Brookings
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brookings clear sky chart from 2005-11-06 to 2024-11-04.

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	12% 8% 3 7% 5% 4 4 4 6% 7% 40%	101430
	Night	10% 8% 3 8% 5% 4 5% 4 6% 7% 42%	97680
Transparency	Day	41% 7% 14% 24% 13% 1	105016
	Night	39% 6% 14% 24% 15% 2	102227
Seeing	Day	15% 10% 31% 28% 13% 3	15983
	Night	13% 9% 35% 33% 10% 1	25853

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	12% 12% 4 10% 12% 8% 7% 5% 6% 6% 19%	2347
	11th to 20th	Day	5% 11% 6% 15% 6% 5% 9% 5% 10% 9% 21%	2543
	21st to end	Day	5% 11% 9% 18% 7% 7% 5% 4 5% 6% 23%	3135
February	1st to 10th	Day	8% 11% 4 11% 9% 7% 5% 5% 7% 7% 27%	1710
	11th to 20th	Day	7% 11% 4 10% 7% 7% 6% 5% 5% 6% 31%	1668
	21st to end	Day	8% 10% 4 11% 6% 6% 5% 4 6% 6% 32%	1570
March	1st to 10th	Day	12% 11% 4 9% 5% 4 4 3 4 6% 39%	3302
	11th to 20th	Day	10% 10% 3 8% 5% 4 4 4 5% 7% 42%	3480
	21st to end	Day	23% 13% 4 11% 4 4 4 3 5% 5% 23%	3814
April	1st to 10th	Day	17% 7% 3 7% 4 4 5% 3 5% 7% 38%	2175
	11th to 20th	Day	19% 11% 4 8% 4 4 3 3 4 6% 35%	2442
	21st to end	Day	20% 10% 3 6% 4 3 4 3 5% 6% 36%	2470
May	1st to 10th	Day	15% 7% 2 7% 4 4 5% 4 6% 7% 38%	4082
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 7% 46%	4141
	21st to end	Day	19% 6% 2 6% 4 4 4 4 5% 8% 39%	4824
June	1st to 10th	Day	11% 5% 2 5% 4 5% 4 4 6% 9% 45%	2830
	11th to 20th	Day	14% 6% 2 5% 4 4 5% 4 6% 7% 43%	2850
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 9% 47%	2850
July	1st to 10th	Day	11% 4 2 5% 5% 5% 5% 4 8% 10% 41%	4750
	11th to 20th	Day	5% 3 1 4 3 3 4 4 6% 8% 59%	4529
	21st to end	Day	5% 4 2 5% 4 4 5% 5% 8% 9% 49%	4501
August	1st to 10th	Day	10% 7% 2 6% 4 4 5% 4 7% 9% 42%	4104
	11th to 20th	Day	14% 7% 3 7% 4 4 5% 4 6% 9% 37%	4041
	21st to end	Day	9% 5% 2 6% 4 4 4 4 5% 8% 51%	4532
September	1st to 10th	Day	12% 5% 2 5% 3 3 4 3 5% 6% 53%	2234
	11th to 20th	Day	10% 6% 2 5% 4 3 4 3 5% 6% 52%	2090
	21st to end	Day	12% 6% 2 4 4 3 4 3 4 5% 53%	2090
October	1st to 10th	Day	15% 8% 2 6% 3 3 3 3 4 7% 47%	1954
	11th to 20th	Day	14% 6% 2 5% 3 4 3 3 5% 7% 47%	1900
	21st to end	Day	15% 9% 3 6% 3 4 4 2 4 5% 43%	1986
November	1st to 10th	Day	12% 9% 3 6% 5% 4 4 4 5% 7% 43%	1700
	11th to 20th	Day	8% 11% 4 10% 6% 6% 4 4 5% 6% 36%	1537
	21st to end	Day	12% 10% 2 7% 4 4 5% 4 6% 9% 37%	1520
December	1st to 10th	Day	8% 9% 3 12% 8% 6% 7% 5% 5% 7% 30%	1520
	11th to 20th	Day	9% 11% 4 13% 8% 6% 4 4 5% 8% 28%	1767
	21st to end	Day	18% 10% 4 12% 7% 5% 4 4 4 6% 25%	2442
January	1st to 10th	Night	8% 12% 4 12% 9% 8% 7% 5% 7% 6% 22%	4605
	11th to 20th	Night	3 9% 4 12% 8% 7% 9% 6% 9% 9% 23%	4425
	21st to end	Night	5% 10% 7% 18% 5% 5% 5% 4 5% 6% 28%	4532
February	1st to 10th	Night	6% 11% 4 10% 7% 6% 5% 4 5% 8% 33%	2470
	11th to 20th	Night	7% 9% 4 9% 6% 6% 5% 4 6% 6% 38%	2403
	21st to end	Night	9% 10% 3 9% 6% 5% 5% 4 6% 7% 37%	1898
March	1st to 10th	Night	8% 7% 3 7% 4 4 5% 3 5% 8% 46%	3556
	11th to 20th	Night	8% 7% 3 7% 4 4 4 4 6% 7% 46%	3480
	21st to end	Night	22% 13% 4 8% 6% 4 4 3 4 5% 27%	3817
April	1st to 10th	Night	14% 10% 3 6% 4 4 4 4 5% 7% 39%	2000
	11th to 20th	Night	16% 10% 4 7% 4 3 3 3 4 5% 39%	1689
	21st to end	Night	16% 9% 4 7% 4 4 4 4 4 6% 38%	1710
May	1st to 10th	Night	18% 6% 2 4 3 3 3 3 4 7% 48%	2823
	11th to 20th	Night	9% 5% 2 5% 3 4 4 4 6% 8% 51%	2760
	21st to end	Night	16% 6% 2 5% 4 4 4 3 6% 8% 43%	2743
June	1st to 10th	Night	8% 4 1 4 3 4 4 4 7% 8% 52%	1346
	11th to 20th	Night	6% 5% 2 5% 4 5% 4 3 7% 8% 51%	1330
	21st to end	Night	7% 3 2 3 3 2 3 3 6% 8% 59%	1330
July	1st to 10th	Night	10% 6% 2 4 3 3 5% 3 6% 9% 48%	2220
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 8% 65%	2437
	21st to end	Night	3 3 1 4 4 4 5% 4 7% 12% 55%	3059
August	1st to 10th	Night	6% 8% 2 6% 3 4 4 4 6% 7% 49%	2836
	11th to 20th	Night	12% 5% 2 5% 3 3 4 4 6% 8% 48%	2798
	21st to end	Night	8% 4 2 5% 3 3 4 3 5% 7% 56%	3135
September	1st to 10th	Night	8% 5% 2 3 3 3 4 3 4 7% 59%	1942
	11th to 20th	Night	9% 5% 1 5% 3 4 3 3 4 7% 56%	2090
	21st to end	Night	11% 5% 2 4 3 2 3 3 3 5% 58%	2090
October	1st to 10th	Night	14% 6% 2 4 3 3 3 3 5% 6% 52%	2206
	11th to 20th	Night	14% 8% 2 5% 3 3 4 2 5% 6% 48%	2280
	21st to end	Night	13% 10% 2 6% 3 3 3 3 4 7% 45%	2608
November	1st to 10th	Night	9% 6% 3 7% 5% 4 4 3 5% 7% 47%	2451
	11th to 20th	Night	8% 10% 3 10% 5% 4 4 4 5% 6% 41%	2641
	21st to end	Night	9% 8% 3 8% 4 4 4 4 6% 7% 43%	2660
December	1st to 10th	Night	6% 10% 3 12% 8% 6% 6% 4 6% 7% 32%	2660
	11th to 20th	Night	10% 10% 3 10% 6% 5% 5% 4 7% 8% 33%	3425
	21st to end	Night	18% 13% 4 13% 5% 5% 4 3 5% 5% 25%	5225

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	61% 6% 11% 15% 5% 1	2348
	11th to 20th	Day	56% 4 10% 23% 7%	2543
	21st to end	Day	60% 6% 12% 15% 7%	3135
February	1st to 10th	Day	55% 6% 14% 16% 9%	1710
	11th to 20th	Day	51% 7% 12% 19% 9% 2	1677
	21st to end	Day	51% 6% 15% 17% 10% 2	1570
March	1st to 10th	Day	45% 6% 12% 28% 8% 1	3302
	11th to 20th	Day	40% 6% 11% 26% 14% 3	3480
	21st to end	Day	62% 7% 12% 13% 5% 1	3814
April	1st to 10th	Day	44% 7% 14% 22% 11% 1	2175
	11th to 20th	Day	49% 5% 11% 22% 12% 1	2442
	21st to end	Day	48% 6% 12% 24% 9%	2470
May	1st to 10th	Day	41% 9% 12% 24% 14%	4120
	11th to 20th	Day	37% 6% 11% 27% 15% 3	4145
	21st to end	Day	41% 8% 13% 24% 14% 1	4837
June	1st to 10th	Day	34% 8% 16% 30% 11% 1	2830
	11th to 20th	Day	38% 8% 15% 24% 13% 2	2850
	21st to end	Day	32% 8% 16% 28% 14% 2	2850
July	1st to 10th	Day	34% 10% 20% 24% 12% 1	4676
	11th to 20th	Day	21% 7% 15% 34% 20% 3	4450
	21st to end	Day	26% 9% 18% 27% 18% 1	4359
August	1st to 10th	Day	36% 7% 14% 26% 14% 2	4090
	11th to 20th	Day	42% 9% 15% 26% 7% 1	4080
	21st to end	Day	31% 7% 19% 26% 14% 2	4531
September	1st to 10th	Day	32% 5% 12% 32% 17% 1	2234
	11th to 20th	Day	31% 7% 17% 30% 14% 1	2090
	21st to end	Day	33% 5% 11% 30% 19% 2	2090
October	1st to 10th	Day	27% 3 9% 29% 30% 1	3240
	11th to 20th	Day	34% 5% 12% 24% 21% 3	3140
	21st to end	Day	44% 5% 14% 21% 16% 1	3255
November	1st to 10th	Day	40% 6% 14% 23% 13% 3	1700
	11th to 20th	Day	47% 7% 13% 21% 11% 1	1537
	21st to end	Day	42% 6% 15% 23% 12% 1	1520
December	1st to 10th	Day	51% 7% 16% 16% 8% 2	1520
	11th to 20th	Day	54% 6% 16% 18% 5%	1764
	21st to end	Day	57% 6% 11% 17% 7% 1	2442
January	1st to 10th	Night	58% 7% 11% 17% 7%	4605
	11th to 20th	Night	53% 6% 13% 19% 9% 1	4425
	21st to end	Night	54% 8% 13% 16% 9% 1	4532
February	1st to 10th	Night	48% 6% 11% 22% 11% 2	2470
	11th to 20th	Night	43% 7% 12% 23% 12% 3	2404
	21st to end	Night	44% 6% 13% 20% 12% 4	1898
March	1st to 10th	Night	35% 7% 12% 26% 17% 2	3556
	11th to 20th	Night	34% 5% 13% 30% 16% 1	3480
	21st to end	Night	59% 7% 12% 15% 5% 1	3817
April	1st to 10th	Night	43% 8% 12% 24% 11% 1	2000
	11th to 20th	Night	44% 5% 11% 23% 15% 2	1689
	21st to end	Night	45% 6% 11% 25% 12% 1	1710
May	1st to 10th	Night	36% 7% 14% 23% 17% 3	2850
	11th to 20th	Night	30% 8% 12% 27% 21% 2	2761
	21st to end	Night	39% 8% 12% 28% 13% 1	2751
June	1st to 10th	Night	28% 7% 16% 31% 15% 4	1346
	11th to 20th	Night	29% 7% 18% 26% 17% 4	1330
	21st to end	Night	22% 7% 16% 31% 21% 2	1330
July	1st to 10th	Night	31% 8% 21% 23% 15% 2	2185
	11th to 20th	Night	16% 7% 12% 41% 20% 3	2393
	21st to end	Night	20% 9% 19% 29% 20% 3	2962
August	1st to 10th	Night	33% 8% 16% 25% 16% 3	2826
	11th to 20th	Night	32% 10% 16% 29% 12% 1	2825
	21st to end	Night	27% 7% 18% 27% 17% 3	3135
September	1st to 10th	Night	26% 7% 14% 31% 21% 2	1942
	11th to 20th	Night	29% 6% 14% 32% 18% 1	2090
	21st to end	Night	29% 5% 10% 31% 23% 2	2090
October	1st to 10th	Night	21% 3 7% 27% 38% 4	3687
	11th to 20th	Night	28% 4 14% 30% 22% 2	3779
	21st to end	Night	38% 4 14% 28% 15% 1	4295
November	1st to 10th	Night	37% 5% 13% 23% 19% 4	2451
	11th to 20th	Night	41% 6% 14% 22% 14% 2	2641
	21st to end	Night	39% 6% 17% 25% 14% 1	2660
December	1st to 10th	Night	48% 7% 17% 19% 8%	2660
	11th to 20th	Night	46% 7% 21% 19% 6%	3427
	21st to end	Night	59% 5% 10% 18% 7% 1	5225

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	17% 8% 29% 32% 12% 1	270
	11th to 20th	Day	14% 12% 36% 29% 7% 2	270
	21st to end	Day	18% 11% 35% 24% 12% 1	297
February	1st to 10th	Day	12% 12% 44% 28% 3	270
	11th to 20th	Day	12% 15% 38% 27% 8%	270
	21st to end	Day	15% 13% 40% 28% 4	225
March	1st to 10th	Day	19% 15% 41% 23% 2 1	270
	11th to 20th	Day	17% 10% 41% 21% 10% 1	270
	21st to end	Day	26% 11% 26% 24% 11% 1	297
April	1st to 10th	Day	26% 15% 34% 20% 5%	355
	11th to 20th	Day	27% 14% 29% 22% 7% 1	640
	21st to end	Day	24% 14% 30% 21% 10% 1	650
May	1st to 10th	Day	20% 13% 31% 27% 8% 1	653
	11th to 20th	Day	21% 12% 29% 24% 12% 3	675
	21st to end	Day	20% 9% 29% 30% 11% 2	734
June	1st to 10th	Day	9% 9% 25% 33% 19% 4	680
	11th to 20th	Day	15% 9% 33% 28% 13% 2	680
	21st to end	Day	11% 8% 31% 33% 15% 2	680
July	1st to 10th	Day	7% 3 24% 37% 22% 6%	671
	11th to 20th	Day	6% 4 33% 34% 18% 4	668
	21st to end	Day	6% 4 25% 39% 22% 5%	739
August	1st to 10th	Day	10% 3 25% 36% 22% 4	676
	11th to 20th	Day	12% 5% 25% 32% 21% 4	665
	21st to end	Day	8% 6% 28% 34% 20% 4	748
September	1st to 10th	Day	12% 8% 30% 31% 15% 4	444
	11th to 20th	Day	11% 7% 34% 31% 14% 2	300
	21st to end	Day	17% 14% 29% 24% 11% 4	300
October	1st to 10th	Day	20% 9% 29% 26% 11% 5%	300
	11th to 20th	Day	14% 19% 33% 23% 8% 2	300
	21st to end	Day	22% 17% 38% 15% 7% 1	330
November	1st to 10th	Day	23% 10% 33% 22% 10% 2	279
	11th to 20th	Day	12% 15% 43% 22% 7% 1	270
	21st to end	Day	19% 19% 29% 25% 7% 1	270
December	1st to 10th	Day	12% 13% 40% 25% 9% 2	270
	11th to 20th	Day	12% 14% 43% 26% 4	270
	21st to end	Day	26% 9% 37% 22% 6% 1	297
January	1st to 10th	Night	11% 10% 41% 29% 8% 1	950
	11th to 20th	Night	11% 10% 39% 32% 7%	950
	21st to end	Night	16% 10% 39% 28% 7%	1045
February	1st to 10th	Night	11% 10% 43% 30% 6% 1	950
	11th to 20th	Night	13% 10% 40% 30% 7% 1	929
	21st to end	Night	13% 11% 35% 32% 7% 2	642
March	1st to 10th	Night	13% 10% 42% 29% 7%	660
	11th to 20th	Night	18% 10% 35% 31% 5%	570
	21st to end	Night	19% 10% 33% 29% 10% 1	627
April	1st to 10th	Night	18% 11% 39% 28% 4	570
	11th to 20th	Night	21% 13% 31% 26% 8% 1	563
	21st to end	Night	19% 10% 35% 28% 7% 1	570
May	1st to 10th	Night	17% 10% 33% 30% 9% 1	570
	11th to 20th	Night	16% 7% 35% 31% 9% 1	561
	21st to end	Night	16% 5% 34% 33% 11% 1	617
June	1st to 10th	Night	9% 5% 26% 42% 17% 1	570
	11th to 20th	Night	9% 5% 36% 41% 9%	570
	21st to end	Night	9% 3 26% 47% 15% 1	570
July	1st to 10th	Night	7% 3 23% 45% 21% 2	555
	11th to 20th	Night	5% 2 29% 47% 18%	552
	21st to end	Night	3 2 25% 49% 19% 1	624
August	1st to 10th	Night	6% 5% 22% 49% 17% 1	567
	11th to 20th	Night	10% 3 23% 42% 21% 2	564
	21st to end	Night	7% 3 29% 41% 19% 2	627
September	1st to 10th	Night	9% 4 31% 40% 15% 2	570
	11th to 20th	Night	9% 6% 33% 37% 13% 3	570
	21st to end	Night	12% 8% 34% 33% 11% 1	570
October	1st to 10th	Night	18% 8% 33% 30% 10% 1	686
	11th to 20th	Night	18% 11% 35% 28% 8%	760
	21st to end	Night	18% 12% 34% 28% 7%	936
November	1st to 10th	Night	12% 10% 39% 30% 8% 1	943
	11th to 20th	Night	13% 13% 38% 27% 9% 1	950
	21st to end	Night	12% 12% 38% 31% 7%	950
December	1st to 10th	Night	13% 12% 39% 29% 7% 1	950
	11th to 20th	Night	16% 9% 38% 29% 7% 1	950
	21st to end	Night	22% 11% 35% 26% 5% 1	1045

Page generated at 2024-11-01 21:47:44. Version ac07

Copyright © 2024 Attilla Danko.