Beaumont
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Beaumont clear sky chart from 2005-11-06 to 2025-03-27.

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	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	109418
	Night	14% 7% 2 6% 4 4 4 3 5% 7% 44%	110108
Transparency	Day	41% 8% 11% 17% 16% 6%	113064
	Night	37% 6% 12% 18% 17% 8%	114602
Seeing	Day	14% 6% 18% 25% 23% 13%	15303
	Night	15% 5% 19% 32% 25% 4	25270

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	21% 9% 2 6% 3 4 3 3 4 5% 40%	4077
	11th to 20th	Day	16% 6% 2 6% 4 3 3 3 3 5% 49%	4080
	21st to end	Day	28% 8% 3 6% 3 3 3 2 4 7% 33%	4488
February	1st to 10th	Day	22% 7% 3 6% 5% 4 3 3 5% 6% 35%	1800
	11th to 20th	Day	22% 10% 3 7% 4 4 3 2 4 4 37%	2035
	21st to end	Day	22% 10% 3 6% 4 3 3 3 3 5% 37%	1815
March	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 4 5% 7% 28%	3546
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	3590
	21st to end	Day	18% 6% 3 6% 5% 5% 4 3 5% 5% 40%	3880
April	1st to 10th	Day	14% 9% 3 6% 5% 5% 4 4 5% 7% 36%	2137
	11th to 20th	Day	17% 7% 3 7% 5% 5% 4 4 6% 7% 36%	2254
	21st to end	Day	10% 7% 2 6% 6% 5% 6% 5% 5% 7% 43%	2280
May	1st to 10th	Day	17% 8% 3 9% 6% 6% 5% 4 5% 7% 28%	3765
	11th to 20th	Day	13% 6% 2 6% 4 4 4 3 6% 8% 42%	3913
	21st to end	Day	8% 6% 2 8% 6% 6% 7% 6% 8% 10% 34%	4477
June	1st to 10th	Day	6% 5% 3 8% 7% 7% 8% 6% 8% 9% 34%	2470
	11th to 20th	Day	5% 5% 2 7% 7% 6% 8% 6% 9% 9% 34%	2470
	21st to end	Day	7% 5% 2 9% 8% 8% 8% 7% 10% 10% 25%	2470
July	1st to 10th	Day	8% 6% 3 9% 7% 7% 8% 7% 10% 11% 24%	4120
	11th to 20th	Day	8% 9% 4 11% 8% 8% 7% 6% 9% 9% 21%	4120
	21st to end	Day	14% 9% 3 9% 7% 7% 7% 5% 7% 10% 23%	4465
August	1st to 10th	Day	2 2 1 4 4 5% 5% 5% 8% 10% 54%	4086
	11th to 20th	Day	3 3 1 5% 5% 5% 6% 5% 10% 13% 44%	3729
	21st to end	Day	9% 6% 3 8% 7% 6% 7% 5% 7% 8% 34%	4180
September	1st to 10th	Day	9% 7% 2 7% 6% 6% 6% 5% 7% 9% 34%	2235
	11th to 20th	Day	14% 6% 2 8% 6% 5% 7% 5% 6% 7% 35%	2090
	21st to end	Day	10% 5% 2 5% 5% 5% 5% 4 6% 8% 44%	2081
October	1st to 10th	Day	7% 4 2 6% 4 4 5% 3 5% 7% 53%	1900
	11th to 20th	Day	9% 5% 2 5% 4 4 4 4 5% 8% 51%	1900
	21st to end	Day	13% 5% 2 6% 3 3 3 2 5% 6% 53%	2090
November	1st to 10th	Day	12% 6% 2 5% 4 5% 5% 4 4 7% 45%	1958
	11th to 20th	Day	11% 5% 3 7% 4 4 4 4 5% 6% 48%	2000
	21st to end	Day	16% 8% 2 6% 4 4 3 3 4 6% 44%	2000
December	1st to 10th	Day	22% 8% 3 6% 3 4 3 3 4 6% 38%	3038
	11th to 20th	Day	14% 9% 3 7% 5% 4 4 3 5% 6% 41%	3391
	21st to end	Day	17% 7% 2 5% 3 3 4 3 5% 5% 46%	4488
January	1st to 10th	Night	18% 7% 3 5% 3 3 3 3 4 6% 45%	5888
	11th to 20th	Night	18% 8% 3 5% 3 3 3 2 3 5% 47%	5900
	21st to end	Night	28% 9% 2 7% 4 3 3 3 4 6% 32%	6490
February	1st to 10th	Night	18% 9% 3 7% 4 4 3 4 4 6% 39%	2600
	11th to 20th	Night	22% 8% 3 5% 3 3 3 2 3 6% 41%	2266
	21st to end	Night	22% 9% 2 7% 4 3 3 3 4 5% 37%	1815
March	1st to 10th	Night	24% 13% 3 7% 4 4 4 3 4 5% 29%	3529
	11th to 20th	Night	23% 8% 4 8% 6% 4 4 3 4 6% 32%	3590
	21st to end	Night	14% 6% 2 6% 4 5% 4 4 5% 6% 44%	3889
April	1st to 10th	Night	15% 6% 3 6% 6% 4 4 4 5% 8% 39%	2043
	11th to 20th	Night	17% 6% 2 4 3 3 3 3 6% 9% 42%	1875
	21st to end	Night	13% 7% 2 5% 5% 4 4 4 4 7% 45%	1900
May	1st to 10th	Night	27% 9% 3 6% 5% 4 4 4 5% 8% 27%	3130
	11th to 20th	Night	14% 6% 3 6% 4 4 4 4 5% 6% 43%	2981
	21st to end	Night	13% 6% 2 6% 4 4 4 4 9% 10% 37%	3090
June	1st to 10th	Night	5% 3 2 4 4 3 4 4 7% 11% 53%	1710
	11th to 20th	Night	5% 3 1 4 4 3 4 4 7% 12% 53%	1710
	21st to end	Night	6% 5% 2 6% 5% 5% 6% 6% 8% 11% 42%	1710
July	1st to 10th	Night	5% 5% 2 6% 5% 4 5% 4 7% 12% 44%	2850
	11th to 20th	Night	3 4 2 6% 6% 5% 6% 5% 8% 11% 41%	2850
	21st to end	Night	8% 7% 3 7% 6% 5% 5% 5% 7% 10% 38%	3098
August	1st to 10th	Night	2 2 1 3 2 3 3 3 5% 10% 66%	2852
	11th to 20th	Night	2 1 1 3 2 3 4 5% 7% 12% 61%	3100
	21st to end	Night	6% 4 2 6% 5% 5% 6% 5% 9% 10% 43%	3476
September	1st to 10th	Night	6% 6% 1 5% 4 4 5% 4 8% 11% 46%	1939
	11th to 20th	Night	11% 6% 2 7% 5% 4 5% 4 6% 7% 43%	2090
	21st to end	Night	8% 4 2 6% 4 3 3 3 5% 6% 57%	2090
October	1st to 10th	Night	6% 3 1 5% 4 4 3 3 6% 7% 59%	2268
	11th to 20th	Night	9% 4 1 4 3 3 3 3 5% 7% 58%	2280
	21st to end	Night	11% 5% 2 4 3 2 3 1 3 5% 61%	2508
November	1st to 10th	Night	10% 5% 2 6% 3 3 4 4 4 7% 52%	2340
	11th to 20th	Night	11% 5% 2 4 3 3 4 2 5% 5% 54%	2400
	21st to end	Night	14% 7% 2 7% 5% 4 3 3 4 6% 46%	2400
December	1st to 10th	Night	21% 9% 4 7% 5% 4 3 3 4 6% 35%	4145
	11th to 20th	Night	14% 10% 3 7% 4 3 3 3 5% 5% 43%	4816
	21st to end	Night	16% 8% 2 6% 4 3 3 3 4 5% 46%	6490

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	47% 4 4 19% 18% 7%	4078
	11th to 20th	Day	38% 5% 5% 14% 27% 11%	4080
	21st to end	Day	53% 3 4 13% 15% 11%	4488
February	1st to 10th	Day	50% 4 7% 13% 17% 9%	1800
	11th to 20th	Day	49% 5% 7% 13% 17% 9%	2045
	21st to end	Day	51% 5% 8% 13% 15% 8%	1815
March	1st to 10th	Day	54% 7% 10% 12% 13% 5%	3546
	11th to 20th	Day	50% 7% 10% 13% 13% 7%	3590
	21st to end	Day	44% 6% 8% 17% 22% 3	3880
April	1st to 10th	Day	46% 7% 9% 15% 15% 9%	2137
	11th to 20th	Day	45% 7% 10% 15% 14% 10%	2254
	21st to end	Day	38% 8% 10% 17% 22% 5%	2280
May	1st to 10th	Day	54% 8% 10% 14% 10% 4	3800
	11th to 20th	Day	39% 7% 8% 20% 24% 3	3917
	21st to end	Day	38% 11% 15% 26% 9% 1	4489
June	1st to 10th	Day	38% 13% 16% 19% 13% 1	2470
	11th to 20th	Day	38% 11% 14% 23% 13% 3	2470
	21st to end	Day	46% 12% 18% 18% 7%	2470
July	1st to 10th	Day	44% 13% 24% 16% 2	4056
	11th to 20th	Day	53% 12% 18% 14% 3	4051
	21st to end	Day	52% 12% 17% 17% 2 1	4325
August	1st to 10th	Day	20% 10% 14% 37% 19%	4072
	11th to 20th	Day	26% 11% 32% 28% 3	3765
	21st to end	Day	44% 10% 14% 17% 14% 1	4179
September	1st to 10th	Day	42% 11% 14% 15% 13% 3	2235
	11th to 20th	Day	45% 9% 13% 14% 14% 4	2090
	21st to end	Day	35% 8% 13% 19% 14% 10%	2081
October	1st to 10th	Day	23% 5% 6% 13% 16% 36%	3160
	11th to 20th	Day	20% 4 5% 18% 35% 18%	3140
	21st to end	Day	26% 4 5% 12% 42% 12%	3428
November	1st to 10th	Day	37% 6% 10% 18% 19% 10%	1958
	11th to 20th	Day	35% 6% 8% 16% 21% 14%	2000
	21st to end	Day	41% 5% 7% 19% 19% 9%	2000
December	1st to 10th	Day	47% 4 7% 16% 21% 5%	3038
	11th to 20th	Day	43% 5% 7% 14% 19% 11%	3389
	21st to end	Day	40% 4 6% 16% 25% 10%	4488
January	1st to 10th	Night	40% 5% 6% 21% 20% 7%	5888
	11th to 20th	Night	41% 3 4 16% 25% 10%	5900
	21st to end	Night	54% 4 5% 12% 15% 11%	6490
February	1st to 10th	Night	47% 4 7% 11% 19% 12%	2600
	11th to 20th	Night	45% 5% 7% 15% 19% 10%	2266
	21st to end	Night	48% 6% 8% 13% 14% 12%	1815
March	1st to 10th	Night	56% 6% 8% 12% 12% 6%	3529
	11th to 20th	Night	53% 7% 8% 13% 13% 5%	3590
	21st to end	Night	39% 7% 11% 14% 23% 6%	3889
April	1st to 10th	Night	42% 7% 10% 17% 15% 10%	2043
	11th to 20th	Night	38% 6% 11% 18% 15% 13%	1875
	21st to end	Night	37% 6% 9% 21% 21% 6%	1900
May	1st to 10th	Night	54% 9% 11% 12% 10% 4	3160
	11th to 20th	Night	39% 7% 9% 18% 22% 4	2982
	21st to end	Night	36% 12% 19% 24% 8% 1	3099
June	1st to 10th	Night	22% 10% 21% 32% 15%	1710
	11th to 20th	Night	23% 8% 20% 32% 15% 2	1710
	21st to end	Night	32% 11% 23% 25% 9%	1710
July	1st to 10th	Night	33% 8% 37% 20% 2	2805
	11th to 20th	Night	33% 11% 31% 22% 4	2796
	21st to end	Night	41% 13% 23% 21% 3	2999
August	1st to 10th	Night	13% 6% 20% 42% 18%	2842
	11th to 20th	Night	15% 8% 38% 34% 5%	3130
	21st to end	Night	33% 13% 20% 21% 12% 1	3476
September	1st to 10th	Night	31% 9% 22% 22% 14% 3	1939
	11th to 20th	Night	38% 8% 17% 18% 15% 5%	2090
	21st to end	Night	28% 6% 13% 23% 18% 12%	2090
October	1st to 10th	Night	18% 4 7% 16% 17% 37%	3788
	11th to 20th	Night	16% 4 6% 25% 30% 21%	3779
	21st to end	Night	21% 3 5% 13% 40% 17%	4120
November	1st to 10th	Night	31% 6% 12% 19% 22% 11%	2340
	11th to 20th	Night	32% 4 9% 18% 24% 13%	2400
	21st to end	Night	40% 4 9% 19% 18% 11%	2400
December	1st to 10th	Night	52% 4 6% 16% 16% 6%	4145
	11th to 20th	Night	44% 4 7% 12% 20% 12%	4817
	21st to end	Night	40% 5% 6% 14% 25% 9%	6490

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	23% 10% 38% 18% 10% 1	300
	11th to 20th	Day	20% 14% 34% 23% 9%	300
	21st to end	Day	23% 13% 35% 22% 7%	330
February	1st to 10th	Day	24% 13% 35% 21% 6%	300
	11th to 20th	Day	31% 14% 28% 24% 3	300
	21st to end	Day	27% 19% 35% 14% 3 1	249
March	1st to 10th	Day	26% 14% 33% 21% 6%	300
	11th to 20th	Day	16% 16% 46% 15% 6% 1	300
	21st to end	Day	22% 13% 34% 23% 7% 1	315
April	1st to 10th	Day	19% 14% 30% 27% 10% 1	317
	11th to 20th	Day	25% 12% 25% 22% 15% 2	452
	21st to end	Day	15% 8% 30% 29% 17% 2	460
May	1st to 10th	Day	19% 8% 23% 30% 17% 2	463
	11th to 20th	Day	12% 4 19% 39% 20% 5%	571
	21st to end	Day	9% 4 23% 35% 22% 7%	734
June	1st to 10th	Day	8% 2 11% 33% 31% 15%	680
	11th to 20th	Day	7% 3 11% 33% 31% 14%	680
	21st to end	Day	10% 3 9% 24% 34% 21%	680
July	1st to 10th	Day	9% 2 4 23% 37% 24%	671
	11th to 20th	Day	8% 2 5% 21% 34% 29%	668
	21st to end	Day	8% 2 4 22% 36% 28%	739
August	1st to 10th	Day	3 1 2 21% 42% 30%	671
	11th to 20th	Day	5% 2 1 10% 43% 39%	479
	21st to end	Day	12% 3 3 17% 32% 32%	539
September	1st to 10th	Day	10% 3 4 20% 37% 27%	445
	11th to 20th	Day	13% 3 6% 20% 35% 22%	300
	21st to end	Day	12% 2 8% 26% 37% 16%	300
October	1st to 10th	Day	7% 2 14% 41% 26% 10%	300
	11th to 20th	Day	10% 4 16% 36% 23% 11%	300
	21st to end	Day	18% 6% 23% 28% 19% 5%	330
November	1st to 10th	Day	16% 6% 20% 33% 21% 3	300
	11th to 20th	Day	16% 7% 24% 37% 13% 2	300
	21st to end	Day	19% 13% 31% 21% 13% 2	300
December	1st to 10th	Day	21% 7% 31% 26% 10% 5%	300
	11th to 20th	Day	18% 9% 36% 27% 9% 1	300
	21st to end	Day	20% 12% 35% 24% 8% 2	330
January	1st to 10th	Night	22% 6% 31% 32% 9%	1000
	11th to 20th	Night	23% 7% 29% 32% 9%	1000
	21st to end	Night	24% 6% 28% 36% 6%	1100
February	1st to 10th	Night	25% 8% 28% 34% 6%	1000
	11th to 20th	Night	28% 9% 26% 30% 8%	710
	21st to end	Night	25% 7% 33% 31% 3	495
March	1st to 10th	Night	24% 7% 29% 34% 6%	600
	11th to 20th	Night	21% 7% 30% 34% 8%	600
	21st to end	Night	18% 8% 28% 34% 11%	647
April	1st to 10th	Night	18% 7% 29% 37% 9%	570
	11th to 20th	Night	20% 9% 23% 34% 14%	563
	21st to end	Night	16% 6% 26% 38% 14% 1	570
May	1st to 10th	Night	15% 5% 24% 43% 12%	570
	11th to 20th	Night	12% 4 20% 42% 22% 1	561
	21st to end	Night	7% 4 17% 40% 30% 3	617
June	1st to 10th	Night	6% 2 5% 34% 48% 5%	570
	11th to 20th	Night	5% 2 6% 35% 44% 7%	570
	21st to end	Night	8% 2 7% 24% 49% 11%	570
July	1st to 10th	Night	7% 2 2 22% 53% 13%	555
	11th to 20th	Night	4 1 1 20% 54% 20%	552
	21st to end	Night	4 2 3 21% 52% 17%	624
August	1st to 10th	Night	2 1 1 17% 64% 15%	567
	11th to 20th	Night	5% 1 1 13% 60% 20%	564
	21st to end	Night	8% 2 3 17% 53% 17%	627
September	1st to 10th	Night	7% 1 5% 22% 51% 15%	570
	11th to 20th	Night	11% 2 3 22% 54% 8%	570
	21st to end	Night	10% 1 4 28% 48% 8%	570
October	1st to 10th	Night	7% 2 7% 33% 45% 6%	748
	11th to 20th	Night	10% 3 16% 38% 29% 4	760
	21st to end	Night	12% 5% 17% 38% 25% 3	836
November	1st to 10th	Night	12% 4 17% 38% 27% 2	780
	11th to 20th	Night	13% 6% 22% 40% 19%	800
	21st to end	Night	18% 5% 28% 33% 15% 1	800
December	1st to 10th	Night	22% 6% 24% 34% 14% 1	934
	11th to 20th	Night	23% 7% 25% 34% 11%	1000
	21st to end	Night	21% 7% 27% 34% 10%	1100

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