%	4440
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 5% 6% 8% 37%	4814
August	1st to 10th	Day	14% 6% 2 8% 6% 5% 6% 5% 7% 9% 32%	4368
	11th to 20th	Day	15% 8% 3 8% 5% 5% 5% 5% 7% 9% 31%	3924
	21st to end	Day	11% 5% 2 6% 4 5% 5% 5% 7% 10% 40%	4180
September	1st to 10th	Day	12% 6% 2 4 4 4 4 3 6% 8% 46%	2280
	11th to 20th	Day	13% 6% 3 5% 4 4 4 3 5% 7% 47%	2147
	21st to end	Day	15% 7% 2 6% 4 4 4 3 6% 8% 40%	2090
October	1st to 10th	Day	21% 7% 3 8% 6% 4 4 3 4 6% 34%	2047
	11th to 20th	Day	14% 11% 3 7% 5% 5% 4 3 5% 7% 36%	1834
	21st to end	Day	21% 13% 4 7% 5% 4 5% 3 4 5% 29%	1881
November	1st to 10th	Day	11% 9% 3 8% 6% 5% 4 5% 6% 6% 37%	1761
	11th to 20th	Day	16% 11% 2 9% 5% 5% 4 4 6% 6% 30%	1719
	21st to end	Day	15% 12% 4 9% 5% 5% 5% 4 6% 7% 28%	1577
December	1st to 10th	Day	17% 15% 3 11% 8% 6% 5% 3 5% 7% 21%	1520
	11th to 20th	Day	20% 13% 2 9% 5% 5% 5% 3 5% 7% 27%	1906
	21st to end	Day	20% 15% 5% 11% 6% 5% 5% 3 4 4 21%	2772
January	1st to 10th	Night	14% 10% 3 10% 6% 5% 5% 5% 7% 7% 27%	4429
	11th to 20th	Night	10% 12% 6% 15% 8% 7% 5% 4 5% 7% 21%	4440
	21st to end	Night	15% 14% 6% 14% 6% 6% 5% 4 5% 4 21%	4884
February	1st to 10th	Night	9% 12% 5% 11% 7% 6% 6% 6% 6% 8% 25%	2509
	11th to 20th	Night	9% 10% 5% 10% 7% 7% 6% 6% 7% 6% 27%	2218
	21st to end	Night	12% 10% 3 10% 7% 5% 5% 4 6% 7% 31%	1884
March	1st to 10th	Night	20% 14% 3 6% 6% 4 4 4 5% 6% 27%	3724
	11th to 20th	Night	11% 12% 4 10% 7% 6% 5% 4 5% 5% 31%	3699
	21st to end	Night	15% 13% 4 9% 5% 5% 3 3 4 5% 34%	3466
April	1st to 10th	Night	15% 11% 3 8% 5% 6% 5% 4 5% 6% 32%	1900
	11th to 20th	Night	17% 10% 3 6% 4 5% 3 4 6% 7% 33%	1875
	21st to end	Night	19% 8% 3 7% 5% 4 4 4 5% 6% 34%	1727
May	1st to 10th	Night	24% 11% 3 7% 4 4 5% 3 5% 8% 26%	2834
	11th to 20th	Night	18% 9% 3 8% 5% 5% 6% 4 5% 5% 31%	2495
	21st to end	Night	13% 6% 2 6% 4 4 5% 4 7% 9% 40%	2738
June	1st to 10th	Night	18% 7% 2 5% 5% 4 5% 4 6% 9% 33%	1520
	11th to 20th	Night	17% 7% 2 5% 4 4 4 4 5% 8% 40%	1520
	21st to end	Night	18% 5% 2 6% 6% 4 4 4 5% 8% 37%	1520
July	1st to 10th	Night	11% 5% 2 7% 6% 6% 5% 6% 7% 8% 37%	2520
	11th to 20th	Night	14% 5% 3 5% 5% 4 4 4 7% 8% 42%	2520
	21st to end	Night	12% 7% 3 6% 5% 5% 4 4 7% 7% 40%	2739
August	1st to 10th	Night	16% 8% 3 9% 5% 4 5% 4 5% 6% 35%	2529
	11th to 20th	Night	14% 6% 3 6% 5% 5% 4 3 6% 8% 40%	2900
	21st to end	Night	9% 5% 2 6% 4 4 4 4 7% 9% 46%	3476
September	1st to 10th	Night	12% 5% 2 5% 4 4 3 4 6% 8% 48%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 3 3 5% 6% 50%	2031
	21st to end	Night	13% 7% 2 4 4 4 4 3 7% 7% 44%	2090
October	1st to 10th	Night	18% 7% 3 7% 4 6% 3 3 6% 7% 35%	2130
	11th to 20th	Night	15% 8% 3 7% 5% 5% 5% 4 5% 7% 35%	2346
	21st to end	Night	21% 9% 2 7% 5% 4 5% 5% 6% 6% 29%	2717
November	1st to 10th	Night	13% 9% 4 8% 5% 5% 5% 3 5% 6% 35%	2537
	11th to 20th	Night	16% 7% 2 9% 4 5% 5% 5% 6% 7% 33%	2484
	21st to end	Night	14% 9% 4 10% 6% 5% 5% 4 6% 8% 30%	2598
December	1st to 10th	Night	17% 13% 5% 11% 7% 5% 5% 4 6% 7% 20%	2660
	11th to 20th	Night	19% 10% 5% 9% 5% 5% 5% 5% 5% 8% 25%	3288
	21st to end	Night	19% 13% 5% 15% 5% 4 4 3 5% 5% 20%	4884

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	58% 2 9% 26% 5%	2518
	11th to 20th	Day	65% 3 9% 18% 5% 1	2520
	21st to end	Day	66% 2 10% 15% 6% 1	2772
February	1st to 10th	Day	55% 4 12% 19% 7% 2	1665
	11th to 20th	Day	57% 4 10% 19% 9% 2	1857
	21st to end	Day	56% 3 12% 16% 11% 2	1570
March	1st to 10th	Day	66% 2 8% 13% 10% 2	3119
	11th to 20th	Day	59% 1 10% 17% 11% 2	3256
	21st to end	Day	58% 2 4 16% 18% 3	4166
April	1st to 10th	Day	55% 2 9% 20% 12% 3	2280
	11th to 20th	Day	50% 4 10% 20% 16% 1	2254
	21st to end	Day	57% 3 9% 18% 11% 2	2451
May	1st to 10th	Day	61% 2 9% 20% 7% 1	4148
	11th to 20th	Day	53% 3 15% 19% 9% 1	4402
	21st to end	Day	41% 3 13% 29% 12% 1	4837
June	1st to 10th	Day	53% 4 14% 19% 10%	2660
	11th to 20th	Day	47% 4 11% 22% 14% 2	2660
	21st to end	Day	53% 5% 12% 19% 9% 1	2660
July	1st to 10th	Day	41% 5% 16% 25% 13%	4370
	11th to 20th	Day	40% 6% 19% 27% 7%	4365
	21st to end	Day	44% 5% 13% 25% 12%	4661
August	1st to 10th	Day	48% 5% 16% 22% 10%	4354
	11th to 20th	Day	49% 5% 16% 25% 6%	3963
	21st to end	Day	38% 5% 17% 25% 13% 1	4180
September	1st to 10th	Day	36% 4 12% 33% 14% 1	2280
	11th to 20th	Day	38% 3 9% 32% 17% 1	2147
	21st to end	Day	42% 3 14% 28% 11% 2	2090
October	1st to 10th	Day	48% 4 10% 23% 13% 1	3398
	11th to 20th	Day	45% 2 13% 26% 13%	3024
	21st to end	Day	44% 3 12% 28% 13% 1	3081
November	1st to 10th	Day	46% 4 13% 23% 13%	1761
	11th to 20th	Day	53% 4 12% 18% 11% 2	1719
	21st to end	Day	55% 3 17% 20% 5% 1	1577
December	1st to 10th	Day	63% 3 14% 15% 5% 1	1520
	11th to 20th	Day	59% 4 10% 18% 8% 1	1906
	21st to end	Day	67% 2 10% 13% 8%	2772
January	1st to 10th	Night	54% 2 17% 21% 6%	4429
	11th to 20th	Night	63% 3 12% 15% 6% 1	4440
	21st to end	Night	66% 2 9% 15% 6% 1	4884
February	1st to 10th	Night	54% 4 13% 19% 8% 1	2509
	11th to 20th	Night	54% 4 9% 22% 11% 1	2220
	21st to end	Night	52% 2 13% 21% 9% 3	1884
March	1st to 10th	Night	60% 2 9% 18% 10% 1	3734
	11th to 20th	Night	56% 2 10% 19% 12% 1	3700
	21st to end	Night	55% 2 6% 16% 18% 4	3466
April	1st to 10th	Night	53% 2 9% 22% 13% 2	1900
	11th to 20th	Night	50% 3 10% 25% 13% 1	1875
	21st to end	Night	51% 3 9% 20% 13% 3	1727
May	1st to 10th	Night	59% 2 10% 19% 9% 1	2840
	11th to 20th	Night	56% 2 13% 19% 9% 1	2496
	21st to end	Night	42% 3 17% 23% 14% 2	2739
June	1st to 10th	Night	47% 4 15% 22% 11%	1520
	11th to 20th	Night	43% 5% 16% 23% 11% 2	1520
	21st to end	Night	46% 4 16% 23% 10% 1	1520
July	1st to 10th	Night	43% 5% 18% 21% 13%	2480
	11th to 20th	Night	40% 6% 16% 28% 10%	2472
	21st to end	Night	42% 6% 12% 29% 11% 1	2651
August	1st to 10th	Night	50% 4 13% 24% 9%	2519
	11th to 20th	Night	44% 5% 19% 23% 10%	2927
	21st to end	Night	33% 5% 22% 27% 12% 1	3476
September	1st to 10th	Night	34% 5% 16% 31% 13%	1900
	11th to 20th	Night	36% 3 12% 33% 16% 1	2031
	21st to end	Night	39% 3 14% 27% 14% 3	2090
October	1st to 10th	Night	50% 4 12% 24% 8% 1	3559
	11th to 20th	Night	43% 5% 12% 24% 15% 1	3895
	21st to end	Night	44% 4 13% 29% 10% 1	4467
November	1st to 10th	Night	49% 4 12% 23% 10% 2	2537
	11th to 20th	Night	49% 3 11% 24% 10% 2	2484
	21st to end	Night	53% 4 15% 21% 7%	2598
December	1st to 10th	Night	64% 3 12% 17% 4	2660
	11th to 20th	Night	57% 4 12% 17% 10% 1	3288
	21st to end	Night	68% 2 9% 17% 4	4884

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% 22% 32% 17% 7% 1	180
	11th to 20th	Day	31% 23% 27% 13% 5% 1	180
	21st to end	Day	21% 26% 28% 18% 6% 1	198
February	1st to 10th	Day	34% 25% 28% 10% 2	253
	11th to 20th	Day	29% 23% 31% 14% 3	456
	21st to end	Day	28% 21% 30% 16% 4	382
March	1st to 10th	Day	29% 16% 32% 18% 4	460
	11th to 20th	Day	32% 21% 28% 14% 5%	460
	21st to end	Day	32% 21% 25% 13% 5% 3	506
April	1st to 10th	Day	35% 16% 26% 16% 5% 2	460
	11th to 20th	Day	35% 20% 24% 13% 6% 2	452
	21st to end	Day	33% 18% 30% 10% 8% 2	460
May	1st to 10th	Day	33% 20% 25% 12% 7% 3	463
	11th to 20th	Day	21% 19% 31% 21% 6% 2	487
	21st to end	Day	18% 18% 33% 21% 9% 2	529
June	1st to 10th	Day	23% 14% 38% 16% 8% 1	490
	11th to 20th	Day	21% 14% 31% 22% 9% 2	490
	21st to end	Day	22% 13% 34% 20% 9% 2	490
July	1st to 10th	Day	17% 11% 30% 27% 11% 3	485
	11th to 20th	Day	15% 8% 36% 27% 10% 4	484
	21st to end	Day	14% 10% 38% 25% 10% 3	532
August	1st to 10th	Day	13% 12% 30% 24% 17% 5%	486
	11th to 20th	Day	19% 9% 25% 24% 14% 8%	479
	21st to end	Day	14% 12% 28% 25% 14% 7%	539
September	1st to 10th	Day	16% 13% 25% 26% 13% 8%	490
	11th to 20th	Day	16% 11% 25% 21% 15% 13%	490
	21st to end	Day	20% 10% 28% 22% 12% 7%	490
October	1st to 10th	Day	24% 13% 26% 18% 13% 6%	490
	11th to 20th	Day	23% 16% 25% 22% 11% 2	455
	21st to end	Day	34% 15% 24% 20% 7% 1	429
November	1st to 10th	Day	24% 17% 23% 22% 13% 1	395
	11th to 20th	Day	28% 20% 24% 19% 8% 1	373
	21st to end	Day	31% 16% 27% 18% 7% 1	237
December	1st to 10th	Day	28% 19% 31% 17% 4 2	180
	11th to 20th	Day	32% 20% 29% 17% 2	180
	21st to end	Day	34% 17% 27% 17% 5%	198
January	1st to 10th	Night	20% 18% 35% 23% 4	760
	11th to 20th	Night	25% 17% 28% 26% 4	760
	21st to end	Night	16% 18% 32% 29% 4	836
February	1st to 10th	Night	19% 18% 34% 26% 3	760
	11th to 20th	Night	20% 18% 35% 23% 3	743
	21st to end	Night	22% 17% 31% 27% 4	628
March	1st to 10th	Night	23% 14% 33% 27% 3	760
	11th to 20th	Night	23% 19% 28% 24% 6% 1	760
	21st to end	Night	27% 16% 26% 24% 8%	836
April	1st to 10th	Night	25% 17% 30% 23% 5%	760
	11th to 20th	Night	24% 19% 26% 23% 7%	751
	21st to end	Night	28% 13% 28% 23% 7%	587
May	1st to 10th	Night	26% 13% 29% 24% 8%	570
	11th to 20th	Night	18% 13% 29% 34% 6% 1	374
	21st to end	Night	18% 9% 27% 34% 12%	411
June	1st to 10th	Night	20% 7% 28% 32% 12%	380
	11th to 20th	Night	20% 8% 22% 36% 14%	380
	21st to end	Night	19% 5% 24% 37% 13% 1	380
July	1st to 10th	Night	16% 4 20% 42% 16% 2	370
	11th to 20th	Night	14% 4 24% 39% 17% 2	368
	21st to end	Night	13% 6% 20% 43% 17% 1	416
August	1st to 10th	Night	15% 3 16% 42% 24%	388
	11th to 20th	Night	16% 6% 19% 36% 20% 3	628
	21st to end	Night	15% 7% 18% 36% 22% 3	836
September	1st to 10th	Night	14% 7% 26% 32% 19% 2	760
	11th to 20th	Night	15% 8% 19% 30% 24% 4	760
	21st to end	Night	16% 7% 25% 32% 18% 2	760
October	1st to 10th	Night	24% 12% 17% 29% 16% 2	760
	11th to 20th	Night	22% 11% 23% 29% 14% 1	760
	21st to end	Night	28% 12% 26% 27% 7%	836
November	1st to 10th	Night	21% 16% 25% 30% 8% 1	780
	11th to 20th	Night	20% 16% 28% 26% 8% 2	765
	21st to end	Night	23% 15% 28% 27% 7%	760
December	1st to 10th	Night	27% 17% 32% 20% 4	760
	11th to 20th	Night	25% 17% 27% 26% 5%	760
	21st to end	Night	26% 17% 30% 23% 3	836

Page generated at 2024-11-08 22:45:36. Version ac07

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