Observatoire Huntingdon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Huntingdon clear sky chart from 2005-11-06 to 2025-01-07.

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	18% 11% 4 8% 5% 4 4 4 5% 6% 31%	105131
	Night	19% 13% 4 9% 5% 4 4 3 5% 5% 28%	103895
Transparency	Day	51% 6% 13% 20% 9% 1	108605
	Night	55% 6% 12% 17% 9% 1	108509
Seeing	Day	22% 17% 29% 21% 9% 2	14729
	Night	23% 16% 29% 23% 8% 1	23825

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	17% 19% 5% 13% 7% 5% 5% 4 3 4 17%	2565
	11th to 20th	Day	14% 18% 8% 14% 8% 6% 4 3 4 4 16%	2520
	21st to end	Day	15% 18% 7% 13% 7% 7% 4 3 5% 6% 14%	2772
February	1st to 10th	Day	15% 18% 5% 13% 7% 5% 5% 3 5% 5% 20%	1706
	11th to 20th	Day	13% 14% 5% 13% 7% 6% 4 4 5% 4 24%	1750
	21st to end	Day	17% 17% 5% 9% 7% 5% 4 3 5% 6% 23%	1570
March	1st to 10th	Day	22% 13% 4 9% 5% 5% 5% 3 5% 6% 24%	3116
	11th to 20th	Day	14% 20% 5% 11% 6% 4 4 3 4 5% 25%	3320
	21st to end	Day	16% 10% 3 10% 5% 3 3 3 4 5% 37%	4132
April	1st to 10th	Day	22% 13% 4 7% 5% 4 3 2 4 5% 32%	2280
	11th to 20th	Day	21% 10% 3 6% 5% 4 3 2 5% 5% 35%	2254
	21st to end	Day	24% 11% 3 6% 4 4 4 3 4 6% 32%	2402
May	1st to 10th	Day	23% 9% 3 8% 4 4 4 3 5% 6% 29%	4385
	11th to 20th	Day	19% 10% 3 8% 5% 4 4 4 5% 7% 32%	4398
	21st to end	Day	15% 7% 2 6% 5% 4 5% 4 7% 8% 36%	4837
June	1st to 10th	Day	24% 8% 3 7% 4 4 5% 3 6% 7% 30%	2660
	11th to 20th	Day	15% 7% 2 7% 4 6% 5% 4 6% 8% 36%	2660
	21st to end	Day	21% 7% 3 6% 5% 5% 5% 4 5% 7% 31%	2660
July	1st to 10th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 9% 38%	4440
	11th to 20th	Day	13% 6% 2 6% 5% 5% 5% 5% 7% 8% 38%	4440
	21st to end	Day	13% 6% 2 5% 4 4 4 4 6% 9% 42%	4814
August	1st to 10th	Day	17% 7% 3 7% 5% 4 5% 4 6% 8% 33%	4423
	11th to 20th	Day	16% 6% 3 7% 4 4 5% 4 6% 7% 38%	3935
	21st to end	Day	17% 5% 2 5% 3 4 5% 4 7% 8% 39%	4180
September	1st to 10th	Day	14% 6% 2 5% 4 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 4 7% 48%	2217
	21st to end	Day	15% 6% 3 7% 4 3 4 4 6% 8% 40%	2090
October	1st to 10th	Day	22% 8% 3 6% 4 4 4 4 5% 7% 33%	1938
	11th to 20th	Day	19% 11% 3 9% 5% 5% 5% 4 4 5% 30%	1886
	21st to end	Day	27% 12% 4 7% 4 4 3 3 4 6% 27%	1881
November	1st to 10th	Day	18% 11% 4 8% 4 5% 4 3 5% 7% 31%	1761
	11th to 20th	Day	17% 13% 5% 9% 5% 4 4 4 6% 6% 27%	1713
	21st to end	Day	19% 20% 5% 10% 5% 4 5% 4 4 5% 20%	1600
December	1st to 10th	Day	20% 19% 7% 16% 7% 5% 4 3 4 4 12%	2600
	11th to 20th	Day	18% 16% 6% 13% 6% 4 5% 3 5% 4 21%	2986
	21st to end	Day	21% 18% 4 11% 5% 4 4 3 5% 4 21%	3960
January	1st to 10th	Night	16% 19% 8% 14% 6% 5% 3 2 4 4 18%	4514
	11th to 20th	Night	13% 17% 7% 18% 7% 5% 5% 3 5% 4 15%	4440
	21st to end	Night	17% 21% 7% 11% 7% 5% 3 3 4 4 18%	4884
February	1st to 10th	Night	15% 16% 6% 14% 8% 6% 4 3 4 5% 18%	2470
	11th to 20th	Night	14% 15% 6% 12% 7% 5% 5% 3 4 5% 24%	2315
	21st to end	Night	15% 17% 5% 10% 6% 4 4 3 4 5% 27%	1884
March	1st to 10th	Night	22% 12% 3 7% 5% 5% 3 2 4 5% 32%	3724
	11th to 20th	Night	18% 21% 5% 9% 5% 4 3 2 3 5% 25%	3622
	21st to end	Night	15% 14% 4 9% 5% 4 4 3 4 4 35%	3499
April	1st to 10th	Night	23% 12% 4 8% 6% 4 4 3 4 4 28%	1900
	11th to 20th	Night	23% 10% 2 8% 5% 4 4 3 4 6% 31%	1875
	21st to end	Night	21% 10% 4 8% 4 4 4 2 5% 5% 33%	1777
May	1st to 10th	Night	25% 10% 3 7% 4 4 4 4 5% 7% 27%	2583
	11th to 20th	Night	22% 9% 3 7% 4 4 4 3 5% 5% 35%	2495
	21st to end	Night	16% 7% 2 6% 5% 4 5% 3 6% 8% 37%	2738
June	1st to 10th	Night	21% 8% 3 7% 4 4 4 4 6% 8% 29%	1520
	11th to 20th	Night	18% 6% 3 5% 5% 5% 3 4 5% 7% 39%	1520
	21st to end	Night	18% 8% 4 7% 5% 5% 4 4 5% 7% 35%	1520
July	1st to 10th	Night	16% 7% 3 8% 5% 4 5% 4 6% 7% 35%	2520
	11th to 20th	Night	16% 5% 2 6% 4 3 4 4 7% 8% 41%	2520
	21st to end	Night	14% 7% 2 7% 4 5% 4 4 6% 7% 40%	2739
August	1st to 10th	Night	18% 8% 3 8% 4 4 3 3 5% 7% 38%	2506
	11th to 20th	Night	18% 7% 3 8% 5% 4 5% 3 5% 7% 36%	2847
	21st to end	Night	15% 6% 2 6% 4 4 4 4 7% 7% 42%	3476
September	1st to 10th	Night	14% 6% 2 7% 4 4 4 3 5% 7% 43%	1900
	11th to 20th	Night	16% 5% 2 6% 3 3 2 4 5% 6% 48%	1962
	21st to end	Night	19% 6% 2 5% 4 4 4 3 6% 6% 42%	2090
October	1st to 10th	Night	20% 8% 3 6% 5% 4 4 4 5% 6% 35%	2239
	11th to 20th	Night	20% 10% 3 8% 4 5% 5% 3 5% 5% 32%	2293
	21st to end	Night	25% 12% 3 8% 5% 4 4 3 4 5% 27%	2717
November	1st to 10th	Night	20% 13% 3 7% 4 5% 3 4 6% 6% 29%	2537
	11th to 20th	Night	19% 12% 4 8% 5% 5% 4 3 4 5% 30%	2685
	21st to end	Night	21% 15% 5% 10% 5% 5% 3 3 4 5% 22%	2800
December	1st to 10th	Night	19% 24% 7% 12% 6% 5% 5% 3 4 3 12%	4580
	11th to 20th	Night	23% 17% 6% 11% 5% 4 4 2 3 3 21%	5208
	21st to end	Night	23% 17% 5% 12% 5% 4 4 3 3 6% 19%	6996

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	66% 7% 15% 10% 2	2566
	11th to 20th	Day	67% 4 16% 8% 5%	2520
	21st to end	Day	67% 7% 14% 7% 4 1	2772
February	1st to 10th	Day	66% 5% 10% 14% 3 1	1706
	11th to 20th	Day	61% 5% 12% 14% 7% 1	1759
	21st to end	Day	62% 5% 10% 13% 8% 1	1570
March	1st to 10th	Day	59% 6% 11% 17% 6% 1	3119
	11th to 20th	Day	59% 5% 14% 12% 9% 1	3320
	21st to end	Day	49% 4 9% 20% 16% 2	4132
April	1st to 10th	Day	55% 4 8% 20% 11% 2	2280
	11th to 20th	Day	51% 4 9% 20% 15% 2	2254
	21st to end	Day	53% 5% 10% 16% 12% 3	2402
May	1st to 10th	Day	53% 7% 11% 18% 10% 1	4399
	11th to 20th	Day	50% 9% 13% 19% 9% 1	4402
	21st to end	Day	42% 8% 12% 24% 12% 1	4837
June	1st to 10th	Day	52% 6% 11% 18% 12% 1	2660
	11th to 20th	Day	44% 7% 12% 23% 12% 2	2660
	21st to end	Day	51% 8% 12% 19% 10% 1	2660
July	1st to 10th	Day	41% 7% 13% 28% 10%	4370
	11th to 20th	Day	40% 8% 15% 30% 7%	4365
	21st to end	Day	37% 8% 13% 32% 9%	4661
August	1st to 10th	Day	47% 7% 15% 22% 8%	4409
	11th to 20th	Day	43% 8% 17% 27% 6%	3976
	21st to end	Day	40% 7% 18% 22% 12%	4180
September	1st to 10th	Day	38% 8% 13% 27% 14%	2280
	11th to 20th	Day	37% 5% 12% 32% 14% 1	2217
	21st to end	Day	42% 7% 15% 26% 10% 1	2090
October	1st to 10th	Day	47% 5% 13% 26% 8%	3224
	11th to 20th	Day	47% 6% 16% 24% 7%	3114
	21st to end	Day	48% 4 19% 22% 6%	3081
November	1st to 10th	Day	53% 6% 13% 20% 7% 1	1761
	11th to 20th	Day	56% 6% 12% 15% 9% 1	1713
	21st to end	Day	67% 7% 12% 11% 3	1600
December	1st to 10th	Day	75% 6% 9% 8% 1	2600
	11th to 20th	Day	64% 8% 9% 14% 5%	2986
	21st to end	Day	65% 7% 9% 14% 5%	3960
January	1st to 10th	Night	68% 7% 13% 9% 3	4514
	11th to 20th	Night	68% 8% 12% 9% 4	4440
	21st to end	Night	69% 6% 12% 8% 5%	4884
February	1st to 10th	Night	67% 7% 9% 12% 5% 1	2470
	11th to 20th	Night	61% 4 11% 16% 7%	2317
	21st to end	Night	59% 5% 9% 16% 11% 1	1884
March	1st to 10th	Night	54% 6% 9% 21% 9% 2	3734
	11th to 20th	Night	61% 5% 11% 13% 7% 2	3623
	21st to end	Night	52% 4 9% 21% 13% 2	3499
April	1st to 10th	Night	58% 4 10% 16% 11% 1	1900
	11th to 20th	Night	54% 5% 11% 18% 11% 1	1875
	21st to end	Night	53% 5% 8% 17% 14% 4	1777
May	1st to 10th	Night	55% 7% 9% 16% 10% 2	2589
	11th to 20th	Night	48% 8% 12% 20% 11% 2	2496
	21st to end	Night	42% 8% 12% 20% 17% 1	2739
June	1st to 10th	Night	51% 8% 11% 17% 12% 1	1520
	11th to 20th	Night	44% 6% 13% 19% 16% 2	1520
	21st to end	Night	48% 7% 13% 21% 11% 1	1520
July	1st to 10th	Night	46% 7% 13% 21% 13%	2480
	11th to 20th	Night	38% 8% 16% 31% 8%	2472
	21st to end	Night	41% 7% 14% 25% 12%	2651
August	1st to 10th	Night	45% 7% 13% 26% 8%	2496
	11th to 20th	Night	47% 7% 17% 21% 7%	2871
	21st to end	Night	39% 8% 16% 23% 13% 1	3476
September	1st to 10th	Night	40% 7% 12% 27% 13% 1	1900
	11th to 20th	Night	36% 6% 13% 32% 12%	1962
	21st to end	Night	42% 7% 12% 25% 14% 1	2090
October	1st to 10th	Night	47% 7% 12% 26% 8%	3733
	11th to 20th	Night	48% 5% 13% 24% 10%	3804
	21st to end	Night	51% 6% 15% 19% 9% 1	4467
November	1st to 10th	Night	54% 7% 13% 17% 8% 1	2537
	11th to 20th	Night	56% 5% 12% 17% 8% 2	2685
	21st to end	Night	64% 7% 11% 13% 4	2800
December	1st to 10th	Night	74% 6% 10% 8% 2	4580
	11th to 20th	Night	66% 5% 9% 12% 7%	5208
	21st to end	Night	65% 6% 9% 11% 8%	6996

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	27% 18% 31% 18% 6%	192
	11th to 20th	Day	28% 28% 29% 12% 3 1	180
	21st to end	Day	20% 21% 36% 19% 4	198
February	1st to 10th	Day	28% 27% 31% 12% 1	268
	11th to 20th	Day	22% 27% 37% 13% 1	357
	21st to end	Day	29% 20% 31% 18% 2	382
March	1st to 10th	Day	27% 22% 28% 17% 6%	460
	11th to 20th	Day	20% 26% 33% 16% 4 1	460
	21st to end	Day	28% 21% 26% 14% 10%	506
April	1st to 10th	Day	27% 21% 30% 16% 6%	460
	11th to 20th	Day	26% 23% 25% 17% 8% 1	452
	21st to end	Day	28% 17% 29% 17% 8% 2	460
May	1st to 10th	Day	25% 15% 33% 18% 8% 1	463
	11th to 20th	Day	18% 15% 32% 21% 13% 1	487
	21st to end	Day	19% 17% 29% 24% 9% 2	529
June	1st to 10th	Day	26% 14% 27% 24% 8% 2	490
	11th to 20th	Day	16% 13% 34% 28% 8% 2	490
	21st to end	Day	24% 13% 32% 19% 10% 2	490
July	1st to 10th	Day	13% 11% 33% 25% 14% 4	485
	11th to 20th	Day	15% 11% 31% 30% 10% 4	484
	21st to end	Day	13% 10% 31% 31% 12% 2	532
August	1st to 10th	Day	16% 8% 29% 29% 15% 3	486
	11th to 20th	Day	14% 9% 27% 31% 14% 5%	479
	21st to end	Day	16% 12% 29% 22% 15% 6%	539
September	1st to 10th	Day	16% 9% 30% 24% 15% 6%	490
	11th to 20th	Day	16% 11% 19% 27% 19% 8%	490
	21st to end	Day	16% 12% 26% 26% 16% 4	490
October	1st to 10th	Day	24% 16% 25% 19% 13% 4	490
	11th to 20th	Day	26% 20% 26% 16% 10% 1	483
	21st to end	Day	34% 15% 27% 17% 7%	429
November	1st to 10th	Day	30% 20% 25% 16% 9%	395
	11th to 20th	Day	30% 24% 24% 15% 7% 1	313
	21st to end	Day	29% 27% 24% 16% 5%	200
December	1st to 10th	Day	32% 18% 28% 17% 6%	200
	11th to 20th	Day	29% 30% 27% 12% 3 1	200
	21st to end	Day	30% 25% 25% 15% 3 1	220
January	1st to 10th	Night	24% 23% 34% 17% 2	785
	11th to 20th	Night	27% 22% 31% 16% 4	760
	21st to end	Night	20% 19% 35% 22% 4	836
February	1st to 10th	Night	21% 23% 32% 20% 3	760
	11th to 20th	Night	21% 22% 35% 19% 2	743
	21st to end	Night	24% 18% 34% 22% 2	628
March	1st to 10th	Night	27% 18% 30% 21% 4	760
	11th to 20th	Night	25% 22% 31% 19% 4	760
	21st to end	Night	26% 15% 28% 25% 6%	836
April	1st to 10th	Night	27% 17% 31% 20% 4	760
	11th to 20th	Night	27% 17% 30% 21% 6%	751
	21st to end	Night	27% 14% 29% 22% 7%	637
May	1st to 10th	Night	27% 11% 28% 25% 9%	423
	11th to 20th	Night	21% 11% 31% 28% 9% 1	374
	21st to end	Night	17% 10% 33% 29% 10%	411
June	1st to 10th	Night	23% 9% 32% 28% 7% 1	380
	11th to 20th	Night	18% 10% 28% 31% 12% 1	380
	21st to end	Night	20% 8% 31% 27% 14% 1	380
July	1st to 10th	Night	11% 8% 33% 34% 13% 1	370
	11th to 20th	Night	11% 7% 29% 38% 14% 1	368
	21st to end	Night	14% 5% 32% 38% 11% 1	416
August	1st to 10th	Night	14% 5% 24% 39% 17% 1	378
	11th to 20th	Night	15% 6% 23% 35% 19% 2	597
	21st to end	Night	15% 6% 28% 32% 16% 1	836
September	1st to 10th	Night	15% 8% 29% 33% 13% 1	760
	11th to 20th	Night	16% 8% 23% 32% 18% 3	760
	21st to end	Night	19% 10% 26% 25% 18% 2	760
October	1st to 10th	Night	24% 12% 28% 21% 14% 1	760
	11th to 20th	Night	26% 16% 25% 24% 8% 1	760
	21st to end	Night	29% 17% 29% 19% 5%	836
November	1st to 10th	Night	28% 19% 25% 21% 6%	780
	11th to 20th	Night	25% 21% 29% 16% 9% 1	800
	21st to end	Night	29% 22% 24% 18% 6%	800
December	1st to 10th	Night	31% 21% 29% 16% 4	800
	11th to 20th	Night	29% 22% 28% 16% 4 1	800
	21st to end	Night	32% 21% 29% 15% 4	880

Page generated at 2025-01-04 03:24:00. Version ac07

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