Roberval
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Roberval clear sky chart from 2005-11-06 to 2024-12-06.

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% 6% 5% 5% 4 6% 7% 28%	101876
	Night	16% 12% 4 10% 6% 5% 5% 4 5% 6% 26%	97878
Transparency	Day	55% 5% 13% 19% 8% 1	105311
	Night	59% 5% 12% 17% 7%	102533
Seeing	Day	21% 10% 29% 25% 12% 3	15271
	Night	24% 10% 28% 27% 9% 1	23715

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	12% 15% 8% 17% 8% 7% 5% 4 5% 6% 15%	2490
	11th to 20th	Day	11% 14% 7% 15% 10% 7% 6% 4 6% 5% 14%	2520
	21st to end	Day	9% 13% 5% 16% 7% 6% 5% 3 5% 6% 26%	2772
February	1st to 10th	Day	7% 13% 5% 12% 10% 9% 9% 4 5% 4 21%	1520
	11th to 20th	Day	12% 15% 6% 14% 8% 7% 6% 4 5% 5% 19%	1748
	21st to end	Day	10% 15% 5% 12% 7% 6% 6% 5% 6% 6% 24%	1570
March	1st to 10th	Day	13% 13% 3 9% 5% 4 4 4 6% 7% 32%	3116
	11th to 20th	Day	14% 17% 5% 12% 6% 5% 5% 3 4 5% 23%	3252
	21st to end	Day	11% 13% 4 10% 5% 4 5% 4 6% 7% 31%	4152
April	1st to 10th	Day	17% 15% 5% 12% 6% 6% 4 3 3 4 25%	2280
	11th to 20th	Day	17% 12% 3 8% 4 4 4 3 5% 6% 34%	2336
	21st to end	Day	20% 12% 4 7% 5% 4 4 3 5% 6% 30%	2470
May	1st to 10th	Day	16% 10% 3 7% 5% 5% 6% 4 6% 6% 31%	4411
	11th to 20th	Day	16% 8% 3 7% 5% 5% 5% 4 6% 8% 33%	4398
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 4 6% 7% 34%	5015
June	1st to 10th	Day	19% 8% 3 8% 5% 5% 5% 5% 5% 7% 31%	2850
	11th to 20th	Day	15% 6% 2 7% 6% 5% 5% 4 6% 8% 34%	2850
	21st to end	Day	21% 7% 3 7% 6% 5% 6% 4 7% 7% 28%	2850
July	1st to 10th	Day	16% 7% 3 7% 4 5% 6% 5% 7% 8% 31%	4646
	11th to 20th	Day	13% 7% 3 9% 6% 6% 6% 5% 8% 9% 29%	4440
	21st to end	Day	12% 7% 3 7% 6% 6% 6% 4 7% 8% 35%	4814
August	1st to 10th	Day	14% 7% 3 9% 7% 7% 7% 5% 7% 9% 25%	4423
	11th to 20th	Day	16% 7% 3 7% 5% 6% 6% 5% 7% 9% 29%	4170
	21st to end	Day	13% 7% 4 8% 5% 5% 6% 4 6% 7% 34%	4316
September	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 4 6% 7% 34%	2280
	11th to 20th	Day	17% 7% 3 7% 5% 5% 4 4 5% 7% 36%	2157
	21st to end	Day	22% 8% 3 7% 5% 5% 4 3 5% 6% 31%	2090
October	1st to 10th	Day	17% 11% 3 8% 6% 6% 4 3 6% 6% 30%	2015
	11th to 20th	Day	24% 15% 4 10% 5% 5% 5% 4 5% 5% 18%	1756
	21st to end	Day	24% 15% 4 9% 4 5% 4 3 4 6% 22%	1881
November	1st to 10th	Day	18% 16% 4 10% 6% 6% 5% 3 4 4 24%	1761
	11th to 20th	Day	19% 16% 4 11% 7% 5% 5% 4 5% 4 21%	1663
	21st to end	Day	20% 18% 5% 12% 5% 6% 5% 4 4 6% 15%	1400
December	1st to 10th	Day	18% 19% 5% 12% 8% 5% 4 3 6% 5% 16%	1365
	11th to 20th	Day	20% 18% 5% 9% 5% 5% 3 3 4 4 24%	1668
	21st to end	Day	17% 17% 6% 12% 9% 6% 5% 4 5% 5% 15%	2431
January	1st to 10th	Night	13% 19% 7% 14% 10% 7% 4 3 4 4 15%	4454
	11th to 20th	Night	11% 15% 6% 16% 11% 7% 4 4 5% 5% 18%	4440
	21st to end	Night	8% 14% 7% 15% 9% 7% 5% 4 5% 6% 21%	4884
February	1st to 10th	Night	9% 14% 5% 11% 7% 7% 6% 5% 5% 6% 24%	2660
	11th to 20th	Night	9% 16% 6% 14% 10% 6% 6% 4 4 4 21%	2312
	21st to end	Night	10% 15% 5% 11% 6% 5% 6% 3 6% 6% 26%	1884
March	1st to 10th	Night	17% 12% 4 9% 6% 5% 7% 5% 5% 6% 24%	3724
	11th to 20th	Night	14% 18% 5% 12% 7% 5% 5% 3 5% 5% 22%	3706
	21st to end	Night	13% 13% 5% 10% 6% 5% 5% 4 5% 6% 28%	3477
April	1st to 10th	Night	19% 15% 4 9% 5% 5% 5% 3 4 5% 25%	1900
	11th to 20th	Night	18% 11% 3 7% 5% 6% 4 3 5% 6% 32%	1792
	21st to end	Night	19% 11% 2 8% 5% 5% 4 3 4 5% 33%	1710
May	1st to 10th	Night	16% 10% 3 8% 6% 5% 5% 3 5% 5% 34%	2559
	11th to 20th	Night	18% 8% 2 8% 5% 5% 4 5% 6% 7% 31%	2495
	21st to end	Night	20% 8% 3 7% 5% 5% 4 3 5% 7% 31%	2566
June	1st to 10th	Night	19% 7% 3 8% 4 5% 5% 6% 5% 7% 30%	1330
	11th to 20th	Night	15% 7% 3 6% 6% 5% 4 4 6% 7% 36%	1330
	21st to end	Night	17% 7% 3 8% 5% 5% 5% 4 6% 8% 32%	1330
July	1st to 10th	Night	13% 5% 3 8% 6% 6% 7% 6% 8% 8% 30%	2317
	11th to 20th	Night	10% 7% 3 8% 6% 6% 6% 5% 7% 8% 34%	2520
	21st to end	Night	11% 5% 3 6% 5% 5% 5% 4 6% 8% 42%	2739
August	1st to 10th	Night	13% 7% 3 7% 5% 6% 6% 5% 7% 9% 33%	2506
	11th to 20th	Night	17% 7% 2 7% 5% 4 4 4 6% 9% 34%	2625
	21st to end	Night	14% 7% 3 7% 4 5% 5% 3 7% 8% 38%	3338
September	1st to 10th	Night	17% 7% 2 6% 3 5% 4 3 5% 7% 40%	1900
	11th to 20th	Night	17% 8% 3 7% 5% 4 4 3 5% 5% 39%	2023
	21st to end	Night	20% 7% 2 7% 4 5% 5% 4 4 5% 36%	2090
October	1st to 10th	Night	19% 9% 3 6% 4 4 5% 3 6% 7% 34%	2161
	11th to 20th	Night	26% 12% 3 7% 5% 5% 5% 3 4 5% 24%	2423
	21st to end	Night	26% 13% 3 7% 4 5% 5% 4 5% 6% 21%	2717
November	1st to 10th	Night	20% 14% 5% 9% 4 5% 5% 4 5% 6% 24%	2537
	11th to 20th	Night	18% 16% 5% 11% 6% 5% 4 4 5% 5% 22%	2730
	21st to end	Night	19% 18% 5% 13% 7% 5% 4 4 5% 5% 15%	3000
December	1st to 10th	Night	18% 18% 7% 13% 8% 4 4 3 4 4 17%	2932
	11th to 20th	Night	19% 16% 5% 11% 6% 4 5% 4 5% 5% 20%	3531
	21st to end	Night	15% 20% 7% 11% 7% 5% 4 3 4 4 19%	5236

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	72% 3 13% 10% 2	2491
	11th to 20th	Day	71% 5% 10% 11% 4	2520
	21st to end	Day	61% 3 10% 17% 9%	2772
February	1st to 10th	Day	65% 3 9% 15% 8% 1	1520
	11th to 20th	Day	68% 4 8% 13% 7%	1757
	21st to end	Day	60% 4 9% 18% 8% 2	1570
March	1st to 10th	Day	52% 3 14% 19% 10% 2	3119
	11th to 20th	Day	64% 2 12% 16% 5%	3252
	21st to end	Day	50% 4 10% 19% 15% 2	4152
April	1st to 10th	Day	63% 3 9% 13% 9% 3	2280
	11th to 20th	Day	52% 2 10% 22% 12% 2	2336
	21st to end	Day	56% 2 9% 18% 13% 1	2470
May	1st to 10th	Day	50% 4 14% 18% 12% 2	4425
	11th to 20th	Day	49% 4 13% 22% 11% 1	4402
	21st to end	Day	47% 4 11% 21% 15% 2	5015
June	1st to 10th	Day	52% 3 10% 22% 11% 1	2850
	11th to 20th	Day	45% 4 14% 23% 12% 2	2850
	21st to end	Day	52% 5% 13% 20% 10%	2850
July	1st to 10th	Day	46% 6% 16% 28% 4	4574
	11th to 20th	Day	48% 6% 19% 21% 4	4365
	21st to end	Day	47% 6% 17% 23% 7%	4661
August	1st to 10th	Day	52% 7% 18% 20% 2	4409
	11th to 20th	Day	48% 7% 22% 20% 4	4212
	21st to end	Day	48% 6% 15% 21% 10%	4316
September	1st to 10th	Day	48% 5% 17% 22% 7%	2280
	11th to 20th	Day	46% 4 19% 23% 7%	2157
	21st to end	Day	55% 5% 15% 19% 7%	2090
October	1st to 10th	Day	54% 6% 13% 22% 4	3353
	11th to 20th	Day	66% 4 15% 14% 2	2894
	21st to end	Day	60% 7% 16% 14% 3	3081
November	1st to 10th	Day	65% 4 11% 14% 5% 1	1761
	11th to 20th	Day	68% 4 10% 13% 4	1663
	21st to end	Day	73% 6% 11% 9% 3	1400
December	1st to 10th	Day	73% 7% 6% 11% 3	1365
	11th to 20th	Day	66% 4 6% 19% 5%	1668
	21st to end	Day	73% 4 8% 9% 6%	2431
January	1st to 10th	Night	75% 3 9% 9% 3	4454
	11th to 20th	Night	69% 5% 8% 13% 5%	4440
	21st to end	Night	66% 4 10% 15% 5%	4884
February	1st to 10th	Night	62% 4 9% 17% 8%	2660
	11th to 20th	Night	68% 4 8% 13% 7%	2314
	21st to end	Night	60% 4 10% 18% 8%	1884
March	1st to 10th	Night	63% 2 11% 16% 7% 1	3734
	11th to 20th	Night	67% 3 10% 13% 6% 1	3707
	21st to end	Night	57% 5% 9% 19% 8% 2	3477
April	1st to 10th	Night	63% 3 8% 16% 8% 2	1900
	11th to 20th	Night	53% 4 8% 23% 11% 1	1792
	21st to end	Night	55% 2 9% 21% 12% 2	1710
May	1st to 10th	Night	52% 5% 10% 18% 13% 1	2565
	11th to 20th	Night	48% 7% 13% 20% 12% 1	2496
	21st to end	Night	53% 5% 9% 17% 15% 1	2567
June	1st to 10th	Night	50% 6% 11% 23% 10% 1	1330
	11th to 20th	Night	47% 5% 12% 21% 12% 3	1330
	21st to end	Night	51% 6% 12% 21% 10%	1330
July	1st to 10th	Night	47% 7% 15% 27% 5%	2279
	11th to 20th	Night	45% 7% 18% 25% 4	2472
	21st to end	Night	40% 6% 20% 22% 12%	2651
August	1st to 10th	Night	46% 8% 17% 22% 6%	2496
	11th to 20th	Night	47% 6% 24% 19% 4	2649
	21st to end	Night	43% 6% 17% 25% 8%	3338
September	1st to 10th	Night	44% 6% 16% 25% 9%	1900
	11th to 20th	Night	48% 5% 17% 24% 6%	2023
	21st to end	Night	50% 6% 13% 24% 7%	2090
October	1st to 10th	Night	51% 6% 15% 23% 5%	3603
	11th to 20th	Night	61% 4 14% 17% 4	4024
	21st to end	Night	62% 7% 13% 13% 5%	4467
November	1st to 10th	Night	63% 4 13% 15% 5%	2537
	11th to 20th	Night	67% 4 11% 13% 4	2730
	21st to end	Night	73% 6% 10% 9% 3	3000
December	1st to 10th	Night	74% 5% 9% 10% 2	2932
	11th to 20th	Night	68% 6% 7% 13% 5%	3532
	21st to end	Night	72% 3 9% 11% 4	5236

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% 11% 36% 19% 9% 2	180
	11th to 20th	Day	14% 12% 32% 28% 14% 1	180
	21st to end	Day	16% 7% 27% 29% 19% 2	198
February	1st to 10th	Day	9% 17% 44% 21% 8% 1	180
	11th to 20th	Day	19% 13% 37% 26% 5% 1	363
	21st to end	Day	19% 13% 42% 19% 6% 1	382
March	1st to 10th	Day	22% 11% 32% 24% 9% 1	460
	11th to 20th	Day	20% 13% 32% 23% 10% 2	460
	21st to end	Day	23% 12% 33% 25% 7% 2	506
April	1st to 10th	Day	24% 14% 30% 22% 8% 2	460
	11th to 20th	Day	22% 14% 26% 24% 11% 3	452
	21st to end	Day	24% 11% 32% 23% 10% 1	460
May	1st to 10th	Day	22% 11% 32% 23% 10% 3	463
	11th to 20th	Day	16% 8% 30% 26% 16% 2	487
	21st to end	Day	20% 12% 33% 27% 7% 1	629
June	1st to 10th	Day	22% 6% 30% 28% 12% 2	680
	11th to 20th	Day	19% 9% 26% 28% 16% 2	680
	21st to end	Day	23% 6% 25% 29% 14% 3	680
July	1st to 10th	Day	17% 5% 26% 35% 14% 3	611
	11th to 20th	Day	17% 7% 23% 29% 20% 4	484
	21st to end	Day	15% 5% 22% 29% 24% 4	532
August	1st to 10th	Day	15% 6% 22% 31% 21% 5%	486
	11th to 20th	Day	16% 4 21% 31% 20% 7%	479
	21st to end	Day	19% 9% 24% 24% 14% 10%	539
September	1st to 10th	Day	20% 9% 26% 27% 13% 5%	490
	11th to 20th	Day	20% 10% 21% 28% 16% 4	490
	21st to end	Day	24% 10% 27% 21% 13% 6%	490
October	1st to 10th	Day	20% 14% 28% 20% 12% 6%	490
	11th to 20th	Day	31% 15% 26% 17% 8% 2	413
	21st to end	Day	33% 11% 29% 19% 7% 1	429
November	1st to 10th	Day	31% 17% 32% 14% 5% 1	395
	11th to 20th	Day	27% 18% 29% 18% 8% 1	275
	21st to end	Day	30% 15% 33% 14% 8% 2	200
December	1st to 10th	Day	22% 7% 30% 23% 16% 2	190
	11th to 20th	Day	23% 15% 37% 18% 4 2	180
	21st to end	Day	26% 15% 30% 21% 8% 1	198
January	1st to 10th	Night	25% 11% 31% 25% 8%	765
	11th to 20th	Night	23% 12% 27% 30% 9% 1	760
	21st to end	Night	14% 8% 30% 34% 13% 2	836
February	1st to 10th	Night	14% 10% 34% 30% 10% 2	760
	11th to 20th	Night	18% 11% 32% 30% 8% 1	743
	21st to end	Night	20% 12% 32% 27% 8% 1	628
March	1st to 10th	Night	20% 12% 32% 28% 8%	760
	11th to 20th	Night	23% 13% 29% 25% 9% 1	760
	21st to end	Night	22% 13% 30% 28% 7%	836
April	1st to 10th	Night	29% 9% 24% 29% 7% 1	760
	11th to 20th	Night	25% 10% 29% 28% 8% 1	668
	21st to end	Night	26% 11% 31% 24% 7%	570
May	1st to 10th	Night	29% 8% 28% 28% 7%	412
	11th to 20th	Night	22% 11% 27% 28% 11% 1	374
	21st to end	Night	23% 10% 35% 23% 7% 1	411
June	1st to 10th	Night	23% 4 32% 30% 9% 1	380
	11th to 20th	Night	17% 7% 31% 30% 13% 1	380
	21st to end	Night	18% 7% 25% 34% 13% 2	380
July	1st to 10th	Night	20% 7% 25% 36% 13%	370
	11th to 20th	Night	15% 4 26% 40% 15%	368
	21st to end	Night	17% 6% 23% 39% 13% 2	416
August	1st to 10th	Night	17% 5% 24% 34% 19% 2	378
	11th to 20th	Night	19% 3 25% 33% 16% 3	466
	21st to end	Night	20% 9% 24% 28% 15% 4	750
September	1st to 10th	Night	21% 9% 26% 31% 13% 1	760
	11th to 20th	Night	23% 9% 27% 26% 13% 3	760
	21st to end	Night	25% 8% 30% 25% 10% 2	760
October	1st to 10th	Night	24% 11% 29% 24% 10% 2	760
	11th to 20th	Night	38% 10% 26% 18% 7% 1	760
	21st to end	Night	37% 11% 26% 18% 8%	836
November	1st to 10th	Night	32% 15% 30% 17% 5% 1	780
	11th to 20th	Night	28% 18% 30% 17% 7%	805
	21st to end	Night	31% 14% 30% 19% 6% 1	900
December	1st to 10th	Night	30% 11% 25% 24% 8% 1	878
	11th to 20th	Night	23% 13% 31% 23% 9% 1	850
	21st to end	Night	26% 13% 25% 27% 8% 1	935

Page generated at 2024-12-03 06:45:08. Version ac07

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